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1.
D. Babala 《Czechoslovak Journal of Physics》1960,10(9):628-632
The cross-section for the two-quantum annihilation-in-flight of partially polarized beams of particles, obtained by using the polarization density matrix, is given. The formula includes the special results of L. A. Page [1]. The annihilation of a longitudinally polarized positron with a transversally polarized electron is discussed. Computations are made in a centre-of-mass system with summing over photon polarizations.
Abbreviated version of a diploma-thesis for the degree graduate physicist.
The author wishes to express his sincere gratitude to Professor V. Votruba and Dr. L. Valenta for suggesting this work and for many helpful discussions and criticisms. 相似文献
. . . . . .
Abbreviated version of a diploma-thesis for the degree graduate physicist.
The author wishes to express his sincere gratitude to Professor V. Votruba and Dr. L. Valenta for suggesting this work and for many helpful discussions and criticisms. 相似文献
2.
F. Roubínek 《Czechoslovak Journal of Physics》1960,10(12):949-953
Zusammenfassung Es wurde der Einfluß eines Bombardements mit Stickstoffionen vor der Erregung untersucht und gezeigt, daß die Stiekstoffatome eine große Rolle bei der Entstehung des Emissionsmaximums bei 150° spielen.
-
, 150°C.相似文献
3.
In a recent paper we developed a method which allows one to control rigorously the finite-size behavior in long cylinders near first-order phase transitions at low temperature. Here we apply this method to asymmetric transitions with two competing phases, and to theq-state Potts model as a typical model of a temperature-driven transition, whereq low-temperature phases compete with one high-temperature phase. We obtain the finite-size scaling of the firstN eigenvalues (whereN is the number of competing phases) of the transfer matrix in a periodic box of volumeL × ... ×L ×t, and, as a corollary, the finite-size scaling of the shape of the order parameter in a hypercubic box (t=L), the infinite cylinder (t=), and the crossover regime from hypercubic to cylindrical scaling. For the two-phase case (N=2 we find that the crossover length
L is given by O(Lw)exp(Lv), where is the inverse temperature, is the surface tension, and w=1/2 if v+1=2 whilew=0 if v+1 >2. For the standard Ising model we also consider free boundary conditions, showing that L=exp[Lv+O(Lv– 1)] for any dimension v+12. For v+1=2 we finally discuss a class of boundary conditions which interpolate between free (corresponding to the interpolating parameter g=0) and periodic boundary conditions (corresponding to g=1), finding that
L=O(Lw)exp(L
v) withw=0 forg=0 andw=1/2 for 0<g1. 相似文献
4.
Alla Margolina Fereydoon Family Vladimir Privman 《Zeitschrift für Physik B Condensed Matter》1984,54(4):321-324
We report analyses of series enumerations for the mean radius of gyration for isotropic and directed lattice animals and for percolation clusters, in two and three dimensions. We allow for the leading correction to the scaling behaviour and obtain estimates of the leading correction-to-scaling exponent . We find -0.640±0.004 and =0.87±0.07 for isotropic animals in 2d, and =0.64±0.06 in 3d. For directed lattice animals we argue that the leading correction has=
or=
; we also estimate
=0.82±0.01 and 0.69 ±0.01 ind=2, 3 respectively. For percolation clusters at and abovep
c, we find (p
c) =0.58±0.06 and (p>p
c)=0.84±0.09 in 2d, and (p
c)=0.42±0.11 and (p>p
c)=0.41 ±0.09 in 3d. 相似文献
5.
E. M. E. Zayed 《International Journal of Theoretical Physics》2000,39(1):189-205
We study the influence of a finite container on an ideal gas. The trace of theheat kernel (t) =
= 1exp(–t), where {}
= 1are the eigenvalues of the negative Laplacian – 2 = – 3
= 1(/x
)2 in the (x
1, x
2, x
3)-space,is studied for a general bounded domain with a smooth bounding surface S, where afinite number of Dirichlet, Neumann, and Robin boundary conditions on thepiecewise smooth parts S
i
(i = 1, ..., n) of S are considered such that S =U
i = 1
S
i
. Some geometrical properties of (the volume, the surface area, the meancurvature, and the Gaussian curvature) are determined. Furthermore,thermodynamic quantities, particularly the energy, for an ideal gas enclosed inthe general bounded domain with Dirichlet, Neumann, and Robin conditionsare examined with the help of the asymptotic expansions of (t) for short timet. We show that these thermodynamic quantities depend on some geometricproperties of . 相似文献
6.
