José M. Gonçalves

The structure and stability of molecular cloud cores in external radiation fields

We have considered the thermal equilibrium in pre-protostellar cores in the approximation where the dust tempera- ture is independent of interactions with the gas and where the gas is heated both by collisions with dust grains and ionization by cosmic rays. We have then used these results to study the stability of cores in hydrostatic equilibrium in the limit where thermal pressure dominates over magnetic field and turbulence. We compare the density distribution derived in this manner with results obtained in the isothermal case. We find that for cores with characteristics similar to those observed in nearby molecular clouds, the gas and dust temperatures are coupled in the core interior with densities above ∼3×10 4 cm −3 . As a consequence, one expects that the gas temperature like the dust temperature decreases towards the center of these objects. However, the regime where gas and dust temperatures are coupled coincides approximately with that in which CO and many other molecular species deplete onto dust grain surfaces. At larger radii and lower densities, the gas and dust temperatures decouple and the gas temperature tends to the value expected for cosmic ray heating alone. The density structure which one computes taking into account such deviations from isothermality are not greatly different from that expected for an isothermal Bonnor-Ebert sphere. It is impossi- ble in the framework of these models to have a stable equilibrium core with mass above ∼5 Mand column density compatible with observed values (NH > 2 × 10 22 cm −2 or AV > 10 mag). We conclude from this that observed high mass cores are either supported by magnetic field or turbulence or are already in a state of collapse. Lower mass cores on the other hand have stable states where thermal pressure alone provides support against gravitation and we conclude that the much studied object B68 may be in a state of stable equilibrium if the internal gas temperature is computed in self-consistent fashion. Finally we note that in molecular clouds such as Ophiuchus and Orion with high radiation fields and pressures, gas and dust temperatures are expected to be well coupled and hence in the absence of an internal heat source, one expects temperatures to decrease towards core centers and to be relatively high as compared to low pressure clouds like Taurus.

Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A

Context. Magnetic fields are believed to play a crucial role in the process of star formation. Aims. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores. Methods. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response. Results. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 M� ,o f age 9× 10 4 yr, formed in a cloud with an initial mass-to-flux ratio ∼2 times the critical value. Conclusions. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields control the evolution and collapse of the molecular cloud cores from which stars form.

Decision Support System for Surface Irrigation Design

The SADREG decision support system was developed to help decision makers in the process of design and selection of farm surface irrigation systems to respond to requirements of modernization of surface irrigation—furrow, basin, and border irrigation. It includes a database, simulation models, user-friendly interfaces, and multicriteria analysis models. SADREG is comprised of two components: design and selection. The first component applies database information, and through several simulation and computational tools, produces a set of design alternatives in agreement with the user options. These alternatives are characterized by several hydraulic, economic, and environmental indicators that allow appropriate selection and ranking. The selection component bases upon multicriteria analysis using composite programming and ELECTRE II ranking models, which support the decision maker to select the best alternative. The decision maker participates in all decision processes through a user-friendly interface that a...

Polarized dust emission of magnetized molecular cloud cores

We compute polarization maps for molecular cloud cores modeled as magnetized singular isothermal toroids, under the assumption that the emitting dust grains are aspherical and aligned with the large-scale magnetic field. We show that, depending on the inclination of the toroid with the line-of-sight, the bending of the magnetic field lines resulting from the need to counteract the inward pull of gravity naturally produces a depolarization effect toward the centre of the map. We compute the decrease of polarization degree with increasing intensity for different viewing angles and frequencies, and we show that an outward increasing temperature gradient, as expected in starless cores heated by the external radiation field, enhances the decrease of polarization. We compare our results with recent observations, and we conclude that this geometrical effect, together with other mechanisms of depolarization, may significantly contribute to the decrease of polarization degrees with intensity observed in the majority of molecular cloud cores. Finally, we consider the dependence of the polarization degree on the dust temperature gradient predicted for externally heated clouds, and we briefly comment on the limits of the Chandrasekhar-Fermi formula to estimate the magnetic field strength in molecular cloud cores.

Analysis of irrigation efficiency and water use efficiency of border irrigation.

The successful worldwide cultivation of hexaploid wheat in a diverse range of environments is because of, in part, breeding and selection for appropriate heading date. To adjust and fine-tune the heading time of hexaploid wheat to particular geographical regions and specific environment within these, there is an urgent need to evaluate and use alternative alleles for heading time. Aegilops tauschii, the donor species of D-genome of hexaploid wheat, has a wide geographic distribution. The present study revealed a wide variation for heading time among 56 Ae. tauschii accessions. All the accessions with short heading dates belonged to the ssp. tauschii, whereas most of ssp. strangulata accessions showed very long heading date. The heading date was also related to distribution of this species. The monotelosomic and monosomic analysis of a synthetic hexaploid wheat showed that chromosome 2D derived from ssp. tauschii accession AS60 had a major effect on promoting heading time with a reduction of more than 5 days. It is postulated that this Ae. tauschii genotype possess the allele Ppd-Dt1 responsible for the insensitivity to photoperiod. This allele is probably different from Ppd-D1 existing in hexaploid wheat. The new allele Ppd-Dt1 derived from Ae. tauschii might be used as a source for hexaploid wheat breeding on photoperiod response.G156S with part drooping leaf,dark-green leaf color and normal flower organs was respectively crossed with restoring lines Minghui 63,Minghui 86,Qianhui 085,Shuhui 527 with straight leaf to study heredity and gene loci of drooping leaf character.The results showed that the drooping leaf character was controlled by a pair of recessive genes according to the phenotypes of F1,F2,BC1 populations and χ2 test,and the gene controlling drooping leaf character was between RM5628 and RM6849 of the short arm of chromosome 3 and its genetic distance was 1.0 cM and 0.9 cM.

