1,251 research outputs found
Introducing Agility in Hybrid Communication Systems and Sensors
This paper presents a new approach in dealing with hybridization issues in communication systems or sensors. The thrust is to separate the logical network (sensor) infrastructure from the physical one. Here we show how we can exploit concepts such as persistent identification which we believe is crucial to be able to connect a variety of heterogeneous devices in a network that grows, and that is robust to failures. A vital characteristic of our architecture is the ability to accommodate a variety of heterogeneous devices and subsystems. Several examples of hybridization of sensors at the physical, logical, and network levels are presented and discussed
Late Holocene isotope hydrology of Lake Qinghai, NE Tibetan Plateau: effective moisture variability and atmospheric circulation changes
A sub-centennial-resolution record of lacustrine carbonate oxygen isotopes (δ<sup>18</sup>O<sub>C</sub>) from the closed-basin Lake Qinghai on the NE Tibetan Plateau shows pronounced variability over the past 1500 years. Changes in δ<sup>18</sup>O<sub>C</sub> in hydrologically closed lakes are often interpreted in terms of changing effective moisture. Under this interpretation our record would imply increasing effective moisture during the Little Ice Age (LIA) compared to the Medieval Warm Period (MWP). However, independent evidence from other archives strongly suggests the Asian summer monsoon was stronger during the MWP and weakened during the LIA. Controls other than effective moisture (the balance of water inputs over evaporative loss) must therefore have contributed to the δ<sup>18</sup>O<sub>C</sub> values. We propose the LIA signal in Lake Qinghai resulted from a reduction in evaporation caused by colder air temperatures, coupled with a decrease in oxygen isotope composition of input waters as a result of an increase in the relative importance of westerly-derived precipitation. Our results caution against simplistic interpretations of carbonate oxygen isotope records from hydrologically closed lakes and suggest all possible controlling factors must be taken into account in order to avoid misleading palaeoclimatic reconstructions
An adaptive inelastic magnetic mirror for Bose-Einstein condensates
We report the reflection and focussing of a Bose-Einstein condensate by a new
pulsed magnetic mirror. The mirror is adaptive, inelastic, and of extremely
high optical quality. The deviations from specularity are less than 0.5 mrad
rms, making this the best atomic mirror demonstrated to date. We have also used
the mirror to realize the analog of a beam-expander, producing an ultra-cold
collimated fountain of matter wavesComment: 4 pages, 4 figure
Ab Initio Evidence for the Formation of Impurity d(3z^2-r^2) Holes in Doped La_{2-x}Sr_xCuO_4
Using the spin unrestricted Becke-3-Lee-Yang-Parr density functional, we
computed the electronic structure of explicitly doped La_{2-x}Sr_xCuO_4 (x =
0.125, 0.25, and 0.5). At each doping level, an impurity hole band is formed
within the undoped insulating gap. This band is well-localized to CuO_6
octahedra adjacent to the Sr impurities. The nature of the impurity hole is
A_{1g} in symmetry, formed primarily from the z^2 orbital on the Cu and p_z
orbitals on the apical O's. There is a strong triplet coupling of this hole
with the intrinsic B_{1g} Cu x^2-y^2/O1 p_{sigma} hole on the same site.
Optimization of the c coordinate of the apical O's in the doped CuO_6
octahedron lead to an asymmetric anti-Jahn-Teller distortion of the O2 atoms
toward the central Cu. In particular, the O2 atom between the Cu and Sr is
displaced 0.26 A while the O2 atom between the Cu and La is displaced 0.10 A.
