Deriving Star Formation Histories: Evolutionary or Population Synthesis Codes versus Color-Magnitude Diagrams     

Danielle Alloin  Carme Gallart  Emmanuel Fleurence  Emanuela Pompei  Daniel Raimann  Uta Fritze- Von Alvensleben  Sukyoung Yi 《Astrophysics and Space Science》2002,281(1-2):109-113

The goal of this project is to analyze the integrated-light spectrum of a region in the LMC bar, for which HST images are already available yielding color-magnitude diagrams reaching the oldest main-sequence turnoff. Then, we can derive the star formation history in this field through evolutionary/population synthesis of the integrated light from 330 to 990 nm by a variety of independent methods and compare the results with the - in principle - more reliable results derived from the analysis of the color-magnitude diagram (CMD). This confrontation is the key ‘truth-test’ needed for the understanding of the abilities and the limitations of the evolutionary/population synthesis methods that must be applied of necessity to unresolved nearby and far-away galaxies. We report here on the observational part of the project. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Chemostatanlage zur kontinuierlichen Kultur von Algen   总被引：1，自引：0，他引：1  

Max Von Hirsburnner 《Aquatic Sciences - Research Across Boundaries》1981,43(2):370-376

The apparatus described was assembled using relatively inexpensive parts and makes the cultivation of various forms of algae under steady-state conditions and different flowrates (variation under 0.5%) possible. There was no difference in the biodensity in the reactor compared to that in the outflow.  相似文献   

W-shaped occultation signatures: Inference of entwined particle orbits in charged planetary ringlets     

Von R. Eshleman  John V. Breakwell  G. Leonard Tyler  Essam A. Marouf 《Icarus》1983,54(2):212-226

Observed W-shaped occultation signatures of certain narrow ringlets in the ring systems of Saturn and Uranus imply a concentration of material near their inner and outer radial edges. A model is proposed where edge bunching is a natural consequence of particles in entwined elliptical orbits, with the same particles alternately defining both edges. While such orbits cross over in radius, collisions would not occur if they have small inclinations, the same fixed argument of periapse ω, and other parameters whereby the particles would “fly in formation” along compressed helical paths relative to the core of the ringlet, which is taken to be a circle in the equatorial plane. For this model to match the observed ring thickness and ringlet widths, orbit inclinations i must be much smaller than their eccentricities e, which themselves would be very small compared to unity. Thus, the meridional cross section of the resultant torus would be a very thin ellipse of thickness proportional to i∣cos ω∣, tilted slightly from the equatorial plane by (i/e)∣sin ω∣ radians. However, gravitational perturbations due to the oblateness of the planet would cause a secular change in ω so that this cross section would collapse periodically to a tilted line, and collisions would then occur. If this collapse could be prevented, the torus could remain in a continuous state of nearly zero viscosity. Stabilization against collapse appears possible due to several remarkable characteristics that are added to the model when the particles are electrically charged. First, because of inherent features of the torus structure, a weak electric force could counter the key effect of the vastly larger oblateness force. Second, because the electric perturbation also affects i, there is a large region in ω,i space where stability against cross-sectional collapse is automatic. For this region, the thickness of the elliptical cross section would expand and contract in concert with the way that the major axis of the ellipse rocks back and forth relative to the equatorial plane. The period of these “rocking and breathing” changes would be from 1 to 3 weeks for a torus in the C ring of Saturn, for example. The electric effects could change considerably without driving the parameters of the torus from the stable domain where cross-sectional collapse does not occur. While specialized and in several important ways still incomplete, the proposed model could account for the W-shaped patterns and explain how very dense ringlets might endure without energy loss due to collisions. It also appears to be capable of explaining the observed sorting of particles by size within a ringlet. Several characteristics of the model suggest definitive tests of its applicability, including its prediction that a nonsymmetrical W-shaped occultation signature could be reversed a half orbit away, and that grazing solar illumination of tilted ringlets might cast shadows that change with time in a prescribed way.  相似文献   

High Resolution Solar Speckle Imaging With the Extended Knox–Thompson Algorithm     

K. Mikurda  O. Von Der Lühe 《Solar physics》2006,235(1-2):31-53

We present an implementation of the extended Knox-Thompson (EKT) speckle reconstruction algorithm dedicated to solar observations. EKT speckle imaging yields nearly diffraction-limited images from bursts of short exposure solar observations under a wide range of seeing conditions. Our implementation supports field dependent amplitude calibration to permit analyzing data obtained with a partially compensating adaptive optics systems. The principles of the method and some technical details of our implementation are discussed. We have performed various tests using simulated data of representative solar scenes. The simulations include the effects of seeing and noise with the exception of anisoplanatism. The expected photometric error of a reconstructed image amounts to a few percent of the mean intensity under seeing conditions ranging from poor to excellent. We also present sample reconstructions of real data and discuss issues arising from anisoplanatism.  相似文献   

