4,974 research outputs found
COMPTEL observations of gamma‐ray flares in October 1991
The COMPTEL experiment on GRO images 0.75–30 MeV celestial gamma‐radiation that falls within its 1 steradian field of view. During observation 12 (primary target Cen A) in October 1991 the sun had been in the fov and several solar flares associated with the active region 6891 had been observed. Time profile and energy spectra had been produced, using COMPTEL’s primary mode of operation (the telescope mode). Additionally the number of counts received in the D2‐single burst detector (the secondary mode of operation) are given. We summarize the preliminary results on all of these flares
The pre-WDVV ring of physics and its topology
We show how a simplicial complex arising from the WDVV
(Witten-Dijkgraaf-Verlinde-Verlinde) equations of string theory is the
Whitehouse complex. Using discrete Morse theory, we give an elementary proof
that the Whitehouse complex is homotopy equivalent to a wedge of
spheres of dimension . We also verify the Cohen-Macaulay
property. Additionally, recurrences are given for the face enumeration of the
complex and the Hilbert series of the associated pre-WDVV ring.Comment: 13 pages, 4 figures, 2 table
COMPTEL’s solar flare catalog
COMPTEL, the imaging gamma‐ray telescope, capable of detecting gamma rays in the range of 0.1–30 MeV, is one of four instruments aboard NASA’s Compton Gamma‐Ray Observatory. The Comptel burst detectors (single Defector Mode) have a field of view of ∼2.5 π sr. These detectors of COMPTEL permit measurements of energy spectra and time histories of solar flare gamma‐ray emission. A search through the Single Detector Mode’s data is being conducted. We summarize the preliminary results of this search
Exploring the role of professional associations in collective learning in London and New York's advertising and law professional service firm clusters.
The value of regional economies for collective learning has been reported by numerous scholars. However often work has been criticised for lacking analytical clarity and failing to explore the architectures of collective learning and the role of the knowledge produced in making firms in a cluster economy successful. This paper engages with these problematics and investigates how collective learning is facilitated in the advertising and law professional service firm clusters in London and New York. It explores the role of professional associations and investigates how they mediate a collective learning process in each city. It argues that professional associations seed urban communities of practice that emerge outside of the formal activities of professional associations. In these communities individual with shared interests in advertising and law learn from one-another and are therefore able to adapt and evolve one-another approaches to common industry challenges. The paper suggests this is another form of the variation Marshall highlighted in relation to cluster-based collective learning. The paper also shows how the collective learning process is affected by the presence, absence and strength of an institutional thickness. It is therefore argued that a richer understanding of institutional affects is needed in relation to CL
Early multi-wavelength emission from Gamma-ray Bursts: from Gamma-ray to X-ray
The study of the early high-energy emission from both long and short
Gamma-ray bursts has been revolutionized by the Swift mission. The rapid
response of Swift shows that the non-thermal X-ray emission transitions
smoothly from the prompt phase into a decaying phase whatever the details of
the light curve. The decay is often categorized by a steep-to-shallow
transition suggesting that the prompt emission and the afterglow are two
distinct emission components. In those GRBs with an initially steeply-decaying
X-ray light curve we are probably seeing off-axis emission due to termination
of intense central engine activity. This phase is usually followed, within the
first hour, by a shallow decay, giving the appearance of a late emission hump.
The late emission hump can last for up to a day, and hence, although faint, is
energetically very significant. The energy emitted during the late emission
hump is very likely due to the forward shock being constantly refreshed by
either late central engine activity or less relativistic material emitted
during the prompt phase. In other GRBs the early X-ray emission decays
gradually following the prompt emission with no evidence for early temporal
breaks, and in these bursts the emission may be dominated by classical
afterglow emission from the external shock as the relativistic jet is slowed by
interaction with the surrounding circum-burst medium. At least half of the GRBs
observed by Swift also show erratic X-ray flaring behaviour, usually within the
first few hours. The properties of the X-ray flares suggest that they are due
to central engine activity. Overall, the observed wide variety of early
high-energy phenomena pose a major challenge to GRB models.Comment: Accepted for publication in the New Journal of Physics focus issue on
Gamma Ray Burst
Exact Dynamical Correlation Functions of Calogero-Sutherland Model and One-Dimensional Fractional Statistics
One-dimensional model of non-relativistic particles with inverse-square
interaction potential known as Calogero-Sutherland Model (CSM) is shown to
possess fractional statistics. Using the theory of Jack symmetric polynomial
the exact dynamical density-density correlation function and the one-particle
Green's function (hole propagator) at any rational interaction coupling
constant are obtained and used to show clear evidences of the
fractional statistics. Motifs representing the eigenstates of the model are
also constructed and used to reveal the fractional {\it exclusion} statistics
(in the sense of Haldane's ``Generalized Pauli Exclusion Principle''). This
model is also endowed with a natural {\it exchange } statistics (1D analog of
2D braiding statistics) compatible with the {\it exclusion} statistics.
(Submitted to PRL on April 18, 1994)Comment: Revtex 11 pages, IASSNS-HEP-94/27 (April 18, 1994
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