Adhesion and spreading of cultured endothelial cells on modified and unmodified poly(ethylene terephthalate): a morphological study

The in vitro adhesion and spreading of human endothelial cells (HEC) on hydrophobic poly(ethylene terephthalate) (PETP) and moderately wettable tissue culture polyethylene terephthalate) (TCPETP) were studied with light microscopy and electron microscopy. Numbers of HEC adhering on TCPETP were always higher than those found on PETP. When cells were seeded in the presence of serum, extensive cell spreading on both PETP and TCPETP was observed after the first 30 min. Thereafter, spread cells appeared to withdraw from the PETP surface, resulting in irregularly shaped cells. Complete cell spreading occurred on TCPETP. Complete cell spreading also occurred on PETP and TCPETP when HEC had first been seeded from phosphate buffer solution and serum was supplied after 30 min. Furthermore, HEC spread on both PETP and TCPETP when the surfaces were precoated with protein(s), which promotes cell adhesion. However, when plasma was used for the coating, spread cells did not proliferate in a monolayer pattern. This study shows that TCPETP is, in general, a better surface for adhesion and proliferation of HEC than is PETP, suggesting that vascular prostheses with a TCPETP-like surface will perform better in vivo than prostheses made of PETP

Hypervelocity Stars. I. The Spectroscopic Survey

We discuss our targeted search for hypervelocity stars (HVSs), stars traveling with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Our survey, now half complete, has successfully identified a total of four probable HVSs plus a number of other unusual objects. Here we report the most recently discovered two HVSs: SDSS J110557.45+093439.5 and possibly SDSS J113312.12+010824, traveling with Galactic rest-frame velocities at least +508+-12 and +418+-10 km/s, respectively. The other late B-type objects in our survey are consistent with a population of post main-sequence stars or blue stragglers in the Galactic halo, with mean metallicity [Fe/H]=-1.3 and velocity dispersion 108+-5 km/s. Interestingly, the velocity distribution shows a tail of objects with large positive velocities that may be a mix of low-velocity HVSs and high-velocity runaway stars. Our survey also includes a number of DA white dwarfs with unusually red colors, possibly extremely low mass objects. Two of our objects are B supergiants in the Leo A dwarf, providing the first spectroscopic evidence for star formation in this dwarf galaxy within the last ~30 Myr.Comment: 10 pages, uses emulateapj, accepted by Ap

Young Globular Clusters and Dwarf Spheroidals

Most of the globular clusters in the main body of the Galactic halo were formed almost simultaneously. However, globular cluster formation in dwarf spheroidal galaxies appears to have extended over a significant fraction of a Hubble time. This suggests that the factors which suppressed late-time formation of globulars in the main body of the Galactic halo were not operative in dwarf spheroidal galaxies. Possibly the presence of significant numbers of ``young'' globulars at R_{GC} > 15 kpc can be accounted for by the assumption that many of these objects were formed in Sagittarius-like (but not Fornax-like) dwarf spheroidal galaxies, that were subsequently destroyed by Galactic tidal forces. It would be of interest to search for low-luminosity remnants of parental dwarf spheroidals around the ``young'' globulars Eridanus, Palomar 1, 3, 14, and Terzan 7. Furthermore multi-color photometry could be used to search for the remnants of the super-associations, within which outer halo globular clusters originally formed. Such envelopes are expected to have been tidally stripped from globulars in the inner halo.Comment: 18 pages, with 2 figures, in LaTeX format; to appear in the Astrophysical Journal in February 200

Duhamel versus transanal endorectal pull through (TERPT) for the surgical treatment of Hirschsprung’s disease

For the surgical treatment of Hirschsprung’s disease, several surgical techniques are used to resect the distal aganglionic colon. Two frequently used techniques are the Duhamel procedure and the transanal endorectal pull-through procedure. During the ‘8th Pediatric Colorectal Course’ in Nijmegen, November 2015, a workshop was organized to share experiences of both techniques by several experts in the field and to discuss (long term) outcomes. Specifically, the objective of the meeting was to discuss the main controversies in relation to the technical execution of both procedures in order to make an initial assessment of the limitations of available evidence for clinical decision-making and to formulate a set of preliminary recommendations for current clinical care and future research

Hypervelocity Stars: Predicting the Spectrum of Ejection Velocities

The disruption of binary stars by the tidal field of the black hole in the Galactic Center can produce the hypervelocity stars observed in the halo. We use numerical models to simulate the full spectrum of observable velocities of stars ejected into the halo by this binary disruption process. Our model includes a range of parameters for binaries with 3-4 M_Solar primaries, consideration of radial orbits of the ejected stars through an approximate mass distribution for the Galaxy, and the impact of stellar lifetimes. We calculate the spectrum of ejection velocities and reproduce previous results for the mean ejection velocity at the Galactic center. The model predicts that the full population of ejected stars includes both the hypervelocity stars with velocities large enough to escape from the Galaxy and a comparable number of ejected, but bound, stars of the same stellar type. The predicted median speeds of the population of ejected stars as a function of distance in the halo are consistent with current observations. Combining the model with the data also shows that interesting constraints on the properties of binaries in the Galactic Center and on the mass distribution in the Galaxy can be obtained even with modest samples of ejected stars.Comment: 26 pages, including 6 figures, accepted for publication in the Astrophysical Journa

