Data for Modeling of Positron Collisions and Transport in Gases

We review the current status of positron cross sections for collisions with atoms and molecules from the viewpoint of their use in studies of positron transport processes in gases, liquids and human tissue. The data include cross sections for positron scaThis work is supported by MNPRS Projects ON171037 and III41011 and the Australian Research Council’s Centre of Excellence Program

Breakdown, scaling and volt-ampere characteristics of low current micro-discharges

Abstract We give preliminary results on the breakdown and low current limit of volt-ampere characteristics of simple parallel plate non-equilibrium dc discharges at standard (centimetre size) and micro-discharge conditions. Experiments with micro-discharges are reported attempting to establish the maintenance of E/N, pd and j/p 2 scalings at small dimensions down to 20 µm. It was found that it may not be possible to obtain properly the left-hand side of the Paschen curve. The possible causes are numerous but we believe that it is possible that long path prevention techniques do not work at high pressures. Nevertheless, the standard scaling laws seem to be maintained down to these dimensions which are consistent with simulations that predict violation of scaling below 10 µm. Volt-ampere characteristics are also presented and compared with those of the standard size discharges

Application of Non-Eqilibrium Plasmas in Top-Down and Bottom-Up Nanotechnologies and Biomedicine

In this paper we discuss how a better understanding of thermal and mainly non-thermal plasmas provides basis for their application in a number or nanotechnologies. One should bear in mind that one may design unique properties of plasmas thus affecting very directly properties of the resulting nanostructures. A number of examples where plasmas contribute to production of nanomaterials, modification of surfaces and functionalization at nanoscales are given here. Plasmas are not a panacea but in nanotechnology their application may be the best strategy to convert production of individual structures to massively parallel production that may become a viable industrial technology

Positrons in gas filled traps and their transport in molecular gases

In this paper we give a review of two recent developments in positron transport, calculation of transport coefficients for a relatively complete set of collision cross sections for water vapour and for application of they Monte Carlo technique to model gas filled subexcitation positron traps such as Penning Malmberg Surko (Surko) trap. Calculated transport coefficients, very much like those for argon and other molecular gases show several new kinetic phenomena. The most important is the negative differential conductivity (NDC) for the bulk drift velocity when the flux drift velocity shows no sign of NDC. These results in water vapour are similar to the results in argon or hydrogen. The same technique that has been used for positron (and previously electron) transport may be applied to model development of particles in a Surko trap. We have provided calculation of the ensemble of positrons in the trap from an initial beam like distribution to the fully thermalised distribution. This model, however, does not include plasma effects (interaction between charged particles) and may be applied for lower positron densities

On new developments in the physics of positron swarms

Recently a new wave of swarm studies of positrons was initiated based on more complete scattering cross section sets. Initially some interesting and new physics was discovered, most importantly negative differential conductivity (NDC) that occurs only for the bulk drift velocity while it does not exist for the flux property. However the ultimate goal was to develop tools to model positron transport in realistic applications and the work that is progressing along these lines is reviewed here. It includes studies of positron transport in molecular gases, thermalization in generic swarm situations and in realistic gas filled traps and transport of positrons in crossed electric and magnetic fields. Finally we have extended the same technique of simulation (Monte Carlo) to studies of thermalization of positronium molecule. In addition, recently published first steps towards including effects of dense media on positron transport are summarized here

Kinetic phenomena in transport of electrons and positrons in gases caused by the properties of scattering cross sections

Collisions of electrons, atoms, molecules, photons and ions are the basic processes in plasmas and ionized gases in general. This is especially valid for low temperature collisional plasmas. Kinetic phenomena in transport are very sensitivitive to the shape of the cross sections and may at the same time affect the macroscopic applications. We will show how transport theory or simulation codes, phenomenology, kinetic phenomena and transport data may be used to improve our knowledge of the cross sections, our understanding of the plasma models, application of the swarm physics in ionized gases and similar applications to model and improve gas filled traps of positrons. Swarm techniques could also be a starting point in applying atomic and molecular data in models of electron or positron therapy/diagnostics in radiation related medicine

