Blind separation of positive sources by globally convergent gradient search

The instantaneous noise-free linear mixing model in independent component analysis is largely a solved problem under the usual assumption of independent nongaussian sources and full column rank mixing matrix. However, with some prior information on the sources, like positivity, new analysis and perhaps simplified solution methods may yet become possible. In this letter, we consider the task of independent component analysis when the independent sources are known to be nonnegative and well grounded, which means that they have a nonzero pdf in the region of zero. It can be shown that in this case, the solution method is basically very simple: an orthogonal rotation of the whitened observation vector into nonnegative outputs will give a positive permutation of the original sources. We propose a cost function whose minimum coincides with nonnegativity and derive the gradient algorithm under the whitening constraint, under which the separating matrix is orthogonal. We further prove that in the Stiefel manifold of orthogonal matrices, the cost function is a Lyapunov function for the matrix gradient flow, implying global convergence. Thus, this algorithm is guaranteed to find the nonnegative well-grounded independent sources. The analysis is complemented by a numerical simulation, which illustrates the algorithm.     

High power density beam from narrow diode-laser arrays in axial symmetry

A multiplexing method based on narrow diode-laser arrays (DLAs) in an axially symmetric configuration is described. The use of submillimeter narrow DLAs improves beam quality considerably in the slow-axis direction compared with typical 1-cm-wide DLAs. The axially symmetric geometry is advantageous for efficient spatial, wavelength, and polarization multiplexing. With narrow DLAs and an axially symmetric geometry, a small circular focus with more than 10-kW/mm2 average power density is possible. Theoretical calculations and preliminary experimental results are presented.     

Compact stacking of diode lasers for pulsed light sources of high brightness

A compact stacking architecture for high-power diode-laser arrays is proposed and compared with traditional stacks. The objective of compact stacking is to achieve high brightness values without the use of microlenses. The calculated brightness for a compact stack is over 300 W mm(-2) sr(-1), which is approximately 40 times higher than that of a traditional stack made of similar laser emitters. Even higher brightness values of over 600 W mm(-2) sr(-1) were reached in practice. A laser head was manufactured in which the light from several compact laser stacks could be fiber coupled or the light could be transformed to a highly uniform beam.     

The validity and reliability of a portable slip meter for determining floor slipperiness during simulated heel strike

A previously developed test rig was used as starting point for designing a portable slip meter with two new features. First, an inflatable pneumatic test wheel, consisting of six slider units, was introduced as the impacting contact element relative to floor surface. Second, an inductive trigger was built into the system to facilitate a precise timing of the slider-floor contact during the test. This new test rig was designed to measure transitional friction properties of contaminated floor surfaces during simulated heel strike, which is considered the most critical phase of gait from the slip and fall point of view. Another objective was to quantify the validity and reliability of this test method in the laboratory, but not yet in the field. The measurement process was evaluated on eight wet and oily floor surfaces (vinyl and ceramic tile floorings) using two slider materials (plain, profiled), two normal loads (100, 200 N), and two sliding velocities (0.15, 0.30 m/s) as independent variables. The outputs of the portable slip meter, in terms of transitional friction coefficients, were compared to force platform-based friction values and to slip resistance values obtained with a slip simulator apparatus for laboratory testing of shoes and floor surfaces. The outputs were also evaluated against slipperiness ratings made by three male subjects in paired comparison trials, in which the subjects walked over eight wet floor surfaces wearing shoes with the plain soling material. The results showed that test option 200 N and 0.15m/s led to optimum validity despite its tendency to promote frictional vibrations (stick-slip) in the contact surface. Compared to the lower sliding speed, the higher speed reduced both stick-slip and measurement bias. Test option 200 N and 0.30 m/s was the most reliable one in this experiment. It yielded lower friction coefficients than any other test option and reduced the likelihood of underestimating slip and fall hazards. The results implied that the minimum friction coefficient was 0.25 for preventing a fall on wet floor surfaces, whereas the limit for preventing a slip was in the range 0.30-0.35. Transitional friction measurement was found to be a valid and reliable indicator for slip resistance. A more accurate control of the normal force during testing is needed for actual field use of the test method.     

Remote sensing support for national forest inventories

National forest inventory programs are tasked to produce timely and accurate estimates for a wide range of forest resource variables for a variety of users and applications. Time, cost, and precision constraints cause these programs to seek technological innovations that contribute to measurement and estimation efficiencies and that facilitate the production and distribution of an increasing array of inventory data, estimates, and derived products. Many of the recent innovations have involved remotely sensed data and related statistical estimation techniques. Current applications of remote sensing in support of national forest inventories are reviewed for three areas: (1) observation or measurement, meaning using remotely sensed data in lieu of field observations or measurements; (2) estimation, meaning calculation of traditional inventory areal estimates such as forest area or volume per unit area; and (3) mapping. Future applications focus on two areas: augmenting field measurements with remotely sensed data obtained from lidar sensors and Internet accessible map-based estimation.     

