Sorption of Radioactive Iodine and Fluoride Ion on Hydroxyapatite from the Aqueous Phase

Sorption of the ¹³¹I^-, ¹³¹IO₃ ^-, and F^- ions on various samples of hydroxyapatite (HAP) from aqueous solutions was studied. The HAP samples were prepared by the following reactions: Ca(OH)₂ + H₃PO₄ HAP, CACl₂ + Na₃PO₄ + NaOH HAP, and Ca(NO₃)₂ + HAP seed + (NH₄)₂HPO₄ + NH₃ HAP. None of the HAP samples sorb ionic species of radioactive iodine from aqueous solutions. As for F^-, the best sorption properties are exhibited by the HAP sample prepared by the second reaction. The degree of recovery of fluoride ion with the HAP precipitate in 5 min, 4 h, and 5 days of the contact of the solid and liquid phases is 54, 66, and >95% of the initial F^- amount, respectively. The distribution factor K _d of the fluoride ion between the HAP solid phase and solution decreases with increasing V/m ratio and pH of the initial solution.     

Cooling Mechanism of Spin Polarized Atomic Hydrogen Adsorbed on Dilute 3He-4He Mixture Film

We cooled down the two-dimensional (2-D) spin-polarized atomic hydrogen (H) adsorbed on a small surface called cold spot, whose temperature was kept much colder than the rest of the sample cell. The 2-D density of H was controlled by an input flux of H into the sample cell. We investigated the surface recombination of H adsorbed on 3% ³ He ³ He- ⁴ He mixture. ESR at 129GHz was carried out to detect H by mirror cavity with the cold spot located at the confocal point. We calculated the thermal boundary resistance between the absorbed H and the mixture. From the temperature dependence of the surface recombination together with calculated boundary resistance, we obtained the temperature dependence of _a. The result agrees with the previous measurement. Two-D H on the mixture film was cooled well down to 40mK.     

Thermal transport properties of helium near the superfluid transition. II. Dilute3He-4He mixtures in the superfluid phase

Measurements of the average thermal conductivity _exp hQ/T and of the thermal relaxation time to reach steady-state equilibrium conditions are reported in the superfluid phase for dilute mixtures of³He in⁴He. Hereh is the cell height,Q is the heat flux, andT is the temperature difference across the fluid layer. The measurements were made over the impurity range 2×10^–9<X(³He)<3×10^–2 and with heat fluxes 0.3<Q<160 µW/cm². Assuming the boundary resistanceR _b , measured forX<10^–5, to be independent ofX over the whole range ofX, a calculation is given for _exp. ForQ smaller than a well-defined critical heat fluxQ _c (X) X ^0.9, _exp is independent of Q and can be identified with the local conductivity _eff, which is found to be independent of the reduced temperature = (T–T)/T for –10^–2. Its extrapolated value at T is found to depart forX10^–3 from the prediction X ^–1 , tending instead to a weaker divergence X ^–a witha0.08. A finite conductivity asX tends to zero is not excluded by the data, however. ForQ >Q _c (X), a nonlinear regime is entered. ForX10^–6, the measurements with the available temperature resolution are limited to the nonlinear conditions, but can be extrapolated into the linear regime forX2×10^–7. The results for _exp(Q),Q _c (X), and _eff(XX) are found to be internally consistent, as shown by comparison with a theory by Behringer based on Khalatnikov's transport equations. Furthermore, the observed relaxation times (X) in the linear regime are found to be consistent forX>10^–5 with the hydrodynamic calculations using the measured _eff(X). ForX<10^–5, a faster relaxation mechanism than predicted seems to dominate. The transport properties in the nonlinear regimes are presented and unexplained observations are discussed.     

Thermal detection of ESR on spin-polarized hydrogen: Study of surface recombination

We introduce a new method for the detection of electron-spin resonance in spin-polarized atomic hydrogen gas (H). Instead of observing the microwave power absorbed in the ESR transition, we monitor the recombination heat deposited by ESR-induced spin-up atoms (H) onto a liquid-helium coated carbon bolometer. The signal from this sensor reproduces well the ESR absorption lineshape registered by our 128 GHz homodyne spectrometer. Using the recombination detection we have achieved a density detection limit of n=3·10¹⁰ atoms/cm³ for 0.2 nW microwave power incident on the resonant cavity at the temperature T=150 mK. We have studied the decay rate of recombination heat absorbed by the bolometer after an ESR excitation pulse and the dependence of this rate on T, n and nuclear polarization of the H sample. The bolometer signal is found to be related mainly to second-order H + H recombination to ortho-H₂ on the surfaces of the sample cell. From the signals we have determined the rate constant K _bc ^c =3.2(5)·10^–5T cm²/s·K^–1/2 in the interval from T=250 to 425 mK in a field of 4.5 T.     

