A decrease in the density of trapping centers in silicon oxide as a result of radiation-thermal treatment

The results of processing the experimental drain-gate characteristics of test MOS transistors after irradiation with fast electrons and subsequent heat treatment are reported. It is shown that the concentration of trapping centers in the oxide is lowered as a result of radiation-thermal treatment.     

Numerical approximation of the Ginzburg-Landau equation with memory effects in the dynamics of phase transitions

We consider the out-of-equilibrium time evolution of a nonconserved order parameter using the Ginzburg-Landau equation including memory effects. Memory effects are expected to play important role on the nonequilibrium dynamics for fast phase transitions, in which the time scales of the rapid phase conversion are comparable to the microscopic time scales. We consider two numerical approximation schemes based on Fourier collocation and finite difference methods and perform a numerical analysis with respect to the existence, stability and convergence of the schemes. We present results of direct numerical simulations for one and three spatial dimensions, and examine numerically the stability and convergence of both approximation schemes.     

STRINGVACUA. A Mathematica package for studying vacuum configurations in string phenomenology

We give a simple tutorial introduction to the Mathematica package STRINGVACUA, which is designed to find vacua of string-derived or inspired four-dimensional N=1 supergravities. The package uses powerful algebro-geometric methods, as implemented in the free computer algebra system Singular, but requires no knowledge of the mathematics upon which it is based. A series of easy-to-use Mathematica modules are provided which can be used both in string theory and in more general applications requiring fast polynomial computations. The use of these modules is illustrated throughout with simple examples.

Program summary

Program title: STRINGVACUACatalogue identifier: AEBZ_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBZ_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: GNU GPLNo. of lines in distributed program, including test data, etc.: 31 050No. of bytes in distributed program, including test data, etc.: 163 832Distribution format: tar.gzProgramming language: “Mathematica” syntaxComputer: Home and office spec desktop and laptop machines, networked or stand aloneOperating system: Windows XP (with Cygwin), Linux, Mac OS, running Mathematica V5 or aboveRAM: Varies greatly depending on calculation to be performedClassification: 11.1External routines: Linux: The program “Singular” is called from Mathematica. Windows: “Singular” is called within the Cygwin environment from Mathematica.Nature of problem: A central problem of string-phenomenology is to find stable vacua in the four-dimensional effective theories which result from compactification.Solution method: We present an algorithmic method, which uses techniques of algebraic geometry, to find all of the vacua of any given string-phenomenological system in a huge class.Running time: Varies greatly depending on calculation requested.     

Dynamics of the deconfinement transition of quarks and gluons in a finite volume

We employ finite elements methods for the approximation of solutions of the Ginzburg-Landau equations describing the deconfinement transition in quantum chromodynamics. These methods seem appropriate for situations where the deconfining transition occurs over a finite volume as in relativistic heavy ion collisions, where in addition expansion of the system and flow of matter are important. Simulation results employing finite elements are presented for a Ginzburg-Landau equation based on a model free energy describing the deconfining transition in pure gauge SU(2) theory. Results for finite and infinite system are compared.     

The role of IAEA in coordinating research and transferring technology in radiation chemistry and processing of polymers

The IAEA has been playing a significant role in fostering developments in radiation technology in general and radiation processing of polymers in particular, among its Member States (MS) and facilitate know-how/technology transfer to developing MS. The former is usually achieved through coordinated research projects (CRP) and thematic technical meetings, while the latter is mainly accomplished through technical cooperation (TC) projects. Coordinated research projects encourage research on, and development and practical application of, radiation technology to foster exchange of scientific and technical information. The technical cooperation (TC) programme helps Member States to realize their development priorities through the application of appropriate radiation technology.The IAEA has implemented several coordinated research projects (CRP) recently, including one on-going project, in the field of radiation processing of polymeric materials. The CRPs facilitated the acquisition and dissemination of know-how and technology for controlling of degradation effects in radiation processing of polymers, radiation synthesis of stimuli-responsive membranes, hydrogels and absorbents for separation purposes and the use of radiation processing to prepare biomaterials for applications in medicine.The IAEA extends cooperation to well-known international conferences dealing with radiation technology to facilitate participation of talented scientists from developing MS and building collaborations. The IAEA published technical documents, covering the findings of thematic technical meetings (TM) and coordinated research projects have been an important source of valuable practical information.     

