5,486 research outputs found

    Manifestly Haraway by Donna J. Haraway

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    Review of Donna J. Haraway\u27s Manifestly Haraway

    A New Index for Predicting Catastrophes by Madhur Anand

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    A Review of Madhur Anand\u27s A New Index for Predicting Catastrophes

    Abrupt Longitudinal Magnetic Field Changes and Ultraviolet Emissions Accompanying Solar Flares

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    We have used Transition Region and Coronal Explorer (TRACE) 1600 \AA images and Global Oscillation Network Group (GONG) magnetograms to compare ultraviolet (UV) emissions from the chromosphere to longitudinal magnetic field changes in the photosphere during four X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred across more than ten pixels in the GONG magnetograms for each flare. These magnetic changes lagged the GOES flare start times in all cases, showing that they were consequences and not causes of the flares. Ultraviolet emissions were spatially coincident with the field changes. The UV emissions tended to lag the GOES start times for the flares, and led the changes in the magnetic field in all pixels except one. The UV emissions led the photospheric field changes by 4 minutes on average with the longest lead being 9 minutes, however, the UV emissions continued for tens of minutes, and more than an hour in some cases, after the field changes were complete. The observations are consistent with the picture in which an Alfv\'{e}n wave from the field reconnection site in the corona propagates field changes outward in all directions near the onset of the impulsive phase, including downwards through the chromosphere and into the photosphere, causing the photospheric field changes, whereas the chromosphere emits in the UV in the form of flare kernels, ribbons and sequential chromospheric brightenings during all phases of the flare

    Theoretical models of free-free microwave emission from solar magnetic loops

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    The free-free microwave emission is calculated from a series of model magnetic loops. The loops are surrounded by a cooler external plasma, as required by recent simultaneous X ray and microwave observations, and a narrow transition zone separating the loops from the external plasma. To be consistent with the observational results, upper limits on the density and temperature scale lengths in the transition zone are found to be 360 km and 250 km, respectively. The models which best produce agreement with X ray and microwave observations also yielded emission measure curves which agree well with observational emission measure curves for solar active regions

    The collisional relaxation of electrons in hot flaring plasma and inferring the properties of solar flare accelerated electrons from X-ray observations

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    X-ray observations are a direct diagnostic of fast electrons produced in solar flares, energized during the energy release process and directed towards the Sun. Since the properties of accelerated electrons can be substantially changed during their transport and interaction with the background plasma, a model must ultimately be applied to X-ray observations in order to understand the mechanism responsible for their acceleration. A cold thick target model is ubiquitously used for this task, since it provides a simple analytic relationship between the accelerated electron spectrum and the emitting electron spectrum in the X-ray source, with the latter quantity readily obtained from X-ray observations. However, such a model is inappropriate for the majority of solar flares in which the electrons propagate in a hot megaKelvin plasma, because it does not take into account the physics of thermalization of fast electrons. The use of a more realistic model, properly accounting for the properties of the background plasma, and the collisional diffusion and thermalization of electrons, can alleviate or even remove many of the traditional problems associated with the cold thick target model and the deduction of the accelerated electron spectrum from X-ray spectroscopy, such as the number problem and the need to impose an ad hoc low energy cut-off.Comment: 6 pages, 14th Annual International Astrophysics Conference Tampa proceeding

    Why Is There Corporate Taxation In a Small Open Economy? The Role of Transfer Pricing and Income Shifting

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    Several recent papers argue that corporate income taxes should not be used by small, open economies. With capital mobility, the burden of the tax falls on fixed factors (e.g., labor), and the tax system is more efficient if labor is taxed directly. However, corporate taxes not only exist but rates are roughly comparable with the top personal tax rates. Past models also forecast that multinationals should not invest in countries with low corporate tax rates, since the surtax they owe when profits are repatriated puts them at a competitive disadvantage. Yet such foreign direct investment is substantial. We suggest that the resolution of these puzzles may be found in the role of income shifting, both domestic (between the personal and corporate tax bases) and cross-border (through transfer pricing). Countries need cash-flow corporate taxes as a backstop to labor taxes to discourage individuals from converting their labor income into otherwise untaxed corporate income. We explore how these taxes can best be modified to deal as well with cross-border shifting.
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