Bystander responses induced by low LET radiation

Radiation-induced bystander responses are observed when cells respond to their neighbours being irradiated. Considerable evidence is now available regarding the importance of these responses in cell and tissue models. Most studies have utilized two approaches where either a media-transferable factor has been assessed or cells have been exposed to low fluences of charged particles, where only a few percent are exposed. The development of microbeams has allowed nontargeted responses such as bystander effects to be more carefully analysed. As well as charged particle microbeams, X-ray microprobes have been developed, and several groups are also developing electron microbeams. Using the Gray Cancer Institute soft X-ray microprobe, it has been possible to follow the response of individual cells to targeted low doses of carbon-characteristic soft X-rays. Studies in human fibroblasts have shown evidence of a significant radiation quality-dependent bystander effect, measured as chromosomal damage in the form of micronuclei which is radiation quality dependent. Other studies show that even under conditions when only a single cell is targeted with soft X-rays, significant bystander-mediated cell killing is observed. The observation of bystander responses with low LET radiation suggests that these may be important in understanding radiation risk from background levels of radiation, where cells observe only single electron track traversals. Also, the indirect evidence for these responses in vivo indicates that they may have a role to play in current radiotherapy approaches and future novel strategies involving modulating nontargeted responses.

A multiple-radical model for radiation action on DNA and the dependence of OER on LET

We have a developed a multiple-radical model of the chemical modification reactions involving oxygen and thiols relevant to the interactions of ionizing radiations with DNA. The treatment is based on the Alper and Howard-Flanders equation but considers the case where more than one radical may be involved in the production of lesions in DNA. This model makes several predictions regarding the induction of double strand breaks in DNA by ionizing radiation and the role of sensitizers such as oxygen and protectors such as thiols which act at the chemical phase of radiation action via the involvement of free radicals. The model predicts a decreasing OER with increasing LET on the basis that as radical multiplicity increases so will the probability that, even under hypoxia, damage will be fixed and lead to lesion production. The model can be considered to provide an alternative hypothesis to those of 'interacting radicals' or of 'oxygen-in-the-track'.

Plasma parameter characterization of a reflex plasma source operating in oxygen

A reflex discharge plasma, obtained as a hybrid between a Penning discharge plasma (PDP) and a hollow-cathode discharge (HCD) plasma, is analysed as a possible direction-current, high-density plasma source. The experiment is run in oxygen at pressures of 10 mTorr and 1 mTorr, and for discharge currents of 100 to 200 mA. Although the gas pressure is considerably lower than those used in HCDs, the hollow-cathode effect (HCE) occurs for current levels higher than 100 mA and leads to plasma densities comparable with those obtained using inductive plasma sources. The presence of a constant magnetic field leads to the enhancement of electron emission from cathodes under ion bombardment, and to the decreasing of the ion loss by diffusion to the wall.

STUDY OF THE DISCHARGE OF A MULTICUSP ION-SOURCE OPERATING WITH H2 AND D2

The plasma parameters and relative positive and negative ion concentrations in a small, filtered, multicusp ion source, operating at low plasma density (

Corruption and subsidiary profitability: US MNC subsidiaries in the Asia Pacific region

Would multinational corporation (MNC) subsidiaries be more profitable in host countries where corruption is less severe? Would MNC subsidiaries be more profitable in less corrupt countries if they focus on local sales? This paper examines the impact of the level of corruption on the profitability of US MNCs in the Asia Pacific region. Using foreign direct investment (FDI) data archived by the US Bureau of Economic Analysis and corruption data reported by the World Bank, we find that MNC subsidiaries located in countries with a lower level of corruption are more profitable. In addition, MNC subsidiaries with a greater focus on local sales are more profitable when the corruption level is low. This study contributes to the literature by showing that when local sales are important to MNC subsidiaries, a lower level of corruption by host countries positively affects the profitability of the MNC subsidiaries.

High-efficiency low-voltage-stress Class-EF PA with extended maximum operating frequency

The Class-EF power amplifier (PA) introduced recently has a peak switch voltage much lower than the well-known Class-E PA. However, the value of the transistor output capacitance at high frequencies is typically larger than the required Class-EF optimum shunt capacitance. As a result, softswitching operation that minimizes power dissipation during OFF-to-ON transient cannot be achieved at high frequencies. A novel Class-EF topology with transmission-line load network proposed in this paper allows the PA to operate at much higher frequencies without trading the other figures of merit. Closed-form formulations are derived to simultaneously satisfy the Class-EF impedances requirement at fundamental frequency, all even harmonics, and the first two odd harmonics as well as to provide matching to 50O load. © 2011 Institut fur Mikrowellen.