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1.
The Fredholm representation theory is well adapted to the construction of homotopy invariants of non-simply-connected manifolds by means of the generalized Hirzebruch formula [σ(M)] = 〈L(M)ch A f*ξ, [M]〉 ∈ K A 0(pt) ⊗ Q, where A = C*[π] is the C*-algebra of the group π, π = π 1(M). The bundle ξK A 0() is the canonical A-bundle generated by the natural representation πA. Recently, the first author constructed a natural family of Fredholm representations that lead to a symmetric vector bundle on the completion of the fundamental group with a modification of the Higson-Roe corona, provided that the completion is a closed manifold.  相似文献   

2.
Using a sample of over 400 million φ→KSKL decays produced during the years 2001 and 2002 at the DAΦNE e+e- collider, the ratio RS π=Γ(KS→π+π-(γ))/Γ(KS→π0π0) has been measured with the KLOE detector. The result is RS π=2.2555±0.0012stat±0.0021corr-stat±0.0050syst, which is in good agreement with the previously published result based on the KLOE data sample from the year 2000. The average of the KLOE results is RS π=2.2549±0.0054, reducing the total error by a factor of three, to 0.25%.  相似文献   

3.
A magnetic phase transition in carbon-doped (0.1 and 0.7 at. %) Fe70Ni30 Invar alloys was investigated by the method of depolarization of a transmitted neutron beam and by small-angle scattering of polarized neutrons. It is shown that for both alloys, two characteristic length scales of magnetic correlations coexist above T c. Small-angle scattering by critical correlations with radius R c is described well by the Ornstein-Zernike (OZ) expression. The longer-scale (second) correlations, whose size can be estimated from depolarization data, are not described by the OZ expression, and hypothetically can be modeled by a squared OZ expression, which in coordinate space corresponds to the relation 〈M(r)M(0)〉∝exp(−r/R d), where R d is the correlation length of the second scale. The temperature dependence of the correlation radius R c was obtained: R c ∝ ((TT c)/Tc)ν , where ν≈2/3 is the critical exponent for ferromagnets, over a wide temperature range up to T c exp , at which the correlation radius becomes constant and equals its maximum value R c(T c)=R c max . The maximum correlation radius established (R c max =140 Å and 230 Å for the first and second alloys, respectively) characterizes the length-scale of the fluctuation for which the appearance of critical correlations first results in the formation of a ferromagnetic phase, and the phenomenon itself exhibits a “disruption” of the second-order phase transition at T=T c exp , as a result of which a first-order transition arises. Temperature hysteresis was also detected in the measured polarization of the transmitted beam and intensity of small-angle neutron scattering in the alloy above T c, confirming the character of this magnetic transition as a first-order transition close to a second-order transition. Zh. éksp. Teor. Fiz. 112, 2134–2155 (December 1997)  相似文献   

4.
A combined analysis of photoproduction data on γp↦ πN, ηN was performed including the data on KΛ and KΣ. The data are interpreted in an isobar model with s-channel baryon resonances and π, ρ (ω), K, and K * exchange in the t-channel. Three baryon resonances have a substantial coupling to ηN, the well-known N(1535)S 11, N(1720)P 13, and N(2070)D 15. The inclusion of data with open strangeness reveals evidence for further new resonances, N(1840)P 11, N(1875)D 13 and, with weaker evidence, for N(2170)D 13.  相似文献   

5.
Minamisono  T.  Matsuta  K.  Minamisono  K.  Kudo  S.  Ogura  M.  Fukuda  S.  Sato  K.  Mihara  M.  Fukuda  M. 《Hyperfine Interactions》2001,136(3-8):225-231
In order to precisely determine the |eqQ(41Sc)/h| of 41Sc(I π=7/2, T 1/2=0.596 s) implanted in a TiO2 single crystal the electric field gradient tensor and anisotropic chemical shift were determined by detecting the Fourier Transformed Pulse-NMR of 45Sc(I π=7/2, stable) in the crystal at a high field of 7.0 T and 9.4 T. Combining the new |eqQ(41Sc)/h| value with the Q(45Sc)=−(23.6±0.2) fm2, also renewed by using the known atomic hyperfine interaction constants and Sternheimer polarization effect, the |Q(41Sc;I π=7/2,T 1/2=0.596 s)|=(15.6±0.3) fm2 has been precisely determined. The value is compared with the theoretical Q(41Sc) given by a shell model code. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

6.
Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M+)/<A part> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/ <A part> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/ <A part> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected. Received: 10 December 1999 / Accepted: 14 November 2000  相似文献   

