共查询到20条相似文献，搜索用时 312 毫秒
1.
The gravitational field of a global monopole in the context of Einstein–Cartan theory is investigated. A comparison is made
with the corresponding results predicted by general relativity.
PACS Nos: 98.80cq; 04.20 jb; 04.50 相似文献
2.
The analysis of application of two dynamical models (``Earth–Moon' and``barycentre' model) in the motion of Near Earth Asteroids was performed. Mainaim was the quantitative estimation of the influence of lunar perturbations on the motionof NEA. Additionally, basic tests of application of numerical methods weremade (RMVS3 and B–S methods). The orbits of 1083 Apollo–Aten–Amor and 7selected AAA objects were adopted as test particles in numerical integrationof the motion. The comparison between results obtained by both dynamicalmodels is discussed in detail. In specific cases, the application of the``Earth–Moon' dynamical model is very important and cannot be neglected incomputations of orbits. 相似文献
3.
It is shown that an analog of Birkhoff’s theorem of general relativity exists in the Einstein–Cartan–Kalb–Ramond (ECKR) theory
of gravity when Kalb–Ramond (KR) field strength, which occurs in the theory is independent of time. 相似文献
4.
Vanscheidt R. Bleul H. Manthey E. Jütte M. Pohlen M. Schmidtobreick L. Altmann M. Dieball A. Geffert M. Sanner J. Notni P. Schmoll J. 《Earth, Moon, and Planets》1998,81(3):223-231
Extensive widefield CCD direct imaging of C/1995 O1 (Hale-Bopp) at UBVRI was carried out at Hoher List Observatory with the
1.06 m telescope (field of view 20′ × 20′) and at Potsdam Observatory with the 0.70 m telescope (field of view 8′ × 8′). The
corresponding spatial resolution is 850–1000 km pix-1and 525–590 km pix-1, respectively. The data covers 25 nights from February 20 to April 21, 1997.
In order to quantify the various features in the apparent inner coma we introduce a new tomographic method that minimizes
the morphological bias caused by image processing. The tomographic analysis leads to quantitative maps refering to the position
and intensity of the dust ejections for each image frame. Variability and periodicity within the inner coma can be thoroughly
deduced due to various sets of consecutive nights in the observation period mentioned above. The results are compared with
applications of adaptive Laplace filtering.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
E. Paunzen 《Astrophysics and Space Science》1999,266(3):379-387
In this article the current status of the knowledge forthe group of λ Bootis stars is reviewed. These metal poor objectsare
quite outstanding compared to other chemically peculiar stars of theupper main sequence. Up to now no conclusive theory has
been developedwhich is able to explain the majority of observational results. There is,however, an increasing interest in
observational as well as theoreticalresults in order to develop and test astrophysical models such asaccretion of circumstellar
matter and diffusion processes in stellaratmospheres.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
R. Ramesh 《Solar physics》2000,196(1):213-220
We report low-frequency observations of an enhancement in the solar corona prior to the halo coronal mass ejection of 23 October 1997, with the Gauribidanur radioheliograph. The Sun was `quiet' and no radio bursts were observed either prior to or in the aftermath of the event. The radio method would be useful in studying the pre-event structures associated with the eruptive solar activity, particularly from the ground. 相似文献
7.
Using the teleparallel gravity versions of the Einstein and Landau–Lifshitz’s energy and/or momentum complexes, I obtain the
energy and momentum of the universe in viscous Kasner-type cosmological models. The energy and momentum components (due to
matter plus field) are found to be zero and this agree with a previous work of Rosen and Johri et al., who investigated the
problem of the energy in Friedmann–Robertson–Walker (FRW) universe. The result that the total energy and momentum components
of the universe in these models is zero same as Bergmann–Thomson’s energy–momentum and props the viewpoint of Tryon. Rosen
found that the energy of the FRW space–time is zero, which agrees with the studies of Tryon.
PACs Numbers: 04.20.-q; 04.50.+h
An erratum to this article is available at . 相似文献
8.
We report the observation of an outburst of comet Hale–Bopp (C/1995 O1) happened on September 10–11, 1996, carried by the
1.56 m telescope of Shanghai Astronomical Observatory. Two ejecta were found in CCD images during the outburst. According
to the positions of ejecta, we discuss the motion of the ejecta considering dust particles are subjected to the gravity and
the Solar radiation pressure, and conclude that the mean radii of dust grains in the ejecta were about submicron-sized. So
the observed X-ray emission are most likely produced by small size particles scattering the Solar X-ray.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
We compare various objects as the possible parent comet of the1998 June Boötid, by using the Tisserand invariant and the D-discriminant. Furthermore,in order to investigate the behaviour of the meteoric stream orbit, wesimulate the orbital evolution of test particles that are released from7P/Pons–Winnecke. We show firstly that the parent comet of the 1998 June Boötids, is 7P/Pons–Winnecke, and secondly that the meteoroids which constitute 1998 June Boötids were released in 1819 and 1869 from the parent comet. In themid-1900s the meteoroids started to transfer to Earth-colliding orbitsby Jovian perturbations. 相似文献
10.
