Static Domain Research Articles

Monitoring of ageing campaigns of PEM fuel cell stacks using a model-based method

Nowadays, Proton Exchange Membrane Fuel Cells (PEMFC) are considered as a promising solution for transportation applications, especially for the aeronautical field in the context of development of a “More Electrical Aircraft”. Due to various operating conditions, the State of Health (SoH) of a Proton Exchange Membrane Fuel Cell (PEMFC) could be degraded implying a possible decrease of its performance and durability. Hence, there must be a development of tools dedicated to the PEMFC diagnosis and ageing monitoring. In this context, this paper introduces a model-based method contributing to the monitoring of the SoH of a PEMFC in aircraft applications. The proposed methodology consists of the tracking of the temporal evolution a chosen Quasi-Static (QS) model parameters, these parameters being associated with the various physicochemical phenomena involved in a Fuel Cell (FC): activation, diffusion and ohmic. Parameters of the model are identified from a measurement regularly carried out throughout the fuel cell life: the polarization curve (V–I curve). The present model uses also high-frequency resistance measured via Electrochemical Impedance Spectroscopies (EIS) performed at various current values of the polarization curve. This methodology is evaluated here in the framework of three ageing campaigns carried out with three 1 kW PEM stacks operating at low temperature (50 – 80 °C). In this paper, a particular attention is paid to calculations and results relating to the first ageing campaign. A comparison of the results related to the three campaigns is achieved as a part of this work. In addition to the good reproduction of experimental data and the separation of losses in the static domain, the QS model presented in this paper makes it possible to monitor the FC SoH via the follow-up of losses and their related parameters.

Fundamental solutions and integral equations of first-order laminated composite beams

Laminated composite materials consist of oriented plies usually bonded together to provide desirable mechanical properties such as high stiffness and strength to weight ratio. The result is a feasible solution for many technological problems, principally in the naval, aerospace, and automotive industries. Laminated composite beams have been represented in many mathematical models since 3D elasticity to laminated beam theories such as discrete-layer approaches and equivalent single-layer models (ESL). In this article, the mathematical steps for deriving the fundamental solutions and integral equations of an ESL model, called first-order laminated composite beam theory (FOBT), under static loading are presented. The direct boundary element method (BEM) solution is properly addressed, incorporating topics such as: (a) explicit forms of influence matrices, (b) load vectors for concentrated loading and (trapezoidal, sinusoidal) distributed loading, and (c) reduction of BEM solution to the classical laminated beam theory. Numerical results are presented for beams under different static load cases, boundary conditions, and domain discontinuity problems associated with stepped beams and continuous beams. The results suggest the correctness and effectiveness of this direct BEM formulation.

HDRS: Hindi Dialogue Restaurant Search Corpus for Dialogue State Tracking in Task-Oriented Environment

Due to the rapid increase in the development of Task-oriented dialogue systems, the need for labelled dialogue corpus has become inevitable. For the Hindi language, there is no such dialogue corpus yet available. As a first attempt, we release a Hindi Dialogue Restaurant Search (HDRS) corpus and compare various state-of-the-art dialogue state tracking (DST) models on it. The corpus consists of 1.4 k human-to-human typed dialogues collected using Wizard-of-Oz paradigm. The paper starts with a brief description of the corpus by providing the details of features, corpus collection process and statistical analysis, then the performance of baseline NLU and DST models are investigated. Further, we experimented two categories of state-of-the-art belief state trackers: (1) Non-contextual pre-trained word embedding based DST models; (2) Contextual pre-trained BERT based DST models. All belief trackers follow a three-layered generic architecture. The category-1 models use the static domain ontology, while category-2 models have the capability to handle the dynamic ontology. The DST models are compared on joint-goal and turn-request accuracy. Global encoder and Slot-ATtentive decoders (GSAT) outperforms all the models with 83.25% joint-goal accuracy, followed by SUMBT.

