bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure of the near-wall layer of filtration-induced colloidal assembly
Authors: Mokrane Mohand Larbi , Desclaux Térence , Morris Jeffrey F. , Joseph Pierre , Liot Olivier
Published: September 2020

A colloidal suspension clogs model pores. Microstructure of the near-wall layer of colloids is studied. That reveals a transition inside the clog from amorphous to crystalline organisation. It can be related to a competition between drag forces and electrostatic repulsion.
Effects of Stimulus Repetition Rates on the Auditory Brainstem Response to Level-Specific CE-Chirp in Normal-Hearing Adults
Authors: Dzulkarnain Ahmad Aidil Arafat , Shahrudin Fatin Amira , Jamal Fatin Nabilah , Marzuki Muhammad Nasrullah , Mazlan Mohd Naufal Shah
Published: September 2020

Purpose

The purpose of this study is to investigate the influence of stimulus repetition rates on the auditory brainstem response (ABR) to Level-Specific (LS) CE-Chirp and click stimuli at multiple intensity levels in normal-hearing adults.

Method

A repeated-measure study design was used on 13 normal-hearing adults. ABRs were acquired from the study participants using LS CE-Chirp and click stimuli at four stimulus repetition rates (19.1, 33.3, 61.1, and 81.1 Hz) and four intensity levels (80, 60, 40, and 20 dB nHL). The ABR test was stopped at 40-nV residual noise level.

Results

High-stimulus repetition rates caused the ABR latencies to be longer and have reduced amplitudes in both ABR to LS CE-Chirp and click stimuli. The ABR to LS CE-Chirp Wave I, III, and V amplitudes were larger than ABR to click in almost all the stimulus repetition rates. However, there were no differences in the number of averages required to reach the stopping criterion between ABR to LS CE-Chirp and click stimulus, and between high-stimulus repetition rates and low-stimulus repetition rates.

Conclusion

The LS CE-Chirp at standard low-stimulus repetition rates can be used to elicit ABR for both neurodiagnostic and threshold seeking procedure.
Transient stability enhancement of power system with instability tolerant synchronous generator
Authors: Yaghobi Hamid
Published: September 2020

Out‐of‐step or out‐of‐synchronism is the loss of magnetic coupling between the rotor and the stator of a synchronous generator. Recent research has shown that loss of synchronism condition of a synchronous generator due to the local and inter‐area oscillations can cause severe damage to the machine and power system. In other words, if these oscillations do not damp, the power system will become unstable. It is worth highlighting that, along with the growth of grid interconnections, the stability has been a significant concern in the operation of the power systems, and the generators play a substantial role in this issue. Consequently, to reduce these oscillations and failures, the instability tolerant synchronous generator (ITSG), presented in this study, applied in the critical points of the network. The proposed generator is designed in such a way that it has a higher specific magnetic loading to stabilise the power system much more. The simulation tests demonstrate that the applied generator is effective in stabilising the network and improving the transient stability of the system in response to oscillations.
High‐fidelity large‐signal order reduction approach for composite load model
Authors: Ma Zixiao , Wang Zhaoyu , Zhao Dongbo , Cui Bai
Published: September 2020

With the increasing penetration of electronic loads and distributed energy resources, conventional load models cannot capture their dynamics. Therefore, a new comprehensive composite load model is developed by Western Electricity Coordinating Council (WECC). However, this model is a complex high‐order non‐linear system with multi‐time‐scale property, which poses challenges on power system studies with heavy computational burden. In order to reduce the model complexity, the authors firstly develop a large‐signal order reduction (LSOR) method using singular perturbation theory. In this method, the fast dynamics are integrated into the slow ones to preserve transient characteristics of the former. Then, accuracy assessment conditions are proposed and embedded into the LSOR to improve and guarantee the accuracy of reduced‐order model. Finally, the reduced‐order WECC composite load model is derived by using the proposed algorithm. Simulation results show that the reduced‐order large‐signal model significantly alleviates the computational burden while maintaining similar dynamic responses as the original composite load model.
Monitoring truck's operations at freight intermodal terminals: traffic observation by scanning on‐board devices
Authors: Carboni Angela , Deflorio Francesco , Dalla Chiara Bruno
Published: September 2020

Monitoring operations at freight intermodal terminals are useful for estimating their performance, while collecting traffic data allows them to properly manage and control truck flows. Nevertheless, the key role of observation can be in contrast with users’ privacy. A valuable solution to obtain traffic information preserving players’ anonymity may be provided by scanning radio signals emitted by commonly used on‐board devices, which can be locally identified by their unique media access control address. In this solution, no personal, freight or vehicle information is collected. An uncommon application of bluetooth scanners for monitoring operation of truck flows inside terminals is presented, based on a simple methodology for data processing. The algorithm starts from the data collection and the selection of information at relevant points of the terminal, then the network observation is composed by matching the data recorded in connected points. Finally, key performance indicators are estimated, starting from vehicle trajectories, node by node, and their travel time. The method is applied with on‐field tests in a large‐size rail–road terminal, where the detected counting results are lower than the ground truth, being not all the users equipped with bluetooth devices; however, the pioneering application results replicable in other contexts related to logistics.
More planetary candidates from K2 Campaign 5 using TRAN_K2
Authors: Kovacs Geza
Published: September 2020

Context. The exquisite precision of space-based photometric surveys and the unavoidable presence of instrumental systematics and intrinsic stellar variability call for the development of sophisticated methods that distinguish these signal components from those caused by planetary transits.

