684 research outputs found
Quantum kinetic approach to the calculation of the Nernst effect
We show that the strong Nernst effect observed recently in amorphous
superconducting films far above the critical temperature is caused by the
fluctuations of the superconducting order parameter. We employ the quantum
kinetic approach for the derivation of the Nernst coefficient. We present here
the main steps of the calculation and discuss some subtle issues that we
encountered while calculating the Nernst coefficient. In particular, we
demonstrate that in the limit T=0 the contribution of the magnetization ensures
the vanishing of the Nernst signal in accordance with the third law of
thermodynamics. We obtained a striking agreement between our theoretical
calculations and the experimental data in a broad region of temperatures and
magnetic fields.Comment: 24 pages, 13 figure
Direct Radiation Pressure Measurements for Lightsail Membranes
Ultrathin lightsails propelled by laser radiation pressure to relativistic
speeds are currently the most promising route for flyby-based exoplanet
exploration. However, there has been a notable lack of experimental
characterization of key parameters essential for lightsail propulsion.
Therefore, a model platform for optomechanical characterization of lightsail
prototypes made from realistic materials is needed. We propose an approach for
simultaneous measurement of optical forces and driving powers, which
capitalizes on the multiphysics dynamics induced by the driving laser beam. By
modelling the lightsail with a 50-nm thick silicon nitride membrane suspended
by compliant micromechanical springs, we quantify force from off-resonantly
driven displacement and power from heating-induced mechanical mode softening.
This approach allows us to calibrate the measured forces to the driving powers
by operating the device as a mechanical bolometer. We report radiation pressure
forces of 80 fN using a collimated pump beam of 100 W/cm2 and noise-robust
common-path interferometry. As lightsails will inevitably experience non-normal
forces, we quantify the effects of incidence angle and spot size on the optical
force and explain the nonintuitive trend by edge scattering. Our results
provide a framework for comprehensive lightsail characterization and laboratory
optomechanical manipulation of macroscopic objects by radiation pressure
forces
Anti-GnRH antibodies can induce castrate levels of testosterone in patients with advanced prostate cancer
D17DT consists of the GnRH decapeptide linked to diphtheria toxoid. The aim of this pilot study was to assess the tolerance of D17DT and the production of anti-GnRH antibodies from two doses, 30 and 100 μg, in patients with locally advanced prostate cancer. Twelve patients with histologically proven prostate cancer in whom hormonal therapy was indicated were recruited. Patients received either 30 or 100 μg given intramuscularly on three separate occasions over six weeks. Patients were followed up and blood was taken for estimation of serum testosterone, PSA and anti-GnRH antibody titre. Overall the drug was well tolerated. In 5 patients a significant reduction in serum testosterone and PSA was seen. Castrate levels of testosterone were achieved in 4 and maintained for up to 9 months. Patients with the highest antibody titre had the best response in terms of testosterone suppression. This study shows that it is possible to immunize a patient with prostate cancer against GnRH to induce castrate levels of testosterone. This state appears to be reversible. This novel form of immunotherapy may have advantages over conventional forms of hormonal therapy and further studies are warranted in order to try and increase the proportion of responders. © 2000 Cancer Research Campaig
Pseudorandom Selective Excitation in NMR
In this work, average Hamiltonian theory is used to study selective
excitation in a spin-1/2 system evolving under a series of small flip-angle
pulses that are applied either periodically [which
corresponds to the DANTE pulse sequence] or aperiodically. First, an average
Hamiltonian description of the DANTE pulse sequence is developed; such a
description is determined to be valid either at or very far from the DANTE
resonance frequencies, which are simply integer multiples of the inverse of the
interpulse delay. For aperiodic excitation schemes where the interpulse delays
are chosen pseudorandomly, a single resonance can be selectively excited if the
-pulses' phases are modulated in concert with the time delays. Such a
selective pulse is termed a pseudorandom-DANTE or p-DANTE sequence, and the
conditions in which an average Hamiltonian description of p-DANTE is found to
be similar to that found for the DANTE sequence. It is also shown that
averaging over different p-DANTE sequences that are selective for the same
resonance can help reduce excitations at frequencies away from the resonance
frequency, thereby improving the apparent selectivity of the p-DANTE sequences.
Finally, experimental demonstrations of p-DANTE sequences and comparisons with
theory are presented.Comment: 23 pages, 8 figure
Quantum kinetic approach for studying thermal transport in the presence of electron-electron interactions and disorder
A user friendly scheme based on the quantum kinetic equation is developed for
studying thermal transport phenomena in the presence of interactions and
disorder. We demonstrate that this scheme is suitable for both a systematic
perturbative calculation as well as a general analysis. We believe that we
present an adequate alternative to the Kubo formula, which for the thermal
transport is rather cumbersome.Comment: 30 pages, 16 figure
Ноосферная проблематика в философии Тейяра де Шардена
Современная экологическая ситуация остается одной их актуальных. Она требует всестороннего, комплексного анализа, в том числе и философского осмысления. В XX в. сформировались несколько концептуальных представлений, получивших название "ноосферных". Одним из теоретиков ноосферной концепции был Тейяр де Шарден. Исследование его подхода дает основание избежать ошибок и сформировать научное последовательное представление во взаимоотношениях между Природой и Обществом
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