3,500 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
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
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
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
Condensation phase transitions of symmetric conserved-mass aggregation model on complex networks
We investigate condensation phase transitions of symmetric conserved-mass
aggregation (SCA) model on random networks (RNs) and scale-free networks (SFNs)
with degree distribution . In SCA model, masses diffuse
with unite rate, and unit mass chips off from mass with rate . The
dynamics conserves total mass density . In the steady state, on RNs and
SFNs with for , we numerically show that SCA
model undergoes the same type condensation transitions as those on regular
lattices. However the critical line depends on network
structures. On SFNs with , the fluid phase of exponential mass
distribution completely disappears and no phase transitions occurs. Instead,
the condensation with exponentially decaying background mass distribution
always takes place for any non-zero density. For the existence of the condensed
phase for at the zero density limit, we investigate one
lamb-lion problem on RNs and SFNs. We numerically show that a lamb survives
indefinitely with finite survival probability on RNs and SFNs with ,
and dies out exponentially on SFNs with . The finite life time
of a lamb on SFNs with ensures the existence of the
condensation at the zero density limit on SFNs with at which
direct numerical simulations are practically impossible. At ,
we numerically confirm that complete condensation takes place for any on RNs. Together with the recent study on SFNs, the complete condensation
always occurs on both RNs and SFNs in zero range process with constant hopping
rate.Comment: 6 pages, 6 figure
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
On the supercritically diffusive magneto-geostrophic equations
We address the well-posedness theory for the magento-geostrophic equation,
namely an active scalar equation in which the divergence-free drift velocity is
one derivative more singular than the active scalar. In the presence of
supercritical fractional diffusion given by (-\Delta)^\gamma, where 0<\gamma<1,
we discover that for \gamma>1/2 the equations are locally well-posed, while for
\gamma<1/2 they are ill-posed, in the sense that there is no Lipschitz solution
map. The main reason for the striking loss of regularity when \gamma goes below
1/2 is that the constitutive law used to obtain the velocity from the active
scalar is given by an unbounded Fourier multiplier which is both even and
anisotropic. Lastly, we note that the anisotropy of the constitutive law for
the velocity may be explored in order to obtain an improvement in the
regularity of the solutions when the initial data and the force have thin
Fourier support, i.e. they are supported on a plane in frequency space. In
particular, for such well-prepared data one may prove the local existence and
uniqueness of solutions for all values of \gamma \in (0,1).Comment: 24 page
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
Rigorous steps towards holography in asymptotically flat spacetimes
Scalar QFT on the boundary at null infinity of a general
asymptotically flat 4D spacetime is constructed using the algebraic approach
based on Weyl algebra associated to a BMS-invariant symplectic form. The
constructed theory is invariant under a suitable unitary representation of the
BMS group with manifest meaning when the fields are interpreted as suitable
extensions to of massless minimally coupled fields propagating in the
bulk. The analysis of the found unitary BMS representation proves that such a
field on coincides with the natural wave function constructed out of
the unitary BMS irreducible representation induced from the little group
, the semidirect product between SO(2) and the two dimensional
translational group. The result proposes a natural criterion to solve the long
standing problem of the topology of BMS group. Indeed the found natural
correspondence of quantum field theories holds only if the BMS group is
equipped with the nuclear topology rejecting instead the Hilbert one.
Eventually some theorems towards a holographic description on of QFT in
the bulk are established at level of algebras of fields for strongly
asymptotically predictable spacetimes. It is proved that preservation of a
certain symplectic form implies the existence of an injective -homomorphism
from the Weyl algebra of fields of the bulk into that associated with the
boundary . Those results are, in particular, applied to 4D Minkowski
spacetime where a nice interplay between Poincar\'e invariance in the bulk and
BMS invariance on the boundary at is established at level of QFT. It
arises that the -homomorphism admits unitary implementation and Minkowski
vacuum is mapped into the BMS invariant vacuum on .Comment: 62 pages, amslatex, xy package; revised section 2 and the
conclusions; corrected some typos; added some references; accepted for
pubblication on Rev. Math. Phy
A family of diameter-based eigenvalue bounds for quantum graphs
We establish a sharp lower bound on the first non-trivial eigenvalue of the
Laplacian on a metric graph equipped with natural (i.e., continuity and
Kirchhoff) vertex conditions in terms of the diameter and the total length of
the graph. This extends a result of, and resolves an open problem from, [J. B.
Kennedy, P. Kurasov, G. Malenov\'a and D. Mugnolo, Ann. Henri Poincar\'e 17
(2016), 2439--2473, Section 7.2], and also complements an analogous lower bound
for the corresponding eigenvalue of the combinatorial Laplacian on a discrete
graph. We also give a family of corresponding lower bounds for the higher
eigenvalues under the assumption that the total length of the graph is
sufficiently large compared with its diameter. These inequalities are sharp in
the case of trees.Comment: Substantial revision of v1. The main result, originally for the first
eigenvalue, has been generalised to the higher ones. The title has been
changed and the proofs substantially reorganised to reflect the new result,
and a section containing concluding remarks has been adde
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