Terms Of Moments Research Articles

Physicists research practices: A perspective to rethink inquiry-based science education

Inquiry-Based Science Education (IBSE) is presented as derived from a scientific approach where students are invited to work in the way scientists work. Studying the proximity between IBSE and scientific approach can be done through different perspectives; the focus here is on the scientific approach. The goal of this case study consists in exploring the ways in which scientists perform their research by interviewing 8 French physicists volunteers to participate in the study. This preliminary research is the first step to analyze the contemporary physicists’ through research practices, and then to enrich and question IBSE in a different way. The interviews are analyzed in terms of moments, specifically a moment called “to explore/to experiment” with the ck¢ (conception, knowing, concept)framework allowing to model the conceptions of researchers. The results only show two common operators (R) related to the moment “to explore/ to experiment” concerning the research processes of the 8 physicists. However, zero control structures (∑) are common to any of them.

Numerical and experimental study of anti-slosh performance of combined baffles in partially filled tank vehicles

A numerical model based on VOF (Volume of Fluid) method is established to analyze liquid sloshing phenomenon in a partially filled cylindrical tank with or without various baffle arrangements. A series of slosh experiments were conducted on a scaled tank under harmonic acceleration excitations. The model is validated by comparing the slosh responses in terms of forces and moments with the measured data. The validated model is further employed to investigate the effect of combined baffles—proposed in the paper—on liquid sloshing motion. The results imply that conventional baffles could only limit liquid slosh in the longitudinal direction. The addition of combined baffles could suppress liquid slosh in both the longitudinal and lateral directions and the braking performance and roll stability limits of tank vehicles are thus improved.

Analysis of a Novel Two-Dimensional Lattice Hydrodynamic Model Considering Predictive Effect

In actual driving, the driver can estimate the traffic condition ahead at the next moment in terms of the current traffic information, which describes the driver’s predictive effect. Due to this factor, a novel two-dimensional lattice hydrodynamic model considering a driver’s predictive effect is proposed in this paper. The stability condition of the novel model is obtained by performing the linear stability analysis method, and the phase diagram between the driver’s sensitivity coefficient and traffic density is drawn. The nonlinear analysis of the model is conducted and the kink-antikink of modified Korteweg-de Vries (mKdV) equation is derived, which describes the propagation characteristics of the traffic density flow waves near the critical point. The numerical simulation is executed to explore how the driver’s predictive effect affects the traffic flow stability. Numerical results coincide well with theoretical analysis results, which indicates that the predictive effect of drivers can effectively avoid traffic congestion and the fraction of eastbound cars can also improve the stability of traffic flow to a certain extent.

Tunnel shape optimization method considering the interaction between lining and soil

Recent tunnel shape optimization considers only the stress distribution in the soil around the tunnel or the lining’s mechanical performance and frequently ignores the influence of the interaction between the lining and soil. Thus, this study presents a tunnel shape optimization method considering this interaction. First, the concept of a lining rational arch axis is employed to derive an analytical expression for the tunnel shape, which is subjected to earth pressure recommended by the International Tunneling Association (ITA). Further, the rationality of the obtained tunnel shape is verified using a finite element method (FEM) simulation, which considers the interaction between the lining and soil. Thus, an iterative FEM is further proposed to minimize the lining’s eccentricity. The tunnel shape is gradually modified via the iterative FEM by offsetting the lining axis along the normal vector using the corresponding eccentricity to obtain the optimal tunnel shape. The results reveal that, with the optimal tunnel shape based on the rational arch axis, the tunnel lining is mainly subjected to axial compressive force and exhibits good performance in terms of deformation and bending moment.

Quark anomalous magnetic moment and its effects on the ρ meson properties

A symmetry-preserving treatment of mesons, within a Dyson-Schwinger and Bethe-Salpeter equations approach, demands an interconnection between the kernels of the quark gap equation and meson Bethe-Salpeter equation. Appealing to those symmetries expressed by the vector and axial-vector Ward-Green-Takahashi identitiges (WGTI), we construct a two-body Bethe-Salpeter kernel and study its implications in the vector channel; particularly, we analyze the structure of the quark-photon vertex, which explicitly develops a vector meson pole in the timelike axis and the quark anomlaous magnetic moment term, as well as a variety of $\rho$ meson properties: mass and decay constants, electromagnetic form factors, and valence-quark distribution amplitudes.

A method for calculating the nonequilibrium entropy of a flowing polymer melt via atomistic simulation.

