Comment on "Quantum Confinement and Optical Gaps in Si Nanocrystals"

We show that the method used by Ogut, Chelikowsky and Louie (Phys. Rev. Lett. 79, 1770 (1997)) to calculate the optical gap of Si nanocrystals omits an electron-hole polarization energy. When this contribution is taken into account, the corrected optical gap is in excellent agreement with semi-empirical pseudopotential calculations.Comment: 3 pages, 1 figur

Mortality following a brain tumour diagnosis in patients with multiple sclerosis

Objectives: As brain tumours and their treatment may theoretically have a poorer prognosis in inflammatory central nervous system diseases such as multiple sclerosis (MS), all-cause mortality following a brain tumour diagnosis was compared between patients with and without MS. The potential role of age at tumour diagnosis was also examined. Setting: Hospital inpatients in Sweden with assessment of mortality in hospital or following discharge. Participants: Swedish national registers identified 20 543 patients with an MS diagnosis (1969-2005) and they were matched individually to produce a comparison cohort of 204 163 members of the general population without MS. Everyone with a primary brain tumour diagnosis was selected for this study: 111 with MS and 907 without MS. Primary and secondary outcome measures: 5-year mortality risk following brain tumour diagnosis and age at brain tumour diagnosis. Results: A non-statistically significant lower mortality risk among patients with MS (lower for those with tumours of high-grade and uncertain-grade malignancy and no notable difference for low-grade tumours) produced an unadjusted HR (and 95% CI) of 0.75 (0.56 to 1.02). After adjustment for age at diagnosis, grade of malignancy, sex, region of residence and socioeconomic index, the HR is 0.91 (0.67-1.24). The change in estimate was largely due to adjustment for age at brain tumour diagnosis, as patients with MS were on average 4.7 years younger at brain tumour diagnosis than those in the comparison cohort (p<0.001). Conclusions: Younger age at tumour diagnosis may contribute to mortality reduction in those with highgrade and uncertain-grade brain tumours. Survival following a brain tumour is not worse in patients with MS; even after age at brain tumour diagnosis and grade of malignancy are taken into account

Graphene Oxidation: Thickness Dependent Etching and Strong Chemical Doping

Patterned graphene shows substantial potential for applications in future molecular-scale integrated electronics. Environmental effects are a critical issue in a single layer material where every atom is on the surface. Especially intriguing is the variety of rich chemical interactions shown by molecular oxygen with aromatic molecules. We find that O2 etching kinetics vary strongly with the number of graphene layers in the sample. Three-layer-thick samples show etching similar to bulk natural graphite. Single-layer graphene reacts faster and shows random etch pits in contrast to natural graphite where nucleation occurs at point defects. In addition, basal plane oxygen species strongly hole dope graphene, with a Fermi level shift of ~0.5 eV. These oxygen species partially desorb in an Ar gas flow, or under irradiation by far UV light, and readsorb again in an O2 atmosphere at room temperature. This strongly doped graphene is very different than graphene oxide made by mineral acid attack.Comment: 15 pages, 5 figure

An experimental and theoretical approach for the carbon deposition problem during steam reforming of model biogas

The conversion of biogas to electricity presents an attractive niche application for solid oxide fuel cells (SOFCs). A number of attempts have been made to use biogas as a fuel for high temperature fuel cell systems such as SOFCs. Biogas can be converted to a hydrogen-rich fuel in a reforming process which can use steam or carbon dioxide as the reforming agent. Conventionally, the reforming process is conducted at around 850◦C using several different catalysts depending on application. Biogas naturally contains the reforming agent, carbon dioxide, however, for typical biogas the content of carbon dioxide is insufficient to conduct the reforming process safely. Fore those cases, steam is added to prevent carbon deposition. Carbon formation occurs between the catalyst and the metal support, creating fibers which damage the catalytic property of the reactor. A number of papers have dealt with the problem of carbon deposition during both methane steam reforming and dry reforming. However, from the standpoint of solid oxide fuel cells, not every carbon-free condition is optimal for its operation. This paper treats this subject, explaining the mechanism of carbon formation during the steam reforming of biogas and using a numerical analysis to determine efficient and carbon-free working conditions

Evolution of the electronic structure with size in II-VI semiconductor nanocrystals

In order to provide a quantitatively accurate description of the band gap variation with sizes in various II-VI semiconductor nanocrystals, we make use of the recently reported tight-binding parametrization of the corresponding bulk systems. Using the same tight-binding scheme and parameters, we calculate the electronic structure of II-VI nanocrystals in real space with sizes ranging between 5 and 80 {\AA} in diameter. A comparison with available experimental results from the literature shows an excellent agreement over the entire range of sizes.Comment: 17 pages, 4 figures, accepted in Phys. Rev.

Magnetic phase transition in V2O3 nanocrystals

V2O3 nanocrystals can be synthesized through hydrothermal reduction of VO(OH)2 using hydrazine as a reducing agent. Addition of different ligands to the reaction produces nanoparticles, nanorods and nanoplatelets of different sizes. Small nanoparticles synthesized in this manner show suppression of the magnetic phase transition to lower temperatures. Using muon spin relaxation spectroscopy and synchrotron x-ray diffraction, it is determined that the volume fraction of the high-temperature phase, characterized by a rhombohedral structure and paramagnetism, gradually declines with decreasing temperature, in contrast to the sharp transition observed in bulk V2O3.Comment: 6 pages, 6 figure

Residential radon-222 exposure and lung cancer: exposure assessment methodology

Although occupational epidemiological studies and animal experimentation provide strong evidence that radon-222 (222Rn) progeny exposure causes lung cancer, residential epidemiological studies have not confirmed this association. Past residential epidemiological studies have yielded contradictory findings. Exposure misclassification has seriously compromised the ability of these studies to detect whether an association exists between 222Rn exposure and lung cancer. Misclassification of 222Rn exposure has arisen primarily from: 1) detector measurement error; 2) failure to consider temporal and spatial 222Rn variations within a home; 3) missing data from previously occupied homes that currently are inaccessible; 4) failure to link 222Rn concentrations with subject mobility; and 5) measuring 222Rn gas concentration as a surrogate for 222Rn progeny exposure. This paper examines these methodological dosimetry problems and addresses how we are accounting for them in an ongoing, population-based, case-control study of 222Rn and lung cancer in Iowa

Work participation, social roles, and empowerment of Q-fever fatigue syndrome patients ≥10 years after infection

Objective:To determine work participation, social roles, and empowerment of QFS patients ≥10-year after infection. Methods:QFS patients ≥10-year after acute infection, who were of working age, participated in a cross-sectional survey study. Work participation, fulfilment of social roles, and empowerment outcomes were studied for the total population, as well as for subgroups based on employment type and current work status. Associations between empowerment, work and social roles were examined. Results:291 participants were included. Of the 250 participants who had paid work before Q-fever, 80.4% stopped working or worked less hours due to QFS. For each social role, more than half of the participants (56.6–87.8%) spent less time on the role compared to before Q-fever. The median empowerment score was 41.0 (IQR: 37.0–44.0) out of 60. A higher empowerment score was significantly associated with lower odds of performing all social roles less due to QFS (OR = 0.871–0.933; p&lt;0.001–0.026), except for parenting and informal care provision (p = 0.070–0.460). No associations were found between empowerment and current work status. Conclusion: Work participation and fulfilment of social roles is generally low in QFS patients. Many of the participants stopped working or are working less hours due to QFS, and most spent less time on social roles compared to before Q-fever. Minor variation was seen in total empowerment scores of participants; however, these slight differences were associated with the fulfilment of social roles, but not work participation. This new insight should be further explored in future studies.</p