Critical radius and critical number of gas atoms for cavities containing a Van der Waals gas

The effect of gas on void nucleation and growth is particularly important for structural materials in fusion reactors because of the high production of helium by neutron-induced transmutation reactions. Gas reduces the critical radius for bias driven growth and there is a critical number of gas atoms, n/sub g/*, at which the critical radius is reduced essentially to zero. The significance of this is that the time interval to the accumulation of n/sub g/* gas atoms may determine the time to the onset of bias driven swelling where n/sub g/* is large. In previous papers these critical quantities were given for an ideal gas. Recently, we presented the results for a Van der Waals gas. Here the derivation of these relations is presented and further results of calculations are given. At low temperatures (high pressures) the results depart from those of the ideal gas, with the critical number affected more strongly than the critical radius. Comparisons are made with earlier calculations

KEANEKARAGAMAN FUNGI MIKORIZA ARBUSKULA (FMA) PADA RIZOSFER TANAMAN PEGAGAN (Centella asiatica (L.) Urban)

ABSTRAKDefisiensi hara fosfor (P) menjadi salah satu faktor pembatas dalamsistem produksi pertanian di Indonesia yang umumnya diusahakan padatanah-tanah masam. Pemanfaatan fungi mikoriza arbuskula (FMA)merupakan salah satu alternatif dalam menanggulangi permasalahan padatanah masam, karena FMA dapat membantu tanaman menyerap unsur Pdan unsur hara lainnya dari dalam tanah. Untuk mempelajari potensi FMA,hal pertama yang harus diketahui adalah keanekaragaman dari organismetersebut. Dengan adanya data tentang keanekaragaman FMA, maka dapatdilakukan seleksi guna mendapatkan isolat FMA yang potensial danefektif dalam meningkatkan pertumbuhan dan produktivitas tanamanpegagan. Penelitian ini bertujuan untuk mengisolasi dan mengidentifikasijenis-jenis FMA pada rizosfer tanaman pegagan. Penelitian dilaksanakanbulan Januari sampai Agustus 2008. Pengambilan contoh tanah dilakukanpada tiga lokasi pertanaman pegagan di Kebun Percobaan Gunung Putri,Sukamulya, dan Cicurug, sedangkan isolasi, identifikasi, dan pemerang-kapan spora dilakukan di Laboratorium Ekofisiologi dan rumah kaca BalaiPenelitian Tanaman Obat dan Aromatik Bogor. Hasil penelitianmenunjukkan bahwa sebelum pemerangkapan diperoleh 2 genus (Glomusdan Acaulospora) pada contoh tanah di KP Gunung Putri, 3 genus(Glomus, Acaulospora dan Scutellospora) di KP Sukamulya, dan 2 genus(Glomus dan Acaulospora) di KP Cicurug. Setelah dilakukan trappingjenis FMA, di KP Gunung Putri didapatkan 5 jenis FMA (4 tipe Glomusdan 1 tipe Acaulospora), di KP Sukamulya terdapat 5 jenis FMA (3 tipeGlomus, 1 tipe Acaulospora, dan 1 tipe Scutellospora), dan di KP Cicurugterdapat 4 jenis FMA (3 tipe Glomus dan 1 tipe Acaulospora).Keanekaragaman FMA pada rizosfer pertanaman pegagan cukup beragamdan berpotensi dimanfaatkan untuk meningkatkan efisiensi pemupukan,khususnya ketersediaan dan serapan hara P.Kata kunci : Centella asiatica (L.) Urban, keanekaragaman, fungimikoriza arbuskula (FMA), pegaganABSTRACTArbuscular Mycorrhizae Fungi (AMF) diversity on asiaticpennywort Centella asiatica (L.) Urban) rhizosphereDeficiency of phosphorus (P) is one of the limiting factors ofagricultural production system in Indonesia which is generally managed onacid soils. Utilizing arbuscular mycorrhizae fungi (AMF) is one of thealternative solutions on acid soils problem, because of its ability to take upP and other nutrients from soils. The first concern which must be studied isdiversity of the organism. Data on AMF diversity obtained is useful toselect potential and effective AMF by increasing plant growth andproduction of asiatic pennywort. The aim of this research was to isolateand identify types of AMF in asiatic pennywort rhizosphere. The experi-ment was conducted from January until August 2008. Soil samples weretaken from three locations of asiatic pennywort plantations i.e. GunungPutri, Sukamulya, and Cicurug experimental stations. Isolation, identifi-cation, and trapping of spore were conducted at the Eco-physiology labo-ratory and glasshouse of Indonesian Medicinal and Aromatic CropsResearch Institute (IMACRI), Bogor. The laboratory results of soil sam-ples before trapping showed that there were two genus of AMF spores(Glomus and Acaulospora) in the samples from Gunung Putri, three genus(Glomus, Acaulospora, and Scutellospora) from Sukamulya, and twogenus (Glomus and Acaulospora) from Cicurug. After trapping, it wasidentified that the soil samples from Gunung Putri, Sukamulya, andCicurug contained five AMF species (four types of Glomus and one typeof Acaulospora), five AMF species (three types of Glomus, one type ofAcaulospora and Scutellospora), and four AMF species (three types ofGlomus and one type of Acaulospora) from Cicurug. Diversity of AMFvariety can be utilized to get potential to increase the efficiency offertilizer, specifically availability and uptake of nutrient P.Key words : Centella  asiatica  (L.)  Urban,  diversity,  ArbuscularMycorrhizae Fungi (AMF), asiatic pennywor

