Can Fluffy Dust Alleviate the "Subsolar" Interstellar Abundance Problem?

What might be the most appropriate set of interstellar reference abundances of chemical elements (both in gas and in dust) relative to hydrogen has been a subject of much discussion in the past decade. While historically the Sun has been taken as the reference standard, it has recently been suggested that the interstellar abundances might be better represented by those of B stars (because of their young ages) which are just ~60--70% of the widely adopted solar values (``subsolar''). On the other hand, the most recent estimates of the solar carbon and oxygen abundances are also close to those of B stars. If the interstellar abundances are indeed ``subsolar'' like B stars or the newly-determined solar C,O values, there might be a lack of raw material to form the dust to account for the interstellar extinction. In literature it has been argued that this problem could be solved if interstellar grains have a fluffy, porous structure since fluffy grains are more effective in absorbing and scattering optical and ultraviolet starlight than compact grains (on a per unit mass basis). However, we show in this work that, using the Kramers-Kronig relation, fluffy dust is not able to overcome the abundance shortage problem. A likely solution is that the abundances of refractory elements in stellar photospheres may under-represent the composition of the interstellar material from which stars are formed, resulting either from the possible underestimation of the degree of heavy-element settling in stellar atmospheres, or from the incomplete incorporation of heavy elements in stars during the star formation process.Comment: 15 pages, 2 figures, 1 table. To appear in The Astrophysical Journal, vol. 622 (the April-01-2005 issue

SuperWASP: Wide Angle Search for Planets

SuperWASP is a fully robotic, ultra-wide angle survey for planetary transits. Currently under construction, it will consist of 5 cameras, each monitoring a 9.5 x 9.5 deg field of view. The Torus mount and enclosure will be fully automated and linked to a built-in weather station. We aim to begin observations at the beginning of 2003.Comment: 4 pages, 1 figure, to be published in proceedings of "Scientific Frontiers in Research on Extrasolar Planets

Continuous measurement of global difference coupling using a phase-locked-loop tune meter in the Relativistic Heavy Ion Collider

We present a new technique to continuously measure and compensate the global difference coupling coefficient through the continuous measurements of eigenmode projection parameters, using a high resolution phase-locked-loop tune meter. First, four eigenmode projection parameters are defined as the observables for weak difference coupling. Then, their analytical expressions are obtained using the strict matrix treatment and the Hamiltonian perturbation theory of linear coupling. From these parameters, the complex global coupling coefficient can be fully determined and compensated. This method was successfully demonstrated in the Relativistic Heavy Ion Collider (RHIC) 2006 run

Questioning Identity: How a Diverse Set of Respondents Answer Standard Questions About Ethnicity and Race

Ethnoracial identity refers to the racial and ethnic categories that people use to classify themselves and others. How it is measured in surveys has implications for understanding inequalities. Yet how people self-identify may not conform to the categories standardized survey questions use to measure ethnicity and race, leading to potential measurement error. In interviewer-administered surveys, answers to survey questions are achieved through interviewer–respondent interaction. An analysis of interviewer–respondent interaction can illuminate whether, when, how, and why respondents experience problems with questions. In this study, we examine how indicators of interviewer–respondent interactional problems vary across ethnoracial groups when respondents answer questions about ethnicity and race. Further, we explore how interviewers respond in the presence of these interactional problems. Data are provided by the 2013–2014 Voices Heard Survey, a computer-assisted telephone survey designed to measure perceptions of participating in medical research among an ethnoracially diverse sample of respondents

Simulating Reionization: Character and Observability

In recent years there has been considerable progress in our understanding of the nature and properties of the reionization process. In particular, the numerical simulations of this epoch have made a qualitative leap forward, reaching sufficiently large scales to derive the characteristic scales of the reionization process and thus allowing for realistic observational predictions. Our group has recently performed the first such large-scale radiative transfer simulations of reionization, run on top of state-of-the-art simulations of early structure formation. This allowed us to make the first realistic observational predictions about the Epoch of Reionization based on detailed radiative transfer and structure formation simulations. We discuss the basic features of reionization derived from our simulations and some recent results on the observational implications for the high-redshift Ly-alpha sources.Comment: 3 pages, to appear in the Proceedings of First Stars III, Santa Fe, July 2007, AIP Conference Serie

Adaptation to Variable Environments, Resilience to Climate Change: Investigating Land, Water and Settlement in Indus Northwest India

This paper explores the nature and dynamics of adaptation and resilience in the face of a diverse and varied environmental and ecological context using the case study of South Asia’s Indus Civilization (ca. 3000–1300 BC). Most early complex societies developed in regions where the climatic parameters faced by ancient subsistence farmers were varied but rain falls primarily in one season. In contrast, the Indus Civilization developed in a specific environmental context that spanned a very distinct environmental threshold, where winter and summer rainfall systems overlap. There is now evidence to show that this region was directly subject to climate change during the period when the Indus Civilization was at its height (ca. 2500–1900 BC). The Indus Civilization, therefore, provides a unique opportunity to understand how an ancient society coped with diverse and varied ecologies and change in the fundamental environmental parameters. This paper integrates research carried out as part of the Land, Water and Settlement project in northwest India between 2007 and 2014. Although coming from only one of the regions occupied by Indus populations, these data necessitate the reconsideration of several prevailing views about the Indus Civilization as a whole and invigorate discussion about human-environment interactions and their relationship to processes of cultural transformation