Competitive mechanism of temperature-dependent electrical properties in BiFeO3-BaTiO3 ferroelectrics controlled by domain evolution

To understand the structure nature and physical mechanisms of property evolution under electric and temperature fields, temperature-dependent electrical properties of bismuth ferrite-barium titanate (BiFeO3-BaTiO3, BF-BT) ceramics were analyzed from both static structure and domain dynamics. Intriguingly, temperature coefficient of remanent polarization (Pr) and negative strain (Sneg) changes from positive to negative as BT component increases, leading to a nearly zero temperature coefficient of Pr at critical component (BT=0.35). Combined with multi-scale structure characterization techniques and polarization switching/backswitching described by the temperature-dependent Ps and Ps-Pr, such behavior is explained by the evolution of domain size for the first time and a competitive mechanism is also proposed. That is, the evolution of macro stripe domain (0.25≤BT≤0.30) to nanodomain (0.35≤BT≤0.45) determines the transition from the dominated polarization switching process to the dominated backswitching process, further greatly determining the temperature-stability of strain properties: variation of unipolar strain changes from 136% (BT=0.25) to 25% (BT=0.45) with increasing BT content. We believe that these results significantly guide the performance improvement (especially temperature-dependent properties) of BF-BT solid solutions.

Crystallization of magnetic skyrmions in MnSi investigated by neutron spin echo spectroscopy

The authors study crystallization process of magnetic skyrmions in a chiral magnet MnSi by means of a resonance-type neutron spin echo spectroscopy in a magnetic field, and find that the skyrmions aggregate into small static triangular-lattice domains near the critical temperature.

Examination of WRF-ARW Experiments Using Different Planetary Boundary Layer Parameterizations to Study the Rapid Intensification and Trajectory of Hurricane Otto (2016)

Hurricane Otto (2016) was characterised by remarkable meteorological features of relevance for the scientific community and society. Scientifically, among the most important attributes of Otto is that it underwent a rapid intensification (RI) process. For society, this cyclone severely impacted Costa Rica and Nicaragua, leaving enormous economic losses and many fatalities. In this study, a set of three numerical simulations are performed to examine the skill of model estimations in reproducing RI and trajectory of Hurricane Otto by comparing the results of a global model to a regional model using three different planetary boundary layer parameterizations (PBL). The objective is to set the basis for future studies that analyse the physical reasons why a particular simulation (associated with a certain model setup) performs better than others in terms of reproducing RI and trajectory. We use the regional model Weather Research and Forecasting—Advanced Research WRF (WRF-ARW) with boundary and initial conditions provided by the Global Forecast System (GFS) analysis (horizontal resolution of 0.5 degrees). The PBL used are the Medium Range Forecast, the Mellor-Yamada-Janjic (MYJ), and the Yonsei University (YSU) parameterizations. The regional model is run in three static domains with horizontal grid spacing of 27, 9 and 3 km, the latter covering the spacial extent of Otto during the simulation period. WRF-ARW results improve the GFS forecast, in almost every aspect evaluated in this study, particularly, the simulated trajectories in WRF-ARW show a better representation of the cyclone path and movement compared to GFS. Even though the MYJ experiment was the only one that exhibited an abrupt 24-h change in the storm’s surface wind, close to the 25-knot threshold, the YSU scheme presented the fastest intensification, closest to reality.

Study Recognizes and Assists in Mitigation of Bottomhole Assembly Lateral Vibration Chatter

