Close frequency pairs in Delta Scuti stars

The majority of the well-studied Delta Scuti stars show frequency pairs in the power spectra with frequency separations less than 0.06 c/d(0.7 microHz) as well as amplitude variability. We examine the interpretation in terms of separate excited stellar pulsation modes,single modes with variable amplitudes, and observational problems. The variable-phase technique, which examines the phase jumps near the times of minimum amplitude of an assumed single frequency, is applied to the extensive data of the star BI CMi, which shows some of the most extreme behavior. The following results are found for the 5 features in the power spectrum which could be explained as single modes with variable amplitudes or as double modes: for three features it can be shown that these are indeed pairs of separate pulsation modes beating with each other: at times of minimum amplitude the phase jumps are observed and both the observed amplitude and phase variations can be predicted correctly by assuming two separate modes of nearly equal frequencies. Artifacts caused by observational error,insufficient frequency resolution or variable amplitudes can be ruled out. A fourth pair has a probable origin in two excited modes, while a 5th case is inconclusive due to long time scales of variability and small amplitudes.The existence of close frequencies need to be taken into account in planning the lengths of earth-based as well as space campaigns so that sufficient frequency resolution is obtained. Possible reasons for the existence of close frequencies in Delta Scuti stars are considered.They include the dense frequency spacing caused by the presence of mixed modes, rotational splitting as well as near-coincidence of the frequencies of modes with different l values (the so-called Small Spacing).Comment: 9 Pages, 5 Figures, Accepted by Astronomy and Astrophysics; alternative Download from ftp://ftp.deltascuti.net/pub/CloseFrequencies.pd

Factors affecting trauma outcomes and mortality: a comparison of an established level one trauma unit and a secondary hospital in South Africa

MT201

Magnetic domain walls in constrained geometries

Magnetic domain walls have been studied in micrometer-sized Fe20Ni80 elements containing geometrical constrictions by spin-polarized scanning electron microscopy and numerical simulations. By controlling the constriction dimensions, the wall width can be tailored and the wall type modified. In particular, the width of a 180 degree Neel wall can be strongly reduced or increased by the constriction geometry compared with the wall in unconstrained systems.Comment: 4 pages, 6 figure

A necdin/MAGE-like gene in the chromosome 15 autism susceptibility region: expression, imprinting, and mapping of the human and mouse orthologues

BACKGROUND: Proximal chromosome 15q is implicated in neurodevelopmental disorders including Prader-Willi and Angelman syndromes, autistic disorder and developmental abnormalities resulting from chromosomal deletions or duplications. A subset of genes in this region are subject to genomic imprinting, the expression of the gene from only one parental allele. RESULTS: We have now identified the NDNL2 (also known as MAGE-G) gene within the 15q autistic disorder susceptibility region and have mapped its murine homolog to the region of conserved synteny near necdin (Ndn) on mouse Chr 7. NDNL2/MAGE-G is a member of a large gene family that includes the X-linked MAGE cluster, MAGED1 (NRAGE), MAGEL2 and NDN, where the latter two genes are implicated in Prader-Willi syndrome. We have now determined that NDNL2/Ndnl2 is widely expressed in mouse and human fetal and adult tissues, and that it is apparently not subject to genomic imprinting by the PWS/AS Imprinting Center. CONCLUSION: Although NDNL2/MAGE-G in the broadly defined chromosome 15 autistic disorder susceptibility region, it is not likely to be pathogenic based on its wide expression pattern and lack of imprinted expression

Benzene C−H Bond Activation in Carboxylic Acids Catalyzed by O-Donor Iridium(III) Complexes: An Experimental and Density Functional Study

The mechanism of benzene C−H bond activation by [Ir(μ-acac-O,O,C^3)(acac-O,O)(OAc)]_2 (4) and [Ir(μ-acac-O,O,C^3)(acac-O,O)(TFA)]_2 (5) complexes (acac = acetylacetonato, OAc = acetate, and TFA = trifluoroacetate) was studied experimentally and theoretically. Hydrogen−deuterium (H/D) exchange between benzene and CD_(3)COOD solvent catalyzed by 4 (ΔH^‡ = 28.3 ± 1.1 kcal/mol, ΔS^‡ = 3.9 ± 3.0 cal K^(−1) mol^(−1)) results in a monotonic increase of all benzene isotopologues, suggesting that once benzene coordinates to the iridium center, there are multiple H/D exchange events prior to benzene dissociation. B3LYP density functional theory (DFT) calculations reveal that this benzene isotopologue pattern is due to a rate-determining step that involves acetate ligand dissociation and benzene coordination, which is then followed by heterolytic C−H bond cleavage to generate an iridium-phenyl intermediate. A synthesized iridium-phenyl intermediate was also shown to be competent for H/D exchange, giving similar rates to the proposed catalytic systems. This mechanism nicely explains why hydroarylation between benzene and alkenes is suppressed in the presence of acetic acid when catalyzed by [Ir(μ-acac-O,O,C^3)(acac-O,O)(acac-C^3)]_2 (3) (Matsumoto et al. J. Am. Chem. Soc. 2000, 122, 7414). Benzene H/D exchange in CF_(3)COOD solvent catalyzed by 5 (ΔH^‡ = 15.3 ± 3.5 kcal/mol, ΔS^‡ = −30.0 ± 5.1 cal K^(−1) mol^(−1)) results in significantly elevated H/D exchange rates and the formation of only a single benzene isotopologue, (C_(6)H_(5)D). DFT calculations show that this is due to a change in the rate-determining step. Now equilibrium between coordinated and uncoordinated benzene precedes a single rate-determining heterolytic C−H bond cleavage step

Ocean acidification effects on calcifying macroalgae

Since the Industrial Revolution, the partial pressure of carbon dioxide (pCO2) has been increasing and global ocean surface waters have absorbed 30% of the anthropogenic CO2 released into the atmosphere. An increase in pCO2 in surface ocean waters causes an increase in bicarbonate ions (HCO3-) and protons (H+) and a decrease in carbonate ions (CO32-), thereby decreasing the pH and the saturation state of the seawater with respect to CO32-. These changes in ocean chemistry (termed ocean acidification) are expected to have negative impacts on marine calcifying organisms. Because calcifying marine primary producers are important to the carbon cycle and rocky shore habitat structure and stability, investigating how they will respond to future oceanic pCO2 levels is a relevant and important topic of research. Due to a recent strong increase in the number of studies investigating the responses of calcifying marine macroalgae to elevated pCO2, this review aims to present the state of knowledge on the response of calcifying macroalgae to ocean acidification alone and in combination with global and local stressors. We discuss the physiological responses of calcifying macroalgae to elevated pCO2 within the contexts biogeography, taxonomy, and calcification mechanisms. Generally, coralline algae that deposit high-Mg calcite are most susceptible to high pCO2, and polar species are particularly at risk. However, some dolomite-depositing species may be able to acclimate to high pCO2. Calcifiers generally show sensitivity to overgrowth and outcompetition by noncalcifying algae when grown under elevated CO2 conditions, and this trend could be amplified under conditions of high inorganic nutrients. However, it still remains unknown whether or not calcifiers will be able to adapt to their rapidly changing environments. We discuss the lack of research on this topic, and provide some suggestions for how this knowledge gap can be filled by future research