Chromium-doped CdF2 crystals by ESR spectroscopy

Single crystals of Cr-doped CdF₂ in which only Cr²⁺ ions were present were obtained by heating CdF₂:CrF₃ samples in Cd vapors. The crystals produced were studied by ESR spectroscopy at X band at 4.2 ^oK. The spectrum obtained is described by the effective spin Hamiltonian:

g⁽²⁾_eff = 4g_zcosΘ, g⁽¹⁾_eff = 2g_zcosΘ, where i = 1 for the doublet of the spin S = 1, and i = 2 for the doublet of the spin S = 2; net effective spin $\text{S}\text{=}\text{1}\text{2}$; g_z=1.85±0.03; |Δ₍₂₎|=3.08±0.07 GHz; |Δ₍₁₎|=5.85±0.07 GHz; $\text{1}\text{6}\text{(Δ}{}^{\mathrm{o}}{}_{\mathrm{(2)}}\text{? Δ}{}^{\mathrm{o}}{}_{\mathrm{(1)}}\text{)=?11.01±0.02}\text{GHz}$.     

Discrimination of the threat of direct versus tangential approach to the nest by incubating herring and great black-backed gulls.

Examined the ability of incubating herring (Larus argentatus) and black-backed (L. marinus) gulls to discriminate between people walking directly toward their nests and those merely walking tangentially by their nests. Study groups varied in their habitat (open vs vegetated) and previous exposure to human disturbance. Herring gulls responded when the experimenter (E) was at a greater distance from the nest if the approach was directly toward the nest with the person looking at the incubating bird, and gulls in disturbed areas responded sooner than birds in undisturbed areas. In habitats with low visibility (dense bush cover), the gulls could not see E early enough to show different responses to the 2 treatments. Black-backed gulls nested only in undisturbed areas, and only slight differences were evident in the distance at which they left the nest. However, they called more when E was approaching the nest directly. In this study, gulls habituated to the continual presence of humans by modifying their responses, but even habituated birds continued to reassess the potential danger of a nearby human and perceived subtle differences between a direct and a tangential approach. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prevalence of microbial biofilms on selected fresh produce and household surfaces

Investigations of biofilms in domestic environments are sparsely represented in the literature. In this study, samples of various household surfaces, including food, laundry and kitchen items, were analyzed for evidence of biofilm presence. Visualization of the surfaces was carried out using cryostage scanning electron microscopy (CSEM) and light microscopy. Qualitative evidence of the presence of biofilm formation was obtained from all of the sample groups analyzed, suggesting the widespread existence of microorganisms in biofilms on domestic surfaces. This suggests that biofilms may be important in household hygiene, and highlights the need for standardized, approved biofilm methods suitable for consumer products testing.     

Geochemical signature of contaminated sediment remobilization revealed by spatially resolved X-ray microanalysis of annual rings of Salix nigra

An X-ray microprobe was used to determine the concentration and distribution of Ni, U, and other metals within annual rings of willows (Salix nigra L.) from a former de facto radiological settling basin (Steed Pond; SP) and a depositional environment downstream (Tims Branch; TB) on the Savannah River Site (SRS). Geochemical and historical information about both areas are well documented. Following spillway breaches at SP in 1984 and the early 1990s, TB is inundated with contaminated sediments during storms. Bulk elemental composition of tree cores was determined using ICP-OES. Synchrotron X-rayfluorescence (SXRF) analysis showed that the metal contents of SP and TB cores were an order of magnitude higher than those from a reference site. TB cores were enriched with Ni in 1984 and 1991, corresponding with SP spillway breaches (containing 790 mg kg(-1) Ni in 1991). Cores from SP exhibited an extremely high Ni peak in 1996, approximately 5000 mg kg(-1), even though contaminant levels at SP did not change. The geochemical signature of contaminants recorded in TB annual rings reflected the significant sediment remobilization events consistent with the detailed history of the site, and at concentrations relative to their proximity to the source term. However, physiological processes occurring within impacted trees strongly influence the chronological accuracy of dendroanalysis and must be investigated further.     

DNA hybridization using surface plasmon-coupled emission

We describe a new approach to measuring DNA hybridization using surface plasmon-coupled emission (SPCE). Excited fluorophores are known to couple with surface oscillations of electrons in thin metal films, typically 50 nm thick silver on a glass prism. These surface plasmons then radiate into the glass at a sharply defined angle determined by the emission wavelength and the optical properties of the glass and metal. This radiation has the same spectral profile as the emission spectrum of the fluorophores. We studied the emission due to Cy3-labeled DNA oligomers bound to complementary unlabeled oligomers which were themselves bound to the metal surface. Hybridization resulted in SPCE due to Cy3-DNA into the prism. Directional SPCE was observed whether the sample was illuminated from the sample side or through the glass substrate at the surface plasmon angle for the excitation wavelength. A large fraction of the total potential emission is coupled to the surface plasmons resulting in improved sensitivity. When illuminated through the prism at the surface plasmon angle, the sensitivity is increased due to the enhanced intensity of the resonance evanescent field. It is known that SPCE depends on proximity to the silver surface. As a result, changes in emission intensity are observed due to fluorophore localization even if hybridization does not affect the quantum yield of the fluorophore. The use of SPCE resulted in suppression of interfering emission from a noncomplementary Cy5-DNA oligomers due to weaker coupling of the more distant fluorophores with the surface plasmons. We expect SPCE to have numerous applications to nucleic acid analysis and for the measurement of bioaffinity reactions.     

