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Biomedical subjects

Z Rácz

Publications and source records attributed to Z Rácz.

At least 19 recordsLinked to original sources
PubMed2003

Magnetization distribution in the transverse Ising chain with energy flux.

The zero-temperature transverse Ising chain carrying an energy flux j(E) is studied with the aim of determining the nonequilibrium distribution functions, P(M(z)) and P(Mx) of its transverse and longitudinal magnetizations, respectively. An exact calculation reveals that P(M(z)) is a Gaussian both at j(E)=0 and at j(E) not equal to 0, and the width of the distribution decreases with increasing energy flux. The distribution of the order-parameter fluctuations, P(Mx), is evaluated numerically for spin chains of up to 20 spins. For the equilibrium case (j(E)=0), we find the expected Gaussian fluctuations away from the critical point, while the critical order-parameter fluctuations are shown to be non-Gaussian with a scaling function Phi(x)=Phi(M(x)/ )= P(Mx) strongly dependent on the boundary conditions. When j(E) not equal to 0, the system displays long-range, oscillating correlations but P(Mx) is a Gaussian nevertheless, and the width of the Gaussian decreases with increasing j(E). In particular, we find that, at critical transverse field, the width has a j(-3/8)(E) asymptotic in the j(E)-->0 limit.

Journal Article↗
PubMed2002

Roughness distributions for 1/f alpha signals.

The probability density function (PDF) of the roughness, i.e., of the temporal variance, of 1/f(alpha) noise signals is studied. Our starting point is the generalization of the model of Gaussian, time periodic, 1/f noise, discussed in our recent Letter [Phys. Rev. Lett. 87, 240601 (2001)], to arbitrary power law. We investigate three main scaling regions (alpha < or = 1/2, 1/2 < alpha < or = 1, and 1< alpha), distinguished by the scaling of the cumulants in terms of the microscopic scale and the total length of the period. Various analytical representations of the PDF allow for a precise numerical evaluation of the scaling function of the PDF for any alpha. A simulation of the periodic process makes it possible to study also nonperiodic, thus experimentally more relevant, signals on relatively short intervals embedded in the full period. We find that for alpha < or = 1/2 the scaled PDFs in both the periodic and the nonperiodic cases are Gaussian, but for alpha > 1/2 they differ from the Gaussian and from each other. Both deviations increase with growing alpha. That conclusion, based on numerics, is reinforced by analytic results for alpha = 2 and alpha-->infinity, in the latter limit the scaling function of the PDF being finite for periodic signals, but developing a singularity for the aperiodic ones. Finally, an overview is given for the scaling of cumulants of the roughness and the various scaling regions in arbitrary dimensions. We suggest that our theoretical and numerical results open a different perspective on the data analysis of 1/f(alpha) processes.

Journal Article↗
PubMed2002

Width distributions and the upper critical dimension of Kardar-Parisi-Zhang interfaces.

Simulations of restricted solid-on-solid growth models are used to build the width distributions of d=2-5 dimensional Kardar-Parisi-Zhang (KPZ) interfaces. We find that the universal scaling function associated with the steady-state width distribution changes smoothly as d is increased, thus strongly suggesting that d=4 is not an upper critical dimension for the KPZ equation. The dimensional trends observed in the scaling functions indicate that the upper critical dimension is at infinity.

Journal Article↗
PubMed2001

1/f noise and extreme value statistics.

We study finite-size scaling of the roughness of signals in systems displaying Gaussian 1/f power spectra. It is found that one of the extreme value distributions, the Fisher-Tippett-Gumbel (FTG) distribution, emerges as the scaling function when boundary conditions are periodic. We provide a realistic example of periodic 1/f noise, and demonstrate by simulations that the FTG distribution is a good approximation for the case of nonperiodic boundary conditions as well. Experiments on voltage fluctuations in GaAs films are analyzed and excellent agreement is found with the theory.

Journal Article↗
PubMed2001

[Biological aspects of the effectiveness/ineffectiveness of thrombocyte transfusions].

The clinical effect of platelet transfusions depends on a series of different factors and therefore it is not easy to explain the cause of inefficiency or that of the side-effects. Not only the immunhematological state of the patient, but the medical treatment and the properties of the platelet preparations should be taken into account. Platelet products prepared by standard techniques and stored according to the international recommendations possess different hemostatic effect. The effect of platelet storage conditions, aspects of platelet thermophysiology and current international tendencies regarding preparation and storage of platelet products are discussed. The choice of the proper platelet product has an essential impact on the clinical outcome.

Animals↗
PubMed2000

Characteristics of the specific removal of lymphocytes and granulocytes from whole blood in an automated bottom-and-top processing system.

