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

A supersymmetric 3-3-1 model

We build the complete supersymmetric version of a 3-3-1 gauge model using the superfield formalism. We point out that a discrete symmetry, similar to the R-symmetry in the minimal supersymmetric standard model, is possible to be defined in this model. Hence we have both R-conserving and R-violating possibilities. Analysis of the mass spectrum of the neutral real scalar fields shown that in this model the lightest scalar Higgs has a mass upper limit, and at the tree level it is 124.5 GeV for a given illustrative set of parameters.Comment: RevTex, extended and revised version, 20 pages, one eps figur

Left-right asymmetries and exotic vector-boson discovery in lepton-lepton colliders

By considering left-right (L-R) asymmetries we study the capabilities of lepton colliders in searching for new exotic vector bosons. Specifically we study the effect of a doubly charged bilepton boson and an extra neutral vector boson appearing in a 3-3-1 model on the L-R asymmetries for the processes $e^-e^-\to e^-e^-$, $\mu^-\mu^-\to\mu^-\mu^-$ and $e^-\mu^-\to e^-\mu^-$ and show that these asymmetries are very sensitive to these new contributions and that they are in fact powerful tools for discovery this sort of vector bosons.Comment: RevTeX, 22 pages, 12 eps figure

FCNC in the minimal 3-3-1 model revisited

We show that in the minimal 3-3-1 model the flavor changing neutral currents (FCNCs) do not impose necessarily strong constraints on the mass of the $Z^\prime$ of the model if we also consider the neutral scalar contributions to such processes, like the neutral mesons mass difference and rare semileptonic decays. We first obtain numerical values for all the mixing matrices of the model i.e., the unitary matrices that rotate the left- and right-handed quarks in each charge sector which give the correct mass of all the quarks and the CKM mixing matrix. Then, we find that there is a range of parameters in which the neutral scalar contributions to these processes may interfere with those of the $Z^\prime$, implying this vector boson may be lighter than it has been thought.Comment: Extended version including the effect of a pseudoscalar. 37 pags. and 12 figures. New references added. Version matches the published versio

Concerning CP violation in 331 models

We consider the implementation of CP violation in the context of 331 models. In particular we treat a model where only three scalar triplets are needed in order to give all fermions a mass while keeping neutrino massless. In this case all CP violation is provided by the scalar sector.Comment: Revtex, 5 pages, no figures. Talk given by O. Ravinez at the 7th Workshop on Particles and Fields, Morelia, Mexico, 21-27 Nov 1997; typos correcte

Neutrinoless double beta decay with and without Majoron-like boson emission in a 3-3-1 model

We consider the contributions to the neutrinoless double beta decays in a $SU(3)_L\otimes U(1)_N$ electroweak model. We show that for a range of the parameters in the model there are diagrams involving vector-vector-scalar and trilinear scalar couplings which can be potentially as contributing as the light massive Majorana neutrino exchange one. We use these contributions to obtain constraints upon some mass scales of the model, like the masses of the new charged vector and scalar bosons. We also consider briefly the decay in which besides the two electrons a Majoron-like boson is emitted.Comment: Revtex, 10 pages and 8 eps figures. Extended version to be published in Physical Review