Plastic nets in agriculture ; a general review of types and applications

At the moment, there are a large number of agricultural net types on the market characterized by different structural features such as type of material, type and dimensions of threads, texture, mesh size, porosity / solidity and weight; by radiometric properties like color, transmissivity/reflectivity/shading factor; by physical properties like air permeability and several mechanical characteristics such as tensile stress, strength, elongation at break, and durability. Protection from hail, wind, snow, or strong rainfall in fruit-farming and ornamentals, shading nets for greenhouses and nets moderately modifying the microenvironment for a crop are the most common applications. A systematic review of the current state-of-the-art of structural parameters, standard and regulations, most common agricultural net applications, and their supporting structures has been developed by means of a literature study, technical investigations, concerning characteristics and use of nets. As a result, the survey highlighted that in many cases different, not even similar, net types were adopted for the same application and the same cultivations by various growers. Results show that neither growers nor net producers have clear ideas about the relationship between the net typology optimization for a specific application and the construction parameters of the net. The choice often depends on empirical or economic criteria and not on scientific considerations. Moreover, it appears that scientifically justified technical requirements for nets used in specific agricultural applications have not been established yet

Thermodynamic Behavior of a Model Covalent Material Described by the Environment-Dependent Interatomic Potential

Using molecular dynamics simulations we study the thermodynamic behavior of a single-component covalent material described by the recently proposed Environment-Dependent Interatomic Potential (EDIP). The parameterization of EDIP for silicon exhibits a range of unusual properties typically found in more complex materials, such as the existence of two structurally distinct disordered phases, a density decrease upon melting of the low-temperature amorphous phase, and negative thermal expansion coefficients for both the crystal (at high temperatures) and the amorphous phase (at all temperatures). Structural differences between the two disordered phases also lead to a first-order transition between them, which suggests the existence of a second critical point, as is believed to exist for amorphous forms of frozen water. For EDIP-Si, however, the unusual behavior is associated not only with the open nature of tetrahedral bonding but also with a competition between four-fold (covalent) and five-fold (metallic) coordination. The unusual behavior of the model and its unique ability to simulation the liquid/amorphous transition on molecular-dynamics time scales make it a suitable prototype for fundamental studies of anomalous thermodynamics in disordeered systems.Comment: 48 pages (double-spaced), 13 figure

Economic and environmental analysis of energy efficiency measures in agriculture. Case Studies and trade offs.

This report is the result of the collaboration of the partners of the AGREE work-package “Economic and environmental analysis”, which is based on case study analyses of the partners in seven countries of the EU. The case studies show economic and environmental trade-offs in the different regions in the EU, for which each partner is responsible. Nevertheless prior to the reporting of the case studies an intensive discussion on a common methodological approach has been accomplished and applied to the case studies. The case studies show a wide range of different perspectives of energy efficiency in agriculture, but they are all based on the common methodology presented in Chapter 3. In Chapter 4, the case studies are presented, with authors indicated at the beginning of each section. Each section of Chapter 4 ends with a synthesis analysis of the results from the different case studies. Chapter 5 summarizes and concludes the report by highlighting the major findings of the analyses. The report builds upon the “State of the Art in Energy Efficiency in Europe” published separately by the AGREE consortium (Gołaszewski et al. 2012), which shows the status quo of energy use and possible energy efficiency measures in agriculture across different production systems and regions in Europe. This report presents an economic and environmental analysis based on in-depth case studies which show the potential for, and constraints on, energy efficiency measures in agriculture with respect to the specific environments in Europe

Activation of tumor suppressor LKB1 by honokiol abrogates cancer stem-like phenotype in breast cancer via inhibition of oncogenic Stat3

