Knight shifts for short-lived β emitters in Pt

The Knight shifts K for short-lived β emitters ¹²N and ²⁷Si implanted in Pt have been measured by means of β-NMR technique. The results were K(¹²N in Pt)= +(5.8 ± 2.1)× 10^-4 and K(²⁷Si in Pt)= +(1.4 ± 0.8)× 10^-3. The spin–lattice relaxation time T₁ was measured for ¹²N in Pt. The result was T₁(¹²N in Pt, T=300 K)= 66 ± 8 ms, thus, T₁T= 20 ± 2 Ks. The present Knight shifts are in good agreement with the KKR band structure calculation with local lattice relaxation determined theoretically. This revised version was published online in August 2006 with corrections to the Cover Date.     

Zur ann?hernden Bestimmung von Harzim Ceresin

Ohne Zusammenfassung     

Die Unterscheidung des Reismehles von Buchweizenmehl

Ohne Zusammenfassung     

Zur Unterscheidung der verschiedenen St?rkearten

Ohne Zusammenfassung     

Momentum dependence of spin polarization for beta emitting nuclei produced through charge exchange reaction at intermediate energy

Hyperfine interactions were studied in the intermetallic compound GdRh₂Si₂ by perturbed angular correlation (PAC) technique using ¹⁸¹Hf(¹⁸¹Ta) probe nuclei. The measurements were performed in the temperature range 15–285 K. The PAC spectra above the antiferromagnetic ordering temperature of the GdRh₂Si₂ compound (T _N ～ 106 K), were analyzed using a model that included only electric quadrupole interactions. The observed major fraction was assigned to the ¹⁸¹Hf(¹⁸¹Ta) probe substituting the Gd atoms. The PAC spectra below Néel temperature were analyzed using combined electric quadrupole and magnetic dipole interactions. The B_hf value at Gd, measured at 15 K was found to be 1.4(1) T which, is smaller, when compared with the values obtained in this compound using other nuclear probes, ¹⁵⁵Gd (B_hf ～ 30 T) and ¹⁴⁰Ce (B_hf ～ 26 T). The present result using ¹⁸¹Hf(¹⁸¹Ta) probe is quite interesting since it shows that the contribution to B_hf at Gd due the host is smaller than other components which contribute to the hyperfine field. The temperature dependence of B_hf shows an anomalous behavior.     

E.S.R. evidence for the planarity of the t-butyl radical

Monte Carlo calculations are reported for the radial distribution function g ₂(r; λ) of a fluid in which the intermolecular pair potential is [u ^ref(r) + λu ^p(r)], u ^ref(r) being the Weeks-Chandler-Andersen (WCA) reference fluid, and [u ^ref(r) + u ^p(r)] being the Lennard-Jones (6, 12) fluid. The calculations are performed for λ values in the range 0 to 1, at the state condition ρσ³ = 0·80, kT/ε = 0·719. It is shown that at high densities the perturbation expansion of g ₂(r; λ = 1) about g ₂(r; λ = 0) is rapidly convergent, but that the corresponding expansion for y ₂(r; λ) = exp [βu(r; λ)] × g ₂(r; λ) is not. In addition Monte Carlo estimates of the individual terms that contribute to the first-order perturbation term, (?g ₂/?λ)_λ=0, are presented. It is shown that these terms are individually large, but that (?g ₂/?λ)_λ=0 is small because there is strong cancellation between the various terms. Consequently, the calculation of (?g ₂/?λ)_λ=0 is highly sensitive to the approximation used to evaluate the individual terms.     

Radicals containing β-muonium and α or β substituents:

A range of radicals, CH₂(Mu) HX (1) and XCH(Mu)CR₂ (2), where X is a second-row substituent, have been studied by transverse-fieldμ ⁺SR spectroscopy. The reduced muon—electron hyperfine coupling constants (A′_Mu) for class (1) were all close to 37.3 G, the value for the parent radical CH₂(Mu)CH₂. However, for class (2)A′ _Mu values are greatly reduced, as is the case for the corresponding hydrogen derivatives, XCH₂CR₂, relative to CH₃CH₂. Nevertheless, the reduction in coupling for Mu in (2] is appreciably less that that for¹H in XCH₂CR₂ radicals, suggesting significant competition between Mu and X for the out-of-plane site. In addition to theμ ⁺ SR studies, the ESR spectra for the radicals (MeO)₃SiCHCH₃ and (MeO)₃SiCH₂CH₂ have been measured for comparative purposes.     

Precise Nuclear Quadrupole Moments of 8B and 13B

The electric quadrupole coupling constants eqQ/h of ⁸B (, T _1/2 = 769 ms) and ¹³B (, T _1/2 = 17.4 ms) in single crystal TiO₂ have been precisely measured by the β-NQR technique. The ratios of these Q moments to Q(¹²B) were determined as ∣Q(⁸B)/Q(¹²B)∣ = 4.882(32) and ∣Q(¹³B)/Q(¹²B)∣ = 2.768(24).     

Actuation of the Kagome Double-Layer Grid. Part 1: Prediction of performance of the perfect structure

The Kagome Double-Layer Grid (KDLG) is a sandwich-like structure, based on the planar Kagome pattern, which has properties that make it attractive for application as a morphing material. In order to understand the passive and active properties of the KDLG with rigid joints, an analysis is made of the determinacy of the pin-jointed version. The number of internal mechanisms and states of self-stress of the finite pin-jointed structure are calculated as a function of the size of the structure. A statically and kinematically determinate version is obtained by relocating the internal nodes and by prescribing a set of patch bars around the periphery. The actuation performance of the rigid-jointed version is then explored theoretically by replacing a single bar in the structure by an actuator. The resistance to actuation is determined in terms of the stiffness and the allowable actuation strain as dictated by yield and buckling. The paper concludes with the optimal design of a double-layer grid to maximise actuation performance.     

Maximum likelihood factor analysis with rank-deficient sample covariance matrices

This paper characterises completely the circumstances in which maximum likelihood estimation of the factor model is feasible when the sample covariance matrix is rank deficient. This situation will arise when the number of variables exceeds the number of observations.