2,129 research outputs found
Correlation between Subjective Nasal Patency and Intranasal Airflow Distribution
Objectives
(1) Analyze the relationship between intranasal airflow distribution and subjective nasal patency in healthy and nasal airway obstruction (NAO) cohorts using computational fluid dynamics (CFD). (2) Determine whether intranasal airflow distribution is an important objective measure of airflow sensation that should be considered in future NAO virtual surgery planning. Study Design
Cross-sectional. Setting
Academic tertiary medical center and academic dental clinic. Subjects and Methods
Three-dimensional models of nasal anatomy were created based on computed tomography scans of 15 patients with NAO and 15 healthy subjects and used to run CFD simulations of nasal airflow and mucosal cooling. Subjective nasal patency was quantified with a visual analog scale (VAS) and the Nasal Obstruction Symptom Evaluation (NOSE). Regional distribution of nasal airflow (inferior, middle, and superior) was quantified in coronal cross sections in the narrowest nasal cavity. The Pearson correlation coefficient was used to quantify the correlation between subjective scores and regional airflows. Results
Healthy subjects had significantly higher middle airflow than patients with NAO. Subjective nasal patency had no correlation with inferior and superior airflows but a high correlation with middle airflow (|r| = 0.64 and |r| = 0.76 for VAS and NOSE, respectively). Anterior septal deviations tended to shift airflow inferiorly, reducing middle airflow and reducing mucosal cooling in some patients with NAO. Conclusion
Reduced middle airflow correlates with the sensation of nasal obstruction, possibly due to a reduction in mucosal cooling in this region. Further research is needed to elucidate the role of intranasal airflow distribution in the sensation of nasal airflow
A SVM and k-NN Restricted Stacking to Improve Land Use and Land Cover Classification
Land use and land cover (LULC) maps are remote sensing products that are used to classify areas into different landscapes. The newest techniques have been applied to improve the final LULC classification and most of them are based on SVM classifiers. In this paper, a new method based on a multiple classifiers ensemble to improve LULC map accuracy is shown. The method builds a statistical raster from LIDAR and image fusion data following a pixel-oriented strategy. Then, the pixels from a training area are used to build a SVM and k-NN restricted stacking taking into account the special characteristics of spatial data. A comparison between a SVM and the restricted stacking is carried out. The results of the tests show that our approach improves the results in the context of the real data from a riparian area of Huelva (Spain)
Base-accelerated degradation of nanosized platinum electrocatalysts
In the pursuit of a hydrogen economy, extensive research has been directed at developing acidic and alkaline hydrogen fuel cells. Such fuel cells often utilize platinum-based catalysts. These materials have been studied extensively in acidic conditions but not in alkaline ones. This focus on acidic systems creates a marked knowledge gap, since recent studies indicate that carbon-supported platinum (Pt/C) electrocatalysts degrade more rapidly in bases than in acids. Addressing this gap, the present work investigates Pt/C degradation at pH 2 and pH 12 using electrochemistry, transmission electron microscopy (TEM), and in situ X-ray absorption spectroscopy (XAS). TEM and XAS reveal accelerated Pt/C degradation at high pH levels, which results in increased Ostwald ripening, Smoluchowski agglomeration, and nanoparticle detachment. These processes are driven by platinum-catalyzed carbon corrosion and the dissolution and redeposition of platinum nanoparticles. Although these processes take place at both low and high pH levels, basic conditions accelerate the degradation. Base-enhanced Pt dissolution and redeposition was assessed in further detail, revealing an oxidation onset reduction of 100 mV in the base; however, there were no significant differences between undissolved Pt oxidation in acid and in base. The results suggest that soluble Pt oxidation products are stabilized in the base instead. These conclusions are important for translating acidbased literature to alkaline conditions.Catalysis and Surface Chemistr
Efficient electrochemical water oxidation in neutral and near-neutral systems with a nanoscale silver-oxide catalyst
Solid state NMR/Biophysical Organic Chemistr
Brane Interaction as the Origin of Inflation
We reanalyze brane inflation with brane-brane interactions at an angle, which
include the special case of brane-anti-brane interaction. If nature is