Contrary to expectations, investigation of a 0.1 A enhanced Jahn-Teller
distortion of this octahedron does not force formation of an x^2-y^2 hole, but
instead leads to migration of the z^2 hole to the four other CuO_6 octahedra
surrounding the Sr impurity. This latter observation offers a simple
explanation for the bifurcation of the Sr-O2 distance revealed in x-ray
absorption fine structure data.Comment: Submitted to Phys. Rev. B. See http://www.firstprinciples.com for
more informatio
Instanton propagator and instanton induced processes in scalar model
The propagator in the instanton background in the
scalar model in four dimensions is studied.Leading and sub-leading terms of its
asymptotics for large momenta and its on-shell double residue are calculated
analytically. These results are applied to the analysis of the initial-state
and initial-final-state corrections and the calculation of the next-to-leading
(propagator) correction to the exponent of the cross section of instanton
induced multiparticle scattering processes.Comment: 44 pages, 7 postscript figures, LaTe
Linear and Second-order Optical Response of the III-V Mono-layer Superlattices
We report the first fully self-consistent calculations of the nonlinear
optical properties of superlattices. The materials investigated are mono-layer
superlattices with GaP grown on the the top of InP, AlP and GaAs (110)
substrates. We use the full-potential linearized augmented plane wave method
within the generalized gradient approximation to obtain the frequency dependent
dielectric tensor and the second-harmonic-generation susceptibility. The effect
of lattice relaxations on the linear optical properties are studied. Our
calculations show that the major anisotropy in the optical properties is the
result of strain in GaP. This anisotropy is maximum for the superlattice with
maximum lattice mismatch between the constituent materials. In order to
differentiate the superlattice features from the bulk-like transitions an
improvement over the existing effective medium model is proposed. The
superlattice features are found to be more pronounced for the second-order than
the linear optical response indicating the need for full supercell calculations
in determining the correct second-order response.Comment: 9 pages, 4 figures, submitted to Phy. Rev.
Boundary States for the Rolling D-branes in NS5 Background
In this paper we construct the time dependent boundary states describing the
``rolling D-brane solutions'' in the NS5 background discovered recently by
Kutasov by means of the classical DBI analysis. We first survey some aspects of
non-compact branes in the NS5 background based on known boundary states in the
N=2 Liouville theory. We consider two types of non-compact branes, one of which
is BPS and the other is non-BPS but stable. Then we clarify how to Wick-rotate
the non-BPS one appropriately. We show that the Wick-rotated boundary state
realizes the correct trajectory of rolling D-brane in the classical limit, and
leads to well behaved spectral densities of open strings due to the existence
of non-trivial damping factors of energy. We further study the cylinder
amplitudes and the emission rates of massive closed string modes.Comment: 25 pages, 2 figures, v2: typos corrected, reference added, v3:
emission rates of closed strings correcte
Hyperbolic phase and squeeze-parameter estimation
We define a new representation, the hyperbolic phase representation, which enables optimal estimation of a squeeze parameter in the sense of quantum estimation theory. We compare the signal-to-noise ratio for such measurements, with conventional measurement based on photon counting and homodyne detection. The signal-to-noise ratio for hyperbolic phase measurements is shown to increase quadratically with the squeezing parameter for fixed input power
Inelastic lifetimes of confined two-component electron systems in semiconductor quantum wire and quantum well structures
We calculate Coulomb scattering lifetimes of electrons in two-subband quantum
wires and in double-layer quantum wells by obtaining the quasiparticle
self-energy within the framework of the random-phase approximation for the
dynamical dielectric function. We show that, in contrast to a single-subband
quantum wire, the scattering rate in a two-subband quantum wire contains
contributions from both particle-hole excitations and plasmon excitations. For
double-layer quantum well structures, we examine individual contributions to
the scattering rate from quasiparticle as well as acoustic and optical plasmon
excitations at different electron densities and layer separations. We find that
the acoustic plasmon contribution in the two-component electron system does not
introduce any qualitatively new correction to the low energy inelastic
lifetime, and, in particular, does not produce the linear energy dependence of
carrier scattering rate as observed in the normal state of high-
superconductors.Comment: 16 pages, RevTeX, 7 figures. Also available at
http://www-cmg.physics.umd.edu/~lzheng
Fractional quantum revivals in the atomic gravitational cavity
In this paper we discuss the quantum dynamics and fractional quantum revivals of an integrable nonlinear system, consisting of an atom bouncing vertically from an evanescent field, for two cases with the simplified infinite-potential and the more practical exponential potential, respectively. We study the two cases separately, then contrast and compare the results and reach the conclusion that provided the starting position of the atoms is not too close to the reflecting surface supporting the evanescent wave (this condition is always satisfied in present experiments in this field), the two cases will produce the same results. This means that the idealized infinite potential is a good approximation to the more realistic exponential potential. Because the quantum analysis of the infinite-potential case is quite simple and straighforward (since its Schrödinger equation has analytical solutions), this will greatly simplify the quantum analysis of the more complicated exponential potential case and hence has practical significance
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