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Search Results: 1 - 10 of 532892 matches for " Betina M. P.;Steffen "
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Haste intramedular polimérica bioreabsorvível (PLLA/PHBV) para uso na recupera??o de fraturas ósseas
Ferreira, Betina M. P.;Steffen, Alfredo M.;Cardoso, Túlio P.;Alberto-Rincon, Maria do Carmo;Duek, Eliana A. R.;
Polímeros , 2008, DOI: 10.1590/S0104-14282008000400010
Abstract: the growing interest in medicine with the use of bioreabsorbable polymeric materials has been stimulating researchers from orthopedic area to develop more biological solutions, substituting threads, stems and metallic plates for bioreabsorbable polymers in the treatment of fractures. so, we decided to study implants of the plla/phbv blends (two bioreabsorbable polymers) moulded in a mini-injector. those implants were used for recovery of fractures of rabbit femur and assessed in comparison with the thread of steinmann (stainless steel, commercially used). after euthanasia with 6, 12 and 24 weeks of implantation of the artifacts, the bones were studied with x ray, histological exam and mechanic test, while the polymeric implants were submitted the scanning electron microscopy (sem), mechanic test and modular differential scanning calorimetry (mdsc). the x ray showed good calluses bone with the use of the polymer stem as well as with the metallic control. the histological study showed absence of inflammatory reactions or osteolysis. the mechanical test showed bone consolidation in the two groups. in the mechanical test and in the calorimetry studies, the polymeric stem presented signs of progressive degradation within the studied time. with the data obtained, we can state that the implant plla/phbv demonstrated to be as effective in repairing fractures of rabbit femur as the metallic control.
Estudo da intera??o células Vero/PLGA após a modifica??o da superfície por plasma de oxigênio
Esposito, Andrea R.;Lucchesi, Carolina;Ferreira, Betina M. P.;Duek, Eliana A. R.;
Matéria (Rio de Janeiro) , 2007, DOI: 10.1590/S1517-70762007000100021
Abstract: the application of bioreabsorbable polymers as support for cells culture is an alternative method to treat lesions and loss of tissues. the surface modifications of these polymers by plasma is an effective and economical technique to make it more hydrophilic. the aim of this work was to study the interactions between vero cells and plga supports previously treated by oxygen plasma, to increase the surface hydrofilicity. the samples were characterized by contact angle, mev and citochemical analysis. the plasma treatment increased the hydrofilicity, improving the adhesion and cell proliferation, in comparison with the membranes without treatment.
A synthesis of atmospheric mercury depletion event chemistry linking atmosphere, snow and water
A. Steffen,T. Douglas,M. Amyot,P. Ariya
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review the history of Hg in Polar Regions, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the roles that the snow pack, oceans, fresh water and the sea ice play in the cycling of Hg are presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between
Impact of granulation effects on the use of Balmer lines as temperature indicators
H. -G. Ludwig,N. T. Behara,M. Steffen,P. Bonifacio
Physics , 2009, DOI: 10.1051/0004-6361/200911997
Abstract: Balmer lines serve as important indicators of stellar effective temperatures in late-type stellar spectra. One of their modelling uncertainties is the influence of convective flows on their shape. We aim to characterize the influence of convection on the wings of Balmer lines. We perform a differential comparison of synthetic Balmer line profiles obtained from 3D hydrodynamical model atmospheres and 1D hydrostatic standard ones. The model parameters are appropriate for F,G,K dwarf and subgiant stars of metallicity ranging from solar to 1/1000 solar. The shape of the Balmer lines predicted by 3D models can never be exactly reproduced by a 1D model, irrespective of its effective temperature. We introduce the concept of a 3D temperature correction, as the effective temperature difference between a 3D model and a 1D model which provides the closest match to the 3D profile. The temperature correction is different for the different members of the Balmer series and depends on the adopted mixing-length parameter in the 1D model. Among the investigated models, the 3D correction ranges from -300K to +300K. Horizontal temperature fluctuations tend to reduce the 3D correction. Accurate effective temperatures cannot be derived from the wings of Balmer lines, unless the effects of convection are properly accounted for. The 3D models offer a physically well justified way of doing so. The use of 1D models treating convection with the mixing-length theory do not appear to be suitable for this purpose. In particular, there are indications that it is not possible to determine a single value of the mixing-length parameter which will optimally reproduce the Balmer lines for any choice of atmospheric parameters.
Weighted Scale-Free Networks with Stochastic Weight Assignments
Dafang Zheng,Steffen Trimper,Bo Zheng,P. M. Hui
Physics , 2003, DOI: 10.1103/PhysRevE.67.040102
Abstract: We propose and study a model of weighted scale-free networks incorporating a stochastic scheme for weight assignments to the links, taking into account both the popularity and fitness of a node. As the network grows the weights of links are driven either by the connectivity with probability $p$ or by the fitness with probability $1-p$. Results of numerical simulations show that the total weight associated with a selected node exhibits a power law distribution with an exponent $\sigma$, the value of which depends on the probability $p$. The exponent $\sigma$ decreases continuously as $p$ increases. For $p=0$, the total weight distribution displays the same scaling behavior as that of the connectivity distribution with $\sigma= \gamma = 3$, where $\gamma$ is the exponent characterizing the connectivity distribution. An analytical expression for the total weight is derived so as to explain the features observed in the numerical results. Numerical results are also presented for a generalized model with a fitness-dependent link formation mechanism.
