The aim of this work is to study the behaviour of a crack with its tip at the interface between two polymer materials. A numerical model of a cracked bi-material tension specimen is investigated and different stability criteria are tested. The stability criterion of a general stress concentrator usually needs a relation between the critical value of the generalized stress intensity factor (HIC) and critical value of the stress intensity factor KIC (fracture toughness). This relation is a function of the elastic mismatch of particular mterials; the fracture toughness of the main material and the critical distance d ahead of the stress concentrator, where the criterion is applied. Estimation of distance d is usually not straightforward and different authors use different approaches for its determination. Therefore the main aim of this study is the mutual comparison of published approaches for d estimaton and to quantify the influence of d choice on the critical load value. The results obtained can lead to a better residual lifetime prediction and safer design of layered structures. and Obsahuje seznam literatury
Prolamellar bodies (PLBs) isolated from dark-grown, 6.5-d-old leaves of wheat (Triticum aesíivum L. cv. Kosack) were treated with the carboxylic acid cross-linker l-ethyl-3-[3-(diniethylaniino)propyl]carbodiimide (EDC) or with the lysině specific cross-linker 2-iniinothiolane. SDS-PAGE showed that the most prominenent cross- linked product was a dimer of the NADPH-protochlorophyllide oxidoreductase (PCR), but also larger aggregates of the polypeptide were identified by inununological detection on electro-blots. A two-dimensional diagonál gel showed that much of the cross-linking was between the PCR polypeptides. The cross-linkers induced a shift of the fluorescence peak to shorter wavelengths, a bandwidth increase of the fluorescence peak, and an increase of the fluorescence yield. In the presence of NADPH the blue shift was reduced, but the increase in the fluorescence yield still occmred. A cross-linker treatment of PLBs prior to solubilization with 1-0-n-octyl-P -D-glucopyranoside (octylglucoside) delayed, but did not prevent the spectral shifts from 657 to 646 nm and from 646 to 635 nm observed in non-cross-linked detergent- treated PLBs. The cross-linking did not prevent a spectral shift, corresponding to the Shibata shift, of Chlide. Thus the spectral shifts are not strictly coupled to disaggregation of the PCR polypeptides.
The proportion of proliferating erythroblasts, i.e. proerythroblasts, basophilic erythroblasts and polychromatophilic erythroblasts in blood islands of the chick embryo yolk sac, were counted during embryonic days 2-10. From day 2 when high amounts of erythroblasts signalized the onset of embryonic erythropoiesis, the percentage of less mature erythroid cells gradually decreased. Intraamniotic injection of cyclosporin A in doses 1.5 or 15.0 /rg per embryo on day 5 led to significant changes in the proportion of proliferating erythroblasts in the yolk sac blood islands. We speculate that these changes were caused initially by the release of the more mature cells into the circulation and later by a dose-dependent decrease in the number of stem cells. The estimation of proerythroblast percentage from all proliferating erythroblasts in the yolk sac blood islands may serve as a valuable indication of toxic damage in the late avian embryo.
Cardiac repolarization is prolonged in diabetes mellitus (DM), however the distribution of repolarization durations in diabetic hearts is unknown. We estimated the ventricular repolarization pattern and its relation to the ECG phenomena in diabetic mice. Potential mapping was performed on the anterior ventricular surface in healthy (n=18) and alloxan-induced diabetic (n=12) mice with the 64-electrode array. Activation times, end of repolarization times, and activation-recovery intervals (ARIs) were recorded along with limb lead ECGs. ARIs were shorter in the left as compared to right ventricular leads (P<0.05). The global dispersion of repolarization, interventricular and apicobasal repolarization gradients were greater in DM than in healthy animals (P<0.03). The increased dispersion of repolarization and apicobasal repolarization gradient in DM correlated with the prolonged QTc and Tpeak-Tend intervals, respectively. The increased ventricular repolarization heterogeneity corresponded to the electrocardiographic markers was demonstrated in DM., M. A. Vaykshnorayte, A. O. Ovechkin, J. E. Azarov., and Obsahuje seznam literatury
The effect of 3 months feeding with diets of different protein and sucrose content (9 % casein -f 70 % sucrose vs. 18 % casein + 61 % sucrose) on the development of diabetic nephropathy and changes in serum lipid spectrum was investigated in rats with insulin-dependent diabetes (streptozotocin 45 mg.kg-1). Metabolism of diabetic animals (before the nutritional regimen) was characterized by hyperglycaemia, moderate hyperlipidaemia, lipid accumulation in the liver and elevated creatinine concentration in the blood. Kidney weight and protein content were not significantly changed. Histological picture of kidneys showed initial changes of glomerular structure. After three months hyperlipoproteinaemia was more accentuated in animals given either of the two diets, the kidneys were hypertrophic with a higher protein content and displayed morphological changes of diabetic nephropathy. Animals given the low-protein diet developed smaller morphological changes both in glomeruli and tubuli. The study indicates that dietary protein and not hyperlipoproteinaemia is the major factor, which may significantly influence the progress of diabetic nephropathy.
