Limits on HDS/H2S abundance ratios in hot molecular cores

We have searched for HDS emission in a small number of hot cores. Using observations of (H2S)-S-34, we have derived upper limits to the [HDS]/[H2S] abundance ratio. The upper limits, which are close to 10(-3) can be interpreted in two ways, depending on whether grain surface reactions contribute to the formation of H2S. If grains do not dominate, then the H2S observed is formed in hot, post-shocked gas and a ratio close to the cosmic [D]/[H] ratio is expected for [HDS]/[H2S]. This scenario is consistent with our upper limits and with the relatively low abundance ratio found for [HDO]/[H2O] in hot cores but does not seem to account for all of the molecular [D]/[H] ratios observed in hot cores. If grains do dominate the formation of HBS, then the observed upper limit to the ratio is consistent with the formation of 'hot core ices' at a temperature of 60-80 K, close to the temperature at which cometary ices are thought to form.

Calculated rotational and rovibrational spectra of D2S and HDS

Rovibrational energy levels, transition frequencies, and linestrengths are computed variationally for the sulfur hydrides D2S and HDS, using ab initio potential energy and dipole surfaces. Wave-numbers for the pure rotational transitions agree to within 0.2 cm−1 of the experimental lines. For the fundamental vibrational transitions, the band origins for D2S are 860.4, 1900.6, and 1912.0 cm−1 for ν2, ν1, and ν3, respectively, compared with the corresponding experimental values of 855.4, 1896.4, and 1910.2 cm−1. For HDS, we compute ν2 to be 1039.4 cm−1, compared with the experimental value of 1032.7 cm−1. The relative merits of local and normal mode descriptions for the overtone stretching band origins are discussed. Our results confirm the local mode nature of the H2S, D2S, and HDS system.

In situ UV-vis and EXAFS studies of ZnO quantum-sized nanocrystals and Zn-HDS formations from sol-gel route

We have pointed Out that. zinc-based particles obtained from zinc acetate sol-gel route is a mixture of quantum-sized ZnO nanoparticles, zinc acetate, and zinc hydroxide double salt (Zn-HDS). Aiming the knowledge of the mechanisms involved in the formation of ZnO and Zn-HDS phases, the thermohydrolysis of ethanolic zinc acetate solutions induced by lithium hydroxide ([LiOH]/[Zn2+] = 0.1) or water ([H2O]/[Zn2+] = 0.05) addition was investigated at different isothermal temperatures (40, 50, 60 and 70 degrees C) by in situ measurements of turbidity, UV-vis absorption spectra and extended X-ray absorption fine structures (EXAFS). Only the growth of ZnO nanoparticles was observed in sol prepared with LiOH, while a two-step process was observed in that prepared with water addition, leading the fast growth of Zn-HDS and the formation of ZnO nanoparticles at advanced stage. A mechanism of dissolution/reprecipitation governed by the water/ethanol proportion is proposed to account for relative amount of ZnO. (c) 2007 Elsevier Ltd. All rights reserved.

Dynamical study of ZnO nanocrystal and Zn-HDS layered basic zinc acetate formation from sol-gel route

We have pointed out that zinc based particles obtained from ethanolic solution of a zinc acetate derivative (zinc oxy-acetate, Zn4O(Ac)(6)) are a mixture of nanometer sized ZnO, zinc oxy-acetate, and zinc hydroxide double salt (Zn-HDS). The knowledge of the mechanisms involved in the formation of ZnO and Zn-HDS phases, and the evolution of Zn species in reaction medium was monitored in situ during 14 h by simultaneous measurements of UV-vis absorption and extended X-ray absorption fine structures (EXAFS) spectra. This spectroscopic monitoring was initialized just after the addition of an ethanolic lithium hydroxide solution ([LiOH]/[Zn] = 0. 1) to the reaction medium kept under controlled temperature (40 degrees C). This study points out the first direct evidence of the reaction between ZnO nanoparticles and unreacted zinc oxy-acetate to form a Zn-HDS phase. The dissolution of ZnO and the reprecipitation of Zn-HDS are induced by the gradual release of water mainly produced by ethanol esterification well evidenced by gas chromatography coupled to mass spectroscopy and FT-IR measurements.