The Galactic evolution of phosphorus
E. Caffau,P. Bonifacio,R. Faraggiana,M. Steffen
Physics , 2011, DOI: 10.1051/0004-6361/201117313
Abstract: As a galaxy evolves, its chemical composition changes and the abundance ratios of different elements are powerful probes of the underlying evolutionary processes. Phosphorous is an element whose evolution has remained quite elusive until now, because it is difficult to detect in cool stars. The infrared weak P I lines of the multiplet 1, at 1050-1082 nm, are the most reliable indicators of the presence of phosphorus. The availability of CRIRES at VLT has permitted access to this wavelength range in stellar spectra.We attempt to measure the phosphorus abundance of twenty cool stars in the Galactic disk. The spectra are analysed with one-dimensional model-atmospheres computed in Local Thermodynamic Equilibrium (LTE). The line formation computations are performed assuming LTE. The ratio of phosphorus to iron behaves similarly to sulphur, increasing towards lower metallicity stars. Its ratio with respect to sulphur is roughly constant and slightly larger than solar, [P/S]=0.10+- 0.10. We succeed in taking an important step towards the understanding of the chemical evolution of phosphorus in the Galaxy. However, the observed rise in the P/Fe abundance ratio is steeper than predicted by Galactic chemical evolution model model developed by Kobayashi and collaborators. Phosphorus appears to evolve differently from the light odd-Z elements sodium and aluminium. The constant value of [P/S] with metallicity implies that P production is insensitive to the neutron excess, thus processes other than neutron captures operate. We suggest that proton captures on 30Si and alpha captures on $27Al are possibilities to investigate. We see no clear distinction between our results for stars with planets and stars without any detected planet.
Pure-hydrogen 3D model atmospheres of cool white dwarfs
P. -E. Tremblay,H. -G. Ludwig,M. Steffen,B. Freytag
Physics , 2013, DOI: 10.1051/0004-6361/201220813
Abstract: A sequence of pure-hydrogen CO5BOLD 3D model atmospheres of DA white dwarfs is presented for a surface gravity of log g = 8 and effective temperatures from 6000 to 13,000 K. We show that convective properties, such as flow velocities, characteristic granulation size and intensity contrast of the granulation patterns, change significantly over this range. We demonstrate that these 3D simulations are not sensitive to numerical parameters unlike the 1D structures that considerably depend on the mixing-length parameters. We conclude that 3D spectra can be used directly in the spectroscopic analyses of DA white dwarfs. We confirm the result of an earlier preliminary study that 3D model spectra provide a much better characterization of the mass distribution of white dwarfs and that shortcomings of the 1D mixing-length theory are responsible for the spurious high-log g determinations of cool white dwarfs. In particular, the 1D theory is unable to account for the cooling effect of the convective overshoot in the upper atmospheres.
Spectroscopic analysis of DA white dwarfs with 3D model atmospheres
P. -E. Tremblay,H. -G. Ludwig,M. Steffen,B. Freytag
Physics , 2013, DOI: 10.1051/0004-6361/201322318
Abstract: We present the first grid of mean three-dimensional (3D) spectra for pure-hydrogen (DA) white dwarfs based on 3D model atmospheres. We use CO5BOLD radiation-hydrodynamics 3D simulations instead of the mixing-length theory for the treatment of convection. The simulations cover the effective temperature range of 6000 < Teff (K) < 15,000 and the surface gravity range of 7 < log g < 9 where the large majority of DAs with a convective atmosphere are located. We rely on horizontally averaged 3D structures (over constant Rosseland optical depth) to compute <3D> spectra. It is demonstrated that our <3D> spectra can be smoothly connected to their 1D counterparts at higher and lower Teff where the 3D effects are small. Analytical functions are provided in order to convert spectroscopically determined 1D effective temperatures and surface gravities to 3D atmospheric parameters. We apply our improved models to well studied spectroscopic data sets from the Sloan Digital Sky Survey and the White Dwarf Catalog. We confirm that the so-called high-log g problem is not present when employing <3D> spectra and that the issue was caused by inaccuracies in the 1D mixing-length approach. The white dwarfs with a radiative and a convective atmosphere have derived mean masses that are the same within ~0.01 Msun, in much better agreement with our understanding of stellar evolution. Furthermore, the 3D atmospheric parameters are in better agreement with independent Teff and log g values from photometric and parallax measurements.
Optimal Determination of the Equilibrium Displacement of a Damped Harmonic Oscillator in the Presence of Thermal Noise
M. W. Moore,J. H. Steffen,P. E. Boynton
Physics , 2004, DOI: 10.1063/1.1994985
Abstract: Using a matched filter technique, we derive the minimum variance, unbiased estimator for the equilibrium displacement of a damped harmonic oscillator in thermal equilibrium when interactions with the thermal bath are the leading source of noise. We compare the variance in this optimal estimator with the variance in other, commonly used estimators in the presence of pure thermal noise and pure white noise. We also compare the variance in these estimators for a mixture of white and thermal noise. This result has implications for experimental design and the collection and analysis of data.
Epidemics and Dimensionality in Hierarchical Networks
Dafang Zheng,P. M. Hui,Steffen Trimper,Bo Zheng
Quantitative Biology , 2003,
Abstract: Epidemiological processes are studied within a recently proposed hierarchical network model using the susceptible-infected-refractory dynamics of an epidemic. Within the network model, a population may be characterized by $H$ independent hierarchies or dimensions, each of which consists of groupings of individuals into layers of subgroups. Detailed numerical simulations reveal that for $H>1$, global spreading results regardless of the degree of homophily of the individuals forming a social circle. For H=1, a transition from global to local spread occurs as the population becomes decomposed into increasingly homophilous groups. Multiple dimensions in classifying individuals (nodes) thus make a society (computer network) highly susceptible to large scale outbreaks of infectious diseases (viruses).
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