A kinetic model for the ultrasound catalyzed hydrolysis of solventless TEOS-water mixtures and the role of the initial additions of ethanol

The acid and ultrasound catalyzed hydrolysis of solventless TEOS-water mixtures are studied, as a function of the initial additions of ethanol to the mixtures, by means of flux calorimetry measurements. A device was specially designed for this purpose. Under acid conditions, our proposed method has been able to resolve hydrolysis from other condensation reactions, by detecting the exothermal hydrolysis reaction heat. The process has been explained by a dissolution and reaction mechanism. Ultrasound forces the dissolution process to start the reaction. The alcohol produced in the reaction helps the dissolution process to further enhance the hydrolysis. Initial amounts of pure ethanol added to the mixtures shorten the start time of the reaction, due to an additional effect of dissolution, and diminish the reaction rate, as a result of the solvent dilution effect. Our dissolution and reaction mechanism modeling describes the main points arising from the experimental data and yields k(H) = 0.24 M(-1) min(-1) for the second-order hydrolysis rate constant at 39 degrees C.

Study of the hydrolysis of TEOS-TMOS mixtures under ultrasound stimulation

Pure and mixed tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS) were hydrolyzed at 35 degrees C, using oxalic acid as a catalyst and ultrasound stimulation. The hydrolysis reaction was carried out in a specially designed device, in which a heat flow steady state, between the ultrasound source and an external thermostatic bath, was maintained, in the absence of reactions. The exothermic hydrolysis causes a time dependent thermal peak. An induction time is apparent in pure TEOS before the hydrolysis peaks starts, which has been explained by the initial immiscibility gap of the TEOS-water system. The induction time was found to be approximately of the same magnitude as in the HCl catalyzed hydrolysis, in spite of the uncertainty accompanying the peak definition. No induction period is apparent in pure TMOS, so that the hydrolysis starts with its maximum rate. Two independent thermal peaks in the mixed TMOS-TEOS samples were found, both associated to the respective hydrolyses of the pure component. The induction time for the TEOS hydrolysis is decreased as more alcohol (and silanol) is produced in the earlier TMOS hydrolysis. This effect is explained by improvement of homogenization by alcohol.

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.

Ovulation synchronization following commercial application of ultrasound-guided follicle ablation during the estrous cycle in mares

A regimen of progesterone plus estradiol (P&E) was used as a standard for ovarian synchronization to test the efficacy and evaluate the commercial application of ultrasound-guided follicle ablation as a non-steroidal alternative for ovulation synchronization in mares. Recipient mares at a private embryo transfer facility were at unknown stages of the estrous cycle at the start of the experiment on Day 1 when they were randomly assigned to an ablation group (n = 18-21 mares) or to a ME group (n = 20-21 mares). In the ablation group, mares were lightly sedated and all follicles > 10 mm were removed by transvaginal ultrasound-guided follicle aspiration. In the ME group, a combination of progesterone (150 mg) plus estradiol (10 mg) prepared in safflower oil was given daily (im) for 10 d. Two doses of prostaglandin FZ, (PGF, 10 mg/dose, im) were given 12 h apart on Day 5 in the ablation group, or a single dose on Day 10 in the ME group. Human chorionic gonadotropin (hCG, 2500 IU/mare, im) was given at a fixed time, 6 and 10 d after PGF treatment in the ablation and ME groups, respectively, with the expectation of a follicle > 30 mm at the time of treatment. In both the ablation and P&E groups, transrectal ultrasonography was done at the start of the study (Day 1) and again on the day of hCG treatment and daily thereafter to determine the presence of a CL, measure diameter of the largest follicle and detect ovulation. The mean interval from the start of the study and from PGF treatment to ovulation was shorter (P < 0.0001) in the ablation group (13.7 and 9.7 d, respectively) compared to the P&E group (22.3 and 13.2 d, respectively). Following fixed-day treatment with hCG after PGF treatment, the degree of ovulation synchronization was not different (P > 0.05) between the ablation and P&E groups within a 2-d (56 and 70%) or 4-d (83% and 90%) period. Although ultrasound-guided follicle ablation may not be practical in all circumstances, it excluded the conventional 10-d regimen of progesterone and estradiol and was considered an efficacious and feasible, non-steroidal alternative for ovulation synchronization in mares during the estrous cycle. (C 2007 Elsevier B.V. All rights reserved.

Clinicopathological features influencing pelvic lymph node metastasis and vaginal and parametrial involvement in patients with carcinoma of the cervix

Purpose: This study was undertaken to evaluate clinical and pathologic findings that predicted pelvic lymph node metastasis and parametrial and vaginal involvement in patients with stage IB carcinoma of the cervix. Methods: 71 patients with diagnosis of stage IB (FIGO) cervical cancer were prospectively studied from December 1997 to August 2002. The patient's age, clinical stage (IB1 or IB2), histological classification, grade of differentiation, tumor volume, and lymphatic vascular space invasion (LVSI) were evaluated. Statistical methods included chi(2) test and Fisher's exact test to evaluate significant differences between the groups. The level of significance was set at p < 0.05. Results: the clinical stage was IB1 in 51 patients (71.8%) and IB2 in 20 patients (28.2%). The histological classification identified squamous cell carcinoma in 60 patients (84.5%) and adenocarcinoma in 11 patients (15.5%). The average tumoral volume was 22.8 &PLUSMN; 8 24.3 cm(3) (0.3-140.0 cm(3)). The tumor was well differentiated (G1) in 8 (11.3%), moderately differentiated (G2) in 40 (56.3%) and poorly differentiated in 23 (32.4%) of the cases. The presence of LVSI was detected in 14 patients (19.7%) and was associated with pelvic lymph node metastasis and vaginal and parametrial involvement (p = 0.002, p = 0.001 and p < 0.001; respectively). The average number of positive pelvic lymph nodes was significantly higher in the patients with LVSI compared with patients without LVSI (2.47 +/- 2.8 vs. 0.33 +/- 0.74; p = 0.001). There was no association of age, clinical stage, histological classification, grade of differentiation or tumor volume with pelvic lymph node metastasis and vaginal and parametrial involvement. Conclusion: the presence of LVSI is significantly associated with pelvic lymph node metastasis and vaginal and parametrial involvement in patients with stage IB cervical carcinoma. Copyright (C) 2005 S. Karger AG, Basel.

