Avances recientes en la programación de los riegos

[ES] Se describe el estado actual de las distintas técnicas de programación de riegos, poniendo el énfasis en las aplicaciones de una nueva generación de sensores de humedad de suelo y de detección de estrés en planta, recientemente desarrollados. Se muestran ejemplos en los que el registro continuo de la humedad volumétrica del suelo a varias profundidades permite detectar de forma casi inmediata una dosis de riego insuficiente. La detección precoz del estrés en el propio cultivo, ya sea por teledetección o por medidas directas o indirectas en el mismo, debe conducir a manejar el riego con un elevado nivel de precisión y a modular las aplicaciones de agua para optimizar el riego. Entre todos los indicadores de estrés en planta existentes, se apunta que las medidas de contracción de tronco pueden estar entre las más sensibles a cambios en el estado hídrico del árbol. Se presentan casos donde las oscilaciones en el diámetro de los troncos pueden servir para programar los riegos de forma automática. Finalmente, se insiste en la necesidad de integrar estas nuevas técnicas en un enfoque mucho más amplio de manejo del riego, de manera que pueda generalizarse su uso.Fereres Castiel, E.; Goldhamer, DA. (2000). Avances recientes en la programación de los riegos. Ingeniería del Agua. 7(1):47-54. https://doi.org/10.4995/ia.2000.2836SWORD475471Caja Rural de Almeria (ed). 1997. Gestión del regadío en El Campo de Dalías: Las Comunidades de Regantes Sol y Arena y Sol-Poniente. 195pCampbell, G.S. y D.J. Mulla, 1990. Measurement of soil water content and potential. p.127-142. In: Irrigation of Agricultural Crops. (B.A. Stewart y D.R. Nielsen, eds.)Amer. Soc. Agric. Engn., Madison, WisFereres, E. 1996. Irrigation Scheduling and its Impact on the 21st Century. En: Proceedings of the International Conference on ET and Irrigation Scheduling. (Camp, C.R., Sadler, E.J. y Yoder, R.E., eds) ASAE, San Antonio, USA, 547-553Fereres, E., D. Goldhamer, M. Cohen, J. Girona y M. Mata. 1999. Continuous trunk diameter recording can reveal water stress in peach trees. California Agriculture. 53(4):21-25.Garnier, E. y A. Berger, 1986. Effect of water stress on stem diameter changes of peach trees growing in the field. J. App. Ecol. 23:193-209.Ginestar, C. y J.R. Caster, 1996. Utilización de dendrómetros como indicadores de estrés hídrico en mandarinos jóvenes regados por goteo. Riegos y Drenajes XXI, 89:40-46.Goldhamer, D.A. E. Fereres, M. Mata, J Girona y M. Cohen. 1999. Sensitivity of continuous and discrete plant and soil water status monitoring in peach trees subjected to deficit irrigation. Journal of the American Society for Horticultural Science. 124:4:437-444.Goldhamer D.A. y E Fereres. 2000. Scheduling fruit tree irrigation using continuous recorded trunk diameter measurements. (enviado a publicación).Grimes D.W. y H. Yamada. 1982. Relation of cotton growth and yield to minimum leaf water potential. Crop Sci. 22:134-139.Heerman, D.F., D.L. Martin, R.D. Jackson y E.C. Stegman. 1990. Irrigation scheduling controls and techniques. En: Irrigation of agricultural crops (B.A. Stewart y D.R. Nielsen, eds) American Society of Agronomy monograph no.30 p.475-508.Huck M.G. y B. Klepper. 1976. Water relation of cotton. II. Continuous estimates of water potential from stem diameter measurements. Agron. J. 69:593-597Jackson, R.D., R.J. Reginato y S.B. Idso. 1977. Wheat canopy temperature: a practical tool for evaluating crop water requirements. Water Resour Res. 13:651-656.Jackson, R.D. 1981. Canopy temperature and crop wáter stress. Adv. Irrig.,1:43-85.Martin, D.L.; E.C. Stegman, y E. Fereres. 1991: Irrigation Scheduling Principles. En: Management of Farm Irrigation Systems. (Hoffman, G.J., Howell, T.A., Solomon, K.H. eds) American Society of Agricultural Engineers, 155-203.Mata M., J. Girona, D. Goldhamer, E Fereres, M Cohen y S Johnson. 1999. Water relations of lysimeter-grown peach trees are sensitive to deficit irrigation. California Agricultural. 53(4):17-21.Moran, M.S. 1994. Irrigation management in Arizona using satellite and airplanes. Irrig. Sci. 15:35-41Paltineanu, I.C., y J.L. Starr. 1997, Real-time soil water dynamics using multisensor capacitance probes: Laboratory calibration. Soil Sci. Soc. Am. J. 61:1576-1585.Shackel, K. A., H. Ahmadi, W. Biasi, R. Buchner, D. Goldhamer, S. Gurusinghe, J. Hasey, D. Kester, B. Krueger, B.Lampinen, G. McGourty, W. Micke, E. Mitcham, B.Olson, K. Pelletrau, H. Philips, D. Ramos, L.Schwankl, S. Sibbett, R. Snyder, S. Southwick, M. Stevenson, M. Thorpe, S. Weinbaum y J. Yeager. 1997. Plant water status as an index of irrigation need in deciduous fruit trees. HortTechnology 7(1):23-29.Starr, J.L., and I.C. Paltineanu. 1998, Soil water dynamics using multisensor capacitance probes in nontraffic interrows of corn. Soil Sci. Soc. Am. J. 62:114-122