Parafluidity in helium near the λ-transition and the generalized time-dependent Landau theory

A phenomenological theory of parafluidity, i.e., an enhancement of fluidity due to order-parameter fluctuations, is presented for helium near the transition. The generalized time-dependent Landau theory of second-order phase transitions is reviewed in general and is applied to the superfluid transition in helium as a particular example. In helium, it is found that parafluidity is manifested in the divergences of the mass diffusivity , the thermal conductivity , the first-sound amplitude attenuation ||^–1, and the second-sound dampling , which are all consistent with the dynamic scaling hypothesis. Here a characteristic relaxation time ₀ ||^–1 is used, where =(T–T _c )/T _c andT _c is the transition temperature. Although there are not enough experimental data to confirm our formulas, the present approach is seen to agree in order of magnitude with available experiments. Finally, the sound absorption above a ferromagnetic transition is calculated by adding a diffusion term to the generalized time-dependent Landau equation. The result thus obtained agrees in order of magnitude with experiments in nickel.Supported in part by the National Science Foundation and the Horace H. Rackham School of Graduate Studies.     

The role of a surface flow in experiments with atomic hydrogen adsorbed on liquid helium

No Heading We apply a quantum hydrodynamics of the surface of ³He-⁴He solutions to account for the in-plane transport of the two-dimensional (2D) spin-aligned atomic hydrogen (H) adsorbed on superfluid helium film. We discuss how the surface flow of 2D H may be traced in experiment thus allowing to study the interaction of the 2D hydrogen with ripplons and surface-bound ³He as well as to observe the superfluidity of the 2D Bose gas of H. As an example we consider the formation of the ESR spectrum of the 2D H and find that in spatially non-uniform case the surface flow contributes significantly to the conditions of the ESR spectrum instability observable at high microwave power. We also analyze the conditions at which the surface flow of the 2D hydrogen plays an important role in thermal compression experiments.PACS numbers: 05.70.Np, 67.40.Pm, 67.65.+z, 68.03.Kn, 68.43.Mn     

Recombination of Spin Polarized Atomic Hydrogen Adsorbed on a Dilute 3He-4He Mixture

We have been searching for two-dimensional (2-D) superfluidity of spin-polarized atomic hydrogen (H) adsorbed on liquid helium surface. We have investigated H adsorbed on ³ He- ⁴ He mixtures instead of pure ⁴ He because the thermal coupling of H to the mixtures is stronger than ⁴ He. ESR at 129 GHz was carried out to detect H at 4.5 T by using the Fabri-Perot confocal cavity with the cold spot located at the confocal point and thus the 2-D H signal was effectively detected. We investigated the two-body bulk and surface recombination processes of H on a 3% ³ He ³ He- ⁴ He mixture film. From the analysis of the surface recombination process, we found the adsorption energy of H was a 0.6 K for the mixture film in the temperature range between 120 mK and 250 mK, greater than the 0.3–0.4 K found previously for pure ³ He and a 67% ³ He ³ He- ⁴ He mixture.     

Influence of Charge Doping on Thermal Diffusivity of Double Perovskite Sr2FeMoO6 Studied by Mirage Effect

Effects of charge doping on thermal diffusivity have been investigated in double perovskite ferromagnetic Sr_2–x La _x FeMoO₆ (0 x 0.4) by means of the mirage effect at 300 K ( the critical temperature T _c 420 K). Substitution of the La³⁺ ions for the Sr²⁺ ions significantly increases the value of the thermal diffusivity from 0.39 cm² · s^–1 at x = 0 to 0.54 cm² · s^–1 at x = 0.4. The increased thermal diffusivity is ascribed to the extra itinerant electrons on the Mo4d band.     

Structure and Magnetism of the Composite Crystal Ca0.824CuO2

We have studied the magnetic state from a viewpoint of crystallographic features of the 1-D chain compound Ca_0.824CuO₂. A possible spin-hole arrangement in the magnetically coexisting state was determined by analyzing the local structural distortion in the CuO₂ chain by means of a modulated-crystal-structure analysis. The essential periodic sequence expected is (: up- and down-spin, : hole), which can be regarded as a kind of spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain.     