described by a stringy realization of the brane world scenario today (with
arbitrary compactification), and if some additional branes were present in the
early universe, we find that an inflationary epoch is generically quite
natural, ending with a big bang when the last branes collide. In an interesting
brane inflationary scenario suggested by generic string model-building, we use
the density perturbation observed in the cosmic microwave background and the
coupling unification to find that the string scale is comparable to the GUT
scale.Comment: 28 pages, 8 figures, 2 tables, JHEP forma
A Comparative Study between Two Regression Methods on LiDAR Data: A Case Study
Airborne LiDAR (Light Detection and Ranging) has become
an excellent tool for accurately assessing vegetation characteristics in
forest environments. Previous studies showed empirical relationships between
LiDAR and field-measured biophysical variables. Multiple linear
regression (MLR) with stepwise feature selection is the most common
method for building estimation models. Although this technique has provided
very interesting results, many other data mining techniques may
be applied. The overall goal of this study is to compare different methodologies
for assessing biomass fractions at stand level using airborne Li-
DAR data in forest settings. In order to choose the best methodology, a
comparison between two different feature selection techniques (stepwise
selection vs. genetic-based selection) is presented. In addition, classical
MLR is also compared with regression trees (M5P). The results when
each methodology is applied to estimate stand biomass fractions from
an area of northern Spain show that genetically-selected M5P obtains
the best results
A Comparative Study of Machine Learning Regression Methods on LiDAR Data: A Case Study
Light Detection and Ranging (LiDAR) is a remote sensor
able to extract vertical information from sensed objects. LiDAR-derived
information is nowadays used to develop environmental models for describing
fire behaviour or quantifying biomass stocks in forest areas. A
multiple linear regression (MLR) with previous stepwise feature selection
is the most common method in the literature to develop LiDAR-derived
models. MLR defines the relation between the set of field measurements
and the statistics extracted from a LiDAR flight. Machine learning has
recently been paid an increasing attention to improve classic MLR results.
Unfortunately, few studies have been proposed to compare the
quality of the multiple machine learning approaches. This paper presents
a comparison between the classic MLR-based methodology and common
regression techniques in machine learning (neural networks, regression
trees, support vector machines, nearest neighbour, and ensembles such
as random forests). The selected techniques are applied to real LiDAR
data from two areas in the province of Lugo (Galizia, Spain). The results
show that support vector regression statistically outperforms the rest of
techniques when feature selection is applied. However, its performance
cannot be said statistically different from that of Random Forests when
previous feature selection is skipped
Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT
The presence of a solar burst spectral component with flux density increasing
with frequency in the sub-terahertz range, spectrally separated from the
well-known microwave spectral component, bring new possibilities to explore the
flaring physical processes, both observational and theoretical. The solar event
of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component
detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the
Owens Valley Solar Array (OVSA). Emissions obtained by instruments in
satellites are discussed with emphasis to ultra-violet (UV) obtained by the
Transition Region And Coronal Explorer (TRACE), soft X-rays from the
Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays
from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz
impulsive component had its closer temporal counterpart only in the higher
energy X- and gamma-rays ranges. The spatial positions of the centers of
emission at 212 GHz for the first flux enhancement were clearly displaced by
more than one arc-minute from positions at the following phases. The observed
sub-THz fluxes and burst source plasma parameters were found difficult to be
reconciled to a purely thermal emission component. We discuss possible
mechanisms to explain the double spectral components at microwaves and in the
THz ranges.Comment: Accepted version for publication in Solar Physic
Surto alimentar por Salmonella Enteritidis no Noroeste do Estado de São Paulo, Brasil
