Nearby Point Research Articles

Twist disclinations mediated transformations in confined nematic liquid crystals

We studied numerically structural transformations in different confined nematic liquid crystals (LC) mediated by chargeless (twist) disclinations. Firstly, we focus on the role of twist disclinations in Moiré-type geometrical setup where LC is confined in a plane-parallel cell. We impose an azimuthal rotation to initially parallel wedge disclinations where the total topological charge of the system equals to zero. Two qualitatively different scenarii are observed depending on the cell thickness. In thin enough cells the disclinations touch in the mid-plane which enables continuous transformation into a final structure consisting of two twist disclinations confined to the limiting substrates. On the other hand, in thinner cells an additional chargeless loop is formed in the mid-plane. In this case, on rotating the initially parallel disclinations periodic structural reentrant behavior is observed. In cylindrical geometry we considered transformations between the initial metastable escaped radial structure with point defects (ERPD) into escaped radial (ER) or planar polar structure with line defects (PPLD). In both cases two nearby ring-like point defects within the ERPD structure collide and temporarily form a chargeless twist disclination loop. The latter in the ERPD-ER transformation shrinks and enables continuous transformation into the final thermodynamically stable structure. On the contrary, in the ERPD-PPLD transformation the twist loop, whose local structure matches PPLD configuration, increases and converts the system continuously into the global PPLD configuration. Detailed understanding of chargeless defect mediated transformations is beneficial for development of future switching devices based on continuous nematic structural transformations between LC structures exhibiting significantly different optical features.

Fish Diversity of East Sea Streams in Nakdong River Region

Fish surveys were conducted near artificial structures installed in eight streams flowing from the Nakdong River region to the east coast of Korea. As a result of the survey, a total of 20,000 individuals belonging to nine orders, 17 families, and 47 species were found. The dominant species was Zacco koreanus, and the subdominant species was Pungtungia herzi. Among the surveyed fish species, endangered species were Pseudobagrus brevicorpus (rank I) and Cottus hangiongensis (rank II). In addition, migratory fish species were Oncorhynchus keta, Plecoglossus altivelis, and Tribolodon hakonensis. As a result of community analysis, the highest diversity, dominance, richness, and evenness indices were Wangpi, Chuksan, Gokgang, and Janggi Stream respectively. The highest number of species was surveyed in Gokgang Stream (25 species). Alpha diversity, the number of species at each survey point in each stream, was the highest at a survey point in Wangpi Stream (20 species), and beta diversity, species at each stream survey point that does not overlap with nearby survey point, was the highest at survey points in Gokgang Stream (12 species). As a result of the similarity analysis, surveyed streams were divided into four groups: group 1 (Chuksan, Baeknok Stream), group 2 (Uljinnamdae, Wangpi, Yungdeokosip Steam), group 3 (Gokgang Stream), and group 4 (Janggi, Hoeya Stream). This study is expected to serve as basic data for managing the aquatic ecosystem of streams flowing from the Nakdong River region to the east coast.

Global fluid turbulence simulations in the scrape-off layer of a stellarator island divertor

Isothermal fluid turbulence simulations have been performed in the edge and scrape-off layer (SOL) of an analytic stellarator configuration with an island divertor, thereby providing numerical insight into edge turbulence in regions around islands in a stellarator. The steady-state transport follows the a curvature drive that is inverse to the major radius ( $1/R$ ) toward the outboard side, but large fluctuations are present throughout the island divertor region, with the average wavelength of similar size to the island width. The system exhibits a prominent $m=2$ , $n=5$ mode, where m is the poloidal mode number and n is the toroidal mode number, although other modes are present. The amplitude and radial extent of the density fluctuations are similar throughout the edge and SOL, but can decrease near island O-points. The fluctuations exhibit a predominantly positive skewness on the outboard midplane, indicating blob-like perturbations for the transport into the outer SOL. It is determined that a point on the separatrix is generally more correlated with regions outside of the SOL than a nearby reference point which does not lie on the separatrix.

A Study of Nanofluid Flow with Free Bio-Convection in 3D Nearby Stagnation Point by Hermite Wavelet Technique

A new wavelet-numerical method for solving a system of partial differential equations describing an incompressible bio-convection nanofluid flow in a three-dimensional region close to the stagnation point is the primary focus of this article. Hermite wavelets form the basis of the algorithm. An assortment of similitude factors is utilized to improve on the overseeing conditions addressing the protection of all out mass, force, nuclear power, nanoparticles, and microorganisms to a bunch of completely connected nonlinear common differential conditions. The most important physical quantities that have a practical impact on the spread of motile bacteria are presented and analyzed in this paper. During bio-convection, the Prandtl, Lewis, Peclet, Schmidt, and Rayleigh numbers can alter the distribution of moving molecules. The dispersion of microorganisms can be emphatically affected by the kinds of nanoparticles and by the varieties in the temperature as well as volumetric part of the nanoparticles between the wall and the encompassing liquid. With excellent agreement for coupled nonlinear differential equations in engineering applications, our result demonstrates how powerful and simple the HWM is for solving these coupled nonlinear ordinary differential equations.

