Coronae of Stars with Super Solar Elemental Abundances

Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the First Ionization Potential (FIP). This study focuses on the coronal composition of stars with super-solar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, $\iota$ Hor, HR 7291, $\tau$ Boo, and $\alpha$ Cen A and B. These stars all have high-statistics X-ray spectra, three of which are presented for the first time. The abundances measured in this paper are obtained using the line-resolved spectra of the Reflection Grating Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera spectra on board the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components is found to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respective photospheres. For 11 LMi and $\tau$ Boo no FIP effect is present, while $\iota$ Hor, HR 7291, and $\alpha$ Cen A and B show a clear FIP trend. These conclusions hold whether the comparison is made with solar abundances or the individual stellar abundances. Unlike the solar corona where low FIP elements are enriched, in these stars the FIP effect is consistently due to a depletion of high FIP elements with respect to actual photospheric abundances. Comparing to solar abundances (instead of stellar) yields the same fractionation trend as on the Sun. In both cases a similar FIP bias is inferred, but different fractionation mechanisms need to be invoked.Comment: 11 pages, 7 figures, submitted to A&A. Comments are welcom

The starting transient of solid propellant rocket motors with high internal gas velocities

A comprehensive analytical model which considers time and space development of the flow field in solid propellant rocket motors with high volumetric loading density is described. The gas dynamics in the motor chamber is governed by a set of hyperbolic partial differential equations, that are coupled with the ignition and flame spreading events, and with the axial variation of mass addition. The flame spreading rate is calculated by successive heating-to-ignition along the propellant surface. Experimental diagnostic studies have been performed with a rectangular window motor (50 cm grain length, 5 cm burning perimeter and 1 cm hydraulic port diameter), using a controllable head-end gaseous igniter. Tests were conducted with AP composite propellant at port-to-throat area ratios of 2.0, 1.5, 1.2, and 1.06, and head-end pressures from 35 to 70 atm. Calculated pressure transients and flame spreading rates are in very good agreement with those measured in the experimental system

An Inequality for Circle Packings Proved by SemidefiniteProgramming

A geometric inequality among three triangles, originating in circle packing problems, is introduced. In order to prove it, we reduce the original formulation to the nonnegativity of a polynomial in four real indeterminates. Techniques based on sum of squares decompositions, semidefinite programming and symmetry reduction are then applied to provide an easily verifiable nonnegativity certificat

System Theory, Operator Models and Scattering: The Time-Varying Case

It is well known that linear system theory, Lax-Phillips scattering theory, and operator model theory for a contraction operator are all intimately related. A common thread in all three theories is a contractive, analytic, operator-valued function on the unit disk W(z) having a representation of the form W(z) = D + zC(I − zA)−1B, known, depending on the context, as the transfer function, the scattering function, or the characteristic function. We present the time-varing analogue of this framework. Also included is a time-varying analogue of the Abstract Interpolation Problem of Katsnelson-Kheifets-Yuditskii

Are there functional consequences of a reduction in selenium intake in UK subjects?

Dietary Se levels in the UK have fallen over the last 20 years and recent surveys indicate that average Se intakes are 30-40 microg/d, which is well below the current UK reference nutrient intake for adult men (75 microg/d) or women (60 microg/d). Functional consequences of this decline have not been recognised, although epidemiological data suggest it may contribute to increased risk of infections and incidence of some cancers. Previous data have indicated that biochemical changes in Se-dependent proteins occur in otherwise healthy UK subjects given small Se supplements. The current studies have focused on the effect of small Se supplements on the immune response since there is evidence of specific interactions between Se intake and viral replication, and since the potential anti-cancer effects of Se may be mediated by non-antioxidant effects of Se such as changes in immune function. Data indicate that subjects given small Se supplements (50 or 100 microg Se/d) have changes in the activity of Se-dependent enzymes and evidence of improved immune function and clearance of an administered live attenuated virus in the form of poliovirus vaccine. Responses of individual subjects to Se supplements are variable, and current work is evaluating potential explanations for this variability, including genetic variability and pre-existing Se status

Developing Preservice Elementary Teachers' Pedagogical Design Capacity for Reform‐Based Curriculum Design

