Biomedical subjects

A Levstik

Publications and source records attributed to A Levstik.

17 recordsLinked to original sources

PubMed2004

Distinctive contributions from organic filler and relaxorlike polymer matrix to dielectric response of CuPc-P(VDF-TrFE-CFE) composite.

The dielectric response of copper-phthalocyanine (CuPc) oligomers embedded in a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer matrix was studied. Although admixture of CuPc strongly increases the dielectric constant of the terpolymer at all temperatures, each of the two constituents determines the dielectric dynamics in a different temperature region-the relaxorlike matrix above and CuPc below the terpolymer's freezing temperature. Two relaxations, reflecting the charge carriers' response in CuPc, were detected. Results on ac conductivity reveal that the tunneling of polarons is the dominating charge transport mechanism.

Chlorofluorocarbons↗

PubMed2001

1/f noise and dynamical heterogeneity in glasses.

We investigate the relationship between two experimental sets of data related to dynamical heterogeneity, the coefficient alpha of 1/f(alpha) dipolar noise derived from the nonexponentiality of the dielectric or magnetic response near and above the mean relaxation time, and the range Delta(z) of the relaxation times. We find that in different classes of glasses, including spin and proton glasses, relaxor materials, and glass-forming liquids, this relationship exhibits the same trend.

Journal Article↗

PubMed2000

Crossover from glassy to inhomogeneous-ferroelectric nonlinear dielectric response in relaxor ferroelectrics.

The temperature dependence of the dielectric nonlinearities in a PMN single crystal and in 9/65/35 PLZT ceramics has been determined by measuring the first and third harmonic response as well as the dielectric behavior as a function of the dc electric field. In zero field a paraelectric-to-glass, and, in a high enough dc field, a glass-to-ferroelectriclike crossover in the temperature dependence of the nonlinear response have been observed. Both crossovers agree with the predictions of the spherical random-bond-random-field model. Relaxors thus undergo in zero field a transition to a spherical glass, while above the critical field a transition into a ferroelectric state occurs.

Journal Article↗

PubMed1999

Proton glass freezing in hydrated lysozyme powders.

At room temperature, the dielectric relaxation of hydrated powder of the protein lysozyme is known to be due to protons migrating between ionized side chains. A recent study of this relaxation at lower temperatures suggested a behavior typical of proton glasses. An analysis of the complex dielectric susceptibility by a temperature-frequency plot presented here has revealed that ergodicity is broken due to the divergence of the longest relaxation time at 266 K, indicating specifically that this hydrated protein is a proton glass. A change in the temperature behavior of the static dielectric constant and the average relaxation frequency at 273 K indicates a further transition occurring at this temperature, whose nature remains to be investigated.

Freezing↗

PubMed1994