Finite volume effects near the chiral crossover

The effect of a finite volume presents itself both in heavy ion experiments as well as in recent model calculations. The magnitude is sensitive to the proximity of a nearby critical point. We calculate the finite volume effects at finite temperature in continuum QCD using lattice simulations. We focus on the vicinity of the chiral crossover. We investigate the impact of finite volumes at zero and small chemical potentials on the QCD transition though the chiral observables.

Anthropogenic CO2 emission estimates in the Tokyo metropolitan area from ground-based CO2 column observations

Abstract. Urban areas are responsible for more than 40 % of global energy-related carbon dioxide (CO2) emissions. The Tokyo metropolitan area (TMA), Japan, one of the most populated regions in the world, includes various emission sources, such as thermal power plants, automobile traffic, and residential facilities. In order to infer a top–down emission estimate, we conducted an intensive field campaign in the TMA from February to April 2016 to measure column-averaged dry-air mole fractions of CO2 (XCO2) with three ground-based Fourier transform spectrometers (one IFS 125HR and two EM27/SUN spectrometers). At two urban sites (Saitama and Sodegaura), measured XCO2 values were generally larger than those at a rural site (Tsukuba) by up to 9.5 ppm, and average diurnal variations increased toward evening. To simulate the XCO2 enhancement (ΔXCO2) resulting from emissions at each observation site, we used the Stochastic Time-Inverted Lagrangian Transport (STILT) model driven by meteorological fields at a horizontal resolution of ∼1 km from the Weather Research and Forecasting (WRF) model, which was coupled with anthropogenic (large point source and area source) CO2 emissions and biogenic fluxes. Although some of the diurnal variation of ΔXCO2 was not reproduced and plumes from nearby large point sources were not captured, primarily because of a transport modeling error, the WRF–STILT simulations using prior fluxes were generally in good agreement with the observations (mean bias, 0.30 ppm; standard deviation, 1.31 ppm). By combining observations with high-resolution modeling, we developed an urban-scale inversion system in which spatially resolved CO2 emission fluxes at >3 km resolution and a scaling factor of large point source emissions were estimated on a monthly basis by using Bayesian inference. The XCO2 simulation results from the posterior CO2 fluxes were improved (mean bias, −0.03 ppm; standard deviation, 1.21 ppm). The prior and posterior total CO2 emissions in the TMA are 1.026 ± 0.116 and 1.037 ± 0.054 Mt-CO2 d−1 at the 95 % confidence level, respectively. The posterior total CO2 emissions agreed with emission inventories within the posterior uncertainty, demonstrating that the EM27/SUN spectrometer data can constrain urban-scale monthly CO2 emissions.

The Lifestyle and Mobility Connection of Community Supported Agriculture (CSA) Users

Because Community Supported Agriculture (CSA) is considered a greener food shopping option, we hypothesized that users would adopt other sustainability-oriented behaviors. We sought, through 16 qualitative interviews with users, to understand whether CSA use in Montreal, Canada was accompanied by more ecological, non-motorized travel behavior. We find that urban users are typically able to subscribe to a nearby drop-off point and that many of them use non-motorized modes to access their weekly baskets. However, because of the weight of large produce baskets and the set time periods for collection, basket pick-ups by new Covid-19 era users are often part of car-based trip chains.

Mapping Strontium Isotope Geographical Variability as a Basis for Multi-regional Human Mobility: The Sybaris Region (S Italy) in the Early 1st Millennium BC

ABSTRACT Archaeological findings from the 8th c. BC settlement at Francavilla Marittima (CS) and its necropolis on the nearby Macchiabate plateau point to multi-regional interactions and the emergence of new identities in connection with the establishment of the Greek colony Sybaris. Strontium isotope analysis (87Sr/86Sr) is an efficient method to reconstruct human mobility and provides new insights into the Iron Age and Archaic period in the Calabria region. A successful interpretation of Sr isotope compositions in human tissues requires a baseline of the bioavailable strontium in the landscape of Francavilla Marittima and its surroundings. This study presents 87Sr/86Sr values of modern vegetation and water from North Calabria to establish the first finely resolved Sr isotope baseline map of this region. Sr isotope compositions vary between 0.7082 and 0.7127 and reflect the geological and lithological diversity of the study region. The regional 87Sr/86Sr variability exceeds the baseline of bioavailable 87Sr/86Sr at Francavilla Marittima and enables the integration of past regional interaction in data interpretation of the human remains. Several mapping and prediction methods were tested to produce surface models of the isotopic landscape, and the isotope group map is proposed as a suitable representation of the bioavailable Sr in the studied region.

