1,719 research outputs found
Fluorescent Plasmodium berghei sporozoites and pre-erythrocytic stages: a new tool to study mosquito and mammalian host interactions with malaria parasites.
To track malaria parasites for biological studies within the mosquito and mammalian hosts, we constructed a stably transformed clonal line of Plasmodium berghei, PbFluspo, in which sporogonic and pre-erythrocytic liver-stage parasites are autonomously fluorescent. A cassette containing the structural gene for the FACS-adapted green fluorescent protein mutant 2 (GFPmut2), expressed from the 5' and 3' flanking sequences of the circumsporozoite (CS) protein gene, was integrated and expressed at the endogenous CS locus. Recombinant parasites, which bear a wild-type copy of CS, generated highly fluorescent oocysts and sporozoites that invaded mosquito salivary glands and were transmitted normally to rodent hosts. The parasites infected cultured hepatocytes in vitro, where they developed into fluorescent pre-erythrocytic forms. Mammalian cells infected by these parasites can be separated from non-infected cells by fluorescence activated cell sorter (FACS) analysis. These fluorescent insect and mammalian stages of P. berghei should be useful for phenotypic studies in their respective hosts, as well as for identification of new genes expressed in these parasite stages
Absorption Systems In Radio-Selected QSO Surveys
Radio-selected samples of quasars with complete optical identifications offer
an ideal dataset with which to investigate dust bias associated with
intervening absorption systems. Here, we review our work on the Complete
Optical and Radio Absorption Line System (CORALS) survey whose aim is to
quantify this bias and assess the impact of dust on absorber statistics. First,
we review previously published results on the number density and gas content of
high column density absorbers over the redshift range 0.6 < z < 3.5. We then
present the latest results from CORALS which focus on measuring the metal
content of our unbiased absorber sample and an investigation of their
optical--IR colours. Overall we find that although dust is unarguably present
in absorption galaxies, the level appears to be low enough that the statistics
of previous magnitude limited samples have not been severely affected and that
the subsequent reddening of background QSOs is small.Comment: Proceedings of IAUC199, Probing Galaxies through Quasar Absorption
Lines, P. R. Williams, C. Shu, and B. Menard, ed
Direct Observation of the Fourth Star in the Zeta Cancri System
Direct imaging of the zeta Cnc system has resolved the fourth star in the
system, which is in orbit around zeta Cnc C. The presence of the fourth star
has been inferred for many years from irregularities in the motion of star C,
and recently from C's spectroscopic orbit. However, its mass is close to that
of C, making its non-detection puzzling. Observing at wavelengths of 1.2, 1.7,
and 2.2 microns with the adaptive-optics system of the CFHT, we have obtained
images which very clearly reveal star D and show it to have the color of an M2
star. Its brightness is consonant with its being two M stars, which are not
resolved in our observations but are likely to be in a short-period orbit,
thereby accounting for the large mass and the difficulty of detection at
optical wavelengths, where the magnitude difference is much larger. The
positions and colors of all four stars in the system are reported and are
consistent with the most recent astrometric observations.Comment: 7 pages including 3 tables, 1 figure; To appear in PAS
Selective effect of thiazides on the human osteoblast-like cell line MG-63
Selective effect of thiazides on the human osteoblast-like cell line MG-63. Thiazide diuretics have been shown to decrease bone-loss rate and to improve bone mineral density in patients using this medication. However, the exact role of thiazides on bone cells is still debated. In the present work, we studied whether thiazides could affect the normal features of osteoblasts using the human model cell line MG-63. Hydrochlorothiazide (HCTZ) did not affect cell growth nor DNA synthesis in these cells, yet slightly increased alkaline phosphatase activity in these cells at pharmacologically relevant concentrations. Under similar conditions, HCTZ dose-dependently inhibited 1,25(OH)2D3-induced osteocalcin secretion by these cells (maximal effect, -40 to 50%, P < 0.005). However, HCTZ did not inhibit the basal production of osteocalcin in MG-63 cells (without 1,25(OH)2D3 induction), which was very low to undectable. Two different thiazide derivatives, chlorothiazide and cyclothiazide, and two structurally related sulfonamides with selective inhibition of carbonic anhydrase (Acetazolamide) or hyperglycemic effects (Diazoxide) were also tested. Chlorothiazide (1000 µm) inhibited osteocalcin secretion (-42 ± 12.7%) at doses 10-fold higher than HCTZ (100 µm) while cyclothiazide was effective at doses of 1 µm(-27 ± 3.6%), and hence 100-fold lower than HCTZ, compatible with the relative natriuretic effect in vivo of these compounds. Acetazolamide (10 µm) poorly affected osteocalcin secretion at doses 100-fold higher than those needed in vivo to inhibit carbonic anhydrase. Likewise, Diazoxide (100 µm) poorly affected osteocalcin secretion at doses known to promote its biological effect. Higher doses of acetazolamide and diazoxide induced cell death. Neither Acetazolamide nor Diazoxide affected alkaline phosphatase, whereas chlorothiazide had a weak positive effect on this enzymatic activity. The production of macrophage colony-stimulating factor (M-CSF) was stimulated in the presence of 1,25(OH)2D3 (50nm), TNF-α (2 ng/ml) both in MG-63 cells. HCTZ (25 µm, 24hr of preincubation) did not modify basal M-CSF production and did not reduce the response to 1,25(OH)2D3 alone. In contrast, HCTZ inhibited the response to TNF-α alone (P < 0,05), and also reduced the response to a combination of 1,25(OH)2D3 and TNF-α (P < 0.01). In conclusion, these results indicate that thiazide diuretics show a selective inhibion of osteocalcin secretion and M-CSF production by MG-63 cells unlike structurally related drugs. Therefore, these features may explain, in part, the positive effect of thiazides on bone mineral density
