Raman microprobe analysis of preforms and optical fibers

The concentration profile of various dopants (germanium, phosphorus, and fluorine) in preforms and optical fibers has been obtained with a Raman microprobe. A 2-microm spatial resolution was achieved. In the case of germanium and phosphorus, the results agree quite well with those obtained with an electron microprobe. Raman spectroscopy easily detects fluorine. From measurements of various F-doped samples, diffusion of fluorine in undoped and doped silica is suggested.     

Accommodation of impurities in α-Al2O3, α-Cr2O3 and α-Fe2O3

Atomic scale computer simulation was used to predict the mechanisms and energies associated with the accommodation of aliovalent and isovalent dopants in three host oxides with the corundum structure. Here we consider a much more extensive range of dopant ions than has previously been the case. This enables a rigorous comparison of calculated mechanism energetics. From this we predict that divalent ions are charge compensated by oxygen vacancies and tetravalent ions by cation vacancies over the full range of dopant radii. When defect associations are included in the model these conclusions remain valid. At equilibrium, defects resulting from extrinsic dopant solution dominate intrinsic processes, except for the largest dopant cations. Solution reaction energies increase markedly with increasing dopant radius. The behaviour of cluster binding energies is more complex.     

Crossover: online pests plaguing the off line world

During the past 10 years, several technological trends have emerged that significantly and positively affected today's world. Two in particular are noteworthy: the apparently unbounded desire to network any and all devices and deployment of Microsoft's operating systems in everything from consumer PCs and business servers to embedded devices. We could well see the telecommunications boom; the rise of the Internet, and the rush to connect everything to it as one of humanity's milestones, not far removed from, that of the invention of the telephone or telegraph. Computer networking, over the Internet, particularly, has democratized the publishing of information, made massive amounts of information and services accessible to the general public, and enabled new business models. But everything has a dark side. Along with its benefits, the Internet has brought about such things as cybercrime, computer worms, online fraud, spam, and denial-of-service attacks, among other online unpleasantness. This down side is considered in the article.     

Pulsed electro-acoustic technique applied to in-situ measurement of charge distribution in electron-irradiated polymers

Dielectric materials are frequently used in satellite structures for substantial savings in weight. Their dielectric nature and the effect of different forms of radiation encountered in space combine to accumulate electrical charges resulting in the occurrence of electrostatic discharges which cause harmful interference with the electronic parts of the satellite, leading to its malfunction or to a total loss of equipment control. Therefore, the behavior of dielectrics under irradiation must be investigated before being used in space. A pulsed electroacoustic (PEA) device was mounted in an irradiation chamber to monitor the spatial distribution of electrons implanted into polymer films during electronic irradiation. Internal charge accumulation was clearly identified. Penetration depth versus energy was double checked by comparing PEA with surface potential data.     

A urine patch framework to simulate nitrogen leaching on New Zealand dairy farms

On New Zealand dairy farms, it is the nitrogen excreted directly onto pasture, particularly urine, that drives nitrogen (N) leaching from the farm. A new framework (UPF: Urine Patch Framework) is presented that post-processes the results of a whole farm model and runs a mechanistic soil model to simulate the urine patches. Two alternative methods to simulate the spatial distribution of urine patches were implemented and compared (Grid: spatially explicit, and Probabilistic: based on the probability of different temporal urination patterns). This paper describes the implementation of these two methods in connection with a Whole Farm Model; and compares the N leaching predictions with observed data. Two examples are provided, one analyzing the impact of urine patch overlap and another, the relative risk of N leaching at different times of urinary N deposition. The model showed good correlation and predictive ability between simulated annual N leaching results and observed data [R² = 94 %, mean relative prediction error (MRPE) = 10 % for Grid and R² = 72 %, MRPE = 20 % for Probabilistic]. The two methods produced similar results across an 8-year period for monthly and annual N leaching (R² = 96 %, MRPE = 10 % and R² = 86 %, MRPE = 8 %; respectively). Only 8 % of the paddock area was covered with multiple urinations during 1 year, but as much as 39 % of the total urine volume was deposited on overlapped patches. Systematically removing all urinary N for 1 month in either May or June reduced N leaching by approximately 20 %. Avoiding urinary N deposition during autumn or early winter could be highly effective in mitigating N leached during the following winter.     

Effects of worker size on the dynamics of fire ant tunnel construction

Social insects work together to complete tasks. However, different individuals within a colony may vary in task proficiency. We investigated if fire ant (Solenopsis invicta) worker body size influenced the ability to construct tunnels—a key component of subterranean nests. We monitored excavation by worker groups in a substrate of small wetted glass particles in quasi-two-dimensional arenas. Morphological and network features of the tunnel system were measured. Total tunnel area did not differ significantly between groups of large and small workers, although the tunnel area of control sized workers was significantly larger than that of large workers. Moreover, large workers created wider but shorter tunnels, with slower growth rate of tunnel number. However, edge–vertex scaling and degree distribution of the tunnel network were similar across all treatments. In all cases, the amount of excavated material was correlated with the number of active workers. Our study reveals that morphological features of excavated tunnels show modest variation when constructed by workers of varying sizes, but topological features associated with the tunnel network are conserved. These results suggest that important behavioural aspects of tunnel construction—and thus nest building—are similar among morphologically distinct members of fire ant societies.     

Entropic Contributions to Protein Stability

Thermodynamic stability is an important property of proteins that is linked to many of the trade-offs that characterize a protein molecule and therefore its function. Designing a protein with a desired stability is a complicated task given the intrinsic trade-off between enthalpy and entropy which applies for both the folded and unfolded states. Traditionally, protein stability is manipulated by point mutations which regulate the folded state enthalpy. In some cases, the entropy of the unfolded state has also been manipulated by means that drastically restrict its conformational dynamics such as engineering disulfide bonds. In this mini-review, we survey various approaches to modify protein stability by manipulating the entropy of either the unfolded or the folded states. We show that point mutations that involve elimination of long-range contacts may have a greater destabilization effect than mutations that eliminate shorter-range contacts. Protein conjugation can also affect the entropy of the unfolded state and thus the overall stability. In addition, we show that entropy can contribute to shape the folded state and yield greater protein stabilization. Hence, we argue that the entropy component can be practically manipulated both in the folded and unfolded state to modify protein stability.     

Soft-Chemistry Synthesis, Characterization, and Stabilization of CGO/Al2O3/Pt Nanostructured Composite Powders

Soft-chemistry routes were used to synthesize Ce_0.9Gd_0.1O_1.95-based powders with attractive and stable structural, morphological, and textural properties. In the intermediate temperature range between 500° and 700°C, the average Gd-doped CeO₂ (CGO) crystallite size is in the range 9–22 nm and the specific surface area varies from 43.4 to 8 m²/g. Above 700°C, a phase separation occurs between ceria and gadolinium oxide. Addition of alumina was found to be useful in stabilizing the CGO nanocrystallites at a high temperature and to avoid phase separation. A homogeneous dispersion of Pt nanoparticles (<10 nm at 1000°C) in the CGO materials was found to be possible by post-impregnation, although direct insertion of the Pt precursors during the synthesis led to aggregated particles, with less potential for catalytic applications.     

空间跟踪与监视系统探测能力分析

基于空间跟踪与监视系统性能参数信息,借鉴国内相关研究成果,建立了空间跟踪与监视系统红外探测能力分析相关模型,分析了其探测距离、探测精度、定位精度、识别能力,对于空间跟踪与监视系统的相关研究工作具有一定的参考价值.