Structure and photoluminescence of the a-Gex Se1-x, system

Alloys of this system in the composition range 0 < x < $\text{1}\text{2}$ are composed of Se chains, Se₈ rings, Ge(Se_{$\text{1}\text{2}$})₄ tetrahedral, Ge₂$\text{(Se}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_6$ ethane-like and Ge(Se_{$\text{1}\text{2}$})₂ structural units in proportions varying to comply with the actual x values. The glass forming tendency has minima at the stoichiometric compositions GeSe₂ and GeSe and maxima at $\text{x =}\text{1}\text{6}$ and $\text{x =}\text{3}\text{7}$ where the fractions of two coexisting structural units are nearly equal, $\text{i.e.}$ the number product of different bounds (Se-Se, Ge-Se) is maximal. Within the $\text{1}\text{3}$ < x < $\text{1}\text{2}$ composition range, and in non-relaxed samples even at smaller x values, ethane-like 2 (Se₃Ge)-[Ge(Se_{$\text{1}\text{2}$})₃]_n -units probably also exist. Photoluminescence (PL) is most efficient in the stoichionetric compound GeSe₂ having a rigid three-dimensional structure. The PL band is strongly Stokes shifted and thus situated in the middle of the forbidden band except for x = 0.5 where the PL is due to band-toband transitions. Defects of the bonding configurations attributable either to distortions in the structure or to irregular under-and over-coordinated atoms formed during preparation or irradiation witn band gap photons serve as PL centres. The decrease of PL intensity (fatigue) during excitation is caused by the creation of non-radiative centres whose concentration can reach 10²⁰ cm^t3?. Different models accounting for most of the observations are coinpared and discrepancies between their predictions and the experimental data are pointed out.     

Monogalactosyl diglyceride and digalactosyl diglyceride from commercial rapessed “lecithin”

By silicic acid column separation small quantities of glycolipid-rich fractions have been isolated from commercial Swedish rapeseed “lecithin.” Major components in these fractions are monogalactosyl diglyceride and digalactosyl diglyceride which have been identified by R_f on thin layer chromatography specific color reactions and IR spectrometry. The fatty acid patterns of the galactolipids are different from those of the major phospholipids of the same product, with less of palmitic and oleic and considerably more of linolenic acid.     

On the design optimization of built-up stiffened steel beams with buckling and frequency constraints

The literature on the structural design optimization of steel-plate girders indicates a need for more refined research studies to obtain optimal designs by formulating and solving the design problem that combines structural sizing and shape parameters in one unified, constrained problem. For this purpose, the structural optimization design problem of stiffened steel-plate girders is formulated with specified loading conditions and constraints on strength and serviceability considerations including limits on fundamental frequency and buckling modes. The finite-element method-based model is used to define the objective function and the structural/geometric response functions, while the geometric domain elements are used to systematically perturb the structural shape during the search for an optimal shape of the structure. The mathematical statement of the gradient-based-design problem is solved for an optimal structural size and shape with buckling and frequency constraints in addition to the traditional strength constraints. The numerical results obtained are compared with results obtained from a less formal ad hoc design procedure, and some conclusions are drawn to emphasize the design benefits obtained from solving the design problem for optimal structural size and shape.     

Comments on: Optimal stochastic control for discrete-time linear systems with interrupted observations

In a recent paper [1] a control law was found, which was claimed to be optimal. Here we point out an error in the proof and give a counterexample. In fact, the control law in [1] can be seen as a “passive open loop approximation”. We suggest also a control law which actively identifies the random variables in the loop.     

