Treatment with bestatin (the exogenous synthetic inhibitor of metalloproteinases) reduces the activity of metalloproteinase 2 and 12 in the spleen and lung tissues of rats in a model of lipopolysaccharide-induced sepsis.

Sepsis is caused by an inadequate or dysregulated host response to infection. Enzymes causing cellular degradation are matrix metalloproteinases (MMPs). Lipopolysaccharide (LPS) is used in models of sepsis in laboratory settings The aim of the study was to measure MMP 2 and 12 concentrations in spleen and lungs in rats in which septic shock was induced by LPS. The experiment was carried out on 40 male Wistar rats (5 groups of 8): 0. controls 1. administered LPS 2. administered bestatin 3. LPS and bestatin 4.bestatin and after 6 hours LPS Animals were decapitated. Lungs and spleens were collected. Concentrations of MMP-2 and MMP-12 were determined using immunoenzymatic methods. Mean (±SD) MMP-2 in the controls was 43.57 ± 20.53 ng/ml in the lungs and 1.7 ± 0.72 ng/ml in the spleen; Group 1: 31.28 ± 13.13 ng/ml, 0.83 ± 0.8 ng/ml; Group 2: 44.24 ± 22.75 ng /ml, 1.01 ± 0.32 ng/ml; Group 3: 35.94 ± 15.13 ng/ml, 0.41 ± 0.03 ng/ml; Group 4:79.42 ± 44.70 ng/ml, 0.45 ± 0.15, respectively. Mean MMP-12 in controls was 19.79 ± 10.01 ng/ml in lungs and 41.13 ± 15.99 ng/ml in the spleen; Group 1:27.97 ± 15.1 ng/ml; 40.44 ± 11.2 ng/ml; Group 2: 37.93 ± 25.38 ng/ml 41.05 ± 18.08 ng/ml; Group 3: 40.59 ± 11.46 ng/ml, 35.16 ± 12.89 ng/ml; Group 4: 39.4 ± 17.83 ng/ml, 42.04 ± 12.35 ng/ml, respectively. CONCLUSIONS: 1. Bestatin reduces MMP 2 and 12 levels in spleen and lungs. 2. Treatment with bestatin minimizes the effect of LPS.

Communication: Nonexistence of a critical point within the Kirkwood superposition approximation.

An analytic argument is given to show that the application of the Kirkwood superposition approximation to the description of fluid correlation functions precludes the existence of a critical point. The argument holds irrespective of the dimension of the system and the specific form of the interaction potential and settles a long-standing controversy surrounding the nature of the critical behavior predicted within the approximation.

Stability of phases of a square-well fluid within superposition approximation.

The analytic and numerical methods introduced previously to study the phase behavior of hard sphere fluids starting from the Yvon-Born-Green (YBG) equation under the Kirkwood superposition approximation (KSA) are adapted to the square-well fluid. We are able to show conclusively that the YBG equation under the KSA closure when applied to the square-well fluid: (i) predicts the existence of an absolute stability limit corresponding to freezing where undamped oscillations appear in the long-distance behavior of correlations, (ii) in accordance with earlier studies reveals the existence of a liquid-vapor transition by the appearance of a "near-critical region" where monotonically decaying correlations acquire very long range, although the system never loses stability.

Structural transitions in hypersphere fluids: predictions of Kirkwood's approximation.

We use an analytic criterion for vanishing of exponential damping of correlations developed previously [J. Piasecki et al., J. Chem. Phys. 133, 164507 (2010)] to determine the threshold volume fractions for structural transitions in hard sphere systems in dimensions D = 3, 4, 5, and 6, proceeding from the Yvon-Born-Green hierarchy and using the Kirkwood superposition approximation. We conclude that the theory does predict phase transitions in qualitative agreement with numerical studies. We also derive, within the superposition approximation, the asymptotic form of the analytic condition for occurrence of a structural transition in the D → ∞ limit.

Casimir force induced by an imperfect Bose gas.

