138 research outputs found
A Full Shell Model Study of a~=~48 Nuclei
Exact diagonalizations with a minimally modified realistic force lead to
detailed agreement with measured level schemes and electromagnetic transitions
in Ca, Sc, Ti, V, Cr and Mn.
Gamow-Teller strength functions are systematically calculated and reproduce the
data to within the standard quenching factor. Their fine structure indicates
that fragmentation makes much strength unobservable. As a by-product, the
calculations suggest a microscopic description of the onset of rotational
motion. The spectroscopic quality of the results provides strong arguments in
favour of the general validity of monopole corrected realistic forces, which is
discussed.Comment: 30 pages, LaTeX with epsf.sty, 14 Postscript figures included and
compressed using uufiles. Completely new version of previous preprint
nucl-th/9307001. FTUAM-93/01, CRN/PT 93-3
Excited States in 52Fe and the Origin of the Yrast Trap at I=12+
Excited states in 52Fe have been determined up to spin 10\hbar in the
reaction 28Si + 28Si at 115 MeV by using \gamma-ray spectroscopy methods at the
GASP array. The excitation energy of the yrast 10+ state has been determined to
be 7.381 MeV, almost 0.5 MeV above the well known \beta+-decaying yrast 12+
state, definitely confirming the nature of its isomeric character. The mean
lifetimes of the states have been measured by using the Doppler Shift
Attenuation method. The experimental data are compared with spherical shell
model calculations in the full pf-shell.Comment: 9 pages, RevTeX, 7 figures include
Primary, new and export production in the NW Pacific subarctic gyre during the vertigo K2 experiments
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1594-1604, doi:10.1016/j.dsr2.2008.04.013.This paper presents results on tracer experiments using 13C and 15N to
estimate uptake rates of dissolved inorganic carbon (DIC) and nitrogen (DIN).
Experiments were carried out at station K2 (47°N, 161°E) in the NW Pacific subarctic
gyre during July-August 2005. Our goal was to investigate relationships between new
and export production. New production was inferred from the tracer experiments using
the f ratio concept (0-50m); while export production was assessed with neutrally
buoyant sediment traps (NBSTs) and the e ratio concept (at 150m). During trap
deployments, K2 was characterized both by changes in primary production (523 to 404
mg C m-2 d-1), new production (119 to 67 mg C m-2 d-1), export production (68 to 24 mg
C m-2 d-1) and phytoplankton composition (high to low proportion of diatoms). The data
indicate that 17 to 23% of primary production is exportable to deeper layers (f ratio) but only 6 to 13% collected as a sinking particle flux at 150m (e ratio). Accordingly, > 80%
of the carbon fixed by phytoplankton would be mineralized in the upper 50m (1 – f),
while < 11% would be within 50-150m (f – e). DIN uptake flux amounted to 0.5 mM m-2
h-1, which was equivalent to about 95% particulate nitrogen (PN) remineralized and/or
grazed within the upper 150 m. Most of the shallow PN remineralization occurred just
above the depth of the deep chlorophyll maximum (DCM), where a net ammonium
production was measured. Below the DCM, while nitrate uptake rates became negligible
because of light limitation, ammonium uptake did continue to be significant. The uptake
of ammonium by heterotrophic bacteria was estimated to be 14-17% of the DIN
assimilation. Less clear are the consequences of this uptake on the phytoplankton
community and biogeochemical processes, e.g. new production. It was suggested that
competition for ammonium could select for small cells and may force large diatoms to
use nitrate. This implies that under Fe stress as observed here, ammonium uptake is
preferred and new production progressively suppressed despite the surplus of nitrate.This research was supported by the Research Foundation Flanders through grant
G.0021.04 and Vrije Universiteit Brussel via grant GOA 22, as well as the US National
Science Foundation programs in Chemical and Biological Oceanography
Activation of the MAPK pathway is a common event in uveal melanomas although it rarely occurs through mutation of BRAF or RAS
In contrast to cutaneous melanoma, there is no evidence that BRAF mutations are involved in the activation of the mitogen-activated protein kinase (MAPK) pathway in uveal melanoma, although there is increasing evidence that this pathway is activated frequently in the latter tumours. In this study, we performed mutation analysis of the RAS and BRAF genes in a panel of 11 uveal melanoma cell lines and 19 primary uveal melanoma tumours. In addition, Western blot and immunohistochemical analyses were performed on downstream members of the MAPK pathway in order to assess the contribution of each of these components. No mutations were found in any of the three RAS gene family members and only one cell line carried a BRAF mutation (V599E). Despite this, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK), ERK and ELK were constitutively activated in all samples. These data suggest that activation of the MAPK pathway is commonly involved in the development of uveal melanoma, but occurs through a mechanism different to that of cutaneous melanoma