A study of geohydrological and rock engineering environment at Lappvattnet experimental mine

The paper describes a hydrogeological and geotechnical study of rock mass at an experimental nickel mine at Lappvattnet, Sweden. The mine is situated 30 km south-west of the twonship of Skelleftea and was mainly developed for the exploration purposes. The mine consists of 1000 m of underground roadways from where a number of diamond cored boreholes were drilled for geotechnical studies and mine valuation. The main problem encountered during the development stage of the mine was very high quantities of ground water inflows at relatively high hydraulic pressures. The geological and hydrogeological conditions along the length of the drifts are described together with the methods used for ground-water inflow control. The study shows that there is a strong need for modifying the grouting methods to suit the rock conditions in order to control the ground-water inflows. A discussion regarding the need for a detailed geotechnical investigation prior to the planning and design stage of the project is also included.     

A novel automatic algorithm for the segmentation of the lumen of the carotid artery in ultrasound B-mode images

A novel algorithm is proposed for the segmentation of the lumen and bifurcation boundaries of the carotid artery in B-mode ultrasound images. It uses the image contrast characteristics of the lumen and bifurcation of the carotid artery in relation to other tissues and structures for their identification. The relevant ultrasound data regarding the artery presented in the input image is identified using morphologic operators and processed by an anisotropic diffusion filter for speckle noise removal. The information obtained is then used to define two initial contours, one corresponding to the lumen and the other one regarding the bifurcation boundaries, for the application of the Chan-Vese level set segmentation model. A set of longitudinal ultrasound B-mode grayscale images of the common carotid artery was acquired using a GE Healthcare Vivid-e ultrasound system. The results reveal that the new algorithm is effective and robust, and that its main advantage relies on the automatic identification of the carotid lumen, which overcomes the known limitations of the traditional algorithms.     

Occupational posture exposure among construction electricians

The aim of this study is to record, objectively describe and compare working postures of Brazilian and Norwegian construction electricians. Postures of the upper arms, head, and neck during work and breaks were quantified by means of inclinometry for a representative sample of 12 Brazilian and 12 Norwegian electricians in the construction industry during a full work-shift. Despite that differences were found between specific work-related factors, Brazilian and Norwegian workers revealed a high and very similar level and pattern of postures for all evaluated body regions, suggesting that results could be extrapolated to other electricians. Upper arm elevation was high and similar for both groups and head flexion and extension was pronounced compared to other occupations. Thus, extreme postures were identified for construction electricians in both countries, with similar exposure pattern also for defined tasks (planning, support and wiredraw), suggesting that this job is risky regardless organizational differences.     

Modelling gross primary production of a tropical semi-deciduous forest in the southern Amazon Basin

Semi-deciduous forest in the Amazon Basin is sensitive to temporal variation in surface water availability that can limit seasonal rates of leaf and canopy gas exchange. We estimated the seasonal dynamics of gross primary production (GPP) over 3 years (2005–2008) using eddy covariance and assessed canopy spectral reflectance using MODIS imagery for a mature tropical semi-deciduous forest located near Sinop, Mato Grosso, Brazil. A light-use efficiency model, known as the Vegetation Photosynthesis Model (VPM), was used to estimate seasonal and inter-annual variations in GPP as a function of the enhanced vegetation index (EVI), the land surface water index (LSWI), and local meteorology. Our results indicate that the standard VPM was incapable of reproducing the seasonal variation in GPP, primarily because the model overestimated dry-season GPP. In the standard model, the scalar function that alters light-use efficiency (ε_g) as a function of water availability (W_scalar) is calculated as a linear function of the LSWI derived from MODIS; however, the LSWI is negatively correlated with several measures of water availability including precipitation, soil water content, and relative humidity (RH). Thus, during the dry season, when rainfall, soil water content, and RH are low, LSWI, and therefore, W_scalar, are at a seasonal maximum. Using previous research, we derived new functions for W_scalar based on time series of RH and photosynthetic photon flux density (PPFD) that significantly improved the performance of the VPM. Whether these new functions perform equally well in water stressed and unstressed tropical forests needs to be determined, but presumably unstressed ecosystems would have high cloud cover and humidity, which would minimize variations in W_scalar and GPP to spatial and/or temporal variation in water availability.