Chlorine in the stratosphere     

T. Von Clarmann 《Atmósfera》2013,26(3):415-458

This paper reviews the various aspects of chlorine compounds in the stratosphere, both their roles as reactants and as tracers of dynamical processes. In the stratosphere, reactive chlorine is released from chlorofluorocarbons and other chlorine-containing organic source gases. To a large extent reactive chlorine is then sequestered in reservoir species ClONO₂ and HCl. Re-activation of chlorine happens predominantly in polar winter vortices by heterogeneous reaction in combination with sunlight. Catalytic cycles involving Cl, ClO, BrO, Cl₂O₂, ClO₂, and others like NO, NO₂, OH, and HO₂ remove odd oxygen (ozone and atomic oxygen) from the atmosphere. Under an ozone hole condition, the ClO dimer cycle is particularly important, while in mid-latitudes the short-lived reservoir HOC1 has some importance. Solar proton events can also affect stratospheric chlorine chemistry, but whether solar protons effectively activate or deactivate chlorine was shown to depend on illumination conditions. The lifetime of chlorofluorocarbons has an impact on the availability of ozone destructing substances in the stratosphere and depends on the Brewer-Dobson circulation which controls at which altitudes and how long an air parcel is exposed to photochemistry. In turn, the chlorine-containing source gases can be used as tracers to constrain the age of stratospheric air and thus to diagnose the Brewer-Dobson circulation. The use of complementary measurement systems was essential to extend our knowledge on chlorine-containing compounds in the stratosphere. ClO is best measured by remote sensing in its rotational bands in the far infrared and microwave region. For HOC1 the far infrared bands are ideal, but some substantial information was also gained with microwave and mid-infrared measurements. ClONO₂ is only measured in the thermal infrared, while HCl has a measurable signal in the microwave, far infrared and mid-infrared regions. The mid-infrared HCl lines, however, are situated at wavelengths where blackbody emission at terrestrial temperatures is so low that infrared measurements of HCl are possible only in solar absorption geometry, but not in thermal emission. Chlorine source gases are most accurately measured by air sampling techniques, while global coverage can only be achieved by satellite-borne thermal infrared measurements. In epistemological terms, research on stratospheric chemistry and particularly the role of chlorine compounds used various scientific concepts from deductive reasoning, falsificationism, abductive reasoning and so-called “puzzle-solving within normal science”. The structuralist theory of science with the concept of non-statement view of theories, however, seems to be best applicable to stratospheric chlorine research of the recent decades.  相似文献   

Predicting the resilience of transport infrastructure to a natural disaster using Cox’s proportional hazards regression model     

Mojtahedi  Mohammad  Newton  Sidney  Von Meding  Jason 《Natural Hazards》2017,85(2):1119-1133

Transport infrastructure is at significant risk of direct damage from extreme climate events such as flooding, where the cost implications of delayed recovery are generally significant. Previous research in this regard has focused on the technical and engineering aspects of infrastructure construction. The risk management of resilient transport infrastructure is poorly considered, and little has been done to quantify the capacity of transport infrastructure to recover from the impact of natural disasters under varying conditions. This paper applies Cox’s proportional hazards regression model to determine the rate of recovery and cumulative probability that recovery occurs for transport infrastructure across regional areas in New South Wales, Australia. Data for post-disaster reconstruction projects over the period 1992–2012 are used to analyze recovery rate against geographic region, natural disaster type and post-disaster transport infrastructure reconstruction cost. Results demonstrate that transport infrastructure recovered slowest when the failure is the result of a flood rather than bushfire or storm, and in regions with a riverine geography. To validate the accuracy of the model, a bootstrap resampling technique is used. The bootstrap result confirms that the model is robust and reasonable.

