3,547 research outputs found
Dynamics of adaptive agents with asymmetric information
We apply path-integral techniques to study the dynamics of agent-based models
with asymmetric information structures. In particular, we devise a batch
version of a model proposed originally by Berg et al. [Quant. Fin. 1 (2001)
203], and convert the coupled multi-agent processes into an effective-agent
problem from which the dynamical order parameters in ergodic regimes can be
derived self-consistently together with the corresponding phase structure. Our
dynamical study complements and extends the available static theory. Results
are confirmed by numerical simulations.Comment: minor revision of text, accepted by JSTA
Experimental study of Pomeron
A Pomeron phenomenon remains a mystery. A short review of the experimental
situation in diffractive physics and an account of some spectacular
manifestations of the Pomeron are given.Comment: 17 pages, 7 Figs, LATEX. Talk given at the conference "From the
smallest to largest distances", ITEP, Moscow, 24-26 May 2001. Changes: Fig.2
replace
Locating very high energy gamma ray sources with arc minute accuracy
The angular accuracy of gamma-ray detectors is intrinsically limited by the physical processes involved in photon detection. Although a number of point-like sources were detected by the COS-B satellite, only two were unambiguously identified by time signature with counterparts at longer wavelengths. By taking advantage of the extended longitudinal structure of Very High Energy gamma-ray showers, measurements in the TeV energy range can pinpoint source coordinates to arc minute accuracy. This was demonstrated using Cerenkov air shower imaging techniques. With two telescopes in coincidence, the individual event circular probable error will be 0.13 deg. The half-cone angle of the field of view is effectively 1 deg
The role of uncertainty, sentiment and cross-country interactions in G7 output dynamics
Output fluctuations in the G7 are characterised using a VAR model of countries' actual and expected outputs and uncertainty over these. New measures are developed to quantify the relative importance of economic prospects-versus-uncertainty, global-versus-national effects and fundamentals-versus-sentiment for countries' persistent output movements. National and global contributions are found to be equally important across the G7 although considerable differences exist between countries. Uncertainty, and especially cross-country uncertainty, is important in propagating the effects of shocks and generates around 20% of countries' persistent output movements on average. Fundamentals dominate output movements although, with an 80:20 split, sentiment plays a non-negligible role
The Host Galaxy of GRB 990123
We present deep images of the field of gamma-ray burst (GRB) 990123 obtained
in a broad-band UV/visible bandpass with the Hubble Space Telescope, and deep
near-infrared images obtained with the Keck-I 10-m telescope. Both the HST and
Keck images show that the optical transient (OT) is clearly offset by 0.6
arcsec from an extended object, presumably the host galaxy. This galaxy is the
most likely source of the metallic-line absorption at z = 1.6004 seen in the
spectrum of the OT. With magnitudes V_{C} ~ 24.6 +/- 0.2 and K = 21.65 +/- 0.30
mag this corresponds to an L ~ 0.7 L_* galaxy, assuming that it is located at z
= 1.6. The estimated unobscured star formation rate is SFR ~ 6 M_sun/yr, which
is not unusually high for normal galaxies at comparable redshifts. The strength
of the observed metallic absorption lines is suggestive of a relatively high
metallicity of the gas, and thus of a chemically evolved system which may be
associated with a massive galaxy. It is also indicative of a high column
density of the gas, typical of damped Ly-alpha systems at high redshifts. We
conclude that this is the host galaxy of GRB 990123. No other obvious galaxies
are detected within the same projected radius from the OT. There is thus no
evidence for strong gravitational lensing magnification of this burst, and some
alternative explanation for its remarkable energetics may be required. The
observed offset of the OT from the center of its apparent host galaxy, 5.5 +/-
0.9 proper kpc (projected) in the galaxy's rest-frame, both refutes the
possibility that GRBs are related to galactic nuclear activity and supports
models of GRBs which involve the death and/or merger of massive stars. Further,
the HST image suggests an intimate connection of GRB 990123 and a star-forming
region.Comment: Updated references. 12 pages including 3 Postscript figures. Camera-
ready reproductions of the figures can be found at
http://astro.caltech.edu/~jsb/GRB/grb990123.htm
Continuous optical monitoring during the prompt emission of GRB 060111B
We present the time-resolved optical emission of GRB 060111B during its
prompt phase, measured with the TAROT robotic observatory. This is the first
time that the optical emission from a gamma-ray burst has been continuously
monitored with a temporal resolution of a few seconds during the prompt
gamma-ray phase. The temporal evolution of the prompt optical emission at the
level of several seconds is used to provide a clue to the origin of this
emission. The optical emission was found to decay steadily from our first
measure, 28s after the trigger, in contrast to the gamma-ray emission, which
exhibits strong variability at the same time. This behaviour strongly suggests
that the optical emission is due to the reverse shock
Very High Energy Gamma-Ray Emission from the Blazar Markarian 421
Very high energy gamma-ray emission from the BL Lac object Markarian 421 has
been detected over three observing seasons on 59 nights between April 1992 and
June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its
initial detection in 1992, its flux above 500 GeV was
1.610photons cm s. Observations in 1993 confirmed
this level of emission. For observations made between December 1993 and April
1994, its intensity was a factor of 2.20.5 lower. Observations on 14 and
15 May, 1994 showed an increase over this quiescent level by a factor of
10 (Kerrick et al. 1995). This strong outburst suggests that 4 episodes
of increased flux measurements on similar time scales in 1992 and 1994 may be
attributed to somewhat weaker outbursts. The variability of the TeV gamma-ray
emission from Markarian 421 stands in contrast to EGRET observations (Lin et
al. 1994) which show no evidence for variability.Comment: gzip compressed tar file including LaTeX text and 4 postscript
figures (14 pages total incl. 4 tables), accepted for publication in the
Astrophysical Journal. Contact address is [email protected]
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