Expression of the SST receptor 2 in uveal melanoma is not a prognostic marker
Introduction: Uveal melanoma (UM) cells and neurohormone-producing cells both originate from the neural crest. Somatostatin receptors subtype 2 (SSTR2) are over-expressed in several tumors, often from neuroendocrine origin, and synthetic antagonists like octreotide and octreotate are being used as diagnostic or therapeutic agents. We investigated the SSTR2 expression in UM, and determined whether this expression was related to prognosis of the disease. Materials and methods: UM cell lines and fresh primary UM samples were tested for SSTR2 expression by autoradiography (AR) using 125I-Tyr3-octreotate. Furthermore, UM cell lines were analyzed for SSTR2 mRNA expression with quantitative real-time RT-PCR. Results: Using AR, cell-surface SSTR2 expression was demonstrated in two UM metastatic cell lines, but no expression was detected in three cell lines derived from primary UM. However, all primary and metastatic UM cell lines showed mRNA expression levels for SSTR2 using quantitative real-time RT-PCR. Only three of 14 primary UM demonstrated moderate SSTR2 expression, and this expression was not significantly associated with tumor-free survival or any tested prognostic factor. Conclusions: Based on the rare and low expression of SSTR2 found in primary UM specimens and in UM cell lines, we conclude that SSTR2 is not widely expressed in UM. Furthermore, SSTR2 expression was not associated with tumor-free survival and prognostic factors. Therefore SSTR2 is not suited as prognostic marker or therapeutic target in UM
Barium in twilight zone suspended matter as a potential proxy for particulate organic carbon remineralization : results for the North Pacific
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1673-1683, doi:10.1016/j.dsr2.2008.04.020.This study focuses on the fate of exported organic carbon in the twilight zone at two
contrasting environments in the North Pacific: the oligotrophic ALOHA site (22°45'
N 158°W; Hawaii; studied during June–July 2004) and the mesotrophic Subarctic
Pacific K2 site (47°N, 161°W; studied during July-August 2005). Earlier work has
shown that non-lithogenic, excess particulate Ba (Baxs) in the mesopelagic water
column is a potential proxy of organic carbon remineralization. In general Baxs
contents were significantly larger at K2 than at ALOHA. At ALOHA the Baxs profiles
from repeated sampling (5 casts) showed remarkable consistency over a period of
three weeks, suggesting that the system was close to being at steady state. In contrast,
more variability was observed at K2 (6 casts sampled) reflecting the more dynamic
physical and biological conditions prevailing in this environment. While for both sites
Baxs concentrations increased with depth, at K2 a clear maximum was present
between the base of the mixed layer at around 50m and 500m, reflecting production
and release of Baxs. Larger mesopelagic Baxs contents and larger bacterial production
in the twilight zone at the K2 site indicate that more material was exported from the
upper mixed layer for bacterial degradation deeper, compared to the ALOHA site.
Furthermore, application of a published transfer function (Dehairs et al., 1997)
relating oxygen consumption to the observed Baxs data indicated that the latter were in
good agreement with bacterial respiration, calculated from bacterial production. These
results corroborate earlier findings highlighting the potential of Baxs as a proxy for
organic carbon remineralization.
The range of POC remineralization rates calculated from twilight zone excess
particulate Ba contents did also compare well with the depth dependent POC flux
decrease as recorded by neutrally buoyant sediment traps, except in 1 case (out of 4).
This discrepancy could indicate that differences in sinking velocities cause an
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uncoupling of the processes occurring in the fine suspended particle pool from those
affecting the larger particle pool which sustains the vertical flux, thus rendering
comparison between both approaches risky.This research was supported by Federal Science Policy
Office, Brussels through contracts EV/03/7A, SD/CA/03A, the Research Foundation
Flanders through grant G.0021.04 and Vrije Universiteit Brussel via grant GOA 22, as
well as the US National Science Foundation programs in Chemical and Biological
Oceanography
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