| 1. |
- Lindholm, Lena, et al.
(författare)
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Regional oxygenation and systemic inflammatory response during cardiopulmonary bypass: influence of temperature and blood flow variations.
- 2003
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Ingår i: Journal of cardiothoracic and vascular anesthesia. - : Elsevier BV. - 1053-0770. ; 17:2, s. 182-7
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To evaluate the role of target temperature (28 degrees or 34 degrees C) in cardiac surgery on regional oxygenation during hypothermia and rewarming and systemic inflammatory response. DESIGN: Prospective, controlled, and randomized clinical study. SETTING: University hospital. PARTICIPANTS: Elderly patients (mean age 70 +/- 2 years) with acquired heart disease with an anticipated bypass time exceeding 120 minutes (n = 30). INTERVENTIONS: The patients were cooled to either 28 degrees C (n = 15) or 34 degrees C (n = 15). At hypothermia, bypass blood flow was reduced twice from full flow (2.4 L/min/m(2) body surface area [BSA]) to 2.0 L/min/m(2). MEASUREMENTS AND MAIN RESULTS: Hepatic and jugular venous oxygen tension and saturation were higher at 28 degrees C than at 34 degrees C. In comparison with the preoperative values, at 28 degrees C hepatic venous values were higher; whereas at 34 degrees C, they were lower. The reduction of pump blood flow during hypothermia, from 2.4 to 2.0 L/min/m(2)was accompanied by reductions of central, jugular, and hepatic oxygenation at both target temperatures. During rewarming, central and regional venous oxygenation decreased irrespective of the preceding temperature. The decrease was most pronounced in hepatic venous blood, with the lowest individual values <10%. Serum concentrations of C3a and IL-6 increased during hypothermia and increased further during rewarming irrespective of the preceding temperature. CONCLUSION: During cardiopulmonary bypass, hypothermia at 28 degrees C increases regional and central venous oxygenation better than at 34 degrees C. In contrast, venous oxygenation decreases during rewarming irrespective of the preceding temperature. No significant difference in the systemic inflammatory response associated with target temperature was detected.
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| 2. |
- Basylko, S. A., et al.
(författare)
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ac conductivity of a Coulomb glass from computer simulations
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:2, s. 024201-
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Tidskriftsartikel (refereegranskat)abstract
- A method for calculating the photon-induced hopping ac conductivity of a Coulomb glass by computer simulation is proposed. Results obtained by using an effective relaxation algorithm for two three-dimensional models of a Coulomb glass are reported. ac conductance data clearly demonstrate the transition from super-linear to a sub-quadratic power law. We argue that the same qualitative behavior should be expected for compensated semiconductors. It is shown that the transition is driven by the Coulomb energy of sites forming resonant pairs and not by the width of the Coulomb gap.
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| 3. |
- Basylko, S. A., et al.
(författare)
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Coulomb gap in a model with finite charge-transfer energy
- 2001
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 6302:2
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Tidskriftsartikel (refereegranskat)abstract
- The Coulomb gap in a donor-acceptor model with finite charge-transfer energy Delta describing the electronic system on the dielectric side of the metal-insulator transition is investigated by means of computer simulations on two- and three-dimensional finite samples with a random distribution of equal amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry of the model presented with respect to the exchange of donors and accepters are derived. In the immediate neighborhood of the Fermi energy mu. the single-particle density of states g(epsilon) is determined solely by finite size effects, and g(epsilon) further away from mu is described by an asymmetric power law with a nonuniversal exponent, depending on the parameter Delta.
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| 4. |
- Basylko, S. A., et al.
(författare)
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Coulomb glass in the random phase approximation
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:2
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional model of the electrons localized on randomly distributed donor sites of density n and with the acceptor charge uniformly smeared on these sites, -Ke on each, is considered in the random phase approximation (RPA). For the case K = 1/2 the free energy, the density of the one-site energies (DOSE) epsilon, and the pair OSE correlators are found. In the high-temperature region (e(2) n(1/3)/T) < 1 (T is the temperature) RPA energies and DOSE are in a good agreement with the corresponding data of Monte Carlo simulations. Thermodynamics of the model in this region is similar to the one of an electrolyte in the regime of Debye screening. In the vicinity of the Fermi level μ = 0 the OSE correlations, depending on sgn(ε(1) . ε(2)) and with very slow decoupling law, have been found. The main result is that even in the temperature range where the energy of a Coulomb glass is determined by Debye screening effects, the correlations of the long-range nature between the OSE still exist.
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| 5. |
- Basylko, S. A., et al.
(författare)
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Coulomb glass in the restricted random phase approximation
- 2002
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Ingår i: Physics Letters A. - 0375-9601 .- 1873-2429. ; 298:06-maj, s. 416-421
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional model of N/2 electrons localized on N randomly distributed donor sites of density n and with the acceptor charge uniformly smeared on these sites, -e/2 on each. has been considered in the restricted random phase approximation (RRPA) which uses the set of 3N Fourier components of the local charge density as the independent collective variables. The energy e(T) per site and the density of one-site excitation energy (DOSE) g(epsilon) are shown to he, respectively, in excellent quantitative and in good qualitative agreement with the Monte Carlo simulation data in the whole temperature region 0.1 < T < 100, where these simulations were performed (e(2)n(1/3)/k(B) being the temperature scale). The pair correlator for the one-site energies g(epsilon,+/-epsilon, r) is found to have the slow decoupling law similar to(+/-1/r) for T less than or similar to 1 and r much greater than r(d) (r(d), Debye screening radius). The status of the commonly accepted asymptotic g(epsilon) similar to (epsilon - mu)(d-1) (d and mu being, respectively, the spatial dimension and the Fermi energy) is discussed. The deduction of this asymptotic is shown to be based on the strong and questionable conjecture about decoupling of correlations between one-site excitation energies in the vicinity of mu.