Simultaneous tune and coupling feedback in the Relativistic Heavy Ion Collider, and possible implications for the Large Hadron Collider commissioning

Simultaneous tune and coupling feedback were successfully implemented during RHIC run 6. In this paper we describe the measurement and control hardware and software used to accomplish this, present some of the results, discuss areas that require further investigation, and finally offer a few comments on possible implications of these results for LHC commissioning

Error Rate of the Kane Quantum Computer CNOT Gate in the Presence of Dephasing

We study the error rate of CNOT operations in the Kane solid state quantum computer architecture. A spin Hamiltonian is used to describe the system. Dephasing is included as exponential decay of the off diagonal elements of the system's density matrix. Using available spin echo decay data, the CNOT error rate is estimated at approsimately 10^{-3}.Comment: New version includes substantial additional data and merges two old figures into one. (12 pages, 6 figures

ROPS: A New Search for Habitable Earths in the Southern Sky

We present the first results from our Red Optical Planet Survey (ROPS) to search for low mass planets orbiting late type dwarfs (M5.5V - M9V) in their habitable zones (HZ). Our observations, with the red arm of the MIKE spectrograph (0.5 - 0.9 microns) at the 6.5 m Magellan Clay telescope at Las Campanas Observatory indicate that >= 92 per cent of the flux lies beyond 0.7 microns. We use a novel approach that is essentially a hybrid of the simultaneous iodine and ThAr methods for determining precision radial velocities. We apply least squares deconvolution to obtain a single high S/N ratio stellar line for each spectrum and cross correlate against the simultaneously observed telluric line profile, which we derive in the same way. Utilising the 0.62 - 0.90 micron region, we have achieved an r.m.s. precision of 10 m/s for an M5.5V spectral type star with spectral S/N ~160 on 5 minute timescales. By M8V spectral type, a precision of ~30 m/s at S/N = 25 is suggested, although more observations are needed. An assessment of our errors and scatter in the radial velocity points hints at the presence of stellar radial velocity variations. Of our sample of 7 stars, 2 show radial velocity signals at 6-sigma and 10-sigma of the cross correlation uncertainties. If the signals are planetary in origin, our findings are consistent with estimates of Neptune mass planets that predict a frequency of 13 - 27 per cent for early M dwarfs.Our current analysis indicates the we can achieve a sensitivity that is equivalent to the amplitude induced by a 6 M_Earth planet orbiting in the habitable zone. Based on simulations, we estimate that <10 M_Earth habitable zone planets will be detected in a new stellar mass regime, with <=20 epochs of observations.Comment: MNRAS accepted: 14 pages, 8 figures, 3 table

A catalogue of galaxies behind the southern Milky Way. - II. The Crux and Great Attractor regions (l = 289deg - 338deg)

In this second paper of the catalogue series of galaxies behind the southern Milky Way, we report on the deep optical galaxy search in the Crux region (289deg <= l <= 318deg and -10deg <= b <= 10deg) and the Great Attractor region (316deg <= l <= 338deg and -10deg <= b <= 10deg). The galaxy catalogues are presented, a brief description of the galaxy search given, as well as a discussion on the distribution and characteristics of the uncovered galaxies. A total of 8182 galaxies with major diameters D >= 0.2 arcmin were identified in this ~850 square degree area: 3759 galaxies in the Crux region and 4423 galaxies in the Great Attractor region. Of the 8182 galaxies, 229 (2.8%) were catalogued before in the optical (3 in radio) and 251 galaxies have a reliable (159), or likely (92) cross-identification in the IRAS Point Source Catalogue (3.1%). A number of prominent overdensities and filaments of galaxies are identified. They are not correlated with the Galactic foreground extinction and hence indicative of extragalactic large-scale structures. Redshifts obtained at the South African Astronomical Observatory (SAAO) for 518 of the newly catalogued galaxies in the Crux and Great Attractor regions (Fairall et al. 1998; Woudt et al. 1999) confirm distinct voids and clusters in the area here surveyed. With this optical galaxy search, we have reduced the width of the optical `Zone of Avoidance' for galaxies with extinction-corrected diameters larger than 1.3 arcmin from extinction levels A_B >= 1.0 mag to A_B >= 3.0 mag: the remaining optical Zone of Avoidance is now limited by |b| <= 3deg (see Fig. 16).Comment: 19 pages, 16 figures, accepted for publication in A&A. Tables will shortly be available in electronic version at the CDS. Full resolution (colour) copies of Figures 1, 2, 3 and 16 are available at http://mensa.ast.uct.ac.za/~pwoud