Eclipsing binary Trojan asteroid Patroclus: Thermal inertia from Spitzer observations     

Michael Mueller  Franck Marchis  Joshua P. Emery  Stefano Mottola  Jérome Berthier 《Icarus》2010,205(2):505-515

We present mid-infrared observations of the binary L5-Trojan system (617) Patroclus-Menoetius before, during, and after two shadowing events, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. For the first time, we effectively observe changes in asteroid surface temperature in real time, allowing the thermal inertia to be determined very directly. A new detailed binary thermophysical model is presented which accounts for the system’s known mutual orbit, arbitrary component shapes, and thermal conduction in the presence of eclipses.We obtain two local thermal-inertia values, representative of the respective shadowed areas: and . The average thermal inertia is estimated to be , potentially with significant surface heterogeneity. This first thermal-inertia measurement for a Trojan asteroid indicates a surface covered in fine regolith. Independently, we establish the presence of fine-grained (<a few μm) silicates on the surface, based on emissivity features near 10 and similar to those previously found on other Trojans.We also report V-band observations and report a lightcurve with complete rotational coverage. The lightcurve has a low amplitude of peak-to-peak, implying a roughly spherical shape for both components, and is single-periodic with a period equal to the period of the mutual orbit, indicating that the system is fully synchronized.The diameters of Patroclus and Menoetius are 106±11 and , respectively, in agreement with previous findings. Taken together with the system’s known total mass, this implies a bulk mass density of , significantly below the mass density of L4-Trojan asteroid (624) Hektor and suggesting a bulk composition dominated by water ice.All known physical properties of Patroclus, arguably the best studied Trojan asteroid, are consistent with those expected in icy objects with devolatilized surface (extinct comets), consistent with what might be implied by recent dynamical modeling in the framework of the Nice Model.  相似文献   

Microbial response to surface microtopography: the role of metabolism in localized mineral dissolution     

Katrina J. Edwards  Andrew D. Rutenberg 《Chemical Geology》2001,180(1-4):19-32

We examine the role of microtopographical surface features on sulfide minerals in localizing and aligning bacterial adhesion. Experimental data shows strong correlation between bacterial cell alignment and principal crystallographic axes of pyrite (100 and 110). While bacteria often adhere to visible surface imperfections such as scratches, in many cases no associated surface features are visible. Additionally, the size of the surface imperfection does not unambiguously determine its effect in localizing and aligning bacterial cells. We theoretically model bacterial adhesion. We find that the depth of a surface feature such as a scratch is less important than its cross-sectional shape. Surface features that conform to the bacterial shape can strongly alter local bacterial adhesion energies, even with heights of only 10 nm. Hence, small local surface alterations due to bacterial metabolism could strongly affect local adhesion parameters, and may account for the observed bacterial distributions on mineral surfaces.  相似文献   

粤北地区夷平面的初步研究   总被引：11，自引：1，他引：11  

张珂  黄玉昆 《热带地理》1995,15(4):295-305

本文首先简要讨论了夷平面和多层地形的几个成因模式，然后提出了夷平面的模糊数学识别方法和野外鉴别标志，在此基础上，鉴别出了粤北地区铁四级夷平面，即：英德面（高程３００￣３６０ｍ）、仁化面（高程４００￣４７０ｍ）、阳山面（高程６００￣７８０ｍ）和粤北面（高程１０１０￣１３５０ｍ），其形成时代分别大致为Ｑ、Ｎ１＾３－Ｎ２、Ｅ３＾２－Ｅ１＾２和Ｋ２－Ｅ３初，其中以粤北面形成的周期最长，代表了华南地区的广泛  相似文献   

Soil morphological variations on the Taoyuan Terrace, Northwestern Taiwan: Roles of topography and groundwater     

Yu-Shih Lin  Yue-Gau Chen  Zueng-Sang Chen  Meng-Long Hsieh 《Geomorphology》2005,69(1-4):138-151

To understand whether soils on the same geomorphic surface have similar properties, this study examines the morphology of soils developed on the 30-kyr-old Taoyuan Terrace, Northwestern Taiwan. Relationships among soil morphology, variations in the groundwater table, and soil forming processes were established based on field investigations and previously published datasets. The soil series in the study area can be grouped into seven types, including three homogeneous groups, two mottled groups, one gley group, and one reworked group. Fifteen hand-core samples collected in the field and borehole data were used to understand spatial variations in soil morphology. The results indicate that soil morphology on the southern Taoyuan Terrace changes systematically from the fore-edge to the back-edge: from red/orange soils to yellow soils, then to mottled soils, and finally to gley soils. The borehole data indicate that the groundwater table is generally parallel to the ground surface but drops significantly near the terrace fore-edge. This pattern matches with the observed soil toposequence, indicating that the pedogenic processes in the study area are mainly controlled by groundwater distribution determined by topography. Although soils on the terrace fore-edge have developed under the well-drained conditions that favor lateritization, at least two distinct soil types (i.e., red and orange) can be observed there, reflecting different geomorphological settings in a paleo-fluvial landscape. This work suggests that geomorphological and hydrological conditions should be examined carefully before using soil morphology for correlating geomorphic surfaces.  相似文献   

