192 research outputs found
First-principles calculations of X-ray absorption spectra at the K-edge of 3d transition metals: an electronic structure analysis of the pre-edge
International audienceWe first present an extended introduction of the various methods used to extract electronic and structural information from the K pre-edge X-ray absorption spectra of 3d transition metal ions. The K pre-edge structure is then modelled for a selection of 3d transition metal compounds and analyzed using first-principles calculations based on the density functional theory (DFT) in the local density approximation (LDA). The selected compounds under study are presented in an ascending order of electronic structure complexity, starting with the Ti K-edge of rutile and anatase, and finishing with the Fe K-edge of the cyanomet-myoglobin. In most cases, the calculations are compared to polarized experimental spectra. It is shown that DFT-LDA methods enable us to reproduce satisfactorily the experimental features and to understand the nature of the electronic transitions involved in the pre-edge region. The limiting aspects of such methods in modelling the core-hole electron interaction and the 3d electron-electron repulsion are also pointed out
Experimental evidence of thermal fluctuations on the X-ray absorption near-edge structure at the aluminum K-edge
After a review of temperature-dependent experimental x-ray absorption
near-edge structure (XANES) and related theoretical developments, we present
the Al K-edge XANES spectra of corundum and beryl for temperature ranging from
300K to 930K. These experimental results provide a first evidence of the role
of thermal fluctuation in XANES at the Al K-edge especially in the pre-edge
region. The study is carried out by polarized XANES measurements of single
crystals. For any orientation of the sample with respect to the x-ray beam, the
pre-edge peak grows and shifts to lower energy with temperature. In addition
temperature induces modifications in the position and intensities of the main
XANES features. First-principles DFT calculations are performed for both
compounds. They show that the pre-edge peak originates from forbidden 1s to 3s
transitions induced by vibrations. Three existing theoretical models are used
to take vibrations into account in the absorption cross section calculations:
i) an average of the XANES spectra over the thermal displacements of the
absorbing atom around its equilibrium position, ii) a method based on the crude
Born-Oppenheimer approximation where only the initial state is averaged over
thermal displacements, iii) a convolution of the spectra obtained for the atoms
at the equilibrium positions with an approximate phonon spectral function. The
theoretical spectra so obtained permit to qualitatively understand the origin
of the spectral modifications induced by temperature. However the correct
treatment of thermal fluctuation in XANES spectroscopy requires more
sophisticated theoretical tools
Virtual patients design and its effect on clinical reasoning and student experience : a protocol for a randomised factorial multi-centre study
Background
Virtual Patients (VPs) are web-based representations of realistic clinical cases. They are proposed as being an optimal method for teaching clinical reasoning skills. International standards exist which define precisely what constitutes a VP. There are multiple design possibilities for VPs, however there is little formal evidence to support individual design features. The purpose of this trial is to explore the effect of two different potentially important design features on clinical reasoning skills and the student experience. These are the branching case pathways (present or absent) and structured clinical reasoning feedback (present or absent).
Methods/Design
This is a multi-centre randomised 2x2 factorial design study evaluating two independent variables of VP design, branching (present or absent), and structured clinical reasoning feedback (present or absent).The study will be carried out in medical student volunteers in one year group from three university medical schools in the United Kingdom, Warwick, Keele and Birmingham. There are four core musculoskeletal topics. Each case can be designed in four different ways, equating to 16 VPs required for the research. Students will be randomised to four groups, completing the four VP topics in the same order, but with each group exposed to a different VP design sequentially. All students will be exposed to the four designs. Primary outcomes are performance for each case design in a standardized fifteen item clinical reasoning assessment, integrated into each VP, which is identical for each topic. Additionally a 15-item self-reported evaluation is completed for each VP, based on a widely used EViP tool. Student patterns of use of the VPs will be recorded.
In one centre, formative clinical and examination performance will be recorded, along with a self reported pre and post-intervention reasoning score, the DTI. Our power calculations indicate a sample size of 112 is required for both primary outcomes
Microdosimetry of electrons in liquid water using the low-energy models of Geant4
The biological effects of ionizing radiation at the cellular level are frequently studied using the well-known formalism of microdosimetry, which provides a quantitative description of the stochastic aspects of energy deposition in irradiated media. Energy deposition can be simulated using Monte Carlo codes, some adopting a computationally efficient condensed-history approach, while others follow a more detailed track-structure approach. In this work, we present the simulation of microdosimetry spectra and related quantities (frequency-mean and dose-mean lineal energies) for incident monoenergetic electrons (50 eV-10 keV) in spheres of liquid water with dimensions comparable to the size of biological targets: base pairs (2 nm diameter), nucleosomes (10 nm), chromatin fibres (30 nm) and chromosomes (300 nm). Simulations are performed using the condensed-history low-energy physics models ( Livermore and Penelope ) and the track-structure Geant4-DNA physics models, available in the Geant4 Monte Carlo simulation toolkit. The spectra are compared and the influence of simulation parameters and different physics models, with emphasis on recent developments, is discussed, underlining the suitability of Geant4-DNA models for microdosimetry simulations. It is further shown that with an appropriate choice of simulation parameters, condensed-history transport may yield reasonable results for sphere sizes as small as a few tens of a nanometer
An implementation of discrete electron transport models for gold in the Geant4 simulation toolkit
Gold nanoparticle (GNP) boosted radiation therapy can enhance the biological effectiveness of radiation treatments by increasing the quantity of direct and indirect radiation-induced cellular damage. As the physical effects of GNP boosted radiotherapy occur across energy scales that descend down to 10 eV, Monte Carlo simulations require discrete physics models down to these very low energies in order to avoid underestimating the absorbed dose and secondary particle generation. Discrete physics models for electron transportation down to 10 eV have been implemented within the Geant4-DNA low energy extension of Geant4. Such models allow the investigation of GNP effects at the nanoscale. At low energies, the new models have better agreement with experimental data on the backscattering coefficient, and they show similar performance for transmission coefficient data as the Livermore and Penelope models already implemented in Geant4. These new models are applicable in simulations focussed towards estimating the relative biological effectiveness of radiation in GNP boosted radiotherapy applications with photon and electron radiation sources
Collisional kinetics of non-uniform electric field, low-pressure, direct-current discharges in H
A model of the collisional kinetics of energetic hydrogen atoms, molecules,
and ions in pure H discharges is used to predict H emission
profiles and spatial distributions of emission from the cathode regions of
low-pressure, weakly-ionized discharges for comparison with a wide variety of
experiments. Positive and negative ion energy distributions are also predicted.
