Late second-early first millennium BC abrupt climate changes in coastal Syria and their possible significance for the history of the Eastern Mediterranean     

D. Kaniewski  E. Paulissen  H. Weiss  J. Bretschneider 《Quaternary Research》2010,74(2):207-215

The alluvial deposits near Gibala-Tell Tweini provide a unique record of environmental history and food availability estimates covering the Late Bronze Age and the Early Iron Age. The refined pollen-derived climatic proxy suggests that drier climatic conditions occurred in the Mediterranean belt of Syria from the late 13th/early 12th centuries BC to the 9th century BC. This period corresponds with the time frame of the Late Bronze Age collapse and the subsequent Dark Age. The abrupt climate change at the end of the Late Bronze Age caused region-wide crop failures, leading towards socio-economic crises and unsustainability, forcing regional habitat-tracking. Archaeological data show that the first conflagration of Gibala occurred simultaneously with the destruction of the capital city Ugarit currently dated between 1194 and 1175 BC. Gibala redeveloped shortly after this destruction, with large-scale urbanization visible in two main architectural phases during the Early Iron Age I. The later Iron Age I city was destroyed during a second conflagration, which is radiocarbon-dated at circa 2950 cal yr BP. The data from Gibala-Tell Tweini provide evidence in support of the drought hypothesis as a triggering factor behind the Late Bronze Age collapse in the Eastern Mediterranean.  相似文献   

星系NGC5018的星族合成研究     

孔旭  张文浩  李成  程福臻  A.Weiss 《天文学报》2002,43(3):264-271

利用星团谱样本的星族合成方法,研究了邻近巨椭圆星系NGC5018中的星族成分和其内部的恒星形成历史,给出了星系中不同年龄和金属丰度星族的成分占有比.星族合成结果表明,NGC5018中不仅存在大量金属丰度低的年老恒星成分,而且较年轻的星族成分(T=5×108yr)对星系光度贡献也很重要.星系吞并和相互作用过程可能是触发这些较年轻星族形成的物理原因,椭圆星系内部的恒星形成历史可能是2次爆发或者多次爆发过程.这些结果可以很好地解释NGC5018颜色偏蓝、Mg2谱指数强度偏弱等观测特征.  相似文献   

Magnetic flux separation in photospheric convection     

N. O. Weiss  M. R. E. Proctor  D. P. Brownjohn 《Monthly notices of the Royal Astronomical Society》2002,337(1):293-304

Three-dimensional non-linear magnetoconvection in a strongly stratified compressible layer exhibits different patterns as the strength of the imposed magnetic field is reduced. There is a transition from a magnetically dominated regime, with small-scale convection in slender hexagonal cells, to a convectively dominated regime, with clusters of broad rising plumes that confine the magnetic flux to narrow lanes where fields are locally intense. Both patterns can coexist for intermediate field strengths, giving rise to flux separation: clumps of vigorously convecting plumes, from which magnetic flux has been excluded, are segregated from regions with strong fields and small-scale convection. A systematic numerical investigation of these different states shows that flux separation can occur over a significant parameter range and that there is also hysteresis. The results are related to the fine structure of magnetic fields in sunspots and in the quiet Sun.  相似文献   

Benthic foraminiferal distribution and sedimentary structures suggest tectonic erosion at the Costa Rica convergent plate margin     

Martin Meschede  Regine Weiss  Gerhard Schmiedl  Christoph Hemleben 《地学学报》2002,14(5):388-396

ABSTRACT Distribution patterns of benthic foraminiferal faunas from ODP Leg 170 Sites 1041 and 1042 show that the Costa Rican convergent margin subsided from coastal to abyssal depth from Middle Miocene to Present. This favours the model of a margin undergoing active subduction erosion. We propose that subduction erosion leads to the removal of material from the base of the forearc wedge and, as a consequence, to progressive subsidence of the forearc. A mean subsidence rate is estimated to be approximately 0.4 mm yr⁻¹.  相似文献   

