19,774 research outputs found

### Source conductance scaling for high frequency superconducting quasiparticle receivers

It has been suggested that the optimum source conductance G(sub s) for the superconductor-insulator-superconductor (SIS) quasiparticle mixer should have a l/f dependence. This would imply that the critical current density of SIS junctions used for mixing should increase as frequency squared, a stringent constraint on the design of submillimeter SIS mixers, rather than in simple proportion to frequency as previously believed. We have used Tucker's quantum theory of mixing for extensive numerical calculations to determine G(sub s) for an optimized SIS receiver. We find that G(sub s) is very roughly independent of frequency (except for the best junctions at low frequency), and discuss the implications of our results for the design of submillimeter SIS mixers

### Constructive Field Theory and Applications: Perspectives and Open Problems

In this paper we review many interesting open problems in mathematical
physics which may be attacked with the help of tools from constructive field
theory. They could give work for future mathematical physicists trained with
the constructive methods well within the 21st century

### Remarkable virtual SUSY effects in $W^{\pm}$ production at high energy hadron colliders

We present a complete 1-loop study of the electroweak corrections to the
process $ug\to dW^+$ in MSSM and SM.
The occurrence of a number of remarkable properties in the behavior of the
helicity amplitudes at high energies is stressed, and the crucial role of the
virtual SUSY contributions in establishing them, is emphasized. The approach to
asymptopia of these amplitudes is discussed, comparing the effects of the
logarithmic and constant contributions to the mass suppressed ones, which are
relevant at lower energies. Applying crossing to $ug\to d W^+$, we obtain all
subprocesses needed for the 1-loop electroweak corrections to
$W^\pm$-production at LHC. The SUSY model dependence of such a production is
then studied, and illustrations are given for the transverse $W^{\pm}$ momentum
distribution, as well as the angular distribution in the subprocess center of
mass.Comment: 21 pages, 12 figures, version to appear in Phys.Rev.

### Determinant Bounds and the Matsubara UV Problem of Many-Fermion Systems

It is known that perturbation theory converges in fermionic field theory at
weak coupling if the interaction and the covariance are summable and if certain
determinants arising in the expansion can be bounded efficiently, e.g. if the
covariance admits a Gram representation with a finite Gram constant. The
covariances of the standard many--fermion systems do not fall into this class
due to the slow decay of the covariance at large Matsubara frequency, giving
rise to a UV problem in the integration over degrees of freedom with Matsubara
frequencies larger than some Omega (usually the first step in a multiscale
analysis). We show that these covariances do not have Gram representations on
any separable Hilbert space. We then prove a general bound for determinants
associated to chronological products which is stronger than the usual Gram
bound and which applies to the many--fermion case. This allows us to prove
convergence of the first integration step in a rather easy way, for a
short--range interaction which can be arbitrarily strong, provided Omega is
chosen large enough. Moreover, we give - for the first time - nonperturbative
bounds on all scales for the case of scale decompositions of the propagator
which do not impose cutoffs on the Matsubara frequency.Comment: 29 pages LaTe

### SIC1 is ubiquitinated in vitro by a pathway that requires CDC4, CDC34, and cyclin/CDK activities

Traversal from G1 to S-phase in cycling cells of budding yeast is dependent on the destruction of the S-phase cyclin/CDK inhibitor SIC1. Genetic data suggest that SIC1 proteolysis is mediated by the ubiquitin pathway and requires the action of CDC34, CDC4, CDC53, SKP1, and CLN/CDC28. As a first step in defining the functions of the corresponding gene products, we have reconstituted SIC1 multiubiquitination in DEAE-fractionated yeast extract. Multiubiquitination depends on cyclin/CDC28 protein kinase and the CDC34 ubiquitin-conjugating enzyme. Ubiquitin chain formation is abrogated in cdc4ts mutant extracts and assembly restored by the addition of exogenous CDC4, suggesting a direct role for this protein in SIC1 multiubiquitination. Deletion analysis of SIC1 indicates that the N-terminal 160 residues are both necessary and sufficient to serve as substrate for CDC34-dependent ubiquitination. The complementary C-terminal segment of SIC1 binds to the S-phase cyclin CLB5, indicating a modular structure for SIC1

### Ultralight reactive metal foams produced as structural shapes in space: System design

This autonomous experiment for foaming metals in space involved: (1) payload support structure; (2) furnace and foaming apparatus; (3) electronic controls; (4) battery power; and (5) metallurgy. Emphasis was laid on a modular design which was easily modifiable and which offered maximum durability, safety, and failure tolerance

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