Extremal Optimization for Graph Partitioning

Extremal optimization is a new general-purpose method for approximating solutions to hard optimization problems. We study the method in detail by way of the NP-hard graph partitioning problem. We discuss the scaling behavior of extremal optimization, focusing on the convergence of the average run as a function of runtime and system size. The method has a single free parameter, which we determine numerically and justify using a simple argument. Our numerical results demonstrate that on random graphs, extremal optimization maintains consistent accuracy for increasing system sizes, with an approximation error decreasing over runtime roughly as a power law t^(-0.4). On geometrically structured graphs, the scaling of results from the average run suggests that these are far from optimal, with large fluctuations between individual trials. But when only the best runs are considered, results consistent with theoretical arguments are recovered.Comment: 34 pages, RevTex4, 1 table and 20 ps-figures included, related papers available at http://www.physics.emory.edu/faculty/boettcher

Efectos de la nutrición y el riego en la producción de pimiento en toba volcánica

In this study aimed at increasing sustainability in soilless cultivation, volcanic tuff was used as substrate and the tested plant material was blocky type pepper (cv. 4-Ever F1). Three experimental factors were evaluated: cultivation system (open or closed), nutrient composition (N1, N2, N3, N4) and irrigation frequency (I1, I2, I3, I4). Macro nutrient concentrations of N2, N3 and N4 were 2-, 3- and 4-fold of N1. Concentrations of micronutrients were the same for all treatments. Irrigation was started when indoor solar radiation reached 6, 4, 2 and 1 MJ m–2 in the treatments I1, I2, I3 and I4, respectively. As a sustainable soilless technique, closed system was found to be recommendable by incorporating the treatment N4 + I2 to provide high yield and quality for blocky type pepper production. In the case of an open system, N2 + I4 proved to be the most efficient strategy.El objetivo de este estudio fue aumentar la sostenibilidad en un cultivo sin suelo, utilizando como sustrato toba volcánica y como material vegetal pimiento tipo rectangular (cv. 4-Ever F1). Se evaluaron tres factores experimentales: sistema de cultivo (abierto o cerrado), composición de nutrientes (N1, N2, N3, N4) y frecuencia de riego (I1, I2, I3, I4). Las concentraciones N2, N3, y N4de macro nutrientes fueron 2, 3 y 4 veces las de N1, siendo las concentraciones de micronutrientes las mismas para todos los tratamientos. El riego se inició cuando la radiación solar bajo cubierta alcanzó 6, 4, 2 y 1 MJ m2 en los tratamientos I1, I2, I3 e I4, respectivamente. Como técnica de cultivo sin suelo sostenible, en el sistema cerrado los tratamientos que proporcionan mayor rendimiento y calidad de pimiento son N4 + I2. En el caso de sistema abierto, la estrategia más eficiente es utilizar los tratamientos N2 + I4

Response of Grafted and Self-Rooted Tomato Plants to Saline Conditions in Closed Substrate System

5th Balkan Symposium on Vegetables and Potatoes -- OCT 09-12, 2011 -- Tirana, ALBANIAWOS: 000323606200061Grafting could be used as a means to alleviate salt stress in some greenhouse vegetables if appropriate rootstock is selected. In this research, the response of tomato rootstocks 'Beaufort' (L. esculentum x L. hirsutum) and 'Resistar' (L. esculentum) against to salinity was compared with self grafted ones (cv. Gokce F-1) in a PE covered greenhouse during the autumn and spring season of 2007-2008. Plants were grown in perlite (6 L plant(-1)) with the density of 3.5 plants m(-2). The electrical conductivity of the nutrient solution supplied to the plants, which had a standard composition for tomato, was adjusted to 2.0 (control), 6.0 or 10.0 dS m(-1) by adding 0, 42 or 84 mmol L-1 NaCl in order to determine rootstock-salt reaction. The experimental design was randomized parcels with 2 factors with 3 replicates. The results showed that rootstocks increased plant height, stem diameter, root and shoot fresh and dry weight, total and marketable yield. These parameters decreased dramatically with the increase of salinity. Salinity stress especially reduced mean fruit weight and increased amount of nonmarketable fruits. Although higher yield was obtained at 2 dS m(-1) in both growing seasons, the plants grafted onto Beaufort had the highest yields under saline conditions. It was concluded that grafting could increase plant vigor and yield resulting in better performance under saline conditions, however detrimental effect of salinity was more severe in spring season.Int Soc Hort Sci (ISHS