Identification of water-soluble selenium-containing proteins in selenized yeast by size-exclusion-reversed-phase HPLC/ICPMS followed by MALDI-TOF and electrospray Q-TOF mass spectrometry

An approach to speciation of selenium incorporated in yeast proteins was developed. The tryptic digest of a water-soluble protein fraction isolated by size-exclusion chromatography was analyzed by reversed-phase HPLC/ICPMS. The selenopeptides selected owing to the detector's elemental specificity were then analyzed by MALDI-TOFMS in order to select target ions for collision-induced dissociation MS. The latter, carried out with an electrospray Q-TOF spectrometer, enabled the sequencing of the selenopeptides detected by HPLC/ICPMS. The approach allowed for the first time the identification of a family of Se-containing proteins resulting from the replacement by selenomethionine of 2-9 methionine residues in a salt-stress-induced protein SIP18 (Mr 8874). The presence of these proteins was confirmed by MALDI-TOFMS of the original (nondigested) protein fraction. Another selenium protein identified was a heat-shock protein HSP12 (Mr 11693) in which the only methionine residue was replaced by selenomethionine. These two Se-containing proteins accounted for more than 95% of selenium in the water-soluble protein fraction.     

Pressure distribution in an assembly of wooden cylinders with various aspect ratios under uniaxial confined compression

Understanding how forces propagate in granular assemblages is important for equipment design and process control in many technologies. Yet, it remains poorly understood. In this study, a cuboidal assembly comprising cylinders of various lengths (aspect ratios AR ranging from 0.9 to 3.6) were subjected to uniaxial confined compression tests. Samples were vertically compressed until the top platen exerted a pressure of 50 kPa on the uppermost particles. This maximum pressure corresponds to the hydrostatic pressure of an approximately 15 m high column of chopped wood that may be encountered in real storage structures. The nonlinear loading curves were obtained depended on the aspect ratios of the cylinders. The modulus of elasticity, calculated from the linear elastic part of the stress–strain curve, monotonically decreased from 10.2 to 8.6 MPa as the aspect ratio increased from 1.2 to 3.6. The elastic modulus and volume fraction exhibited similar trends as functions of the aspect ratio. The horizontal-to-vertical pressure ratio was calculated as the horizontal pressure exerted on the wider walls to the vertical pressure exerted on the top lid during loading–unloading cycles. For ARs up to 3.6, the pressure ratio was approximately 0.31; for the longest cylinders (AR = 3.6), it decreased to approximately 0.27, probably because the assumption of the representative chamber volume was invalidated at this AR.     

A survey on resource allocation in high performance distributed computing systems

An efficient resource allocation is a fundamental requirement in high performance computing (HPC) systems. Many projects are dedicated to large-scale distributed computing systems that have designed and developed resource allocation mechanisms with a variety of architectures and services. In our study, through analysis, a comprehensive survey for describing resource allocation in various HPCs is reported. The aim of the work is to aggregate under a joint framework, the existing solutions for HPC to provide a thorough analysis and characteristics of the resource management and allocation strategies. Resource allocation mechanisms and strategies play a vital role towards the performance improvement of all the HPCs classifications. Therefore, a comprehensive discussion of widely used resource allocation strategies deployed in HPC environment is required, which is one of the motivations of this survey. Moreover, we have classified the HPC systems into three broad categories, namely: (a) cluster, (b) grid, and (c) cloud systems and define the characteristics of each class by extracting sets of common attributes. All of the aforementioned systems are cataloged into pure software and hybrid/hardware solutions. The system classification is used to identify approaches followed by the implementation of existing resource allocation strategies that are widely presented in the literature.     

Potential effects in multi-resolution post-classification change detection

Change detection is one of the primary applications of remote-sensing data, and many techniques have been developed during the past three decades. Although frequently criticized and despite many alternatives, due to its simplicity and intuitive manner, post-classification change detection still remains one of the most applied techniques. Many studies in the field of change detection analysis acknowledge, for instance, the impact of misregistration, inconsistencies in classification schemes or differences in methods for image interpretation. However, there are additional, rarely studied influences that can cause large errors in change detection results, including integrating multi-resolution data, the adjacency effect and the minimum mapping units (MMUs) that are applied to the classification before change detection. This study demonstrates these effects for the complex land cover of the Alvarado mangrove area at the Mexican Gulf Coast, employing 10 m Système Pour l'Observation de la Terre 5 (SPOT-5) high geometric resolution (HRG)‐based and 57 m Landsat Multispectral Scanner (MSS) classifications. As a baseline, the proportion of the fine spatial resolution classes within the coarse spatial resolution cells were derived, from which proportional change matrices were computed. The analysis employs difference measures to compare change matrices and proportional maps. The impact of various tested resampling functions was negligible if coarse resolution data were refined. For coarsening fine spatial resolution data, change matrix comparison was comparatively small but yielded differences of approximately 20% in spatially explicit measures. Incorrect positional alignment indicated differences of up to 5% in the change matrix for a misregistration of 100 m and even higher spatially explicit differences (28%). The discrepancies due to the adjacency effect were rather low. MMUs of 25 ha resulted in differences of up to 36% in the change matrix. The magnitude of the discrepancies of all studied effects depends on the class diversity in the map, and some can also be related to the difference in spatial resolution.     

Field-Assisted Sintering of Nanocrystalline Titanium Nitride

Nanosized TiN powder was densified via field-assisted sintering at temperatures of 1150°–1350°C and a pressure of 66 MPa under vacuum. A maximum relative density of ∼97% and a maximum mean grain size of 150–200 nm were obtained. Densification and microstructural evolution have been discussed, in terms of superplasticity and electric-field effects.