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 197231, “Recognition and Mitigation of the Bottomhole Assembly Lateral Vibration Chatter Mode,” by Jeffrey R. Bailey, SPE, and Harshit Lathi, ExxonMobil, and Matthew T. Prim, SPE, ADNOC, et al., prepared for the 2019 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11-14 November. The paper has not been peer reviewed. Lateral vibration modeling of certain bottomhole assembly (BHA) designs has shown great sensitivity to the proximity of stabilizer blades. This paper explores the nature of the vibrational dysfunction known as BHA chatter. A field-proven frequency-domain model illustrates the cause of the dysfunction, its rotary-speed dependence, and mitigation methods and results. The complete paper provides three case studies exploring this phenomenon, one of which is included in this synopsis. Introduction The authors first describe the similarities and differences of a BHA and a stringed instrument. The string of a violin, for example, typically has two fixed nodal points: the first at the bridge, which does not change, and the second at the position of the musician’s finger, which is moved along the fingerboard in order to play notes of different frequencies. The finger pressing on the string causes it to have zero displacement at that location, which defines a nodal point. Additional nodal points may occur in the motion of the string as harmonics of the fundamental mode, but these are not considered to be fixed nodes because the amplitudes of the harmonics vary. The string is relatively flexible, so it can be described adequately with a second-order differential equation. Significantly, a BHA typically has more than two nodes. A lateral wave propagating along the BHA must satisfy the nodal point constraint of zero lateral deflection at all these locations. These nodes typically are placed without regard to the frequency of the wave traveling along the string, which is governed by the rotary speed and the type of lateral excitation. The geometric compatibility requirement that the pipe has zero displacement at the fixed nodes has ramifications. The nodal point constraints force the pipe to adapt to the locations of these nodes through contact forces that literally push the pipe back into position to honor the constraints. In some scenarios, this process requires large forces. One consequence of large forces pushing the pipe to maintain geometric compatibility is that these forces are applied to the outer diameter of a body that is rotating, so this response may also generate torque and associated wear of the contacting surfaces. This observation applies to both static and dynamic forces but most commonly is recognized in the static domain. It is not typically recognized in dynamics as applied to BHA design.

Numerical analysis of a long-span bridge response to tornado-like winds

This study focused on the non-synoptic, tornado-like wind-induced effects on flexible horizontal structures that are extremely sensitive to winds. More specifically, the nonuniform, intensive vertical wind-velocity and transient natures of tornado events and their effects on the global behavior of a long-span bridge were investigated. In addition to the static part in the modeling of tornado-like wind-induced loads, the motion-induced effects were modeled using the semi-empirical model with a two-dimensional (2-D) indicial response function. Both nonlinear wind-induced static analysis and linear aeroelastic analysis in the time domain were conducted based on a 3-D finite-element model to investigate the bridge performance under the most unfavorable tornado pattern considering wind-structure interactions. The results from the present study highlighted the important effects due to abovementioned tornado natures (i.e., nonuniform, intensive vertical wind-velocity and transient features) on the long-span bridge, and hence may facilitate more appropriate wind design of flexible horizontal structures in the tornado-prone areas.

A dictionary-based method for detecting machine-generated domains

ABSTRACT Internet robots, also known as bots, have transformed the businesses and society with convenience. However, the dynamics of these interactions could be under adversarial circumstances with detrimental effects on network security. Bots that use domain-generation algorithms (DGAs) can generate many random domains dynamically so that static domain blacklists become ineffective in preventing malicious attacks by botnets. Various families of recent botnets have used DGA to establish communication with the bots. Researchers have introduced various detection methods with moderate success. Methods proposed so far either detect only DGAs that use non-variations forms or focus on the classification accuracy instead of time complexity, which would be critical in real-world production. The goal of this article is to explore how machine learning can help in detecting machine-generated domain names. To that end, we propose a dictionary-based n-gram method that can detect 39 DGA variations. We compared our method with existing research and found that our method can improve the performance of the existing classification algorithms. At last, our method can achieve competitive results as the LSTM model while requiring less time and complexity. Our research helps real-time production for DGA detection and provides insight in protecting DNS server and information security.

