Fracture resistance of zirconia-composite veneered crowns in comparison with zirconia-porcelain crowns.

The objectives were to evaluate the fracture resistance and stress concentration in zirconia/composite veneered crowns in comparison to zirconia/porcelain crowns using occlusal fracture resistance and by stress analysis using finite element analysis method. Zirconia substructures were divided into two groups based on the veneering material. A static load was applied occlusally using a ball indenter and the load to fracture was recorded in Newtons (N). The same crown design was used to create 3D crown models and evaluated using FEA. The zirconia/composite crowns subjected to static occlusal load showed comparable results to the zirconia/porcelain crowns. Zirconia/composite crowns showed higher stress on the zirconia substructure at 63.6 and 50.9 MPa on the zirconia substructure veneered with porcelain. In conclusion, zirconia/composite crowns withstood high occlusal loads similar to zirconia/porcelain crowns with no significant difference. However, the zirconia/composite crowns showed higher stress values than the zirconia/porcelain crowns at the zirconia substructure

Micropropagation techniques as tools for studying plant growth, tuberization and sprouting of potatoes

1988 Fall.Covers not scanned.Includes bibliographical references.Several investigations were undertaken to determine if micropropagated potato cultivars of different maturity classes performed under field conditions in a manner similar to that reported for seed tuber propagated plants of the same cultivars. Plant growth analysis was carried out with special emphasis using Richards' function for evaluating growth attributes such as plant height, leaf area, and derived growth quantities such as RGR. Early, medium, and late maturing potato cultivars were grown under field, greenhouse and vitro conditions to measure tuber yields. Two sprouting indices (sprouting rate index, and sprouting ratio index) were developed and used to quantify the sprouting characteristics of field, greenhouse, and in vitro produced tubers. Storage temperatures were 5, 10, and 20° C. The combined field data of 1986 and 1987 indicated that plant growth, development and tuber yield were in general agreement to that of seed tuber propagated plants. The derived growth quantities (i.e. RSER, RLAER, RTGR, and RUGR) provided a useful way of comparing cultivar response and explained how the overall growth and development can be understood. Significant correlations were reported between selected yield characteristics of field grown, greenhouse grown and in vitro produced tubers. Both Kennebec and Spunta had the highest yield under field, greenhouse, and in vitro conditions. Russet Burbank and Norland had the lowest yield while Desiree and Norgold Russet had an intermediate response. Both sprouting indices incorporate the influence of factors such as cultivar, temperature and tuber size. Both indices also indicate that earliest sprouting occurred in Norland followed by Desiree and Russet Burbank. Field grown, and greenhouse grown tubers exhibited earlier sprouting than] in vitro produced tubers. Overall, these investigations illustrate the potential value of micropropagation methods in predicting yielding ability and sprouting characteristics of potato cultivars

Effect of Shape, Orientation and Aging of a Plastic Greenhouse Cover on the Degradation Rate of the Optical Properties in Arid Climates

In arid climates, the optical properties of plastic-covered greenhouses deteriorate very quickly. To examine the effect of greenhouse shape and orientation on the degradation rate of cover optical properties, four greenhouse prototypes were constructed in two shapes (duo-pitched roof and tunnel), covered with a 200  m thick low-density polyethylene film. Two types were oriented in the North–South direction, the other two in the East–West direction, and all were exposed for one year to an arid climate. Samples were taken from the different surfaces of each cover for testing. The total transmittance (Ts) and reflectance (Rs) of the samples were measured and averaged to obtain the whole cover properties (T and R). Measurements were carried out periodically every 30 days for the four prototypes. The degradation behavior of the optical properties of each cover surface (Ts, Rs) and the whole cover (T, R) was investigated for the four film covers during the exposure time. Results show that the degradation rate of Ts depends on the surface location and the cover orientation. Among the different surfaces of the four prototype covers, the maximum difference in the Ts value between the E and N surfaces for the tunnel cover oriented in the N–S direction was 15.5%. Although the variation of the Ts value among the different cover surfaces was found, the time dependences of the whole cover transmittance (T) for the four covers tested were almost similar. Accordingly, the shape and orientation of the small size greenhouses did not significantly affect the degradation rate of the cover optical properties. In the four covers tested, the reduction in the global solar radiation transmittance (T) was 27–31% after one-year exposure compared to the new film. Nonlinear correlation was developed to predict the degradation rate of the cover transmittance as a function of the accumulated solar irradiance