Ultrasonic attenuation and sound velocity of the excitonic state

Ultrasonic attenuation and sound velocity of a metal in the excitonic state are investigated theoretically in the limitq1 1 and/T _c 1, whereq is the sound-wave vector,1 is the electron mean-free path, is the phonon energy, andT _c is the transition temperature of the excitonic state. The attenuation coefficient of the longitudinal wave increases drastically upon entrance into the excitonic state, then passes a maximum and decreases exponentially as temperature tends to 0 K. The attenuation coefficient of the transverse wave, on the other hand, is described in terms of the electric conductivity in the limitq1 1 and generally increases in the excitonic state. Furthermore, we find that the sound velocity of the longitudinal wave increases rapidly in the excitonic state, which is a simple manifestation of the anomaly of the dielectric function in the excitonic state.     

Low-frequency kinetics of high-T c metal oxides

A microscopic explanation of the low-frequency kinetic properties of metal oxides is proposed. It is based on a strong electron-phonon interaction, which forms a charged Bose liquid of small bipolarons. The large value, the nonKorringa temperature dependence above T _c, and the absence below T _c of the coherent peak of the nuclear spin relaxation, as well as an unexpected coherent peak of the low frequency dynamic conductivity and the linear T-dependence of the resistivity are explained.     

The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures

We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe _x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times ₁and ₂ ^* of ¹⁹⁵ Pt strongly depend on x and on the external magnetic field. No temperature dependence of ₁and ₂ ^* could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K.     

Thermal Expansion and Isothermal Compressibility of TlIn1 – xNdxSe2 (0 ≤ x≤ 0.08) Crystals

The thermal expansion coefficient () and isothermal compressibility ( _T ) of TlIn_{1 – x} Nd _x Se₂(0 x 0.08) crystals were measured between 77 and 400 K. In the range 77–160 K, both and _T increase with temperature, the increase in being much steeper. At higher temperatures, and _T change very little. The observed composition dependences of and _T are interpreted in terms of energy-band structure.     

17O Knight shift study in the superconducting state of Sr2RuO4

¹⁷O Knight shift measurements in Sr₂RuO₄ were performed over the wide range of magnetic field 3.2-11.4kOe parallel to the basal RuO₂ planes. The spin susceptibility is totally unchanged through its T_c, evidencing that the spin-triplet superconducting state is realized in Sr₂RuO₄. The result indicates that the Cooper pairs consist of the parallel spin pairs | > and | > with their quantization axis perpendicular to the c-axis direction. The in-plane 2D nearly ferromagnetic spin fluctuations may play a role for the stabilization of this state among various representations of spin-triplet order parameter.     

Nonlinear asymptotic theory of hypersonic flow past a circular cone

Summary The hypersonic small-disturbance theory is reexamined in this study. A systematic and rigorous approach is proposed to obtain the nonlinear asymptotic equation from the Taylor-Maccoll equation for hypersonic flow past a circular cone. Using this approach, consideration is made of a general asymptotic expansion of the unified supersonic-hypersonic similarity parameter together with the stretched coordinate. Moreover, the successive approximate solutions of the nonlinear hypersonic smalldisturbance equation are solved by iteration. Both of these approximations provide a closed-form solution, which is suitable for the analysis of various related flow problems. Besides the velocity components, the shock location and other thermodynamic properties are presented. Comparisons are also made of the zeroth-order with first-order approximations for shock location and pressure coefficient on the cone surface, respectively. The latter (including the nonlinear effects) demonstrates better correlation with exact solution than the zeroth-order approximation. This approach offers further insight into the fundamental features of hypersonic small-disturbance theory.Notation a speed of sound - H unified supersonic-hypersonic similarity parameter, - K hypersonic similarity parameter, M - M freestream Mach number - P pressure - T temperature - S entropy - u, v radial, polar velocities - V freestream velocity - shock angle - cone angle - density - density ratio, /() - ratio of specific heats - polar angle - stretched polar angle, / - (), (), () gage functions     

Susceptibility and X-Ray Absorption Measurements on Superconducting (Hg,Mo)Sr2CuO4+δ System

In continuation of our recent work [1] on superconducting 1201-type (Hg,M)Sr₂CuO₄₊, M = Cr system, the samples of (Hg_1–x Mx)Sr₂CuO₄₊, M = Mo (x = 0.15, 0.25, and 0.30), were synthesised in partial vacuum. The x = 0.15 composition shows a maximum T _c ^onset of 66 K, while x = 0.25 exhibits T _c ^onset of 50 K. For x = 0.30 sample, the observed T _c ^onset of 36 K is discretely different from the reported values of 20 and 58 K. X-ray absorption measurements on (Hg,Mo)-1201 samples show Hg in divalent state and Cu predominantly in Cu²⁺ state. A weak but distinct Cu¹⁺ signature is also observed in the SC (Hg,Mo)-1201 samples, which is absent in the impurity SrCuO₂ and Sr₂CuO₃ phases. On the basis of available reports, it is viewed that Cu¹⁺ can arise because of a small fraction of Cu occupying the Hg site in (Hg,Mo)-1201 system.     