The Prometastatic Microenvironment of the Liver

The liver is a major metastasis-susceptible site and majority of patients with hepatic metastasis die from the disease in the absence of efficient treatments. The intrahepatic circulation and microvascular arrest of cancer cells trigger a local inflammatory reaction leading to cancer cell apoptosis and cytotoxicity via oxidative stress mediators (mainly nitric oxide and hydrogen peroxide) and hepatic natural killer cells. However, certain cancer cells that resist or even deactivate these anti-tumoral defense mechanisms still can adhere to endothelial cells of the hepatic microvasculature through proinflammatory cytokine-mediated mechanisms. During their temporary residence, some of these cancer cells ignore growth-inhibitory factors while respond to proliferation-stimulating factors released from tumor-activated hepatocytes and sinusoidal cells. This leads to avascular micrometastasis generation in periportal areas of hepatic lobules. Hepatocytes and myofibroblasts derived from portal tracts and activated hepatic stellate cells are next recruited into some of these avascular micrometastases. These create a private microenvironment that supports their development through the specific release of both proangiogenic factors and cancer cell invasion- and proliferation-stimulating factors. Moreover, both soluble factors from tumor-activated hepatocytes and myofibroblasts also contribute to the regulation of metastatic cancer cell genes. Therefore, the liver offers a prometastatic microenvironment to circulating cancer cells that supports metastasis development. The ability to resist anti-tumor hepatic defense and to take advantage of hepatic cell-derived factors are key phenotypic properties of liver-metastasizing cancer cells. Knowledge on hepatic metastasis regulation by microenvironment opens multiple opportunities for metastasis inhibition at both subclinical and advanced stages. In addition, together with metastasis-related gene profiles revealing the existence of liver metastasis potential in primary tumors, new biomarkers on the prometastatic microenvironment of the liver may be helpful for the individual assessment of hepatic metastasis risk in cancer patients

Keep safe: the development of a manualised group CBT intervention for adolescents with ID who display harmful sexual behaviours.

Purpose The purpose of this paper is to focus on the development of Keep Safe, a manualised group intervention for adolescents with intellectual disabilities (ID) who display harmful sexual behaviour (HSB) as the initial phase of a feasibility study. National reports have highlighted the need for the development of specialist programmes, as adolescents with ID make up a significant proportion of young people referred to specialist HSB services and there is a lack of evidence or practice-based interventions for them. Aims included taking account of adolescents’ and families’ needs, motivations and practical commitments, integrating best- practice and being accessible and appropriate across different types of services. Design/methodology/approach Keep Safe development progressed from the practitioner/researcher collaborative young sex offender treatment services collaborative-ID through a project team, Keep Safe development group, comprising a range of practitioners with a variety of clinical expertise across services and an Advisory Group of people with ID. An expert-consensus methodology based on the Delphi method was used. The iterative process for the manual draws on the slim practice-based evidence from UK, New Zealand, North America and Australia. Findings Keep Safe comprises six modules distributed through 36 term-time young people’s sessions, alongside 16 concurrent parental/ carer sessions (some joint). The main focus of Keep Safe is to enhance well-being and reduce harm. Four initial sites volunteered as feasibility leads, and two more were added as recruitment was more difficult than foreseen. Originality/value National reports have highlighted the need for the development of specialist programmes, as adolescents with ID make up a significant proportion of young people referred to specialist HSB services and there is a lack of evidence or practice-based interventions for them. This study is innovative and valuable given the recognition that research and practice is significantly lacking in this area

Negative differential conductivity of positrons in gases

This paper reports on a new series of calculations of positron transport properties based on current experimental cross section data. It is found that negative differential conductivity (NDC) occurs in the bulk drift velocity W but not the flux drift velocity w. The origin of the phenomenon lies in the "reactive" nature of positron collisions associated with positronium Ps formation, and is quite different in origin to the better known NDC effect in w arising from certain combinations of inelastic-elastic cross sections. Moreover, while the Ps formation process is qualitatively similar (at least from a kinetic theory perspective) to electron attachment, it is characterized by a cross section several orders of magnitude larger and hence the "reactive" NDC effect is correspondingly more pronounced. In this paper we test both established conditions for NDC, and develop new criteria, using simple mathematics and physical arguments where possible