Nonequilibrium thermodynamics as applied to polymeric liquids is limited by the inability to quantify the configurational entropy. There is no known experimental method to determine it rigorously. Theoretically, entropy is based entirely on the configurational microstate of the material, but for polymer liquids, the number of available configurations is immense and covers long length scales associated with the chain-like nature of the constituent molecules. In principle, however, it should be possible to calculate the entropy from a realistic molecular dynamics simulation that contains positional data for each atomic unit making up the polymer macromolecules. However, there are two challenges in calculating the entropy from an atomistic simulation: it is necessary to relate atomic positions to configurational mesostates, depending on the degree of coarse-graining assumed (if any), and then to entropy, and considerable computational resources are required to determine the three-dimensional probability distribution functions of the configurational mesostates. In this study, a method was developed to calculate nonequilibrium entropy using 3d probability distributions for a linear, entangled polyethylene melt undergoing steady-state shear and elongational flow. An approximate equation expressed in terms of second moments of the 3d distributions was also examined, which turned out to provide almost identical values of entropy as the fully 3d distributions at the mesoscopic level associated with the end-to-end vector of the polymer chains.

Performance analysis of efficient digital modulation schemes over various fading channels

Using a simple yet accurate two-term exponential based approximation of the Gaussian Q function, in this paper, we simplify the intractable yet significant integrals which are used in the symbol error probability (SEP) expressions of various efficient digital modulation schemes over various well known fading statistics like Rayleigh, Nakagami-m, Nakagami-q and Nakagami-n. Precisely, we express these integrals in terms of simple moment generating function (MGF) whose solution for the aforementioned fading channels can be easily obtained from the literature. This MGF based approach simplifies the cumbersome integrals and eventually makes the SEP expressions tractable. The analytical work is further validated with the help of Monte-Carlo simulations.

Gravitational multipole moments for asymptotically de Sitter spacetimes

We provide a prescription to compute the gravitational multipole moments of compact objects for asymptotically de Sitter spacetimes. Our prescription builds upon a recent definition of the gravitational multipole moments in terms of Noether charges associated to specific vector fields, within the residual harmonic gauge, dubbed multipole symmetries. We first derive the multipole symmetries for spacetimes which are asymptotically de Sitter; we also show that these symmetry vector fields eliminate the non-propagating degrees of freedom from the linearized gravitational wave equation in a suitable gauge. We then apply our prescription to the Kerr-de Sitter black hole and compute its multipole structure. Our result recovers the Geroch-Hansen moments of the Kerr black hole in the limit of vanishing cosmological constant.

Searching for Magnetic Monopoles with Earth's Magnetic Field.

Magnetic monopoles have long been predicted in theory and could exist as a stable object in our Universe. As they move around in galaxies, magnetic monopoles could be captured by astrophysical objects like stars and planets. Here, we provide a novel method to search for magnetic monopoles by detecting the monopole moment of Earth's magnetic field. Using over six years of public geomagnetic field data obtained by the Swarm satellites, we apply Gauss's law to measure the total magnetic flux, which is proportional to the total magnetic charge inside Earth. To account for the secular variation of satellite altitudes, we define an altitude-rescaled magnetic flux to reduce the dominant magnetic dipole contribution. The measured magnetic flux is consistent with the existing magnetic field model that does not contain a monopole moment term. We therefore set an upper limit on the magnetic field strength at Earth's surface from magnetic monopoles to be |B_{m}|<0.13 nT at 95%confidence level, which is less than 2×10^{-6} of Earth's magnetic field strength. This constrains the abundance of magnetically charged objects, including magnetic black holes with large magnetic charges.

Biomechanical Analysis of the Knee Joint during Jump Landing of Genu Valgum Women

The purpose of this study was to identify the analysis of kinematics and kinetic of jump landing on lower extremities in women with valgus knees. To this study, 24 adult women without musculoskeletal diseases were selected as participants. They were separated into a normal group (12 women with quadriceps angles (Q angles) of lower than 20 degrees) and a valgus group (12 women with Q angles of greater than 20 degrees). The study analysis variables were the joint angle and the moment by event, and the center of pressure and the ground reaction force during jump landing. Eight motion capture cameras and two ground reaction force measuring devices were employed to measure and analyze these variables. In the study, Cortex 5.0 was used as a motion analysis program and SPSS 25.0 for Windows was used for data processing. In addition, the independent samples t-test was employed to analyze kinematics and kinetics differences between the valgus and normal groups during jump landing. The statistical significance level was set at p<0.05. According to the study results, in terms of the kinematic factors during jump landing, no statistically significant differences were identified in the knee joints. But, in terms of the knee joint moment of kinematic factors during jump landing, the valgus group showed a significant, larger extension and valgus moment than the normal group. A comprehensive review of the study findings suggests that knee extension and valgus moment increases tibial internal rotation in women with valgus, which results in valgus deformity and the following abnormal movements during jump landing.

