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Search Results: 1 - 10 of 224711 matches for " Zoltan Rácz "
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Width of reaction zones in A + B -> C type reaction-diffusion processes: Effects of an electric current
Kirsten Martens,Michel Droz,Zoltan Rácz
Physics , 2009, DOI: 10.1063/1.3148888
Abstract: We investigate the effects of an electric current on the width of a stationary reaction zone in an irreversible A^- + B^+ -> C reaction-diffusion process. The ion dynamics of the electrolytes A = (A^+, A^-) and B = (B^+, B^-) is described by reaction-diffusion equations obeying local electroneutrality, and the stationary state is obtained by employing reservoirs of fixed electrolyte concentrations at the opposite ends of a finite domain. We find that the width of the reaction zone decreases when the current drives the reacting ions towards the reaction zone while it increases in the opposite case. The linear response of the width to the current is estimated by developing a phenomenological theory based on conservation laws, and on electroneutrality. The theory is found to reproduce numerical solutions to a good accuracy.
Pantoprazole before Endoscopy in Patients with Gastroduodenal Ulcer Bleeding: Does the duration of Infusion and Ulcer Location Influence the Effects?
Istvan Rácz,Milan Szalai,Nora Dancs,Tibor Kárász,Andrea Szabó,Mihaly Cs?ndes,Zoltan Horváth
Gastroenterology Research and Practice , 2012, DOI: 10.1155/2012/561207
Abstract: The aim of this study was to investigate the effect of preemptive pantoprazole infusion on early endoscopic findings in patients with acute ulcer bleeding. Records of 333 patients admitted with acute ulcer bleeding were analyzed. Ulcer bleeders were given either 80?mg bolus of pantoprazole followed by continuous infusion of 8?mg per hour or saline infusion until endoscopy. In 93 patients saline infusion whereas in 240 patients bolus plus infusion of pantoprazole was administrated with mean (±SD) durations of hours and hours, respectively ( ). Actively bleeding ulcers were detected in 46/240 (19.2%) of cases in the pantoprazole group as compared with 23/93 (24.7%) in the saline infusion group ( ). Different durations of pantoprazole infusion (0–4 hours, 4 hours, and 6 hours) had no significant effect on endoscopic and clinical outcome parameters in duodenal ulcer bleeders. Gastric ulcer bleeders on pantoprazole infusion longer than 4 and 6 hours before endoscopy had actively bleeding ulcers in 4.3% and 5% compared to the 19.5% active bleeding rate in the saline group ( and ). Preemptive infusion of high-dose pantoprazole longer than 4 hours before endoscopy decreased the ratio of active bleeding only in gastric but not in duodenal ulcer patients. 1. Introduction In patients with bleeding peptic ulcers infusion of high-dose proton pump inhibitor (PPI) after endoscopic hemostasis reduces recurrent bleeding and improves clinical outcomes [1–6]. High-dose proton pump inhibitors administered intravenously increase and maintain gastric pH above 6, which is thought to be beneficial for platelet aggregation and clot formation over bleeding vessels [7–9]. Recent studies have shown that not only postendoscopic but also preendoscopic high-dose proton pump inhibitor therapy significantly reduces the proportion of patients with high-risk stigmata of recent hemorrhage (active bleeding, nonbleeding visible vessel, and adherent clot) at early endoscopy and decreases the need for endoscopic intervention [10, 11]. However, almost no data exist about the minimally required duration of PPI infusion before endoscopy, whose results downstage the endoscopic lesions and decrease the need for endoscopic intervention [12]. We hypothesized that patients undergoing endoscopy almost immediately after PPI administration may likely utilize only few benefits whereas longer duration of preendoscopic PPI infusion more likely generates clinical benefits. The aim of our retrospective case control study was to investigate the effects of preemptive infusion of pantoprazole before endoscopy
Technological Experiments for the Enhancement of Glycerol Content in High Quality Wines  [PDF]
Cs. Csutorás, O. Hudák, K. Rácz, L. Rácz
Journal of Agricultural Chemistry and Environment (JACEN) , 2014, DOI: 10.4236/jacen.2014.32B008

The glycerol content of grape juices and wines has been determined by gas-chromatographic methods using silyl derivatives. The effect of different storage conditions and yeast cultures on glycerol content has been investigated. Grape juice samples with different starting D-Glucose concentrations have been treated with several additives (HPO42?, S2O52?, NADH and HSO3?). Significant glycerol concentration enhancement has been detected in the case of the addition of NADH (5.14 g/L), however the presence of HSO3? prevented the excessive glycerol formation (1.21 g/L).

