The effect of grain size, strain rate, and temperature on the mechanical behavior of commercial purity aluminum

Commercial purity aluminum AA1050 was subjected to equal channel angular extrusion (ECAE) that resulted in an ultrafine-grained (UFG) microstructure with an as-received grain size of 0.35 μm. This UFG material was then annealed to obtain microstructures with grain sizes ranging from 0.47 to 20 μm. Specimens were compressed at quasi-static, intermediate, and dynamic strain rates at temperatures of 77 and 298 K. The mechanical properties were found to vary significantly with grain size, strain rate, and temperature. Yield stress was found to increase with decreasing grain size, decreasing temperature, and increasing strain rate. The work hardening rate was seen to increase with increasing grain size, decreasing temperature, and increasing strain rate. The influence of strain rate and temperature is most significant in the smallest grain size specimens. The rate of work hardening is also influenced by strain rate, temperature, and grain size with negative rates of work hardening observed at 298 K and quasi-static strain rates in the smallest grain sizes and increasing rates of work hardening with increasing loading rate and grain size. Work hardening behavior is correlated with the substructural evolution of these specimens.     

State of polarization changes: Classification and measurement

We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations.     

移动WiMAX的发展现状

基于IEEE 802.16-2004及ETSI HiperMAN空中接口标准的WiMAX,正在被证明是一个高性价比的替代有线和DSL服务的固定无线技术.150多次的WiMAX试验及在五大洲的部署,清楚地证明了世界范围内对WiMAX作为固定无线服务技术的接受程度.     

Duodenal erosions and ulcers in patients with pancreatobiliary obstruction

The authors compared in a controlled clinical study two groups of patients after a first renal transplantation treated by triple drug immunosuppressive therapy. In a group of 31 patients the triple combination comprised Sandimmune Neoral. In the control group there were 30 patients who received Sandimmune. No differences were found between the two groups as regards the effectiveness of this treatment and the authors did not confirm a lower incidence of rejections described in patients treated with Sandimmune Neoral. They confirmed, however, a lower interindividual variability of Cy-A levels assessed specifically in patients treated with Sandimmune Neoral.     

Stability of motor-unit force thresholds in the decerebrate cat

To further test the hypothesis that some fixed property of motoneurons determines their recruitment order, we quantified the variation in force threshold (FT) for motoneurons recruited in muscle stretch reflexes in the decerebrate cat. Motor axons supplying the medial gastrocnemius (MG) muscle were penetrated with micropipettes and physiological properties of the motoneuron and its muscle fibers, i.e., the motor unit, were measured. FT, defined as the amount of MG force produced when the isolated motor unit was recruited, was measured from 20 to 93 consecutive stretch trials for 29 motor units. Trials were selected for limited variation in base force and rate of rise of force, which have been shown to covary with FT, and in peak stretch force, which gives some index of motor-pool excitability. Under these restricted conditions, large variation in FT would have been inconsistent with the hypothesis. Analysis of the variation in FT employed the coefficient of variation (CV), because of the tendency for FT variance and mean to increase together. We found that CV was distributed with a median value of 10% and with only 2 of 29 units exceeding 36%. Some of this variation was associated with measurement error and with intertrial fluctuations in base, peak, and the rate of change of muscle force. CV was not significantly correlated with motor-unit axonal conduction velocity, contraction time, or force. In three cases FT was measured simultaneously from two motor units in the same stretch trials. Changes in recruitment order were rarely observed (5 of 121 stretch trials), even when FT ranges for units in a pair overlapped. We suggest that the large variation in recruitment threshold observed in some earlier studies resulted not from wide variation in the recruitment ranking of motoneurons within one muscle, but rather from variation in the relative activity of different pools of motoneurons. Our findings are consistent with the hypothesis that recruitment order is determined by some fixed property of alpha-motoneurons and/or by some unvarying combination of presynaptic inputs that fluctuate in parallel.     

