5,343 research outputs found
Possible effects of climate change on the early development of pea, broad bean, maize and sunflower in Mediterranean areas.
In Mediterranean-type climates crop yield depends strongly on the early development of individual plants. Extreme variations of soil temperature close to the surface of bare soils and fast changes of soil water content due to irregular rainfall and high evaporative demand reduce the success of germination, emergence and early leaf production, reducing crop productivity. According to IPCC Fourth Assesment report, climate change in Southern Europe “is projected to worsen hygrometric and thermal conditions (high temperature and drought) and to reduce water availability” and, consequently, to decrease general crop productivity.
The aim of this study was to evaluate the thermal conditions in the top soil layer under different climate change scenarios, and their effects on the early development of some representative crops of Mediterranean agriculture (pea, broad bean, maize and sunflower). For this purpose, soil temperatures near the surface of a Luvisol and a Vertisol during the usual sowing season of winter (October) and summer crops (April) were compared to those recorded in the air above ground, to forecast future values. The impact of simulations on the speed, size and dispersion of germination, emergence and early leaf production was estimated using values of bioclimatic parameters of the crops (cardinal temperatures and thermal times for different phases of establishment) found in the literature.
In both seasons, monthly mean temperatures at soil top layer were significantly greater (*P<0.05) than those found in the air above ground. However, the relationships between air and top soil temperatures were different in both soils and in both seasons. Summer crops seem to be less affected by an increase in temperature than winter crops. Otherwise, the former seem to be more affected by a decrease in soil water availability than the later. In addition, final emergence, speed of emergence and leaf production of the different species will be more affected by global warming than the dispersion around the most likely thermal times. The magnitude of these effects depends also on the magnitude of warming
Litter layer influence on the thermal regime of a sandy soil under a pine forest in mediterranean Portugal
Decomposition of needle litter is a relevant process in applied ecology, namely in the nutrient dynamics of forested ecosystems. Soil temperature strongly influences soil microbian activity.
Temperature profiles of a sandy soil (Haplic Podzol) under a pine forest were measured at several depths down to 16 cm, with and without litter layer. Daily cycles were analysed by means of Fourier series. Daily cycles were studied based on data from four days defined according to soil water content.
The daily periodic variations of soil temperature follow closely the time-course of solar irradiance. Daily course of soil temperature is generally well described by the two first Fourier harmonics. The litter layer acts as a thermal insulator, reducing soil temperature gradients and amplitudes and increasing damping depth, particularly in dry soil
Leaf area expansion and dry matter accumulation during establishment of broad bean and sorghum at different temperatures and soil water contents in two types of soil in mediterranean Portugal
Crop establishment is a major factor determining crop productivity in the field and is strongly controlled by soil temperature and soil moisture. Fast leaf expansion and dry matter accumulation during crop establishment are required for an adequate establishment.
Leaf area expansion and accumulation of dry matter during the establishment of broad bean (Vicia faba L.) and sorghum (Sorghum vulgare L.) were studied at different soil temperatures and soil moisture contents in a Vertisol (Lisboa) and a Luvisol (Évora) from November 1993 to November 1996. Soil temperature was measured at 2 and 4 cm depth with thermocouples, air temperature was measured with a ventilated psychrometer and soil moisture was measured using the gravimetric method. Leaf area was estimated non-destructively. Above ground seedling dry matter was weighed after oven drying at 65ºC. Data analysis was based on the thermal time concept.
For each crop no significant differences were found on leaf area at establishment in both soils under favourable water conditions, but significant differences were found on seedling dry matter. In moist soils, leaf area of both species increased linearly with accumulated temperature and dry matter increased exponentially with accumulated temperature.
