An application of gap regenerator/expander precooled by two stage G-M refrigerator

The degradation of regenerator effectiveness below 10K is due to the imbalance of the heat capacity of the regenerator material and helium gas as a working fluid. One of the attractive methods to increase this efficiency could be realized by a gap regenerator system regarding helium gas property. This paper describes an experiment using pressurized helium gas as a regenerator material. A two stage G-M cycle refrigerator has been used for precooling the gap regenerator system. With this method, minimum temperature below 5K has been obtained when the precooling temperature maintained at 10K

Ground-State Properties of a Heisenberg Spin Glass Model with a Hybrid Genetic Algorithm

We developed a genetic algorithm (GA) in the Heisenberg model that combines a triadic crossover and a parameter-free genetic algorithm. Using the algorithm, we examined the ground-state stiffness of the $\pm J$ Heisenberg model in three dimensions up to a moderate size range. Results showed the stiffness constant of $\theta = 0$ in the periodic-antiperiodic boundary condition method and that of $\theta \sim 0.62$ in the open-boundary-twist method. We considered the origin of the difference in $\theta$ between the two methods and suggested that both results show the same thing: the ground state of the open system is stable against a weak perturbation.Comment: 11 pages, 5 figure

An improved method for determining the DC magnetization curve using a ring specimen

When the DC magnetization curve (B-H) of nonoriented material is measured in a ring specimen, there is an intrinsic error due to the assumption that the mean magnetic path length is equal to the mean geometric path length. A novel method for determining the B-H curve accurately is proposed. The validity of the method is verified by experiments</p

Parisi States in a Heisenberg Spin-Glass Model in Three Dimensions

We have studied low-lying metastable states of the $\pm J$ Heisenberg model in two ($d=2$) and three ($d=3$) dimensions having developed a hybrid genetic algorithm. We have found a strong evidence of the occurrence of the Parisi states in $d=3$ but not in $d=2$. That is, in $L^d$ lattices, there exist metastable states with a finite excitation energy of $\Delta E \sim O(J)$ for $L \to \infty$, and energy barriers $\Delta W$ between the ground state and those metastable states are $\Delta W \sim O(JL^{\theta})$ with $\theta > 0$ in $d=3$ but with $\theta < 0$ in $d=2$. We have also found droplet-like excitations, suggesting a mixed scenario of the replica-symmetry-breaking picture and the droplet picture recently speculated in the Ising SG model.Comment: 4 pages, 6 figure

Compact Claude cycle refrigerator for laboratory use

A Claude cycle refrigerator with a three stage reciprocating expansion engine is described. Instead of a cam mechanism, valves are driven directly by magnetic solenoids operated by means of a micro processor control system. A swash plate mechanism is used to convert reciprocating motion of the expander pistons to rotary motion. A refrigeration capacity of 8 watts was achieved at 4.5 K with the operating pressure of 1.1 MPa and flow rate of 2.4 g/sec.. An effect of overintake operation was studied. Experimental results show that the efficiency of the expander has a peak point in the region of overintake operation with constant cycle speed, which agrees with theoretical results. The electrically controlled valve system is useful to vary the valve timing to achieve an optimum condition of operation

Primordial Non-Gaussianity and Analytical Formula for Minkowski Functionals of the Cosmic Microwave Background and Large-scale Structure

We derive analytical formulae for the Minkowski Functions of the cosmic microwave background (CMB) and large-scale structure (LSS) from primordial non-Gaussianity. These formulae enable us to estimate a non-linear coupling parameter, f_NL, directly from the CMB and LSS data without relying on numerical simulations of non-Gaussian primordial fluctuations. One can use these formulae to estimate statistical errors on f_NL from Gaussian realizations, which are much faster to generate than non-Gaussian ones, fully taking into account the cosmic/sampling variance, beam smearing, survey mask, etc. We show that the CMB data from the Wilkinson Microwave Anisotropy Probe should be sensitive to |f_NL|\simeq 40 at the 68% confidence level. The Planck data should be sensitive to |f_NL|\simeq 20. As for the LSS data, the late-time non-Gaussianity arising from gravitational instability and galaxy biasing makes it more challenging to detect primordial non-Gaussianity at low redshifts. The late-time effects obscure the primordial signals at small spatial scales. High-redshift galaxy surveys at z>2 covering \sim 10Gpc^3 volume would be required for the LSS data to detect |f_NL|\simeq 100. Minkowski Functionals are nicely complementary to the bispectrum because the Minkowski Functionals are defined in real space and the bispectrum is defined in Fourier space. This property makes the Minksowski Functionals a useful tool in the presence of real-world issues such as anisotropic noise, foreground and survey masks. Our formalism can be extended to scale-dependent f_NL easily.Comment: 16 pages, 5 figures, accepted for publication in ApJ (Vol. 653, 2006

