High spin states above the 8⁺ isomer in ⁸⁸Zr have been studied using the ⁸⁶Sr(α, 2nγ)⁸⁸Zr reaction. Several high spin states above the isomer and lower excited states have been identified. The energy levels and transition properties are discussed on the basis of the shell model.

View full abstract

The unpaired elastic force model (EFM) developed by Kushwaha and Kushwaha has been extended to study the lattice dynamics of solid Neon (Ne) and Xenon (Xe). The application of the model has been made to calculate the phonon frequencies of Ne and Xe at all the irreducible points of the first Brillouin Zone. Use thereof has been made to calculate the lattice heat capacities and Debye characteristic temperatures in the temperature range 4–24 K and 4–100 K for Ne and Xe respectively. The calculated values of phonon frequencies along the three symmetry directions [100], [110], and [111], heat capacities and the Debye characteristic temperatures have been compared with the recent available experimental data. The merits and demerits of the model have been widely discussed.

View full abstract

A theory of random mixture of antiferromagnetic atoms with different easy axes is developed in which the effect of spin pair correlations is taken into account. A set of integral equations for the distribution functions g_p^(λ)(S) are obtained, where p=A or B atom, λ=α or β sublattice, S is a unit vector pointing to the direction of spin. The integral equations are solved analytically near the transition temperature in the case of small anisotropy and numerically by the computer at low temperatures in general case. The oblique antiferromagnetic phase is clearly recognized.

View full abstract

A Gaussian spectral weight function is derived by solving in a certain approximation the Dyson equation for band electrons interacting with impurities in a magnetic field. The condition for validity is clarified by examining the approximation. In the presence of the interaction with optical phonons as well as impurities, the transverse electric conductivity is calculated in an approximation consistent with the Green function. The effect of impurities on the transverse magnetophonon oscillation is small under the conditions considered here, contrary to the previous prediction by Barker. A possible reason of the discrepancy is discussed.

View full abstract

“Lineal” is a type of relationship between ferroic phases derived from one prototypic phase, as was explained in previous papers. A lineal transition of rank difference 1, i.e., the transition between two lineal phases whose ranks differ by 1 can be second order A lineal transition of rank difference>1 (let the two relevant phases be called α and β) cannot be second order, if in the homophone sequence there is a possible phase that is lineal both to phase α and to phase β and whose rank is intermediate between the ranks of phases α and β On the other hand, if there is no intermediate-rank lineal phase, the lineal transition of rank difference>1—despite being of rank difference>1—can be second order. Detailed elucidations of these are made with two simple examples of homophone sequences.

View full abstract

In the course of the successive transitions caused by the electrohydrodynamic instabilities in a nematic MBBA, the fluctuation of the transmission of light is measured as a function of the applied voltage. The critical regions at both transitions from Williams domain (the roll pattern) to grid pattern (the cellular pattern) and from grid pattern to non-periodic flow are very broad with strong non-linearity, which bears strong resemblance to the phase transition in a thermal equilibrium. The second moments of the fluctuattion increase at the instability points.

View full abstract

In the course of the successive transitions caused by the electrohydrodynamic instabilities in the nematics (MBBA), the fluctuation of the transmission of light is measured as a function of the applied voltage. From the autocorrelation and the power spectrum the behavior of the characteristic modes are studied. The mode-softenings occur at the instability points. The qualitative discussion is described.

View full abstract

An investigation based on GL theory on quasiparticle-injected superconductor leads to the occurrence of oscillation between two superconducting states with different energy gaps. The frequency of the oscillation is found to be proportional to the discrepancy between the chemical potential for superparticle and that for quasiparticle. Detailed calculations with the help of BCS theory are made on the energy gap and the free energy in the nonequilibrium state. In comparison with the calculated result is discussed an experiment on the temperature dependence of the threshold-injection current for S–N transition.

