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Search Results: 1 - 10 of 714479 matches for " A. M. Nikitina "
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Critical Exponents of Superfluid Helium and Pseudo-$ε$ Expansion
A. I. Sokolov,M. A. Nikitina
Physics , 2014,
Abstract: Pseudo-$\epsilon$ expansions ($\tau$-series) for critical exponents of 3D XY model describing $\lambda$-transition in liquid helium are derived up to $\tau^6$ terms. Numerical estimates extracted from the $\tau$-series obtained using Pad\'e-Borel resummation technique, scaling relations and seven-loop ($\tau^7$) estimate for the Fisher exponent $\eta$ are presented including those for exponents $\alpha$ and $\nu$ measured in experiments with record accuracy. For the exponent $\alpha$ the procedure argued to be most reliable gives $\alpha= -0.0117$. This number is very close to the most accurate experimental values differing appreciably from the results of numerous lattice and field-theoretical calculations. It signals that the pseudo-$\epsilon$ expansion is a powerful tool robust enough to evaluate critical exponents with very small absolute error. The arguments in favour of such a robustness are presented.
Fisher Exponent from Pseudo-$ε$ Expansion
A. I. Sokolov,M. A. Nikitina
Physics , 2014, DOI: 10.1103/PhysRevE.90.012102
Abstract: Critical exponent $\eta$ for three-dimensional systems with $n$-vector order parameter is evaluated in the frame of pseudo-$\epsilon$ expansion approach. Pseudo-$\epsilon$ expansion ($\tau$-series) for $\eta$ found up to $\tau^7$ term for $n$ = 0, 1, 2, 3 and within $\tau^6$ order for general $n$ is shown to have a structure rather favorable for getting numerical estimates. Use of Pad\'e approximants and direct summation of $\tau$-series result in iteration procedures rapidly converging to the asymptotic values that are very close to most reliable numerical estimates of $\eta$ known today. The origin of this fortune is discussed and shown to lie in general properties of the pseudo-$\epsilon$ expansion machinery interfering with some peculiarities of the renormalization group expansion of $\eta$.
Pseudo-$ε$ Expansion and Renormalized Coupling Constants at Criticality
A. I. Sokolov,M. A. Nikitina
Physics , 2014, DOI: 10.1103/PhysRevE.89.052127
Abstract: Universal values of dimensional effective coupling constants $g_{2k}$ that determine nonlinear susceptibilities $\chi_{2k}$ and enter the scaling equation of state are calculated for $n$-vector field theory within the pseudo-$\epsilon$ expansion approach. Pseudo-$\epsilon$ expansions for $g_6$ and $g_8$ at criticality are derived for arbitrary $n$. Analogous series for ratios $R_6 = g_6/g_4^2$ and $R_8 = g_8/g_4^3$ figuring in the equation of state are also found and the pseudo-$\epsilon$ expansion for Wilson fixed point location $g_{4}^*$ descending from the six-loop RG expansion for $\beta$-function is reported. Numerical results are presented for $0 \le n \le 64$ with main attention paid to physically important cases $n = 0, 1, 2, 3$. Pseudo-$\epsilon$ expansions for quartic and sextic couplings have rapidly diminishing coefficients, so Pad\'e resummation turns out to be sufficient to yield high-precision numerical estimates. Moreover, direct summation of these series with optimal truncation gives the values of $g_4^*$ and $R_6^*$ almost as accurate as those provided by Pad\'e technique. Pseudo-$\epsilon$ expansion estimates for $g_8^*$ and $R_8^*$ are found to be much worse than that for the lower-order couplings independently on the resummation method employed. Numerical effectiveness of the pseudo-$\epsilon$ expansion approach in two dimensions is also studied. Pseudo-$\epsilon$ expansion for $g_4^*$ originating from the five-loop RG series for $\beta$-function of 2D $\lambda\phi^4$ field theory is used to get numerical estimates for $n$ ranging from 0 to 64. The approach discussed gives accurate enough values of $g_{4}^*$ down to $n = 2$ and leads to fair estimates for Ising and polymer ($n = 0$) models.
Critical Exponents in Two Dimensions and Pseudo-ε Expansion
M. A. Nikitina,A. I. Sokolov
Physics , 2013, DOI: 10.1103/PhysRevE.89.042146
Abstract: The critical behavior of two-dimensional $n$-vector $\lambda\phi^4$ field model is studied within the framework of pseudo-$\epsilon$ expansion approach. Pseudo-$\epsilon$ expansions for Wilson fixed point location $g^*$ and critical exponents originating from five-loop 2D renormalization group series are derived. Numerical estimates obtained within Pad\'e and Pad\'e-Borel resummation procedures as well as by direct summation are presented for $n = 1$, $n = 0$ and $n = -1$, i. e. for the models which are exactly solvable. The pseudo-$\epsilon$ expansions for $g^*$, critical exponents $\gamma$ and $\nu$ have small lower-order coefficients and slow increasing higher-order ones. As a result, direct summation of these series with optimal cut off provides numerical estimates that are no worse than those given by the resummation approaches mentioned. This enables one to consider the pseudo-$\epsilon$ expansion technique itself as some specific resummation method.
