共查询到20条相似文献,搜索用时 15 毫秒
1.
If M 2m is a closed Kähler spin manifold of positive scalar curvature R, then each eigenvalue λ of type r ( r {1, …, [( m + 1)/2]}) of the Dirac operator D satisfies the inequality λ 2 ≥ rR 0/4 r − 2, where R 0 is the minimum of R on M 2m. Hence, if the complex dimension m is odd (even) we have the estimation for the first eigenvalue of D. In the paper is also considered the limiting case of the given inequalities. In the limiting case with m = 2 r − 1 the manifold M 2m must be Einstein. The manifolds S 2, S 2 × S 2, S 2 × T 2, P 3(
), F(
), P 3(
) × T 2 and F(
3) × T 2, where F(
3) denotes the flag manifold and T 2 the 2-dimensional flat torus, are examples for which the first eigenvalue of the Dirac operator realizes the limiting case of the corresponding inequality. In general, if M 2m is an example of odd complex dimension m, then M 2m × T 2 is an example of even complex dimension m + 1. The limiting case is characterized by the fact that here appear eigenspinors of D 2 which are Kählerian twistor-spinors. 相似文献
3.
The βγ circular polarization correlation of the 3 −(β − 621 keV)3 −(γ 1692)2 + cascade in 124Sb, the 4 +(β − 662)4 + (γ 796)2 + (γ 605)0 + in 13Z4Cs and the 6 +(β −529)6 + (γ 937)4 + (γ 885)2 + (γ 658)0 + in 110mAg have been studied by using a Compton effect polarimeter. The measured asymmetry parameters are 0.172±0.004, −0.0702 ±0.0024 and 0.0549±0.0013 respectively. 相似文献
4.
Theoretical studies are given on the (n, d) and (d, 3He) reactions leading to deeply bound pionic atoms in heavy nuclei of configuration [( nl) π· jn−1] J. The cross sections for various pionic and neutron-hole configurations in the case of a 208Pb target are calculated at incident energies 300–1000 MeV/u by using the effective number approach and the eikonal approximation for distortion. The effective number with a pion in the 1s or 2p state and a neutron hole in the
orbit peaks around the same incident energy ( Tn = 600 MeV) as the elementary cross section n+n→d+π −, where the momentum transfer matches the angular-momentum transfer of L = 5–7. The DWIA cross section for (n,d) producing a pion in the 1s or 2p orbit at Tn = 600 MeV is found to be around 42 or 75 μb/sr, respectively. At Tn = 350 MeV, where the momentum transfer is small, quasi-substitutional states of configurations
and
are preferentially populated with (n, d) cross sections of 95 and 190 μb/sr, respectively. The (d, 3He) cross sections are estimated to be an order of magnitude smaller than the (n, d) cross sections. Thus, the (n, d) and (d, 3He) reactions are found to be suited for the production of deeply bound pionic atoms. 相似文献
5.
Five dimensional classical unified field theories as well as Yang-Mills theory with gauge group U (1), are described in terms of a Lorentzian five dimensional space V 5 with metric tensor γβ which admits a space-like Killing vector ζ . It is assumed that: (1) V 5 has the topology of V 4 x S 1, S 1 is a circle and V 4 is a four dimensional Lorentzian space that is asymptotically flat and (2) the Einstein tensor Γ β of V5 satisfies Γ β Uυ β 0 where U and υ are future oriented time-like vectors with γ βυ ζ β = 0. The spinor approach of Witten [4], Nester [3] and Moreschi and Sparling [5] is used to show that the conserved five dimensional energymomentum vector P = ifΓ β = 0 then V 5 must admit a time-like Killing vector. Lichnerowicz's results [1] then imply that V 5 must be flat. A lower bound for P 4 (the mass) similar to that found by Gibbons and Hull [6] is obtained. 相似文献
6.
The chromium(II) antimony(III) sulphide, [Cr((NH 2CH 2CH 2) 3N)]Sb 4S 7, was synthesised under solvothermal conditions from the reaction of Sb 2S 3, Cr and S dissolved in tris(2-aminoethyl)amine (tren) at 438 K. The products were characterised by single-crystal X-ray diffraction, elemental analysis, SQUID magnetometry and diffuse reflectance spectroscopy. The compound crystallises in the monoclinic space group P2 1/n with a=7.9756(7), b=10.5191(9), c=25.880(2) Å and β=90.864(5)°. Alternating SbS 33− trigonal pyramids and Sb 3S 63− semi-cubes generate Sb 4S 72− chains which are directly bonded to Cr(tren) 2+ pendant units. The effective magnetic moment of 4.94(6) μB shows a negligible orbital contribution, in agreement with expectations for Cr(II): d4 in a 5A ground state. The measured band gap of 2.14(3) eV is consistent with a correlation between optical band gap and framework density that is established from analysis of a wide range of antimony sulphides. 相似文献
7.
