Accelerated expansion from structure formation

We discuss the physics of backreaction-driven accelerated expansion. Using the exact equations for the behaviour of averages in dust universes, we explain how large-scale smoothness does not imply that the effect of inhomogeneity and anisotropy on the expansion rate is small. We demonstrate with an analytical toy model how gravitational collapse can lead to acceleration. We find that the conjecture of the accelerated expansion being due to structure formation is in agreement with the general observational picture of structures in the universe, and more quantitative work is needed to make a detailed comparison.Comment: 44 pages, 1 figure. Expanded treatment of topics from the Gravity Research Foundation contest essay astro-ph/0605632. v2: Added references, clarified wordings. v3: Published version. Minor changes and corrections, added a referenc

Biochemical Characterization of Uracil Phosphoribosyltransferase from Mycobacterium tuberculosis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Uracil phosphoribosyltransferase (UPRT) catalyzes the conversion of uracil and 5-phosphoribosyl-alpha-1-pyrophosphate (PRPP) to uridine 5'-monophosphate (UMP) and pyrophosphate (PPi). UPRT plays an important role in the pyrimidine salvage pathway since UMP is a common precursor of all pyrimidine nucleotides. Here we describe cloning, expression and purification to homogeneity of upp-encoded UPRT from Mycobacterium tuberculosis (MtUPRT). Mass spectrometry and N-terminal amino acid sequencing unambiguously identified the homogeneous protein as MtUPRT. Analytical ultracentrifugation showed that native MtUPRT follows a monomer-tetramer association model. MtUPRT is specific for uracil. GTP is not a modulator of MtUPRT ativity. MtUPRT was not significantly activated or inhibited by ATP, UTP, and CTP. Initial velocity and isothermal titration calorimetry studies suggest that catalysis follows a sequential ordered mechanism, in which PRPP binding is followed by uracil, and PPi product is released first followed by UMP. The pH-rate profiles indicated that groups with pK values of 5.7 and 8.1 are important for catalysis, and a group with a pK value of 9.5 is involved in PRPP binding. The results here described provide a solid foundation on which to base upp gene knockout aiming at the development of strategies to prevent tuberculosis.82Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)"Embrapa Recursos Geneticos e Biotecnologia", BrazilFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq [520182/99-5, 304051/1975-06, 304034/2008-8

Appropriateness of carotid plaque and intima-media thickness assessment in routine clinical practice

<p>Abstract</p> <p>Objectives</p> <p>To describe the findings and evaluate appropriateness of a carotid artery study including the measurement of IMT, the presence of atherosclerotic plaque, and their correlation with cardiovascular risk factors.</p> <p>Methods</p> <p>555 patients (220 men; 67.06 ± 12.44 years) were included in the study. 120 patients (21.62%) presented carotid plaque: 108 (19.45%) in patients with at least one risk factor and 12 (2.1%) in patients without risk factors. With respect to appropriateness of the present studies: 65% were appropriate, 22% were uncertain and 13% were inappropriate. The IMT medians were higher in males (0.0280; 95% CI, 00.82 to 0.478; <it>p </it>= 0.0057) and in hypertensive patients (0.391; 95% CI, 0.0190 to 0.0592; <it>p </it>= 0,001). There was a linear increase in mean IMT for each year increased in age (0.0059; 95% CI; 0.0050 to 0.0067). Carotid plaque was more frequent in patients with CAD (<it>p </it>= 0.0002), diabetes (<it>p </it>= 0.024) and hypertension (<it>p </it>= 0.036).</p> <p>Conclusion</p> <p>Assessment of carotid arteries identified increased incidence of plaque in patients with CAD, diabetes and hypertension. IMT was increased in older patients, hypertensive patients and males. Forty-five percent of the patients were studied based on uncertain and inappropriate reasons.</p

Solubility and bacterial sealing ability of MTA and root-end filling materials

ABSTRACT Objective To evaluate solubility and sealing ability of Mineral Trioxide Aggregate (MTA) and root-end filling materials. Material and Methods The materials evaluated were: MTA, Calcium Silicate Cement with zirconium oxide (CSC/ZrO2), and zinc oxide/eugenol (ZOE). Solubility test was performed according to ANSI/ADA. The difference between initial and final mass of the materials was analyzed after immersion in distilled water for 7 and 30 days. Retrograde cavities in human teeth with single straight root canal were performed by using ultrasonic tip CVD 9.5107-8. The cavities were filled with the evaluated materials to evaluate sealing ability using the bacterial leakage test with Enterococcus faecalis. Bacterial leakage was evaluated every 24 hours for six weeks observing the turbidity of Brain Heart infusion (BHI) medium in contact with root apex. Data were submitted to ANOVA followed by Tukey tests (solubility), and Kruskal-Wallis and Dunn tests (sealing ability) at a 5% significance level. Results For the 7-day period, ZOE presented highest solubility when compared with the other groups (p<0.05). For the 30-day period, no difference was observed among the materials. Lower bacterial leakage was observed for MTA and CSC/ZrO2, and both presented better results than ZOE (p<0.05). Conclusion MTA and CSC/ZrO2 presented better bacterial sealing capacity, which may be related to lower initial solubility observed for these materials in relation to ZOE