Penultimate Approximations in Statistics of Extremes and Reliability of Large Coherent Systems

In reliability theory any coherent system can be represented as either a series-parallel or a parallel-series system. Its lifetime can thus be written as the minimum of maxima or the maximum of minima. For large-scale coherent systems it is sensible to assume that the number of system components goes to infinity. Then, the possible non-degenerate extreme value laws either for maxima or for minima are eligible candidates for the system reliability or at least for the finding of adequate lower and upper bounds for the reliability. The identification of the possible limit laws for the system reliability of homogeneous series-parallel (or parallel-series) systems has already been done under different frameworks. However, it is well-known that in most situations such non-degenerate limit laws are better approximated by an adequate penultimate distribution. Dealing with regular and homogeneous parallel-series systems, we assess both theoretically and through Monte-Carlo simulations the gain in accuracy when a penultimate approximation is used instead of the ultimate one.     

Stochastic Equations and Inclusions with Mean Derivatives and Some Applications

The paper is devoted to a brief introduction into the theory of equations and inclusions with mean derivatives and to investigation of a special type of such inclusions called inclusions of geometric Brownian motion type. The existence of optimal solutions maximizing some cost criteria, is proved.     

Estimation Problems for Periodically Correlated Isotropic Random Fields

Spectral theory of isotropic random fields in Euclidean space developed by M. I. Yadrenko is exploited to find a solution to the problem of optimal linear estimation of the functional

$$ A\zeta ={\sum\limits_{t=0}^{\infty}}\,\,\,{\int_{S_n}} \,\,a(t,x)\zeta (t,x)\,m_n(dx) $$

which depends on unknown values of a periodically correlated (cyclostationary with period T) with respect to time isotropic on the sphere S _n in Euclidean space E ⁿ random field ζ(t, x), t?∈?Z, x?∈?S _n . Estimates are based on observations of the field ζ(t, x)?+?θ(t, x) at points (t, x), t?=???1,???2, ..., x?∈?S _n , where θ(t, x) is an uncorrelated with ζ(t, x) periodically correlated with respect to time isotropic on the sphere S _n random field. Formulas for computing the value of the mean-square error and the spectral characteristic of the optimal linear estimate of the functional Aζ are obtained. The least favourable spectral densities and the minimax (robust) spectral characteristics of the optimal estimates of the functional Aζ are determined for some special classes of spectral densities.

     

Using a cognitive architecture with a physiological substrate to represent effects of a psychological stressor on cognition

Adding a physiological representation to a cognitive architecture offers an attractive approach to modeling the effects of stress on cognition. We introduce ACT-R/Φ, an extended version of the ACT-R cognitive architecture that includes an integrative model of physiology. The extension allows the representation of how physiology and cognition interact. This substrate was used to represent potential effects of a startle response and task-based stress during a mental arithmetic (subtraction) task. We compare predictions from two models loaded into the new hybrid architecture to models previously developed within ACT-R. General behavior differed between models in that the ACT-R/Φ models had dynamic declarative memory noise over the course of the task based on varying epinephrine levels. They attempted more subtractions but were less accurate; this more closely matched human performance than the previous ACT-R models. Using ACT-R/Φ allows a more tractable integration of current physiological and cognitive perspectives on stress. ACT-R/Φ also permits further exploration of the interaction between cognition and physiology, and the emergent effects on behavior caused by the interaction among physiological subsystems. This extension is useful for anyone exploring how the human mind can occur in and be influenced by the physical universe.     

Deformations of Charged Axially Symmetric Initial Data and the Mass–Angular Momentum–Charge Inequality

We show how to reduce the general formulation of the mass–angular momentum–charge inequality, for axisymmetric initial data of the Einstein–Maxwell equations, to the known maximal case whenever a geometrically motivated system of equations admits a solution. It is also shown that the same reduction argument applies to the basic inequality yielding a lower bound for the area of black holes in terms of mass, angular momentum, and charge. This extends previous work by the authors (Cha and Khuri, Ann Henri Poincaré, doi: 10.1007/s00023-014-0332-6, arXiv:1401.3384, 2014), in which the role of charge was omitted. Lastly, we improve upon the hypotheses required for the mass–angular momentum–charge inequality in the maximal case.     

Synthesis of phospholipids on a glyceric acid scaffold: design and preparation of phospholipase A2 specific substrates

Synthesis of a new series of phospholipid analogues to serve as activity-based probes of secretory phospholipase A₂ enzymes is reported. The synthesis is based upon (1) preparation of long-chain esters and amides of glyceric acid, followed by (2) regioselective derivatization of the diol function of the molecule to achieve phosphorylation at the primary hydroxyl group, and to introduce the incipient sn-2-ester group of the target compounds. The sequence has been shown to allow incorporation of fluorescent, paramagnetic, and redox-active reporter groups, leading to phospholipid analogues applicable to detect and measure enzyme activity, to develop highly specific, real-time spectroscopic assay of phospholipase A₂ enzymes, as well as to track the metabolic fate of the hydrolysis products. The synthetic method has a great deal of flexibility to open the way to the design and synthesis of activity-probes for other phospholipid metabolizing enzymes as well.     