H. E. Wilhelm 《Applied physics. B, Lasers and optics》1983,31(3):173-177
Based on the (relativistic) Maxwell equations with displacement current E/t, the initial-boundary-value problem for the compression of an initially homogeneous magnetic fieldB={0,B(x,t),0} between a fixed liner atx=0 and a detonation-driven liner atx=s(t) is solved analytically. By homogenizing the boundary conditions at the moving boundary, the transient electromagnetic fields are shown to be a superposition of quasistatic elliptic (E/t=0) and hyperbolic (E/t0) wave solutions. The wave equation is solved by a Fourier expansion in time-dependent eigenfunctionsf
n
=f
n
[nx/s(t)] for the variable region 0xs(t), where the Fourier amplitudes
n
(t) are determined by coupled differential equations of second order. It is concluded that the conventional elliptic flux compression theories (E/t=0) hold approximately for nonrelativistic liner speeds
, whereas the hyperbolic theory (E/t0) is valid for arbitrary liner speeds
. 相似文献
7.
A. D. W. B. Crumey 《Communications in Mathematical Physics》1987,111(2):167-179
The classical non-linear Schrödinger equation associated with a symmetric Lie algebra =km is known to possess a class of conserved quantities which from a realization of the algebrak []. The construction is now extended to provide a realization of the Kac-Moody algebrak[, –1] (with central extension). One can then define auxiliary quantities to obtain the full algebra [, –1]. This leads to the formal linearization of the system. 相似文献
8.
K. Kriŝtiaková O. Ŝauŝa J. Kriŝtiak Ŝ. Jánoŝ 《Zeitschrift für Physik B Condensed Matter》1989,75(2):197-199
We have measured the ac susceptibility of a wire with a Nb core (1.27 mm diam.) and a Cu cladding (0.37 mm thickness) atT50 K andB0.1 mG. Due to its proximity to Nb, the Cu becomes fully superconducting. From the data we find a breakdown fieldH
b
=1.2 (mG) and a coherence length =2.2T
–1/2 (m) for the Cu, as well as a field penetration depth -34T
1/2 (m) at the Cu/Nb interface. 相似文献
9.
Tom Kennedy 《Journal of statistical physics》1984,37(5-6):529-559
We study a classical charge symmetric system with an external charge distributionq in three dimensions in the limit that the plasma parameter zero. We prove that ifq is scaled appropriately then the correlation functions converge pointwise to those of an ideal gas in the external mean field(x) where is given by-+ 2z sinh() =q This is the mean field equation of Debye and Hückel. The proof uses the sine-Gordon transformation, the Mayer expansion, and a correlation inequality.Work partially supported by NSF Grant MCS 82-02115. 相似文献
10.
We study the optimal learning capacity for neural networks withQ-state clock neurons, i.e. the states arecomplex numbers with magnitude 1 and azimuthal anglesn·2/Q, withn=0, 1, ...,Q–1. Performing a phase space analysis, the learning capacity
c
for given stability can be expressed by means of a double-integral with a simple geometrical interpretation, which for vanishing reduces to
c
(Q) = 4Q/(3Q–4), forQ3. Then we define a training algorithm, which generalizes the well-known AdaTron algorithm fromQ=2 toQ3 and converges very fast to the network with optimal stability, if the numberp of random patterns to be learned is smaller than
c
(Q). Finally, in the conclusions, we also give hints on applications for image recognition and in a note added in proof we generalize some results to Potts model networks. 相似文献
11.
We find the asymptotic decrease of correlations <
A +y
,
B
>,yZ
v
+1, |y|, in the Ising model at high temperatures. For the case when monomials
A
and
B
both are odd, using the saddle-point method, we find the asymptotics of the correlations for any dimension . For even monomials
A
,
B
we formulate a general hypothesis about the form of the asymptotics and confirm it in two cases: (1) =1 and the vectory has an arbitrary direction, (2)y is directed along a fixed axis and arbitrary . Here we use besides the saddle-point method, some arguments from scattering theory. 相似文献
12.
We discuss stochastic Schrödinger operators and Jacobi matrices with wave functions, taking values in
l
so there are 2l Lyaponov exponents 1...l0
l+1...2l
=–1. Our results include the fact that if 1=0 on a set positive measure, thenV is deterministic and one that says that {E|exactly 2j 's are zero} is the essential support of the a.c. spectrum of multiplicity 2j.Research partially supported by USNSF under grant DMS-8416049 相似文献
13.
We study the ground state properties of theS=1/2 Heisenberg antiferromagnet (HAF) on the triangular lattice with nearest-neighbour (J) and next-nearest neighbour (J) couplings. Classically, this system is known to be ordered in a 120° Néel type state for values-<1/8 of the ratio of these couplings and in a collinear state for 1/8<<1. The order parameter and the helicity /gC of the 120° structure are obtained by numerical diagonalisation of finite periodic systems of up toN=30 sites and by applying the spin-wave (SW) approximation to the same finite systems. We find a surprisingly good agreement between the exact and the SW results in the entire region-<<1/8. It appears that the SW theory is still valid for the simple triangular HAF (=0) although the sublattice magnetisation is substantially reduced from its classical value by quantum fluctuations. Our numerical results for the order parameterM of the collinear order support the previous conjecture of a first order transition between the 120° and the collinear order at 1/8. 相似文献
14.