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| 6. |
- Basylko, S. A., et al.
(författare)
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Ground-state study of a donor-acceptor model with finite charge-transfer energy
- 2000
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Ingår i: Physics Letters A. - 0375-9601 .- 1873-2429. ; 271:02-jan, s. 134-138
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Tidskriftsartikel (refereegranskat)abstract
- A donor-acceptor model with randomly distributed N donor and N acceptor sites and with finite charge transfer energy Delta is investigated at zero temperature by means of computer simulations on two-dimensional samples of different sizes, We demonstrate that the density of one-electron excitations g(epsilon) for accepters in the vicinity of the Fermi energy mu depends essentially on the size of the sample investigated and that g(epsilon) further away from mu exhibits a size-independent power-law with the non-universal exponent decreasing with increasing Delta. Rigorous relations for mu and for the mapping of g(epsilon) for donors into g(epsilon) for accepters are also given.
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| 7. |
- Belonoshko, Anatoly B., et al.
(författare)
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First-principles study of hydrogen diffusion in α-Al 2O3 and liquid alumina
- 2004
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 69:2, s. 243021-243026
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the energetics and mobility of neutral hydrogen in alumina Al2O3 using ab initio density-functional calculations. The mobility of hydrogen was studied in corundum (α-Al2O 3) as well as in liquid alumina. Using both static as well as molecular-dynamics calculations, and applying classical transition state theory, we derive the temperature-dependent diffusivity of hydrogen in α-Al 2O3 as D(T)=(21.7 × 10-8 m 2/s)exp(-1.24 eV/kT). The corresponding diffusivity of hydrogen in liquid/amorphous alumina, derived directly from ab initio molecular dynamics calculations, is D(T)=(8.71 × 10-7 m2/s)exp(-0.91 eV/kT). The computed diffusivity compares very well to experimental data. We conclude that diffusion of neutral hydrogen through the bulk of alumina is a good approximation of the mechanism for hydrogen mobility in corrosion scales. The representation of grain-boundary structures by amorphous alumina is, probably, realistic at higher temperatures.
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| 8. |
- Bergkvist, Sara, et al.
(författare)
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Ground state of the random-bond spin-1 Heisenberg chain
- 2002
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 66, s. 134407-1-134407-9
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Tidskriftsartikel (refereegranskat)abstract
- Stochastic series expansion quantum Monte Carlo is used to study the ground state of the antiferromagnetic spin-1 Heisenberg chain with bond disorder. Typical spin- and string-correlation functions behave in accordance with real-space renormalization group predictions for the random-singlet phase. The average string-correlation function decays algebraically with an exponent of -0.378(6), in very good agreement with the prediction of -(3-root5)/2similar or equal to-0.382, while the average spin-correlation function is found to decay with an exponent of about -1, quite different from the expected value of -2. By implementing the concept of directed loops for the spin-1 chain we show that autocorrelation times can be reduced by up to two orders of magnitude.
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| 9. |
- Bergkvist, Sara, et al.
(författare)
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Local-density approximation for confined bosons in an optical lattice
- 2004
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 70, s. 053601-1-053601-7
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Tidskriftsartikel (refereegranskat)abstract
- We investigate local and global properties of the one-dimensional Bose-Hubbard model with an external confining potential, describing an atomic condensate in an optical lattice. Using quantum Monte Carlo techniques we demonstrate that a local-density approximation, which relates the unconfined and the confined model, yields quantitatively correct results in most of the interesting parameter range. We also examine claims of universal behavior in the confined system, and demonstrate the origin of a previously calculated fine structure in the experimentally accessible momentum distribution.
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| 10. |
- Bergkvist, Sara, et al.
(författare)
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Reduction of the sign problem using the meron-cluster approach
- 2003
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 68, s. 016122-1-016122-8
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Tidskriftsartikel (refereegranskat)abstract
- The sign problem in quantum Monte Carlo calculations is analyzed using the meron-cluster solution. A meron is a loop that alters the sign of the configuration, and the concept of merons can be used to solve the sign problem for a limited class of models. Here we show that the method can be used to reduce the sign problem in a wider class of models. We investigate how the meron solution evolves between a point in parameter space where it eliminates the sign problem and a point where it does not affect the sign problem at all. In this intermediate regime, the merons can be used to reduce the sign problem. The average sign still decreases exponentially with system size and inverse temperature, but with a different prefactor. The sign exhibits the slowest decrease in the vicinity of points where the meron-cluster solution eliminates the sign problem. We have used stochastic series expansion quantum Monte Carlo combined with the concept of directed loops.
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