Does bicycling contribute to the risk of erectile dysfunction? Results from the Massachusetts Male Aging Study (MMAS)

An association between bicycling and erectile dysfunction (ED) has been described previously, but there are limited data examining this association in a random population of men. Such data would incorporate bicyclists with varied types of riding and other factors. Data from the Massachusetts Male Aging Study (MMAS) were utilized to examine the association between bicycling and ED. Logistic regression was used to test for an association, controlling for age, energy expenditure, smoking, depression and chronic illness. Bicycling less than 3 h per week was not associated with ED and may be somewhat protective. Bicycling 3 h or more per week may be associated with ED. Data revealed that there may be a reduced probability of ED in those who ride less than 3 h per week and ED may be more likely in bikers who ride more than 3 h per week. More population-based research is needed to better define this relationship

Hydrodynamic theory of an electron gas

The generalised hydrodynamic theory of an electron gas, which does not rely on an assumption of a local equilibrium, is derived as the long-wave limit of a kinetic equation. Apart from the common hydrodynamics variables the theory includes the tensor fields of the higher moments of the distribution function. In contrast to the Bloch hydrodynamics, the theory leads to the correct plasmon dispersion and in the low frequency limit recovers the Navies-Stocks hydrodynamics. The linear approximation to the generalised hydrodynamics is closely related to the theory of highly viscous fluids.Comment: 4 pages, revte

Ab initio density functional investigation of B_24 cluster: Rings, Tubes, Planes, and Cages

We investigate the equilibrium geometries and the systematics of bonding in various isomers of a 24-atom boron cluster using Born-Oppenheimer molecular dynamics within the framework of density functional theory. The isomers studied are the rings, the convex and the quasiplanar structures, the tubes and, the closed structures. A staggered double-ring is found to be the most stable structure amongst the isomers studied. Our calculations reveal that a 24-atom boron cluster does form closed 3-d structures. All isomers show staggered arrangement of nearest neighbor atoms. Such a staggering facilitates $sp^2$ hybridization in boron cluster. A polarization of bonds between the peripheral atoms in the ring and the planar isomers is also seen. Finally, we discuss the fusion of two boron icosahedra. We find that the fusion occurs when the distance between the two icosahedra is less than a critical distance of about 6.5a.u.Comment: 8 pages, 9 figures in jpeg format Editorially approved for publication in Phys. Rev.

A real-space, rela-time method for the dielectric function

We present an algorithm to calculate the linear response of periodic systems in the time-dependent density functional thoery, using a real-space representation of the electron wave functions and calculating the dynamics in real time. The real-space formulation increases the efficiency for calculating the interaction, and the real-time treatment decreases storage requirements and the allows the entire frequency-dependent response to be calculated at once. We give as examples the dielectric functions of a simple metal, lithium, and an elemental insulator, diamond.Comment: 17 pages, Latex, 5 figure

The time evolution of aerosol composition over the Mexico City plateau

International audienceThe time evolution of aerosol concentration and chemical composition in a megacity urban plume was determined based on 8 flights of the DOE G-1 aircraft in and downwind of Mexico City during the March 2006 MILAGRO field campaign. A series of selection criteria are imposed to eliminate data points with non-urban emission influences. Biomass burning has urban and non-urban sources that are distinguished on the basis of CH3CN and CO. In order to account for dilution in the urban plume, aerosol concentrations are normalized to CO which is taken as an inert tracer of urban emission, proportional to the emissions of aerosol precursors. Time evolution is determined with respect to photochemical age defined as ?Log10 (NOx/NOy). The geographic distribution of photochemical age and CO is examined, confirming the picture that Mexico City is a source region and that pollutants become more dilute and aged as they are advected towards T1 and T2, surface sites that are located at the fringe of the City and 35 km to the NE, respectively. Organic aerosol (OA) per ppm CO is found to increase 7 fold over the range of photochemical ages studied, corresponding to a change in NOx/NOy from nearly 100% to 10%. In the older samples the nitrate/CO ratio has leveled off suggesting that evaporation and formation of aerosol nitrate are in balance. In contrast, OA/CO increases with age in older samples, indicating that OA is still being formed. The amount of carbon equivalent to the deduced change in OA/CO with age is 56 ppbC per ppm CO. At an aerosol yield of 5% and 8% for low and high yield aromatic compounds, it is estimated from surface hydrocarbon observations that only ~9% of the OA formation can be accounted for. A comparison of OA/CO in Mexico City and the eastern U.S. gives no evidence that aerosol yields are higher in a more polluted environment

