A note on vacuum solutions based on Lyra's manifold     

Harald H. Soleng 《Astrophysics and Space Science》1987,134(2):405-406

In a recent Letter to the Editor, Beesham (1986) has claimed that the models based on the Lyra manifold allow a wider class of solutions of the vacuum field equations than models based on a Riemannian manifold. It was also argued that the cosmological term is introduced in an arbitraryad hoc fashion in general relativity.In this note I will show that all the vacuum solutions found by Beesham, can equally well be solutions of the Friedmann equations of vacuum with a cosmological term. All these solutions are well known.  相似文献   

Stellar kinematics and populations of early-type galaxies with the SAURON and OASIS integral-field spectrographs     

Richard M. McDermid  Roland Bacon  Harald Kuntschner  Eric Emsellem  Kristen L. Shapiro  Martin Bureau  Michele Cappellari  Roger L. Davies  Jesús Falcn-Barroso  Davor Krajnovi&#x;  Reynier F. Peletier  Marc Sarzi  Tim de Zeeuw 《New Astronomy Reviews》2006,49(10-12):521

We summarise the results and achievements of integral-field spectroscopy of early-type galaxies, observed as part of a survey using both the SAURON and OASIS spectrographs. From the perspective of integral-field spectroscopy, these otherwise smooth and featureless objects show a wealth of structure, both in their stellar kinematics and populations. We focus on the stellar content, and examine properties on both kiloparsec scales with SAURON, and scales of 100’s of parsecs with OASIS. These complementary studies reveal two types of kinematically distinct components (KDCs), differing primarily in their intrinsic sizes. In previous studies, KDCs and their host galaxies have generally been found to be unremarkable in other aspects. We show that large KDCs, typical of the well-studied cases, indeed show little or no age differences with their host galaxy. The KDCs detected with the higher spatial-resolution of OASIS are intrinsically smaller and include, in contrast, a significant fraction of young stars. We speculate on the relationship between KDCs and their host galaxies, and the implications for young populations in early-type galaxies.  相似文献   

Primordial magnetic field,inflation and cosmic strings     

Harald H. Soleng 《Astrophysics and Space Science》1987,137(1):201-203

The possibility of a primordial magnetic field is discussed. The formation of closed, superconducting cosmic strings before the end of inflation is pointed out as a mechanism able to preserve a magnetic field inside the loops which could provide seeds for galactic magnetic fields.  相似文献   

EDITORIAL     

Harald LejenäsEditor-in-Chief Tellus A  Henning RodheEditor-in-Chief Tellus B 《地球，A辑:动力气象学与海洋学》2004,56(1):1-1

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Stellar populations in early-type Coma cluster galaxies – I. The data     

Stephen A. W. Moore  John R. Lucey  Harald Kuntschner  Matthew Colless 《Monthly notices of the Royal Astronomical Society》2002,336(2):382-408

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The SAURON project – VI. Line strength maps of 48 elliptical and lenticular galaxies     

Harald Kuntschner  Eric Emsellem  R. Bacon  M. Bureau  Michele Cappellari  Roger L. Davies  P. T. de Zeeuw  Jesús Falcón-Barroso  Davor Krajnovi&#;  Richard M. McDermid  Reynier F. Peletier  Marc Sarzi 《Monthly notices of the Royal Astronomical Society》2006,369(2):497-528

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Movements,failure and climatic control of the Veslemannen rockslide,Western Norway     

Kristensen  Lene  Czekirda  Justyna  Penna  Ivanna  Etzelmüller  Bernd  Nicolet  Pierrick  Pullarello  José Santiago  Blikra  Lars Harald  Skrede  Ingrid  Oldani  Simon  Abellan  Antonio 《Landslides》2021,18(6):1963-1980

On September 5, 2019, the Veslemannen unstable rock slope (54,000 m³) in Romsdalen, Western Norway, failed catastrophically after 5 years of continuous monitoring. During this period, the rock slope weakened while the precursor movements increased progressively, in particular from 2017. Measured displacement prior to the failure was around 19 m in the upper parts of the instability and 4–5 m in the toe area. The pre-failure movements were usually associated with precipitation events, where peak velocities occurred 2–12 h after maximum precipitation. This indicates that the pore-water pressure in the sliding zones had a large influence on the slope stability. The sensitivity to rainfall increased greatly from spring to autumn suggesting a thermal control on the pore-water pressure. Transient modelling of temperatures suggests near permafrost conditions, and deep seasonal frost was certainly present. We propose that a frozen surface layer prevented water percolation to the sliding zone during spring snowmelt and early summer rainfalls. A transition from possible permafrost to a seasonal frost setting of the landslide body after 2000 was modelled, which may have affected the slope stability. Repeated rapid accelerations during late summers and autumns caused a total of 16 events of the red (high) hazard level and evacuation of the hazard zone. Threshold values for velocity were used in the risk management when increasing or decreasing hazard levels. The inverse velocity method was initially of little value. However, in the final phase before the failure, the inverse velocity method was useful for forecasting the time of failure. Risk communication was important for maintaining public trust in early-warning systems, and especially critical is the communication of the difference between issuing the red hazard level and predicting a landslide.