Aims. Here, we introduce the standalone Fortran code TRAN_K2 to search for planetary transits under the colored noise of stellar variability and instrumental effects. We use this code to perform a survey to uncover new candidates.

Methods. Stellar variability is represented by a Fourier series and, when necessary, by an autoregressive model aimed at avoiding excessive Gibbs overshoots at the edges. For the treatment of systematics, a cotrending and an external parameter decorrelation were employed by using cotrending stars with low stellar variability as well as the chip position and the background flux level at the target. The filtering was done within the framework of the standard weighted least squares, where the weights are determined iteratively, to allow a robust fit and to separate the transit signal from stellar variability and systematics. Once the periods of the transit components are determined from the filtered data by the box-fitting least squares method, we reconstruct the full signal and determine the transit parameters with a higher accuracy. This step greatly reduces the excessive attenuation of the transit depths and minimizes shape deformation.

Results. We tested the code on the field of Campaign 5 of the K2 mission. We detected 98% of the systems with all their candidate planets as previously reported by other authors. We then surveyed the whole field and discovered 15 new systems. An additional three planets were found in three multiplanetary systems, and two more planets were found in a previously known single-planet system.
Mono-enriched stars and Galactic chemical evolution
Authors: Hansen C. J. , Koch A. , Mashonkina L. , Magg M. , Bergemann M. , Sitnova T. , Gallagher A. J. , Ilyin I. , Caffau E. , Zhang H.W. , Strassmeier K. G. , Klessen R. S.
Published: September 2020

A long sought after goal using chemical abundance patterns derived from metal-poor stars is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas from which they were born, and hence they are frequently targeted in chemical tagging studies. Here, we use a sample of 14 metal-poor stars observed with the high-resolution spectrograph called the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) to derive abundances of 32 elements (34 including upper limits). We present well-sampled abundance patterns for all stars obtained using local thermodynamic equilibrium (LTE) radiative transfer codes and one-dimensional (1D) hydrostatic model atmospheres. However, it is currently well-known that the assumptions of 1D and LTE may hide several issues, thereby introducing biases in our interpretation as to the nature of the first stars and the chemical evolution of the Galaxy. Hence, we use non-LTE (NLTE) and correct the abundances using three-dimensional model atmospheres to present a physically more reliable pattern. In order to infer the nature of the first stars, we compare unevolved, cool stars, which have been enriched by a single event (“mono-enriched”), with a set of yield predictions to pin down the mass and energy of the Pop III progenitor. To date, only few bona fide second generation stars that are mono-enriched are known. A simple χ2-fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern, and we therefore carried out our study with an improved fitting technique considering dilution and mixing. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars, some of which are promising bona fide second generation (mono-enriched) stars. The unevolved, dwarf BD+09_2190 shows a mono-enriched signature which, combined with kinematical data, indicates that it moves in the outer halo and likely has been accreted onto the Milky Way early on. The Pop III progenitor was likely of 25.5 M⊙ and 0.6 foe (0.6 1051 erg) in LTE and 19.2 M⊙ and 1.5 foe in NLTE, respectively. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements. In BD-10_3742, we find an almost clean r-process trace, as is represented in the star HD20, which is a “metal-poor Sun benchmark” for the r-process, while TYC5481-00786-1 is a promising CEMP-r/-s candidate that may be enriched by an asymptotic giant branch star of an intermediate mass and metallicity.
Performance Study of Maximum Power Point Tracking (MPPT) Based on Type-2 Fuzzy Logic Controller on Active Dual Axis Solar Tracker
Authors: Abadi Imam , Uyuniyah Qurrotul , Nur Fitriyanah Dwi , Jani Yahya , Abdullah Kamaruddin
Published: September 2020

World energy consumption increases with time, so that occur an energy imbalance. Many breakthroughs have developed to utilize renewable energy. The photovoltaic system is one of the easy-to-use renewable energies. The power conversion from PV fixed is still low, so the PV system is designed using the active dual-axis solar tracker. The PV tracker position can be adjusted to change the sun position to get maximum efficiency. The active dual-axis solar tracker system is integrated with the maximum power point tracking (MPPT) algorithm to keep PV operating at a maximum power point even though input variations change. The active dual-axis solar tracker system integrated with the maximum power point tracking (MPPT) algorithm to keep PV operating at a maximum power point even though input variations change. Tracking test simulation had done by comparing the output power of a fixed PV system with the active dual-axis solar tracker. Type-2 fuzzy logic based MPPT successfully increased the average output power by 10.48 % with the highest increase of 17.48 % obtained at 15:00 West Indonesia Time (GMT+7). The difference in power from a fixed PV system with the active dual-axis solar tracker of 36.08 W is from the output power worth 206.3 to 242.4 W.
Design of Supervisory Control for Speed Control of Wind Turbine using Torque-Control Method Based on Buck Converter
Authors: Indriawati Katherin , Mufit Choirul , Rahmadiansah Andi
Published: September 2020

