The synthesis and hydrolysis of dimethyl acetals catalyzed by sulfated metal oxides. An efficient method for protecting carbonyl groups

Sulfated metal oxides including SO₄ ^2–/ZrO₂, SO₄ ^2–/TiO₂, SO₄ ^2–/HfO₂, SO₄ ^2–/Fe₂O₃, SO₄ ^2–/SnO₂, and SO₄ ^2–/Al₂O₃ were highly efficient catalysts for the reaction of aldehydes and ketones with trimethyl orthoformate producing dimethyl acetals under mild reaction conditions. At room temperature, dimethyl acetal yields of 83–100% were obtained for the five carbonyl compounds chosen. These mesoporous solid acids also effectively catalyzed the hydrolysis of dimethyl acetal to regenerate the original carbonyl compounds in aqueous acetone. They not only provided an effective method for synthesizing dimethyl acetals of larger molecular size but also acted as a versatile catalyst for protecting and deprotecting carbonyl groups during organic synthesis.     

Assessment of atrial septal defect morphology by transthoracic three dimensional echocardiography using standard grey scale and Doppler myocardial imaging techniques: comparison with magnetic resonance imaging and intraoperative findings

The properties of chemically cured and light-cured composite resins were recorded at baseline and at intervals over seven years, while the materials were exposed to controlled storage conditions as well as to various conditions typical of clinical situations. For chemically cured resins in clinical conditions, mechanical properties decreased, and working and setting times increased over four years; if refrigerated (controlled), properties remained constant past seven years. For light-cured resins, test results were constant over the entire seven-year test period regardless of storage conditions. An accelerated aging protocol was developed to allow for the evaluation of the relative storage stability of new and similar materials.     

Physical and Mechanical Properties of Nanostructured Titanium Boride (TiB) Ceramic

A comprehensive report on the physical and mechanical properties of titanium boride (TiB), including many recent results that were largely determined in our research, is provided. Fully dense TiB was synthesized by reaction sintering of Ti and TiB₂ powders. A bulk nanostructured TiB ceramic material having a microstructure composed of nanosized and interconnected TiB whiskers was created. The TiB produced by this method has properties comparable with that of certain commercial types of silicon nitride.     

Unit Skin Friction from the Standard Penetration Test Supplemented with the Measurement of Torque

The standard penetration test (SPT) supplemented with the measurement of torque (SPT-T) may be used to obtain a direct measurement of unit skin friction (fs) between the sampler and the surrounding soil. The test is performed after the standard SPT procedure and does not compromise conventional SPT results. In order to perform the SPT-T, the split-barrel sampler is rotated after driving the ASTM specified distance and the maximum torque is measured using a calibrated torque wrench or transducer mounted to the top of the drill string. The measured torque is used along with the known geometry of the split-barrel sampler to determine a value of unit skin friction. SPT-T test results at 12 sites are presented. The results also show that the unit skin friction values obtained from the SPT-T generally correlate well with SPT N60 values. The results may be valuable for making preliminary estimates of unit skin friction for driven piles and provide some rationale for reported correlations between N60 and skin friction from piles.     

Influence of basal release of nitric oxide on systolic and diastolic function of both ventricles

Nitric oxide is continuously released by coronary artery endothelium under basal conditions; it maintains vascular tone and regulates coronary blood flow. The objective of this study was to investigate the influence of this basal release of nitric oxide on right and left ventricular systolic and diastolic function. Isolated pig hearts perfused at a constant pressure with enriched autologous blood were used. Systolic and diastolic pressure-volume relationships of isovolumically contracting hearts were studied in the control setting and after addition of 1 mmol/L L-N(G)-monomethyl-arginine followed by 5 mmol/L L-arginine to the perfusate. Addition of L-N(G)-monomethyl-arginine caused an acute rise in coronary vascular resistance and a reduction in right and left ventricular systolic function as evaluated by the slope values of the pressure-volume curves, but had little effect on the diastolic function of either ventricle. L-Arginine restored the systolic function to the control level. This alteration in ventricular function was not a result of ischemia because myocardial oxygen consumption was not significantly affected by the acute increase in coronary vascular resistance induced by L-N(G)-monomethyl-arginine. We conclude that basal release of nitric oxide has no direct negative inotropic effect, but in fact plays an important role in preserving right and left ventricular systolic function and maintains the basal coronary vascular tone.     

Characterization of the influence of fabrication methods on microstructure failure

Single-crystal silicon microstructures, of identical design, exhibit different failure rates (following fabrication or mechanical shock testing) due to various processes. The microstructures fabricated with a boron diffusion and subsequent removal of the boron-diffused layer have a higher survival rate to the fabrication process and to mechanical shock. The survival rate (a survivor has an intact proof mass and beam) through the process is increased by 26.5%. At a 3680g shock, the boron-diffused devices have a 2.3% lower failure rate but the difference is not statistically significant. These results have been developed with wafer-level shock testing, which permits bulk testing of many samples in a cost-effective manner.     

Category learning deficits in Parkinson's disease.

Sixteen patients with Parkinson's disease (PD), 15 older controls (OCs), and 109 younger controls (YCs) were compared in 2 category-learning tasks. Participants attempted to assign colored geometric figures to 1 of 2 categories. In rule-based tasks, category membership was defined by an explicit rule that was easy to verbalize, whereas in information-integration tasks, there was no salient verbal rule and accuracy was maximized only if information from 3 stimulus components was integrated at some predecisional stage. The YCs performed the best on both tasks. The PD patients were highly impaired compared with the OCs, in the rule-based categorization task but were not different from the OCs in the information-integration task. These results support the hypothesis that learning in these 2 tasks is mediated by functionally separate systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laboratory Experiments on Frazil-Size Characteristics in a Counterrotating Flume

In an attempt to increase the fundamental understanding of the formation and evolution of frazil ice, laboratory experiments have been conducted in a counterrotating flume at the Hydraulics Research and Testing Facility, University of Manitoba. A high-precision thermometer and recently improved digital image processing system were used to acquire data from these experiments, which will hopefully aid in the development of numerical models. The image processing system is described, and results from a series of experiments are presented. The effects of air temperature, water velocity, and bottom roughness on the formation of frazil ice are discussed. A lognormal distribution appears to provide a reasonable fit to the observed frazil particle size distributions.     

Smaller diameters in hypercube-variant networks

A number of hypercube-variant networks attempt to improve the hypercube by adding extra connections and thus reducing the diameter of the constructed network. We briefly outline a model which describes these variant networks. Further, we show that by restricting this model, we can describe hypercube variants with exactly the same number of edges as the hypercube. We mention several such networks which all have diameter about n/2. We describe a new network within this class that has diameter about 2n/5, thus improving the best known previous bound by a constant factor. We show that within a limited construction paradigm our network is best possible. This revised version was published online in June 2006 with corrections to the Cover Date.     

MEMS麦克风促进声学设计

现在,消费类电子设备(如:电话、PDA、MP3、DSC、笔记本电脑等)的设计人员不断地为这些产品加入新的功能.这就不断地推动电子设计向以下两个方向发展:器件的高集成度和器件尺寸的减小.在一些设计中,电路板的空间是非常珍贵的,设计人员千方百计地将所有器件的管脚最小化.还有一些设计,超薄是产品的主要特点,因此器件的高度就更为重要.无论是何种情况,设计人员都希望采用自由灵活和使用方便的器件.