Is the ‘superhot’ hard x-ray component in solar flares consistent with a thermal source?     

A. Gordon Emslie  Victoria Newman Coffey  Richard A. Schwartz 《Solar physics》1989,122(2):313-317

It has been shown by Brown and Emslie (1988) that any optically thin thermal bremsstrahlung source must emit an energy spectrumL () (keV s^–1 keV^–1) which has the property that higher derivatives alternate in sign, i.e., (–) ^j L(^j)() > 0 for allj. In this short note, we apply this test to the superhot component discussed by Linet al. (1981) in order to determine whether a strictly thermal interpretation of this component is valid. We find that all statistically significant higher derivatives do indeed have the correct sign; this strengthens the identification of this component as due to a thermal source.Presidential Young Investigator.  相似文献   

The GeoForschungsZentrum Potsdam/Groupe de Recherche de Gèodésie Spatiale satellite-only and combined gravity field models: EIGEN-GL04S1 and EIGEN-GL04C   总被引：2，自引：1，他引：1  

Christoph Förste  Roland Schmidt  Richard Stubenvoll  Frank Flechtner  Ulrich Meyer  Rolf König  Hans Neumayer  Richard Biancale  Jean-Michel Lemoine  Sean Bruinsma  Sylvain Loyer  Franz Barthelmes  Saskia Esselborn 《Journal of Geodesy》2008,82(6):331-346

The recent improvements in the Gravity Recovery And Climate Experiment (GRACE) tracking data processing at GeoForschungsZentrum Potsdam (GFZ) and Groupe de Recherche de Géodésie Spatiale (GRGS) Toulouse, the availability of newer surface gravity data sets in the Arctic, Antarctica and North-America, and the availability of a new mean sea surface height model from altimetry processing at GFZ gave rise to the generation of two new global gravity field models. The first, EIGEN-GL04S1, a satellite-only model complete to degree and order 150 in terms of spherical harmonics, was derived by combination of the latest GFZ Potsdam GRACE-only (EIGEN-GRACE04S) and GRGS Toulouse GRACE/LAGEOS (EIGEN-GL04S) mean field solutions. The second, EIGEN-GL04S1 was combined with surface gravity data from altimetry over the oceans and gravimetry over the continents to derive a new high-resolution global gravity field model called EIGEN-GL04C. This model is complete to degree and order 360 and thus resolves geoid and gravity anomalies at half- wavelengths of 55 km at the equator. A degree-dependent combination method has been applied in order to preserve the high accuracy from the GRACE satellite data in the lower frequency band of the geopotential and to form a smooth transition to the high-frequency information coming from the surface data. Compared to pre-CHAMP global high-resolution models, the accuracy was improved at a spatial resolution of 200 km (half-wavelength) by one order of magnitude to 3 cm in terms of geoid heights. The accuracy of this model (i.e. the commission error) at its full spatial resolution is estimated to be 15 cm. The model shows a reduced artificial meridional striping and an increased correlation of EIGEN-GL04C-derived geostrophic meridional currents with World Ocean Atlas 2001 (WOA01) data. These improvements have led to select EIGEN-GL04C for JASON-1 satellite altimeter data reprocessing. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Mirdita Zone ophiolites and associated sediments in Albania reveal Neotethys Ocean origin   总被引：1，自引：1，他引：0  

Hans-Jürgen Gawlick  Wolfgang Frisch  Lirim Hoxha  Paulian Dumitrica  Leopold Krystyn  Richard Lein  Sigrid Missoni  Felix Schlagintweit 《International Journal of Earth Sciences》2008,97(4):865-881