Large Scale Experiments on the Investigation of the Effect of High Concentrations of Aflatoxin B1 on the Fermentation of Different Wines  [PDF]
Cs. Csutorás, K. Rácz, G. Z. Nagy, O. Hudák, L. Rácz
Journal of Agricultural Chemistry and Environment (JACEN) , 2014, DOI: 10.4236/jacen.2014.32B007

The change of aflatoxin B1 (AFB1) content during must fermentation processes in different white, rosé and red musts was investigated, using selected yeast strains of Saccharomyces cerevisiae as starter cultures. Levels of AFB1 in must and lees were determined by high-performance liquid chromatography (HPLC) combined with diode array detection (DAD). Reductions of the AFB1 content between 77% - 97% were recorded after 90 days must fermentations in the model systems, while the relative adsorption level of AFB1 in lees was around ~0.63 in case of white wines, ~0.41 in case of rosé wines and ~0.23 in case of red wines. The results show that even extremely high AFB1 levels do not affect the fermentation process and the life-circle of yeast strains. The concentration of AFB1 in wine can be controlled by using appropriate yeast strains during the alcoholic fermentation.

Neuroplastic changes in addiction
Ildikó Rácz
Frontiers in Molecular Neuroscience , 2014, DOI: 10.3389/fnmol.2013.00056
Space-time extensions II
István Rácz
Physics , 2008, DOI: 10.1088/0264-9381/27/15/155007
Abstract: The global extendibility of smooth causal geodesically incomplete spacetimes is investigated. Denote by $\gamma$ one of the incomplete non-extendible causal geodesics of a causal geodesically incomplete spacetime $(M,g_{ab})$. First, it is shown that it is always possible to select a synchronised family of causal geodesics $\Gamma$ and an open neighbourhood $\mathcal{U}$ of a final segment of $\gamma$ in $M$ such that $\mathcal{U}$ is comprised by members of $\Gamma$, and suitable local coordinates can be defined everywhere on $\mathcal{U}$ provided that $\gamma$ does not terminate either on a tidal force tensor singularity or on a topological singularity. It is also shown that if, in addition, the spacetime, $(M,g_{ab})$, is globally hyperbolic, and the components of the curvature tensor, and its covariant derivatives up to order $k-1$ are bounded on $\mathcal{U}$, and also the line integrals of the components of the $k^{th}$-order covariant derivatives are finite along the members of $\Gamma$---where all the components are meant to be registered with respect to a synchronised frame field on $\mathcal{U}$---then there exists a $C^{k-}$ extension $\Phi: (M,g_{ab}) \rightarrow (\widehat{M},\widehat{g}_{ab})$ so that for each $\bar\gamma\in\Gamma$, which is inextendible in $(M,g_{ab})$, the image, $\Phi\circ\bar\gamma$, is extendible in $(\widehat{M},\widehat{g}_{ab})$. Finally, it is also proved that whenever $\gamma$ does terminate on a topological singularity $(M,g_{ab})$ cannot be generic.
On the topology of untrapped surfaces
István Rácz
Physics , 2008, DOI: 10.1088/0264-9381/26/5/055017
Abstract: Recently a simple proof of the generalizations of Hawking's black hole topology theorem and its application to topological black holes for higher dimensional ($n\geq 4$) spacetimes was given \cite{rnew}. By applying the associated new line of argument it is proven here that strictly stable untrapped surfaces do possess exactly the same topological properties as strictly stable marginally outer trapped surfaces (MOTSs) are known to have. In addition, a quasi-local notion of outwards and inwards pointing spacelike directions--applicable to untrapped and marginally trapped surfaces--is also introduced.