Tumor suppressor and upstream master kinase Liver kinase B1 (LKB1) plays a significant role in suppressing cancer growth and metastatic progression. We show that low-LKB1 expression significantly correlates with poor survival outcome in breast cancer. In line with this observation, loss-of-LKB1 rendered breast cancer cells highly migratory and invasive, attaining cancer stem cell-like phenotype. Accordingly, LKB1-null breast cancer cells exhibited an increased ability to form mammospheres and elevated expression of pluripotency-factors (Oct4, Nanog and Sox2), properties also observed in spontaneous tumors in Lkb1-/- mice. Conversely, LKB1-overexpression in LKB1-null cells abrogated invasion, migration and mammosphere-formation. Honokiol (HNK), a bioactive molecule from Magnolia grandiflora increased LKB1 expression, inhibited individual cell-motility and abrogated the stem-like phenotype of breast cancer cells by reducing the formation of mammosphere, expression of pluripotency-factors and aldehyde dehydrogenase activity. LKB1, and its substrate, AMP-dependent protein kinase (AMPK) are important for HNK-mediated inhibition of pluripotency factors since LKB1-silencing and AMPK-inhibition abrogated, while LKB1-overexpression and AMPK-activation potentiated HNK's effects. Mechanistic studies showed that HNK inhibited Stat3-phosphorylation/activation in an LKB1-dependent manner, preventing its recruitment to canonical binding-sites in the promoters of Nanog, Oct4 and Sox2. Thus, inhibition of the coactivation-function of Stat3 resulted in suppression of expression of pluripotency factors. Further, we showed that HNK inhibited breast tumorigenesis in mice in an LKB1-dependent manner. Molecular analyses of HNK-treated xenografts corroborated our in vitro mechanistic findings. Collectively, these results present the first in vitro and in vivo evidence to support crosstalk between LKB1, Stat3 and pluripotency factors in breast cancer and effective anticancer modulation of this axis with HNK treatment

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference

Briassoulis D. Numerical estimation of the internal and external aerodynamic coefficients of a tunnel greenhouse structure with openings. Comput Electron Agric

Abstract The external and internal aerodynamic coefficients on a tunnel (vaulted-roof) structure with openings are numerically calculated in the case of a transverse wind, using the Finite Element method. Ventilation configurations involving (a) both side symmetrical openings; and (b) only a leeward opening have been studied. The numerical results show that the external aerodynamic coefficients are only weakly influenced by the position or the size of the openings. On the contrary, the internal aerodynamic coefficients, and so the total wind pressures on the structure, strongly depend on the ventilation opening configuration. These results are compared with the relevant provisions of prEN13031-1 European standard and the Eurocode-1 and may provide support to future revisions of the codes within the normal standardisation activities. © 2002 Elsevier Science B.V. All rights reserved

Windloads on net covered structures

Agricultural plastic nets are popular materials for constructing crop protecting structures against natural or biological hazards such as hail, wind, or insects and birds. However existing design standards do not provide a methodology for the calculation of wind loads on structures with permeable cladding. Computational Fluid Dynamics (CFD) simulations provide a cheap and easy to use alternative to full-scale or wind tunnel experiments for analysing the wind generated pressure distribution around net-covered structures. In these simulations the permeable cladding is treated as a porous material. In this way, aerodynamic force coefficients are numerically estimated for structures covered with nets of various air permeability characteristics. In the present paper the aerodynamic coefficients of three typical designs used for supporting agricultural nets for various applications have been numerically calculated. In particular the following structures have been studied: a) duo-pitch anti-hail canopy roof, b) vaulted roof anti-insect house, and c) flat roof shading house. The numerical results were compared against the provisions of the Eurocode-1-1-4 for the corresponding impermeable structures

Air flow through net covered arched structures

Permeable coverings facilitate indoor ventilation due to their porosity, the characteristics of the air flow passing through a net depends on the Reynolds number of the system. So far, only the permeability of nets used in application involving low Reynolds numbers have been studied, while the behaviour of nets at high Reynolds numbers, has been poorly studied. The ventilation of a net covered tunnel was numerically and experimentally studied analysing the airflow around and through the structure. The airflow through a two-dimensional tunnel structure (8.0 m wide and 2.5 m high) covered with various nets was numerically calculated by Computational Fluid Dynamics (CFD) simulations. A full scale tunnel structure, of the same geometry, covered with four different nets, characterised by different porosity, was built in order to validate the numerical CFD results. Wind velocity was measured outside and inside the structure by means of two handheld rotary cup anemometers. Data were gathered in the middle of each sector in order to avoid edge effects. The estimation of the indoor/outdoor air velocity reduction ratio shows a good agreement between measured and calculated values, especially for nets with a medium-low solidity ratio. For low solidity ratios the numerical results overestimate the indoor air velocity. Moreover the full scale measurements confirm the dependence of the “a” factor in the Forchheimer equation with the characteristics of the net