Role of coronal mass ejections in the heliospheric Hale cycle

[1] The 11-year solar cycle variation in the heliospheric magnetic field strength can be explained by the temporary buildup of closed flux released by coronal mass ejections (CMEs). If this explanation is correct, and the total open magnetic flux is conserved, then the interplanetary-CME closed flux must eventually open via reconnection with open flux close to the Sun. In this case each CME will move the reconnected open flux by at least the CME footpoint separation distance. Since the polarity of CME footpoints tends to follow a pattern similar to the Hale cycle of sunspot polarity, repeated CME eruption and subsequent reconnection will naturally result in latitudinal transport of open solar flux. We demonstrate how this process can reverse the coronal and heliospheric fields, and we calculate that the amount of flux involved is sufficient to accomplish the reversal within the 11 years of the solar cycle

Evidence for a Molecular Cloud Origin for Gamma-Ray Bursts: Implications for the Nature of Star Formation in the Universe

It appears that the majority of rapidly-, well-localized gamma-ray bursts with undetected, or dark, optical afterglows, or `dark bursts' for short, occur in clouds of size R > 10L_{49}^{1/2} pc and mass M > 3x10^5L_{49} M_{sun}, where L is the isotropic-equivalent peak luminosity of the optical flash. We show that clouds of this size and mass cannot be modeled as a gas that is bound by pressure equilibrium with a warm or hot phase of the interstellar medium (i.e., a diffuse cloud): Such a cloud would be unstable to gravitational collapse, resulting in the collapse and fragmentation of the cloud until a burst of star formation re-establishes pressure equilibrium within the fragments, and the fragments are bound by self-gravity (i.e., a molecular cloud). Consequently, dark bursts probably occur in molecular clouds, in which case dark bursts are probably a byproduct of this burst of star formation if the molecular cloud formed recently, and/or the result of lingering or latter generation star formation if the molecular cloud formed some time ago. We then show that if bursts occur in Galactic-like molecular clouds, the column densities of which might be universal, the number of dark bursts can be comparable to the number of bursts with detected optical afterglows: This is what is observed, which suggests that the bursts with detected optical afterglows might also occur in molecular clouds. We confirm this by modeling and constraining the distribution of column densities, measured from absorption of the X-ray afterglow, of the bursts with detected optical afterglows: We find that this distribution is consistent with the expectation for bursts that occur in molecular clouds, and is not consistent with the expectation for bursts that occur in diffuse clouds. More...Comment: Accepted to The Astrophysical Journal, 22 pages, 6 figures, LaTe

Determinants of propensity of tertiary agricultural students in Ghana to enter agribusiness as a self-employment venture

The study aimed to identify factors that affect the decision of tertiary agricultural students in Ghana to enter agribusiness as a self-employment venture after graduation. The results showed that tertiary agricultural students in Ghana were predominantly males with little or no farming background. They had a rather moderate propensity to enter self-employed agribusiness. The propensity was based on the perception that agribusiness was beneficial, sustainable, and had a bright future. A significant and positive relationship was found between the propensity to enter self-employed agribusiness and availability of inputs, training received by students and supportive policies. However, a significant and negative relationship was found between students' propensity to enter self-employed agribusiness and the desire for other competing enterprises as well as risks and constraints in agribusiness. The most important determinants of the decision of tertiary level agricultural students to enter into agribusiness were found to be attraction to other businesses such as NGOs, non-agricultural manufacturing industries and banks; training received; perceived constraints; and needs for self- employment in agribusiness. The results indicate that the propensity of agricultural graduates to enter self-employed agribusiness may be increased by (1) making agribusiness attractive by increasing its competitiveness with respect to other enterprises, ( 2) modifying the curricula to make agricultural training at the tertiary level more practical, (3) making it easier to acquire production inputs for agribusiness, and (4) improving the policy environment with supportive policies to minimize risk and constraints in agribusiness.. La recherche était entreprise pour identifier les facteurs qui influencent la decision d'étudiants agricoles du niveau supérieur au Ghana de s'établir dans les agro-industries comme une entreprise de travailleur indépendant après l'obtention du diplôme. Les résultats montraient que les étudiants agricoles de l'enseignement supérieur au Ghana étaient principalement mâles avec peu ou sans expérience d'agriculture. Ils avaient plutôt une propension modérée de s'établir dans l'agro-industrie de travailleur indépendant. Cette propension est fondée sur l'idée que l'agro-industrie est bénéfique, durable et avait un avenir brillant. Un rapport considérable et positif était découvert entre la propension de s'établir dans l'agro-industrie de travailleur indépendant et la disponibilité d'intrants, la formation reçue par les étudiants et les politiques d'appui. Un rapport considérable et négatif était toutefois découvert entre la propension d'étudiants de s'établir dans les agro-industries indépendantes et le désir pour d'autres entreprises en concurrence ainsi que les risques et les contraintes d'agro-industries. Les déterminants les plus importants de la decision d'étudiants agricoles du niveau supérieur de s'établir dans les agro-industries étaient découverts d'être l'attrait aux autres entreprises telles que les ONGs, les industries manufacturières non-agricoles et les banques; la formation reçue; les contraintes remarquées; et les besoins requis pour l'indépendant en agro-industrie. Les résultats indiquent que la propension de licenciés agricoles de s'établir dans l'agro-industrie comme travailleurs indépendants pourrait être augmenté par (1) la transformation d'agro-industrie en la rendant attirante par l'augmentation de sa compétitivité relativement aux autres entreprises, (2) la modification du programme scolaire pour rendre la formation agricole au niveau supérieur plus pratique, (3) la facilitation de l'acquisition de resources de production pour l'agro-industrie, et (4) l'amélioration de l'environnement politique avec les politiques d'appui pour réduire au minimum le risque et les contraintes d'agro-industrie. Ghana Journal of Agricultural Science Vol. 39 (1) 2006: pp. 41-5

