Interaction of Pure Marangoni Convection with a Propagating Reactive Interface under Microgravity.

A reactive interface in the form of an autocatalytic reaction front propagating in a bulk phase can generate a dynamic contact line upon reaching the free surface when a surface tension gradient builds up due to the change in chemical composition. Experiments in microgravity evidence the existence of a self-organized autonomous and localized coupling of a pure Marangoni flow along the surface with the reaction in the bulk. This dynamics results from the advancement of the contact line at the surface that acts as a moving source of the reaction, leading to the reorientation of the front propagation. Microgravity conditions allow one to isolate the transition regime during which the surface propagation is enhanced, whereas diffusion remains the main mode of transport in the bulk with negligible convective mixing, a regime typically concealed on Earth because of buoyancy-driven convection.

Wavy fronts and speed bifurcation in excitable systems with cross diffusion.

A bifurcation of excitation fronts induced by cross diffusion in two-component bistable reaction-diffusion systems of activator-inhibitor type is discovered. This bifurcation is similar to the nonequilibrium Ising-Bloch bifurcation. A different type of fronts, whose spatial profiles are characterized by oscillating tails, are associated with this bifurcation. These fronts are described using exact analytical solutions of piecewise linear reaction-diffusion equations.

Flow-field development during finger splitting at an exothermic chemical reaction front.

Fingertip splitting may be observed at chemical reaction fronts subject to buoyancy-induced Rayleigh-Taylor fingering, as investigated in ascending fronts of the iodate-arsenous acid reaction in vertical Hele-Shaw cells. We study the properties of the flow-field evolution during a tip-splitting event both experimentally and theoretically. Experimental particle-image velocimetry techniques show that the flow field associated to a finger displays a quadrupole of vortices. The evolution of the flow field and the reorganization of the vortices after a tip-splitting event are followed experimentally in detail. Numerical integration of a model reaction-diffusion-convection system for an exothermic reaction taking into account possible heat losses through the walls of the reactor shows that the nonlinear properties of the flow field are different whether the walls are insulating or conducting. In insulating systems, the flow field inside one finger features only one pair of vortices. A quadrupole of flow vortices arranged around a saddle-node structure similar to the one observed experimentally is obtained in the presence of heat losses suggesting that heat effects, even if of very small amplitude, are important in understanding the nonlinear properties of fingering of exothermic chemical fronts.

Survival of patients with cancer in a medical critical care unit.

The records of 40 patients with cancer and 684 patients without cancer admitted to a medical critical care unit were reviewed for the purpose of comparing survival. Patients with cancer had a higher mortality (55%, 22/40) than the patients without cancer (17%, 118/864). Patients with cancer and respiratory failure had a higher mortality (75%, 18/24) than patients without cancer but with respiratory failure (25%, 66/273) and a higher mortality than patients with cancer but without respiratory failure (25%, 4/16). In patients with cancer, the manifestation of respiratory failure as the adult respiratory distress syndrome (ARDS) was associated with a high mortality (86%, 12/14), which was not statistically higher than in patients with cancer with non-ARDS respiratory failure (60%, 6/10) or in patients without cancer with ARDS (65%, 28/43). Patients with cancer but without respiratory failure had a mortality of 25% (4/16). All eight patients with cancer admitted to the hospital because of life-threatening metabolic disturbances survived. In deciding whether to apply critical care techniques to a patient with cancer, the physician should consider the specific nature of the life-threatening illness.

Evidence for increased permeability in reexpansion pulmonary edema.

Concurrent analyses of the colloid osmotic pressure of pulmonary edema fluid and serum were performed in two patients with reexpansion pulmonary edema. In addition, pulmonary artery wedge pressure was measured during pulmonary edema in one patient. The colloid osmotic pressure of the pulmonary edema fluid was 73 and 81 percent of the serum value. The pulmonary arterial wedge pressure in one patient was within normal limits (8 mm Hg). Reexpansion pulmonary edema appears to be due to increased pulmonary capillary permeability rather than to hemodynamic mechanisms.

Oscillations in peroxidase-catalyzed reactions and their potential function in vivo.

The peroxidase-oxidase reaction has become a model system for the study of oscillations and complex dynamics in biochemical systems. In the present paper we give an overview of previous experimental and theoretical studies of the peroxidase-oxidase reaction. Recent in vitro experiments have raised the question whether the reaction also exhibits oscillations and complex dynamics in vivo. To investigate this possibility further we have undertaken new experimental studies of the reaction, using horseradish extracts and phenols which are widely distributed in plants. The results are discussed in light of the occurrence and a possible functional role of oscillations and complex dynamics of the peroxidase-oxidase reaction in vivo.