The variation of wind speed causes the electric power generated by the turbine also varies. To obtain maximum power, the rotor speed of wind turbines must be optimally rated. The rotor speed can be controlled by manipulating the torque from the generator; this method is called Torque Control. In that case, a DC-DC converter is needed as the control actuator. In this study, a buck converter-based supervisory control design was performed on the Horizontal-axis wind turbines (HAWT). Supervisory control is composed of two control loops arranged in cascade, and there is a formula algorithm as the supervisory level. The primary loop uses proportional control mode with a proportional gain of 0.3, whereas in the secondary loop using proportional-integral control mode with a proportional gain of 5.2 and an integral gain of 0.1. The Supervisory control has been implemented successfully and resulted in an average increase in turbine power of 4.1 % at 5 m s–1 and 10.58 % at 6 m s–1 and 11.65 % at 7 m s–1, compared to wind turbine systems without speed control.
The Identification of Micro-hydro Power Plants Potential in Irrigation Areas Based on Unmanned Air Vehicle (UAV) Image Processing
Authors: Alatas Masrur , Theresia Sri Budiastuti Maria , Gunawan Totok , Setyono Prabang , Burlakovs Juris , Yandri Erkata
Published: September 2020

Estimation of the energy demand in Indonesia will increase by 8.15 % annually until 2030. Indonesia is committed to preventing climate change through mix energy (new and renewable energy). One of the sources of this energy is waterpower plants with a potential of 75 091 MW have been utilized 6.4 %, mini-hydro, and micro-hydro with a potential of 19 385 MW have been utilized 1 %. In the Industrial Revolution 4.0, it is doable to identify such potential using drone. This study was conducted in the Kalibawang irrigation area, Special Region of Yogyakarta, Indonesia. The procedure starts with the generation of detailed Aerial Photography using Drone DJI Phantom 4. The images from aerial photography were then processed into high-resolution Digital Elevation Model (DEM). DEM data represent the study area topography and can be used to identify the stream gradient potential or height difference (H). Six potential points were identified with height differences between 3 m to 8 m, resulting in the potential generated power ranging from 125 kW to 334 kW. This study demonstrates the identification of micro-hydro energy potential points, height difference, and generated power using Drone. Six points were identified with total potential energy 1 418 kW.
Evaluation and Comparison of DC-DC Power Converter Variations in Solar Panel Systems Using Maximum Power Point Tracking (MPPT) Flower Pollination Algorithm (FPA) Control
Authors: Luthfansyah Mohammad , Suyanto Suyanto , Bakarr Momodu Bangura Abu
Published: September 2020

Maximum Power Point Tracking (MPPT) is a method that can be used to optimize the electrical power output from solar panels. The performance of the MPPT method on solar panel systems can be influenced by many variables. One of them is the selection of a DC-DC power converter. DC-DC-DC Converter is a component that is used to optimize the performance of solar panels. Several types of DC-DC Converter are Buck, Buck-Boost, Single Ended Primary Inductance Converter (SEPIC), and CUK. Each converter has a different effect on solar panels output power. In order to observe and make a comprehensive analysis, simulations are performed through PSIM (Power Simulator) software on the performance of several DC-DC Converters that use Flower Pollination Algorithm (FPA) as the MPPT algorithm. Variables that observed are the output power characteristic, the response of the voltage-current ripple signal, and the accuracy of the converter in the process of reaching the maximum power point condition. As a result, CUK converter can obtain the highest value of solar panel output power, 145.02 W. A low ripple level with a stable power value response is entirely generated by CUK and SEPIC Converter. Overall, for this system, the CUK converter has better performance than the other converters.
Characteristics of Woody Cutting Waste Briquette with Paper Waste Pulp as Binder
Authors: Ayunina Maulida Okta Arifianti Qurrotin , Alvian Gabriel Azmi , Hidayatulloh Syarif , Khoiro Ummatin Kuntum
Published: September 2020

The current research aimed to increase the calorific value of woody cutting waste briquette with paper waste pulp as binder. There were three different binder variation used in this study, they are 5 %, 10 %, and 15 %. To create a briquette, a cylindrical iron mold with diameter of 3.5 cm and height of 3 cm and a hydraulic press with 2 t power were applied. The physical characteristics of the combination woody waste briquette and paper waste pulp, such as moisture content, ash content, volatile matter and carbon fix were examined using proximate analysis. The calorific value of briquetted fuel was tested by bomb calorimeter. The combustion test was performed to determine the combustion characteristic of briquettes, for example initial ignition time, temperature distribution, and combustion process duration. The general result shows that the calorific value of briquette stood in the range of 4 876 kCal kg–1 to 4 993 kCal kg–1. The maximum moisture content of briquette was 5.32 %. The longest burning time was 105 min.
A systematic review on improving the biocompatibility of titanium implants using nanoparticles
Authors: Nhlapo Nthabiseng , Dzogbewu Thywill Cephas , de Smidt Olga
Published: September 2020