View full abstract

Hall voltage V_⊥ as well as resistance voltage V_⁄⁄ of lead films near the superconducting transition temperature was measured by the use of double AC method. As temperature went down, V_⊥ increased to a maximum value and subsequently decreased to a minimum value. This anomalous behavior of V_⊥ is believed to be due to the superconducting fluctuation. The Hall voltage V_⊥ was almost proportional to the sample current and the applied magnetic field. Above the transition temperature the relation between the observed behavior of the Hall voltage and the predicted one (Fukuyama, Ebisawa and Tsuzuki (1971)) is discussed.

View full abstract

Theoretical study is given of the high field transport of surface state electrons on the liquid ⁴He. The explicit form of the electron distribution function is solved by the use of the Boltzmann transport equation where the electron-ripplon and electron-He gas interactions are considered as dominant scattering mechanisms, and the electron-electron interactions are completely neglected. Inter-subband and intra-subband transitions are treated equally. The S-shaped non-linear behaviors predicted to occur at low temperature region in the electron temperature approximation have been removed. Experimentally observed hysteresis, if any, in the widths of the plasmon resonance and cyclotron resonance may thus be attributed to the electron-electron interaction.

View full abstract

Single crystals of the disordered perovskite-type Sr(Fe_0.766W_0.234)O₃ have been grown from a flux of SrCl₂. The crystals grew with a cubical habit with distinct (100) faces. Magnetic measurements indicated antiferromagnetic behavior or weak-ferromagnetic one with very small spontaneous magnetization (∼0.028 emu/g). The existence of Fe⁴⁺ was suggested by the Mössbauer technique. The Néel temperature is 193 K. The differences of structural, magnetic properties and Mössbauer effect between Sr(Fe_0.766W_0.234)O₃ and Sr(Fe_2⁄3W_1⁄3)O₃ are generally explained by assigning the valence states of the two samples as Sr(Fe_0.468³⁺Fe_0.298⁴⁺W_0.234⁶⁺)O₃ and Sr(Fe_1⁄3³⁺W_2⁄3⁶⁺)O₃ respectively.

View full abstract

The temperature dependence of the electric conductivity, the magnetic susceptibility and the ESR spectra of the crystals of an organic ion-radical salt, 1,1′-diethyl-2,2′-cyanine-[7,7′,8,8′-tetracyanoquinodimethane]₂, were measured. The electric conductivity, σ, is fairly large at room temperature (σ_RT=3.5 Ω⁻¹cm⁻¹) and shows a semiconductive temperature dependence, of which activation energy decreases with decreasing temperature. The susceptibility obeys Curie-Weiss’ law above 60 K and shows a maximum near 40 K. Below 15 K the susceptibility increases again with decreasing temperature. However, similarly at high temperatures even at 4.2 K there are two intense ESR absorptions of which interval depends on the orientation of the crystal in the applied magnetic field.

View full abstract

Instantaneous spin correlations (Remark: Graphics omitted.) in CsCoCl₃ have been studied by means of quasi-elastic neutron scattering technique and well defined plane-like intensity distribution characteristic for 1D system has been observed. At temperatures higher than 30 K, the observed temperature variation of (Remark: Graphics omitted.) is in good agreement with the rigorous solution for the 1D Ising antiferromagnet with |J|⁄k=75 K. When the temperature is decreased, 3D critical scattering consistent with the previously worked model can be observed at two Néel points T_N1=21.3 K and T_N2=9.2 K.

View full abstract

Following the previous study on the 1D Ising antiferrormagnet CsCoCl₃, the dynamical spin correlation has been studied in a wide range of temperature. The observed spin wave spectrum is Ising-like with J⁄k=75 K but the temperature dependence is unusual. No softening of the spin wave frequencies occurs, but the peak becomes broad and the intensity falls off with increasing temperature from the high q side. Well behaved spin wave peaks whose wave lengths are much longer than the correlation length κ⁻¹ can be observed. Discussions are given of the criteria for the existing of spin waves. The longitudinal correlation cannot be described by the simple rigorous solution of diffusive type with reasonable parameters especially at T<|J|⁄k. Villain’s theory of propagative relaxation is promising indicating importance of off-diagonal terms contained in the Hamiltonian.

