71,737 research outputs found
Universality in the Large N_c Dynamics of Flavour: Thermal Vs. Quantum Induced Phase Transitions
We show how two important types of phase transition in large N_c gauge theory
with fundamental flavours can be cast into the same classifying framework as
the meson-melting phase transition. These are quantum fluctuation induced
transitions in the presence of an external electric field, or a chemical
potential for R-charge. The classifying framework involves the study of the
local geometry of a special D-brane embedding, which seeds a self-similar
spiral structure in the space of embeddings. The properties of this spiral,
characterized by a pair of numbers, capture some key universal features of the
transition. Computing these numbers for these non-thermal cases, we find that
these transitions are in the same universality class as each other, but have
different universal features from the thermal case. We present a natural
generalization that yields new universality classes that may pertain to other
types of transition.Comment: 22 pages, 4 figures, pdfLaTe
Phase and Power Control in the RF Magnetron Power Stations of Superconducting Accelerators
Phase and power control methods that satisfy the requirements of
superconducting accelerators to magnetron RF sources were considered by a
simplified kinetic model of a magnetron driven by a resonant injected signal.
The model predicting and explaining stable, low noise operation of the tube
below the threshold of self-excitation (the Hatrree voltage in free run mode)
at a highest efficiency, a wide range of power control and a wide-band phase
control was well verified in experiments demonstrating capabilities of the
magnetron transmitters for powering of state of the art superconducting
accelerators. Descriptions of the kinetic model, the experimental verification
and a conceptual scheme of the highly-efficient magnetron RF transmitter for
the accelerators are presented and discussed.Comment: 10 pages, 15 figure
Efficient solution of the Euler and Navier-Stokes equations with a vectorized multiple-grid algorithm
A multiple-grid algorithm for use in efficiently obtaining steady solutions to the Euler and Navier-Stokes equations is presented. The convergence of the explicit MacCormack algorithm on a fine grid is accelerated by propagating transients from the domain using a sequence of successively coarser grids. Both the fine and coarse grid schemes are readily vectorizable. The combination of multiple-gridding and vectorization results in substantially reduced computational times for the numerical solution of a wide range of flow problems. Results are presented for subsonic, transonic, and supersonic inviscid flows and for subsonic attached and separated laminar viscous flows. Work reduction factors over a scalar, single-grid algorithm range as high as 76.8
Development of shape memory metal as the actuator of a fail safe mechanism
A small, compact, lightweight device was developed using shape memory alloy (SMA) in wire form to actuate a pin-puller that decouples the flanges of two shafts. When the SMA is heated it contracts producing a useful force and stroke. As it cools, it can be reset (elongated in this case) by applying a relatively small force. Resistive heating is accomplished by running a current through the SMA wire for a controlled length of time. The electronics to drive the device are not elaborate or complicated, consisting of a timed current source. The total available contraction is 3 percent of the length of the wire. This device, the engineering properties of the SMA, and the tests performed to verify the design concept are described
Radiation induced zero-resistance states in GaAs/AlGaAs heterostructures: Voltage-current characteristics and intensity dependence at the resistance minima
High mobility two-dimensional electron systems exhibit vanishing resistance
over broad magnetic field intervals upon excitation with microwaves, with a
characteristic reduction of the resistance with increasing radiation intensity
at the resistance minima. Here, we report experimental results examining the
voltage - current characteristics, and the resistance at the minima vs. the
microwave power. The findings indicate that a non-linear V-I curve in the
absence of microwave excitation becomes linearized under irradiation, unlike
expectations, and they suggest a similarity between the roles of the radiation
intensity and the inverse temperature.Comment: 3 color figures; publishe
Expectation values of single-particle operators in the random phase approximation ground state
We developed a method for computing matrix elements of single-particle
operators in the correlated random phase approximation ground state. Working
with the explicit random phase approximation ground state wavefunction, we
derived practically useful and simple expression for a molecular property in
terms of random phase approximation amplitudes. The theory is illustrated by
the calculation of molecular dipole moments for a set of representative
molecules.Comment: Accepted to J.Chem.Phy
Degenerate principal series of quantum Harish-Chandra modules
In this paper we study a quantum analogue of a degenerate principal series of
-modules () related to the Shilov boundary of
the quantum -matrix unit ball. We give necessary and sufficient
conditions for the modules to be simple and unitarizable and investigate their
equivalence.
These results are q-analogues of known classical results on reducibility and
unitarizability of SU(n,n)-modules obtained by Johnson, Sahi, Zhang, Howe and
Tan.Comment: 33 pages, 4 figure
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