10,313 research outputs found
Experimental on-stream elimination of resonant whirl in a large centrifugal compressor
Resonant whirl condition during operation of a multi-stage centrifugal compressor at higher than anticipated speeds and loads was reported. The condition was diagnosed by a large scale computerized Machinery Condition Monitoring System (MACMOS). This computerized system verified that the predominant subsynchronous whirl frequency locked in on the first resonant frequency of the compressor rotor and did not vary with compressor speed. Compressor stability calculations showed the rotor system had excessive hearing stiffness and inadequate effective damping. An optimum bearing design which was developed to minimize the unbalance response and to maximize the stability threshold is presented
A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from Radio Pulses
Multipath propagation in the interstellar medium distorts radio pulses, an
effect predominant for distant pulsars observed at low frequencies. Typically,
broadened pulses are analyzed to determine the amount of propagation-induced
pulse broadening, but with little interest in determining the undistorted pulse
shapes. In this paper we develop and apply a method that recovers both the
intrinsic pulse shape and the pulse broadening function that describes the
scattering of an impulse. The method resembles the CLEAN algorithm used in
synthesis imaging applications, although we search for the best pulse
broadening function, and perform a true deconvolution to recover intrinsic
pulse structre. As figures of merit to optimize the deconvolution, we use the
positivity and symmetry of the deconvolved result along with the mean square
residual and the number of points below a given threshold. Our method makes no
prior assumptions about the intrinsic pulse shape and can be used for a range
of scattering functions for the interstellar medium. It can therefore be
applied to a wider variety of measured pulse shapes and degrees of scattering
than the previous approaches. We apply the technique to both simulated data and
data from Arecibo observations.Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
Surface recombination measurements on IIIâV candidate materials for nanostructure light-emitting diodes
Surface recombination is an important characteristic of an optoelectronic material. Although surface recombination is a limiting factor for very small devices it has not been studied intensively. We have investigated surface recombination velocity on the exposed surfaces of the AlGaN, InGaAs, and InGaAlP material systems by using absolute photoluminescence quantum efficiency measurements. Two of these three material systems have low enough surface recombination velocity to be usable in nanoscale photonic crystal light-emitting diodes
On Observing Dynamic Prioritised Actions in SOC
We study the impact on observational semantics for SOC of priority mechanisms which combine dynamic priority with local pre-emption. We define manageable notions of strong and weak labelled bisimilarities for COWS, a process calculus for SOC, and provide alternative characterisations in terms of open barbed bisimilarities. These semantics show that COWSâs priority mechanisms partially recover the capability to observe receive actions (that could not be observed in a purely asynchronous setting) and that high priority primitives for termination impose specific conditions on the bisimilarities
The Index of (White) Noises and their Product Systems
(See detailed abstract in the article.) We single out the correct class of
spatial product systems (and the spatial endomorphism semigroups with which the
product systems are associated) that allows the most far reaching analogy in
their classifiaction when compared with Arveson systems. The main differences
are that mere existence of a unit is not it sufficient: The unit must be
CENTRAL. And the tensor product under which the index is additive is not
available for product systems of Hilbert modules. It must be replaced by a new
product that even for Arveson systems need not coincide with the tensor
product
Spin transport in inhomogeneous magnetic fields: a proposal for Stern-Gerlach-like experiments with conduction electrons
Spin dynamics in spatially inhomogeneous magnetic fields is studied within
the framework of Boltzmann theory. Stern-Gerlach-like separation of spin up and
spin down electrons occurs in ballistic and diffusive regimes, before spin
relaxation sets in. Transient dynamics and spectral response to time-dependent
inhomogeneous magnetic fields are investigated, and possible experimental
observations of our findings are discussed.Comment: 7 pages, 4 figures; revised and extended version, to appear in PR
High-Spin Doublet Band Structures in odd-odd Tl isotopes
The basis space in the triaxial projected shell model (TPSM) approach is
generalized for odd-odd nuclei to include two-neutron and two-proton
configurations on the basic one-neutron coupled to one-proton quasiparticle
state. The generalization allows to investigate odd-odd nuclei beyond the band
crossing region and as a first application of this development, high-spin band
structures recently observed in odd-odd Tl isotopes are
investigated. In some of these isotopes, the doublet band structures observed
after the band crossing have been conjectured to arise from the spontaneous
breaking of the chiral symmetry. The driving configuration of the chiral
symmetry in these odd-odd isotopes is one-proton and three-neutrons rather than
the basic one-proton and one-neutron as already observed in many other nuclei.
It is demonstrated using the TPSM approach that energy differences of the
doublet bands in Tl and Tl are, indeed, small. However, the
differences in the calculated transition probabilities are somewhat larger than
what is expected in the chiral symmetry limit. Experimental data on the
transition probabilities is needed to shed light on the chiral nature of the
doublet bands.Comment: 11 pages, 17 figures, to appear in EPJ
Primary calcified hydatid of spleen: a case report
Most splenic cysts are parasitic. Hydatid disease, a parasitic disease, isendemic in Kashmir. Splenic involvement alone in hydatid disease is very rare. It may remain asymptomatic or, by causing pressure due to increasing size on adjacent viscera, may become symptomatic. A non specific presentation always makes diagnosis difficult. A case of hydatid spleen in a young boy who presented with abdominal pain is reported. Radiology complemented with serology made the diagnosis. Hydatid disease should beconsidered as a differential diagnosis in every patient with a calcified cystic mass of the spleen in endemic areas.KEY WORDS: Calcified hydatid; Spleen; Splenic cyst; Case repor
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