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S Gluzman

Publications and source records attributed to S Gluzman.

At least 19 recordsLinked to original sources
PubMed2003

Self-similar factor approximants.

The problem of reconstructing functions from their asymptotic expansions in powers of a small variable is addressed by deriving an improved type of approximants. The derivation is based on the self-similar approximation theory, which presents the passage from one approximant to another as the motion realized by a dynamical system with the property of group self-similarity. The derived approximants, because of their form, are called self-similar factor approximants. These complement the obtained earlier self-similar exponential approximants and self-similar root approximants. The specific feature of self-similar factor approximants is that their control functions, providing convergence of the computational algorithm, are completely defined from the accuracy-through-order conditions. These approximants contain the Padé approximants as a particular case, and in some limit they can be reduced to the self-similar exponential approximants previously introduced by two of us. It is proved that the self-similar factor approximants are able to reproduce exactly a wide class of functions, which include a variety of nonalgebraic functions. For other functions, not pertaining to this exactly reproducible class, the factor approximants provide very accurate approximations, whose accuracy surpasses significantly that of the most accurate Padé approximants. This is illustrated by a number of examples showing the generality and accuracy of the factor approximants even when conventional techniques meet serious difficulties.

Journal Article↗
PubMed2002

Classification of possible finite-time singularities by functional renormalization.

Starting from a representation of the early time evolution of a dynamical system in terms of the polynomial expression of some observable phi(t) as a function of the time variable in some interval 0 < or = t < or = T, we investigate how to extrapolate/forecast in some optimal stability sense the future evolution of phi(t) for time t>T. Using the functional renormalization of Yukalov and Gluzman, we offer a general classification of the possible regimes that can be defined based on the sole knowledge of the coefficients of a second-order polynomial representation of the dynamics. In particular, we investigate the conditions for the occurrence of finite-time singularities from the structure of the time series, and quantify the critical time and the functional nature of the singularity when present. We also describe the regimes when a smooth extremum replaces the singularity and determine its position and amplitude. This extends previous works by (1) quantifying the stability of the functional renormalization method more accurately, (2) introducing more global constraints in terms of moments, and (3) going beyond the "mean-field" approximation.

Journal Article↗
PubMed2002

Log-periodic route to fractal functions.

Log-periodic oscillations have been found to decorate the usual power-law behavior found to describe the approach to a critical point, when the continuous scale-invariance symmetry is partially broken into a discrete-scale invariance symmetry. For Ising or Potts spins with ferromagnetic interactions on hierarchical systems, the relative magnitude of the log-periodic corrections are usually very small, of order 10(-5). In growth processes [diffusion limited aggregation (DLA)], rupture, earthquake, and financial crashes, log-periodic oscillations with amplitudes of the order of 10% have been reported. We suggest a "technical" explanation for this 4 order-of-magnitude difference based on the property of the "regular function" g(x) embodying the effect of the microscopic degrees of freedom summed over in a renormalization group (RG) approach F(x)=g(x)+mu(-1)F(gamma x) of an observable F as a function of a control parameter x. For systems for which the RG equation has not been derived, the previous equation can be understood as a Jackson q integral, which is the natural tool for describing discrete-scale invariance. We classify the "Weierstrass-type" solutions of the RG into two classes characterized by the amplitudes A(n) of the power-law series expansion. These two classes are separated by a novel "critical" point. Growth processes (DLA), rupture, earthquake, and financial crashes thus seem to be characterized by oscillatory or bounded regular microscopic functions that lead to a slow power-law decay of A(n), giving strong log-periodic amplitudes. If in addition, the phases of A(n) are ergodic and mixing, the observable presents self-affine nondifferentiable properties. In contrast, the regular function of statistical physics models with "ferromagnetic"-type interactions at equilibrium involves unbound logarithms of polynomials of the control variable that lead to a fast exponential decay of A(n) giving weak log-periodic amplitudes and smoothed observables.

