Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821     

Anne-Marie Weijmans  Michele Cappellari  Roland Bacon  P. T. de Zeeuw  Eric Emsellem  Jesús Falcón-Barroso  Harald Kuntschner  Richard M. McDermid  Remco C. E. van den Bosch  Glenn van de Ven † 《Monthly notices of the Royal Astronomical Society》2009,398(2):561-574

We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii ( R _e) in the early-type galaxies NGC 3379 and 821. With our newly developed observing technique, we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all ∼1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius.
We find that the line strength gradients previously observed within 1 R _e remain constant out to at least 4 R _e, which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal poor. By constructing orbit-based Schwarzschild dynamical models, we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and 821, with 30–50 per cent of the total matter being dark within 4 R _e. The radial anisotropy in our best-fitting halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the  Mg  b – V _esc  relation: its slope is steeper when a dark matter halo is added to the model.  相似文献   

On the election of the flat metric in the bimetric theory of gravitation     

Roland M. Avakian  Edward V. Chubarian  Babken V. Khachatrian  Armen V. Sarkissian 《Astrophysics and Space Science》1980,68(2):347-353

The problem of the form of the flat metric in the Rosen bimetric theory is examined in the following work.It is shown, on concrete examples, how necessary it is to write down the flat metric and solve the problem of finding the gravitational field in arbitrary non-inertial frame. It is shown also how to separate the pure gravitational effects from those connected with non-inertiality of the frame by way of comparing both metrics.  相似文献   

Vertical distribution of dissolved aluminium in the mediterranean sea     

Serge Caschetto  Roland Wollast 《Marine Chemistry》1979,7(2):141-155

The vertical distribution of dissolved aluminium in the Mediterranean Sea offshore of Corsica has been followed during a period of high biological activity (April–September). In May and August, the concentration of dissolved aluminium is at a relatively low (1.5 μg Al1^?1) and rather constant value in the surface waters, while exhibiting minimum values of about 0.5 and 0.8 μg Al1^?1 in April and September. It increases under the seasonal thermocline to a depth of 150–500 m. The bottom waters are characterized by a constant and relatively high value of 4 μg Al1^?1.The observed concentrations of dissolved aluminium are not compatible with a precipitation-dissolution mechanism of clay minerals.The general distribution pattern and the seasonal changes of dissolved aluminium exhibit strong analogies with those of dissolved silica and nitrogen, suggesting a pre-dominant role of biological activity. It is not possible at this stage to attribute the aluminium uptake in the photic zone solely to the activity of diatoms, as suggested earlier.  相似文献   

IGU commission on the coastal environment     

Roland Paskoff 《GeoJournal》1988,17(4):666-666

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On the velocity of jets powering hot spots similar to those in Cygnus A     

Guy Pelletier  Jacques Roland 《Astrophysics and Space Science》1984,100(1-2):351-357

Hot spots similar to those in the radio galaxy Cygnus A can be explained by the strong shock produced by a supersonic but classical jet \(\left( {u_{jet}< c/\sqrt 3 } \right)\) . The high integrated radio luminosity (L?2×10⁴⁴ erg s^?1) and the strength of mean magnetic field (B?2×10^?4 G) suggest the hot spots are the downstream flow of a very strong shock which generates the ultrarelativistic electrons of energy ?≥20 MeV. The fully-developed subsonic turbulence amplifies the magnetic field of the jet up to 1.6×10^?4 G by the dynamo effect. If we assume that the post-shock pressure is dominated by relativistic particles, the ratio between the magnetic energy density to the energy density in relativistic particles is found to be ?2×10^?2, showing that the generally accepted hypothesis of equipartition is not valid for hot spots. The current analysis allows the determination of physical parameters inside hot spots. It is found that:

1. The velocity of the upstream flow in the frame of reference of the shock isu ₁?0.2c. Radio observations indicate that the velocity of separation of hot spots isu _sep?0.05c, so that the velocity of the jet isu _jet=u ₁+u _sep?0.25c.
2. The density of the thermal electrons inside the hot spot isn ₂?5×10^?3 e ^? cm^?3 and the mass ejected per year to power the hot spot is ?4M ₀yr^?1.
3. The relativistic electron density is less than 20% of the thermal electron density inside the hot spot and the spectrum is a power law which continues to energies as low as 30 MeV.
4. The energy density of relativistic protons is lower than the energy density of relativistic electrons unlike the situation for cosmic rays in the Galaxy.