Microleakage of super-EBA with and without finishing as determined by the fluid filtration method.

Super-EBA (SEBA) has been used as a root-end filling material because of its superior sealing properties and clinical success. The purpose of this study was to evaluate whether finishing SEBA after it had set would affect the apical seal. Sixty-five extracted maxillary anterior teeth were instrumented and obturated with a single gutta-percha master cone. The root end was resected, and a 3 mm deep root-end preparation was made using ultrasonic tips. Teeth were randomly divided into three groups. Group 1 received SEBA and was finished with a 30-flute high-speed finishing bur. Group 2 received SEBA, which was cold-burnished with a ball burnisher. Temporary Endodontic Restorative Material was used as the negative control in group 3. Microleakage (microliter/min) was measured under 10 psi using the fluid filtration method at days 1, 7, 30, 90, and 180. SEBA/finished exhibited significant microleakage at day 1 when compared with the burnished group. The differences in leakage were not significant at any other time period.

The adult respiratory distress syndrome.

The adult respiratory distress syndrome (ARDS) is an extreme form of noncardiogenic pulmonary edema associated with alveolar-capillary damage. Clinical features include acute respiratory distress, dyspnea and tachypnea, severe hypoxemia refractory to oxygen therapy, and diffuse bilateral pulmonary infiltrates. Any number of serious disorders can cause ARDS, but the processes leading to the alveolar permeability defect are not understood. Therefore, therapy remains nonspecific and supportive. Treatment includes positive end-expiratory pressure, careful fluid management, steroid therapy, and adequate nutrition. Unfortunately, even with the most sophisticated intensive care, the mortality of ARDS is still greater than 50%.

Professionals' attitudes towards sex between institutionalized patients.

Sexual activity among institutionalized patients has always been an issue of concern to institutions. Despite this fact, there has been little consensus about how patient sexuality should be dealt with. Nor have clinical insights with respect to patient sexuality been empirically tested. Given the diversity of beliefs and policies in this area, guidelines concerning sexual activity among hospitalized mental patients seem to be badly needed. We examined the following six factors that we thought might influence staff decisions: (1) the competence of a patient to engage in sexual activity, (2) the degree of consent, (3) the nature of sexual activity (e.g., hugging vs. genital relations), (4) the location of sexual activity (e.g., in bedroom vs. on grounds), (5) the sex of the initiating patient (6) the sex of the other patients. We hypothesized that mental health professionals, both as members of the community at large and as professionals, would have conventional moral views (as defined by Kohlberg) towards sexual activity. Supporting this hypothesis, of the six factors listed above, only location of the sexual activity and form of the sexual activity affected judgements on sexual activity significantly. The professionals interviewed appeared to be most condemning of homosexual acts, and least condemning of hugging. Although we had hypothesized that profession norms of consent and competence would be significant factors, they were not. The core implication of our study is that mental health professionals need training on competence assessment and its use in decision making and must reexamine their own prejudices (e.g., homophobia) to clarify their decision making about institutional policies.

Buoyancy-driven convection may switch between reactive states in three-dimensional chemical waves.

Traveling waves in an extended reactor, whose width cannot be neglected, represent a three-dimensional (3D) reaction-diffusion-convection system. We investigate the effects of buoyancy-driven convection in such a setting. The 3D waves traveled through horizontal layers of the iodate-arsenous acid (IAA) reaction solution containing excess of arsenous acid. The depth of the reaction solution was the examined parameter. An increase in the intensity of buoyancy-driven flow caused an increase of the traveling wave velocities. Convection distorted the front of the chemical waves. For layers deeper than h>13 mm, heat release became smaller than heat production causing the emergence of Rayleigh-Bénard convection cells. At the interface, a dependency of wave shape on solution depth was observed. For h<7 mm, the waves adopted a stable V-like shape, while for h>13 mm a parabolic shape dominated. For 7

Modeling of glycolytic wave propagation in an open spatial reactor with inhomogeneous substrate influx.

The spatio-temporal dynamics of traveling waves in glycolysis as it occurs in yeast extract have been studied, both theoretically and experimentally. We describe this phenomenon with the distributed Selkov model that accounts for the reactions of phosphofructokinase, which is a key enzyme of the glycolytic reaction cascade. To describe the experimentally observed phase waves in an open spatial reactor we introduce a non-homogeneous flux of substrate in the model. The experimental observation that waves can change their direction of propagation during the experiment is considered in the model. The mechanism for such a change in wave direction is discussed.