PEMANFAATAN VERMIKOMPOS UNTUK PRODUKSI BIOMASSA LEGUM PENUTUP TANAH DAN INOKULUM FUNGI MIKORIZA ARBUSKULA

[THE USE OF VERMICOMPOST FOR BIOMASS PRODUCTION OF LEGUME COVER CROP AND INOCULUM OF ARBUSCULAR MYCORRHIZAL FUNGUS]. Vermicompost is an organic fertilizer produced through the digestive system and microorganism inside the earthworm gut. Vermicompost is recognized to have positive effects on the plant growth and development of mycorrhizal symbiosis.The study was aimed to determine the optimum size (diameter and weight) of vermicompost for producing biomass of legume cover crop (LCC) and inoculum of arbuscular mycorrhiza fungus (AMF) of G. etunicatum. A glasshouse experiment was arranged in a randomized block design, involving different diameter size and weight of vermicompost as the treatments. Results showed that vermicompost is a potential substitute to inorganic fertilizer for production of LCC biomass and AMF inoculum.Vermicompost applied with  diameter < 250 µm weighing 150 – 172 mg produced  the highest  root dry weight of LCC, root colonization, and number of spores of G. etunicatum. A linear relation was found between root colonization and number of spores of G. etunicatum

Radiation effects on microstructures and properties of irradiated materials

Development of structural materials to withstand aggressive radiation environments has been carried out on an international scale over the past four decades. Major radiation-induced changes in properties include swelling, creep and embrittlement. The basic work, stimulated by technology, to understand and control these phenomena, has been heavily oriented toward the evolution of microstructures and their effects on properties. Microstructural research has coupled analyses by high resolution techniques with theoretical modeling to describe and predict microscopic features and the resulting macroscopic properties. A short summary is presented of key physical considerations that drive these changes during irradiation. Such processes begin with displacement cascades, and lead to property changes through the diffusion and clustering of defects

Irradiation creep by climb-enabled glide of dislocations resulting from preferred absorption of point defects

A mechanism of irradiation creep is proposed that arises from the climb-enabled glide of dislocations due to stress-induced preferred absorption of radiation-produced point defects. This creep component we term preferred absorption glide, PAG. PAG-creep operates in addition to the previously studied components of creep from climb by stress-induced preferred absorption, PA-creep, and the climb-enabled glide due to excess absorption of interstitials on dislocations during swelling, l-creep. A formulation of the various climb and climb-enabled glide processes is presented which includes earlier results. PAG-creep is comparable in magnitude to PA-creep in the parameter range of applications. While the PA-creep rate and the l-creep rate are linear in stress, the PAG creep rate is quadratic stress and thus dominates at high stress

Effects of point defect trapping and solute segregation on irradiation-induced swelling and creep

The theory of irradiation swelling and creep, generalized to include impurity trapping of point defects and impurity-induced changes in sink efficiencies for point defects, is reviewed. The mathematical framework is developed and significant results are described. These include the relation between vacancy and interstitial trapping and the effectiveness of trapping as compared to segregation-induced changes in sink efficiencies in modifying void nucleation, void growth, and creep. Current understanding is critically assessed. Several areas requiring further development are identified. In particular those given special attention are the treatment of nondilute solutions and the consequences of current uncertainties in fundamental materials properties whose importance has been identified using the theory

Kinetic theory of radiation effects

To help achieve the quantitative and mechanistic understanding of these processes, the kinetic theory of radiation effects has been developed in the DOE basic energy sciences radiation effects and fusion reactor materials programs, as well as in corresponding efforts in other countries. This discipline grapples with a very wide range of phenomena and draws on numerous sub-fields of theory such as defect physics, diffusion, elasticity, chemical reaction rates, phase transformations and thermodynamics. The theory is cast in a mathematical framework of continuum dynamics. Issues particularly relevant to the present inquiry can be viewed from the standpoints of applications of the theory and areas requiring further progress

Proceedings of the international workshop on spallation materials technology

This document contains papers which were presented at the International Workshop on Spallation Materials Technology. Topics included: overviews and thermal response; operational experience; materials experience; target station and component design; particle transport and damage calculations; neutron sources; and compatibility