Identifying an Environment-Induced Localization Transition from Entropy and Conductance.

Environment-induced localization transitions (LT) occur when a small quantum system interacts with a bath of harmonic oscillators. At equilibrium, LTs are accompanied by an entropy change, signaling the loss of coherence. Despite extensive efforts, equilibrium LTs have yet to be observed. Here, we demonstrate that ongoing experiments on double quantum dots that measure entropy using a nearby quantum point contact realize the celebrated spin-boson model and allow to measure the entropy change of its LT. We find a Kosterlitz-Thouless flow diagram, leading to a universal jump in the spin-bath interaction, reflected in a discontinuity in the zero temperature QPC conductance.

QUICK‐B‐WIM: Large scale application of a moving force identification method on a railway bridge

AbstractGlobally, infrastructure faces the challenge of aging bridges and increasing traffic loads. Extended operational availability and safety of the bridge structures can be enabled by Structural Health Monitoring (SHM) methods. For this, knowledge of the actual vehicle loads is of crucial importance for evaluation of the remaining service life. Direct measurement of the moving loads, however, is either very cumbersome and requires considerable financial effort or in some cases even impossible. Bridge Weigh‐In‐Motion (B‐WIM) methods use the structural responses of bridge structures to determine the external vehicle loads. The present contribution deals with the testing of a novel moving force identification (MFI) method, denoted as Quick‐BWIM (QBWIM) under real operating conditions. In this study, 43 train crossings within 18 hours were investigated and compared with a nearby axle load measurement point. QBWIM achieves an average error of only 1.1% with a standard deviation of 7.5% for individual axles and an average error of 2.1% with a standard deviation of 1.5% for the identification of gross vehicle weights (GVW). This study shows that QBWIM can meet European and US guidelines even under poor conditions and is able to reliably determine axle loads in real time.

One-Step Out-of-Place Resetting for Redirected Walking in VR.

Redirected walking (RDW) allows users to explore virtual environments in limited physical spaces by imperceptibly steering them away from obstacles and space boundaries. However, even with those techniques, the risk of collision cannot always be avoided. For such situations, resetting techniques have been proposed to provide an immediate adjustment of the physical walking direction of a user. Existing resetting techniques are either applied in-place, where the user changes orientation but stays in the same position or out-of-place methods where the user is guided to move from the current position to a safe location all while freezing the movement in the virtual world. While out-of-place methods have the potential to provide more freedom to user movements after resetting, current out-of-place methods do not provide enough guidance for the users to move to optimal locations. In this work, we propose a novel out-of-place resetting strategy that guides users to optimal physical locations with the most potential for free movement and a smaller amount of resetting required for their further movements. For this purpose, we calculate a heat map of the walking area according to the average walking distance using a simulation of the currently used RDW algorithm. Based on this heat map, we identify the most suitable position for a one-step reset within a predefined searching range and use this one as the reset point. Our results show that our method increases the average moving distance within one cycle of resetting. Furthermore, our resetting method can be applied to any physical area with obstacles. That means that RDW methods that were not suitable for such environments (e.g., Steer to Center) combined with our resetting can also be extended to such complex walking areas. In addition, we present a user interface to provide a similar visual experience between these methods, using a two-arrows indicator to help users adjust their position and direction.

Directive Emergency Evacuation Procedures Using MATLAB

This paper presents the development of directive emergency evacuation procedures for occupants of academic buildings. The development has four steps: determining a location as a starting point for evacuation, identifying the number of occupants in the building, referring to regulations and guidelines of emergency evacuation procedures, and designing an algorithm to be programmed in MATLAB software for desktop application. One academic building of the chemical and energy engineering faculty in Universiti Teknologi Malaysia is chosen to demonstrate the evacuation simulation. The algorithm is developed to direct occupants from any room in the building to a nearby assembly point. Occupants must provide inputs to the evacuation simulation, particularly the room’s number and level. Based on the inputs, occupants will get a word-based direction to the assembly point within an estimated time. Fifty students demonstrated the use of an emergency evacuation simulation in MATLAB. They are provided feedback concerning their awareness of emergency evacuation and the interaction with the simulation. Half of them responded that the evacuation simulation in MATLAB and their satisfaction was good and excellent. However, the algorithm is for one potential hazard and its location at a time, making it incapable of having inputs for many hazards. It is recommended that the algorithm is programmed to be used on a smartphone, allowing much easier dynamic emergency calling.

