共查询到20条相似文献,搜索用时 31 毫秒
1.
G. Fabritius G. Flik J. Golczewski D. Herlach G. Jünemann M. Krenke K. Maier A. P. Pathak H. Rempp A. Seeger W. Sigle E. Widmann D. W. Cooke 《Hyperfine Interactions》1986,31(1-4):229-234
By means of π+/μ+ channelling, positive pions (π+) implanted intoTa, Mo, andW are investigated up to high temperatures. A striking observation is that the channelling effect disappears in a rather narrow
temperature interval centred at 0.26 (Ta) to 0.51 (W) of the melting temperature. From studies of π+ trapping by oxygen atoms inTa estimates for the low-temperature π+ diffusivity inTa [D
π(23K)=1.4·10−10±0.3 m2s−1,D
π(47K)=5.7·10−10±0.3 m2s−1] as well as for the binding enthalpy of π+ to 0 atoms (H
B=7·10−2 eV) have been obtained. The diffusion data are in reasonable agreement with the theory of phonon-assisted tunnelling. 相似文献
2.
D. E. Feldman 《JETP Letters》1999,70(2):135-140
The random field and random anisotropy N-vector models are studied with the functional renormalization group in 4−ε dimensions. The random anisotropy Heisenberg (N=3) model has a phase with an infinite correlation length at low temperatures and weak disorder. The correlation function
of the magnetization obeys a power law 〈m(r
1)m(r
2)〉∼|r
1−r
2|− 0.62ε. The magnetic susceptibility diverges at low fields as χ∼H
−1+0.15ε. In the random field N-vector model the correlation length is finite at arbitrarily weak disorder for any N>3.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 130–135 (25 July 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
3.
Preliminary data on the reactions e
+
e
−→φ→γ f
0(980)→γπ0π0 together with data on ππ scattering and the reactions J/ψ→φπ+π− and K
−
p→π +π−(Λ,Σ) are analyzed. The analysis shows that the mass of the f
0(980) meson is
= 950 MeV, and BR(φ→γf
0→γπ0π0)≃ 1× 10−4, indicating that the f
0(980) resonance is of a four-quark nature.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 445–449 (10 April 1998) 相似文献
4.
The excess 1/f noise in a random lattice with bond resistances r∼exp(−λx), where x is a random variable and λ≪1, is studied theoretically. It is shown that if the correlation function {δr
2}∼r
r
θ+2, then the relative spectral density of the noise in the system is expressed as C
e∼λm exp(−λ(1−p
c)), where p
c is the percolation threshold and m=νd (ν is the critical exponent of the correlation length and d is the dimensionality of the problem). It is hypothesized that the exponent m possesses a dual universality: It is independent of 1) the geometry of the lattice and 2) the θ-mechanism responsible for
the generation of the local noise. Numerical modeling in a three-dimensional lattice gives m=52.3 for θ=1 and θ=0, in agreement with the hypothesis.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 614–618 (25 April 1996) 相似文献
5.
V. M. Aul’chenko M. N. Achasov A. V. Bozhenok A. D. Bukin D. A. Bukin S. V. Burdin I. A. Gaponenko V. B. Golubev T. V. Dimova S. I. Dolinskii V. P. Druzhinin M. S. Dubrovin V. N. Ivanchenko P. M. Ivanov A. A. Korol’ S. V. Koshuba A. A. Mamutkin E. V. Pakhtusova S. I. Serednyakov V. A. Sidorov Z. K. Silagadze Yu. V. Usov V. V. Sharyi Yu. M. Shatunov 《JETP Letters》1999,69(2):97-102
A search for the process e
+
e
−→φ(1020)→η″(958) γ in the decay channel η″→π
+
π
−
η, η→γγ was made in an experiment at the VEPP-2M e
+
e
− collider with the SND detector. Analysis confirms the occurrence of φ→η″γ decay with probability B(φ→η″ γ)=(6.7
−2.9
+3.4
)×10−5.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 87–91 (25 January 1999) 相似文献
6.