View full abstract

Torque measurements have been made for a thin disc specimen of Co of which the disc plane was parallel to the (10\bar10) plane at various temperatures between 4.2 K and the room temperature in an external magnetic field of 16.9 kOe which was strong enough to saturate the magnetization. The obtained values of K_u1 and K_u2 were in good agreement with those obtained by Rebouillat and Sucksmith and Thompson. The temperature dependence of K_u1 below about 200 K could well be explained with a model based on the itinerant electron theory by considering the thermal expansion of the lattice parameter ratio.

View full abstract

Low temperature specific heat of an itinerant electron ferromagnet Sc₃In was measured in magnetic fields of 0, 5 and 10 kOe in the temperature range between 1.0 and 20.0 K. Experimental results on the magnetic field dependence of the specific heat is explained reasonably well by the self-consistently renormalized spin fluctuation theory, in which the effect of magnetic field was taken into account.

View full abstract

The magnetic moments of Co atom in Fe–Co–Ni alloys have been determined over whole concentration range of the fcc structure by polarized neutron diffuse scattering experiment. The results support qualitatively the theoretical calculations under the coherent potential approximation. The magnetic moments of Fe atoms have also been obtained in the alloys by means of Mössbauer effect. The results lie in between the theoretical values obtained either by the coherent potential or by the rigid band approximation.

View full abstract

The electronic structure of V–D alloys was studied by the angular correlation measurements of positron annihilation photons using single crystals of VD_0.002, VD_0.02 and VD_0.68. Marked differences are observed in the correlation curves of pure vanadium and VD_0.68 with the [100], [110] and [111] orientations; the characteristic fine structures of vanadium arising from the hole band structures disappear in VD_0.68. The results are interpreted as evidences that deuterium donates its electron to the conduction band of vanadium and the hole band fills gradually. The measurements on polycrystals of VD_0.51−0.67 and VH_0.51 were also made to compare with the results of the single crystals.

View full abstract

A model calculation of inner core photoelectron and photoabsorption spectra in transition metals is made by extending our previous theory such that incomplete shell states (d-state) construct a narrow energy band due to the transfer interaction among them and the hybridization with a conduction band. When a core electron is excited, the d-level of the excited atom is assumed to be lowered due to the core hole left behind. On account of this final state interaction, the photoelectron spectrum has a singular peak tailing off on the high energy side and a satellite, relative intensity of which depends sensitively on the banding effect of d-states. The density of states of the d-band is reflected in the photoabsorption spectrum, but due to the final state interaction it is highly deformed and remains only as a weak structure on the tail of a singular peak appearing at the threshold.

View full abstract

Optical absorption spectra and infrared photoconductivity have been measured for amorphous Si_100−x–Au_x films. From the optical absorption in the energy range from 0.5 eV to 3.0 eV, it is found that the square root of the product of the absorption coefficient and the photon energy is proportional to the photon energy in the region of x<30% and that the optical gap decreases with increasing Au concentration. The result of photoconductivity with photon energy less than the optical gap suggests that the energy level of the localized states due to Au atoms lies at about 0.3 eV above the mobility edge of the valence band. These results are discussed in relation to the metal-nonmetal transition observed in this system.

View full abstract

Self-trapping of a Frenkel exciton in binary mixed crystal A_cB_1−c, with excitation energy difference Δ=ε_B−ε_A and exciton-phonon coupling constant g, is studied. Impurity-assisted self-trapping is possible through cooperation of Δ and g even when neither of them alone is enough for localization. In this situation, one expects amalgamated absorption spectrum representing unrelaxed extended exciton and Stokes-shifted broad emission band representing relaxed localized exciton. We study whether relaxed exciton is localized (S-state) at a particular site of, or extended (B-state) throughout, the A-cluster of various sizes, and how such cluster state changes, as c increases, into free (F) state extended throughout the crystal. The results are compared with recent experiments on TlBr_cCl_1−c. Sudden appearance of edge emission (due to F) at c∼0.3, at the cost of broad band (due to S and B), is ascribed to the combined effect of size-dependent discontinuity of S-B transition in Br-clusters and their percolation.