Arterial hypertension in patients with rheumatoid arthritis
N.M. Nikitina,A.P. Rebrov
Rational Pharmacotherapy in Cardiology , 2009,
Abstract: Aim. To study a prevalence and peculiarities arterial hypertension (HT) in patients with rheumatoid arthritis (RA).Patients and methods. 584 patients with RA were involved in the study. RA was diagnosed according to ACR criteria (1987).Results. 58,6% of the patients with RA had HT. It is significantly more often than this in common population. HT prevalence was directly related with RA duration and RA activity.Conclusion. High HT prevalence in patients with RA and fast growth of morbidity at the beginning of RA requires accurate blood pressure control for HT early diagnosis and timely therapy. Taking into account wide usage of non steroid antiinflammatory drugs calcium antagonists or angiotensin II receptor antagonists are more preferable in this group of patients.
Варианты хирургического лечения омфалоцеле (RUS)
Morozov D.A.,Filippov Yu.V.,Nikitina A.S.,Antonov M.A.
Saratov Journal of Medical Scientific Research , 2007,
Abstract: The variants of surgical treatment of different forms of omphalocelis in newborns were analyzed and made in the pediatric surgery department of Saratov state medical university in period 2000–2006.
The c-axis transport in naturally-grown Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ cross-whisker junctions
Yu. I. Latyshev,A. P. Orlov,A. M. Nikitina,P. Monceau,R. A. Klemm
Physics , 2004, DOI: 10.1103/PhysRevB.70.094517
Abstract: We studied the c-axis transport of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212) cross-whisker junctions formed by annealing ``naturally'' formed whisker junctions. These frequently appear during growth when the $ab$-faces of neighboring whiskers come in contact. We obtained Fraunhofer patterns of the cross-junction critical currents in a parallel magnetic field, and found a sharp increase in the quasiparticle tunneling conductance at $eV=50-60$ mV, indicating high junction quality. For our weak junctions, the interface critical current density is about 0.03 of the critical current density across the stack of bulk intrinsic junctions, as is the room temperature conductivity, and is independent of the twist angle, in contrast to most of the data reported on ``artificial'' cross-whisker junctions [Y. Takano {\it et al.}, Phys. Rev. B {\bf 65}, 140513(R) (2002)]. Our results provide strong evidence of incoherent interface tunneling and for at least a small s-wave order parameter component in the bulk of Bi2212 for $T\le T_c$. They are also consistent with the bicrystal twist experiments of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)].
Polymetabolic disorders after hysterectomy: a chance or a rule?
V.I. Podzolkov,T.I. Nikitina,A.E. Bragina,N.M. Podzolkova
Rational Pharmacotherapy in Cardiology , 2011,
Abstract: Aim. To study the dynamic of metabolic disorders in patients after hysterectomy with intact ovaries.Material and methods. 104 women (aged 44.0±2.1) after hysterectomy with intact ovaries were examined. All patients were split into three subgroups according to time after hysterectomy (1, 3, and 5 years). 25 women (aged 43.0±1.6) with normal menstrual function were included into the control group. Blood pressure (BP) levels and body mass index were measured. Serum lipids profile, plasma levels of immune-reactive insulin (IRI) and C-peptide were investigated in fasting condition and after oral glucose tolerance test.Results. Increase in time after hysterectomy was associated with significant elevation of body mass index, systolic and diastolic BP, basal and stimulated IRI and C-peptide levels, as well as serum levels of total cholesterol and low density lipoprotein cholesterol. These parameters had significant positive correlations with time after hysterectomy.Conclusion. Polymetabolic disorders were more prominent in patients with longer time after hysterectomy. These findings can be basis for definition of post-hysterectomy metabolic syndrome stages.
Data Of Daily Blood Pressure Monitoring In Patients With Rheumatoid Arthritis
N.M. Nikitina,O.S. Lobanova,A.P. Rebrov
Saratov Journal of Medical Scientific Research , 2009,
Abstract: The aim of present work is to study the frequency of hypertension and the peculiarity of 24-hour blood pressure monitoring in patients with rheumatoid arthritis. We studied 584 patients with rheumatoid arthritis. Daily blood pressure monitoring was carried out in 46 patients with arthritis and 18 patients with essential hypertension. Frequency of hypertension was higher in patients with arthritis then in general population. Elevation of systolic blood pressure, heart rate and arterial blood pressure adequate decrease at night were developed to associate with advance of the disease.
Cytoprotective effect of cytoflavinum at treatment of thermal injury of various severity level
Bozhedomov A.J.,Morrison V.V.,Shulaeva N.M.,Nikitina V.V.
Saratov Journal of Medical Scientific Research , 2012,
Abstract: The purpose of research was studying of cytoprotective effect of cytoflavinum at a thermal trauma of different severity level. Materials and methods. 169 patients with thermal burns with a favorable outcome and gravity of a thermal trauma from 30 to 170 points on Franc were under research. 28 patients took standard dosage of cytoflavinum while complex therapy. Results. Patients with thermal trauma more than 60 points on Franc took Cytoflavinumuse and demonstrated decrease in intensity of system inflammatory response syndrome (SIRS), reduction of band neutrophils portion, lowering of erythrocyte number, smaller activation ofthrombocytopoiesis, dicrease of concentration of vascular endothelial growth factor. Positive effect was not revealed in group of patients with thermal trauma less than 60 points who received cytoflavinum. Conclusion. Use of cytoflavinum was the most effective at thermal trauma gravity more than 60 points on Franc
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