Energy losses to surface plasmons by charged particles

The theory of charged particle energy loss to the surface plasmon field is reviewed for a swift charged particle incident on a model metallic system. The expected energy loss is estimated for some representative cases. (GHT

Space-time evolution of electron cascades in diamond

Here we describe model calculations to follow the spatio-temporal evolution of secondary electron cascades in diamond. The band structure of the insulator has been explicitly incorporated into the calculations as it affects ionizations from the valence band. A Monte-Carlo model was constructed to describe the path of electrons following the impact of a single electron of energy E 250 eV. The results show the evolution of the secondary electron cascades in terms of the number of electrons liberated, the spatial distribution of these electrons, and the energy distribution among the electrons as a function of time. The predicted ionization rates (5-13 electrons in 100 fs) lie within the limits given by experiments and phenomenological models. Calculation of the local electron density and the corresponding Debye length shows that the latter is systematically larger than the radius of the electron cloud. This means that the electron gas generated does not represent a plasma in a single impact cascade triggered by an electron of E 250 eV energy. This is important as it justifies the independent-electron approximation used in the model. At 1 fs, the (average) spatial distribution of secondary electrons is anisotropic with the electron cloud elongated in the direction of the primary impact. The maximal radius of the cascade is about 50 A at this time. As the system cools, energy is distributed more equally, and the spatial distribution of the electron cloud becomes isotropic. At 90 fs maximal radius is about 150 A. The Monte-Carlo model described here could be adopted for the investigation of radiation damage in other insulators and has implications for planned experiments with intense femtosecond X-ray sources.Comment: 26 pages, latex, 13 figure

Recall and patient perceptions of hip precautions 6 weeks after total hip arthroplasty

Background and purpose — There is a lack of evidence to support the role of hip precautions in preventing dislocation following total hip arthroplasty (THA). We report an exploratory study which assesses recall, adherence, and the impact of precautions on activities of daily living in the first 6 weeks postoperatively. Patients and methods — We designed a new questionnaire based on the education patients receive and refined by professionals within our multidisciplinary team. 129 patients underwent primary elective THA during the study period and received the questionnaire at 6 weeks postoperatively. Results — 97 (75%) patients responded before the 8th week postoperatively. Most of these (83 patients) could remember all the precautions. Of the 97 who responded only 22 claimed to adhere to all of the precautions. 48 admitted to putting their own underwear on without the use of aids or assistance, and 38 had started walking without an aid. Due to the precautions 67 avoided leaving the house at some point and 63 were unable to perform desired activities. 84 stated that their sleep was affected. There were no dislocations among the 97 patients who responded; however, there was 1 dislocation among the 32 non-responders. Interpretation — We found that most patients did not adhere to hip precaution advice. Precautions have a detrimental effect on patient activity and sleep. In view of the limited efficacy in reducing dislocation rate, we question the use of precautions in the primary arthroplasty setting

Social marketing and social influences: Using social ecology as a theoretical framework

Social marketing has traditionally been dominated by an individualistic model of design. In this work, the authors apply a social ecology model to the theory and practice of social marketing, demonstrating that a multilevel framework is required to fully expose and account for the complexity of sociocultural and environmental effects. The authors have generated a diagnostic tool for this use. The paper then provides a detailed demonstration of the potential power of the tool by applying it to three illustrative case studies: one on encouraging safer driving, the second promoting sustainable travel, and the third increasing early detection of lung cancer. © 2010 Westburn Publishers Ltd

