9,523 research outputs found
Coarsening Dynamics of a One-Dimensional Driven Cahn-Hilliard System
We study the one-dimensional Cahn-Hilliard equation with an additional
driving term representing, say, the effect of gravity. We find that the driving
field has an asymmetric effect on the solution for a single stationary
domain wall (or `kink'), the direction of the field determining whether the
analytic solutions found by Leung [J.Stat.Phys.{\bf 61}, 345 (1990)] are
unique. The dynamics of a kink-antikink pair (`bubble') is then studied. The
behaviour of a bubble is dependent on the relative sizes of a characteristic
length scale , where is the driving field, and the separation, ,
of the interfaces. For the velocities of the interfaces are
negligible, while in the opposite limit a travelling-wave solution is found
with a velocity . For this latter case () a set of
reduced equations, describing the evolution of the domain lengths, is obtained
for a system with a large number of interfaces, and implies a characteristic
length scale growing as . Numerical results for the domain-size
distribution and structure factor confirm this behavior, and show that the
system exhibits dynamical scaling from very early times.Comment: 20 pages, revtex, 10 figures, submitted to Phys. Rev.
Does a loaded warm-up influence jump asymmetry and badminton-specific change of direction performance?
Purpose: Previously, it has been shown that loaded warm-up (LWU) can improve change of direction speed (CODS) in professional badminton players. However, the effect of asymmetry on CODS in badminton players and the influence of LWU on asymmetry has not been examined.
Methods: Twenty-one amateur badminton players (age: 29.5 ± 8.4; playing experience: 8.4 ± 4.2 years) completed two trials. In the first, they performed a control warm-up (CWU). In the second, they performed the same warm-up but with three exercises loaded with a weight vest (LWU). Following both warm-ups, players completed single leg jump (SLCMJ) and badminton-specific CODS tests.
Results: No significant differences between CWU and LWU were observed for CODS, SLCMJ or SLCMJ asymmetry. However, small effect sizes suggested faster CODS (mean difference: -5%; d = -0.32) and lower asymmetries (mean difference: -3%; d = -0.39) following LWU. Five players (24%) experienced CODS improvements greater than the minimum detectable change whilst two (10%) responded negatively. Asymmetry was not correlated with CODS following CWU (ρ = 0.079; p = 0.733) but was negatively associated with CODS after LWU (ρ = -0.491; p = 0.035).
Conclusion: LWU may prove a strategy to trial on an individual basis but generic recommendations should not be applied
Macrorealism from entropic Leggett-Garg inequalities
We formulate entropic Leggett-Garg inequalities, which place constraints on
the statistical outcomes of temporal correlations of observables. The
information theoretic inequalities are satisfied if macrorealism holds. We show
that the quantum statistics underlying correlations between time-separated spin
component of a quantum rotor mimics that of spin correlations in two spatially
separated spin- particles sharing a state of zero total spin. This brings
forth the violation of the entropic Leggett-Garg inequality by a rotating
quantum spin- system in similar manner as does the entropic Bell inequality
(Phys. Rev. Lett. 61, 662 (1988)) by a pair of spin- particles forming a
composite spin singlet state.Comment: 5 pages, RevTeX, 2 eps figures, Accepted for publication in Phys.
Rev.
Dynamics of Ordering of Heisenberg Spins with Torque --- Nonconserved Case. I
We study the dynamics of ordering of a nonconserved Heisenberg magnet. The
dynamics consists of two parts --- an irreversible dissipation into a heat bath
and a reversible precession induced by a torque due to the local molecular
field. For quenches to zero temperature, we provide convincing arguments, both
numerically (Langevin simulation) and analytically (approximate closure scheme
due to Mazenko), that the torque is irrelevant at late times. We subject the
Mazenko closure scheme to systematic numerical tests. Such an analysis, carried
out for the first time on a vector order parameter, shows that the closure
scheme performs respectably well. For quenches to , we show, to , that the torque is irrelevant at the Wilson-Fisher fixed
point.Comment: 13 pages, REVTEX, and 19 .eps figures, compressed, Submitted to Phys.
Rev.
