Searching for momentum enhancement in hypervelocity impacts

In conjunction with the Los Alamos National Laboratory hypervelocity microparticle impact (HMI) team effort to produce higher impact velocities and to understand the physics of crater formation and momentum transfer, we have implemented a low noise microphone as a momentum detector on both the 6 MV Van de Graaff and 85 KV “test stand” particle accelerators. Calculations are presented showing that the impulse response of a circular membrane. When used as a momentum impulse detector, the microphone theoretically may detect impulses as small as 8.8 × 10⁻¹⁵ N s. Sensitivity of the microphone in this application is limited by the noise threshold of the electronic amplifiers and the ambient microphonic vibration of the system. Calculations lead us to anticipate detection of particles over the full range of the Van de Graaff acceleration capability and up to 7 km/s on the test stand. We present momentum enhancement data in the velocity range between 10 km/s and 20 km/s. Preliminary work is presented on momentum impulse calibration of the microphone using laser-pulse photon momentum as an impulse source.     

Structured data in structural analysis software

This paper discusses the use of computer data structures in finite-element structural analysis programs. A number of data structure types that have been shown to be useful in such programs are introduced and described. A simple finite-element model is used to demonstrate how the given set of data structure types naturally lend themselves to developing software for the model. Different methods of implementing data structures in the context of a program are discussed.     

应用研究与发展设施

项目地点:美国亚利桑那州旗竿市项目类型:建筑(教育)开工日期:2005年5月该项目获2005年豪瑞可持续建筑大奖赛北美地区提名奖     

Water distribution and mobility in meat during the conversion of muscle to meat and ageing and the impacts on fresh meat quality attributes--a review

This paper reviews current knowledge on the distribution and mobility of water in muscle (myowater) ante- and post mortem and factors affecting these in relation to fresh meat quality parameters; water-holding capacity (WHC), tenderness and juiciness. NMR transverse relaxometry (T(2)) using bench-top Low-Field Nuclear Magnetic Resonance (LF-NMR) has characterised myowater distribution and mobility as well as structural features in meat which directly affect WHC. The current literature demonstrates that WHC is correlated to the water located outside the myofibrillar network (extra-myofibrillar). This review identifies the critical stages which affect the translocation of water into the extra-myofibrillar space and thus the potential for decreased WHC during proteolysis (the conversion of muscle to meat). This review discusses how the intrinsic properties of the water held within the meat could contribute to juiciness and tenderness. Tenderness has been shown to correlate to T(2), however breed and species differences made it difficult to draw firm conclusions. Further understanding of the inherent water properties of fresh meat and the factors affecting water distribution and mobility using NMR technologies will increase the understanding of WHC and tenderisation of fresh meat.     

The conserved arginine in rho-GTPase-activating protein is essential for efficient catalysis but not for complex formation with Rho.GDP and aluminum fluoride

The Rho family of small GTP-binding proteins are downregulated by an intrinsic GTPase, which is enhanced by GTPase-activating proteins (GAPs). RhoGAPs contain a single conserved arginine residue that has been proposed to be involved in catalysis. Here, the role of this arginine has been elucidated by mutagenesis followed by determination of catalytic and equilibrium binding constants using single-turnover kinetics, isothermal titration calorimetry, and scintillation proximity assays. The turnover numbers for wild-type, R282A, and R282K RhoGAPs were 5.4, 0.023, and 0.010 s-1, respectively. Thus, the function of this arginine could not be replaced by lysine or alanine. Nevertheless, the R282A mutation had a minimal effect on the binding affinity of RhoGAP for either Rho. GTP or Rho.GMPPNP, which confirms the importance of the arginine residue for catalysis as opposed to formation of the protein-protein complex. The R282A mutant RhoGAP still increased the hydrolysis rate of Rho.GTP by 160-fold, whereas the wild-type enzyme increased it by 38000-fold. We conclude that this arginine contributes half of the total reduction of activation energy of catalysis. In the presence of aluminum fluoride, the R282A mutant RhoGAP binds almost as well as the wild type to Rho.GDP, demonstrating that the conserved arginine is not required for this interaction. The affinity of wild-type RhoGAP for the triphosphate form of Rho is similar to that for Rho.GDP with aluminum fluoride. These last two observations show that this complex is not associated with the free energy changes expected for the transition state, although the Rho.GDP.AlF4-.RhoGAP complex might well be a close structural approximation.     

Imaging of the pediatric orbit and visual pathways: computed tomography and magnetic resonance imaging

Tumors of the small bowel are uncommon and seldom suspected on a clinical basis. Together with the relative inaccessibility of the small bowel to endoscopic investigation, the rarity of these tumors undoubtedly delays the diagnosis. Small bowel tumors may be an interesting field of application for enteroscopy, which now can be readily performed with dedicated enteroscopic evaluation in patients with suspected small bowel neoplasia could improve prognosis and treatment. Enteroscopy may also play an important role in the surveillance of inherited polyposis syndromes, as in other precancerous condition of the small bowel. In Peutz-Jeghers syndrome it may reduce polyp-induced complications and improve planning for surgery; in familial adenomatous polyposis it may contribute to preventing upper gastrointestinal tract cancer.     

