Analytical expression for Risken-Nummedal-Graham-Haken instability threshold in quantum cascade lasers.

We have obtained a closed-form expression for the threshold of Risken-Nummedal-Graham-Haken (RNGH) multimode instability in a Fabry-Pérot (FP) cavity quantum cascade laser (QCL). This simple analytical expression is a versatile tool that can easily be applied in practical situations which require analysis of QCL dynamic behavior and estimation of its RNGH multimode instability threshold. Our model for a FP cavity laser accounts for the carrier coherence grating and carrier population grating as well as their relaxation due to carrier diffusion. In the model, the RNGH instability threshold is analyzed using a second-order bi-orthogonal perturbation theory and we confirm our analytical solution by a comparison with the numerical simulations. In particular, the model predicts a low RNGH instability threshold in QCLs. This agrees very well with experimental data available in the literature.

Comparative ultrastructural studies on mitochondrial pathology in the liver of AIDS patients: clusters of mitochondria, protuberances, "minimitochondria," vacuoles, and virus-like particles.

The present comparative conventional electron microscopic studies of the liver biopsy in 20 AIDS patients revealed numerous disintegrated mitochondria in hepatocytes, Kupffer cells lymphocytes, and eosinophile leukocytes. It was observed that (1) AIDS mitochondria are clustered, disorganized, and with protuberances; (2) the number of cristae is reduced and they are branched dichotomously; (3) vacuoles are located both within the mitochondria and, in their vicinity, (4) " minimitochondria" are within the ordinary mitochondria; (5) virus-like particles are at the periphery of electron-dense mitochondrial remains.

[Characteristics of arterial blood pressure responses in the treadmill stress test in patients with post-traumatic stress disorder during the war in Sarajevo]. / Karakteristike odgovora arterijskog krvnog pritiska na opterecenje na pokretnom sagu kod pacijenata sa post-traumatskim stres poremecajem (PTSP) u Sarajevu tokom ratnog perioda.

The health problems associated with PTSD include multiple physical symptoms and signs. It was observed that PTSD was often accompanied with cardiovascular problems. The aim of this study was to estimate the characteristics of arterial blood pressure response on stress exercise in PTSD patients who were forced to stay in a war zone of Sarajevo. This study was carried out in 1995, during the period of intensive war activities in Sarajevo. Exercise stress testing was performed on treadmill, under the Bruce protocol in age matched 9 male PTSD patients and 14 healthy young volunteers (age 18-23 years). Arterial blood pressure was obtained by the cuff method in rest, at the last minute of each exercise stage and four times in the recovery period (1, 3, 6 and 9 minutes). Our results did not confirm previous reports related to the resting values of arterial blood pressure in PTSD patients. In rest, there were no significant differences in systolic, diastolic and mean arterial pressure between PTSD and control group. Systolic blood pressure (SBP) increased during exercise in both groups, especially at advanced exercise stages. Maximal mean SBP values were 222.00 +/- 24.80 mm Hg (control group), and 179.80 +/- mm Hg (PTSD). Exaggerated systolic blood pressure response (over 200 mm Hg) was observed only in the control group. This is probably due to physiological hyperreactive with enhanced sympathetic activity in response to stress caused by war. The luck of hyperreactive response in PTSD patients could be explained by diminished sympathetic influence on systolic blood pressure probably caused by psychoactive medication.

Diapedesis of thrombocytes from capillary into the intercellular space of interscapular brown adipose tissue and their increase by Ca-Sandoz.

Diapedetic capacity of the rat thrombocytes to leave capillaries of the interscapular brown adipose tissue (IBAT) and infiltrate the interstitium has been observed by conventional electron-microscopy. Thrombocytes that reach IBAT interstitium are morphologically completely different from lumenary ones. The interstitial thrombocyte has a prominet head region (1.51 x 2.12 microns) and very long phylopodium (3.43 microns). Experimental conditions which induced drastic changes in morphology of interstitial thrombocytes were: sucrose overfeeding (10% over 2 days); a 24 hour starving after sucrose overfeeding and Ca-Sandoz drinking (480 mg/L Ca2+ during 2 days). The thrombocytes in the IBAT interstitium can be classified as activated according to: a) pseudopode extension; b) swollen open canalicullar system (OCS); c) endocytosis via coated pits and vesicles; and d) structural changes in alpha granules excreted to the interstitium through OCS. In the IBAT interstitium of 24-hour starved rats after sucrose overfeeding, a thrombocytic layer was observed. It was suggested that thrombocyte adrenalin, stored in dense bodies, was selectively included in the IBAT supply without mediation of the central nervous system.

