Using the Ca II Triplet to Trace Abundance Variations in Individual Red Giant Branch stars in Three Nearby Galaxies

Spectroscopic abundance determinations for stars spanning a Hubble time in age are necessary in order to unambiguously determine the evolutionary histories of galaxies. Using FORS1 in Multi-Object Spectroscopy mode on ANTU (UT1) at the ESO-VLT on Paranal we obtained near infrared spectra from which we measured the equivalent widths of the two strongest Ca II triplet lines to determine metal abundances for a sample of Red Giant Branch stars, selected from ESO-NTT optical (I, V-I) photometry of three nearby, Local Group, galaxies: the Sculptor Dwarf Spheroidal, the Fornax Dwarf Spheroidal and the Dwarf Irregular NGC 6822. The summed equivalent width of the two strongest lines in the Ca II triplet absorption line feature, centered at 8500A, can be readily converted into an [Fe/H] abundance using the previously established calibrations by Armandroff & Da Costa (1991) and Rutledge, Hesser & Stetson (1997). We measured metallicities for 37 stars in Sculptor, 32 stars in Fornax, and 23 stars in NGC 6822, yielding more precise estimates of the metallicity distribution functions for these galaxies than it is possible to obtain photometrically. In the case of NGC 6822, this is the first direct measurement of the abundances of the intermediate-age and old stellar populations. We find metallicity spreads in each galaxy which are broadly consistent with the photometric width of the Red Giant Branch, although the abundances of individual stars do not always appear to correspond to their colour. This is almost certainly predominantly due to a highly variable star formation rate with time in these galaxies, which results in a non-uniform, non-globular-cluster-like, evolution of the Ca/Fe ratio.Comment: Accepted for publication in MNRA

Rydberg-Atom Population Transfer By Population Trapping in a Chirped Microwave Pulse

We demonstrate that Rydberg atoms can be transferred to states of lower principal quantum number by exposing them to a frequency chirped microwave pulse. Specifically, we have transferred n=75 atoms to n=66 with a 400-ns pulse chirped from 7.8 to 11.8 GHz. In spite of the large number of coupled levels, using a simplified model we can describe the process reasonably well as a sequence of adiabatic rapid passages

Rydberg-Atom Population Transfer By Population Trapping in a Chirped Microwave Pulse

We demonstrate that Rydberg atoms can be transferred to states of lower principal quantum number by exposing them to a frequency chirped microwave pulse. Specifically, we have transferred n=75 atoms to n=66 with a 400-ns pulse chirped from 7.8 to 11.8 GHz. In spite of the large number of coupled levels, using a simplified model we can describe the process reasonably well as a sequence of adiabatic rapid passages

Intramolecular C-H...O and intermolecular N-H...O and C-H...O interactions in N-ferrocenoylglycine benzyl ester, an effective dihydrogen phosphate anion sensing agent

The title compound, benzyl N-(ferrocenecarbonyl)glycinate, [Fe(C₅H₅)(C₁₅H₁₄NO₃)], a glycine benzyl ester derivative, is an effective anion sensor for electrochemically sensing the dihydrogen phosphate anion (H₂PO₄-). Intermolecular N--H...O hydrogen bonds form onedimensional chains with graph set C(4) [N...O 2.811 (3)Å,]. A two-dimensional network is formed by linking the chains through Car--H...0=Cester interactions about inversion centres [graph set R²₂(14); C...O 3.406 (4)Å]. An intramolecular Ccp-H...0=Cester interaction [C...O 3.540 (3)Å,] with graph set S(9) completes the hydrogen bonding