An ideal biomaterial should be biointegratable with minimum adverse immune response. Titanium (Ti) and its alloys are widely used biomaterials for manufacturing clinical implants because of their innate biocompatibility. However, the bioinert property of Ti may hinder tissue–implant integration and its bio compatibility nature allows for attachment of bacterial cells on implant surfaces. Nanoparticles (NPs) have been proposed as a possible intervention to overcome these biological shortcomings of Ti-based implants. The aim of the current systematic review was to identify literature that demonstrates enhanced biocompatibility of Ti-based implants by incorporating NPs. Electronic searches were conducted through the PubMed/MEDLINE, ScienceDirect, Web of Science and EBSCOhost databases. Studies published in English were extracted, without restrictions on the year of publication, using the following keywords: ‘biocompatibility’, ‘nanoparticles’, ‘titanium’ and ‘implant’. The guidelines stipulated in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement were followed. A total of 630 articles were identified in the initial search and upon reviewing, 21 articles were selected according to the eligibility criteria. The selected literature showed robust evidence to support the hypothesis that the inclusion of NPs improves biocompatibility of Ti implants. The studies further indicated a close correlation between biocompatibility and antibacterial properties, of which NPs have been proven to characteristically achieve both.
Two-fold singularities in nonsmooth dynamics—Higher dimensional analogs
Authors: Webber Simon , Jeffrey Mike R.
Published: September 2020

When a system of ordinary differential equations is discontinuous along some threshold, its flow may become tangent to that threshold from one side or the other, creating a fold singularity, or from both sides simultaneously, creating a two-fold singularity. The classic two-fold exhibits intricate local dynamics and accumulating sequences of local bifurcations and is by now rather well understood, but it is just the simplest of an infinite hierarchy of two-folds and multi-folds in higher dimensions. These arise when a system is discontinuous along multiple intersecting thresholds, and the induced sliding flows on those thresholds become tangent to their intersections. We show here, surprisingly, that these higher dimensional analogs of the two-fold reduce to the equations of the classic two-fold, providing the first step into their study and a new tool to understand higher dimensional systems with discontinuities.
Interference and electro-optical effects in cubic GaN/GaAs heterostructures prepared by molecular beam epitaxy
Authors: Zendejas-Leal B. E. , Casallas-Moreno Y. L. , Yee-Rendon C. M. , González-Pedreros G. I. , Santoyo-Salazar J. , Aguilar-Hernández J. R. , Vázquez-López C. , Gallardo-Hernández S. , Huerta-Ruelas J. , López-López M.
Published: September 2020

Cubic GaN (c-GaN) samples on GaAs (0 0 1) substrates were grown by RF-plasma-assisted molecular beam epitaxy, in which an As4 overpressure was employed for the nucleating layer. Photoreflectance spectra were obtained in the temperature range from 14 to 300 K. Two independent phenomena were noticed. The first one consisted in optical interference features below the c-GaN bandgap, whose origin is a thermo-optical effect: the ultraviolet perturbation beam changes the refractive index of the c-GaN. The second one represents electro-optical phenomena in which two classical band-to-band transitions occur: the first transition for c-GaN layer in which the temperature dependence reveals defects in the film attributed to a hexagonal fraction estimated previously between 3% and 10%, and a second transition for the GaAs substrate that shows Franz–Keldysh oscillations.
Screening of thermoelectric silicides with atomistic transport calculations
Authors: Løvvik Ole Martin , Flage-Larsen Espen , Skomedal Gunstein
Published: September 2020

More than 1000 crystalline silicide materials have been screened for thermoelectric properties using first-principles atomistic calculations coupled with the semi-classical Boltzmann transport equation. Compounds that contain radioactive, toxic, rare, and expensive elements as well as oxides, hydrides, carbides, nitrides, and halides have been neglected in the study. The already well-known silicides with good thermoelectric properties, such as SiGe, Mg2Si, and MnSix, are successfully predicted to be promising compounds along with a number of other binary and ternary silicide compositions. Some of these materials have only been scarcely studied in the literature, with no thermoelectric properties being reported in experimental papers. These novel materials can be very interesting for thermoelectric applications provided that they can be heavily doped to give a sufficiently high charge carrier concentration and that they can be alloyed with isoelectronic elements to achieve adequately low phonon thermal conductivity. The study concludes with a list of the most promising silicide compounds that are recommended for further experimental and theoretical investigations.
Regularity of weak solutions to a class of nonlinear problem with non-standard growth conditions
Authors: Zhou Jianfeng , Tan Zhong
Published: September 2020

In this paper, we study the interior differentiability of a weak solution u ∈ Vp(x) to a nonlinear problem (1.2), which arises in electroheological fluids (ERFs) in an open bounded domain Ω⊂Rd, d = 2, 3. At first, by establishing a reverse Hölder inequality, we show that the weak solution u of (1.2) has bounded energy that satisfies |Du|p(x)∈Llocδ(Ω) with some δ > 1 and p(x)∈(3dd+2,2). Next, based on the higher integrability of Du, we then derive the higher differentiability of u by the theory of difference quotient and a bootstrap argument, from which we obtain the Hölder continuity of u. Here, the analysis and the existence theory of the weak solution to (1.2)–(1.5) have been established by Diening et al. [Lebesgue and Sobolev Spaces with Variable Exponents (Springer-Verlag Berlin Heidelberg, 2011)].
High power factor due to multi-scale engineering in ultra-thin bismuth telluride films
Authors: Singh Sukhdeep , Tripathi S. K.
Published: September 2020

