1,849 research outputs found
Projeto aerodinâmico de turbinas eólicas
Este trabalho apresenta uma metodologia simplificada de dimensionamento do rotor de turbinas eólicas de eixo horizontal, tendo conhecidas as propriedades do ar, velocidade do vento, potência nominal, e outros parâmetros relevantes para seu projeto aerodinâmico. É feita uma estimativa dos esforços atuantes sobre a turbina
Subregional DXA-derived vertebral bone mineral measures are stronger predictors of failure load in specimens with lower areal bone mineral density, compared to those with higher areal bone mineral density
Measurement of areal bone mineral density (aBMD) in intravertebral subregions may increase the diagnostic sensitivity of dual-energy X-ray absorptiometry (DXA)-derived parameters for vertebral fragility. This study investigated whether DXA-derived bone parameters in vertebral subregions were better predictors of vertebral bone strength in specimens with low aBMD, compared to those with higher aBMD. Twenty-five lumbar vertebrae (15 embalmed and 10 fresh-frozen) were scanned with posteroanterior- (PA) and lateral-projection DXA, and then mechanically tested in compression to ultimate failure. Whole-vertebral aBMD and bone mineral content (BMC) were measured from the PA- and lateral-projection scans and within 6 intravertebral subregions. Multivariate regression was used to predict ultimate failure load by BMC, adjusted for vertebral size and specimen fixation status across the whole specimen set, and when subgrouped into specimens with low aBMD and high aBMD. Adjusted BMC explained a substantial proportion of variance in ultimate vertebral load, when measured over the whole vertebral area in lateral projection (adjusted R2 0.84) and across the six subregions (ROIs 2–7) (adjusted R2 range 0.58–0.78). The association between adjusted BMC, either measured subregionally or across the whole vertebral area, and vertebral failure load, was increased for the subgroup of specimens with identified ‘low aBMD’, compared to those with ‘high aBMD’, particularly in the anterior subregion where the adjusted R2 differed by 0.44. The relative contribution of BMC measured in vertebral subregions to ultimate failure load is greater among specimens with lower aBMD, compared to those with higher aBMD, particularly in the anterior subregion of the vertebral body
Biocompatibility and stability of polysaccharide polyelectrolyte complexes aimed at respiratory delivery
Chitosan (CS) and chondroitin sulfate (CHS) are natural polymers with
demonstrated applicability in drug delivery, while nanoparticles are one of the most explored
carriers for transmucosal delivery of biopharmaceuticals. In this work we have prepared
CS/CHS nanoparticles and associated for the first time the therapeutic protein insulin.
Fluorescein isothiocyanate bovine serum albumin (FITC-BSA) was also used to enable
comparison of behaviors regarding differences in molecular weight (5.7 kDa versus 67 kDa).
Nanoparticles of approximately 200 nm and positive zeta potential around +20 mV were
obtained. These parameters remained stable for up to 1 month at 4 C. Proteins were
associated with efficiencies of more than 50%. The release of FITC-BSA in PBS pH 7.4
was more sustained (50% in 24 h) than that of insulin (85% in 24 h). The biocompatibility
of nanoparticles was tested in Calu-3 and A549 cells by means of three different assays.
The metabolic assay MTT, the determination of lactate dehydrogenase release, and the
quantification of the inflammatory response generated by cell exposure to nanoparticles have
indicated an absence of overt toxicity. Overall, the results suggest good indications on the
application of CS/CHS nanoparticles in respiratory transmucosal protein delivery, but the set
of assays should be widened to clarify obtained results
Relationship between FEV1 change and patient-reported outcomes in randomised trials of inhaled bronchodilators for stable COPD: a systematic review.
BACKGROUND: Interactions between spirometry and patient-reported outcomes in COPD are not well understood. This systematic review and study-level analysis investigated the relationship between changes in FEV1 and changes in health status with bronchodilator therapy.
METHODS: Six databases (to October 2009) were searched to identify studies with long-acting bronchodilator therapy reporting FEV1 and health status, dyspnoea or exacerbations. Mean and standard deviations of treatment effects were extracted for each arm of each study. Relationships between changes in trough FEV1 and outcomes were assessed using correlations and random-effects regression modelling. The primary outcome was St George's Respiratory Questionnaire (SGRQ) total score.