Reversible and irreversible domain wall (DW) motions have been investigated in La 0.7Sr 0.3MnO 3 ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10 5 A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10 4 A/m. The Rayleigh constant η increases from 5.45×10 −2 to 1.54×10 −1 (A/m) −1 as the temperature rises from 293 to 343 K, and η decreases from 5.58×10 −2 to 3.67×10 −2 (A/m) −1 with increasing DC field from 1.99×10 3 to 4.22×10 4 A/m. 相似文献
8.
The static quadrupole moments of the first excited Jπ = 2 + states in 20Ne and 22Ne and the reduced electric quadrupole transition probabilities of these states to the ground states were measured via projectile Coulomb excitation. The quadrupole moments were deduced from the shapes of γ-ray angular distributions. The results are: Q( 20Ne, 2 +) = −0.20±0.05 b and Q( 22Ne, 2 +) = −0.11±0.05 b. The transition strengths were deduced from yield measurements and by comparison with the yields of target γ-rays. The results are: B(E2; 0 + → 2 +, 20Ne) = 0.037±0.003 e2 · b 2 and B(E2; 0 + → 2 +, 22Ne) = 0.025±0.002 e2· b 2. The results for the transition strengths are consistent with the results of accurate timing methods and resolve discrepancies between previous experiments. The results for the quadrupole moments are consistent with earlier measurements, although the mean values we obtain are slightly lower. The experimental measurements are compared with theoretical predictions and a detailed discussion is given of corrections to this type of reorientation experiment. 相似文献
9.
Angular distribution of the reaction 12C( d,τ) 11B leading to the 3/2 − ground state and the 4.44 MeV excited (5/2 − state 11B have measured at Ed = 80 MeV up to about 70° and 40°, respectively. The inclusion of second-order processes in the framework of CCBA calculations gives a good reproduction of the 3/2 − as well as of the DWBA forbidden 3/2 − angular distribution. The strong dependence of the cross section on the sign of the deformation supports a positive β 2 value for 11B. 相似文献
10.
Lifetimes of excited 0 + states in 166Er have been measured with the (n,n′γ) reaction. The first and second excited 0 + states have no significant collective enhancements of their decays, and their properties are suggestive of pair-type excitations rather than those of a β vibration or phonon excitation built on the γ vibration. The third excited 0 + state at 1934 keV has an enhanced decay to the ground state band with B( E2; 0 4+ → 2 gsb+) = 8.8 ± 0.9 W.u., consistent with that expected for a β vibration. 相似文献
11.
The results of the impedance spectroscopy measurements on eutectic samples based on zirconium oxide are presented here. Samples of CaZrO 3---ZrO 2(cubic) and MgO---ZrO 2(cubic) have been grown by a directional solidification procedure such that the different phases appear nearly oriented along the growth direction (lamellae in the system of CaZrO 3-ZrO 2(cubic) and fibers of MgO in a ZrO 2 matrix in the other system). The DC electrical conductivity has been measured by impedance spectroscopy along and across the growth axis. For CaZrO 3---ZrO 2 the coductivity is clearly anisotropic. The following values for σ T have been obtained: the conductivity at 600 °C equals 2.0 × 10 −6 Ω −1 cm −1 perpendicular to the fiber axis and 1.4 × 10 −5 Ω −1 cm −1 parallel to it and with an activation energy of 1.3 eV for σ T. For MgO---ZrO 2(cubic) the isotropic value of the conductivity at 600 °C is 10 −4 Ω −1 cm−1 with activation energy for σ T of 1.5 eV. The anisotropic conductivity in the CaZrO 3---ZrO 2 (cubic) system has been explained by a model of an ordered stacking of oxygen conducting (cubic ZrO 2) and non-conducting (CaZrO 3 or MgO) phases. 相似文献
12.
The theoretical mechanisms for the decays ψ′ → ψπ 0 and ψ′ → ψη, which violate SU 2 and SU 3, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π 0 −η −η′ mixing. The π 0 −η mechanism ψ′ → ψν → ψπ 0 leads to Γ(ψ′ → ψπ 0) = (3.3±1.0) × 10 −3 Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π 0−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed. 相似文献
13.
The A( e, e′K+) YX reaction has been investigated in Hall C at Jefferson Lab. Data were taken for Q2 ≈ 0.35 and 0.5 GeV 2 at a beam energy of 3.245 GeV for 3He, 4He. The missing mass spectra are fitted with Monte Carlo simulations including Λ, Σ 0, Σ − hyperon production. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Λ-hypernuclear bound states is seen for 3,4He targets. 相似文献
14.
The reaction γ p → π °γ′ p has been measured with the TAPS BaF 2 calorimeter at the Mainz Microtron accelerator facility MAMI for energies between √2 = 1221–1331 MeV. Cross sections differential in angle and energy have been determined for the photon γ′ in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the Δ +(1232) resonance and, for the first time, a value of μ Δ+ = (2.7 +1.0−1.3( stat) ± 1.5( syst) ± ( theor)) π N has been extracted. 相似文献
15.
