375 research outputs found
Allylsulfones through Palladium-Catalyzed Allylic CâH Sulfonylation of Terminal Alkenes
Two previously unknown protocols for Pd-catalyzed allylic C-H sulfonylation of terminal alkenes have been developed. While the former consists of a direct Pd(II)-catalyzed oxidative C-H allylic sulfonylation in the presence of sulfinate anions, the latter involves a sequential one-pot Pd(II)-catalyzed C-H allylic acetoxylation followed by a Pd(0)-catalyzed sulfonylation. The scope of both protocols was studied on 25 examples
Different vimentin expression in two clones derived from a human colocarcinoma cell line (LoVo) showing different sensitivity to doxorubicin.
We selected two clones, isolated from the human colocarcinoma cell line LoVo, showing a sensitivity to doxorubicin similar to (LoVo clone 5) or three times lower than (LoVo clone 7) the parental cell line. Since vimentin was atypically expressed in a human breast carcinoma cell line made resistant to doxorubicin, we looked at vimentin expression in these two clones with spontaneously different sensitivity to the drug. For comparison we used the parental cell line LoVo WT and LoVo/DX made resistant pharmacologically. mRNA for vimentin was undetectable by Northern blot analysis in LoVo WT and in LoVo clone 5, while expression of this gene was high in LoVo clone 7 and in LoVo/DX. This increase in mRNA levels was not related to an amplification of DNA, as suggested by Southern blot analysis. Immunofluorescence and immunocytochemistry findings confirmed, at protein level, the mRNA data. In LoVo clones 5 and 7, there were respectively 8.6% and 71% vimentin-positive cells, although the two clones showed similar expression of multidrug resistance gene 1 (mdr-1) and accumulated intracellular doxorubicin at similar levels. Similarly, drug efflux was the same for both clones. Our results show for the first time that cells resistant to doxorubicin express vimentin independently of the mdr glycoprotein. However when cells from clone 5 were transfected with human vimentin cDNA, they did not become resistant, indicating that vimentin can be considered as a marker of resistance in these cells but does not give rise to a resistant phenotype by itself
A new study of Mg(,n)Si angular distributions at = 3 - 5 MeV
The observation of Al gives us the proof of active nucleosynthesis in
the Milky Way. However the identification of the main producers of Al is
still a matter of debate. Many sites have been proposed, but our poor knowledge
of the nuclear processes involved introduces high uncertainties. In particular,
the limited accuracy on the Mg(,n)Si reaction cross
section has been identified as the main source of nuclear uncertainty in the
production of Al in C/Ne explosive burning in massive stars, which has
been suggested to be the main source of Al in the Galaxy. We studied
this reaction through neutron spectroscopy at the CN Van de Graaff accelerator
of the Legnaro National Laboratories. Thanks to this technique we are able to
discriminate the (,n) events from possible contamination arising from
parasitic reactions. In particular, we measured the neutron angular
distributions at 5 different beam energies (between 3 and 5 MeV) in the
\ang{17.5}-\ang{106} laboratory system angular range. The presented results
disagree with the assumptions introduced in the analysis of a previous
experiment.Comment: 9 pages, 9 figures - accepted by EPJ
A new FSA approach for in situ -ray spectroscopy
An increasing demand of environmental radioactivity monitoring comes both
from the scientific community and from the society. This requires accurate,
reliable and fast response preferably from portable radiation detectors. Thanks
to recent improvements in the technology, -spectroscopy with sodium
iodide scintillators has been proved to be an excellent tool for in-situ
measurements for the identification and quantitative determination of
-ray emitting radioisotopes, reducing time and costs. Both for
geological and civil purposes not only K, U, and Th have
to be measured, but there is also a growing interest to determine the
abundances of anthropic elements, like Cs and I, which are used
to monitor the effect of nuclear accidents or other human activities.
The Full Spectrum Analysis (FSA) approach has been chosen to analyze the
-spectra. The Non Negative Least Square (NNLS) and the energy
calibration adjustment have been implemented in this method for the first time
in order to correct the intrinsic problem related with the
minimization which could lead to artifacts and non physical results in the
analysis.
A new calibration procedure has been developed for the FSA method by using in
situ -spectra instead of calibration pad spectra. Finally, the new
method has been validated by acquiring -spectra with a 10.16 cm x 10.16
cm sodium iodide detector in 80 different sites in the Ombrone basin, in
Tuscany. The results from the FSA method have been compared with the laboratory
measurements by using HPGe detectors on soil samples collected in the different
sites, showing a satisfactory agreement between them. In particular, the
Cs isotopes has been implemented in the analysis since it has been
found not negligible during the in-situ measurements.Comment: accepted by Science of Total Environment: 8 pages, 10 figures, 3
table
Neutron-induced background by an alpha-beam incident on a deuterium gas target and its implications for the study of the 2H(alpha,gamma)6Li reaction at LUNA
The production of the stable isotope Li-6 in standard Big Bang
nucleosynthesis has recently attracted much interest. Recent observations in
metal-poor stars suggest that a cosmological Li-6 plateau may exist. If true,
this plateau would come in addition to the well-known Spite plateau of Li-7
abundances and would point to a predominantly primordial origin of Li-6,
contrary to the results of standard Big Bang nucleosynthesis calculations.
