55,688 research outputs found
Fast recharge circuit for q-switched lasers
Cavity-dumped lasers employ electrooptic-effect cell to alternately block and release laser pulse. Cell requires high-speed switching circuit that can apply and remove high voltage. Solid-state circuit employs complementary transistor switches which can switch at rates greater than 5 kHz, eliminate warmup time, provide variable voltage wave-form, and allow polarity reversal
Coherent adiabatic theory of two-electron quantum dot molecules in external spin baths
We derive an accurate molecular orbital based expression for the coherent
time evolution of a two-electron wave function in a quantum dot molecule where
the electrons interact with each other, with external time dependent
electromagnetic fields and with a surrounding nuclear spin reservoir. The
theory allows for direct numerical modeling of the decoherence in quantum dots
due to hyperfine interactions. Calculations result in good agreement with
recent singlet-triplet dephasing experiments by Laird et. al. [Phys. Rev. Lett.
97, 056801 (2006)], as well as analytical model calculations. Furthermore, it
is shown that using a much faster electric switch than applied in these
experiments will transfer the initial state to excited states where the
hyperfine singlet-triplet mixing is negligible.Comment: 4 pages, 3 figure
Facilitating Humanitarian Access to Pharmaceutical and Agricultural Innovation
Calls for intellectual property licensing strategies in the pharmaceutical and agricultural sectors that promote humanitarian access to product innovations for the benefit of the disadvantaged. Includes profiles of successful and promising strategies
The application of the global isomorphism to the study of liquid-vapor equilibrium in two and three dimensional Lenard-Jones fluids
We analyze the interrelation between the coexistence curve of the
Lennard-Jones fluid and the Ising model in two and three dimensions within the
global isomorphism approach proposed earlier [V. L. Kulinskii, J. Phys. Chem. B
\textbf{114} 2852 (2010)]. In case of two dimensions we use the exact Onsager
result to construct the binodal of the corresponding Lennard-Jones fluid and
compare it with the results of the simulations. In the three dimensional case
we use available numerical results for the Ising model for the corresponding
mapping. The possibility to observe the singularity of the binodal diameter is
discussed.Comment: 9 pages, 2 figure
Multiple-channel generalization of Lellouch-Luscher formula
We generalize the Lellouch-Luscher formula, relating weak matrix elements in
finite and infinite volumes, to the case of multiple strongly-coupled decay
channels into two scalar particles. This is a necessary first step on the way
to a lattice QCD calculation of weak decay rates for processes such as D -> pi
pi and D -> KK. We also present a field theoretic derivation of the
generalization of Luscher's finite volume quantization condition to multiple
two-particle channels. We give fully explicit results for the case of two
channels, including a form of the generalized Lellouch-Luscher formula
expressed in terms of derivatives of the energies of finite volume states with
respect to the box size. Our results hold for arbitrary total momentum and for
degenerate or non-degenerate particles.Comment: 16 pages, 2 figures. v3: Added references, clarified relation to and
corrected comments about previous work, and minor stylistic improvements. v4:
Minor clarifications added, typos fixed, references updated---matches
published versio
Infall near clusters of galaxies: comparing gas and dark matter velocity profiles
We consider the dynamics in and near galaxy clusters. Gas, dark matter and
galaxies are presently falling into the clusters between approximately 1 and 5
virial radii. At very large distances, beyond 10 virial radii, all matter is
following the Hubble flow, and inside the virial radius the matter particles
have on average zero radial velocity. The cosmological parameters are imprinted
on the infall profile of the gas, however, no method exists, which allows a
measurement of it. We consider the results of two cosmological simulations
(using the numerical codes RAMSES and Gadget) and find that the gas and dark
matter radial velocities are very similar. We derive the relevant dynamical
equations, in particular the generalized hydrostatic equilibrium equation,
including both the expansion of the Universe and the cosmological background.
This generalized gas equation is the main new contribution of this paper. We
combine these generalized equations with the results of the numerical
simulations to estimate the contribution to the measured cluster masses from
the radial velocity: inside the virial radius it is negligible, and inside two
virial radii the effect is below 40%, in agreement the earlier analyses for DM.
We point out how the infall velocity in principle may be observable, by
measuring the gas properties to distance of about two virial radii, however,
this is practically not possible today.Comment: 7 pages, 3 figures, to appear in MNRA
Testing Asteroseismic Radii of Dwarfs and Subgiants with Kepler and Gaia
We test asteroseismic radii of Kepler main-sequence and subgiant stars by
deriving their parallaxes which are compared with those of the first Gaia data
release. We compute radii based on the asteroseismic scaling relations as well
as by fitting observed oscillation frequencies to stellar models for a subset
of the sample, and test the impact of using effective temperatures from either
spectroscopy or the infrared flux method. An offset of 3%, showing no
dependency on any stellar parameters, is found between seismic parallaxes
derived from frequency modelling and those from Gaia. For parallaxes based on
radii from the scaling relations, a smaller offset is found on average;
however, the offset becomes temperature dependent which we interpret as
problems with the scaling relations at high stellar temperatures. Using the
hotter infrared flux method temperature scale, there is no indication that
radii from the scaling relations are inaccurate by more than about 5%. Taking
the radii and masses from the modelling of individual frequencies as reference
values, we seek to correct the scaling relations for the observed temperature
trend. This analysis indicates that the scaling relations systematically
overestimate radii and masses at high temperatures, and that they are accurate
to within 5% in radius and 13% in mass for main-sequence stars with
temperatures below 6400 K. However, further analysis is required to test the
validity of the corrections on a star-by-star basis and for more evolved stars.Comment: 12 pages, 9 figures. Accepted for publication in MNRA
Absence of magnetic long range order in YCrSbO: bond-disorder induced magnetic frustration in a ferromagnetic pyrochlore
The consequences of nonmagnetic-ion dilution for the pyrochlore family
Y()O ( = magnetic ion, = nonmagnetic
ion) have been investigated. As a first step, we experimentally examine the
magnetic properties of YCrSbO ( = 0.5), in which the magnetic
sites (Cr) are percolative. Although the effective Cr-Cr spin exchange
is ferromagnetic, as evidenced by a positive Curie-Weiss temperature,
= 20.1(6) K, our high-resolution neutron powder
diffraction measurements detect no sign of magnetic long range order down to 2
K. In order to understand our observations, we performed numerical simulations
to study the bond-disorder introduced by the ionic size mismatch between
and . Based on these simulations, bond-disorder ( 0.23)
percolates well ahead of site-disorder ( 0.61). This model
successfully reproduces the critical region (0.2 < < 0.25) for the N\'eel
to spin glass phase transition in Zn(CrGa)O, where
the Cr/Ga-sublattice forms the same corner-sharing tetrahedral network as the
-sublattice in Y()O, and the rapid drop in
magnetically ordered moment in the N\'eel phase [Lee , Phys. Rev. B
77, 014405 (2008)]. Our study stresses the nonnegligible role of bond-disorder
on magnetic frustration, even in ferromagnets
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