408 research outputs found
Effects of Intravenous Aspirin on Prostaglandin Synthesis and Kidney Function in Intensive Care Patients
The effects of intravenous acetylsalicylic acid (1.0 g bolus) on renal function and prostaglandin synthesis were evaluated in a prospective, controlled study in eight patients in an intensive care unit. Four of these patients had congestive heart failure. Administration of acetylsalicylic acid caused significant antidiuresis (−56%), antinatriuresis (−82%), renin suppression (−26%) and decreased GFR (−41%). All of these changes were completely reversible within 1-2 hours and tended to be more pronounced in the patients with congestive heart failure. Urinary excretion of prostaglandin E was depressed profoundly (−93%) and did not return to more than 45% of control 6 h after the administration of acetylsalicylic acid. We conclude that intravenous acetylsalicylic acid affects kidney function in a manner similar to other prostaglandin synthesis inhibitors. Its effects are, however, short-lived. The inhibition of urinary PGE2 excretion outlasts GFR depression, antidiuresis, antinatriuresis and renin suppression by several hour
The Critical Behaviour of Potts models with symmetry breaking fields
The -state Potts model in two dimensions in the presence of external
magnetic fields is studied. For general special choices of these
magnetic fields produce effective models with smaller symmetry . The phase diagram of these models and their critical behaviour are
explored by conventional finite-size scaling and conformal invariance. The
possibility of multicritical behavior, for finite values of the symmetry
breaking fields, in the cases where is also analysed. Our results
indicate that for effective models with symmetry the
multicritical point occurs at zero field. This last result is also corroborated
by Monte Carlo simulations.Comment: 15 pages (standart LaTex), 2 figure (PostScript) available by request
to [email protected]
Whole body and hepatic insulin action in normal, starved, and diabetic rats
In normal (N), 3-days starved (S), and streptozotocin-treated (65 mg/kg) 3-days diabetic (D) rats we examined the in vivo dose-response relationship between plasma insulin levels vs. whole body glucose uptake (BGU) and inhibition of hepatic glucose production (HGP) in conscious rats, as determined with the four-step sequential hyperinsulinemic euglycemic clamp technique, combined with [3-3H]glucose infusion. Twelve-hour fasting (basal) HGP was 3.0 +/- 0.2, 2.1 +/- 0.2, and 5.4 +/- 0.5 mg/min in N, S, and D rats, respectively. Next, all rats were clamped at matched glycemia (6 mM). Lowering plasma glucose in D rats from +/- 20 to 6.0 mM did not increase plasma norepinephrine, epinephrine, glucagon, and corticosterone levels. For BGU, insulin sensitivity was increased (70 +/- 11 microU/ml) in S and unchanged (113 +/- 21 microU/ml) in D compared with N rats (105 +/- 10 microU/ml). Insulin responsiveness was unchanged (12.4 +/- 0.8 mg/min) in S and decreased (8.5 +/- 0.8 mg/min) in D compared with N rats (12.3 +/- 0.7 mg/min). For HGP, insulin sensitivity was unchanged (68 +/- 10 microU/ml) in S and decreased (157 +/- 21 microU/ml) in D compared with N rats (71 +/- 5 microU/ml). Insulin responsiveness was identical among N, S, and D rats (complete suppression of HGP). In summary, 1) insulin resistance in D rats is caused by hepatic insensitivity and by a reduction in BGU responsiveness. 2) S rats show normal hepatic insulin action, but insulin sensitivity for BGU is increased. Therefore, S and D rats both suffering from a comparable catabolic state (10-15% body wt loss in 3 days) show opposite effects on in vivo insulin action. This indicates that in vivo insulin resistance in D rats is not caused by the catabolic state per se
Resonant Tunneling Between Quantum Hall Edge States
Resonant tunneling between fractional quantum Hall edge states is studied in
the Luttinger liquid picture. For the Laughlin parent states, the resonance
line shape is a universal function whose width scales to zero at zero
temperature. Extensive quantum Monte Carlo simulations are presented for which confirm this picture and provide a parameter-free prediction for the
line shape.Comment: 14 pages , revtex , IUCM93-00
Classical XY Model in 1.99 Dimensions
We consider the classical XY model (O(2) nonlinear sigma-model) on a class of
lattices with the (fractal) dimensions 1<D<2. The Berezinskii's harmonic
approximation suggests that the model undergoes a phase transition in which the
low temperature phase is characterized by stretched exponential decay of
correlations. We prove an exponentially decaying upper bound for the two-point
correlation functions at non-zero temperatures, thus excluding the possibility
of such a phase transition.Comment: LaTeX 8 pages, no figure
Oblique Confinement and Phase Transitions in Chern-Simons Gauge Theories
We investigate non-perturbative features of a planar Chern-Simons gauge
theory modeling the long distance physics of quantum Hall systems, including a
finite gap M for excitations. By formulating the model on a lattice, we
identify the relevant topological configurations and their interactions. For M
bigger than a critical value, the model exhibits an oblique confinement phase,
which we identify with Lauglin's incompressible quantum fluid. For M smaller
than the critical value, we obtain a phase transition to a Coulomb phase or a
confinement phase, depending on the value of the electromagnetic coupling.Comment: 8 pages, harvmac, DFUPG 91/94 and MPI-PhT/94-9
Evidence of exactness of the mean field theory in the nonextensive regime of long-range spin models
The q-state Potts model with long-range interactions that decay as 1/r^alpha
subjected to an uniform magnetic field on d-dimensional lattices is analized
for different values of q in the nonextensive regime (alpha between 0 and d).
We also consider the two dimensional antiferromagnetic Ising model with the
same type of interactions. The mean field solution and Monte Carlo calculations
for the equations of state for these models are compared. We show that, using a
derived scaling which properly describes the nonextensive thermodynamic
behaviour, both types of calculations show an excellent agreement in all the
cases here considered, except for alpha=d. These results allow us to extend to
nonextensive magnetic models a previous conjecture which states that the mean
field theory is exact for the Ising one.Comment: 10 pages, 4 figure
Effective electron-electron and electron-phonon interactions in the Hubbard-Holstein model
We investigate the interplay between the electron-electron and the
electron-phonon interaction in the Hubbard-Holstein model. We implement the
flow-equation method to investigate within this model the effect of correlation
on the electron-phonon effective coupling and, conversely, the effect of
phonons in the effective electron-electron interaction. Using this technique we
obtain analytical momentum-dependent expressions for the effective couplings
and we study their behavior for different physical regimes. In agreement with
other works on this subject, we find that the electron-electron attraction
mediated by phonons in the presence of Hubbard repulsion is peaked at low
transferred momenta. The role of the characteristic energies involved is also
analyzed.Comment: 23 pages, 5 figure
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