Satiation of juveniles ofCoregonus lavaretus L. fed onDaphnia pulicaria     

Roland Rösch 《Aquatic Sciences - Research Across Boundaries》1986,48(1):44-52

Juveniles ofCoregonus lavaretus L. of a body weight (wet weight) between 0.5 and 11g were fed on pond reared livingDaphnia pulicaria. The fish were held in groups of 4 to 8 fish in tanks of a volume of 10 to 20 l at water temperatures of 8, 12, 16 and 20°C. After a deprivation time of 24 h the fish were fed an amount of livingDaphnia of about 1000 specimen/l. Fish of a body weight (wet weight) less than 1 g showed a continuous food intake until satiation, whereas the food intake of bigger fish was divided into three phases: During a first feeding period 50 to 73% of the satiation amount were consumed. This feeding period was followed by a period of no food intake, which was followed by a second feeding period. At the end of the second feeding period the fish were satiated. The period of no food intake is considered to be a specific adaptation to planctivory. The satiation time (min) increased with increasing body weight and increasing water temperature. The satiation amount, i.e. the amount of food eaten until satiation (mg stomach content, dry weight) increased with increasing body weight. The satiation amount expressed in % body weight (dry weight/dry weight) reached a maximum of 10% for fish of a body weight of 1 g. With increasing body weight it decreased to 5% for fish of 11 g b.wt. At 8°C the satiation amount was significantly lower than at 12°C. The experiments were performed at the Limnological Institute, University of Constance, D-7750 Constance, Federal Republic of Germany.  相似文献   

Chairman''s report     

Roland Pusch 《Engineering Geology》1981,18(1-4):111-114

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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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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   

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   

Recent quick-clay studies, an introduction     

Roland Pusch 《Engineering Geology》1966,1(6):413-414

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Initial reports of the deep sea drilling project: National Science Foundation,Washington, D.C., 1969, 672 pp., U.S. $ 10.25     

Roland von Huene 《Marine Geology》1971

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