Series-system reliability-estimation using very small binomialsamples

This investigation explored the effect of incorporating prior information into series-system reliability estimates, where the inferences are made using very small sets (less than 10 observations) of binomial test-data. To capture this effect, the performance of a set of Bayes interval estimators was compared to that of a set of classical estimators over a wide range of subsystem beta prior-distribution parameters. During a Monte Carlo simulation, the Bayes estimators tended to provide shorter interval estimators when the mean of the prior system-reliability differed from the true reliability by 20 percent of less, but the classical estimators dominated when the difference was greater. Based on these results, the authors conclude that there is no clear advantage to using Bayes interval estimation for sample sizes less than 10 unless the poor mean system reliability is believed to be within 20 percent of the true system reliability. Otherwise, the Lindstrom-Madden estimator, a useful classical alternative for very small samples, should be used     

Gain enhancement of multistage parametric intracavity frequencyconversion

Multistage intracavity frequency conversion in optical parametric oscillators (OPOs) can generate new frequencies efficiently over a large dynamic range of pump intensity. These frequencies can be either higher or lower than the pump frequency. High efficiency is correlated with steady states exhibiting nearly complete pump depletion (CPD). Placing a second OPO crystal with high small-signal gain in the cavity does not affect the steady states with CPD, if the pump is depleted and the idler out-coupled before these fields reach the high-gain crystal. However, the high-gain crystal promotes rapid saturation, and hence higher time-averaged efficiency, in Q-switched devices. Numerical modeling of injection-seeded Q-switched devices in three spatial dimensions suggests that excellent beam quality at high peak power is obtainable. However, instabilities can occur in this modeling, and it is not known if these numerical instabilities entail instabilities in the physical devices     

Properties of high-voltage stress generated traps in thin siliconoxide

It has previously been shown that trap generation inside thin oxides during high voltage stressing can be coupled to time-dependent-dielectric-breakdown distributions through the statistics linking wearout to breakdown. Since the stress-generated traps play a crucial role in the wearout/breakdown process, it is important to understand the properties of these traps. The properties of the traps in oxides with thicknesses between 2.5 nm and 22 nm have been studied, with emphasis on oxides in the 8.5-nm to 13-nm thickness range. The Coulombic scattering cross section of the traps responsible for the reduction in the tunneling current, an estimate of the spatial and energy distribution of the traps, and the charging/discharging properties of the traps have been measured. It will be shown that the measured properties of the high-voltage, stress-generated traps can be adequately described by the tunneling of electrons into and out of traps     

Bounds on bearing and symbol estimation with side information

We develop Cramer-Rao bounds (CRBs) for bearing, symbol, and channel estimation of communications signals in flat-fading channels. We do this using the constrained CRB formulation of German and Hero (1990), and Stoica and Ng (see IEEE Signal Processing Lett., vol.5, p.177-79, 1998), with the unknown parameters treated as deterministic constants. The equality constraints may be combined arbitrarily, e.g., we may develop CRBs for bearing estimation of constant modulus (CM) signals where a subset of the symbols are known (semi-blind, CM case). The results establish the value of side information in a large variety of communications scenarios. We focus on the CM and semi-blind properties and develop closed-form CRBs for these cases. Examples are presented indicating the relative value of the training and CIM property. These show the significant amount of signal processing information provided under these two conditions. In addition, we consider the performance of the maximum-likelihood beamformer for the semi-blind case, assuming the bearings are known. This semi-blind beamformer achieves the appropriate (constrained) CRB with finite data at finite SNR. Analysis also reveals that in a semi-blind scenario with two closely spaced sources, ten or more training symbols are sufficient to achieve the asymptotic training regime. Together with previous results on angle estimation for known sources, these results indicate that relatively few training samples enable both angle estimation and closely spaced co-channel source separation that approaches the CRB with finite data and finite SNR     

A model for diffraction-limited high-power multimode fiberamplifiers using seeded stimulated Brillouin scattering phaseconjugation

Diffraction-limited polarized stimulated Brillouin scattering (SBS) Stokes output from a multimode fiber is possible when the Stokes beam is the phase conjugate of diffraction-limited polarized pump light from a narrow-band master oscillator. Net amplification can be obtained by interposing a gain medium, such as a fiber amplifier between the master oscillator and the region of SBS generation. This paper proposes and studies numerically a model which describes the space-time dynamics of SBS generation, including phase conjugation, attenuation, phonon decay, thermal noise, inhomogeneous broadening, and amplifier gain. Noise reduction and phase locking are obtained by seeding the low-power end of the fiber at the Stokes frequency. Simulations are described for the case of 1.064 μm light amplification in a dual-clad Yb-doped multimode fiber amplifier     

A 15-mW fully integrated I/Q synthesizer for Bluetooth in 0.18-/spl mu/m CMOS

A low-power fully integrated synthesizer for Bluetooth applications is presented. The circuit with quadrature output signals at 2.45 GHz and 15-mW power dissipation has been designed in a digital 0.18-/spl mu/m CMOS process with 1.8-V supply voltage. The only external component is a 64-MHz crystal. Measurements have been performed on packaged samples mounted on an FR-4 board and show that the Bluetooth requirements are met. The measured phase noise is below -120 dBc/Hz at 3-MHz offset, and the resulting residual frequency modulation is 7.4-kHz rms. The tuning range consists of an analog and digital tuning mechanism, resulting in more than 15% overall tuning range.     

Super-resolved time-frequency analysis of wideband backscattereddata

A time-frequency super-resolution procedure is presented for processing wideband backscattered data containing both scattering center and natural resonance information. In this procedure, Prony's method is first applied in the frequency domain to locate scattering centers. The data is processed one slice at a time through the use of a sliding window function. Parameterized models for the scattering centers are obtained by a weighted average of the results from each segment. A similar procedure is used in the time domain to fully parameterize the natural resonances. In contrast to other time-frequency techniques, the time-frequencg display from the present super-resolution procedure is not constrained in resolution by the Fourier limit     

Elemental Powder Approaches to Ni3Al-Matrix Composites

Reactive sintering and hot isostatic compaction of mixed elemental powders have been combined to fabricate full density NiAl intermetallic-matrix composites. This process involves the formation of the matrix compound from its elemental constituents through an exothermic reaction. Dispersed ceramic phases inhibit direct consolidation, necessitating superposition of external pressure via hot isostatic compaction to obtain full density. The latter process is termed reactive hot isostatic pressing (RHIP). Because of its flexibility and low cost, this fabrication process merits attention as a means of preparing monolithic compounds and intermetallic-matrix composites.