View full abstract

Electronic properties of doped chalcogenide glasses are discussed on the basis of the Street-Mott model by taking a finite width of gap states into account. The conduction activation energy depends strongly on the shape of the gap state energy distribution. A rather gradual change in the activation energy with the increas of impurity concentrations, often observed in experiments, is well reproduced by introducing relatively small values for the distribution width. It is then possible to estimate the fraction of dopant atoms, which actually change conductivity, by comparing the results of the present model with experiments.

View full abstract

It is shown that the crystal binding energies of the IV–VI narrow gap semiconductors are calculated using the Heitler-London-Löwdin treatment modified so as to include the effect of covalent binding. The numerical calculations performed for PbS show that the calculated crystal binding energy, which is in good agreement with observation, consists of two parts, namely the binding energy in ionic approximation and the covalent binding correction and the former is almost equal to the one obtained by the classical Born-Mayer-Sherman treatment. The covalent bonding correction for PbS, PbSe, PbTe, SnTe, and GeTe are found to be 2.1, 2.9, 3.3, 3.2, and 3.9 eV/molecule, respectively.

View full abstract

The quantum mechanical treatment of the crystal energy of the IV–VI semiconductors developed in our previous paper is extended so as to be applicable to the case in which there exists a relative ionic displacement corresponding to the TO phonon at point Γ. It is shown that the unusually large transverse effective charges in these crystals come partly from rather large electronic polarizabilities of their constituent ions and partly from covalent bonds contained partially in the interatomic bonds in these crystals. The theory contains only one adjustable parameter concerning local field correction which is related with penetration between nearest neighboring ions. Using its numerical value determined for PbS, we can explain the transverse effective charges of the IV–VI semiconductors quantitatively. The relation between Katayama–Kawamura’s treatment and ours is discussed briefly.

View full abstract

A net charge of drops has been measured with a photocurrent method and a photoluminescence method at 1.5 K in pure and doped Ge. The sign of the net charge obtained from the two methods is in agreement with each other. The sign is negative in pure Ge (N_D<10¹³ cm⁻³) and p-type Ge (N_A=8×10¹⁴ cm⁻³). The sign is positive in n-type Ge (10¹³ cm⁻³\lesssimN_D≤2×10¹⁴ cm⁻³), and the sign cannot be obtained for N_D≥8×10¹⁴ cm⁻³ and N_A=5×10¹¹ cm⁻³. The sign reversals are not observed under ⟨111⟩ uniaxial stress (\lesssim10³ kg/cm²).

View full abstract

Resonant Brillouin scattering by longitudinal acoustic phonons has been observed for the first time in CdS by using mode converted phonons generated by partial reflection of acoustoelectric domains. Analysis based upon resonant Brillouin scattering theory and piezobirefringence theory shows a good agreement with the present observation, and predicts a weak cancellation at 750 nm.

View full abstract

Energy transfer mechanisms from the host lattice to bromine ions in NaCl : Br crystals have been investigated by observing host-sensitized luminescence. The migration of excitons and that of holes are both found to be responsible for the energy transfer mechanisms. Separation of the two migration processes is shown to be possible by investigating the temperature dependence of the emission intensity. The results obtained reveal that, when the exciting photon energy is increased beyond the Γ-band edges of NaCl, probability of the energy transfer due to exciton diffusion decreases rapidly with the complementary enhancement of that due to hole migration. This situation is consistent with the results obtained recently in KBr : I crystals.

View full abstract

Low-temperature luminescence associated with bound multiexciton complexes in boron-doped silicon has been investigated with emphasis on the excitation-level dependence of the luminescence spectra. In order to interpret the experimental results, we have proposed a model for the formation and decay processes of bound multiexciton complexes. It has been found that the excitation-level dependence of the bound multiexciton luminescence in boron-doped silicon is consistent with the excitation behavior calculated from the rate equations based on the model for the recombination kinetics of bound multiexciton complexes.

