1,882 research outputs found
Strong spectral evolution during the prompt emission of GRB 070616
Swift has revealed features in GRB early light curves, such as steep decays
and X-ray flares, whose properties are consistent with an internal origin
though they are far from understood. The steep X-ray decay is often explained
using the curvature effect; however a significant number of GRBs display strong
spectral evolution during this phase, and a new mechanism must be invoked to
explain this. Of particular interest are the longest duration GRBs in which the
early emission can be studied in most detail. Here we present data for GRB
070616, in which the prompt emission shows a complex multipeaked structure,
leading to one of the longest prompt emission durations ever recorded. We take
advantage of extensive coverage of such a long burst by all Swift instruments.
Combining data from Swift and Suzaku we study the evolution of the prompt
emission spectrum, following the temporal variability of the peak energy and
spectral slope.Comment: 4 pages, 2 figures (Fig 1 in colour), contributed talk, submitted to
the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9
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TALON - The Telescope Alert Operation Network System: Intelligent Linking of Distributed Autonomous Robotic Telescopes
The internet has brought about great change in the astronomical community,
but this interconnectivity is just starting to be exploited for use in
instrumentation. Utilizing the internet for communicating between distributed
astronomical systems is still in its infancy, but it already shows great
potential. Here we present an example of a distributed network of telescopes
that performs more efficiently in synchronous operation than as individual
instruments. RAPid Telescopes for Optical Response (RAPTOR) is a system of
telescopes at LANL that has intelligent intercommunication, combined with
wide-field optics, temporal monitoring software, and deep-field follow-up
capability all working in closed-loop real-time operation. The Telescope ALert
Operations Network (TALON) is a network server that allows intercommunication
of alert triggers from external and internal resources and controls the
distribution of these to each of the telescopes on the network. TALON is
designed to grow, allowing any number of telescopes to be linked together and
communicate. Coupled with an intelligent alert client at each telescope, it can
analyze and respond to each distributed TALON alert based on the telescopes
needs and schedule.Comment: Presentation at SPIE 2004, Glasgow, Scotland (UK
Quantum dynamics of a high-finesse optical cavity coupled with a thin semi-transparent membrane
We study the quantum dynamics of the cavity optomechanical system formed by a
Fabry-Perot cavity with a thin vibrating membrane at its center. We first
derive the general multimode Hamiltonian describing the radiation pressure
interaction between the cavity modes and the vibrational modes of the membrane.
We then restrict the analysis to the standard case of a single cavity mode
interacting with a single mechanical resonator and we determine to what extent
optical absorption by the membrane hinder reaching a quantum regime for the
cavity-membrane system. We show that membrane absorption does not pose serious
limitations and that one can simultaneously achieve ground state cooling of a
vibrational mode of the membrane and stationary optomechanical entanglement
with state-of-the-art apparatuses.Comment: 14 pages, 7 figure
Gamma-ray Bursts, Classified Physically
From Galactic binary sources, to extragalactic magnetized neutron stars, to
long-duration GRBs without associated supernovae, the types of sources we now
believe capable of producing bursts of gamma-rays continues to grow apace. With
this emergent diversity comes the recognition that the traditional (and newly
formulated) high-energy observables used for identifying sub-classes does not
provide an adequate one-to-one mapping to progenitors. The popular
classification of some > 100 sec duration GRBs as ``short bursts'' is not only
an unpalatable retronym and syntactically oxymoronic but highlights the
difficultly of using what was once a purely phenomenological classification to
encode our understanding of the physics that gives rise to the events. Here we
propose a physically based classification scheme designed to coexist with the
phenomenological system already in place and argue for its utility and
necessity.Comment: 6 pages, 3 figures. Slightly expanded version of solicited paper to
be published in the Proceedings of ''Gamma Ray Bursts 2007,'' Santa Fe, New
Mexico, November 5-9. Edited by E. E. Fenimore, M. Galassi, D. Palme
Aurophilic interactions in polynuclear Au(I) complexes with phosphine ligands containing imidazole rings
Aurophilic interactions in polynuclear Au(I)
complexes with phosphine ligands containing
imidazole rings
Fiorella Bachechiaa*, Alfredo Burinib, Rossana Galassib
aIstituto di Strutturistica Chimica, C.N.R., Area della Ricerca di Roma,
C.P. 10, 00016 Monterotondo St. (Roma), Italy., bDipartimento di Scienze
Chimiche, UniversitĂ di Camerino, 62032 Camerino, Italy. E-mail:
[email protected]
Keywords: gold complexes, aurophilicity, crystal
structures
The tertiary phosphines of the type (Bzim)3-nPhnP, where Bzim
is 1-benzyl-2-imidazolylphosphine and n varies from 0 to 2,
were synthesised as part of a program aimed to the study of
the coordination chemistry of phosphines containing imidazole
rings. The softer character of imidazole, with respect to other
heterocycles, turned out to be useful in the stabilization of
complexes with soft metals as those of Group 11 in low oxidation
states. These ligands can behave as monodentate or as P, N
bidentate forming dinuclear cationic complexes. With Au(I)
they were found to be able to favour the formation of intraand
intermolecular aurophilic interactions. TheAu(I) complexes
assume considerable interest when aurophilic bonds occur
between gold atoms, since their chemical and physical properties
change to particular characteristics with potential applications
in electronic, optical or sensor devices. In particular short
Au•••Au interactions are considered related to optoelectronic
properties as observed in a number of polynuclear gold
compounds. Here the structures of two Au(I) complexes are
reported. The binuclear complex [ÎĽ-(Bzim)Ph2PAu2(C6F5)2]
adopts a folded conformation with parallel, eclipsed C6F5
rings and a corresponding short AucccAu contact of 3.033(2)Ă….
