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Physics

New submissions

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New submissions for Thu, 22 Feb 18

[1]  arXiv:1802.07256 [pdf, ps, other]
Title: Hampering Görtler vortices via optimal control in the framework of nonlinear boundary region equations
Subjects: Fluid Dynamics (physics.flu-dyn)

The control of stream-wise vortices in high Reynolds number boundary layer flows often aims at reducing the vortex energy as a means of mitigating the growth of secondary instabilities, which eventually delay the transition from laminar to turbulent flow. In this paper, we aim at utilizing such an energy reduction strategy using optimal control theory to limit the growth of G\"{o}rtler vortices developing in an incompressible laminar boundary layer flow over a concave wall, and excited by a row of roughness elements with span-wise separation in the same order of magnitude as the boundary layer thickness. Commensurate with control theory formalism, we transform a constrained optimization problem into an unconstrained one by applying the method of Lagrange multipliers. A high Reynolds number asymptotic framework is utilized, wherein the Navier-Stokes equations are reduced to the boundary region equations (BRE), in which wall deformations enter the problem through an appropriate Prandtl transformation. In the optimal control strategy, the wall displacement or the wall transpiration velocity serve as control variables, while the cost functional is defined in terms of the wall shear stress. Our numerical results indicate, among other things, that the optimal control algorithm is very effective in reducing the amplitude of the G\"{o}rtler vortices, especially for the control based on wall displacement.

[2]  arXiv:1802.07258 [pdf, other]
Title: Rank dynamics of word usage at multiple scales
Comments: 19 pages (main text) + 24 pages (supplementary information)
Subjects: Physics and Society (physics.soc-ph)

The recent dramatic increase in online data availability has allowed researchers to explore human culture with unprecedented detail, such as the growth and diversification of language. In particular, it provides statistical tools to explore whether word use is similar across languages, and if so, whether these generic features appear at different scales of language structure. Here we use the Google Books $N$-grams dataset to analyze the temporal evolution of word usage in several languages. We apply measures proposed recently to study rank dynamics, such as the diversity of $N$-grams in a given rank, the probability that an $N$-gram changes rank between successive time intervals, the rank entropy, and the rank complexity. Using different methods, results show that there are generic properties for different languages at different scales, such as a core of words necessary to minimally understand a language. We also propose a null model to explore the relevance of linguistic structure across multiple scales, concluding that $N$-gram statistics cannot be reduced to word statistics. We expect our results to be useful in improving text prediction algorithms, as well as in shedding light on the large-scale features of language use, beyond linguistic and cultural differences across human populations.

[3]  arXiv:1802.07259 [pdf, ps, other]
Title: Multigrid Renormalization
Comments: 18 pages, 17 figures, 1 table
Subjects: Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)

We combine the multigrid (MG) method with state-of-the-art concepts from the variational formulation of the numerical renormalization group. The resulting MG renormalization (MGR) method is a natural generalization of the MG method for solving partial differential equations. When the solution on a grid of $N$ points is sought, our MGR method has a computational cost scaling as $\mathcal{O}(\log(N))$, as opposed to $\mathcal{O}(N)$ for the best standard MG method. Therefore MGR can exponentially speed up standard MG computations. To illustrate our method, we develop a novel algorithm for the ground state computation of the nonlinear Schr\"{o}dinger equation. Our algorithm acts variationally on tensor products and updates the tensors one after another by solving a local nonlinear optimization problem. We compare several different methods for the nonlinear tensor update and find that the Newton method is the most efficient as well as precise. The combination of MGR with our nonlinear ground state algorithm produces accurate results for the nonlinear Schr\"{o}dinger equation on $N = 10^{18}$ grid points in three spatial dimensions.

[4]  arXiv:1802.07261 [pdf, ps, other]
Title: The Mathematics of Human Contact: Developing a Model for Social Interaction in School Children
Comments: 18 pages, 5 figures, 5 tables
Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)

In this paper, we provide a statistical analysis of high-resolution contact pattern data within primary and secondary schools as collected by the SocioPatterns collaboration. Students are graphically represented as nodes in a temporally evolving network, in which links represent proximity or interaction between students. This article focuses on link- and node-level statistics, such as the on- and off-durations of links as well as the activity potential of nodes and links. Parametric models are fitted to the on- and off-durations of links, inter-event times and node activity potentials and, based on these, we propose a number of theoretical models that are able to reproduce the collected data within varying levels of accuracy. By doing so, we aim to identify the minimal network-level properties that are needed to closely match the real-world data, with the aim of combining this contact pattern model with epidemic models in future work.

[5]  arXiv:1802.07292 [pdf, other]
Title: Bots sustain and inflate striking opposition in online social systems
Comments: 10 pages, 5 figures
Subjects: Physics and Society (physics.soc-ph); Computers and Society (cs.CY); Human-Computer Interaction (cs.HC); Multiagent Systems (cs.MA); Social and Information Networks (cs.SI)

Societies are complex systems which tend to polarize into sub-groups of individuals with dramatically opposite perspectives. This phenomenon is reflected -- and often amplified -- in online social networks where, however, humans are no more the only players, and co-exist alongside with social bots, i.e. software-controlled accounts. Analyzing large-scale social data collected during the Catalan referendum for independence on October 1 2017, consisting of nearly 4 millions Twitter posts generated by almost 1 million users, we identify the two polarized groups of Independentists and Constitutionalists and quantify the structural and emotional roles played by social bots. We show that bots act from peripheral areas of the social system to target influential humans of both groups, mostly bombarding Independentists with negative and violent contents, sustaining and inflating instability in this online society. These results quantify the potential dangerous influence of political bots during voting processes.

[6]  arXiv:1802.07305 [pdf, other]
Title: Comparison of collimated blue light generation in ${}^{85}$Rb atoms via the D${}_1$ and D${}_2$ lines
Comments: 7 pages, 11 figures
Subjects: Atomic Physics (physics.atom-ph); Optics (physics.optics)

We experimentally studied the characteristics of the collimated blue light (CBL) produced in ${}^{85}$Rb vapor by two resonant laser fields exciting atoms into the $5D_{3/2}$ state, using either the $5P_{1/2}$ or the $5P_{3/2}$ intermediate state. We compared the CBL output at different values of frequency detunings, powers, and polarizations of the pump lasers in these two cases, and confirmed the observed trends using a simple theoretical model. We also demonstrated that the addition of the repump laser, preventing the accumulation of atomic population in the uncoupled hyperfine ground state, resulted in nearly an order of magnitude increase in CBL power output. Overall, we found that the $5S_{1/2} - 5P_{1/2} - 5D_{3/2}$ excitation pathway results in stronger CBL generation, as we detected up to $4.25~\mu$W using two pumps of the same linear polarization. The optimum CBL output for the $5S_{1/2} - 5P_{3/2} - 5D_{3/2}$ excitation pathway required the two pump lasers to have the same circular polarization, but resulted only in a maximum CBL power of $450$~nW.

[7]  arXiv:1802.07312 [pdf]
Title: Why are Megaprojects, Including Nuclear Power Plants, Delivered Overbudget and Late? Reasons and Remedies
Journal-ref: Center for Advanced Nuclear Energy Systems (CANES), Massachusetts Institute of Technology, 2018
Subjects: Physics and Society (physics.soc-ph); General Finance (q-fin.GN)

In the first section, this report analyses Nuclear Power Plants (NPPs) in the context of megaprojects, explaining why they are often delivered over budget and late. In the second section, the report discusses how Small Modular Reactors (SMRs) might address these issues. Megaprojects are extremely risky and often implemented after a sub-optimal phase of project planning leading to underestimations of the costs and overestimation of short-term benefits. When considering adherence to schedule and budget, often megaprojects might be considered a failure, and optimism bias, strategic mis-rapresentation, complexity, poor planning, poor risk allocation, poor scope management are all reasons to explain their over budget and delay. For megaprojects, especially in the nuclear field, a key strategy to achieve good performances appears to be the standardization. This standardization needs to be twofold: (i) technical standardisation, i.e. the construction of very similar design over and over, and (ii) the project delivery chain standardisation, i.e. the same stakeholders involved in the delivery of a project that is replicable multiple times. Under this perspective, given their size and standardisation potential, SMRs, might be a suitable class of NPP for several countries. Yet, if the economy of scale is the only driver considered, SMRs are hardly competitive with large NPPs (or even with gas or coal power plants). However, a fleet of standard SMRs might balance the lack of economy of scale with the economy of multiples, and the delivery of several standardised SMR projects might be the key to achieve good project management performances in the nuclear sector. However, the deployment of SMRs faces a number of challenges from several perspectives, such as the licencing, supply chain and financing ones. These challenges might be enormous, but so are the potential rewards too.

