44,127 research outputs found
A correlative investigation of the propagation of ULF wave power through the dayside magnetosphere
Three different ULF wave phenomena (azimuthally polarized Pc 3 pulsations, radially polarized Pc 4 pulsations, and solitary Pc 5 pulsations related to solar wind pressure pulses) were studied. The main problems covered are: (1) how do magnetospheric Pc 3-4 pulsations, which appear to originate in the solar wind, enter the magnetosphere, and how is this wave energy transported throughout the magnetosphere once it enters; (2) what is the ULF response of the outer dayside magnetosphere to solar wind pressure pulses; and (3) how do Pc 3-4 pulsations modulate ELF-VLF emissions in the dayside magnetosphere
The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey
Context. Thanks to recent and ongoing large scale surveys, hundreds of brown
dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf
Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam
camera on the Canada-France-Hawaii Telescope telescope. Aims. Our objectives
are to find ultracool brown dwarfs and to constrain the field brown-dwarf
luminosity function and the mass function from a large and homogeneous sample
of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i' and z'
images and follow them up with pointed near infrared (NIR) imaging on several
telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or
ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical
ultracool dwarfs i' - z' colours, found in 780 square degrees. Results. We have
currently completed the NIR follow-up on a large part of the survey for all
candidates from mid-L dwarfs down to the latest T dwarfs known with utracool
dwarfs' colours. This allows us to draw on a complete and well defined sample
of 102 ultracool dwarfs to investigate the luminosity function and space
density of field dwarfs. Conclusions. We found the density of late L5 to T0
dwarfs to be 2.0pm0.8 x 10-3 objects pc-3, the density of T0.5 to T5.5 dwarfs
to be 1.4pm0.3 x 10-3 objects pc-3, and the density of T6 to T8 dwarfs to be
5.3pm3.1 x 10-3 objects pc-3 . We found that these results agree better with a
flat substellar mass function. Three latest dwarfs at the boundary between T
and Y dwarfs give the high density 8.3p9.0m5.1 x 10-3 objects pc-3. Although
the uncertainties are very large this suggests that many brown dwarfs should be
found in this late spectral type range, as expected from the cooling of brown
dwarfs, whatever their mass, down to very low temperature.Comment: Accepted for publication in A&
Three-dimensional structure of the Upper Scorpius association with the Gaia first data release
Using new proper motion data from recently published catalogs, we revisit the
membership of previously identified members of the Upper Scorpius association.
We confirmed 750 of them as cluster members based on the convergent point
method, compute their kinematic parallaxes and combined them with Gaia
parallaxes to investigate the 3D structure and geometry of the association
using a robust covariance method. We find a mean distance of ~pc
and show that the morphology of the association defined by the brightest (and
most massive) stars yields a prolate ellipsoid with dimensions of
~pc, while the faintest cluster members define a more
elongated structure with dimensions of ~pc. We
suggest that the different properties of both populations is an imprint of the
star formation history in this region.Comment: 5 pages, 1 figure, MNRAS letters (in press
Adrenomedullin prevents apoptosis in prostate cancer cells
The 52-aminoacid peptide adrenomedullin (AM) is expressed in the normal and malignant prostate. We have previously shown that prostate cancer cells produce and secrete AM, which acts as an autocrine growth inhibitory factor. We have evaluated in the present study the role of AM in prostate cancer cell apoptosis, induced either by serum deprivation or treatment with the chemotherapeutic agent etoposide (which acts as an inhibitor of topoisomerase II). For this purpose we over-expressed AM in PC-3, DU 145 and LNCaP cells, which were transfected with an expression vector carrying AM. We also treated the parental cell lines with synthetic AM in normal culture conditions and in conditions of induced-apoptosis. After serum removal, AM prevented apoptosis in DU 145 and PC-3 cells, but not in LNCaP cells. When treated with etoposide, AM prevented apoptosis in PC-3 and LNCaP cells, but not in DU 145 cells. Cell cycle analysis demonstrated a significant decrease in the percentage of AM-overexpressing PC-3 cells in the subG0/G1 phase after treatment with etoposide, as compared to the percentage of mock-transfected PC-3 treated cells. Western blot showed that protein levels of phosphorylated ERK1/2 increased in parental PC-3 cells after treatment with etoposide. In PC-3 cells overexpressing AM, phosphorylated ERK1/2 basal levels were lower than basal levels of parental PC-3 cells, and treatment with etoposide did not result in such an increase. Etoposide produced a significant increase in cleaved PARP in parental PC-3 cells. However, PC-3 clones overexpressing AM that were treated with etoposide only showed a mild increase in fragmented PARP. The ratio Bcl-2/Bax was reduced in parental or mock-transfected PC-3 cells after treatment with etoposide. On the contrary, this ratio was not reduced in PC-3 clones with AM overexpression that were treated with etoposide. All these data demonstrate that AM plays a protective role against induced apoptosis in prostate cancer cells. These results may have important implications in prostate cancer resistance to chemotherapeutic agents
The central density of R136 in 30 Doradus
The central density rho_0 of a stellar cluster is an important physical
parameter for determining its evolutionary and dynamical state. How much mass
segregation there is, or whether the cluster has undergone core collapse both
depends on rho_0. We reanalyze the results of a previous paper that gives the
mass density profile of R136 and combine them with both a conservative upper
limit for the core parameter and a more uncertain recent measurement. We thus
place a lower limit on rho_0 under reasonable and defensible assumptions about
the IMF, finding rho_0 >~ 1.5x10^4 Msun/pc^3 for the conservative assumption a
< 0.4 pc for the cluster core parameter. If we use the lower, but more
uncertain value a = 0.025 pc, the central density estimate becomes greater than
10^7 Msun/pc^3. A mechanism based on the destruction of a large number of
circumstellar disks is posited to explain the hitherto unexplained increase in
reddening presented in that same work.Comment: 6 pages, 2 figure
Fatty-acid uptake in prostate cancer cells using dynamic microfluidic raman technology
It is known that intake of dietary fatty acid (FA) is strongly correlated with prostate cancer progression but is highly dependent on the type of FAs. High levels of palmitic acid (PA) or arachidonic acid (AA) can stimulate the progression of cancer. In this study, a unique experimental set-up consisting of a Raman microscope, coupled with a commercial shear-flow microfluidic system is used to monitor fatty acid uptake by prostate cancer (PC-3) cells in real-time at the single cell level. Uptake of deuterated PA, deuterated AA, and the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were monitored using this new system, while complementary flow cytometry experiments using Nile red staining, were also conducted for the validation of the cellular lipid uptake. Using this novel experimental system, we show that DHA and EPA have inhibitory effects on the uptake of PA and AA by PC-3 cells
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