Susceptibilities of the S = 12 XY model on the square lattice at T = 0

For the $\text{S =}\text{1}\text{2}\text{XY}$ model at T = 0 four susceptibilities have been calculated exactly on a sequence of finite square lattices and extrapolated to the infinite square lattice. For the ferromagnet χ_zz = 0 while χ_xx ～ N^2.9; for the antiferromagnet $\text{J}{}_{\mathrm{\chi xx}}\text{N(gμ}{}_{\mathrm{<mtext>B</mtext>}}\text{)}{}^2\text{= 0.025 ± 0.002}$ and $\text{J}{}_{\mathrm{\chi xx}}\text{N(gμ}{}_{\mathrm{<mtext>B</mtext>}}\text{)}{}^2\text{= 0.13 ± 0.03}$.     

Total width of the lowest T = 2 state in 24Mg

By analyzing thick-target excitation functions of the $\text{E}{}_{\mathrm{<mtext>p</mtext>}}\text{= 3906}\text{keV}{}^{23}\text{Na}\text{(}\text{p}\text{, γ)}$ resonance we have determined Γ_c.m ≦ 530⁺⁴⁰_?70 eV for the width of the lowest T = 2 state of ²⁴Mg. The beam energy resolution function was measured using a narrow ²⁷Al(p, γ) resonance at E_p = 3671 keV, for which we obtain Γ_c.m. = 180 ±50 eV.     

Contributions of operators of twist two and higher in large n moments of structure functions

Though high twist terms are becoming important as x→1, or equivalently, in large n moments, their detection in this regime in deep inelastic lepton scattering needs special caution. The high order terms in the twist two component are strongly dependent on n; one finds that at $\text{Q}{}^2\text{?Q}{}^2{}_7\text{?Λ}{}^2\text{a}{}_{\mathrm{k}}\text{exp}\text{[α}{}_{\mathrm{k}}\text{(}\text{log}\text{n)}{}^{\mathrm{<mtext>2?1</mtext><mtext>k</mtext>}}\text{(}\text{1+b}{}_{\mathrm{k}}\text{log}\text{n}\text{)]}$ the perturbative expansion is invalid whereas higher twist terms are important at $\text{Q}{}^2\text{?Q}{}_1{}^2\text{= Λ}{}^2\text{nC}$. Since $\text{Q}{}_7{}^2$ grows very fast with n the necessary requirement for any deep inelastic phenomenological analysis, namely $\text{Q}{}_1{}^2\text{?Q}{}_7{}^2$, cannot hold for too large moments. The scheme dependence of a_k, α_k and b_k is also discussed.     

Critical slowing down of fluctuations in squaric acid (H2C4O4) at the phase transition observed by 13C spin-lattice relaxation

Spin lattice relaxation T₁ of naturally abundant ¹³C nuclei in squaric acid was measured close to the antiferroelectric-paraelectric phase transition temperature T_c = 373 K. A rapid increase in $\text{1}\text{T}{}_1$ is observed close to T_c coming from above, which follows the power law $\text{1}\text{T}{}_1\text{～ ε}{}^{\mathrm{?1.4}}$ where $\text{ε =}\text{(T ? T}{}_{\mathrm{c}}\text{)}\text{T}{}_{\mathrm{c}}$. This behaviour is explained on the basis of the two-dimensional character of the fluctuations.     

The effective T = 1 two-particle matrix elements in the fp shell

The ⁴¹Ca($\text{d}$, p)⁴²Ca reaction has been used to locate the strength distributions for $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ transfer in ⁴²Ca. Effective $\text{(}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^2$, $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and ${}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ two-body matrix elements are derived from the data and compared to theoretical predictions.     

Classical stochastic diffusion theory for desorption from solid surfaces

We present a theory of desorption of atoms and molecules from solid surfaces based on a classical stochastic diffusion formulation. We obtain a simple rate expression which has the form $\text{R = (}\text{Ω}{}_{\mathrm{o}}\text{2π}$f(T) exp($\text{?D}{}_{\mathrm{e}}\text{K}{}_{\mathrm{T}}$), where T is the temperature, k is Boltzmann's constant, the bond enthalpy, and Ω_o is the surface-adsorbate vibrational frequency. For atoms √(T) = 1, while for molecules f(T) depends on the parameters for the frustrated rotations at the surface. Application of this theory is reported for the desorption of atoms and molecules. We find that molecules lead to a greatly increased (factor of 100) Arrhenius preexponential factor in excellent agreement with experiment.     