We present a study of the Casimir effect in an imperfect (mean-field) Bose gas contained between two infinite parallel plane walls. The derivation of the Casimir force follows from the calculation of the excess grand-canonical free energy density under periodic, Dirichlet, and Neumann boundary conditions with the use of the steepest descent method. In the one-phase region, the force decays exponentially fast when distance D between the walls tends to infinity. When the Bose-Einstein condensation point is approached, the decay length in the exponential law diverges with critical exponent ν(IMP) = 1, which differs from the perfect gas case where ν(P) = 1/2. In the two-phase region, the Casimir force is long range and decays following the power law D(-3), with the same amplitude as in the perfect gas.

Prediction of a structural transition in the hard disk fluid.

Starting from the second equilibrium equation in the BBGKY hierarchy under the Kirkwood superposition closure, we implement a new method for studying the asymptotic decay of correlations in the hard disk fluid in the high density regime. From our analysis and complementary numerical studies, we find that exponentially damped oscillations can occur only up to a packing fraction η(∗)∼0.718, a value that is in substantial agreement with the packing fraction, η∼0.723, believed to characterize the transition from the ordered solid phase to a dense fluid phase, as inferred from Mak's Monte Carlo simulations [Phys. Rev. E 73, 065104 (2006)]. Next, we show that the same method of analysis predicts that the exponential damping of oscillations in the hard sphere fluid becomes impossible when λ=4nπσ(3)[1+H(1)]≥34.81, where H(1) is the contact value of the correlation function, n is the number density, and σ is the sphere diameter in exact agreement with the condition, λ≥34.8, which is first reported in a numerical study of the Kirkwood equation by Kirkwood et al. [J. Chem. Phys. 18, 1040 (1950)]. Finally, we show that our method confirms the absence of any structural transition in hard rods for the entire range of densities below close packing.

Less invasive posterior surgical approach for hip joint replacement--complications and limitations.

BACKGROUND: We attempted to analyse the difficulties and risk of complications associated with total hip replacement using a limited posterior approach and standard instrumentation. MATERIAL AND METHODS: A series of 85 consecutive cases (47 females and 38 males; age range 22-87 years; mean age: 65.6 +/- 10.4) of total hip replacement using a modified Gibson approach were analyzed prospectively. Bilateral surgery was performed in 7 patients. There were 44 non-cemented arthroplasties. Body mass index varied from 22 to 36 (body weight 78-104 kg) and the length of the operative wound varied from 6.5 to 14 cm (mean 9.8 +/- 1.3 cm). The wound was 14 centimeters long in six subjects with a BMI of 35-36. The procedure was performed in a lateral decubitus position using an appropriately limited posterior approach. After careful coagulation of blood vessels surrounding the base of the femoral head posteriorly, the obturator and gemelli tendons and the posterior part of the joint capsule were cut through as close to the femoral attachment (T) as possible. This made it possible to dislocate the joint posteriorly. Further stages of the procedure were performed in a typical manner, with special attention paid to the preservation of the tendon of the piriformis muscle. Continuity of the muscle was re-examined following the reposition of the artificial joint. RESULTS: Two injuries to the piriform tendon were observed. Persistent bleeding from vessels surrounding the femoral neck base occurred in 5 patients while in four others there was transient paresis of the peroneal muscles and dorsal extensors of the ipsilateral foot, probably caused by extension of the sciatic nerve. There was one oblique fracture of the proximal femoral shaft. We did not observe significant errors in postoperative joint geometry. Mean intraoperative blood loss was 400 ml. We did not note postoperative dislocations or infections. CONCLUSIONS: On the basis of our observations of a series of 85 patients, minimizing the extent of the posterior surgical approach for hip joint replacement seems an attractive alternative to the classical extensive technique. Our material reveals a relatively high incidence of transient paresis of the peroneal part of the sciatic nerve. The introduction of appropriate instrumentation and the accumulation of experience will certainly decrease the risk of extension of the sciatic nerve in the operative wound.

Bose gas beyond mean field.

