133 research outputs found
Modeling of the Continuous Absorption of Electromagnetic Radiation in Dense Hydrogen Plasma
In this work is examined a new modeling way of describing the continuous
absorption of electromagnetic (EM) radiation in a dense partially ionized
hydrogen plasmas with electron densities about cm -
cm and temperatures about K - K in the wavelength region . The obtained results can be applied to the plasmas of the
partially ionized layers of different stellar atmospheres
Modélisation thermo-hydraulique de la congélation artificielle des terrains
Artificial ground freezing is a ground sealing and reinforcement technique regularly used in civil and mining engineering. In order to reliably predict the freezing evolution in the porous medium, this research offers two new numerical models allowing the simulation of the global problem of artificial ground freezing. A first model aims at representing the thermo-hydraulic coupled mechanisms associated with the material freezing while a second model focuses on the estimation of heat transfers between a freeze pipe and the surrounding ground. The thermo-hydraulic model, in addition to being thermodynamically consistent, has been verified both with respect to analytical solutions and large- scale experimental results obtained under conditions of high water flow velocity. The pipe-ground model adopts an innovative approach compared with literature. It allows to determine the boundary conditions of the ground freezing models, not readily available in practice, and to optimize the operating conditions of the system thanks to limited simulation times. By the considered assumptions, their reliability and their practicality, these two models are particularly well adapted to industrial sites like the uranium mine Cigar Lake (Canada) which presents two major constraints: the potential presence of high seepage-flow velocities and the strong ground heterogeneity. In these contexts, applications of the two models, jointly used or not, are presented with respect to simple cases and to the industrial case of Cigar Lake. They can be employed to predict the freezing evolution in the ground considering the thermo-hydraulic interactions, to optimize the freezing system, or to evaluate the impact of specific geological, hydrogeological and operating conditions on the freezing progress.La congélation artificielle des terrains est une technique d'imperméabilisation et de renforcement des terrains régulièrement employée dans le génie civil et l'industrie minière. Dans un objectif de prédiction fiable de l'évolution de la congélation dans le milieu poreux, cette recherche propose deux nouveaux modèles numériques permettant la simulation du problème global de la congélation artificielle des terrains. Un premier modèle a pour objectif la représentation des mécanismes couplés thermo-hydrauliques associés à la congélation du matériau tandis qu'un deuxième modèle se concentre sur l'estimation des échanges de chaleur entre un puits de congélation et le terrain environnant. Le modèle thermo-hydraulique, en plus d'être cohérent sur le plan thermodynamique, a été vérifié à la fois par rapport à des solutions analytiques et par rapport à des résultats expérimentaux obtenus à grande échelle en conditions d'écoulements importants. Le modèle puits-terrain adopte une approche innovante par rapport à la bibliographie. Il permet de déterminer les conditions aux limites des modèles de congélation des terrains, difficiles à connaître en pratique, et d'optimiser les conditions opératoires du système grâce à des temps de simulation limités. De par les hypothèses considérées, leur fiabilité et leur praticité d'utilisation, ces deux modèles sont particulièrement adaptés à des sites industriels comme celui de la mine d'uranium de Cigar Lake (Canada) qui présente deux contraintes majeures : la présence potentielle d'écoulements importants et la forte hétérogénéité des terrains à congeler. Dans de tels contextes, des applications d'utilisation conjointe des deux modèles ou non sont présentées par rapport à des cas simples et au cas industriel de Cigar Lake. Ils peuvent ainsi être employés pour prédire l'évolution de la congélation dans le terrain en tenant compte des interactions thermo-hydrauliques, pour optimiser le système de congélation, ou encore pour évaluer l'impact sur la progression des zones congelées de conditions géologiques, hydrogéologiques et opératoires particulières
Modelagem da dinâmica do desmatamento de uma fronteira em expansão, Lábrea, Amazonas
Brazil’s “arc of deforestation” continues to expand across the Amazon region and has already
reached the southeastern part of the state of Amazonas. A new focus of the deforestation has
already affected a part of Lábrea, which is the municipality (county) that was recently found
to have one of the highest deforestation rates in Amazonas. Pressure from the Arc originates
in the neighboring states of Acre and Rondônia, which already have intense deforestation
processes underway for the expansion and consolidation of the agricultural and ranching
frontier. In addition to the impacts caused to natural ecosystems in Lábrea, land-use changes
have induced a series of social conflicts through the process of “grilagem” (fraudulent
appropriation of large areas of public land) and from agricultural and ranching activities that
have contributed to the expulsion of extractive workers such as rubber tappers and Brazil nut
gatherers. Consequently, traditional families demanded the creation of extractive reserves to
protect themselves. In addition, as a part of the Program for the Acceleration of Growth
(PAC) the Ministry of Transportation plans to reconstruct the BR-319 (Porto Velho- Manaus)
Highway (which has been abandoned since 1988) and to recuperate a part of the marginally
passable Transamazon Higway (BR-230) that connects the BR-319 to Lábrea. To avoid the
environmental consequences of these projects, in 2006 the government proposed a series of
protected areas in the area of influence of the BR-319, four of which have been recently
created in the municipality of Lábrea. This study had the objective of modeling the future
spatial dynamics of deforestation in Lábrea and evaluating the usefulness of the recently
created protected areas in containing deforestation. Chapter I analyzes the effectiveness of
protected areas that have already been created in Acre, Rondônia and southern Amazonas.
