The application of prolate spheroidal wave functions to the detection and estimation of bandlimited signals

Prolate spheroidal wave functions for solution of Fredholm equation for bandlimited signal detectio

Band limited image restoration by linear mean-square estimation

Linear estimator optimum for data on finite interval for restoration of image

Ionospheric scintillation studies

The diffracted field of a monochromatic plane wave was characterized by two complex correlation functions. For a Gaussian complex field, these quantities suffice to completely define the statistics of the field. Thus, one can in principle calculate the statistics of any measurable quantity in terms of the model parameters. The best data fits were achieved for intensity statistics derived under the Gaussian statistics hypothesis. The signal structure that achieved the best fit was nearly invariant with scintillation level and irregularity source (ionosphere or solar wind). It was characterized by the fact that more than 80% of the scattered signal power is in phase quadrature with the undeviated or coherent signal component. Thus, the Gaussian-statistics hypothesis is both convenient and accurate for channel modeling work

Factorization of spectra by discrete Fourier transforms

Discrete Fourier transform factorization of arbitrary spectral density function

Photo and electroluminescence behavior of Tb(ACAC)3phen complex used as emissive layer on organic light emitting diodes

This work shows the luminescence properties of a rare-earth organic complex, the Tb(ACAC)3phen. The results show the 5D4 -> 7F3,4,5,6 transitions with no influence of any ligand emission. The photoluminescence excitation spectrum is tentatively interpreted by the ligands absorption. An OLED was made by thermal evaporation (total thickness of 1200 Å) using TPD and Alq3 as hole and electron transport layers, respectively. The light emission reproduces the photoluminescence spectrum of the terbium complex at room temperature, with CIE (x,y) color coordinates of (0.28, 0.55). No presence of any bands from the ligands was observed. The potential use of this compound in efficient devices is discussed

Incoherent Scatter Radar Observations of Westward Electric Fields and Plasma Densities in the Auroral Ionosphere, 1

This paper reports the results of incoherent scatter radar observations of high-altitude ion drifts and other plasma parameters made February 24, 1972, at Chatanika, Alaska (L = 5.7), during a period of magnetic disturbance. For this experiment, conducted between 0909 to 1303 UT (2309 to 0303 AST), the radar line of sight was held fixed in the magnetic meridian plane so that the observed north-south ion drifts could be interpreted in terms of a westward electric field that ranged in magnitude from −10 to +35 mV m−1. The results confirm many effects found previously through other experimental techniques. Southward ion drifts predominated during the 4-hour observation period. Several times the westward electric field inside large regions of enhanced electron density was substantially smaller than the field outside these regions. In addition, on several occasions these walls or bands of ionization were found to drift southward at about the same speed as the E⊥ × B drift in the surrounding plasma. The plasma inside the enhanced region, however, did not share the drift motion but remained relatively stationary with respect to the radar. The present observations of F 2 layer densities and temperatures indicate an unusual increase in electron density just before the onset of a large substorm. Finally, measurements of the height and peak density of the auroral E layer show significant variations in the intensity and average energy of the electron flux. These variations appear to be related to auroral breakup and a transition to steady precipitation of moderately soft electrons

Tuning hole mobility in InP nanowires

Transport properties of holes in InP nanowires were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature and strain fields. Using molecular dynamics, we simulate nanowire structures, LO-phonon energy renormalization and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the nanowire size are changed. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands.Comment: 4 pages, 4 figure

Incoherent-Scatter Radar Observations of Westward Electric Fields, 2

In this paper we describe the results of a series of geomagnetic meridian plane radar incoherent scatter plasma transport measurements. From such data the eastward (zonal) component of the electric field can be deduced. The results show that the electric field has an eastward component whenever the discrete auroras are northward of the region of the measurement. The zonal field component turns westward as the discrete auroras move equatorward of the region of the measurement. Thus there is an eastward electric field boundary near the equatorward limit of the discrete aurora, which is the poleward boundary of the diffuse aurora during undisturbed periods. During a particularly disturbed period we also observed three pronounced substorm-related enhancements of the westward-directed zonal field. For midnight and morning sector substorms the enhancements preceded the substorm onset times by 20-30 min. We show from meridian chain all-sky camera data that all three enhancements coincided with equatorward expansions of the auroral oval

A Comprehensive Statistical Analysis of the Gas Distribution in Lyman-limit and Damped Lyman-alpha Absorption Systems

In this paper we show how to use data on Lyman-limit and Damped Lyman-alpha absorption systems to derive the hydrogen ionization fractions and the distribution of the face-on total gas column density. We consider axially symmetric, randomly oriented absorbers, ionized by an external background radiation field in order to relate the face-on total gas distribution to that of the neutral hydrogen observed along the line of sight. We devise a statistical procedure based on the Maximum Likelihood criterion, that is able to treat simultaneously data coming from different surveys and statistically recovers the "true" column densities in the presence of large uncertainties: this is especially important for Lyman-limit systems which leave an unmeasurable residual flux at wavelengths shorter than the Lyman break. We make use of simulated data to look for possible observational biases and extensively test our procedure. For a large statistical sample of real data in the redshift range [1.75,3.25] (collected from all published surveys) our Maximum Likelihood procedure gives a power-law slope for the total hydrogen distribution of -2.7. All together Lyman-limit systems therefore contain more gas than Damped Lyman-alpha systems. Analysis of data at other redshifts shows that more observations are needed to reach a compelling evidence for a cosmological evolution of the slope of the gas distribution.Comment: 30 pages with 7 eps figures, LaTeX accepted for publication in ApJ main journa