We study a homogeneous Bose gas with purely repulsive forces. Using the Kac scaling of the binary potential we derive analytically the form of the thermodynamic functions of the gas for small but finite values of the scaling parameter in the low density regime. In this way we determine dominant corrections to the mean-field theory. It turns out that repulsive forces increase the pressure at fixed density and decrease the density at given chemical potential (the temperature is kept constant). They also flatten the Bose momentum distribution. However, the present analysis cannot be extended to the region where the mean-field theory predicts the appearance of condensate.

Kinetic models of ion transport through a nanopore.

Kinetic equations for the stationary state distribution function of ions moving through narrow pores are solved for a number of 1D models of single ion transport. Ions move through pores of length L, under the action of a constant external field and of a concentration gradient. The interaction of single ions with the confining pore surface and with water molecules inside the pore are modeled by a Fokker-Planck term in the kinetic equation, or by uncorrelated collisions with thermalizing centers distributed along the pore. The temporary binding of ions to polar residues lining the pore is modeled by stopping traps or energy barriers. Analytic expressions for the stationary ion current through the pore are derived for several versions of the model, as functions of key physical parameters. In all cases, saturation of the current at high fields is predicted. Such simple models, for which results are analytic, may prove useful in the study of the current/voltage relations of ion channels through membranes.

Self-consistent equation for an interacting Bose gas.

We consider interacting Bose gas in thermal equilibrium assuming a positive and bounded pair potential V(r) such that 0< integral dr V(r)=a< infinity. Expressing the partition function by the Feynman-Kac functional integral yields a classicallike polymer representation of the quantum gas. With the Mayer graph summation techniques, we demonstrate the existence of a self-consistent relation rho(mu)=F(mu-(a)rho(mu)) between the density rho and the chemical potential mu, valid in the range of convergence of Mayer series. The function F is equal to the sum of all rooted multiply connected graphs. Using Kac's scaling V(gamma)(r)=gamma3V(gamma(r)), we prove that in the mean-field limit gamma-->0, only the tree diagrams contribute and function F reduces to the free gas density. We also investigate how to extend the validity of the self-consistent relation beyond the convergence radius of the Mayer series (vicinity of Bose-Einstein condensation), and study the dominant corrections to the mean field. At the lowest order, the form of function F is shown to depend on a single polymer partition function for which we derive the lower and the upper bounds and on the resummation of ring diagrams which can be analytically performed.

Some exact results for Boltzmann's annihilation dynamics.

The problem of ballistic annihilation for a spatially homogeneous system is revisited within Boltzmann's kinetic theory in two and three dimensions. Analytical results are derived for the time evolution of the particle density for some isotropic discrete bimodal velocity modulus distributions. According to the allowed values of the velocity modulus, different behaviors are obtained: power law decay with nonuniversal exponents depending continuously upon the ratio of the two velocities, or exponential decay. When one of the two velocities is equal to zero, the model describes the problem of ballistic annihilation in the presence of static traps. The analytical predictions are shown to be in agreement with the results of two-dimensional molecular dynamics simulations.

Dynamics of ballistic annihilation.

The problem of ballistically controlled annihilation is revisited for general initial velocity distributions and an arbitrary dimension. An analytical derivation of the hierarchy equations obeyed by the reduced distributions is given, and a scaling analysis of the corresponding spatially homogeneous system is performed. This approach points to the relevance of the nonlinear Boltzmann equation for dimensions larger than 1 and provides expressions for the exponents describing the decay of the particle density n(t) proportional, variant t(-xi) and the root-mean-square velocity v proportional, variant t(-gamma) in terms of a parameter related to the dissipation of kinetic energy. The Boltzmann equation is then solved perturbatively within a systematic expansion in Sonine polynomials. Analytical expressions for the exponents xi and gamma are obtained in arbitrary dimension as a function of the parameter mu characterizing the small velocity behavior of the initial velocity distribution. Moreover, the leading non-Gaussian corrections to the scaled velocity distribution are computed. These expressions for the scaling exponents are in good agreement with the values reported in the literature for continuous velocity distributions in d=1. For the two-dimensional case, we implement Monte Carlo and molecular dynamics simulations that turn out to be in excellent agreement with the analytical predictions.