The formation and evolution of a large amplitude MHD perturbation propagating perpendicular to the magnetic field in a perfectly conducting low plasma is studied. The perturbation is generated by an abrupt expansion of the source region. Explicit expressions for the time and the distance needed for the transformation of the perturbation's leading edge into a shock wave are derived. The results are applied to coronal conditions and the dynamic spectra of the radio emission excited by the shock are synthesized, reproducing metric and kilometric type II bursts. The features corresponding to the metric type II burst precursor and the moving type IV burst in the case of kilometric type II bursts are identified. A specific radio signature that is sometimes observed at the onset of a metric type II burst is found to appear immediately before the shock wave formation due to the associated growth of the magnetic field gradient. Time delays and starting frequencies of bursts' onsets are calculated and presented as a function of the impulsiveness of the source-region expansion, using different values of the ambient Alfvén velocity and various time profiles of the expansion velocity. The results are confronted with the observations of metric and kilometric type II solar radio bursts. 相似文献
11.
Burša Milan Kenyon Steve Kouba Jan Müller Achim Raděj Karel Vatrt Viliam Vojtíšková Marie Vítek Vojtěch 《Earth, Moon, and Planets》1999,84(3):163-176
The TOPEX/POSEIDON (T/P) satellite altimeter data from January 1, 1993to October 24, 1999 (cycles 11–261) was used for investigating
thelong-term variations in the geoidal geopotential W0 and/orin the geopotential scale factor R0 = GM/W0 (GM is theadopted geocentric gravitational constant). The mean valuesdetermined for the whole period covered are: W0 =(62 636 856.161 ± 0.002) m2 s-2, R0 =(6 363 672.5448 ± 0.0002) m. The actual accuracy is limited bythe altimeter calibration error (2–3 cm) and it isestimated
to be about ± 0.5 m2 s-2 (± 5 cm).The yearly variations of the above mean values are at the formalerror level. No long-term trend in W0, representing the oceanvolume change, was found for the seven years period 1993–9 on thebasis of T/P altimeter (AVISO) data.
No sea surface topography modelwas used in the solution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
The normalised Hénon–Heiles family exhibits a degenerate bifurcation when passing through the separable case =0. We clarify the relation between this degeneracy and the integrability at =0. Furthermore we show that the degenerate bifurcation carries over to the Hénon–Heiles family itself. 相似文献
13.
We interpret the historical activity of comet 55P/Tempel–Tuttle in terms of the observed characteristics of present-day short
period comets. In this respect, it is now realized that such comets are liable to undergo significant outburst and mantle
loss events at intervals separated by of order a few hundred years. On this basis one might well expect comet 55P/Tempel–Tuttle
to have undergone several outbursts since its earliest sighing in 1366. The limited absolute magnitude data available for
55P/Tempel–Tuttle is not inconsistent with the suggestion that the comet underwent outbursts during its 1699 and 1865 perihelion
returns. If the outbursts of comet 55P/Tempel–Tuttle are interpreted in terms of mantle loss events then the bright, electrophonic
sound producing fireballs reported during the great Leonid meteor storm of 1833 may have been due to the Earth sampling mantle
material ejected during the outburst of 1699.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Using polarimetric spectra obtained with the SOFIN spectrograph installed at the Nordic Optical Telescope, we detect a longitudinal magnetic field 〈Bz〉 = –168±35 G in the Of?p star HD 108. This result is in agreement with the longitudinal magnetic field measurement of the order of –150 G recently reported by the MiMeS team. The measurement of the longitudinal magnetic field in the Of?p star HD 191612 results in 〈Bz〉 = +450±153 G. The only previously published magnetic field measurement for this star showed a negative longitudinal magnetic field 〈Bz〉 = –220±38 G, indicating a change of polarity over ∼100 days. Further, we report the detection of distinct Zeeman features in the narrow Ca II and Na I doublet lines for both Of?p stars, hinting at the possible presence of material around these stars. The origin of these features is not yet clear and more work is needed to investigate how magnetic fields interact with stellar wind dynamics (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
Anirudh Pradhan G. S. Khadekar Deepak Srivastava 《Astrophysics and Space Science》2006,305(4):415-421
Implications of cosmological model with a cosmological term of the form , where β is a constant, are analyzed in multidimensional space time. The proper distance, the luminosity distance-redshift, the angular diameter distance-redshift, and look back time-redshift for the model are presented. It has been shown that models are found to be compatible with the present observations. This work, has thus generalized to higher dimensions the well-known result in four dimensional space time. It is found that the difference is significant at least in the principal to the anologous situation in four dimensional space time. 相似文献
16.