The Mirdita Ophiolite Zone in Albania is associated with widespread mélanges containing components of up to nappe-size. We dated matrix and components of the mélange by radiolarians, conodonts, and other taxa. The components consist of radiolarites, pelagic limestones and shallow-water limestones, all of Triassic age, as well as ophiolites. Triassic radiolarite as a primary cover of ophiolite material proves Middle Triassic onset of Mirdita ocean-floor formation. The mélange contains a turbiditic radiolarite-rich matrix (“radiolaritic flysch”), dated as Late Bajocian to Early Oxfordian. It formed as a synorogenic sediment during west-directed thrusting of ophiolite and sediment-cover nappes representing ocean floor and underplated fragments of the western continental margin. The tectonic structures formed during these orogenic events (“Younger Kimmeridian or Eohellenic Orogeny”) are sealed by Late Jurassic platform carbonates. The geological history conforms with that of the Inner Dinarides and adjoining areas; we therefore correlate the Mirdita-Pindos Ophiolite Zone with the Vardar Zone and explain its present position by far-distance west-directed thrusting.  相似文献   

Distribution and Trophic Importance of Anthropogenic Nitrogen in Narragansett Bay: An Assessment Using Stable Isotopes     

Autumn Oczkowski  Scott Nixon  Kelly Henry  Peter DiMilla  Michael Pilson  Stephen Granger  Betty Buckley  Carol Thornber  Richard McKinney  Joaquin Chaves 《Estuaries and Coasts》2008,31(1):53-69

Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary (macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ¹⁵N) and carbon (δ¹³C). The δ¹⁵N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source loading. There is also evidence of a west to east gradient of heavy to light values of δ¹⁵N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ¹⁵N values in macroalgae there reflected preferential uptake of ¹⁴N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of dissolved C species may control the observed δ¹³C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ¹⁵N (13.2 ± 0.54‰ SD) and δ¹³C (−16.76 ± 0.61‰ SD) throughout the bay, and the δ¹⁵N values were 2–5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources.  相似文献   

Microlites and "nanolites" in rhyolitic glass: microstructural and chemical characterization     

Thomas G. Sharp  Richard J. Stevenson  Donald B. Dingwell 《Bulletin of Volcanology》1996,57(8):631-640

 We used transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to study magmatic crystals in the Ben Lomond rhyolite lava dome, Taupo Volcanic Center, New Zealand. Using TEM and SEM to investigate the size distributions of these crystals, we identified three size populations: microphenocrysts (>1.2 μm wide), microlites (>0.6 μm wide), and smaller crystals (<0.6 μm wide) which we term "nanolites". The predominant mineral phases of the microlites and nanolites are augites, pigeonites, and hypersthenes. The compositions and microstructures within these pyroxenes indicate disequilibrium crystallization at approximately 850–900  °C and undercoolings as high as 300  °C from equilibrium crystallization temperatures. Complex microstructures resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian layer of the Ben Lomond rhyolite dome. This study demonstrates the existence of sub-micron magmatic crystals in a rhyolite and illustrates the potential of TEM to provide unique information about the crystallization and cooling histories of glassy volcanic rocks. Received: May 8, 1995 / Accepted: November 27, 1995  相似文献   

A model of an exploding,radiating star in general relativity     

Richard C. Adams  Jeffrey M. Cohen  John C. Peterson 《Astrophysics and Space Science》1996,236(2):229-256

In a previous paper Adams, Cary and Cohen (1994) presented a model of a supernova. In that paper the equations of General Relativity describing the evolution of a spherically symmetric, radiating star were solved analytically. The evolution of the star was determined by the application of boundary conditions at the center and at the edge. Due to lmitations in the presupernova model, only the very slow inward motion of an unstable, degenerate core could be considered. The solution was also limited by the need to exclude a runaway term, one that increased exponentially with time. Without the exclusion of the runaway, the luminosity would have increased without bound and the mass would have become negative.This paper presents a completely analytic solution to the equations of General Relativity describing the evolution of a Type II supernova. Professor S.E. Woosley kindly gave us data on the physical variables of a 12M ₀ presupernova star. In our model the core collapses within 1 s, leaving a 1.3M ₀ remnant. Shortly afterward 10.6M ₀ is ejected to infinity, and 0.17M ₀ is radiated away in the form of neutrinos. The distance of the edge from the center increases proportionally to the two-thirds power of the time. The luminosity decreases proportionally to the inverse four-thirds power.Although the runaway solution was modified by the exploding rather than a static envelope, it must still be excluded by adjusting initial conditions. Its character is changed from an exponential to a very large power (55) of time. The removal of a degree of freedom by this exclusion leads to physically non-sensical results such as negative luminosity. The inclusion of a term describing motion of the mantle due to neutrino interactions provides the additional degree of freedom necessary for physically reasonable results.  相似文献   

