Thermal stability of poly(methyl methacrylate-co-butyl acrylate) and poly(styrene-co-butyl acrylate) polymers

Thermal stability of poly(methyl methacrylate-co-butyl acrylate) and poly(styrene-co-butyl acrylate) modified with a small amount of acrylic acid and/or N-methylolacrylamide as a crosslinking agent was studied in this work. Programmed thermogravimetric analysis has been used to study the effect of copolymer composition on thermal stability, over a temperature range from 50 to 450°C, under a constant flow of nitrogen. Kinetic parameters of thermal degradation, activation energy, pre-exponential factor, and reaction order were obtained by using MacCallum-Tanner's approach. Kinetic data indicate that the thermal degradation of the investigated copolymer systems is the first order reaction, and that the increase of activation energy may be an indication of thermal stability changes in copolymer systems.     

Rheological investigation of poly(vinyl alcohol)/poly(N-vinyl pyrrolidone) mixtures in aqueous solution and hydrogel state

Rheological behavior of poly(vinyl alcohol) (PVA) and poly(N-vinyl pyrrolidone) (PVP) mixtures in aqueous solutions and hydrogel state was investigated. The complex dependence of the viscosity on PVA/PVP mixture composition could be attributed to cumulative effects of electrostatic interactions, hydrogen bonding or association phenomena. Physical hydrogels were prepared by freezing/thawing method and their viscoelastic properties were followed as a function of number of cryogenic cycles and aging time at 37 °C. From swelling experiments, it was observed that the diffusion of water molecules into the hydrogel pores is Fickian (for low number of cryogenic cycles) and it becomes pseudo-Fickian as the sample is submitted to more than 10 freezing/thawing cycles. PVA/PVP hydrogels obtained by physical interactions present a high degree of tailorability and they are suitable candidates for biomedical applications.     

Towards highly available and scalable high performance clusters

In recent years, we have witnessed a growing interest in high performance computing (HPC) using a cluster of workstations. This growth made it affordable to individuals to have exclusive access to their own supercomputers. However, one of the challenges in a clustered environment is to keep system failure to the minimum and to achieve the highest possible level of system availability. High-Availability (HA) computing attempts to avoid the problems of unexpected failures through active redundancy and preemptive measures. Since the price of hardware components are significantly dropping, we propose to combine both HPC and HA concepts and layout the design of a HA-HPC cluster, considering all possible measures. In particular, we explore the hardware and the management layers of the HA-HPC cluster design, as well as a more focused study on the parallel-applications layer (i.e. FT-MPI implementations). Our findings show that combining HPC and HA architectures is feasible, in order to achieve HA cluster that is used for High Performance Computing.     

Holographic optical coherence imaging of rat osteogenic sarcoma tumor spheroids

Holographic optical coherence imaging is a full-frame variant of coherence-domain imaging. An optoelectronic semiconductor holographic film functions as a coherence filter placed before a conventional digital video camera that passes coherent (structure-bearing) light to the camera during holographic readout while preferentially rejecting scattered light. The data are acquired as a succession of en face images at increasing depth inside the sample in a fly-through acquisition. The samples of living tissue were rat osteogenic sarcoma multicellular tumor spheroids that were grown from a single osteoblast cell line in a bioreactor. Tumor spheroids are nearly spherical and have radial symmetry, presenting a simple geometry for analysis. The tumors investigated ranged in diameter from several hundred micrometers to over 1 mm. Holographic features from the tumors were observed in reflection to depths of 500-600 microm with a total tissue path length of approximately 14 mean free paths. The volumetric data from the tumor spheroids reveal heterogeneous structure, presumably caused by necrosis and microcalcifications characteristic of some human avascular tumors.     

State dependence and trait stability of perfectionism: A short-term longitudinal study.

The authors examined state dependency on depression, trait stability, and state-trait characteristics of perfectionism in a short-term longitudinal study of university students. Relative stability of perfectionism was assessed with test-retest correlations across 3 time points, and results showed higher rank order and relative stability for perfectionism scores compared with depression scores. Regression and path analyses to disentangle directions of effects revealed that initial maladaptive perfectionism scores remained robust predictors of later perfectionism scores, even after the authors controlled for prior and concurrent depression and other dimensions of perfectionism. Perfectionism proved to be quite stable and was a significant predictor of later depression. Perfectionism was also not meaningfully altered by state changes in depression. The overall findings indicate that perfectionism appears to have substantial relative stability, and perfectionistic discrepancy in particular is a clear vulnerability factor for depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing Ti-25Ta-5Zr Bioalloy via Anodic Oxidation Procedure at High Voltage

The current paper reports the processing of Ti-25Ta-5Zr bioalloy via anodic oxidation in NH4BF4 solution under constant potentiostatic conditions at high voltage to obtain more suitable properties for biomedical application. The maximum efficiency of the procedure is reached at highest applied voltage, when the corrosion rate in Hank’s solution is decreased approxomately six times. The topography of the anodic layer has been studied using atomic force microscopy (AFM), and the results indicated that the anodic oxidation process increases the surface roughness. The AFM images indicated a different porosity for the anodized surfaces as well. After anodizing, the hydrophilic character of Ti-25Ta-5Zr samples has increased. A good correlation between corrosion rate obtained from potentiodynamic curves and corrosion rate from ions release analysis was obtained.     