[8]  arXiv:1802.07333 [pdf, ps, other]
Title: Modeling of Supersonic Radiative Marshak waves using Simple Models and Advanced Simulations
Comments: 12 pages, 8 figures
Subjects: Computational Physics (physics.comp-ph); Statistical Mechanics (cond-mat.stat-mech); Plasma Physics (physics.plasm-ph)

We study the problem of radiative heat (Marshak) waves using advanced approximate approaches. Supersonic radiative Marshak waves that are propagating into a material are radiation dominated (i.e. hydrodynamic motion is negligible), and can be described mainly by the Boltzmann equation. However, the exact thermal radiative transfer problem is a nontrivial one, and there still exists a need for approximations that are simple to solve. The discontinuous asymptotic $P_1$ approximation, which is a combination of the asymptotic $P_1$ and the discontinuous asymptotic diffusion approximations, was tested in previous work via theoretical benchmarks. Here we analyze a fundamental and typical experiment of a supersonic Marshak wave propagation in a low-density $\mathrm{SiO_2}$ foam cylinder, embedded in gold walls. First, we offer a simple analytic model, that grasps the main effects dominating the physical system. We find the physics governing the system to be dominated by a simple, one-dimensional effect, based on the careful observation of the different radiation temperatures that are involved in the problem. The model is completed with the main two-dimensional effect which is caused by the loss of energy to the gold walls. Second, we examine the validity of the discontinuous asymptotic $P_1$ approximation, comparing to exact simulations with good accuracy. Specifically, the heat front position as a function of the time is reproduced perfectly.

[9]  arXiv:1802.07340 [pdf, other]
Title: Influence of non-linearity of medium on the laser induced filamentation instability in magnetized plasma
Comments: 13 pages 5 figures
Subjects: Plasma Physics (physics.plasm-ph); Optics (physics.optics)

The effects of the non-linearity of the medium on the growth rate of filamentation instability in a magnetized plasma interacting with an intense laser pulse, is investigated. The non-linearity of the medium, modeled by Kerr non-linearity, is an important factor, which determines the rate of instability growth. Sensitivity of the rate of filamentation growth, to the Kerr non-linear coefficient could be adjusted by the external magnetic field and laser intensity.

[10]  arXiv:1802.07349 [pdf, other]
Title: New regime of plasma wake field acceleration in the extreme blowout regime
Authors: David Tsiklauri (Queen Mary University of London)
Comments: submitted for publication, in peer review.arXiv admin note: text overlap with arXiv:1711.09766
Subjects: Plasma Physics (physics.plasm-ph); Accelerator Physics (physics.acc-ph)

Three dimensional particle in cell simulations are used for studying proton driven plasma wake-field acceleration that uses a high-energy proton bunch to drive a plasma wake-field for electron beam acceleration. A new parameter regime was found which generates essentially constant electric field that is three orders magnitudes larger than that of AWAKE design, i.e. of the order of $2 \times 10^{3}$ GV/m. This is achieved in the the extreme blowout regime, when number density of the driving proton bunch exceeds plasma electron number density 100 times.

[11]  arXiv:1802.07353 [pdf, ps, other]
Title: Non-relativistic Arbitrary l-states of Quarkonium through Asymptotic Iteration Method
Subjects: General Physics (physics.gen-ph)

The energy eigenvalues with any l-states and mass of heavy quark- antiquark system (quarkonium) are obtained by using Asymptotic Iteration Method in the view of non-relativistic quantum chromodynamics, in which the quarks are considered as spinless for easiness, and are bounded by Cornell potential. A semi-analytical formula for energy eigenvalues and mass is achieved via the method in scope of the perturbation theory. The accuracy of this formula is checked by comparing the eigenvalues with the ones numerically obtained in this study, and with exact ones in literature. Furthermore, semi-analytical formula is applied to some meson systems for comparing the masses with the experimental data.

[12]  arXiv:1802.07393 [pdf]
Title: A lateral-type spin-photodiode based on Fe/x-AlOx/p-InGaAs junctions with a refracting-facet side window
Comments: 27 pages, 8 figures, 1 appendix
Subjects: Applied Physics (physics.app-ph)

A lateral-type spin-photodiode having a refracting facet on a side edge of the device is proposed and demonstrated at room temperature. The light shed horizontally on the side of the device is refracted and introduced directly into a thin InGaAs active layer under the spin-detecting Fe contact in which spin-polarized carriers are generated and injected into the Fe contact through a crystalline AlOx tunnel barrier. Experiments have been carried out with a circular polarization spectrometry set up, through which helicity-dependent photocurrent component, dI, is obtained with the conversion efficiency F ~ 0.4 %, where F is the ratio between dI and total photocurrent Iph. This value is the highest reported so far for pure lateral-type spin-photodiodes. It is discussed through analysis with a model consisting of drift-diffusion and quantum tunneling equations that a factor that limits the F value is unoccupied spin-polarized density-of-states of Fe in energy region into which spin-polarized electrons in a semiconductor are injected.

[13]  arXiv:1802.07399 [pdf]
Title: Arbitrary helicity control of circularly polarized light from lateral-type spin-polarized light-emitting diodes at room temperature
Subjects: Optics (physics.optics); Applied Physics (physics.app-ph)

We demonstrate arbitrary helicity control of circularly polarized light (CPL) emitted at room temperature from the cleaved side-facet of a lateral-type spin-polarized light-emitting diode (spin-LED) with two ferromagnetic electrodes in an anti-parallel magnetization configuration. Driving alternate currents through the two electrodes results in polarization switching of CPL with frequencies up to 100 kHz. Furthermore, tuning the current density ratio in the two electrodes enables manipulation of the degree of circular polarization. These results demonstrate arbitrary electrical control of polarization with high speed, which is required for the practical use of lateral-type spin-LEDs as monolithic CPL light sources.

[14]  arXiv:1802.07404 [pdf]
Title: Radiative Entropy Analysis of Solar Energy Conversion Systems
Authors: Bolin Liao
Comments: 21 pages, 5 figures
Subjects: Applied Physics (physics.app-ph)

The hotness of the sun and the coldness of the outer space are inexhaustible thermodynamic resources for human beings. From a thermodynamic point of view, any energy conversion systems that receive energy from the sun and/or dissipate energy to the universe are heat engines with photons as the "working fluid" and can be analyzed using the concept of entropy. While entropy analysis provides a particularly convenient way to understand the efficiency limits, it is typically taught in the context of thermodynamic cycles among quasi-equilibrium states and its generalization to solar energy conversion systems running in a continuous and non-equilibrium fashion is not straightforward. In this educational article, we present a few examples to illustrate how the concept of photon entropy, combined with the radiative transfer equation, can be used to analyze the entropy generation processes and the efficiency limits of different solar energy conversion systems. We provide explicit calculations for the local and total entropy generation rates for simple emitters and absorbers, as well as photovoltaic cells, which can be readily reproduced by students. We further discuss the connection between the entropy generation and the device efficiency, particularly the exact spectral matching condition that is shared by infinite-junction photovoltaic cells and reversible thermoelectric materials to approach their theoretical efficiency limit.

[15]  arXiv:1802.07413 [pdf, other]
Title: Dysprosium-doped ZBLAN fiber laser tunable from 2.8 μm to 3.4 μm, pumped at 1.7 μm
Journal-ref: Optics Letters 43, 971 (2018)
Subjects: Optics (physics.optics)

We demonstrate a mid-infrared dysprosium-doped fluoride fiber laser with a continuously tunable output range of 573 nm, pumped by a 1.7 {\mu}m Raman fiber laser. To the best of our knowledge, this represents the largest tuning range achieved to date from any rare-earth-doped fiber laser and, critically, spans the 2.8-3.4 {\mu}m spectral region, which contains absorption resonances of many important functional groups and is uncovered by other rare-earth ions. Output powers up to 170 mW are achieved, with 21% slope efficiency. We also discuss the relative merits of the 1.7 {\mu}m pump scheme, including possible pump excited-state absorption.