High thermoelectric (TE) power factors were obtained for bismuth telluride by deploying confinement and multi-scale engineering in synergy. The thickness of the film was kept in the ultra-thin range (41 nm) following which a high magnitude of 1.9 × 104 S m−1 was obtained at room temperature (RT). Films were deposited at an elevated substrate temperature to enhance the grain quality and high mobility bearing (00l) grain growth. Thus, relatively large crystallite sizes (∼26 nm) with less grain boundaries and directional growth with a low defect profile were the prime reasons for highly enhanced electrical conductivity. Apart from the multiple effects that were deployed, ultra-thin dimensions of the films proved to be effective in further enhancing Seebeck coefficient values. The co-alloyed In minimized the hole concentration through reducing antisite defects and also preserved the reduced bipolar effect at elevated temperatures. The inclusion of excess tellurium induced Te segregates in the film that helped in energy dependent scattering of carriers in addition to its donor-like effect. Hot carrier filtering, induced by excess Te along with ultra-thin dimensions resulted in a Seebeck coefficient (S) of −223.6 μV K−1 at RT. A soaring value of −338.1 μV K−1 was obtained at 90 °C. Following the synergetic employment of multiple enhancement strategies, a high power factor of 959.9 μW m−1 K−2 was obtained at room temperature with a towering magnitude of 2537.7 μW m−1 K−2 at 90 °C.
Foucault pendulum properties of spherical oscillators
Authors: Flückiger P. , Vardi I. , Henein S.
Published: September 2020

The Foucault pendulum provides a demonstration of the turning of the Earth. The principle at work is that linear oscillations of a two-degree-of-freedom isotropic harmonic oscillator remain unchanged in an inertial frame of reference, so appear to precess in a rotating frame of reference. In recent work, we applied two-degree-of-freedom isotropic oscillators to mechanical timekeeping. In this paper, we note that the spherical oscillators we considered have qualitatively different behavior in a non-inertial frame. We show that when in a rotating frame, linear oscillations precess at one half the rotational speed of the rotating frame. We validate this result experimentally by designing and constructing a proof of concept demonstrator placed on a motorized rotating table. The demonstrator consists of a spherical isotropic oscillator, a launcher to place the oscillator on planar orbits, a motorized rotating table, video recording for qualitative observation, and a laser measurement setup for quantitative results. The experimental data recorded by the lasers strongly validate the physical phenomenon.
Membrane permeability of small molecules from unbiased molecular dynamics simulations
Authors: Krämer Andreas , Ghysels An , Wang Eric , Venable Richard M. , Klauda Jeffery B. , Brooks Bernard R. , Pastor Richard W.
Published: September 2020

Permeation of many small molecules through lipid bilayers can be directly observed in molecular dynamics simulations on the nano- and microsecond timescale. While unbiased simulations provide an unobstructed view of the permeation process, their feasibility for computing permeability coefficients depends on various factors that differ for each permeant. The present work studies three small molecules for which unbiased simulations of permeation are feasible within less than a microsecond, one hydrophobic (oxygen), one hydrophilic (water), and one amphiphilic (ethanol). Permeabilities are computed using two approaches: counting methods and a maximum-likelihood estimation for the inhomogeneous solubility diffusion (ISD) model. Counting methods yield nearly model-free estimates of the permeability for all three permeants. While the ISD-based approach is reasonable for oxygen, it lacks precision for water due to insufficient sampling and results in misleading estimates for ethanol due to invalid model assumptions. It is also demonstrated that simulations using a Langevin thermostat with collision frequencies of 1/ps and 5/ps yield oxygen permeabilities and diffusion constants that are lower than those using Nosé–Hoover by statistically significant margins. In contrast, permeabilities from trajectories generated with Nosé–Hoover and the microcanonical ensemble do not show statistically significant differences. As molecular simulations become more affordable and accurate, calculation of permeability for an expanding range of molecules will be feasible using unbiased simulations. The present work summarizes theoretical underpinnings, identifies pitfalls, and develops best practices for such simulations.
The thermoelectric effect of a refined heat equation during the photothermal excitation due to two-temperature theory with laser pulses
Authors: Lotfy Kh. , El-Bary A. , Atef Haitham M.
Published: September 2020

A novel model of two temperatures in generalized thermoelasticity theory in the context of the photothermal transport process is studied. The medium is excited at the free surface of semi-infinite semiconductor by normal load subjected to pulsed laser during refined multi-phase-lag thermal memory of heat conduction equation. All coupled between multi-waves such as thermal, elastic, and plasma waves are investigated. The exact solutions of main physical fields in this investigation are obtained analytically in two dimensions using the normal mode technique. Some mechanical and thermal loads are applied on the free surface of the medium. Some comparisons of the numerical results are shown. All physical fields are very sensitive to the variation of the laser pulses and two temperatures’ parameter. The influence of thermoelectric coupling parameter and thermal memory of physical fields of silicon (Si) material have been displayed graphically and discussed to illustrate the physical meaning of the problem.
Materials loss measurements using superconducting microwave resonators
Authors: McRae C. R. H. , Wang H. , Gao J. , Vissers M. R. , Brecht T. , Dunsworth A. , Pappas D. P. , Mutus J.
Published: September 2020