The moon’s permanent magnetic field: a cratered-shell model     

H. Weiss  P. J. Coleman Jr. 《Earth, Moon, and Planets》1977,16(3):311-315

As part of our study of the larger-scale remanent magnetic field of the Moon, we have examined the effects of cratering in an otherwise spherically symmetrical shell magnetized by a concentric dipolar magnetic fieldH _o to an intensity of magnetizationc H _o, wherec is a constant. In our initial model, we assume that the material excavated from the craters is distributed with random orientation and thus does not contribute to the remanent dipole momentM _g . We further assume that the mare fill does not contribute significantly toM _g . We choose the magnetizing dipole momentM _o and the constantc such that the magnitude of the productcH _o ≃ 3 × 10⁻⁴Г at the outer surface of the shell in the equatorial plane of the dipole. This value of the intensity of remanent magnetization was chosen to be within the range 10⁻⁷−10⁻³Г’; the intensities of thermo-remanent magnetization exhibited by Apollo samples. Finally, we use the locations and diameters of the 10 largest craters on the Moon and the depth-to-diameter ratios of Pike’s formulation to model approximately the excavation of the magnetized shell. The remanent dipole momentM _g was calculated for each of three orthogonal orientations of the magnetizing dipoleM _o. The three magnitudes ofM _g fall in the range 4 × 10¹⁸−1 × 10¹⁹Г cm³ which is close to the upper limit of 10¹⁹Г cm³ estimated forM _g from the field measurements obtained with the Apollo subsatellites. Further, the distribution of the craters is such as to produce a significant transverse component ofM _g with acute angles between the spin axis andM _g in the range 51°–77°.  相似文献   

The law of the sea: R.R. Churchill and A.V. Lowe Manchester University Press,Manchester, 1983, xxxiii and 321 pp     

Freidl Weiss 《Marine Policy》1984,8(3):282-284

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Trapped Ar isotopes in meteorite ALH 84001 indicate Mars did not have a thick ancient atmosphere     

William S. Cassata  David L. Shuster  Paul R. Renne  Benjamin P. Weiss 《Icarus》2012,221(1):461-465

Water is not currently stable in liquid form on the martian surface due to the present mean atmospheric pressure of ～7 mbar and mean global temperature of ～220 K. However, geomorphic features and hydrated mineral assemblages suggest that Mars’ climate was once warmer and liquid water flowed on the surface. These observations may indicate a substantially more massive atmosphere in the past, but there have been few observational constraints on paleoatmospheric pressures. Here we show how the ⁴⁰Ar/³⁶Ar ratios of trapped gases within martian meteorite ALH 84001 constrain paleoatmospheric pressure on Mars during the Noachian era [～4.56–3.8 billion years (Ga)]. Our model indicates that atmospheric pressures did not exceed ～1.5 bar during the first 400 million years (Ma) of the Noachian era, and were <400 mbar by 4.16 Ga. Such pressures of CO₂ are only sufficient to stabilize liquid water on Mars’ surface at low latitudes during seasonally warm periods. Other greenhouse gases like SO₂ and water vapor may have played an important role in intermittently stabilizing liquid water at higher latitudes following major volcanic eruptions or impact events.  相似文献   

CoRoT/ESTA–TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models     

Yveline Lebreton  Josefina Montalbán  Jørgen Christensen-Dalsgaard  Ian W. Roxburgh  Achim Weiss 《Astrophysics and Space Science》2008,316(1-4):187-213

We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT.  相似文献   

Study of a thermal drill head for the exploration of subsurface planetary ice layers     

P. Weiss  K.L. Yung  N. Kömle  E. Kaufmann 《Planetary and Space Science》2008,56(9):1280-1292

The recently discovered water vapor plumes on Saturn's moon Enceladus, the polar caps of planet Mars and the possible ice volcanism on the Jovian satellites call for suitable techniques to explore deep ice layers of the solar system bodies. This paper presents a novel approach to deliver scientific probes into deeper layers of planetary ice. Several existing locomotion concepts and techniques for such probes are presented. After studying the mathematical framework of the melting locomotion process, melting tests with different head forms were done to evaluate the influence of the head's geometry on the melting process. This work led to a novel concept of a thermal drill head, using heat and mechanical drill in combination to penetrate the ice. We compare the performance of such a hybrid concept versus the melting penetration alone by a mathematical model and tests in ice with a prototype of the melting drill head.  相似文献   

The Uncertainty in the True End Point of a Fossil's Stratigraphic Range When Stratigraphic Sections Are Sampled Discretely     

Weiss  Robert E.  Marshall  Charles R. 《Mathematical Geosciences》1999,31(4):435-453

Stratigraphic sections are often sampled at well-defined discrete points. Because of the incompleteness of the fossil record, a particular species may not be observed even when it is extant at a sampling point. We introduce a model and Bayesian analysis for estimating the true time of disappearance of a lineage from a section in the face of the possibility that failure to find the species beyond its observed stratigraphic range may represent false negatives. We incorporate proper prior information, including an estimated longevity of the species and the probability that it will be observed if extant. Our analysis produces a posterior density for the true extinction time of the species. Summaries of this probability distribution provide a point estimate of the extinction time, a standard deviation for the uncertainty in the estimate, and confidence intervals for the time of extinction. We apply our model to stratigraphic ranges of benthic foraminifera collected from the early Late Cretaceous (Cenomanian and Turonian) from Eastbourne, England.  相似文献