Cauchy problem as a two-surface based `geometrodynamics'
István Rácz
Physics , 2014, DOI: 10.1088/0264-9381/32/1/015006
Abstract: Four-dimensional spacetimes foliated by a two-parameter family of homologous two-surfaces are considered in Einstein's theory of gravity. By combining a 1+(1+2) decomposition, the canonical form of the spacetime metric and a suitable specification of the conformal structure of the foliating two-surfaces a gauge fixing is introduced. It is shown that, in terms of the chosen geometrically distinguished variables, the 1+3 Hamiltonian and momentum constraints can be recast into the form of a parabolic equation and a first order symmetric hyperbolic system, respectively. Initial data to this system can be given on one of the two-surfaces foliating the three-dimensional initial data surface. The 1+3 reduced Einstein's equations are also determined. By combining the 1+3 momentum constraint with the reduced system of the secondary 1+2 decomposition a mixed hyperbolic-hyperbolic system is formed. It is shown that solutions to this mixed hyperbolic-hyperbolic system are also solutions to the full set of Einstein's equations provided that the 1+3 Hamiltonian constraint is solved on the initial data surface $\Sigma_0$ and the 1+2 Hamiltonian and momentum type expressions vanish on a world-tube yielded by the Lie transport of one of the two-surfaces foliating $\Sigma_0$ along the time evolution vector field. Whenever the foliating two-surfaces are compact without boundary in the spacetime and a regular origin exists on the time-slices---this is the location where the foliating two-surfaces smoothly reduce to a point---it suffices to guarantee that the 1+3 Hamiltonian constraint holds on the initial data surface. A short discussion on the use of the geometrically distinguished variables in identifying the degrees of freedom of gravity are also included.
On rigidity of spacetimes with a compact Cauchy horizon
István Rácz
Physics , 2001,
Abstract: Smooth spacetimes with a compact Cauchy horizon ruled by closed null geodesics are considered. The compact Cauchy horizon is assumed to be non-degenerate. Then, supporting the validity of Penrose's strong cosmic censor hypothesis, the existence of a smooth Killing vector field in a neighbourhood of the horizon on the Cauchy development side is shown.
Stationary Black Holes as Holographs II
István Rácz
Physics , 2013, DOI: 10.1088/0264-9381/31/3/035006
Abstract: Smooth four-dimensional electrovac spacetimes in Einstein's theory are considered each possessing a pair of null hypersurfaces, $H_1$ and $H_2$, generated by expansion and shear free geodesically complete null congruences such that they intersect on a two-dimensional spacelike surface, $Z=H_1\cap H_2$. By making use of a combination of the Newman-Penrose formalism and the null characteristic initial value problem it is shown that both the spacetime geometry and the electromagnetic field are uniquely determined, in the domain of dependence of $H_1\cup H_2$ once a complex vector field $\xi^A$ (determining the metric induced on $Z$), the $\tau$ spin coefficient and the $\phi_1$ electromagnetic potential are specified on $Z$. The existence of a Killing vector field---with respect to which the null hypersurfaces $H_1$ and $H_2$ comprise a bifurcate type Killing horizon---is also justified in the domain of dependence of $H_1\cup H_2$. Since, in general, the freely specifiable data on $Z$ do not have any sort of symmetry the corresponding spacetimes do not possess any symmetry in addition to the horizon Killing vector field. Thereby, they comprise the class of generic `stationary' distorted electrovac black hole spacetimes. It is also shown that there are stationary distorted electrovac black hole configurations such that parallelly propagated curvature blow up occurs both to the future and to the past ends of some of the null generators of their bifurcate Killing horizon, and also that this behavior is universal. In particular, it is shown that, in the space of vacuum solutions to Einstein's equations, in an arbitrarily small neighborhood of the Schwarzschild solution this type of distorted vacuum black hole configurations always exist. A short discussion on the relation of these results and some of the recent claims on the instability of extremal black holes is also given.
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