13,118 research outputs found

    Observation of the dielectric-waveguide mode of light propagation in p-n junctions

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    Theoretical considerations of the propagation of electromagnetic energy near a p-n junction (1) show that the “sandwich” formed by having a depletion layer bounded by the p and n regions can act as a dielectric waveguide. (1,2

    Application of XFaster power spectrum and likelihood estimator to Planck

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    We develop the XFaster Cosmic Microwave Background (CMB) temperature and polarization anisotropy power spectrum and likelihood technique for the Planck CMB satellite mission. We give an overview of this estimator and its current implementation and present the results of applying this algorithm to simulated Planck data. We show that it can accurately extract the power spectrum of Planck data for the high-l multipoles range. We compare the XFaster approximation for the likelihood to other high-l likelihood approximations such as Gaussian and Offset Lognormal and a low-l pixel-based likelihood. We show that the XFaster likelihood is not only accurate at high-l, but also performs well at moderately low multipoles. We also present results for cosmological parameter Markov Chain Monte Carlo estimation with the XFaster likelihood. As long as the low-l polarization and temperature power are properly accounted for, e.g., by adding an adequate low-l likelihood ingredient, the input parameters are recovered to a high level of accuracy.Comment: 25 pages, 20 figures, updated to reflect published version: slightly extended account of XFaster technique, added improved plots and minor corrections. Accepted for publication in MNRA

    Signal-to-Noise Eigenmode Analysis of the Two-Year COBE Maps

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    To test a theory of cosmic microwave background fluctuations, it is natural to expand an anisotropy map in an uncorrelated basis of linear combinations of pixel amplitudes --- statistically-independent for both the noise and the signal. These S/NS/N-eigenmodes are indispensible for rapid Bayesian analyses of anisotropy experiments, applied here to the recently-released two-year COBE {\it dmr} maps and the {\it firs} map. A 2-parameter model with an overall band-power and a spectral tilt ΜΔT\nu_{\Delta T} describes well inflation-based theories. The band-powers for {\it all} the {\it dmr} 53,90,3153,90,31 aa+bb GHz and {\it firs} 170 GHz maps agree, {(1.1±0.1)×10−5}1/2\{(1.1\pm 0.1)\times 10^{-5}\}^{1/2}, and are largely independent of tilt and degree of (sharp) S/NS/N-filtering. Further, after optimal S/NS/N-filtering, the {\it dmr} maps reveal the same tilt-independent large scale features and correlation function. The unfiltered {\it dmr} 5353 aa+bb index ΜΔT+1\nu_{\Delta T}+1 is 1.4±0.41.4\pm 0.4; increasing the S/NS/N-filtering gives a broad region at (1.0--1.2)±\pm0.5, a jump to (1.4--1.6)±\pm0.5, then a drop to 0.8, the higher values clearly seen to be driven by S/NS/N-power spectrum data points that do not fit single-tilt models. These indices are nicely compatible with inflation values (∌\sim0.8--1.2), but not overwhelmingly so.Comment: submitted to Phys.Rev.Letters, 4 pages, uuencoded compressed PostScript; also bdmr2.ps.Z, via anonymous ftp to ftp.cita.utoronto.ca, cd to /pub/dick/yukawa; CITA-94-2

    In Nightingale's footsteps: A qualitative analysis of the impact of leadership development within the clinical learning environment

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    Aim To identify and describe the impact areas of a newly developed leadership development programme focussed on positioning leaders to improve the student experience of the clinical learning environment. Background There is a need to consider extending traditional ways of developing leaders within the clinical learning in order to accommodate an increased number of students and ensure their learning experience is fulfilling and developmental. The Florence Nightingale Foundation implemented a bespoke leadership development programme within the clinical learning environment. Identifying the areas of impact will help to inform organisational decision making regarding the benefits of encouraging and supporting emerging leaders to undertake this type of programme. Method For this qualitative descriptive study, eight health care professionals who took part in a bespoke leadership development programme were interviewed individually and then collectively. The Florence Nightingale Foundation fellowship/scholarship programme is examined to determine impact. Results Two key themes were described in relation to impact of the programme. These were ‘Personal Development’ and ‘Professional Impact’. The two key themes comprised several subthemes. The notion of time and space to think was subsumed within each theme. Conclusion Data highlights that the Florence Nightingale Foundation programme had a distinct impact on participants by transforming thinking and increasing self-confidence to enable changes to make improvements both within their organisations and at national level. Implications for Nursing Management Health care managers must continue to invest in building leadership capacity and capability through programmes that can help position individuals to realize their potential to positively influence health outcomes and wider society

