HST Images and Spectra of the Remnant of SN 1885 in M31

Near UV HST images of the remnant of SN 1885 (S And) in M31 show a 0"70 +- 0"05 diameter absorption disk silhouetted against M31's central bulge, at SN 1885's historically reported position. The disk's size corresponds to a linear diameter of 2.5 +- 0.4 pc at a distance of 725 +- 70 kpc, implying an average expansion velocity of 11000 +- 2000 km/s over 110 years. Low-dispersion FOS spectra over 3200-4800 A; reveal that the absorption arises principally from Ca II H & K (equivalent width ~215 A;) with weaker absorption features of Ca I 4227 A; and Fe I 3720 A;. The flux at Ca II line center indicates a foreground starlight fraction of 0.21, which places SNR 1885 some 64 pc to the near side of the midpoint of the M31 bulge, comparable to its projected 55 pc distance from the nucleus. The absorption line profiles suggest an approximately spherically symmetric, bell-shaped density distribution of supernova ejecta freely expanding at up to 13100 +- 1500 km/s. We estimate Ca I, Ca II, and Fe I masses of 2.9(+2.4,-0.6) x 10^-4 M_o, 0.005(+0.016,-0.002) M_o, and 0.013(+0.010,-0.005) M_o respectively. If the ionization state of iron is similar to the observed ionization state of calcium, M_CaII/M_CaI = 16(+42,-5), then the mass of Fe II is 0.21(+0.74,-0.08) M_o, consistent with that expected for either normal or subluminous SN Ia.Comment: 8 pages, including 4 embedded EPS figures, emulateapj.sty style file. Color image at http://casa.colorado.edu/~mcl/sand.shtml . Submitted to Ap

Cost-effectiveness of malaria diagnosis using rapid diagnostic tests compared to microscopy or clinical symptoms alone in Afghanistan

Background Improving access to parasitological diagnosis of malaria is a central strategy for control and elimination of the disease. Malaria rapid diagnostic tests (RDTs) are relatively easy to perform and could be used in primary level clinics to increase coverage of diagnostics and improve treatment of malaria.<p></p> Methods A cost-effectiveness analysis was undertaken of RDT-based diagnosis in public health sector facilities in Afghanistan comparing the societal and health sector costs of RDTs versus microscopy and RDTs versus clinical diagnosis in low and moderate transmission areas. The effect measure was ‘appropriate treatment for malaria’ defined using a reference diagnosis. Effects were obtained from a recent trial of RDTs in 22 public health centres with cost data collected directly from health centres and from patients enrolled in the trial. Decision models were used to compare the cost of RDT diagnosis versus the current diagnostic method in use at the clinic per appropriately treated case (incremental cost-effectiveness ratio, ICER).<p></p> Results RDT diagnosis of Plasmodium vivax and Plasmodium falciparum malaria in patients with uncomplicated febrile illness had higher effectiveness and lower cost compared to microscopy and was cost-effective across the moderate and low transmission settings. RDTs remained cost-effective when microscopy was used for other clinical purposes. In the low transmission setting, RDTs were much more effective than clinical diagnosis (65.2% (212/325) vs 12.5% (40/321)) but at an additional cost (ICER) of US$4.5 per appropriately treated patient including a health sector cost (ICER) of US$2.5 and household cost of US$2.0. Sensitivity analysis, which varied drug costs, indicated that RDTs would remain cost-effective if artemisinin combination therapy was used for treating both P. vivax and P. falciparum. Cost-effectiveness of microscopy relative to RDT is further reduced if the former is used exclusively for malaria diagnosis. In the health service setting of Afghanistan, RDTs are a cost-effective intervention compared to microscopy.<p></p> Conclusions RDTs remain cost-effective across a range of drug costs and if microscopy is used for a range of diagnostic services. RDTs have significant advantages over clinical diagnosis with minor increases in the cost of service provision.<p></p&gt

From Selection to Instruction and Back: Competing Conformational Selection and Induced Fit Pathways in Abiotic Hosts

Two limiting cases of molecular recognition, induced fit (IF) and conformational selection (CS), play a central role in allosteric regulation of natural systems. The IF paradigm states that a substrate “instructs” the host to change its shape after complexation, while CS asserts that a guest “selects” the optimal fit from an ensemble of preexisting host conformations. With no studies that quantitatively address the interplay of two limiting pathways in abiotic systems, we herein and for the first time describe the way by which twisted capsule M-1, encompassing two conformers M-1(+) and M-1(−), trap CX4 (X=Cl, Br) to give CX4⊂M-1(+) and CX4⊂M-1(−), with all four states being in thermal equilibrium. With the assistance of 2D EXSY, we found that CBr4 would, at its lower concentrations, bind M-1 via a M-1(+)→M-1(−)→CBr4⊂M-1(−) pathway corresponding to conformational selection. For M-1 complexing CCl4 though, data from 2D EXSY measurements and 1D NMR line-shape analysis suggested that lower CCl4 concentrations would favor CS while the IF pathway prevailed at higher proportions of the guest. Since CS and IF are not mutually exclusive, we reason that our work sets the stage for characterizing the dynamics of a wide range of already existing hosts to broaden our fundamental understanding of their action. The objective is to master the way in which encapsulation takes place for designing novel and allosteric sequestering agents, catalysts and chemosensors akin to those found in nature