Study of the 58Ni(τ, α)57Ni reaction at 25 MeV

The ⁵⁸Ni(τ, α)⁵⁷Ni reaction has been studied at 25 MeV incident energy. Angular distributions have been measured from 5° to 50° with a split-pole spectrometer up to 13.5 MeV excitation energy. A local zero-range DWBA analysis has been carried out, allowing l-assignments for about eighty levels, most of them previously unknown. An isospin-dependent potential has been used in the calculation of the neutron form factor for both T_<and T_> states, and the C²S values deduced using this procedure are compared to those obtained with the usual separation energy method. Analog states of eleven ⁵⁷Co levels have been identified and the eventuality for isospin mixing in ⁵⁷Ni has been discussed. A sum rule analysis has been carried out and energy centroids of hole states have been determined. About 60% of the $\text{1}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{T}{}_{\mathrm{<}}$ strengths and the full $\text{1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ hole strengths are observed. It is shown that the two excess neutrons in the ⁵⁸Ni ground state mainly populate the $\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{, 1}\text{f}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{and}\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbitals, whereas the occupancy number of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ subshell is found to be smaller than 0.1%. Some non-pickup angular distributions have also been observed and a CRC analysis assuming two-step processes in the (τ, α) reaction and weak-coupling wave functions for final states has been attempted. Assignments of J^π values are proposed for four ⁵⁷Ni levels, based on this analysis.     

Jahn-Teller analysis of the 3T1(P) absorption band of Ni2+ in GaP

Comparison between experimental absorption due to the ${}^3\text{T}{}_1\text{(F)?}{}^3\text{T}{}_1\text{(P)}$ transition of substitutional Ni²⁺(d⁸) in GaP and theoretical predictions based on the Jahn-Teller model is presented. Numerical solution of the Hamiltonian, in which spin-orbit interaction and T₂-mode Jahn-Teller coupling are included, is in very good agreement with the energy position and intensities of the observed absorption lines.     

Magnetic circular dichroism of transition metal ions in solids—II K2NaGaF6: Cr3+

The absorption and MCD spectra of the ${}^4\text{A}{}_{\mathrm{2g}}\text{→}{}^4\text{T}{}_{\mathrm{2g}}$, ${}^4\text{A}{}_{\mathrm{2g}}$, ${}^4\text{A}{}_{\mathrm{2g}}\text{→}{}^4\text{T}{}_{\mathrm{1g}}{}^{\mathrm{a}}$ and ${}^4\text{A}{}_{\mathrm{2g}}\text{→}{}^4\text{T}{}_{\mathrm{1g}}{}^{\mathrm{b}}$ spin-allowed transitions of Cr³⁺ in K₂NaGaF₆ are reported. It is shown that transitions to the ${}^4\text{T}{}_{\mathrm{1g}}$. states are induced by T_1u vibratio the other spin-allowed transition, ${}^4\text{A}{}_{\mathrm{2g}}\text{→}{}^4\text{T}{}_{\mathrm{2g}}$, there are three competing intensity mechanisms: electric dipole induced by T_1u vibrations, electric dipole induced by T_2u vibrations and magnetic dipole, and an estimate is made of the relative importance of these. The magnetic dipole ${}^4\text{A}{}_{\mathrm{2g}}\text{→}{}^2\text{E}{}_{\mathrm{g}}$ zero-phonon line is observed to be accompanied by a vibrational sideband for which the coupling is predominantly with T_2u vibrations. Other weak transitions are observed in MCD spectra and their origin briefly discussed.     

A Mössbauer study of amorphous Fe40Ni40B20

Amorphous Fe₄₀Ni₄₀B₂₀ (VITROVAC 0040) alloy has been investigated using ⁵⁷Fe Mössbauer Spectroscopy. The Curie temperature T_c is found to be well defined and is 695 ± 1 K. The quadrupole splitting just above T_c is 0.64 mm sec^?1. The crystallization temperature is 698 ± 2 K, close to but definitely above T_c. The average hyperfine field H_eff(T) of the glassy state shows a temperature dependence of $\text{H}{}_{\mathrm{<mtext>eff</mtext>}}\text{(0)[1 ? B}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{(T/T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{? C}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{(T/T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{? …]}$ indicative of the existence of spin wave excitations. The values of $\text{B}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{C}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ are found to be 0.40 and 0.06, respectively, for T/T_c ? 0.72. At temperatures close to T_c, H_eff(T) varies as (1 ? T/T_c)^β where β is one of the critical exponents and its value is found to be 0.29 ± 0.02.     

