149 research outputs found
Physiological aspects of educational training adaptation of students
20 healthy male and female students of Artsakh State University aged 18-20 years have participated in an experiment to study the mechanisms of training adaptation. Surveys were conducted during the academic semester in 2 stages: the non-examination period (March-April) - Monday and Friday, before and after school and during the examination period (May-June) - before and after the exam. In order to study the impact of mental stress a survey was also conducted among students once they complete mental or intellectual Eysenck test. A psychological testing of students was carried out to identify the level of intelligence (IQ) by Eysenck, personal and situational anxiety by Spielberger and health, activity, mood by SAN (HAM) questionnaire. Basic hemodynamic parameters were measured: heart rate, systolic and diastolic blood pressure. ECG examination was conducted using R.M. Baevsky's cardio-ervalography method. Comparative analysis of the dynamics of the studied parameters showed that the process of adaptation of students to the teaching load is accompanied by periods of decline during non-examination period, more vividly expressed when doing mental or intellectual work, and tension of the studied parameters during the examination period
Multimodal transcriptional control of pattern formation in embryonic development
Predicting how interactions between transcription factors and regulatory DNA sequence dictate rates of transcription and, ultimately, drive developmental outcomes remains an open challenge in physical biology. Using stripe 2 of the even-skipped gene in Drosophila embryos as a case study, we dissect the regulatory forces underpinning a key step along the developmental decision-making cascade: the generation of cytoplasmic mRNA patterns via the control of transcription in individual cells. Using live imaging and computational approaches, we found that the transcriptional burst frequency is modulated across the stripe to control the mRNA production rate. However, we discovered that bursting alone cannot quantitatively recapitulate the formation of the stripe and that control of the window of time over which each nucleus transcribes even-skipped plays a critical role in stripe formation. Theoretical modeling revealed that these regulatory strategies (bursting and the time window) respond in different ways to input transcription factor concentrations, suggesting that the stripe is shaped by the interplay of 2 distinct underlying molecular processes
Transfer ionization and its sensitivity to the ground-state wave function
We present kinematically complete theoretical calculations and experiments
for transfer ionization in HHe collisions at 630 keV/u. Experiment and
theory are compared on the most detailed level of fully differential cross
sections in the momentum space. This allows us to unambiguously identify
contributions from the shake-off and two-step-2 mechanisms of the reaction. It
is shown that the simultaneous electron transfer and ionization is highly
sensitive to the quality of a trial initial-state wave function
Back-to-back emission of the electrons in double photoionization of helium
We calculate the double differential distributions and distributions in
recoil momenta for the high energy non-relativistic double photoionization of
helium. We show that the results of recent experiments is the pioneering
experimental manifestation of the quasifree mechanism for the double
photoionization, predicted long ago in our papers. This mechanism provides a
surplus in distribution over the recoil momenta at small values of the latter,
corresponding to nearly "back-to-back" emission of the electrons. Also in
agreement with previous analysis the surplus is due to the quadrupole terms of
the photon-electron interaction. We present the characteristic angular
distribution for the "back-to-back" electron emission. The confirmation of the
quasifree mechanism opens a new area of exiting experiments, which are expected
to increase our understanding of the electron dynamics and of the bound states
structure. The results of this Letter along with the recent experiments open a
new field for studies of two-electron ionization not only by photons but by
other projectiles, e.g. by fast electrons or heavy ions.Comment: 10 pages, 2 figure
Conductance distribution between Hall plateaus
Mesoscopic fluctuations of two-port conductance and four-port resistance
between Hall plateaus are studied within a realistic model for a
two-dimensional electron gas in a perpendicular magnetic field and a smooth
disordered potential. The two-port conductance distribution is concave
between and and is nearly flat between and . These
characteristics are consistent with recent observations. The distribution is
found to be sharply peaked near the end-points and . The
distribution functions for the three independent resistances in a four-port
Hall bar geometry are, on the other hand, characterized by a central peak and a
relatively large width.Comment: 11 pages, 5 ps figures, submitted to Phys. Rev.
Le Chatelier principle in replicator dynamics
The Le Chatelier principle states that physical equilibria are not only
stable, but they also resist external perturbations via short-time
negative-feedback mechanisms: a perturbation induces processes tending to
diminish its results. The principle has deep roots, e.g., in thermodynamics it
is closely related to the second law and the positivity of the entropy
production. Here we study the applicability of the Le Chatelier principle to
evolutionary game theory, i.e., to perturbations of a Nash equilibrium within
the replicator dynamics. We show that the principle can be reformulated as a
majorization relation. This defines a stability notion that generalizes the
concept of evolutionary stability. We determine criteria for a Nash equilibrium
to satisfy the Le Chatelier principle and relate them to mutualistic
interactions (game-theoretical anticoordination) showing in which sense
mutualistic replicators can be more stable than (say) competing ones. There are
globally stable Nash equilibria, where the Le Chatelier principle is violated
even locally: in contrast to the thermodynamic equilibrium a Nash equilibrium
can amplify small perturbations, though both this type of equilibria satisfy
the detailed balance condition.Comment: 12 pages, 3 figure
Scaling Properties of Conductance at Integer Quantum Hall Plateau Transitions
We investigate the scaling properties of zero temperature conductances at
integer quantum Hall plateau transitions in the lowest Landau band of a
two-dimensional tight-binding model. Scaling is obeyed for all energy and
system sizes with critical exponent nu =7/3 . The arithmetic average of the
conductance at the localization-delocalization critical point is found to be
_c = 0.506 e^2 / h, in agreement with the universal longitudinal conductance
predicted by an analytical theory. The probability distribution of the
conductance at the critical point is broad with a dip at small G.Comment: 4 pages, 3 postscript figures, Submitted to PR
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