Distributed Design of Wireless Powered Fog Computing Networks With Binary Computation Offloading

This paper investigates a multi-user wireless powered fog computing (FC) network, where multiple energy-limited wireless sensor devices (WSDs) first harvest energy from a nearby hybrid access point (HAP), and then compute their tasks locally (i.e., the local computing (LC) mode) or offload the tasks to the HAP (i.e., the FC mode) via a binary offloading policy. In order to pursue the green computing network design, an optimization problem is formulated to minimize the transmit power at the HAP by jointly optimizing the time allocation ratio and the computing mode selection vector, under the energy causality constraints and the WSDs’ computing rate requirements constraints. To efficiently solve the formulated non-convex problem in a distributed manner, it is first transformed into an approximate form, and then an alternating direction method of multipliers (ADMM)-based algorithm is designed to solve the transformed problem, based on which the successive convex approximation (SCA) is adopted to improve the approximating precision in an iterative way. With the proposed ADMM-based distributed algorithm, each WSD is able to optimize its computing mode and offloading time with local channel state information (CSI), which thus is more suitable for large-scale networks. For comparison, a channel-sorting-based (CSB) centralized algorithm with global CSI is also presented, and the computational complexities of the proposed ADMM-based algorithm and the CSB algorithm are analyzed. Simulation results show that the proposed distributed algorithm achieves a comparable performance with the CSB centralized algorithm and the exhaustive search method. It is also observed that to minimize the transmit power at the HAP, the WSDs with the better channel quality are inclined to select the LC mode, which is much different from traditional sum-computation-rate maximization design.

Realistic Protocol to Measure Entanglement at Finite Temperatures.

It is desirable to relate entanglement of many-body systems to measurable observables. In systems with a conserved charge, it was recently shown that the number entanglement entropy (NEE)-i.e., the entropy change due to an unselective subsystem charge measurement-is an entanglement monotone. Here we derive finite-temperature equilibrium relations between Rényi moments of the NEE, and multipoint charge correlations. These relations are exemplified in quantum dot systems where the desired charge correlations can be measured via a nearby quantum point contact. In quantum dots recently realizing the multichannel Kondo effect we show that the NEE has a nontrivial universal temperature dependence which is now accessible using the proposed methods.

Superdiffusive Energy Transport in Kinetically Constrained Models

Universal nonequilibrium properties of isolated quantum systems are typically probed by studying transport of conserved quantities, such as charge or spin, while transport of energy has received considerably less attention. Here, we study infinite-temperature energy transport in the kinetically-constrained PXP model describing Rydberg atom quantum simulators. Our state-of-the-art numerical simulations, including exact diagonalization and time-evolving block decimation methods, reveal the existence of two distinct transport regimes. At moderate times, the energy-energy correlation function displays periodic oscillations due to families of eigenstates forming different su(2) representations hidden within the spectrum. These families of eigenstates generalize the quantum many-body scarred states found in previous works and leave an imprint on the infinite-temperature energy transport. At later times, we observe a broad superdiffusive transport regime that we attribute to the proximity of a nearby integrable point. Intriguingly, strong deformations of the PXP model by the chemical potential do not restore diffusion, but instead lead to a stable superdiffusive exponent $z\approx3/2$. Our results suggest constrained models to be potential hosts of novel transport regimes and call for developing an analytic understanding of their energy transport.

Noise suppression of transport through double quantum dots by feedback control

A controllable low noise current lies at the heart of high-precision measurements in quantum transport and metrology. While the previous research dealt with the suppression of noise in transport through a tunneling junction or a single quantum dot (QD) device, the present work investigates noise inhibition of a double quantum dot (DQD) transport system based on closed-loop feedback control. The unique advantage of a DQD device is that bidirectional transport at low bias can be measured by a nearby quantum point contact. However, the continuous monitoring of the DQD states inevitably leads to a measurement-induced dephasing. To appropriately characterize its transport properties in the presence of feedback action, we here develop a numerical method dubbed auxiliary density matrix approach, motivated by the hierarchical expansion of the moment-generating function in the hierarchy equations of motion [J. Cerrillo et al., Phys. Rev. B 94, 214308 (2016)]. This generic method has no restriction on the system structure and parameters and is able to evaluate the feedback current cumulants to an arbitrary order. It is revealed that the feedback control of the tunnel coupling between the two dots is the most effective to suppress the noise under various tunnel coupling configurations. The influence of interdot Coulomb interaction, measurement-induced dephasing, and finite time delay on feedback is also analyzed in detail.