High-pressure behavior of dielectric constant in a binary critical mixture

An alternative design of the measurement capacitor for high-pressure studies of complex liquids or soft matter systems is presented. Subsequently, results for the precritical anomaly of dielectric constant in 1-nitropropane-octane critical mixture are reported. First, the pressure dependence of the critical consolute temperature T_{C} up to P=0.55GPa was determined and portrayed using the derivative-based analysis. Second, temperature and pressure evolutions of dielectric constant on approaching the critical consolute point at (T_{C}=304.1K and P_{C}=403MPa) were studied. They revealed that the pretransitional anomaly ɛ(P→P_{C}) is notably more pronounced than for ɛ(T→T_{C}). For both paths, the static domain extends even to as low frequency as f=100Hz, whereas for tests under atmospheric pressure, they require at least f=100kHz. The discussion of the impact of correction-to-scaling terms, including the unique case of the pressure paths, is also presented.

Application of enstrophy dissipation to analyze energy loss in a centrifugal pump as turbine

Pump as turbine (PAT) is a type of energy recovery equipment. However, the mechanism of performance degradation when it deviates from the design working condition is inadequately reported. Hence, the steady performance of a centrifugal PAT with a design specific speed (nsd=3.65ndQd∕Hd0.75) of 90 was simulated by ANSYS-CFX 18.0. The shear stress transport (SST) k-ω turbulence model was used to close the Reynolds-averaged Navier–Stokes (RANS) equations and the simulation results of performance were verified by comparing the experimental. To explore the energy loss mechanism of the PAT under different flow conditions, the energy loss of each part of PAT was calculated by the enstrophy dissipation method, which not only accurately calculate the energy loss but also diagnose where and how hydraulic loss occurs. Compared with the traditional pressure drop assessment method, the enstrophy dissipation method has higher prediction accuracy for the rotating domain, almost the same prediction accuracy in the static domain. The energy loss of the PAT mainly occurs in the cavity, volute and impeller. Hydraulic loss is dominated by fluctuating enstrophy dissipation power and wall enstrophy dissipation power. Adverse flow phenomena such as backflow and shock flow could evidently increase the volume and wall enstrophy dissipation rates. Therefore, the proposed method can be used intuitively to provide a reference for PAT performance optimization and actual operation regulation.

Conformal scale factor inversion for domain walls and holography

We describe a correspondence between domain wall solutions of Einstein gravity with a single scalar field and self-interaction potential. The correspondence we call conformal scale factor inversion (CSFI) is a map comprising the inversion of the scale factor in conformal coordinates, and a transformation of the field and its potential which preserves the form of the Einstein equations for static and isotropic domain walls. By construction, CSFI maps the asymptotic anti--de Sitter boundary to the vicinity of a naked singularity in a theory with a special Liouville (exponential) scalar field potential; it is also a map in the parameter space of exponential potentials. The correspondence can be extended to linear fluctuations, being akin to an S-duality, and can be interpreted in terms of ``SUSY quantum mechanics'' for the fluctuation modes. The holographic implementation of CSFI relates the UV and IR regimes of a pair of holographic renormalization group flows; in particular, it is a symmetry of the GPPZ flow.

The leopard never changes its spots

Previous research in pattern formation using reaction-diffusion mostly focused on static domains, either for computational simplicity or mathematical tractability. In this work, we have explored the expressiveness of combining simple mechanisms as a possible explanation for pigmentation pattern formation, where tissue growth plays a crucial role. Our motivation is not only to realistically reproduce natural patterns but also to get insights into the underlying biological processes. Therefore, we present a novel approach to generate realistic animal skin patterns. First, we describe the approximation of tissue growth by a series of discrete matrix expansion operations. Then, we combine it with an adaptation of Turing's non-linear reaction-diffusion model, which enforces upper and lower bounds to the concentrations of the involved chemical reagents. We also propose the addition of a single-reagent continuous autocatalytic reaction, called reinforcement, to provide a mechanism to maintain an already established pattern during growth. By careful adjustment of the parameters and the sequencing of operations, we closely match the appearance of a few real species. In particular, we reproduce in detail the distinctive features of the leopard skin, also providing a hypothesis for the simultaneous productions of the most common melanin types, eumelanin and pheomelanin.