Galaxy Morphology - Halo Gas Connections
We studied a sample of 38 intermediate redshift MgII absorption-selected
galaxies using (1) Keck/HIRES and VLT/UVES quasar spectra to measure the halo
gas kinematics from MgII absorption profiles and (2) HST/WFPC-2 images to study
the absorbing galaxy morphologies. We have searched for correlations between
quantified gas absorption properties, and host galaxy impact parameters,
inclinations, position angles, and quantified morphological parameters. We
report a 3.2-sigma correlation between asymmetric perturbations in the host
galaxy morphology and the MgII absorption equivalent width. We suggest that
this correlation may indicate a connection between past merging and/or
interaction events in MgII absorption-selected galaxies and the velocity
dispersion and quantity of gas surrounding these galaxies.Comment: 6 pages; 3 figures; contributed talk for IAU 199: Probing Galaxies
through Quasar Absorption Line
Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height
Recent studies show that shrubs are colonizing higher latitudes and altitudes
in the Arctic. Shrubs affect the wind transport, accumulation and melt of
snow, but there have been few sensitivity studies of how shrub expansion
might affect snowmelt rates and timing. Here, a three-source energy balance model
(3SOM), which calculates vertical and horizontal energy fluxes – thus
allowing within-cell advection – between the atmosphere, snow, snow-free
ground and vegetation, is introduced. The three-source structure was specifically
adopted to investigate shrub–tundra processes associated with patchy
snow cover that single- or two-source models fail to address. The ability of
the model to simulate the snow regime of an upland tundra valley is
evaluated; a blowing snow transport and sublimation model is used to simulate
premelt snow distributions and 3SOM is used to simulate melt. Some success at
simulating turbulent fluxes in point simulations and broad spatial pattern in
distributed runs is shown even if the lack of advection between cells causes
melt rates to be underestimated. The models are then used to investigate the
sensitivity of the snow regime in the valley to varying shrub cover and
topography. Results show that, for domain average shrub fractional cover
≤0.4, topography dominates the pre- and early melt energy budget but
has little influence for higher shrub cover. The increase in domain average
sensible heat fluxes and net radiation with increasing shrub cover is more
marked without topography where shrubs introduce wind-induced spatial
variability of snow and snow-free patches. As snowmelt evolves, differences
in the energy budget between simulations with and without topography remain
relatively constant and are independent of shrub cover. These results suggest
that, to avoid overestimating the effect of shrub expansion on the energy
budget of the Arctic, future large-scale investigations should consider wind
redistribution of snow, shrub bending and emergence, and sub-grid topography
as they affect the variability of snow cover
Submillimetre dust polarisation and opacity in the HD163296 protoplanetary ring system
We present ALMA images of the sub-mm continuum polarisation and spectral
index of the protoplanetary ringed disk HD163296. The polarisation fraction at
870{\mu}m is measured to be ~0.9% in the central core and generally increases
with radius along the disk major axis. It peaks in the gaps between the dust
rings, and the largest value (~4%) is found between rings 1 and 2. The
polarisation vectors are aligned with the disk minor axis in the central core,
but become more azimuthal in the gaps, twisting by up to +/-9degrees in the gap
between rings 1 and 2. These general characteristics are consistent with a
model of self-scattered radiation in the ringed structure, without requiring an
additional dust alignment mechanism. The 870/1300{\mu}m dust spectral index
exhibits minima in the centre and the inner rings, suggesting these regions
have high optical depths. However, further refinement of the dust or the disk
model at higher resolution is needed to reproduce simultaneously the observed
degree of polarisation and the low spectral index.Comment: 5 pages +2 pages supplemental data. v2 - revised figures and final
values; conclusions unchange
Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows
We study the kinematically narrow, low-ionization line emission from a
bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with
Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance
transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas
outflow. Emission in MgII near and redward of systemic velocity, in concert
with the observed absorption, yields a P Cygni-like line profile similar to
those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the
MgII emission is spatially resolved, and extends significantly beyond the
emission from stars and HII regions within the galaxy. Assuming the emission
has a simple, symmetric surface brightness profile, we find that the gas
extends to distances > ~7 kpc. We also detect several narrow FeII*
fine-structure lines in emission near the systemic velocity, arising from
energy levels which are radiatively excited directly from the ground state. We
suggest that the MgII and FeII* emission is generated by photon scattering in
the observed outflow, and emphasize that this emission is a generic prediction
of outflows. These observations provide the first direct constraints on the
minimum spatial extent and morphology of the wind from a distant galaxy.
Estimates of these parameters are crucial for understanding the impact of
outflows in driving galaxy evolution.Comment: Submitted to ApJL. 6 pages, 4 figures. Uses emulateapj forma
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