Preparation of Nanocomposites from Styrene and Modified Graphite Oxides

Graphite oxide was prepared and modified with several ammonium salts and these modified graphite oxides were used to prepare nanocomposites with polystyrene by in situ polymerization of styrene monomer and by melt blending with polystyrene. Nanocomposites were characterized by X-ray diffraction, cone calorimetry, thermogravimetric analysis and the evaluation of mechanical properties. Nanocomposites are formed by in situ polymerization but not by melt blending; the graphite oxide undergoes thermal degradation at the temperature of melt blending so nanocomposite formation would be unlikely. Mechanical properties of the melt blended nanocomposites are improved relative to the virgin polystyrene while those prepared by in situ polymerization are decreased, except in the case of Young\u27s Modulus, where melt blended and in situ polymerized materials show similar results

Expandable Graphite/Polyamide-6 Nanocomposites

Polyamide-6 (PA-6)/graphite nanocomposites were prepared by melt blending, using a variety of graphites, including virgin graphite, expandable graphites and expanded graphite. The resulting nanocomposites were characterized by X-ray diffraction, thermogravimetric analysis, cone calorimetry, and tensile mechanical analysis. Nanocomposite formation does occur, as denoted by the nanometre dispersion of graphite layers in the polymer matrix, and the dispersion depends on the graphite treatment. The material properties of the resulting composites are improved relative to the virgin/unfilled polymer; in particular, there is an enhancement of the thermal stability without any significant deterioration of the mechanical properties

Blending bias impacts the host halo masses derived from a cross-correlation analysis of bright sub-millimetre galaxies

Placing bright sub-millimetre galaxies (SMGs) within the broader context of galaxy formation and evolution requires accurate measurements of their clustering, which can constrain the masses of their host dark matter halos. Recent work has shown that the clustering measurements of these galaxies may be affected by a `blending bias,' which results in the angular correlation function of the sources extracted from single-dish imaging surveys being boosted relative to that of the underlying galaxies. This is due to confusion introduced by the coarse angular resolution of the single-dish telescope and could lead to the inferred halo masses being significantly overestimated. We investigate the extent to which this bias affects the measurement of the correlation function of SMGs when it is derived via a cross-correlation with a more abundant galaxy population. We find that the blending bias is essentially the same as in the auto-correlation case and conclude that the best way to reduce its effects is to calculate the angular correlation function using SMGs in narrow redshift bins. Blending bias causes the inferred host halo masses of the SMGs to be overestimated by a factor of $\sim6$ when a redshift interval of $\delta z=3$ is used. However, this reduces to a factor of $\sim2$ for $\delta z=0.5$. The broadening of photometric redshift probability distributions with increasing redshift can therefore impart a mild halo `downsizing' effect onto the inferred host halo masses, though this trend is not as strong as seen in recent observational studies.Comment: 10 pages, 9 figures, 1 table. Accepted to MNRA

Microlensing and the Search for Extraterrestrial Life

Are microlensing searches likely to discover planets that harbor life? Given our present state of knowledge, this is a difficult question to answer. We therefore begin by asking a more narrowly focused question: are conditions on planets discovered via microlensing likely to be similar to those we experience on Earth? In this paper I link the microlensing observations to the well-known "Goldilocks Problem" (conditions on the Earth-like planets need to be "just right"), to find that Earth-like planets discovered via microlensing are likely to be orbiting stars more luminous than the sun. This means that light from the planetary system's central star may contribute a significant fraction of the baseline flux relative to the star that is lensed. Such blending of light from the lens with light from the lensed source can, in principle, limit our ability to detect these events. This turns out not to be a significant problem, however. A second consequence of blending is the opportunity to determine the spectral type of the lensed spectral type of the lensed star. This circumstance, plus the possibility that finite-source-size effects are important, implies that some meaningful follow-up observations are likely to be possible for a subset Earth-like planets discovered via microlensing. In addition, calculations indicate that reasonable requirements on the planet's density and surface gravity imply that the mass of Earth-like planets is likely to be within a factor of $\sim 15$ of an Earth mass.Comment: 15 pages, 2 figures. To be published in the Astrophysical Journa

Optimizing Ground-based Observations of O2 in Earth Analogs

We present the result of calculations to optimize the search for molecular oxygen (O2) in Earth analogs transiting around nearby, low-mass stars using ground-based, high-resolution, Doppler shift techniques. We investigate a series of parameters, namely spectral resolution, wavelength coverage of the observations, and sky coordinates and systemic velocity of the exoplanetary systems, to find the values that optimize detectability of O2. We find that increasing the spectral resolution of observations to R = 300,000 - 400,000 from the typical R ~ 100,000, more than doubles the average depth of O2 lines in planets with atmospheres similar to Earth's. Resolutions higher than about 500,000 do not produce significant gains in the depths of the O2 lines. We confirm that observations in the O2 A-band are the most efficient except for M9V host stars, for which observations in the O2 NIR-band are more efficient. Combining observations in the O2 A, B, and NIR -bands can reduce the number of transits needed to produce a detection of O2 by about 1/3 in the case of white noise limited observations. However, that advantage disappears in the presence of typical levels of red noise. Therefore, combining observations in more than one band produces no significant gains versus observing only in the A-band, unless red-noise can be significantly reduced. Blending between the exoplanet's O2 lines and telluric O2 lines is a known problem. We find that problem can be alleviated by increasing the resolution of the observations, and by giving preference to targets near the ecliptic.Comment: 15 pages, 7 figures, accepted for publication in The Astronomical Journa

Microlensing planet detection via geosynchronous and low Earth orbit satellites

Planet detection through microlensing is usually limited by a well-known degeneracy in the Einstein timescale $t_E$, which prevents mass and distance of the lens to be univocally determined. It has been shown that a satellite in geosynchronous orbit could provide masses and distances for most standard planetary events ($t_E \approx 20$ days) via a microlens parallax measurement. This paper extends the analysis to shorter Einstein timescales, $t_E \approx 1$ day, when dealing with the case of Jupiter-mass lenses. We then study the capabilities of a low Earth orbit satellite on even shorter timescales, $t_E \approx 0.1$ days. A Fisher matrix analysis is employed to predict how the 1-$\sigma$ error on parallax depends on $t_E$ and the peak magnification of the microlensing event. It is shown that a geosynchronous satellite could detect parallaxes for Jupiter-mass free floaters and discover planetary systems around very low-mass brown dwarfs. Moreover, a low Earth orbit satellite could lead to the discovery of Earth-mass free-floating planets. Limitations to these results can be the strong requirements on the photometry, the effects of blending, and in the case of the low orbit, the Earth's umbra.Comment: 5 pages, 3 figures. Minor language edits. Accepted for publication in Astronomy & Astrophysic

Creating effective focus cues in multi-plane 3D displays.

Focus cues are incorrect in conventional stereoscopic displays. This causes a dissociation of vergence and accommodation, which leads to visual fatigue and perceptual distortions. Multi-plane displays can minimize these problems by creating nearly correct focus cues. But to create the appearance of continuous depth in a multi-plane display, one needs to use depth-weighted blending: i.e., distribute light intensity between adjacent planes. Akeley et al. [ACM Trans. Graph. 23, 804 (2004)] and Liu and Hua [Opt. Express 18, 11562 (2009)] described rather different rules for depth-weighted blending. We examined the effectiveness of those and other rules using a model of a typical human eye and biologically plausible metrics for image quality. We find that the linear blending rule proposed by Akeley and colleagues [ACM Trans. Graph. 23, 804 (2004)] is the best solution for natural stimuli