    Power Spectrum of Primordial Inhomogeneity Determined from the 4-Year COBE DMR Sky Maps

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    Fourier analysis and power spectrum estimation of the cosmic microwave background anisotropy on an incompletely sampled sky developed by Gorski (1994) has been applied to the high-latitude portion of the 4-year COBE DMR 31.5, 53 and 90 GHz sky maps. Likelihood analysis using newly constructed Galaxy cuts (extended beyond |b| = 20deg to excise the known foreground emission) and simultaneously correcting for the faint high latitude galactic foreground emission is conducted on the DMR sky maps pixelized in both ecliptic and galactic coordinates. The Bayesian power spectrum estimation from the foreground corrected 4-year COBE DMR data renders n ~ 1.2 +/- 0.3, and Q_{rms-PS} ~ 15.3^{+3.7}_{-2.8} microK (projections of the two-parameter likelihood). These results are consistent with the Harrison-Zel'dovich n=1 model of amplitude Q_{rms-PS} ~ 18 microK detected with significance exceeding 14sigma (dQ/Q < 0.07). (A small power spectrum amplitude drop below the published 2-year results is predominantly due to the application of the new, extended Galaxy cuts.)Comment: 9 pages of text in LaTeX, 1 postscript Table, 4 postscript figures (2 color plates), submitted to The Astrophysical Journal (Letters

    Power Spectrum Estimators For Large CMB Datasets

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    Forthcoming high-resolution observations of the Cosmic Microwave Background (CMB) radiation will generate datasets many orders of magnitude larger than have been obtained to date. The size and complexity of such datasets presents a very serious challenge to analysing them with existing or anticipated computers. Here we present an investigation of the currently favored algorithm for obtaining the power spectrum from a sky-temperature map --- the quadratic estimator. We show that, whilst improving on direct evaluation of the likelihood function, current implementations still inherently scale as the equivalent of the cube of the number of pixels or worse, and demonstrate the critical importance of choosing the right implementation for a particular dataset.Comment: 8 pages LATEX, no figures, corrected misaligned columns in table

    Exactly solvable model of A + A \to 0 reactions on a heterogeneous catalytic chain

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    We present an exact solution describing equilibrium properties of the catalytically-activated A + A \to 0 reaction taking place on a one-dimensional lattice, where some of the sites possess special "catalytic" properties. The A particles undergo continuous exchanges with the vapor phase; two neighboring adsorbed As react when at least one of them resides on a catalytic site (CS). We consider three situations for the CS distribution: regular, annealed random and quenched random. For all three CS distribution types, we derive exact results for the disorder-averaged pressure and present exact asymptotic expressions for the particles' mean density. The model studied here furnishes another example of a 1D Ising-type system with random multi-site interactions which admits an exact solution.Comment: 7 pages, 3 Figures, appearing in Europhysics Letter

    2-Point Correlations in the COBE DMR 4-Year Anisotropy Maps

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    The 2-point temperature correlation function is evaluated from the 4-year COBE DMR microwave anisotropy maps. We examine the 2-point function, which is the Legendre transform of the angular power spectrum, and show that the data are statistically consistent from channel to channel and frequency to frequency. The most likely quadrupole normalization is computed for a scale-invariant power-law spectrum of CMB anisotropy, using a variety of data combinations. For a given data set, the normalization inferred from the 2-point data is consistent with that inferred by other methods. The smallest and largest normalization deduced from any data combination are 16.4 and 19.6 uK respectively, with a value ~18 uK generally preferred.Comment: Sumbitted to ApJ Letter

    Current cosmological constraints from a 10 parameter CMB analysis

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    We compute the constraints on a ``standard'' 10 parameter cold dark matter (CDM) model from the most recent CMB and data and other observations, exploring 30 million discrete models and two continuous parameters. Our parameters are the densities of CDM, baryons, neutrinos, vacuum energy and curvature, the reionization optical depth, and the normalization and tilt for both scalar and tensor fluctuations. Our strongest constraints are on spatial curvature, -0.24 < Omega_k < 0.38, and CDM density, h^2 Omega_cdm <0.3, both at 95%. Including SN 1a constraints gives a positive cosmological constant at high significance. We explore the robustness of our results to various assumptions. We find that three different data subsets give qualitatively consistent constraints. Some of the technical issues that have the largest impact are the inclusion of calibration errors, closed models, gravity waves, reionization, nucleosynthesis constraints and 10-dimensional likelihood interpolation.Comment: Replaced to match published ApJ version. More details added. 13 ApJ pages. CMB movies and color figs at http://www.hep.upenn.edu/~max/10par_frames.html or from [email protected]