DFT calculation of the intermolecular exchange interaction in the magnetic Mn4_4 dimer

The dimeric form of the single-molecule magnet [Mn$_4$O$_3$Cl$_4$(O$_2$CEt)$_3$(py)$_3$]$_2$ recently revealed interesting phenomena: no quantum tunneling at zero field and tunneling before magnetic field reversal. This is attributed to substantial antiferromagnetic exchange interaction between different monomers. The intermolecular exchange interaction, electronic structure and magnetic properties of this molecular magnet are calculated using density-functional theory within generalized-gradient approximation. Calculations are in good agreement with experiment.Comment: 4 page

Greedy Parabolics: Wind flow direction within the deflation basin of parabolic dunes is governed by deflation basin width and depth

Parabolic dunes are ‘U’ or ‘V’-shaped aeolian landforms that form on pre-existing sand deposits. Their morphology consists of an upwind deflation basin, bordered by often vegetated trailing arms and a downwind depositional lobe. The orientation of parabolic dunes is commonly attributed to the prevailing or resultant wind direction. Consequently, the orientation of parabolic dunes stabilised by vegetation growth has been used as a proxy for wind direction during past climates in several studies. However, the ability or extent of parabolic dune morphology to steer incident wind flow parallel to the orientation of the landform, and thus migrate in the direction of the current landform orientation rather than prevailing wind direction, is unknown. By numerically modelling wind flow within the deflation basin of eight parabolic dunes, we demonstrate for the first time that wind flow direction within the deflation basin of a parabolic dune is highly controlled by the depth and width of the deflation basin. The greater the depth–width ratio of the landform (i.e. the deeper and narrower the deflation basin), the greater the degree of flow steering relative to the axis orientation of the landform. These results demonstrate that future studies must exercise caution when using parabolic dune orientation as a direct proxy for prevailing wind direction, especially where parabolic dunes have a relatively high deflation basin depth–width ratio, as the deflation basin of these landforms may continue to migrate in an antecedent wind direction

Second harmonic generation and birefringence of some ternary pnictide semiconductors

A first-principles study of the birefringence and the frequency dependent second harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC$_2$ (A = Zn, Cd; B = Si, Ge; C = As, P) with the chalcopyrite structures was carried out. We show that a simple empirical observation that a smaller value of the gap is correlated with larger value of SHG is qualitatively true. However, simple inverse power scaling laws between gaps and SHG were not found. Instead, the real value of the nonlinear response is a result of a very delicate balance between different intraband and interband terms.Comment: 13 pages, 12 figure

A viewpoint on material and design considerations for oesophageal stents with extended lifetime

Oesophageal stents are meshed tubular implants designed to maintain patency of the oesophageal lumen and attenuate the symptoms of oesophageal cancer. Oesophageal cancers account for one in twenty cancer diagnoses and can lead to dysphasia, malnutrition and the diminishment of patient quality of life (QOL). Self-expanding oesophageal stents are the most common approach to attenuate these symptoms. Recent advances in oncological therapy have enabled patient survival beyond the lifetime of current devices. This introduces new complications for palliation, driving the need for innovation in stent design. This review identifies the factors responsible for stent failure. It explores the challenges of enhancing the longevity of stent therapies and outlines solutions to improving clinical outcomes. Discussions focus on the role of stent materials, construction methods, and coatings upon device performance. We found three key stent enhancement strategies currently used; material surface treatments, anti-migratory modifications, and biodegradable skeletons. Furthermore, radioactive and drug eluting stent designs were identified as emerging novel treatments. In conclusion, the review offers an overview of remaining key challenges in oesophageal stent design and potential solutions. It is clear that further research is needed to improve the clinical outcome of stents and patient QOL