Spin-Glass and Chiral-Glass Transitions in a ±J\pm J Heisenberg Spin-Glass Model in Three Dimensions

The three-dimensional $\pm J$ Heisenberg spin-glass model is investigated by the non-equilibrium relaxation method from the paramagnetic state. Finite-size effects in the non-equilibrium relaxation are analyzed, and the relaxation functions of the spin-glass susceptibility and the chiral-glass susceptibility in the infinite-size system are obtained. The finite-time scaling analysis gives the spin-glass transition at $T_{\rm sg}/J=0.21_{-0.02}^{+0.01}$ and the chiral-glass transition at $T_{\rm cg}/J=0.22_{-0.03}^{+0.01}$. The results suggest that both transitions occur simultaneously. The critical exponent of the spin-glass susceptibility is estimated as $\gamma_{\rm sg}= 1.7 \pm 0.3$, which makes an agreement with the experiments of the insulating and the canonical spin-glass materials.Comment: 4 pages, 2 figure

A simulation of high energy cosmic ray propagation 1

High energy cosmic ray propagation of the energy region 10 to the 14.5 power - 10 to the 18th power eV is simulated in the inter steller circumstances. In conclusion, the diffusion process by turbulent magnetic fields is classified into several regions by ratio of the gyro-radius and the scale of turbulence. When the ratio becomes larger then 10 to the minus 0.5 power, the analysis with the assumption of point scattering can be applied with the mean free path E sup 2. However, when the ratio is smaller than 10 to the minus 0.5 power, we need a more complicated analysis or simulation. Assuming the turbulence scale of magnetic fields of the Galaxy is 10-30pc and the mean magnetic field strength is 3 micro gauss, the energy of cosmic ray with that gyro-radius is about 10 to the 16.5 power eV

Ordering of the Heisenberg Spin Glass in High Dimensions

Ordering of the Heisenberg spin glass with the nearest-neighbor Gaussian coupling is investigated by equilibrium Monte Carlo simulations in four and five dimensions. Ordering of the mean-field Heisenberg spin-glass is also studied for comparison. Particular attention is paid to the nature of the spin-glass and the chiral-glass orderings. Our numerical data suggest that, in five dimensions, the model exhibits a single spin-glass transition at a finite temperature, where the spin-glass order accompanying the simultaneous chiral-glass order sets in. In four dimensions, by contrast, the model exhibits a chiral-glass transition at a finite temperature, not accompanying the standard spin-glass order. The critical region associated with the chiral-glass transition, however, is very narrow, suggesting that dimension four is close to the marginal dimensionality.Comment: 18 pages, 12 figure

Gamma rays of energy or = 10(15) eV from Cyg X-3

The experimental data of extensive air showers observed at Akeno have been analyzed to detect the gamma ray signal from Cyg X-3. After muon poor air showers are selected, the correlation of data acquisition time with 4.8 hours X-ray period is studied, giving the data concentration near the phase 0.6, the time of X-ray maximum. The probability that uniform backgrounds create the distribution is 0.2%. The time averaged integral gamma ray flux is estimated as (1.1 + or - 0.4)x 10 to the -14th power cm(-2) sec(-1) for Eo 10 to the 15th power eV and (8.8 + or - 5.0)x 10 to the 14th power cm(-2) sec(-1) for Eo 6 x 10 to the 14th power eV