Journal Article↗
PubMed2002

Stress and well-being in mothers of young children 11 years after the Chornobyl nuclear power plant accident.

BACKGROUND: This paper examines the association between exposure to the Chornobyl nuclear power plant explosion and the psychological and physical well-being of mothers with young children. The study also examines whether exposure to Chornobyl increased the vulnerability of mothers to subsequent economic and social stress, and thus represents a unique test of the stress-vulnerability model in a non-Western setting. METHOD: The sample consisted of mothers evacuated from the contamination zone surrounding the plant (evacuees) and mothers who had never lived in a radiation-contaminated area (controls). In addition to exposure status, the interview obtained data on perceived economic stress, social stress and stress moderators. The dependent variables were measured by the SCL-90 global severity index (GSI), perceived physical health and number of days unable to work due to illness. RESULTS: Overall, evacuees reported fewer stressors and greater personal and social resources than control mothers. Nevertheless, evacuees scored higher on the GSI, reported lower perceived physical health and took more sick days relative to control mothers, even after controlling for demographic factors, stressors and stress moderators. Tests of interaction effects were not statistically significant. CONCLUSIONS: The findings confirmed that married women with young children evacuated to Kyiv following the Chornobyl nuclear power plant explosion reported significantly poorer psychological and perceived physical health than controls 11 years later. Although perceived social and economic adversities also affected these outcomes, there was no evidence that exposure to the Chornobyl accident increased the vulnerability of mothers to these stressors, giving support to the additive burden model of stress.

Adult↗
PubMed2001

Self-consistent theory of rupture by progressive diffuse damage.

We analyze a self-consistent theory of crack growth controlled by a cumulative damage variable d(t) dependent on stress history, in the quasistatic regime where the sound wave velocity is taken as infinite. Depending upon the damage exponent m, which controls the rate of damage dd/dt~sigma(m) as a function of local stress sigma, we find two regimes. For 0 /=2, the rupture dynamics is not defined without the introduction of a regularizing scheme. We investigate three regularization schemes involving, respectively, a saturation of damage, a minimum distance of approach to the crack tip, and a fixed stress maximum. In the first and third schemes, the finite-time singularity is replaced by a crack dynamics defined for all times but which is controlled by either the existence of a microscopic scale at which the stress is regularized or by the maximum sustainable stress. In the second scheme, a finite-time singularity is again found. In the first two schemes within this regime m>/=2, the theory has no continuous limit.

Journal Article↗
PubMed2001

Ukrainian application of the Children's Somatization Inventory: psychometric properties and associations with internalizing symptoms.

This paper examines the psychometric properties of the Children's Somatization Inventory (CSI) in 600 10-12-year old children in Kyiv, Ukraine, replicating and extending the original findings from a sample in Nashville, Tennessee (J. Garber et al. 1991). The Kyiv children had significantly lower CSI total scores and reported significantly fewer symptoms than the American children. The Kyiv mothers, however, reported significantly more somatization symptoms in their children than did the American mothers. A factor analysis of the children's data yielded four similar factors encompassing pseudoneurologic, cardiovascular, gastrointestinal, and pain/weakness symptoms. Consistent with the findings from the Nashville study, the CSI was significantly related to the children's self-reports of health and depressive and anxiety symptoms and to maternal reports of child depression and anxiety symptoms. In addition, although more children with the highest CSI scores (25+) reported various illness experiences than those with 0-1 symptoms, no differences were found in the school absentee records. Thus, the results were congruent with the findings of the Nashville study, indicating that the CSI reliably measured somatization in this Ukrainian sample.

Anxiety↗
PubMed2000

School and neuropsychological performance of evacuated children in Kyiv 11 years after the Chornobyl disaster.

