980 resultados para selective catalytic reduction
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Cetyltrimethylammonium bromide (CTAB) and n-hexadecylamine (HDA) have been used as template in the synthesis of a mesolamellar xerogel tungsten oxide phase (WO(3)/CTAB/HDA). The catalytic properties of the resulting material were investigated in the oxidation of cis-cyclooctene, styrene, and cyclohexane, using hydrogen peroxide (H(2)O(2)), terc-butyl hydroperoxide (t-BOOH), or m-chlorperbenzoic acid (m-CPBA) as oxygen transfer agent. In general, the catalytic results were comparable to those obtained with related systems, thus suggesting the potential application of this material as catalyst for epoxidation reactions. (C) 2011 Elsevier B.V. All rights reserved.
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A substituted porphyrin bearing four crown ether units, H(2)(TCP), was synthesized from the reaction between (5,10,15,20-tetra(o-aminophenyl) porphyrin) and the acyl derivative of the ether (4-carboxy-18-crown-6). The free-base porphyrin was characterized by C, N, and H elemental analysis; UV-vis and IR spectroscopies; and (1)H NMR. The corresponding ironporphyrin, Fe(TCP)Cl, was obtained via iron insertion into H(2)(TCP). Fe(TCP)Cl was employed as catalyst for carbamazepine (CBZ) oxidation by iodosylbenzene (PhIO), 3-chloroperoxybenzoic acid (m-CPBA) or sodium hypochlorite (NaOCl), in methanol or in a biphasic water/dichloroethane system. The crowned ironporphyrin proved to be a highly efficient and selective catalyst for CBZ epoxidation even in the biphasic dichloroethane /H(2)O system, with no need for an additional phase transfer agent.
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Studies on the involvement of 5-HT1-mediated mechanisms in the dorsal periaqueductal gray (dPAG) of animals with past stressful experiences have not been conducted so far. We investigated the role of 5-HT1 receptors in the dPAG of rats previously submitted to contextual fear conditioning. Defensive behaviors induced by activation of the dPAG were assessed by measuring the lowest electric current applied to this structure (threshold) able to produce freezing and escape responses during testing sessions of contextual fear conditioning, in which animals were placed in a context previously paired to footshocks. The 5-HT1A function of the dPAG was evaluated by local injections of 8-OH-DPAT (4 and 8 nmol/0.2 mu L) and WAY-100635 (10 nmol/0.2 mu L), selective agonist and antagonist of 5-HT1A receptors, respectively. In accordance with previous studies, 8-OH-DPAT increased aversive thresholds (antiaversive effects) but injections of WAY 100635 into the dPAG did not produce significant effects on the aversive thresholds in naive rats. However, the aversive thresholds of animals exhibiting contextual fear remained unchanged with both treatments. Moreover, 8-OH-DPAT and WAY 100635 did not change the dPAG post-stimulation freezing. The present results suggest that the stressful experience of being fear conditioned has an effect on the role of the 5-HT1A receptors in mediating unconditioned fear. Also, the reduction in the regulation of the defensive behaviors by 5-HT1A-mediated mechanisms in the dPAG of these animals may underlie the stress precipitated psychopathology associated with the neural substrates of aversion of the dPAG. (c) 2007 Elsevier Inc. All rights reserved.
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Independent brain circuits appear to underlie different forms of conditioned fear, depending on the type of conditioning used, such as a context or explicit cue paired with footshocks. Several clinical reports have associated damage to the medial temporal lobe (MTL) with retrograde amnesia. Although a number of studies have elucidated the neural circuits underlying conditioned fear, the involvement of MTL components in the aversive conditioning paradigm is still unclear. To address this issue, we assessed freezing responses and Fos protein expression in subregions of the rhinal cortex and ventral hippocampus of rats following exposure to a context, light or tone previously paired with footshock (Experiment 1). A comparable degree of freezing was observed in the three types of conditioned fear, but with distinct patterns of Fos distribution. The groups exposed to cued fear conditioning did not show changes in Fos expression, whereas the group subjected to contextual fear conditioning showed selective activation of the ectorhinal (Ect), perirhinal (Per), and entorhinal (Ent) cortices, with no changes in the ventral hippocampus. We then examined the effects of the benzodiazepine midazolam injected bilaterally into these three rhinal subregions in the expression of contextual fear conditioning (Experiment 2). Midazolam administration into the Ect, Per, and Ent reduced freezing responses. These findings suggest that contextual and explicit stimuli endowed with aversive properties through conditioning recruit distinct brain areas, and the rhinal cortex appears to be critical for storing context-, but not explicit cue-footshock, associations. (C) 2010 Elsevier B.V. All rights reserved.
