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Search Results: 1 - 10 of 32376 matches for " Peter Takacs "
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Biomechanical Mapping of the Female Pelvic Floor: Prolapse versus Normal Conditions  [PDF]
Vladimir Egorov, S. Abbas Shobeiri, Peter Takacs, Lennox Hoyte, Vincent Lucente, Heather van Raalte
Open Journal of Obstetrics and Gynecology (OJOG) , 2018, DOI: 10.4236/ojog.2018.810093
Abstract: Background: Quantitative biomechanical characterization of pelvic supportive structures and functions in vivo is thought to provide insight into pathophysiology of pelvic organ prolapse (POP). An innovative approach—vaginal tactile imaging—allows biomechanical mapping of the female pelvic floor to quantify tissue elasticity, pelvic support, and pelvic muscle functions. The Vaginal Tactile Imager (VTI) records high definition pressure patterns from vaginal walls under an applied tissue deformation and during pelvic floor muscle contractions. Objective: To explore an extended set of 52 biomechanical parameters for differentiation and characterization of POP relative to normal pelvic floor conditions. Methods: 96 subjects with normal and POP conditions were included in the data analysis from multi-site observational, case-controlled studies; 42 subjects had normal pelvic floor conditions and 54 subjects had POP. The VTI, model 2S, was used with an analytical software package to calculate automatically 52 biomechanical parameters for 8 VTI test procedures (probe insertion, elevation, rotation, Valsalva maneuver, voluntary muscle contractions in 2 planes, relaxation, and reflex contraction). The groups were equalized for subject age and parity. Results: The ranges, mean values, and standard deviations for all 52 VTI parameters were established. 33 of 52 parameters were identified as statistically sensitive (p < 0.05; t-test) to the POP development. Among these 33 parameters, 11 parameters show changes (decrease) in tissue elasticity, 8 parameters
Asymptotic scattering and duality in the one-dimensional three-state quantum Potts model on a lattice
Akos Rapp,Peter Schmitteckert,Gabor Takacs,Gergely Zarand
Physics , 2011, DOI: 10.1088/1367-2630/15/1/013058
Abstract: We determine numerically the single-particle and the two-particle spectrum of the three-state quantum Potts model on a lattice by using the density matrix renormalization group method, and extract information on the asymptotic (small momentum) S-matrix of the quasiparticles. The low energy part of the finite size spectrum can be understood in terms of a simple effective model introduced in a previous work, and is consistent with an asymptotic S-matrix of an exchange form below a momentum scale $p^*$. This scale appears to vanish faster than the Compton scale, $mc$, as one approaches the critical point, suggesting that a dangerously irrelevant operator may be responsible for the behavior observed on the lattice.
Approximation error estimates and inverse inequalities for B-splines of maximum smoothness
Stefan Takacs,Thomas Takacs
Mathematics , 2015,
Abstract: In this paper, we develop approximation error estimates as well as corresponding inverse inequalities for B-splines of maximum smoothness, where both the function to be approximated and the approximation error are measured in standard Sobolev norms and semi-norms. The presented approximation error estimates do not depend on the polynomial degree of the splines but only on the grid size. We will see that the approximation lives in a subspace of the classical B-spline space. We show that for this subspace, there is an inverse inequality which is also independent of the polynomial degree. As the approximation error estimate and the inverse inequality show complementary behavior, the results shown in this paper can be used to construct fast iterative methods for solving problems arising from isogeometric discretizations of partial differential equations.
How to improve poor system efficiencies of ESP installations controlled by surface chokes
Gabor Takacs
Journal of Petroleum Exploration and Production Technologies , 2011, DOI: 10.1007/s13202-011-0011-9
Abstract: Electrical submersible pumping is the most inflexible of any artificial lift system because a specific ESP pump can only be used in a definite, quite restricted range of pumping rates. If it is used outside the specified range, pump and system efficiencies rapidly deteriorate and eventually mechanical problems leading to a complete system failure develop. When serious deviation from the design production rate is experienced, the possible solutions are (a) running a different pump with the proper recommended operating range, or (b) using a variable speed drive (VSD) unit. However, in case the ESP system produces a higher than desired liquid rate, a simple and frequently used solution is the installation of a wellhead choke. The wellhead choke restricts the pumping rate and forces the ESP pump to operate within its recommended liquid rate range. This solution, of course, is very detrimental to the economy of the production system because of the high hydraulic losses across the choke that cause a considerable waste of energy. The paper utilizes NODAL analysis to investigate the negative effects of surface production chokes on the energy efficiency of ESP systems as compared to the application of VSD drives. The power flow in the ESP system is described and the calculation of energy losses in system components is detailed. Based on these, a calculation model is proposed to evaluate the harmful effects of wellhead choking and to find the proper parameters of the necessary VSD unit. By presenting a detailed calculation on an example well using the proposed model the detrimental effects of wellhead choking are illustrated and the beneficial effects of using a VSD drive are presented. Using data of a group of wells placed on ESP production a detailed investigation is presented on the field-wide effects of choking. The energy flows and the total energy requirements are calculated for current and optimized cases where VSD units providing the required electrical frequencies are used. Final results clearly indicate that substantial electric power savings are possible if production control is executed by VSDs instead of the present practice of using surface chokes.
