Low Luminosity States of the Black Hole Candidate GX 339-4. I. ASCA and Simultaneous Radio/RXTE Observations

We discuss a series of observations of the black hole candidate GX 339-4 in low luminosity, spectrally hard states. We present spectral analysis of three separate archival Advanced Satellite for Cosmology and Astrophysics (ASCA) data sets and eight separate Rossi X-ray Timing Explorer (RXTE) data sets. Three of the RXTE observations were strictly simultaneous with 843 MHz and 8.3-9.1 GHz radio observations. All of these observations have (3-9 keV) flux approximately < 10^{-9} ergs s^{-1} cm^{-2}. The ASCA data show evidence for an 6.4 keV Fe line with equivalent width 40 eV, as well as evidence for a soft excess that is well-modeled by a power law plus a multicolor blackbody spectrum with peak temperature 150-200 eV. The RXTE data sets also show evidence of an Fe line with equivalent widths 20-140 eV. Reflection models show a hardening of the RXTE spectra with decreasing X-ray flux; however, these models do not exhibit evidence of a correlation between the photon index of the incident power law flux and the solid angle subtended by the reflector. `Sphere+disk' Comptonization models and Advection Dominated Accretion Flow (ADAF) models also provide reasonable descriptions of the RXTE data. The former models yield coronal temperatures in the range 20-50 keV and optical depths of \tau ~ 3. The model fits to the X-ray data, however, do not simultaneously explain the observed radio properties. The most likely source of the radio flux is synchrotron emission from an extended outflow of size greater than O(10^7 GM/c^2).Comment: 18 pages in latex emulateapj.sty. Accepted for publication in the Astrophysical Journa

Path integral Monte Carlo simulations of silicates

We investigate the thermal expansion of crystalline SiO$_2$ in the $\beta$-- cristobalite and the $\beta$-quartz structure with path integral Monte Carlo (PIMC) techniques. This simulation method allows to treat low-temperature quantum effects properly. At temperatures below the Debye temperature, thermal properties obtained with PIMC agree better with experimental results than those obtained with classical Monte Carlo methods.Comment: 27 pages, 10 figures, Phys. Rev. B (in press

A proposed emendation of the Gray Flycatchers type locality and formal designation of its lectotype\u27

The Gray Flycatcher (Empidonax wrightii) now bears the specific epithet that Spencer Fullerton Baird provisionally designated\u27 for a potential new species of this genus—which he described from two seemingly undated Smithsonian Institution museum skins (i.e., USNM 7234 and 7237), and which the United States and Mexican Boundary Survey botanist Charles Wright had purportedly collected at El Paso, El Paso County, Texas presumably in the early 1850s. However, our research indicates that: (a) the latter locality did not exist as such when Wright collected these specimens, which respective dates we have determined were almost certainly 4 May and 3 April 1852; and (b) he had instead obtained them at the U.S. Boundary Commission\u27s operational headquarters located upstream along the Rio Grande at nearby Frontera, Texas. That facility was soon destroyed by a massive flood that swept down this river on the night of 25 June 1852—since which date a series of international and interstate agreements resulted in its former site having been variously shifted between Chihuahua, Texas, and New Mexico until 1930, when it was officially placed in present Sunland Park, Doña Ana County in the latter state. Consequently, it is this latest location that we are here proposing as the emended type locality of E. wrightii Baird, while at the same time also formally designating the taxon\u27s sole remaining Smithsonian syntype (USNM 7234) as its lectotype.\u2

Highly polarized alkenes as organocatalysts for the polymerization of lactones and trimethylene carbonate

