1,874 research outputs found
Development of a superconducting protection switch for the HERA P-ring: design study and demonstration models
The electrical circuit of the HERA (Hadron Electron Ring Accelerator) proton ring (p-ring) is divided in octants so that in the case of a quench, the current has to be commutated to dumping resistors. The authors describe the application of superconducting switches which would enable the main circuit to remain at 4 K during a quench while the current is forced to flow through instantaneously loaded leads and dumping resistors. The main specifications of the required switches are: current of 6.5 kA, minimum off-resistance 12 Omega , energy absorbed 1 MJ, and self protecting. The various design and feasibility aspects of superconducting switches for this application are discussed. The requirement of being passively protected against a self-quench is considered the most critical design problem. It is still uncertain whether it remains necessary to apply an active protection scheme to enable safe operation of the switch
Effective sigma models and lattice Ward identities
We perform a lattice analysis of the Faddeev-Niemi effective action
conjectured to describe the low-energy sector of SU(2) Yang-Mills theory. To
this end we generate an ensemble of unit vector fields ("color spins") n from
the Wilson action. The ensemble does not show long-range order but exhibits a
mass gap of the order of 1 GeV. From the distribution of color spins we
reconstruct approximate effective actions by means of exact lattice
Schwinger-Dyson and Ward identities ("inverse Monte Carlo"). We show that the
generated ensemble cannot be recovered from a Faddeev-Niemi action, modified in
a minimal way by adding an explicit symmetry-breaking term to avoid the
appearance of Goldstone modes.Comment: 25 pages, 17 figures, JHEP styl
Relation between chiral symmetry breaking and confinement in YM-theories
Spectral sums of the Dirac-Wilson operator and their relation to the Polyakov
loop are thoroughly investigated. The approach by Gattringer is generalized to
mode sums which reconstruct the Polyakov loop locally. This opens the
possibility to study the mode sum approximation to the Polyakov loop
correlator. The approach is re-derived for the ab initio continuum formulation
of Yang-Mills theories, and the convergence of the mode sum is studied in
detail. The mode sums are then explicitly calculated for the Schwinger model
and SU(2) gauge theory in a homogeneous background field. Using SU(2) lattice
gauge theory, the IR dominated mode sums are considered and the mode sum
approximation to the static quark anti-quark potential is obtained numerically.
We find a good agreement between the mode sum approximation and the static
potential at large distances for the confinement and the high temperature
plasma phase.Comment: 17 pages, 10 figures, typos corrected, references added, final
version to appear in PR
Amino Acid Transporter Inventory of the Selaginella Genome
Amino acids play fundamental roles in a multitude of functions including protein synthesis, hormone metabolism, nerve transmission, cell growth, production of metabolic energy, nucleobase synthesis, nitrogen metabolism, and urea biosynthesis. Selaginella as a member of the lycophytes is part of an ancient lineage of vascular plants that had arisen ∼400 million years ago. In angiosperms, which have attracted most of the attention for nutrient transport so far, we have been able to identify many of the key transporters for nitrogen. Their role is not always fully clear, thus an analysis of Selaginella as a representative of an ancient vascular plant may help shed light on the evolution and function of these diverse transporters. Here we annotated and analyzed the genes encoding putative transporters involved in cellular uptake of amino acids present in the Selaginella genome
Phase Structure of Z(3)-Polyakov-Loop Models
We study effective lattice actions describing the Polyakov loop dynamics
originating from finite-temperature Yang-Mills theory. Starting with a
strong-coupling expansion the effective action is obtained as a series of
Z(3)-invariant operators involving higher and higher powers of the Polyakov
loop, each with its own coupling. Truncating to a subclass with two couplings
we perform a detailed analysis of the statistical mechanics involved. To this
end we employ a modified mean field approximation and Monte Carlo simulations
based on a novel cluster algorithm. We find excellent agreement of both
approaches concerning the phase structure of the theories. The phase diagram
exhibits both first and second order transitions between symmetric,
ferromagnetic and anti-ferromagnetic phases with phase boundaries merging at
three tricritical points. The critical exponents nu and gamma at the continuous
transition between symmetric and anti-ferromagnetic phases are the same as for
the 3-state Potts model.Comment: 20 pages, 22 figure
Characterization of an embedded RF-MEMS switch
An RF-MEMS capacitive switch for mm-wave integrated circuits, embedded in the BEOL of 0.25μm BiCMOS process, has been characterized. First, a mechanical
model based on Finite-Element-Method (FEM) was developed by taking the residual stress of the thin film membrane into account. The pull-in voltage and the capacitance values obtained with the mechanical model agree very well with the
measured values. Moreover, S-parameters were extracted using Electromagnetic (EM) solver. The data observed in this way also agree well with the experimental ones measured up to 110GHz. The developed RF model was applied to a transmit/receive (T/R) antenna switch design. The results proved the feasibility of using the FEM model in circuit simulations for the development of RF-MEMS switch embedded, single-chip multi-band RF ICs
Daily Eastern News: November 10, 1975
https://thekeep.eiu.edu/den_1975_nov/1005/thumbnail.jp
Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d)
Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d) have been studied by means
of magnetization measurements in the temperature range between 1.95 K and Tc,
in an external magnetic field up to 9 T. Flux jumps were found in the
temperature range 1.95 K - 6 K, with the external magnetic field parallel to
the c axis of the investigated sample. The effect of sample history on magnetic
flux jumping was studied and it was found to be well accounted for by the
available theoretical models. The magnetic field sweep rate strongly influences
the flux jumping and this effect was interpreted in terms of the influence of
both flux creep and the thermal environment of the sample. Strong flux creep
was found in the temperature and magnetic field range where flux jumps occur
suggesting a relationship between the two. The heat exchange conditions between
the sample and the experimental environment also influence the flux jumping
behavior. Both these effects stabilize the sample against flux instabilities,
and this stabilizing effect increases with decreasing magnetic field sweep
rate. Demagnetizing effects are also shown to have a significant influence on
flux jumping.Comment: 10 pages, 6 figures, RevTeX4, submitted to Phys. Rev.
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