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The use of egg shells to infer the historical presence of copepods in alpine lakes     

Roland Knapp  Jodi Garton  Orlando Sarnelle 《Journal of Paleolimnology》2001,25(4):539-543

Copepods (Class Crustacea, Order Copepoda) are rarely included in paleoecological studies of lakes because they lack long-lasting exoskeletal remains. We describe the remains of eggs (egg shells) from Hesperodiaptomus copepods that are well preserved and abundant in alpine lake sediments. We demonstrate that the egg shells are the remains of Hesperodiaptomus eggs based on (i) the similar size and morphology of egg shells collected from sediments and those produced from the hatching of eggs obtained from laboratory-maintained Hesperodiaptomus, and (ii) the finding that diapausing eggs collected from lake sediments and hatched in the laboratory produced copepod nauplii that were morphologically indistinguishable from those hatched from eggs produced by laboratory-maintained Hesperodiaptomus. Egg shells were approximately two orders of magnitude more abundant in sediment cores than were viable diapausing eggs, making egg shells superior to viable diapausing eggs for quantifying the historical presence and abundance of Hesperodiaptomus. These results have important implications for alpine lake restoration as egg shells can be used to identify lakes in which Hesperodiaptomus was eliminated by fish introductions but has failed to return after fish eradication, lakes in which the pre-disturbance conditions are likely to be restored only by reintroductions of this important taxon.  相似文献   

Physico/chemical stability of smectite clays     

Roland Pusch  Ola Karnland 《Engineering Geology》1996,41(1-4):73-85

There is convincing evidence from field data that smectite clay undergoes conversion primarily to illite and chlorite if it is fully water-saturated and heated. The conversion may take place through mixed-layer formation with increasing illite/smectite ratio at higher temperatures and pressures. This process requires dehydration of the interlamellar space, for which either an external pressure or drying are needed. An alternative mechanism that takes place without dehydration, is dissolution of smectite and neoformation of illite. Both processes imply reorganization of the smectite crystal lattice for which the activation energy is fairly high, meaning that the conversion is negligible at temperatures lower than about 60°C. At elevated temperatures the conversion rate is controlled by the access to potassium for either mechanism.

An ongoing detailed investigation of this subject has led to a tentative model for the smectite-to-illite conversion in natural sediments and in canister-embedding clay in high-level radioactive waste (HLW) repositories.  相似文献   

Seismic hazard evaluation for dams in northern Colorado, U.S.A.     

Ute R. Vetter  Jon P. Ake  Roland C. Laforge 《Natural Hazards》1996,14(2-3):227-240

A seismic hazard evaluation for three dams in the Rocky Mountains of northern Colorado is based on a study of the historical seismicity. To model earthquake occurrence as a random process utilizing a maximum likelihood method, the catalog must exhibit random space-time characteristics. This was achieved using a declustering procedure and correction for completeness of recording. On the basis of the resulting a- and b-values, probabilistic epicentral distances for a 2 × 10^–5 annual probability were calculated. For a random earthquake of magnitude M _L 6.0–6.5, this distance is 15 km. Suggested ground motion parameters were estimated using a probabilistic seismic hazard analysis. Critical peak horizontal accelerations at the dams are 0.22g if median values are assumed and 0.39g if variable attenuation and seismicity rates are taken into account. For structural analysis of the dams, synthetic acceleration time series were calculated to match the empirical response spectra. In addition, existing horizontal strong motion records from two Mammoth Lakes, California earthquakes were selected and scaled to fit the target horizontal acceleration response spectra.  相似文献   

Time-dependent thermal convection, mantle differentiation and continental-crust growth     

Uwe Walzer  Roland Hendel 《Geophysical Journal International》1997,130(2):303-325

The thermal evolution of the Earth is controlled by radioactive elements whose heat production rate decays with time and whose spatial distribution depends on chemical segregation processes.
We present a 2-D and finite-difference Boussinesq convection model with temperature-dependent viscosity and time- and space-dependent radioactive heat sources. We used Newtonian rheology, boxes of aspect ratio 3, and heating from within. Starting from the geochemical results of Hofmann (1988), it is assumed that the radioactive heat sources of the mantle were initially distributed homogeneously. In a number of calculations, however, higher starting abundances of radioactive sources were assumed in the upper mantle. For the present geological situation, this also results in a depleted upper mantle. It was assumed that, if the viscosity falls below a certain critical value, chemical segregation will take place. In this way, model continental crust develops, leaving behind areas of a depleted mantle. We obtained the heat source, flow line, temperature, viscosity and heat-flow distribution as a function of time with realistic values, especially for the present time. The present viscosity of the upper mantle is approximately at the standard value obtained for postglacial uplift modelling; the deeper-mantle viscosity is considerably higher. The time dependence of the computed mean of the kinetic energy of mantle convection bears a resemblance to that of the magmatic and orogenetic activity of the Earth. We assumed that the 670 km discontinuity cannot be penetrated by the flow.  相似文献   

Zero velocity hypersurfaces for the general three-dimensional three-body problem     

Roland Sergysels 《Celestial Mechanics and Dynamical Astronomy》1986,38(3):207-214

The equation of zero velocity surfaces for the general three-body problem can be derived from Sundman's inequality. The geometry of those surfaces was studied by Bozis in the planar case and by Marchal and Saari in the three-dimensional case. More recently, Saari, using a geometrical approach, has found an inequality stronger than Sundman's. Using Bozis' algebraic method, and a rotating frame which does not take into account entirely the rotation of the three-body system, we also find an inequality stronger than Sundman's. The comparison with Saari's inequality is more difficult. However, our result can be expressed in four-dimensional space and the regions where motion is allowed can be seen (numerically) to lie inside those obtained by the use of Sundman's inequality.Agrégé de Faculté.  相似文献