3,386 research outputs found
Sky survey at far infrared wavelengths using a balloon-borne telescope
Localized sources of far infrared radiation (approximately 50 microns) have been detected during a high altitude balloon flight with a 40 cm telescope and silicon detectors. The flight system is described and preliminary results are presented. A large area of the sky has been scanned for localized sources of far infrared radiation, using a balloon-borne system that was sensitive to wavelengths beyond about 55 microns. Two Molectron silicon bolometers were used, with a Newtonian telescope having a 40 cm primary. The telescope was driven in azimuth at a fixed elevation; this mode of scanning was carried out for the duration of each of two balloon flights. The flight system is described
Linear instability criteria for ideal fluid flows subject to two subclasses of perturbations
In this paper we examine the linear stability of equilibrium solutions to
incompressible Euler's equation in 2- and 3-dimensions. The space of
perturbations is split into two classes - those that preserve the topology of
vortex lines and those in the corresponding factor space. This classification
of perturbations arises naturally from the geometric structure of
hydrodynamics; our first class of perturbations is the tangent space to the
co-adjoint orbit. Instability criteria for equilibrium solutions are
established in the form of lower bounds for the essential spectral radius of
the linear evolution operator restricted to each class of perturbation.Comment: 29 page
The origin and propagation of VVH primary cosmic ray particles
Several source spectra were constructed from combinations of 4- and s-process nuclei to match the observed charge spectrum of VVH particles. Their propagation was then followed, allowing for interactions and decay, and comparisons were made between the calculated near-earth spectra and those observed during high altitude balloon flights. None of the models gave good agreement with observations
Bose-Einstein condensate and Spontaneous Breaking of Conformal Symmetry on Killing Horizons
Local scalar QFT (in Weyl algebraic approach) is constructed on degenerate
semi-Riemannian manifolds corresponding to Killing horizons in spacetime.
Covariance properties of the -algebra of observables with respect to the
conformal group PSL(2,\bR) are studied.It is shown that, in addition to the
state studied by Guido, Longo, Roberts and Verch for bifurcated Killing
horizons, which is conformally invariant and KMS at Hawking temperature with
respect to the Killing flow and defines a conformal net of von Neumann
algebras, there is a further wide class of algebraic (coherent) states
representing spontaneous breaking of PSL(2,\bR) symmetry. This class is
labeled by functions in a suitable Hilbert space and their GNS representations
enjoy remarkable properties. The states are non equivalent extremal KMS states
at Hawking temperature with respect to the residual one-parameter subgroup of
PSL(2,\bR) associated with the Killing flow. The KMS property is valid for
the two local sub algebras of observables uniquely determined by covariance and
invariance under the residual symmetry unitarily represented. These algebras
rely on the physical region of the manifold corresponding to a Killing horizon
cleaned up by removing the unphysical points at infinity (necessary to describe
the whole PSL(2,\bR) action).Each of the found states can be interpreted as a
different thermodynamic phase, containing Bose-Einstein condensate,for the
considered quantum field. It is finally suggested that the found states could
describe different black holes.Comment: 36 pages, 1 figure. Formula of condensate energy density modified.
