VALIDATION OF A DXA-BASED METHOD FOR OBTAINING INERTIA TENSORS: 'WHEN PIGS FLY'

This paper examines the accuracy of body segment inertia tensors estimated by combining information from dual-energy X-ray absorptiometry and a three-dimensional modelling technique proposed by Zatsiorsky et al. (1 990) (DXAIVol method). The inertia tensor of a frozen pig cadaver was estimated using the novel DXAlVol method and traditional compound pendulum techniques. The pig cadaver was projected through the air and the experimental 'ground truth kinematics' were recorded. Simulated kinematics of the pig cadaver flight were generated using the inertia tensor derived from the DXAlVol and compound pendulum methods and compared to the ground truth kinematics. Simulations based on the novel D W o l method's inertia tensor traded the experimentally recorded flight of the frozen pig cadaver with superior accuracy

Estudo da estrutura porosa de empacotamento compacto aleatório de esferas rígidas.

No início, o estudo dos empacotamentos compactos de corpos tinha a simples função de otimizar espaço físico. Os estudos pioneiros obtiveram grandes resultados em empacotamento de corpos com geometrias simples, proporcionado a utilização deste estudo para modelar a nascente estrutura atômica. Os estudos foram avançando até o ponto de serem utilizados para modelar estruturas complexas, como aglomerados de células e materiais heterogêneos porosos, sendo este último foco deste trabalho. Para esse objetivo, construímos empacotamentos compactos aleatórios de esferas rígidas, gerados por algoritmos computacionais comumente reportados na literatura. Nossos estudos caracterizaram do ponto de vista estatístico o meio poroso formado pelas regiões vazias do empacotamento aleatório de esferas. Seus descritores estatísticos, a função de autocorrelação estatística de dois-pontos 𝑆2(𝑟) e distribuição de tamanho de poros foram calculados e analisados. Particular ênfase foi dada ao cálculo da entropia da distribuição de tamanhos de poros e a sua interpretação em termos da proximidade do sistema ao limite de máxima densidade. Por último, fizemos a reconstrução da função de autocorrelação calculada numa rocha natural da formação Lagoa-Salgada, a partir de medidas estatísticas realizadas sobre um empacotamento compacto aleatório de esferas interpenetráveis. Este último ponto estudado é relevante no sentido que o estudo mostrou que é possível reconstruir, mesmo que parcialmente, a estrutura porosa de um material poroso natural. De forma geral, os resultados encontrados neste trabalho reproduziram resultados abordados na literatura sobre a caracterização morfológica de meios heterógenos, além de fornecer novas ideias acerca da possibilidade de utilizar ferramentas estatísticas visando reproduzir a morfologia porosa observada em rochas naturais

Development of a GPU-based Monte Carlo dose calculation code for coupled electron-photon transport

Monte Carlo simulation is the most accurate method for absorbed dose calculations in radiotherapy. Its efficiency still requires improvement for routine clinical applications, especially for online adaptive radiotherapy. In this paper, we report our recent development on a GPU-based Monte Carlo dose calculation code for coupled electron-photon transport. We have implemented the Dose Planning Method (DPM) Monte Carlo dose calculation package (Sempau et al, Phys. Med. Biol., 45(2000)2263-2291) on GPU architecture under CUDA platform. The implementation has been tested with respect to the original sequential DPM code on CPU in phantoms with water-lung-water or water-bone-water slab geometry. A 20 MeV mono-energetic electron point source or a 6 MV photon point source is used in our validation. The results demonstrate adequate accuracy of our GPU implementation for both electron and photon beams in radiotherapy energy range. Speed up factors of about 5.0 ~ 6.6 times have been observed, using an NVIDIA Tesla C1060 GPU card against a 2.27GHz Intel Xeon CPU processor.Comment: 13 pages, 3 figures, and 1 table. Paper revised. Figures update

Monte Carlo investigations of the effect of beam divergence on thick, segmented crystalline scintillators for radiotherapy imaging

The use of thick, segmented scintillators in electronic portal imagers offers the potential for significant improvement in x-ray detection efficiency compared to conventional phosphor screens. Such improvement substantially increases the detective quantum efficiency (DQE), leading to the possibility of achieving soft-tissue visualization at clinically practical (i.e. low) doses using megavoltage (MV) cone-beam computed tomography. While these DQE increases are greatest at zero spatial frequency, they are diminished at higher frequencies as a result of degradation of spatial resolution due to lateral spreading of secondary radiation within the scintillator—an effect that is more pronounced for thicker scintillators. The extent of this spreading is even more accentuated for radiation impinging the scintillator at oblique angles of incidence due to beam divergence. In this paper, Monte Carlo simulations of radiation transport, performed to investigate and quantify the effects of beam divergence on the imaging performance of MV imagers based on two promising scintillators (BGO and CsI:Tl), are reported. In these studies, 10–40 mm thick scintillators, incorporating low-density polymer, or high-density tungsten septal walls, were examined for incident angles corresponding to that encountered at locations up to ~15 cm from the central beam axis (for an imager located 130 cm from a radiotherapy x-ray source). The simulations demonstrate progressively more severe spatial resolution degradation (quantified in terms of the effect on the modulation transfer function) as a function of increasing angle of incidence (as well as of the scintillator thickness). Since the noise power behavior was found to be largely independent of the incident angle, the dependence of the DQE on the incident angle is therefore primarily determined by the spatial resolution. The observed DQE degradation suggests that 10 mm thick scintillators are not strongly affected by beam divergence for detector areas up to ~30 × 30 cm2. For thicker scintillators, the area that is relatively unaffected is significantly reduced, requiring a focused scintillator geometry in order to preserve spatial resolution, and thus DQE.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85404/1/pmb10_13_006.pd

Emerging Opportunities: Monitoring and Evaluation in a Tech-Enabled World

Various trends are impacting on the field of monitoring and evaluation in the area of international development. Resources have become ever more scarce while expectations for what development assistance should achieve are growing. The search for more efficient systems to measure impact is on. Country governments are also working to improve their own capacities for evaluation, and demand is rising from national and community-based organizations for meaningful participation in the evaluation process as well as for greater voice and more accountability from both aid and development agencies and government.These factors, in addition to greater competition for limited resources in the area of international development, are pushing donors, program participants and evaluators themselves to seek more rigorous – and at the same time flexible – systems to monitor and evaluate development and humanitarian interventions.However, many current approaches to M&E are unable to address the changing structure of development assistance and the increasingly complex environment in which it operates. Operational challenges (for example, limited time, insufficient resources and poor data quality) as well as methodological challenges that impact on the quality and timeliness of evaluation exercises have yet to be fully overcome

GATE : a simulation toolkit for PET and SPECT

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols, and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at the address http://www-lphe.epfl.ch/GATE/

IMPACT OF EMPLOYEE FAMILY-FRIENDLY SUPPORTIVENESS ON WORK PERFORMANCE OF EMPLOYEES IN ORGANIZATIONS

The Study investigated impact of Employee Family -friendly supportiveness on work performance of Employees in organizations.860 participants drawn from services, manufacturing and distributive organizations made up sample for the study. Instruments used to collect data .from the study included the Family - friendly Support Inventory (FFSI) and Work PeTjormance Rating Scale1 and 2 (WPRS 1 and WPRS 2) One way ANOVA was used to analyze data at 0.05 level of signifzcance. Findings revealed that there is no significant difference between the work performance of single and married workers who benefitted from family:friendly support services (F1 ~.8421 = .01, p>.05). Findings further revealed that there is no signifzcant difference between work performance of married workers having long or short years working experience who benefited from FFSS (F0•7961 = 3.4; p>.05)