Thermal conductivity measurements of porous dust aggregates: I. Technique, model and first results     

M. Krause  J. Blum  M. Trieloff 《Icarus》2011,214(1):286-296

We present a non-invasive technique for measuring the thermal conductivity of fragile and sensitive materials. In the context of planet-formation research, the investigation of the thermal conductivity of porous dust aggregates provide important knowledge about the influence of heating processes, like internal heating by radioactive decay of short-lived nuclei, e.g. ²⁶Al, on the evolution and growth of planetesimals. The determination of the thermal conductivity was performed by a combination of laboratory experiments and numerical simulations. An IR camera measured the temperature distribution of the sample surface heated by a well-characterized laser beam. The thermal conductivity as free parameter in the model calculations, exactly emulating the experiment, was varied until the experimental and numerical temperature distributions showed best agreement. Thus, we determined for three types of porous dust samples, consisting of spherical, 1.5 μm-sized SiO₂ particles, with volume filling factors in the range of 15-54%, the thermal conductivity to be 0.002-0.02 W m⁻¹ K⁻¹, respectively. From our results, we can conclude that the thermal conductivity mainly depends on the volume filling factor. Further investigations, which are planned for different materials and varied contact area sizes (produced by sintering), will prove the appropriate dependencies in more detail.  相似文献   

A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight,Brazilian shelf     

Troy A. Dexter  Darrell S. Kaufman  Richard A. Krause Jr.  Susan L. Barbour Wood  Marcello G. Simões  John Warren Huntley  Yurena Yanes  Christopher S. Romanek  Michał Kowalewski 《Quaternary Research》2014

To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São Paulo Bight (São Paulo State, Brazil). The resulting ¹⁴C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges from modern to 10,307 cal yr BP, is right skewed, and represents a remarkably complete time series: the completeness of the Holocene record is 66% at 250-yr binning resolution and 81% at 500-yr binning resolution. Extensive time-averaging is observed for all sites across the sampled bathymetric range indicating long water depth-invariant survival of carbonate shells at the sediment surface with low net sedimentation rates. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can contain time-rich shell accumulations that record the entire Holocene, not just the present.  相似文献   

Simulations of multiphase turbulence in jet cocoons     

M. Krause  P. Alexander 《Monthly notices of the Royal Astronomical Society》2007,376(2):465-478

The interaction of optically emitting clouds with warm X-ray gas and hot, tenuous radio plasma in radio jet cocoons is modelled by 2D compressible hydrodynamic simulations. The initial setup is the Kelvin–Helmholtz instability at a contact surface of density contrast 10⁴. The denser medium contains clouds of higher density. Optically thin radiation is realized via a cooling source term. The cool phase effectively extracts energy from the other gas which is both, radiated away and used for acceleration of the cold phase. This increases the system's cooling rate substantially and leads to a massively amplified cold mass dropout. We show that it is feasible, given small seed clouds of the order of  100 M_⊙  , that all of the optically emitting gas in a radio jet cocoon may be produced by this mechanism on the propagation time-scale of the jet. The mass is generally distributed as   T ^−1/2  with temperature, with a prominent peak at 14 000 K. This peak is likely to be related to the counteracting effects of shock heating and a strong rise in the cooling function. The volume filling factor of cold gas in this peak is of the order of  10⁻⁵–10⁻³  and generally increases during the simulation time.
The simulations tend towards an isotropic scale-free Kolmogorov-type energy spectrum over the simulation time-scale. We find the same Mach-number density relation as Kritsuk & Norman and show that this relation may explain the velocity widths of emission lines associated with high-redshift radio galaxies, if the environmental temperature is lower, or the jet-ambient density ratio is less extreme than in their low-redshift counterparts.  相似文献   

Large Scale Simulations of the Jet-Igm Interaction     

Martin G. H. Krause 《Astrophysics and Space Science》2004,293(1-2):255-262

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New high‐resolution age data from the Ediacaran–Cambrian boundary indicate rapid,ecologically driven onset of the Cambrian explosion     

Ulf Linnemann  Maria Ovtcharova  Urs Schaltegger  Andreas Grtner  Michael Hautmann  Gerd Geyer  Patricia Vickers‐Rich  Tom Rich  Birgit Plessen  Mandy Hofmann  Johannes Zieger  Rita Krause  Les Kriesfeld  Jeff Smith 《地学学报》2019,31(1):49-58