The paper deals with the motion of 90° wedge domains in BaTiO3 in an alternating field of 50 c/s. The critical field, the positional hysteresis loops with double asymmetry, the production of wedges with polarization perpendicular to the field and 180° substructure in the wedges were studied. The differences between the behaviour of the wedges and the individual 90° walls are pointed out which are caused by differences in the energy balance of these formations and by different interactions with 180° processes. The upper limit of contribution of the wedge motion to the initial permittivity is estimated. The results are discussed from the phenomenological point of view.
90° BaTiO3
90° BaTiO3 , 50 Hz. , , , , , , 180° . 90° , 180° . , . .相似文献
15.
Hidetoshi Nishimori Kenn Kubo Yukiyasu Ozeki Yasuhiro Tomita Tatsuya Kishi 《Journal of statistical physics》1989,55(1-2):259-277
The existence of long-range order is proved under certain conditions for the antiferromagnetic quantum spin system with anisotropic interactions (XXZ model) on the simple cubic or the square lattice. In three dimensions (the simple cubic lattice), finite long-range order exists at sufficiently low temperatures for any anisotropy(0) ifS1, and for 0<0.29 (XY-like) or>1.19 (Ising-like) ifS=1/2. In two dimensions (the square lattice), ground-state long-range order exists under the following conditions: for any anisotropy (0) ifS3/2; 0<0.032 (XY-like) or 0.67<<1.34 (almost isotropic) or>1.80 (Ising-like) ifS=1;>1.93 (Ising-like) ifS=1/2. We conjecture that the two-dimensional spin-1/2XY model (=0) has finite ground-state long-range order. Numerical evidence supporting this conjecture is given. 相似文献
16.
András Sütő 《Communications in Mathematical Physics》1987,111(3):409-415
The spectrum (H) of the tight binding Fibonacci Hamiltonian (H
mn=
m,n+1+
m+1,n
+
m,n
v(n),v(n)=
((n–1)), 1/ is the golden number) is shown to coincide with the dynamical spectrum, the set on which an infinite subsequence of traces of transfer matrices is bounded. The point spectrum is absent for any , and (H) is a Cantor set for 4. Combining this with Casdagli's earlier result, one finds that the spectrum is singular continuous for 16.On leave from the Central Research Institute for Physics, Budapest, Hungary 相似文献
17.
F. Lukeš 《Czechoslovak Journal of Physics》1960,10(1):59-65
The paper gives the values of the optical constants of thin films of germanium obtained by evaporating germanium in a vacuum onto glass slides in the region of 0·35–0·78 for an index of absorptionk and 0·35–2·5 for refractive indexn. The results are compared with the values obtained by other authors and with the values ofn andk for single crystals. It is shown that these values for thin films and single crystals slightly differ quantitatively but agree fairly well qualitatively, which had not been sufficiently the case in previous papers.
, , 0,35 0,78 k 0,35–2,5 n. n, k . , , , , .相似文献
18.
Many one-dimensional quasiperiodic systems based on the Fibonacci rule, such as the tight-binding HamiltonianH(n)=(n+1)+(n–1)+v(n)
(n),n,l
2(),, wherev(n)=[(n+1)]–[n],[x] denoting the integer part ofx and the golden mean
, give rise to the same recursion relation for the transfer matrices. It is proved that the wave functions and the norm of transfer matrices are polynomially bounded (critical regime) if and only if the energy is in the spectrum of the Hamiltonian. This solves a conjecture of Kohmoto and Sutherland on the power-law growth of the resistance in a one-dimensional quasicrystal. 相似文献
19.
S. Albeverio G. Gallavotti R. Høegh-Krohn 《Communications in Mathematical Physics》1979,70(2):187-192
We show that for the regularized exponential interaction :e
: ind space-time dimensions the Schwinger functions converge to the Schwinger functions for the free field ifd>2 for all or ifd=2 for all such that ||>0.Partially sponsored by the I.H.E.S. through the Stiftung Volkswagenwerk 相似文献
20.
An approximate evaluation of the pair distribution and the structure factor is performed analytically for the two-dimensional, one-component plasma at any value of the coupling constant. The approximate distribution remains positive and satisfies three sum rules, including the compressibility one. When 0 or 2, exact results are found. At=2 the transition from monotonie (<2) to oscillatory (>2) decay of correlations takes place. Comparison with the Monte Carlo simulations shows good agreement for 0<<4. 相似文献