Buffer gas beam coolers may become excellent beam preparation devices for high-resolution mass separation. The small beam
emittance provided makes efficient isobar resolution a realistic goal. In order to fulfill the needs of future facilities
providing high-intensity beams of rare isotopes, it is desirable to increase the beam intensity limit of such devices from
typically several tens of nanoamperes to microamperes. This requires the usage of high-voltage radiofrequencies in a low-pressure
gas environment. A buffer gas beam cooler, dedicated to this purpose, is under development at the NSCL. The study of voltage
breakdowns under such conditions and the design of an electrode system minimizing them is mandatory.
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An extension of the Parikh-Wilczek's semi-classical quantum tunneling method, the tunneling radiation of the charged particle from a torus-like black hole is investigated. Difference from the uncharged mass-less particle, the geodesics of the charged massive particle tunneling from the black hole is not light-like, but determined by the phase velocity. The derived result shows that the tunneling rate depends on the emitted particle's energy and electric charge, and takes the same functional form as uncharged particle. It proves also that the exact emission spectrum is not strictly pure thermal, but is consistent with the underlying unitary theory.
PACS Numbers: 04.70.Dy, 97.60.Lf, 05.30.Ch. 相似文献
The rate-equation approach is used to describe sequential tunneling through a molecular junction in the Coulomb blockade regime.
Such device is composed of molecular quantum dot (with discrete energy levels) coupled with two metallic electrodes via potential
barriers. Based on this model, we calculate nonlinear transport characteristics (conductance-voltage and current-voltage dependences)
and compare them with the results obtained within a self-consistent field approach. It is shown that the shape of transport
characteristics is determined by the combined effect of the electronic structure of molecular quantum dots and by the Coulomb
blockade. In particular, the following phenomena are discussed in detail: the suppression of the current at higher voltages,
the charging-induced rectification effect, the charging-generated changes of conductance gap and the temperature-induced as
well as broadening-generated smoothing of current steps. 相似文献
One of the most pervasive laws in biology is the allometric scaling, whereby a biological variable Y is related to the mass M of the organism by a power law, Y=Y0Mb, where b is the so-called allometric exponent. The origin of these power laws is still a matter of dispute mainly because biological laws, in general, do not follow from physical ones in a simple manner. In this work, we review the interspecific allometry of metabolic rates, where recent progress in the understanding of the interplay between geometrical, physical and biological constraints has been achieved.
For many years, it was a universal belief that the basal metabolic rate (BMR) of all organisms is described by Kleiber's law (allometric exponent b=3/4). A few years ago, a theoretical basis for this law was proposed, based on a resource distribution network common to all organisms. Nevertheless, the 3/4-law has been questioned recently. First, there is an ongoing debate as to whether the empirical value of b is 3/4 or 2/3, or even nonuniversal. Second, some mathematical and conceptual errors were found these network models, weakening the proposed theoretical arguments. Another pertinent observation is that the maximal aerobically sustained metabolic rate of endotherms scales with an exponent larger than that of BMR. Here we present a critical discussion of the theoretical models proposed to explain the scaling of metabolic rates, and compare the predicted exponents with a review of the experimental literature. Our main conclusion is that although there is not a universal exponent, it should be possible to develop a unified theory for the common origin of the allometric scaling laws of metabolism. 相似文献
New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM(H) (∞ critical current densityJc(H)) in isothermalMH scans in a weakly pinned single crystal of Ca3Rh4Sn13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles
of vortices injected through the sample edges towards the destined equilibrium vortex state at a givenH. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence inJc(H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state
between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of
Ca3Rh4Sn13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the
onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point
and a critical point in the (H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light
of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb. 相似文献
The effect of transverse geometries of the slab of composite high-Tc superconductors on their stable and unstable thermal and electrodynamics transient states in the incomplete and complete penetration modes during the current charging are discussed. The transient period when the electric field that is induced by the charged current becomes more homogeneous during the initial stage of the complete penetration mode in the sub-critical voltage range is studied. In the over-critical voltage range, the cross-section shape of the slab affects its stable and unstable temperature variation. As a result, the current instability condition is not identical for high-Tc superconducting composite tapes that have the same cross-sectional area with various shapes of the cross-section. The condition depends on their thickness: the less thickness, the more stable the current distribution in the composite superconductors with the same cross-sectional area. This feature is a result of the unavoidable reduction of the current-carrying capacity of a high-Tc superconducting composite by the temperature increase. This reduction is caused by the relevant temperature dependence of electrodynamics states of the composite. This temperature dependence happens even during a stable stage of the current charging. These mechanisms must be considered during experiments at which the critical or quenching currents are defined. 相似文献
Applying Parikh-Wilzcek‘s semi-classical quantum tunneling model, we study the Hawking radiation of charged particles as tunneling from the event horizon of a cylindrically symmetric black hole in anti-de Sitter space-time.The derived result shows that the tunneling rate of charged particles is related to the change of Bekenstein-Hawking entropy and that the radiation spectrum is not strictly pure thermal after taking the black hole background dynamical and self-gravitation interaction into account, but is consistent with the underlying unitary theory. 相似文献
Dual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH2CH2)2NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10?10 cm3 molecule?1 s?1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10?10 cm3 molecule?1 s?1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH2 and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour. 相似文献