5,694 research outputs found
Field Quantization, Photons and Non-Hermitean Modes
Field quantization in three dimensional unstable optical systems is treated
by expanding the vector potential in terms of non-Hermitean (Fox-Li) modes in
both the cavity and external regions. The cavity non-Hermitean modes (NHM) are
treated using the paraxial and monochromaticity approximations. The NHM
bi-orthogonality relationships are used in a standard canonical quantization
procedure based on introducing generalised coordinates and momenta for the
electromagnetic (EM) field. The quantum EM field is equivalent to a set of
quantum harmonic oscillators (QHO), associated with either the cavity or the
external region NHM. This confirms the validity of the photon model in unstable
optical systems, though the annihilation and creation operators for each QHO
are not Hermitean adjoints. The quantum Hamiltonian for the EM field is the sum
of non-commuting cavity and external region contributions, each of which is sum
of independent QHO Hamiltonians for each NHM, but the external field
Hamiltonian also includes a coupling term responsible for external NHM photon
exchange processes. Cavity energy gain and loss processes is associated with
the non-commutativity of cavity and external region operators, given in terms
of surface integrals involving cavity and external region NHM functions on the
cavity-external region boundary. The spontaneous decay of a two-level atom
inside an unstable cavity is treated using the essential states approach and
the rotating wave approximation. Atomic transitions leading to cavity NHM
photon absorption have a different coupling constant to those leading to photon
emission, a feature resulting from the use of NHM functions. Under certain
conditions the decay rate is enhanced by the Petermann factor.Comment: 38 pages, tex, 2 figures, ps. General expression for decay rate
added. To be published in Journal of Modern Optic
The Apm Galaxy Survey IV: Redshifts of Rich Clusters of Galaxies
We present redshifts for a sample of 229 clusters selected from the APM
Galaxy Survey, 189 of which are new redshift determinations. Non-cluster galaxy
redshifts have been rejected from this sample using a likelihood ratio test
based on the projected and apparent magnitude distributions of the cluster
fields. We test this technique using cluster fields in which redshifts have
been measured for more than 10 galaxies. Our redshift sample is nearly complete
and has been used in previous papers to study the three dimensional
distribution of rich clusters of galaxies. 157 of the clusters in our sample
are listed in the Abell catalogue or supplement, and the remainder are new
cluster identifications.Comment: 15 pages UUencoded compressed postscript. Submitted to Monthly
Notices of the R.A.
Exploration Using Without-Replacement Sampling of Actions Is Sometimes Inferior
In many statistical and machine learning applications, without-replacement sampling is considered superior to with-replacement sampling. In some cases, this has been proven, and in others the heuristic is so intuitively attractive that it is taken for granted. In reinforcement learning, many count-based exploration strategies are justified by reliance on the aforementioned heuristic. This paper will detail the non-intuitive discovery that when measuring the goodness of an exploration strategy by the stochastic shortest path to a goal state, there is a class of processes for which an action selection strategy based on without-replacement sampling of actions can be worse than with-replacement sampling. Specifically, the expected time until a specified goal state is first reached can be provably larger under without-replacement sampling. Numerical experiments describe the frequency and severity of this inferiority
Neuromyelitis optica spectrum disorder in three generations of a Chinese family
© 2019 Neuromyelitis optica spectrum disorder is an inflammatory demyelinating disease that is largely sporadic. Familial disease has been reported in one or two generations, although its basis remains unknown. We report here three subjects meeting diagnostic criteria for NMOSD in one family: a father and son, and the maternal aunt of the father. Anticipation, of 27 years, was apparent in transmission from father to son. Aquaporin-4 antibodies were observed in the aunt but not the father and son, nor in other family members. A putative pathogenic mutation in the NECL2 gene was not found in this pedigree. This first report of NMOSD in three generations of one family underlines the heterogeneity of familial NMOSD
Differential neuroproteomic and systems biology analysis of spinal cord injury
Acute spinal cord injury (SCI) is a devastating condition with many consequences and no known effective treatment. Although it is quite easy to diagnose traumatic SCI, the assessment of injury severity and projection of disease progression or recovery are often challenging, as no consensus biomarkers have been clearly identified. Here rats were subjected to experimental moderate or severe thoracic SCI. At 24h and 7d postinjury, spinal cord segment caudal to injury center versus sham samples was harvested and subjected to differential proteomic analysis. Cationic/anionic-exchange chromatography, followed by 1D polyacrylamide gel electrophoresis, was used to reduce protein complexity. A reverse phase liquid chromatography-tandem mass spectrometry proteomic platform was then utilized to identify proteome changes associated with SCI. Twenty-two and 22 proteins were up-regulated at 24 h and 7 day after SCI, respectively; whereas 19 and 16 proteins are down-regulated at 24 h and 7 day after SCI, respectively, when compared with sham control. A subset of 12 proteins were identified as candidate SCI biomarkers - TF (Transferrin), FASN (Fatty acid synthase), NME1 (Nucleoside diphosphate kinase 1), STMN1 (Stathmin 1), EEF2 (Eukaryotic translation elongation factor 2), CTSD (Cathepsin D), ANXA1 (Annexin A1), ANXA2 (Annexin A2), PGM1 (Phosphoglucomutase 1), PEA15 (Phosphoprotein enriched in astrocytes 15), GOT2 (Glutamic-oxaloacetic transaminase 2), and TPI-1 (Triosephosphate isomerase 1), data are available via ProteomeXchange with identifier PXD003473. In addition, Transferrin, Cathepsin D, and TPI-1 and PEA15 were further verified in rat spinal cord tissue and/or CSF samples after SCI and in human CSF samples from moderate/severe SCI patients. Lastly, a systems biology approach was utilized to determine the critical biochemical pathways and interactome in the pathogenesis of SCI. Thus, SCI candidate biomarkers identified can be used to correlate with disease progression or to identify potential SCI therapeutic targets
Theory of Pseudomodes in Quantum Optical Processes
This paper deals with non-Markovian behaviour in atomic systems coupled to a
structured reservoir of quantum EM field modes, with particular relevance to
atoms interacting with the field in high Q cavities or photonic band gap
materials. In cases such as the former, we show that the pseudo mode theory for
single quantum reservoir excitations can be obtained by applying the Fano
diagonalisation method to a system in which the atomic transitions are coupled
to a discrete set of (cavity) quasimodes, which in turn are coupled to a
continuum set of (external) quasimodes with slowly varying coupling constants
and continuum mode density. Each pseudomode can be identified with a discrete
quasimode, which gives structure to the actual reservoir of true modes via the
expressions for the equivalent atom-true mode coupling constants. The quasimode
theory enables cases of multiple excitation of the reservoir to now be treated
via Markovian master equations for the atom-discrete quasimode system.
