5,853 research outputs found
Out Of The Dusk To You
https://digitalcommons.library.umaine.edu/mmb-vp/5766/thumbnail.jp
Redefinition of salinity
Two definitions of salinity have been in use since the early part of the present century (Knudsen 1901, Forch et al. 1902). According to the procedural definition, salinity is the amount (in grams) of dissolved solid material in a kilogram of seawater after all the bromine has been replaced by an equivalent quantity of chlorine, after all the carbonate has been converted to oxide, and after all of the organic matter has been destroyed...
Exploration and exploitation in the presence of network externalities
This paper examines the conditions under which exploration of a new, incompatible technologyis
conducive to firm growth in the presence of network externalities. In particular,
this studyis motivated bythe divergent evolutions of the PC and the workstation markets in
response to a new technology: reduced instruction set computing (RISC). In the PC market,
Intel has developed new microprocessors bymaintaining compatibilitywith the established
architecture, whereas it was radicallyr eplaced byRISC in the workstation market. History
indicates that unlike the PC market, the workstation market consisted of a large number
of power users, who are less sensitive to compatibilitythan ordinaryusers. Our numerical
analysis indicates that the exploration of a new, incompatible technologyis more likelyto
increase the chance of firm growth when there are a substantial number of power users or
when a new technologyis introduced before an established technologytakes off.
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Monopoles and the Emergence of Black Hole Entropy
One of the remarkable features of black holes is that they possess a
thermodynamic description, even though they do not appear to be statistical
systems. We use self-gravitating magnetic monopole solutions as tools for
understanding the emergence of this description as one goes from an ordinary
spacetime to one containing a black hole. We describe how causally distinct
regions emerge as a monopole solution develops a horizon. We define an entropy
that is naturally associated with these regions and that has a clear connection
with the Hawking-Bekenstein entropy in the critical black hole limit.Comment: 6 pages, one figure RevTe
Tailoring the surface charge of dextran-based polymer coated SPIONs for modulated stem cell uptake and MRI contrast
Tracking stem cells in vivo using non-invasive techniques is critical to evaluate the efficacy and safety of stem cell therapies. Superparamagnetic iron oxide nanoparticles (SPIONs) enable cells to be tracked using magnetic resonance imaging (MRI), but to obtain detectable signal cells need to be labelled with a sufficient amount of iron oxide. For the majority of SPIONs, this can only be obtained with the use of transfection agents, which can adversely affect cell health. Here, we have synthesised a library of dextran-based polymer coated SPIONs with varying surface charge from −1.5 mV to +18.2 mV via a co-precipitation approach and investigated their ability to be directly internalised by stem cells without the need for transfection agents. The SPIONs were colloidally stable in physiological solutions. The crystalline phase of the particles was confirmed with powder X-ray diffraction and their magnetic properties were characterised using SQUID magnetometry and magnetic resonance. Increased surface charge led to six-fold increase in uptake of particles into stem cells and higher MRI contrast, with negligible change in cell viability. Cell tracking velocimetry was shown to be a more accurate method for predicting MRI contrast of stem cells compared to measuring iron oxide uptake through conventional bulk iron quantification
The Stellar and Gaseous Contents of the Orion Dwarf Galaxy
We present new KPNO 0.9-m optical and VLA HI spectral line observations of
the Orion dwarf galaxy. This nearby (D ~ 5.4 Mpc), intermediate-mass (M_dyn =
1.1x10^10 Solar masses) dwarf displays a wealth of structure in its neutral
ISM, including three prominent "hole/depression" features in the inner HI disk.
We explore the rich gas kinematics, where solid-body rotation dominates and the
rotation curve is flat out to the observed edge of the HI disk (~6.8 kpc). The
Orion dwarf contains a substantial fraction of dark matter throughout its disk:
comparing the 4.7x10^8 Solar masses of detected neutral gas with estimates of
the stellar mass from optical and near-infrared imaging (3.7x10^8 Solar masses)
implies a mass-to-light ratio of ~13. New H alpha observations show only
modest-strength current star formation (~0.04 Solar masses per year); this star
formation rate is consistent with our 1.4 GHz radio continuum non-detection.Comment: Astronomical Journal, in press. Full-resolution version available
from http://www.macalester.edu/~jcannon/pubs.htm
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