273 research outputs found
Quantitative analysis of numerical estimates for the permeability of porous media from lattice-Boltzmann simulations
During the last decade, lattice-Boltzmann (LB) simulations have been improved
to become an efficient tool for determining the permeability of porous media
samples. However, well known improvements of the original algorithm are often
not implemented. These include for example multirelaxation time schemes or
improved boundary conditions, as well as different possibilities to impose a
pressure gradient. This paper shows that a significant difference of the
calculated permeabilities can be found unless one uses a carefully selected
setup. We present a detailed discussion of possible simulation setups and
quantitative studies of the influence of simulation parameters. We illustrate
our results by applying the algorithm to a Fontainebleau sandstone and by
comparing our benchmark studies to other numerical permeability measurements in
the literature.Comment: 14 pages, 11 figure
Impact of the new Chilean air-tightness regulation on indoor air pollution in dwellings with inefficient heating sources
In 2014, the Chilean Ministry of Housing and Urban Planning (MINVU) began to develop regulations for maximum levels of air infiltration in dwellings. This paper investigates the impacts of increased air-tightness on indoor air quality (IAQ) and energy use. The study uses computer simulations representative of social housing in Temuco, a city with heavy urban air pollution and cold winters. Results show infiltration measures produced reductions of -49% in air changes and -17% in heating loads. Emissions from six different types of wood, gas and paraffin burners including PM10, PM2.5, NO2, CO, SO2 and PAHs were modelled. changes of between -3% to +35% in individual contaminant concentrations, revealing that increased air-tightness does not necessarily imply a reduction in IAQ due to variations in deposition rates and reduced external pollutant ingress. As heater emissions exceeded pollutant concentration limits between 1-41% of the time, adopting cleaner heating technology is recommende
Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents
Chaotic micromixers such as the staggered herringbone mixer developed by
Stroock et al. allow efficient mixing of fluids even at low Reynolds number by
repeated stretching and folding of the fluid interfaces. The ability of the
fluid to mix well depends on the rate at which "chaotic advection" occurs in
the mixer. An optimization of mixer geometries is a non trivial task which is
often performed by time consuming and expensive trial and error experiments. In
this paper an algorithm is presented that applies the concept of finite-time
Lyapunov exponents to obtain a quantitative measure of the chaotic advection of
the flow and hence the performance of micromixers. By performing lattice
Boltzmann simulations of the flow inside a mixer geometry, introducing massless
and non-interacting tracer particles and following their trajectories the
finite time Lyapunov exponents can be calculated. The applicability of the
method is demonstrated by a comparison of the improved geometrical structure of
the staggered herringbone mixer with available literature data.Comment: 9 pages, 8 figure
Galaxy properties from J-PAS narrow-band photometry
We study the consistency of the physical properties of galaxies retrieved
from SED-fitting as a function of spectral resolution and signal-to-noise ratio
(SNR). Using a selection of physically motivated star formation histories, we
set up a control sample of mock galaxy spectra representing observations of the
local universe in high-resolution spectroscopy, and in 56 narrow-band and 5
broad-band photometry. We fit the SEDs at these spectral resolutions and
compute their corresponding the stellar mass, the mass- and luminosity-weighted
age and metallicity, and the dust extinction. We study the biases,
correlations, and degeneracies affecting the retrieved parameters and explore
the r\^ole of the spectral resolution and the SNR in regulating these
degeneracies. We find that narrow-band photometry and spectroscopy yield
similar trends in the physical properties derived, the former being
considerably more precise. Using a galaxy sample from the SDSS, we compare more
realistically the results obtained from high-resolution and narrow-band SEDs
(synthesized from the same SDSS spectra) following the same spectral fitting
procedures. We use results from the literature as a benchmark to our
spectroscopic estimates and show that the prior PDFs, commonly adopted in
parametric methods, may introduce biases not accounted for in a Bayesian
framework. We conclude that narrow-band photometry yields the same trend in the
age-metallicity relation in the literature, provided it is affected by the same
biases as spectroscopy; albeit the precision achieved with the latter is
generally twice as large as with the narrow-band, at SNR values typical of the
different kinds of data.Comment: 26 pages, 15 figures. Accepted for publication in MNRA
pyFIT3D and pyPipe3D -- The new version of the Integral Field Spectroscopy data analysis pipeline
We present a new version of the FIT3D and Pipe3D codes, two packages to
derive properties of the stellar populations and the ionized emission lines
from optical spectroscopy and integral field spectroscopy data respectively.
