Bibliothek

Notizen: Bilayers of yttrium and amorphous silicon were irradiated with 600-keV Ar++, Kr++, and Xe++ ions at temperatures between 80 and 372 K. The mixing rates were considerably larger than rates predicted by a model based on overlapping thermal spikes, as well as predictions generated by an extension of the model to the case of nonoverlapping thermal spikes. However, the experimental mixing rates did exhibit a linear dependence on the nuclear energy deposited at the interface. This agrees qualitatively with the premise of nonoverlapping thermal spikes. We compare our results with other ion-mixed medium-Z, metal/metal systems which also show this tendency.

Notizen: Low temperature ion beam mixing rates for Cu-Ti, Ni-Ti, and Fe-Ti layers have been found to be significantly lower than predicted by a popular semi-empirical thermal spike model. It has been proposed that the unavoidable hydrogen contamination of the as-deposited Ti films may have reduced the mixing rates, but the measurement of even lower mixing rates for Fe-V and Fe-Co bilayers shows the discrepancy to be more fundamental. Still, a systematic dependence on heat of mixing suggests that some sort of diffusional (thermal spike?) mechanism is involved.

Notizen: Galantamine hydrobromide is a tertiary alkaloid drug that has been developed and approved in a number of countries including the USA and several countries in Europe as a treatment for mild-to-moderate Alzheimer's disease (AD). Galantamine has a unique, dual mode of action. It is a reversible, competitive inhibitor of acetylcholinesterase (AChE), and is the only drug actively marketed for the treatment of AD with proven activity as an allosteric modulator of nicotinic acetylcholine receptors (nAChRs). This latter activity is thought to be particularly important since decreases in the expression and activity of nAChRs make a large contribution to the reduction in central cholinergic neurotransmission in patients with AD. Galantamine exhibits favorable pharmacokinetic characteristics including predictable linear elimination kinetics at the recommended maintenance doses (16 and 24 mg/day), a relatively short half-life (approximately 7 h) and high bioavailability. It is extensively metabolized in numerous pathways, mainly in the liver via cytochrome P450 enzymes CYP2D6 and CYP3A4, and has a low potential for clinically significant drug-drug interactions. During four large randomized, double-blind, placebo-controlled trials of up to 6 months duration, galantamine 16 and 24 mg/day significantly benefited cognitive and global function, ability to perform activities of daily living (ADL) and behavior, relative to placebo and baseline, for up to 6 months. Caregiver burden (time spent by caregivers supervising patients or assisting them with ADL), and caregiver distress (related to patients' behavioral symptoms) were also reduced. Cognitive and functional abilities were preserved at or near baseline for at least 12 months in patients who received galantamine 24 mg/day for 12 months in a long-term US study. These benefits were maximized by early and continued galantamine treatment and, again, were associated with significant reductions in caregiver burden. Trials of the efficacy of galantamine in dementia related to cerebrovascular disease have also yielded positive results. There are no safety concerns associated with the use of galantamine. The incidence of adverse events, particularly cholinergically mediated events affecting the gastrointestinal system, is generally low and can be minimized using the recommended slow dose-escalation scheme. Galantamine may, therefore, help to reduce the overall burden and cost involved in caring for dementia patients. Taking all evidence into account, galantamine has the potential to become a first-line therapy for dementia.

Notizen: Bilayers of yttrium and amorphous silicon have been irradiated with 60 keV inert ions. Between liquid-nitrogen temperature and 100 °C, ion mixing resulted in an amorphous alloy of Y and Si. For temperatures of 125–190 °C, we observed formation of the YSi phase. YSi is not formed during thermal anneals of bilayers. Ion mixing at higher temperatures (≥205 °C) results in the formation of the stable YSi1.7 phase. Such sequential silicide formation has not been observed for comparable rare-earth silicides. The minimum temperatures for ion-induced YSi1.7 formation agrees with the prediction by a simple model which correlates vacancy mobility to phase transformation. The YSi formation temperature is associated with the onset of radiation-enhanced diffusion. This temperature does not correlate well with the prediction of the model, but agrees with a scaling based on the average cohesive energy.

Notizen: Low-temperature ion beam mixing rates for Ni-Ti, Zr-Ni, and Pd-Ni bilayers significantly exceeded binary collision estimates, and appeared quite sensitive to thermodynamic driving forces. In the absence of a temperature dependence such a behavior is commonly ascribed to interdiffusion within thermal spikes. However, the Ni-Ti mixing rate was seen to vary linearly with nuclear damage energy for irradiation with 600 keV Xe, Kr, or Ar, 300 keV Ne or N, or 200 keV N ions, or 1 MeV Au ions (literature value). This excludes overlapping thermal spikes. An expression was derived for mixing due to nonoverlapping thermal spikes, but this could also not explain our results.

Notizen: Measurements of the low-temperature mixing of several 5d–4d bilayers by 600 keV Xe ions have strongly supported the assumption of a thermal spike mechanism. Quite disturbingly, however, the Au-Ag mixing rate appeared to exceed theoretical predictions by about a factor of 3. A closer examination of this system shows the discrepancy to be caused by the formation of a strongly nonuniform Au surface structure during irradiation. An improved value for the mixing rate is in reasonable agreement with predictions.