Low soil water during establishment reduced leaf expansion and dry matter accumulation of both crops, mainly if it occurred before seedling emergence. In mediterranean type climates meteorological extremes of low rainfall associated to high temperatures are expected to be more frequent on the wake of global climate change, reducing crop establishment and productivity
Considering Human Aspects on Strategies for Designing and Managing Distributed Human Computation
A human computation system can be viewed as a distributed system in which the
processors are humans, called workers. Such systems harness the cognitive power
of a group of workers connected to the Internet to execute relatively simple
tasks, whose solutions, once grouped, solve a problem that systems equipped
with only machines could not solve satisfactorily. Examples of such systems are
Amazon Mechanical Turk and the Zooniverse platform. A human computation
application comprises a group of tasks, each of them can be performed by one
worker. Tasks might have dependencies among each other. In this study, we
propose a theoretical framework to analyze such type of application from a
distributed systems point of view. Our framework is established on three
dimensions that represent different perspectives in which human computation
applications can be approached: quality-of-service requirements, design and
management strategies, and human aspects. By using this framework, we review
human computation in the perspective of programmers seeking to improve the
design of human computation applications and managers seeking to increase the
effectiveness of human computation infrastructures in running such
applications. In doing so, besides integrating and organizing what has been
done in this direction, we also put into perspective the fact that the human
aspects of the workers in such systems introduce new challenges in terms of,
for example, task assignment, dependency management, and fault prevention and
tolerance. We discuss how they are related to distributed systems and other
areas of knowledge.Comment: 3 figures, 1 tabl
Effects of Irrigation and Tree Spacing on Soil and Air Temperature Profiles of Olive Orchards
Changes on the climate of the boundary layer occur when a vegetation cover
above a bare soil is introduced, namely on temperatures and humidity profiles,
above and under soil surface. Since air and soil temperatures affect crop growth and
development and also soil moisture, they have been used as driving variables in
numerous crop growth and development models as well as in those referred to soil
mineralization, evaporation, transpiration, etc. The aim of this work was to evaluate
(a) the soil thermal behavior in two olive orchards (Olea europaea sp. europaea),
both grown on soils with little profile development (Regosol and Cambisol) and
subject to drip irrigation but with different spacing between trees, and (b) the air
thermal profile over olive rows. Experiments were performed from April to June
2012 in Southern Portugal. Soil and air temperatures were measured by
thermocouples. The two orchards changed spatial distribution of soil surface
temperature, soil temperature profiles and air temperature within the canopy, either
on a daily or hourly basis. Olive tree spacing and irrigation affected both the soil
thermal behavior and air thermal profiles. Tree spacing affected the horizontal
gradients established along the interrows (intensity and rhythm). Irrigation reduced
hourly and daily mean soil surface temperatures and daily thermal amplitudes of
both profiles. Differences were also found on damping depths of the thermal wave
estimated for the driest and the wettest profiles. Along the row, the effect of shading
seems to overlap that of irrigation in a hourly basis
The Montado agroforestry system microclimatic specificity in the context of global change
The effects of oak trees on microclimatic
parameters in Quercus rotundifolia Lam. woodland in the
Alentejo, Southern Portugal, are reported. Results show that
oak tree create a marked differentiation in the grass matrix,
between open and undercanopy areas. Compared to open
areas, it presents lower soil moisture beneath the oak canopy,
lower soil temperatures and lower photosynthetically active
radiation (PAR). Soil temperatures outside trees canopy
were generally higher than undercanopy areas, reaching
twice its values during the winter. The decrease of soil water
content is more rapid in areas outside the trees canopy
action, but the replenishment starts early and is faster in
those areas. PAR intercepted by tree canopy is greater than
60%, and affects dramatically herbaceous production.
Different climatic conditions due to the presence of the tree,
associated with greater variability in chemistry environment
undercanopy, if combined with the IPCC forecasts for
Mediterranean region, pose new challenges in the
management of the montado areas
Controlo de qualidade dos dados de posicionamento em reflexão sísmica de muito alta resolução
The quality control is a very important operation in the seismic data acquisition
surveys and its main goals are to assess the quality of the acquired data, to
detect problems during acquisition and finally to guarantee that the data has the
required quality to be accepted for further processing, or if it must be rejected.
The time spent in operations makes its cost to grow up and therefore the QC
must be done efficiently and as early as possible., It is critical that the most
relevant factors that can seriously compromise the data are evaluated onboard.
Navigation quality control is extremely important because the navigation errors
can contribute to the feathering effect that by itself is one of the main rejections
criteria. On the other hand, the quality of the positioning data can have strong
influence on the seismic resolution, as it is used to calculate positioning for every
reflection point. Thus, wrong positioning data affect offsets computing and can
move the reflection midpoints to erroneous position causing a discrepancy
between the actual geology and the seismic section obtained. This causes errors
in the exact location of boulders and the identification of other in-depth hazards
that threat the optimization of wind turbine installations, which is one of
Geosurveys goals in this type of surveys.
The main sources of these problems are related to the bad functioning of GPS
antennas used in the acquisition system and other systematic problems such as
geometry assignment. There are typical errors which affect the geometry such
as distance measurement between lead buoy center and first channel, distance
measurements and assignment between channels in the different streamer
sections. The solution proposed in this work consists on the development of
effective methods to diagnose these types of problems, where through a
graphical scheme it becomes possible to detect different types of positioning
errors and their causes.
The method developed in the scope of this work was based on the quality control
of the offsets calculated with the positioning data and the direct arrivals time.