7.
Recently [see V.V. Anisovich et al., Yad. Fiz. 63, 1489 (2000)], the K-matrix solutions for the wave IJ PC=00++ were obtained in the mass region 450–1900 MeV, where four resonances f 0(980), f 0(1300), f 0(1500), f 0(1750) and the broad state f 0(1530 −250 +90 ) are located. Based on these solutions, partial widths are determined for scalar-isoscalar states decaying into the channels ππ, KK ηη, ηη′, ππππ and corresponding decay couplings. From Yadernaya Fizika, Vol. 65, No. 8, 2002, pp. 1583–1590. Original English Text Copyright ? 2002 by Anisovich, Nikonov, Sarantsev. This article was submitted by the authors in English.  相似文献   

8.
The light cone QCD sum rules are derived for the K * Kπ coupling g K * Kπ and the ρππ coupling g ρππ. The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with respect to the two external momenta, p 1 2, p 2 2= (pq)2. Our result g K * Kπ= (8.7 ± 0.5) and g ρππ= (11.5 ± 0.8) is in good agreement with the experimental value. Received: 31 July 1998 / Revised version: 20 November 1998  相似文献   

9.
A quantum Monte Carlo procedure is used to calculate the energy, sublattice magnetization, Néel temperature, and the slopes of the S=[1/T N(x=0)]dT N(x)/dx curves as functions of the hole concentration and the exchange anisotropy Δ=1−J x,y/J z in the Heisenberg model with anisotropic negative interactions between nearest neighbors in a square lattice with dilution among the lattice sites. The slope diverges in the limit Δ→0: S∼ln(6.5/Δ). Fiz. Tverd. Tela (St. Petersburg) 39, 898–900 (May 1997)  相似文献   

10.
Hyperfine interactions of β-emitting17F implanted in single crystals of NaF and CaF2 were studied. The nuclear magnetic moment of theT π=5/2+ state was determined with an improved precision to be |μ(17F;π=5/2+,T 1/2=64.5s|=4.72130±0.00025. nm. Isoscalar magnetic moments of the doubly closed shell ±1 nucleon nuclei around mass number 16 were derived and the effective nucleon mass in the nucleus was discussed.  相似文献   

11.
Tanigaki  M.  Ohkubo  Y.  Taniguchi  A.  Kawase  Y.  Goto  J.  Sasanuma  T. 《Hyperfine Interactions》2001,136(3-8):391-396
A 140La(I π=3, T 1/2=40.3 h)-doped layer has been produced in CaB6 by means of radioactive isotope (RI) beam technique: 140Cs(I π=1, T 1/2=63.7 s) was implanted into CaB6 and the radioactive equilibrium of 140Ba–140La was achieved. The concentration of La in CaB6 was La/Ca ∼0.001. Obtained TDPAC spectra of the 2083 keV level of 140Ce (I π=4+, T 1/2=3.4 ns, μ=+4.35±0.10 μ N ) followed by the β decay of 140La showed the existence of hyperfine magnetic fields: B hyp=−15.0±0.5 T and −1.00±0.15 T. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

12.
The real part R s and the imaginary part X s of the surface impedance Z s=R s+ iX s of Tl2Ba2CaCu2O8−δ and YBa2Cu3O6.95 single crystals have been measured with high precision at frequency ω/2π=9.4 GHz in the temperature range 0<T<140 K. In the Tl2Ba2CaCu2O8−δ crystal a linear temperature dependence R s(T) has been found for T⩽50 K, and the magnetic field penetration depth λ(4.2 K)=X s(4.2 K)/ω μ 0≈3760 Å has been measured. Along with well known features of the function Z s(T) in high-quality YBa2Cu3O6.95 single crystals, such as the linearity of λ(T) and R s(T) for T<T c/3 and a maximum of R s(T) at TT c/2, the linearity range of λ(T) extends to T≃50 K, and this curve has a plateau in the range 60<T<85 K. The curve of R s(T) in both the superconducting and normal states of YBa2Cu3O6.95 is well described by a two-fluid model with the electron-phonon mechanism of quasiparticle relaxation. A formula describing the curve of λ 2(0)/λ 2(T) throughout the studied temperature range is also given. Zh. éksp. Teor. Fiz. 112, 2210–2222 (December 1997)  相似文献   