The imbalance between nitric oxide (NO) and reactive oxygen species (ROS) production appears to be a common feature of experimental and human hypertension. Previously, different antioxidants and/or scavengers of oxygen free radicals were shown to activate nitric oxide synthase (NO synthase, NOS) and to increase the expression of both endothelial and neuronal NO synthase isoforms leading to blood pressure reduction. On the other hand, various antihypertensive drugs have been documented to possess antioxidant properties, which may contribute to their beneficial effect on blood pressure. This review is focused on the effects of antioxidant treatment in different models of
experimental hypertension with a special attention to the prevention of oxidative damage and the augmentation of NO synthase activity and expression of NOS isoforms.
The aim of the study was to determine the effect of selective dopaminergic agents [(±)-SKF-81297 (Di agonist), R(-)-2,10,ll-trihydroxy-N-propyl-noraporphine (D2 agonist), pergolid (D agonist), R( + )-SCH-23390 (Di antagonist), S(—)-eticlopride (D2 antagonist) and cis-(Z)-flupenthixol (D antagonist)] on cell-mediated immune response in vivo and in vitro and to verify the presence of dopamine receptors on murine splenocytes. The tested dopaminergic compounds exhibited a pronounced inhibitory effect on T-dependent immunity. They suppressed alloantigen-induced immune response in vivo and in vitro, IL-2 production was also markedly reduced. No substantial difference was found between the effect of dopamine agonists and antagonists or among ligands of subtypes of dopamine receptors. The effect of dopaminergic agents in vitro indicates a direct interaction with immunocompetent cells at the peripheral level. As the binding studies did not confirm the presence of dopamine receptors on splenocytes, the immunosuppressive efficacy of dopaminergic agents does not seem to be mediated via specific dopamine receptors.
DPC played an important role in regulating the production, translocation and partítioning of i‘*C-assimilates in cotton {Gossypium hirsutum L.) plants. Seed soaking with DPC increased the partítioning of cotton assimilates into roots aitd main stem, and decreased the partítioning into seedling tip which was beneficial for the seedling. After the appearance of a square, spraying with DPC decreased the partítioning of assimilates into the main stem, branches and their growing points, and increased the partítioning into reproductíve organs and roots. This helped to avoid or reduce spindling, ensured a steady growth, coordination of the relatíon between vegetatíve and reproductíve organs, and improved the development of floral buds. From bloom to boll-setting,. sprayings with DPC greatly increased the partítioning of assimilates into reproductíve organs and decreased the partítioning into vegetatíve organs, which was usefiil for the growth and development of squares and bolls.
Water-withholding for 5 to 7 weeks and subsequent re-watering were made on potted plants of two epiphytic (E) and two terrestrial (T) fern species, which were collected from a seasonal tropical rainforest and had been grown in a screenhouse with 5 % irradiance for 4 months. During the water stress, the two E species completely closed stomata when frond relative water content (RWC) reached about 70 % with fairly constant maximum photochemistry efficiency (Fv/Fm), while the two T species kept partial stomata opening until RWC reached 45 % and reduction in Fv/Fm at the late stage. Also, chlorophyll content as indicated by a spectral reflectance index was gradually reduced in three species. Physiological recovery was completed after 3-d re-watering for the E species, which was more rapid than for the T species. The gas exchange measurements and regression analyses indicated higher photosynthetic water use efficiency in the E species than in the T species. and Q. Zhang ... [et al.].
Infection and tumors provoke substantial changes accompanied with the disbalance of many neuroendocrine factors which in their summarizing effects influence the life span of animals. Our previous results showed enhanced mortality after one injection of morphine in association with Friend leukaemia virus infection. The aim of this study was to examine the effects of some other opioids (pethidine and pentazocine) and an acetylcholine esterase inhibitor neostigmine on the survival of animals under two conditions: (1) Friend leukaemia virus infection which mostly depressed immune functions, and (2) Toxoplasma gondii infection which in general enhanced the immune status. In contrast to our previous observation with morphine, the mortality induced by single doses of pethidine (150 mg/kg) or pentazocine (50-75 mg/kg) was unchanged during the Friend leukaemia virus infection. A single injection of neostigmine (0.42 or 0.56 mg/kg) was significantly more lethal in DBA-2 mice infected with Friend leukaemia virus. Neostigmine in doses of 0.33 and 0.4 mg/kg caused death in 46 % and 57 %, respectively, of animals infected with Toxoplasma gondii which was significantly higher in comparison with only 8 % and 12.5 % in control groups. Pethidine (150 mg/kg) killed 70 % of Toxoplasma gondii infected animals and even 90 % of non-infected mice. Thus, the Friend leukaemia virus and Toxoplasma gondii infections increased toxicity only of some drugs which may, at least partly, be associated with altered immune status during infection and involvement of the cholinergic system.