11,008 research outputs found
The detection of extragalactic N: Consequences for nitrogen nucleosynthesis and chemical evolution
Detections of extragalactic N are reported from observations of the
rare hydrogen cyanide isotope HCN toward the Large Magellanic Cloud
(LMC) and the core of the (post-) starburst galaxy NGC 4945. Accounting for
optical depth effects, the LMC data from the massive star-forming region N113
infer a N ratio of 111 17, about twice the C
value. For the LMC star-forming region N159HW and for the central region of NGC
4945, N ratios are also 100. The N ratios
are smaller than all interstellar nitrogen isotope ratios measured in the disk
and center of the Milky Way, strongly supporting the idea that N is
predominantly of `primary' nature, with massive stars being its dominant
source. Although this appears to be in contradiction with standard stellar
evolution and nucleosynthesis calculations, it supports recent findings of
abundant N production due to rotationally induced mixing of protons into
the helium-burning shells of massive stars.Comment: 15 pages including one postscript figure, accepted for publication by
ApJ Letter, further comments: please contact Yi-nan Chi
Abundances and Isotope Ratios in the Magellanic Clouds: The Star Forming Environment of N113
With the goal of deriving the physical and chemical conditions of star
forming regions in the Large Magellanic Cloud (LMC), a spectral line survey of
the prominent star forming region N113 is presented. The observations cover
parts of the frequency range from 85 GHz to 357 GHz and include 63 molecular
transitions from a total of 16 species, among them spectra of rare
isotopologues. Maps of selected molecular lines as well as the 1.2 mm continuum
distribution are also presented. Molecular abundances in the core of the
complex are found to be consistent with a photon dominated region (PDR) that is
nitrogen deficient, with the potential exception of N2H+. Densities range from
5x10^3 cm-3 for CO to almost 10^6 for CS and HCN, indicating that only the
densest regions provide sufficient shielding even for some of the most common
species. An ortho- to para-H_2CO ratio of ~3 hints at H_2CO formation in a warm
(>=40 K) environment. Isotope ratios are 12C/13C ~ 49+-5, 16O/18O ~ 2000+-250,
18O/17O ~ 1.7+-0.2 and 32S/34S ~ 15. Agreement with data from other star
forming clouds shows that the gas is well mixed in the LMC . The isotope ratios
do not only differ from those seen in the Galaxy. They also do not form a
continuation of the trends observed with decreasing metallicity from the inner
to the outer Galaxy. This implies that the outer Galaxy, is not providing a
transition zone between the inner Galaxy and the metal poor environment of the
Magellanic Clouds. A part of this discrepancy is likely caused by differences
in the age of the stellar populations in the outer Galaxy and the LMC.Comment: 50 pages, 13 figures, accepted for publication in Ap
Ocean warming-acidification synergism undermines dissolved organic matter assembly.
Understanding the influence of synergisms on natural processes is a critical step toward determining the full-extent of anthropogenic stressors. As carbon emissions continue unabated, two major stressors--warming and acidification--threaten marine systems on several scales. Here, we report that a moderate temperature increase (from 30°C to 32°C) is sufficient to slow--even hinder--the ability of dissolved organic matter, a major carbon pool, to self-assemble to form marine microgels, which contribute to the particulate organic matter pool. Moreover, acidification lowers the temperature threshold at which we observe our results. These findings carry implications for the marine carbon cycle, as self-assembled marine microgels generate an estimated global seawater budget of ~1016 g C. We used laser scattering spectroscopy to test the influence of temperature and pH on spontaneous marine gel assembly. The results of independent experiments revealed that at a particular point, both pH and temperature block microgel formation (32°C, pH 8.2), and disperse existing gels (35°C). We then tested the hypothesis that temperature and pH have a synergistic influence on marine gel dispersion. We found that the dispersion temperature decreases concurrently with pH: from 32°C at pH 8.2, to 28°C at pH 7.5. If our laboratory observations can be extrapolated to complex marine environments, our results suggest that a warming-acidification synergism can decrease carbon and nutrient fluxes, disturbing marine trophic and trace element cycles, at rates faster than projected
Cardiovascular magnetic resonance reference ranges for the heart and aorta in Chinese at 3T.
