Workshop on Measurement Needs for Local-Structure Determination in Inorganic Materials

The functional responses (e.g., dielectric, magnetic, catalytic, etc.) of many industrially-relevant materials are controlled by their local structure—a term that refers to the atomic arrangements on a scale ranging from atomic (sub-nanometer) to several nanometers. Thus, accurate knowledge of local structure is central to understanding the properties of nanostructured materials, thereby placing the problem of determining atomic positions on the nanoscale—the so-called “nanostructure problem”—at the center of modern materials development. Today, multiple experimental techniques exist for probing local atomic arrangements; nonetheless, finding accurate comprehensive, and robust structural solutions for the nanostructured materials still remains a formidable challenge because any one of these methods yields only a partial view of the local structure. The primary goal of this 2-day NIST-sponsored workshop was to bring together experts in the key experimental and theoretical areas relevant to local-structure determination to devise a strategy for the collaborative effort required to develop a comprehensive measurement solution on the local scale. The participants unanimously agreed that solving the nanostructure problem—an ultimate frontier in materials characterization—necessitates a coordinated interdisciplinary effort that transcends the existing capabilities of any single institution, including national laboratories, centers, and user facilities. The discussions converged on an institute dedicated to local structure determination as the most viable organizational platform for successfully addressing the nanostructure problem. The proposed “institute” would provide an intellectual infrastructure for local structure determination by (1) developing and maintaining relevant computer software integrated in an open-source global optimization framework (Fig. 2), (2) connecting industrial and academic users with experts in measurement techniques, (3) developing and maintaining pertinent databases, and (4) providing necessary education and training.Open in a separate windowFig. 2A schematic representation of the complex modeling idea: integration of combined inputs from multiple experimental techniques and theory into the global optimization framework [Billinge and Levin, unpublished]. In this concept, the structural model evolves toward the correct solution as more data is provided for the fit.     

Use of thermolysin metalloprotein affinity metal chromatography in the decontamination of actinide-bearing solutions

Thermolysin metalloprotein affinity metal chromatography (MAMC) has been shown to be effective for the removal and concentration of lanthanide and actinide ions from aqueous solution. Using solution of trivalent lanthanide ions of appropriate radii and of Th⁴⁺ and UO ions as models, the calciumbinding sites of immobilized thermolysin have shown appreciable potential for the decontamination of actinide-bearing waster solutions. The zinc-binding site of the affixed protein may also be used for the removal and concentration of divalent transition metal ions.     

Rat strain minimally influences anesthetic and convulsant requirements of inhaled compounds in rats

We assessed the effect of rat strain on susceptibility to anesthesia and convulsions produced by inhaled compounds. We determined the minimum alveolar anesthetic concentration (MAC) of desflurane and nitrous oxide, and the convulsive 50% effective dose (ED50) of 1,2-dichlorohexafluorocyclobutane, flurothyl, and difluoromethyl-1-chlorotetrafluoroethyl ether in five strains (three inbred [Long Evans, Sprague-Dawley, and Wistar] and two outbred [Fischer and Brown Norway]). Strain had slight effects on anesthetic potency, the strains with the highest MAC values (Long Evans and Brown Norway) having values < or =28% greater than the strains with the lowest values (Sprague Dawley and Wistar). MAC for nitrous oxide correlated directly with MAC for desflurane as a function of strain. MAC for either desflurane or nitrous oxide correlated inversely with the convulsive ED50 of 1,2-dichlorohexafluorocyclobutane, but correlated poorly (and directly) with the convulsive ED50 of the remaining compounds. Convulsivity varied little as a function of strain (greatest difference 21%) and did not vary consistently as a function of strain. No consistent difference was seen between inbred versus outbred strains. IMPLICATIONS: Rat strain has a minimal effect on the potency of inhaled anesthetics or the convulsant activity of inhaled compounds. It seems that the sites acted on by inhaled compounds to produce anesthesia and convulsions are conserved across common rat strains.     