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Human hypoxanthine-guanine phosphoribosyltransferase (HGPRT) catalyses the synthesis of the purine nucleoside monophosphates, IMP and GMP, by the addition of a 6-oxopurine base, either hypoxanthine or guanine, to the 1-beta-position of 5-phospho-U-D-ribosyl-1-pyrophosphate (PRib-PP). The mechanism is sequential, with PRib-PP binding to the free enzyme prior to the base. After the covalent reaction, pyrophosphate is released followed by the nucleoside monophosphate. A number of snapshots of the structure of this enzyme along the reaction pathway have been captured. These include the structure in the presence of the inactive purine base analogue, 7-hydroxy [4,3-d] pyrazolo pyrimidine (HPP) and PRib-PP. Mg2+, and in complex with IMP or GMP. The third structure is that of the immucillinHP.Mg2+.PPi complex, a transition-state analogue. Here, the first crystal structure of free human HGPRT is reported to 1.9 angstrom resolution, showing that significant conformational changes have to occur for the substrate(s) to bind and for catalysis to proceed. Included in these changes are relative movement of subunits within the tetramer, rotation and extension of an active-site alpha-helix (D137-D153), reorientation of key active-site residues K68, D137 and K165, and the rearrangement of three active-site loops (100-128, 165-173 and 186-196). Toxoplasina gondii HGXPRT is the only other 6-oxopurine phosphoribosyltransferase structure solved in the absence of ligands. Comparison of this structure with human HGPRT reveals significant differences in the two active sites, including the structure of the flexible loop containing K68 (human) or K79 (T gondii). (c) 2005 Elsevier Ltd. All rights reserved.
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Pulmonary interstitial emphysema is a common complication of mechanical ventilation in preterm babies. We report a case of severe unilateral pulmonary interstitial emphysema in a premature newborn, treated with high-frequency oscillatory ventilation, lateral decubitus positioning and selective intubation. After complete radiological resolution of the pulmonary emphysema in the left lung, the patient was studied by electrical impedance tomography and a marked reduction of ventilation was identified in the left lung despite radiological resolution of the cysts. This finding indicates that functional abnormalities may persist for longer periods after radiologic resolution of such lesions.
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Symptomatic benign prostatic hyperplasia (BPH) typically occurs in the sixth and seventh decades, and the most frequent obstructive urinary symptoms are hesitancy, decreased urinary stream, sensation of incomplete emptying, nocturia, frequency, and urgency. Various medications, specifically 5-alpha-reductase inhibitors and selective alpha-blockers, can decrease the severity of the symptoms secondary to BPH, but prostatectomy is still considered to be the traditional method of management. We report the preliminary results for two patients with acute urinary retention due to BPH, successfully treated by prostate artery embolization (PAE). The patients were investigated using the International Prostate Symptom Score, by digital rectal examination, urodynamic testing, prostate biopsy, transrectal ultrasound (US), and magnetic resonance imaging (MRI). Uroflowmetry and postvoid residual urine volume complemented the investigation at 30, 90, and 180 days after PAE. The procedure was performed under local anesthesia; embolization of the prostate arteries was performed with a microcatheter and 300- to 500-mu m microspheres using complete stasis as the end point. One patient was subjected to bilateral PAE and the other to unilateral PAE; they urinated spontaneously after removal of the urethral catheter, 15 and 10 days after the procedure, respectively. At 6-month follow-up, US and MRI revealed a prostate reduction of 39.7% and 47.8%, respectively, for the bilateral PAE and 25.5 and 27.8%, respectively, for the patient submitted to unilateral PAE. The early results, at 6-month follow-up, for the two patients with BPH show a promising potential alternative for treatment with PAE.