Cardiovascular magnetic resonance (CMR) reference ranges have not been well established in Chinese. Here we determined normal cardiac and aortic reference ranges in healthy Singaporean Chinese and investigated how these data might affect clinical interpretation of CMR scans.In 180 healthy Singaporean Chinese (20 to 69 years old; males, n = 91), comprehensive cardiac assessment was performed using the steady state free precision technique (3T Ingenia, Philips) and images were analysed by two independent observers (CMR42, Circle Cardiovascular Imaging). Measurements were internally validated using standardized approaches: left ventricular mass (LVM) was measured in diastole and systole (with and without papillary muscles) and stroke volumes were compared in both ventricles. All reference ranges were stratified by sex and age; and indeterminate/borderline regions were defined statistically at the limits of the normal reference ranges. Results were compared with clinical measurements reported in the same individuals.LVM was equivalent in both phases (mean difference 3.0 ± 2.5 g; P = 0.22) and stroke volumes were not significantly different in the left and right ventricles (P = 0.91). Compared to females, males had larger left and right ventricular volumes (P 0.05 for all measures). In both sexes, age correlated negatively with left and right ventricular volumes; and positively with aortic sinus and sinotubular junction diameters (P < 0.0001 for all). There was excellent agreement in indexed stroke volumes in the left and right ventricles (0.1±5.7 mL/m2, 0.7±6.2 mL/m2, respectively), LVM (0.6±6.4 g/m2), atrial sizes and aortic root dimensions between values reported in clinical reports and our measured reference ranges.Comprehensive sex and age-corrected CMR reference ranges at 3T have been established in Singaporean Chinese. This is an important step for clinical practice and research studies of the heart and aorta in Asia
Anharmonicity Induced Resonances for Ultracold Atoms and their Detection
When two atoms interact in the presence of an anharmonic potential, such as
an optical lattice, the center of mass motion cannot be separated from the
relative motion. In addition to generating a confinement-induced resonance (or
shifting the position of an existing Feshbach resonance), the external
potential changes the resonance picture qualitatively by introducing new
resonances where molecular excited center of mass states cross the scattering
threshold. We demonstrate the existence of these resonances, give their
quantitative characterization in an optical superlattice, and propose an
experimental scheme to detect them through controlled sweeping of the magnetic
field.Comment: 6 pages, 5 figures; expanded presentatio
Organisational transformation through CRM implementation: a descriptive case study
CRM is becoming critical to organisations worldwide as global competition increases and technological innovations in communication continue to emerge. In this descriptive case study, we have investigated a utility provider – with a geographical monopoly, who has successfully implemented a complaint management system, as part of their CRM process transformation. We have applied the teleological process theory (Ven de Ven and Poole 1995) to describe the organisational change, based on our empirical research.<br /
Stability of Horava-Lifshitz Black Holes in the Context of AdS/CFT
The anti--de Sitter/conformal field theory (AdS/CFT) correspondence is a
powerful tool that promises to provide new insights toward a full understanding
of field theories under extreme conditions, including but not limited to
quark-gluon plasma, Fermi liquid and superconductor. In many such applications,
one typically models the field theory with asymptotically AdS black holes.
These black holes are subjected to stringy effects that might render them
unstable. Ho\v{r}ava-Lifshitz gravity, in which space and time undergo
different transformations, has attracted attentions due to its power-counting
renormalizability. In terms of AdS/CFT correspondence, Ho\v{r}ava-Lifshitz
black holes might be useful to model holographic superconductors with Lifshitz
scaling symmetry. It is thus interesting to study the stringy stability of
Ho\v{r}ava-Lifshitz black holes in the context of AdS/CFT. We find that
uncharged topological black holes in Ho\v{r}ava-Lifshitz theory are
nonperturbatively stable, unlike their counterparts in Einstein gravity, with
the possible exceptions of negatively curved black holes with detailed balance
parameter close to unity. Sufficiently charged flat black holes for
close to unity, and sufficiently charged positively curved black
holes with close to zero, are also unstable. The implication to the
Ho\v{r}ava-Lifshitz holographic superconductor is discussed.Comment: 15 pages, 6 figures. Updated version accepted by Phys. Rev. D, with
corrections to various misprints. References update
Differential effects of calcium- and vitamin D-fortified milk with FOS-inulin compared to regular milk, on bone biomarkers in Chinese pre- and postmenopausal women
PURPOSE:
To compare the effects of a high-calcium vitamin D-fortified milk with added FOS-inulin versus regular milk on serum parathyroid hormone, and bone turnover markers in premenopausal (Pre-M) and postmenopausal (PM) women over 12 weeks.
METHODS:
Premenopausal women (n = 136, mean age 41 (±5) years) and postmenopausal women [n = 121, mean age 59 (±4) years] were recruited, and each age group randomised into two groups to take two glasses per day of control = regular milk (500 mg calcium per day) or intervention (Int) = fortified milk (1000 mg calcium for pre-M women and 1200 mg calcium for PM women, 96 mg magnesium, 2.4 mg zinc, 15 µg vitamin D, 4 g FOS-inulin per day). At baseline, week 4 and week 12 serum minerals and bone biochemical markers were measured and bone density was measured at baseline.
RESULTS:
Mean 25-hydroxyvitamin D [25(OH) vitamin D3] levels among groups were between 49 and 65 nmol/L at baseline, and over the 12 weeks of supplementation, the fortified milk improved vitamin D status in both Int groups. CTx-1 and PINP reduced significantly in both Pre-M and PM groups over the 12 weeks, with the changes in CTx-1 being significantly different (P < 0.035) between PM control and PM Int groups at week 12. Parathyroid hormone levels were significantly reduced in all groups over time, except for control PM group where levels increased at 12 weeks.
CONCLUSION:
The overall pattern of responses indicates that while both regular milk and fortified milk reduce bone resorption in young and older women, fortified milk is measurably more effective
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