[16]  arXiv:1802.07428 [pdf, other]
Title: Writing and Erasing of Temporal Kerr Cavity Solitons via Intensity Modulation of the Cavity Driving Field
Comments: 5 pages, 5 figures
Subjects: Optics (physics.optics)

We experimentally and numerically study the use of intensity modulation for the controlled addressing of temporal Kerr cavity solitons. Using a coherently driven fiber ring resonator, we demonstrate that a single temporally broad intensity modulation pulse applied on the cavity driving field permits systematic and efficient writing and erasing of ultrashort cavity solitons. We use numerical simulations based on the mean-field Lugiato-Lefever model to investigate the addressing dynamics, and present a simple physical description of the underlying physics.

[17]  arXiv:1802.07436 [pdf, other]
Title: Time-resolved optical emission spectroscopic studies of picosecond laser produced Cr plasma
Subjects: Plasma Physics (physics.plasm-ph)

Time-resolved optical emission spectroscopic measurements of a plasma generated by irradiating a Cr target using 60 picosecond (ps) and 300 ps laser pulses is carried out to investigate the variation in the linewidth ($\delta\lambda$) of emission from neutrals and ions for increasing ambient pressures. Measurements ranging from 10$^{-6}$ Torr to 10$^2$ Torr show a distinctly different variation in the $\delta\lambda$ of neutrals (Cr I) compared to that of singly ionized Cr (Cr II), for both irradiations. $\delta\lambda$ increases monotonously with pressure for Cr II, but an oscillation is evident at intermediate pressures for Cr I. This oscillation does not depend on the laser pulse widths used. In spite of the differences in the plasma formation mechanisms, it is experimentally found that there is an optimum intermediate background pressure for which $\delta\lambda$ of neutrals drops to a minimum. Importantly, these results underline the fact that for intermediate pressures, the usual practice of calculating the plasma number density from the $\delta\lambda$ of neutrals needs to be judiciously done, to avoid reaching inaccurate conclusions.

[18]  arXiv:1802.07443 [pdf]
Title: Space Elevator Propulsion with Mechanical Waves
Authors: Mark A. Wessels
Comments: 10 pages, 6 figures
Subjects: Popular Physics (physics.pop-ph)

The current preferred envisioned method for transmitting power to a space elevator climber is a laser/photovoltaic (PV) system. In this, a ground-based laser beam would transmit megawatts of optical power through the atmosphere to an arrangement of PV panels mounted on the ascending climber. Although this technique has been successfully demonstrated in small models, this method will likely suffer from serious shortcomings in a realistic full-scale system, including poor conversion efficiency, obscuration by clouds, and mechanical fragility of the panels. Worse, the PV method provides no means of regenerative energy recovery. Furthermore, the laser would need to operate continuously at multi-megawatt levels for as long as 14 days (the time for the climber to reach geosynchronous altitudes). No such laser has ever been demonstrated.
This paper presents a radical alternative method for propelling a space elevator car: by using the cable to transmit power in the form of transverse mechanical waves propagated on the cable. A ground-based mechanical driving oscillator would excite the waves. Traveling at hypersonic speeds, the waves encounter the climber. This mechanical power is then extracted by an engine in the climber to propel the climber upward. The oscillator may be manifested by a pair of opposing pistons contacting the cable on opposite sides of the cable, near the anchor point. Most importantly, existing engines can easily provide the required amount of power to send a 10 metric-ton car from the ground to geosynchronous altitudes.

[19]  arXiv:1802.07471 [pdf]
Title: Degressive representation of Member States in the European Parliament 2019-2024
Subjects: Physics and Society (physics.soc-ph); History and Overview (math.HO)

Primary law of the European Union demands that the allocation of the seats of the European Parliament between the Member States must obey the principle of degressive proportionality. The principle embodies the political aim that the more populous states agree to be underrepresented in order to allow the less populous states to be better represented. This paper reviews four allocation methods achieving this goal: the Cambridge Compromise, the Power Compromise, the Modified Cambridge Compromise, and the 0.5-DPL Method. After a year of committee deliberations, Parliament decreed on 7 February 2018 an allocation of seats for the 2019 elections that realizes degressive proportionality, but otherwise lacks methodological grounding. The allocation emerged from haggling and bargaining behind closed doors.

[20]  arXiv:1802.07477 [pdf, ps, other]
Title: Shape Dynamics of Freely Falling Droplets
Comments: 2 figures
Subjects: Fluid Dynamics (physics.flu-dyn); Biological Physics (physics.bio-ph)

Oscillating shape motion of a freely falling water droplet has long fascinated and inspired scientists. We propose dynamic non-linear equations for closed, two dimensional surfaces in gravity and apply it to analyze shape dynamics of freely falling water drops. The analytic solutions qualitatively well explain why drops oscillate among prolate/oblate morphologies and display a number of features consistent with experiments.

[21]  arXiv:1802.07480 [pdf, other]
Title: Collective Dynamics of Self-propelled Semiflexible Filaments
Subjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Subcellular Processes (q-bio.SC)

The collective behavior of active semiflexible filaments is studied with a model of tangentially driven self-propelled worm-like chains. The combination of excluded-volume interactions and self-propulsion leads to several distinct dynamic phases as a function of bending rigidity, activity, and aspect ratio of individual filaments. We consider first the case of intermediate filament density. For high-aspect-ratio filaments, we identify a transition with increasing propulsion from a state of free-swimming filaments to a state of spiraled filaments with nearly frozen translational motion. For lower aspect ratios, this gas-of-spirals phase is suppressed with growing density due to filament collisions; instead, filaments form clusters similar to self-propelled rods, as activity increases. Finite bending rigidity strongly effects the dynamics and phase behavior. Flexible filaments form small and transient clusters, while stiffer filaments organize into giant clusters, similarly as self-propelled rods, but with a reentrant phase behavior from giant to smaller clusters as activity becomes large enough to bend the filaments. For high filament densities, we identify a nearly frozen jamming state at low activities, a nematic laning state at intermediate activities, and an active-turbulence state at high activities. The latter state is characterized by a power-law decay of the energy spectrum as a function of wave number. The resulting phase diagrams encapsulate tunable non-equilibrium steady states that can be used in the organization of living matter.

[22]  arXiv:1802.07486 [pdf, other]
Title: Data-Driven Forecasting of High-Dimensional Chaotic Systems with Long-Short Term Memory Networks
Comments: 25 pages
Subjects: Computational Physics (physics.comp-ph); Learning (cs.LG); Chaotic Dynamics (nlin.CD)

We introduce a data-driven forecasting method for high dimensional, chaotic systems using Long-Short Term Memory (LSTM) recurrent neural networks. The proposed LSTM neural networks perform inference of high dimensional dynamical systems in their reduced order space and are shown to be an effective set of non-linear approximators of their attractor. We demonstrate the forecasting performance of the LSTM and compare it with Gaussian processes (GPs) in time series obtained from the Lorenz 96 system, the Kuramoto-Sivashinsky equation and a prototype climate model. The LSTM networks outperform the GPs in short-term forecasting accuracy in all applications considered. A hybrid architecture, extending the LSTM with a mean stochastic model (MSM-LSTM), is proposed to ensure convergence to the invariant measure. This novel hybrid method is fully data-driven and extends the forecasting capabilities of LSTM networks.

[23]  arXiv:1802.07488 [pdf, other]
Title: From jamming to collective cell migration through a boundary induced transition
Comments: 6 figures
Subjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Cell Behavior (q-bio.CB)

Cell monolayers provide an interesting example of active matter, exhibiting a phase transition from a flowing to jammed state as they age. Here we report experiments and numerical simulations illustrating how a jammed cellular layer rapidly reverts to a flowing state after a wound. Quantitative comparison between experiments and simulations shows that cells change their self-propulsion and alignement strength so that the system crosses a phase transition line, which we characterize by finite-size scaling in an active particle model. This wound-induced unjamming transition is found to occur generically in epithelial, endothelial and cancer cells.

[24]  arXiv:1802.07492 [pdf]
Title: Surface texturing of Ti6Al4V alloy using femtosecond laser for superior antibacterial performance
Comments: 21 pages, 10 figures
Subjects: Medical Physics (physics.med-ph)

Titanium and its alloy are most widely used implant materials in dental and orthopaedic fields. However, infections occurring during implantation leads to implant failure in most of the cases. Here, we have demonstrated antibacterial behavior of Ti6Al4V alloy achieved when surface modified using femtosecond laser beam. Post laser treatment conical microstructures were observed on the Ti6Al4V alloy surface. Generation of different sub-oxide phases of titanium dioxide were detected on laser treated samples using X-ray diffraction and X-ray photoelectron spectroscopy. Wettability of Ti6Al4V alloy surface changed significantly after interaction with the laser. Adhesion and growth of two gram positive; Staphylococcus aureus and Streptococcus mutans and one gram negative Pseudomonas aeruginosa bacteria have been explored on pristine, as well as, on laser textured Ti6Al4V alloy surfaces. In-vitro investigation on agar plate showed inhibition of bacterial growth on most of the laser treated surface. Superior surface roughness and occurrence of magneli phases of titanium dioxide on laser treated surface were probably responsible for the antibacterial behavior exhibited by the laser treated samples. Therefore, femtosecond laser surface treatment of Ti6Al4V alloy could find potential application in the development of infection free medical implants for dental and orthopedic usages.