View full abstract

Pyroelectric and dielectric measurements have been made on Rb₂Cd₂(SO₄)₃ crystals with the simultaneous optical examination of the domain texture of the specimens. An unusual temperature dependence of the spontaneous polarization was found in the ferroelectric phases, which is similar to that found in (NH₄)₂SO₄. As the temperature is lowered, the spontaneous polarization appears at the Curie point (−144°C), gradually decreases and changes its sign below −160°C without an appreciable change at the second transition temperature of −170°C. The reversal in polarization was confirmed to take place by both pyroelectric measurement and optical observation. An abrupt change of dielectric constant ε_b at the Curie point was revealed by using single domain specimens.

View full abstract

All the elastic stiffness constants in the I and II phases of Ca₂Sr(C₂H₅CO₂)₆ were determined in an ultrasonic frequency region in the temperature range from −80°C to 70°C. The anomalies in the velocities of the longitudinal modes show the logarithmic divergence above the I–II phase transition temperature, whereas the velocities of the transverse modes show no anomaly in the I phase. These phenomena can be well explained by the Levanyuk-Dvo\v{r}ák theory of the nonpiezoelectric material.

View full abstract

Pure E-TO excitation and pure E-LO mode in KDP have been separately observed. Lineshape anomaly in mixed mode spectra of E-TO and E-LO excitation has been found to come only from the E-TO response. The plateau response in E-TO spectra is essentially attributed to the collective proton motion in x-y plane.

View full abstract

Dielectric and dilatometric measurements were made for the deuterated crystal (ND₄)₃D(SeO₄)₂. For comparison the dilatometric measurement was also made for the undeuterated crystal (NH₄)₃(SeO₄)₂. Two phase transitions were found at +55°C and at about +29°C for (NH₄)₃H(SeO₄)₂ besides the two phase transitions previously reported. Deuteration rises the Curie temperature by about 34°C, showing important role of the O–H–O bonds playing in the ferroelectric transition. The Curie-Weiss constant and spontaneous polarization of the deuterated crystal are 3.7×10³ K and 2.4 μC·cm⁻² at −170°C, respectively.

View full abstract

The crystal structure analysis of the low temperature phase of SrTiO₃ has been made at 77 K using the method of X-ray oscillation photograph. The space group is determined as I4/mcm and the rotational shift of oxygen octahedra with respect to Sr ion frame is by 1.6°; this is slightly larger than those estimated from a previous ESR experiment, neutron diffraction study and from X-ray lattice parameter measurement. Observed temperature parameters are in reasonable agreement with previously reported ones estimated from a rigid shell model.

View full abstract

Electrical resistivity in c-direction (ρ_c) as a function of temperature (T) has been investigated of a number of highly crystalline specimens of kish and pyrolytic graphites in relation to their structural perfection evaluated by the basal-plane resistivity ratio between 300 K and 4.2 K (R_T=ρ_a(300)⁄ρ_a(4.2)). The ρ_c vs R_T plot indicates a Λ-shaped curve, and the ρ_c vs T relationship becomes gradually metallic-like as R_T increases. For pyrolytic graphite, the thinner the specimen the higher the perfection in the range 0.016 to 0.73 mm. Based on these observations, the intrinsic c-axis conduction is concluded to be described within the framework of band theory, while it is impeded by laminar defects and short-circuited sometimes by misaligned basal-planes especially in the pyrolytic specimens. Comparison is made with the theory of Ono who has taken into account the scattering of carriers by stacking faults.

View full abstract

The core structure of an a⁄2[110](1\bar10) edge dislocation in sodium chrolide crystal was studied by computer simulation under a cyclic boundary condition. It is found that each dislocation is dissociated into two partials with Burgers vectors a⁄2[100] and a⁄2[010], forming a crack on the expanded side of the dislocation and that the average interatomic distance in the crystal increases by 5.5 per cent, when the crystal contains dislocations with a density of one dislocation per 30 atomic rows parallel to [001]. Using this value, we can explain the large expansion on melting of the salt on the basis of the dislocation theory of liquid. The energy of an edge dislocation per an interatomic distance is 1.19 eV for the above-mentioned dislocation density, which agrees with the observed value of the heat of fusion.