Yttrium Substitution in CaS

Substitution of Y³⁺ in CaS results in the cubic rock-salt-type solid-solution Ca_{1− x} Y_{2 x /3}□ _{x /3}S, with x 0.37 and where □ denotes cation vacancies that form for charge compensation. The substitution range determined from polycrystalline samples prepared at 1025°C corresponds to a solubility limit of 16 mol% Y₂S₃ in CaS. Evolution of the unit cell edge with x indicates that the CaS lattice expands about the cation vacancies. Single-crystal X-ray diffraction studies of samples grown from a eutectic CaCl₂–KCl flux revealed no indication of superstructure formation, indicating that Ca²⁺, Y³⁺, and vacancies are disordered across the cation sites. Thermogravimetric analysis curves for Ca_0.7Y_0.2S, CaS, and the ternary compound CaY₂S₄ indicate oxidative stability up to 430°, 410°, and 490°C, respectively.     

New computation approaches for open-loop SSTDMA network synchronization

This paper presents two new open-loop synchronization algorithms for computing the satellite position. One is based on a three-rotational co-ordinate transformation, the other is based on a numerical iteration method. A detailed comparison of these two algorithms with other available algorithms is given with respect to accuracy of the computed separation distances between ground stations and the satellite, sensitivity to measurement and implementation errors, computation speed, and implementation complexity.     

The effects of PECVD silicon dioxide passivation on the electrical characteristics of Sol-Gel deposited PZT film capacitors

Abstract

Plasma-enhanced chemical vapor deposition (PECVD) of doped and undoped silicon dioxide layers is widely used throughout the semiconductor industry for the passivation of processed devices before the final metallization processing steps. However, a reduction in the remanent polarization of PZT platinum-electrode capacitors has been observed when the capacitors were passivated with PECVD silicon dioxide films. This paper presents the results of a study to determine the effects of a standard PECVD silicon dioxide process on the retained polarization of Sol-Gel derived PZT capacitors with platinum electrodes. The retained polarization of the capacitors was measured before and after the silicon dioxide depositions. Measurements indicate that for PZT capacitors with temperature-stabilized top electrodes, there is relatively little change in the retained polarization after the depositions. However, for the PZT capacitors without the temperature-stabilized top electrodes, reductions in excess of 70% in the retained polarization can occur.     

Passive cooling systems for cement-based roofs

In warmer climates, buildings made of cement-based materials often exhibit unfavorable thermal characteristics including higher interior temperature, especially in the absence of an active cooling mechanical system. The purpose of this research project was to investigate the thermal effects of newly designed passive cooling systems on concrete roofs in existing buildings. Each tested passive cooling system consists of a combination of materials that can reduce net heat load in buildings. Commercially available materials such as aluminum 1100 and galvanized steel were used as radiation reflectors; and polyurethane, polystyrene, polyethylene, and an air gap were used as insulation. Experimental results based on laboratory-scale prototypes show that the radiation reflector shape as well as the material selection of each passive cooling system led to reductions in heat conduction between 65 and 88% when compared to a control prototype. Each passive cooling system showed a slow thermal time response when compared to a plain concrete roof, which is a desirable characteristic for controlling thermal fluctuations when heat conduction is also reduced simultaneously. Transient empirical models to predict accurately the midpoint temperature of a cement roof were formulated with and without passive cooling systems in use.     

An Approximation Technique for Pseudo-Boolean Maximization Problems

A partitioning procedure is proposed for obtaining approximate solutions to pseudo-Boolean optimization problems (e.g., zero-one polynomial programs). Such a procedure is useful not only in its ability to provide a bound value but further as a means for initializing optimum seeking methods, such as implicit enumeration techniques, employed to insure optimality.     

Reaction time in normal and defective subjects following varied warning conditions.

As a test of a stimulus-trace theory of behavioral inadequacy, normal and mentally defective Ss performed on a simple reaction-time task with warning intervals of 2, 4, 8, 12 sec. The warning stimulus was a light which for ? of the Ss in each group was on for 1.5 sec. at the beginning of the warning interval. For the other Ss the warning signal was on throughout the warning interval. The signal to respond was a buzzer. The normal Ss performance did not differ for the 2 warning conditions but there were marked differences between the defective groups. A 2nd experiment using only defective Ss provided a control for a possible task artifact. The results were interpreted as suggesting a deficiency in short-term memory in defective Ss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Digital single-sideband modulators

A new derivation of Darlington's digital s.s.b./f.d.m. modulator1 implementation is presented, giving additional structural insight.