154 research outputs found
Orientations of two coupled molecules
Orientation states of two coupled polar molecules controlled by laser pulses
are studied theoretically. By varying the period of a series of periodically
applied laser pulse, transition from regular to chaotic behavior may occur.
Schmidt decomposition is used to measure the degree of entanglement. It is
found that the entanglement can be enhanced by increasing the strength of laser
pulse.Comment: 4 pages, 4 figures, to appear in Chem. Phys. Lett.(2004
Oscillations of a solid sphere falling through a wormlike micellar fluid
We present an experimental study of the motion of a solid sphere falling
through a wormlike micellar fluid. While smaller or lighter spheres quickly
reach a terminal velocity, larger or heavier spheres are found to oscillate in
the direction of their falling motion. The onset of this instability correlates
with a critical value of the velocity gradient scale
s. We relate this condition to the known complex rheology of wormlike
micellar fluids, and suggest that the unsteady motion of the sphere is caused
by the formation and breaking of flow-induced structures.Comment: 4 pages, 4 figure
Possible experiment for determination of the role of microscopic vortex rings in the \lambda-transition in He-II
It is suggested that microscopic vortex rings (MVR) play an important role in
the \lambda-transition in helium-II and substantially determine the value of
T_{\lambda}. For very thin films of He-II, with thickness d less than the size
of the smallest MVR, the rings do not fit in and, therefore, do not exist in
such films. Consequently, for superfluid films of He-II, a peculiarity in the
form of a smoothed-out jump should be observed in the curve T_{m}(d) at the
values of thickness approximately equal to the size of the smallest MVR, d= 3 -
9 A (T_{m} is the temperature of the maximum of the broad peak on the curve of
the dependence of the specific heat on temperature). The absence of a similar
peculiarity will be an evidence that MVR do not influence the values of
T_{\lambda} and T_{m}, and do not play any key role in the \lambda-transition.
The currently available experimental data are insufficient for revealing the
predicted peculiarity.Comment: 6 pages, 2 figure
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
A Study of Cosmic Ray Secondaries Induced by the Mir Space Station Using AMS-01
The Alpha Magnetic Spectrometer (AMS-02) is a high energy particle physics
experiment that will study cosmic rays in the to range and will be installed on the International Space Station
(ISS) for at least 3 years. A first version of AMS-02, AMS-01, flew aboard the
space shuttle \emph{Discovery} from June 2 to June 12, 1998, and collected
cosmic ray triggers. Part of the \emph{Mir} space station was within the
AMS-01 field of view during the four day \emph{Mir} docking phase of this
flight. We have reconstructed an image of this part of the \emph{Mir} space
station using secondary and emissions from primary cosmic rays
interacting with \emph{Mir}. This is the first time this reconstruction was
performed in AMS-01, and it is important for understanding potential
backgrounds during the 3 year AMS-02 mission.Comment: To be submitted to NIM B Added material requested by referee. Minor
stylistic and grammer change
Development of Motorized Slewing Mirror Stage for the UFFO Project
The Ultra-Fast Flash Observatory (UFFO) is a space observatory for optical follow-ups of
gamma ray bursts (GRBs), aiming to explore the first 60 seconds of GRBs optical emission.
UFFO is utilized to catch early optical emissions from GRBs within few sec after trigger
using a Gimbal mirror which redirects the optical path rather than slewing entire
spacecraft. We have developed a 15 cm two-axis Gimbal mirror stage for the UFFO-Pathfinder
which is going to be on board the Lomonosov satellite which is to be launched in 2013. The
stage is designed for fast and accurate motion with given budgets of 3 kg of mass and 3
Watt of power. By employing stepping motors, the slewing mirror can rotate faster than 15
deg/sec so that objects in the UFFO coverage (60 deg × 60 deg) can be targeted in
~1 sec. The obtained targeting resolution is better 2 arcmin using a close-loop
control with high precision rotary encoder. In this presentation, we will discuss details
of design, manufacturing, space qualification tests, as well as performance tests
A new strategy for enhancing imputation quality of rare variants from next-generation sequencing data via combining SNP and exome chip data
Background: Rare variants have gathered increasing attention as a possible alternative source of missing heritability. Since next generation sequencing technology is not yet cost-effective for large-scale genomic studies, a widely used alternative approach is imputation. However, the imputation approach may be limited by the low accuracy of the imputed rare variants. To improve imputation accuracy of rare variants, various approaches have been suggested, including increasing the sample size of the reference panel, using sequencing data from study-specific samples (i.e., specific populations), and using local reference panels by genotyping or sequencing a subset of study samples. While these approaches mainly utilize reference panels, imputation accuracy of rare variants can also be increased by using exome chips containing rare variants. The exome chip contains 250 K rare variants selected from the discovered variants of about 12,000 sequenced samples. If exome chip data are available for previously genotyped samples, the combined approach using a genotype panel of merged data, including exome chips and SNP chips, should increase the imputation accuracy of rare variants. Results: In this study, we describe a combined imputation which uses both exome chip and SNP chip data simultaneously as a genotype panel. The effectiveness and performance of the combined approach was demonstrated using a reference panel of 848 samples constructed using exome sequencing data from the T2D-GENES consortium and 5,349 sample genotype panels consisting of an exome chip and SNP chip. As a result, the combined approach increased imputation quality up to 11 %, and genomic coverage for rare variants up to 117.7 % (MAF < 1 %), compared to imputation using the SNP chip alone. Also, we investigated the systematic effect of reference panels on imputation quality using five reference panels and three genotype panels. The best performing approach was the combination of the study specific reference panel and the genotype panel of combined data. Conclusions: Our study demonstrates that combined datasets, including SNP chips and exome chips, enhances both the imputation quality and genomic coverage of rare variants
Cosmic-ray positron fraction measurement from 1 to 30 GeV with AMS-01
A measurement of the cosmic ray positron fraction e+/(e+ + e-) in the energy range of 1-30 GeV is presented. The measurement is based on data taken by the AMS-01 experiment during its 10 day Space Shuttle flight in June 1998. A proton background suppression on the order of 10^6 is reached by identifying converted bremsstrahlung photons emitted from positrons
Modern temporal network theory: A colloquium
The power of any kind of network approach lies in the ability to simplify a
complex system so that one can better understand its function as a whole.
Sometimes it is beneficial, however, to include more information than in a
simple graph of only nodes and links. Adding information about times of
interactions can make predictions and mechanistic understanding more accurate.
The drawback, however, is that there are not so many methods available, partly
because temporal networks is a relatively young field, partly because it more
difficult to develop such methods compared to for static networks. In this
colloquium, we review the methods to analyze and model temporal networks and
processes taking place on them, focusing mainly on the last three years. This
includes the spreading of infectious disease, opinions, rumors, in social
networks; information packets in computer networks; various types of signaling
in biology, and more. We also discuss future directions.Comment: Final accepted versio
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