[en] Nuclear magnetic resonance (NMR) experiments were carried out in two heavy fermion superconductors, CeCu₂Si₂ and U/sub 1-x/Th/sub x/Be₁₃ (x = 0,0.0331). The unusual normal state and superconducting state behavior of CeCu₂Si₂ and UBe₁₃ has recently been discovered. Both compounds exhibit enormous values of the normal state low temperature magnetic susceptibility chi and the linear specific heat coefficient γ. Standard analyses of chi and γ results in a two order of magnitude enhancement of the conduction electron mass, but the ratio chi/γ retains a value appropriate to a free-electron gas. It is of interest to obtain as much microscopic information as possible. In one of the CeCu₂Si₂ superconducting specimens, the observed temperature dependence of the spin-lattice relaxation rate 1/T₁ (T) is consistent with a conventional quasi-particle excitation spectrum below the superconducting transition temperature T/sub c/. In the other superconducting CeCu₂Si₂ sample, the nuclear spin-lattice relaxation rate decreases drastically just below T/sub c/ without the apparent enhancement observed in the first sample. The spin lattice relaxation rate in UBe₁₃ varies approximately as T³ well below the transition temperature T/sub c/., This behavior is consistent with a class of anisotropic pairing models for which the superconducting gap vanishes along lines on the Fermi surface

[en] Purpose: As three-dimensional diode arrays increase in popularity for patient-specific quality assurance for intensity-modulated radiation therapy (IMRT), it is important to evaluate an array’s susceptibility to setup errors. The ArcCHECK phantom is set up by manually aligning its outside marks with the linear accelerator’s lasers and light-field. If done correctly, this aligns the ArcCHECK cylinder’s central axis (CAX) with the linear accelerator’s axis of rotation. However, this process is prone to error. This project has developed an analytical expression including a perturbation factor to quantify the effect of shifts. Methods: The ArcCHECK is set up by aligning its machine marks with either the sagittal room lasers or the light-field of the linear accelerator at gantry zero (IEC). ArcCHECK has sixty-six evenly-spaced SunPoint diodes aligned radially in a ring 14.4 cm from CAX. The detector response function (DRF) was measured and combined with inverse-square correction to develop an analytical expression for output. The output was calculated using shifts of 0 (perfect alignment), +/−1, +/−2 and +/−5 mm. The effect on a series of simple inputs was determined: unity, 1-D ramp, steps, and hat-function to represent uniform field, wedge, evenly-spaced modulation, and single sharp modulation, respectively. Results: Geometric expressions were developed with perturbation factor included to represent shifts. DRF was modeled using sixth-degree polynomials with correlation coefficient 0.9997. The output was calculated using simple inputs such as unity, 1-D ramp, steps, and hat-function, with perturbation factors of: 0, +/−1, +/−2 and +/−5 mm. Discrepancies have been observed, but large fluctuations have been somewhat mitigated by aliasing arising from discrete diode placement. Conclusion: An analytical expression with perturbation factors was developed to estimate the impact of setup errors on an ArcCHECK phantom. Presently, this has been applied to simple functions, but is being developed to handle more realistic clinical cases

[en] Gamma irradiation was found to be an effective method for the improvement of both barrier and mechanical properties of the edible films and coatings based on calcium and sodium caseinates alone or combined with some globular proteins. Our current studies concern gamma irradiation influence on the physical properties of calcium caseinate-whey protein isolate-glycerol (1:1:1) solutions and gels, used for films preparation. Irradiation of solutions was carried out with Co-60 gamma rays applying 0 and 32 kGy dose. The increase in viscosity of solutions was found after irradiation connected to induced crosslinking. Lower viscosity values were detected, however, after heating of the solutions irradiated with a 32 kGy dose than after heating of the non-irradiated ones regarding differences in the structure of gels and resulting in different temperature-viscosity curves that were recorded for the irradiated and the non-irradiated samples during heating and cooling. Creation of less stiff but better ordered gels after irradiation arises probably from reorganisation of aperiodic helical phase and β-sheets, in particular from increase of β-strands, detected by FTIR. Films obtained from these gels are characterised by improved barrier properties and mechanical resistance and are more rigid than those prepared from the non-irradiated gels. The route of gel creation was investigated for the control and the irradiated samples during heating and the subsequent cooling

