1,648 research outputs found
Scale-invariant statistics of period in directed earthquake network
A new law regarding structure of the earthquake networks is found. The
seismic data taken in California is mapped to a growing directed network. Then,
statistics of period in the network, which implies that after how many
earthquakes an earthquake returns to the initial location, is studied. It is
found that the period distribution obeys a power law, showing the fundamental
difficulty of statistical estimate of period.Comment: 11 pages including 3 figure
Effect of Compton Scattering on the Electron Beam Dynamics at the ATF Damping Ring
Compton scattering provides one of the most promising scheme to obtain
polarized positrons for the next generation of -- colliders.
Moreover it is an attractive method to produce monochromatic high energy
polarized gammas for nuclear applications and X-rays for compact light sources.
In this framework a four-mirror Fabry-P\'erot cavity has been installed at the
Accelerator Test Facility (ATF - KEK, Tsukuba, Japan) and is used to produce an
intense flux of polarized gamma rays by Compton scattering
\cite{ipac-mightylaser}. For electrons at the ATF energy (1.28 GeV) Compton
scattering may result in a shorter lifetime due to the limited bucket
acceptance. We have implemented the effect of Compton scattering on a 2D
tracking code with a Monte-Carlo method. This code has been used to study the
longitudinal dynamics of the electron beam at the ATF damping ring, in
particular the evolution of the energy spread and the bunch length under
Compton scattering. The results obtained are presented and discussed. Possible
methods to observe the effect of Compton scattering on the ATF beam are
proposed
Dynamical evolution of clustering in complex network of earthquakes
The network approach plays a distinguished role in contemporary science of
complex systems/phenomena. Such an approach has been introduced into seismology
in a recent work [S. Abe and N. Suzuki, Europhys. Lett. 65, 581 (2004)]. Here,
we discuss the dynamical property of the earthquake network constructed in
California and report the discovery that the values of the clustering
coefficient remain stationary before main shocks, suddenly jump up at the main
shocks, and then slowly decay following a power law to become stationary again.
Thus, the network approach is found to characterize main shocks in a peculiar
manner.Comment: 10 pages, 3 figures, 1 tabl
Magnetic-field effects on the charge-spin stripe order in La-214 high-Tc cuprates
Magnetic-field effects on the charge-spin stripe order in La-214 high-Tc
cuprates have been investigated from measurements of the in-plane
electrical-resistivity, Rho_ab_. In La_2-x_Ba_x_CuO_4_ with x=0.10 and
La_2-x_Sr_x_CuO_4_ with x=0.115 where the incommensurate charge peaks are weak
and unobservable in zero field in elastic neutron-scattering measurements,
respectively, the normal-state value of Rho_ab_ at low temperatures markedly
increases with increasing field up to 27 T. For La_2-x_Ba_x_CuO_4_ with x=0.11
and Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with x=0.115 and y=0.02 where
the charge stripe order is fairly stabilized in zero field, on the other hand,
the increase in Rho_ab_ with increasing field is negligibly small. In
conclusion, when the charge-spin stripe order is not fully stable in zero
field, magnetic field operates to stabilize the charge-spin stripe order. The
value of Rho_ab_ increases with increasing field depending on the stability of
the charge stripe order.Comment: 4 pages, 2 figures, Proceedings of Yamada Conference LX on Research
in High Magnetic Fields (RHMF2006) (Satellite of ICM2006
Photon generation by laser-Compton scattering at the KEK-ATF
We performed a photon generation experiment by laser-Compton scattering at
the KEK-ATF, aiming to develop a Compton based polarized positron source for
linear colliders. In the experiment, laser pulses with a 357 MHz repetition
rate were accumulated and their power was enhanced by up to 250 times in the
Fabry-Perot optical resonant cavity. We succeeded in synchronizing the laser
pulses and colliding them with the 1.3 GeV electron beam in the ATF ring while
maintaining the laser pulse accumulation in the cavity. As a result, we
observed 26.0 +/- 0.1 photons per electron-laser pulse crossing, which
corresponds to a yield of 10^8 photons in a second.Comment: 3 pages, 5 figures, Preprint submitted to TIPP09 Proceedings in NIM