Exact Fermi energy,susceptibilities, and their singularities for an electron gas in a uniform magnetic field at T = 0 °K

Exact analysis is presented to derive the magnetic response functions and their singularities of free-electron gas in a uniform magnetic field of arbitrary strength at T = 0 °K. The newly defined functions, Λ_μ(s) = ∑₀^[s])(s ? n)^μ of $\text{μ =}\text{?1}\text{2}\text{,}\text{1}\text{2}\text{,}\text{3}\text{2}$, are employed to obtain the Fermi energy, magnetization, and susceptibility as functions of B. It is revealed that the spin susceptibility is composed of two parts, χ_s1 and χ_s2, where χ_s2 is purely oscillatory diamagnetic. A graphical method of finding the Fermi energy ?_F(B) as a function of B has been obtained. The system is shown to become totally one-dimensional electron gas in the field B greater than $\text{B}{}_{\mathrm{\downarrow }}\text{= (2ηn)}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ and the total energy satisfies $\text{E}{}_{\mathrm{t}}\text{=}\text{1}\text{3}\text{?}{}_{\mathrm{F}}\text{(B)N}$. The obvious extension of the present theory to the Bloch electrons on the ellipsoidal constant energy surface is also discussed.     

CPT symmetry and neutral kaons

We discuss the accuracy of CPT invariance tests in the neutral kaon decays. The possible CPT non-invariance is parametrized by amplitudes of two types: (i) CP violating, but T conserving, and (ii) T violating, but CP conserving. It is shown that the experimental data are consistent with CPT symmetry essentially within two standard deviations.The source of this not quite satisfactory agreement is the experimental value of the phase φ₀₀ of the ratio $\text{A(}\text{K}{}_{\mathrm{L}}{}^0\text{→π}{}^0\text{π}{}^0\text{)}\text{A(}\text{K}{}_{\mathrm{S}}{}^0\text{→π}{}^0\text{π}{}^0\text{)}$, which differs by two standard deviations from the phase φ_+? of the ratio $\text{A(}\text{K}{}_{\mathrm{L}}{}^0\text{→π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{)}\text{A(}\text{K}{}_{\mathrm{S}}{}^0\text{→π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{)}$ decay amplitude. We argue that to get better agreement with CPT invariance, the value of the phase φ₀₀ has to be equal to the value of the phase φ_+? within the errors of the latter. New, more accurate measurements of the phase φ₀₀ would be very interesting to rest CPT invariance, especially taking into account that neutral kaons allow the test with much better accuracy than any other particle.     

General kinematical characteristics of fitted events from four-, six-, eight-, and ten-prong topologies in pp interactions at 13.1 GeV/c

Partial cross sections are presented for the various topologies in 13.1 GeV/c pp interactions. The transverse and c.m. longitudinal momenta distributions for nucleons and pions are given. The variation of〈p_T〉 and are presented as a function of the multiplicity The best fit of the p_T and $\text{p}{}_{\mathrm{L}}{}^1$ distributions is obtained with functions suggested by the thermodyanamical model. The collimation and asymmetry parameters are given. Di-pions and tripions correlations are studied.     

The effect of a non-minimally coupled scalar field upon classical thermodynamics

It is known that a scalar field that is non-minimally coupled to the geometry implies a varying gravitational “constant” G_eff, and hence a violation of the continuity equations, $\text{T}\text{?}{}^{\mathrm{ik}}{}_{\mathrm{;k}}\text{≠ 0}$, where $\text{T}\text{?}{}_{\mathrm{ij}}$ is the uncorrected energy-momentum tensor. This in turn upsets classical thermodynamics. 3he simplest resolution of this difficulty is to multiply all energetic quantities by $\text{G}{}_{\mathrm{<mtext>eff</mtext>}}\text{G}{}_{\mathrm{<mtext>N</mtext>}}$, where G_N is the newtonian gravitational constant. This modified thermodynamics is applied to the scalar-field version of the cosmological model of Zee, for which it is shown to cause restoration of the symmetry above some critical temperature T_c close to the Planck temperature. We also illustrate how the second law of thermodynamics is always obeyed, correcting a recent discussion by Davies.     