Environmental studies data base development and data synthesis activities of the US Subseabed Disposal Program

The US Subseabed Disposal Program is assessing the scientific feasibility of subseabed emplacement of high-level nuclear wastes. Studies of disposal methods and of the barriers to radionuclide migration (canister, waste form and sediment) suggest that environmental information will be needed to address the impact of accidental release of radionuclides in the deep sea. Biological, physical, and geochemical data are being collected from field and laboratory studies as well as from literature searches. These data are being analyzed using a multicompartmental radionuclide transport model and appropriate physical oceanographic models. The data integrated into this framework will help answer two questions: what are the environmental effects of radionuclides which may be released in the deep sea, and what are the effects of such a release upon man

What do young athletes implicitly understand about psychological skills?

One reason sport psychologists teach psychological skills is to enhance performance in sport; but the value of psychological skills for young athletes is questionable because of the qualitative and quantitative differences between children and adults in their understanding of abstract concepts such as mental skills. To teach these skills effectively to young athletes, sport psychologists need to appreciate what young athletes implicitly understand about such skills because maturational (e.g., cognitive, social) and environmental (e.g., coaches) factors can influence the progressive development of children and youth. In the present qualitative study, we explored young athletes’ (aged 10–15 years) understanding of four basic psychological skills: goal setting, mental imagery, self-talk, and relaxation. Young athletes (n = 118: 75 males and 43 females) completed an open-ended questionnaire to report their understanding of these four basic psychological skills. Compared with the older youth athletes, the younger youth athletes were less able to explain the meaning of each psychological skill. Goal setting and mental imagery were better understood than self-talk and relaxation. Based on these findings, sport psychologists should consider adapting interventions and psychoeducational programs to match young athletes’ age and developmental level

Emergence of Anti-Cancer Drug Resistance: Exploring the Importance of the Microenvironmental Niche via a Spatial Model

Practically, all chemotherapeutic agents lead to drug resistance. Clinically, it is a challenge to determine whether resistance arises prior to, or as a result of, cancer therapy. Further, a number of different intracellular and microenvironmental factors have been correlated with the emergence of drug resistance. With the goal of better understanding drug resistance and its connection with the tumor microenvironment, we have developed a hybrid discrete-continuous mathematical model. In this model, cancer cells described through a particle-spring approach respond to dynamically changing oxygen and DNA damaging drug concentrations described through partial differential equations. We thoroughly explored the behavior of our self-calibrated model under the following common conditions: a fixed layout of the vasculature, an identical initial configuration of cancer cells, the same mechanism of drug action, and one mechanism of cellular response to the drug. We considered one set of simulations in which drug resistance existed prior to the start of treatment, and another set in which drug resistance is acquired in response to treatment. This allows us to compare how both kinds of resistance influence the spatial and temporal dynamics of the developing tumor, and its clonal diversity. We show that both pre-existing and acquired resistance can give rise to three biologically distinct parameter regimes: successful tumor eradication, reduced effectiveness of drug during the course of treatment (resistance), and complete treatment failure

On the gravitodynamics of moving bodies

In the present work we propose a generalization of Newton's gravitational theory from the original works of Heaviside and Sciama, that takes into account both approaches, and accomplishes the same result in a simpler way than the standard cosmological approach. The established formulation describes the local gravitational field related to the observables and effectively implements the Mach's principle in a quantitative form that retakes Dirac's large number hypothesis. As a consequence of the equivalence principle and the application of this formulation to the observable universe, we obtain, as an immediate result, a value of Omega = 2. We construct a dynamic model for a galaxy without dark matter, which fits well with recent observational data, in terms of a variable effective inertial mass that reflects the present dynamic state of the universe and that replicates from first principles, the phenomenology proposed in MOND. The remarkable aspect of these results is the connection of the effect dubbed dark matter with the dark energy field, which makes it possible for us to interpret it as longitudinal gravitational waves.Comment: 18 pages, 4 figures. Final version: almost identical to the reference journal; Cent. Eur. J. Phys. 201