26,752 research outputs found
Zero torque gear head wrench
A gear head wrench particularly suited for use in applying torque to bolts without transferring torsional stress to bolt-receiving structures is introduced. The wrench is characterized by a coupling including a socket, for connecting a bolt head with a torque multiplying gear train, provided within a housing having an annulus concentrically related to the socket and adapted to be coupled with a spacer interposed between the bolt head and the juxtaposed surface of the bolt-receiving structure for applying a balancing counter-torque to the spacer as torque is applied to the bolt head whereby the bolt-receiving structure is substantially isolated from torsional stress. As a result of the foregoing, the operator of the wrench is substantially isolated from any forces which may be imposed
Bolt installation tool for tightening large nuts and bolts
Large bolts and nuts are accurately tightened to structures without damaging torque stresses. There are two models of bolt installation tool. One is rigidly mounted and one is hand held. Each model includes torque-multiplier unit
High Frequency Behavior of the Infrared Conductivity of Cuprates
We analyze recent infrared conductivity data in the normal state of the
cuprates.
We find that the high frequency behavior, which has been suggested as
evidence for quantum critical scaling, is generally characteristic of electrons
interacting with a broad spectrum of bosons.
From explicit calculations, we find a frequency exponent for the modulus of
the conductivity, and a phase angle, in good agreement with experiment. The
data indicate an upper cut-off of the boson spectrum of order 300 meV. This
implies that the bosons are of electronic origin rather than phonons.Comment: 4 page
Odd Parity and Line Nodes in Heavy Fermion Superconductors
Group theory arguments have demonstrated that a general odd parity order
parameter cannot have line nodes in the presence of spin-orbit coupling. In
this paper, it is shown that these arguments do not hold on the
zone face of a hexagonal close packed lattice. In particular, three of the six
odd parity representations vanish identically on this face. This has potential
relevance to the heavy fermion superconductor .Comment: 5 pages, revte
The Temperature Evolution of the Spectral Peak in High Temperature Superconductors
Recent photoemission data in the high temperature cuprate superconductor
Bi2212 have been interpreted in terms of a sharp spectral peak with a
temperature independent lifetime, whose weight strongly decreases upon heating.
By a detailed analysis of the data, we are able to extract the temperature
dependence of the electron self-energy, and demonstrate that this intepretation
is misleading. Rather, the spectral peak loses its integrity above Tc due to a
large reduction in the electron lifetime.Comment: 5 pages, revtex, 4 encapsulated postscript figure
Incoherent pair tunneling in the pseudogap phase of cuprates
Motivated by a recent experiment by Bergeal et al., we reconsider incoherent
pair tunneling in a cuprate junction formed from an optimally doped
superconducting lead and an underdoped normal metallic lead. We study the
impact of the pseudogap on the pair tunneling by describing fermions in the
underdoped lead with a model self-energy that has been developed to reproduce
photoemission data. We find that the pseudogap causes an additional temperature
dependent suppression of the pair contribution to the tunneling current. We
discuss consistency with available experimental data and propose future
experimental directions.Comment: 5 pages, 3 figure
A new extensive catalog of optically variable AGN in the GOODS Fields and a new statistical approach to variability selection
Variability is a property shared by practically all AGN. This makes
variability selection a possible technique for identifying AGN. Given that
variability selection makes no prior assumption about spectral properties, it
is a powerful technique for detecting both low-luminosity AGN in which the host
galaxy emission is dominating and AGN with unusual spectral properties. In this
paper, we will discuss and test different statistical methods for the detection
of variability in sparsely sampled data that allow full control over the false
positive rates. We will apply these methods to the GOODS North and South fields
and present a catalog of variable sources in the z band in both GOODS fields.
Out of 11931 objects checked, we find 155 variable sources at a significance
level of 99.9%, corresponding to about 1.3% of all objects. After rejection of
stars and supernovae, 139 variability selected AGN remain. Their magnitudes
reach down as faint as 25.5 mag in z. Spectroscopic redshifts are available for
22 of the variability selected AGN, ranging from 0.046 to 3.7. The absolute
magnitudes in the rest-frame z-band range from ~ -18 to -24, reaching
substantially fainter than the typical luminosities probed by traditional X-ray
and spectroscopic AGN selection in these fields. Therefore, this is a powerful
technique for future exploration of the evolution of the faint end of the AGN
luminosity function up to high redshifts.Comment: Accepted for publication in The Astrophysical Journal (version 2:
minor changes to text after receiving comments
PRISM: a tool for automatic verification of probabilistic systems
Probabilistic model checking is an automatic formal verification technique for analysing quantitative properties of systems which exhibit stochastic behaviour. PRISM is a probabilistic model checking tool which has already been successfully deployed in a wide range of application domains, from real-time communication protocols to biological signalling pathways. The tool has recently undergone a significant amount of development. Major additions include facilities to manually explore models, Monte-Carlo discrete-event simulation techniques for approximate model analysis (including support for distributed simulation) and the ability to compute cost- and reward-based measures, e.g. "the expected energy consumption of the system before the first failure occurs". This paper presents an overview of all the main features of PRISM. More information can be found on the website: www.cs.bham.ac.uk/~dxp/prism
Quasiparticle mirages in the tunneling spectra of d-wave superconductors
We illustrate the importance of many-body effects in the Fourier transformed
local density of states (FT-LDOS) of d-wave superconductors from a model of
electrons coupled to an Einstein mode with energy Omega_0. For bias energies
significantly larger than Omega_0 the quasiparticles have short lifetimes due
to this coupling, and the FT-LDOS is featureless if the electron-impurity
scattering is treated within the Born approximation. In this regime it is
important to include boson exchange for the electron-impurity scattering which
provides a `step down' in energy for the electrons and allows for long
lifetimes. This many-body effect produces qualitatively different results,
namely the presence of peaks in the FT-LDOS which are mirrors of the
quasiparticle interference peaks which occur at bias energies smaller than ~
Omega_0. The experimental observation of these quasiparticle mirages would be
an important step forward in elucidating the role of many-body effects in
FT-LDOS measurements.Comment: revised text with new figures, to be published, Phys Rev
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