A Covariant Non-Local Model of Bohm's Quantum Potential

Assuming that the energy of a gas depends non-locally on the logarithm of its mass density, the body force in the resulting equation of motion consists of the sum of density gradient terms. Truncating this series after the second term, Bohm's quantum potential and the Madelung equation are obtained, showing explicitly that some of the hypotheses that led to the formulation of quantum mechanics do admit a classical interpretation based on non-locality. Here, we generalize this approach imposing a finite speed of propagation of any perturbation, thus determining a covariant formulation of the Madelung equation.

Mixing Improvement in a T-Shaped Micro-Junction through Small Rectangular Cavities

The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities in the lateral walls of the mixing channel just downstream of the confluence region. The aim is to preserve the simple geometry that has contributed to spread the practical use of the T-shaped micro-junction while suggesting a modification that should, in principle, work jointly with the vortical structures present in the mixing channel, further enhancing their efficiency in mixing without significant additional pressure drops. The performance is analyzed in the different flow regimes occurring by increasing the Reynolds number. The cavities are effective in the two highly-mixed flow regimes, viz., the steady engulfment and the periodic asymmetric regimes. This presence does not interfere with the formation of the vortical structures that promote mixing by convection in these two regimes, but it further enhances the mixing of the inlet streams in the near-wall region of the mixing channel without any additional cost, leading to better performance than the classical configuration.

Dissolution or Growth of a Liquid Drop via Phase-Field Ternary Mixture Model Based on the Non-Random, Two-Liquid Equation

We simulate the diffusion-driven dissolution or growth of a single-component liquid drop embedded in a continuous phase of a binary liquid. Our theoretical approach follows a diffuse-interface model of partially miscible ternary liquid mixtures that incorporates the non-random, two-liquid (NRTL) equation as a submodel for the enthalpic (so-called excess) component of the Gibbs energy of mixing, while its nonlocal part is represented based on a square-gradient (Cahn-Hilliard-type modeling) assumption. The governing equations for this phase-field ternary mixture model are simulated in 2D, showing that, for a single-component drop embedded in a continuous phase of a binary liquid (which is highly miscible with either one component of the continuous phase but is essentially immiscible with the other), the size of the drop can either shrink to zero or reach a stationary value, depending on whether the global composition of the mixture is within the one-phase region or the unstable range of the phase diagram.

Diffusion-Driven Dissolution or Growth of a Liquid Drop Embedded in a Continuous Phase of Another Liquid via Phase-Field Ternary Mixture Model

We simulate the diffusion-driven dissolution or growth of a single-component (resp. two-component) drop embedded in a continuous phase of a binary (resp. single-component) liquid. Our theoretical approach follows a standard diffuse-interface model of partially miscible ternary liquid mixtures, which is based on a regular solution model assumption together with a Flory-Huggins and Cahn-Hilliard representation of the excess and nonlocal components of the Gibbs free energy of mixing. Based on 2D simulation results, we show that for a single-component drop embedded in a continuous phase of a binary liquid (which is highly miscible with either one component of the continuous phase but essentially immiscible with the other) the size of the drop can either shrink to zero or reach a stationary value, depending on whether the global composition of the mixture is within the one-phase region or the unstable range of the phase diagram. On the other hand, for an isolated two-component drop embedded in a continuous phase of a single-component liquid (which is essentially immiscible with either one component of the drop but miscible with the other) the size of the drop can either grow or shrink and, in particular, it will eventually go to zero if the global composition of the mixture is within the one-phase region; otherwise, for system locations in the unstable range the size of the drop tends to a constant value as the composition within the drop reaches its final equilibrium value.

Spinodal decomposition of chemically reactive binary mixtures

We simulate the influence of a reversible isomerization reaction on the phase segregation process occurring after spinodal decomposition of a deeply quenched regular binary mixture, restricting attention to systems wherein material transport occurs solely by diffusion. Our theoretical approach follows a diffuse-interface model of partially miscible binary mixtures wherein the coupling between reaction and diffusion is addressed within the frame of nonequilibrium thermodynamics, leading to a linear dependence of the reaction rate on the chemical affinity. Ultimately, the rate for an elementary reaction depends on the local part of the chemical potential difference since reaction is an inherently local phenomenon. Based on two-dimensional simulation results, we express the competition between segregation and reaction as a function of the Damköhler number. For a phase-separating mixture with components having different physical properties, a skewed phase diagram leads, at large times, to a system converging to a single-phase equilibrium state, corresponding to the absolute minimum of the Gibbs free energy. This conclusion continues to hold for the critical phase separation of an ideally perfectly symmetric binary mixture, where the choice of final equilibrium state at large times depends on the initial mean concentration being slightly larger or less than the critical concentration.

