Effect of Sintering Duration on Some Properties of Pure Magnesium

Powder Metallurgy and Metal Ceramics - Tribological and physical properties of pure magnesium (Mg) are investigated during sintering for 2, 4, and 6 h at the temperature of 600°C. The pure...     

The elasto-plastic impact analysis of functionally graded circular plates under low-velocities

In this study, three-dimensional elasto-plastic analysis of functionally graded (FG) circular plates under low-velocity impact loads is presented. The FG circular plate is composed of ceramic (SiC) and metal (Al) phases, varying in a predetermined fashion through the plate thickness. The elasto-plastic behaviour of the FG circular plate is described by the TTO model. In the analyses, the ceramic phase is taken to be an isotropic elastic material whereas the metal phase is taken to be elasto-plastic material in accordance with the TTO model. The locally effective material properties were evaluated using homogenization method which is based on the Mori–Tanaka scheme. The effects of compositional gradient exponent and impactor velocity on the elasto-plastic impact response of the FG circular plates are investigated, and results are presented graphical form. The compositional gradient exponent and impactor velocity have significant effects on the elasto-plastic impact response of the FG circular plates. The elasto-plastic impact response of FG circular plates is similar to those of homogeneous plates. Therefore, the TTO model can be used to describe the mechanical behaviour of FG plates beyond the elastic range, assuming that the material response is essentially governed by the spreading of plasticity in the metal phase.     

Activation of cysteine proteases in cowpea plants during the hypersensitive response--a form of programmed cell death

The matrix metalloproteinases appear to play a key role in mammary tissue remodeling during involution. By immunoprecipitation and immunoblot using antibodies against 60K gelatinase which appears during involution a 90K polypeptide has been identified as its inactive proenzyme in the early involuting rat mammary gland. 90K polypeptide was isolated from the second day involuting rat mammary gland by immunoaffinity chromatography. On proteolytic digestion, the inactive 90K polypeptide was converted to active gelatinase. Primary cultures of mammary epithelial cells secreted the 90K polypeptide. These results indicated that the 60K inducible MMP involved in mammary gland involution and remodeling is produced as a 90K proenzyme which is activated by proteolysis in the extracellular sites.     

Benzodiazepine use and cognitive function among community-dwelling elderly

OBJECTIVE: To evaluate the relation between benzodiazepine use and cognitive function among community-dwelling elderly. METHODS: This prospective cohort study included 2765 self-reporting subjects from the Duke Established Populations for Epidemiologic Studies of the Elderly. The subjects were cognitively intact at baseline (1986-1987) and alive at follow-up data collection 3 years later. Cognitive function was assessed with the Short Portable Mental Status Questionnaire (unimpaired versus impaired and change in score) and on the basis of the number of errors on the individual domains of the Orientation-Memory-Concentration Test. Benzodiazepine use was determined during in-home interviews and classified by dose, half-life, and duration. Covariates included demographic characteristics, health status, and health behaviors. RESULTS: After control for covariates, current users of benzodiazepine made more errors on the memory test (beta coefficient, 0.35; 95% confidence interval [CI], 0.10 to 0.61) than nonusers. Further assessment of the negative effects on memory among current users suggested a dose response in which users taking the recommended or higher dose made more errors (beta coefficient, 0.57; 95% CI, 0.26 to 0.88) and a duration response in which long-term users made more errors (beta coefficient, 0.39; 95% CI, 0.05 to 0.73) than nonusers. Users of agents with long half-lives and users of agents with short half-lives both had increased memory impairment (beta coefficient, 0.32; 95% CI, 0.01 to 0.64 and beta coefficient, 0.38; 95% CI, 0.02 to 0.75, respectively) relative to nonusers. Previous benzodiazepine use was unrelated to memory problems, and current and previous benzodiazepine use was unrelated to level of cognitive functioning as measured with the other 4 tests. CONCLUSIONS: The results suggested that current benzodiazepine use, especially in recommended or higher doses, is associated with worse memory among community-dwelling elderly.     

Identification of a novel endogenous memory facilitating cyclic dipeptide cyclo-prolylglycine in rat brain

Using high-performance liquid chromatography, gas-chromatography and chromato-mass spectrometry methods a novel endogenous cyclic dipeptide cyclo-prolylglycine was identified in rat brain. Its content according to gas chromatography is 2.8 +/- 0.3 nmol/g wet brain. Synthetic cyclo-prolylglycine has demonstrated antiamnesic activity in the passive avoidance test in rats at a dose of 0.1 mg/kg i.p. Cyclic dipeptide cyclo-prolylglycine seems to be a memory facilitating substance and its presence in rat brain suggests the existence of a new mechanism of memory regulation.     

Epithelial V-like antigen (EVA), a novel member of the immunoglobulin superfamily, expressed in embryonic epithelia with a potential role as homotypic adhesion molecule in thymus histogenesis

Granule cells in the rat hippocampal dentate gyrus contain intracellular receptors for the adrenal hormone corticosterone. Activation of these receptors seems essential for granule cell viability, since removal of the adrenal gland (adrenalectomy) results within three days in apoptotic-like degeneration of granule cells. In the present study we used extracellular in vitro recording methods to study the synaptic transmission in the dentate gyrus of adrenalectomized animals, in sham-operated controls and adrenalectomized rats treated with a low dose of corticosterone. We found that particularly three days after adrenalectomy orthodromic field responses in the dentate gyrus were reduced in amplitude. Corticosterone-treated rats did not show this impairment of synaptic transmission. Antidromically-evoked field responses were also reduced after adrenalectomy, which indicates that postsynaptic cell properties rather than signal transduction in the synapses are under steroid control. Responses to paired pulse stimulation were only marginally affected, suggesting that interneuronal networks may be less affected by the hormones than the principal cells. These electrophysiological data indicate that adrenalectomy induced apoptotic-like degeneration in the hippocampal dentate gyrus is clearly associated with impaired processing of incoming information.     

The role of operative arthroscopy for the diagnosis and treatment of lesions about the distal ulna

Operative arthroscopy of the wrist compliments the physical examination and radiographic imaging to improve diagnosis and treatment of lesions about the distal ulna. This article reviews the relevant anatomy, biomechanics, and classification of acute and degenerative lesions of the triangular fibrocartilage complex (TFCC). Minimally invasive diagnostic and management techniques for TFCC tears are described in detail.     

Efficacy of anterior, posterior and total fundoplication in an experimental model

BACKGROUND: This study examined the effect of different types of laparoscopic fundoplication on an incompetent lower oesophageal sphincter to test their effectiveness at preventing gastro-oesophageal reflux in the early postoperative period. METHODS: An experimental porcine model was used. Initial oesophageal myotomy ensured an incompetent lower oesophageal sphincter with free reflux of 'intragastric fluid'. Anterior, posterior or total fundoplication was then performed laparoscopically in 15 laboratory pigs (five in each group). Fundoplication competence and efficacy were determined 2 weeks after laparoscopic antireflux surgery by inflating the stomach with liquid through a gastrostomy cannula. Some animals were also studied at 4 and 6 weeks. Lower oesophageal sphincter pressure was determined using a water-perfused oesophageal manometry catheter incorporating a Dent sleeve. RESULTS: All three types of fundoplication produced similar increases in postoperative resting lower oesophageal sphincter pressure and restored adequate competence to the gastro-oesophageal junction. CONCLUSION: All three variants of laparoscopic fundoplication restore gastro-oesophageal competence in the early postoperative period.