RESULTS: Thirty-six studies (≥ 3 months) were included. Twenty-two studies (23,654 patients) with 49 treatment arms each contributing one data point provided SGRQ data. Change in trough FEV1 and change in SGRQ total score were negatively correlated (r = -0.46, p < 0.001); greater increases in FEV1 were associated with greater reductions (improvements) in SGRQ. The correlation strengthened with increasing study duration from 3 to 12 months. Regression modelling indicated that 100 mL increase in FEV1 (change at which patients are more likely to report improvement) was associated with a statistically significant reduction in SGRQ of 2.5 (95% CI 1.9, 3.1), while a clinically relevant SGRQ change (4.0) was associated with 160.6 (95% CI 129.0, 211.6) mL increase in FEV1. The association between change in FEV1 and other patient-reported outcomes was generally weak.
CONCLUSIONS: Our analyses indicate, at a study level, that improvement in mean trough FEV1 is associated with proportional improvements in health status
Assessment of the effect of interval from presentation to surgery on outcome in patients with peri-ampullary malignancy
Background: Delay between diagnosis of peri-ampullary cancer (PC) and surgery may allow tumour progression and affect outcome. This study aims to explore associations of interval to surgery (IS) with pathological outcomes and survival in patients with PC. Method: A database review of all patients undergoing surgery between 2006 and 2014 was undertaken. IS was measured from diagnosis by imaging. Potential association between IS and survival was measured using Cox regression analysis, and between IS and pathological outcome with multivariate logistic analysis. Results: 388 patients underwent surgery. The median IS was 49 days (1-551 days), and was not associated with any of the evaluated outcomes in patients with pancreatic (149) or distal bile duct (46) cancer. For patients with ampullary cancer (71) longer IS was associated with improved survival, with median survival of 1.3, 3.1 and 4.3 years for patients waiting 2 (25) months for surgery (p=0.036). A higher rate of margin positivity (31.4%) was also noted among patients who waited less than the median IS compared to those waiting longer than this interval (11.4%) (p=0.032). Conclusion: For patients with ampullary cancer there is a paradoxical improvement in outcome among those with a longer IS, which may be explained by progression to inoperability of more aggressive lesions
Evaluation of rate law approximations in bottom-up kinetic models of metabolism.
BackgroundThe mechanistic description of enzyme kinetics in a dynamic model of metabolism requires specifying the numerical values of a large number of kinetic parameters. The parameterization challenge is often addressed through the use of simplifying approximations to form reaction rate laws with reduced numbers of parameters. Whether such simplified models can reproduce dynamic characteristics of the full system is an important question.ResultsIn this work, we compared the local transient response properties of dynamic models constructed using rate laws with varying levels of approximation. These approximate rate laws were: 1) a Michaelis-Menten rate law with measured enzyme parameters, 2) a Michaelis-Menten rate law with approximated parameters, using the convenience kinetics convention, 3) a thermodynamic rate law resulting from a metabolite saturation assumption, and 4) a pure chemical reaction mass action rate law that removes the role of the enzyme from the reaction kinetics. We utilized in vivo data for the human red blood cell to compare the effect of rate law choices against the backdrop of physiological flux and concentration differences. We found that the Michaelis-Menten rate law with measured enzyme parameters yields an excellent approximation of the full system dynamics, while other assumptions cause greater discrepancies in system dynamic behavior. However, iteratively replacing mechanistic rate laws with approximations resulted in a model that retains a high correlation with the true model behavior. Investigating this consistency, we determined that the order of magnitude differences among fluxes and concentrations in the network were greatly influential on the network dynamics. We further identified reaction features such as thermodynamic reversibility, high substrate concentration, and lack of allosteric regulation, which make certain reactions more suitable for rate law approximations.ConclusionsOverall, our work generally supports the use of approximate rate laws when building large scale kinetic models, due to the key role that physiologically meaningful flux and concentration ranges play in determining network dynamics. However, we also showed that detailed mechanistic models show a clear benefit in prediction accuracy when data is available. The work here should help to provide guidance to future kinetic modeling efforts on the choice of rate law and parameterization approaches
Cold gas accretion in galaxies
Evidence for the accretion of cold gas in galaxies has been rapidly
accumulating in the past years. HI observations of galaxies and their
environment have brought to light new facts and phenomena which are evidence of
ongoing or recent accretion:
1) A large number of galaxies are accompanied by gas-rich dwarfs or are
surrounded by HI cloud complexes, tails and filaments. It may be regarded as
direct evidence of cold gas accretion in the local universe. It is probably the
same kind of phenomenon of material infall as the stellar streams observed in
the halos of our galaxy and M31. 2) Considerable amounts of extra-planar HI
have been found in nearby spiral galaxies. While a large fraction of this gas
is produced by galactic fountains, it is likely that a part of it is of
extragalactic origin. 3) Spirals are known to have extended and warped outer
layers of HI. It is not clear how these have formed, and how and for how long
the warps can be sustained. Gas infall has been proposed as the origin. 4) The
majority of galactic disks are lopsided in their morphology as well as in their
kinematics. Also here recent accretion has been advocated as a possible cause.
