共查询到18条相似文献，搜索用时 187 毫秒
1.
In light of the Ф-mapping method,the contribution of disclination linges to the free energy density of 2-dimensional liquid crystals is studied in the single-elastic constant approximation.It is pointed out that ,compared with the previous theory ,the free energy density can be divided into two parts.One is the usual distorted energy density of director field around the disclination lines.The other is the free endrgy density of the disclination lines themselves which is centralized at the disclination lines and topoligically quantized in a unit of 1/2kπ .The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines,i.e.,the disclination strength.From the method of Lagrangian multipliers,the equilibrium equation and the molecular field of 2-dimensional liquid crystals are also obtained.It is shown that the physical meaning of the Lagrangian multiplier is just the distorted energy density. 相似文献
2.
In the light of Ф-mapping method and the relationship between entropy and the Euler characteristic, the intrinsic topological structure of entropy of Kerr black holes is studied. From the Ganss-Bonnet-Chem theorem, it is shown that the entropy of Kerr black hole is determined by singularities of the Killing vector field of spacetime. These singularities naturally carry topological numbers, Hopf indices and Brouwer degrees, which can also be viewed as topological quantization of entropy of Kerr black holes. Specific results S = A/4 for non-extreme Kerr black holes and S = 0 for extreme ones are calculated independently by using the above-mentioned methods. 相似文献
3.
A method is proposed to monitor and control Hopf bifurcations in multi-machine power systems using the information from wide area measurement systems （WAMSs）. The power method （PM） is adopted to compute the pair of conjugate eigenvalues with the algebraically largest real part and the corresponding eigenvectors of the Jacobian matrix of a power system. The distance between the current equilibrium point and the Hopf bifurcation set can be monitored dynamically by computing the pair of conjugate eigenvalues. When the current equilibrium point is close to the Hopf bifurcation set, the approximate normal vector to the Hopf bifurcation set is computed and used as a direction to regulate control parameters to avoid a Hopf bifurcation in the power system described by differential algebraic equations （DAEs）. The validity of the proposed method is demonstrated by regulating the reactive power loads in a 14-bus power system. 相似文献
4.
For reconstructing a freeform feature from point cloud, a deformation-based method is proposed in this paper. The freeform feature consists of a secondary surface and a blending surface. The secondary surface plays a role in substituting a local region of a given primary surface. The blending surface acts as a bridge to smoothly connect the unchanged region of the primary surface with the secondary surface. The secondary surface is generated by surface deformation subjected to line constraints, i.e., character lines and limiting lines, not designed by conventional methods. The lines are used to represent the underlying information of the freeform feature in point cloud, where the character lines depict the feature＇s shape, and the limiting lines determine its location and orientation. The configuration of the character lines and the extraction of the limiting lines are discussed in detail. The blending surface is designed by the traditional modeling method, whose intrinsic parameters are recovered from point cloud through a series of steps, namely, point cloud slicing, circle fitting and regression analysis. The proposed method is used not only to effectively and efficiently reconstruct the freeform feature, but also to modify it by manipulating the line constraints. Typical examples are given to verify our method. 相似文献
5.
Exceptional family of elements and the solvability of complementarity problems in uniformly smooth and uniformly convex Banach spaces 总被引：1，自引：0，他引：1
ISACG. LIJin-lu 《浙江大学学报(A卷英文版)》2005,6(4):289-295
INTRODUCTION New topological method in complementaritytheory is now developing. This method is based on thenotion of “exceptional family of elements (EFE)”initially defined in 1991–1993 by G. Isac as “radialfamily of elements”. The name of EFE was given in(Isac et al., 1997), after the authors found a connectionbetween this notion and the topological degree in Rn. We note that after 1997, this notion was extendedto completely continuous fields and to other classes ofm… 相似文献
6.
The clock generator and OOK modulator for RFID (Radio Frequency Identification) presented in this paper consist of a current source and delay elements. The simple constant-gm structure is adopted in the current source design and the current consumption of the current source is only about 2 μA. The delay elements, the clock generator and OOK modulator are introduced in detail in the paper. The designed circuits are fabricated by 0.6 μm CMOS process. The area of the core circuit is only about 400 μmμ0 μm. The delay time of all three samples is in the range of 9 μs to 21 μs when the supply voltage varies from 2 V to 4 V. As the measured results satisfy the system requirements, these circuit structures are suitable for RFID application. 相似文献
7.