Buoyancy-driven detachment of a wall-bound pendant drop: interface shape at pinchoff and nonequilibrium surface tension

We present numerical results from phase-field simulations of the buoyancy-driven detachment of an isolated, wall-bound pendant emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. Our theoretical approach follows a diffuse-interface model for partially miscible binary mixtures which has been extended to include the influence of static contact angles other than 90^{∘}, based on a Hermite interpolation formulation of the Cahn boundary condition as first proposed by Jacqmin [J. Fluid Mech. 402, 57 (2000)JFLSA70022-112010.1017/S0022112099006874]. In a previous work, this model has been successfully employed for simulating triphase contact line problems in stable emulsions with nearly immiscible components, and, in particular, applied to the determination of critical Bond numbers for buoyancy-driven detachment as a function of static contact angle. Herein, the shapes of interfaces at pinchoff are investigated as a function of static contact angle and distance to the critical condition. Furthermore, we show numerical results on the nonequilibrium surface tension that help to explain the discrepancy between our numerically determined static contact angle dependence of the critical Bond number and its sharp-interface counterpart based on a static stability analysis of equilibrium shapes after numerical integration of the Young-Laplace equation. Finally, we show the influence of static contact angle and distance to the critical condition on the temporal evolution of the minimum neck radius in the necking regime of drop detachment.

[EMG and forces during manoeuvring of ceiling-based and floor-based patient transfer devices]

A laboratory and on-the-field study was conducted to compare Floor-Based (FB) and Ceiling-Based (CB) patients transfer devices. Pushing and pulling forces were measured by means of computer assisted dynamometer. EMG signals were measured. Standardized patient transfers were setup in the room (bed-chair-door-return). FB devices showed pushing and pulling forces higher than CB ones. CB paths were the smoothest and EMG data related to upper arms and trunk muscles showed stable lower loads for CB. The study suggests that CB patient transfer devices reduced the load. CBs seem the best tools for patient handling.

Continuous veno-venous hemofiltration with regional citrate anticoagulation: a four-year single-center experience

BACKGROUND

Hemofiltration protocols using a citrate-buffered replacement solution offer the advantage of regional anticoagulation and a buffer effect. The role played by such fluids in clinical practice is not yet well established. The risk of electrolytic disorders, acid-base imbalance, or citrate accumulation should be clarified. We report on a renal therapy protocol based on a citrate isonatremic replacement solution.

METHOD

We considered all patients needing renal replacement therapy admitted to our cardiovascular intensive care unit between January 2003 and June 2007. A citrate-buffered fluid was delivered in predilution mode to a post-filter ionized calcium target < or = 0.25 mmol/L. Extracorporeal blood flow was set at a constant of 140+/-10 ml/min. Blood calcemia was maintained by a 5% calcium-chloride solution infused into the patient. We recorded the patients' acid-base variables, ionized calcium, daily electrolytes, albumin, urea and filter life-span.

RESULTS

We observed 101 consecutive patients out of 2,523; incidence 4%, overall mortality was 57% at ICU discharge. Mean replacement rate was 2,554+/-475 ml/h corresponding to 34+/-5 ml/kg/h. Mean patient ionized calcium level was 1.07+/-0.04 mmo/L, maintained by 13+/-2 ml/h of infused calcium-chloride. All other electrolytes remained in the normal range. The Stewart biophysical approach confirmed a strong anion gap of 3.1+/- 3 meq/L. Acid-base balance showed a buffer effect. Mean filter life-span was 52+/-11 h.

CONCLUSION

Renal replacement therapy based on citrate-buffered fluid may be useful in clinical practice. This methodology presented an adequate metabolic control and allowed regional anticoagulation. A sufficient calcium supply was mandatory to avoid hypocalcemia. The small strong ion gap suggested a modest citrate accumulation.

Experimental evidence of the motion of a single out-of-equilibrium drop

We show experimentally that when a single, neutrally buoyant drop is injected into a binary mixture either it remains quiescent or it moves, depending on whether the composition of the drop and that of the surrounding phase coincide with the equilibrium concentrations. In general, the movement of out-of-equilibrium drops, which is called diffusiophoresis, is induced by the Korteweg body force. This force is proportional to the chemical potential gradient and is therefore nonzero only when the system is in chemical nonequilibrium. In this letter, we show experimentally that this movement occurs for a single drop as well, even when the initial condition is (almost) isotropic. This instability, although it does not have a complete analytical explanation, has been predicted in the numerical simulations by Vladimirova et al. (Vladimirova, N.; Malagoli, A.; Mauri, R. Phys. Rev. E 1999, 60, 2037).