EXPLORING EFL TEACHERS� UNDERSTANDING AND BELIEFS IN INTERCULTURAL COMMUNICATIVE COMPETENCE IN INDONESIAN CONTEXT

As the result of globalization, the English language teaching goals in many countries have shifted from communicative competence to intercultural communicative competence (ICC). However, among the small number of studies on ICC in Indonesia, most of them focus on ICC in the tertiary level which shows there is a gap of work in the secondary level of education. Thus, this article attempts to seek the truth about senior high school teachers� understanding and beliefs as well as revealing their attempts in promoting ICC in the classroom. The case study was employed with two novice teachers as participants through interview and document analysis. The finding shows some interesting facts that both teachers viewed concept of ICC similarly as cross-cultural understanding in a way both to overcome misunderstanding and culture shock. Both teachers believed that language is culture bound, yet, only a very small trace of cultural aspects were shown in the documents; and as they viewed culture as dynamic, yet, the content being taught mainly covered static domain of culture.��Keywords: Byram�s five savoirs; culture education; intercultural communicative competence.

InvaliDB

Traditional databases are optimized for pull-based queries, i.e. they make information available in direct response to client requests. While this access pattern is adequate for mostly static domains, it requires inefficient and slow workarounds (e.g. periodic polling) when clients need to stay up-to-date. Acknowledging reactive and interactive workloads, modern real-time databases such as Firebase, Meteor, and RethinkDB proactively deliver result updates to their clients through push-based real-time queries. However, current implementations are only of limited practical relevance, since they are incompatible with existing technology stacks, fail under heavy load, or do not support complex queries to begin with. To address these issues, we propose the system design InvaliDB which combines linear read and write scalability for real-time queries with superior query expressiveness and legacy compatibility. We compare InvaliDB against competing system designs to emphasize the benefits of our approach. To validate our claims of linear scalability, we further present an experimental evaluation of the InvaliDB prototype that has been serving customers at the Database-as-a-Service company Baqend since July 2017.

Domain wall contributions to piezoelectricity in relaxor-lead titanate single crystals

It is demonstrated that the dielectric permittivity and piezoelectric coefficients in relaxor-PbTiO3 single crystals close to the morphotropic phase boundary (MPB) can be augmented by contributions from domain walls. Landau-Ginzburg-Devonshire models, incorporating both polarization and strain gradients through the domain walls, show that wall contributions in domain engineered single crystals originate from enhanced, field-induced polarization rotation in static domain walls, unlike ceramics, in which piezoelectricity is enhanced by domain wall translation. For 71° domain walls in 0.7 Pb(Mg1/3Nb2/3)O3 – 0.3PbTiO3 the piezoelectric charge coefficient d33 at the center of the wall ranges from 5000 to >30,000 pC N−1 depending on the wall width. Thus, a sufficiently high domain wall density can account for the experimentally observed augmentation in the measured properties compared to single domain models. The symmetry of the domain walls explains both the variety of average symmetries observed close to the MPB and the experimentally observed switching of the [001]-oriented crystals into the tetragonal phase via a symmetry-improbable MC phase. For a crystal of rhombohedral ground state, the presence of domain walls will impart monoclinic symmetry, the predominance of which increases with increasing domain wall density.

Facial Paralysis and Communicative Participation: The Importance of Facial Symmetry at Rest.

