Pučko praznovjerje i mitologija

Ukoliko netko namjerava izučavati mitologiju Slavena, on mora najprije dobro upoznati pretkršćanski religijski život starih Slavena, cijeli kršćanski život i tradiciju slavenskog prostoga puka, a naročito »pučko praznovjerje

Optimized Effective Potentials in Finite Basis Sets

The finite basis optimized effective potential (OEP) method within density functional theory is examined as an ill-posed problem. It is shown that the generation of nonphysical potentials is a controllable manifestation of the use of unbalanced, and thus unsuitable, basis sets. A modified functional incorporating a regularizing smoothness measure of the OEP is introduced. This provides a condition on balanced basis sets for the potential, as well as a method to determine the most appropriate OEP potential and energy from calculations performed with any finite basis set.Comment: 23 pages, 28 figure

Ignition of premixed air/fuel mixtures by microwave steamer discharge

A variety of methods exists for fast and efficient combustion of air-fuel mixtures. In this study, a microwave subcritical streamer discharge is used to ignite propane-air mixtures at atmospheric pressure. The streamer is initiated at the inner surface of a dielectric tube with the help of a passive half-wave vibrator. By creating a network of ignition lines, the streamer discharge forms the network of burning channels with large total surface area. This leads to the apparent speed of combustion propagation along the cylinder in excess of 100 m/s, which is more than 200 times the laminar flame propagation speed. The axial propagation of the combustion front in a cylindrical tube filled with the air/propane mixture is investigated by high speed video recording in visible light. A simple model is presented to explain observed results

INTERFERENCE OF UNIDIRECTIONAL SHOCK WAVES

Subject of study.We consider interference of unidirectional shock waves or, as they are called, catching up shock waves. The scope of work is to give a classification of the shock-wave structures that arise in this type of interaction of shock waves, and the area of their existence. Intersection of unidirectional shock waves results in arising of a shock-wave structure at the intersection point, which contains the main shock wave, tangential discontinuity and one more reflected gas-dynamic discontinuity of unknown beforehand type. The problem of determining the type of reflected discontinuity is the main problem that one has to solve in the study of catching shock waves interference. Main results.The paper presents the pictures of shock-wave structures arising at the interaction of catching up shock waves. The areas with a regular and irregular unidirectional interaction of shocks are described. Characteristic shock-wave structures are of greatest interest, where reflected gas-dynamic discontinuity degenerates into discontinuous characteristics. Such structures have a number of extreme properties. We have found the areas of existence for such shock-wave structures. There are also areas in which the steady-state solution is not available. The latter has determined revival of interest for the theoretical study of the problem, because the facts of sudden shock-wave structure destruction inside the air intake of supersonic aircrafts at high Mach numbers have been discovered. Practical significance.The theory of interference for unidirectional shock waves and design procedure are usable in the design of supersonic air intakes. It is also relevant for application possibility investigation of catching up oblique shock waves to create overcompressed detonation in perspective detonation air-jet and rocket engines

ENVIRONMENTALLY FRIENDLY METHOD OF GASEOUS FUEL COMBUSTION WITH THE USE OF QUASI-OPTICAL MICROWAVE

Subject of Research.The paper deals with the problem of developing low emission combustors operating on natural gas or LPG, to reduce emissions of nitrogen oxides NOx. The possibility of burning very lean fuel mixtures is studied. To initiate the ignition and combustion stabilization the discharge generated by the quasi-optical microwave is used. Main Results. Initiating ignition by streamer microwave discharge increases the rate of combustion and combustion efficiency about four times as compared with the conventional spark ignition. Streamer discharge ignition by very lean fuel-air mixture is demonstrated with the factor of oxiding agent excess greater than the limit of explosive range under normal conditions. According to indirect indicators, ignition by microwave discharge created by quasi-optical radiation is of non-thermal nature. Microwave discharge excites oxygen atoms, and intense ultra-violet radiation is generated as a result that causes formation of cold nonequilibrium plasma with avalanche growth of free electrons. Streamer discharge propagates at a speed of 5 km /s, so the initiation of the ignition occurs immediately throughout. The temperature of the fuel mixture at the point of ignition initiation does not exceed 400 К.There is no area with a temperature sufficient to initiate thermal Zeldovich mechanism of emission of nitrogen oxides. Combustion rate is high. As a result the Fenimore mechanism of "fast nitrogen oxides" has no chance to be progressing, and NOx emissions in appreciable quantities are excluded. Energy costs are comparable with spark ignition.Practical Relevance. The studied technology is designed for low emission internal combustion engines, power gas turbines, gas compressor units, fueled by natural gas

Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution

A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the ball milling using different technological modes. Cold and hot pressing at different conditions and also SPS process were used for consolidation of the powder into a bulk nanostructure and nanocomposites. The main factors allowing slowing-down of the growth of nanograins as a result of recrystallization are the reduction of the temperature and of the duration of the pressing, the increase of the pressure, as well as addition of small value additives (like MoS2, thermally expanded graphite or fullerenes). It was reached the thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of the thermoelectric efficiency in bulk nanocrystalline semiconductors based on BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead to improvement of the thermoelectric figure of merit. The theoretical dependence of the electric and heat conductivities and the thermoelectric power as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite accurately correlates with the experimental data.Comment: 35 pages, 24 figures, 4 tables, 52 reference

Nickel’s Role in Pancreatic Ductal Adenocarcinoma: Potential Involvement of microRNAs

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancer types with a limited overall survival rate due to the asymptomatic progression of symptoms in metastatic stages of the malignancy and the lack of an early reliable diagnostic biomarker. MicroRNAs (miRs/miRNAs) are small (~18–24 nucleotides), endogenous, non-coding RNAs, which are closely linked to the development of numerous malignancies comprising PDAC. Recent studies have described the role of environmental pollutants such as nickel (Ni) in PDAC, but the mechanisms of Ni-mediated toxicity in cancer are still not completely understood. Specifically, Ni has been found to alter the expression and function of miRs in several malignancies, leading to changes in target gene expression. In this study, we found that levels of Ni were significantly higher in cancerous tissue, thus implicating Ni in pancreatic carcinogenesis. Hence, in vitro studies followed by using both normal and pancreatic tumor cell lines and increasing Ni concentration increased lethality. Comparing LC50 values, Ni-acetate groups demonstrated lower values needed than in NiCl2 groups, suggesting greater Ni-acetate. Panc-10.05 cell line appeared the most sensitive to Ni compounds. Exposure to Ni-acetate resulted in an increased phospho-AKT, and decreased FOXO1 expression in Panc-10.05 cells, while NiCl2 also increased PTEN expression in Panc-10.05 cells. Specifically, following NiCl2 exposure to PDAC cells, the expression levels of miR-221 and miR-155 were significantly upregulated, while the expression levels of miR-126 were significantly decreased. Hence, our study has suggested pilot insights to indicate that the environmental pollutant Ni plays an important role in the progression of PDAC by promoting an association between miRs and Ni exposure during PDAC pathogenesis

Combustion of lean fuel mixtures with subcritical streamer microwave discharge

A sub-critical microwave discharge is used to achieve a stable ignition and combustion of lean air-fuel mixtures in a long tube. The microwave discharge is burnt at the presence of initiator with the quasi-optical microwave beam. The resonance way of initiation of a microwave discharge is more effective compared to traditional plasma-assisted ways of ignition and stabilization of combustion. The experimental observations show that ignition and combustion of a lean air and propane mixture in a long tube is achieved at low ignition limit with fuel/air ratio lower than 0.55. The results obtained are useful for design of new and improvement of the existing plasma-assisted technologies in aviation industry