The analyses revealed the usefulness of protected areas in containing deforestation: 90% of
the protected areas had deforestation rates inferior to those in a 10-km-wide strip surrounding
the protected areas. In addition, weights of evidence that represent the probabilities used in
the AGROECO model to simulate future deforestation inside the proposed areas have been
determined for the protected areas in this region, as well for the areas surrounding the
protected areas (10-km buffer). These weights of evidence have been determined specifically
for the category of use of each protected area and for the category of use in accord with its
administrative level (federal or state). Indigenous reserves were the most effective in repelling
deforestation, with a weight of -2.57; Integral Protected Areas were less efficient with a
weight of -1.23, and, finally, Sustainable Use Protected Areas were the most vulnerable with a
weight of -0.15. When considering weights of evidence as a function of the internal Euclidian
distance, weights declined when the internal distance was progressing from the edge of the
protected area to the center. Protected areas had weights of evidence that varied with the
internal Euclidian distance. These weights have been used in Chapter II, where eight scenarios
have been produced for the Lábrea region up to 2040 using the AGROECO model. Of the two
groups of scenarios, one didn’t consider the recent creation of protected areas (I), Business As
Usual while the other considered these areas, (II) Governance. In each scenario group, four
study cases have been considered including: 1- homogenously distributed weights of evidence
over the protected areas, 2- gradually distributed weights of evidence according to the internal
Euclidian distance, 3- homogenously distributed weights of evidence over the protected areas
and weights of evidence for the 10-km buffer areas, 4- gradually distributed weights of
evidence according to the internal Euclidian distance and weights of evidence for the 10-km
buffer areas. Creation of the protected areas has been little efficient because the majority of
the Governance group scenarios had slightly less deforested area in 2040 than did the
corresponding scenarios in the Business As Usual group. The use of gradually distributed
weights of evidence according to the internal Euclidian distance appears to be the most
realistic approach because it reduces the influence of deforestation occurrence in areas far
from the protected area limits. Considering the weights of evidence for the 10-km buffer area,
the surroundings of the protected areas have concentrated deforestation inside their limits
because their high weights of evidence make them more attractive to deforestation in the
simulations. However, this is believed to be a consequence of the years for which satellite data were available for calibrating the model, when the areas outside of the reserve buffers
had already been heavily deforested, leaving little left to clear. The most realistic scenarios for
our dataset are therefore considered to be those that use gradually distributed weights of
evidence but do not use separate weights for the buffer areas. In the scenario (GOV-2),
deforestation was reduced in the study area by 5,1 % (2.596 km 2 ) as a result of the creation of
the reserves, when compared to the corresponding baseline scenario (BAU-2).O Arco do Desmatamento da Amazônia Brasileira, em seu avanço contínuo, já alcançou a
parte sul do Amazonas. Nessa região, a pressão que estimula seu crescimento se origina nos
estados vizinhos, Acre e Rondônia, estados que já conheceram processos de desmatamento
intensos relacionados pela expansão da fronteira agropecuária e sua consolidação. Os novos
focos de desmatamento já afetaram o sul do município de Lábrea. Nos últimos anos, Lábrea
foi o município que apresentou taxas recordes de desmatamento no Estado do Amazonas.