[25]  arXiv:1802.07495 [pdf]
Title: Rapid voltage sensing with single nanorods via the quantum confined Stark effect
Subjects: Applied Physics (physics.app-ph); Optics (physics.optics)

Properly designed colloidal semiconductor quantum dots (QDs) have already been shown to exhibit high sensitivity to external electric fields via the quantum confined Stark effect (QCSE). Yet, detection of the characteristic spectral shifts associated with the effect of QCSE has traditionally been painstakingly slow, dramatically limiting the sensitivity of these QD sensors to fast transients. We experimentally demonstrate a new detection scheme designed at achieving shot-noise limited sensitivity to emission wavelength shifts in QDs, showing feasibility for their use as local electric field sensors on the millisecond time scale. This regime of operation is already potentially suitable for detection of single action potentials in neurons at a high spatial resolution.

[26]  arXiv:1802.07500 [pdf, other]
Title: Passive Decoupling of Two Closely Located Dipole Antennas
Subjects: Applied Physics (physics.app-ph)

In this paper, we prove that two parallel dipole antennas can be decoupled by a similar but passive dipole located in the middle between them. The decoupling is proved for whatever excitation of these antennas and for ultimately small distances between them. Our theoretical model based on the method of induced electromotive forces is validated by numerical simulations and measurements. A good agreement between theory, simulation and measurement proves the veracity of our approach.

[27]  arXiv:1802.07520 [pdf, other]
Title: Synchrotron emission from nanowire-array targets irradiated by ultraintense laser pulses
Subjects: Plasma Physics (physics.plasm-ph)

We present a numerical study, based on two-dimensional particle-in-cell simulations, of the synchrotron emission induced during the interaction of femtosecond laser pulses of intensities $I=10^{21}-10^{23}\,\mathrm{Wcm}^{-2}$ with nanowire arrays. Through an extensive parametric scan on the target parameters, we identify and characterize several dominant radiation mechanisms, mainly depending on the transparency or opacity of the plasma produced by the wire expansion. At $I=10^{22}\,\mathrm{Wcm}^{-2}$, the emission of high-energy ($>10\,\mathrm{keV}$) photons attains a maximum conversion efficiency of $\sim 10\%$ for $36-50\,\mathrm{nm}$ wire widths and $1\,\mu\mathrm{m}$ interspacing. This maximum radiation yield is similar to that achieved in uniform plasma of same average (sub-solid) density, but nanowire arrays provide efficient radiation sources over a broader parameter range. We examine the variations of the photon spectra with the laser intensity and the wire material. Finally, we demonstrate that the radiation efficiency can be further enhanced by adding a plasma mirror at the backside of the nanowire array.

[28]  arXiv:1802.07565 [pdf, ps, other]
Title: Fluctuation Analysis of the Atmospheric Energy Cycle
Comments: 17 pages, 5 figures
Subjects: Atmospheric and Oceanic Physics (physics.ao-ph)

The atmosphere gains available potential energy by solar radiation and dissipates kinetic energy mainly in the atmospheric boundary layer. We analyze the fluctuations of the global mean energy cycle defined by Lorenz (1955) in a simulation with a simplified hydrostatic model. The energy current densities are well approximated by the generalized Gumbel distribution (Bramwell, Holdsworth and Pinton, 1998) and the Generalized Extreme Value (GEV) distribution. In an attempt to assess the fluctuation relation of Evans, Cohen, and Morriss (1993) we define entropy production by the injected power and use the GEV location parameter as a reference state. The fluctuation ratio reveals a linear behavior in a finite range.

[29]  arXiv:1802.07567 [pdf, other]
Title: Measurement of optical to electrical and electrical to optical delays with ps-level uncertainty
Subjects: Optics (physics.optics)

We present a new measurement principle to determine the absolute time delay of a waveform from an optical reference plane to an electrical reference plane and vice versa. We demonstrate a method based on this principle with 2 ps uncertainty. This method can be used to perform accurate time delay determinations of optical transceivers used in fibre-optic time-dissemination equipment. As a result the time scales in optical and electrical domain can be related to each other with the same uncertainty. We expect this method to break new grounds in high-accuracy time transfer and absolute calibration of time-transfer equipment.

[30]  arXiv:1802.07573 [pdf, other]
Title: Asymmetric Cryptography with Physical Unclonable Keys
Comments: 20 pages, 8 figures
Subjects: Optics (physics.optics); Quantum Physics (quant-ph)

Secure communication is of paramount importance in modern society. Asymmetric cryptography methods such as the widely used RSA method allow secure exchange of information between parties who have not shared secret keys. However, the existing asymmetric cryptographic schemes rely on unproven mathematical assumptions for security. Further, the digital keys used in their implementation are susceptible to copying that might remain unnoticed. Here we introduce a secure communication method that overcomes these two limitations by employing Physical Unclonable Keys (PUKs). Using optical PUKs realized in opaque scattering materials and employing off-the-shelf equipment, we transmit messages in an error-corrected way. Information is transmitted as patterned wavefronts of few-photon wavepackets which can be successfully decrypted only with the receiver's PUK. The security of PUK-Enabled Asymmetric Communication (PEAC) is not based on any stored secret but on the hardness of distinguishing between different few-photon wavefronts.

[31]  arXiv:1802.07580 [pdf]
Title: Numerical Investigation on Local Non-equilibrium Flows Using a Diatomic Nonlinear Constitutive Model
Subjects: Fluid Dynamics (physics.flu-dyn); Computational Physics (physics.comp-ph)

The linear Navier-Stokes-Fourier (NSF) constitutive relations are capable of simulating the near-continuum flows, but fail in description of those flows which are removed far away from local equilibrium. In this paper, a diatomic nonlinear model named as nonlinear coupled constitutive relations (NCCR), derived from Eu's generalized hydrodynamics and proposed by Myong, is presented as an alternative for simulating these hypersonic gas flows with a goal of recovering NSF's solutions in continuum regime and being superior in transition regime. To guarantee stable computation, a reliable and efficient coupled algorithm is proposed for this diatomic nonlinear constitutive model. Constitutive-curve analysis is carried out in detail to compare this coupled algorithm with Myong's previous algorithm. Local flow regions are investigated carefully in these hypersonic flows past a cone tip, a hollow cylinder-flare and a HTV-type vehicle. The convergent solutions of NCCR model are compared with NSF, DSMC calculations and experiment. It is demonstrated that the NCCR model works as efficiently as the NSF model in continuum regime, but more accurately compared with DSMC and experiment than NSF in non-equilibrium flows. The discrepancies of flow- field and surface parameters, imply a potential for remedying NSF's deficiency in local non-equilibrium regions.

[32]  arXiv:1802.07582 [pdf, other]
Title: Axisymmetric inertial modes in a spherical shell at low Ekman numbers
Comments: 38 pages, 25 figures, to appear in J. Fluid Mechanics
Subjects: Fluid Dynamics (physics.flu-dyn); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We investigate the asymptotic properties of axisymmetric inertial modes propagating in a spherical shell when viscosity tends to zero. We identify three kinds of eigenmodes whose eigenvalues follow very different laws as the Ekman number $E$ becomes very small. First are modes associated with attractors of characteristics that are made of thin shear layers closely following the periodic orbit traced by the characteristic attractor. Second are modes made of shear layers that connect the critical latitude singularities of the two hemispheres of the inner boundary of the spherical shell. Third are quasi-regular modes associated with the frequency of neutral periodic orbits of characteristics. We thoroughly analyse a subset of attractor modes for which numerical solutions point to an asymptotic law governing the eigenvalues. We show that three length scales proportional to $E^{1/6}$, $E^{1/4}$ and $E^{1/3}$ control the shape of the shear layers that are associated with these modes. These scales point out the key role of the small parameter $E^{1/12}$ in these oscillatory flows. With a simplified model of the viscous Poincar\'e equation, we can give an approximate analytical formula that reproduces the velocity field in such shear layers. Finally, we also present an analysis of the quasi-regular modes whose frequencies are close to $\sin(\pi/4)$ and explain why a fluid inside a spherical shell cannot respond to any periodic forcing at this frequency when viscosity vanishes.