CONTENTS OF CYTOCHROMES IN YEAST

The contents of cytochromes in yeast were determined quantitatively from the absorption spectra, using a solid cell paste of intact yeast. During the industrial production of baker's yeast, the contents of the cytochromes, particularly of cytochrome aa₃ at successive stages, increased gradually with increasing aeration. In semi-aerobically grown baker's yeast, the contents of cytochromes aa₃, b and c were 0·9, 2·9 and 2·9 × 10^?5 moles/litre of fresh yeast (total amount 6·7 × 10^?5 moles/litre), while in vigorously aerated commercial baker's yeast the respective values were 2·3, 4·8 and 5·2 × 10^?5 moles/litre (total amount 12·3 × 10^?5 moles/litre). In brewer's yeasts separated after the brewing process, the contents of cytochromes were markedly lower than in baker's yeast grown with limited aeration, whereas in top-fermenting yeast the total cytochrome content, aa₃ + b + c, was in some samples markedly higher, 7·1 × 10^?5 moles/litre, than in bottom-fermenting brewer's yeast, 2·4 × 10^?5 moles/litre. When brewer's bottom yeast was grown on a laboratory scale under increasing aeration, a maximum appeared in the cytochrome contents when aeration was moderate, and increased aeration inhibited the formation of cytochromes. The cytochrome contents in brewer's bottom yeast may exceed the amounts found in commercial baker's yeast. In addition to aeration, the type of metabolism influences the amounts of cytochromes in yeast.     

Variation among and within mountain birch trees in foliage phenols,carbohydrates, and amino acids,and in growth ofEpirrita autumnata larvae

Leaf quality of the mountain birch (Betula pubescens ssp.tortuosa) for herbivores was studied at several hierarchical levels: among trees, among ramets within trees, among branches within ramets, and among short shoots within branches. The experimental units at each level were chosen randomly. The indices of leaf quality were the growth rate of the larvae of a geometrid,Epirrita autumnata, and certain biochemical traits of the leaves (total phenolics and individual phenolic compounds, total carbohydrates and individual sugars, free and protein-bound amino acids). We also discuss relationships between larval growth rate and biochemical foliage traits. Larval growth rates during two successive years correlated positively at the level of tree, the ramet, and the branch, indicating that the relationships in leaf quality remained constant between seasons both among and within trees. The distribution of variation at different hierarchical levels depended on the trait in question. In the case of larval growth rate, ramets and short shoots accounted for most of the explained variation. In the case of biochemical compounds, trees accounted for most of the variance in the content of total phenolics and individual low-molecular-weight phenolics. In the content of carbohydrates (total carbohydrates, starch, fructose, glucose, and sucrose) and amino acids, variation among branches was generally larger than variation among trees. Variation among ramets was low for most compounds. No single leaf trait played a paramount role in larval growth. Secondary compounds, represented by phenolic compounds, or primary metabolites, particularly sugars, may both be important in determining the suitability of birch leaves for larvae. If phenols are causally more important, genet-specific analyses of foliage chemistry are needed. If sugars are of primary importance, within-genet sampling and analysis of foliage chemistry are necessary.     

Toxicological screening with formula-based metabolite identification by liquid chromatography/time-of-flight mass spectrometry

An analytical procedure was evaluated for the comprehensive toxicological screening of drugs, metabolites, and pesticides in 1-mL urine samples by TurboIon spray liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) in the positive ionization mode and continuous mass measurement. The substance database consisted of exact monoisotopic masses for 637 compounds, of which an LC retention time was available for 392. A macroprogram was refined for extracting the data into a legible report, utilizing metabolic patterns and preset identification criteria. These criteria included +/-30 ppm mass tolerance, a +/-0.2-min window for absolute retention time, if available, and a minimum area count of 500. The limit of detection, determined for 90 compounds, was <0.1 mg/L for 73% of the compounds studied and >1.0 mg/L for 6% of the compounds. For method comparisons, 50 successive autopsy urine samples were analyzed by this method, and the results confirmed by gas chromatography/mass spectrometry (GC/MS). Findings for parent drugs were consistent with both methods; in addition, LC/TOFMS regularly revealed apparently correct findings for metabolites not shown by GC/MS. Mean and median mass accuracy by LC/TOFMS was 7.6 and 5.4 ppm, respectively. The procedure proved well-suited for tentative identification without reference substances. The few false positives emphasized the fact that all three parameters, exact mass, retention time, and metabolite pattern, are required for unequivocal identification.