基于我们最近所构建的Ar+H+2→ArH++H(12A′)反应的新势能面,采用准经典轨线法研究了碰撞能分别为0.48,0.77,1.24 eV以及能量为0.48 eV时反应物不同振动态下Ar+H+2→ArH++H反应的立体动力学性质.结果显示在给定的碰撞能情况下,以及当反应物振动量子数由0变到2时计算的积分反应截面与实验值符合得较好.通过比较发现,碰撞能对此反应k-j′关联函数P(θr)分布的影响大于其受振动激发的影响,并且关于k-k′-j′三矢量相关的函数P(?r)分布以及极化微分反应截面对碰撞能较敏感,同时发现振动激发对P(?r)分布和极化微分反应截面也有较大的影响. 相似文献
7.
Kalyani Desikan 《Pramana》1995,45(6):511-517
BD-FRW universe filled with imperfect fluid having bulk viscosity is investigated under the framework of Israel-Stewart-Hiscock
causal theory. The field equations have been solved by using the relationφ=KR
α
whereK andα are constants, between the Brans-Dicke scalar fieldϕ and the scale factorR. This relation, in fact, leads to a constant deceleration parameterq. It is shown that the constancy of the deceleration parameter permits only two possibilities i.e. eitherH=constant withm=1 orm=(1+b −α)/(2(1+b) −α), irrespective of the value ofɛ. 相似文献
8.
M R M Witwit 《Pramana》1994,42(2):159-165
Eigenenergies are calculated for the potentialsV
1(r)=−(a/r)[1+(1+br)e−2br
] andV
2(r)=−(v/r)[1 −λr(1−Z
−1)(1+λr)−1], using renormalized series technique. Accurate results produced here for various eigenstates agree with those available
in the literature. 相似文献
9.
Let (A,α) be a C*-dynamical system. We introduce the notion of pressure P
α(H) of the automorphism α at a self-adjoint operator H∈A. Then we consider the class of AF-systems satisfying the following condition: there exists a dense α-invariant *-subalgebra
? of A such that for all pairs a,b∈? the C*-algebra they generate is finite dimensional, and there is p=p(a,b)∈ℕ such that [α
j
(a),b]= 0 for |j|≥p. For systems in this class we prove the variational principle, i.e. show that P
α(H) is the supremum of the quantities h
φ(α) −φ(H), where h
φ(α) is the Connes–Narnhofer–Thirring dynamical entropy of α with respect to the α-invariant state φ. If H∈A, and P
α(H) is finite, we show that any state on which the supremum is attained is a KMS-state with respect to a one-parameter automorphism
group naturally associated with H. In particular, Voiculescu's topological entropy is equal to the supremum of h
φ(α), and any state of finite maximal entropy is a trace.
Received: 19 April 2000 / Accepted: 14 June 2000 相似文献
10.
Comparative studies of the emission of quasi-thermal atomic and cluster ions from V, Nb, Ta, Au, and In targets bombarded
by cluster ions Au
m
−(m = 1–9), as well as from Si and Bi targets bombarded by cluster ions Au
m
−(m = 1–9) and Bi
m
−(m = 1–5), with energy E
0 ranging from 6 to 21 keV are carried out. In the case of bombardment by heavy cluster ions, the fraction of the quasi-thermal
component in the energy spectra of sputtered atomic ions reaches 50 (for V, In, and Au), 70 (Nb), or more than 90% (Ta). In
addition, quasi-thermal ions play a considerable part in the emission of small cluster ions Au2+, In2+, In3+, and Bi
n
+(n = 2–7). The results of the generalizing investigation favor the presence of thermal spike conditions at cluster bombardment
and their appreciable contribution to the emission of atomic and small cluster ions. 相似文献
11.
A variational approach is developed for bound state calculations in three- and four-electron atomic systems. This approach
can be applied to determine, in principle, an arbitrary bound state in three- and four-electron ions and atoms. Our variational
wave functions are constructed from four- and five-body Gaussoids that respectively depend on six (r
12, r
13, r
14, r
23, r
24, r
34) and ten (r
12, r
13, r
14, r
15, r
23, r
24, r
25, r
34, r
35 and r
45) relative coordinates. The approach allows operating with the more than one electron spin functions. In particular, the trial
wave functions for the 1
S states in four-electron atomic systems include the two independent spin functions χ1 = αβαβ + βαβα − βααβ − αββα and χ2 = 2ααββ + 2ββαα − βααβ − αββα − βαβα − αβαβ. We also discuss the construction of variational wave functions for the excited
23
S states in four- electron atomic systems. 相似文献
12.