Study of polypropylene/polybutene blends modified by gamma irradiation and (high melt strength polypropylene)/polybutene blends

It is well-known that polypropylene (PP) is difficult to process as a consequence of its linear structure. It is also known that grafting of long-chain branches on PP backbone using ionizing radiation is an effective approach to achieve high melt strength polypropylene (HMS PP). Chain-scission and, in minor extend, crosslinking and grafting are the predominant reaction in order to branch PP backbone. However, if multifunctional monomers are used to promote the grafting reaction, crosslinking can surpass chain scission and grafting, reducing drawability. Therefore, in an effort to enhance the processability and so the drawability, it has been found helpful to add a small amount of polybutene-1. Gamma irradiation technique was used to induce chemical changes in blends of PP and polybutene in acetylene atmosphere (crosslinker promoter) and in HMSPP/polybutene blends. The samples were irradiated with a ⁶⁰Co source with doses of 12.5 and 20 kGy in the presence of acetylene. In this work, two different methods of blends processing were compared regarding rheological and mechanical properties. Effects on the strength and elongation at the yield point and at rupture were observed by mechanical tests and showed decrease of tensile strength and increase of elongation at rupture for samples obtained by irradiation of blends. The results from rheology demonstrated an increase in melt strength and drawability of blends.     

Radiation-induced degradation of galactomannan polysaccharides

In this study, guar gum, tara gum and locust bean gum were irradiated in a gamma cell in the solid state. The change in their molecular weights were determined by size exclusion chromatography analysis and the change in their viscosity values with change of temperature and irradiation dose were determined. Chain scission yield, G(s), and degradation rate values were calculated. The calculated G(s) values is 1.09 ± 0.16, 1.07 ± 0.06, 0.85 ± 0.10 for GG, TG and LBG, respectively. The effect of mannose-galactose ratio and initial molecular weight of these gums on the degradation behavior were discussed.     

Combined addition of nano diamond and nano SiO2, an effective method to improve the in-field critical current density of MgB2 superconductor

MgB₂ bulk samples added with nano SiO₂ and/or nano diamond were prepared by powder-in-sealed-tube (PIST) method and the effects of addition on structural and superconducting properties were studied. X-ray diffraction (XRD) analysis revealed that the addition caused systematic reduction in ‘a’ lattice parameter due to the substitution of C atoms at B sites and the strain caused by reacted intragrain nano particles of Mg₂Si as evinced by transmission electron microscope image. Scanning electron microscopy images showed distinct microstructural variations with SiO₂/diamond addition. It was evident from DC magnetization measurements that the in-field critical current density [J_C(H)] of doped samples did not fall drastically like the undoped sample. Among the doped samples the J_C(H) of co-doped samples were significantly higher and the best co-doped sample yielded a J_C, an order of magnitude more than the undoped one at 5 K and 8 T.     

Electron beam-induced thickening of the protective oxide layer around Fe nanoparticles

There are many circumstances in science where the process of measuring the properties of a system alters the system. An imaging process can exert an inadvertent effect on the object being observed. Consequently, what we observe does not necessarily represent what had been present before the observation. Normally, this effect can be ignored if the consequence of such a change is believed not to be significant. The expansion of nanostructured materials has made high-resolution transmission electron microscopy one of the indispensable tools for probing the characteristics of nanomaterials. Modification of nanoparticles by the electron beam during their imaging has been widely noticed and this is generally believed to be due to electron beam-induced heating effect, defect formation in the particles, charging of the particle, or excitation of surrounding gases. However, an explicit experimental identification of which process dominates is often very hard to establish. We report the thickening of native oxide layer on iron nanoparticle under electron beam irradiation. Based on atomic level imaging, electron diffraction, and computer simulation, we have direct evidence that the protecting oxide layer formed on Fe nanoparticle at room temperature in air or oxygen continues to grow during an electron beam bombardment in the vacuum system typical of most TEM systems. Typically, the oxide layer increases from approximately 3 to approximately 6 nm following approximately 1h electron beam exposure typically with an electron flux of 7 x 10(5)nm(-2)s(-1) and an vacuum of approximately 3 x 10(-5)Pa. Partial illumination of a nanoparticle and observation of the shell thickening conclusively demonstrates that many of the mechanisms postulated to explain such processes are not occurring to a significant extent. The observed growth is not related to the electron beam-induced heating of the nanoparticle, or residual oxygen ionization, or establishment of an electrical field, rather it is related to electron beam-facilitated mass transport across the oxide layer (a defect-related process). The growth follows a parabolic growth law.