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On singularities in electrodynamics and gravitational theory     

H.-H. Von Borzeszkowski  H.-J. Treder  W. Yourgrau 《Astronomische Nachrichten》1979,300(2):57-62

The singularity and particle problems in electrodynamics and gravitational theory are discussed. Comparing different modifications of MAXWELL 's electrodynamics and general theory of relativity, arguments are given which show possibilities of solving these problems by a modification that replaces EINSTEIN 's equations by those of the EINSTEIN -BACH -WEYL -type.  相似文献   

Particle size distributions in Saturn's rings from voyager 1 radio occultation     

Essam A. Marouf  G. Leonard Tyler  Howard A. Zebker  Richard A. Simpson  Von R. Eshleman 《Icarus》1983,54(2):189-211

Observations of microwave opacity τ[λ] and near forward scatter from Saturn's rings at wavelengths λ of 3.6 and 13 cm from the Voyager 1 ring occultation experiment contain information regarding ring particle sizes in the range of about a = 0.01 to 15 m radius. The opacity measurements τ[3.6] and τ[13] are sufficient to constrain the scale factor n(a₀) and index q of a power law incremental size distribution n(a) = n(a₀)[a₀/a]^q, assuming known minimum and maximum sizes and a many-particle-thick model. The families of such distributions are highly convergent in the centimeter-size range. Forward scatter at 3.6 cm can be used to solve for a general distribution over the radius range $\text{1 ? a ? 15}\text{m}$ by integral inversion and inverse scattering methods, again assuming a many-particle-thick slab-type radiative transfer model. Distributions n(a) valid over $\text{0.01 ? a ? 15}\text{m}$ are obtained by combining the results from the two types of measurements above. Mass distributions may be computed directly from n(a). Such distributions, partly measured and partly synthesized, have been obtained for four features in the ring system centered at 1.35, 1.51, 2.01, and 2.12 Saturn radii (R_s). The size and mass distributions both cut off sharply at a ? 4–5 m; the mass distribution peaks over the narrow size range $\text{3 ? a ? 4}\text{m}$ for all four locations. No single power law distribution is consistent with the data over the entire interval $\text{0.01 ? a ? 5}\text{m}$, although a power law-type model is consistent with the data over a limited size range of $\text{0.01 ? a ? 1}\text{m}$, where the indices q = 3.4 and 3.3 are obtained from the slab model for the features located at 1.51 and 2.01 R_s. The fractional contribution of the suprameter particles to the microwave opacity in each feature appears to be about $\text{1}\text{3}\text{,}\text{1}\text{3}\text{,}\text{2}\text{3}\text{,}\text{and}\text{1}$, respectively, with the fraction at 2.12 R_s being the least certain. The cumulative surface mass per unit area obtained for the classical slab model is approximately 11, 16, 41, and 132 g/cm² for the four features, respectively, if the particles are solid H₂O ice. Both the fractional opacity and the mass density estimates represent upper bounds implied by the assumption of a uniformly mixed set of particles in a many-particle-thick vertical profile; lower estimates would result if the rings were assumed to be nearly a monolayer or if the vertical distribution of particles were size dependent.  相似文献   

Coordinated Observations of Comet Hale–Bopp between 32 and 860 GHz     

Wink  J. E.  Altenhoff  W. J.  Bieging  J.  Butler  B.  Butner  H.  Haslam  C.G.T.  Kreysa  E.  Martin  R.  Mauersberger  R.  McMullin  J.  Muders  D.  Peters  W.  Schmidt  J.  Schraml  J. B.  Sievers  A.  Stumpff  P.  Von Kapp-Herr  A.  Thum  C.  Zylka  R. 《Earth, Moon, and Planets》1997,77(3):165-165

Earth, Moon, and Planets - The concept of simultaneous multifrequency continuum observations, successfully tested on Comet Hyakutake, was applied to Comet Hale-Bopp, using the Heinrich Hertz...  相似文献   

Spectral investigation of chromospheric fine structure     

Ulrich Grossmann-Doerth  Marina Von Uexküll 《Solar physics》1971,20(1):31-46

H spectra and effectively simultaneous filtergrams were taken at the Fraunhofer Observatory on Capri with the 35 cm domeless Coudé. The spatial resolution of the 19 best spectra selected for analysis was estimated to be 1–2 arc sec. The comparison of several hundred H line profiles emitted by typical chromospheric structure elements with theoretical prediction yielded strong evidence to suggest that the chromosphere consists of two parts: A lower, rather uniform layer at rest superposed by clouds (condensations of great spatial variability) which constitute the well-known structure pattern of H filtergrams. For most image points the line-of-sight velocity, optical thickness, source function and Doppler broadening of these clouds could be determined. While the values of the latter three quantities were found to be similar to what Beckers (1968) has found for limb spicules the velocity of the bright and of the dark mottles is considerably smaller than to be expected if these features were the spicules as seen on the disk. However, our results do not rule out the possibility that the spicules rise at the centers of rosettes where they are difficult to detect.Mitteilung aus dem Fraunhofer Institut No. 105.  相似文献