Triple-flame propagation in a parallel flow: an analytical study

We present an analytical study of triple-flame propagation in a two-dimensional mixing layer against a parallel flow. The problem is formulated within a constant density thermo-diffusive model, and solved analytically in the asymptotic limit of large activation energy of the chemical reaction for flames thin compared with their typical radius of curvature. Explicit expressions are obtained in this limit, describing the influence of the flow on the triple-flame. The results are expected to be applicable when the ratio between the flow-scale and the flame-front radius of curvature (which is mainly dictated by concentration gradients) is of order unity, or larger. When this ratio is large, as in the illustrative case of a Poiseuille flow in a porous channel considered here, the flow is found to negligibly affect the flame structure except for a change in its speed by an amount which depends on the stoichiometric conditions of the mixture. On the other hand, when this ratio is of order unity, the flow is able to significantly wrinkle the flame-front, modify its propagation speed, and shift its leading edge away from the stoichiometric line. The latter situation is investigated in the illustrative case of spatially harmonic flows. The results presented describe, in particular, how the leading-edge of the flame-front can be determined in terms of the flow amplitude A which is critical in determining the flame speed. The latter is found to depend linearly on A in the first approximation with a correction proportional to the flame thickness multiplied by , for |A| sufficiently large. The effect of varying the flow-scale on flame propagation in this context is also described, with explicit formulae provided, and interesting behaviours, such as non-monotonic dependence on the scale, identified.     

Statistical properties of curved polymer

Intrinsic curvature of biopolymers is emerging as an essential feature in various biological phenomena. Examples of polymers with intrinsic curvature are microtubule in eukaryotic cells or FtsZ filaments in prokaryotic cells. We consider the general model for polymers with intrinsic curvature. We aim to study both equilibrium and dynamic properties of such polymers. Here we report preliminary results on the equilibrium distribution function P(R) of the end-to-end distance R. We employ transfer matrix method for this study.      

Burning velocity of triple flames with gentle concentration gradient

We investigated the local flame speed of a two-dimensional, methane-air triple flame in a rectangular burner. The velocity fields and the concentration profiles were measured with particle image velocimetry and the Rayleigh scattering method, respectively. There was a requisite combination of initial velocity and initial concentration gradient for consistency of the local concentration gradient at the leading edge of the flame. In these cases, the flame curvatures were also consistent. Accordingly, the burning velocity, defined as local flow velocity at the triple point, was determined by the flame curvature. The burning velocity increased with increasing flame curvature, when the curvature was near zero. After that, the burning velocity decreased with increasing curvature. The peak value thus exceeded the adiabatic one-dimensional laminar burning velocity. Comparing the effects of the measured flame stretch rate on the flow strain κ_s and flame curvature κ_c, κ_s is larger and increases more rapidly than κ_c for flame curvatures satisfying 1/R_f < 250 m⁻¹ and then becomes constant while κ_c still increases for 250 m⁻¹ < 1/R_f, so that κ_c becomes much larger than κ_s. There is also a peak in burning velocity at roughly the transition in flame curvature specified above. Therefore, the burning velocity for a low concentration gradient correlates with the flame stretch rate.     

基于Contourlet变换与FLD的人脸表情识别方法

提出了一种基于Contourlet变换与FLD的人脸表情特征提取方法。Contourlet变换是一种新的多尺度几何分析方法,它在具备小波变换的多分辨率特性和时频局部特性的同时,还具有很强的多方向选择性和各向异性。图像经过Contourlet变换后的低频分量可体现表情的概貌,高频方向子带可体现表情的轮廓和纹理等细节。将低频分量与部分高频方向子带结合起来作为整体特征,可压缩图像的数据量,并能够体现表情的本质特征。首先用Fisher线性判别法(FLD)进行特征提取,然后采用K-近邻法进行分类。实验证明,该方法比经典的FLD方法有着更快的特征提取速度和更高的表情识别率。     

Gauge theory onR×S 3 topology

A model for gauge theories over a compact Lie group is described using R × S³ as background space. The U(1) and SU(2) gauge theories are considered as particular examples, and a comparison with other results is given. Our results differ from those of Carmeli and MalinFound. Phys. 16, 791 (1986);17, 193 (1987)] by a supplementary term in the curvature tensor due to the noncommutativity of derivatives used on R × S³ space. Some observations about supersymmetry and gravity on R × S³ space are also given.     

Method for edge contour extraction of a scanning probe microscope image

A method for edge contour extraction of a scanning probe microscope image is proposed. This method is developed to process an image that has the large size irregularity and/or objects bound together. It is based on definition of the local minimum points of brightness data function and permits one to obtain the correct edge contour line. The advantages of the proposed method over traditional methods are demonstrated using model results. This method can be used to process different images.     

