A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source

We present a quantitative model of the magnetic energy stored and then released through magnetic reconnection for a flare on 26 Feb 2004. This flare, well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only for a brief, early phase. Throughout the main period of energy release there is a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare loops. Our model describes the heating and compression of such a source by localized, transient magnetic reconnection. It is a three-dimensional generalization of the Petschek model whereby Alfven-speed retraction following reconnection drives supersonic inflows parallel to the field lines, which form shocks heating, compressing, and confining a loop-top plasma plug. The confining inflows provide longer life than a freely-expanding or conductively-cooling plasma of similar size and temperature. Superposition of successive transient episodes of localized reconnection across a current sheet produces an apparently persistent, localized source of high-temperature emission. The temperature of the source decreases smoothly on a time scale consistent with observations, far longer than the cooling time of a single plug. Built from a disordered collection of small plugs, the source need not have the coherent jet-like structure predicted by steady-state reconnection models. This new model predicts temperatures and emission measure consistent with the observations of 26 Feb 2004. Furthermore, the total energy released by the flare is found to be roughly consistent with that predicted by the model. Only a small fraction of the energy released appears in the super-hot source at any one time, but roughly a quarter of the flare energy is thermalized by the reconnection shocks over the course of the flare. All energy is presumed to ultimately appear in the lower-temperature T<20 MK, post-flare loops

Vascular Remodeling in Health and Disease

The term vascular remodeling is commonly used to define the structural changes in blood vessel geometry that occur in response to long-term physiologic alterations in blood flow or in response to vessel wall injury brought about by trauma or underlying cardiovascular diseases.1, 2, 3, 4 The process of remodeling, which begins as an adaptive response to long-term hemodynamic alterations such as elevated shear stress or increased intravascular pressure, may eventually become maladaptive, leading to impaired vascular function. The vascular endothelium, owing to its location lining the lumen of blood vessels, plays a pivotal role in regulation of all aspects of vascular function and homeostasis.5 Thus, not surprisingly, endothelial dysfunction has been recognized as the harbinger of all major cardiovascular diseases such as hypertension, atherosclerosis, and diabetes.6, 7, 8 The endothelium elaborates a variety of substances that influence vascular tone and protect the vessel wall against inflammatory cell adhesion, thrombus formation, and vascular cell proliferation.8, 9, 10 Among the primary biologic mediators emanating from the endothelium is nitric oxide (NO) and the arachidonic acid metabolite prostacyclin [prostaglandin I2 (PGI2)], which exert powerful vasodilatory, antiadhesive, and antiproliferative effects in the vessel wall

Botrypus virginianus

Pteridophyte

Texas Root Rot: If You Can't Kill it, Put it Under Arrest

This item is part of the Arizona Land and People (formerly Progressive Agriculture in Arizona) archive. It was digitized from a physical copy provided by the College of Agriculture and Life Sciences at The University of Arizona. For more information about this periodical, please email CALS Publications at [email protected]

An Implementation of Statistical Default Logic

Abstract. Statistical Default Logic (SDL) is an expansion of classical (i.e., Reiter) default logic that allows us to model common inference patterns found in standard inferential statistics, e.g., hypothesis testing and the estimation of a population‘s mean, variance and proportions. This paper presents an embedding of an important subset of SDL theories, called literal statistical default theories, into stable model semantics. The embedding is designed to compute the signature set of literals that uniquely distinguishes each extension on a statistical default theory at a pre-assigned error-bound probability.

Darwin’s progress and the problem of slavery

Legendary as a ‘genius’ out of time, Charles Darwin is said to have revolutionized our understanding of life on earth by explaining nature-history as the purposeless product of directionless variation naturally selected through a chancy struggle for existence. Yet, whatever may be deduced from his theory of natural selection as understood today, Darwin himself was not bound by any such conclusions. His vision of nature-history, for all its haphazardness, was directional, meliorative and hopeful. In the 1830s he went out of his way to develop privately a subversive theory of human evolution, and he pursued the subject with tenacity for three decades before publishing The descent of man in 1871. Underpinning his research was a belief in racial brotherhood rooted in the greatest moral movement of the age, for the abolition of slavery. Darwin extended the abolitionists’ common-descent image to the rest of life, making not just the races, but all races, kin. Human slavery, however, did not evolve into or out of existence. To Darwin it was a ‘sin’ to ‘expiate’ by moral action, and the Origin of species was written with a view towards undermining slavery’s creationist ideologues, most notably the Harvard professor Louis Agassiz. Intractable slavery collided with Darwin’s post-Christian progressivism in the US Civil War, clouding his hopes for humanity, but the Northern victory in 1865 enabled him to carry ‘the grand idea of God hating sin and loving righteousness’ into The descent of man, where the driving of formerly enslaved races out of existence is naturalized as a byproduct of historical progress in which ‘virtue will be triumphant’ at last