Association of human leucocyte antigen phenotype with vaccine efficacy in patients receiving vaginal mucosal immunization for recurrent urinary tract infection

CONTEXT: One or both commercial tuberculin skin test reagents (Aplisol and Tubersol) may have a high rate of false-positive reactions. OBJECTIVE: To compare the reaction size and specificity of skin testing with Aplisol, Tubersol, and the standard purified protein derivative (PPD-S1). DESIGN: Double-blind trial, conducted between May 14, 1997, and October28, 1997, in which each individual received 4 tuberculin skin reagents at sites assigned at random. SETTING: Health departments and universities in 6 US cities. PARTICIPANTS: A total of 1555 persons at low risk of latent tuberculosis infection. INTERVENTION: Simultaneous skin tests with Aplisol, Tubersol, PPD-S1, and either a second PPD-S1 or PPD-S2 (a proposed new standard). MAIN OUTCOME MEASURE: Reaction size at each injection site measured by 2 investigators blinded to type of reagent. RESULTS: Aplisol produced slightly larger reactions than Tubersol, but this difference did not significantly change skin test interpretation. The mean +/- SD reaction sizes were 3.4+/-4.2 mm with Aplisol, 2.1+/-3.2 mm with Tubersol, and 2.5+/-3.6 mm with PPD-S1. Assuming that all participants were uninfected and using a 10-mm cutoff, the specificities of the tests were high: Aplisol, 98.2%; Tubersol, 99.2%; and PPD-S1, 98.9%. Significant variability was not detected in interobserver, host, and lot-to-lot reagent comparisons. CONCLUSION: Using a cutoff of at least 10 mm, testing with 3 different PPD reagents resulted in similar numbers of uninfected persons being correctly classified.     

The influence of metals and carbides during laser surface modification of low alloy steel

The addition of both elements (Cr and Ni) and carbides (SiC and WC) during laser surface alloying under different processing speeds produced surfaces with both enhanced hardness wear resistance and corrosion properties compared to the base AISI 4340 steel material. These effects were due to the evolution of unique microstructures within the laser-processed region, which includes austenite, ferrite, martensite, Fe- and Si-based carbides and the retention of the original carbides (SiC and WC) in various combinations. The chromium and nickel stabilized the austenite and ferrite but reduced the formation of martensite that is useful to increase the hardness and prevent cracking. Also, the substantial dissociation of the original carbides (SIC and WC) into elemental silicon and tungsten supplemented the stabilization of ferrite and reduction in the hardness. The presence of the undissociated carbides and some martensite formation provided substantial increases in the microhardness. The improvement of both the mechanical properties and corrosion resistance might be self-exclusive due to the reduction of the carbides and the subsequent inability of the matrix to prevent cracking.     

Purification and crystallization of complexes modeling the active state of the fragile histidine triad protein

Fragile histidine triad protein (Fhit) is a diadenosine triphosphate (ApppA) hydrolase encoded at the human chromosome 3 fragile site which is frequently disrupted in tumors. Reintroduction of FHIT coding sequences to cancer cell lines with FHIT deletions suppressed the ability of these cell lines to form tumors in nude mice even when the reintroduced FHIT gene had been mutated to allow ApppA binding but not hydrolysis. Because this suggested that the tumor suppressor activity of Fhit protein depends on substrate-dependent signaling rather than ApppA catabolism, we prepared two crystalline forms of Fhit protein that are expected to model its biologically active, substrate-bound state. Wild-type and the His96Asn forms of Fhit were overexpressed in Escherichia coli, purified to homogeneity and crystallized in the presence and absence of ApppA and an ApppA analog. Single crystals obtained by vapor diffusion against ammonium sulfate diffracted X-rays to beyond 2.75 A resolution. High quality native synchrotron X-ray data were collected for an orthorhombic and a hexagonal crystal form.      

Effect of annealing on the optical quality of AgGaS2 and AgGaSe2 single crystals

Single crystals of AgGaS₂ and AgGaSe₂ were grown by a modified Bridgman-Stockbarger technique. Pieces of sizes 10 mm × 6 mm × 4 mm and 11 mm × 6 mm × 5 mm of AgGaS₂ and AgGaSe₂ free from lamellar twins, were cut from the crystals for detailed investigations. The results of infrared transmittance and absorbance measurements indicate that the optical quality of the annealed crystals was much better than that of the as-grown crystals. Experiments on thermal etching were also carried out to study the microscopic defects in the crystals.