4,306 research outputs found
The electric quadrupole channel of the 7.8 eV transition
The unique isomeric transition at 7.8 eV in has a
magnetic dipole () and an electric quadrupole () multipole mixing. So
far, the component has been widely disregarded. Here, we investigate the
nuclear physics nature and the impact of the decay channel for the nuclear
coupling to the atomic shell based on the newest theoretical predictions for
the corresponding reduced nuclear transition probabilities. Our results show
that the contribution of the channel is dominant or at least of the same
order of magnitude for internal conversion or electronic bridge transitions
involving the atomic orbitals , and . Notable exceptions are the
internal conversion of the electron and the electronic bridge between the
electronic states and , for which the component dominates by two
to three orders of magnitude. Caution is therefore advised when considering
isomeric excitation or decay via nuclear coupling to the atomic shell, as the
involved orbitals determine which multipole transition component dominates
Nuclear-resonant electron scattering
We investigate nuclear-resonant electron scattering as occurring in the
two-step process of nuclear excitation by electron capture (NEEC) followed by
internal conversion. The nuclear excitation and decay are treated by a
phenomenological collective model in which nuclear states and transition
probabilities are described by experimental parameters. We present capture
rates and resonant strengths for a number of heavy ion collision systems
considering various scenarios for the resonant electron scattering process. The
results show that for certain cases resonant electron scattering can have
significantly larger resonance strengths than NEEC followed by the radiative
decay of the nucleus. We discuss the impact of our findings on the possible
experimental observation of NEEC.Comment: 24 pages, 2 plots, 5 table
Endocannabinoid Metabolome of Human Breast Milk
Human breast milk (HBM) is an extremely complex yet fascinating biofluid tailored to meet an infant’s nutritional requirements for development. Amongst the nutrients present in HBM, the long-chain polyunsaturated fatty acids (LCPUFAs) are of high importance due to the pivotal role they play in infant cognitive and visual development, and growth. In addition, the LCPUFAs are precursors to endocannabinoids (EC) which are endogenous lipid mediators. EC exert metabolic responses including appetite and food intake regulation, and they have been identified to play a role in establishing the suckling response of the newborn that is needed to nurse. Thus, we aimed to characterize and quantify the EC present in HBM, termed the EC metabolome (ECM). HBM samples were collected from two different populations, one in Guatemala (n = 26) and the other one in the United States (n = 24). We collected HBM at different lactation stages: transitional (2 weeks postpartum) and mature (4 weeks and 16-24 weeks postpartum) milk. Using liquid chromatography-mass spectrometry analyses, we identified 15 members of the ECM in both lactation stages: arachidonoylethanolamine, palmitoylethanolamine, oleoylethanolamine, docosahexaenoylethanolamine, eicoapentaenoylethanolamine, eicosenoylethanolamine, arachidonoylglycerol, palmitoyglycerol, oleoylglycerol, docosahexaenoylglycerol, eicosapentaenoylglycerol, eiconenooylglycerol, arachidonic acid, docosahexaenoic acid, and eicosapentaenoic acid. Overall, members in the glycerol group were higher in concentration than those of the ethanolamide group. To date, the mechanisms of action and the role of the ECM in HBM and infant development are not fully understood. Data from the present study provides a foundation to develop future studies to help elucidate how the ECM modulates infant health and development
Searching for new thermally emitting isolated neutron stars in the 2XMMp catalogue - Discovery of a promising candidate
The group of 7 thermally emitting and radio-quiet isolated neutron stars
(INSs) discovered by ROSAT constitutes a nearby population which locally
appears to be as numerous as that of the classical radio pulsars. So far,
attempts to enlarge this particular group of INSs finding more remote objects
failed to confirm any candidate. We found in the 2XMMp catalogue a handful of
sources with no catalogued counterparts and with X-ray spectra similar to those
of the ROSAT discovered INSs, but seen at larger distances and thus undergoing
higher interstellar absorptions. In order to rule out alternative
identifications such as an AGN or a CV, we obtained deep ESO-VLT and SOAR
optical imaging for the X-ray brightest candidates. We report here on the
current status of our search and discuss the possible nature of our candidates.
We focus particularly on the X-ray brightest source of our sample, 2XMM
J104608.7-594306, observed serendipitously over more than four years by the
XMM-Newton Observatory. A lower limit on the X-ray to optical flux ratio of ~
300 together with a stable flux and soft X-ray spectrum make it the most
promising thermally emitting INS candidate. Beyond the finding of new members,
our study aims at constraining the space density of this population at large
distances and at determining whether their apparently high local density is an
anomaly or not.Comment: 3 pages, 2 figures, proceedings of the conference "40 Years of
Pulsars", 12-17 August 2007, Montreal, Canad
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