[33]  arXiv:1802.07583 [pdf]
Title: Time-series analysis of fissure-fed multi-vent activity: a snapshot from the July 2014 eruption of Etna volcano (Italy)
Comments: 10 figures
Journal-ref: Bull Volcanol (2017) 79: 51
Subjects: Geophysics (physics.geo-ph)

On 5 July 2014, an eruptive fissure opened on the eastern flank of Etna volcano (Italy) at ~3.000 m a.s.l. Strombolian activity and lava effusion occurred simultaneously at two neighbouring vents. In the following weeks, eruptive activity led to the build-up of two cones, tens of meters high, here named Crater N and Crater S. To characterize the short-term (days) dynamics of this multi-vent system, we performed a multi-parametric investigation by means of a dense instrumental network. The experimental setup, deployed on July 15-16th at ca. 300 m from the eruption site, comprised two broadband seismometers and three microphones as well as high speed video and thermal cameras. Thermal analyses enabled us to characterize the style of eruptive activity at each vent. In particular, explosive activity at Crater N featured higher thermal amplitudes and a lower explosion frequency than at Crater S. Several episodes of switching between puffing and Strombolian activity were noted at Crater S through both visual observation and thermal data; oppositely, Crater N exhibited a quasi-periodic activity. The quantification of the eruptive style of each vent enabled us to infer the geometry of the eruptive system: a branched conduit, prone to rapid changes of gas flux accommodated at the most inclined conduit (i.e. Crater S). Accordingly, we were able to correctly interpret acoustic data and thereby extend the characterization of this twovent system.

[34]  arXiv:1802.07599 [pdf]
Title: Graphene-enabled, directed nanomaterial placement from solution for large-scale device integration
Comments: 17 pages, 5 figures
Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Controlled placement of nanomaterials at predefined locations with nanoscale precision remains among the most challenging problems that inhibit their large-scale integration in the field of semiconductor process technology. Methods based on surface functionalization have a drawback where undesired chemical modifications can occur and deteriorate the deposited material. The application of electric-field assisted placement techniques eliminates the element of chemical treatment; however, it requires an incorporation of conductive placement electrodes that limit the performance, scaling, and density of integrated electronic devices. Here, we report a method for electric-field assisted placement of solution-processed nanomaterials by using large-scale graphene layers featuring nanoscale deposition sites. The structured graphene layers are prepared via either transfer or synthesis on standard substrates, then are removed without residue once nanomaterial deposition is completed, yielding material assemblies with nanoscale resolution that cover surface areas larger than 1mm2. In order to demonstrate the broad applicability, we have assembled representative zero-, one-, and two-dimensional semiconductors at predefined substrate locations and integrated them into nanoelectronic devices. This graphene-based placement technique affords nanoscale resolution at wafer scale, and could enable mass manufacturing of nanoelectronics and optoelectronics involving a wide range of nanomaterials prepared via solution-based approaches.

[35]  arXiv:1802.07602 [pdf, other]
Title: Wake of inertial waves of a horizontal cylinder in horizontal translation
Comments: Accepted for publication in Physical Review Fluids
Subjects: Fluid Dynamics (physics.flu-dyn); Geophysics (physics.geo-ph)

We analyze theoretically and experimentally the wake behind a horizontal cylinder of diameter $d$ horizontally translated at constant velocity $U$ in a fluid rotating about the vertical axis at a rate $\Omega$. Using particle image velocimetry measurements in the rotating frame, we show that the wake is stabilized by rotation for Reynolds number ${\rm Re}=Ud/\nu$ much larger than in a non-rotating fluid. Over the explored range of parameters, the limit of stability is ${\rm Re} \simeq (275 \pm 25) / {\rm Ro}$, with ${\rm Ro}=U/2\Omega d$ the Rossby number, indicating that the stabilizing process is governed by the Ekman pumping in the boundary layer. At low Rossby number, the wake takes the form of a stationary pattern of inertial waves, similar to the wake of surface gravity waves behind a ship. We compare this steady wake pattern to a model, originally developed by [Johnson, J. Fluid Mech. 120, 359 (1982)], assuming a free-slip boundary condition and a weak streamwise perturbation. Our measurements show a quantitative agreement with this model for ${\rm Ro}\lesssim 0.3$. At larger Rossby number, the phase pattern of the wake is close to the prediction for an infinitely small line object. However, the wake amplitude and phase origin are not correctly described by the weak-streamwise-perturbation model, calling for an alternative model for the boundary condition at moderate rotation rate.

[36]  arXiv:1802.07603 [pdf, other]
Title: RichMol: A general variational approach for rovibrational molecular dynamics in external electric fields
Subjects: Chemical Physics (physics.chem-ph)

A general variational approach for computing the rovibrational dynamics of polyatomic molecules in the presence of external electric fields is presented. Highly accurate, full-dimensional variational calculations provide a basis of field-free rovibrational states for evaluating the rovibrational matrix elements of high-rank Cartesian tensor operators, and for solving the time-dependent Schr\"odinger equation. The effect of the external electric field is treated as a multipole moment expansion truncated at the second hyperpolarizability interaction term. Our fully numerical and computationally efficient method has been implemented in a new program, RichMol, which can simulate the effects of multiple external fields of arbitrary strength, polarization, pulse shape and duration. Illustrative calculations of two-color orientation and rotational excitation with an optical centrifuge of NH$_3$ are discussed.

[37]  arXiv:1802.07630 [pdf, other]
Title: Diffractive shear interferometry for extreme ultraviolet high-resolution lensless imaging
Subjects: Optics (physics.optics)

We demonstrate a novel imaging approach and associated reconstruction algorithm for far-field coherent diffractive imaging, based on the measurement of a pair of laterally sheared diffraction patterns. The differential phase profile retrieved from such a measurement leads to improved reconstruction accuracy, increased robustness against noise, and faster convergence compared to traditional coherent diffractive imaging methods. We measure laterally sheared diffraction patterns using Fourier-transform spectroscopy with two phase-locked pulse pairs from a high harmonic source. Using this approach, we demonstrate spectrally resolved imaging at extreme ultraviolet wavelengths between 28 and 35 nm.

[38]  arXiv:1802.07638 [pdf, ps, other]
Title: Theoretical Modeling of KHz to THz Simultaneous Energy Harvesting and Magneto-Inductive Communications with Molecular Magnets on Vibrating Graphene
Authors: Burhan Gulbahar
Comments: 18 pages, 11 figures, 3 tables
Subjects: Applied Physics (physics.app-ph); Medical Physics (physics.med-ph)

Magneto-inductive (MI) THz wireless communications is recently shown to provide significant theoretical performances for nanoscale applications with microscale transceivers and microwatt transmission powers. The energy harvesting (EH) based generation of carrier signals for MI transceivers is critical for the autonomous and noninvasive operation. State-of-the-art electromagnetic (EM) vibrational devices have millimeter dimensions while targeting only low frequency EH without any real-time communications purpose. In this article, graphene nanoscale resonators are combined with single molecular magnets (SMMs) to realize a simultaneous EH and MI transceiver by exploiting the unique advantages of graphene such as atomic thickness, ultra-low weight, high strain and the resonance frequencies reaching THz with the high magnetic moment of Terbium(III) bis(phthalocyanine) ($\mbox{TbPc}_2$) SMM. The special low complexity design is improved by novel modulation methods achieving simultaneous wireless information and power transfer (SWIPT). The numerical simulations provide tens of nanowatt powers and efficiencies of $10^4 \, W/m^3$ in acoustic and ultrasound frequencies comparable with state-of-the-art vibrational EH devices while millimeter wave carrier generation is numerically simulated. The proposed design presents a practical framework for nanoscale communications including cellular tracking.