In situ and simultaneous nanostructural and spectroscopic studies of ZnO nanoparticle and Zn-HDS formations from hydrolysis of ethanolic zinc acetate solutions induced by water

The simultaneous formation of nanometer sized zinc oxide (ZnO), and acetate zinc hydroxide double salt (Zn-HDS) is described. These phases, obtained using the sol-gel synthesis route based on zinc acetate salt in alcoholic media, were identified by direct characterization of the reaction products in solution using complementary techniques: nephelometry, in situ Small-Angle X-ray Scattering (SAXS), UV-Vis spectroscopy and Extended X-ray Absorption Fine Structures (EXAFS). In particular, the hydrolytic pathway of ethanolic zinc acetate precursor solutions promoted by addition of water with the molar ratio N = [H2O]/[Zn2+] = 0.05 was investigated in this paper. The aim was to understand the formation mechanism of ZnO colloidal suspension and to reveal the factors responsible for the formation of Zn-HDS in the final precipitates. The growth mechanism of ZnO nanoparticles is based on primary particle (radius approximate to 1.5 nm) rotation inside the primary aggregate (radius < 3.5 nm) giving rise to an epitaxial attachment of particles and then subsequent coalescence. The growth of second ZnO aggregates is not associated with the Otswald ripening, and could be associated with changes in equilibrium between solute species induced by the superficial etching of Zn-HDS particles at the advanced stage of kinetic.

Use of the HDS system (hydric depuration with soils) associated to other constructed wetlands techniques for public water supply

Two projects of water treatment for public water supply were developed and operated by using combined systems of constructed wetlands. One of the projects was carried out in the town of Analandia, Sao Paulo, Brazil and wetlands with floating aquatic plants associated to the HDS system were used. Nearly 6480 inhabitants were supplied. The other conducted project was an experimental station in partnership with SABESP (Sao Paulo State Sanitation Agency/Brazil), for the pretreatment of 1700 l.s-1 of waters from the Cotia River, which is used for the population's supply after conventional treatment at the Lower Cotia Water Treatment Station. For this pilot project, wetlands with emergents and floating plants associated to the HDS system were used. The proposed objectives were achieved in both projects.

A Simpler and More Accurate AUTO-HDS Framework for Clustering and Visualization of Biological Data

In [1], the authors proposed a framework for automated clustering and visualization of biological data sets named AUTO-HDS. This letter is intended to complement that framework by showing that it is possible to get rid of a user-defined parameter in a way that the clustering stage can be implemented more accurately while having reduced computational complexity

Discrimination in Metropolitan Housing Markets: National Results from Phase 1 of the Housing Discrimination Study (HDS)

The Housing Discrimination Study 2000 (HDS 2000) is the third nationwide effort sponsored by HUD to measure the amount of discrimination faced by minority home seekers. This report provides national estimates of discrimination faced by African Americans and Hispanics in 2000 as they searched for housing in the sales and rental markets. It also provides an accurate measure of how housing discrimination has changed since 1989. The report shows large decreases between 1989 and 2000 in the level of discrimination experienced by Hispanics and African Americans seeking to a buy a home. There are, however, worrisome upward trends of discrimination in the areas of geographic steering in home sales for African Americans and the amount of help agents provide to Hispanics with obtaining financing. There has also been a modest decrease in discrimination toward African Americans seeking to rent a unit. This downward trend, however, has not been seen for Hispanic renters. Hispanic renters now are more likely to experience discrimination in their housing search than do African American renters.

Dynamics of pattern writing and erasure in photorefractive lithium niobate for data storage applications