In this work, the activity of N-heterocyclic olefins (NHOs), a newly emerging class of organopolymerization catalyst, is investigated to affect the metal-free polymerization of lactones and trimethylene carbonate (TMC). A decisive structure−activity relationship is revealed. While catalysts of the simplest type bearing an exocyclic CH2 moiety polymerize L-lactide (L-LA) and δ-valerolactone (δ-VL) in a non-living and non-quantitative manner, the introduction of methyl substituents on the exocyclic carbon radically changes this behavior. 2-Isopropylidene-1,3,4,5-tetramethylimidazoline is found to be highly active for a range of monomers such as L-LA, δ-VL, ε-caprolactone (ε-CL), and TMC, with quantitative conversion occurring within seconds with catalyst loadings of just 0.2 mol %. The high activity of this NHO further enables the ring-opening polymerization (ROP) of the macrolactone ω-pentadecalactone (PDL). However, this broad applicability is offset by a lack of control over the polymerizations, including side reactions as a consequence of its strong basicity. To overcome this, a saturated, imidazolinium-derived analogue was synthesized and subsequently demonstrated to possess a harnessed reactivity which enables it to polymerize both L-LA and TMC in a controlled manner (ĐM < 1.2). NMR spectroscopic and MALDI-ToF MS experiments highlight the differences in polymerization pathways for 2-methylene-1,3,4,5-tetramethylimidazoline, in which the exocyclic carbon is not substituted, in contrast to 2-isopropylidene-1,3,4,5-tetramethylimidazoline, with the former operating via its nucleophilicity and the latter acting as a base with enolizable δ-VL

Identification of Ancient Feather Fragments Found in Melting Alpine Ice Patches in Southern Yukon

Twelve ancient artifacts or fragmented feather samples recovered from melting alpine ice patches in southern Yukon were analyzed in order to identify the species of birds associated with the ice patches or used on weapons recovered from these sites. The identification of bird species used by ancient hunters as long ago as 4500 BP enhances our insight into the customs, culture, and sophistication of life at that time. Downy feather barbs were found on two samples and microscopically identified as duck (Anatidae) and falcon (Falconidae). Further examination and comparisons using museum specimens resulted in a total of six identifications: Anatidae, eagle (Aquila or Haliaeetus), gyrfalcon (Falco rusticolus), white-tailed ptarmigan (Lagopus leucurus), short-eared owl (Asio flammeus), and northern flicker (Colaptes auratus luteus). Three of the feather samples were complete enough to show apparent modification, or notching, along the feather shaft. The identification of non-game birds such as gyrfalcon and eagles, together with evidence of possible worked or notched feathers, indicates that as long as 4500 years ago, Subarctic hunters selected feathers not only for their utility in fletching, but also possibly for symbolic or decorative purposes.On a analysé 12 anciens artefacts ou échantillons de fragments de plumes découverts dans le sud du Yukon lors de la fonte de plaques de glace alpine, afin d’identifier les espèces aviaires associées à ces plaques de glace ou utilisées sur les armes provenant de ces sites. L’identification des espèces aviaires utilisées par les anciens chasseurs à une époque aussi reculée que 4500 BP nous permet de mieux comprendre les coutumes, la culture et le degré de sophistication de la vie à cette époque. On a trouvé des barbes duveteuses sur deux échantillons et l’analyse au microscope a révélé qu’elles appartenaient à un canard (anatidé) et à un faucon (falconidé). Un examen plus poussé et des comparaisons avec des spécimens présents dans des musées ont permis d’établir six provenances: anatidé, aigle (Aquila ou Haliaeetus), faucon gerfaut (Falco rusticolus), lagopède à queue blanche (Lagopus leucurus), hibou des marais (Asio flammeus) et pic flamboyant (Colaptes auratus luteus). Trois des échantillons de plumes étaient assez complets pour révéler des modifications apparentes ou encoches, le long de la tige de la plume. L’identification d’oiseaux non cynégétiques tels que le faucon gerfaut et les aigles, combinée avec la découverte de plumes encochées ou éventuellement travaillées, révèle qu’il y a 4500 ans, les chasseurs subarctiques sélectionnaient déjà les plumes non seulement dans un but utilitaire pour en faire des empennes de flèches, mais peut-être aussi à des fins symboliques ou d’ornementation

