Computational aspects of probit model

Sometimes the maximum likelihood estimation procedure for the probit model fails. There may be two reasons: the maximum likelihood estimate (MLE) just does not exist or computer overflow error occurs during the computation of the cumulative distribution function (cdf). For example, the approximation explosive effect due to an inaccurate computation of the cdf for a large value of the argument occurs in a popular statistical package S-plus. The goal of the paper is to provide remedies for these two abnormalities. First, despite the availability of a criterion for the MLE existence, expressed in terms of a separation plane in the covariate space, there are no constructive criteria to verify whether such a separation exists. We develop constructive criteria for the MLE existence that are valid also for other link functions. Second, to avoid the overflow problem we suggest approximate formulae for the log-likelihood function and its derivatives in the case of possiblelarge value of the argument. Standard algorithms of the log-likelihood maximization like Newton-Raphson or Fisher Scoring are very sensitive to large values of the linear predictor, particularly outliers. Five algorithms are compared by the time to converge and reliability via statistical simulations. The corrected algorithms, based on the approximate formulae are more reliable and almost as fast as the standard one

Aqueous vapour substitution for hydrogen in the process of pyrolysis

In order to decrease hydrocarbons fractional pressure in the process of ethylene pyrolysis, 0.5-1.5 kilograms of aqueous vapour is added to each kilo of feedstock. In the pyrolysis of hydrocarbon feed, a considerable part of the process' power consumption is connected with water vaporization; heating up of the diluent to 800°C and more with the subsequent condensation. The aim of this work is to reduce specific energy consumption and improve selectivity to ethylene of pyrolysis process. The same hydrocarbons fractional pressure can be created as during diluting by aqueous vapour if we use hydrogen as a diluent with its mass 9 times less. It was found that if hydrogen is purged to the furnace inlet under different feedstock temperatures prior to the pyrolitic reaction, hydrogen will become a homogeneous catalyst for the subsequent radical-chain reactions. The depth of the reaction (according to Korzun and Magaril in Thermal processes of refining 2008) will be greater, under otherwise equal conditions, than without hydrogen. Specific heat energy consumption for the production of ethylene, as well as for the amount of ethylene and propylene, with aqueous vapour substitution to hydrogen decreases. When replacing the vapour for a considerably smaller amount of hydrogen, the latter is involved in a radical chain process, providing greater selectivity for ethylene production, thereby increasing the yield of ethylene at 15% relative. As a result, ethylene production costs are significantly reduced. © 2014 WIT Press.International Journal of Safety and Security Engineering;International Journal of Sustainable Development and Planning;WIT Transactions on Ecology and the Environmen

Armas arrojadizas de caza de yacimientos del Paleolítico Superior Final de Byki (centro de Europa del Este): Coexistencia de puntas de hueso y puntas de sílex

The article deals with a specific Late Upper Paleolithic Byki site complex, situated in the Seim river basin, in the center of Eastern Europe. Main feature of Byki 1, 2, 3, 7 (cultural layers I and Ia) sites is presence of geometric microliths (triangles) in their flint assemblages. The sites’ radiocarbon uncalibrated dates are in between 18000 and 16 000 BP. Late Upper Paleolithic human visitors at Byki sites have been not living for a long time there. Byki site fauna collections are characterized by a dominance of ungulate and fur game species, while the rest known Late Last Glacial sites in the center of Eastern Europe and in the Seim river basin show a clear prevalence of mammoth. The aim of the present study was to understand a relationship between bone and flint hunting projectile weaponry at Byki sites. Our study showed a singleness of bone points there, although rather numerous and various bone / antler and ivory artifacts are well known in the Byki assemblages. At the same time, serial flint triangles serving, high likely, as arrowheads, have been basic hunting projectile weaponry elements for Byki site human inhabitants.El artículo trata de un complejo específico de yacimientos de Byki del Paleolítico Superior Reciente, situado en la cuenca del río Seim, en el centro de Europa del Este. La característica principal de los yacimientos Byki 1, 2, 3, 7 (horizontes culturales I y Ia) es la presencia de microlitos geométricos (triángulos) en su industria de sílex. Las fechas de radiocarbono sin calibrar se distribuyen entre 18000 y 16000 BP. Losvisitantes humanos del Paleolítico Superior Reciente en los yacimientos de Byki no han estado viviendo allí durante mucho tiempo. Las colecciones de fauna se caracterizan por el predominio de especies de ungulados y animales de caza, mientras que el resto de los yacimientos conocidos del final del último Glacial en el centro de Europa del Este y en la cuenca del río Seim muestran una clara prevalencia del mamut. El objetivo del presente estudio es comprender la relación entre los proyectiles de caza de hueso y de sílex de los yacimientos de Byki. Nuestro estudio muestra una singularidad de las puntas óseas, aunque se conocen bastante numerosos y diversos artefactos de huesos/ asta y marfil de los conjuntos de Byki. Al mismo tiempo, las series de triángulos de sílex que probablemente sirvieron como puntas de flecha, han sido los elementos básicos de los proyectiles de caza para los habitantes de Byki.

Electron-phonon interaction via Pekar mechanism in nanostructures

We consider an electron-acoustic phonon coupling mechanism associated with the dependence of crystal dielectric permittivity on the strain (the so-called Pekar mechanism) in nanostructures characterized by strong confining electric fields. The efficiency of Pekar coupling is a function of both the absolute value and the spatial distribution of the electric field. It is demonstrated that this mechanism exhibits a phonon wavevector dependence similar to that of piezoelectricity and must be taken into account for electron transport calculations in an extended field distribution. In particular, we analyze the role of Pekar coupling in energy relaxation in silicon inversion layers. Comparison with the recent experimental results is provided to illustrate its potential significance

The Concept of Ecologically Oriented Progress and Natural Resource Preservation

The most important issue of scientific and technological progress is considering the environment challenges of industrial development. It means that the progress must be ecologically oriented and environmentally friendly. The most adequate concept for the approach to the issue of "man - society – nature" relations is the ontology of the noosphere - the idea of a common space for human beings and nature. It presents an ideal example of an optimistic attitude towards the coordination between accelerating the scientific and technological development and natural resource saving. However, to maintain the balance between human needs and environmental processes determined by this concept, it is essential to include the lean production training into technological development of society

A flexible low-cost, high-precision, single interface electrical impedance tomography system for breast cancer detection using FPGA

Typically, in multi-frequency Electrical Impedance Tomography (EIT) systems, a current is applied and the voltages developed across the subject are detected. However, due to the complexity of designing stable current sources, there has been mention in the literature of applying a voltage to the subject whilst measuring the consequent current flow. This paper presents a comparative study between the two techniques in a novel design suitable for the detection of breast cancers. The suggested instrument borrows the best features of both the injection of current and the application of voltage, circumventing their limitations. Furthermore, the system has a common patient-electrode interface for both methodologies, whilst the control of the system and the necessary signal processing is carried out in a field programmable gate array (FPGA). Through this novel system, wide-bandwidth, low-noise, as well as high-speed (frame rate) can be achieved

Stimulation of reparation in a linear wound model in rats by Bischofit gel

The article is to evaluate Bischofit gel reparative activity in a linear wound model in rat