White-light enhancements and small-scale chromospheric activities in an active region     

Reizaburo Kitai  Richard Muller 《Solar physics》1996,165(1):155-167

A microflare or a group of Ellerman bombs was found to be associated with several points of white-light enhancements. These points had similar sizes as facular points (d 0.3 arc sec). Temporal evolution of these activities is described. Origins of these activities are discussed to be deeply seated excess heating in chromospheric and photospheric levels.  相似文献   

Lidar observations of turbulent vortex shedding by an isolated topographic feature     

William P. Hooper  Jeffrey E. James  Richard J. Lind 《Boundary-Layer Meteorology》1996,80(1-2):95-108

Scanning measurements by a single wavelength lidar (1.06 m) were made downwind of the Pt. Sur rock, an isolated hill (height 110 m) along the California coast. Turbulent eddies (approximate diameter 50 m) were observed detaching from a stationary aerosol feature above the rock and moving downwind. Under conditions with a high Froude number [1.8], the Strouhal number [0.22] of vortex shedding was close to that observed in tank experiments with a Reynolds number of 200.  相似文献   

On solving Kepler's equation for nearly parabolic orbits     

Richard A. Serafin 《Celestial Mechanics and Dynamical Astronomy》1996,65(4):389-398

We deal here with the efficient starting points for Kepler's equation in the special case of nearly parabolic orbits. Our approach provides with very simple formulas that allow calculating these points on a scientific vest-pocket calculator. Moreover, srtarting with these points in the Newton's method we can calculate a root of Kepler's equation with an accuracy greater than 0.001 in 0–2 iterations. This accuracy holds for the true anomaly || 135° and |e – 1| 0.01. We explain the reason for this effect also.Dedicated to the memory of Professor G.N. Duboshin (1903–1986).  相似文献   

Pore pressure profiles in fractured and compliant rocks1     

zdoan Yilmaz  Richard C. Nolen-Hoeksema  Amos Nur 《Geophysical Prospecting》1994,42(6):693-714

Fluid permeability in fractured rocks is sensitive to pore-pressure changes. This dependence can have large effects on the flow of fluids through rocks. We define the permeability compliance γ= 1/k(k/δp_p)_pc, which is the sensitivity of the permeability k to the pore pressure p_p at a constant confining pressure p_c, and solve the specific problems of constant pressure at the boundary of a half-space, a cylindrical cavity and a spherical cavity. The results show that when the magnitude of permeability compliance is large relative to other compliances, diffusion is masked by a piston-like pressure profile. We expect this phenomenon to occur in highly fractured and compliant rock systems where γ may be large. The pressure profile moves rapidly when fluids are pumped into the rock and very slowly when fluids are pumped out. Consequently, fluid pressure, its history and distribution around injection and production wells may be significantly different from pressures predicted by the linear diffusion equation. The propagation speed of the pressure profile, marked by the point where δp_p/δx is a maximum, decreases with time approximately as and the amplitude of the profile also dissipates with time (or distance). The effect of permeability compliance can be important for fluid injection into and withdrawal from reservoirs. For example, excessive drawdown could cause near-wellbore flow suffocation. Also, estimates of the storage capacity of reservoirs may be greatly modified when γ is large. The large near-wellbore pressure gradients caused during withdrawal by large γ can cause sanding and wellbore collapse due to excessive production rates.  相似文献