Structure and stability of an immunoglobulin superfamily domain from twitchin, a muscle protein of the nematode Caenorhabditis elegans

The NMR solution structure of an immunoglobulin superfamily module of twitchin (Ig 18') has been determined and the kinetic and equilibrium folding behaviour characterised. Thirty molecular coordinates were calculated using a hybrid distance geometry-simulated annealing protocol based on 1207 distance and 48 dihedral restraints. The atomic rms distributions about the mean coordinate for the ensemble of structures is 0.55( +/- 0.09) A for backbone atoms and 1.10( +/- 0.08) A for all heavy atoms. The protein has a topology very similar to that of telokin and the titin Ig domains and thus it falls into the I set of the immunoglobulin superfamily. The close agreement between the predicted and observed structures of Ig 18' demonstrates clearly that the I set profile can be applied in the structure prediction of immunoglobulin-like domains of diverse modular proteins. Folding studies reveal that the protein has relatively low thermodynamic stability, deltaG(H2O)U-F = 4.0 kcal mol(-1) at physiological pH. Unfolding studies suggest that the protein has considerable kinetic stability, the half life of the unfolding is greater than 40 minutes in the absence of denaturant.     

Dynamic endocrine testing. The Mayo Clinic model

An endocrine testing center (ETC) is a universal requirement for the practice of endocrinology. Modifications of the Mayo Clinic model for an ETC should be applicable to most endocrine practices. Key components of an ETC include a centralized testing area, registered nurse-physician team, detailed testing protocols, and patient education programs.     

A noncompetitive peptide inhibitor of the nicotinic acetylcholine receptor from Conus purpurascens venom

A paralytic peptide, psi-conotoxin Piiie has been purified and characterized from Conus purpurascens venom. Electrophysiological studies indicate that the peptide inhibits the nicotinic acetylcholine receptor (nAChR). However, the peptide does not block the binding of alpha-bungarotoxin, a competitive nAChR antagonist. Thus, psi-conotoxin Piiie appears to inhibit the receptor at a site other than the acetylcholine-binding site. As ascertained by sequence analysis, mass spectrometry, and chemical synthesis, the peptide has the following covalent structure: HOOCCLYGKCRRYOGCSSASCCQR* (O = 4-trans hydroxyproline; * indicates an amidated C-terminus). The disulfide connectivity of the toxin is unrelated to the alpha- or the alphaA-conotoxins, the Conus peptide families that are competitive inhibitors of the nAChR, but shows homology to the mu-conotoxins (which are Na+ channel blockers).     

Intralesional radiolabeled human monoclonal IgM in human tumor xenografts

Sensory-perceptual abnormalities in people with autism are discussed from two perspectives: published firsthand accounts and existing psychological research evidence. A range of abnormalities, including hyper- and hyposensitivity, sensory distortion and overload, and multichannel receptivity and processing difficulties, are described in firsthand accounts and frequently portrayed as central to the autistic experience. A number of dangers are inherent in uncritically accepting these accounts at face value and in any wider generalization to the autistic population as a whole. Evidence from clinical studies suggests that unusual sensory responses are present in a majority of autistic children, that they are manifested very early in development, and that they may be linked with other aspects of autistic behavior. In addition, experimental studies using a range of indices have found evidence of unusual responses to sensory stimuli in autistic subjects. However the clinical and experimental research to date suffers from serious methodological limitations and more systematic investigation is warranted. Key issues for future psychological research in the area are identified.     

Microflora of periodontal pockets in advanced periodontitis

The aim of study was the evaluation of periodontal pockets microflora in patients with advanced periodontitis. From each subject 16-20 samples were taken using paper points. Pooled sample after 60 s. mixing was serially diluted in reduced BHI. For total cell counts and for the isolation of black pigmented anaerobes Brucella agar supplemented with 5% sheep blood, hemin, menadione, with and without Kanamycin-Vancomycin mixture and BM agar plates were used. For isolation of A. actinomycetemcomitans TSBV agar plates were used. Cultures were incubated in anaerobic chamber at 37 degrees C for 7 days and TSBV agar plates in an atmosphere of 95% air-5% CO2 at 37 degrees C for 5 days. Microorganisms were identified by Gram staining, colony morphology, fluorescence in UV-light, haemagglutination of 3% sheep erythrocytes, fermentation of sugars, production of indole, urease (API 20A), specific enzymes (Rapid ID 32A). Twenty seven subjects with clinically recognized periodontitis were examined. Microorganisms important in periodontitis were isolated from periodontal pockets of almost all examined subjects. The number of bacteria obtained from the sample of one patient ranged from 1 x 10(4) CFU/ml to 3,6 x 10(6) CFU/ml. Porphyromonas gingivalis was identified in the samples taken from 17 patients, Prevotella intermedia-19, Actinobacillus actinomycetemcomitans -11, Fusobacterium nucleatum-9, Peptostreptococcus spp.-22.