Diffusion of 111Cd probes in Ga7Pt3 studied via nuclear quadrupole relaxation

Diffusion of ¹¹¹In/Cd impurity atoms was studied in Ga₇Pt₃ at the atomic level using the method of perturbed angular correlation of gamma rays (PAC). As in previous measurements on Ga₇Pd₃, probes were observed to occupy two inequivalent Ga-sublattices. Quadrupole interaction perturbation functions for each site exhibited damping at elevated temperatures that is attributed to nuclear relaxation caused by stochastic jumps of the probe atoms accompanied by reorientation of axes of the electric field gradient tensor. Fitted relaxation frequencies, proportional to mean jump frequencies of the probe, were thermally activated. Arrhenius plots revealed jump-frequency activation enthalpies of 0.94 (8) and 0.67 (4) eV for the two sites and frequency prefactors close to 1 THz. Results were similar to those found previously for Ga₇Pd₃, although jump frequencies are about 100 times lower in Ga₇Pt₃.     

NEUROTOXICITY OF TETRAPHENYLPORPHINESULFONATE TPPS4 and ITS RELATION TO PHOTODYNAMIC THERAPY*

Abstract Tetraphenylporphinesulfonate (TPPS₄) is a synthetic porphyrin that localizes in certain tumors to a higher absolute concentration and with more favorable tumor to other tissue ratios than any other porphyrin yet studied. Its utilization for photodynamic therapy and other applications has been inhibited by reported neurotoxicity. We injected TPPS₄ over a broad dose range of 5-150 mg kg^?1 and observed the effects on peripheral nerve in groups of animals sacrificed 35, 70 and 140 days later. No immediate deaths or phototoxic manifestations were seen. Light and electron microscopy, however, revealed cytoskeletal abnormalities and nerve fiber degeneration affecting both myelinated and unmyelinated fibers in all the time and dose groups. These findings have similarities to those of other experimental toxic neuropathies, and may also be related to the preponderance of autonomic manifestations in patients with porphyric neuropathy. The morphological changes consisted of tangles of fibrillar material in the myelinated fibers and loss of neurotubules in the unmyelinated fibers. Our studies indicate a direct interaction of TPPS₄ with tubulin. This biological mechanism may be involved in the selective distribution of certain parenterally administered porphyrins.     

Vladimir Evgen’evich Dmitrienko (On the occasion of his 60th birthday)

Crystallography Reports -     

Individual interface states and their implications for low-frequency noise in MOSFETs

We show that the wide distribution of time constants required to explain 1/ƒ noise in MOSFETs arises as a natural consequence of the multi-phonon model of carrier trapping into individual Si-SiO₂ interface states. A new class of random telegraph signal found in the drain current of small-area silicon MOSFETs is described. These signals are a result of defect metastability and are shown to be a source of non-Gaussian noise.     

Site Preferences of Hyperfine Impurities in Ni2Al3 Phases

The site occupation of indium solutes in Ni₂Al₃-type compounds was determined using perturbed angular correlation of gamma rays. Measurements were made for compositions on both sides of the stoichiometric composition. Sites were identified through their quadrupole interactions. For transition-metal (TM) rich aluminides and galliumides, indium solutes occupy only one of two inequivalent trivalent-metal sites (Al or Ga). For TM-poor aluminides, indium solutes tend to locate at noncrystallographic sites such as in grain boundaries. For TM-poor galliumides, the solutes occupy nickel sites while close to the stoichiometric composition they also occupy sites on an empty Ni-sublattice. Composition dependences of site preference for indium solutes in Pt₂Al₃ and Ni₂Ga₃ are examined in terms of a recently developed thermodynamic model. This revised version was published online in September 2006 with corrections to the Cover Date.