9,425 research outputs found
Indirect methods for measuring variations of the solar constant
The difference between the methods that measure delta S, and those that measure variations in the solar luminosity, delta L, is discussed. It is shown that the past practice of simply relating delta S to delta L by geometrical arguments is not valid because of anisotropy of the solar radiation. It is concluded that direct techniques prove the existence of short term variability that is fully explainable in terms of the passage of active regions (spots and faculae) on the face of the Sun. The obervations of changes in the solar diameter support the existence of structurally induced variations of the solar luminosity on timescales of tens of years, which are significant in the understanding of climatic variations
The evolution of rotating stars. 1: Method and exploratory calculations for a 7 solar mass star
A method was developed which allows us to study the evolution of rotating stars beyond the main sequence stage. Four different cases of redistribution of angular momentum in an evolving star are considered. Evolutionary sequences for a 7 solar mass star, rotating according to these different cases, were computed from the ZAMS to the double shell source stage. Each sequence was begun with a (typical) equatorial velocity of 210 km/sec. On the main sequence, the effects of rotation are of minor importance. As the core contracts during later stages, important effects arise in all physically plausible cases. The outer regions of the cores approach critical velocities and develop unstable angular velocity distributions. The effects of these instabilities should significantly alter the subsequent evolution
Isospin in Reaction Dynamics. The Case of Dissipative Collisions at Fermi Energies
A key question in the physics of unstable nuclei is the knowledge of the
for asymmetric nuclear matter () away from normal conditions. We
recall that the symmetry energy at low densities has important effects on the
neutron skin structure, while the knowledge in high densities region is crucial
for supernovae dynamics and neutron star properties. The way to probe
such region of the isovector in terrestrial laboratories is through very
dissipative collisions of asymmetric (up to exotic) heavy ions from low to
relativistic energies. A general introduction to the topic is firstly
presented. We pass then to a detailed discussion on the
process as the main dissipative mechanism at the Fermi energies and to the
related isospin dynamics. From Stochastic Mean Field simulations the isospin
effects on all the phases of the reaction dynamics are thoroughly analysed,
from the fast nucleon emission to the mid-rapidity fragment formation up to the
dynamical fission of the residues. Simulations have been performed
with an increasing stiffness of the symmetry term of the .
Some differences have been noticed, especially for the fragment charge
asymmetry. New isospin effects have been revealed from the correlation of
fragment asymmetry with dynamical quantities at the freeze-out time. A series
of isospin sensitive observables to be further measured are finally listed.Comment: 16 pages, 6 figures, Contribution to the 5th Italy-Japan Symposium,
Recent Achievements and Perspectives in Nuclear Physics, Naples Nov.3-7 2004,
World Sci. in press. Latex in WorldSci/proc/styl
Peranan Media Pengajaran dalam Pembelajaran Bahasa
Teaching language is like the adults (father-mother) teach their baby to practice speaking. Naturally, a child or a baby just imitates or repeat what the adults say. However, to accelerate and to grow up their skill in uttering the word media is needed, because it has function to make something abstract to be real and concret, as well as, to ease baby or children understand what they hear. Such this case accure in teaching and learning process where media is treated as a means of transferring knowledge. Good media leads a teacher or lecturer to good educative interactions in which it could strengthen the method of learnin
Variation of the Diameter of the Sun as Measured by the Solar Disk Sextant (SDS)
The balloon-borne Solar Disk Sextant (SDS) experiment has measured the
angular size of the Sun on seven occasions spanning the years 1992 to 2011. The
solar half-diameter -- observed in a 100-nm wide passband centred at 615 nm --
is found to vary over that period by up to 200 mas, while the typical estimated
uncertainty of each measure is 20 mas. The diameter variation is not in phase
with the solar activity cycle; thus, the measured diameter variation cannot be
explained as an observational artefact of surface activity. Other possible
instrument-related explanations for the observed variation are considered but
found unlikely, leading us to conclude that the variation is real. The SDS is
described here in detail, as is the complete analysis procedure necessary to
calibrate the instrument and allow comparison of diameter measures across
decades.Comment: 41 pages; appendix and 2 figures added plus some changes in text
based on referee's comments; to appear in MNRA
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