View full abstract

Aluminum L_2,3- and 3d-transition metal M_2,3-absorption spectra of Al-3d-transition metal alloys are measured. Main alloying effects are the shift of M_2,3 edge and the broadening of L_2,3 edge. The amount of charge transfer between constituent atoms is estimated from the shift and the parameters of the virtual bound states, and a possibility that the d state of Mn in Al is spin split is suggested. The width of broadening of L_2,3 edge varies with solute elements from Ti to Ni in paralled to the dc resistivity (R_imp⁄c), but is observed to be narrower by 5 to 9 times than that expected from the R_imp⁄c.

View full abstract

Second harmonic generation measurement has been performed to see whether or not K₂SeO₄ crystal is centrosymmetric in its hexagonal phase. All examined SHG signals were weaker than the detectable limit of our experimental setup, implying that SHG coefficient d₃₃ of K₂SeO₄ is estimated to be smaller than 5.3×10⁻³·d₁₁ of quartz. The present experiment indicates that the space group of the hexagonal phase of K₂SeO₄ is nonpolar D_6h⁴–P6₃/mmc rather than polar C_6v⁴–P6₃mc.

View full abstract

Phase diagram has been determined with X-rays for bilayer membranes of mixed lipids of dioleoyl-phosphatidylcholine/dipalmitoyl-phosphatidylcholine in water. Observed liquidus lines were reproduced well by calculation on the assumption of ideal mixing of the two lipids. In the fluid state there seems to be a transition temperature where a small discontinuous structural change takes place.
Obtained X-Ray data suggest that the direction of tilting of the lipid hydrocarbon chains becomes indefinite with regard to the longitudinal angle keeping the latitudinal angle constant in the intermediate phase of the membranes of dipalmitoyl-phosphatidylcholine between 35°C and 42.5°C.

View full abstract

Quasi-elastic neutron scattering experiment was performed on FeCl₃, NiCl₂ and MgCl₂ aqueous solutions. The whole shape of energy spectra of incoherently scattered neutrons was analyzed. The hydration number of Fe³⁺ ion was estimated to be 2.6, being independent of solute concentration. Based on a jump diffusion model, the diffusion constant and the rest time for the water molecules bound to Ni²⁺ ion in the NiCl₂ solution were estimated as 0.2×10⁻⁵ cm² sec⁻¹ and 3.0×10⁻¹² sec at 25°C, and 0.6×10⁻⁵ cm² sec⁻¹ and 2.0×10⁻¹² sec at 55°C, respectively. Those to Mg²⁺ ion in the MgCl₂ solution were estimated as 0.8×10⁻⁵ cm² sce⁻¹ and 3.0×10⁻¹² sec at 25°C, respectively. The present results justify the structure model proposed by Brady et al. for the FeCl₃ solution and the simplified “hard sphere model” originally proposed by Quirke et al. for the NiCl₂ solution. The diffusion process of Mg²⁺ ion in the MgCl₂ solution is discussed.

View full abstract

Single-center secular equations are obtained in the MS–Xα formalism. Furthermore, it is shown how one may return to a multicenter representation after determining the coefficients of the partial-wave expansion in the single-center representation.

View full abstract

The anisotropy of the spin-lattice relaxation time T_1D of dipolar energy, that T_1ρ in the rotating frame and that T₁ in the high magnetic field have been studied in tetrahedrally coordinated four-spin-1/2 system. The expression of T_1D and T_1ρ is presented when tetrahedron reorientates about the four three-fold axes and three two-fold axes. The anisotropy of T_1D and T_1ρ of proton spins in NH₄Cl and NH₄Br has been measured and compared with the present model of relaxation times. The measurement of T_1ρ is more useful because of the larger anisotropy to determine the model of the reorientation of NH₄-ion than that of T_1D and T₁. The present model is in good agreement with the experimental results in NH₄Cl, but the agreement is worse in NH₄Br. Some possible origins for the disagreement in the latter case are discussed. We have also compared the present model of spin-lattice relaxation times with those which were derived by the other authors.