Measurement of Lagrangian velocity in fully developed turbulence
We have developed a new experimental technique to measure the Lagrangian
velocity of tracer particles in a turbulent flow, based on ultrasonic Doppler
tracking. This method yields a direct access to the velocity of a single
particule at a turbulent Reynolds number . Its dynamics is
analyzed with two decades of time resolution, below the Lagrangian correlation
time. We observe that the Lagrangian velocity spectrum has a Lorentzian form
, in agreement
with a Kolmogorov-like scaling in the inertial range. The probability density
function (PDF) of the velocity time increments displays a change of shape from
quasi-Gaussian a integral time scale to stretched exponential tails at the
smallest time increments. This intermittency, when measured from relative
scaling exponents of structure functions, is more pronounced than in the
Eulerian framework.Comment: 4 pages, 5 figures. to appear in PR
Providing accessibility through implementation of electronic laboratory notebooks
Electronic Laboratory Notebooks (ELNs) have recently gained popularity in academia and industry while paper laboratory notebooks (PLNs) are becoming obsolete from the digital world. This is due to the many benefits of ELNs such as efficiency, accessibility, and data integrity (Bird, Willoughby, & Frey, 2013; Colabroy & Bell, 2019). In tertiary education, ELNs have been implemented to help students develop skills that are easily transferrable and prepare them for a technological rich workplace. Learning and understanding students’ and teaching staff perceptions’ of their experience with using ELNs, particularly during the COVID-19 pandemic, is key to successful implementation in education. A series of surveys were distributed and interviews were conducted across various undergraduate chemistry units from first to third year level and post-graduate teaching staff to gather insight into their perceptions of using PLNs and ELNs and the software platform, LabArchives.
This presentation will provide some insight into students’ and teaching staff’s experiences with using ELNs. In general, it was found that students had positive perceptions of ELNs, even though there is a higher learning curve compared to PLNs. Reasons for this include increased communication, accessibility, and the ease of presenting work legibility. Also, the COVID-19 pandemic is associated with students having a positive experience with using ELNs mainly due to increased communication and accessibility from home where otherwise not possible.
REFERENCES
Bird, C. L., Willoughby, C., & Frey, J. G. (2013). Laboratory notebooks in the digital era: The role of ELNs in record keeping for chemistry and other sciences. Chemical Society Review, 42(20), 8157-8175.
Colabroy, K. & Bell, J. K. (2019). Lab eNotebooks. In Biochemistry Education: From Theory to Practice, 1337, 173-195. American Chemical Society
Spinodal Decomposition and the Tomita Sum Rule
The scaling properties of a phase-ordering system with a conserved order
parameter are studied. The theory developed leads to scaling functions
satisfying certain general properties including the Tomita sum rule. The theory
also gives good agreement with numerical results for the order parameter
scaling function in three dimensions. The values of the associated
nonequilibrium decay exponents are given by the known lower bounds.Comment: 15 pages, 6 figure
A comparison of four functional test in discriminating fallers from non-fallers in older people
Purpose : Which functional tests on mobility and balance can better screen older people at risk of falls is unclear. This study aims to compare the Berg Balance Scale (BBS), Tinetti Mobility Score (TMS), Elderly Mobility Scale (EMS) and Timed Up and Go test (TUG) in discriminating fallers from non-fallers in older people. Method : This was a case-control study involving one rater who conducted a mobility and balance assessment on subjects using the four functional tests in random sequence. Subjects recruited included 17 and 22 older people with a history of single and multiple falls respectively from a public Falls Clinic, and 39 community-dwellers without fall history and whose age, sex and BMI matched those of the fallers. All subjects underwent the mobility and balance assessment within one day. Results : Single fallers performed better than multiple fallers in all four functional tests but were worse than non-fallers in the BBS, TMS and TUG. The BBS demonstrated the best discriminating ability, with high sensitivity and specificity. The BBS item \u27pick up an object from the floor\u27 was the best at screening fallers. Conclusion : BBS was the most powerful functional test of the four in discriminating fallers from non-faller
Evolution of speckle during spinodal decomposition
Time-dependent properties of the speckled intensity patterns created by
scattering coherent radiation from materials undergoing spinodal decomposition
are investigated by numerical integration of the Cahn-Hilliard-Cook equation.
For binary systems which obey a local conservation law, the characteristic
domain size is known to grow in time as with n=1/3,
where B is a constant. The intensities of individual speckles are found to be
nonstationary, persistent time series. The two-time intensity covariance at
wave vector can be collapsed onto a scaling function , where and . Both analytically and numerically, the covariance
is found to depend on only through in the
small- limit and in the large-
limit, consistent with a simple theory of moving interfaces that applies to any
universality class described by a scalar order parameter. The speckle-intensity
covariance is numerically demonstrated to be equal to the square of the
two-time structure factor of the scattering material, for which an analytic
scaling function is obtained for large In addition, the two-time,
two-point order-parameter correlation function is found to scale as
, even for quite large
distances . The asymptotic power-law exponent for the autocorrelation
function is found to be , violating an upper bound
conjectured by Fisher and Huse.Comment: RevTex: 11 pages + 12 figures, submitted to PR
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