1,882 research outputs found
Experimental and numerical investigation of Helmholtz resonators and perforated liners as attenuation devices in industrial gas turbine combustors
This paper reports upon developments in the simulation of the passive control of combustion dynamics in industrial gas turbines using acoustic attenuation devices such as Helmholtz resonators and perforated liners. Combustion instability in gas turbine combustors may, if uncontrolled, lead to large-amplitude pressure fluctuations, with consequent serious mechanical problems in the gas turbine combustor system. Perforated combustor walls and Helmholtz resonators are two commonly used passive instability control devices. However, experimental design of the noise attenuation device is time-consuming and calls for expensive trial and error practice. Despite significant advances over recent decades, the ability of Computational Fluid Dynamics to predict the attenuation of pressure fluctuations by these instability control devices is still not well validated. In this paper, the attenuation of pressure fluctuations by a group of multi-perforated panel absorbers and Helmholtz resonators are investigated both by experiment and computational simulation. It is demonstrated that CFD can predict the noise attenuation from Helmholtz resonators with good accuracy. A porous material model is modified to represent a multi-perforated panel and this perforated wall representation approach is demonstrated to be able to accurately predict the pressure fluctuation attenuation effect of perforated panels. This work demonstrates the applicability of CFD in gas turbine combustion instability control device design
Resonant Transport in Nb/GaAs/AlGaAs/GaAs Microstructures
Resonant transport in a hybrid semiconductor-superconductor microstructure
grown by MBE on GaAs is presented. This structure experimentally realizes the
prototype system originally proposed by de Gennes and Saint-James in 1963 in
\emph{all}-metal structures. A low temperature single peak superimposed to the
characteristic Andreev-dominated subgap conductance represents the mark of such
resonant behavior. Random matrix theory of quantum transport was employed in
order to analyze the observed magnetotransport properties and ballistic effects
were included by directly solving the Bogoliubov-de Gennes equations.Comment: 7 pages REVTeX, 4 figures, to be published by World Scientific in
Proceedings of International Symposium on Mesoscopic Superconductivity and
Spintronics (NTT R&D Center Atsugi, Japan, March 2002
Behaviour of acoustic waves in a duct with Helmholtz resonator in presence of a temperature gradient
Understanding the behaviour of one-dimensional acoustical wave propagation in ducts is very important for controlling combustion instabilities in propulsion, household burners, gas turbine combustors, and designing engineering mufflers. This paper is concerned with ducts in which temperature gradient exist. Computational Fluid Dynamics (CFD) simulation of the acoustic wave propagations through a duct with Helmholtz resonators in the presence of a mean temperature gradient without mean air flow has been investigated. Acoustic pressure and axial velocity amplitudes have been calculated as a function of time. Time and axial distance dependent acoustic pressure and velocity are visualised as 3D surface plots
Behaviour of acoustic waves in a duct with Helmholtz resonator in presence of a temperature gradient
Understanding the behaviour of one-dimensional acoustical wave propagation in ducts is very important for controlling combustion instabilities in propulsion, household burners, gas turbine combustors, and designing engineering mufflers. This paper is concerned with ducts in which temperature gradient exist. Computational Fluid Dynamics (CFD) simulation of the acoustic wave propagations through a duct with Helmholtz resonators in the presence of a mean temperature gradient without mean air flow has been investigated. Acoustic pressure and axial velocity amplitudes have been calculated as a function of time. Time and axial distance dependent acoustic pressure and velocity are visualised as 3D surface plots
Early predictive response to multi-tyrosine kinase inhibitors in advanced refractory radioactive-iodine differentiated thyroid cancer: A new challenge for [18 f]fdg pet/ct
Differentiated thyroid cancer (DTC) represents the most common thyroid cancer histotype. Generally, it exhibits a good prognosis after conventional treatments; nevertheless, about 20% of patients can develop a local recurrence and/or distant metastasis. In one-third of advanced DTC, the metastatic lesions lose the ability to take up iodine and become radioactive iodine-refractory (RAI-R) DTC. In this set of patients, the possibility to perform localized treatments should always be taken into consideration before the initiation of systemic therapy. In the last decade, some multi-tyrosine kinase inhibitor (MKI) drugs were approved for advanced DTC, impacting on patient’s survival rate, but at the same time, these therapies have been associated with several adverse events. In this clinical context, the role of 2-deoxy-2-[18 F]fluoro-D-glucose positron emission tomography/computed tomography ([18 F]FDG PET/CT) in the early treatment response to these innovative therapies was investigated, in order to assess the potentiality of this diagnostic tool in the early recognition of non-responders, avoiding unnecessary therapy. Herein, we aimed to present a critical overview about the reliability of [18 F]FDG PET/CT in the early predictive response to MKIs in advanced differentiated thyroid cancer
Sex-determinants and their distribution in various populations of Musca domestica L. of Western Europe
SUMMARYThe distribution of sex-determinants in field populations ofMusca domestica domesticaL. was studied in 62 samples of flies collected at 53 sites (animal farms) between 1975 and 1981 in an area stretching North–South from Denmark (+ Iceland) to Sicily.Karyological observations and genetic analyses demonstrated the existence of three types of population along a latitudinal cline. Populations of Northern Europe were of the standard type (XXfemales andXYmales) with theYchromosome determining sex. Those of Central and Southern Italy from sites below 100 m.a.s.l. (metres above sea level) were autosomal (XXfemales and males), sex in them being determined by autosomal sex-determinants for both femaleness and maleness. In the large intermediate zone the populations were mixed and had several karyotypes in both sexes. In this zone an altitudinal gradient was also observed, with autosomal determinants less common at higher altitudes. Genetic tests showed, in the autosomal and in the mixed populations, the presence of two autosomal male factors:MIII, the most common, on autosome III andMII, on autosome II.The gradient in sex determinants found in flies of Western Europe appears to be a dynamic phenomenon of relatively recent origin. Both climatic influence and selective pressure with insecticides have probably contributed towards the micro-evolution of populations with different sex-determinants in the houseflies of the area studied
Mitotic recombination in Musca domestica L. and its influence on mosaicism, gynandromorphism and recombination in males
SUMMARYIn the housefly, mosaics appear spontaneously but rarely. Sexual mosaics or gynandromorphs also appear in strains in which sex determination is based on autosomal sex factors. Rare cases of recombination in the male have been reported by some authors. In field and laboratory populations, mitotic plates with figures indicating exchange of chromatid segments are regularly observed in tissues of individuals of both sexes and at all stages of development. All these anomalies are interpreted as outward manifestation of the same phenomenon: mitotic recombination. The cytological basis of mitotic recombination, its relative frequency, its influence on linkage and genetic variability are discussed
Nonpuerperal inversion of uterus secondary to leiomyoma in menopause: a rare case report
Inversion of uterus is a rare clinical condition if not associated with third stage of labor or puerperium. Non-puerperal uterine inversion usually occurs secondary to tumor arising from the fundus of uterus. We report an unusual case of non-puerperal uterine inversion caused by large submucous fibroid in a 65 year old postmenopausal woman which was managed by combined abdomino-perineal approach
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