[39]  arXiv:1802.07656 [pdf]
Title: Effects of CO2 flushing on crystal textures and compositions: experimental evidence from recent K trachybasalts erupted at Mt. Etna
Subjects: Geophysics (physics.geo-ph)

Changes in magmatic assemblages and crystal stability as a response of CO2 flushing in basaltic systems have been never directly addressed experimentally, making the role of CO2 in magma dynamics still controversial and object of scientific debate. We conducted a series of experiments to understand the response of magmas from Etna volcano to CO2 flushing. We performed a first experiment at 300 MPa to synthesize a starting material composed of crystals of some hundreds of m and melt pools. This material is representative of an initial magmatic assemblage composed of plagioclase, clinopyroxene and a water undersaturated melt. In a second step, the initial assemblage was equilibrated at 300 and 100 MPa with fluids having different XCO2fl . Our experiments demonstrate that flushing basaltic systems with fluids may drastically affect crystal textures and phase equilibria depending on the amount of H2O and CO2 in the fluid phase. Since texture and crystal proportions are among the most important parameters governing the rheology of magmas, fluid flushing will also influence magma ascent to the Earths surface. The experimental results open new perspectives to decipher the textural and compositional record of minerals observed in volcanic rocks from Mt. Etna, and at the same time offer the basis for interpreting the information preserved in minerals from other basaltic volcanoes erupting magmas enriched in CO2.

[40]  arXiv:1802.07659 [pdf, ps, other]
Title: 3D modelling of self-organized patterns of spots on anodes of DC glow discharge
Subjects: Plasma Physics (physics.plasm-ph)

Self-organized patterns of spots on a at metallic anode in a cylindrical glow dis- charge tube are simulated self-consistently. A standard model of a glow discharge is used, comprising conservation and transport equations for a single species of ion and electrons, written with the use of the drift-diffusion and local-field approximations, and the Poisson equation. The computation domain is the region from the anode to the discharge column; only processes in the near-anode region are considered. Multiple solutions, existing in the same range of discharge current and describing modes with and without anode spots, are computed by means of a stationary solver. The computed spots exhibited unexpected behavior. A reversal of the local anode current density in the middle of each of the spots was found, i.e. mini-cathodes are formed inside the spots. The solutions do not fit into the conventional pattern of self-organization in bistable nonlinear dissipative systems; e.g. the modes are not joined by bifurcations.

[41]  arXiv:1802.07664 [pdf, ps, other]
Title: Robustness of flow networks against cascading failures under partial load redistribution
Subjects: Physics and Society (physics.soc-ph)

We study the robustness of flow networks against cascading failures under a partial load redistribution model. In particular, we consider a flow network of $N$ lines with initial loads $L_1, \ldots, L_N$ and free-spaces $S_1, \ldots, S_N$ that are independent and identically distributed with joint distribution $P_{LS}(x,y)=P(L \leq x, S \leq y)$. The capacity $C_i$ is the maximum load allowed on line $i$, and is given by $C_i=L_i + S_i$. When a line fails due to overloading, it is removed from the system and $(1-\varepsilon)$-fraction of the load it was carrying (at the moment of failing) gets redistributed equally among all remaining lines in the system; hence we refer to this as the partial load redistribution model. The rest (i.e., $\varepsilon$-fraction) of the load is assumed to be lost or absorbed, e.g., due to advanced circuitry disconnecting overloaded power lines or an inter-connected network/material absorbing a fraction of the flow from overloaded lines. We analyze the robustness of this flow network against random attacks that remove a $p$-fraction of the lines. Our contributions include (i) deriving the final fraction of alive lines $n_{\infty}(p,\varepsilon)$ for all $p, \varepsilon \in (0,1)$ and confirming the results via extensive simulations; (ii) showing that partial redistribution might lead to (depending on the parameter $0<\varepsilon \leq 1$) the order of transition at the critical attack size $p^{*}$ changing from first to second-order; and (iii) proving analytically that the widely used robustness metric measuring the area $\int_{0}^{1} n_{\infty}(p,\varepsilon) \mathrm{d}p$ is maximized when all lines have the same free-space regardless of their initial load.

[42]  arXiv:1802.07671 [pdf, ps, other]
Title: Stokes waves with constant vorticity: I. numerical computation
Subjects: Fluid Dynamics (physics.flu-dyn)

Periodic traveling waves are numerically computed in a constant vorticity flow subject to the force of gravity. The Stokes wave problem is formulated via a conformal mapping as a nonlinear pseudo-differential equation, involving a periodic Hilbert transform for a strip, and solved by the Newton-GMRES method. It works well with a fast Fourier transform and is more effective than a boundary integral method. The result is in excellent agreement, qualitatively and quantitatively, with earlier ones.
For strong positive vorticity, in the finite or infinite depth, overhanging profiles are found as the steepness increases and tend to a touching wave, whose profile self-intersects somewhere along the trough line, trapping an air bubble; the numerical solutions become unphysical as the steepness increases further and make a gap in the wave speed versus steepness plane; a touching wave then takes over and the physical solutions follow in the wave speed versus steepness plane until they ultimately tend to an extreme wave, which exhibits a sharp corner at the crest. Overhanging waves of nearly maximum heights are found to approach rigid body rotation of a fluid disk as the strength of positive vorticity increases.

[43]  arXiv:1802.07674 [pdf, other]
Title: Odd-time reversal $PT$ symmetry induced by anti-$PT$-symmetric medium
Comments: 5 pages + Supplemental Material; 4 figures; accepted for Phys. Rev. Lett
Subjects: Optics (physics.optics); Pattern Formation and Solitons (nlin.PS)

We introduce an optical system (a coupler) obeying parity-time ($PT$) symmetry with odd-time reversal, $T^2=-1$. It is implemented with two birefringent waveguides embedded in an anti-$PT$-symmetric medium. The system possesses properties which are untypical for most physical systems with the conventional even-time reversal. Having symmetry-protected degeneracy of the linear modes, the coupler allows for realization of a coherent switch operating with a superposition of binary states which are distinguished by their polarizations. When a Kerr nonlinearity is taken into account, each linear state, being double degenerated, bifurcates into several distinct nonlinear modes, some of which are dynamically stable. The nonlinear modes are characterized by amplitude and by polarization and come in $PT$-conjugate pairs.

[44]  arXiv:1802.07679 [pdf, other]
Title: The STELLA Apparatus for Particle-Gamma Coincidence Fusion Measurements with Nanosecond Timing
Comments: 18 pages, 11 figures
Subjects: Instrumentation and Detectors (physics.ins-det)

The STELLA (STELlar LAboratory) experimental station for the measurement of deep sub-barrier light heavy-ion fusion cross sections has been installed at the Androm\`{e}de accelerator at the Institut de Physique Nucl\'{e}aire, Orsay (France). The setup is designed for the direct experimental determination of heavy-ion fusion cross sections as low as tens of picobarn. The detection concept is based on the coincident measurement of emitted gamma rays with the UK FATIMA (FAst TIMing Array) and evaporated charged particles using a silicon detector array. Key developments relevant to reaching the extreme sub-barrier fusion region are a rotating target mechanism to sustain beam intensities above 10$\mu$A, an ultra-high vacuum to prevent carbon built-up and gamma charged-particle timing in the order of nanoseconds sufficient to separate proton and alpha particles.

[45]  arXiv:1802.07719 [pdf, other]
Title: Unlimited Accumulation of Electromagnetic Energy Using Time-Varying Reactive Elements
Subjects: Applied Physics (physics.app-ph)

Accumulation of energy by reactive elements is limited by the amplitude of time-harmonic external sources. In the steady-state regime, all incident power is fully reflected back to the source, and the stored energy does not increase in time, although the external source continuously supplies energy. Here, we show that this claim is not true if the reactive element is time-varying, and time-varying lossless loads of a transmission line or lossless metasurfaces can accumulate electromagnetic energy supplied by a time-harmonic source continuously in time without any theoretical limit. We analytically derive the required time dependence of the load reactance and show that it can be in principle realized as a series connection of mixers and filters. Furthermore, we prove that properly designing time-varying LC circuits one can arbitrarily engineer the time dependence of the current in the circuit fed by a given time-harmonic source. As an example, we theoretically demonstrate a circuit with a linearly increasing current through the inductor. Such LC circuits can accumulate huge energy from both the time-harmonic external source and the pump which works on varying the circuit elements in time. Finally, we discuss how this stored energy can be released in form of a time-compressed pulse.

Cross-lists for Thu, 22 Feb 18

[46]  arXiv:1802.06815 (cross-list from cond-mat.quant-gas) [pdf, other]
Title: Floquet engineering of optical solenoids and quantized charge pumping along tailored paths in two-dimensional Chern insulators
Comments: 6 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

The insertion of a local magnetic flux, as the one created by a thin solenoid, plays an important role in gedanken experiments of quantum Hall physics. By combining Floquet engineering of artificial magnetic fields with the ability of single-site addressing in quantum-gas microscopes, we propose a scheme for the realization of such local solenoid-type magnetic fields in optical lattices. We show that it can be employed to manipulate and probe elementary excitations of a topological Chern insulator. This includes quantized adiabatic charge pumping along tailored paths inside the bulk, as well as the controlled population of edge modes.

