4,150 research outputs found
Single-file diffusion on self-similar substrates
We study the single file diffusion problem on a one-dimensional lattice with
a self-similar distribution of hopping rates. We find that the time dependence
of the mean-square displacement of both a tagged particle and the center of
mass of the system present anomalous power laws modulated by logarithmic
periodic oscillations. The anomalous exponent of a tagged particle is one half
of the exponent of the center of mass, and always smaller than 1/4. Using
heuristic arguments, the exponents and the periods of oscillation are
analytically obtained and confirmed by Monte Carlo simulations.Comment: 12 pages, 6 figure
ChatGPT in the Classroom: Boon or Bane for Physics Students' Academic Performance?
This study investigates the influence of ChatGPT, an AI-based language model,
on student performance in a physics course. We conducted an experimental
analysis with two cohorts of students in a second-semester engineering physics
course. The control group (Physics 2 2022B) used traditional teaching methods,
while the experimental group (Physics 2 2023A) integrated ChatGPT as a learning
tool. Our results indicate that the use of ChatGPT led to a significant
decrease in student performance, as evidenced by lower grades and negative Hake
factors compared to the control group. In addition, a survey of students
revealed conflicting perceptions of the usefulness of ChatGPT in teaching
physics. While most recognized its usefulness in understanding concepts and
providing information, concerns were raised about its potential to reduce
critical thinking and independent learning. These findings suggest that while
ChatGPT can be a useful tool, it should be used with caution and as a
supplement to traditional teaching methods, rather than as a stand-alone
solution. The study underlines the importance of critical and reflective use of
AI tools in educational settings and highlights the irreplaceable role of
teachers in providing comprehensive educational support.Comment: 9 pages and 13 figure
Vibration-induced granular segregation: a phenomenon driven by three mechanisms
The segregation of large spheres in a granular bed under vertical vibrations
is studied. In our experiments we systematically measure rise times as a
function of density, diameter and depth; for two different sinusoidal
excitations. The measurements reveal that: at low frequencies, inertia and
convection are the only mechanisms behind segregation. Inertia (convection)
dominates when the relative density is greater (less) than one. At high
frequencies, where convection is suppressed, fluidization of the granular bed
causes either buoyancy or sinkage and segregation occurs.Comment: 4 pages. 3 figures, revtex4, to appear in PRL (in press
Causation, Measurement Relevance and No-conspiracy in EPR
In this paper I assess the adequacy of no-conspiracy conditions employed in
the usual derivations of the Bell inequality in the context of EPR
correlations. First, I look at the EPR correlations from a purely
phenomenological point of view and claim that common cause explanations of
these cannot be ruled out. I argue that an appropriate common cause explanation
requires that no-conspiracy conditions are re-interpreted as mere common
cause-measurement independence conditions. In the right circumstances then,
violations of measurement independence need not entail any kind of conspiracy
(nor backwards in time causation). To the contrary, if measurement operations
in the EPR context are taken to be causally relevant in a specific way to the
experiment outcomes, their explicit causal role provides the grounds for a
common cause explanation of the corresponding correlations.Comment: 20 pages, 1 figur
Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?
A unified semiclassical time propagator is used to calculate the
semiclassical time-correlation function in three cartesian dimensions for a
particle moving in an attractive Coulomb potential. It is demonstrated that
under these conditions the singularity of the potential does not cause any
difficulties and the Coulomb interaction can be treated as any other
non-singular potential. Moreover, by virtue of our three-dimensional
calculation, we can explain the discrepancies between previous semiclassical
and quantum results obtained for the one-dimensional radial Coulomb problem.Comment: 8 pages, 4 figures (EPS
Direct Measurements of the Transport of Nonequilibrium Electrons in Gold Films with Different Crystal Structures
The transport of femtosecond-laser-excited nonequilibrium electrons across polycrystalline and single-crystalline gold films has been investigated through time-of-flight measurements. The thicknesses of the films range from 25 to 400 nm. Ballistic electrons as well as electrons interacting with other electrons and/or with the lattice have been observed. The ballistic component dominates the transport in the thinner films, whereas the interactive transport mechanism is dominant at the upper end of the thickness range. A slower effective velocity of the interactive component is observed in the polycrystalline samples, and is assumed to arise from the presence of grain boundaries. The reflection coefficient of excited electrons at the grain boundaries is extracted from the experiment and is estimated to be r=0.12. The experiment also suggests that thermal equilibrium among the excited electrons is not fully established in the first 500 fs after excitation. © 1993 The American Physical Society
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