The replacement of the late Precambrian Ediacaran biota by morphologically disparate animals at the beginning of the Phanerozoic was a key event in the history of life on Earth, the mechanisms and the time‐scales of which are not entirely understood. A composite section in Namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the Ediacaran–Cambrian boundary to 538.6–538.8 Ma, more than 2 Ma younger than previously assumed. The U–Pb‐CA‐ID TIMS zircon ages demonstrate an ultrashort time frame for the LAD of the Ediacaran biota to the FAD of a complex, burrowing Phanerozoic biota represented by trace fossils to a 410 ka time window of 538.99 ± 0.21 Ma to 538.58 ± 0.19 Ma. The extremely short duration of the faunal transition from Ediacaran to Cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the Phanerozoic.  相似文献   

Water sensor network applications: Time to move beyond the technical?          下载免费PDF全文

Feng Mao  Julian Clark  Wouter Buytaert  Stefan Krause  David M. Hannah 《水文研究》2018,32(16):2612-2615

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A water cycle for the Anthropocene     

Benjamin W. Abbott  Kevin Bishop  Jay P. Zarnetske  David M. Hannah  Rebecca J. Frei  Camille Minaudo  F.Stuart Chapin  Stefan Krause  Lafe Conner  David Ellison  Sarah E. Godsey  Stephen Plont  Jean Marais  Tamara Kolbe  Amanda Huebner  Tyler Hampton  Sen Gu  Madeline Buhman  Sayedeh Sara Sayedi  Ovidiu Ursache  Melissa Chapin  Kathryn D. Henderson  Gilles Pinay 《水文研究》2019,33(23):3046-3052

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Groundwater-surface water interactions: New methods and models to improve understanding of processes and dynamics     

Jan H. Fleckenstein  Stefan Krause  David M. Hannah  Fulvio Boano 《Advances in water resources》2010

Interest in groundwater (GW)-surface water (SW) interactions has grown steadily over the last two decades. New regulations such as the EU Water Framework Directive (WFD) now call for a sustainable management of coupled ground- and surface water resources and linked ecosystems. Embracing this mandate requires new interdisciplinary research on GW-SW systems that addresses the linkages between hydrology, biogeochemistry and ecology at nested scales and specifically accounts for small-scale spatial and temporal patterns of GW-SW exchange. Methods to assess these patterns such as the use of natural tracers (e.g. heat) and integrated surface-subsurface numerical models have been refined and enhanced significantly in recent years and have improved our understanding of processes and dynamics. Numerical models are increasingly used to explore hypotheses and to develop new conceptual models of GW-SW interactions. New technologies like distributed temperature sensing (DTS) allow an assessment of process dynamics at unprecedented spatial and temporal resolution. These developments are reflected in the contributions to this Special Issue on GW-SW interactions. However, challenges remain in transferring process understanding across scales.  相似文献   

Copper bioavailability and toxicity to Mytilus galloprovincialis in Shelter Island Yacht Basin,San Diego,CA     

Casey Bosse  Gunther Rosen  Marienne Colvin  Patrick Earley  Robert Santore  Ignacio Rivera-Duarte 《Marine pollution bulletin》2014

The bioavailability and toxicity of copper (Cu) in Shelter Island Yacht Basin (SIYB), San Diego, CA, USA, was assessed with simultaneous toxicological, chemical, and modeling approaches. Toxicological measurements included laboratory toxicity testing with Mytilus galloprovincialis (Mediterranean mussel) embryos added to both site water (ambient) and site water spiked with multiple Cu concentrations. Chemical assessment of ambient samples included total and dissolved Cu concentrations, and Cu complexation capacity measurements. Modeling was based on chemical speciation and predictions of bioavailability and toxicity using a marine Biotic Ligand Model (BLM). Cumulatively, these methods assessed the natural buffering capacity of Cu in SIYB during singular wet and dry season sampling events. Overall, the three approaches suggested negligible bioavailability, and isolated observed or predicted toxicity, despite an observed gradient of increasing Cu concentration, both horizontally and vertically within the water body, exceeding current water quality criteria for saltwater.  相似文献   

Reconstruction of historical pressure patterns over Japan using two-point pressure–temperature datasets since the nineteenth century     

Masumi Zaiki  Gunther P. Können  Keiji Kimura  Takehiko Mikami  Togo Tsukahara 《Climatic change》2009,95(1-2):231-248

The temperature and pressure differences between Tokyo and Nagasaki were used to reconstruct past climate conditions. January and July in each available year since the 1820s were classified into several types with characteristic sea level atmospheric pressure patterns. This results in 18 years of pre-1881 data and a continuous series thereafter. The series indicate that the warming after 1900 (after the end of the so-called Little Ice Age) and again after 1960 can at least partly be attributed to an increase in the frequency of warm circulation pattern types at the expense of cold types. The difference in nature of the shifts in circulation types that occurred in the late nineteenth century compared with that in the late twentieth centuries suggests that the mechanism behind the warming in the late nineteenth century differs from that in the late twentieth century.  相似文献