190,864 research outputs found
Dynamic Model and Phase Transitions for Liquid Helium
This article presents a phenomenological dynamic phase transition theory --
modeling and analysis -- for superfluids. As we know, although the
time-dependent Ginzburg-Landau model has been successfully used in
superconductivity, and the classical Ginzburg-Landau free energy is still
poorly applicable to liquid helium in a quantitative sense. The study in this
article is based on 1) a new dynamic classification scheme of phase
transitions, 2) new time-dependent Ginzburg-Landau models for general
equilibrium transitions, and 3) the general dynamic transition theory. The
results in this article predict the existence of a unstable region H, where
both solid and liquid He II states appear randomly depending on fluctuations
and the existence of a switch point M on the lambda-curve, where the
transitions changes types
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Using the Values-Practice Framework to adopt lifetime optimising behaviours: the case of maintenance
The influence that consumers have on the lifespan of products has attracted increased attention in recent years. Studies have provided an overall understanding of the factors that influence consumer attitudes and behaviours towards product longevity, categorised around the physical properties of a product, and individual and societal characteristics. However, such studies do not yet adequately explain how people could adopt product lifetime optimising behaviours. To fill this gap, the paper analyses a range of studies on what influences product lifetimes, focusing on maintenance activities. It proposes the use of the Values-Practice framework derived from two theoretical positions, social psychology and social practice theory, to consider how to facilitate the adoption of lifetime optimising behaviours. To build this framework, it analyses studies that classify factors influencing attitudes and behaviours towards product lifetimes and then links these to the âmeaningâ, âcompetenceâ and âmaterialâ elements of practice. The framework could be used as a tool to aid designers under stand the different elements and factors that engage people in maintenance activities. The paper concludes by considering the research requirements for the future application of the framework
Stratified Rotating Boussinesq Equations in Geophysical Fluid Dynamics: Dynamic Bifurcation and Periodic Solutions
The main objective of this article is to study the dynamics of the stratified
rotating Boussinesq equations, which are a basic model in geophysical fluid
dynamics. First, for the case where the Prandtl number is greater than one, a
complete stability and bifurcation analysis near the first critical Rayleigh
number is carried out. Second, for the case where the Prandtl number is smaller
than one, the onset of the Hopf bifurcation near the first critical Rayleigh
number is established, leading to the existence of nontrivial periodic
solutions. The analysis is based on a newly developed bifurcation and stability
theory for nonlinear dynamical systems (both finite and infinite dimensional)
by two of the authors [16]
Muscle Fatigue Analysis Using OpenSim
In this research, attempts are made to conduct concrete muscle fatigue
analysis of arbitrary motions on OpenSim, a digital human modeling platform. A
plug-in is written on the base of a muscle fatigue model, which makes it
possible to calculate the decline of force-output capability of each muscle
along time. The plug-in is tested on a three-dimensional, 29 degree-of-freedom
human model. Motion data is obtained by motion capturing during an arbitrary
running at a speed of 3.96 m/s. Ten muscles are selected for concrete analysis.
As a result, the force-output capability of these muscles reduced to 60%-70%
after 10 minutes' running, on a general basis. Erector spinae, which loses
39.2% of its maximal capability, is found to be more fatigue-exposed than the
others. The influence of subject attributes (fatigability) is evaluated and
discussed
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A critical analysis of COA research.
Five experts respected for their significant contributions to the scientific literature on children of alcoholics (COA's) offer their perspectives in a panel discussion format. The panel members reflect on the historical roots of COA research and comment on its current status and future direction. Enriched by the panelists' variety of backgrounds, research interests, and approaches, the discussion emphasizes the need to consider multiple variables that influence the risk for alcoholism among COA's
Shubnikov-de Haas oscillations of a single layer graphene under dc current bias
Shubnikov-de Haas (SdH) oscillations under a dc current bias are
experimentally studied on a Hall bar sample of single layer graphene. In dc
resistance, the bias current shows the common damping effect on the SdH
oscillations and the effect can be well accounted for by an elevated electron
temperature that is found to be linearly dependent on the current bias. In
differential resistance, a novel phase inversion of the SdH oscillations has
been observed with increasing dc bias, namely we observe the oscillation maxima
develop into minima and vice versa. Moreover, it is found that the onset
biasing current, at which a SdH extremum is about to invert, is linearly
dependent on the magnetic field of the SdH extrema. These observations are
quantitatively explained with the help of a general SdH formula.Comment: 5 pages, 4 figures, A few references adde
Anomalous Pinning Fields in Helical Magnets: Screening of the Quasiparticle Interaction
The spin-orbit interaction strength g_so in helical magnets determines both
the pitch wave number q and the critical field H_c1 where the helix aligns with
an external magnetic field. Within a standard Landau-Ginzburg-Wilson (LGW)
theory, a determination of g_so in MnSi and FeGe from these two observables
yields values that differ by a factor of 20. This discrepancy is remedied by
considering the fermionic theory underlying the LGW theory, and in particular
the effects of screening on the effective electron-electron interaction that
results from an exchange of helical fluctuations.Comment: 4pp, 2 fig
Dynamic Transitions for Quasilinear Systems and Cahn-Hilliard equation with Onsager mobility
The main objectives of this article are two-fold. First, we study the effect
of the nonlinear Onsager mobility on the phase transition and on the
well-posedness of the Cahn-Hilliard equation modeling a binary system. It is
shown in particular that the dynamic transition is essentially independent of
the nonlinearity of the Onsager mobility. However, the nonlinearity of the
mobility does cause substantial technical difficulty for the well-posedness and
for carrying out the dynamic transition analysis. For this reason, as a second
objective, we introduce a systematic approach to deal with phase transition
problems modeled by quasilinear partial differential equation, following the
ideas of the dynamic transition theory developed recently by Ma and Wang
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