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

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

Modelling of low-pressure gas breakdown in uniform DC electric field by PIC technique with realistic secondary electron emission

This paper compares the basic phenomenological model based on the Townsends theory and the detailed simulation of the gas breakdown in argon in uniform DC electric field. Calculations were carried out by using a one-dimensional particle-in-cell/Monte Carlo (PIC/MCC) code with three velocity components with a new secondary emission model. The simulation results clearly show how different models of the secondary electron emission affect the breakdown voltage. The fact that results of simulation are in a good agreement with the available experimental data merely means that phenomenological secondary electron yields were developed to fit the experiment. However, oversimplified models cannot predict all features of Townsend discharges and cannot be reconciled with binary collision data. One such example is the need to predict the DC volt-ampere characteristics in order to reveal the predominant physical processes by studying the j/p(2) scaling.22nd Symposium on Plasma Physics and Technology, Jun 26-29, 2006, Prague, Czech Republi

On application of transport coefficients in plasma modelling

In this paper we review recent developments in the transport theory as developed to deal with the so-called swarm experiments. We analyze where and how such results can affect the outcome of the plasma models [1]. In principle it is well understood that modeling of plasmas requires representing a large number of processes, and for a large group of these one does not know all the pertinent physical processes and even more so there is a general shortage of data. In that respect insisting on purity in the representation of the charged particle, in particular electron transport seems unnecessary. Nevertheless we wish to draw attention that neglecting some aspects of electron transport may lead to neglecting some important aspects of physics. We wish to draw attention to proper representation of the transport in crossed electric and magnetic fields, differences between flux and bulk transport properties under appreciable influence of non-conservative processes, temporal development of transport coefficients, anisotropy of diffusion and anomalous longitudinal diffusion when field changes direction and many more. Finally we wish to draw attention that plasma models should be benchmarked against basic swarm test models to verify how adequate the representation of some processes is. The stage of development of plasma models has reached such sophistication that perhaps requires that all aspects should be developed at the best available level. [1] RE Robson et al. Rev.Modern Phys. 77 (4) (2005) 1303

Structure and proton conductivity of 12-tungstophosphoric acid doped silica

Sol-gel syntheses offer a wide range of possibilities for introduction of materials with specific properties (electronic, optic and ion-conductive, etc.) into optically clear matrices. Preparation of silica gel bulk, containing 12-tungstophosphoric acid (WPA) in mesopores, as well as its structural and conduction characteristics are reported. Characteristics of the obtained doped gels depend on the gel preparation, gelation process and the WPA content. According to the obtained results, especially for the high conductivity (sigma similar to 0.1 S/cm), WPA doped silica gel is a promising material for solid electrolytes.VIII International Conference on Solid State Protonic Conductors, Aug 18-23, 1996, Gol, Norwa

Economic evaluation alongside a randomised controlled crossover trial of modified group cognitive behavioural therapy for anxiety compared to treatment-as-usual in adults with Asperger Syndrome

<strong>Background:</strong> There is a growing interest in using group cognitive behavioural therapy (CBT) with people who have Asperger Syndrome (AS) and comorbid mental health problems. This study aims to assess the cost-effectiveness of modified group CBT for adults with AS experiencing co-occurring anxiety compared to treatment-as-usual. <strong>Methods:</strong> Economic evaluation alongside a pilot, multi-centre, single-blind, randomised controlled crossover trial. Costs from the UK public sector (National Health Service and Social Services) and societal perspectives, quality-adjusted life-years (QALYs), incremental net (monetary) benefit (INB), expected value of perfect information, expected value of sample information, expected net gain of sampling, and efficient sample size of a future trial are reported. <strong>Results:</strong> Over 48 weeks, from the societal perspective, CBT results in additional costs of £6647, with only a 0.015 incremental gain in QALYs, leading to a negative INB estimate of £6206 and a 23% probability of cost-effectiveness at a threshold of £30,000/QALY. Results from sensitivity analyses support the unlikely cost-effectiveness of CBT, but indicate the potential for cost-effectiveness over longer time horizons. Eliminating decision uncertainty is valued at £277 million and the efficient sample size for a future trial is estimated at 1,200 participants per arm. <strong>Limitations:</strong> Relatively small sample size and prevalence of missing data present challenges to the interpretation of the results. <strong>Conclusions:</strong> Current evidence from this small pilot study suggests that on average, modified group CBT is not cost-effective. However, there is much decision uncertainty so such a conclusion could be wrong. A large, full scale trial to reduce uncertainty would be an efficient investment for the UK health economy

Plasma induced DNA damage: Comparison with the effects of ionizing radiation

We use human primary fibroblasts for comparing plasma and gamma rays induced DNA damage. In both cases, DNA strand breaks occur, but of fundamentally different nature. Unlike gamma exposure, contact with plasma predominantly leads to single strand breaks and base-damages, while double strand breaks are mainly consequence of the cell repair mechanisms. Different cell signaling mechanisms are detected confirming this (ataxia telangiectasia mutated - ATM and ataxia telangiectasia and Rad3 related - ATR, respectively). The effective plasma doses can be tuned to match the typical therapeutic doses of 2Gy. Tailoring the effective dose through plasma power and duration of the treatment enables safety precautions mainly by inducing apoptosis and consequently reduced frequency of micronuclei. (C) 2014 AIP Publishing LLC