View full abstract

Electrical resistivity ρ of liquid semiconductors Te, Ga₂Te₃, In₂Te₃ and Tl₂Te has been measured up to 30 kbar and 900°C. The resistivity ρ of liquid Ga₂Te₃ and In₂Te₃ rapidly decreases with pressure in the low pressure region (\lesssim5 kbar), while ρ of liquid Tl₂Te gradually decreases in the wide pressure range. This difference is discussed in connection with the bonding character of constituent atoms.

View full abstract

The behavior of the sideband wave is studied analytically in a one-dimensional plasma in which a large-amplitude, monochromatic electron plasma wave is applied. The distortion of the electron distribution function is calculated by the Liouville operator formalism. It is shown that the damping rate of the sideband wave, which is proportional to the amplitude of the applied field under usual experimental conditions, changes to be proportional to its square root in the restricted region.

View full abstract

Resonance absorption is studied for a steady-state, cold, magnetized plasma irradiated by a laser-light. A magnetic field perpendicular to the plane of incidence of the light enables the plasma to absorb a normally incident light, because an upper-hybrid wave is excited in the plasma. An obliquely incident light enhances remarkably the resonance absorption of the upper-hybrid wave. Numerical-integrations of the wave equation show that the maximum absorption-rate exceeds 90% for reasonable plasma parameters. When the magnetic field has a component parallel to the plane of incidence of the light, coupling occurs between the ordinary wave and the extraordinary wave in the plasma. This coupling reduces the dependence of absorption-rate on the polarity of light.

View full abstract

A possibility that the collapse of a long coherent Langmuir wave is suppressed by the effect of acoustic turbulence is shown. The local depression of the plasma density caused by the ponderomotive force of the long coherent Langmuir wave makes the parametric instability possible and leads to the excitation of the turbulent ion acoustic waves and turbulent plasma waves which are trapped in the modulated Langmuir wave. The scattering of the Langmuir wave by the turbulent waves is effective to the stabilization of the modulation instability as the turbulent energy is increased. The condition for the suppression of the collapse is examined.

View full abstract

Statistical analysis is made of the inhomogeneous turbulence with unidirectional mean flow in infinite fluid. The velocity is assumed to depend on the coordinate normal to the flow. Considering that the space variation of the mean flow is small compared with that of the fluctuating one, two space scales corresponding to mean and fluctuating flows are introduced into the Navier-Stokes equations. The direct-interaction approximation is applied to the equation thus found, and Reynolds stress is evaluated. Results obtained are applied to the calculation of grid-scale Reynolds stress used frequently in a numerical simulation of turbulent flows.

View full abstract

The flow through a single or multiple parallel planar periodic arrays of small spheres is considered on the basis of the Stokes equation. In analysis the relation between the force on a sphere and the average fluid velocity is obtained. As examples, the flows through several semi-infinite lattices, a single lattice and two lattices are discussed.

View full abstract

An exact solution describing a multiple collision of periodic waves is obtained for the Benjamin-Ono equation. It is shown that the solution reduces to the rational multi-soliton solution in a long wave limit.

View full abstract

From ⁵⁹Co NMR experiments in metallic compounds Co(S_xSe_1−x)₂ with pyrite structure, it is shown that the concentration and external field dependences of the magnetism are manifested by inhomogeneous distribution of ferromagnetic Co atoms with 0.85 μ_B and nonmagnetic Co atoms. Particularly, the field induced metamagnetic transition found in x=0.88 and 0.86 is concluded to be due to the progressive-discontinuous transitions from the nonmagnetic to the ferromagnetic states with increasing external field. The field dependence of the NMR intensity associated with the nonmagnetic Co atoms accounts entirely for the magnetization vs field curves.

View full abstract