Mechanical and Fatigue Properties of Diamond-Reinforced Cu and Al Metal Matrix Composites Prepared by Cold Spray.

Diamond-reinforced metal matrix composites (DMMC) prepared by cold spray are emerging materials simultaneously featuring outstanding thermal conductivity and wear resistance. In our paper, their mechanical and fatigue properties relevant to perspective engineering applications were investigated using miniature bending specimens. Two different diamond mass concentrations (20 and 50%) embedded in two metal matrices (Al-lighter than diamond, Cu-heavier than diamond) were compared with the respective cold-sprayed pure metals, as well as bulk Al and Cu references. The pure Al, Cu coatings showed properties typical for cold spray deposits, i.e., decreased elastic moduli (50 GPa for Al, 80 GPa for Cu), limited ductility (< 1 × 10-3) and low fracture toughness (3.8 MPa·m0.5 for Al, 5.6 MPa·m0.5 for Cu) when compared to the bulks. Significantly improved properties (strain at fracture, ultimate strength, fatigue crack growth resistance, fracture toughness) were then observed for the produced DMMC. The improvement can be explained by a combination of two factors: changes in the properties of the metallic matrix triggered by the reinforcement particles peening effect and stress redistribution due to the particles presence.

Positron annihilation spectroscopy study of radiation-induced defects in W and Fe irradiated with neutrons with different spectra.

The paper presents new knowledge on primary defect formation in tungsten (W) and iron (Fe) irradiated by fission and high-energy neutrons at near-room temperature. Using a well-established method of positron-annihilation lifetime-spectroscopy (PALS), it was found that irradiation of W in the fission reactor and by high-energy neutrons from the p(35 MeV)-Be generator leads to the formation of small radiation-induced vacancy clusters with comparable mean size. In the case of Fe, smaller mean size of primary radiation-induced vacancy clusters was measured after irradiation with fission neutrons compared to irradiation with high-energy neutrons from the p(35 MeV)-Be generator. It was found that one of the reasons of the formation of the larger size of the defects with lower density in Fe is lower flux in the case of irradiation with high-energy neutrons from the p(35 MeV)-Be source. The second reason is enhanced defect agglomeration and recombination within the energetic displacement cascade at high energy primary knock-on-atoms (PKAs). This is consistent with the concept of the athermal recombination corrected (arc-dpa) model, although the measured dpa cross-section of both fission neutrons and wide-spectrum high-energy neutrons in W is between the conventional Norgett-Robinson-Torrens (NRT-dpa) and arc-dpa predictions. This means that the physics of the primary radiation effects in materials is still not fully known and requires further study through a combination of modeling and experimental efforts. The present data serve as a basis for the development of an improved concept of the displacement process.

Increasing Fatigue Endurance of Hydroxyapatite and Rutile Plasma Sprayed Biocomponents by Controlling Deposition In-Flight Properties.

Three sets of hydroxyapatite and rutile-TiO2 coatings were plasma sprayed onto metallic substrates. The spray parameters of the sets were modified so as to obtain different in-flight temperatures and velocities of the powder particles within the plasma jet (ranging from 1778 to 2385 K and 128 to 199 m s-1, respectively). Fatigue endurance of the coated specimens was then tested. The samples were subjected to a symmetric cyclical bend loading, and the crack propagation was monitored until it reached a predefined cross-section damage. The influence of the coating deposition was evaluated with respect to a noncoated reference set and the in-flight characteristics. Attributed to favorable residual stress development in the sprayed samples, it was found that the deposition of the coatings generally led to a prolongation of the fatigue lives. The highest lifetime increase (up to 46% as compared to the noncoated set) was recorded for the coatings deposited under high in-flight temperature and velocity. Importantly, this was achieved without significantly compromising the microstructure or phase composition of the deposited HA and TiO2 layers.

Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations.

Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime, which is shorter than the CdTe bulk lifetime. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities.

Novel neuroimaging findings in a patient with cerebral Whipple's disease: a magnetic resonance imaging and positron emission tomography study.

The authors report a 43-year-old patient with histopathologically proven cerebral Whipple's disease. Magnetic resonance imaging (MRI) revealed a multilayered left frontal lesion without mass effect, no perifocal brain edema, no contrast enhancement, and a thin shell of fluid signal that presented as an incomplete, open ring. An [11C]methionine positron emission tomography (PET) study showed low uptake below the threshold that is characteristic for brain tumors. In precise co-registration to the MR images, the PET data showed that increased uptake was mainly located in the direct adjacent part of the MRI lesion. The fluid signal on MRI corresponded to the extensive outflow of fluid from the lesion, which was observed during neurosurgical resection, and also to the neuropathological findings. The authors conclude that this cerebral manifestation of Whipple's disease made a unique and hitherto undescribed appearance on MRI; uptake pattern of PET amino acid tracer may help in the preoperative distinction of inflammatory from neoplastic lesions.

[Viral hepatitis in users of addictive drugs in the Czech Republic]. / Virové hepatitidy u problémových uzivatelu návykových látek v CR.

INTRODUCTION: Prevalence of viral hepatitis A-C markers in problematic drug users was studied. MATERIAL AND METHODS: Two groups of drug users, i.e. addicts enrolled in a mid-term drug withdrawal community program (group 1) and penitentiary prisoners (group 2), were tested for the presence of viral hepatitis A-C markers. Group 1 of 546 addicts (335 males and 211 females) included 163 male and 91 female injection drug users (IDUs) and 172 male and 120 female mostly alcohol abusers. Group 2 of 197 male prisoners included 150 injection drug users and 47 mostly alcohol abusers. Serological markers of viral hepatitis were detected by EIA within the entry check-up; RT PCR was used for detection of HCV nucleic acid. RESULTS: The prevalence rates of anti-HAV antibodies among group 1 addicts were 33.6% for IDUs and 39.5% for the remaining mostly alcohol abusers. HBsAg was found in 4.2% of IDUs and 0.0% in the remaining addicts. Two IDUs also tested positive for HBeAg. Anti-HCV positivity was recorded in 22.4% of IDUs and 5.6% of the remaining addicts. The prevalence rates of anti-HAV antibodies among group 2 penitentiary prisoners were 40.7% for IDUs and 28.6% for the remaining mostly alcohol abusers. Anti-HAV IgM antibodies were detected in 4.2% prisoner IDUs. HBsAg was found in 3.4% of IDUs and 6.5% in the remaining addicts. Anti-HCV positivity was recorded in 18.1% of IDUs and 16.3% of the remaining addicts. CONCLUSION: The prevalence rates of the markers studied in the addicts are several times as high as in the general population; therefore, the population of addicts is a potential source of the spread of viral hepatitis.

Brain studies--image co-registration and template creation.

Image co-registration requires special software, which is usually available for Unix workstations. This work presents two programs running under MS Windows, one for study co-registration and one for template creation. The co-registration can be done by minimising/maximising the count difference, squared difference, shape and mutual information. The quality of the fit can be estimated by evaluating the contours with different tools. The aligned images can be used for template creation. Both programs can be downloaded from http://www.homolka.cz/nm.

WKB approach to calculating the lifetime of quasistationary states.

A novel WKB approach to calculating the lifetime of quasistationary states in the potential wells of the form V(x)=P(x)-muQ(x), where P(x) is the radial part of the potential for the spherically symmetric harmonic oscillator or the hydrogen atom and Q(x) is a polynomial, is suggested. In this approach, the usual explicit procedure of the asymptotic matching of the perturbative and WKB wave functions is avoided and a simple formula for the imaginary part of the energy is found. The leading and the first correction terms for the imaginary part of the energy and the related lifetime are analytically calculated.