23,105 research outputs found
A sensitive infrared imaging up converter and spatial coherence of atmospheric propagation
An infrared imaging technique based on the nonlinear interaction known as upconversion was used to obtain images of several astronomical objects in the 10 micrometer spectral region, and to demonstrate quantitatively the sharper images allowed for wavelengths beyond the visible region. The deleterious effects of atmospheric inhomogeneities on telescope resolution were studied in the infrared region using the technique developed. The low quantum efficiency of the device employed severely limited its usefulness as an astronomical detector
A simple method for estimation of coagulation efficiency in mixed aerosols
Aerosols of KBr and AgNO3 were mixed, exposed to light in a glass tube and collected in the dark. About 15% of the collected material was reduced to silver upon development. Thus, two aerosols of particles that react to form a photo-reducible compound can be used to measure coagulation efficiency
True Airspeed Measurement by Ionization-Tracer Technique
Ion bundles produced in a pulse-excited corona discharge are used as tracers with a radar-like pulse transit-time measuring instrument in order to provide a measurement of airspeed that is independent of all variables except time and distance. The resulting instrumentation need not project into the air stream and, therefore, will not cause any interference in supersonic flow. The instrument was tested at Mach numbers ranging from 0.3 to 3.8. Use of the proper instrumentation and technique results in accuracy of the order of 1 percent
Mixed perturbative expansion: the validity of a model for the cascading
A new type of perturbative expansion is built in order to give a rigorous
derivation and to clarify the range of validity of some commonly used model
equations.
This model describes the evolution of the modulation of two short and
localized pulses, fundamental and second harmonic, propagating together in a
bulk uniaxial crystal with non-vanishing second order susceptibility
and interacting through the nonlinear effect known as ``cascading'' in
nonlinear optics.
The perturbative method mixes a multi-scale expansion with a power series
expansion of the susceptibility, and must be carefully adapted to the physical
situation. It allows the determination of the physical conditions under which
the model is valid: the order of magnitude of the walk-off, phase-mismatch,and
anisotropy must have determined values.Comment: arxiv version is already officia
SU(3) Spin-Orbit Coupling in Systems of Ultracold Atoms
Motivated by the recent experimental success in realizing synthetic
spin-orbit coupling in ultracold atomic systems, we consider N-component atoms
coupled to a non-Abelian SU(N) gauge field. More specifically, we focus on the
case, referred to here as "SU(3) spin-orbit-coupling," where the internal
states of three-component atoms are coupled to their momenta via a matrix
structure that involves the Gell-Mann matrices (in contrast to the Pauli
matrices in conventional SU(2) spin-orbit-coupled systems). It is shown that
the SU(3) spin-orbit-coupling gives rise to qualitatively different phenomena
and in particular we find that even a homogeneous SU(3) field on a simple
square lattice enables a topologically non-trivial state to exist, while such
SU(2) systems always have trivial topology. In deriving this result, we first
establish an exact equivalence between the Hofstadter model with a 1/N Abelian
flux per plaquette and a homogeneous SU(N) non-Abelian model. The former is
known to have a topological spectrum for N>2, which is thus inherited by the
latter. It is explicitly verified by an exact calculation for N=3, where we
develop and use a new algebraic method to calculate topological indices in the
SU(3) case. Finally, we consider a strip geometry and establish the existence
of three gapless edge states -- the hallmark feature of such an SU(3)
topological insulator.Comment: 4.2 pages, 1 figur
Big Bang Nucleosynthesis with Long Lived Charged Massive Particles
We consider Big Bang Nucleosynthesis (BBN) with long lived charged massive
particles. Before decaying, the long lived charged particle recombines with a
light element to form a bound state like a hydrogen atom. This effect modifies
the nuclear reaction rates during the BBN epoch through the modifications of
the Coulomb field and the kinematics of the captured light elements, which can
change the light element abundances. It is possible that the heavier nuclei
abundances such as Li and Be decrease sizably, while the ratios ,
D/H, and He/H remain unchanged. This may solve the current discrepancy
between the BBN prediction and the observed abundance of Li. If future
collider experiments found signals of a long-lived charged particle inside the
detector, the information of its lifetime and decay properties could provide
insights to understand not only the particle physics models but also the
phenomena in the early universe in turn.Comment: 20 pages, 6 figures, published version in Physical Review
The effect of composition on the mechanism of stress-corrosion cracking of titanium alloys in nitrogen tetroxide, and aqueous and hot- salt environments Annual summary report, 1 May 1967 - 30 Apr. 1968
Stress corrosion data for titanium alloys in aqueous, hot salt, and nitrogen dioxide environment
Interior Point Decoding for Linear Vector Channels
In this paper, a novel decoding algorithm for low-density parity-check (LDPC)
codes based on convex optimization is presented. The decoding algorithm, called
interior point decoding, is designed for linear vector channels. The linear
vector channels include many practically important channels such as inter
symbol interference channels and partial response channels. It is shown that
the maximum likelihood decoding (MLD) rule for a linear vector channel can be
relaxed to a convex optimization problem, which is called a relaxed MLD
problem. The proposed decoding algorithm is based on a numerical optimization
technique so called interior point method with barrier function. Approximate
variations of the gradient descent and the Newton methods are used to solve the
convex optimization problem. In a decoding process of the proposed algorithm, a
search point always lies in the fundamental polytope defined based on a
low-density parity-check matrix. Compared with a convectional joint message
passing decoder, the proposed decoding algorithm achieves better BER
performance with less complexity in the case of partial response channels in
many cases.Comment: 18 pages, 17 figures, The paper has been submitted to IEEE
Transaction on Information Theor
Optically mediated nonlinear quantum optomechanics
We consider theoretically the optomechanical interaction of several
mechanical modes with a single quantized cavity field mode for linear and
quadratic coupling. We focus specifically on situations where the optical
dissipation is the dominant source of damping, in which case the optical field
can be adiabatically eliminated, resulting in effective multimode interactions
between the mechanical modes. In the case of linear coupling, the coherent
contribution to the interaction can be exploited e.g. in quantum state swapping
protocols, while the incoherent part leads to significant modifications of cold
damping or amplification from the single-mode situation. Quadratic coupling can
result in a wealth of possible effective interactions including the analogs of
second-harmonic generation and four-wave mixing in nonlinear optics, with
specific forms depending sensitively on the sign of the coupling. The
cavity-mediated mechanical interaction of two modes is investigated in two
limiting cases, the resolved sideband and the Doppler regime. As an
illustrative application of the formal analysis we discuss in some detail a
two-mode system where a Bose-Einstein condensate is optomechanically linearly
coupled to the moving end mirror of a Fabry-P\'erot cavity.Comment: 11 pages, 8 figure
Polarization squeezing of light by single passage through an atomic vapor
We have studied relative-intensity fluctuations for a variable set of
orthogonal elliptic polarization components of a linearly polarized laser beam
traversing a resonant Rb vapor cell. Significant polarization squeezing
at the threshold level (-3dB) required for the implementation of several
continuous variables quantum protocols was observed. The extreme simplicity of
the setup, based on standard polarization components, makes it particularly
convenient for quantum information applications.Comment: Revised version. Minor changes. four pages, three figure
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