In our view, accretion takes place both through the arrival and merging of
gas-rich satellites and through gas infall from the intergalactic medium (IGM).
The infall may have observable effects on the disk such as bursts of star
formation and lopsidedness. We infer a mean ``visible'' accretion rate of cold
gas in galaxies of at least 0.2 Msol/yr. In order to reach the accretion rates
needed to sustain the observed star formation (~1 Msol/yr), additional infall
of large amounts of gas from the IGM seems to be required.Comment: To appear in Astronomy & Astrophysics Reviews. 34 pages.
Full-resolution version available at
http://www.astron.nl/~oosterlo/accretionRevie
Poly(N-Isopropylacrylamide) surface-grafted ghitosan membranes as a new substrate for cell sheet engineering and manipulation
The immobilization of poly(N-isopropylacrylamide)
(PNIPAAm) on chitosanmembranes was performed in
order to render membranes with thermo-responsive surface
properties. The aim was to create membranes suitable for cell
culture and in which confluent cell sheets can be recovered by
simply lowering the temperature. The chitosan membranes
were immersed in a solution of the monomer that was
polymerized via radical initiation. The composition of the
polymerization reaction solvent, which was a mixture of a
chitosan non-solvent (isopropanol) and a solvent (water),
provided a tight control over the chitosan membranes
swelling capability. The different swelling ratio, obtained
at different solvent composition of the reaction mixture,
drives simultaneously the monomer solubility and diffusion
into the polymeric matrix, the polymerization reaction rate,
as well as the eventual chain transfer to the side substituents
of the pyranosyl groups of chitosan. A combined analysis of
the modified membranes chemistry by proton nuclear magnetic
resonance (1H-NMR), Fourier transform spectroscopy
with attenuated total reflection (FTIR-ATR) and X-ray
photoelectron spectroscopy (XPS) showed that it was possible
to control the chitosan modification yield and depth in the
solvent composition range between 75% and 100% of isopropanol.
Plasma treatment was also applied to the original
chitosan membranes in order to improve cell adhesion and
proliferation. Chitosan membranes, which had been previously
subjected to oxygen plasma treatment, were then modified by
means of the previously describedmethodology. A human fetal
lung fibroblast cell line was cultured until confluence on the plasma-treated thermo-responsive chitosan membranes and
cell sheets were harvested lowering the temperature.Contract grant sponsor: European NoE EXPERTISSUESContract grant number: NMP3-CT-2004-500283Contract grant sponsor: European UnionContract grant number: NMP3-CT-2003-50575
Scale-invariance of galaxy clustering
Some years ago we proposed a new approach to the analysis of galaxy and
cluster correlations based on the concepts and methods of modern statistical
Physics. This led to the surprising result that galaxy correlations are fractal
and not homogeneous up to the limits of the available catalogs. The usual
statistical methods, which are based on the assumption of homogeneity, are
therefore inconsistent for all the length scales probed so far, and a new, more
general, conceptual framework is necessary to identifythe real physical
properties of these structures. In the last few years the 3-d catalogs have
been significatively improved and we have extended our methods to the analysis
of number counts and angular catalogs. This has led to a complete analysis of
all the available data that we present in this review. The result is that
galaxy structures are highly irregular and self-similar: all the available data
are consistent with each other and show fractal correlations (with dimension ) up to the deepest scales probed so far (1000 \hmp) and even more
as indicated from the new interpretation of the number counts. The evidence for
scale-invariance of galaxy clustering is very strong up to 150 \hmp due to
the statistical robustness of the data but becomes progressively weaker
(statistically) at larger distances due to the limited data. In These facts
lead to fascinating conceptual implications about our knowledge of the universe
and to a new scenario for the theoretical challenge in this field.Comment: Latex file 165 pages, 106 postscript figures. This paper is also
available at http://www.phys.uniroma1.it/DOCS/PIL/pil.html To appear in
Physics Report (Dec. 1997
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