13.
The low spin states of 223Ra have been populated via α-decay from 227Th which was itself produced following β decay of an 227Ac source. α–γ and α−e K,L,M angular correlation measurements have been analysed using the correct ground state spins of 227Th(=1/2+) and 223Ra(=3/2+) for the first time. The analysis has allowed unique Jπ values to be assigned to almost all levels below 400 keV excitation in 223Ra. Values of (g Kg R)/Q 0 have been deduced for several members of the K= 3/2± bands (for the first time in an odd N nucleus in this mass region) allowing estimates of g K and g R to be extracted. The values of g K and g R are not significantly different for the positive and negative parity band members and tend to support other strong evidence that stable octupole deformation exists in 223Ra at low excitation energies. Received: 17 November 1997 / Revised version: 8 January 1998  相似文献   

14.
An analysis is made of the relation between accurate formulas for the coefficients of turbulent diffusion D T and the alpha effect α T for a magnetic field in the Lagrange and Euler representations. It is shown that the quadratic term with respect to α T in the diffusion coefficient derived by Moffatt and Kraichnan is incorrect and should be dropped. First, a numerical solution of the nonlinear equation (DIA equation) for the Green function is presented, describing the transport of a magnetic field for the case of incompressible, uniform, isotropic, steady-state turbulence possessing helicity. These solutions are used to calculate the steady-state coefficients D T and α T for various values of the parameters ξ 0=u 0 σ 0/R 0, a=H 0/u 0 2 p 0, σ 0/σ 1, and R 0/R 1, where u 0, σ 0, and R 0 are the characteristic velocity, lifetime, and scale of the turbulent pulsations, and H 0, σ 1, and R 1 are similar values describing the helicity of the medium h(1,2)=〈u(1)· (∇×u(2))〉, and the parameter α characterizes the degree of helicity. The DIA values of D T and α T and the self-consistent values of these quantities calculated using the Green tensor in the diffusion approximation are in qualitative agreement. It is shown that the coefficient of turbulent diffusion is always positive for all the types of turbulence studied. Nonsteady-state values of D T(t) and α T(t) calculated by a self-consistent method are given. Zh. éksp. Teor. Fiz. 112, 1312–1331 (October 1997)  相似文献   

15.
16.
By means of π++ 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   

17.
The spin-spin relaxation rate 63 T 2 −1 of 63Cu nuclei in CuO2 layers is measured in the normal and superconducting states of the compound YBa2Cu3O6.9 (T c onset =94 K) subjected to radiation-induced disordering by a fast-neutron flux Φ to T c onset =68 K (Φ=7×1018 cm−2) and T c onset <4 K (Φ=12×1018 cm−2). It is found that as the structural disorder increases, the contribution of the indirect spin-spin interaction 63 T 2G −1 , which is related to the value of the spin susceptibility at the boundary of the Brillouin zone of the copper planes χs(q={π/a; π/a}), decreases slightly at the transition to the superconducting state for the initial sample and remains unchanged for the weakly disordered sample. This behavior of the short-wavelength contribution to the spin susceptibility attests to the stability of the x 2y 2 symmetry of the energy gap against structural disorder, in accordance with proposed theoretical models of Cooper pairing for high-T c cuprates. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 172–177 (10 February 1998)  相似文献   

18.
The dipion spectrum for the ϒ(nS) → ϒ(n′S) transition with n < 4 has the form dw/dq ∼ (phase space) |η − x|2, with x = q 2 − 4m π2 / (ΔM)2 − 4m π2 < q 2M ππ2, and ΔM = M(nS) − M(n′S). The parameter η is calculated and the spectrum is shown to reproduce the experimental data for all three types of decays: 3 → 1, 2 → 1, and 3 → 2 with η ≈ 0.5, 0, and −3, respectively. The text was submitted by the author in English.  相似文献   

19.
Abstact: High-spin states in 183Re have been studied using the 176Yb(11B,4n) reaction at 52 and 57 MeV. Two high-K bands have been observed directly by a time-correlated γ-γ coincidence measurement. One of the bands is built on an isomeric K π=(25/2)+ state at E x= 1908 keV with a half-life of 0.82(2) ms. The other band, assigned as K π=(29/2) at E x= 2739 keV, decays to the (25/2)+ band. These bands are interpreted as three-quasiparticle structures, π(5/2)+[402] &⊗ν(9/2)+[624] ⊗ν(11/2)+[615] for the (25/2)+ band and π(9/2)[514] ⊗ν(9/2)+[624] ⊗ν(11/2)+[615] for the (29/2) band. The K π= (29/2) band becomes strongly Coriolis mixed with increasing spin and is gradually changing into a low-K s-band structure. Received: 20 April 1998  相似文献   

20.
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   

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