Post-Outburst Observations of V1647 Ori: Detection of a Brief Warm, Molecular Outflow

We present new observations of the fundamental ro-vibrational CO spectrum of V1647 Ori, the young star whose recent outburst illuminated McNeil's Nebula. Previous spectra, acquired during outburst in 2004 February and July, had shown the CO emission lines to be broad and centrally peaked-similar to the CO spectrum of a typical classical T Tauri star. In this paper, we present CO spectra acquired shortly after the luminosity of the source returned to its pre-outburst level (2006 February) and roughly one year later (2006 December and 2007 February). The spectrum taken in 2006 February revealed blue-shifted CO absorption lines superimposed on the previously observed CO emission lines. The projected velocity, column density, and temperature of this outflowing gas was 30 km/s, 3^{+2}_{-1}E18 cm^{-2$, and 700^{+300}_{-100} K, respectively. The absorption lines were not observed in the 2006 December and 2007 February data, and so their strengths must have decreased in the interim by a factor of 9 or more. We discuss three mechanisms that could give rise to this unusual outflow.Comment: 14 pages, 2 figures, accepted for publication in ApJ

The Gas/Dust Ratio of Circumstellar Disks: Testing Models of Planetesimal Formation

We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6–5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust columndensity ratio and disk inclination similar to that found by Rettig et al

Dust Stratification in Young Circumstellar Disks

We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S, RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO, and C18O as well as broad emission lines of gas phase12CO. The narrow absorption lines of CO are shown to originate from the colder circumstellar gas. We find that the line of sight gas column densities resulting from the CO absorption lines are much higher than expected for the measured extinction for each source and suggest the gas to dust ratio is measuring the dust settling and/or grain coagulation in these extended disks. We provide a model of turbulence, dust settling and grain growth to explain the results. The techniques presented here allow us to provide some observationally-motivated bounds on accretion disk alpha in protostellar systems

Suicide genes: Monitoring cells in patients with a safety switch

Clinical trials increasingly incorporate suicide genes either as direct lytic agents for tumors or as safety switches in therapies based on genetically modified cells. Suicide genes can also be used as non-invasive reporters to monitor the biological consequences of administering genetically modified cells to patients and gather information relevant to patient safety. These genes can monitor therapeutic outcomes addressable by early clinical intervention. As an example, our recent clinical trial used 18F-9-(4-fluoro-3-hydroxymethylbutyl)guanine (18FHBG) and PET/CT scans to follow T cells transduced with herpes simplex virus thymidine kinase (TK) after administration to patients. Guided by preclinical data we ultimately hope to discern whether a particular pattern of transduced T cell migration within patients reflects early development of Graft vs. Host Disease (GvHD). Current difficulties in terms of choice of suicide gene, biodistribution of radiolabeled tracers in humans versus animal models, and threshold levels of genetically modified cells needed for detection by PET/CT are discussed. As alternative suicide genes are developed, additional radiolabel probes suitable for imaging in patients should be considered

Scale-dependent Associations among Fish Predation, Littoral Habitat, and Distributions of Crayfish Species

To predict how species establish and disperse within novel communities, the spatial scale at which competition, predation, and habitat interact must be understood. We explored how these factors affect the distribution and abundance of the exotic crayfishes Orconectes rusticus and O. propinquus and the native O. virilis at both the site-specific and whole-lake scales in northern Wisconsin lakes. During summer 1990, we quantified crayfish, fish predators, and fish diets in cobble and macrophyte sites in Trout Lake, comparing resulting patterns to those in 21 lakes surveyed during summer 1987. Within and across lakes, fish abundance was unrelated to habitat. Within Trout Lake, O. rusticus and O. propinquus were common in both cobble and macrophyte. Orconectes virilis was restricted to macrophyte, probably due to strong displacement by the invaders in cobble. Across lakes, O. rusticus increased where habitat was more than 16.7% cobble, O. propinquus was generally rare, and O. virilis abundance was unrelated to cobble. Crayfish were generally small in cobble and large in macrophyte, perhaps because of habitat-specific, size-selective fish predation or because large crayfish leave cobble when it no longer provides refuge. Orconectes virilis, the largest of three congeners, may have a size refuge in macrophyte but not in cobble. Across lakes, O. rusticus was only abundant when fish biomass was low; O. virilis abundance varied positively with fish. Effects of fish predation and habitat on the ability of invaders Orconectes rusticus and O. propinquus to establish and replace O. virilis appear to be scale dependent. At local (site-specific) scales, cobble likely interacts with selective predation for O. virilis to allow the invaders to establish and replace the native. At the lake-wide scale, high cobble facilitates invaders but predation may curb their successful dispersal and establishment at new sites. Models of community assembly and invasions need to incorporate scale dependencies in habitat availability and biotic interactions to effectively assess the invasion potential of novel species