There is a paucity of research devoted to understanding the communication restrictions encountered by facial paralysis patients. We aim to explore the relationship between patient-reported restrictions in communicative participation and objective facial paralysis severity using validated scales of facial movement. We performed a pilot retrospective study using a consecutive series of adult patients with a diagnosis of unilateral facial paralysis. In addition to baseline demographics, subjects were evaluated using the Communicative Item Participation Bank Short Form (CPIB), Electronic Facial Assessment by Computer Evaluation (eFACE), and Sunnybrook Facial Grading System (SFGS). Twenty patients were included, 10 (50%) of whom were female with a mean age of 61 ± 13 years and mean duration of facial paralysis of 53 ± 82 months. The mean CPIB score was 14.6 ± 10.0 (range 0-29) and was comparable to scores of patients with conditions known to cause significant communicative disability. The mean eFACE scores were 67.4 ± 29.2, 44.2 ± 30.1, and 73.8 ± 30.0 for the static, dynamic, and synkinesis domains, respectively, with a composite smile score of 58.5 ± 16.9. After adjusting for age, gender, and duration of facial paralysis, significant moderate correlations were observed between the CPIB and the static eFACE domain (r = -0.51, P = .03) and smile composite score (r = 0.48, P = 0.0049), in addition to between the CPIB and SFGS synkinesis domain (r = 0.48, P = 0.04). Patients with unilateral facial paralysis experience significant limitations in communicative participation. These restrictions demonstrate moderate to strong correlations with objective assessments of facial paralysis and quality of life measures. Communicative participation may be a helpful means of tracking response to treatment. IV.

Cell Size, Mechanical Tension, and GTPase Signaling in the Single Cell.

Cell polarization requires redistribution of specific proteins to the nascent front and back of a eukaryotic cell. Among these proteins are Rac and Rho, members of the small GTPase family that regulate the actin cytoskeleton. Rac promotes actin assembly and protrusion of the front edge, whereas Rho activates myosin-driven contraction at the back. Mathematical models of cell polarization at many levels of detail have appeared. One of the simplest based on "wave-pinning" consists of a pair of reaction-diffusion equations for a single GTPase. Mathematical analysis of wave-pinning so far is largely restricted to static domains in one spatial dimension. Here, we extend the analysis to cells that change in size, showing that both shrinking and growing cells can lose polarity. We further consider the feedback between mechanical tension, GTPase activation, and cell deformation in both static, growing, shrinking, and moving cells. Special cases (spatially uniform cell chemistry, the absence or presence of mechanical feedback) are analyzed, and the full model is explored by simulations in 1D. We find a variety of novel behaviors, including "dilution-induced" oscillations of Rac activity and cell size, as well as gain or loss of polarization and motility in the model cell.

Electro-optic evolution driven by static and relaxational nano ferroelectric domains in KTa1−xNbxO3

Both the relaxational nano-domains driven by biased electric fields under ordered static domains and strong anisotropy determined by the deformation of the NbO6/TaO6 realize enhancements of EO properties in the vicinity of Tf.

The annual surface temperature patterns across the Dead Sea as retrieved from thermal images

Satellite images capture a large scene instantaneously, enabling direct comparisons of surface–atmosphere interactions in a static time domain. The annual course of surface temperature of the Dead Sea is investigated using thermal images obtained from Band 10 onboard Landsat 8. Retrieved sea surface temperature varied from around 20 °C in February to ~ 35 °C in July. Retrieved sea surface temperature is commensurate with extensive field measurements, with a root mean square error of 1.25 °C. Satellite images reveal three distinct thermal patterns. The first one is the presence of temperature variations across the open sea which may reflect differences in local meteorology and/or differential mixing with the deeper layers. The second feature is the different temperature skewness patterns between winter and summer months. A slight negative temperature skewness is observed during the period November through February, and a steep positive one during the rest of the year, with large values occurring during summer. These skewness patterns reflect the variations in the annual course of heating and cooling mechanisms occurring in the open sea and along the shallow shorelines. The third distinct feature is the presence of cold finger plumes during the cold months, extending around 4 km inside the open sea and covering an area in excess of 3 km2. The influence of freshwater flux on evaporation from large hypersaline water bodies is investigated using a theoretical formulation derived in this paper. Results show that the effect of freshwater flux on evaporation from hypersaline lakes is a complex process determined by activity and temperature departures. Satellite images provide an excellent surrogate to field observations which are money and labor intensive, time consuming, and very limited in their spatial coverage.