The model developed for spatially uniform electric fields and current densities
less than A/m is extended to non-uniform electric fields, current
densities of A/m, and electric field to gas density ratios MTd at 0.002 to 5 Torr pressure. (1 Td = V m and 1 Torr =
133 Pa) The observed far-wing Doppler broadening and spatial distribution of
the H emission is consistent with reactions among H, H,
H, and H ions, fast H atoms, and fast H molecules, and with
reflection, excitation, and attachment to fast H atoms at surfaces. The
H excitation and H formation occur principally by collisions of
fast H, fast H, and H with H. Simplifications include using a
one-dimensional geometry, a multi-beam transport model, and the average
cathode-fall electric field. The H emission is linear with current
density over eight orders of magnitude. The calculated ion energy distributions
agree satisfactorily with experiment for H and H, but are only in
qualitative agreement for H and H. The experiments successfully modeled
range from short-gap, parallel-plane glow discharges to beam-like,
electrostatic-confinement discharges.Comment: Submitted to Plasmas Sources Science and Technology 8/18/201
Proposed Standards for Medical Education Submissions to the Journal of General Internal Medicine
To help authors design rigorous studies and prepare clear and informative manuscripts, improve the transparency of editorial decisions, and raise the bar on educational scholarship, the Deputy Editors of the Journal of General Internal Medicine articulate standards for medical education submissions to the Journal. General standards include: (1) quality questions, (2) quality methods to match the questions, (3) insightful interpretation of findings, (4) transparent, unbiased reporting, and (5) attention to human subjects’ protection and ethical research conduct. Additional standards for specific study types are described. We hope these proposed standards will generate discussion that will foster their continued evolution
Utilization of case presentations in medical microbiology to enhance relevance of basic science for medical students
Background : Small-group case presentation exercises (CPs) were created to increase course relevance for medical students taking Medical Microbiology (MM) and Infectious Diseases (ID) Methods : Each student received a unique paper case and had 10 minutes to review patient history, physical exam data, and laboratory data. Students then had three minutes to orally present their case and defend why they ruled in or out each of the answer choices provided, followed by an additional three minutes to answer questions. Results : Exam scores differed significantly between students who received the traditional lecture-laboratory curriculum (Group I) and students who participated in the CPs (Group II). In MM, median unit exam and final exam scores for Group I students were 84.4% and 77.8%, compared to 86.0% and 82.2% for Group II students (P < 0.018; P < 0.001; Mann-Whitney Rank Sum Test). Median unit and final ID exam scores for Group I students were 84.0% and 80.0%, compared to 88.0% and 86.7% for Group II students (P < 0.001; P < 0.001). Conclusion : Students felt that the CPs improved their critical thinking and presentation skills and helped to prepare them as future physicians
Benefits of knowledge-based interprofessional communication skills training in medical undergraduate education
OBJECTIVES: Good interprofessional communication is fundamental to effective teamworking in medicine. Finalmed is a private course that teaches the principles and methods of clinical presenting as an iterative technique of reasoning though clinical data. We have tested the efficacy of this technique using a questionnaire-based study. DESIGN: An anonymized 10-point Likert scale questionnaire was designed. SETTING: Questionnaires were distributed at five UK courses and two UAE courses. PARTICIPANTS: Questionnaires were given to all students attending these courses. MAIN OUTCOME MEASURES: The questionnaire included pre- and post-course questions addressing self-reported confidence in clinical presenting (CCP) and effectiveness in clinical presenting (ECP). We also asked whether attendees felt that clinical presenting should be integrated formally into medical school curricula. RESULTS: A total of 331/395 questionnaires were returned. Median improvement in CCP was 50% (P < 0.0001) and in ECP was 40% (P < 0.0001), irrespective of country of study, graduate entry status and whether the student felt that they had been exposed to these techniques previously. Students recorded a strong opinion in favour of integrating the content and style of the Finalmed course into their medical school curriculum, with 286 students (86%) recording a score of ≥8. CONCLUSION: Our study suggests that after a two- or three-day dedicated course, both self-reported confidence and effectiveness in clinical presenting significantly improve. Furthermore, students in the UK and the UAE returned a desire for integration into medical school curricula of IPC through the teaching of clinical presenting
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