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排序方式: 共有548条查询结果,搜索用时 15 毫秒
71.
Cha??Koren Ronan?VicquelinEmail author Olivier?Gicquel 《Flow, Turbulence and Combustion》2018,101(1):77-102
A multi-physics simulation combining large-eddy simulation, conjugate heat transfer and radiative heat transfer is used to predict the wall temperature field of a confined premixed swirling flame operating under atmospheric pressure. The combustion model accounts for the effect of enthalpy defect on the flame structure whose stabilization is here sensitive to the wall heat losses. The conjugate heat transfer is accounted for by solving the heat conduction within the combustor walls and with the Hybrid-Cell Neumann-Dirichlet coupling method, enabling to dynamically adapt the coupling period. The latter coupling procedure is enhanced to determine statistics (mean, RMS, \(\ldots \)) in a permanent regime accurately and efficiently thanks to an acceleration technique which is derived and validated. The exact radiative heat transfer equation is solved with an advanced Monte Carlo method with a local control of the statistical error. The coupled simulation is carried out with or without accounting for radiation. Excellent results for the wall temperature are achieved by the fully coupled simulation which are then further analyzed in terms of radiative effects, global energy budget and fluctuations of wall heat flux and temperature. 相似文献
72.
Purpose
To prospectively evaluate diffusion-weighted (DW) magnetic resonance (MR) imaging for differentiation of postobstructive consolidation from centrally located lung carcinomas by using apparent diffusion coefficients (ADCs).Materials and Methods
An institutional review board approved this study; informed consent was obtained from patients. Forty-nine consecutive patients (3 women, 46 men; mean age, 63.6 years; age range, 42–85 years) with lung carcinoma underwent DW MR imaging. Forty patients had central and nine patients had peripheral lung carcinomas. ADC of each lung carcinoma was calculated from DW MR images obtained with two different b values (0, 1000 s/mm2).In the final study group including 27 patients with central lung carcinoma accompanying distal lung consolidation (mean age, 67.2 years; 3 women, 24 men), ADCs of lung carcinomas were statistically compared among cytologic/histologic types and accompanying postobstructive consolidations. Unpaired t test was used for measurable variables with normal distribution, and Kruskal–Wallis variance analysis and Mann–Whitney U tests were used for the measurable variables without normal distribution.Results
There was no significant difference between mean ADC values of all types of carcinomas (P=.302) and also between mean ADC values of central (1.91 ± 0.7×10−3 mm2/s) and peripheral carcinomas (1.58 ± 0. 6×10−3 mm2/s) (P=.224). The mean ADC value for the masses of central lung carcinoma with postobstructive consolidations was 1.83 ± 0.75×10−3 mm2/s, and for consolidation was 2.50 ± 0.76×10−3 mm2/s. ADC of central carcinoma masses was significantly lower than that of postobstructive consolidations (P=.003).Conclusions
ADC values of central lung carcinoma masses appear to be lower than accompanying postobstructive consolidations. ADC values could be considered useful as a differentiating parameter among central lung carcinomas and accompanying postobstructive consolidations. 相似文献73.
Michal?Landa Petr?Sedlák Hanu??Seiner Luděk?Heller Lucie?Bicanová Petr??ittner Václav?Novák 《Applied Physics A: Materials Science & Processing》2009,96(3):557-567
Recent experimental and theoretical improvements of resonant ultrasound spectroscopy (RUS) are summarized to investigate elastic
constants of phases in shape memory alloys. The proposed inversion procedure, described in this work, is particularly suitable
to reliable evaluation of the temperature dependence of elastic constants of low-symmetry ferroelastic materials which may
be strongly elastically anisotropic and tend to exist in twinned forms. The method is applicable even for the evaluation of
single-crystal elastic constants from RUS measurements on microtwinned crystals, since it involves a homogenization algorithm
based on the macroscopic deformation response of the layered structure. This potentially allows performing meaningful acoustic
studies on samples with a general submicron-size layered structure. 相似文献
74.
Daniel Ha??ko Jaroslav Bruncko Andrej Vincze Franti??ek Uherek 《Central European Journal of Physics》2009,7(2):345-349
Two series of polycrystalline zinc oxide (ZnO) layers, from Zn or ZnO targets, were grown on silicon (1 1 1) substrates by
pulsed laser deposition (PLD) at ambient oxygen pressure levels, stepwise increased from 1 to 35 Pa. For ablation of targets,
a pulsed Nd:YAG laser was used. The structural and morphological properties of the layers were investigated by scanning electron
microscopy (SEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS). The SEM images of ZnO layers
in SE mode show a uniform granular structure and modified surface morphology, depending on oxygen pressure. The mean grain
size in height and lateral directions decreases with an increase of oxygen pressure from 1 to 5 Pa, while a subsequent rise
of oxygen pressure from 5 to 35 Pa will cause an increase in the grain size. The AFM measurement revealed that the surface
structures of zinc oxide layers grown from different targets were similar, and the layers formed at an ambient oxygen pressure
of 5 Pa exhibited the smallest values of calculated roughness and granularity. SIMS depth profiling analyses confirmed that
the ZnO composition was homogenous across the layer, up to the abrupt change of chemical composition at the interface between
the ZnO layer and the Si substrate.