On the Energy Growth of Some Periodically Driven Quantum Systems with Shrinking Gaps in the Spectrum
We consider quantum Hamiltonians of the form H(t)=H+V(t) where the spectrum of H is semibounded and discrete, and the eigenvalues behave as E
n
∼n
α
, with 0<α<1. In particular, the gaps between successive eigenvalues decay as n
α−1. V(t) is supposed to be periodic, bounded, continuously differentiable in the strong sense and such that the matrix entries with
respect to the spectral decomposition of H obey the estimate ‖V(t)
m,n
‖≤ε|m−n|−p
max {m,n}−2γ
for m≠n, where ε>0, p≥1 and γ=(1−α)/2. We show that the energy diffusion exponent can be arbitrarily small provided p is sufficiently large and ε is small enough. More precisely, for any initial condition Ψ∈Dom(H
1/2), the diffusion of energy is bounded from above as 〈H〉
Ψ
(t)=O(t
σ
), where
. As an application we consider the Hamiltonian H(t)=|p|
α
+ε
v(θ,t) on L
2(S
1,dθ) which was discussed earlier in the literature by Howland. 相似文献
13.
N. N. Achasov 《JETP Letters》1996,63(8):601-606
It is shown that BR(χ
b1(1 P)→e
+
e
−)≃3.3· 10−7 and BR(χ
c1(1 P)→e
+
e
−)≃10−8. This gives realistic possibilities for searching for the production of χ
b1(1 P) and ξ
c1(1 P) states in e
+
e
− collisions, even on the present-day colliders, to say nothing of b and c-τ factories.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 569–574 (25 April 1996) 相似文献
14.
V. V. Tarasov P. O. Varlamov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(4):458-463
We report our observations on the resonance signals of masses of 1520, 1670, 1810 (1 820), and 2100 MeV c
−2, produced inclusively in the reaction Σ− + C(Cu) → p + K− + X, and the signals of masses of 1020 and 1525 MeV c
−2, produced inclusively in the reaction Σ− + C(Cu) → K+ + K− + X, with a 600-GeV c
−1- momentum hyperon beam in the SELEX experiment at the Fermilab. The masses, widths, and branching ratios were measured. The
resonance signal of mass of 1520 MeV c
−2 correspond to the known Λ(1520) hyperon. The signals of masses of 1020 and 1525 MeV c
−2 in the K+K− system correspond to the φ0(1020)- and f
2′(1525) mesons, respectively. The branching ratio of the resonance of mass of 1670 MeV c
−2 relative to Λ(1520) is (24.92 ± 0.45 ± 0.48)%, while that of the resonance of mass of 1810 (or 1 820) MeV c
−2 relative to Λ(1520) is (16.13 ± 0.38 ± 0.45)%. The branching ratio of the f
2′(1525) resonance relative to φ0(1020) is (10.75 ± 0.25 ± 0.45)%. Data analysis was performed over 6 × 107 trigger events registered by the SELEX setup on the FNAL Tevatron. 相似文献
15.
A theoretical study is carried out of quantum beats (QB) in the time-dependent intensities of absorption of a test pulse and
of spontaneous luminescence in a Cu2O crystal under conditions of double optical resonance. It is assumed that pumping is effected by a CO2-laser pulse which dynamically couples the exciton levels 1s(Γ
5
+
) and 2p(Γ
4
−
,Γ
5
−
,Γ
3
−
Γ
2
−
) and splits them into two or three pairs of quasi-energy levels. The frequency of the test pulse is in resonance with the
frequency Γ
5
+
of the exciton. The corresponding intensities for various directions of the electric vector of the pump field E
L, the polarization vector ξ, and the wave vector q of the test pulse are obtained. The frequency of the quantum beats is twice the Rabi frequency, which for different values
of E
L, ξ and q contains different sets of matrix elements of the dipole transitions between the levels 1s(Γ
5
+
) and 2p(Γ
4
−
,Γ
5
−
,Γ
3
−
Γ
2
−
). Thus, by measuring the period of the quantum beats it is possible to determine the unknown matrix elements of the indicated
transitions.
Fiz. Tverd. Tela (St. Petersburg) 39, 844–847 (May 1997) 相似文献
16.
