Chemical etching of (100) GaAs in the (NH4)2Cr2O7-H2SO4-N H4Cl-H2O system

The etching solution containing ammonium dichromate, sulphuric acid and ammonium chloride in water solution allows for the investigation of the influence of individual active components and their concentration on the etching reaction with GaAs. The influence of these agents on etching as well as the temperature and stirring were examined. The etching rate increases with increasing Cl^– ion concentration, increases and subsequently decreases with the increasing of H⁺ ion concentration and remains constant in the wide range of oxidant anion concentration. The effect of stirring on etching rate allows us to estimate regions dominated by diffusion kinetics. The activation energy in the wide range of parameters is constant and equal to 60 kJ mol^–1. Microscopic observations reveal surfaces of various morphologies: smooth; covered with round hills; or with a network of veins. Various profiles of grooves arranged in various directions are revealed due to the preferential characteristic of etching; these profiles are also influenced by the mask material.     

Interactions of phospholipase D with 1,2 diacyl-sn-glycerol-3-phosphorylcholine,dodecylsulfate, and Ca2+

Some properties of the pure, soluble phospholipase D (phosphatidycholine phosphatido hydrolase, EC 3.1.4.4) interactions with phosphatidyl choline (1,2 diacyl-sn-glycerol-3-phosphoryl choline) in a system also containing dodecylsulfate and Ca²⁺ ions were studied. Concentrations of Ca²⁺ greater than 50 mM were necessary both for activity and adsorption of the enzyme to the “supersubstrate.” Ethylenediamine tetraacetic acid caused inhibition of activity, greater than one would expect from its chelating capacity. A nonlinear increase in activity with the increase of enzyme protein was observed, suggesting a subunit aggregation into a higher mol wt protein, catalytically more active. Upon centrifugation of the supersubstrate-enzyme complex at 4.5×10⁵ g·min at 30 C, most of the substrate molecules sedimented regardless of the pH. The reverse was true when centrifugation was done at 1 C. Phospholipase D hydrolyzed phosphatidylcholine molecules present in the supersubstrate at temperatures around 0 C at a rate 1/5 that of a maximal value measured at 30C. The Arrhenius plot was linear in the range from 0 to 30 C, and at that temperature the curve broke with a smaller slope. Activation energy of 9.1 Kcal/mol, below 30 C, was calculated. Adsorption of the enzyme to the sedimentable supersubstrate occurred at pH 8.0, regardless of temperature. At pH 5.6, a considerable portion of phosphatidylcholine was degraded at 30 C, thus minimizing the capacity of the supersubstrate to adsorb the enzyme. Although Mg²⁺ could replace Ca²⁺ in the formation of sedimentable supersubstrate, it neither assists in adsorption of the enzyme nor in activation of the phosphatidylcholine hydrolysis.     

(S)-(+)-linalool,a mate attractant pheromone component in the bee Colletes cunicularius

Enantiomerically pure (S)-(+)-linalool was the main constituent in the extracts of the cephalic secretions of virgin females, mated females, freshly emerged males, and patrolling males of the solitary bee Colletes cunicularius. After copulation, the content of (S)-(+)-linalool emitted by the female was strongly reduced. Electrophysiological experiments revealed that both enantiomers of linalool elicited responses from the antennae of the males. Field tests using the pure enantiomers and the racemate of linalool showed that the number of male bees attracted was highest for (S)-(+)-linalool. The search flight activity in the mating flight area increased dramatically when patrolling males were presented with (S)-(+)-linalool vs (R)-(–)-linalool. Taken together, these data indicate a mate attractant pheromone function of (S)-(+)-linalool.     

