13,971 research outputs found

    A new, large-scale map of interstellar reddening derived from HI emission

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    We present a new map of interstellar reddening, covering the 39\% of the sky with low {\rm HI} column densities (NHI<4×1020 cm−2N_{\rm HI} < 4\times10^{20}\,\rm cm^{-2} or E(B−V)≈45 mmagE(B-V)\approx 45\rm\, mmag) at 16.′116\overset{'}{.}1 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 NHI/E(B−V)=8.8×1021  cm2 mag−1N_{\rm HI}/E(B-V) = 8.8\times10^{21}\, \rm\, cm^{2}\, mag^{-1} for gas with ∣vLSR∣<90 km s−1|v_{\rm LSR}| < 90\,\rm km\, s^{-1} 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 ≃5 mmag\simeq 5\,\rm mmag. Further, the differences between our map and the SFD map are in excellent agreement with the low resolution (4.∘54\overset{\circ}{.}5) 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

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    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 BB to the rate of the analog-to-digital converter fsf_s to comply with the well-known Nyquist-Shannon sampling theorem. In contrast, here we consider a transceiver that by design violates the common paradigm B≤fsB\leq f_s. To this end, at the receiver, we allow for a higher pre-filter bandwidth B>fsB>f_s 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

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    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

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    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

    Stress - structure correlations in grafted polymer films

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    CP parameters of the B systems from Tevatron

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    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

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    The charged fermion mass matrices are invariant under U(1)3U(1)^3 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 BdB_d and BsB_s mixing. In particular, there is a range of parameters in which new phases do not contribute to the KK meson CP violation but give identical new physics phases in the BdB_d and BsB_s 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

    The Family Name Dilemma: A Question of Fairness

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    Quantum Electrodynamics in the Light-Front Weyl Gauge

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    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 A−=0A^-=0. 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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