Aircraft and ground-based measurements of hydroperoxides during the 2006 MILAGRO field campaign

International audienceMixing ratios of hydrogen peroxide and hydroxymethyl hydroperoxide were determined aboard the US Department of Energy G-1 Research Aircraft during the March 2006 MILAGRO field campaign in Mexico. Ground measurements of total hydroperoxide were made at the T1 site at Universidad Technologica de Tecámac, about 35 km NW of Mexico City. In the air and on the ground, peroxide mixing ratios near the source region were generally near 1 ppbv, much lower than had been predicted from photochemical models based on the 2003 Mexico City study. Strong southerly flow resulted in transport of pollutants from the T0 to T1 and T2 surface sites on several flight days. On these days, it was observed that peroxide concentrations slightly decreased as the G-1 flew progressively downwind. This observation is consistent with low or negative net peroxide production rates calculated for the source region and is due to the very high NOx concentrations above the Mexico City plateau. However, relatively high values of peroxide were observed at takeoff and landing near Veracruz, a site with much higher humidity and lower NOx concentrations

Theoretical Study of Cubic Structures Based on Fullerene Carbon Clusters: C28_{28}C and (C28)2_{28})_{2}

We study a new hypothetical form of solid carbon \csc, with a unit cell which is composed of the \cs \ fullerene cluster and an additional single carbon atom arranged in the zincblende structure. Using {\it ab initio} calculations, we show that this new form of solid carbon has lower energy than hyperdiamond, the recently proposed form composed of \cs \ units in the diamond structure. To understand the bonding character of of these cluster-based solids, we analyze the electronic structure of \csc \ and of hyperdiamond and compare them to the electronic states of crystalline cubic diamond.Comment: 15 pages, latex, no figure

An efficient k.p method for calculation of total energy and electronic density of states

An efficient method for calculating the electronic structure in large systems with a fully converged BZ sampling is presented. The method is based on a k.p-like approximation developed in the framework of the density functional perturbation theory. The reliability and efficiency of the method are demostrated in test calculations on Ar and Si supercells

Timesaving Double-Grid Method for Real-Space Electronic-Structure Calculations

We present a simple and efficient technique in ab initio electronic-structure calculation utilizing real-space double-grid with a high density of grid points in the vicinity of nuclei. This technique promises to greatly reduce the overhead for performing the integrals that involves non-local parts of pseudopotentials, with keeping a high degree of accuracy. Our procedure gives rise to no Pulay forces, unlike other real-space methods using adaptive coordinates. Moreover, we demonstrate the potential power of the method by calculating several properties of atoms and molecules.Comment: 4 pages, 5 figure

Evidence that pneumococcal serotype replacement in Massachusetts following conjugate vaccination is now complete

Invasive pneumococcal disease (IPD) has been reduced in the US following conjugate vaccination (PCV7) targeting seven pneumococcal serotypes in 2000. However, increases in IPD due to other serotypes have been observed, in particular 19A. How much this serotype replacement will erode the benefits of vaccination and over what timescale is unknown. We used a population genetic approach to test first whether the selective impact of vaccination could be detected in a longitudinal carriage sample, and secondly how long it persisted for following introduction of vaccine in 2000. To detect the selective impact of the vaccine we compared the serotype diversity of samples from pneumococcal carriage in Massachusetts children collected in 2001, 2004 and 2007 with others collected in the pre-vaccine era in Massachusetts, the UK and Finland. The 2004 sample was significantly (p \u3e0.0001) more diverse than pre-vaccine samples, indicating the selective pressure of vaccination. The 2007 sample showed no significant difference in diversity from the pre-vaccine period, and exhibited similar population structure, but with different serotypes. In 2007 the carriage frequency of 19A was similar to that of the most common serotype in pre-vaccine samples. We suggest that serotype replacement involving 19A may be complete in Massachusetts due to similarities in population structure to pre-vaccine samples. These results suggest that the replacement phenomenon occurs rapidly with high vaccine coverage, and may allay concerns about future increases in disease due to 19A. For other serotypes, the future course of replacement disease remains to be determined