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Vagal Denervation and Neurally Mediated Syncope. A 15-year-old female patient presented with frequent episodes of vasovagal syncope refractory to non-pharmacological and pharmacological measures. Two tilt-table tests performed before and after conventional therapy were positive and reproduced the patient`s clinical symptoms. Selective vagal denervation, guided by HFS, was performed. Six radiofrequency pulses were applied on the left and right sides of the interatrial septum, abolishing vagal responses at these locations. Basal sinus node and Wenckebach cycle lengths changed significantly following ablation. A tilt test performed after denervation was negative and revealed autonomic tone modification. The patient reported significant improvement in quality of life and remained asymptomatic for 9 months after denervation. After this period, three episodes of NMS occurred during a 4-month interval and a tilt test performed 11 months after the procedure demonstrated vagal activity recovery. (J Cardiovasc Electrophysiol, Vol. 20, pp. 558-563, May 2009).
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OBJECTIVE: The aim of this article is to describe the anatomy of the cavernous sinus and to provide a guide for use when performing surgery in this complex area. Clinical cases are used to illustrate routes to the cavernous sinus and its contents and to demonstrate how the cavernous sinus can be used as a pathway for exposure of deeper structures. METHODS: Thirty cadaveric cavernous sinuses were examined using X3 to X40 magnification after the arteries and veins were injected with colored silicone. Distances between the entrance of the oculomotor and trochlear nerves and the posterior clinoid process were recorded. Stepwise dissections (if the cavernous sinuses, performed to demonstrate the intradural and extradural routes, are accompanied by intraoperative photographs of those approaches. RESULTS: The anatomy of the cavernous sinus is complex because of the high density of critically important neural and vascular structures. Selective cases demonstrate how a detailed knowledge of cavernous sinus anatomy can provide for safer surgery with low morbidity. CONCLUSION: A precise understanding of the bony relationships and neurovascular contents of the cavernous sinus, together with the use of cranial base and microsurgical techniques, has allowed neurosurgeons to approach the cavernous sinus with reduced morbidity and mortality, changing the natural history of selected lesions in this region. Complete resection of cavernous sinus meningiomas has proven to be difficult and, in many cases, impossible without causing significant morbidity. However, surgical reduction of such lesions enhances the chances for success of subsequent therapy.
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Background There are multitudes of procedures in plastic surgery used to correct hypertrophic and pendulous breasts in patients with heavy and ptotic breasts who need great resections of breast tissue, where the suprasternal notch-to-nipple distance is long and the use of nipple-areola transposition techniques is a challenge for the plastic surgeon. The purpose of this study is to present a technique of reduction mammaplasty that could solve these problems based on the following principles: mammary reduction utilizing a thin superior medial pedicle (0.8-1.5 cm thick) and the resection performed in two steps: (1) the base excess at a plane perpendicular to the breast (this determines the cone`s height) and (2) central half keel (this determines the breast diameter reduction). Methods Ninety patients with mammary hypertrophy were operated on at the ""Hospital das Clinicas,"" Sao Paulo University Medical School, between January 2000 and November 2005. Inclusion in this study required a minimum of 12-cm change in nipple position and a 750-g breast resection. Results The mean change in nipple position was 16 cm (range = 12-21 cm). The mean weight of each breast was 1400 (range = 750-3000 g).Considering the great amount of volume removed and the size of the operated breasts, few complications were observed and were similar to those reported following other techniques described in the literature. Patient satisfaction following this procedure was high. Conclusion The results of this study clearly demonstrate that thin superior medial pedicle reduction mammaplasty is a safe and reliable technique in cases of severe mammary hypertrophy.