Towards More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere

Motivated by the recognition that variation in the optical transmission of the atmosphere is probably the main limitation to the precision of ground-based CCD measurements of celestial fluxes, we review the physical processes that attenuate the passage of light through the Earth's atmosphere. The next generation of astronomical surveys, such as PanSTARRS and LSST, will greatly benefit from dedicated apparatus to obtain atmospheric transmission data that can be associated with each survey image. We review and compare various approaches to this measurement problem, including photometry, spectroscopy, and LIDAR. In conjunction with careful measurements of instrumental throughput, atmospheric transmission measurements should allow next-generation imaging surveys to produce photometry of unprecedented precision. Our primary concerns are the real-time determination of aerosol scattering and absorption by water along the line of sight, both of which can vary over the course of a night's observations.Comment: 41 pages, 14 figures. Accepted PAS

Preparation of an ion with the highest calculated proton affinity: ortho-diethynylbenzene dianion

Owing to the increased proton affinity that results from additional negative charges, multiply-charged anions have been proposed as one route to prepare and access a range of new and powerful superbases . Paradoxically, while the additional electrons in polyanions increase basicity they serve to diminish the electron binding energy and thus, it had been thought, hinder experimental synthesis. We report the synthesis and isolation of the ortho-diethynylbenzene dianion (ortho-DEB2−) and present observations of this novel species undergoing gas-phase proton-abstraction reactions. Using a theoretical model based on Marcus-Hush theory, we attribute the stability of ortho-DEB2− to the presence of a barrier that prevents spontaneous electron detachment. The proton affinity of 1843 kJ mol−1 calculated for this dianion superbase using high-level quantum chemistry calculations significantly exceeds that of the lithium monoxide anion, the most basic system previously prepared. The ortho-diethynylbenzene dianion is therefore the strongest base that has been experimentally observed to date

Cost-effectiveness of malaria diagnosis using rapid diagnostic tests compared to microscopy or clinical symptoms alone in Afghanistan.

BACKGROUND: Improving access to parasitological diagnosis of malaria is a central strategy for control and elimination of the disease. Malaria rapid diagnostic tests (RDTs) are relatively easy to perform and could be used in primary level clinics to increase coverage of diagnostics and improve treatment of malaria. METHODS: A cost-effectiveness analysis was undertaken of RDT-based diagnosis in public health sector facilities in Afghanistan comparing the societal and health sector costs of RDTs versus microscopy and RDTs versus clinical diagnosis in low and moderate transmission areas. The effect measure was 'appropriate treatment for malaria' defined using a reference diagnosis. Effects were obtained from a recent trial of RDTs in 22 public health centres with cost data collected directly from health centres and from patients enrolled in the trial. Decision models were used to compare the cost of RDT diagnosis versus the current diagnostic method in use at the clinic per appropriately treated case (incremental cost-effectiveness ratio, ICER). RESULTS: RDT diagnosis of Plasmodium vivax and Plasmodium falciparum malaria in patients with uncomplicated febrile illness had higher effectiveness and lower cost compared to microscopy and was cost-effective across the moderate and low transmission settings. RDTs remained cost-effective when microscopy was used for other clinical purposes. In the low transmission setting, RDTs were much more effective than clinical diagnosis (65.2% (212/325) vs 12.5% (40/321)) but at an additional cost (ICER) of US$4.5 per appropriately treated patient including a health sector cost (ICER) of US$2.5 and household cost of US$2.0. Sensitivity analysis, which varied drug costs, indicated that RDTs would remain cost-effective if artemisinin combination therapy was used for treating both P. vivax and P. falciparum. Cost-effectiveness of microscopy relative to RDT is further reduced if the former is used exclusively for malaria diagnosis. In the health service setting of Afghanistan, RDTs are a cost-effective intervention compared to microscopy. CONCLUSIONS: RDTs remain cost-effective across a range of drug costs and if microscopy is used for a range of diagnostic services. RDTs have significant advantages over clinical diagnosis with minor increases in the cost of service provision. TRIAL REGISTRATION: The trial was registered at ClinicalTrials.gov under identifier NCT00935688

The Quasar / Galaxy Pair PKS 1327-206 / ESO 1327-2041: Absorption Associated with a Recent Galaxy Merger

We present HST/WFPC2 broadband and ground-based Halpha images, H I 21-cm emission maps, and low-resolution optical spectra of the nearby galaxy ESO 1327-2041, which is located 38 arcsec (14 kpc in projection) west of the quasar PKS 1327-206. Our HST images reveal that ESO 1327-2041 has a complex optical morphology, including an extended spiral arm that was previously classified as a polar ring. Our optical spectra show Halpha emission from several H II regions in this arm located ~5 arcsec from the quasar position (~2 kpc in projection) and our ground-based Halpha images reveal the presence of several additional H II regions in an inclined disk near the galaxy's center. Absorption associated with ESO 1327-2041 is found in H I 21-cm, optical, and near-UV spectra of PKS 1327-206. We find two absorption components at cz = 5255 and 5510 km/s in the H I 21-cm absorption spectrum, which match the velocities of previously discovered metal-line components. We attribute the 5510 km/s absorber to disk gas in the extended spiral arm and the 5255 km/s absorber to high-velocity gas that has been tidally stripped from the disk of ESO 1327-2041. The complexity of the galaxy/absorber relationships for these very nearby H I 21-cm absorbers suggests that the standard view of high redshift damped Lyman-alpha absorbers is oversimplified in many cases.Comment: Replaced with accepted version; 16 page