Covering Materials Incorporating Radiation-Preventing Techniques to Meet Greenhouse Cooling Challenges in Arid Regions: A Review

Cooling greenhouses is essential to provide a suitable environment for plant growth in arid regions characterized by brackish water resources. However, using conventional cooling methods are facing many challenges. Filtering out near infra-red radiation (NIR) at the greenhouse cover can significantly reduce the heating load and can solve the overheating problem of the greenhouse air. This paper is to review (i) the problems of using conventional cooling methods and (ii) the advantages of greenhouse covers that incorporate NIR reflectors. This survey focuses on how the cover type affects the transmittance of photosynthetically active radiation (PAR), the reflectance or absorptance of NIR and the greenhouse air temperature. NIR-reflecting plastic films seem to be the most suitable, low cost and simple cover for greenhouses under arid conditions. Therefore, this review discusses how various additives should be incorporated in plastic film to increase its mechanical properties, durability and ability to stand up to extremely harsh weather. Presently, NIR-reflecting covers are able to reduce greenhouse air temperature by no more than 5°C. This reduction is not enough in regions where the ambient temperature may exceed 45°C in summer. There is a need to develop improved NIR-reflecting plastic film covers

The cientificWorldJOURNAL Review Article Covering Materials Incorporating Radiation-Preventing Techniques to Meet Greenhouse Cooling Challenges in Arid Regions: A Review

Cooling greenhouses is essential to provide a suitable environment for plant growth in arid regions characterized by brackish water resources. However, using conventional cooling methods are facing many challenges. Filtering out near infra-red radiation (NIR) at the greenhouse cover can significantly reduce the heating load and can solve the overheating problem of the greenhouse air. This paper is to review (i) the problems of using conventional cooling methods and (ii) the advantages of greenhouse covers that incorporate NIR reflectors. This survey focuses on how the cover type affects the transmittance of photosynthetically active radiation (PAR), the reflectance or absorptance of NIR and the greenhouse air temperature. NIR-reflecting plastic films seem to be the most suitable, low cost and simple cover for greenhouses under arid conditions. Therefore, this review discusses how various additives should be incorporated in plastic film to increase its mechanical properties, durability and ability to stand up to extremely harsh weather. Presently, NIR-reflecting covers are able to reduce greenhouse air temperature by no more than 5 • C. This reduction is not enough in regions where the ambient temperature may exceed 45 • C in summer. There is a need to develop improved NIR-reflecting plastic film covers

DESIGNING AN INTEGRATED COMPUTER PROGRAM FOR VEGETABLE PRODUCTION IN THE KINGDOM OF SAUDI ARABIA

Vegetable production provide great value in the agricultural production sector in the Kingdom of Saudi Arabia. Growers and agricultural engineers need a comprehensive database in Arabic lan-guage that can be available for use any time any where. Therefore, this research project was initiat-ed. The computer program was developed using Visual Basic Net 2005 which is one of the ad-vanced visual programming languages. We took into consideration easy usage and coherence be-tween all program components. Main results in-clude computer program with the data base, which includes: vegetable crops, diseases, insect pests and other pests that attacks vegetable crops, management tactics, cultural practices, irrigation requirements, planting dates, data search. Fur-thermore, field trips have been carried out to some vegetable farms in all the Kingdom regions. A digit-ized map of the Kingdom has been added to the program in addition to crop water and heat re-quirements. Various search capabilities have been developed in the program. After the completion of the program build up, verification trips have been carried out for five regions in the presence of farm-ers and extension specialists of the different direc-torate of the Ministry of Agriculture to test the accu-racy of steps used in the program. A manual for the computer program as well as leaflet on pro-gram set up and usage have been included. It is recommended to make this program available at the internet and distribute copies to the Ministry of Agriculture and its directorates as well as farmers

Engineering Melon Plants with Improved Fruit Shelf Life Using the TILLING Approach