Selective and Sequential Catalytic Chemical Depolymerization and Upcycling of Mixed Plastics

Chemical recycling to monomer (CRM) provides a useful technique to allow for polymer-to-monomer-to-polymer circular economies. A significant challenge remains, however, in the treatment of mixed plastics by CRM in which unselective depolymerization requires either presorting of plastics or purification processes postdepolymerization, both of which add cost to waste plastic processing. We report a simple, yet selective, chemical depolymerization of three commonly used polymers, poly(lactic acid) (PLA), bisphenol A polycarbonate (BPA-PC), and polyethylene terephthalate (PET), using inexpensive and readily available common metal salt/organobase dual catalysts. By a judicious choice of catalyst and conditions, selective and sequential depolymerization of mixtures of the polymers was demonstrated. Furthermore, the potential for upcycling of polymers to value-added monomers was explored through the application of alternative nucleophiles within the depolymerization.</p

The utilisation of hydrogels for iPSC-cardiomyocyte research

Cardiac fibroblasts' (FBs) and cardiomyocytes' (CMs) behaviour and morphology are influenced by their environment such as remodelling of the myocardium, thus highlighting the importance of biomaterial substrates in cell culture. Biomaterials have emerged as important tools for the development of physiological models, due to the range of adaptable properties of these materials, such as degradability and biocompatibility. Biomaterial hydrogels can act as alternative substrates for cellular studies, which have been particularly key to the progression of the cardiovascular field. This review will focus on the role of hydrogels in cardiac research, specifically the use of natural and synthetic biomaterials such as hyaluronic acid, polydimethylsiloxane and polyethylene glycol for culturing induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The ability to fine-tune mechanical properties such as stiffness and the versatility of biomaterials is assessed, alongside applications of hydrogels with iPSC-CMs. Natural hydrogels often display higher biocompatibility with iPSC-CMs but often degrade quicker, whereas synthetic hydrogels can be modified to facilitate cell attachment and decrease degradation rates. iPSC-CM structure and electrophysiology can be assessed on natural and synthetic hydrogels, often resolving issues such as immaturity of iPSC-CMs. Biomaterial hydrogels can thus provide a more physiological model of the cardiac extracellular matrix compared to traditional 2D models, with the cardiac field expansively utilising hydrogels to recapitulate disease conditions such as stiffness, encourage alignment of iPSC-CMs and facilitate further model development such as engineered heart tissues (EHTs)

The Utilisation of Hydrogels for iPSC-Cardiomyocyte Research

Cardiac fibroblasts’ (FBs) and cardiomyocytes’ (CMs) behaviour and morphology are influenced by their environment such as remodelling of the myocardium, thus highlighting the importance of biomaterial substrates in cell culture. Biomaterials have emerged as important tools for the development of physiological models, due to the range of adaptable properties of these materials, such as degradability and biocompatibility. Biomaterial hydrogels can act as alternative substrates for cellular studies, which have been particularly key to the progression of the cardiovascular field. This review will focus on the role of hydrogels in cardiac research, specifically the use of natural and synthetic biomaterials such as hyaluronic acid, polydimethylsiloxane and polyethylene glycol for culturing induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The ability to fine-tune mechanical properties such as stiffness and the versatility of biomaterials is assessed, alongside applications of hydrogels with iPSC-CMs. Natural hydrogels often display higher biocompatibility with iPSC-CMs but often degrade quicker, whereas synthetic hydrogels can be modified to facilitate cell attachment and decrease degradation rates. iPSC-CM structure and electrophysiology can be assessed on natural and synthetic hydrogels, often resolving issues such as immaturity of iPSC-CMs. Biomaterial hydrogels can thus provide a more physiological model of the cardiac extracellular matrix compared to traditional 2D models, with the cardiac field expansively utilising hydrogels to recapitulate disease conditions such as stiffness, encourage alignment of iPSC-CMs and facilitate further model development such as engineered heart tissues (EHTs)