5,247 research outputs found
Secular Dynamics of S-type Planetary Orbits in Binary Star Systems: Applicability Domains of First- and Second-Order Theories
We analyse the secular dynamics of planets on S-type coplanar orbits in tight
binary systems, based on first- and second-order analytical models, and compare
their predictions with full N-body simulations. The perturbation parameter
adopted for the development of these models depends on the masses of the stars
and on the semimajor axis ratio between the planet and the binary.
We show that each model has both advantages and limitations. While the
first-order analytical model is algebraically simple and easy to implement, it
is only applicable in regions of the parameter space where the perturbations
are sufficiently small. The second-order model, although more complex, has a
larger range of validity and must be taken into account for dynamical studies
of some real exoplanetary systems such as -Cephei and HD 41004A.
However, in some extreme cases, neither of these analytical models yields
quantitatively correct results, requiring either higher-order theories or
direct numerical simulations.
Finally, we determine the limits of applicability of each analytical model in
the parameter space of the system, giving an important visual aid to decode
which secular theory should be adopted for any given planetary system in a
close binary.Comment: 32 pages, 8 figures, accepted for publication in Celestial Mechanics
and Dynamical Astrophysic
Tougher Educational Exam Leading to Worse Selection
This paper shows a somehow counterintuitive result: an increase in the exam diculty may reduce the average quality (productivity) of selected individuals. Since the exam does not verify all skills, when its standard rises, candidates with relatively low skills emphasized in the test and high skills demanded in the job may no longer qualify. Hence, an increase in the testing standard may be counterproductive. One implication is that policies should emphasize alignment between the skills tested and those required in the actual jobs.school standard, signaling model, cognitive skill, noncog- nitive skill
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国立大学法人長岡技術科学大
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