Werner Lohmann 《Astrophysics and Space Science》1975,32(1):153-163
The mean velocities of the stars in 58 globular clusters are derived from the photometric measurements of Kron and Mayall (1960). The mass-visual brightness ratio
is used. The velocities are falling in the interval 2.9v11.6 km s–1, their mean value is 6.75 km s–1.
Mitteilungen Serie A. 相似文献
Mitteilungen Serie A. 相似文献
17.
Bernard R. Durney 《Solar physics》2000,196(1):1-18
The torsional oscillations at the solar surface have been interpreted by Schüssler and Yoshimura as being generated by the Lorentz force associated with the solar dynamo. It has been shown recently that they are also present in the upper half of the solar convection zone (SCZ). With the help of a solar dynamo model of the Babcock–Leighton type studied earlier, the longitudinal component of the Lorentz force, L
, is calculated, and its sign or isocontours, are plotted vs. time, t, and polar angle, (the horizontal and vertical axis respectively). Two cases are considered, (1) differential rotation differs from zero only in the tachocline, (2) differential rotation as in (1) in the tachocline, and purely latitudinal and independent of depth in the bulk of the SCZ. In the first case the sign of L
is roughly independent of latitude (corresponding to vertical bands in the t, plot), whereas in the second case the bands show a pole–equator slope of the correct sign. The pattern of the bands still differs, however, considerably from that of the helioseismic observations, and the values of the Lorentz force are too small at low latitudes. It is all but certain that the toroidal field that lies at the origin of the large bipolar magnetic regions observed at the surface, must be generated in the tachocline by differential rotation; the regeneration of the corresponding poloidal field, B
p has not yet been fully clarified. B
p could be regenerated, for example, at the surface (as in Babcock–Leighton models), or slightly above the tachocline, (as in interface dynamos). In the framework of the Babcock-Leighton models, the following scenario is suggested: the dynamo processes that give rise to the large bipolar magnetic regions are only part of the cyclic solar dynamo (to distinguish it from the turbulent dynamo). The toroidal field generated locally by differential rotation must contribute significantly to the torsional oscillations patterns. As this field becomes buoyant, it should give rise, at the surface, to the smaller bipolar magnetic regions as, e.g., to the ephemeral bipolar magnetic regions. These have a weak non-random orientation of magnetic axis, and must therefore also contribute to the source term for the poloidal field. Not only the ephemeral bipolar regions could be generated in the bulk of the SCZ, but many of the smaller bipolar regions as well (at depths that increase with their flux), all contributing to the source term for the poloidal field. In contrast to the butterfly diagram that provides only a very weak test of dynamo theories, the pattern of torsional oscillations has the potential of critically discriminating between different dynamo models. 相似文献
18.
Woodward Charles E. Gehrz R. D. Mason C. G. Jones T. J. Williams D. M. 《Earth, Moon, and Planets》1998,81(3):217-222
Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed
to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric
and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization
near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron
sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather
than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = Tcolor/TBB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity)
of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135°
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
20.
We carried out a statistical test on the peak position of the big blue bump (BBB) of medium/small redshift AGNs of different luminosities. The main method is to compare the spectral index in the soft X-ray, SX and the power law index for the straight line joining 1050 Å in UV and 0.5 keV of soft X-ray, UV-SX. The distributions of these two quantities proved to be similar from their mean values and by the K-S test. Hence, between 1050 Å and 0.5 keV, a power law possibly holds. The statistics predict that the BBB peaks around 1050 Å. This statistical result can also be obtained in the soft X-ray-selected, low luminosity AGN sample, WF 93. This shows that, even though a soft X-ray excess generally exists in WF 93, the BBB may still peak around 1050 Å. However, there is no correlation between SX and UV-SX, indicating that there is still an unknown factor operating in the far and extreme ultraviolet (FUV and EUV), which while ensuring overall similarity in distribution, inhibits one-to-one correspondence between individual values. 相似文献