Longitudinal magnetic relaxation in superfluid 3He

Longitudinal magnetic relaxation in both ³He-A and ³He-B is studied in a variety of magnetic fields and three different geometries. Relaxation as described by Leggett and Takagi is observed for particular geometries in both ³He-A and ³He-B within a very limited range of magnetic field and temperature near T _c. Under certain other conditions the longitudinal magnetization in ³He-A does not relax monotonically in time. Relaxation in ³He-B very near the critical temperature is shown to be remarkably different following nominal 90 and 180 pulses. Other observations using RF pulses with a time-dependent frequency provide evidence for a negative frequency shift in ³He-B at large tipping angles in certain geometries.Supported by the U.S. Department of Energy under contract number EY-76-S-03-0034, P.A. 143.     

The viscosity and some related properties of liquid3He at the melting curve between 1 and 100 mK

The viscosity of liquid ³ He has been measured along the melting curve from 1 to 100 mK by means of a vibrating wire viscometer. In the normal Fermiliquid region we find 1/T² = 1.17–3.10T, where is in P and T in K. At the transition temperature T _A = 2.6 mK a rapid decrease occurs in _n , the viscosity of the normal component. Within 0.3 mK below T _A , _n decreases to about 25% of _A, but then becomes essentially constant. In the B phase _n first decreases to 20% of _A and then seems to increase below 1.4 mK. Data on _n , the density of the normal component, are also presented in the A and B phases. The results show that viscous flow is accompanied by a flow of zero dissipation, thus proving superfluidity in the A and B phases. The viscosity data at magnetic fields up to 0.9T have been related to theoretical calculations of the energy gap of superfluid ³ He near T _A . The splitting of the A transition and the suppression of the B phase in an external field were also measured.     

Non fermi liquid ground states in strongly correlated f-electron materials

Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for three f-electron systems: M_1–xU_xPd₃ (M = Sc, Y), U_1–xTh_xPd₂Al₃, and UCu_5–xPd_x. The emerging systematics of NFL behavior in f-electron systems, based on the present sample of nearly ten f-electron systems, is updated. Many of the f-electron systems exhibit the following temperature dependences of the electrical resistivity p, specific heat C, and magnetic susceptibility for T T₀, where T_o is a characteristic temperature: P(T) 1 –aT/T ₀, where a < 0 or > 0, C(T)/T (-1/T _o) In (T/bT ₀), and (T) 1 –c(T/T_o)^1/2. In several of the f-electron systems, the characteristic temperature T_o can be identified with the Kondo temperature T_k.     

Flow visualization glass-ceramic: Preliminary experimental and modelling results

A glass-ceramic material was developed to act as a flow visualization material. Preliminary experiments indicate that aperiodic, thermally induced, convective flows can be sustained at normal processing conditions. These flows and the stress and temperature gradients induced are most likely responsible for the anomalous behaviour seen in these materials and the difficulties encountered in their development and in their production on industrial and experimental scales. A simple model describing the dynamics of variable-viscosity fluids was developed and was shown to be in qualitative agreement with more sophisticated models as well as with experimental results. The model was shown to simulate the dependence of the critical Rayleigh number for the onset of convection on the viscous properties of the fluid at low T, and also to simulate quenching behaviour when the temperature differences were high.Nomenclature C _p Heat capacity - D, E, F Expansion coefficients - H Height of the roll cell - Pr Prandtl number - R _a Rayleigh number - R _c Critical Rayleigh number for the onset of convection in a constant-viscosity fluid - S Dimensionless stream function - T Temperature - T _m Mean temperature - T ₀ Bottom surface temperature - T _r Reference temperature - a Aspect ratio of cell - g Acceleration due to gravity - k Thermal conductivity - k ₁ Function related to ²v/T ² - k ₂ Function related to ⁴v/T ⁴ - r Rayleigh number ratioR _a/R _c - t Time - w Dimensionless vertical coordinate - w _m Mean cell height - x Horizontal coordinate - y Dimensionless horizontal coordinate - z Vertical coordinate - , Constants - _t Thermal expansion coefficient - Constant in viscosity function - T Temperature difference between top and bottom surfaces - _i Viscosity coefficients - Kinematic viscosity - _m Mean kinematic viscosity - Dimensionless kinematic viscosity - Thermal diffusivity - Non-linear temperature function - Dimensionless non-linear temperature function - _o - Stream function - Dimensionless time - Eigenvalues