[47]  arXiv:1802.07402 (cross-list from quant-ph) [pdf, other]
Title: Microwave device characterisation using a widefield diamond microscope
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)

Devices relying on microwave circuitry form a cornerstone of many classical and emerging quantum technologies. A capability to provide in-situ, noninvasive and direct imaging of the microwave fields above such devices would be a powerful tool for their function and failure analysis. In this work, we build on recent achievements in magnetometry using ensembles of nitrogen vacancy centres in diamond, to present a widefield microwave microscope with few-micron resolution over a millimeter-scale field of view, 130nT/sqrt-Hz microwave amplitude sensitivity, a dynamic range of 48 dB, and sub-ms temporal resolution. We use our microscope to image the microwave field a few microns above a range of microwave circuitry components, and to characterise a novel atom chip design. Our results open the way to high-throughput characterisation and debugging of complex, multi-component microwave devices, including real-time exploration of device operation.

[48]  arXiv:1802.07409 (cross-list from cond-mat.stat-mech) [pdf, other]
Title: Metastable state en route to traveling-wave synchronization state
Authors: Jinha Park, B. Kahng
Journal-ref: Phys. Rev. E 97, 020203(R) (2018)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Chaotic Dynamics (nlin.CD); Biological Physics (physics.bio-ph)

The Kuramoto model with mixed signs of couplings is known to produce a traveling-wave synchronized state. Here, we consider an abrupt synchronization transition from the incoherent state to the traveling-wave state through a long-lasting metastable state with large fluctuations. Our explanation of the metastability is that the dynamic flow remains within a limited region of phase space and circulates through a few active states bounded by saddle and stable fixed points. This complex flow generates a long-lasting critical behavior, a signature of a hybrid phase transition. We show that the long-lasting period can be controlled by varying the density of inhibitory/excitatory interactions. We discuss a potential application of this transition behavior to the recovery process of human consciousness.

[49]  arXiv:1802.07507 (cross-list from hep-ph) [pdf, ps, other]
Title: Electron-seeded ALP production and ALP decay in an oscillating electromagnetic field
Authors: B. King
Comments: 7 pages, 4 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); Optics (physics.optics); Plasma Physics (physics.plasm-ph)

Certain models involving ALPs (axion-like-particles) allow for the coupling of scalars and pseudoscalars to fermions. A derivation of the total rate for production of massive scalars and pseudoscalars by an electron in a monochromatic, circularly-polarised electromagnetic background is presented. In addition, a derivation and the total rate for the decay of massive scalars and pseudoscalars into electron-positron pairs in the same electromagnetic background is given. We conclude by approximating the total yield of ALP production for a typical laser-particle experimental scenario.

[50]  arXiv:1802.07540 (cross-list from math.NA) [pdf, other]
Title: Operator splitting technique using streamline projection for two-phase flow in highly heterogeneous and anisotropic porous media
Subjects: Numerical Analysis (math.NA); Computational Physics (physics.comp-ph)

In this paper, we present a fast streamline-based numerical method for the two-phase flow equations in high-rate flooding scenarios for incompressible fluids in heterogeneous and anisotropic porous media. A fractional flow formulation is adopted and a discontinuous Galerkin method (DG) is employed to solve the pressure equation. Capillary effects can be neglected in high-rate flooding scenarios. This allows us to present an improved streamline approach in combination with the one-dimensional front tracking method to solve the transport equation. To handle the high computational costs of the DG approximation, domain decomposition is applied combined with an algebraic multigrid preconditioner to solve the linear system. Special care at the interior interfaces is required and the streamline tracer has to include a dynamic communication strategy. The method is validated in various two- and three-dimensional tests, where comparisons of the solutions in terms of approximation of flow front propagation with standard fully-implicit finite volume methods are provided.

[51]  arXiv:1802.07549 (cross-list from astro-ph.HE) [pdf, ps, other]
Title: Evolution of 3-dimensional Relativistic Current Sheets and Development of Self-Generated Turbulence
Authors: Makoto Takamoto
Comments: 9 pages, 10 figures, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph)

In this paper, the temporal evolution of 3-dimensional relativistic current sheets in Poynting-dominated plasma is studied for the first time. Over the past few decades, a lot of efforts have been conducted on studying the evolution of current sheets in 2-dimensional space, and concluded that sufficiently long current sheets always evolves into the so-called "plasmoid-chain", which provides fast reconnection rate independent of its resistivity. However, it is suspected that plasmoid-chain can exist only in the case of 2-dimensional approximation, and would show transition to turbulence in 3-dimensional space.
We performed 3-dimensional numerical simulation of relativistic current sheet using resistive relativistic magnetohydrodynamic approximation. The results showed that the 3-dimensional current sheet evolve not into plasmoid-chain but turbulence. The resulting reconnection rate is $0.004$ which is much smaller than that of plasmoid-chain. The energy conversion from magnetic field to kinetic energy of turbulence is just 0.01\% which is much smaller than typical non-relativistic cases. Using the energy principle, we also showed that the plasmoid is always unstable for a displacement in opposite direction to its acceleration, probably interchange-type instability, and this always results in seeds of turbulence behind the plasmoids. Finally, the temperature distribution along the sheet is discussed, and it is found that the sheet is less active than plasmoid-chain. Our finding can be applied for many high energy astrophysical phenomena, and can provide a basic model of the general current sheet in Poynting-dominated plasma.

[52]  arXiv:1802.07643 (cross-list from math.AP) [pdf, other]
Title: Floating structures in shallow water: local well-posedness in the axisymmetric case
Authors: Edoardo Bocchi (IMB)
Subjects: Analysis of PDEs (math.AP); Atmospheric and Oceanic Physics (physics.ao-ph); Fluid Dynamics (physics.flu-dyn)

The floating structure problem describes the interaction between surface water waves and a floating body, generally a boat or a wave energy converter. As shown by Lannes in [18] the equations for the fluid motion can be reduced to a set of two evolution equations on the surface elevation and the horizontal discharge. The presence of the object is accounted for by a constraint on the discharge under the object; the pressure exerted by the fluid on this object is then the Lagrange multiplier associated to this constraint. Our goal in this paper is to prove the well-posedness of this fluid-structure interaction problem in the shallow water approximation under the assumption that the flow is axisymmetric without swirl. We write the fluid equations as a quasilinear hyperbolic mixed initial boundary value problem and the solid equation as a second order ODE coupled to the fluid equations. Finally we prove the local in time well-posedness for this coupled problem, provided some compatibility conditions on the initial data are satisfied.

[53]  arXiv:1802.07684 (cross-list from math.NA) [pdf, other]
Title: Multiscale finite elements through advection-induced coordinates for transient advection-diffusion equations
Comments: 26 pages, 13 figures, 6 tables
Subjects: Numerical Analysis (math.NA); Data Structures and Algorithms (cs.DS); Computational Physics (physics.comp-ph)

Long simulation times in climate sciences typically require coarse grids due to computational constraints. Nonetheless, unresolved subscale information significantly influences the prognostic variables and can not be neglected for reliable long term simulations. This is typically done via parametrizations but their coupling to the coarse grid variables often involves simple heuristics. We explore a novel up-scaling approach inspired by multi-scale finite element methods. These methods are well established in porous media applications, where mostly stationary or quasi stationary situations prevail. In advection-dominated problems arising in climate simulations the approach needs to be adjusted. We do so by performing coordinate transforms that make the effect of transport milder in the vicinity of coarse element boundaries. The idea of our method is quite general and we demonstrate it as a proof-of-concept on a one-dimensional passive advection-diffusion equation with oscillatory background velocity and diffusion.