Além dos danos causados aos ecossistemas naturais, as mudanças de uso da terra têm
provocado conflitos sociais graves através do processo de grilagem de terras e da atividade
agropecuária, contribuindo para a expulsão de trabalhadores extrativistas da região. Ao
mesmo tempo, foram propostas em 2006 quatro áreas protegidas federais em Lábrea, dentro
do grupo de áreas propostas na Área sob Limitação Administrativa Provisória (ALAP) da BR-
319 (rodovia Manaus-Porto Velho), sugeridas em prevenção dos impactos ambientais que
poderão ser causados pela reconstrução da BR-319 e a pavimentação da BR-230 (rodovia
Transamazônica). Esses projetos federais são integrados ao Programa de Aceleração do
Crescimento (PAC). Este estudo teve como objetivo modelar, com o modelo AGROECO, a
dinâmica futura do desmatamento de Lábrea e avaliar a efetividade das áreas protegidas
recém criadas em conter o desmatamento. No Capítulo I, foi analisada a vulnerabilidade ao
desmatamento de áreas protegidas já implementadas na parte Sudoeste do Arco do
Desmatamento, nos Estados do Acre, Rondônia e Sul do Amazonas para entender como as
áreas recém criadas poderão ser futuramente afetadas. As análises revelaram a efetividade das
áreas protegidas em conter o desmatamento dentro dos seus limites, sendo que 90% das áreas
protegidas apresentaram taxas de desmatamento inferiores às taxas da área de seu entorno de
10 km. Também, pesos de evidência que representam a influência de uma variável espacial no
desmatamento e modificam posteriormente as chances de ocorrer o evento desmatamento
foram calculados para as áreas protegidas e suas áreas de amortecimento, especificamente
para cada categoria de uso associada à esfera administrativa. Os pesos de evidência, quando
apresentarem valores negativos tem uma influencia negativa no evento considerado, ou seja,
no caso do desmatamento, tendem a repelir o avanço do desmatamento. As terras indígenas
foram as mais repulsivas com um peso de evidência médio de -2,57, as áreas de proteção
integral foram um pouco menos eficientes com um peso médio de -1,23 e finalmente, as
unidades de uso sustentável foram as mais vulneráveis com um valor médio de -0,15.
Considerando os pesos de evidência em relação à distância euclidiana interna das áreas
protegidas, estes declinaram quando a distância euclidiana aumentou desde a borda interna da
área protegida. As áreas protegidas apresentaram um peso de evidência variando com a
distância interna delas, mais negativos quando a distância interna aumenta. Esses pesos de
evidência foram utilizados na modelagem do desmatamento de Lábrea elaborada do Capítulo
II. No Capítulo II, foram simulados oito cenários futuros de desmatamento da região de
Lábrea até 2040 com o modelo AGROECO. Dos dois grupos de cenários simulados, um não
considera a criação das áreas protegidas BAU-Business As Usual (ou Mesmo de Sempre) e
outro considera GOV-Governança. Dentro desses dois grupos de cenários foram considerados
quatro casos de simulação, incluindo: 1- pesos de evidência das áreas protegidas
homogeneamente distribuídos, 2- pesos de evidência das áreas protegidas gradualmente
distribuídos em relação à distância euclidiana interna da área protegida, 3- pesos de evidência
das áreas protegidas homogeneamente distribuídos e pesos específicos às áreas de
amortecimento, 4- pesos de evidência das áreas protegidas gradualmente distribuídos e pesos
específicos às áreas de amortecimento. A criação de áreas protegidas foi pouco eficiente em
conter desmatamento sendo que na maioria, os cenários do grupo GOV apresentaram em
2040, áreas de desmatamento acumulado levemente inferiores àquelas obtidas para os
cenários BAU. A utilização de pesos de evidência evoluindo com a distância euclidiana
interna da área protegida parece ser mais realista, reduzindo a influência de ocorrência de
desmatamento nas áreas mais distantes da borda das áreas protegidas. Quanto ao efeito
provocado pela consideração de pesos de evidência das áreas de entorno às áreas protegidas, foi constatado que o desmatamento aumentou dentro dos limites das áreas de entorno por
serem mais atrativas em termos de peso de evidência. No entanto, acredita-se que seja uma
conseqüência dos anos para os quais os dados de uso/cobertura da terra foram disponíveis
para calibrar o modelo, quando as áreas fora dos buffers das reservas já haviam sofrido muito
desmatamento. O cenário mais realista para o conjunto de dados, portanto, é considerado
aquele que usa pesos de evidência gradativamente distribuídos, mas que não usa pesos de
evidência específicos às áreas de buffers. No cenário GOV-2, o desmatamento foi reduzido na
área de estudo em 5,1 % (2.596 km 2 ) como resultado da criação das reservas, quando
comparado com o cenário correspondente da linha de base (BAU-2)
Soil organic carbon, carbon stock and their relationships to physical attributes under forest soils in Central Amazonia.