With this information it was possible to establish a classification criterion for the
positioning data according to its quality, to calculate the errors and obtain
indicators about its source of error, always considering that the various factors
have different influences on the errors and some problems appear more
frequently than others. Based on this, rejection criteria for data with positioning
errors was established and solutions were tested in the software packages
RadExPro and Kingdom Suite, in order to evaluate the effect of these errors on
the seismic volumes.O controle de qualidade é uma operação muito importante durante as
campanhas de aquisição de dados sísmicos. Tem como objetivo avaliar a
qualidade dos dados adquiridos, detetar problemas ocorridos durante a
aquisição, e finalmente assegurar que os dados têm a qualidade necessária
para serem aceites ou se devem ser rejeitados. O tempo de operação tem
consequências diretas sobre os custos e, por esta razão, esta é uma operação
que deve ser feita rapidamente. Assim, devem ser avaliados os fatores mais
relevantes que podem comprometer seriamente a qualidade dos dados.
O controle de qualidade da navegação é de extrema importância, visto que os
erros de navegação contribuem para o feathering, que por sua vez constitui um
dos principais critérios de rejeição. Por outro lado, a qualidade da navegação ou
dos dados de posicionamento pode afetar fortemente a resolução sísmica pelo
facto de serem usados para a determinação das posições das reflexões. Assim,
dados de posicionamentos errados afetam os cálculos dos offsets e podem
deslocar os pontos médios de reflexões para posições erradas, provocando uma
discrepância entre a geologia real e a secção sísmica obtida. Deste modo, fica
mais difícil a localização exata de blocos rochosos e a identificação de outros
perigos em profundidade que colocam em risco a otimização das instalações
das turbinas eólicas, trabalhos que a Geosurveys tem vindo a realizar.
As principais causas na origem destes problemas estão relacionadas com o mau
funcionamento das antenas GPS usadas no sistema de aquisição, e outros
problemas sistemáticos, como a atribuição de geometria. Existem erros típicos
que afetam a geometria, tais como o erro na medição da distância entre o centro
da antena da lead buoy e o primeiro canal, e erros na medição e atribuição das
distâncias entre canais para as diferentes secções dos streamers. A solução
proposta neste trabalho passou pelo desenvolvimento de métodos eficientes
para diagnóstico destes tipos de problemas, onde através de padrões gráficos
se torna possível detetar diferentes tipos de erros de posicionamentos e as
respetivas causas.
O método desenvolvido baseou-se no controle de qualidade dos offsets
calculados com os dados de posicionamento e no tempo de chegada das ondas
diretas. Com essas duas informações foi possível estabelecer um critério de
classificação dos dados de posicionamento quanto à sua qualidade, calcular os
erros e obter indícios sobre a sua origem, levando sempre em consideração que
os vários fatores têm diferentes influências sobre os erros e que alguns
problemas são mais frequentes que outros. Com base neste procedimento,
foram estabelecidos critérios de rejeição de dados com erros de
posicionamento. As soluções obtidas foram testadas no software RadExPro e
Kingdom Suite de modo a avaliar o efeito que esses erros têm sobre a sísmica.Mestrado em Engenharia Geológic
Identificação eletrónica, assinatura e serviço de confiança
A generalização do uso de comunicações eletrónicas em todas as esferas das atividades humanas traz a necessidade de uma nova perspetiva legal. Esta necessidade é particularmente sentida a nível da União Europeia com o objetivo assumido de construir um mercado digital único e fiável. O Regulamento 910/2014 foi estabelecido como o principal quadro jurídico europeu destinado a harmonizar o entendimento de instrumentos como identificação eletrónica, autenticação eletrónica, serviços eletrónicos e também outros serviços de confiança da sociedade de informação, como selos eletrónicos, carimbos, serviços de entrega registrada eletrónica e autenticação de sites. No seu conjunto, o Regulamento 910/2014 visa estabelecer um quadro jurídico comum que permitisse aos cidadãos europeus tirarem pleno partido dos serviços digitais num ambiente técnica e juridicamente seguro.The generalization of the use of electronic communications in all spheres of human activities brings along a need for a new legal perspective. This need is particularly felt at European Union level with the assumed aim of building a trustable Digital Single Market. Regulation 910/2014 was set as the main European legal framework aimed at harmonizing the understanding of instruments such as electronic identification, electronic authentication, electronic services, and other trust services of information society, such as electronic seals, electronic time stamps, electronic registered delivery services and website authentication. In the whole, Regulation 910/2014 is intended to establish a common legal framework allowing European citizens to take full advantage of digital services in a technically and legally secure environment
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