Replacements for Thu, 22 Feb 18

[54]  arXiv:1601.07750 (replaced) [pdf, ps, other]
Title: Identification and acceptation of macroscopic magnetism energy levels results in better understanding of the linkages between the traditional theory with quantum electrodynamics and revelation of the limited validity of the Faraday's Law
Comments: We remove the myth of modern electrodynamics that solving Faraday's homopolar generator (FHG) could exist independently of brushes and electronic elements using a homogenised magnetic field. 10 pages, 10 figures, this https URL, this https URL, this http URL
Subjects: Classical Physics (physics.class-ph)
[55]  arXiv:1608.03976 (replaced) [pdf]
Title: Topological transport of sound mediated by spin-redirection geometric phase
Comments: 26 pages, 8 figures
Journal-ref: Sci. Adv. 4, eaaq1475 (2018)
Subjects: Classical Physics (physics.class-ph); Optics (physics.optics)
[56]  arXiv:1703.08833 (replaced) [pdf, ps, other]
Title: Subdiffraction incoherent optical imaging via spatial-mode demultiplexing: semiclassical treatment
Authors: Mankei Tsang
Comments: 20 pages, 8 figures, 1 table. v5: same as the accepted version except Appendix C, which is much simplified here---the simplification was discovered too late to be included in the published version
Journal-ref: Physical Review A 97, 023830 (2018)
Subjects: Optics (physics.optics)
[57]  arXiv:1704.07779 (replaced) [pdf, ps, other]
Title: Disparities of Larmor's/Liénard's formulations with special relativity and energy-momentum conservation
Authors: Ashok K. Singal
Comments: 8 pages, 1 figure
Subjects: General Physics (physics.gen-ph)
[58]  arXiv:1706.06321 (replaced) [pdf, other]
Title: Rapid decay in the relative efficiency of quarantine to halt epidemics in networks
Comments: 10 pages, 7 figures
Journal-ref: Phys. Rev. E 97, 022308 (2018)
Subjects: Physics and Society (physics.soc-ph); Populations and Evolution (q-bio.PE)
[59]  arXiv:1706.09844 (replaced) [pdf]
Title: Optimization and Testing of a novel Photoacoustic Spectromicroscopy Cell in the Mid-IR Spectrum
Subjects: Instrumentation and Detectors (physics.ins-det)
[60]  arXiv:1707.08131 (replaced) [pdf, other]
Title: Signal tracking beyond the time resolution of an atomic sensor by Kalman filtering
Comments: 15 pages, 4 figures
Journal-ref: Phys. Rev. Lett. 120, 040503 (2018)
Subjects: Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph); Instrumentation and Detectors (physics.ins-det)
[61]  arXiv:1708.06505 (replaced) [pdf, ps, other]
Title: Imaging Spectroscopy of Solar Radio Burst Fine Structures
Comments: 20 pages, 9 figures
Journal-ref: Nature Communications 8, Article number: 1515 (2017)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); Plasma Physics (physics.plasm-ph); Space Physics (physics.space-ph)
[62]  arXiv:1708.07410 (replaced) [pdf, ps, other]
Title: Fermion inter-particle potentials in 5D and a dimensional restriction prescription to 4D
Comments: In this version, new comments and results have been added in Sections IV, V and Concluding Comments. To be published in Phys. Rev. D
Subjects: General Physics (physics.gen-ph); High Energy Physics - Theory (hep-th)
[63]  arXiv:1708.07508 (replaced) [pdf, other]
Title: Which spike train distance is most suitable for distinguishing rate and temporal coding?
Comments: 14 pages, 6 Figures, 1 Table
Subjects: Neurons and Cognition (q-bio.NC); Data Analysis, Statistics and Probability (physics.data-an)
[64]  arXiv:1708.08324 (replaced) [pdf, ps, other]
Title: Rainbow gravity corrections to the entropic force
Comments: 8 pages
Subjects: General Physics (physics.gen-ph); High Energy Physics - Theory (hep-th)
[65]  arXiv:1708.08556 (replaced) [pdf, other]
Title: Modeling flow and transport in fracture networks using graphs
Comments: 11 pages, 10 figures, 2 tables
Subjects: Computational Physics (physics.comp-ph)
[66]  arXiv:1709.07054 (replaced) [pdf, other]
Title: Effective description of anisotropic wave dispersion in mechanical band-gap metamaterials via the relaxed micromorphic model
Comments: 46 pages, 14 figures
Subjects: Applied Physics (physics.app-ph)
[67]  arXiv:1709.10026 (replaced) [pdf]
Title: Optimization and Performance of Bifacial Solar Modules: A Global Perspective
Subjects: Applied Physics (physics.app-ph); Optics (physics.optics)
[68]  arXiv:1710.08037 (replaced) [pdf]
Title: Phase Locking Value revisited: teaching new tricks to an old dog
Subjects: Signal Processing (eess.SP); Chaotic Dynamics (nlin.CD); Data Analysis, Statistics and Probability (physics.data-an); Neurons and Cognition (q-bio.NC)
[69]  arXiv:1710.09559 (replaced) [pdf, other]
Title: From global scaling to the dynamics of individual cities
Comments: Revised version 8 pages, 9 figures+5 pages of Supp. Information. Accepted for publication in PNAS
Subjects: Physics and Society (physics.soc-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
[70]  arXiv:1711.01679 (replaced) [pdf, other]
Title: SIR-Hawkes: Linking Epidemic Models and Hawkes Processes to Model Diffusions in Finite Populations
Journal-ref: Proceedings of WWW 2018
Subjects: Social and Information Networks (cs.SI); Physics and Society (physics.soc-ph)
[71]  arXiv:1711.04580 (replaced) [pdf, other]
Title: Turbulence appearance and non-appearance in thin fluid layers
Comments: Main text: 4 pages with 5 figures; Supplemental information: 5 pages with 6 figures
Subjects: Fluid Dynamics (physics.flu-dyn)
[72]  arXiv:1712.04439 (replaced) [pdf, other]
Title: Two-level Chebyshev filter based complementary subspace method: pushing the envelope of large-scale electronic structure calculations
Comments: Resubmitted version (version 2)
Subjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
[73]  arXiv:1712.04442 (replaced) [pdf]
Title: Capacitor-within-Capacitor: Electrically Controlled Capacitors
Authors: Haim Grebel
Comments: 11 pages,11 figures, 1 table
Subjects: General Physics (physics.gen-ph)
[74]  arXiv:1712.04829 (replaced) [pdf, ps, other]
Title: Localization of multilayer networks by the optimized single-layer rewiring
Comments: 10 pages, 8 figures
Subjects: Signal Processing (eess.SP); Adaptation and Self-Organizing Systems (nlin.AO); Physics and Society (physics.soc-ph)
[75]  arXiv:1801.01358 (replaced) [pdf, ps, other]
Title: Budden's Paradox Resolved
Authors: J. A. Grzesik
Comments: version i: Budden's energy nonconservation paradox is dispelled herein along truly elementary analytic lines in slightly under three double column pages; version ii: no changes whatsoever have been made as to analytic content, but several overly florid locutions have been reluctantly purged so as not to unduly alarm uptight scientific types
Subjects: General Physics (physics.gen-ph); Classical Analysis and ODEs (math.CA)
[76]  arXiv:1801.03471 (replaced) [pdf, other]
Title: Rapid calculation of maximum particle lifetime for diffusion in complex geometries
Comments: 10 pages, 1 figure
Subjects: Biological Physics (physics.bio-ph); Computational Physics (physics.comp-ph)
[77]  arXiv:1801.09233 (replaced) [pdf, other]
Title: Random matrix approach to plasmon resonances in the random impedance network model of disordered nanocomposites
Comments: 6 pages, 3 figures; References added
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
[78]  arXiv:1802.03588 (replaced) [pdf, other]
Title: Single SiV$^-$ centers in low-strain nanodiamonds with bulk-like spectral properties and nano-manipulation capabilities
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics); Quantum Physics (quant-ph)
[79]  arXiv:1802.04952 (replaced) [pdf, other]
Title: Spin-state ice in geometrically frustrated spin-crossover materials
Comments: The scale on the right-hand side of Fig. 4b was incorrect. This has been corrected. No other changes from v1
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
[80]  arXiv:1802.05112 (replaced) [pdf]
Title: Estimating Un-propped Fracture Conductivity and Fracture Compliance from Diagnostic Fracture Injection Tests
Comments: arXiv admin note: substantial text overlap with arXiv:1710.06464
Subjects: Geophysics (physics.geo-ph)
[81]  arXiv:1802.06721 (replaced) [pdf, ps, other]
Title: Segregation in Religion Networks
Comments: 11 pages, 2 figures
Subjects: Physics and Society (physics.soc-ph); Social and Information Networks (cs.SI)
[82]  arXiv:1802.06729 (replaced) [pdf, ps, other]
Title: Analytical model of a 3D beam dynamics in a wakefield device
Comments: 5 pages, 3 figures
Subjects: Accelerator Physics (physics.acc-ph)
[83]  arXiv:1802.07014 (replaced) [pdf, ps, other]
Title: Electromechanical coupling of waves in nerve fibres
Subjects: Biological Physics (physics.bio-ph); Numerical Analysis (math.NA)
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