Colloidal templating at a cholesteric - oil interface: Assembly guided by an array of disclination lines

We simulate colloids (radius $R \sim 1\mu$m) trapped at the interface between a cholesteric liquid crystal and an immiscible oil, at which the helical order (pitch p) in the bulk conflicts with the orientation induced at the interface, stabilizing an ordered array of disclinations. For weak anchoring strength W of the director field at the colloidal surface, this creates a template, favoring particle positions eitheron top of or midway between defect lines, depending on $\alpha = R/p$. For small $\alpha$, optical microscopy experiments confirm this picture, but for larger $\alpha$ no templating is seen. This may stem from the emergence at moderate W of a rugged energy landscape associated with defect reconnections.Comment: 5 pages, 4 figure

A New Look At Carbon Abundances In Planetary Nebulae. III. DDDM1, IC 3568, IC4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009

This paper is the third in a series reporting on a study of carbon abundances in a carefully chosen sample of planetary nebulae representing a large range in progenitor mass and metallicity. We make use of the IUE Final Archive database containing consistently-reduced spectra to measure line strengths of C III] 1909 along with numerous other UV lines for the planetary nebulae DDDM1, IC 3568, IC 4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009. We combine the IUE data with line strengths from optical spectra obtained specifically to match the IUE slit positions as closely as possible, to determine values for the abundance ratios He/H, O/H, C/O, N/O, and Ne/O. The ratio of C III] 1909/C II 4267 is found to be effective for merging UV and optical spectra when He II 1640/4686 is unavailable. Our abundance determination method includes a 5-level program whose results are fine-tuned by corrections derived from detailed photoionization models constrained by the same set of emission lines. All objects appear to have subsolar levels of O/H, and all but one show N/O levels above solar. In addition, the seven planetary nebulae span a broad range in C/O values. We infer that many of our objects are matter bounded, and thus the standard ionization correction factor for N/O may be inappropriate for these PNe. Finally, we estimate C/O using both collisionally-excited and recombination lines associated with C+2 and find the well established result that abundances from recombination lines usually exceed those from collisionally-excited lines by several times.Comment: 36 pages, 7 tables, 2 figures, latex. Tables and figures supplied as two separate postscript files. Accepted for publication in Ap

12^{12}C/13^{13}C ratio in planetary nebulae from the IUE archives

We investigated the abundance ratio of $^{12}$C/$^{13}$C in planetary nebulae by examining emission lines arising from \ion{C}{3} 2s2p ^3P_{2,1,0} \to 2s^2 ^1S_0. Spectra were retrieved from the International Ultraviolet Explorer archives, and multiple spectra of the same object were coadded to achieve improved signal-to-noise. The $^{13}$C hyperfine structure line at 1909.6 \AA was detected in NGC 2440. The $^{12}$C/$^{13}$C ratio was found to be $\sim4.4\pm$1.2. In all other objects, we provide an upper limit for the flux of the 1910 \AA line. For 23 of these sources, a lower limit for the $^{12}$C/$^{13}$C ratio was established. The impact on our current understanding of stellar evolution is discussed. The resulting high signal-to-noise \ion{C}{3} spectrum helps constrain the atomic physics of the line formation process. Some objects have the measured 1907/1909 flux ratio outside the low-electron density theoretical limit for $^{12}$C. A mixture of $^{13}$C with $^{12}$C helps to close the gap somewhat. Nevertheless, some observed 1907/1909 flux ratios still appear too high to conform to the presently predicted limits. It is shown that this limit, as well as the 1910/1909 flux ratio, are predominantly influenced by using the standard partitioning among the collision strengths for the multiplet $^1S_0$--$^3P_J$ according to the statistical weights. A detailed calculation for the fine structure collision strengths between these individual levels would be valuable.Comment: ApJ accepted: 19 pages, 3 Figures, 2 Table

