Heat capacity and phonon mean free path of wurtzite GaN

We report on lattice specific heat of bulk hexagonal GaN measured by the heat flow method in the temperature range 20-300 K and by the adiabatic method in the range 5-70 K. We fit the experimental data using two temperatures model. The best fit with the accuracy of 3 % was obtained for the temperature independent Debye's temperature $\theta_{\rm D}=365$ {\rm K} and Einstein's temperature $\theta_{\rm E}=880$ {\rm K}. We relate these temperatures to the function of density of states. Using our results for heat conduction coefficient, we established in temperature range 10-100 K the explicit dependence of the phonon mean free path on temperature $\it{l}_{\rm ph}\propto T^{-2}$. Above 100 K, there is the evidence of contribution of the Umklapp processes which limit phonon free path at high temepratures. For phonons with energy $k_{\rm B}\times 300$ {\rm K} the mean free path is of the order 100 {\rm nm}Comment: 5 pages, 4 figure

Synthesis and characterization of hydroxyapatite-gelatine composite materials for orthopaedic application

The composite materials based on hydroxyapatite (HA) and gelatine (Gel) with addition of silver and zirconium oxide were obtained. The study investigates a combination of low powered ultrasonic irradiation and low concentration of gelatine in the co-precipitation synthesis. These composites have different weight ratios of organic/inorganic components and may be synthesized in two ways: simple mixing and co-precipitation. Both of which were compared. The estimation of porosity, in vivo testing, surface morphology and phase composition as well as the IR-analysis were provided. Hydroxyapatite was the main crystalline phase in obtained composites. While around powdered HA-Gel composite the connective tissue capsule is formed without bone tissue formation, HA-Gel-Ag porous composite implantation leads to formation of new bone tissue and activation of cell proliferation. Addition of silver ions into composite material allows decreasing inflammation on the first stage of implantation and has positive effect on bone tissue formation. Some of the obtained composite materials containing silver or ZrO2 are biocompatible. bio-resorbable and osteoconductive with high level of porosity (75e85%)

Structural and crystal-chemical characteristics of the apatite deposits from human aortic walls

Thermal behavior of biological apatite is the object of several studies. Crystal size, carbonate content, phase composition, and other parameters change during annealing up to 900 °C in biological minerals with apatite structure. The way these parameters change reflects the specific properties of the initial bioapatite. This work presents data on thermal transformations of pathological bioapatite from the human cardiovascular system, namely aortic wall deposits. Some minor elements, foreign to calcium hydroxyapatite (e.g., Na and Mg), can be both incorporated in the apatite structure and localized in the surface layers of crystals, modifying functions of the mineral. A new approach was proposed to determine the predominant location of minor elements, such as Mg, Na, and K, in the mineral of pathological deposits. Mg and Na in pathological apatite can be in both structurally bound (substituting calcium in lattice) and labile (localized on the crystal surface) states, while K is not able to join the apatite structure in significant amount or be chemically bound to it. This approach, based on atomic spectrometry, can be used effectively in combination with a set of traditional techniques, such as like EDS, IRS, and XRD

Low-frequency Noise in Individual Carbon Nanotube Field-Effect Transistors with Top, Side and Back Gate Configurations: Effect of Gamma Irradiation

We report on the influence of low gamma irradiation (10^4 Gy) on the noise properties of individual carbon nanotube (CNT) field-effect transistors (FETs) with different gate configurations and two different dielectric layers, SiO2 and Al2O3. Before treatment, strong generation-recombination (GR) noise components are observed. These data are used to identify several charge traps related to dielectric layers of the FETs by determining their activation energy. Investigation of samples with a single SiO2 dielectric layer as well as with two dielectric layers allows us to separate traps for each of the two dielectric layers. We reveal that each charge trap level observed in the side gate operation splits into two levels in top gate operation due to a different potential profile along the CNT channel. After gamma irradiation, only reduced flicker noise is registered in the noise spectra, which indicates a decrease of the number of charge traps. The mobility, which is estimated to be larger than 2x10^4 cm2V-1s-1 at room temperature, decreases only slightly after radiation treatment demonstrating high radiation hardness of the CNTs. Finally, we study the influence of Schottky barriers at the metal-nanotube interface on the transport properties of FETs analyzing the behavior of the flicker noise component.Comment: 19 pages, 9 figures, 1 table, accepted for publication in "Nanotechnology" journa

CLINICAL AND IMMUNOLOGICAL FEATURES OF KIDNEY TRANSPLANT RECIPIENTS WITH CYTOMEGALOVIRUS INFECTION MANIFESTATION IN THE EARLY POSTOPERATIVE PERIOD

Aim. To optimize the management of postoperative renal allograft recipients through the introduction of methods for predicting risk of manifestation of cytomegalovirus infection on the basis of a comprehensive assessment of the clinical and immunological status. Materials and methods. We retrospectively analyzed the medical records of 303 patients with end-stage renal disease, among them – were the recipients of renal allograft – 136, among whom 29 within 2 months after the operation had clinical signs of CMV infection. Assessable "CMV syndrome", laboratory evidence of CMV infection, the incidence of antigens (genes) of HLA A, B and DRB *1, calculated goodness of fit χ2 and relative risk RR, changes MCP-1 in urine. Results. In renal allograft recipients with clinical and laboratory evidence of CMV infection in the early postoperative period, significantly more (χ2 > 3,8) met antigen B35. A positive association with CMV infection was detected also for DRB1 * 08, B21, B22, B41, A24 (9), B51 (5), DRB1*14 and DRB1*15. Protective effects possessed antigens / alleles of genes A26 (10), B14, B38 (16) B61 (40) and DRB1*16. MCP-1 levels in this group of recipients were raised to 2174,7 ± 296,3 pg/ml with a strong negative correlation with the levels of urea and creatinine in serum (r = 0,9, p < 0.001). Conclusion. Immunological markers of risk manifestation of CMV infection in recipients of kidneys in the early postoperative period are: the carriage of В35 и В55,56(22), В49(21), В41, DRB1*08 и DRB1*15, an increase of levels of MCP-1 in urine without increasing the levels of urea and creatinine in the serum