Study on gingival tissue reaction to the materials used for making dental prosthesis

Fixed prosthetic restorations may generate periodontal irritation by various and complex mechanisms especially in the presence of the microbial factor. In this regard, changes that compromise the functional value of the support structures of the teeth occur. Studies on patients wearing fixed denture show that those prosthetic structures facilitate plaque accumulation. Close supervision leads to prevention of periodontal diseases, through learning of a proper hygiene. Between the marginal periodontium and the prosthetic restoration, there must be a relation of ‘mutual protection’ or at least ‘mutual respect’. In this study, we tried to analyze the reaction of the periodontal tissue in contact with fixed prosthesis depending on the prosthetic material used. There were 102 fixed prostheses considered by this study that have generated reactions in the periodontal tissues with which came into contact. Thus, from the total number of 102 fixed dental prostheses, 75% were made from metal alloys based on copper, 18% from Cr–Ni alloys, 2% from Cr–Co alloys, 4% from gold alloys, and one from stainless steel. In 35% of the cases, the patients had multiple fixed dentures made from different types of dental alloys, cases in which the symptoms of the periodontal problems may be also linked to the phenomenon of oral galvanism. The histological study showed various morphological changes from one patient to another, depending on the intensity of the inflammatory and reparative response, the associated diseases (diabetes, dyslipidemia, cardiovascular diseases) and especially on the dental hygiene status. Fixed prosthesis, in the absence of a proper cervical adaptation and an adequate local hygiene, may act as an irritative thorn and may induce gingivitis and periodontitis phenomena.     

Morphological and molecular pathology of CCL4‐induced hepatic fibrosis in connexin43‐deficient mice

Gap junction channels, formed by connexins (Cx), are involved in the maintenance of tissue homeostasis, cell growth, differentiation, and development. Several studies have shown that Cx43 is involved in the control of wound healing in dermal tissue. However, it remains unknown whether Cx43 plays a role in the control of liver fibrogenesis. Our study investigated the roles of Cx43 heterologous deletion on carbon tetrachloride (CCl₄)‐induced hepatic fibrosis in mice. We administered CCl₄ to both Cx43‐deficient (Cx43^+/?) and wild‐type mice and examined hepatocellular injury and collagen deposition by histological and ultrastructural analyses. Serum biochemical analysis was performed to quantify liver injury. Hepatocyte proliferation was analyzed immunohistochemically. Protein and messenger RNA (mRNA) expression of liver connexins were evaluated using immunohistochemistry as well as immunoblotting analysis and quantitative real‐time PCR. We demonstrated that Cx43^+/? mice developed excessive liver fibrosis compared with wild‐type mice after CCl₄‐induced chronic hepatic injury, with thick and irregular collagen fibers. Histopathological evaluation showed that Cx43^+/? mice present less necroinflammatory lesions in liver parenchyma and consequent reduction of serum aminotransferase activity. Hepatocyte cell proliferation was reduced in Cx43^+/? mice. There was no difference in Cx32 and Cx26 protein or mRNA expression in fibrotic mice. Protein expression of Cx43 increased in CCl₄‐treated mice, although with aberrant protein location on cytoplasm of perisinusoidal cells. Our results demonstrate that Cx43 plays an important role in the control and regulation of hepatic fibrogenesis. Microsc. Res. Tech., 2011. © 2010 Wiley‐Liss, Inc.     

The Multiple Gyrotron System on the DIII-D Tokamak

The electron cyclotron heating and current drive complex on the DIII-D tokamak presently comprises six gyrotrons injecting rf power from the low field side at 110 GHz, the 2f _ce resonance at the center of the vacuum chamber. Typical injected rf power is 600–650 kW per gyrotron. The launched rf can be directed over ±20° toroidally to create both co- and counter-current drive and scanned over 40° poloidally to permit the injected rf beams to intersect, and be absorbed at, the second harmonic resonance anywhere in the tokamak upper half plane. The elliptical polarization is controlled so that the desired extraordinary or ordinary modes are excited for any injection geometry. The maximum injected energy on a single plasma shot has been 16.6 MJ for six gyrotrons injecting a total of 3.4 MW for 5 seconds.