Characteristics of lymphocyte and granulocyte removal were studied during processing of fresh and overnight-stored human blood in a bottom-and-top semiautomated system using the buffy coat (BC) technique. Blood cells were counted in the resulting components. Removal efficiency of lymphocytes and granulocytes correlated with the loss of erythrocytes due to removal of the BC. Sigmoidal curves showed a good fit to experimental data. Variables of the equations differed substantially concerning removal of lymphocytes and granulocytes. Overnight storage of blood at 20-22 degrees C prior to processing resulted in changes in efficiency of leukocyte removal. Removal of lymphocytes decreased, while that of granulocytes increased due to overnight processing. Lymphocytes may be removed almost quantitatively with less than 10% (fresh blood) or 15% (overnight-stored blood) loss in erythrocyte content of the donated blood, corresponding to less than 28 ml packed red cells in the BC. Granulocytes seem to represent the residual amount of the final leukocyte content in the erythrocyte product. The present study may contribute to the production of erythrocyte products with fewer contaminating leukocytes and to the standardizing of semiautomated blood processing.

Blood Component Removal↗
PubMed1999

Transport in the XX chain at zero temperature: emergence of flat magnetization profiles.

We study the connection between magnetization transport and magnetization profiles in zero-temperature XX chains. The time evolution of the transverse magnetization m(x,t) is calculated using an inhomogeneous initial state that is the ground state at fixed magnetization but with m reversed from -m(0) for x<0 to m(0) for x>0. In the long-time limit, the magnetization evolves into a scaling form m(x,t)=Phi(x/t) and the profile develops a flat part (m=Phi=0) in the (x/t) 1/2 while it expands with the maximum velocity c(0)=1 for m(0)-->0. The states emerging in the scaling limit are compared to those of a homogeneous system where the same magnetization current is driven by a bulk field, and we find that the expectation values of various quantities (energy, occupation number in the fermionic representation) agree in the two systems.

Journal Article↗
PubMed1997

Differential reduction in lymphocyte and granulocyte content by removal of the buffy coat from fresh and overnight-stored blood. Comparison of manual and automated blood processing systems.

The efficiency of leukocyte removal was studied by the removal of the buffy coat layer from fresh and overnight-stored whole blood. Manual blood processing was compared with two types of automated separators: the T-ACE (Terumo) and the OPTI system (with the top-and-bottom bag, Baxter). The main characteristics of leukocyte removal were similar for the systems studied. The efficiency of leukocyte removal was consistently higher with overnight-stored blood. When the net red cell content of the buffy coat was 20-30 mL, the figures were: 70% (n = 103) vs 45% (n = 87, manual method), 78% (n = 6) vs 60% (n = 100, T-ACE) and 82% (n = 10) vs 71% (n = 20, OPTI system), respectively. The increase in the efficiency in leukocyte removal was due to a rapid increase in the efficiency of removal of granulocytes: 65% (n = 65) vs 45% (n = 57, manual method), 80% (n = 4) vs 46% (n = 83, T-ACE) and 74% (n = 9) vs 57% (n = 17, OPTI system), respectively. Processing of overnight stored blood may provide red cell concentrates with fewer contaminating leukocytes and granulocytes.

Automation↗
PubMed1997

Increased yield of F VIII from pooled plasma vs. single-donor plasma in the production of cryoprecipitates.

Coagulation factor VIII:C yield was studied in two types of cryoprecipitates. The first group contained products from single-donor plasma units. The other group contained cryoprecipitates which were produced from pooled plasma. The volume of plasma/bag was not different between the two groups, but both the yield and the total content of F VIII:C in cryoprecipitates were significantly different. The yield of F VIII:C was higher (+20% in relative terms) in cryoprecipitates produced from pooled plasma, resulting in higher potency of such products. The positive effect of plasma pooling on the recovery of F VIII:C might be a result of reassembly of factor VIII subunits of different individuals in the plasma pools. The findings may have a role also in large-scale production of F VIII concentrates.

Chemical Precipitation↗
PubMed1995

Storage of platelet concentrates from overnight-stored blood and overnight-stored buffy coat: in vitro studies.

Platelet concentrates (PCs) were prepared from single buffy coats derived from fresh blood and from blood units stored overnight, as well as from buffy coats that were stored overnight. The platelet yield from overnight-stored buffy coats was similar to that of fresh blood or overnight-stored blood. PCs were stored at 20-24 degrees C and on day 5 of storage, platelet aggregation with ADP was tested both at 37 and 25 degrees C. Stored platelets aggregated better at 25 degrees C than 37 degrees C. The maximal, aggregation (10 microM ADP) of stored platelets from overnight-stored buffy coats was 46 +/- 23% (n = 30), while that of stored platelets prepared either from fresh or overnight-stored blood was 27 +/- 21% (n = 29) and 22 +/- 15% (n = 29), respectively. Extracellular lactate dehydrogenase and ammonia levels, as well as elastase activity were similar in stored PCs of different origin. Our conclusion is that PCs prepared from overnight-stored buffy coat might also be suitable for storage and clinical use. In vivo studies are needed to confirm our findings.

Blood Component Removal↗