Colloid-stabilized emulsions: behaviour as the interfacial tension is reduced

We present confocal microscopy studies of novel particle-stabilized emulsions. The novelty arises because the immiscible fluids have an accessible upper critical solution temperature. The emulsions have been created by beginning with particles dispersed in the single-fluid phase. On cooling, regions of the minority phase nucleate. While coarsening these nuclei become coated with particles due to the associated reduction in interfacial energy. The resulting emulsion is arrested, and the particle-coated interfaces have intriguing properties. Having made use of the binary-fluid phase diagram to create the emulsion we then make use of it to study the properties of the interfaces. As the emulsion is re-heated toward the single-fluid phase the interfacial tension falls and the volume of the dispersed phase drops. Crumpling, fracture or coalescence can follow. The results show that the elasticity of the interfaces has a controlling influence over the emulsion behaviour.Comment: Submitted for the proceedings of the 6th Liquid Matter Conference, held in Utrecht (NL) in July 200

Observations of rotationally resolved C3 in translucent sight lines

The rotationally resolved spectrum of the A ^1Pi_u <- X ^1Sigma^+_g 000-000 transition of C3, centered at 4051.6A, has been observed along 10 translucent lines of sight. To interpret these spectra, a new method for the determination of column densities and analysis of excitation profiles involving the simulation and fitting of observed spectra has been developed. The populations of lower rotational levels (J<14) in C3 are best fit by thermal distributions that are consistent with the kinetic temperatures determined from the excitation profile of C2. Just as in the case of C2, higher rotational levels (J>14) of C3 show increased nonthermal population distributions in clouds which have been determined to have total gas densities below ~500 cm-3.Comment: 12 pages, 4 figures, accepted for publication in The Astrophysical Journa

Global Governance Behind Closed Doors : The IMF Boardroom, the Enhanced Structural Adjustment Facility, and the Intersection of Material Power and Norm Change in Global Politics

Up on the 12th floor of its 19th Street Headquarters, the IMF Board sits in active session for an average of 7 hours per week. Although key matters of policy are decided on in the venue, the rules governing Boardroom interactions remain opaque, resting on an uneasy combination of consensual decision-making and weighted voting. Through a detailed analysis of IMF Board discussions surrounding the Enhanced Structural Adjustment Facility (ESAF), this article sheds light on the mechanics of power in this often overlooked venue of global economic governance. By exploring the key issues of default liability and loan conditionality, I demonstrate that whilst the Boardroom is a more active site of contestation than has hitherto been recognized, material power is a prime determinant of both Executive Directors’ preferences and outcomes reached from discussions. And as the decisions reached form the backbone of the ‘instruction sheet’ used by Fund staff to guide their everyday operational decisions, these outcomes—and the processes through which they were reached—were factors of primary importance in stabilizing the operational norms at the heart of a controversial phase in the contemporary history of IMF concessional lending

Hubble Space Telescope Survey of Interstellar ^12CO/^13CO in the Solar Neighborhood

We examine 20 diffuse and translucent Galactic sight lines and extract the column densities of the ^12CO and ^13CO isotopologues from their ultraviolet A--X absorption bands detected in archival Space Telescope Imaging Spectrograph data with lambda/Deltalambda geq 46,000. Five more targets with Goddard High-Resolution Spectrograph data are added to the sample that more than doubles the number of sight lines with published Hubble Space Telescope observations of ^13CO. Most sight lines have 12-to-13 isotopic ratios that are not significantly different from the local value of 70 for ^12C/^13C, which is based on mm-wave observations of rotational lines in emission from CO and H_2CO inside dense molecular clouds, as well as on results from optical measurements of CH^+. Five of the 25 sight lines are found to be fractionated toward lower 12-to-13 values, while three sight lines in the sample are fractionated toward higher ratios, signaling the predominance of either isotopic charge exchange or selective photodissociation, respectively. There are no obvious trends of the ^12CO-to-^13CO ratio with physical conditions such as gas temperature or density, yet ^12CO/^13CO does vary in a complicated manner with the column density of either CO isotopologue, owing to varying levels of competition between isotopic charge exchange and selective photodissociation in the fractionation of CO. Finally, rotational temperatures of H_2 show that all sight lines with detected amounts of ^13CO pass through gas that is on average colder by 20 K than the gas without ^13CO. This colder gas is also sampled by CN and C_2 molecules, the latter indicating gas kinetic temperatures of only 28 K, enough to facilitate an efficient charge exchange reaction that lowers the value of ^12CO/^13CO.Comment: 1-column emulateapj, 23 pages, 9 figure