The new codes have been fully transcribed to Python from the original Perl and
C versions, modifying the algorithms when needed to make use of the unique
capabilities of this language with the main goals of (1) respecting as much as
possible the original philosophy of the algorithms, (2) maintaining a full
compatibility with the original version in terms of the format of the required
input and produced output files, and (3) improving the efficiency and accuracy
of the algorithms, and solving known (and newly discovered) bugs. The complete
package is freely distributed, with an available repository online. pyFIT3D and
pyPipe3D are fully tested with data of the most recent IFS data surveys and
compilations (e.g. CALIFA, MaNGA, SAMI and AMUSING++), and confronted with
simulations. We describe here the code, its new implementation, its accuracy in
recovering the parameters based on simulations, and a showcase of its
implementation on a particular dataset.Comment: New Astronomy - 29 pages, 19 figures - Received on 7 Dec 2021 -
Accepted for publication on 8 Jul 202
Optimization of chaotic micromixers using finite time Lyapunov exponents
In microfluidics mixing of different fluids is a highly non-trivial task due to the absence of turbulence. The dominant process allowing mixing at low Reynolds number is therefore diffusion, thus rendering mixing in plain channels very inefficient. Recently, passive chaotic micromixers such as the staggered herringbone mixer were developed, allowing efficient mixing of fluids by repeated stretching and folding of the fluid interfaces. The optimization of the geometrical parameters of such mixer devices is often performed by time consuming and expensive trial and error experiments. We demonstrate that the application of the lattice Boltzmann method to fluid flow in highly complex mixer geometries together with standard techniques from statistical physics and dynamical systems theory can lead to a highly efficient way to optimize micromixer geometries. The strategy applies massively parallel fluid flow simulations inside a mixer, where massless and noninteracting tracer particles are introduced. By following their trajectories we can calculate finite time Lyapunov exponents in order to quantify the degree of chaotic advection inside the mixer. The current report provides a review of our results published in [1] together with additional details on the simulation methodology
Nanomaterial-based Sensors for the Study of DNA Interaction with Drugs
The interaction of drugs with DNA has been searched thoroughly giving rise to an endless number of findings of undoubted importance, such as a prompt alert to harmful substances, ability to explain most of the biological mechanisms, or provision of important clues in targeted development of novel chemotherapeutics. The existence of some drugs that induce oxidative damage is an increasing point of concern as they can cause cellular death, aging, and are closely related to the development of many diseases. Because of a direct correlation between the response, strength/ nature of the interaction and the pharmaceutical action of DNA-targeted drugs, the electrochemical analysis is based on the signals of DNA before and after the interaction with the DNA-targeted drug. Nowadays, nanoscale materials are used extensively for offering fascinating characteristics that can be used in designing new strategies for drug-DNA interaction detection. This work presents a review of nanomaterials (NMs) for the study of drug-nucleic acid interaction. We summarize types of drug-DNA interactions, electroanalytical techniques for evidencing these interactions and quantification of drug and/or DNA monitoring
Tecnologias sociais: as organizações não governamentais no enfrentamento das mudanças climáticas e na promoção de desenvolvimento humano
De acordo com o quarto relatório do Intergovernmental Panel on Climate Change (IPCC), as regiões semiáridas do mundo estarão entre as mais afetadas pelos impactos das mudanças climáticas globais. Estudos realizados pelo Ministério do Meio Ambiente (MMA), em 2007, confirmam que, no Nordeste brasileiro, não apenas choverá menos e mais irregularmente, mas, também, haverá mais secas, devido ao aquecimento da temperatura. Diante dos diversos impactos sociais, ambientais e econômicos possíveis nesses cenários, é de fundamental importância a verificação de alternativas sustentáveis para o semiárido brasileiro. Este artigo tem por objetivo avaliar o potencial de algumas das tecnologias sociais (TS) de convivência com o semiárido, desenvolvidas por diversas organizações, para a mitigação das mudanças climáticas e a promoção de desenvolvimento humano. Constata-se que as TS tem grande potencial para auxiliar na mitigação e na adaptação das mudanças climáticas, ao mesmo tempo que promovem melhorias na qualidade de vida das localidades onde estão sendo desenvolvidas
Available evidence and outcome of off-label use of rituximab in clinical practice
Purpose: To analyze the therapeutic indications for off-label use of rituximab, the available evidence for its use, the outcomes, and the cost. Methods: This was a retrospective analysis of patients treated with rituximab for off-label indications from January 2007 to December 2009 in two tertiary hospitals. Information on patient characteristics, medical conditions, and therapeutic responses was collected from medical records. Available evidence for the efficacy of rituximab in each condition was reviewed, and the cost of treatment was calculated. Results: A total of 101 cases of off-label rituximab use were analyzed. The median age of the patients involved was 53 [interquartile range (IQR) 37.5-68.0] years; 55.4 % were women. The indications for prescribing rituximab were primarily hematological diseases (46 %), systemic connective tissue disorders (27 %), and kidney diseases (20 %). Available evidence supporting rituximab treatment for these indications mainly came from individual cohort studies (53.5 % of cases) and case series (25.7 %). The short-term outcome (median 3 months, IQR 2-4 months) was a complete response in 38 % of cases and partial response in 32.6 %. The highest short-term responses were observed for systemic lupus erythematosus and membranous glomerulonephritis, and the lowest was for neuromyelitis optica, idiopathic thrombocytopenic purpura, and miscellaneous indications. Some response was maintained in long-term follow-up (median 23 months IQR 12-30months) in 69.2%of patients showing a short-term response. Median cost per patient was 5,187.5 (IQR 5,187.5-7,781.3). Conclusions: In our study, off-label rituximab was mainly used for the treatment of hematological, kidney, and systemic connective tissue disorders, and the response among our patient cohort was variable depending on the specific disease. The level of evidence supporting the use of rituximab for these indications was low and the cost was very high. We conclude that more clinical trials on the off-label use of rituximab are needed, although these may be difficult to conduct in some rare diseases. Data from observational studies may provide useful information to assist prescribing in clinical practice
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