Effects of thermal annealing on the optical characteristics of k -na + waveguides

We present a systematic study of the changes induced in the refractive-index profile of different sets of K -Na + ion-exchanged waveguides on soda-lime and BK7 substrates because of thermal annealing in the presence or absence of salt vapors. The concentration of potassium is recovered by secondary ion mass spectrometry, and the propagation losses are measured by means of the three-prism configuration.     

Probabilistic methods for eigenvalue estimates

Some probabilistic techniques are discussed regarding their use in estimating the principal eigenvalue of an elliptic operator. Such estimates are useful when studying models for biochemical reactions governed by lateral diffusion.In this paper we summarize recent results on some mathematical techniques that were developed to study certain biological models.     

A parametric study of AlN thin films grown by pulsed laser deposition

High quality AlN thin films were grown at 200–450°C on sapphire substrates by laser ablation of Al targets in nitrogen reactive atmosphere. The nitrogen pressure was varied between 10⁻³ and 10⁻¹ mbar. The reactive gas pressure during irradiation and the temperature of the substrate were found to essentially influence the quality of the layers. X-ray diffraction analysis evidenced the formation of highly orientated layers for a very restrictive set of parameters. Other analysis techniques, like X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, optical transmission spectroscopy have been used to evidence the good stoichiometry and purity of the films. The characteristics of these films were compared with those of AlN thin films deposited in similar experimental conditions, on Si (100) and Si (111) substrates.     

Pattern Perturbation Method for Multicanonical Monte Carlo Simulations in Optical Communications

In this letter, we present a novel method to efficiently account for pattern dependence in the bit-error-ratio (BER) estimation of an optical communication system through multi-canonical Monte Carlo (MMC) simulations. The proposed method considers the transmitted pattern as random, extending the MMC random-walk to the overall state space comprising noise and pattern. The resulting complexity is only linear in the intersymbol interference length, allowing us to account for long pattern dependence in a feasible computational time. The accuracy of the method is confirmed by the agreement of simulations with the exact probability density functions and BER values evaluated through the Karhunen-Loeve series expansion method.     

Peculiar aspects of nanocrystal memory cells: data and extrapolations

Nanocrystal memory cell are a promising candidate for the scaling of nonvolatile memories in which the conventional floating gate is replaced by an array of nanocrystals. The aim of this paper is to present the results of a thorough investigation of the possibilities and the limitations of such new memory cell. In particular, we focus on devices characterized by a very thin tunnel oxide layer and by silicon nanocrystals formed by chemical vapor deposition. The direct tunneling of the electrons through the tunnel oxide, their storage into the silicon nanocrystals, and furthermore, retention, endurance, and drain turn-on effects, well-known issues for nonvolatile memories, are all investigated. The cell can be also programmed by channel hot electron injection, allowing the possibility to multibit storage. The suppression of the drain turn-on and the possibility of using this cell for multibit storage give us a clear evidence of the distributed nature of the charge storage.     

A controlled comparison of thermal biofeedback and relaxation training in the treatment of essential hypertension: II. Effects on cardiovascular reactivity.

Compared progressive muscle relaxation (PMR), thermal biofeedback (BFB), and drug withdrawal (DW) as possible substitutes for 2nd-stage (sympatholytic) antihypertensive medications, using 73 hypertensive adults. Reactivity (heart rate, systolic blood pressure, and diastolic blood pressure) to 3 stressors (mental arithmetic, cold pressor, and negative mental imagery) was measured before and after PMR, BFB, and DW. PMR led to more reductions in some aspect of reactivity than did BFB. Reductions in reactivity were seen more for mental arithmetic and systolic blood pressure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparative review of charged particle microbeam facilities

At the low doses (and low dose rates) relevant to environmental and occupational radiation exposure (0-50 mSv), which are of practical concern for radiation protection, very few cells in the human organism experience more than one traversal by densely ionising particles in their lifetime, the intervals between the tracks, if any, typically being months or years. The biological effects of exactly one particle are not well known and cannot be simulated in vitro by conventional broad-beam exposures, due to the random Poisson distribution of tracks. Charged particle microbeam facilities are a unique tool that allows targeting of single cells and analysis of the induced damage on a cell-by-cell basis. In the past few years, many charged particle microbeam facilities for radiobiology have come into operation or are under development worldwide. Different experimental designs have been adopted at various laboratories regarding the achievement of micrometre (or sub-micrometre) ion beam size, by mechanical collimation or focusing, particle detection, and cell recognition and positioning systems. The different approaches are reviewed and discussed in this paper.     

Analytical model of the effects of a nonuniform distribution of stored charge on the electrical characteristics of discrete-trap nonvolatile memories

We propose an analytical model of the effects of a nonuniform distribution of trapped charge on the electrical characteristics and on the perspectives of 2-bit operation of discrete-trap memories. To keep the model tractable, we consider an idealized nonuniform distribution, represented by a step function, so that the concentration of trapped charge can assume only two possible values in two different regions. Notwithstanding the simplicity of our assumptions, which limits the range of validity of our model to the subthreshold and weak inversion regions of the I-V characteristics, we can investigate a series of important aspects for 2-bit storage of nonvolatile memories. Our model is then validated through comparison with detailed numerical simulations performed with a commercial technology computer-aided design tool, and with the experimental electrical characteristics of nanocrystal flash memories under different bias conditions. Finally, we provide a method, based on our model, to extract an "effective" distribution of trapped charge, in which all charge is uniformly distributed in a localized region close to the drain.