The performance of superconducting circuits for quantum computing is limited by materials losses. In particular, coherence times are typically bounded by two-level system (TLS) losses at single photon powers and millikelvin temperatures. The identification of low loss fabrication techniques, materials, and thin film dielectrics is critical to achieving scalable architectures for superconducting quantum computing. Superconducting microwave resonators provide a convenient qubit proxy for assessing performance and studying TLS loss and other mechanisms relevant to superconducting circuits such as non-equilibrium quasiparticles and magnetic flux vortices. In this review article, we provide an overview of considerations for designing accurate resonator experiments to characterize loss, including applicable types of losses, cryogenic setup, device design, and methods for extracting material and interface losses, summarizing techniques that have been evolving for over two decades. Results from measurements of a wide variety of materials and processes are also summarized. Finally, we present recommendations for the reporting of loss data from superconducting microwave resonators to facilitate materials comparisons across the field.
Charge collection efficiency in the presence of non-uniform carrier drift mobilities and lifetimes in photoconductive detectors
Authors: Kasap S. O. , Kabir M. Z. , Ramaswami Kieran O. , Johanson Robert E. , Curry Richard J.
Published: September 2020

We consider the charge collection efficiency (CCE) for semiconductors in which the charge transport parameters, the drift mobility μ, and the carrier lifetime τ have spatial dependence, i.e., μ = μ(x) and τ = τ(x), where x is the distance from the radiation receiving top electrode toward the rear electrode. The small signal carrier packet drift analysis (CPDA) is re-examined, and the CCE efficiency for electrons and holes is formulated in terms of μ(x)τ(x)F(x), where F is the field. We use two model mobility and lifetime variations that are linear and exponential and then calculate and compare CCE determined from the CPDA equation, numerical solution of the continuity equation and Monte Carlo simulations as a function of the parameters characterizing the linear and exponential changes. The use of standard CCE equations for nonuniform samples is extensively examined, and errors are quantified by introducing a spatial average (SA) ⟨τ(x)⟩, average inverse (AI) ⟨1/τ(x)⟩, a new effective lifetime, and a kth order average. The SA lifetime works best when τ(x) monotonically decreases with x and AI works best when τ(x) monotonically increases with x. Stabilized a-Se x-ray photoconductors were considered as a practical application of this work. Both hole and electron lifetimes decrease in a-Se upon x-ray irradiation. Using the empirical equations derived recently for τh(x) and τe(x) as a function of dose D(x) in the sample, the CCE for two a-Se samples corresponding to a low-end device quality and the “best” was determined as a function of applied field.
Investigating the validity of Schrage relationships for water using molecular dynamics simulations
Authors: Chandra Anirban , Keblinski Pawel
Published: September 2020

Recently, molecular dynamics (MD) simulations were utilized to show that Schrage theory predicts evaporation/condensation mass fluxes with good accuracy in the case of monoatomic and non-polar molecular fluids. Here, we examine if they are equally accurate for molecular polar fluids, such as water. In particular, using molecular dynamics (MD) simulations, we study the steady state evaporation/condensation processes of water in a one-dimensional heat-pipe geometry to ascertain the validity of Schrage relationships. Non-equilibrium mass flow is driven by controlling the temperatures of the source/sink. Equilibrium simulations are utilized to evaluate the saturation properties and the mass accommodation coefficients as a function of temperature. Our results indicate that Schrage equations predict the evaporation/condensation rates of water with good accuracy. Moreover, we show that molecular velocity distributions in the vapor phase are indeed Maxwellian distributions shifted by the velocity of the macroscopic vapor flow, as assumed in Schrage’s theoretical analysis.
A combination of machine learning and infrequent metadynamics to efficiently predict kinetic rates, transition states, and molecular determinants of drug dissociation from G protein-coupled receptors
Authors: Lamim Ribeiro João Marcelo , Provasi Davide , Filizola Marta
Published: September 2020

Determining the drug-target residence time (RT) is of major interest in drug discovery given that this kinetic parameter often represents a better indicator of in vivo drug efficacy than binding affinity. However, obtaining drug-target unbinding rates poses significant challenges, both computationally and experimentally. This is particularly palpable for complex systems like G Protein-Coupled Receptors (GPCRs) whose ligand unbinding typically requires very long timescales oftentimes inaccessible by standard molecular dynamics simulations. Enhanced sampling methods offer a useful alternative, and their efficiency can be further improved by using machine learning tools to identify optimal reaction coordinates. Here, we test the combination of two machine learning techniques, automatic mutual information noise omission and reweighted autoencoded variational Bayes for enhanced sampling, with infrequent metadynamics to efficiently study the unbinding kinetics of two classical drugs with different RTs in a prototypic GPCR, the μ-opioid receptor. Dissociation rates derived from these computations are within one order of magnitude from experimental values. We also use the simulation data to uncover the dissociation mechanisms of these drugs, shedding light on the structures of rate-limiting transition states, which, alongside metastable poses, are difficult to obtain experimentally but important to visualize when designing drugs with a desired kinetic profile.
Dynamic behaviors of interfacial water on the self-assembly monolayer (SAM) heterogeneous surface
Authors: Tian Ranran , Hu Guorong , Ou Xinwen , Luo Mengbo , Li Jingyuan
Published: September 2020