Ballistic transport and spin-orbit interaction of two-dimensional electrons on a cylindrical surface

The components of the ballistic magnetoconductance tensor of a two-dimensional electron gas placed on a cylindrical sector are calculated for various geometries. For a quasiclassical system a method is proposed for finding the conductance based only on the Bohr-Sommerfeld quantization condition and not requiring a knowledge of the matrix elements of the velocity. The effect of curvature of the surface on the spin-orbit interaction in a two-dimensional electron gas is investigated. As examples, the microwave absorption and longitudinal conductance of a hollow cylindrical wire are calculated, and also the conductance of a cylindrical sector. There are qualitative differences from planar systems, in particular the relative sign of the curvature and the spin-orbit coupling constant becomes important. Zh. éksp. Teor. Fiz. 113, 1411–1428 (April 1998)     

Polarized Infrared and Raman Spectra and Ab-initio Calculations of Benzotriazole

Abstract

The i. r. spectra of benzotriazole have been measured from 4000 to 60 cm^?1: polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been investigated. The structural parameters and vibrational frequencies have been determined from ab-initio Hartree-Fock gradient calculations using the 6–31G* basis set. A detailed arsignment of most of the observed bands has been proposed on the basis of the i. r. dichroism, Raman polarization data and frequency calculations.

     

CD Spectroscopic Study of Absolute Conformation and Configuration of Some 4-Hydroxychromans

CD data of the optically active 4-hydroxy (1–5) and 4-acetoxy chromans (6–8) were analyzed by two different approaches. The Snatzke-Antus treatment of chiraly perturbed chromane chromophore revealed M absolute conformation and 4S absolute configuration of the alcohols, i.e. P absolute conformation and 4R absolute configuration of the acetates. The proposed absolute configuration of the optically active alcohols was confirmed for 1 and 2 by the chiral excitone coupling method applied on their benzoates 9 and 10.     

13C Nuclear Magnetic Resonance Studies of the Conformations of Serine‐3′‐ and 5′‐Thymidine Monophosphate Conjugates

The differences in the backbone conformation between O‐thymidine‐3′‐(1) and 5′‐yl O‐alkyl N‐phosphoryl serine methyl esters (2) have been investigated by solution ¹³C NMR spectroscopy. The stereo‐sensitive vicinal ³¹P–¹³C coupling constants were measured and used in the conformational analysis for the P–O5′–C5′, P–O3′–C3′, and P–N–C_α bonds. Three‐dimensional structural characteristics of dephosphorylation reactions of Compounds are also discussed.     

An analysis of the destabilizing curvature effects on the turbulent flow over a rotating cylinder

An analysis based on the available experimental data and second-order closures is made for a turbulent shear flow over a rotating cylinder in a quiescent fluid. The near-wall behaviour of the non-linear model for the pressure-strain correlation proposed by Speziale, Sarkar and Gatski [J. Fluid Mech. 245, 227 (1991)] is enlarged; and the methodology proposed by Lai and So [J. Fluid Mech. 221, 641 (1990)] is adopted to take into account the wall-effects. The radial profile of the curvature parameter, R_s, is examined in connection with the logarithmic law. It is shown that the log-layer is associated to the region where the mean velocity profile, V, is related to the power of the radial distance as Computations reveal that this region corresponds to the state with the most destabilizing curvature effects; which can be chararacterized by the minimum value of the parameter B _c =2R _s (1+2R _s ), and not that one of the parameter B=2R _s (1+2R _s )/(1+R _s )² firstly introduced by Bradshaw [J. Fluid Mech. 36, 171 (1969)] and extensively used to characterize the turbulence structure in curved flows. Received 9 December 1997     

Weighted iterative inversion method for T2 spectrum in nuclear magnetic resonance

Abstract

In traditional nuclear magnetic resonance T₂ inversion methods, the components with long T₂ absorb the components with short T₂, especially for low magnetic field intensity. As a result, the true distribution of all components often cannot be reflected by their solutions, and thus obtaining short T₂ components is an important T₂ inversion problem. Herein, a weighted iterative inversion method for T₂ spectrum in nuclear magnetic resonance is proposed to solve this problem. The weight-based method is applied to ensure that the short T₂ components are not eliminated. The weight scheme is determined by two parameters: the number of weights and maximum weight. The number of weights is determined by the rate of decay, and the maximum weight is mainly determined by three parameters: signal-noise ratio, curvature, and slope of collected signal. To avoid the mutations of results caused by weights, the iteration process was adopted to obtain the optimal solution. The proposed method provides good results, and it was verified to be robust and accurate though simulations and experiments.     