C?t?lin I. Carstea 《Communications in Mathematical Physics》2010,300(2):487-528
The existence of co-rotational finite time blow up solutions to the wave map problem from ${\mathbb{R}^{2+1} \to N}The existence of co-rotational finite time blow up solutions to the wave map problem from
\mathbbR2+1 ? N{\mathbb{R}^{2+1} \to N} , where N is a surface of revolution with metric d
ρ
2 + g(ρ)2
dθ2, g an entire function, is proven. These are of the form u(t,r)=Q(l(t)t)+R(t,r){u(t,r)=Q(\lambda(t)t)+\mathcal{R}(t,r)} , where Q is a time independent solution of the co-rotational wave map equation −u
tt
+ u
rr
+ r
−1
u
r
= r
−2
g(u)g′(u), λ(t) = t
−1-ν, ν > 1/2 is arbitrary, and R{\mathcal{R}} is a term whose local energy goes to zero as t → 0. 相似文献
17.
W. Schwarz E. H. Brandt K. -P. Döring U. Essmann K. Fürderer M. Gladisch D. Herlach G. Majer H. -J. Mundinger H. Orth A. Seeger M. Schmolz 《Hyperfine Interactions》1986,31(1-4):247-253
The diffusivityD
μ of positive muons (μ+) in the mixed state of superconducting high-purity, high-perfection niobium single crystals is investigated by measurements
of the relaxation of the transverse muon spin polarization (μ+SR). The method makes use of the strong magnetic field gradients existing in the mixed state of Type-II superconductors and
monitorsD
μ through the variation of the magnetic field felt by the μ+ during their diffusion through the crystals. For μ+ near the centres of the flux lines inNb it givesD
μ(4.6 K)=(8±2)·10−11m2S−1. The positive temperature coefficient ofD
μ indicates that at liquid-helium temperatures the diffusivity of μ+ inNb is mainly due to phonon-assisted tunnelling processes. 相似文献
18.
Edward A. Desloge 《International Journal of Theoretical Physics》1976,15(5):357-363
On the basis of elementary symmetry arguments it is shown that (1) if in classical mechanics there exists a quantity λ+Σiμiυi+1/2νυ
2 that is conserved, where λ,μ
i, andν are particle parameters, then theμ
i andν are all proportional to a single parameterμ and the quantityAμ+ΣiBiμυi+C(λ+ 1/2Dμυ
2), whereD ≡ν/μ, is conserved for all values ofA, B
i, andC; (2) if in relativistic mechanics there exists a quantity λ+Σiμiυi[1−(υ
2/c
2)]−1/2+νc[1−(υ
2/c
2)]−1/2 that is conserved, then theμ
i andν are all proportional to a single parameterμ and the quantityAλ+ΣiBiμνi[1−(υ
2/c
2)]−1/2+Cμc [1−(υ
2/c
2)]−1/2 is conserved for all values ofA, B
i, andC. 相似文献
19.
Edward A. Desloge 《International Journal of Theoretical Physics》1976,15(5):349-356
On the basis of simple kinematic arguments it is shown that any quantity, depending only on the nature and velocity of a particle,
that is conserved in a collision must, in classical mechanics, be of the form λ+Σiμiυi+1/2vυ
2 or in relativistic mechanics of the form λ+Σiμiυi[1−(υ
2/c
2)]−1/2+νc [1−(υ
2/c
2)]−1/2 where λ,μ
i, andν are particle parameters. 相似文献
20.
The value of adjustable parameterC in the four-parameter potentialU(r) =D
e [(1 - exp[-b(r -r
e)])/(1 -C exp[-b(r -r
e)])]2 has been expressed in terms of molecular parameters and its significance has been brought out. The potential so constructed,
withC derived from the molecular parameters, has been applied to ten electronic states in addition to the states studied by Wei
Hua. Average mean deviation for these 25 states has been found to be 3.47 as compared to 6.93, 6.95 and 9.72 obtained from
Levine, Varshni and Morse potentials, respectively. Also Dunham’s method has been used to express rotation-vibration interaction
constant (αe) and anharmonicity constant (ωexe) in terms ofC and other molecular constants. These relations have been employed to determine these quantities for 37 electronic states.
For αe, the average mean deviation is 7.2% compared to 19.7% for Lippincott’s potential which is known to be the best to predict
these values. Average mean deviation for (ωexe) turns out to be 17.4% which is almost the same as found from Lippincott’s potential function. 相似文献