This paper presents a new type of fault current limiter(FCL) based on fast-closing switch,which is composed of a capacitor bank and a reactor in series.The main control component is a fast-closing switch connected in parallel with the capactitors,which is drien by the electromagnetic repulsion force.It can response the order within 1 ms.When fault occurs,the switch closes and the capacitors are bypassed.and the fault current is limited by the reactor,Simulation analysis and experiment show that the electromagnetic repulsion force actuator can meet the demand of fast-closing switch,it is feasible to develop the FCL with low cost and high reliability. 相似文献
8.
PWM逆变器载波方式的选择 总被引：1，自引：2，他引：1
In this paper the influence of different carrier waveforms upon the output characteristics of PWM inverter is described in detail. When a triangular carrier waveform is used in hard-switching PWM inverters, harmonics exist in the neighborhood of the output frequency of the inverter output voltage and current due to the dead time. The triangular carrier waveform used in soft-switching PWM inverter will cause difficulties in controlling resonance-trigger time, higher loss in the resonant circuit, and less utilization of the DC bus voltage. If a sawtooth carrier is used in hard-switching PWM inverter, there will be severe distortion in the current waveform. When sawtooth carriers with alternate positive and negative slopes are used in soft-switching PWM inverters, the resonancetrigger time is easy to control, and distortion in the output voltage and current caused by the dead time will not appear. 相似文献
9.
This paper proposes an engineering approach to examine the stability margin of cascade circuits. The proposed measurement injects an external perturbation current into the cascade interface and measures the load-side response current. The system stability margin can be figured out by comparing the magnitudes of the perturbation current and the response current. The proposed measurement is strictly derived in theory, implemented with details, and demonstrated by experiment. 相似文献
10.
The indirect boundary element method (IBEM) is used to study the surface motion of an alluvial valley in layered half-space for incident plane P-waves based on Wolf’s theory. Firstly, the free field response can be solved by the direct stiffness method, and the scattering wave response is calculated by Green’s functions of distributed loads acting on inclined lines in a layered half-space. The method is verified by comparing its results with literature and numerical analyses are performed by taking the amplification of incident plane P-waves by an alluvial valley in one soil layer resting on bedrock as an example. The results show that there exist distinct differences between the wave amplification by an alluvial valley embedded in layered half-space and that in homogeneous half-space and there is interaction between the valley and the soil layer. The amplitudes are relatively large when incident frequencies are close to the soil layer’s resonant frequencies. 相似文献
11.
姜海益 《浙江大学学报(A卷英文版)》2004,5(7):754-758
Let k,m,n be positive integers,and k≥2,α∈(0,1],0＜r＜min {m,n} an integer,d=r (m-r)/(k α),and iff∈ Ck,α(Rm,R″),A =Cr(f)= {x ∈ Rm ,rank(Df(x))≤r},thenf(A)is d-null.Thus the statement posed by Arthur Sard in 1965 can be completely solved when k≥2. 相似文献
12.
Let R be a ring, a ,b ∈ R, ( D , α ) and (G , β ) be two generalized derivations of R . It is proved that if aD ( x ) = G ( x )b for all x ∈ R, then one of the following possibilities holds: (i) If either a or b is contained in C , then α = β= 0 and there exist p , q ∈ Qr ( RC) such that D ( x )= px and G ( x )= qx for all x ∈ R;(ii) If both a and b are contained in C , then either a = b= 0 or D and G are C-linearly dependent;(iii) If neither a nor b is contained in C , then there exist p , q ∈ Qr ( RC) and w ∈ Qr ( R) such that α ( x ) = [ q ,x] and β ( x ) = [ x ,p] for all x ∈ R, whence D ( x )= wx-xq and G ( x )= xp + avx with v ∈ C and aw-pb= 0. 相似文献
13.