Effect of Grafting on Salinity Tolerance in Tomato Production

International Symposium on Strategies Towards Sustainability of Protected Cultivation in Mild Winter Climate -- JAN 31, 2009 -- Antalya, TURKEYWOS: 000305334500094The response of tomato rootstocks to salinity was studied in a PE covered greenhouse during the spring season of 2005. 'Maxifort' and 'Vigomax' hybrid rootstocks grafted with commercial cultivar 'Durinta F-1' were used. Self grafted plants were used as control treatment. Two EC levels of nutrient solution (2 and 6 dS m(-1)) were applied to the plants in perlite culture. Salinity level of the nutrient solution was increased using NaCl three weeks after planting. Irrigation timing was based on indoor integrated solar radiation level of 1.0 MJ m(-2). The amount of nutrient solution was adjusted according to the ratio of drain water/applied volume. Yield parameters (total and marketable yield, fruit number and mean fruit weight) and fresh and dry weight of plant parts were measured. Increasing of EC level from 2 to 6 dS m(-1) caused a significant reduction in yield parameters. The use of rootstocks increased the marketable yield. The reduction of yield by the increasing salinity levels was lower in the grafted treatments. Yield and WUEs were higher in grafted plants. Higher water consumption was observed when rootstocks were used.ECOPONICS project - European Union [ICA3-CT-2002-10020]This research was supported by ECOPONICS project financed by the European Union (Project No: ICA3-CT-2002-10020)

Crop coefficients in simplified hydroponic systems

International Symposium on Greenhouse Cooling -- APR 24-27, 2006 -- Almeria, SPAINWOS: 000243532400064This study was carried out during the spring growing season of 2003 in order to determine tomato crop evapotranspiration and to develop crop coefficients under different irrigation treatments in open and closed systems. The experiment was conducted in a non-heated plastic covered greenhouse. Tomato plants were grown in perlite and irrigation was applied according to the indoor integrated solar radiation levels viz 1, 2, and 4 MJ m(-2). The results showed that evapotranspiration of tomato plants varied according to the treatments and ranged between 229 and 371 mm. The highest daily evapotranspiration values were 4.4 mm and 5.0 mm in the closed and open systems, respectively. Regarding the irrigation treatments, the highest evapotranspiration rate was obtained with the 1 MJ m(-2) treatment. Crop coefficient curves were obtained from the ratio of crop evapotranspiration (ET) to the reference evapotranspiration (ET0) estimated by pan evaporation, solar radiation and FAO Penman-Monteith equation methods on a weekly basis during growing season. The maximum crop coefficient value for tomato derived from the Penman-Monteith formula was 1.5 in the open system.ISHS Commiss Horticultural Engn, ISHS Commiss Protected CultivatINCO-DC Project ECOPONICS [ICA3-CT-2002-10020]This research has been supported by the INCO-DC Project ECOPONICS with the contract number ICA3-CT-2002-10020

Effects of grafting in saline conditions

International Symposium on Advances in Environmental Control, Automation and Cultivation Systems for Sustainable, High-Quality Crop Production Under Protected Cultivation -- AUG 13-19, 2006 -- Seoul, SOUTH KOREAWOS: 000255678800048Grafting could be used as a strategy to increase tolerance of plants to salinity and to promote water use efficiency. In these experiments tomato cultivar 'Durinta' was grafted on two rootstocks, namely Beaufort and Heman and grown at two EC levels of nutrients solution (2 and 6 dS/m) comparing with ungrafted plants between the years 2004 and 2005. Plants were grown in plastic containers. The substrate was perlite and substrate volume was 6 liters per plant. The seedlings were transferred to the greenhouse on 24 March 2004 and 26 August 2004 in spring and autumn season productions respectively with a plant density of 3.48 plants per in. Irrigation timing was based on indoor integrated solar radiation level of 1.0 MJ.m(-2). The amount of nutrient solution was adjusted according to the ratio of drainwater/applied volume, which was kept approximately 30% in 2 dS/m and 40% in 6 dS/m. By the use of rootstocks, marketable yield increased in 6 dS/m compared with ungrafted plants. The average marketable yield increase in Beaufort and Heman was 47.5% and 24.3%, respectively. Also the average increase in water use efficiency was 46.5% with Beaufort and 24.4% with Heman

Response of Pepino (Solanum muricatum Aiton) to Salinity

5th Balkan Symposium on Vegetables and Potatoes -- OCT 09-12, 2011 -- Tirana, ALBANIAWOS: 000323606200060Two experiment were conducted in a polyethylene greenhouse in order to determine the effects of salinity on plant growth, yield, fruit quality and water consumption of pepino (Solanum muricatum Aiton). In the first experiment plant growth, yield and fruit quality response to three different salinity levels of nutrient solution (2 dS m(-1) control, 5 dS m(-1) and 8 dS m(-1)) in closed soilless system were tested. In second experiment, seedlings were screened in water culture in order to identify the response of pepino to gradually increased salinity. Salinity level was increased up to 300 mM by adding 50 mM NaCl weekly and plants were left for 7 days at that salinity level. The results showed that plant height, stem diameter, stem fresh and dry weights, cluster dry weight, fruit fresh weight, total and marketable yield, mean fruit weight and plant water consumption were decreased at the level of 8 dS m(-1) while EC of fruit juice and vitamin C increased at 8 dS m(-1) EC level in first experiment. In second experiment, plants were damaged at higher salinity level (200-300 mM). It was concluded that pepino could be grown under medium salinity stress conditions as an alternative crop in greenhouses.Int Soc Hort Sci (ISHS