Lubricated sliding wear behaviour of aluminium alloy composites

Interest in aluminium alloy (Al-alloy) composites as wear resistant materials continues to grow. However, the use of the popular Al-alloy-SiC composite can be limited by the abrasive nature of the SiC, leading to increased counterface wear rates. This study reports new Al-alloy composites that offer high wear resistance, to a level similar to Al-alloy-SiC. Aluminium alloy (2124, 5056) matrix composites reinforced by nominally 15 vol.% of Cr3Si, MoSi2, Ni3Al and SiC particles were prepared by a powder metallurgy route. The aluminium alloy matrix was produced by gas atomisation, and the Cr3Si, MoSi2 and Ni3Al were prepared by self-propagating high temperature synthesis (SHS), while the SiC was from a standard commercial supply. Following blending, the particulates were consolidated by extrusion, producing a homogenous distribution of the reinforcement in the matrix. Wear testing was undertaken using a pin-on-ring configuration against an M2 steel counterface, with a commercial synthetic oil lubricant, at 0.94 m/s and a normal load of 630 N, corresponding to initial Hertzian contact pressures of 750–890 MPa (the exact value depending on the material properties). Specific wear rates at sliding distances exceeding 400 km were in the range 4.5–12.7 × 10?10 mm3/Nm. The monolithic alloys gave the highest specific wear rates, while the MoSi2 and Cr3Si reinforced alloys exhibited the lowest. The worn surface has been analysed in detail using focused ion beam (FIB) microscopy to determine the sub-surface structural evolution and by tomographic reconstruction of tilted scanning electron microscopy (SEM) images, to determine the local worn surface topography. Consequently, the wear mechanisms as a function of alloy composition and reinforcement type are discussed.<br/

COLD COMPACTING OF UOsub2sub 2 + ZrHsub2sub 2 FUEL PELLETS FOR CRITICAL EXPERIMENTS

This describes about Cold Compacting of Uo$Sub 2$ + Zrh$Sub 2$ Fuel Pellets for Critical Experiments

Human acylpeptide hydrolase. Studies on its thiol groups and mechanism of action.

The presence of a cysteine residue(s) near the active site of acylpeptide hydrolase was suggested by inactivation of the enzyme with sulfhydryl-modifying agents and by the substantial protection against inactivation afforded by the competitive inhibitor acetylmethionine. 5,5'-dithiobis-(2-nitrobenzoate) titrations of the native and the denatured enzyme together with analysis for cysteic acid after performic acid oxidation showed that the enzyme contained 12 free SH groups and three disulfide bonds/monomer. Chemical modification with radiolabeled iodoacetamide led to the labeling of Cys-30 and Cys-64 suggesting that one or both of these Cys residues are close to the active site. Modification of one or both of them probably inhibits the enzyme either because of a distortion of the active site or because the adducts present a barrier to the efficient diffusion of substrates into and products out of the active site. Studies on the mechanism of action of acylpeptide hydrolase have employed p-nitrophenyl-N-propyl carbamate as a potent active site-directed inhibitor. Enzyme inactivation, which follows pseudo first-order kinetics, is diminished by the competitive inhibitor acetylmethionine. The inhibited enzyme slowly regains activity at a rate that is increased in the presence of the nucleophile hydroxylamine. A general mechanism involving an acyl-enzyme intermediate is supported by evidence for the formation of acetyl-alanyl hydroxamate during hydrolysis of acetyl-alanine p-nitroanilide in the presence of hydroxylamine. The effect on Vmax and Km during this reaction indicate that hydrolysis of the acyl-enzyme intermediate is rate-limiting

Bi flux-dependent MBE growth of GaSbBi alloys

AbstractThe incorporation of Bi in GaSb1−xBix alloys grown by molecular beam epitaxy is investigated as a function of Bi flux at fixed growth temperature (275°C) and growth rate (1μmh−1). The Bi content is found to vary proportionally with Bi flux with Bi contents, as measured by Rutherford backscattering, in the range 0<x≤4.5%. The GaSbBi samples grown at the lowest Bi fluxes have smooth surfaces free of metallic droplets. The higher Bi flux samples have surface Bi droplets. The room temperature band gap of the GaSbBi epitaxial layers determined from optical absorption decreases linearly with increasing Bi content with a reduction of ~32meV/%Bi

Narrowband UVB phototherapy for clinically isolated syndrome: A trial to deliver the benefits of Vitamin D and other UVB-Induced molecules

Low vitamin D and insufficient sun exposure are additive independent risk factors for the development of multiple sclerosis (MS). The usual measure of vitamin D status, serum 25-hydroxy vitamin D [25(OH)D], is also a marker of recent exposure to the UVB rays of sunshine. The main evidence for a protective effect for MS development of higher 25(OH)D comes from observational studies, but this study design cannot separate out whether 25(OH)D is acting as a marker of vitamin D status, sun exposure, or both. In light of a lack of definitive outcomes in MS patients after trials of vitamin D supplementation and the ability of narrowband UVB to induce vitamin D, as well as other immune-regulatory molecules in skin, the Phototherapy for Clinically Isolated Syndrome (PhoCIS) trial was established to investigate the benefits of narrowband UVB, in addition to supplemented vitamin D, on MS development in individuals with Clinically Isolated Syndrome. We propose that the PhoCIS trial provides a fresh approach to re-defining the reported associations of 25(OH)D levels with MS development and progression

