5,628 research outputs found
Greenhouse technology for sustainable production in mild winter climate areas: Trends and needs
Greenhouse production in the near future will need to reduce significantly its environmental impact. For this purpose, elements such as the structure, glazing materials, climate equipments and controls have to be developed and wisely managed to reduce the dependence on fossil fuels, achieve maximum use of natural resources such as solar radiation and water, and minimize the input of chemicals and fertilizers. This paper discusses the most relevant developments in greenhouse technology for mild winter climates. Regarding greenhouse structures, recent studies based on computational fluid dynamics have been conducted to investigate the effect of parameters such as ventilator size and arrangement, roof slope and greenhouse width and height on the air exchange rate. Next generation greenhouses are expected to incorporate some of the innovations derived from recent ventilation studies. Covering crops with screens is becoming a common practice. Main advantages and limitations of screenhouses are discussed in this paper. Thermal storage is increasingly applied in closed or semi-closed greenhouses. Under some conditions semi-closed greenhouses could mitigate day/night while reducing the use of water and the entrance of pest. Photo selective films that reflect a fraction of NIR radiation are effective at lowering greenhouse temperature and, in some cases, may be cost effective. NIR reflective films have side effects of major importance in greenhouse production. The CO2 enrichment strategy in computer-controlled greenhouses is based on determining the benefits of increasing the CO2 concentration against the cost of it. No clear strategies have been defined for the application of CO2 in unheated greenhouses, where most of the time the source of carbon dioxide is the external air. Some authors suggest ventilating as little as possible and fertilizing with bottled carbon dioxide at least up to the external concentration. Improving greenhouses by introducing new technologies may have an additional impact on the environment. From an environmental point of view, the incorporation of technology needs to increase yield to compensate for its associated environmental burden. Previous results have shown that forced ventilation and heating are the main reasons for the increase in environmental impact in climate controlled greenhouses. Additional results on the area of technology and its associated impact are discussed in this pape
Non-monotonic entanglement of physical EM field states in non-inertial frames
We develop a general technique to analyse the quantum effects of acceleration
on realistic spatially-localised electromagnetic field states entangled in the
polarization degree of freedom. We show that for this setting, quantum
entanglement may build up as the acceleration increases, providing a clear
signature of the quantum effects of relativistic acceleration.Comment: 5 pages, 3 figure
Greenhouse engineering: New technologies and approaches
Firstly, this article discusses the greenhouse engineering situation in three geographic areas which are relevant in the field of protected cultivation: Northern Asia, The Netherlands and the Mediterranean. For each area, the prevailing greenhouse type and equipment is briefly described. Secondly, the main technological constraints are pointed out and finally the research directions are discussed. For all areas under consideration, attempts to design more efficient greenhouse systems are under way. In Northern Asia progress is being made towards the optimisation of greenhouses as a solar collector and to the development of new heating strategies. Important subjects addressed in The Netherlands are energy conservation and the replacement or alleviation of human labour by increasing mechanisation. In the Mediterranean there is growing interest in semi-closed greenhouses with CO2 enrichment and control of excessive humidity. All geographic areas share the need of having an optimised climate control based on the crop response to the greenhouse environment. All areas also share the requirement of being respectful to the environment, therefore future greenhouses are expected to use engineering to produce with minimal or zero emissions
Patologías en edificaciones con grado de protección 1 en la zona a del centro histórico urbano de Cienfuegos
La investigación ofrece resultados científicos sobre el estudio de las patologías que afectan las obras de fabrica en la zona A del Centro Histórico urbano de la ciudad de Cienfuegos, analiza una muestra de quince edificaciones de valor patrimonial con grado de protección 1, aplicando una metodología para el estudio de esta problemática adaptándola a las características de estas edificaciones con alto grado de protección.
El presente trabajo utiliza metodologías científicamente confiables para el estudio del problema adecuándola a la condicionante de que se está en presencia de obras de fábrica de edificaciones de alto grado de protección de sus valores patrimoniales.