Investigating the spatial distribution of summit flats in the Uinta Mountains of northeastern Utah, USA     

Jeffrey S. Munroe 《Geomorphology》2006,75(3-4):437

Isolated, laterally extensive, gently sloping surfaces known as summit flats are present at high elevations in many Laramide ranges, and are particularly well developed in the Uinta Mountains of northeastern Utah. To investigate the spatial distribution of these surfaces, and to consider possible controls on this pattern, a map of summit flats in the Uintas was developed from digital elevation data. Summit flats were identified as unglaciated areas of the landscape above an elevation of 3400 m, having a slope of less than 0.3 m m^− 1, and an area greater than 5 × 10^− 2 km². As defined, summit flats comprise 43% of the unglaciated land area above 3400 m in the Uintas, with the largest individual flat covering nearly 34 km². To quantitatively evaluate the distribution of summit flats in the Uintas, the area of summit flats was normalized to the total unglaciated area above 3400 m in 10-km-wide swaths oriented normal to the range axis. Values of percent summit flats obtained by this method decrease dramatically westward, from a high of more than 60% at the eastern end of the Uintas, to 0% at the western end. Given that individual summit flats can be diminished through lateral erosion by surrounding valley glaciers, and that the summit flats themselves were apparently never glaciated, this result suggests that glacial erosion has been more effective in the western Uintas over the course of the Quaternary. Focused glacial erosion at the upwind end of the range is consistent with the hypothesis that the proximity of Lake Bonneville enhanced precipitation over the western Uintas during the Last Glacial Maximum [Munroe, J.S., and, Mickelson, D.M., 2002. Last Glacial Maximum equilibrium-line altitudes and paleoclimate, northern Uinta Mountains, Utah, U.S.A. Journal of Glaciology, 48, 257–266].  相似文献   

Temperature–Humidity Dissimilarity and Heat-to-water-vapour Transport Efficiency Above and Within a Pine Forest Canopy: the Role of the Bowen Ratio     

E. Lamaud  M. Irvine 《Boundary-Layer Meteorology》2006,120(1):87-109

Over the past 15 years atmospheric surface-layer experiments over heterogeneous canopies have shown that the vertical transfer of sensible heat and water vapour exhibit a strong dissimilarity. In particular, the sensible-heat-to-water-vapour transport efficiencies generally exceed unity. One of the main consequences is that evaporation (latent heat flux) computed by the flux-variance method is overestimated, as persistently demonstrated by comparisons with evaporation obtained with the eddy-correlation method. Various authors proposed to take into account the temperature–humidity dissimilarity to extend the applicability of the flux-variance method in order to compute evaporation from non-uniform surfaces. They attempted to connect the sensible-heat-to-water-vapour transport efficiency (λ) to the correlation coefficient between temperature and humidity turbulent fluctuations (R _Tq ). This approach was found to be successful over ‘wet’ surfaces for which λ can be approximated by R _Tq and ‘dry’ surfaces for which λ can be approximated by 1/R _Tq . However, no solution has been proposed until now for intermediate hydrological conditions. We investigated this question using eddy-correlation measurements above and inside a pine forest canopy. For both levels, our data present a strong likeness with previously published results over heterogeneous surfaces. In particular, they confirm that λ is R _Tq in wet conditions and 1/R _Tq in dry conditions. Moreover, we defined the range of the Bowen ratio (Bo) values for which those two approximations are valid (below 0.1 and greater than 1, respectively) and established a relationship between λ, R _Tq and Bo for the intermediate range of Bo. We are confident that this new parameterization will enlarge the applicability of the flux-variance method to all kinds of heterogeneous surfaces in various hydrological conditions  相似文献   

Simulation of surface energy fluxes using high-resolution non-hydrostatic simulations and comparisons with measurements for the LITFASS-2003 experiment     

Günther Heinemann  Michael Kerschgens 《Boundary-Layer Meteorology》2006,121(1):195-220

