756 research outputs found
Paradigm of modern pharmacology: development and current approaches
The article focuses on the current approach to understanding pharmaceutical products’ effect. It describes a paradigm shift in views on pharmaceutical action in correlation to the processes occurring under pathology. The paper discusses the role of regulatory processes in the development of a disease and a recovery. It points out the necessity of disease registration in order to early start a therap
Pharmacological vector of Rudolf Buchheim
The article is dedicated to the author of experimental pharmacology, professor of University of Dorpat, German pharmacologist Rudolf Buchheim (1820-1879
Charge and Statistics of Quasiparticles in Fractional Quantum Hall Effec
We have studied here the charge and statistics of quasiparticle excitations
in FQH states on the basis of the Berry phase approach incorporating the fact
that even number of flux quanta can be gauged away when the Berry phase is
removed to the dynamical phase. It is observed that the charge and
statistical parameter of a quasiparticle at filling factor
are given by and
, with the fact that the charge of the quasihole is
opposite to that of the quasielectron. Using Laughlin wave function for
quasiparticles, numerical studies have been done following the work of
Kj{\o}nsberg and Myrheim \cite{KM} for FQH states at and it is
pointed out that as in case of quasiholes, the statistics parameter can be well
defined for quasielectrons having the value .Comment: 12 pages, 4 figure
Detection of non-Gaussian Fluctuations in a Quantum Point Contact
An experimental study of current fluctuations through a tunable transmission
barrier, a quantum point contact, are reported. We measure the probability
distribution function of transmitted charge with precision sufficient to
extract the first three cumulants. To obtain the intrinsic quantities,
corresponding to voltage-biased barrier, we employ a procedure that accounts
for the response of the external circuit and the amplifier. The third cumulant,
obtained with a high precision, is found to agree with the prediction for the
statistics of transport in the non-Poissonian regime.Comment: 4 pages, 4 figures; published versio
Direct Observation of a Fractional Charge
We performed measurements of Quantum Shot Noise in order to determine the
quasiparticle charge in the Fractional Quantum Hall regime. The noise is
generated by a current flow through a partially transmitting Quantum Point
Contact in a 2DEG. The noise is directly proportional to the charge of the
quasiparticles, thus allowing direct determination of the charge. We measured
Quantum Shot Noise at a filling factor of 1/3 and found that the charge is e/3;
as predicted by Laughlin.Comment: 3 pages, PostScript, 4 figures. Submitted to Natur
On the Cooling of Electrons in a Silicon Inversion Layer
The cooling of two-dimensional electrons in silicon-metal-oxide semiconductor
field effect transistors is studied experimentally. Cooling to the lattice is
found to be more effective than expected from the bulk electron-phonon coupling
in silicon. Unexpectedly, the extracted heat transfer rate to phonons at low
temperatures depends cubically on electron temperature, suggesting that
piezoelectric coupling (absent in bulk silicon) dominates over deformation
potential. According to our findings, at 100 mK, electrons farther than 0.1 mm
from the contacts are mostly cooled by phonons. Using long devices and low
excitation voltage we measure electron resistivity down to 100 mK and find that
some of the "metallic" curves, reported earlier, turn insulating below about
300 mK. This finding renders the definition of the claimed 2D metal-insulator
transition questionable. Previous low temperature measurements in silicon
devices are analyzed and thumb rules for evaluating their electron temperatures
are provided.Comment: 5 pages, 4 figures. Discussion corrected and a few references adde
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