Dynamic behaviors of water molecules near the surface with mixed hydrophobic and hydrophilic areas are studied by molecular dynamics simulation. More specifically, the diffusion coefficient and hydrogen bond lifetime of interfacial water on the self-assembly monolayer composed of hydrophobic and hydrophilic groups and their dependence on the mixing ratio are studied. The diffusion dramatically slows down, and the hydrogen bond lifetime considerably increases when a few hydrophilic groups are added to the hydrophobic surface. When the percentage of hydrophilic groups increases to 25%, the behavior of interfacial water is similar to the case of the pure hydrophilic surface. The sensitivity to the hydrophilic group can be attributed to the fact that the grafted hydrophilic groups can not only retard the directly bound water molecules but also affect indirectly bound water by stabilizing hydrogen bonds among interfacial water molecules.
Catalyst free approach for the fabrication of CoN//Zn3N2 asymmetric configuration for highly efficient flexible supercapacitor
Authors: Adalati Ravikant , Kumar Ashwani , Sharma Meenakshi , Tiwari Pranjala , Chandra Ramesh
Published: September 2020

This report presents a single-step deposition of crystalline and catalyst-free cobalt nitride (CoN) and zinc nitride (Zn3N2) electrodes on a flexible current collector for highly efficient flexible supercapacitors. These proposed electrodes take full advantage of mechanical strength, electrochemical stability, and tremendous electrical conductivity with excellent adhesion to a flexible current collector and show high capacitive performance with outstanding cyclic life. The asymmetric supercapacitor (ASC) was constructed using CoN as a negative electrode and Zn3N2 as a positive electrode, assembled with 1 M Na2SO4 aqueous electrolyte soaked Whatman filter paper as the separator. This ASC exhibits a wider voltage window (up to 2 V), good capacitance (75.4 Fg−1), and high specific energy (42 Wh kg−1) with good capacitance retention (93.6% for the flat cell and 80.1% for the 80° bend cell) over 5000 charging discharging cycles. Therefore, this design of ASC potentially expands the performance of high frequency and flexible electronics.
Structure and vibrational properties of sodium silicate glass surfaces
Authors: Zhang Zhen , Ispas Simona , Kob Walter
Published: September 2020

Using molecular dynamics simulations, we investigate how the structural and vibrational properties of the surfaces of sodo-silicate glasses depend on the sodium content as well as the nature of the surface. Two types of glass surfaces are considered: A melt-formed surface (MS) in which a liquid with a free surface has been cooled down into the glass phase and a fracture surface (FS) obtained by tensile loading of a glass sample. We find that the MS is more abundant in Na and non-bridging oxygen atoms than the FS and the bulk glass, whereas the FS has higher concentration of structural defects such as two-membered rings and under-coordinated Si than the MS. We associate these structural differences to the production histories of the glasses and the mobility of the Na ions. It is also found that for Na-poor systems, the fluctuations in composition and local atomic charge density decay with a power-law as a function of distance from the surface, while Na-rich systems show an exponential decay with a typical decay length of ≈2.3 Å. The vibrational density of states shows that the presence of the surfaces leads to a decrease in the characteristic frequencies in the system. The two-membered rings give rise to a pronounce band at ≈880 cm−1, which is in good agreement with experimental observations.
GXPS: A Geant4-based Monte Carlo code for x-ray polycapillary simulation
Authors: Chi Zhijun
Published: September 2020

With the rapid development of the x-ray polycapillary optics, there is an increasing demand for an effective simulation tool, considering the real physical process and geometry model, to optimize their performance. In this paper, a Geant4-based Monte Carlo code for X-ray Polycapillary Simulation (GXPS) is developed. Based on the classical electromagnetic theory, an x-ray boundary process is developed using the dielectric model, including total external reflection, Fresnel reflection, and Fresnel refraction. The surface roughness of x-ray polycapillary is taken into account using a classical Gaussian slope distribution model. A new geometry solid for x-ray polycapillary modeling is constructed using a cubic function whose coefficients can be derived based on the parameters of a practical lens. To validate the effectiveness of this code, a point-to-parallel x-ray polycapillary lens is simulated with an x-ray energy of 8.04 keV (Cu Kα) and the simulation result is compared with the experiment. Well agreement between the simulation and the experimental result is verified considering the transmission efficiency, the output beam profile, and the divergence angle of the lens. The focusing characteristics of the lens are also demonstrated using this code. The simulation result of the focal spot size agrees well with the predicted value calculated using the empirical relation.
Decoding the 2D IR spectrum of the aqueous proton with high-level VSCF/VCI calculations
Authors: Carpenter William B. , Yu Qi , Hack John H. , Dereka Bogdan , Bowman Joel M. , Tokmakoff Andrei
Published: September 2020