La muestra estudiada es representativa de las edificaciones con alto grado de protección, en esta zona A del Centro Histórico de la ciudad objeto de estudio. A partir de la muestra intencional, definida por interés de la Oficina del Conservador de la ciudad, se desarrolla el proceso de análisis diagnostico y recomendaciones para el tratamiento de las patologías detectadas, representa un 44,5 % del total de edificaciones con grado de protección 1 en esta zona A. Se enumeran en cada caso las afectaciones que tienen los edificios, arribando a conclusiones sobre las patologías que afectan las obras de fábrica en este lugar
Thirty Femtograms Detection of Iron in Mammalian Cells
Inorganic nanomaterials and particles with enhanced optical, mechanical or
magnetic attributes are currently being developed for a wide range of
applications. Safety issues have been formulated however concerning their
potential cyto- and genotoxicity. For in vivo and in vitro experimentations,
recent developments have heightened the need of simple and facile methods to
measure the amount of nanoparticles taken up by cells or tissues. In this work,
we present a rapid and highly sensitive method for quantifying the uptake of
iron oxide nanoparticles in mammalian cells. Our approach exploits the
digestion of incubated cells with concentrated hydrochloric acid reactant and a
colorimetric based UV-Visible absorption technique. The technique allows the
detection of iron in cells over 4 decades in masses, from 0.03 to 300 picograms
per cell. Applied on particles of different surface chemistry and sizes, the
protocol demonstrates that the coating is the key parameter in the
nanoparticle/cell interactions. The data are corroborated by scanning and
transmission electron microscopy and stress the importance of resiliently
adsorbed nanoparticles at the plasma membrane.Comment: 18 pages, 6 figure
Hydrodynamic Character of the Non-equipartition of Kinetic Energy in Binary Granular Gases
The influence of the heating mechanism on the kinetic energy densities of the
components of a vibrated granular mixture is investigated. Collisions of the
particles with the vibrating wall are inelastic and characterized by two
coefficients of normal restitution, one for each of the two species. By means
of molecular dynamics simulations, it is shown that the non-equipartition of
kinetic energy is not affected by the differential mechanism of energy
injection, aside the usual boundary layer around the wall. The macroscopic
state of the mixture in the bulk is defined by intensive variables that do not
include the partial granular temperatures of the components
Composition and Self-Adaptation of Service-Based Systems with Feature Models
The adoption of mechanisms for reusing software in pervasive systems has not yet become standard practice. This is because the use of pre-existing software requires the selection, composition and adaptation of prefabricated software parts, as well as the management of some complex problems such as guaranteeing high levels of efficiency and safety in critical domains. In addition to the wide variety of services, pervasive systems are composed of many networked heterogeneous devices with embedded software. In this work, we promote the safe reuse of services in service-based systems using two complementary technologies, Service-Oriented Architecture and Software Product Lines. In order to do this, we extend both the service discovery and composition processes defined in the DAMASCo framework, which currently does not deal with the service variability that constitutes pervasive systems. We use feature models to represent the variability and to self-adapt the services during the composition in a safe way taking context changes into consideration. We illustrate our proposal with a case study related to the driving domain of an Intelligent Transportation System, handling the context information of the environment.Work partially supported by the projects TIN2008-05932,
TIN2008-01942, TIN2012-35669, TIN2012-34840 and CSD2007-0004 funded by
Spanish Ministry of Economy and Competitiveness and FEDER; P09-TIC-05231 and
P11-TIC-7659 funded by Andalusian Government; and FP7-317731 funded by EU. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec
In vitro toxicity of nanoceria: effect of coating and stability in biofluids
Due to the increasing use of nanometric cerium oxide in applications,
concerns about the toxicity of these particles have been raised and have
resulted in a large number of investigations. We report here on the
interactions between 7 nm anionically charged cerium oxide particles and living
mammalian cells. By a modification of the particle coating including
low-molecular weight ligands and polymers, two generic behaviors are compared:
particles coated with citrate ions that precipitate in biofluids and particles
coated with poly(acrylic acid) that are stable and remain nanometric. We find
that nanoceria covered with both coating agents are taken up by mouse
fibroblasts and localized into membrane-bound compartments. However, flow
cytometry and electron microscopy reveal that as a result of their
precipitation, citrate-coated particles interact more strongly with cells. At
cerium concentration above 1 mM, only citrate-coated nanoceria (and not
particles coated with poly(acrylic acid)) display toxicity and moderate
genotoxicity. The results demonstrate that the control of the surface chemistry
of the particles and its ability to prevent aggregation can affect the toxicity
of nanomaterials.Comment: 33 pages 10 figures, accepted at Nanotoxicolog
The influence of individual characteristics on getting involved in an entrepreneurial team: The contingent role of individualism
A traditional stereotype of the entrepreneur is that of a lone hero. However, many entrepreneurs engage in new businesses as members of entrepreneurial teams. These teams usually perform better in terms of employment generation, innovation, and profits. Thus, a relevant question is why some individuals get involved in entrepreneurship through a team rather than alone. Our explanation is focused on two variables related to the entrepreneur''s human capital: their educational level and their intrapreneurial experience. There are conflicting arguments on how these variables lead an entrepreneur to join a team, and we argue that the degree of individualism of the society helps us understand the discrepancies. We use a sample of 66, 716 early-stage entrepreneurs from 66 countries surveyed by the Global Entrepreneurship Monitor between 2014 and 2017. Our results show that entrepreneurs with higher levels of education and intrapreneurial experience are more likely to be involved in the entrepreneurship process as members of teams. However, the effect of educational level is less pronounced in individualist contexts. In addition, we find that the motivation to enter entrepreneurship partially mediates these relationships, as individuals endowed with higher human capital are likely to enter entrepreneurship driven by an opportunistic motivation, which in turns makes them likely to need or join teams to reach their goals
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