13,517 research outputs found
A new, large-scale map of interstellar reddening derived from HI emission
We present a new map of interstellar reddening, covering the 39\% of the sky
with low {\rm HI} column densities (
or ) at resolution, based on
all-sky observations of Galactic HI emission by the HI4PI Survey. In this low
column density regime, we derive a characteristic value of for gas with and find no significant reddening associated with gas at
higher velocities. We compare our HI-based reddening map with the Schlegel,
Finkbeiner, and Davis (1998, SFD) reddening map and find them consistent to
within a scatter of . Further, the differences between our
map and the SFD map are in excellent agreement with the low resolution
() corrections to the SFD map derived by Peek and Graves
(2010) based on observed reddening toward passive galaxies. We therefore argue
that our HI-based map provides the most accurate interstellar reddening
estimates in the low column density regime to date. Our reddening map is made
publicly available (http://dx.doi.org/10.7910/DVN/AFJNWJ).Comment: Re-submitted to ApJ. The reddening map is available at
http://dx.doi.org/10.7910/DVN/AFJNW
Joint Transmit and Receive Filter Optimization for Sub-Nyquist Delay-Doppler Estimation
In this article, a framework is presented for the joint optimization of the
analog transmit and receive filter with respect to a parameter estimation
problem. At the receiver, conventional signal processing systems restrict the
two-sided bandwidth of the analog pre-filter to the rate of the
analog-to-digital converter to comply with the well-known Nyquist-Shannon
sampling theorem. In contrast, here we consider a transceiver that by design
violates the common paradigm . To this end, at the receiver, we
allow for a higher pre-filter bandwidth and study the achievable
parameter estimation accuracy under a fixed sampling rate when the transmit and
receive filter are jointly optimized with respect to the Bayesian
Cram\'{e}r-Rao lower bound. For the case of delay-Doppler estimation, we
propose to approximate the required Fisher information matrix and solve the
transceiver design problem by an alternating optimization algorithm. The
presented approach allows us to explore the Pareto-optimal region spanned by
transmit and receive filters which are favorable under a weighted mean squared
error criterion. We also discuss the computational complexity of the obtained
transceiver design by visualizing the resulting ambiguity function. Finally, we
verify the performance of the optimized designs by Monte-Carlo simulations of a
likelihood-based estimator.Comment: 15 pages, 16 figure
Analysis of light scattering off photonic crystal slabs in terms of Feshbach resonances
Techniques to deal with Feshbach resonances are applied to describe resonant
light scattering off one dimensional photonic crystal slabs. Accurate
expressions for scattering amplitudes, free of any fitting parameter, are
obtained for isolated as well as overlapping resonances. They relate the
resonance properties to the properties of the optical structure and of the
incident light. For the most common case of a piecewise constant dielectric
function, the calculations can be carried out essentially analytically. After
establishing the accuracy of this approach we demonstrate its potential in the
analysis of the reflection coefficients for the diverse shapes of overlapping,
interacting resonances.Comment: 12 pages, 5 figure
EVS: Head-up or Head Down? Evaluation of Crew Procedure and Human Factors for Enhanced Vision Systems
Feasibility of an EVS head-down procedure is examined that may provide the same operational benefits under low visibility as the FAA rule on Enhanced Flight Visibility that requires the use of a head-up display (HUD). The main element of the described EVS head-down procedure is the crew procedure within cockpit for flying the approach. The task sharing between Pilot-Flying and Pilot-Not-Flying is arranged such that multiple head-up/head-down transitions can be avoided. The pilot-flying is using the head-down display for acquisition of the necessary visual cues in the EVS image. The pilot-not-flying is monitoring the instruments and looking for the outside visual cues
CP parameters of the B systems from Tevatron
Recent results on CP parameters of the B systems obtained by the CDF and D0
collaborations using the data samples collected at the Tevatron Collider in the
period 2002 - 2007 were presented at the QCD 2008 conference (Montpellier,
France). These results include measurements of the mixing phase, decay width
difference, and CP violation parameters in the Bs and Bu decays.Comment: Presented at the QCD 2008 Conference (Montpellier, France); added
references; corrected RCP+ paramete
Implications of CP violating 2HDM in B physics
The charged fermion mass matrices are invariant under symmetry
linked to the fermion number transformation. Under the condition that the
definition of this symmetry in arbitrary weak basis does not depend upon Higgs
parameters such as ratio of vacuum expectation values, a class of two Higgs
doublet models (2HDM) can be identified in which tree level flavor changing
neutral currents normally present in 2HDM are absent. However unlike the type I
or type II Higgs doublet models, the charged Higgs couplings in these models
contain additional flavor dependent CP violating phases. These phases can
account for the recent hints of the beyond standard model CP violation in the
and mixing. In particular, there is a range of parameters in which
new phases do not contribute to the meson CP violation but give identical
new physics phases in the and meson mixing.Comment: 7 pages, 1 figure, Talk given by Bhavik P. Kodrani at 16th
International Symposium on Particles, Strings and Cosmology, July 19th -
23rd, 2010, Valencia, Spai
Quantum Electrodynamics in the Light-Front Weyl Gauge
We examine QED(3+1) quantised in the `front form' with finite `volume'
regularisation, namely in Discretised Light-Cone Quantisation. Instead of the
light-cone or Coulomb gauges, we impose the light-front Weyl gauge . The
Dirac method is used to arrive at the quantum commutation relations for the
independent variables. We apply `quantum mechanical gauge fixing' to implement
Gau{\ss}' law, and derive the physical Hamiltonian in terms of unconstrained
variables. As in the instant form, this Hamiltonian is invariant under global
residual gauge transformations, namely displacements. On the light-cone the
symmetry manifests itself quite differently.Comment: LaTeX file, 30 pages (A4 size), no figures. Submitted to Physical
review D. January 18, 1996. Originally posted, erroneously, with missing
`Weyl' in title. Otherwise, paper is identica
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