Effects of quenching rate and viscosity on spinodal decomposition

Spinodal decomposition of deeply quenched mixtures is studied experimentally, with particular emphasis on the domain growth rate during the late stage of coarsening. We provide some experimental evidence that at high Péclet number, the process is isotropic and the domain growth is linear in time, even at finite quenching rates. In fact, the quenching rate appears to influence the magnitude of the growth rate, but not its scaling law. In the second part of the work we analyze the effect of viscosity on the growth rate. As predicted by the diffuse interface model, we do not find any effect of viscosity on the growth rate of the nucleating drops, although, as expected, the viscosity of the continuous phase does influence the settling speed and thus the total separation time.

Transport Properties of EVAl-Starch-α Amylase Membranes

We investigated the influence of various physicochemical parameters on the morphology and time-porosity formation of membranes composed of ethylene-vinyl alcohol, starch, and alpha-amylase. In particular, we determined that (1) it is possible to obtain a membrane with desired porosity by phase inversion in an appropriate water-ethanol mixture and (2) the enzymatic bioerosion is controlled by the amount of alpha-amylase present in the blend. Although no experiments involving drugs were carried out, the delivery properties of the film were determined by measuring the Darcy permeability, the effective diffusivity, and the mean reaction rate of the membranes, relating them to the modality of membrane preparation, the amount of enzyme present within the membrane, and the incubation time of the samples in a buffer solution. Simple theoretical models of the delivery properties of the membranes were developed, leading to predictions that were in good agreement with the experimental results.

Stapled transanal rectal resection for outlet obstruction: a prospective, multicenter trial

PURPOSE

This prospective, multicenter trial was designed to assess the safety and effectiveness of a novel technique in the treatment of outlet obstruction caused by the combination of intussusception and rectocele by using a double-transanal, 33-mm circular stapler.

METHODS

From January to October 2001, 90 patients with outlet obstruction were operated on and followed (mean, 16.3 +/- 2.9 months) by the validated Constipation Scoring and Continence Grading Systems, clinical examination, defecography, and anorectal manometry. Anal ultrasound also was performed in 58 multiparous patients.

RESULTS

Operative time and hospital stay were short (mean, 43.3 +/- 8.7 minutes and 2.1 +/- 0.8 days, respectively), and postoperative pain was minimal. The mean time to resume normal activity was 10.2 +/- 4.5 days. Complications were 17.8 percent fecal urgency, 8.9 percent incontinence to flatus, 5.5 percent urinary retention, 4.4 percent bleeding, 3.3 percent anastomotic stenosis, and 1.1 percent pneumonia. All constipation symptoms significantly improved (P < 0.001) without worsening of anal continence. No patient complained of dyspareunia. At postoperative defecography, all patients had a double incisure of the lower rectal outline in the site of anastomosis, with the disappearance of both intussusception and rectocele. Anal pressure was not significantly modified, whereas rectal compliance was restored (P < 0.05). No lesions of anal sphincters caused by the operation were found in multiparous patients. The outcome at one year was excellent in 48 of 90 patients, good in 33, fairly good in 5, and poor in 4.

CONCLUSIONS

This novel technique seems to be safe and effective in the treatment of outlet obstruction caused by the combination of intussusception and rectocele. Randomized trials are required to confirm these findings.

Heat and mass transport in nonhomogeneous random velocity fields

The effective equation describing the transport of passive tracers in nonsolenoidal velocity fields is determined, assuming that the velocity field U(r,t) is a function of both position r and time t, albeit remaining locally random. Assuming a strong separation of scales and applying the method of homogenization, we find a Fickian constitutive relation for the coarse-grained particle flux, as the sum of a convective part, V(E)c, and a diffusive term, -D(s). Inverted Delta c, where V(E) is the Eulerian mean tracer velocity, c the average particle concentration, and D(s) the effective diffusivity. The latter can be written as D(s)(r,t)=D(0)I+D(r,r,t), where D0 is the molecular diffusivity, I the unit dyadic and D(r(1),r(2),t) the cross diffusion dyadic. Conversely, the Eulerian mean velocity V(E)(r,t) is the sum of the microscale mean tracer velocity V(r,t) and a particle drift velocity, V(d)(r,t)=-[(delta/delta r(2)).D(T)(r,r(2),t)](r(2)=r), which depends on the nonhomogeneity of the velocity field at the macroscale. The microscale mean particle velocity, in turn, is the sum of the mean fluid velocity and the ballistic tracer velocity, which is due to the local nonuniformity of the concentration field and is therefore structurally different from the tracer drift velocity. In the limit of large Peclet numbers, D(s) coincides with the self-diffusion dyadic, as it measures the local temporal growth of the mean square displacement of a tracer particle from its average position. In this case, the motion of a tracer particle is a random process in the manner of Stratonovich, where the smoothly varying mean tracer velocity equals the microscale mean tracer velocity and the fluctuating term is described through the cross diffusion dyadic D(r(1),r(2),t).