Teachers use curriculum materials as a guide in their planning, critiquing and adapting them to address reform‐based goals and practices and specific contextual needs. To become well‐started beginners in planning lessons, novice teachers need opportunities to develop their pedagogical design capacity—that is, their ability to use personal and curricular resources in designing instruction for students. This study investigated the use of reform‐based criteria in supporting 24 preservice teachers enrolled in an elementary science methods course. In learning about and applying criteria, the preservice teachers developed aspects of their pedagogical design capacity by expanding their analysis ideas and refining their knowledge and beliefs about curriculum design. However, many struggled with analyzing lesson plans in a reform‐oriented way during student teaching. This occurred, in part, because the preservice teachers navigated different settings that conveyed conflicting ideas about the reasons why teachers make modifications. The methods course emphasized the importance of modifying materials to promote reform‐based science teaching, but few preservice teachers observed their mentor teachers make adaptations for this reason. These findings have important implications for theoretical models on curriculum materials use and the design of science teacher education.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91354/1/j.1467-873X.2012.00599.x.pd

M-current inhibition rapidly induces a unique CK2-dependent plasticity of the axon initial segment

Alterations in synaptic input, persisting for hours to days, elicit homeostatic plastic changes in the axon initial segment (AIS), which is pivotal for spike generation. Here, in hippocampal pyramidal neurons of both primary cultures and slices, we triggered a unique form of AIS plasticity by selectively targeting M-type K+ channels, which predominantly localize to the AIS and are essential for tuning neuronal excitability. While acute M-current inhibition via cholinergic activation or direct channel block made neurons more excitable, minutes to hours of sustained M-current depression resulted in a gradual reduction in intrinsic excitability. Dual soma–axon patch-clamp recordings combined with axonal Na+ imaging and immunocytochemistry revealed that these compensatory alterations were associated with a distal shift of the spike trigger zone and distal relocation of FGF14, Na+, and Kv7 channels but not ankyrin G. The concomitant distal redistribution of FGF14 together with Nav and Kv7 segments along the AIS suggests that these channels relocate as a structural and functional unit. These fast homeostatic changes were independent of l-type Ca2+ channel activity but were contingent on the crucial AIS protein, protein kinase CK2. Using compartmental simulations, we examined the effects of varying the AIS position relative to the soma and found that AIS distal relocation of both Nav and Kv7 channels elicited a decrease in neuronal excitability. Thus, alterations in M-channel activity rapidly trigger unique AIS plasticity to stabilize network excitability

Diesel Exhaust Inhalation Elicits Acute Vasoconstriction in Vivo

BACKGROUND: Traffic-related air pollution is consistently associated with cardiovascular morbidity and mortality. Recent human and animal studies suggest that exposure to air pollutants affects vascular function. Diesel exhaust (DE) is a major source of traffic-related air pollution. OBJECTIVES: Our goal was to study the effects of short-term exposure to DE on vascular reactivity and on mediators of vascular tone. METHODS: In a double-blind, crossover, controlled exposure study, 27 adult volunteers (10 healthy and 17 with metabolic syndrome) were exposed in randomized order to filtered air (FA) and each of two levels of diluted DE (100 or 200 μg/m3 of fine particulate matter) in 2-hr sessions. Before and after each exposure, we assessed the brachial artery diameter (BAd) by B-mode ultrasound and collected blood samples for endothelin-1 (ET-1) and catecholamines. Postexposure we also assessed endothelium-dependent flow-mediated dilation (FMD). RESULTS: Compared with FA, DE at 200 μg/m3 elicited a decrease in BAd (0.11 mm; 95% confidence interval, 0.02–0.18), and the effect appeared linearly dose related with a smaller effect at 100 μg/m3. Plasma levels of ET-1 increased after 200 μg/m3 DE but not after FA (p = 0.01). There was no consistent impact of DE on plasma catecholamines or FMD. CONCLUSIONS: These results demonstrate that short-term exposure to DE is associated with acute endothelial response and vasoconstriction of a conductance artery. Elucidation of the signaling pathways controlling vascular tone that underlie this observation requires further study