Irrigation Water-Saving Technologies to Adapt to Global Changes in the Yellow River Basin, China: A Hetao Case Study

Water resources management in the Yellow River basin, China, is facing a paradigmatic change in consequence of an unbalanced supply and demand due to an increased demand for water from non-agricultural sectors and a reduced supply due to climate change that reduced precipitation and increased climatic demand. The problem is aggravated by low equity of spatial water allocation in the basin. A supply reduction in the upstream basin area aims to control the water scarcity conditions occurring in the middle and lower reaches of the basin. Forecasted scenarios on water resources allocation and use for agriculture in the upper reaches of the Yellow River basin point out for the need to reduce irrigation water withdrawal and increasing land and water productivity. This paper focus on the Hetao Irrigation District, Inner Mongolia, in upper reaches of Yellow River, where sustainable water saving irrigation is being implemented in response to global changes occurring in the Yellow River basin. That implementation requires technological adaption referring to modernization of canal water conveyance and delivery, which refers to upgrading the hydraulic regulation and control structures, reducing operational runoff wastages, and improving system management. At field level, modern irrigation technologies adapted to local conditions are under implementation. The paper focus on an application to Dengkou area.

Improving Water Productivity in Irrigated Agriculture: Challenges from Climate Change and New Water Resources Paradigms

The increasing pressure on water resources is due to continuously growing consumption, which itself results from demographic and economic developments and the effect of expected climate change. Therefore, action to encourage the more efficient and productive use of water is urgent. Water management needs to focus on regulating the use of this limited resource by multiple users; the allocation of water to non-agricultural users, in particular, is increasing steadily. Moreover, increased variability in climate regimes is expected to modify the volume, temporal and spatial distribution of water storage and fluxes, and therefore to affect the distribution, availability and sustainability of regional water resources. Irrigated agriculture is one of the sectors also facing new challenges. Given that water scarcity is expected to worsen in large agricultural production areas, one such challenge is how to maintain or increase sustainable agricultural production under growing water use restrictions. Improvements in agricultural water management should seek to conserve not only water but energy and soil, too, while still satisfying society’s relentless demand for high quality food and fiber crops, and livestock, aquatic and forest products. This work addresses the main problems related to this topic, illustrated with case studies from Europe and Asia.

A Web-based Decision Support System for Surface Irrigation Design. Sofware Development

This paper presents the Web-based decision support system SADREG for design and selection of farm surface irrigation systems: furrows, basin and border irrigation. The design component applies database information and produces a set of design alternatives in agreement with the user options through several simulation and computational tools. The selection component applies multicriteria analysis to rank those alternatives. Comparing with the conventional stand-alone PC-program, an Internet application has a larger flexibility enabling the access by users worldwide, particularly in areas where expert technical support for surface irrigation improvement is more incipient. Moreover, it allows an easier transfer and share of knowledge and tools to improve the procedures of irrigation design. The Web SADREG application includes the Web module that creates the user interface, data fluxes, showing numerical and graphical data, and the simulation engine, which runs the simulation models on the server. The development applies the PHP and C++ languages to achieve a better flexibility and to minimize client system requirements and SQLServer for data storing, thus allowing a simultaneous connection of several users. During the simulation process the users are informed about the input parameters, the design process and the output. An online help and information about irrigation equipments and guidelines for a good irrigation practices is available. This approach results on a better service quality, avoiding package installation and is more versatile to upgrade and to integrate other data and models. This software, available on http://sadreg.safe-net.eu Web site, is currently being tested.

Irrigation Scheduling For Water Savings And Salinity Control In The Yellow River Basin, China

Water saving in irrigation is a main issue in the Yellow River basin. Field studies were conducted in two areas. The Huinong system, Ningxia, in the upper reaches, where excess irrigation water is applied giving rise to waterlogging and salinity problems, and the Bojili system, Shandong, in the lower reaches of the river basin, where water availability is insufficient and salinity is related to drainage reuse. To control such problems, improved irrigation scheduling may play an important role. The irrigation scheduling simulation model ISAREG is used to evaluate the current schedules and to generate improved ones. It computes the capillary rise from the water table and deep percolation when excess water is applied, and considers the effects of salinity in crop evapotranspiration, crop water stress and yields, as well as the leaching requirements. The model has been previously calibrated and validated for North China. The model is explored interactively with surface irrigation simulation models to take into consideration the limitations imposed by the field systems concerning depths to be applied and irrigation performances. For Huinong, improvements consist in reducing the number of irrigations and adopting new calendars according to the depth of water table and the soil salinity conditions. Percolation could then be reduced from the current 60 % of the applied depths to only the volumes required for leaching. Water saving would represent more than 33 % and salinity could be controlled when also drainage would be improved. For Bojili, current schedules are appropriate and main issues concern deficit irrigation to cope with present water shortages. For both applications, it is concluded that effectiveness of irrigation scheduling improvements highly depend on required betterment in the basin irrigation systems mainly relative to land levelling, inflow discharges and field sizes.