Cognition commands change.

Problematic behavior can be viewed as the result of the interaction between parents and children as guided by operating assumptions. Preliminary research suggests that enduring and generalized adaptive changes in problematic behavior are engendered when behavior modification techniques like praise are augmented with cognitive techniques like self talk. The changes may be more enduring and generalized when these techniques are used not only with children but also with and by parents. However, research is needed to validate this working hypothesis as well as to determine the most effective behaviors and cognitions of parents necessary to bring about and maintain change. Until this research has been validated, clinicians may utilize these techniques both with and by parents and with children on the bases of face validity and of extending logically the findings in the areas of behavior modification and cognitive-behavioral techniques.

The role of naturally occurring phenols in inducing oscillations in the peroxidase-oxidase reaction.

The influence of a series of naturally occurring phenolic compounds on the dynamics of the horseradish peroxidase-catalyzed oxidation of NADH by oxygen (the peroxidase-oxidase reaction) was investigated. Various types of dynamic behaviors are induced in the peroxidase-oxidase reaction upon addition of low concentrations of different phenols. The identity of the particular phenol determines the type of dynamics shown (inhibition of the reaction, monotonic reaction, damped oscillations, sustained oscillations, and complex oscillations). The kind of behavior that a given phenolic compound is able to induce is governed by the reduction potentials for the formation of the phenoxyl radical. The phenolic compounds are shown not to be consumed during the reaction. Mechanistic considerations are made on the basis of the reduction potentials of the different reactants present in the peroxidase-oxidase system. We interpret the role of the phenols as electron mediators of the electron transfer between some enzyme intermediates or O2- and NADH.

Problem solving revisited.

In this paper the increasing problems and need for novel solutions in today's world are discussed. A framework consisting of the combination of the problem-solving process and the creative thinking process is considered. Inherent in each process is a predominant mode of thought: reasoning or vertical thinking in the problem-solving process, and imagination or lateral thinking in the creative thinking process. These processes directed in a complementary manner are suggested as a means of solving problems creatively in situations which call for unique and novel solutions.

Interactions of isoniazid with foods.

We reviewed reactions previously reported in patients treated with isoniazid, who ate certain fish and cheeses. We observed similar reactions in two patients after they ingested cheese and wine. Isoniazid is an inhibitor of both monoamine and diamine oxidases, which contribute to the metabolism of histamine that may be present in some fish and cheeses. Monoamine oxidase also acts in the metabolism of tyramine, present in some cheeses and wines. Reactions reported after eating fish or cheese, in patients treated with isoniazid, are similar in that both are characterized by headache, palpitations, skin flushing, nausea, vomiting, and pruritus. Reactions after fish have not been associated with increased blood pressure, whereas those following cheese ingestion frequently result in modest increases in blood pressure. Patients treated with isoniazid should be alerted to the possibility of reactions after eating certain foods.

Oscillatory dynamics protect enzymes and possibly cells against toxic substances.

We have used the oscillating peroxidase-oxidase (PO) reaction as a model system to study how oscillatory dynamics may affect the influence of toxic reaction intermediates on enzyme stability. In the peroxidase-oxidase reaction reactive intermediates, such as hydrogen peroxide, superoxide, and hydroxyl radical are formed. Such intermediates inactivate many cellular macromolecules such as proteins and nucleic acids. These reaction intermediates also react with peroxidase itself to form an inactive enzyme. The fact that the PO reaction shows bistability between an oscillatory and a steady state gives us a unique possibility to compare such inactivation when the system is in one of these two states. We show that inactivation of peroxidase is slower when the system is in an oscillatory state, and using numerical simulations we provide evidence that oscillatory dynamics lower the average concentration of the reactive intermediates.

pH oscillations in the hemin-hydrogen peroxide-sulfite reaction.

Oscillatory behaviour in the pH value has been observed during the oxidation of sulfite by hydrogen peroxide mediated by hemin, a well known enzyme model compound, in a continuous-flow stirred tank reactor. The dynamics of this reaction has been studied for a variety of flow rates of the reactants. As the flow rates increase, the oscillations evolve from relaxation oscillations to more complex shapes, displaying, among others, bursting behaviour. A reaction mechanism is proposed that involves the autocatalytic oxidation of HSO3- by H2O2, while slow equilibria between different pH-dependent forms of hemin account for the feedback loop which gives rise to oscillatory dynamics. It is shown in experiments that no participation of CO2 is required for oscillations to occur.