The 1863 Invasion of Pennsylvania

Confederate General Robert E. Lee’s invasion of Pennsylvania in 1863 was a grave mistake, on a variety of levels, which ultimately culminated in a crippling defeat at Gettysburg. After the Army of Northern Virginia successfully defended southern territory against northern attacks, the transition to an offensive strategy, advancing north in to Pennsylvania was a vast miscalculation. Lee’s army now traversed enemy territory, leaving behind the advantages of a campaign on southern territory and abandoning a defensive posture. This transition to fighting on enemy territory brought several difficulties that Lee seemingly overlooked, and presented challenges for which Lee was unprepared. Lee sought to bring the fighting, which was primarily on Southern soil, in to Northern territory, in hopes of breaking the will of Northerners and forcing the Federal government in to suing for peace. However, while in Pennsylvania, Lee continuously miscalculated enemy positions, all the while compromising his own while moving among a hostile populace. While amongst that populace, which Lee hoped would help push for capitulation upon seeing the Army of Northern Virginia in Pennsylvania, Lee’s men found themselves at a significant intelligence and psychological disadvantage. Lee’s push north in pursuit of one decisive victory over the Army of the Potomac ultimately failed to achieve its ultimate goal. This illusive triumph very likely could have been successfully achieved through other means, and should not have been sought after at the expense of a crushing defeat such as that the Army of Northern Virginia experienced at Gettysburg. Lee’s move into Pennsylvania proved foolhardy, as he failed to appropriately supervise his commanders, calling in to question his own capabilities as a General. These questions about Lee’s competency and capabilities litter the historical record when examining the Pennsylvania campaign, and functionally reshape the legacy of the General Lee. Ultimately, Lee sought recognition through success on Northern soil, but misjudged how attainable a decisive victory up North would be. As the Federal 3 government considered relenting to a peace agreement, the push north into Pennsylvania by the Lee’ army, riding high on victorious engagements in Virginia, forced the North’s hand, all the while Robert E. Lee was overplaying his own

Intermolecular N-H...N and C-H...O interactions from one-dimensional chains comprising the two independent molecules of N,N'-dicyclohexyl-N-nicotinoylurea

The title_compound, C₁₉H₂₇N₃0₂, crystallizes in space group P1 with two molecules in the asymmetric unit which differ slightly in conformation. Intermolecular N--H...N and C--H...O interactions generate a hydrogen-bonded ring system between the alternating molecules, graph set R²₂(16), with N...N distances of 3.021 (3) and 3.041 (3)Å, and C...O distances of 3.219(3) and 3.296(3)Å along the hydrogen-bonded chains

Examining the Connectivity of Antarctic Krill on the West Antarctic Peninsula: Implications for Pygoscelis Penguin Biogeography and Population Dynamics

Antarctic krill (Euphausia superba) are considered a keystone species for higher trophic level predators along the West Antarctic Peninsula (WAP) during the austral summer. The connectivity of these populations may play a critical role in predator biogeography, especially for central-place foragers such as the Pygoscelis penguins that breed along the WAP during the austral summer. Here, we used a physical ocean model to examine adult krill connectivity in this region using simulated krill with realistic diel vertical migration behaviors across four austral summers. Specifically, we examined krill connectivity around the Adélie gap, a 400 km long region along the WAP with a distinct absence of Adélie penguin colonies, to determine if krill population connectivity around this feature played a role in its persistence. Our results indicate that krill populations north and south of the Adélie gap are nearly isolated from each other and that persistent current features play a role in this inter-region connectivity, or lack thereof. Our results indicate that simulated krill released within the Adélie gap are quickly advected from the region, suggesting that the lack of local krill recruit retention may play a role in the persistence of this biogeographic feature

Peptide Antigen Concentration Modulates Digital NFAT1 Activation in Primary Mouse Naive CD8(+) T Cells as Measured by Flow Cytometry of Isolated Cell Nuclei

Circulating naive T cells exist in a quiescent state. After TCR contact with the cognate peptide presented by APCs in secondary lymphoid structures, T cells undergo a period of rapid transcriptional changes that set the stage for fate-determining effector or memory programming. We describe a novel method to analyze TCR signaling pathway activation in nuclei isolated from primary mouse naive T cells after stimulation with natural peptide Ags. We prelabeled cells with cell tracking dye to easily distinguish CD8(+) T cell nuclei from APC nuclei by conventional flow cytometry. Using this approach, we observed clear digital activation of NFAT1 transcription factor in OT-I T cells stimulated with OVA peptide presented by bulk splenocytes. OVA concentration had discrete control over the fraction of the cells that translocated NFAT1, indicating that a distinct threshold amount of TCR signaling is required to switch on NFAT1 in naive T cells. This behavior was cell contact dependent and qualitatively more exact than the NFAT1 response in ionomycin-stimulated naive T cells. These data contribute to our understanding of the digital behavior of TCR signaling components documented in other studies and indicate how T cells might discriminate log-fold changes in Ag availability during an actual infection. Overall, these results highlight the potential of this coculture nuclei isolation protocol to address stimulation-dependent translocation of proteins in primary lymphocytes