Potential Analysis - In this paper we present a short proof of the following classification Theorem for g ?harmonic functions in half-spaces. Assume that u is a nonnegative solution to... 相似文献
This paper presents a further analysis of results of airfoil self-noise prediction obtained in the previous work using large eddy simulation and acoustic analogy. The physical mechanisms responsible for airfoil noise generation in the aerodynamic flows analyzed are a combination of turbulent and laminar boundary layers, as well as vortex shedding (VS) originated due to trailing edge bluntness. The primary interest here consists of evaluating the effects of mean flow convection, quadrupole sources and vortex shedding tonal noise on the overall sound pressure level (OASPL) of a NACA0012 airfoil at low and moderate freestream Mach numbers. The overall sound pressure level is the measured quantity which eventually would be the main concern in terms of noise generation for aircraft and wind energy companies, and regulating agencies. The Reynolds number based on the airfoil chord is fixed at Rec=408,000 for all flow configurations studied. The results demonstrate that, for moderate Mach numbers, mean flow effects and quadrupole sources considerably increase OASPL and, therefore, should be taken into account in the acoustic prediction. For a low Mach number flow with vortex shedding, it is observed that OASPL is higher when laminar boundary layer separation is the VS driving mechanism compared to trailing edge bluntness. 相似文献
Franck-Condon factors and R-centroids for the B-X transition of I2 have been calculated from recent molecular parameters. From our radiative lifetimes and others reported in the literature, the validity of several proposed electronic transition moment functions has been checked. Acombination of the Bhale and Koffend functions seems to give the best fitting with the experimental radiative lifetimes. 相似文献
BaTiO3 thin films were deposited by pulsed laser deposition on Pt–Si at different laser pulse repetition frequencies. X-ray diffraction spectra show that preferred oriented films can be grown by adjusting the pulse repetition frequency. Enhanced dielectric and ferroelectric properties obtained in films deposited at 1 Hz is attributed to preferred orientation, low strain and homogeneous grain distribution. The films deposited at 1 Hz show an impressive remanent polarization of 21.4 μC/cm2 with a coercive field of 70.0 kV/cm. The shift in Curie temperature, which stems from changing the laser pulse repetition frequency, is associated with the strain state in the film. 相似文献
Pd/C-Sb2O5·SnO2 and PdAu/C-Sb2O5·SnO2 electrocatalysts with different PdAu atomic ratio (90:10, 70:30, and 50:50) were prepared by borohydride reduction method, and characterized by X-ray diffraction, transmission electron microscopy, cyclic voltammetry, chronoamperommetry, and performance test on direct formic acid fuel cell at 100 °C. X-ray diffraction showed for Pd/C-Sb2O5·SnO2 the presence of Pd face-centered cubic (fcc) system, while for PdAu/C-Sb2O5·SnO2 it showed the presence of Pd fcc phase, PdAu fcc alloys and a segregated phases fcc Pd-rich and Au-rich phases. TEM micrographs and histograms for all electrocatalysts showed that the nanoparticles where not well dispersed on the support and some agglomerates were present. The electrochemical studies showed that PdAu/C-Sb2O5·SnO2 (70:30) had superior performance for formic acid electro-oxidation at 25 °C compared to others electrocatalysts prepared while PdAu/C-Sb2O5·SnO2 (90:10) showed superior performance in direct formic acidic fuel cell at 100 °C. These results indicated that the addition of 10–30 % Au to Pd favor the electro-oxidation of formic acid. This effect could be attributed to the synergy between the constituents of the electrocatalyst (metallic Pd and Au, SnO2, and Sb2O5·SnO2). 相似文献
The functional integration over the auxiliary bosonic variables of cubic order related with the effective action of the Nambu–Jona–Lasinio
model with ’t Hooft term has recently been obtained in the form of a loop expansion. Even numbers of loops contribute to the
action, while odd numbers of loops are assigned to the measure. We consider the two-loop corrections and analyse their effect
on the low-lying pseudoscalar and scalar mass spectra, quark condensates and weak decay constants. The results are compared
to the leading order calculations and other approaches.
PACS 12.39.Fe, 11.30.Rd, 11.30.Qc 相似文献
OIT's oxidation condition is very harsh for pure and irradiated polymers, particularly PP. PP undergoes pronounced molecular weight degradation in the course of processing and is prone to very fast oxidation and consequently very fast degradation, especially on samples submitted to previous aging and irradiation.
We developed a more useful method applicable by a much broader set of resins. Our group has recently introduced a new procedure to determine OIT, in non-stabilized and stabilized, irradiated and non-irradiated polypropylene. The new procedure was based on two main features: (1) starting the oxidation on melted samples at temperatures as low as possible; (2) oxidation under slow heating conditions. So each sample has a set of two values of time and temperature, as the new method is not isothermal any longer, so we better call it “Temperature dependent oxidative induction-time”. The new method showed itself as reproducible, sensitive to small changes in additive compositions and simple and inexpensive. 相似文献
The use of a laser-Doppler velocimeter has been extended to the analysis of turbulent heat transfer in a strongly sheared
disc-stabilised propane-air flame through its combination with either laser Rayleigh scattering or digitally-compensated fine-wire
thermocouples. The laser velocimeter was based on a conventional forward scattering system from the green light of a 5W Argon-Ion
laser, while the Rayleigh signals used the blue line of the same laser. The procedure for the numeric compensation of the
thermocouple signals included analysis of the effect of velocity and temperature on the time constant of the thermocouple
and was optimised to allow combined velocity–temperature samples acquired by a purpose-built digital interference with a frequency
up to 2000 Hz, without deterioration of the thermocouple by particle accretion. The maximum effective data rate for the combined
Rayleigh/LDV system is shown to be around 130 Hz, which corresponds to a data rate of valid Doppler signals around 400 Hz
and statistics based on more than 15 000 measurements is made possible. The results obtained with the two systems agree qualitatively,
although the use of thermocouples attenuates the measured velocity-temperature correlations. The results are used to assess
the extent to which turbulent mixing in flames is altered by the accompanying heat release and quantify the processes of non-gradient
diffusion in a strongly recirculating premixed flame.
Received: 15 November 1996/Accepted: 2 September 1997 相似文献
We consider a cylindrical fiber whose core is a liquid crystal (LC) subject to the action of a low frequency field applied parallel to the axis of the cylinder and having initially the escaped configuration. We find the distorted textures of the nematic inside the cylinder by assuming arbitrary anchoring boundary conditions. In the optical limit we calculate the ray trajectories followed by a low intensity beam along the fiber parametrized by a low frequency electric field. Finally, we calculate exactly the spatial dependence of the transverse magnetic modes distribution in the guide, on the electric field, by using a numerical scheme. We summarize our paper and discuss our results. 相似文献