A foodborne outbreak which affected 211 persons occurred, in a School, in 1993. The epidemiological data obtained by interviewing the affected and non affected persons sampled showed as predominant symptoms: diarrhoea, fever (77.7%), abdominal cramps (67.7%), vomiting (65.8%), hot-and-cold sensations (54.5%) and headache (44.5%). The median incubation period was of 17 hours, the limits being 3 and 29 hours. The disease period was of from 3 to 4 days. The food concerned was a kind of paté, a mayonnaise mixture prepared with fresh eggs with boiled potatoes that was consumed with bread. The biological material analysis - 3 coprocultures, and leftovers of the food revealed the presence of one and the same organism: Salmonella Enteritidis. In the food, the numbers of this bacterium per gram were sufficient to account for the manifestation of the disease (104 and 105/g). The antibiogram of all the isolates showed the same sensibility pattern. The preparation related to this outbreak suggests the endogenous contamination of the eggs; the cross contamination - the outbreak affected three school periods, as the food was prepared separately for each school period; and the conditions under which the food was kept during the time from preparation to consumption. The observation of the 3 food handlers, by successive coprocultures, for one week, indicates that they were not asymptomatic carriers nor were they affected as a result of this outbreak by the causal bacteria.Em 1993 ocorreu um surto alimentar em escola, com 211 afetados. Os dados epidemiológicos levantados por entrevista de amostragem de afetados e não afetados mostraram que os sintomas predominantes foram diarréia, febre (77,7%), dor abdominal (67,7%), vômito (65,8%), calafrios (54,5%) e cefaléia (44,5%). A mediana de incubação foi de 17 horas, com limites entre 3 e 29 horas. A duração da doença foi de 3 a 4 dias. O alimento consumido foi um tipo de patê, mistura de molho de maionese preparada com ovos crus com batata cozida, passado em pão. A análise de material biológico (3 coproculturas) e de restos de alimentos revelou a presença do mesmo microrganismo, a Salmonella Enteritidis. No caso dos alimentos, o número encontrado desta bactéria por gramo de produto era compatível com a quantidade de células necessária para desencadear a doença (10(4)e 10(5)/g). O antibiograma de todas as cepas isoladas revelou o mesmo padrão de sensibilidade. As falhas no preparo do alimento relacionadas com o levantamento indicam a possibilidade de contaminação endógena dos ovos; contaminação cruzada - o surto afetou três períodos escolares, sendo que para cada um o alimento foi preparado em separado - e as condições de manutenção do alimento após preparo e até o consumo. A observação por uma semana seguida das 3 merendeiras envolvidas, através de coprocultura, não indicaram que as mesmas fossem portadoras assintomáticas desta bactéria ou que tivessem sido envolvidas no surto em questão
Assessing the role of multiple mechanisms increasing the age of dengue cases in Thailand
The mean age of dengue hemorrhagic fever (DHF) cases increased considerably in Thailand from 8.1 to 24.3 y between 1981 and 2017 (mean annual increase of 0.45 y). Alternative proposed explanations for this trend, such as changes in surveillance practices, reduced mosquito–human contact, and shifts in population demographics, have different implications for global dengue epidemiology. To evaluate the contribution of each of these hypothesized mechanisms to the observed data, we developed 20 nested epidemiological models of dengue virus infection, allowing for variation over time in population demographics, infection hazards, and reporting rates. We also quantified the effect of removing or retaining each source of variation in simulations of the age trajectory. Shifts in the age structure of susceptibility explained 58% of the observed change in age. Adding heterogeneous reporting by age and reductions in per-serotype infection hazard to models with shifts in susceptibility explained an additional 42%. Reductions in infection hazards were mostly driven by changes in the number of infectious individuals at any time (another consequence of shifting age demographics) rather than changes in the transmissibility of individual infections. We conclude that the demographic transition drives the overwhelming majority of the observed change as it changes both the age structure of susceptibility and the number of infectious individuals. With the projected Thai population age structure, our results suggest a continuing increase in age of DHF cases, shifting the burden toward individuals with more comorbidity. These insights into dengue epidemiology may be relevant to many regions of the globe currently undergoing comparable changes in population demographics
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