Accepted for pubblication in Journal of Mathematical Physic
Primary cosmic ray particles with z 35 (VVH particles)
Large areas of nuclear emulsions and plastic detectors were exposed to the primary cosmic radiation during high altitude balloon flights. From the analysis of 141 particle tracks recorded during a total exposure of 1.3 x 10 to the 7th power sq m ster.sec., a charge spectrum of the VVH particles has been derived
Relationships between various characterisations of wave tails
One can define several properties of wave equations that correspond to the
absence of tails in their solutions, the most common one by far being Huygens'
principle. Not all of these definitions are equivalent, although they are
sometimes assumed to be. We analyse this issue in detail for linear scalar
waves, establishing some relationships between the various properties. Huygens'
principle is almost always equivalent to the characteristic propagation
property, and in two spacetime dimensions the latter is equivalent to the
zeroth order progressing wave propagation property. Higher order progressing
waves in general do have tails, and do not seem to admit a simple physical
characterisation, but they are nevertheless useful because of their close
association with exactly solvable two-dimensional equations.Comment: Plain TeX, 26 page
"Peeling property" for linearized gravity in null coordinates
A complete description of the linearized gravitational field on a flat
background is given in terms of gauge-independent quasilocal quantities. This
is an extension of the results from gr-qc/9801068. Asymptotic spherical
quasilocal parameterization of the Weyl field and its relation with Einstein
equations is presented. The field equations are equivalent to the wave
equation. A generalization for Schwarzschild background is developed and the
axial part of gravitational field is fully analyzed. In the case of axial
degree of freedom for linearized gravitational field the corresponding
generalization of the d'Alembert operator is a Regge-Wheeler equation. Finally,
the asymptotics at null infinity is investigated and strong peeling property
for axial waves is proved.Comment: 27 page
Molecular evidence for the clonal origin of blast crisis in chronic myeloid leukaemia.
Cytogenetic and enzymatic studies have shown that chronic myeloid leukemia (CML) represents the clonal proliferation of a pluripotent stem cell. The Philadelphia chromosome (Ph') is the characteristic karyotypic abnormality seen in this disease, although the exact role of this clonal marker in the pathogenesis of CML is uncertain. At a molecular level, the Ph' has recently been shown to represent the translocation of c-abl to a limited (breakpoint cluster region, bcr) on chromosome 22. We have used probes for the bcr gene to obtain molecular evidence for the clonal origin of blast crisis in 2 patient with CML. In both cases, the first with myeloid and the second with lymphoid blast crisis, there was rearrangement of the bcr gene. The patterns of rearrangement varied between patients but were identical when comparing acute and chronic phases within the same individual. As the Ph' translocation is thought to represent a random recombination event these data not only provide further evidence for the clonal origin of blast crisis in CML, but also suggest that in the second patient this translocation event had already occurred at the pluripotent stem cell
Algebraic approach to quantum field theory on non-globally-hyperbolic spacetimes
The mathematical formalism for linear quantum field theory on curved
spacetime depends in an essential way on the assumption of global
hyperbolicity. Physically, what lie at the foundation of any formalism for
quantization in curved spacetime are the canonical commutation relations,
imposed on the field operators evaluated at a global Cauchy surface. In the
algebraic formulation of linear quantum field theory, the canonical commutation
relations are restated in terms of a well-defined symplectic structure on the
space of smooth solutions, and the local field algebra is constructed as the
Weyl algebra associated to this symplectic vector space. When spacetime is not
globally hyperbolic, e.g. when it contains naked singularities or closed
timelike curves, a global Cauchy surface does not exist, and there is no
obvious way to formulate the canonical commutation relations, hence no obvious
way to construct the field algebra. In a paper submitted elsewhere, we report
on a generalization of the algebraic framework for quantum field theory to
arbitrary topological spaces which do not necessarily have a spacetime metric
defined on them at the outset. Taking this generalization as a starting point,
in this paper we give a prescription for constructing the field algebra of a
(massless or massive) Klein-Gordon field on an arbitrary background spacetime.
When spacetime is globally hyperbolic, the theory defined by our construction
coincides with the ordinary Klein-Gordon field theory on aComment: 21 pages, UCSBTH-92-4
Performance requirements analysis for payload delivery from a space station
Operations conducted from a space station in low Earth orbit which have different constraints and opportunities than those conducted from direct Earth launch were examined. While a space station relieves many size and performance constraints on the space shuttle, the space station's inertial orbit has different launch window constraints from those associated with customary Earth launches which reflect upon upper stage capability. A performance requirements analysis was developed to provide a reference source of parametric data, and specific case solutions and upper stage sizing trade to assist potential space station users and space station and upper stage developers assess the impacts of a space station on missions of interest
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