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Simulations of VLBI observations of a geodetic satellite providing co-location in space     

James M. Anderson  Georg Beyerle  Susanne Glaser  Li Liu  Benjamin Männel  Tobias Nilsson  Robert Heinkelmann  Harald Schuh 《Journal of Geodesy》2018,92(9):1023-1046

We performed Monte Carlo simulations of very-long-baseline interferometry (VLBI) observations of Earth-orbiting satellites incorporating co-located space-geodetic instruments in order to study how well the VLBI frame and the spacecraft frame can be tied using such measurements. We simulated observations of spacecraft by VLBI observations, time-of-flight (TOF) measurements using a time-encoded signal in the spacecraft transmission, similar in concept to precise point positioning, and differential VLBI (D-VLBI) observations using angularly nearby quasar calibrators to compare their relative performance. We used the proposed European Geodetic Reference Antenna in Space (E-GRASP) mission as an initial test case for our software. We found that the standard VLBI technique is limited, in part, by the present lack of knowledge of the absolute offset of VLBI time to Coordinated Universal Time at the level of microseconds. TOF measurements are better able to overcome this problem and provide frame ties with uncertainties in translation and scale nearly a factor of three smaller than those yielded from VLBI measurements. If the absolute time offset issue can be resolved by external means, the VLBI results can be significantly improved and can come close to providing 1 mm accuracy in the frame tie parameters. D-VLBI observations with optimum performance assumptions provide roughly a factor of two higher uncertainties for the E-GRASP orbit. We additionally simulated how station and spacecraft position offsets affect the frame tie performance.  相似文献   

Heterogeneity preserving upscaling for heat transport in fractured geothermal reservoirs     

Anna Nissen  Eirik Keilegavlen  Tor Harald Sandve  Inga Berre  Jan Martin Nordbotten 《Computational Geosciences》2018,22(2):451-467

In simulation of fluid injection in fractured geothermal reservoirs, the characteristics of the physical processes are severely affected by the local occurence of connected fractures. To resolve these structurally dominated processes, there is a need to develop discretization strategies that also limit computational effort. In this paper, we present an upscaling methodology for geothermal heat transport with fractures represented explicitly in the computational grid. The heat transport is modeled by an advection-conduction equation for the temperature, and solved on a highly irregular coarse grid that preserves the fracture heterogeneity. The upscaling is based on different strategies for the advective term and the conductive term. The coarse scale advective term is constructed from sums of fine scale fluxes, whereas the coarse scale conductive term is constructed based on numerically computed basis functions. The method naturally incorporates the coupling between solution variables in the matrix and in the fractures, respectively, via the discretization. In this way, explicit transfer terms that couple fracture and matrix solution variables are avoided. Numerical results show that the upscaling methodology performs well, in particular for large upscaling ratios, and that it is applicable also to highly complex fracture networks.  相似文献   

Dissolution–precipitation reactions in hydrothermal experiments with quartz–feldspar aggregates     

Ansgar Schepers  Harald Milsch 《Contributions to Mineralogy and Petrology》2013,165(1):83-101

Batch and flow-through experiments were performed on quartz–feldspar granular aggregates at hydrothermal conditions (up to ≈150 °C, up to 5 MPa effective pressure, and near-neutral pH) for up to 141 days. The effect of dissolution–precipitation reactions on the surface morphology of the mineral grains was investigated. The starting materials as well as the solids and fluids resulting from the experiments were characterized using BET, energy dispersive X-ray spectroscopy, electron microprobe analysis, inductively coupled plasma-optical emission spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and X-ray fluorescence spectroscopy. The electrical conductivity of fluid samples was used as a proxy for the evolution of the fluid composition in the experiments. The chemical analyses of the fluids in combination with hydrogeochemical simulations with PHREEQC suggested the precipitation of Al–Si-bearing solid phases. Electron microscopy confirmed the formation of secondary amorphous Al–Si-bearing solid phases. The microscopic observations are consistent with a process of stoichiometric dissolution of the mineral grains, transport of dissolved ions in the fluid phase, and spatially coupled precipitation of sub-μm sized amorphous particles on mineral surfaces. These findings shed light onto early stages of diagenesis of quartz–feldspar sands and indicate that amorphous phases may be precursors for the formation of crystalline phases, for example, clay minerals.  相似文献