90,825 research outputs found
Connexin 40 promoter-based enrichment of embryonic stem cell-derived cardiovascular progenitor cells
Background: Pluripotent embryonic stem (ES) cells that can differentiate into functional cardiomyocytes as well as vascular cells in cell culture may open the door to cardiovascular cell transplantation. However, the percentage of ES cells in embryoid bodies (EBs) which spontaneously undergo cardiovascular differentiation is low (< 10%), making strategies for their specific labeling and purification indispensable. Methods: The human connexin 40 (Cx40) promoter was isolated and cloned in the vector pEGFP. The specificity of the construct was initially assessed in Xenopus embryos injected with Cx40-EGFP plasmid DNA. Stable Cx40-EGFP ES cell clones were differentiated and fluorescent cells were enriched manually as well as via fluorescence-activated cell sorting. Characterization of these cells was performed with respect to spontaneous beating as well as via RT-PCRs and immunofluorescent stainings. Results: Cx40-EGFP reporter plasmid injection led to EGFP fluorescence specifically in the abdominal aorta of frog tadpoles. After crude manual enrichment of highly Cx40-EGFP- positive EBs, the appearance of cardiac and vascular structures was increased approximately 3-fold. Immuno fluorescent stainings showed EGFP expression exclusively in vascular-like structures simultaneously expressing von Willebrand factor and in formerly beating areas expressing alpha-actinin. Cx40-EGFP-expressing EBs revealed significantly higher numbers of beating cardiomyocytes and vascular-like structures. Semiquantitative RT-PCRs confirmed an enhanced cardiovascular differentiation as shown for the cardiac markers Nkx2.5 and MLC2v, as well as the endothelial marker vascular endothelial cadherin. Conclusions: Our work shows the feasibility of specific labeling and purification of cardiovascular progenitor cells from differentiating EBs based on the Cx40 promoter. We provide proof of principle that the deleted CD4 (Delta CD4) surface marker-based method for magnetic cell sorting developed by our group will be ideally suitable for transference to this promoter. Copyright (c) 2008 S. Karger AG, Basel
Diagnostics Of Disks Around Hot Stars
We discuss three different observational diagnostics related to disks around hot stars: absorption line determinations of rotational velocities of Be stars; polarization diagnostics of circumstellar disks; and X-ray line diagnostics of one specific magnetized hot star, theta(1) Ori C. Some common themes that emerge from these studies include (a) the benefits of having a specific physical model as a framework for interpreting diagnostic data; (b) the importance of combining several different types of observational diagnostics of the same objects; and (c) that while there is often the need to reinterpret traditional diagnostics in light of new theoretical advances, there are many new and powerful diagnostics that are, or will soon be, available for the study of disks around hot stars
Structure of Fermionic Density Matrices: Complete N-representability Conditions
We present a constructive solution to the N-representability problem---a full
characterization of the conditions for constraining the two-electron reduced
density matrix (2-RDM) to represent an N-electron density matrix. Previously
known conditions, while rigorous, were incomplete. Here we derive a hierarchy
of constraints built upon (i) the bipolar theorem and (ii) tensor
decompositions of model Hamiltonians. Existing conditions D, Q, G, T1, and T2,
known classical conditions, and new conditions appear naturally. Subsets of the
conditions are amenable to polynomial-time computations of strongly correlated
systems
Groundwater characteristics at Seabee Hook, Cape Hallett, Antarctica
Seabee Hook is a low lying gravel spit adjacent to Cape Hallett, northern Victoria Land, in the Ross Sea region of Antarctica and hosts an Adélie penguin (Pygoscelis adeliae) rookery. Dipwells were inserted to monitor changes in depth to, and volume of, groundwater and tracer tests were conducted to estimate aquifer hydraulic conductivity and groundwater velocity. During summer (November–February), meltwater forms a shallow, unconfined, aquifer perched on impermeable ice cemented soil. Groundwater extent and volume depends on the amount of snowfall as meltwater is primarily sourced from melting snow drifts. Groundwater velocity through the permeable gravel and sand was up to 7.8 m day−1, and hydraulic conductivities of 4.7 × 10−4 m s−1 to 3.7 × 10−5 m s−1 were measured. The presence of the penguin rookery, and the proximity of the sea, affects groundwater chemistry with elevated concentrations of salts (1205 mg L−1 sodium, 332 mg L−1 potassium) and nutrients (193 mg L−1 nitrate, 833 mg L−1 ammonia, 10 mg L−1 total phosphorus) compared with groundwater sourced away from the rookery, and with other terrestrial waters in Antarctica
Radio Synchrotron Emission from Secondary Leptons in the Vicinity of Sgr A*
A point-like source of ~TeV gamma-rays has recently been seen towards the
Galactic center by HESS and other air Cerenkov telescopes. In recent work
(Ballantyne et al. 2007), we demonstrated that these gamma-rays can be
attributed to high-energy protons that (i) are accelerated close to the event
horizon of the central black hole, Sgr A*, (ii) diffuse out to ~pc scales, and
(iii) finally interact to produce gamma-rays. The same hadronic collision
processes will necessarily lead to the creation of electrons and positrons.
Here we calculate the synchrotron emissivity of these secondary leptons in the
same magnetic field configuration through which the initiating protons have
been propagated in our model. We compare this emission with the observed ~GHz
radio spectrum of the inner few pc region which we have assembled from archival
data and new measurements we have made with the Australia Telescope Compact
Array. We find that our model predicts secondary synchrotron emission with a
steep slope consistent with the observations but with an overall normalization
that is too large by a factor of ~ 2. If we further constrain our theoretical
gamma-ray curve to obey the implicit EGRET upper limit on emission from this
region we predict radio emission that is consistent with observations, i.e.,
the hadronic model of gamma ray emission can, simultaneously and without
fine-tuning, also explain essentially all the diffuse radio emission detected
from the inner few pc of the Galaxy.Comment: 11 pages, 2 figures. Two references missing from published version
added and acknowledgements extende
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