Recommending people to people: the nature of reciprocal recommenders with a case study in online dating

People-to-people recommenders constitute an important class of recommender systems. Examples include online dating, where people have the common goal of finding a partner, and employment websites where one group of users needs to find a job (employer) and another group needs to find an employee. People-to-people recommenders differ from the traditional items-to-people recommenders as they must satisfy both parties; we call this type of recommender reciprocal. This article is the first to present a comprehensive view of this important recommender class. We first identify the characteristics of reciprocal recommenders and compare them with traditional recommenders, which are widely used in e-commerce websites. We then present a series of studies and evaluations of a content-based reciprocal recommender in the domain of online dating. It uses a large dataset from a major online dating website. We use this case study to illustrate the distinctive requirements of reciprocal recommenders and highlight important challenges, such as the need to avoid bad recommendations since they may make users to feel rejected. Our experiments indicate that, by considering reciprocity, the rate of successful connections can be significantly improved. They also show that, despite the existence of rich explicit profiles, the use of implicit profiles provides more effective recommendations. We conclude with a discussion, linking our work in online dating to the many other domains that require reciprocal recommenders. Our key contributions are the recognition of the reciprocal recommender as an important class of recommender, the identification of its distinctive characteristics and the exploration of how these impact the recommendation process in an extensive case study in the domain of online dating.     

Comparison of tribological parameters of surfaces determined by the stylus method and by the immersion method of holographic interferometry

The investigation of surface roughness by the use of the improved immersion method of holographic interferometry is reported in this paper; the results obtained for some engineering surfaces are given.The application of the holographic microscope, specially designed imersion cell and transparent replicas that reproduce details of the differently machined engineering surfaces allows us to obtain contour maps of the surface asperities with intervals between contour lines of about 1 μm.The contour maps were used for determining the tribological parameters of the surface which were compared with those obtained by the use of stylus methods.It is shown with a few examples that the roughness parameters determined from the contour maps have greater values than those obtained by the profilometry.     

Simulation of the high-octane alkylates manufacturing considering the process unsteadiness

The aim of this paper work is to study the model of the process of sulphuric-acid alkylation of isobutane using a mathematical model. The model of the object was developed considering the physicochemical regularities of the process. The paper analyzes the main processes occurring at the installation and performs the results of model verification. In addition, the technological scheme of one of the sulphuric-acid alkylation existing installations were considered. The developed program is able to calculate the composition of the obtained alkylate, to determine the yield of target products and by-products, to select optimal technological process conditions for a given raw material composition. It was noted, that the consumption of sulfuric acid increases as a result of the accumulation of high-molecular organic compounds in it, as well as its dilution with water, which enters the reactor along with the raw material and forms during the side reactions of the process.     

Das Problem des Datenschutzes in Polen im Hinblick auf die ACTA-Debatte

Das themenüberschneidende Problem des Daten- und Menschenrechtsschutzes, welches in den letzten Wochen die ?ffentliche Debatte in Polen, aber auch in Europa dominiert hat, bezieht sich auf das ACTA-Abkommen. Die Darstellung dieses schwierigen Gebietes soll dem Leser eine Analyse der Zusammenh?nge zwischen Privatschutz, Bürgerrechten und Datenschutz aus polnischer Sicht vermitteln.     

Comparison of Age-dependent Quantitative Changes in the Male Labial Gland Secretion of <Emphasis Type="Italic">Bombus Terrestris</Emphasis> and <Emphasis Type="Italic">Bombus Lucorum</Emphasis>

Age-related changes of antennal-active components of male labial gland extracts were studied in two closely related bumblebee species, Bombus terrestris and B. lucorum. In B. terrestris, compounds eliciting electroantennogram (EAG) responses of virgin queens were ethyl dodecanoate, 2,3-dihydrofarnesal, 2,3-dihydrofarnesol, hexadecan-1-ol, octadeca-9,12,15-trien-1-ol, and geranylcitronellol. Compounds that elicited EAG responses from queens of B. lucorum were ethyl dodecanoate, ethyl tetradec-7-enoate, ethyl tetradec-9-enoate, ethyl hexadec-9-enoate, hexadecan-1-ol, hexadec-7-enal, octadeca-9,12-dien-1-ol, octadeca-9,12,15-trien-1-ol, and octadecan-1-ol. Quantities of these compounds in the labial glands changed significantly over the lifetime of the respective males of the two species. In both species, concentrations of the respective compounds reached their maximum within seven days after eclosion. Subsequently, a rapid decrease in the amount of EAG-active compounds occurred in B. terrestris, whereas in B. lucorum the amount of active compounds stayed approximately constant or decreased at a slow rate. Microscopy showed that in B. terrestris secretory cells of the labial glands undergo apoptosis from the fifth to the tenth day of life, whilst in B. lucorum labial gland cells remain unchanged throughout the life of the males.