An attempt to establish an in vitro-in vivo correlation: case of paracetamol immediate-release tablets.

The purpose of this study was to investigate the possibility of developing different levels of in vitro-in vivo correlation for immediate-release paracetamol tablets using in vitro dissolution data obtained under various experimental conditions. The influence of agitation intensity and pH value of the dissolution media was investigated. The level B approach, using statistical moment analysis led to poor correlation results. The results obtained by numerical deconvolution in order to study level A correlation indicated that good correlation should be sought with moderate levels of agitation (beyond 50 rpm in rotating basket apparatus). Results obtained by numerical convolution showed the highest level of correlation, level A, with one-to-one relationship between observed and predicted in vivo profiles.

The influence of Eudragit type on the dissolution rate of acetylsalicylic acid from matrix tablets.

The effect of four Eudragits used as matrix substances on the physical characteristics of tablets and on the dissolution rate of acetylsalicylic acid has been investigated. The concentration of matrix substance necessary for achieving the appropriate effect of sustained release of acetylsalicylic acid (ASA) depends on the type of Eudragit used. For tablets prepared using Eudragit RS-100, Eudragit L-100-55 and Eudragit S-100, the acceptable dissolution rate of ASA was obtained with only 3% of polymer. In the case of Eudragit RL-100, to obtain the same effect, 10% of polymer was required. The dissolution data were evaluated on the basis of theoretical dissolution equations and by linear transformation of dissolution curves. The following mathematical models were employed: zero order equation, first order kinetics, Hixon-Crowell's cube root kinetics and diffusion model. The results indicated that the fitness of the kinetic model was dependent on the type of Eudragit used.

Erythrophagocytosis by brown adipocytes of rat interscapular tissue.

In this investigation the following phenomena were observed: 1. Rat interscapular brown adipocytes were found to be capable of erythrophagocytosis; 2. Before leaving the capillary lumen, erythrocytes took some material from the blood plasma by endocytosis and passed the endothelial junction carrying endocytotic vacuole. Some erythrocytes were in transit: the so-called "head" was in the process of engulfment by brown adipocytes while the rest of the cell had not left the capillary lumen. Fragmentation of erythrocytes was observed during passage through the endothelial junction as well as in the cytoplasm of adipocytes. 3. In some brown adipocytes erythrocytes retained the same shape as in the capillary, but in many cases they exhibited unusual form. Intracytoplasmic erythrocytes were seen in a semithin sections stained with toluidine blue. 4. Erythrocytes either became cells which phagocytized mitochondria and lipid droplets before their transformation into lipofuscin bodies or they were degraded into ferritin-like particles observed (on unstained sections) in the mitochondrial matrix, intercristal space, on the periphery of lipid droplets and in brown adipocyte cytoplasm.

[Effect of microwave irradiation on biological systems]. / Efekti mikrotalasnog zracenja na bioloske sisteme.

Use of microwave radiation as a source of energy has been increased in recent years. The existence of high-power microwave emitting sources, such as satellite and television communications systems, radar systems and heating devices, in both the general public and industrial environments raises the question of whether exposure to microwave radiation is detrimental to health. The use of microwave devices in home and in medicine, e.g. in clinical diagnosis and in therapy, also makes the investigation of the biological effects of acute and repetitive exposure imperative. In this work we present some characteristics of microwave radiation, and the possible effects on some systems under the conditions of different forms of microwave irradiation, on experimental animals and on the people who have been professionally or ignorantly irradiated.

A stereological investigation of rat endocrine pancreas after a long-term low-protein diet.

Stereological analysis of rat endocrine pancreas was carried out after 4 months of low-protein intake. Thirty make Wistar rats, aged 2 months at the beginning of the experiment, were divided into three groups. The control group (NP) received a standard laboratory diet. The experimental group (LP) received a low-protein diet, and the pair-fed animals also received a standard laboratory diet, as the NP rats did, but restricted to the amounts consumed by the LP group. All groups were offered drinking water ad lib. Weibel's multipurpose lattice was used to determine the volume fraction of cells and numerical density of islets in the endocrine pancreas. The results showed that the long-term low-protein diet decreased the volume fraction of B-cells and increased that of A-cells. Numerical density of islets was significantly increased, whereas the absolute number was decreased. The mean number of B-cells per islet was found to be decreased and that of D-cells increased. The mean radius of the islets was decreased, as was the mean surface area.