Biomedical subjects

J Schmelzer

Publications and source records attributed to J Schmelzer.

6 recordsLinked to original sources

PubMed2002

Finite-size effects in the conductivity of cluster assembled nanostructures.

Atomic clusters have been deposited between lithographically defined contacts with nanometer scale separations. The design of the contacts is based on an appropriate application of percolation theory to conduction in cluster deposited devices and allows finite-size effects to be clearly observed. It is demonstrated, both by experiment and by simulation, that for small contact separations the percolation threshold is shifted to extremely low surface coverages. The selected rectangular contact geometry ensures that wirelike structures are formed close to the percolation threshold.

Journal Article↗

PubMed2002

Kinetics of formation of a phase with an arbitrary stoichiometric composition in a multicomponent solid solution.

A kinetic theory of nucleation and growth of a evolving phase with a given stoichiometric composition in a multicomponent solid solution is developed. It is assumed naturally that the phase grows as a result of individual atom incorporation into the phase domain in a stoichiometric ratio. As it is shown, for the case of phase formation in a multicomponent system the basic kinetic equations, describing the nucleation-growth process, can be reduced formally to the respective expression derived for nucleation-growth processes in one-component systems. However, the effective diffusion coefficients and the effective supersaturation are expressed as nontrivial combinations of the thermodynamic and kinetic parameters of the different components involved in the phase formation process. In the determination of these properties, the theory is not restricted in its applicability to perfect solutions but extended to phase formation in real mixtures. Thus, the theory may be applied directly towards the interpretation of experimental data. In the present paper, particular attention is devoted to the analysis of the two stages of the overall transformation process: (1) the stage of quasi-steady-state nucleation and (2) the transient stage of coarsening. As the results of this analysis, the quasi-steady-state nucleation rate, the number of clusters formed via nucleation and growth, and the time evolution of the cluster size distributions are established. Moreover, estimates are given for the duration of the different stages of the transformation process.

Journal Article↗

PubMed1999

Kinetics of Nucleation at Increasing Supersaturation.

The kinetics of homogeneous nucleation-growth processes under increasing supersaturation is investigated. The increase of the supersaturation is hereby caused by an appropriate variation of external parameters such as pressure and temperature. Analytic expressions are formulated for the dependence of the number of supercritical clusters both on the rate of change of the supersaturation and on time. In generalization of previous studies, both thermal and athermal nucleation are taken into consideration. It turns out that in dependence on the rate of change of the external parameters, either thermal (for moderate rates) or athermal (for higher rates) nucleation, dominates the process. It is shown further that, in the range where thermal nucleation dominates, the onset of nucleation-growth processes, i.e., the minimum value of the supersaturation required for intensive nucleation, depends weakly (logarithmically) on the rate of increase of the supersaturation. Criteria are formulated under which conditions the commonly employed assumption-independence of the nucleation-growth process on the way the initial unstable state is established-is applicable. As shown, quite generally these criteria are not fulfilled. In a further step of the analysis, simultaneously to external variations of the thermodynamic parameters, internally generated changes of the state of the system (depletion effects) are accounted for. For segregation processes in solutions (bubble formation), which are analyzed here as an example, such effects result from a decrease of the supersaturation due to the consumption of solute particles by the clusters of the newly formed phase. Basic characteristics of the nucleation-growth process, such as the maximum number of clusters formed in the system, are determined in dependence on both externally (rate of change of the external parameters) and internally (depletion effects) induced changes of the thermodynamic state of the system. It is shown, in particular, that the interplay of both factors is, in general, of comparable importance for the outcome of the nucleation-growth process. Copyright 1999 Academic Press.

Journal Article↗

PubMed1996

Least restrictive alternatives: do they really work?

Seclusion and restraint continue to spark debate regarding their therapeutic value and ethical, legal, and humanitarian implications, yet they remain frequently used forms of treatment in psychiatric settings. Identifying specific alternatives to seclusion and restraint use, teaching nursing staff how and when to use them, and determining their effect on patient outcome are important quality improvement issues. A quality improvement study conducted at a long-term care psychiatric facility identified alternatives that nursing staff used and their effect on reducing seclusion and restraint rates. A total of 773 incidents of disruptive behavior were managed with least restrictive alternatives and did not require the use of seclusion or restraint. One-to-one verbal intervention followed by medication as needed represented the most frequently used alternative. Total seclusion and restraint hours decreased by 31 percent, and restraint hours decreased by 47 percent.

Colorado↗

PubMed1982

Endoneurial effects of sera from patients with acute inflammatory polyradiculoneuropathy: electrophysiologic studies on normal and demyelinated rat nerves.

Serum from 10 patients with acute inflammatory demyelinative polyradiculoneuropathy (AIDP) and 10 age-matched controls was injected into rat sciatic nerve. No statistically significant changes in any electrophysiologic parameters were found at 1 week. In nerves studied with serial recordings over 60 minutes, a small but significantly greater reduction in compound muscle action potential (CMAP) was observed at 60 minutes with AIDP serum injected into normal or focally demyelinated nerves. The small reduction in CMAP amplitude in the first hour is of uncertain clinical significance.

Action Potentials↗

PubMed1982

Electrophysiological studies of Guillain-Barré syndrome with different susceptibilities to develop EAN serum on 2 strains of rats.

Sera from 10 patients with AIDP and 10 age-matched controls were microinjected into the tibial division of rat sciatic nerve using improved microinjection techniques and coded sera. No statistically significant changes in conduction velocity or amplitude of the compound muscle action potential (CMAP) or in the monophasic compound action potential (CAP) parameters was found at 1 week. In nerves studied with serial recording over 1 h a small but significantly greater reduction in CMAP amplitude was observed at 60 min in the AIDP group and at both 30 and 60 min when only sera from very severely affected (bed-ridden) patients were considered. A similar reduction was found following microinjection into focally demyelinated nerves. The finding of a small reduction in CMAP amplitude in the first hour suggests the presence in some AIDP patients of serum blocking or demyelinating factors but the clinical significance of this small reduction is uncertain.

Action Potentials↗