Publications

A bright idea: By restricting the rotation between receptor and reporter units of the fluorescent chemosensor Mercury Green 1 (MG1), a remarkably high quantum efficiency is achieved in its Hg2+-ion-bound form in water (Φ=0.72). MG1 is specific to environmentally and biologically relevant mercury levels (ppm to ppb range), and can assay levels of Hg2+ ion in living cells and in edible fish.

We describe the rational design of oligothiophene semiconductors to facilitate solution-based fabrication of environmentally stable organic field-effect transistors (OFETs). Ultrathin films of α,ω-distyryl quaterthiophene (DS4T), pentathiophene (DS5T), and sexithiophene (DS6T) were prepared via solution processing to probe the effect of styryl end groups, oligomer length, and thin film structure on air stability. These films were prepared via solution deposition and thermal annealing of precursors featuring thermally labile ester solubilizing groups. A detailed study of the thin film structure was performed using atomic force microscopy (AFM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and grazing incidence X-ray diffraction (GIXD). Functional OFETs were obtained for DS5T and DS6T and have, respectively, hole mobilities of 0.051 and 0.043 cm2/(V s) and on/off ratios of 1 × 105 to 1 × 106, whereas DS4T OFETs failed to function because of poor film continuity. The effect of both short-term and long-term exposure to air is tracked in OFETs revealing remarkable stability for both DS5T and DS6T. This stability is attributed to the elimination of reactive sites in α,ω-distyryl oligothiophenes and suggests that careful choice of end-group structure can stabilize these molecules against oxidative degradation.

Copper specimens were exposed to Sulfate-Reducing Bacteria (SRB) for 10 months under the conditions corresponding to the final disposal of high-level nuclear waste. In-situ electrochemical impedance spectroscopy (EIS) measurements were carried out to characterize the surface-environment interface after various times of exposure. The EIS results are interpreted in terms of the Point Defect Model (PDM), in order to obtain kinetic information on the formation of the Cu2S passive film. The standard rate constant and the rate constants for the surface reactions revealed that the Cu2S layer is a p-type semiconductor. The diffusion constant for cation vacancies in the barrier layer and the average bulk cation vacancy concentration in the barrier layer were found to be on the orders of 10−13 cm2⋅s−1 and 1022 cm−3, respectively, i.e., both slightly higher than reported in literature for corresponding electrochemically developed Cu2S layers. The electric field strength was approximately 3⋅105 Vcm−1 at all measurement points. These results are presented and discussed in this work in the light of storage of high-level nuclear waste.

SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to ∼ 500 d after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with <it>Hubble Space Telescope</it>/Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the <it>BVrRiIZYJH</it> bands. SN 2013dy has a broad and slowly declining light curve (Δ<it>m</it><inf>15</inf>(<it>B</it>) = 0.92 mag), shallow <f>$\\mathrm{Si}\\,\\small {II}\\,\\lambda 6355$</f> absorption, and a low velocity gradient. We detect strong C <scp>ii</scp> in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of <f>$10.0^{+4.8}_{-3.8} \\times 10^{42}$</f> erg s−1. We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.

We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of SN 2005hk. These data reveal that SN 2005hk was nearly identical in its observed properties to SN 2002cx, which has been called ``the most peculiar known type Ia supernova.'' Both supernovae exhibited high ionization SN 1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities that were roughly half those of typical type Ia supernovae. The R and I light curves of both supernovae were also peculiar in not displaying the secondary maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk reveals the same peculiarity in the near-infrared. By combining our optical and near-infrared photometry of SN 2005hk with published ultraviolet light curves obtained with the Swift satellite, we are able to construct a bolometric light curve from ~10 days before to ~60 days after B maximum. The shape and unusually low peak luminosity of this light curve, plus the low expansion velocities and absence of a secondary maximum at red and near-infrared wavelengths, are all in reasonable agreement with model calculations of a 3D deflagration which produces ~0.25 M_sun of 56Ni.

Objective To examine the extent to which accountable care organizations ( ACO s) formally incorporate postacute care providers. Data Sources The National Survey of ACO s ( N = 269, response rate 66 percent). Study Design We report statistics on ACO s' formal inclusion of postacute care providers and the organizational characteristics and clinical capabilities of ACO s that have postacute care. Principal Findings Half of ACO s formally include at least one postacute service, with inclusion at higher rates in ACO s with commercial (64 percent) and Medicaid contracts (70 percent) compared to ACO s with Medicare contracts only (45 percent). ACO s that have a formal relationship with a postacute provider are more likely to have advanced transition management, end of life planning, readmission prevention, and care management capabilities. Conclusions Many ACO s have not formally engaged postacute care, which may leave room to improve service integration and care management.

A transcriptional enhancer element has been localized 3 kilobases 3' of the murine T-cell receptor C gamma 1 locus using a chloramphenicol acetyltransferase reporter gene construct. As a monomer the enhancer functions only in PEER gamma delta cells and Jurkat alpha beta cells of the T-cell lines tested. However, a tetramer of the enhancer functions in virtually all T-cell lines tested, including alpha beta T-cell lines, but not in other cell types. These results suggest that elements other than the enhancer are responsible for the failure of rearranged C gamma 1 genes to be expressed in alpha beta T cells. The enhancer has been localized to a 200-base-pair Rsa I restriction fragment, which contains sequence motifs similar to those found in the other T-cell receptor enhancers but not in the immunoglobulin enhancers.