Novel genetic loci associated with hippocampal volume

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness

Brain volumetric deficits in MAPT mutation carriers: a multisite study

Objective: MAPT mutations typically cause behavioral variant frontotemporal dementia with or without parkinsonism. Previous studies have shown that symptomatic MAPT mutation carriers have frontotemporal atrophy, yet studies have shown mixed results as to whether presymptomatic carriers have low gray matter volumes. To elucidate whether presymptomatic carriers have lower structural brain volumes within regions atrophied during the symptomatic phase, we studied a large cohort of MAPT mutation carriers using a voxelwise approach. Methods: We studied 22 symptomatic carriers (age 54.7 ± 9.1, 13 female) and 43 presymptomatic carriers (age 39.2 ± 10.4, 21 female). Symptomatic carriers’ clinical syndromes included: behavioral variant frontotemporal dementia (18), an amnestic dementia syndrome (2), Parkinson’s disease (1), and mild cognitive impairment (1). We performed voxel-based morphometry on T1 images and assessed brain volumetrics by clinical subgroup, age, and mutation subtype. Results: Symptomatic carriers showed gray matter atrophy in bilateral frontotemporal cortex, insula, and striatum, and white matter atrophy in bilateral corpus callosum and uncinate fasciculus. Approximately 20% of presymptomatic carriers had low gray matter volumes in bilateral hippocampus, amygdala, and lateral temporal cortex. Within these regions, low gray matter volume

Expanding the clinical phenotype of individuals with a 3-bp in-frame deletion of the NF1 gene (c.2970_2972del): an update of genotype–phenotype correlation

Purpose: Neurofibromatosis type 1 (NF1) is characterized by a highly variable clinical presentation, but almost all NF1-affected adults present with cutaneous and/or subcutaneous neurofibromas. Exceptions are individuals heterozygous for the NF1 in-frame deletion, c.2970_2972del (p.Met992del), associated with a mild phenotype without any externally visible tumors. Methods: A total of 135 individuals from 103 unrelated families, all carrying the constitutional NF1 p.Met992del pathogenic variant and clinically assessed using the same standardized phenotypic checklist form, were included in this study. Results: None of the individuals had externally visible plexiform or histopathologically confirmed cutaneous or subcutaneous neurofibromas. We did not identify any complications, such as symptomatic optic pathway gliomas (OPGs) or symptomatic spinal neurofibromas; however, 4.8% of individuals had nonoptic brain tumors, mostly low-grade and asymptomatic, and 38.8% had cognitive impairment/learning disabilities. In an individual with the NF1 constitutional c.2970_2972del and three astrocytomas, we provided proof that all were NF1-associated tumors given loss of heterozygosity at three intragenic NF1 microsatellite markers and c.2970_297

Stopping powers of solids for low-energy protons

Electron gas models are useful approximations for describing the valence electron response of a solid to the passage of a charged particle. A simple free-electron gas model was used by Fermi and Teller to estimate the time required for a mesotron to be stopped in various solids. More recent work has employed the Lindhard dielectric response function, or approximations thereto, for calculations of the valence electron contributions to energy loss per unit pathlength for protons. Such calculations have generally shown rather poor agreement with experimental data for low-energy protons (velocity small compared to the Fermi velocity, v<<v/sub F/). The purpose of this paper is to draw attention to a recent calculation of the stopping power for slow protons using a density-functional formalism. These new results have been shown to give good agreement with experimental data and thus should provide valuable theoretical guidance in estimating stopping powers of solids for which no experimental data are available

Energy loss and scattering of subexcitation electrons in SiO/sub 2/

For electrons with energies below the band gap energy of approx. 9 eV in SiO/sub 2/, energy loss or gain occurs through phonon emission or absorption. Coupling to the longitudinal optical (LO) modes has been considered by several workers in connection with ''electron-runaway'' and subsequent ''breakdown'' when high electric fields are applied to this insulator. The important role played by acoustic phonon modes in predicting the breakdown field in SiO/sub 2/ was recently discussed by Fischetti and Fischetti, et al. following the theoretical formulations described by Sparks, et al. We have re-examined these interactions and evaluated the energy loss per unit pathlength and transport mean free path to aid in a qualitative description of the behavior of subexcitation electrons in SiO/sub 2/. For example, energy losses and angular deflections experienced by subexcitation electrons in matter are very important in establishing whether geminate recombination occurs between an ejected electron and its parent ion in radiation physics. The response of solid-state devices to ionizing radiation is determined in part by recombination processes, which in turn may depend importantly on the kinds of cross sections that we consider here. 11 refs., 6 figs