321 research outputs found
Three-boson problem at low energy and Implications for dilute Bose-Einstein condensates
It is shown that the effective interaction strength of three bosons at small
collision energies can be extracted from their wave function at zero energy. An
asymptotic expansion of this wave function at large interparticle distances is
derived, from which is defined a quantity named three-body scattering
hypervolume, which is an analog of the two-body scattering length. Given any
finite-range interaction potentials, one can thus predict the effective
three-body force from a numerical solution of the Schr\"{o}dinger equation. In
this way the constant for hard-sphere bosons is computed, leading to the
complete result for the ground state energy per particle of a dilute
Bose-Einstein condensate (BEC) of hard spheres to order , where
is the number density. Effects of are also demonstrated in the three-body
energy in a finite box of size , which is expanded to the order ,
and in the three-body scattering amplitude in vacuum. Another key prediction is
that there is a violation of the effective field theory (EFT) in the condensate
fraction in dilute BECs, caused by short-range physics. EFT predictions for the
ground state energy and few-body scattering amplitudes, however, are
corroborated.Comment: 24 pages, no figur
Superconductivity at 5.2 K in ZrTe3 polycrystals and the effect of Cu, Ag intercalation
We report the occurrence of superconductivity in polycrystalline samples of
ZrTe3 at 5.2 K temperature at ambient pressure. The superconducting state
coexists with the charge density wave (CDW) phase, which sets in at 63K. The
intercalation of Cu or Ag, does not have any bearing on the superconducting
transition temperature but suppresses the CDW state. The feature of CDW anomaly
in these compounds is clearly seen in the DC magnetization data. Resistivity
data is analysed to estimate the relative loss of carriers and reduction in the
nested Fermi surface area upon CDW formation in the ZrTe3 and the intercalated
compounds.Comment: 5 pages, 8 figure
Correlation of high energy muons with primary composition in extensive air shower
An experimental investigation of high energy muons above 200 GeV in extensive air showers has been made for studying high energy interaction and primary composition of cosmic rays of energies in the range 10 to the 14th power approx. 10 to the 15th power eV. The muon energies are estimated from the burst sizes initiated by the muons in the rock, which are measured by four layers of proportional counters, each of area 5 x 2.6 sq m, placed at 30 m.w.e. deep, Funasaka tunnel vertically below the air shower array. These results are compared with Monte Carlo simulations based on the scaling model and the fireball model for two primary compositions, all proton and mixed
Quantum noise in ideal operational amplifiers
We consider a model of quantum measurement built on an ideal operational
amplifier operating in the limit of infinite gain, infinite input impedance and
null output impedance and with a feddback loop. We evaluate the intensity and
voltage noises which have to be added to the classical amplification equations
in order to fulfill the requirements of quantum mechanics. We give a
description of this measurement device as a quantum network scattering quantum
fluctuations from input to output ports.Comment: 4 pages, 2 figures, RevTe
Fluctuation-dissipation theorem and quantum tunneling with dissipation at finite temperature
A reformulation of the fluctuation-dissipation theorem of Callen and Welton
is presented in such a manner that the basic idea of Feynman-Vernon and
Caldeira -Leggett of using an infinite number of oscillators to simulate the
dissipative medium is realized manifestly without actually introducing
oscillators. If one assumes the existence of a well defined dissipative
coefficient which little depends on the temperature in the energy
region we are interested in, the spontanous and induced emissions as well as
induced absorption of these effective oscillators with correct Bose
distribution automatically appears.
Combined with a dispersion relation, we reproduce the tunneling formula in
the presence of dissipation at finite temperature without referring to an
explicit model Lagrangian. The fluctuation-dissipation theorem of Callen-Welton
is also generalized to the fermionic dissipation (or fluctuation) which allows
a transparent physical interpretation in terms of second quantized fermionic
oscillators. This fermionic version of fluctuation-dissipation theorem may
become relevant in the analyses of, for example, fermion radiation from a black
hole and also supersymmetry at the early universe.Comment: 19 pages. Phys. Rev. E (in press
VERTICAL AND HORIZONTAL FORCES DURING CUTIING IN BASKETBALL UNDER DIFFERENT CONDITIONS
The purpose of this study is to evaluate ground reaction force responses in professional basketball athletes while executing this sport's typical cutting maneuver with and without ankle bracing: taping, aircast-type orthosis and basketball shoes. Eight athletes were dynamically analyzed during a basketball cutting maneuver with a force platform. We collected vertical and medial-lateral forces under these three conditions and analyzed force peaks of foot contact with the ground and propulsion and growth gradient for these forces. Results show that bracing did not significantly change Fymax1 and GCFymax1; significantly reduced Fymax2 and GG Fymax2. With respect to the medial-lateral component, there were no significant differences in relation to force magnitudes between the three study conditions. However, GG Fzmax1 was significantly greater for the sport shoe condition than for the taping condition. Bracing decreased ground reaction force at some instances, but increased in others
NGC2180: a disrupting open cluster
The spatial dependence of luminosity and mass functions of evolved open
clusters is discussed in this work using J and H 2MASS photometry. The target
objects are the overlooked open cluster NGC2180 and the intermediate-age open
cluster NGC3680. We conclude that, although in an advanced dynamical state
(mass segregated), NGC3680 does not present strong signs of dissolution. On the
other hand, NGC2180 presents flat, eroded LFs throughout its structure,
indicating that in addition to mass segregation, Galactic tidal stripping has
been effective in depleting this cluster of stars. Accordingly, NGC2180 may be
the missing link between evolved open clusters and remnants. We study both
clusters in the context of dynamical states estimated from diagnostic-diagrams
involving photometric and structural parameters. Both clusters are dynamically
evolved systems. In particular, NGC2180 is closer to open cluster remnants than
NGC3680.Comment: 9 pages, 8 figure
Crystal structure of RIG-I C-terminal domain bound to blunt-ended double-strand RNA without 5′ triphosphate
RIG-I recognizes molecular patterns in viral RNA to regulate the induction of type I interferons. The C-terminal domain (CTD) of RIG-I exhibits high affinity for 5′ triphosphate (ppp) dsRNA as well as blunt-ended dsRNA. Structures of RIG-I CTD bound to 5′-ppp dsRNA showed that RIG-I recognizes the termini of dsRNA and interacts with the ppp through electrostatic interactions. However, the structural basis for the recognition of non-phosphorylated dsRNA by RIG-I is not fully understood. Here, we show that RIG-I CTD binds blunt-ended dsRNA in a different orientation compared to 5′ ppp dsRNA and interacts with both strands of the dsRNA. Overlapping sets of residues are involved in the recognition of blunt-ended dsRNA and 5′ ppp dsRNA. Mutations at the RNA-binding surface affect RNA binding and signaling by RIG-I. These results provide the mechanistic basis for how RIG-I recognizes different RNA ligands
Quantum Communication with Correlated Nonclassical States
Nonclassical correlations between the quadrature-phase amplitudes of two
spatially separated optical beams are exploited to realize a two-channel
quantum communication experiment with a high degree of immunity to
interception. For this scheme, either channel alone can have an arbitrarily
small signal-to-noise ratio (SNR) for transmission of a coherent ``message''.
However, when the transmitted beams are combined properly upon authorized
detection, the encoded message can in principle be recovered with the original
SNR of the source. An experimental demonstration has achieved a 3.2 dB
improvement in SNR over that possible with correlated classical sources.
Extensions of the protocol to improve its security against eavesdropping are
discussed.Comment: 8 pages and 4 figures (Figure 1; Figures 2a, 2b; Figure 2
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