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An important consideration in the development of mathematical models for dynamic simulation, is the identification of the appropriate mathematical structure. By building models with an efficient structure which is devoid of redundancy, it is possible to create simple, accurate and functional models. This leads not only to efficient simulation, but to a deeper understanding of the important dynamic relationships within the process. In this paper, a method is proposed for systematic model development for startup and shutdown simulation which is based on the identification of the essential process structure. The key tool in this analysis is the method of nonlinear perturbations for structural identification and model reduction. Starting from a detailed mathematical process description both singular and regular structural perturbations are detected. These techniques are then used to give insight into the system structure and where appropriate to eliminate superfluous model equations or reduce them to other forms. This process retains the ability to interpret the reduced order model in terms of the physico-chemical phenomena. Using this model reduction technique it is possible to attribute observable dynamics to particular unit operations within the process. This relationship then highlights the unit operations which must be accurately modelled in order to develop a robust plant model. The technique generates detailed insight into the dynamic structure of the models providing a basis for system re-design and dynamic analysis. The technique is illustrated on the modelling for an evaporator startup. Copyright (C) 1996 Elsevier Science Ltd
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In this second paper, the three structural measures which have been developed are used in the modelling of a three stage centrifugal synthesis gas compressor. The goal of this case study is to determine the essential mathematical structure which must be incorporated into the compressor model to accurately model the shutdown of this system. A simple, accurate and functional model of the system is created via three structural measures. It was found that the model can be correctly reduced into its basic modes and that the order of the differential system can be reduced from 51(st) to 20(th). Of the 31 differential equational 21 reduce to algebraic relations, 8 become constants and 2 can be deleted thereby increasing the algebraic set from 70 to 91 equations. An interpretation is also obtained as to which physical phenomena are dominating the dynamics of the compressor add whether the compressor will enter surge during the shutdown. Comparisons of the reduced model performance against the full model are given, showing the accuracy and applicability of the approach. Copyright (C) 1996 Elsevier Science Ltd
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We consider the case of two cavity modes of the electromagnetic field, which are coupled via the action of a parametric amplifier. The fields are allowed to leak from the cavity and homodyne measurement is performed on one of the modes. Because of the correlations between the modes, this leads to a reduction of the variance in a quadrature of the other mode, although no measurement is performed on it directly. We discuss how this relates to the Einstein-Podolky-Rosen Gedankenexperiment.
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We analyzed the effect of a 6-week aerobic exercise training program on the in vivo macrophage reverse cholesterol transport (RCT) in human cholesteryl ester transfer protein (CETP) transgenic (CETP-tg) mice. Male CETP-tg mice were randomly assigned to a sedentary group or a carefully supervised exercise training group (treadmill 15 m/min, 30 min sessions, five sessions per week). The levels of plasma lipids were determined by enzymatic methods, and the lipoprotein profile was determined by fast protein liquid chromatography (FPLC). CETP activity was determined by measuring the transfer rate of (14)C-cholesterol from HDL to apo-B containing lipoproteins, using plasma from CETP-tg mice as a source of CETP. The reverse cholesterol transport was determined in vivo by measuring the [(3)H]-cholesterol recovery in plasma and feces (24 and 48 h) and in the liver (48 h) following a peritoneal injection of [(3)H]-cholesterol labeled J774-macrophages into both sedentary and exercise trained mice. The protein levels of liver receptors were determined by immunoblot, and the mRNA levels for liver enzymes were measured using RT-PCR. Exercise training did not significantly affect the levels of plasma lipids or CETP activity. The HDL fraction assessed by FPLC was higher in exercise-trained compared to sedentary mice. In comparison to the sedentary group, a greater recovery of [(3)H]-cholesterol from the injected macrophages was found in the plasma, liver and feces of exercise-trained animals. The latter occurred even with a reduction in the liver CYP7A1 mRNA level in exercised trained animals. Exercise training increased the liver LDL receptor and ABCA-1 protein levels, although the SR-BI protein content was unchanged. The RCT benefit in CETP-tg mice elicited by exercise training helps to elucidate the role of exercise in the prevention of atherosclerosis in humans.