蒋岳祥 《浙江大学学报(A卷英文版)》2004,5(3):335-342
Suppose {Xi,i≥1} and {Yi, i≥1} are two independent sequences with distribution functions and , respectively. Zi,n is the combination of Xi and Yi with a probability for each I with 1≤ i≤n. The extreme value distribution GZ(x) of this particular triangular array of the i.i.d. Random variables Z1,n,… Z2,n, Zn,n is discussed. We found a new form of the extreme value distributions i)ΦAα1(x)Φα2 and ii) ψAα(x)ψα2(x)α1<α2), which are not max-stable. It occurs if FX and FY belong to the same MDA(Φ) or MDA(Ψ). 相似文献
14.
Let Bnp={x ∈ Rn‖|x ‖p≤l} be the unit ball ofp norm in the n-dimensional normed space p. The formula for the volume of Bnp was obtained and its asymptotic properties were found out as n→∞and p→∞. 相似文献
15.
Ahmad Faiz 《上海大学学报(英文版)》1998,2(2):108-111
The diagonal Padé approximants for exp (x), tan x and tanh x are obtained in a simple manner by using the property of Legendre polynomials that on [−1,1] P
r1(x) is orthogonal to every polynomial of lower degree. Gauss’s quadrature formula is used to find the denominators of some functions. 相似文献
16.
Well-cubic perovskite lanthanum aluminate (LaAlO3) film on (110) silicon substrate was fabricated by sol-gel method with corresponding inorganic salts. Lanthanum acetate and
aluminum acetate glacial acetic acid solutions were prepared via ligand exchange starting from lanthanum nitrate hexahydrate
and aluminum nitrate hexahydrate after being refluxed. (CH3CO)2O removed nitrates and the crystallized H2O completely, acetylacetone (AcAc) was partially bidentated with metallic ion of the metallic acetates and formed La(OAc)3−x
(AcAc)
x
which were hydrolyzed into La(AcAc)3−x(OH)
x
by adding 10 ml 0.4% methyl cellulose (MCL) solution. The La(AcAc)3−x
(OH)
x
, polymerizing and combining with MCL, formed the LaAlO3 sol precursor with heteropolymeric structure and formed film easily. The epitaxial LaAlO3 film on Si(110) substrate was crystallized after being annealed in thermal annealing furnace for 650–750 °C/30 min. The morphologies
and microstructures were characterized. The refractive index of the LAO film was 1.942 to 2.007; the dielectric constant and
the dissipation factors were estimated to be 23–26 and 2.1×10−4−2.4×10−4 respectively.
Project (No. 2002CB613305) supported by the National Basic Research Program (973) of China 相似文献
17.
WANG Ya-qin 《浙江大学学报(A卷英文版)》2007,8(10):1691-1694
Let K be a closed convex subset of a real reflexive Banach space E, T：K→K be a nonexpansive mapping, and f：K→K be a fixed weakly contractive （may not be contractive） mapping. Then for any t∈（0, 1）, let x1∈K be the unique fixed point of the weak contraction x1→tf（x）＋（1-t）Tx. If T has a fixed point and E admits a weakly sequentially continuous duality mapping from E to E^＊, then it is shown that {xt} converges to a fixed point of T as t→0. The results presented here improve and generalize the corresponding results in （Xu, 2004）. 相似文献
18.
Shailesh A. Shirali 《Resonance》2007,12(7):27-43
For non-negative integers k, n, let P
k
(n) denote the sum {fx27-1}. We show by two different means that if k ≥ 3 and odd, then n
2(n+1)2 iss a factor of the polynomial P
k
(n); and if k ≥ 2 and even, then n (n+1) (2n+1) is a factor of the polynomial P
k
(n). We also derive a relatively unknown result first obtained by Johann Faulhaber in the 17th century.
Shailesh Shirali has been at Rishi Valley School, Andhra Pradesh (Krishnamurti Foundation India) since the 1980’s. He has
a deep interest in teaching and writing about mathematics at the high school/post school levels, with particular emphasis
on problem solving and on historical aspects of the subject. He has been involved in the Mathematics Olympiad movement at
the national and international level for the past two decades. He is the author of several expository books and articles aimed
at interested high school students. 相似文献