Interactions with membrane lipids and SNARE complex underlie dual roles for calcium-dependent activator protein for secretion (CAPS) in large dense-core vesicles (LDCVS) priming

CAPS (Calcium-dependent activator protein for secretion), was discovered as a soluble factor required for catecholamine secretion from PC12 cells. CAPS facilitates release of dense-core vesicles and release of neurotransmitters. In vertebrates CAPS is required for priming of synaptic vesicles and dense-core vesicles in neurons and in catecholamine release from the adrenal medulla. The pleckstrin homology domain of CAPS has been shown to mediate an interaction with the plasma membrane. An interaction with SNARE proteins and assembled SNARE complexes requires the Munc13 homology domain. The interaction with SNARE components facilitates SNARE complex formation, the molecular basis of the priming reaction, while interactions with the phosphoinositol 4,5 bisphosphate (PI(4,5)P2) rich areas of the plasma membrane localize CAPS at the release site but may also promote the fusion of primed vesicles. CAPS splice variants lacking the Munc13 homology domain but with an intact pleckstrin homology domain promote priming to the readily releasable pool while CAPS splice variants with a deletion in the pleckstrin homology domain promote catecholamine release, albeit at slower rates. These results confirm a dual action of CAPS dependent on the Munc13 homology- and the pleckstrin homology domains, respectively.Sociedad Argentina de Fisiologí

Dust Settling in Magnetorotationally-Driven Turbulent Discs II: The Pervasiveness of the Streaming Instability and its Consequences

We present a series of simulations of turbulent stratified protostellar discs with the goal of characterizing the settling of dust throughout a minimum-mass solar nebula. We compare the evolution of both compact spherical grains, as well as highly fractal grains. Our simulations use a shearing-box formulation to study the evolution of dust grains locally within the disc, and collectively our simulations span the entire extent of a typical accretion disc. The dust is stirred by gas that undergoes MRI-driven turbulence. This establishes a steady state scale height for the dust that is different for dust of different sizes. This sedimentation of dust is an important first step in planet formation and we predict that ALMA should be able to observationally verify its existence. When significant sedimentation occurs, the dust will participate in a streaming instability that significantly enhances the dust density. We show that the streaming instability is pervasive in the outer disc. We characterize the scale heights of dust whose size ranges from a few microns to a few centimeters. We find that for spherical grains, a power-law relationship develops for the scale height with grain size, with a slope that is slightly steeper than -1/2. The sedimentation is strongest in the outer disc and increases for large grains. The results presented here show that direct measurements of grain settling can be made by ALMA and we present favorable conditions for observability. The streaming instability should also be directly observable and we provide conditions for directly observing it. We calculate collision rates and growth rates for the dust grains in our simulations of various sizes colliding with other grains, and find that these rates are significantly enhanced through the density enhancement arising from the streaming instability.Comment: 39 pages, 13 figures, submitted to MNRAS. Abstract is abridge

CAPS facilitates filling of the rapidly releasable pool of large dense-core vesicles

Calcium-activator protein for secretion (CAPS) is a cytosolic protein that associates with large dense-core vesicles and is involved in their secretion. Mammals express two CAPS isoforms, which share a similar domain structure including a Munc13 homology domain that is believed to be involved in the priming of secretory vesicles. A variety of studies designed to perturb CAPS function indicate that CAPS is involved in the secretion of large dense-core vesicles, but where in the secretory pathway CAPS acts is still under debate. Mice in which one allele of the CAPS-1 gene is deleted exhibit a deficit in catecholamine secretion from chromaffin cells. We have examined catecholamine secretion from chromaffin cells in which both CAPS genes were deleted and show that the deletion of both CAPS isoforms causes a strong reduction in the pool of rapidly releasable chromaffin granules and of sustained release during ongoing stimulation. We conclude that CAPS is required for the adequate refilling and/or maintenance of a rapidly releasable granule pool