Background: Fruit ripening and softening are key traits that have an effect on food supply, fruit nutritional value and consequently, human health. Since ethylene induces ripening of climacteric fruit, it is one of the main targets to control fruit over ripening that leads to fruit softening and deterioration. The characterization of the ethylene pathway in Arabidopsis and tomato identified key genes that control fruit ripening. [br/] Methodology/Principal Findings: To engineer melon fruit with improved shelf-life, we conducted a translational research experiment. We set up a TILLING platform in a monoecious and climacteric melon line, cloned genes that control ethylene production and screened for induced mutations that lead to fruits with enhanced shelf life. Two missense mutations, L124F and G194D, of the ethylene biosynthetic enzyme, ACC oxidase 1, were identified and the mutant plants were characterized with respect to fruit maturation. The L124F mutation is a conservative mutation occurring away from the enzyme active site and thus was predicted to not affect ethylene production and thus fruit ripening. In contrast, G194D modification occurs in a highly conserved amino acid position predicted, by crystallographic analysis, to affect the enzymatic activity. Phenotypic analysis of the G194D mutant fruit showed complete delayed ripening and yellowing with improved shelf life and, as predicted, the L124F mutation did not have an effect. [br/] Conclusions/Significance: We constructed a mutant collection of 4023 melon M2 families. Based on the TILLING of 11 genes, we calculated the overall mutation rate of one mutation every 573 kb and identified 8 alleles per tilled kilobase. We also identified a TILLING mutant with enhanced fruit shelf life. This work demonstrates the effectiveness of TILLING as a reverse genetics tool to improve crop species. As cucurbits are model species in different areas of plant biology, we anticipate that the developed tool will be widely exploited by the scientific community

Water sorption isotherms of vegetable seeds as influenced by seed species and storage temperature

The water sorption isotherms of seeds of four vegetable species; carrot, cucumber, onion, and tomato were determined using the static method of eight saturated salt solutions (relative humidity range from 11 to 98%) at four storage temperatures; 5, 15, 25, and 35°C. The water sorption isotherms of each crop exhibited a reverse sigmoid shape. When seeds were stored at low relative humidity (RH), their equilibrium moisture contents (EMC) were relatively low. At 5°C, no major changes in moisture sorption up to 80% RH. Beyond this point, a sharp increase in EMC occurred. In general, no major differences in water sorption isotherms were observed between species at low relative humidities. Differences became obvious when seeds were stored at RH higher than 60% except for seeds held at 5°C and 15°C. In general, the increase in storage temperature increased the water activity (aw) of seeds. At 97% RH, seeds held at 25 and 35 °C deteriorated before reaching equilibrium. The experimental data were fitted well with GAB and Henderson equations. Equilibrium moisture content varied from a minimum of 0.00236 (g water/g dry matter) for tomato to a maximum of 0.0388 for carrot. The correlation coefficients (0.968 to 0.999 for GAB model and 0.922 to 0.961 for Henderson model) indicated a good fit to experimental data. The GAB model fits experimental data better than Henderson model as indicated by the higher correlation coefficient values

PHOTOAUTOTROPHIC AND PHOTOMIXOTROPHIC MICROPROPAGATION OF THREE POTATO CULTIVARS

The present study was aimed to compare the photoautotrophic (PAM) and photomixotrophic micropropagation (PMM) of three potato cultivars (Hermes, Rosetta and Asterix). Cultures were initiated from single node explants and established in MS basal medium with some modifications. Potato plantlets responded in sugar-free media although sugar-containing media (PMM1 and PMM2) performed better as compared to that of sugar-free (PAM1 and PAM2) media. The PMM1 produced shoot length averaging 6.25 cm with 8.08 nodes and weighing 0.24 g fresh weight of plantlet. On the other hand, PAM1 grown culture produced 4.03 cm shoot length, 8 nodes and 0.06 g of fresh weight. Shoot length and fresh weight of plantlets were significantly higher in PMM1 and PMM2 based media. Whereas the number of nodes per shoot was not significantly different on media with or without sugar (except the media PAM2). Sugar and vitamin-free media ( PAM2) performed inferior in all the traits. Key words: Potato, Photoautotrophic and Photomixotrophic Micropropagation