On some recent results concerning the superconducting transition temperature

The Eliashberg gap equations relate the transition temperature T_c of an isotropic superconductor to its electron-phonon spectral function α²F(ω) and Coulomb pseudopotential parameter $\text{μ}{}^1$. Recently the Eliashberg theory has been used to derive some supposedly rigorous results bearing on the problem of attaining higher superconducting transition temperatures: Bergmann and Rainer derived an expression for the functional derivative $\text{δT}{}_{\mathrm{c}}\text{δα}{}^2\text{F(ω)}$; Allen and Dynes showed that in the asymptotic limit of very large $\text{λ(λ?10)k}{}_{\mathrm{B}}\text{T}{}_{\mathrm{c}}\text{=f(μ}{}^1\text{)(λ〈ω}{}^2\text{〉)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and Leavens proved that for any isotropic superconductor k_BT_c ?0.2309A, where A is the area under its electron-phonon spectral function. In this letter we show that the result of Allen and Dynes is not compatible with the other results and is, in fact, incorrect.     

Density of states in dirty type II superconductors near Tc

We have determined the behavior of the density of states in the mixed state of superconducting alloys for T → T_c. The local density of states tends towards the BCS expression with the order parameter playing the role of the energy gap. The singularities are smeared out by the spatial average. The effective normal core radius of a vortex diverges like $\text{(1 ?}\text{T}\text{T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$ for T → T_c unlike the coherence length which diverges like $\text{(1 ?}\text{T}\text{T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$.     

Structure magnetique en champ applique nul de l'acetate de manganese tetrahydrate Mn(CH3COO)2, 4H2O

The magnetic structure of manganous acetate Mn(CH₃COO)₂, 4H₂O has been solved by neutron diffraction. Manganous acetate crystallizes in the space group $\text{P2}{}_1\text{c}$ with Z = 6. Manganese atoms (in position 2a and 4e) are located in (100) planes. Below T_N = 3.18 K this compound is antiferromagnetic in a zero applied field with the k vector [$\text{1}\text{2}$ 00]. The plane (100) is ferromagnetic. The magnetic group is $\text{P}{}_{\mathrm{2a}}\text{2}{}_1\text{c}$.     

Further neighbour interactions in the quasi b.c.c. Heisenberg ferromagnets M2 Cu X4 · 2H2 O (M = NH4, K,Rb or Cs; X = Cl or Br)

The Curie-Weiss constant θ of the quasi b.c.c., $\text{S =}\text{1}\text{2}$, Heisenberg ferromagnets, (NH₄)₂ Cu Br₄ · 2H₂ O and Rb₂ Cu Br₄ · 2H₂ O, have been derived from measurements of the susceptibility in the paramagnetic region (4.2 < T < 100 K) and of the high-field magnetization curves at $\text{T = 4.2}\text{K}\text{(}\text{T}\text{T}{}_{\mathrm{c}}\text{? 2.3)}$. The $\text{T}{}_{\mathrm{c}}\text{θ}$ values obtained point to the presence of further neighbour interactions considerably stronger than previously assumed. The effective number of equivalently interacting magnetic neighbours is estimated to be at least seventeen.     

Monte Carlo study on dynamical behaviour of spins and spin clusters in the 2D ± J Ising spin-glass

To investigate dynamical (time-dependent) behavior of spins and spin clusters in the two-dimensional ± J Ising spin-glass, we have evaluated the relaxation time τ_i of individual spins by the Monte Carlo simulation. An interesting finding is that, at least in the temperature range $\text{T ? 0.8J}$, most of τ_i are described by $\text{τ}{}_{\mathrm{i}}\text{∝}\text{exp}\text{{}\text{E}{}_{\mathrm{i}}\text{(T ? T}{}_0\text{}}$ with T₀?0.5J (E_i being a constant), which suggests that the system undergoes a glass transition obeying Fulcher's law.