The tetranuclear cluster complex {[μ-N,N’-(Bzim)3PAuCl]2
Au2}2+c AuCl2
- c AuCl4
- consists in a 12-membered macrocycle
with two gold atoms coordinated to two (Bzim)3P
molecules, in bridging mode, through the nitrogen atoms of the
imidazole rings and two gold atoms coordinated to the
phosphorus atoms of the (Bzim)3P ligands. Two chloride atoms
complete the Au bicoordination. Three strong aurophilic interactions,
Au(1)cccAu(4) [2.989(2)Ă…], Au(2)cccAu(3) [3.014(2)Ă…]
andAu(1)cccAu(2) [3.257(3)Ă…], occur.Aweak gold-gold contact,
Au(3)cccAu(4) [3.766(2)Ă…], is also present.
Understanding molecular interactions
23r
GRBs and the thermalization process of electron-positron plasmas
We discuss the temporal evolution of the pair plasma created in Gamma-Ray
Burst sources. A particular attention is paid to the relaxation of the plasma
into thermal equilibrium. We also discuss the connection between the dynamics
of expansion and the spatial geometry of the plasma. The role of the baryonic
loading parameter is emphasized.Comment: 4 pages, 3 figures, in the Proceedings of the "Gamma Ray Bursts 2007"
meeting, November 5-9, 2007, Santa Fe, New Mexico, US
SkyDOT (Sky Database for Objects in the Time Domain): A Virtual Observatory for Variability Studies at LANL
The mining of Virtual Observatories (VOs) is becoming a powerful new method
for discovery in astronomy. Here we report on the development of SkyDOT (Sky
Database for Objects in the Time domain), a new Virtual Observatory, which is
dedicated to the study of sky variability. The site will confederate a number
of massive variability surveys and enable exploration of the time domain in
astronomy. We discuss the architecture of the database and the functionality of
the user interface. An important aspect of SkyDOT is that it is continuously
updated in near real time so that users can access new observations in a timely
manner. The site will also utilize high level machine learning tools that will
allow sophisticated mining of the archive. Another key feature is the real time
data stream provided by RAPTOR (RAPid Telescopes for Optical Response), a new
sky monitoring experiment under construction at Los Alamos National Laboratory
(LANL).Comment: to appear in SPIE proceedings vol. 4846, 11 pages, 5 figure
The antiquity of hydrocephalus: the first full palaeo-neuropathological description
The Pathology Museum of the University of Florence houses a rich collection of anatomical specimens and over a hundred waxworks portraying pathological conditions occurring in the nineteenth century, when the museum was established. Clinical and autopsy findings of these cases can still be retrieved from the original museum catalogue, offering a rare opportunity for retrospective palaeo-pathological diagnostics. We present a historical case of severe hydrocephalus backed by modern-day anthropological, radiological and molecular analyses conducted on the skeleton of an 18-month-old male infant deceased in 1831. Luigi Calamai (1796-1851), a wax craftsman of La Specola workshop in Florence, was commissioned to create a life-sized wax model of the child's head, neck and upper thorax. This artwork allows us to appreciate the cranial and facial alterations determined by 30 lb of cerebrospinal fluid (CSF) accumulated within the cerebral ventricular system. Based on the autopsy report, gross malformations of the neural tube, tumours and haemorrhage could be excluded. A molecular approach proved helpful in confirming sex. We present this case as the so-far most compelling case of hydrocephalus in palaeo-pathological research
Path-integral calculation of the third virial coefficient of quantum gases at low temperatures
We derive path-integral expressions for the second and third virial
coefficients of monatomic quantum gases. Unlike previous work that considered
only Boltzmann statistics, we include exchange effects (Bose-Einstein or
Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials
to calculate the third virial coefficient of 3He and 4He in the temperature
range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited
experimental data. Inclusion of exchange effects is necessary to obtain
accurate results below about 7 K.Comment: The following article has been accepted by The Journal of Chemical
Physics. After it is published, it will be found at http://jcp.aip.org/
Version 2 includes the corrections detailed in the Erratu
DNA-Protein Binding Rates: Bending Fluctuation and Hydrodynamic Coupling Effects
We investigate diffusion-limited reactions between a diffusing particle and a
target site on a semiflexible polymer, a key factor determining the kinetics of
DNA-protein binding and polymerization of cytoskeletal filaments. Our theory
focuses on two competing effects: polymer shape fluctuations, which speed up
association, and the hydrodynamic coupling between the diffusing particle and
the chain, which slows down association. Polymer bending fluctuations are
described using a mean field dynamical theory, while the hydrodynamic coupling
between polymer and particle is incorporated through a simple heuristic
approximation. Both of these we validate through comparison with Brownian
dynamics simulations. Neither of the effects has been fully considered before
in the biophysical context, and we show they are necessary to form accurate
estimates of reaction processes. The association rate depends on the stiffness
of the polymer and the particle size, exhibiting a maximum for intermediate
persistence length and a minimum for intermediate particle radius. In the
parameter range relevant to DNA-protein binding, the rate increase is up to
100% compared to the Smoluchowski result for simple center-of-mass motion. The
quantitative predictions made by the theory can be tested experimentally.Comment: 21 pages, 11 figures, 1 tabl
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