A ring R is called almost-quasi-commutative if for each x, y ∈ R there exist nonzero relatively prime integers j = j(x, y) and k = k(x, y) and a non-negative integer n = n(x, y) such that jxy = k(yx)n. We establish some general properties of such rings, study commutativity of almost-quasi-commutative R, and consider several examples.
Authors:C. L. Beaudry, L. C. Klein, and R. A. McCauley
Thermogravimetric analyses of sol-gel derived silica and silica-poly(vinyl acetate) (PVAc) materials show that the loss in weight between 35 and 900°C can be attributed to three distinct reactions. Samples were prepared by dissolving the reactants tetraethyl orthosilicate (TEOS), poly(vinyl acetate) (PVAc), and water in mixtures of ethanol and formamide. The lowest temperature weight loss is due to the decomposition/removal of the solvents, while the intermediate weight loss corresponds to decomposition of the PVAc. The highest temperature weight loss is related to the dehydroxylation of the silica surface. The relative amounts of ethanol and formamide have a considerable effect on processing time, drying behavior, and the resulting thermal behavior of the gels.
Authors:Á. Klein, Margit Kulcsár, Virág Krízsik, R. Mátics, P. Rudas, J. Török, and Gy. Huszenicza
The basic patterns of thyroid hormones [thyroxine (T4) and 3,3',5-triiodothyronine (T3)] and the T4 and T3 responses induced by thyrotropin releasing hormone (TRH) are reported in captive female barn owls (Tyto alba) during the non-breeding period. The main findings of the study, conducted on a total of 10 owls, are as follow: (1) The thyroid gland of barn owl can be stimulated by the classical TRH stimulation test. (2) T3 response was much more pronounced both under cold (around 10°C) and warm (around 20°C) conditions, whereas T4 response ranged so widely that we could not point out any significant change in it. (3) Basal T3 plasma level was significantly (p = 0.036) higher in birds exposed to cold temperature, and they responded to TRH treatment with a lower plasma T3 elevation than the birds kept in a warm chamber. This pattern, however, cannot be explained by increased food intake, but is in agreement with the fact that enhanced T3 level may account for higher avUCP mRNA expression, which results in higher heat production on the cell level. From the results it is concluded that altering T3 plasma level plays a significant role in cold-induced thermoregulation.
Authors:Andrei Jitianu, Kristin Lammers, Georgia A. Arbuckle-Kiel, and Lisa C. Klein
Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted siloxane and a di-substituted siloxane, methyltrimethoxysilane (MTES) together with dimethyldimethoxysilane (DMDES). Five gel compositions were prepared with concentrations between 50% MTES–50% DMDES and 75% MTES–25% DMDES (in mol.%). The consolidation temperature, the treatment temperature after which the melting gel no longer softens, increased from 135 to 160 °C with a decrease in the amount of the mono-substituted siloxane. The glass transition temperature, recorded with differential scanning calorimetry, decreased from −0.3 to −56.7 °C with a decrease in the amount of the mono-substituted siloxane. When a sample was heat treated isothermally for 2 h at the consolidation temperature, the glass transition temperature increased by about 15°, indicating further crosslinking of the siloxane network.
Authors:Peter Lukovich, A. Zsirka-Klein, T. Vanca, L. Szpaszkij, and P. Benkő
The technical background of pure Natural Orifice Translumenal Endoscopic Surgery (NOTES) surgery has not been created yet, but ever more reports are being published on hybrid NOTES surgery and single-port surgical interventions, which have appeared as a result of device development inspired by NOTES. Surgery carried out through single ports only differ from pure NOTES in respect of the access orifice, which makes learning this technique extremely important for anyone whishing to implement a surgical intervention through a natural orifice. Numerous publications have appeared by now on the single port or hybrid NOTES surgery of various organs (gall bladder, kidney, large bowel). Based on these, most surgery is safely feasible through one port as well, but the surgery takes longer and it is not significantly less painful than a “traditional” laparoscopic intervention. Long-term results are still missing, primarily in what concerns the frequency of infections and post-operative hernia. We have received an answer to part of the dilemmas formulated in the White Paper. Besides specially bent laparoscopic devices robot technology and devices controlled by extracorporal magnets may both be a solution to the problem of triangulation. The transvaginal and transgastric paths do not seem to cause significant risks from the viewpoint of infections, but the closing of viscerotomy in the case of the stomach is far from being solved. In respect of learning and practicing new surgical techniques no method exists at the moment that could be considered the “gold standard”. Besides the earlier questions there are new ones as well awaiting partial solutions (e.g. necessity of drain following a NOTES surgery, oncologic principles).
Authors:K. Zutin, V. M. Nogueira, A. E. Mauro, G. R. de Souza, and S. I. Klein
The compounds [Fe(bda)(CO)2L] and [Fe(ch)(CO)2L], (bda=benzylideneacetone; ch=chalcone; L=CO, PPh3) were investigated by thermogravimetry and derivative thermogravimetry (TG and DTG). The fragmentation patterns suggest that the iron atom protects the enone fragment, so that the organic ligands break up with the loss of the pendant aromatic rings.