相似文献
75.
Peter Bury Hikaru Kobayashi Masao Takahashi Kentaro Imamura Peter Sidor Franti??ek ??ernobila 《Central European Journal of Physics》2009,7(2):237-241
Ultrathin silicon dioxide (SiO2) layers formed on Si substrate with nitric acid have been investigated using both acoustic deep-level transient spectroscopy
(A-DLTS) and electrical methods to characterize the interface states. The set of SiO2/Si structures formed in different conditions (reaction time, concentrations of nitric acid (HNO3), and SiO2 thickness [3–9 nm]) was prepared. The leakage current density was decreased by post-oxidation annealing (POA) treatment at
250°C in pure nitrogen for 1 h and/or post-metallization annealing (PMA) treatment at 250°C in a hydrogen atmosphere for 1
h. All structures of the set, except electrical investigation, current-voltage (I - V), and capacitance — voltage (C - V) measurements, were investigated using A-DLTS to find both the interface states distribution and the role of POA and/or PMA
treatment on the interface-state occurrence and distribution. The evident decreases of interface states and shift of their
activation energies in the structures with PMA treatment in comparison with POA treatment were observed in most of the investigated
structures. The results are analyzed and discussed.
相似文献
76.
Michal Novotn?? P??emysl Fitl Anna Krasilnikova Sytchkova Ji???- Bul?-?? Jan Lanaok Petr Pokorna David Najdek Jia Boan 《Central European Journal of Physics》2009,7(2):327-331
The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated
by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen
atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm−2 to 250 mJ·cm−2 was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface
structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy
(SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence
of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of
applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black
gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm−2 and 3.5 mJ·cm−2 for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase
in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film
were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser
treatment.
相似文献
77.
On textured n-type silicon substrates for solar cell manufacturing, the relation between light trapping behavior, structural
imperfections, energetic distribution of interface state densities and interface recombination losses were investigated by
applying surface sensitive techniques. The field-modulated surface photovoltage (SPV), in-situ photoluminescence (PL) measurements, total hemispherical UV-NIR-reflectance measurements and electron microscopy (SEM) were
employed to yield detailed information on the influence of wet-chemical treatments on preparation induced micro-roughness
and electronic properties of polished and textured silicon substrates. It was shown that isotropic as well as anisotropic
etching of light trapping structures result in high surface micro-roughness and density of interface states. Removing damaged
surface layers in the nm range by wet-chemical treatments, the density of these states and the related interface recombination
loss can be reduced. In-situ PL measurements were applied to optimise HF-treatment times aimed at undamaged, oxide-free and hydrogen-terminated substrate
surfaces as starting material for subsequent solar cell preparations.
相似文献
78.
V.?Dmitra?inovi? Toru?Sato Milovan??uvakov 《The European Physical Journal C - Particles and Fields》2009,62(2):383-397
We calculate the energies of three-quark states with definite permutation symmetry (i.e. of SU(6) multiplets) in the N=0, 1, 2 shells, confined by the Y-string three-quark potential. The exact Y-string potential consists of one term, the so-called
three-string term, and three angle-dependent two-string terms. Due to this technical complication we treat the problem at
three increasingly accurate levels of approximation: (1) the (approximate) three-string potential expanded to first order
in trigonometric functions of hyper-spherical angles; (2) the (approximate) three-string potential to all orders in the power
expansion in hyper-spherical harmonics, but without taking into account the transition(s) to two-string potentials; (3) the
exact minimal-length string potential to all orders in a power expansion in the hyper-spherical harmonics, and taking into
account the transition(s) to two-string potentials. We show the general trend of improvement of these approximations: the
exact non-perturbative corrections to the total energy are of the order of one per cent, as compared with approximation (2),
yet the exact energy differences between the [20,1+],[70,2+],[56,2+],[70,0+]-plets are shifted to 2:2:0.9, from the Bowler and Tynemouth separation rule 2:2:1, which is obeyed by approximation (2)
at the one per cent level. The precise value of the energy separation of the first radial excitation (“Roper”) [56′,0+]-plet from the [70,1−]-plet depends on the approximation, but does not become negative, i.e. the “Roper” remains heavier than the odd-parity [70,1−]-plet in all of our approximations. 相似文献
79.
The structure of covariant observables—normalized positive operator measures (POMs)—is studied in the case of a type I symmetry
group. Such measures are completely determined by kernels which are measurable fields of positive semidefinite sesquilinear
forms. We produce the minimal Kolmogorov decompositions for the kernels and determine those which correspond to the extreme
covariant observables. Illustrative examples of the extremals in the case of the Abelian symmetry group are given.
Dedicated to Pekka J. Lahti in honor of his sixtieth birthday 相似文献
80.
Marijana??akovi?Email author Maja?Do?en Zora?Popovi?Email author 《Journal of chemical crystallography》2011,41(2):180-185