Finite temperature expectation values of boundary operators
G. Takacs
Physics , 2008, DOI: 10.1016/j.nuclphysb.2008.06.014
Abstract: A conjecture is presented for the thermal one-point function of boundary operators in integrable boundary quantum field theories in terms of form factors. It is expected to have applications in studying boundary critical phenomena and boundary flows, which are relevant in the context of condensed matter and string theory. The conjectured formula is verified by a low-temperature expansion developed using finite size techniques, which can also be used to evaluate higher point functions both in the bulk and on the boundary.
Quantum Affine Symmetry and Scattering Amplitudes of the Imaginary Coupled d_4(3) Affine Toda Field Theory
Gabor Takacs
Physics , 1997, DOI: 10.1016/S0550-3213(97)00443-4
Abstract: An exact S-matrix is conjectured for the imaginary coupled d_4(3) affine Toda field theory, using the U_q(g_2(1)) symmetry. It is shown that this S-matrix is consistent with the results for the case of real coupling using the breather-particle correspondence. For q a root of unity it is argued that the theory can be restricted to yield Phi(11|14) perturbations of WA_2 minimal models and the restriction is performed for the (3,p') minimal models.
Form factor perturbation theory from finite volume
G. Takacs
Physics , 2009, DOI: 10.1016/j.nuclphysb.2009.10.001
Abstract: Using a regularization by putting the system in finite volume, we develop a novel approach to form factor perturbation theory for nonintegrable models described as perturbations of integrable ones. This permits to go beyond first order in form factor perturbation theory and in principle works to any order. The procedure is carried out in detail for double sine-Gordon theory, where the vacuum energy density and breather mass correction is evaluated at second order. The results agree with those obtained from the truncated conformal space approach. The regularization procedure can also be used to compute other spectral sums involving disconnected pieces of form factors such as those that occur e.g. in finite temperature correlators.
A New RSOS Restriction of the Zhiber-Mikhailov-Shabat Model and $Φ_{(1,5)}$ Perturbations of Nonunitary Minimal Models
Gabor Takacs
Physics , 1996, DOI: 10.1016/S0550-3213(97)00057-6
Abstract: The RSOS restriction of the Zhiber-Mikhailov-Shabat (ZMS) model is investigated. It is shown that in addition to the usual RSOS restriction, corresponding to $\Phi_{(1,2)}$ and $\Phi_{(2,1)}$ perturbations of minimal CFT, there is another one which yields $\Phi_{(1,5)}$ perturbations of non-unitary minimal models. The new RSOS restriction is carried out and the particular case of the minimal models ${\cal M}_{(3,10)}$, ${\cal M}_{(3,14)}$ and ${\cal M}_{(3,16)}$ is discussed in detail. In the first two cases, while the mass spectra of the two RSOS restrictions are the same, the bootstrap systems and the detailed amplitudes are different. In the third case, even the spectra of the two RSOS restrictions are different. In addition, for ${\cal M}_{(3,10)}$ an interpretation in terms of the tensor product of two copies of ${\cal M}_{(2,5)}$ is given.
Form factors of boundary exponential operators in the sinh-Gordon model
G. Takacs
Physics , 2008, DOI: 10.1016/j.nuclphysb.2008.01.025
Abstract: Using the recently introduced boundary form factor bootstrap equations, the form factors of boundary exponential operators in the sinh-Gordon model are constructed. The ultraviolet scaling dimension and the normalization of these operators are checked against previously known results. The construction presented in this paper can be applied to determine form factors of relevant primary boundary operators in general integrable boundary quantum field theories.
The R-matrix of the U_q(d_4(3)) algebra and g_2(1) affine Toda field theory
Gabor Takacs
Physics , 1997, DOI: 10.1016/S0550-3213(97)80612-8
Abstract: The R-matrix of the U_q(d_4(3)) algebra is constructed in the 8-dimensional fundamental representation. Using this result an exact S-matrix is conjectured for the imaginary coupled g_2(1) affine Toda field theory, the structure of which is found to be very similar to the previously investigated S-matrix of d_4(3) Toda theory. It is shown that this S-matrix is consistent with the results for the case of real coupling using the breather-particle correspondence. For q a root of unity it is argued that the theory can be restricted to yield Phi(11|12) perturbations of WA_2 minimal models.
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