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101.
The shadow of a black hole is usually calculated, either analytically or numerically, on the assumption that the black hole is eternal, i.e., that it has existed for all time. Here we ask the question of how this shadow comes about in the course of time when a black hole is formed by gravitational collapse. To that end we consider a star that is spherically symmetric, dark and non-transparent and we assume that it begins, at some instant of time, to collapse in free fall like a ball of dust. We analytically calculate the dependence on time of the angular radius of the shadow, first for a static observer who is watching the collapse from a certain distance and then for an observer who is falling towards the centre following the collapsing star. 相似文献
102.
P. Betz E. Bitterwolf A. Burkard F. Glatz F. Heidinger Th. Kern R. Lehmann S. Norbert H. Röpke C. Schneider J. Siefert 《Zeitschrift für Physik A Hadrons and Nuclei》1982,309(2):163-176
Particleγ-ray coincidences have been measured in the28Si (d,pγ) reaction at 6.5 and 7 MeV bombarding energy, in the26Mg (α,nγ) reaction at 12, 14 and 15 MeV, and in the27A1 (τ,pγ) reaction at 9 MeV. Theγ-decay has been observed for all bound states of29Si and for 56 unbound states up to 12,960 KeV excitation energy. Particleγ-ray angular correlations were measured in the28Si (d,pγ) reaction at 6.5 MeV and in the26Mg (α,nγ) reaction at 12 MeV. Spin (-parity) assignments or restrictions were obtained for nearly all bound states and some high-spin states above the binding energy. The assignment of mirror levels in29Si and29P has been extended to 8.2 MeV excitation energy. The excitation energies of 41 positive-parity states are reproduced by shell model calculations. The possible existence of aK π=5/2+ band with prolate deformation is discussed. 相似文献
103.
B. Pümpin H. Keller W. Kündig I. M. Savić J. W. Schneider H. Simmler P. Zimmermann E. Kaldis S. Rusiecki C. Rossel 《Hyperfine Interactions》1991,63(1-4):25-31
A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa2Cu3O
x
samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content
of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen
contentx was found to have strong similarities with the behavior of the critical temperatureT
c
as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups. 相似文献
104.
105.
Theodor Sexl 《Zeitschrift für Physik A Hadrons and Nuclei》1933,81(3-4):178-185
106.
107.
108.
Resistivity and thermal conductivity of the intermediate valence compound CePd3 between 1.3 and 300 K are compared with those of the nonmagnetic and magnetic reference compounds YPd3 and GdPd3 and of alloys of the type Ce1–xRE
x
Pd3 with RE=Y, Gd and 0.01<x<0.5. The analysis reveals the existence of a maximum metallic resistivity of 300 cm for CePd3. The intrinsic resistivity of CePd3 rises proportional toT
2 up to 100 K, with a coefficientB about 107 times larger than e.g. in copper. We interpret this with indirect electron-electron scattering mediated through valence transitions. 相似文献
109.
S.A. Nepijko M. Klais G. Schönhense N. Cramer Z. Celinski C.M. Schneider S. Zennaro N. Zema N.N. Sedov 《Applied Physics A: Materials Science & Processing》2003,76(5):809-815
Micromagnetic properties of the Fe19Ni81 (5 nm)/NiO (50 nm)/Fe19Ni81 (30 nm) structured system have been investigated in a photoemission electron microscope in the magnetic X-ray circular dichroism
operating mode. The microstructured Fe19Ni81 (5 nm) film contained two-dimensional islands with the aspect ratio varying from 1:1 to 10:1, and the linear size of their
long axis comprised 24, 12 and 6 μm. It is shown that the magnetic domains have the direction of magnetization preferentially
parallel and antiparallel to the magnetic field direction in which this system was prepared. Their number is determined by
the particles’ sizes, their shape as well as by the direction of the external magnetizing field and can be characterized by
a non-monotonic size dependence. The magnetization of domains with different lateral sizes was found to be 0.4 T with an accuracy
better than 20%.
Received: 29 May 2002 / Accepted: 17 July 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +49-6131/392-3807, E-mail: nepijko@mail.uni-mainz.de 相似文献
110.
D. Schneider 《Acta Physica Hungarica A》1996,3(3-4):229-244
A short review of the experimental program in highly-charged heavy ion physics conducted at the Lawrence Livermore National Laboratory Electron Beam Ion Trap (EBIT) facility is presented. The heavy-ion research, involving ions up to fully stripped U92+, includes precision x-ray spectroscopy and lifetime studies, electron impact ionization and excitation cross section measurements. The investigations of ion-surface interactions following the impact of high-Z highly charged ions on surfaces are aimed to study the neutralization dynamics effecting the ion and the response of the surface as well. The combination of an EBIT% with a cryogenic Penning Trap (“RETRSP”) allows to conduct experiments with ultra cold (e.g. 10 K) very highly charged ions. These studies of charge exchange processes, Coulomb crystals and measurements of hyperfine transitions using laser spectroscopy are in progress. 相似文献