Local Pulsars; A note on the Birth-Velocity Distribution

We explore a simple model for the representation of the observed distributions of the motions, and the characteristic ages of the local population of pulsars. The principal difference from earlier models is the introduction of a unique value, S, for the kick velocity with which pulsars are born. We consider separately the proper motion components in galactic longitude and latitude, and find that the distributions of the velocity components parallel and perpendicular to the galactic plane are represented satisfactorily by S=200 km/sec, and leave no room for a significant fraction of much higher velocities. The successful proposition of a unique value for the kick velocity may provide an interesting tool in attempts to understand the physical process leading to the expulsion of the neutron star.Comment: To be published in JAA, 14 pages, 7 figure

The Role of Mass and Environment in Multiple Star Formation: A 2MASS Survey of Wide Multiplicity in Three Young Associations

We present the results of a search for wide binary systems among 783 members of three nearby young associations: Taurus-Auriga, Chamaeleon I, and two subgroups of Upper Scorpius. Near-infrared (JHK) imagery from 2MASS was analyzed to search for wide (1-30"; ~150-4500 AU) companions to known association members, using color-magnitude cuts to reject likely background stars. We identify a total of 131 candidate binary companions with colors consistent with physical association, of which 39 have not been identified previously in the literature. Our results suggest that the wide binary frequency is a function of both mass and environment, with significantly higher frequencies among high-mass stars than lower-mass stars and in the T associations than in the OB association. We discuss the implications for wide binary formation and conclude that the environmental dependence is not a direct result of stellar density or total association mass, but instead might depend on another environmental parameter like the gas temperature. We also analyze the mass ratio distribution as a function of mass and find that it agrees with the distribution for field stars to within the statistical uncertainties. The binary populations in these associations generally follow the empirical mass-maximum separation relation observed for field binaries, but we have found one candidate low-mass system (USco-160611.9-193532; Mtot~0.4 Msun) which has a projected separation (10.8"; 1550 AU) much larger than the suggested limit for its mass. (Abridged)Comment: Accepted to ApJ; 27 pages in emulateapj format. The full version of table 2 can be downloaded via http://www.astro.caltech.edu/~alk/tab2.pdf (PDF) or http://www.astro.caltech.edu/~alk/tab2.txt (text

A 25,000 years climate record from the East African equator: Half-precessional climate forcing and the history of temperature and hydrological change

Particularly in tropical and subtropical regions, high-resolution climate records have demonstrated major variability in the hydrological cycle at orbital, millennial and sub-millennial time scales in the last 25,000 years. Geographical patterns of past climate change (from the equator to both poles, and among continents and ocean basins at similar latitude) at these various time scales hold the key to understanding the climate-dynamical processes governing them, and to resolution of longstanding questions about the relative importance of tropical and high-latitude climate dynamics in translating external climate-forcing mechanisms into regional climate variability. Currently, dynamical analysis of past tropical climate variability is being hampered by the fragmentary or poorly dated nature of available records from key continental regions, debate to what extent marine records are representative for climate history on the continents, and uncertainty about whether traditional isotopic tracers applied to tropical continental records mainly reflect temperature or hydrological change. What has been missing is a continuous, high-resolution climate record from the tropics that adequately separates the evolution of temperature and hydrological change, and covers the period from the Last Glacial Maximum until the present with sufficient age control to establish supra-regional phase relationships in past climate anomalies at millennial and century time scales.In this context, the EuroCLIMATE project CHALLACEA here presents a reconstruction of climate history on the East African equator, based on multiple proxy-indicator analyses in the sediment record of a permanently stratified crater lake (Lake Challa, a 4.2 km2, 92 m deep crater lake on the lower East slope of Mt. Kilimanjaro, Tanzania) with stable physical limnology and sedimentation dynamics over the past 25,000 years. This has resulted in a unique combination of high temporal resolution, excellent radiometric (210Pb, 14C) age control, and confidence that the recording parameters of the climatic proxies (i.e. the relationship between climate change and its proxy signals extracted from the sediment record) have remained constant through time. The equatorial (3° S) location of our study site in East Africa, where seasonal migration of the Intertropical Convergence Zone spans the widest latitude range, provides unique information on how varying rainfall contributions from the Indian Ocean monsoons have shaped the region’s climate history. The detailed reconstruction of the temperature and moisture-balance history of equatorial East Africa from before the Last Glacial Maximum to the present uniquely weaves together tropical climate variability at orbital, millennial and century time scales. The temporal pattern of reconstructed climate changes bears the clear signature of half-precessional insolation forcing of tropical monsoon dynamics on the East African equator, modified by high southern latitude influence on the timing of post-glacial temperature rise, and by high northern latitude influence on tropical hydrological variability at millennial and century time scales