Time dependent transformations in deformation quantization
We study the action of time dependent canonical and coordinate
transformations in phase space quantum mechanics. We extend the covariant
formulation of the theory by providing a formalism that is fully invariant
under both standard and time dependent coordinate transformations. This result
considerably enlarges the set of possible phase space representations of
quantum mechanics and makes it possible to construct a causal representation
for the distributional sector of Wigner quantum mechanics.Comment: 16 pages, to appear in the J. Math. Phy
1 um Excess Sources in the UKIDSS - I. Three T Dwarfs in the SDSS Southern Equatorial Stripe
We report the discovery of two field brown dwarfs, ULAS J0128-0041 and ULAS
J0321+0051, and the rediscovery of ULAS J0226+0051 (IfA 0230-Z1), in the Sloan
Digital Sky Survey (SDSS) southern equatorial stripe. They are found in the
course of our follow-up observation program of 1 um excess sources in the
United Kingdom Infrared Telescope Infrared Deep Sky Survey. The Gemini
Multi-Object Spectrographs spectra at red optical wavelengths (6500-10500 A)
are presented, which reveal that they are early-T dwarfs. The classification is
also supported by their optical to near-infrared colors. It is noted that ULAS
J0321+0051 is one of the faintest currently known T dwarfs. The estimated
distances to the three objects are 50-110 pc, thus they are among the most
distant field T dwarfs known. Dense temporal coverage of the target fields
achieved by the SDSS-II Supernova Survey allows us to perform a simple
time-series analysis, which leads to the finding of significant proper motions
of 150-290 mas/yr or the transverse velocities of 40-100 km/s for ULAS
J0128-0041 and ULAS J0226+0051. We also find that there are no detectable,
long-term (a-few-year) brightness variations above a few times 0.1 mag for the
two brown dwarfs.Comment: Accepted for publication in the Astronomical Journal; Typos correcte
Generalized Weyl-Wigner map and Vey quantum mechanics
The Weyl-Wigner map yields the entire structure of Moyal quantum mechanics
directly from the standard operator formulation. The covariant generalization
of Moyal theory, also known as Vey quantum mechanics, was presented in the
literature many years ago. However, a derivation of the formalism directly from
standard operator quantum mechanics, clarifying the relation between the two
formulations is still missing. In this paper we present a covariant
generalization of the Weyl order prescription and of the Weyl-Wigner map and
use them to derive Vey quantum mechanics directly from the standard operator
formulation. The procedure displays some interesting features: it yields all
the key ingredients and provides a more straightforward interpretation of the
Vey theory including a direct implementation of unitary operator
transformations as phase space coordinate transformations in the Vey idiom.
These features are illustrated through a simple example.Comment: 15 pages, LaTe
Scaling and memory of intraday volatility return intervals in stock market
We study the return interval between price volatilities that are above
a certain threshold for 31 intraday datasets, including the Standard &
Poor's 500 index and the 30 stocks that form the Dow Jones Industrial index.
For different threshold , the probability density function
scales with the mean interval as
, similar to that found in daily
volatilities. Since the intraday records have significantly more data points
compared to the daily records, we could probe for much higher thresholds
and still obtain good statistics. We find that the scaling function is
consistent for all 31 intraday datasets in various time resolutions, and the
function is well approximated by the stretched exponential, , with and , which indicates the
existence of correlations. We analyze the conditional probability distribution
for following a certain interval , and find
depends on , which demonstrates memory in intraday
return intervals. Also, we find that the mean conditional interval
increases with , consistent with the memory found for
. Moreover, we find that return interval records have long
term correlations with correlation exponents similar to that of volatility
records.Comment: 19 pages, 8 figure
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