Effects of the water quantity on the solventless TEOS hydrolysis under ultrasound stimulation

The acid hydrolysis under ultrasound stimulation of solventless tetraethoxysilane(TEOS)-water mixtures was studied at 40 degrees C, by means of a heat flux calorimetric method, as a function of the initial water/TEOS molar ratio (r) ranging from 2 to 10. The method is based on the time record of the exothermic heat peak of hydrolysis, arising after an induction time under ultrasound stimulation, which is a measure of the reaction rate. The hydrolysed quantity was found to be approximately independent of the water/TEOS molar ratio, even for r < 4. Polycondensation reaction takes place mainly for low water/TEOS molar ratio in order to supply water to allow almost complete hydrolysis. The overall process of dissolution and hydrolysis has reasonably been described by a previous modelling. The dissolution process of water in TEOS, under ultrasound stimulation and acid conditions, was found to be rather dependent of the alcohol produced in the hydrolysis reaction instead of the initial water quantity present in the mixture.

A dissolution and reaction modeling for hydrolysis of TEOS in heterogeneous TEOS-water-HCl mixtures under ultrasound stimulation

A simplified dissolution and reaction modeling was employed to study the hydrolysis of heterogeneous tetraethoxysilane (TEOS)-water-HCl mixtures under ultrasound stimulation. The nominal pH was changed from 0.8 to 2.0. The acid specific hydrolysis rate constant was determined as k = 6.1 mol(-1) 1 min(-1) [H+](-1) at 39 degreesC, in good agreement with the literature. Along the heterogeneous step of the reaction, the ultrasound maintains an additional quantity of water under a virtual state of dissolution besides the water dissolved due to the homogenizing effect of the alcohol produced in the reaction. The forced virtually dissolved water is probably represented by water at the TEOS-water interface during the heterogeneous step of the reaction. The mean radius of the heterogeneity represented by water dispersed in TEOS phase, while hydrolysis has not started yet, was evaluated as about 290 A. The HCl concentration accordingly increases the hydrolysis rate constant but its fundamental role on the immiscibility gap of the TEOS-water-ethanol system has not been unequivocally established. (C) 2002 Elsevier B.V. B.V. All rights reserved.

A study of the hydrolysis pathway in oxalic acid catalyzed reacting TMOS-water mixtures under ultrasound stimulation

The hydrolysis of TMOS in oxalic acid catalyzed reacting TMOS-water mixtures, under ultrasound stimulation, was studied by fitting a simplified dissolution and reaction modeling for samples, the hydrolysis rate of which had been measured in a previous work. The reaction pathway represented in a ternary diagram shows a heterogeneous step for the reaction which gradually progresses until complete homogenization of the system. Besides the water dissolved due to the homogenizing effect of the alcohol, ultrasound maintains a virtual and additional dissolution of water located at the interface between the TMOS and water during the heterogeneous step of the reaction. The mean radius of the heterogeneity represented by water dispersed in TMOS was evaluated as around 150 Angstrom. The oxalic acid concentration accordingly increases the hydrolysis rate constant but its fundamental role on the solubility of water in TMOS could not unequivocally be established.

EFFECT OF CHOLINERGIC STIMULATION OF THE AMYGDALOID COMPLEX ON WATER AND SALT INTAKE

The effect of carbachol (80 nmol/mul) injection into the amygdaloid nuclear complex (AMG) on sodium appetite and water intake was studied in male Holtzman rats weighing 240-270 g. Twenty-five satiated rats and 38 water-deprived rats were used in the experiment on water intake. In the experiment on sodium intake, 19 rats were injected with atropine + carbachol and 9 rats with hexamethonium + carbachol. After carbachol injection into the AMG, water intake decreased in rats submitted to 30 h of water deprivation (10.28 +/- 1.04 ml/120 min vs 0.69 +/- 0.22 ml/120 min). The decrease in water intake was blocked by prior local injection of a tropine (20 nmol/1 mul)(11.66 +/- 1.46 ml/120 min vs 0.69 +/- 0.22 ml/120 min), but not of hexamethonium (30 nmol/1 mul), into the AMG. In water-deprived animals, carbachol injection into the AMG caused a decrease in sodium chloride intake (6.16 +/- 1.82 ml/h vs 0.88 +/- 0.54 ml/h) which was blocked by previous injection of hexamethonium but not of a tropine. These results suggest that the cholinergic system of the AMG plays a role in the control of water and salt intake.