The present rate of technological advance continues to place significant demands on data storage devices. The sheer amount of digital data being generated each year along with consumer expectations, fuels these demands. At present, most digital data is stored magnetically, in the form of hard disk drives or on magnetic tape. The increase in areal density (AD) of magnetic hard disk drives over the past 50 years has been of the order of 100 million times, and current devices are storing data at ADs of the order of hundreds of gigabits per square inch. However, it has been known for some time that the progress in this form of data storage is approaching fundamental limits. The main limitation relates to the lower size limit that an individual bit can have for stable storage. Various techniques for overcoming these fundamental limits are currently the focus of considerable research effort. Most attempt to improve current data storage methods, or modify these slightly for higher density storage. Alternatively, three dimensional optical data storage is a promising field for the information storage needs of the future, offering very high density, high speed memory. There are two ways in which data may be recorded in a three dimensional optical medium; either bit-by-bit (similar in principle to an optical disc medium such as CD or DVD) or by using pages of bit data. Bit-by-bit techniques for three dimensional storage offer high density but are inherently slow due to the serial nature of data access. Page-based techniques, where a two-dimensional page of data bits is written in one write operation, can offer significantly higher data rates, due to their parallel nature. Holographic Data Storage (HDS) is one such page-oriented optical memory technique. This field of research has been active for several decades, but with few commercial products presently available. Another page-oriented optical memory technique involves recording pages of data as phase masks in a photorefractive medium. A photorefractive material is one by which the refractive index can be modified by light of the appropriate wavelength and intensity, and this property can be used to store information in these materials. In phase mask storage, two dimensional pages of data are recorded into a photorefractive crystal, as refractive index changes in the medium. A low-intensity readout beam propagating through the medium will have its intensity profile modified by these refractive index changes and a CCD camera can be used to monitor the readout beam, and thus read the stored data. The main aim of this research was to investigate data storage using phase masks in the photorefractive crystal, lithium niobate (LiNbO3). Firstly the experimental methods for storing the two dimensional pages of data (a set of vertical stripes of varying lengths) in the medium are presented. The laser beam used for writing, whose intensity profile is modified by an amplitudemask which contains a pattern of the information to be stored, illuminates the lithium niobate crystal and the photorefractive effect causes the patterns to be stored as refractive index changes in the medium. These patterns are read out non-destructively using a low intensity probe beam and a CCD camera. A common complication of information storage in photorefractive crystals is the issue of destructive readout. This is a problem particularly for holographic data storage, where the readout beam should be at the same wavelength as the beam used for writing. Since the charge carriers in the medium are still sensitive to the read light field, the readout beam erases the stored information. A method to avoid this is by using thermal fixing. Here the photorefractive medium is heated to temperatures above 150�C; this process forms an ionic grating in the medium. This ionic grating is insensitive to the readout beam and therefore the information is not erased during readout. A non-contact method for determining temperature change in a lithium niobate crystal is presented in this thesis. The temperature-dependent birefringent properties of the medium cause intensity oscillations to be observed for a beam propagating through the medium during a change in temperature. It is shown that each oscillation corresponds to a particular temperature change, and by counting the number of oscillations observed, the temperature change of the medium can be deduced. The presented technique for measuring temperature change could easily be applied to a situation where thermal fixing of data in a photorefractive medium is required. Furthermore, by using an expanded beam and monitoring the intensity oscillations over a wide region, it is shown that the temperature in various locations of the crystal can be monitored simultaneously. This technique could be used to deduce temperature gradients in the medium. It is shown that the three dimensional nature of the recording medium causes interesting degradation effects to occur when the patterns are written for a longer-than-optimal time. This degradation results in the splitting of the vertical stripes in the data pattern, and for long writing exposure times this process can result in the complete deterioration of the information in the medium. It is shown in that simply by using incoherent illumination, the original pattern can be recovered from the degraded state. The reason for the recovery is that the refractive index changes causing the degradation are of a smaller magnitude since they are induced by the write field components scattered from the written structures. During incoherent erasure, the lower magnitude refractive index changes are neutralised first, allowing the original pattern to be recovered. The degradation process is shown to be reversed during the recovery process, and a simple relationship is found relating the time at which particular features appear during degradation and recovery. A further outcome of this work is that the minimum stripe width of 30 ìm is required for accurate storage and recovery of the information in the medium, any size smaller than this results in incomplete recovery. The degradation and recovery process could be applied to an application in image scrambling or cryptography for optical information storage. A two dimensional numerical model based on the finite-difference beam propagation method (FD-BPM) is presented and used to gain insight into the pattern storage process. The model shows that the degradation of the patterns is due to the complicated path taken by the write beam as it propagates through the crystal, and in particular the scattering of this beam from the induced refractive index structures in the medium. The model indicates that the highest quality pattern storage would be achieved with a thin 0.5 mm medium; however this type of medium would also remove the degradation property of the patterns and the subsequent recovery process. To overcome the simplistic treatment of the refractive index change in the FD-BPM model, a fully three dimensional photorefractive model developed by Devaux is presented. This model shows significant insight into the pattern storage, particularly for the degradation and recovery process, and confirms the theory that the recovery of the degraded patterns is possible since the refractive index changes responsible for the degradation are of a smaller magnitude. Finally, detailed analysis of the pattern formation and degradation dynamics for periodic patterns of various periodicities is presented. It is shown that stripe widths in the write beam of greater than 150 ìm result in the formation of different types of refractive index changes, compared with the stripes of smaller widths. As a result, it is shown that the pattern storage method discussed in this thesis has an upper feature size limit of 150 ìm, for accurate and reliable pattern storage.

Noise robust voice activity detection using normal probability testing and time-domain histogram analysis

This paper presents a method of voice activity detection (VAD) suitable for high noise scenarios, based on the fusion of two complementary systems. The first system uses a proposed non-Gaussianity score (NGS) feature based on normal probability testing. The second system employs a histogram distance score (HDS) feature that detects changes in the signal through conducting a template-based similarity measure between adjacent frames. The decision outputs by the two systems are then merged using an open-by-reconstruction fusion stage. Accuracy of the proposed method was compared to several baseline VAD methods on a database created using real recordings of a variety of high-noise environments.