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

Fourier analysis of wave turbulence in a thin elastic plate

The spatio-temporal dynamics of the deformation of a vibrated plate is measured by a high speed Fourier transform profilometry technique. The space-time Fourier spectrum is analyzed. It displays a behavior consistent with the premises of the Weak Turbulence theory. A isotropic continuous spectrum of waves is excited with a non linear dispersion relation slightly shifted from the linear dispersion relation. The spectral width of the dispersion relation is also measured. The non linearity of this system is weak as expected from the theory. Finite size effects are discussed. Despite a qualitative agreement with the theory, a quantitative mismatch is observed which origin may be due to the dissipation that ultimately absorbs the energy flux of the Kolmogorov-Zakharov casade.Comment: accepted for publication in European Physical Journal B see http://www.epj.or

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

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

Mutagenicity of tamoxifen DNA adducts in human endometrial cells and in silico prediction of p53 mutation hotspots

Tamoxifen elevates the risk of endometrial tumours in women and α-(N2-deoxyguanosinyl)-tamoxifen adducts are reportedly present in endometrial tissue of patients undergoing therapy. Given the widespread use of tamoxifen there is considerable interest in elucidating the mechanisms underlying treatment-associated cancer. Using a combined experimental and multivariate statistical approach we have examined the mutagenicity and potential consequences of adduct formation by reactive intermediates in target uterine cells. pSP189 plasmid containing the supF gene was incubated with α-acetoxytamoxifen or 4-hydroxytamoxifen quinone methide (4-OHtamQM) to generate dG-N2-tamoxifen and dG-N2-4-hydroxytamoxifen, respectively. Plasmids were replicated in Ishikawa cells then screened in Escherichia coli. Treatment with both α-acetoxytamoxifen and 4-OHtamQM caused a dose-related increase in adduct levels, resulting in a damage-dependent increase in mutation frequency for α-acetoxytamoxifen; 4-OHtamQM had no apparent effect. Only α-acetoxytamoxifen generated statistically different supF mutation spectra relative to the spontaneous pattern, with most mutations being GC→TA transversions. Application of the LwPy53 algorithm to the α-acetoxytamoxifen spectrum predicted strong GC→TA hotspots at codons 244 and 273. These signature alterations do not correlate with current reports of the mutations observed in endometrial carcinomas from treated women, suggesting that dG-N2-tam adduct formation in the p53 gene is not a prerequisite for endometrial cancer initiation in women

Somersault of Paramecium in extremely confined environments

We investigate various swimming modes of Paramecium in geometric confinements and a non-swimming self-bending behavior like a somersault, which is quite different from the previously reported behaviors. We observe that Paramecia execute directional sinusoidal trajectories in thick fluid films, whereas Paramecia meander around a localized region and execute frequent turns due to collisions with adjacent walls in thin fluid films. When Paramecia are further constrained in rectangular channels narrower than the length of the cell body, a fraction of meandering Paramecia buckle their body by pushing on the channel walls. The bucking (self-bending) of the cell body allows the Paramecium to reorient its anterior end and explore a completely new direction in extremely confined spaces. Using force deflection method, we quantify the Young’s modulus of the cell and estimate the swimming and bending powers exerted by Paramecium. The analysis shows that Paramecia can utilize a fraction of its swimming power to execute the self-bending maneuver within the confined channel and no extra power may be required for this new kind of self-bending behavior. This investigation sheds light on how micro-organisms can use the flexibility of the body to actively navigate within confined spaces

Inactivation of the transforming growth factor β type II receptor in human small cell lung cancer cell lines

Transforming growth factor β (TGF-β) exerts a growth inhibitory effect on many cell types through binding to two types of receptors, the type I and II receptors. Resistance to TGF-β due to lack of type II receptor (RII) has been described in some cancer types including small cell lung cancer (SCLC). The purpose of this study was to examine the cause of absent RII expression in SCLC cell lines. Northern blot analysis showed that RII RNA expression was very weak in 16 of 21 cell lines. To investigate if the absence of RII transcript was due to mutations, we screened the poly-A tract for mutations, but no mutations were detected. Additional screening for mutations of the RII gene revealed a GG to TT base substitution in one cell line, which did not express RII. This mutation generates a stop codon resulting in predicted synthesis of a truncated RII of 219 amino acids. The nature of the mutation, which has not previously been observed in RII, has been linked to exposure to benzo[a]-pyrene, a component of cigarette smoke. Since RII has been mapped to chromosome 3p22 and nearby loci are often hypermethylated in SCLC, it was examined whether the lack of RII expression was due to hypermethylation. Southern blot analysis of the RII promoter did not show altered methylation patterns. The restriction endonuclease pattern of the RII gene was altered in two SCLC cell lines when digested with Sma 1. However, treatment with 5-aza-2′-deoxycytidine did not induce expression of RII mRNA. Our results indicate that in SCLC lack of RII mRNA is not commonly due to mutations and inactivation of RII transcription was not due to hypermethylation of the RII promoter or gene. Thus, these data show that in most cases of the SCLC cell lines, the RII gene and promoter is intact in spite of absent RII expression. However, the nature of the mutation found could suggest that it was caused by cigarette smoking. © 1999 Cancer Research Campaig