1,567 research outputs found
Markov evolutions and hierarchical equations in the continuum I. One-component systems
General birth-and-death as well as hopping stochastic dynamics of infinite
particle systems in the continuum are considered. We derive corresponding
evolution equations for correlation functions and generating functionals.
General considerations are illustrated in a number of concrete examples of
Markov evolutions appearing in applications.Comment: 47 page
Vlasov scaling for stochastic dynamics of continuous systems
We describe a general scheme of derivation of the Vlasov-type equations for
Markov evolutions of particle systems in continuum. This scheme is based on a
proper scaling of corresponding Markov generators and has an algorithmic
realization in terms of related hierarchical chains of correlation functions
equations. Several examples of the realization of the proposed approach in
particular models are presented.Comment: 23 page
Lowering and raising operators for the free Meixner class of orthogonal polynomials
We compare some properties of the lowering and raising operators for the
classical and free classes of Meixner polynomials on the real line
Pulsar Science with the Green Bank 43m Telescope
The 43m telescope at the NRAO site in Green Bank, WV has recently been
outfitted with a clone of the Green Bank Ultimate Pulsar Processing Instrument
(GUPPI \cite{Ransom:2009}) backend, making it very useful for a number of
pulsar related studies in frequency ranges 800-1600 MHz and 220-440 MHz. Some
of the recent science being done with it include: monitoring of the Crab
pulsar, a blind search for transient sources, pulsar searches of targets of
opportunity, and an all-sky mapping project. For the Crab monitoring project,
regular observations are searched for giant pulses (GPs), which are then
correlated with -ray photons from the \emph{Fermi} spacecraft. Data
from the all-sky mapping project are first run through a pipeline that does a
blind transient search, looking for single pulses over a DM range of 0-500
pc~cm. These projects are made possible by MIT Lincoln Labs.Comment: 2 pages, 1 figure, to appear in AIP Conference Proceedings of Pulsar
Conference 2010 "Radio Pulsars: a key to unlock the secrets of the Universe",
Sardinia, October 201
A Search for Pulsed and Bursty Radio Emission from X-ray Dim Isolated Neutron Stars
We have carried out a search for radio emission from six X-ray dim isolated
neutron stars (XDINSs) observed with the Robert C. Byrd Green Bank Radio
Telescope (GBT) at 820 MHz. No bursty or pulsed radio emission was found down
to a 4sigma significance level. The corresponding flux limit is 0.01-0.04 mJy
depending on the integration time for the particular source and pulse duty
cycle of 2%. These are the most sensitive limits yet on radio emission from
these objects.Comment: 3 pages, 3 figures, to be appeared in the Proceedings of the
conference "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More"
held on August 12-17, 2007, McGill University, Montreal, Canad
The Inklings in America
Transcription of a panel discussion at the 19th Mythopoeic Conference
A Giant Sample of Giant Pulses from the Crab Pulsar
We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a
timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and
seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses
(GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken
with the same telescope and backend and analyzed as one data set. We calculated
power-law fits to amplitude distributions for main pulse (MP) and interpulse
(IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz
and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also
correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank
Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9
GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2
GHz and 39900 GPs from the GBT were recorded during these contemporaneous
observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at
8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP
GPs were detected within one spin period of high-frequency IP GPs, with a
chance probability of 9%. This indicates that the emission processes at high
and low radio frequencies are related, despite significant pulse profile shape
differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to
see if increased pair production in the magnetosphere is the mechanism
responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons
were used in this correlation analysis. No significant correlations were found
between GPs and gamma-ray photons. This indicates that increased pair
production in the magnetosphere is likely not the dominant cause of GPs.
Possible methods of GP production may be increased coherence of synchrotron
emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap
Phase transitions and quantum effects in anharmonic crystals
The most important recent results in the theory of phase transitions and
quantum effects in quantum anharmonic crystals are presented and discussed. In
particular, necessary and sufficient conditions for a phase transition to occur
at some temperature are given in the form of simple inequalities involving the
interaction strength and the parameters describing a single oscillator. The
main characteristic feature of the theory is that both mentioned phenomena are
described in one and the same setting, in which thermodynamic phases of the
model appear as probability measures on path spaces. Then the possibility of a
phase transition to occur is related to the existence of multiple phases at the
same values of the relevant parameters. Other definitions of phase transitions,
based on the non-differentiability of the free energy density and on the
appearance of ordering, are also discussed
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