К ОБРАТНОЙ ЗАДАЧЕ НЕБЕСНОЙ МЕХАНИКИ

The link between exterior solutions to the Einstein gravitational field equations such as the exact Erez-Rosen metric and approximate Hartle-Thorne metric is established here for the static case in the limit of linear mass quadrupole moment (Q) and second order terms in total mass (M). To this end, the Geroch-Hansen multipole moments are calculated for the Erez-Rosen and Hartle-Thorne solutions in order to find the relationship among the parameters of both metrics. The coordinate transformations are sought in a general form with two unknown functions in the corresponding limit of ~Q and ~M^2. By employing the perturbation theory, the approximate Erez-Rosen metric is written in the same coordinates as the Hartle-Thorne metric. By equating the radial and azimuthal components of the metric tensor of both solutions the sought functions are found in a straightforward way. It is shown that the approximation ~Q and ~M^2, which is used throughout the article, is physical and suitable for solving most problems of celestial mechanics in post-Newtonian physics. This approximation does not require the use of the Zipoy-Voorhees transformation, which is a necessary strict mathematical requirement in the ~Q approximation, i.e. when no other approximations are made. This implies that the explicit form of the coordinate transformations depends entirely on the approximation that is adopted in each particular case. The results obtained here are in agreement with the previous results in the literature and can be applied to different astrophysical goals. The paper pursues not only pure scientific, but also academic purposes and can be used as an auxiliary and additional material to the special courses of general theory of relativity, celestial mechanics and relativistic astrophysics.

A resilient column with angular friction damper for seismic performance upgrading of underground structures

Underground structures can be vulnerable due to seismic-induced deformation. A resilient underground structure is preferable for seismic response mitigation and quick recovery. In this study, a resilient central column with angular friction damper (RC-AFD) was constructed for the seismic performance upgrading of underground structures, and a practical design procedure was developed for the RC-AFD to enable the two-state control for underground structures subject to seismic excitations with multi-intensity. The RC-AFD consists of a self-centering column characterized by relaxed constraints at the top and bottom column that is restricted by unbounded prestressed tendons, whereas a pair of angular friction dampers are placed at the top of the central column. The mechanical model and its physical realization are detailed, whereas the two-state control mechanism is proposed by following the enhanced demand of seismic performance upgrading. The effectiveness and robustness of the proposed RC-AFD for structural seismic response mitigation of typical underground structures were investigated in terms of structural displacement, shear force, bending moments, and energy-based responses. The obtained results show that the two flexible connection joints concentrated at the top and bottom of the RC-AFD produce a significant isolation effect, through which the multiple responses of the central column can be reduced significantly. Benefiting from the two-state design and the employed angular friction damper with a large radius plate, the RC-AFD exhibits an enhanced energy dissipation capacity, which robustly dissipates the intense plastic energy for multi-intensity excitations. As a consequence, the plastic energy dissipation burden of the primary structures can be significantly relieved and residual deformation can be avoided due to the excellent self-centering ability.

The future of autonomous underwater vehicle control

The future of autonomous underwater vehicle control

Shake table testing for the seismic response of a container crane with uplift and derailment

In the seismic analysis, the boundary condition of a container crane is a complex problem when dealing with the contact between the crane's toes and the ground surface or wharf deck. In operation, the wheels of container cranes move on rails freely but are usually anchored when at rest. Therefore, the wheels could be lifted up and derailed due to seismic excitation. The boundary condition of a container crane has not been fully addressed in past research. It has mostly been simplified as pin supports without considering the possibilities of uplift and derailment of the crane legs. Hence, there is a need to conduct a study focusing on the effects of derailment and uplift on a container crane's seismic response. This paper investigates the seismic response of a container crane via a shake table testing of a 1/20 scale crane constructed according to the similitude law, with a simulation of the boundary condition of the scale crane as a pin and a friction boundary. A white noise test was conducted to determine the natural frequencies of the scale crane, then the seismic response of the container crane was determined via three input ground motions. The three input ground motions were designed by matching real earthquakes to the Korean design elastic response spectrum and scaling down for the shake table testing. Under these seismic excitations, the responses of the container crane were considered in terms of uplift, derailment, portal movement, and bending moments. The shake table testing shows that the maximum difference in the natural frequencies of the crane for the portal sway mode, between the friction boundary and pin support, was 2.1%. Due to the effects of derailment and uplift of the landside legs, the bending moments in the crane's seaside legs with a friction boundary were 109% higher than those with a pinned boundary. In addition, a residual deformation was observed in the portal frame after the vibration had stopped when the scale crane was assigned a friction boundary.