Implementation of the k 0-standardization method for analysis of geological samples at the Neutron Activation Analysis Laboratory, São Paulo, Brazil

The Neutron Activation Analysis Laboratory (LAN-IPEN) has been analysing geological samples for many years with the INAA comparative method, for geochemical and environmental research. This study presents the results obtained in the implementation of the k ₀-standardization method at LAN-IPEN, for geological samples analysis, by using the program k ₀-IAEA, provided by the International Atomic Energy Agency (IAEA). The thermal to epithermal flux ratio f and the shape factor α of the epithermal flux distribution of the IEA-R1 nuclear reactor of IPEN were determined for the pneumatic irradiation facility and one selected irradiation position, for short and long irradiations, respectively. To obtain these factors, the “bare triple-monitor” method with ¹⁹⁷Au–⁹⁶Zr–⁹⁴Zr was used. In order to validate the methodology, the geological reference materials basalts JB-1 (GSJ) and BE-N (IWG-GIT), andesite AGV-1 (USGS), granite GS-N (ANRT), SOIL-7 (IAEA) and sediment Buffalo River Sediment (NIST–BRS-8704), which represent different geological matrices, were analysed. The concentration results obtained agreed with assigned, with bias <10 % except for Zn in AGV-1. The U-score test showed that all results, except Mg in JB-1, are within 95 % confidence interval. These results indicate excellent possibilities of using this parametric method at the LAN-IPEN for geochemical and environmental studies.     

Development and characterization of a small electromembrane extraction probe coupled with mass spectrometry for real-time and online monitoring of in vitro drug metabolism

A small and very simple electromembrane extraction probe (EME-probe) was developed and coupled directly to electrospray ionization mass spectrometry (ESI-MS), and this system was used to monitor in real time in vitro metabolism by rat liver microsomes of drug substances from a small reaction (incubation) chamber (37 °C). The drug-related substances were continuously extracted from the 1.0 mL metabolic reaction mixture and into the EME-probe by an electrical potential of 2.5 V. The extraction probe consisted of a 1-mm long and 350-μm ID thin supported liquid membrane (SLM) of 2-nitrophenyl octyl ether. The drugs and formed metabolites where extracted through the SLM and directly into a 3 μL min^?1 flow of 60 mM HCOOH inside the probe serving as the acceptor solution. The acceptor solution was directed into the ESI-MS-system, and the MS continuously monitored the drug-related substances extracted by the EME-probe. The extraction efficiency of the EME-probe was dependant on the applied electrical potential and the length of the SLM, and these parameters as well as the volume of the reaction chamber were set to the values mentioned above to avoid serious depletion from the reaction chamber (soft extraction). Soft extraction was mandatory in order not to affect the reaction kinetics by sample composition changes induced by the EME-probe. The EME-probe/MS-system was used to establish kinetic profiles for the in vitro metabolism of promethazine, amitriptyline and imipramine as model substances.     

Online dynamic pH junction–sweeping for the determination of benzoic and sorbic acids in food products by capillary electrophoresis

A simple, low-cost, and efficient online focusing method that combines a dynamic pH junction and sweeping by capillary electrophoresis with polymer solutions was developed and optimized for the simultaneous determination of benzoic acid (BA) and sorbic acid (SA). A sample solution consisting of 2.5 mM phosphate at pH 3.0 and a buffer solution containing 15 mM tetraborate (pH 9.2), 40 mM sodium dodecyl sulfate, and 0.100 % (w/v) poly(ethylene oxide) were utilized to realize dynamic pH junction–sweeping for BA and SA. Under the optimized conditions, the entire analysis process was completed in 7 min, and a 900-fold sensitivity enhancement was achieved with limits of detection (S/N?=?3) as low as 8.2 and 6.1 nM for BA and SA, respectively. The linear ranges were between 20 nM and 20 μM for BA and 20 nM and 10 μM for SA, with correlation coefficients greater than 0.992. The recoveries of the proposed method ranged from 90 to 113 %. These satisfactory results indicate that this method has the potential to be an effective analytical tool for the rapid screening of BA and SA in different food products.

Open image in new window

Figure An online focusing strategy combining dynamic pH junction and sweeping for sensitive determination of benzoic and sorbic acid in food products using capillary electrophoresis wit polymer solutions