Treatment of urinary stress incontinence by intravaginal electrical stimulation and pelvic floor physiotherapy

Treatment of urinary stress incontinence (USI) by intravaginal electrical stimulation (IES) and pelvic floor physiotherapy represents an alternative to other therapies. The purpose of this work was to evaluate the effectiveness of this treatment inpatients with urinary incontinence. From January 1998 to May 2000, 30 women (mean age 54 years) were studied. All patients had USI and 70% urge incontinence; average follow-up was 7 months. Selection criteria were based on clinical history, objective evaluation of perineal musculature by perineometry, and urodynamics. The treatment protocol consisted of three sessions of IES per week for 14 weeks using INNOVA equipment. Physiotherapy was initiated in the fifth week of IES. A significant decrease in the number of micturitions and urgency was observed after treatment (P<0.01). The pad test showed a reduction in urinary leakage from 13.9 to 5.9 g after treatment (P<0.01). Objective evaluation of perineal muscle strength showed a significant improvement in all patients after treatment (P<0.01). A positive correlation was observed between maximum flow rate (Q(max)) and all three variables: urethral pressure profile at rest and on straining (stop test), and abdominal leak-point pressure (ALPP). A positive correlation was also observed between ALPP and the stop test. Over 100 different surgical and conservative treatments have been tried to manage USI. The majority of these procedures reveal that despite progress already made in this area, there is no ideal treatment. Satisfactory results can be achieved with this method, especially with patients who are reluctant to undergo surgery because of personal or clinical problems.

Effects of Transcranial Magnetic Stimulation on the Cognitive Event-Related Potential P300: A Literature Review

The objective of this study was to perform a systematic review regarding the effects of transcranial magnetic stimulation (TMS) on the cognitive event-related potential P300. A search was performed of the PubMed database, using the keywords "transcranial magnetic stimulation" and "P300." Eight articles were selected and, after analysis of references, one additional article was added to the list. We found the comparison among studies to be difficult, as the information regarding the effects of TMS on P300 is both scarce and heterogeneous with respect to the parameters used in TMS stimulation and the elicitation of P300. However, 7 of 9 studies found positive results. New studies need to be carried out in order to understand the contribution of these variables and others to the alteration in the latency and amplitude of the P300 wave.

Effects of prenatal exposure to deltamethrin on forced swimming behavior, motor activity, and striatal dopamine levels in male and female rats

The effects of prenatal exposure of rat pups to 0.08 mg/kg deltamethrin (DTM) on physical, reflex and behavioral developmental parameters, on forced swimming and open-field behaviors, and on striatal monoamine levels at 60 days of age were observed. Maternal and offspring body weight, physical and reflex development were unaffected by the exposure to the pesticide. At 21 days of age, open-field locomotion frequency and immobility duration of male and female offspring were not different between control and exposed animals. However, male rearing frequency was increased in experimental animals. A decreased immobility latency to float and in general activity after the swimming test in male offspring was observed at adult age; no interference was detected in the float duration during the swimming test. In addition, these animals presented higher striatal 3,4-dihydroxyphenylacetic acid (DOPAC) levels without modification in dopamine (DA) levels and an increased DOPAC/DA ratio. These data indicate a higher activity of the dopaminergic system in these animals. Noradrenaline (NA) levels were increased, while MHPG levels were not detectable in the system studied. Serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels, as well as the homovanillic acid (HVA)/DA ratio, were not modified by the exposure to the pesticide. No changes were observed in swimming and open-field behaviors nor were there any changes in striatal monoamines or their metabolites in the female experimental group. In relation to the pesticide formula, the present data showing that prenatal exposure to DTM alters latency to float and the activity of striatal dopaminergic system might reflect a persistent effect of the pesticide on animal motor activity, mainly in males. on the other hand, the decrease in general activity observed in experimental male rats suggests higher levels of emotionality induced by previous exposure to the swimming behavior test in relation to control animals. Data gathered in the present study may be important for the assessment of the safety of pyrethroid insecticides. (C) 2001 Elsevier B.V. All rights reserved.