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S Russ

Publications and source records attributed to S Russ.

10 recordsLinked to original sources
PubMed2002

Increased damping of irregular resonators.

It is shown that fractal drums and jagged geometry resonators may be more damped than ordinary Euclidean systems. Several damping mechanisms are examined and studied by numerical calculations. The results depend on the dissipation mechanisms but globally they increase with localization, frequency, and the irregularity of the resonator. The increased dissipation is due to the uneven spatial distribution of the vibrational amplitude in two different ways. First, it is related to the partial confinement of the vibrational modes. Secondly, increased dissipation may be due to singularities in the amplitude distribution. This is the case when a few points exist where the vibration is pinned to zero inducing local logarithmic singularities. This last effect can be spectacular: a single defect can dominate the surface damping by viscous forces of a square drum.

Journal Article↗
PubMed2001

Energy fluctuations of pseudointegrable systems with growing surface roughness.

The eigenfrequencies of two-dimensional systems with fractal boundaries and with nonscaling rough boundaries are calculated numerically by the Lanczos algorithm and analyzed by means of level statistics. The systems are pseudointegrable and the fluctuations of their eigenvalue spectra show a global statistical behavior between the Poisson and the Wigner distributions. With increasing irregularity of the boundary, the systems approach the Wigner limit and the results seem to depend only on the genus number of the geometry and not on details, such as the asymptotic shape of the geometry, the type of roughness (scaling or nonscaling), and the boundary conditions (Neumann or Dirichlet). No transition between localized and extended states is found in fractal drums.

Journal Article↗
PubMed1997

Seasonal variations of rheological and hemostatic parameters and acute-phase reactants in young, healthy subjects.

The incidence of cardiovascular diseases is increased in winter months. Recent studies have shown seasonal changes in plasma viscosity, fibrinogen, and factor VII activity with elevated levels during winter. An increase in these factors generates a "hypercoagulable state," which may lead to a rise in cardiovascular morbidity and mortality. It has been suggested that an increase in upper respiratory infections might be the underlying cause for the raised acute-phase reactants, in particular fibrinogen, during the winter season. We investigated seasonal variations of 26 parameters, determining blood rheology and hemostasis in 16 healthy volunteers (8 men and 8 women) aged 20 to 41 years. They were seen at monthly intervals over a period of 1 year. Seasonal variation with peak fitted values in the winter months was found for plasma viscosity (P < .001 for the seasonal difference), red blood cell deformability (P < .001), whole blood viscosity (P < .001), hemoglobin (P < .001), hematocrit (P < .001), mean corpuscular volume (P = .001), platelet count (P = .01), alpha 1-glycoprotein (P < .001), fibrinogen (measured by immunonephelometry; P < .001), plasminogen activator inhibitor-1 (P = .002), LDL cholesterol (P = .003), and triglyceride levels (P < .001). HDL cholesterol (P < .001) and cortisol (P = .001) showed inverse seasonal patterns, with a maximum during summertime. No statistically significant seasonal variations were seen for red blood cell aggregation, complement factor C4, total cholesterol, ceruloplasmin, haptoglobin, white blood cell count, and plasminogen. These data do not support the hypothesis that increased morbidity and mortality from cardiovascular diseases during winter may be mainly attributable to increased synthesis of acute-phase proteins due to infections. The cause for the seasonal variations in rheological and hemostatic parameters remains unclear and should be studied in more detail.

Acute-Phase Proteins↗
PubMed1996

Fractal geometry impact on nuclear relaxation in irregular pores.

We apply a fractal description of pore surface irregularity to study the nuclear relaxation of a confined liquid. From the introduction of a length characteristic of diffusive and surface relaxing properties we describe three different relaxation regimes. These regimes show that the nuclear relaxation can be drastically modified by pore surface irregularity.

Fractals↗
PubMed1981

Adaptive regression and types of cognitive flexibility.

The relationship between adaptive regression and cognitive flexibility was explored in a group of 42 college students. Adaptive regression was measured with the Holt scoring system for the Rorschach. One type of cognitive flexibility was measured by Guilford's tests of divergent production (Word Fluency, Associational Fluency, and Alternate Uses) and a second type by Mednick's Remote Associates Test. Adaptive regression was found to be significantly positively related to the Remote Associates Test in males but not in females. Adaptive regression was found to be unrelated to divergent production tests. These relationships were not found to be mediated by Rorschach productivity or verbal intelligence. A two-stage process was proposed to account for the cognitive operations underlying adaptive regression and the Remote Associates Test. The first stage is seen as a generative (primary process) stage, while the second stage is seen as an evaluative (secondary process) stage. Possible reasons for sex differences were also discussed.

Journal Article↗