This paper examines the cognitive and neuropsychological functioning of children who were in utero to age 15 months at the time of the Chornobyl disaster and were evacuated to Kyiv from the 30-kilometer zone surrounding the plant. Specifically, we compared 300 evacuee children at ages 10-12 with 300 non-evacuee Kyiv classmates on objective and subjective measures of attention, memory, and school performance. The evacuee children were not significantly different from their classmates on the objective measures (grades; Symbolic Relations subtest of the Detroit Test; forms 1 and 2 of the Visual Search and Attention Test; Benton Form A; Trails A; Underline the Words Test) or on most of the subjective measures (the attention subscale of the Child Behavior Checklist completed by mothers; the attention items of the Iowa Conners Teacher's Rating Scale; mother and child perceptions of school performance). The one exception was that 31.3% of evacuee mothers compared to 7.4% of classmate mothers indicated that their child had a memory problem. However, this subjective measure of memory problems was not significantly related to neuropsychological or school performance. No significant differences were found in comparisons of evacuees and classmates who were in utero at the time of the explosion, children from Pripyat vs. other villages in the 30-kilometer zone, and children manifesting greater generalized anxiety. For both groups, children with greater Chornobyl-focused anxiety performed significantly worse than children with less Chornobyl-focused anxiety on measures of attention. The results thus fail to confirm two previous reports that relatively more children from areas contaminated by radiation had cognitive deficits compared to controls. Possible reasons for the differences in findings among the studies are discussed.

Achievement↗
PubMed1993

Soviet special psychiatric hospitals. Where the system was criminal and the inmates were sane.

The subversion of psychiatric intervention for political purposes in the USSR during the 1970s and 1980s resulted in both intra-psychic and subsequent adaptational dysfunction in those dissidents who physically survived it. Incarceration in special psychiatric hospitals subjected the inmates to a sense of helplessness under the control of a malevolent power, futility, despair, danger from close and contentious contact with hardened criminals and the violently insane, overdosage with mind-altering and body-distorting neuroleptic drugs, and a Kafkaesque ambiguity concerning the specific terms of instutionalisation. Discharge did not bring release from continued threats and the eroded social networks to which the inmates returned subjected them to a new set of stressors. While some families remained intact and provided necessary support during the re-entry period, many families had been destroyed either by the circumstances of the family member's incarceration or by the length of the victim's stay in the psychiatric hospital. Wives left, people died, friends deserted, jobs evaporated, and often there was not even a home to accept them. Social agencies were either hostile or indifferent to their plight. Many felt like they had been thrown overboard from a prison ship without a life preserver. It was the proverbial transition from the frying pan into the fire.

Crime↗
PubMed1989

Insulin-like growth factor-II in nonislet cell tumors associated with hypoglycemia: increased levels of messenger ribonucleic acid.

The role of insulin-like growth factor-II (IGF-II) in the hypoglycemia associated with nonislet cell tumors is controversial. In this study we have addressed this question by measuring the IGF-II mRNA levels in extracts of these tumors. Hybridization of a 32P-labeled IGF-II cDNA to a Northern blot of RNA from three nonislet cell tumors associated with hypoglycemia (a hemangiopericytoma, fibrosarcoma, and malignant mesenchymal tumor) demonstrated six hybridizing bands, 6.8, 5.6, 4.7, 3.6, 2.6, and 2.1 kilobases in length. These bands were similar to those described by others in a range of tumors and normal tissues. Tissue IGF-II mRNA levels were quantitated using a solution hybridization/RNase protection assay. IGF-II mRNA levels in the tumors were similar to the level present in one line of human hepatoblastoma-derived Hep G2 cells, 5- to 6-fold higher than that in another line of Hep G2 cells, and 2- to 3-fold higher than that in term placenta. In contrast, little or no IGF-II mRNA was detected in a nonfunctioning islet cell adenoma or normal spleen. There was no evidence for amplification of the IGF-II gene in the one tumor in which it was sought. These data suggest that nonislet cell tumors associated with hypoglycemia produce large amounts of IGF-II mRNA and that this IGF-II mRNA appears to be the product of an IGF-II gene, which is apparently normal in the region encoding mature IGF-II peptide.

Adult↗