Convective Instability Of The Solar Corona: Why The Solar Wind Blows

Chapman's (1957) conductive model of the solar corona is characterized by a temperature varying as r**(-2/7) with heliocentric distance r. The density distribution in this non-isothermal hydrostatic model has a minimum value at 123 RS, and increases with r above that altitude. It is shown that this hydrostatic model becomes convectively unstable above r = 35 RS, where the temperature lapse rate becomes superadiabatic. Beyond this radial distance heat conduction fails to be efficient enough to keep the temperature gradient smaller than the adiabatic lapse rate. We report the results obtained by Lemaire (1968) who showed that an additional mechanism is then required to transport the energy flux away from the Sun into interplanetary space. He pointed out that this additional mechanism is advection: i.e. the stationary hydrodynamic expansion of the corona. In other words the corona is unable to stay in hydrostatic equilibrium. The hydrodynamic solar wind expansion is thus a physical consequence of the too steep (superadiabatic) temperature gradient beyond the peak of coronal temperature that can be determined from white light brightness distributions observed during solar eclipses. The thermodynamic argument for the existence of a continuous solar wind expansion which is presented here, complements Parker's classical argument based on boundary conditions imposed to the solutions of the hydrodynamic equations for the coronal expansion: i.e. the inability of the mechanical forces to hold the corona in hydrostatic equilibrium. The thermodynamic argument presented here is based on the energy transport equation. It relies on the temperature distribution which becomes super-adiabatic above a certain altitude in the inner corona.Comment: 4 pages, 3 figures, presented at SW12 conference (2009); Copyright 2010 American Institute of Physics 978-0-7354-0759-6/10. This article may be downloaded for personal use only. The following article appeared in CP1216 and may be found at http://proceedings.aip.or

Half a Century of Kinetic Solar Wind Models

I outline the development of four generations of kinetic models, starting with Chamberlain's solar breeze exospheric model. It is shown why this first kinetic model did not give apposite supersonic evaporation velocities, like early hydrodynamic models of the solar wind. When a self-consistent polarization electric potential distribution is used in the coronal plasma, instead of the Pannekoek-Rosseland's one, supersonic bulk velocities are readily obtained in the second generation of kinetic models. It is outlined how the third and fourth generations of these models have improved the agreement with observations of slow and fast speed solar wind streams.Comment: 10 pages, 3 figures, presented at SW12 conf. ; Copyright (2010 AIP 978-0-7354-0759-6/10) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics The following article appeared in (CP1216) and may be found at (http://proceedings.aip.org

Radial Distributions of Coronal Electron Temperatures: specificities of the DYN model

This paper is a follow up of the article where Lemaire and Stegen (2016) introduced their DYN method to calculate coronal temperature profiles from given radial distributions of the coronal and solar wind (SW) electron densities. Several such temperature profiles are calculated and presented corresponding to a set of given empirical density models derived from eclipse observations and in-situ measurements of the electron density and bulk velocity at 1 AU. The DYN temperature profiles obtained for the equatorial and polar regions of the corona challenge the results deduced since 1958 from singular hydrodynamical models of the SW. In these models - where the expansion velocity transits through a singular saddle point - the maximum coronal temperature is predicted to be located at the base of the corona, while in all DYN models the altitude of the maximum temperature is found at significantly higher altitudes in the mid-corona. Furthermore, the maximum of the DYN-estimated temperatures is found at much higher altitudes over the polar regions and coronal holes, than over the equator. However, at low altitudes, in the inner corona, the DYN temperatures are always smaller at high latitudes, than at low equatorial latitudes. This appears well in agreement with existing coronal hole observations. These findings have serious implications on the open questions: what is the actual source of the coronal heating, and where is the maximum energy deposited within the solar corona?Comment: 13 pages, 3 figures. Submitted to the Solar Physics journa

Magnetic Behavior Of Rare-earth Iron-rich Intermetallic Compounds

The thermal variation of lattice parameters of rare earth-transition metal intermetallic compounds rich in Fe, Co, or Ni in the temperature range of 25-900oK is studied. For the Fe compounds, negative thermal expansion is observed below their magnetic ordering temperatures regardless of the nature of substitutional ordering. For Co and Ni compounds, the thermal expansion behavior is normal. It is then concluded that for the Fe compounds, the magnetic properties are mainly determined by the Fe-Fe interatomic distances and the number of Fe nearest neighbors, whereas for Co and Ni compounds the magnetic properties are determined by the conduction electron transfer from the rare earth to the 3 d band of Co or Ni, The anomalous thermal expansion of Fe compounds and the metamagnetic transition of the Lu compound is explained in terms of the distance dependence. of the interaction energy as proposed by Neel. © 1971, IEEE. All rights reserved

Outcomes of concomitant aortic valve replacement and coronary artery bypass grafting at teaching hospitals versus nonteaching hospitals