On the nature of the fishtail effect in the magnetic hysteresis loop of high-T c superconductors

An explanation is proposed for the fishtail effect observed in the magnetic hysteresis loops of high-T _c superconductors. It is shown that anisotropy of the pinning and curvature of the flux lines in the sample are sufficient for this effect to appear. The design of experiments for checking the proposed explanation is discussed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 538–542 (25 October 1996)     

Compressibility of a zinc single crystal under confining pressure

Abstract

In the present study, the two compressibility moduli of a zinc single crystal were measured at room temperature up to 18 GPa. The results are compared with those obtained by Bridgman from a different experimental method. This study required a gaseous hydrostatic confining pressure, and then it has been necessary to develop an original diamond anvil cell with a large optical aperture allowing the use of sophisticated video imaging and image analysis techniques. A model is proposed for the zinc volume-pressure relation.     

图像分割中采用自适应三次B样条修饰轮廓线

大多数由像素灰度值或灰度相关参数获得图像轮廓线的方法由于受到图像噪声、量化误差以及灰阶的梯度分布等方面的影响 ,获得的边缘轮廓线是不光滑的 ,带有小而密集的不规则锯齿或毛刺 ,这不仅不符合实际情况 ,而且会给进一步的图像处理带来困难。为了获得连续光滑的轮廓线 ,提出了一种方法 :先以动态规划算法提取全局最优的轮廓线 ,然后用一种自适应三次B样条对获得的轮廓线进行修饰和平滑处理。该样条可根据轮廓线不同处的曲率变化情况 ,自适应地调整控制点的分布。在各类图像上的试验表明 ,该方法即有效的消除了轮廓线上的小锯齿 ,又保留了轮廓线的特征细节     

Using the local density approximation and the LYP,BLYP and B3LYP functionals within reference-state one-particle density-matrix theory

For closed-shell systems, the local density approximation (LDA) and the LYP, BLYP and B3LYP functionals are shown to be compatible with reference-state one-particle density-matrix theory, where this recently introduced formalism is based on Brueckner-orbital theory and an energy functional that includes exact exchange and a non-universal correlation-energy functional. The method is demonstrated to reduce to a density functional theory when the exchange-correlation energy-functional has a simplified form, i.e. its integrand contains only the coordinates of two electrons, say r ₁ and r ₂, and it has a Dirac delta function δ(r ₁ - r ₂ as a factor. Since Brueckner and Hartree–Fock orbitals are often very similar, any local exchange functional that works well with Hartree–Fock theory is a reasonable approximation with reference-state one-particle density-matrix theory. The LDA approximation is also a reasonable approximation. However, the Colle–Salvetti correlation-energy functional and the LYP variant are not ideal for the method, since these are universal functionals. Nevertheless, they appear to provide reasonable approximations. The B3LYP functional is derived using a linear combination of two functionals: one is the BLYP functional; the other uses exact exchange and a correlation-energy functional from the LDA.     

TheB (3) field as a link between gravitation and electromagnetism in the vacuum

The emergence of theB ⁽³⁾ field in vacuo has shown that electromagnetism is non-Abelian and similar in structure to gravitation. In this paper the Christoffel symbol used in general relativity is developed for electromagnetism in curvilinear coordinates: The former becomes describable as the antisymmetric part of the gravitational Ricci tensor. Therefore gravitation and electromagnetism are respectively the symmetric and antisymmetric parts of thesame Ricci tensor within a proportionality factor. Both fields are obtained from the Riemann curvature tensor, both are expressions of curvature in spacetime.     

Solute-second phase interaction for Mg,Ag and Zn in Al–Li alloys

ABSTRACT

Early experiments have shown the promises of alloying with Mg?+?Ag (or Mg?+?Zn) on the performance of Al–Li alloys. To better understand the interaction between solutes and second phases in Al–Li alloys, Mg, Ag and Zn segregation to Al/δ′ interface as well as their substitution in δ′ bulk were investigated at the atomic level using first principles modelling and calculations. Energetics results and local charge analyses revealed that Mg, Ag and Zn can segregate to Al/δ′ interface by different preference, but have no significant influence on the interface adhesion. Ag and Zn can also dissolve into δ′ bulk, and enhance the local metallic bonding with nearest-neighboring Al atoms. Based on these results, a multi-fold benefit mechanism was suggested for the combined alloying with Mg?+?Ag (or Mg?+?Zn) in Al–Li alloys.