Service Home Identification of Multiple-Source IoT Applications in Edge Computing

The real-time communication requirement of the Internet of Things (IoT) applications promotes the convergence of IoT and Mobile Edge Computing (MEC). The MEC paradigm greatly shortens the IoT service delay by leveraging cloudlets (edge servers) of MEC in the proximity of IoT devices. Considering limited computing and storage resources in an MEC network, it is challenging to provide efficient IoT-enabled service provisioning in such a network. In this article, we study the service home identification problem of service provisioning for multi-source IoT applications in an MEC network, by identifying a service home (cloudlet) of each multi-source IoT application for its data processing, querying and storage. Each multi-source IoT application consists of multiple sources located at different geographical locations and each source uploads its data stream via a gateway (its nearby access point) to the MEC network and the uploaded data then is aggregated with the stream data of the other sources of the IoT application at the service home. We here focus on two novel service home identification problems: the service operational cost minimization problem with the aim to minimize the total service operational cost by admitting as many multi-source IoT applications as possible, and the online throughput maximization problem with the aim to maximize the number of multi-source IoT application requests admitted. We first show that both the problems are NP-hard. We then formulate an Integer Linear Programming (ILP) solution to the service operational cost minimization problem, and propose a randomized algorithm with high probability and a deterministic approximation algorithm respectively, at moderate resource capacity violations. We third develop an efficient heuristic algorithm for the problem without any resource violation. Furthermore, we deal with the online throughput maximization problem under an assumption that multi-source IoT application requests arrive one by one without the knowledge of future arrivals, for which we formulate an Integer Linear Programming (ILP) solution to its offline version, followed by devising an online algorithm with competitive ratio. We finally evaluate the performance of the proposed algorithms through experimental simulations. Simulation results demonstrate that the proposed algorithms are promising, and outperform their comparison counterparts.

A digital hologram-based encryption and compression method for 3D models

This study proposes a novel method to compress and decompress the 3D models for safe transmission and storage. The 3D models are first extracted to become 3D point clouds, which would be classified by the K-means algorithm. Then, these nearby 3D point clouds are converted into a computer-generated hologram (CGH) by calculating the point distribution on the hologram plane using the optical wavefront propagation method. The computer-generated hologram (CGH) contains the spatial coordinate information on point clouds, which can be decompressed using the convolutional neural network (CNN) method. The decompression accuracy of 3D point clouds is quantitatively assessed by normalized correlation coefficients (NCCs), reflecting the correlation between two points and influenced by the hologram resolution, the convolution kernel, and the diffraction distance. Numerical simulations have shown that the novel method can reconstruct a high-quality 3D point cloud with an accuracy of 0.1 mm.

An X-Ray Proper-motion Study of the Large Magellanic Cloud Supernova Remnant 0509-67.5

We present a third epoch of Chandra observations of the Type Ia Large Magellanic Cloud Supernova remnant 0509-67.5. With these new observations from 2020, the baseline for proper-motion measurements of the expansion has grown to 20 yr (from the earliest Chandra observations in 2000). We report here the results of these new expansion measurements. The lack of nearby bright point sources renders absolute image alignment difficult. However, we are able to measure the average expansion of the diameter of the remnant along several projection directions. We find that the remnant is expanding with an average velocity of 6120 (4900–7360) km s−1. This high shock velocity is consistent with previous works, and also consistent with the inference that 0509-67.5 is expanding into a very low density surrounding medium. At the distance of the LMC, this velocity corresponds to an undecelerated age of 600 yr, with the real age somewhat smaller.

Federated edge learning for the wireless physical layer: Opportunities and challenges

Deep learning (DL) has been applied to the physical layer of wireless communication systems, which directly extracts environment knowledge from data and outperforms conventional methods either in accuracy or computation complexity. However, most related research works employ centralized training that inevitably involves collecting training data from edge devices. The data uploading process usually results in excessive communication overhead and privacy disclosure. Alternatively, a distributed learning approach named federated edge learning (FEEL) is introduced to physical layer designs. In FEEL, all devices collaborate to train a global model only by exchanging parameters with a nearby access point. Because all datasets are kept local, data privacy is better protected and data transmission overhead can be reduced. This paper reviews the studies on applying FEEL to the wireless physical layer including channel state information acquisition, transmitter, and receiver design, which represent a paradigm shift of the DL-based physical layer design. In the meantime they also reveal several limitations inherent in FEEL, particularly when applied to the wireless physical layer, thus motivating further research efforts in the field.