Therefore, the nuclear physics underlying Big Bang Li-6 production must be
revisited. The main production channel for Li-6 in the Big Bang is the
2H(alpha,gamma)6Li reaction. The present work reports on neutron-induced
effects in a high-purity germanium detector that were encountered in a new
study of this reaction. In the experiment, an {\alpha}-beam from the
underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium
gas target are used. A low neutron flux is induced by energetic deuterons from
elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the
ultra-low laboratory neutron background at LUNA, the effect of this weak flux
of 2-3 MeV neutrons on well-shielded high-purity germanium detectors has been
studied in detail. Data have been taken at 280 and 400 keV alpha-beam energy
and for comparison also using an americium-beryllium neutron source.Comment: Submitted to EPJA; 13 pages, 8 figure
Sensitivities of Low Energy Reactor Neutrino Experiments
The low energy part of the reactor neutrino spectra has not been
experimentally measured. Its uncertainties limit the sensitivities in certain
reactor neutrino experiments. The origin of these uncertainties are discussed,
and the effects on measurements of neutrino interactions with electrons and
nuclei are studied. Comparisons are made with existing results. In particular,
the discrepancies between previous measurements with Standard Model
expectations can be explained by an under-estimation of the low energy reactor
neutrino spectra. To optimize the experimental sensitivities, measurements for
\nuebar-e cross-sections should focus on events with large (1.5 MeV)
recoil energy while those for neutrino magnetic moment searches should be based
on events 100 keV. The merits and attainable accuracies for
neutrino-electron scattering experiments using artificial neutrino sources are
discussed.Comment: 25 pages, 9 figure
First Direct Measurement of the ^{17}O(p,\gamma)^{18}F Reaction Cross-Section at Gamow Energies for Classical Novae
Classical novae are important contributors to the abundances of key isotopes,
such as the radioactive ^{18}F, whose observation by satellite missions could
provide constraints on nucleosynthesis models in novae. The
^{17}O(p,\gamma)^{18}F reaction plays a critical role in the synthesis of both
oxygen and fluorine isotopes but its reaction rate is not well determined
because of the lack of experimental data at energies relevant to novae
explosions. In this study, the reaction cross section has been measured
directly for the first time in a wide energy range Ecm = 200 - 370 keV
appropriate to hydrogen burning in classical novae. In addition, the E=183 keV
resonance strength, \omega \gamma=1.67\pm0.12 \mueV, has been measured with the
highest precision to date. The uncertainty on the ^{17}O(p,\gamma)^{18}F
reaction rate has been reduced by a factor of 4, thus leading to firmer
constraints on accurate models of novae nucleosynthesis.Comment: accepted by Phys. Rev. Let
22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na
We investigate the impact of the new LUNA rate for the nuclear reaction NeNa on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range , and metallicities , , and . We find that the new LUNA measures have much reduced the nuclear uncertainties of the Ne and Na AGB ejecta, which drop from factors of to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of Na, the uncertainties that still affect the Ne and Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available
Class II phosphoinositide 3-kinase C2 beta regulates a novel signaling pathway involved in breast cancer progression
It is now well established that the enzymes phosphoinositide 3-kinases (PI3Ks) have a key role in the development and progression of many cancer types and indeed PI3Ks inhibitors are currently being tested in clinical trials. Although eight distinct PI3K isoforms exist, grouped into three classes, most of the evidence currently available are focused on one specific isoform with very little known about the potential role of the other members of this family in cancer. Here we demonstrate that the class II enzyme PI3K-C2ÎČ is overexpressed in several human breast cancer cell lines and in human breast cancer specimens. Our data indicate that PI3K-C2ÎČ regulates breast cancer cell growth in vitro and in vivo and that PI3K-C2ÎČ expression in breast tissues is correlated with the proliferative status of the tumor. Specifically we show that downregulation of PI3K-C2ÎČ in breast cancer cell lines reduces colony formation, induces cell cycle arrest and inhibits tumor growth, in particular in an estrogen-dependent in vivo xenograft. Investigation of the mechanism of the PI3K-C2ÎČ-dependent regulation of cell cycle progression and cell growth revealed that PI3K-C2ÎČ regulates cyclin B1 protein levels through modulation of microRNA miR-449a levels. Our data further demonstrate that downregulation of PI3K-C2ÎČ inhibits breast cancer cell invasion in vitro and breast cancer metastasis in vivo. Consistent with this, PI3K-C2ÎČ is highly expressed in lymph-nodes metastases compared to matching primary tumors. These data demonstrate that PI3K-C2ÎČ plays a pivotal role in breast cancer progression and in metastasis development. Our data indicate that PI3K-C2ÎČ may represent a key molecular switch that regulates a rate-limiting step in breast tumor progression and therefore it may be targeted to limit breast cancer spread
Preparation and characterisation of isotopically enriched TaO targets for nuclear astrophysics studies
The direct measurement of reaction cross sections at astrophysical energies
often requires the use of solid targets of known thickness, isotopic
composition, and stoichiometry that are able to withstand high beam currents
for extended periods of time. Here, we report on the production and
characterisation of isotopically enriched TaO targets for the study of
proton-induced reactions at the Laboratory for Underground Nuclear Astrophysics
facility of the Laboratori Nazionali del Gran Sasso. The targets were prepared
by anodisation of tantalum backings in enriched water (up to 66% in O
and up to 96% in O). Special care was devoted to minimising the presence
of any contaminants that could induce unwanted background reactions with the
beam in the energy region of astrophysical interest. Results from target
characterisation measurements are reported, and the conclusions for proton
capture measurements with these targets are drawn.Comment: accepted to EPJ
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