ObjectiveHospitals with a high volume and academic status produce better patient outcomes than other hospitals after complex surgical procedures. Risk models show that concomitant aortic valve replacement and coronary artery bypass grafting pose a greater risk than isolated coronary artery bypass grafting or aortic valve replacement. We examined the relationship of hospital teaching status and the presence of a thoracic surgery residency program with aortic valve replacement/coronary artery bypass grafting outcomes.MethodsBy using the Nationwide Inpatient Sample database, we identified patients who underwent concomitant aortic valve replacement/coronary artery bypass grafting from 1998 to 2007 at nonteaching hospitals, teaching hospitals without a thoracic surgery residency program, and teaching hospitals with a thoracic surgery residency program. Multivariate analysis was performed to identify intergroup differences. Risk-adjusted multivariable logistic regression analysis was used to assess independent predictors of in-hospital mortality and complication rates.ResultsThe 3 groups of patients did not differ significantly in their baseline characteristics. Patients who underwent aortic valve replacement/coronary artery bypass grafting had higher overall risk-adjusted complication rates in nonteaching hospitals (odds ratio 1.58; 95% confidence interval, 1.39–1.80; P < .0001) and teaching hospitals without a thoracic surgery residency program (odds ratio 1.42; 95% confidence interval, 1.26–1.60; P < .0001) than in thoracic surgery residency program hospitals. However, no difference was observed in the adjusted mortality rate for nonteaching hospitals (odds ratio 0.95; 95% confidence interval, 0.87–1.04; P = .25) or teaching hospitals without a thoracic surgery residency program (odds ratio 1.00; 95% confidence interval, 0.92–1.08; P = .98) when compared with thoracic surgery residency program hospitals. Robust statistical models were used for analysis, with c-statistics of 0.98 (complications) and 0.82 (mortality).ConclusionPatients who require complex cardiac operations may have better outcomes when treated at teaching hospitals with a thoracic surgery residency program

Endovascular repair of thoracic aortic pseudoaneurysms and patch aneurysms

Pseudoaneurysms and patch aneurysms are life-threatening late complications after thoracoabdominal aortic aneurysm (TAAA) repair. We treated four patients who presented with a pseudoaneurysm or patch aneurysm involving the descending thoracic portion of a previously implanted TAAA graft. In each patient, stent grafts were placed within the existing graft to cover the aneurysm endoluminally. All patients recovered without major complications, and computed tomography performed after a mean follow-up of 51.5 ± 19.7 months showed that the repairs remained intact

Magnetic Structure Investigations at the Nuclear Center

The magnetic structure of the compounds UOS, ß-CoSO4, YCO5, and HoCO5 is briefly described. UOS is antiferromagnetic. The Néel temperature is Tn=55°K. The magnetic cell is doubled in the c direction with a ++ - - sequence of U moments along c. The apparent spin is S∼1. The negative interaction corresponds to U-O-U links. In ß-CoSO4 (high-temperature modification, space group Pbnm), Co atoms are in 000, 00½, ½½½, ½½0. Here three different antiferromagnetic spin modes, mutually perpendicular, Ax(+ - - +), Gy(+-+-), and Cz(++ - - ), in the Wollan-Koehler notation, are coupled. Direction cosines are 0.71, 0.50, and 0.50, respectively. The Co moment is about 3,84 µB at 4.2°K. A field-induced spin flip to the configuration Fx, Cy, Gz is predicted. YCO5 is ferromagnetic at room temperature with a moment value of Co practically equal to that of metallic Co and moment direction along c, which is conserved down to 4.2°K. In HoCO5 the moment of Ho is opposite to those of the Co atoms. When cooling from room to liquid helium temperature, the direction of easy magnetization changes from near c to a direction in the basal plane and the Ho moment increases from 4 to about 9 µB. The compensation temperature is 70°K

Endovascular versus open repair of ruptured descending thoracic aortic aneurysms: A nationwide risk-adjusted study of 923 patients

ObjectiveRecent studies support the use of endovascular treatment for ruptured abdominal aortic aneurysms, but few studies have examined the use of thoracic endovascular aortic repair (TEVAR) for ruptured descending thoracic aortic aneurysm. We evaluated nationwide data regarding short-term outcomes of TEVAR and open aortic repair (OAR) for ruptured descending thoracic aortic aneurysm.MethodsFrom US Nationwide Inpatient Sample data, we identified 923 patients who underwent ruptured descending thoracic aortic aneurysm repair in 2006–2008 and who had no concomitant aortic disorders. Of these patients, 364 (39.4%) underwent TEVAR and 559 (60.6%) underwent OAR. Multivariable regression was used to assess the effect of TEVAR versus OAR after adjusting for potential confounding factors. Outcomes assessed were in-hospital mortality, complications, failure to rescue (defined as the mortality among patients in whom a complication develops), and disposition. Backward stepwise logistic regression was used to identify independent predictors of outcomes for each approach.ResultsPatients undergoing TEVAR were older (72 ± 12 years vs 65 ± 15 years; P < .001) and had a higher Deyo comorbidity index (4.19 ± 1.79 vs 3.14 ± 2.05; P < .001) than patients undergoing OAR. Unadjusted mortality was 23.4% (85/364) for TEVAR and 28.6% (160/559) for OAR. After risk adjustment, the odds of mortality, complications, and failure to rescue were similar for TEVAR and OAR (P > .1 for all), but patients undergoing TEVAR had a greater chance of routine discharge (odds ratio [OR] = 3.3; P < .001). An interaction was identified that linked hospital size and operative approach with risk of complications (P < .001). In smaller hospitals, TEVAR was associated with lower complication rates than OAR (OR = 0.21; P < .05). Regression analysis revealed that smaller hospital size predicted significantly higher rates of mortality (OR = 2.4; P < .05), complications (OR = 4.0; P < .005), and failure to rescue (OR = 51.12; P < .001) in those undergoing OAR but not in those undergoing TEVAR. Preexisting renal disorders substantially increased mortality risk (OR = 10.81; P < .001) and failure to rescue (OR = 309.54; P < .001) in patients undergoing TEVAR.ConclusionsNationwide data for ruptured descending thoracic aortic aneurysm reveal equivalent mortality, complication rates, and failure to rescue for TEVAR and OAR but more frequent routine discharge with TEVAR. Unlike OAR outcomes, TEVAR outcomes were not poorer in smaller hospitals, where TEVAR produced fewer complications than OAR. Therefore, TEVAR may be an ideal alternative to OAR for ruptured descending thoracic aortic aneurysm, particularly in small hospitals where expertise in OAR may be lacking and immediate transfer to a higher echelon of care may not be feasible