Histomorphometrical analysis of bone formed after maxillary sinus floor augmentation by grafting with a combination of autogenous bone and demineralized freeze-dried bone allograft or hydroxyapatite

Background: Maxillary sinus floor augmentation procedures are currently the treatment of choice when the alveolar crest of the posterior maxilla is insufficient for dental implant anchorage. This procedure aims to obtain enough bone with biomaterial association with the autogenous bone graft to create volume and allow osteo conduction. The objective of this study was to histologically and histometrically evaluate the bone formed after maxillary sinus floor augmentation by grafting with a combination of autogenous bone, from the symphyseal area mixed with DFDBA or hydroxyapatite.Methods: Ten biopsies were taken from 10 patients 10 months after sinus floor augmentation using a combination of 50% autogenous bone plus 50% dernineralized freeze-dried bone allograft (DFDBA group) or 50% autogenous bone plus 50% hydroxyapatite (HA group). Routine histological processing and staining with hernatoxylin and eosin and Masson's trichrome were performed.Results: the histomorphometrical analysis indicated good regenerative results in both groups for the bone tissue mean in the grafted area (50.46 +/- 16.29% for the DFDBA group and 46.79 +/- 8.56% for the HA group). Histological evaluation revealed the presence of mature bone with compact and cancellous areas in both groups. The inflammatory infiltrate was on average nonsignificant and of mononuclear prevalence. Some biopsies showed blocks of the biomaterial in the medullary spaces close to the bone wall, with absence of osteogenic activity.Conclusions: the results indicated that both DFDBA and HA associated with an autogenous bone graft were biocompatible and promoted osteoconduction, acting as a matrix for bone formation. However, both materials were still present after 10 months.

A CALORIMETRIC STUDY OF THE ULTRASOUND-STIMULATED HYDROLYSIS OF SOLVENTLESS TEOS-WATER MIXTURES

The kinetics of ultrasound-stimulated and HCl-catalyzed hydrolysis of solventless TEOS-water mixtures was studied as a function of temperature ranging from 10 degrees C up to 65 degrees C by means of flux calorimetry measurements. A specially designed device was utilized for this purpose. The exothermic peak arising few minutes after sonication began has been attributed mainly to the hydrolysis reaction. The overall hydrolysis process, which was measured through the irradiation time up to the hydrolysis peak, was found to be thermally activated, with an apparent activation energy Delta E = 36.4 kJ/mol. The alcohol produced at the early hydrolysis due to sonication seems to further enhance the reaction, via a parallel autocatalytic path, which is controlled by a faster pseudo second order rate constant (k'). Our modeling yielded k' = 6.3 x 10(-2) M(-1) min(-1) at 20 degrees C, which is in a reasonable agreement with the literature, and an activation energy Delta E = 40.4 kJ/mol for the specific process of hydrolysis in presence of alcohol.

Predicting beef carcass retail products of Mediterranean buffaloes by real-time ultrasound measures

Twenty eight Mediterranean buffaloes bulls were scanned with real-time ultrasound (RTU), slaughtered, and fabricated into retail cuts to determine the potential for ultrasound measures to predict carcass retail yield. Ultrasound measures of fat thickness, ribeye area and rump fat thickness were recorded three to five days prior to slaughter. Carcass measurements were taken, and one side of each carcass was fabricated into retail cuts. Stepwise regression analysis was used to compare possible models for prediction of either kilograms or percent retail product from carcass mesaurements and ultrasound measures. Results indicate that possible prediction models for percent or kilograms of retail products using RTU measures were similar in their predictive power and accuracy when compared to models derived from carcass measurements. Both fat thickness and ribeye area were over-predicted when measured ultrasonically compared to measurements taken on the carcass in the cooler. The mean absolute differences for both traits are larger than the mean differences, indicating that some images were interpreted to be larger and some smaller than actual carcass measurements. Ultrasound measurements of REA and FT had positive correlations with carcass measures of the same traits (r=.96 for REA and r=.99 for FT). Standard errors of prediction currently are being used as the standard to certify ultrasound technicians for accuracy. Regression equations using live weight (LW), rib eye area (REAU) and subcutaneous fat thickness (FTU) between 12(th) and 13 (th) ribs and also over the biceps femoris muscle (FTP8) by ultrasound explained 95% of the variation in the hot carcass weight when measure immediately before slaughter.

Linear analysis of building floor structures by a BEM formulation based on Reissner's theory

In this work, the plate bending formulation of the boundary element method (BEM) based on the Reissner's hypothesis is extended to the analysis of zoned plates in order to model a building floor structure. In the proposed formulation each sub-region defines a beam or a slab and depending on the way the sub-regions are represented, one can have two different types of analysis. In the simple bending problem all sub-regions are defined by their middle surface. on the other hand, for the coupled stretching-bending problem all sub-regions are referred to a chosen reference surface, therefore eccentricity effects are taken into account. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. The bending and stretching values defined on the interfaces are approximated along the beam width, reducing therefore the number of degrees of freedom. Then, in the proposed model the set of equations is written in terms of the problem values on the beam axis and on the external boundary without beams. Finally some numerical examples are presented to show the accuracy of the proposed model.