Effects of Methylene Blue and Polyethelene Glycol on Facial Nerve Axotomy Recovery

poster abstractInjury and disease are common factors affecting peripheral nerves and can lead to loss of function. Recovery time after an injury is slow and not very efficient in humans. Treatment methods involving methylene blue (MB) and polyethylene glycol (PEG) have shown combinational effects in sciatic nerve axotomies. We are using behavior analysis of eye blink reflex and vibrissae orientation and movement as a measurement of rate of functional recovery. We will have treatment groups of both cut and crush rats. For each group we will be testing the effect of PEG/MB or no treatment control groups. The results of these treatment groups are significant to finding treatment options for clinical use

A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35Cl, 113Cd, and 139La

An apparatus for measuring parity-violating asymmetries in gamma-ray emission following polarized cold neutron capture was constructed as a 1/10th scale test of the design for the forthcoming n+p->d+gamma experiment at LANSCE. The elements of the polarized neutron beam, including a polarized 3He neutron spin filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl) detectors and photodiode current mode readout, measurements were made of asymmetries in gamma-ray emission following neutron capture on 35Cl, 113Cd, and 139La targets. Upper limits on the parity-allowed asymmetry $s_n \cdot (k_{\gamma} \times k_n)$ were set at the level of 7 x 10^-6 for all three targets. Parity-violating asymmetries $s_n \cdot k_{\gamma}$ were observed in 35Cl, A_gamma = (-29.1 +- 6.7) x 10^-6, and 139La, A_gamma = (-15.5 +- 7.1) x 10^-6, values consistent with previous measurements.Comment: 19 pages, 4 figures, submitted to Nucl. Instr. and Meth.

Acylpeptide hydrolase: inhibitors and some active site residues of the human enzyme.

Acylpeptide hydrolase may be involved in N-terminal deacetylation of nascent polypeptide chains and of bioactive peptides. The activity of this enzyme from human erythrocytes is sensitive to anions such as chloride, nitrate, and fluoride. Furthermore, blocked amino acids act as competitive inhibitors of the enzyme. Acetyl leucine chloromethyl ketone has been employed to identify one active site residue as His-707. Diisopropylfluorophosphate has been used to identify a second active site residue as Ser-587. Chemical modification studies with a water-soluble carbodiimide implicate a carboxyl group in catalytic activity. These results and the sequence around these active site residues, especially near Ser-587, suggest that acylpeptide hydrolase contains a catalytic triad. The presence of a cysteine residue in the vicinity of the active site is suggested by the inactivation of the enzyme by sulfhydryl-modifying agents and also by a low amount of modification by the peptide chloromethyl ketone inhibitor. Ebelactone A, an inhibitor of the formyl aminopeptidase, the bacterial counterpart of eukaryotic acylpeptide hydrolase, was found to be an effective inhibitor of this enzyme. These findings suggest that acylpeptidase hydrolase is a member of a family of enzymes with extremely diverse functions

Changes in serum neurofilament light chain levels following narrowband ultraviolet B phototherapy in clinically isolated syndrome

Objective To determine whether serum neurofilament light chain (sNfL) levels are suppressed in patients with the clinically isolated syndrome (CIS) following narrowband ultraviolet B phototherapy (UVB-PT). Methods sNfL levels were measured using a sensitive single-molecule array assay at baseline and up to 12 months in 17 patients with CIS, 10 of whom received UVB-PT, and were compared with healthy control (HC) and early relapsing remitting multiple sclerosis (RRMS) group. sNfL levels were correlated with magnetic resonance imaging total lesion volume (LV) determined using icobrain version 4.4.1 and with clinical outcomes. Results Baseline median sNfL levels were significantly higher in the CIS (20.6 pg/mL, interquartile range [IQR] 13.7–161.4) and RRMS groups (36.6 pg/ml [IQR] 16.2–212.2) than in HC (10.7 pg/ml [IQR] 4.9–21.5) (p = .012 and p = .0002, respectively), and were strongly correlated with T2 and T1 LV at 12 months (r = .800; p = .014 and r = .833; p = .008, respectively) in the CIS group. Analysis of changes in sNfL levels over time in the CIS group showed a significant cumulative suppressive effect of UVB-PT in the first 3 months (UVB-PT −10.6% vs non-UVB-PT +58.3%; p = .04) following which the levels in the two groups converged and continued to fall. Conclusions Our findings provide the basis for further studies to determine the utility of sNfL levels as a marker of neuro-axonal damage in CIS and early MS and for assessing the efficacy of new therapeutic interventions such as UVB-PT