Investigating Candidates’ Research Experience Beyond the Thesis: The Peripheral World of the Doctorate

This article focuses on both the process and the results of a recently completed research project that concentrated on what are commonly seen as peripheral aspects of the doctorate; that is, aspects of candidature that lie beyond, and outside of, the core work of what is widely understood to be research training. The project saw 18 candidates from the creative arts and humanities – and creative writing in particular – gather to reflect upon their learning journeys, and then analyse and theorise the ‘human’ dimensions of undertaking a doctorate. These often peripheral aspects were revealed to have a major influence on undertaking a research degree, as well as affecting candidates’ progress and satisfaction with their studies, and career potential beyond the research degree. This article first outlines how candidates were able to develop a language with which to identify some of the major human dimensions – the lived experience – of undertaking a doctorate that emerged from the project. It then explores how candidates were able to articulate their own growth in the form of producing an edited collection of essays in order that others might benefit from this reflective learning

Uncertainties in determining parton distributions at large x

We critically examine uncertainties in parton distribution functions (PDFs) at large x arising from nuclear effects in deuterium F2 structure function data. Within a global PDF analysis, we assess the impact on the PDFs from uncertainties in the deuteron wave function at short distances and nucleon off-shell effects, the use of relativistic kinematics, as well as the use of less a restrictive parametrization of the d/u ratio. We find that in particular the d-quark and gluon PDFs vary significantly with the choice of nuclear model. We highlight the impact of these uncertainties on the determination of the neutron structure function, and on W boson production and parton luminosity at the Tevatron and the LHC. Finally, we discuss prospects for new measurements sensitive to the d-quark and gluon distributions but insensitive to nuclear corrections.Comment: 37 pages, 13 figures. Final published versio

The X-ray afterglow of the Gamma-ray burst of May 8, 1997: spectral variability and possible evidence of an iron line

We report the possible detection (99.3% of statistical significance) of redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst GRB970508 observed by BeppoSAX. Its energy is consistent with the redshift of the putative host galaxy determined from optical spectroscopy. The line disappeared about 1 day after the burst. We have also analyzed the spectral variability during the outburst event that characterizes the X-ray afterglow of this GRB. The spectrum gets harder during the flare, turning to steep when the flux decreases. The variability, intensity and width of the line indicate that the emitting region should have a mass approximately greater than 0.5 solar masses (assuming the iron abundance similar to its solar value), a size of about 3 times 10^15 cm, be distributed anisotropically, and be moving with sub-relativistic speed. In contrast to the fairly clean environment expected in the merging of two neutron stars, the observed line properties would imply that the site of the burst is embedded in a large mass of material, consistent with pre-explosion ejecta of a very massive star. This material could be related with the outburst observed in the afterglow 1 day after the GRB and with the spectral variations measured during this phase.Comment: To appear in The Astrophysical Journal Letters, AASTEX LateX, 2 PostScript figure

Improved Rheometry of Yield Stress Fluids Using Bespoke Fractal 3D Printed Vanes

To enable robust rheological measurements of the properties of yield stress fluids, we introduce a class of modified vane fixtures with fractal-like cross-sectional structures. A greater number of outer contact edges leads to increased kinematic homogeneity at the point of yielding and beyond. The vanes are 3D printed using a desktop stereolithography machine, making them inexpensive (disposable), chemically-compatible with a wide range of solvents, and readily adaptable as a base for further design innovations. To complete the tooling set, we introduce a textured 3D printed cup, which attaches to a standard rheometer base. We discuss general design criteria for 3D printed rheometer vanes, including consideration of sample volume displaced by the vanes, stress homogeneity, and secondary flows that constrain the parameter space of potential designs. We also develop a conversion from machine torque to material shear stress for vanes with an arbitrary number of arms. We compare a family of vane designs by measuring the viscosity of Newtonian calibration oils with error <5% relative to reference measurements made with a cone-and-plate geometry. We measure the flow curve of a simple Carbopol yield stress fluid, and show that a 24-arm 3D printed fractal vane agrees within 1% of reference measurements made with a roughened cone-and-plate geometry. Last, we demonstrate use of the 24-arm fractal vane to probe the thixo-elasto-visco-plastic (TEVP) response of a Carbopol-based hair gel, a jammed emulsion (mayonnaise), and a strongly alkaline carbon black-based battery slurry

Cost-effectiveness of a potential vaccine for Coccidioides immitis.

Coccidioidomycosis, a systemic fungal infection, affects Americans living in the Southwest. We evaluated the cost- effectiveness of a potential vaccine against Coccidioides immitis. Using a decision model we developed, we estimate that among children, vaccination would saved 1.9 quality-adjusted life days (QALD) and $33 per person. Among adults, screening followed by vaccination would save 0.5 QALD per person and cost$62,000 per quality adjusted life year gained over no vaccination. If the birth cohort in highly endemic counties of California and Arizona were immunized in 2001, 11 deaths would be averted and $3 million would be saved (in net present value) over the lifetime of these infants. Vaccination of adults to prevent disseminated coccidioidomycosis would provide a modest health benefit similar in magnitude to other vaccines but would increase net expenditures. Vaccination of children in highly endemic regions would provide a larger health benefit and would reduce total health care expenditures