Land-surface heterogeneity effects on the subgrid scale of regional climate and numerical weather prediction models are of vital interest for the energy and mass exchange between the surface and the atmospheric boundary layer. High-resolution numerical model simulations can be used to quantify these effects, and are a tool used to obtain area-averaged surface fluxes over heterogeneous land surfaces. We present high-resolution model simulations for the LITFASS area near Berlin during the LITFASS-2003 experiment, which were carried out using the non-hydrostatic model FOOT3DK of the University of Köln with horizontal resolutions of 1 km and 250 m. The LITFASS-2003 experimental dataset is used for comparison. The screen level quantities show good quality for the simulated pressure, temperature, humidity and wind speed and direction. Averaged over the four week experimental period, simulated surface energy fluxes at land stations show a small bias for the turbulent heat fluxes and an underestimation of the net radiation caused by excessive cloudiness in the simulations. For eight selected days with low cloud amounts, the net radiation bias is close to zero, but the sensible heat flux shows a strong positive bias. Large differences are found for latent heat fluxes over a lake, which are partly due to local effects on the measurements, but an additional problem seems to be the overestimation of the turbulent exchange under stable conditions in the daytime internal boundary layer over the lake. In the area average over the LITFASS area of 20 ×  20 km², again a strong positive bias of 70 W m^?2 for the sensible heat is present. For the low soil moisture conditions during June 2003, the simulation of the turbulent heat fluxes is sensitive to variations in the soil type and its hydrological properties. Under these conditions, the supply of ground water to the lowest soil layer should be accounted for. Different area-averaging methods are tested. The experimental set-up of the LITFASS-2003 experiment is found to be well suited for the computation of area-averaged turbulent heat fluxes.  相似文献   

闭合裂纹面相互作用的实验研究   总被引：4，自引：0，他引：4       下载免费PDF全文

尹祥础  李世愚  李红  王敏 《地球物理学报》1988,31(3):306-314

为了研究地震过程中断层面的相互作用,设计了四类裂纹面状况不同的断裂力学实验。实验结果表明,裂纹面的状况对于含裂纹材料的σ_c(2^1/2)值有强烈的影响,并利用断裂力学的原理对结果进行了分析。 实验中解决了如下技术关键: 1.可用三点弯曲、局部受拉、单面启裂、双面贯穿的方法,在脆性材料板状试件（玻璃板、岩石板）以及有机玻璃板中预制中心穿透裂纹。 2.在裂纹端部预计裂纹扩展的区域内粘贴电阻应变片,用以判断并测量裂纹初始扩展及其相应的破坏应力σ_c的方法。  相似文献   

Numerical results to the Sitnikov-problem     

R. Dvorak 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):71-80

We present numerical results of the so-called Sitnikov-problem, a special case of the three-dimensional elliptic restricted three-body problem. Here the two primaries have equal masses and the third body moves perpendicular to the plane of the primaries' orbit through their barycenter. The circular problem is integrable through elliptic integrals; the elliptic case offers a surprisingly great variety of motions which are until now not very well known. Very interesting work was done by J. Moser in connection with the original Sitnikov-paper itself, but the results are only valid for special types of orbits. As the perturbation approach needs to have small parameters in the system we took in our experiments as initial conditions for the work moderate eccentricities for the primaries' orbit (0.33e _primaries 0.66) and also a range of initial conditions for the distance of the 3 ^rd body (= the planet) from very close to the primaries orbital plane of motion up to distance 2 times the semi-major axes of their orbit. To visualize the complexity of motions we present some special orbits and show also the development of Poincaré surfaces of section with the eccentricity as a parameter. Finally a table shows the structure of phase space for these moderately chosen eccentricities.  相似文献   

Advances in travel geometry and urban modelling   总被引：1，自引：0，他引：1  

Geoffrey Hyman  Les Mayhew 《GeoJournal》2004,59(3):191-207

Urban travel geometry is a generalization of patterns of movement in cities and regions where route configuration and prevailing traffic speeds constrain or direct movement in distinctive and repeatable patterns. In this paper we use these properties to construct time surfaces on which distance equates to the time of travel in the urban plane. Such surfaces can be two- or three-dimensional and are useful in the study of urban structure, locational analysis, transport planning and traffic management. A particular niche addressed in this paper is non-conformal time surface transformations in which speed or the cost of travel is constrained according to co-ordinate directions. It is argued that such models may be more suited to gridded and orbital-radial cities than previously used conformal transformations. After explaining the rationale behind the approach, a mathematical basis is developed and several calibrated examples are provided based on regions in the UK. The paper concludes with some examples of potential applications, and an annex provides a detailed mathematical framework. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献