Microscopic theory of magnetoconductivity at low magnetic fields in terms of Berry curvature and orbital magnetic moment

Using a microscopic theory for the magnetoconductivity at low magnetic fields we show how the Hall and longitudinal conductivity can be calculated in the low scattering rate limit. In the lowest order of the scattering rate, we recover the result of the semiclassical Boltzmann transport theory. At higher order, we get corrections containing the Berry curvature and the orbital magnetic moment. We use this formalism to study the linear longitudinal magnetoconductivity in tilted Weyl semimetals. We discuss how our result is related to the semiclassical Boltzmann approach and show the differences that arise compared to previous studies related to the orbital magnetic moment.

The EUREC&amp;lt;sup&amp;gt;4&amp;lt;/sup&amp;gt;A turbulence dataset derived from the SAFIRE ATR 42 aircraft

Abstract. During the EUREC4A field experiment that took place over the tropical Atlantic Ocean east of Barbados, the French ATR 42 environment research aircraft of SAFIRE aimed to characterize the shallow cloud properties near cloud base and the turbulent structure of the subcloud layer. For this purpose, the aircraft payload included radar and lidar remote sensing, microphysical probes, a laser spectrometer, and meteorological sensors. In particular, the aircraft was equipped with a five-hole radome nose as well as several temperature and moisture sensors allowing for measurements of wind, temperature and humidity at 25 Hz. This paper presents the high-frequency measurements made with these sensors and their translation in terms of turbulent fluctuations, turbulent moments and characteristic length scales of turbulence. A particular focus is on the calibration and the quality control of the air moisture measurements, which remain a challenge at fine scales. Level-2 and Level-3 data are distributed as an ensemble of NetCDF files available to the public at AERIS (https://doi.org/10.25326/128, Lothon and Brilouet, 2020).

Characterization of Monochromatic Aberrated Metalenses in Terms of Intensity-Based Moments.

Consistent with wave-optics simulations of metasurfaces, aberrations of metalenses should also be described in terms of wave optics and not ray tracing. In this respect, we have shown, through extensive numerical simulations, that intensity-based moments and the associated parameters defined in terms of them (average position, spatial extent, skewness and kurtosis) adequately capture changes in beam shapes induced by aberrations of a metalens with a hyperbolic phase profile. We have studied axial illumination, in which phase-discretization induced aberrations exist, as well as non-axial illumination, when coma could also appear. Our results allow the identification of the parameters most prone to induce changes in the beam shape for metalenses that impart on an incident electromagnetic field a step-like approximation of an ideal phase profile.

Polynomial Series Expansions and Moment Approximations for Conditional Mean Risk Sharing of Insurance Losses

This paper exploits the representation of the conditional mean risk sharing allocations in terms of size-biased transforms to derive effective approximations within insurance pools of limited size. Precisely, the probability density functions involved in this representation are expanded with respect to the Gamma density and its associated Laguerre orthonormal polynomials, or with respect to the Normal density and its associated Hermite polynomials when the size of the pool gets larger. Depending on the thickness of the tails of the loss distributions, the latter may be replaced with their Esscher transform (or exponential tilting) of negative order. The numerical method then consists in truncating the series expansions to a limited number of terms. This results in an approximation in terms of the first moments of the individual loss distributions. Compound Panjer-Katz sums are considered as an application. The proposed method is compared with the well-established Panjer recursive algorithm. It appears to provide the analyst with reliable approximations that can be used to tune system parameters, before performing exact calculations.

A generalized sextic Freud weight

ABSTRACT We discuss the recurrence coefficients of orthogonal polynomials with respect to a generalized sextic Freud weight with parameters and . We show that the coefficients in these recurrence relations can be expressed in terms of Wronskians of generalized hypergeometric functions . We derive a nonlinear discrete as well as a system of differential equations satisfied by the recurrence coefficients and use these to investigate their asymptotic behaviour. We conclude by highlighting a fascinating connection between generalized quartic, sextic, octic and decic Freud weights when expressing their first moments in terms of generalized hypergeometric functions.

On Inheritances

In this presentation for the Asian American Writers’ Workshop, Tamara K. Nopper analyzes the emergent discourses of “anti-Asian violence” and “Black-Asian solidarity” within historical and sociological contexts. She begins with a discussion of the importance of the 1980s and 1990s as formative moments in terms of post-Asian American Movement organizational infrastructure. She then discusses interracial violence, the coeval growth of hate crime data and legislation, and the hashtag #StopAAPIHate. Her primary concern in this discussion is to reveal what work these narrative framings do in service of or in opposition to anti-Blackness and carcerality.