Effect of Statistical Fluctuation in Monte Carlo Based Photon Beam Dose Calculation on Gamma Index Evaluation

The gamma-index test has been commonly adopted to quantify the degree of agreement between a reference dose distribution and an evaluation dose distribution. Monte Carlo (MC) simulation has been widely used for the radiotherapy dose calculation for both clinical and research purposes. The goal of this work is to investigate both theoretically and experimentally the impact of the MC statistical fluctuation on the gamma-index test when the fluctuation exists in the reference, the evaluation, or both dose distributions. To the first order approximation, we theoretically demonstrated in a simplified model that the statistical fluctuation tends to overestimate gamma-index values when existing in the reference dose distribution and underestimate gamma-index values when existing in the evaluation dose distribution given the original gamma-index is relatively large for the statistical fluctuation. Our numerical experiments using clinical photon radiation therapy cases have shown that 1) when performing a gamma-index test between an MC reference dose and a non-MC evaluation dose, the average gamma-index is overestimated and the passing rate decreases with the increase of the noise level in the reference dose; 2) when performing a gamma-index test between a non-MC reference dose and an MC evaluation dose, the average gamma-index is underestimated when they are within the clinically relevant range and the passing rate increases with the increase of the noise level in the evaluation dose; 3) when performing a gamma-index test between an MC reference dose and an MC evaluation dose, the passing rate is overestimated due to the noise in the evaluation dose and underestimated due to the noise in the reference dose. We conclude that the gamma-index test should be used with caution when comparing dose distributions computed with Monte Carlo simulation

Influence of Copper Vapor on Dielectric Properties of Hot CO2 at Different Pressures from 0.4 MPa to 0.8 MPa

The influence of copper vapor on dielectric properties of hot CO 2 at different pressures has beenanalyzed in this paper . By solving the Boltzmann equation the electron energy distribution functions andthe critical reduced electric fie ld strength (E/N) cr were obtained. The results indicate that copper markedlyreduces (E/N) cr of the CO 2 Cu gas mixtures because of copper’s large ionization cross section.Additionally, increasing the gas pressure effectively delays the pick temperature of (E/N) cr

Social isolation, rather than loneliness, is associated with cognitive decline in older adults: the China Health and Retirement Longitudinal Study

BACKGROUND: Social isolation and loneliness have each been associated with cognitive decline, but most previous research is limited to Western populations. This study examined the relationships of social isolation and loneliness on cognitive function among Chinese older adults. METHODS: This study used two waves of data (2011 and 2015) from the China Health and Retirement Longitudinal Study and analyses were restricted to those respondents aged 50 and older. Social isolation, loneliness, and cognitive function were measured at baseline. Follow-up measures on cognitive function were obtained for 7761 participants (mean age = 60.97, s.d. = 7.31; male, 50.8%). Lagged dependent variable models adjusted for confounding factors were used to evaluate the association between baseline isolation, loneliness, and cognitive function at follow-up. RESULTS: Loneliness was significantly associated with the cognitive decline at follow-up (episodic memory: β = -0.03, p 0.05). By contrast, social isolation was significantly associated with decreases in all cognitive function measures at follow-up (episodic memory: β = -0.05, p < 0.001; mental status: β = -0.03, p < 0.01) even after controlling for loneliness and all confounding variables. CONCLUSIONS: Social isolation is associated with cognitive decline in Chinese older adults, and the relationships are independent of loneliness. These findings expand our knowledge about the links between social relationships and the cognitive function in non-Western populations

Graphenized carbon nanofiber: a novel light-trapping and conductive material to achieve an efficiency breakthrough in silicon solar cells

A study was conducted to demonstrate graphenized carbon nanofiber as a novel light-trapping and conductive material to achieve an efficiency breakthrough in silicon solar cells. The study presented a new pathway to solve the bottleneck issues and provide a significant performance improvement on silicon-based solar cells with the latest efficiencies. The concept of the novel nanomaterial and solar cell design was based on a novel synthesis process in which graphitized carbon fibers were used as the synthesis precursor. It was demonstrated that an innovative 1D graphenized carbon nanofiber (GCNF) could be achieved through longitudinal wall cutting by the wet chemical method