The aqueous proton is a common and long-studied species in chemistry, yet there is currently intense interest devoted to understanding its hydration structure and transport dynamics. Typically described in terms of two limiting structures observed in gas-phase clusters, the Zundel H5O2+ and Eigen H9O4+ ions, the aqueous structure is less clear due to the heterogeneity of hydrogen bonding environments and room-temperature structural fluctuations in water. The linear infrared (IR) spectrum, which reports on structural configurations, is challenging to interpret because it appears as a continuum of absorption, and the underlying vibrational modes are strongly anharmonically coupled to each other. Recent two-dimensional IR (2D IR) experiments presented strong evidence for asymmetric Zundel-like motifs in solution, but true structure–spectrum correlations are missing and complicated by the anharmonicity of the system. In this study, we employ high-level vibrational self-consistent field/virtual state configuration interaction calculations to demonstrate that the 2D IR spectrum reports on a broad distribution of geometric configurations of the aqueous proton. We find that the diagonal 2D IR spectrum around 1200 cm−1 is dominated by the proton stretch vibrations of Zundel-like and intermediate geometries, broadened by the heterogeneity of aqueous configurations. There is a wide distribution of multidimensional potential shapes for the proton stretching vibration with varying degrees of potential asymmetry and confinement. Finally, we find specific cross peak patterns due to aqueous Zundel-like species. These studies provide clarity on highly debated spectral assignments and stringent spectroscopic benchmarks for future simulations.
Molecular dynamics study of grain boundaries and triple junctions in ice
Authors: Yagasaki Takuma , Matsumoto Masakazu , Tanaka Hideki
Published: September 2020

We perform classical molecular dynamics simulations of polycrystalline ice at 250 K using the TIP4P/Ice model. The structures of polycrystalline ice are prepared by growing ice particles in supercooled water. An order parameter developed recently is used to characterize local structures in terms of the liquid–liquid phase transition scenario. It is shown that the grain boundaries and triple junctions in ice are structurally similar to low-density liquid water in which most water molecules form four hydrogen bonds and the O–O–O angles deviate from the tetrahedral angle of 109.47°. The thickness of the grain boundaries is ∼1 nm. The diffusion coefficient of water molecules along the grain boundaries calculated in this study, 5.0 × 10−13 m2 s−1, is in good agreement with experimental data. The diffusion along the triple junctions is 3.4 times faster than that along the grain boundaries. We model the grain size dependence of diffusivity of water molecules in polycrystalline ice using the simulation results and find that the impact of the grain boundaries and the triple junctions on the diffusivity is negligible for typical polycrystalline ice samples having grain sizes of the order of millimeters. We also demonstrate that the properties of the grain boundaries are quite different from those of the ice/vapor interface at the same temperature: the quasi-liquid layer at the ice/vapor interface is similar to high-density liquid water and the diffusion coefficient along the ice/vapor interface is two orders of magnitude larger than that along the grain boundaries.
Ratchet current in nontwist Hamiltonian systems
Authors: Mugnaine Michele , Batista Antonio M. , Caldas Iberê L. , Szezech José D. , Viana Ricardo L.
Published: September 2020

Non-monotonic area-preserving maps violate the twist condition locally in phase space, giving rise to shearless invariant barriers surrounded by twin island chains in these regions of phase space. For the extended standard nontwist map, with two resonant perturbations with distinct wave numbers, we investigate the presence of such barriers and their associated island chains and compare our results with those that have been reported for the standard nontwist map with only one perturbation. Furthermore, we determine in the control parameter space the existence of the shearless barrier and the influence of the additional wave number on this condition. We show that only for odd second wave numbers are the twin island chains symmetrical. Moreover, for even wave numbers, the lack of symmetry between the chains of twin islands generates a ratchet effect that implies a directed transport in the phase space.
Clustering of extreme events in time series generated by the fractional Ornstein–Uhlenbeck equation
Authors: Telesca Luciano , Czechowski Zbigniew
Published: September 2020

We analyze the time clustering phenomenon in sequences of extremes of time series generated by the fractional Ornstein–Uhlenbeck (fO-U) equation as the source of long-term correlation. We used the percentile-based definition of extremes based on the crossing theory or run theory, where a run is a sequence of L contiguous values above a given percentile. Thus, a sequence of extremes becomes a point process in time, being the time of occurrence of the extreme the starting time of the run. We investigate the relationship between the Hurst exponent related to the time series generated by the fO-U equation and three measures of time clustering of the corresponding extremes defined on the base of the 95th percentile. Our results suggest that for persistent pure fractional Gaussian noise, the sequence of the extremes is clusterized, while extremes obtained by antipersistent or Markovian pure fractional Gaussian noise seem to behave more regularly or Poissonianly. However, for the fractional Ornstein–Uhlenbeck equation, the clustering of extremes is evident even for antipersistent and Markovian cases. This is a result of short range correlations caused by differential and drift terms. The drift parameter influences the extremes clustering effect—it drops with increasing value of the parameter.