Monte Carlo Simulation for Polychromatic X-ray Fluorescence Computed Tomography with Sheet-Beam Geometry

X-ray fluorescence computed tomography based on sheet-beam can save a huge amount of time to obtain a whole set of projections using synchrotron. However, it is clearly unpractical for most biomedical research laboratories. In this paper, polychromatic X-ray fluorescence computed tomography with sheet-beam geometry is tested by Monte Carlo simulation. First, two phantoms (A and B) filled with PMMA are used to simulate imaging process through GEANT 4. Phantom A contains several GNP-loaded regions with the same size (10 mm) in height and diameter but different Au weight concentration ranging from 0.3% to 1.8%. Phantom B contains twelve GNP-loaded regions with the same Au weight concentration (1.6%) but different diameter ranging from 1mm to 9mm. Second, discretized presentation of imaging model is established to reconstruct more accurate XFCT images. Third, XFCT images of phantom A and B are reconstructed by fliter backprojection (FBP) and maximum likelihood expectation maximization (MLEM) with and without correction, respectively. Contrast to noise ratio (CNR) is calculated to evaluate all the reconstructed images. Our results show that it is feasible for sheet-beam XFCT system based on polychromatic X-ray source and the discretized imaging model can be used to reconstruct more accurate images

Sensitive frequency-dependence of the carrier-envelope phase effect on bound-bound transition: an interference perspective

We investigate numerically with Hylleraas coordinates the frequency dependence of the carrier-envelope phase (CEP) effect on bound-bound transitions of helium induced by an ultrashort laser pulse of few cycles. We find that the CEP effect is very sensitive to the carrier frequency of the laser pulse, occurring regularly even at far-off resonance frequencies. By analyzing a two-level model, we find that the CEP effect can be attributed to the quantum interference between neighboring multi-photon transition pathways, which is made possible by the broadened spectrum of the ultrashort laser pulse. A general picture is developed along this line to understand the sensitivity of the CEP effect to laser's carrier frequency. Multi-level influence on the CEP effect is also discussed

Time-varying multivariate causal processes

In this paper, we consider a wide class of time-varying multivariate causal processes that nests many classical and new examples as special cases. We first show the existence of a weakly dependent stationary approximation to initiate our theoretical investigation. We then consider a quasi-maximum likelihood estimation (QMLE), and provide both point-wise and uniform inferences to coefficient functions of interest. The theoretical findings are further examined through extensive simulations. Finally, we show empirical relevance of our study by evaluating both temporal and contemporaneous connectedness between the stock markets of China and U.S

Increasing Coverage of Hepatitis B Vaccination in China: A Systematic Review of Interventions and Implementation Experiences.

This study used a system evaluation method to summarize China's experience on improving the coverage of hepatitis B vaccine, especially the strategies employed to improve the uptake of timely birth dosage. Identifying successful methods and strategies will provide strong evidence for policy makers and health workers in other countries with high hepatitis B prevalence.We conducted a literature review included English or Chinese literature carried out in mainland China, using PubMed, the Cochrane databases, Web of Knowledge, China National Knowledge Infrastructure, Wanfang data, and other relevant databases.Nineteen articles about the effectiveness and impact of interventions on improving the coverage of hepatitis B vaccine were included. Strong or moderate evidence showed that reinforcing health education, training and supervision, providing subsidies for facility birth, strengthening the coordination among health care providers, and using out-of-cold-chain storage for vaccines were all important to improving vaccination coverage.We found evidence that community education was the most commonly used intervention, and out-reach programs such as out-of-cold chain strategy were more effective in increasing the coverage of vaccination in remote areas where the facility birth rate was respectively low. The essential impact factors were found to be strong government commitment and the cooperation of the different government departments.Public interventions relying on basic health care systems combined with outreach care services were critical elements in improving the hepatitis B vaccination rate in China. This success could not have occurred without exceptional national commitment