Applications of the theory to one, two and many discrete quasimodes are made.
For a simple photonic band gap model, where the reservoir structure is
associated with the true mode density rather than the coupling constants, the
single quantum excitation case appears to be equivalent to a case with two
discrete quasimodes
Ultra-short silicon-organic hybrid (SOH) modulator for bidirectional polarization-independent operation
We propose a bidirectional, polarization-independent, recirculating IQ-modulator scheme based on the silicon-organic hybrid (SOH) platform. We demonstrate the viability of the concept by using an SOH Mach-Zehnder modulator, operated at 10 GBd BPSK and 2ASK-2PSK
Controlled coupling of counterpropagating whispering-gallery modes by a single Rayleigh scatterer: a classical problem in a quantum optical light
We present experiments where a single subwavelength scatterer is used to
examine and control the back-scattering induced coupling between
counterpropagating high-Q modes of a microsphere resonator. Our measurements
reveal the standing wave character of the resulting symmetric and antisymmetric
eigenmodes, their unbalanced intensity distributions, and the coherent nature
of their coupling. We discuss our findings and the underlying classical physics
in the framework common to quantum optics and provide a particularly intuitive
explanation of the central processes.Comment: accepted for publication in Pysical Review Letter
A Flux-limited Sample of Bright Clusters of Galaxies from the Southern Part of the ROSAT All-Sky Survey: the Catalog and the LogN-LogS
We describe the selection of an X-ray flux-limited sample of bright clusters
of galaxies in the southern hemisphere, based on the first analysis of the
ROSAT All-Sky Survey data (RASS1). The sample is constructed starting from an
identification of candidate clusters in RASS1, and their X-ray fluxes are
remeasured using the Steepness Ratio Technique. This method is better suited
than the RASS1 standard algorithm for measuring flux from extended sources. The
final sample is count-rate-limited in the ROSAT hard band (0.5-2.0 keV), so
that due to the distribution of NH, its effective flux limit varies between
about 3-4 x 10**-12 ergs cm**-2 s**-1 over the selected area. This covers the
Decl<2.5 deg part of the south Galactic cap region (b<-20 deg) - with the
exclusion of patches of low RASS1 exposure time and of the Magellanic Clouds
area - for a total of 8235 deg**2. 130 candidate sources fulfill our selection
criteria for bonafide clusters of galaxies in this area. Of these, 101 are
Abell/ACO clusters, while 29 do not have a counterpart in these catalogs. Of
these clusters, 126 (97%) clusters have a redshift and for these we compute an
X-ray luminosity. 20% of the cluster redshifts come from new observations, as
part of the ESO Key Program REFLEX Cluster Survey that is under completion.
Considering the intrinsic biases and incompletenesses introduced by the flux
selection and source identification processes, we estimate the overall
completeness to be better than 90%. The observed number count distribution,
LogN-LogS, is well fitted by a power law with slope alpha = 1.34 +/- 0.15 and
normalization A = 11.87 +/- 1.04 sr**-1 (10**-11 ergs cm**-2 s**-1)**alpha, in
good agreement with other measurements.Comment: 27 pages, 8 figures and 3 tables included, LaTex, emulateapj.sty and
epsf.sty, accepted for publication in ApJ: scheduled for the March 20, 1999,
Vol.514. The cluster catalog is available at
http://www.merate.mi.astro.it/~degrand
Separately contacted electron-hole double layer in a GaAs/AlxGa1âxAs heterostructure
We describe a method for creating closely spaced parallel two-dimensional electron and hole gases confined in 200 Ă
GaAs wells separated by a 200 Ă
wide AlxGa1âxAs barrier. Low-temperature ohmic contacts are made to both the electrons and holes, whose densities are individually adjustable between 10^(10)/cm^2 to greater than 10^(11)/cm^2
- âŠ