A C.W. multi-mode dye laser is used to obtain by optical pumping an orientation of the 2p 5 3s 3P 0 ( F = 3/2) state of 21Ne. A magnetic resonance experiment leads to the measurement of the g factor g ( 3P 0) = 3.027 (8) × 10 −4 to be compared with the theoretical prediction (3.025(6) × 10 −4). One obtains also the metastability exchange cross section σ( 3P 0) = 18.4 ± 4 Å 2 for collisions between metastable ( 3P 0) Ne atoms and ground state Ne atoms. This result is compared with other measurements and theoretical evaluation. 相似文献
16.
The reactions π −p → 2π −π +p, π −p → 2π −π +π op and π −p → 2π −2π +n are analysed at 11 and 16 GeV/ c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π −p → 2π −π +p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π −p → (2π −π +)p, and of the proton, π −p → π −(π −π +p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π −p → (2π)(πp) decrease with increasing energy. In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π−p → π−(π−π+πop); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π−p → π−(π−2π+)n. Another strong maximum corresponds to the pion dissociation π−p → (2π−π+πo)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π−p → (2π−2π+)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π−p → (2π−π+)(πop) and π−p → (2π−π+)(π+n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed. An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy. 相似文献
17.
The time-dependence of the decay rate of initially pure K 0 into the final state (π +π −π 0) has been studied in search for the decay k S0→π +π −π 0. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K S0 amplitude and the K L0 amplitude is η +−0 = (0.13 −0.20+0.17) + i(0.17 −0.26+0.27); the ratio of the CP-conserving K S0 amplitude and the K L0 amplitude is < 0.4. The energy dependence of the K 0→π +π −π 0 matrix element is found to be a+−0 = −0.31 ± 0.03. 相似文献
18.
Polycrystalline (1− x)Ta 2O 5− xTiO 2 thin films were formed on Si by metalorganic decomposition (MOD) and annealed at various temperatures. As-deposited films were in the amorphous state and were completely transformed to crystalline after annealing above 600 °C. During crystallization, a thin interfacial SiO 2 layer was formed at the (1− x)Ta 2O 5− xTiO 2/Si interface. Thin films with 0.92Ta 2O 5–0.08TiO 2 composition exhibited superior insulating properties. The measured dielectric constant and dissipation factor at 1 MHz were 9 and 0.015, respectively, for films annealed at 900 °C. The interface trap density was 2.5×10 11 cm −2 eV −1, and flatband voltage was −0.38 V. A charge storage density of 22.8 fC/μm 2 was obtained at an applied electric field of 3 MV/cm. The leakage current density was lower than 4×10 −9 A/cm 2 up to an applied electric field of 6 MV/cm. 相似文献
19.
We present an analytic three-loop calculation for thermodynamic quantities of the O(n) symmetric Φ 4 theory below Tc within the minimal subtraction scheme at fixed dimension d = 3. Goldstone singularities arising at an intermediate stage in the calculation of O( n) symmetric quantities cancel among themselves leaving a finite result in the limit of zero external field. From the free energy we calculate the three-loop terms of the amplitude functions ƒ Φ, F+ and F− of the order parameter and the specific heat above and below Tc, respectively, without using the e = 4- d expansion. A Borel resummation for the case n = 2 yields resummed amplitude functions fΦ and F− that are slightly larger than the one-loop results. Accurate knowledge of these functions is needed for testing the renormalization-group prediction of critical-point universality along the λ −line of superfluid 4He. Combining the three-loop result for F− with a recent five-loop calculation of the additive renormalization constant of the specific heat yields excellent agreement between the calculated and measured universal amplitude ratio A+/ A- of the specific heat of 4He. In addition we use our result for fΦ to calculate the universal combination Rc of the amplitudes of the order parameter, the susceptibility and the specific heat for n = 2 and n = 3. Our Borel-resummed three-loop result for Rc is significantly more accurate than the previous result obtained from the ε-expansion up to O(ε 2. 相似文献
20.
We present predictions for flavour-violating charged-lepton decays induced by the seesaw mechanism implemented within the constrained minimal supersymmetric standard model (CMSSM) with universal input soft supersymmetry breaking terms. We assume that one heavy singlet neutrino almost decouples from the seesaw mechanism, as suggested by the pattern of light neutrino masses and mixing angles. This is suggested independently by sneutrino inflation with a low reheating temperature, TRH10 7 GeV, so as to avoid overproducing gravitinos. This requirement further fixes the mass of the weakly-coupled sneutrino, whose decays may lead to leptogenesis. We find that BR(μ→ eγ)10 −13 but BR(τ→μγ)10 −9 in the bulk of the acceptable parameter space, apart from a few isolated points. The ratio BR(μ→ eγ)/ BR(τ→ eγ) depends on only one complex parameter, and is particularly interesting to compare with experiment. 相似文献
|