Magnetically Focused Proton Irradiation of Small Volume Radiosurgery Targets Using a Triplet of Quadrupole Magnets

Proton therapy is an advantageous choice for the irradiation of tumors in proximity of critical structures due to rapid dose fall off and high dose deposition at target compared to dose at the surface of the patient (ie, peak-to-entrance dose ratio (P/E)). However, with target fields below 1.0 cm, as often encountered in proton radiosurgery, multiple Coulomb scattering (MCS) broadens proton beams leading to diminished P/E advantages and reduced dose delivery efficiency (DDE). Magnetic focusing tends to counteract MCS and is a promising method to reduce these undesirable effects. The purpose of this research is to investigate the advantages of proton magnetic focusing with a triplet of quadrupole rare earth permanent magnets

Defect Formation Energies without the Band-Gap Problem: Combining DFT and GW for the Silicon Self-Interstitial

We present an improved method to calculate defect formation energies that overcomes the band-gap problem of Kohn-Sham density-functional theory (DFT) and reduces the self-interaction error of the local-density approximation (LDA) to DFT. We demonstrate for the silicon self-interstitial that combining LDA with quasiparticle energy calculations in the G0W0 approach increases the defect formation energy of the neutral charge state by ~1.1 eV, which is in good agreement with diffusion Monte Carlo calculations (E. R. Batista et al. Phys. Rev. B 74, 121102(R) (2006), W.-K. Leung et al. Phys. Rev. Lett. 83, 2351 (1999)). Moreover, the G0W0-corrected charge transition levels agree well with recent measurements.Comment: 4 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Analytical modelling of stable isotope fractionation of volatile organic compounds in the unsaturated zone

Analytical models were developed that simulate stable isotope ratios of volatile organic compounds (VOCs) near a point source contamination in the unsaturated zone. The models describe diffusive transport of VOCs, biodegradation and source ageing. The mass transport is governed by Fick's law for diffusion, and the equation for reactive transport of VOCs in the soil gas phase was solved for different source geometries and for different boundary conditions. Model results were compared to experimental data from a one-dimensional laboratory column and a radial-symmetric field experiment, and the comparison yielded a satisfying agreement. The model results clearly illustrate the significant isotope fractionation by gas-phase diffusion under transient state conditions. This leads to an initial depletion of heavy isotopes with increasing distance from the source. The isotope evolution of the source is governed by the combined effects of isotope fractionation due to vaporization, diffusion and biodegradation. The net effect can lead to an enrichment or depletion of the heavy isotope in the remaining organic phase depending on the compound and element considered. Finally, the isotope evolution of molecules migrating away from the source and undergoing degradation is governed by a combined degradation and diffusion isotope effect. This suggests that in the unsaturated zone, the interpretation of biodegradation based on isotope data must always be based on a model combining gas-phase diffusion and degradation.Comment: 11 pages, 6 figure

Testing for sexually transmitted infections in general practice: cross-sectional study

Background: Primary care is an important provider of sexual health care in England. We sought to explore the extent of testing for chlamydia and HIV in general practice and its relation to associated measures of sexual health in two contrasting geographical settings.Methods: We analysed chlamydia and HIV testing data from 64 general practices and one genitourinary medicine (GUM) clinic in Brent (from mid-2003 to mid-2006) and 143 general practices and two GUM clinics in Avon (2004). We examined associations between practice testing status, practice characteristics and hypothesised markers of population need (area level teenage conception rates and Index of Multiple Deprivation, IMD scores).Results: No HIV or chlamydia testing was done in 19% (12/64) of general practices in Brent, compared to 2.1% (3/143) in Avon. In Brent, the mean age of general practitioners (GPs) in Brent practices that tested for chlamydia or HIV was lower than in those that had not conducted testing. Practices where no HIV testing was done had slightly higher local teenage conception rates (median 23.5 vs. 17.4/1000 women aged 15-44, p = 0.07) and served more deprived areas (median IMD score 27.1 vs. 21.8, p = 0.05). Mean yearly chlamydia and HIV testing rates, in practices that did test were 33.2 and 0.6 (per 1000 patients aged 15-44 years) in Brent, and 34.1 and 10.3 in Avon, respectively. In Brent practices only 20% of chlamydia tests were conducted in patients aged under 25 years, compared with 39% in Avon.Conclusions: There are substantial geographical differences in the intensity of chlamydia and HIV testing in general practice. Interventions to facilitate sexually transmitted infection and HIV testing in general practice are needed to improve access to effective sexual health care. The use of routinely-collected laboratory, practice-level and demographic data for monitoring sexual health service provision and informing service planning should be more widely evaluated