The soil carbon under Amazonian forests has an important roles in global changing, making information on the soil content and depths of these stocks are considerable interest in efforts to quantify soil carbon emissions to the atmosphere.This study quantified the content and soil organic carbon stock under primary forest up to 2 m depth, at different topographic positions, at Cuieiras Biological Reserve, Manaus/ ZF2, km 34, in the Central Amazon, evaluating the soil attributes that may influence the permanence of soil carbon. Soil samples were collected along a transect of 850 m on topographic gradient Oxisol (plateau), Ultisol (slope) and Spodosol (valley). The stocks of soil carbon were obtained by multiplying the carbon content, soil bulk density and trickiness of soil layers. The watershed was delimited by using STRM and IKONOS images and the carbon contend obtained in the transects was extrapolated as a way to evaluate the potential for carbon stocks in an area of 2678.68 ha. The total SOC was greater in Oxisol followed by Spodosol and Ultisol. It was found direct correlations between the SOC and soil physical attributes. Among the clay soils (Oxisol and Ultisol), the largest stocks of carbon were observed in Oxisol at both the transect (90 to 175.5 Mg C ha-1) as the level of watershed (100.2 to 195.2 Mg C ha-1). The carbon stocks under sandy soil (Spodosol) was greater to clay soils along the transect (160-241 Mg C ha-1) and near them in the Watershed (96.90 to 146.01 Mg C ha-1)
Reliability Analysis of In-person and Virtual Goniometric Measurements of the Upper Extremity
# Background
Virtual healthcare has forced clinicians to modify or eliminate parts of the musculoskeletal evaluation such as motion assessment. Although acceptable to excellent levels of in-person goniometric reliability is achievable, reliability of virtual assessments is unknown.
# Purpose
To determine if similar upper extremity goniometric measurements could be obtained in-person and virtually.
# Study Design
Reliability study; classroom setting
# Methods
Publicly recruited sample over 18 years of age with no upper extremity injuries. Each subject was tested in a standing position with dominant arm facing the clinicians to visualize the landmarks for goniometer placement. Flexion and extension of the shoulder, elbow and wrist were measured. Prior to performing in-person goniometric measurements for each joint, an image was captured of each pre-determined joint position using a mobile device with a camera. This image represented the screenshot on a virtual platform. Four clinicians performed in-person measurements twice during the same session on each subject. The following week clinicians measured virtual images using the same techniques. Inter-rater and intra-rater reliability were determined via intraclass correlation coefficients (ICC).
# Results
Inter-rater reliability for five of the six in-person (ICC≥0.81) and virtual measurements (ICC≥0.78 ) were classified as excellent. In-person wrist extension (ICC=0.60) and virtual wrist flexion (ICC=0.65) were classified as good. Intra-rater reliability for individual clinicians were between good and excellent for the in-person measurements (ICC:0.61-0.96) and virtual measurements (ICC:0.72-0.97). There were a greater number of excellent ICC values for the virtual measurements (90%) compared to in-person measurements (70%). There were statistically significant differences between in-person and virtual sessions for five of six measurements (p≤0.006). Only elbow extension did not differ between sessions (p=0.966).
# Conclusion
Virtual assessment compared to goniometric measurements showed good to excellent inter- and intra-rater reliabilities (ICC \> 0.60), which suggests clinicians can utilize goniometry either in person or on a virtual platform.
# Level of Evidence
3b
©The Author(s
Electrical conductivity of plasmas of DB white dwarf atmospheres
The static electrical conductivity of non-ideal, dense, partially ionized
helium plasma was calculated over a wide range of plasma parameters:
temperatures and mass density . Calculations of
electrical conductivity of plasma for the considered range of plasma parameters
are of interest for DB white dwarf atmospheres with effective temperatures
.
Electrical conductivity of plasma was calculated by using the modified random
phase approximation and semiclassical method, adapted for the case of dense,
partially ionized plasma. The results were compared with the unique existing
experimental data, including the results related to the region of dense
plasmas. In spite of low accuracy of the experimental data, the existing
agreement with them indicates that results obtained in this paper are correct
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