Extremes of random fields over arbitrary domains with application to concrete rupture stresses

To find the exact probability distribution of the global maximum or minimum of a random field within a bounded domain is a pending problem even for Gaussian fields. Except for very special examples of fields, recourse must be taken to approximate reasoning or asymptotic considerations to be judged with respect to accuracy by simulations. In this paper, the problem is addressed through a functional equation that leads to the definition of a class of distribution functions that depend solely on process or field characteristics and domain quantities that can be calculated explicitly. This distribution function class is studied for Gaussian processes in earlier works by the author and it has been obtained explicitly for Gaussian fields on rectangular domains in the plane. Simulation studies show that rather good predictions are obtained for sufficiently smooth wide band Gaussian processes and fields. In this paper, the distribution function is obtained in general for Gaussian fields over arbitrary bounded domains with piecewise continuous and differentiable boundaries, and as in earlier works the distribution function is tested against empirical distribution functions obtained by simulation of sample functions of a smooth approximately Gaussian field, herein called a broken line Hino field. For completeness this particular field type is defined in appendix a and appendix b. The paper concludes with a statistical application on data for plain concrete tensile strength.     

Dual-trap technique for reduction of low-frequency noise in force measuring optical tweezers

High-resolution long-time force measurements by optical tweezers are often limited by low-frequency (1/f) noise. A dual-trap technique is presented that can reduce such noise in the force signal. It incorporates a second trap (a reference trap) that probes the noise in the system and it is based upon the assumption that the low-frequency parts of the noise from the two traps are correlated. A subtraction of the low-frequency signal from the reference trap from the signal from the force measuring trap will therefore yield a net signal that is significantly less influenced by noise. It is shown that this dual-trap technique can reduce the noise in the force signal up to 60% depending on detection bandwidth.     

The effect of phosphate additives on the lubrication of rolling element bearings in a refrigerant environment

Chlorine free replacement refrigerants, HFC (hydrofluorocarbons) and HC (hydrocarbons), have shown less lubricating properties. Phosphate based additives were used to improve the lubricity with refrigerant R-134a, demonstrating positive effects. In the present paper, the ability to form lubricating film and wear of two additives, phosphate ester and acid phosphate, was investigated in a bearing test apparatus.The results show that phosphate additive in polyolester oil, in an R-134a environment, increases the lubricating film and reduce wear. Surface topography during the initial run-in changes to a more favorable profile with lower RMS angle and longer wavelengths that promote load-carrying capacity and film build-up.     

Cognitive decline from estimated premorbid status predicts neurodegeneration in Alzheimer's disease.

This study investigated the relationship between premorbid and current cognitive function with respect to the clinical features of patients with various types of neurodegeneration in the form of Alzheimer's disease (AD), mild cognitive impairment (MCI), and subjective cognitive impairment (SCI), as compared with a healthy control group (C). Clinical features (MMSE, cognitive and depressive symptoms), genetics (apolipoprotein E; APOE) and measures of neurodegeneration (Aβ42, t-tau, and p-tau) were examined, as well as present cognitive function. Various methods of assessing premorbid cognitive function were compared, including a Swedish NART-analogous test (Irregularly Spelled Words; ISW), a Swedish lexical decision test (SLDT), a Hold test (Information in WAIS-R), Best current performance test, and combined demographic characteristics. Results showed that cognitive decline (premorbid minus current cognitive function) based on SLDT and ISW was a significant predictor for MMSE and Aβ42, whereas corresponding associations for present cognitive function and decline measures based on other methods were less powerful. Results also showed that specific verbal abilities (e.g., SLDT and ISW) were insensitive to AD and that these abilities indicated premorbid cognitive function in retrospect. In conclusion, cognitive decline from premorbid status reflects the disease processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The occurrence of organochlorines in marine avian top predators along a latitudinal gradient

The aim of this study was to determine the role of cold condensation and fractionation on the occurrence of organochlorine contaminants (OCs) in avian marine top predators along a latitudinal gradient. We measured 24 polychlorinated biphenyl (PCB) congeners and six pesticide OCs in blood of great black-backed gulls (Larus marinus) from the Norwegian Coast (58 degrees N-70 degrees N) and glaucous gulls (Larus hyperboreus) from Bjornoya in the Norwegian Arctic (74 degrees N). Glaucous gulls had up to 3 times higher sigmaOC concentrations compared to the great black-backed gulls, and a OC pattern dominated largely by persistent and low volatile compounds such as highly chlorinated PCBs and metabolites such as oxychlordane. This was not consistent with cold condensation and fractionation theory, but probably related to diet and elevated biomagnification. Among great black-backed gulls, however, there were indications of both cold condensation and fractionation. Higher and lower chlorinated PCBs had highest absolute concentrations in the south and in the north, respectively, except for one location at an intermediate latitude, where concentrations of most OCs exceeded all other locations. In terms of proportional contribution to sigmaOC (pattern), relatively volatile OCs such as HCB, oxychlordane and tri- to penta- PCB congeners were more important at northern latitudes, while hexa- to nona-PCBs made up a larger proportion of sigmaOC in the south. The results thus showed that differences in global distribution of compounds with different physicochemical properties could be detected in avian top predators such as large gulls, even if biomagnification and biotransformation influence both the absolute concentrations and the patterns of OCs.     

Fire research in scandinavia—A long-term program

The author contends a great imbalance exists between two fundamental concepts in designing buildings. On the one hand, considerable care and thought go into designing for static and dynamic loads; but design for fire resistance is dealt with in an extremely conventional and stereotyped way. He feels it is essential—in Scandinavian and in other countries—that long-term experimental and theoretical research programs be undertaken so that design for fire resistance can be carried out in conformity with fundamental principles conventionally used in static design of load-bearing structures. Note: This article is based on Proceeding No. 129 (1964), “General Programme for Scandinavian Long-term Research,” of the National Swedish Institute for Materials Testing, (Statens Provningsanstalt), Stockholm, Sweden.     

Influence of crosslinking on the characteristics of thermally expandable microspheres expanding at high temperature

Free‐radical suspension polymerization was used to synthesize thermally expandable microspheres (TEMS); in this process, a poly(acrylonitrile‐co‐methacrylonitrile) shell encapsulated isooctane. Different amounts of dimethacrylate, diacrylate, or divinyl ether functional crosslinker were added to investigate the effects on the crosslinking density of the polymer and the expansion properties of the TEMS. The optimum amount of crosslinker was found to be approximately 0.05–0.1 mol %. However, a significantly better expansion could be obtained with 1,4‐butanediol dimethacrylate as a crosslinker, compared to 1,4‐butanediol divinyl ether or 1,4‐butanediol diacrylate. From monitoring the conversion of monofunctional analogues by gas chromatography, we suggest that the differences in expansion obtained with different crosslinkers, originated from the difference in the reactivity of the radicals in the system toward the vinyl functionalities of the crosslinkers. This regulated the incorporation of the crosslinker into the polymer and, thereby, the mechanical properties of the microsphere shell. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Picosecond Fluorescence Spectroscopy in the Analysis of Structure and Motion of Biopolymers

INTRODUCTION

The dynamic aspects of molecular structures at atomic resolution have become of increasing importance. The analysis of molecular motions of individual residues and structural domains of biomolecules is essential for an understanding of the functional aspects of biopolymers at the molecular level.