Taphonomic experiments resolve controls on the preservation of melanosomes and keratinous tissues in feathers

Fossils are a key source of data on the evolution of feather structure and function through deep time, but their ability to resolve macroevolutionary questions is compromised by an incomplete understanding of their taphonomy. Critically, the relative preservation potential of two key feather components, melanosomes and keratinous tissue, is not fully resolved. Recent studies suggesting that melanosomes are preferentially preserved conflict with observations that melanosomes preserve in fossil feathers as external moulds in an organic matrix. To date, there is no model to explain the latter mode of melanosome preservation. We addressed these issues by degrading feathers in systematic taphonomic experiments incorporating decay, maturation and oxidation in isolation and combination. Our results reveal that the production of mouldic melanosomes requires interactions with an oxidant and is most likely to occur prior to substantial maturation. This constrains the taphonomic conditions under which melanosomes are likely to be fossilized. Critically, our experiments also confirm that keratinous feather structures have a higher preservation potential than melanosomes under a range of diagenetic conditions, supporting hitherto controversial hypotheses that fossil feathers can retain degraded keratinous structures

Development of Personalized Health Messages to Promote Engagement in Advance Care Planning

Objectives: To develop and test the acceptability of personalized intervention materials to promote advance care planning (ACP) based on the Transtheoretical Model (TTM), in which readiness to change is a critical organizing construct. Design: Development study creating an expert system delivering TTM‐personalized feedback reports and stage‐matched brochures with more‐general information on ACP and modifications based on participant reviews. Setting: Senior centers. Participants: Community‐living persons aged 65 and older (N = 77). Measurements: Participant ratings of length, attractiveness, and trustworthiness of and reactions to reports and brochures. Results: The expert system assessed participants’ readiness to engage in each of four ACP behaviors: completion of a living will, naming a health care proxy, communication with loved ones about quality vs quantity of life, and communication with clinicians about quality vs quantity of life. The system also assessed pros and cons of engagement and values and beliefs that influence engagement. The system provided individualized feedback based on the assessment, with brochures providing additional general information. Initial participant review indicating unacceptable length led to revision of feedback reports from full‐sentence paragraph format to bulleted format. After review, the majority of participants rated the materials as easy to read, trustworthy, providing new information, making them more comfortable reading about ACP, and increasing interest in participating in ACP. Conclusion: Older adults found an expert system individualized feedback report and accompanying brochure to promote ACP engagement to highly acceptable and engaging. Additional research is necessary to examine the effects of these materials on behavior change

Emission of Circularly Polarized Terahertz Wave from Inhomogeneous Intrinsic Josephson Junctions

We have theoretically demonstrated the emission of circularly-polarized terahertz (THz) waves from intrinsic Josephson junctions (IJJs) which is locally heated by an external heat source such as the laser irradiation. We focus on a mesa-structured IJJ whose geometry is slightly deviate from a square and find that the local heating make it possible to emit circularly-polarized THz waves. In this mesa, the inhomogeneity of critical current density induced by the local heating excites the electromagnetic cavity modes TM (1,0) and TM (0,1), whose polarizations are orthogonal to each other. The mixture of these modes results in the generation of circularly-polarized THz waves. We also show that the circular polarization dramatically changes with the applied voltage. The emitter based on IJJs can emit circularly-polarized and continuum THz waves by the local heating, and will be useful for various technological application.Comment: 5 pages, 3 figure

Changing use of Lizard Island over the past 4000 years and implications for understanding Indigenous offshore island use on the Great Barrier Reef

Archaeological records documenting the timing and use of northern Great Barrier Reef offshore islands by Aboriginal and Torres Strait Islander peoples throughout the Holocene are limited when compared to the central and southern extents of the region. Excavations on Lizard Island, located 33 km from Cape Flattery on the mainland, provide high resolution evidence for periodic, yet sustained offshore island use over the past 4000 years, with focused exploitation of diverse marine resources and manufacture of quartz artefacts. An increase in island use occurs from around 2250 years ago, at a time when a hiatus or reduction in offshore island occupation has been documented for other Great Barrier Reef islands, but concurrent with demographic expansion across Torres Strait to the north. Archaeological evidence from Lizard Island provides a previously undocumented occupation pattern associated with Great Barrier Reef Late Holocene island use. We suggest this trajectory of Lizard Island occupation was underwritten by its place within the Coral Sea Cultural Interaction Sphere, which may highlight its significance both locally and regionally across this vast seascape