[en] ⁶³Cu nuclear quadrupole resonance (NQR) has been observed in a heavy-fermion system CeCu₂Si₂. In the superconducting CeCu₂Si₂ specimens (T_c congruent 0.6 K), NQR experiments have revealed an onset of a phase transition below ∼1 K. Zero- and longitudinal-field muon-spin-relaxation measurements suggest a static magnetic ordering below ∼0.8 K, either in the spin-glass or in incommensurate spin-density-wave states. The exotic transition observed in NQR measurements should be closely related to the static magnetic ordering in muon-spin-relaxation measurements. NQR data from a nonsuperconducting CeCu₂Si₂ sample are consistent with extensive disorder in Cu site occupation. Therefore, the spin-density wave may be depressed in the nonsuperconducting CeCu₂Si₂. The superconducting transition temperature T_c can be enhanced by the presence of spin-density waves such that, if the spin-density wave is depressed, CeCu₂Si₂ will lose its superconducting properties

[en] The magnetic-phase diagram of the system CeRu₂(Si_1-xGe_x)₂ is studied by specific-heat, magnetic-susceptibility and electrical resistance measurements (x=0.1, 0.2, 0.3, 0.6, 0.8, 0.9, 1.0). The susceptibility χ was measured by zero-field-cooling (ZFC) and field-cooling (FC) methods. If x < 0.1, there is no clear long-range magnetic order. When x>0.1, χ_FC(T) starts to deviate from χ_ZFC(T) at T_sf. This suggests a spin-glass state below T_sf. In the range 0.9 ≥ x ≥ 0.2, the specific-heat measurements of CeRu₂(Si_1-xGe_x)₂ show multiple magnetic phase transitions. There are three phase transitions in CeRu₂Si_0.4Ge_1.6 and CeRu₂Si_0.2Ge_1.8. Except for x=0, below 30 K, electrical resistivity ρ(T) increases continuously up to a temperature of 10 K. The drastic drop of ρ(T) below 10 K is due to magnetic ordering. The multiple phase transitions of CeRu₂(Si_1-xGe_x)₂ are not observed in the resistance measurements. However, the slope of ρ(T)/ρ(285 K) of CeRu₂Si_0.4Ge_1.6 changes at ∼7 K, which further supports multiple phase transitions in CeRu₂(Si_1-xGe_x)₂. (author)

[en] The acoustic properties are investigated of the Fibonacci Nb-Cu metallic superlattices from surface waves by means of light scattering. The measured velocities of surface waves do not show a dramatic difference between quasiperiodic superlattices and periodic superlattices. The velocity of Rayleigh surface is found to be 9 to 16% less than the theoretical value calculated from bulk elastic constants and densities. (author)

[en] The zero-field-cooled and field-cooled magnetizations, magnetization versus field, and remanent magnetization were measured for a cermet on the base of Al₂O₃ using a SQUID magnetometer in the temperature range of 2-360 K. It was shown that magnetic properties of the cermet are determined by independent ferromagnetic, paramagnetic and spin-glass contributions. The spin-glass behavior was studied

[en] Small amount of Fe substituted for Cu in Bi₂Ca₁Sr₂Cu₂O_y has been found to decrease T_c drastically, suggesting that the exchange interaction between the superconducting pairs and the magnetic moment is still the dominant mechanism responsible for the loss of high T_c superconductivity in Fe-doped Bi₂Ca₁Sr₂Cu₂O_y. 1 at.% Zn substituted for Cu in Bi₂Ca₁Sr₂Cu₂O_y is quite effectively in reducing T_c, but a further increase in Zn concentration does not vary T_c significantly. The T_c of Bi₂Ca₁Sr₂Cu₂O_y is not affected at all by replacing Cu by Al. The magnitude of the magnetic susceptibility at low temperatures decreases with increasing Fe concentration, but increases with increasing Zn and Al concentrations

[en] We report magnetic-susceptibility, specific-heat, and electrical resistivity measurements of Pr₂CuSi₃. This compound exhibits ferromagnetism at T_c=10 K and upon further cooling shows spin-glass properties below about T_f=8 K. The coefficient of the term linear in temperature in the specific heat γ of Pr₂CuSi₃ is 0.505 Jmol^-1K^-2 which is much larger than that of normal metals. This compound might be classified as a nonmagnetic atom-disorder spin glass. copyright 1997 The American Physical Society

[en] New specific methods have been developed for the detection of chromium(VI) and of vanadium(V), based on the formation of a purple color with primaquin in concentrated sulfuric acid solution. The identification limits and dilution limits have been determined to be 0.05 μg, 1 : 1 000 000 for chromium(VI) and 0.1 μg, 1 : 500 000 for vanadium(V) respectively. (Author)