Two-dimensional model of phase segregation in liquid binary mixtures

The hydrodynamic effects on the late stage kinetics of phase separation in liquid mixtures is studied using the model H. Mass and momentum transport are coupled via a nonequilibrium body force, which is proportional to the Peclet number alpha, i.e., the ratio between convective and diffusive molar fluxes. Numerical simulations based on this theoretical model show that phase separation in low viscosity, liquid binary mixtures is mostly driven by convection, thereby explaining the experimental findings that the process is fast, with the typical size of single-phase domains increasing linearly with time. However, as soon as sharp interfaces form, the linear growth regime reaches an end, and the process appears to be driven by diffusion, although the condition of local equilibrium is not reached. During this stage, the typical size of the nucleating drops increases like t(n), where 1/3< n <1/2, depending on the value of the Peclet number. As the Peclet number increases, the transition between convection- and diffusion-driven regimes occurs at larger times, and therefore for larger sizes of the nucleating drops.

Diffusiophoresis of two-dimensional liquid droplets in a phase-separating system

The motion of phase-separating liquid drops was simulated in two dimensions following the model H, where convection and diffusion are coupled via a body force, expressing the tendency of demixing systems to minimize their free energy. This driving force depends on the capillary number, i.e., the ratio of viscous to thermal forces, which in a typical case is of order 10(-4), inducing a convective material flux much larger than its diffusive counterpart. Three problems were considered. In the first, we studied the motion of a single drop immersed in a continuum field with constant concentration gradient, finding that the drop speed is proportional to the concentration gradient and inversely proportional to the capillary number. In the second problem, we found that the motion of a single drop immersed in a homogeneous concentration field depends on the difference (Delta(phi))(0) between the initial concentration of the continuum phase and its equilibrium value. In fact, when (Delta(phi))(0)<0, the drop shrinks without moving, while when (Delta(phi))(0)>0, the drop consumes material from the surrounding field and moves randomly, propelled by the induced capillary driving force. During its movement, the drop grows linearly in time, with a growth rate proportional to the ratio between molecular diffusivity and interface thickness. In addition, during its random motion, the drop mean square displacement grows linearly with time, with an effective diffusion coefficient which is of the same magnitude as the molecular diffusivity. The predicted drop growth rate and mean velocity are in good agreement with experimental observations. Finally, the motion of two drops is studied, showing that the capillary forces induce a mutual attraction between the two drops. When (Delta(phi))(0)<0, the attractive force is unchallenged, thus leading always to coalescence, while when (Delta(phi))(0)>0 a screening effect arises which may keep the two drops apart from each other.

[Invaginating colonic lipoma as a cause of intestinal occlusion]

The authors describe three cases of single invaginating colon lipoma, causing ileus. They review the literature and make some remarks.

[Serology study for HBV and HIV-1 in a cohort of parenteral drug addicts]

We studied 335 subjects, all drug addicts for the presence of the following serological markers: HIV1 antibody, HBsAg, HBsAb, HBcAb totals. We conclude that subjects HIV1 positive (n. 149) present HBsAb in a significantly lower number (p greater than 0.001) than HIV1 negative subjects (n. 95). The presence of HBcAb isolated is significantly higher (p greater than 0.001) in subjects HIV1 positive. They show an altered serological response to HBV compared to subjects HIV1 negative.

The pineal gland-opioid system relation: melatonin-naloxone interactions in regulating GH and LH releases in man

Several observations have demonstrated that the opioid system can modulate melatonin secretion from the pineal gland and that the effects of opioids may require a pineal participation. In contrast, the role played by the pineal gland in regulating the synthesis and secretion of endorphins and enkephalins in still obscure. To establish whether the neuroendocrine activity of melatonin are mediated by endogenous opioids and to demonstrate a possible action exerted by the pineal gland on opioid peptides, GH and LH serum mean levels were evaluated by RIA in 12 healthy subjects of both sexes after melatonin injection alone (0.4 mg/kg bw im at 09:00 h) and on a separate occasion after a simultaneous administration of melatonin and naloxone (1.2 mg iv as a bolus, followed by an iv infusion of 1.6 mg/h for 3h). On an other occasion, the study was performed during saline or naloxone infusion alone. In each test, venous blood samples were collected at -20, 0, 30, 60, 90, 120 and 180 min. A significant rise of GH was observed after melatonin injection alone. The simultaneous infusion of naloxone blocked melatonin-induced GH rise. Melatonin did not affected LH serum levels, while it was able to reduce LH increase induced by naloxone. These preliminary results suggest that some neuroendocrine effects of melatonin might be mediated by a modulation on the opioid tone.