175 research outputs found
School context and gender differences in mathematical performance among school graduates in Russia
publication-status: Acceptedtypes: ArticleGender differences in mathematical performance have received considerable scrutiny in the fields of sociology, economics, and psychology. We analyse a large data set of high school graduates who took a standardized mathematical test in Russia in 2011 (n=738,456) and find no substantial difference in mean test scores across boys and girls. However, boys have a greater variance of scores and are more numerous at the top of the distribution. We apply quantile regression to model the association between school characteristics and gender differences in test scores throughout the distribution of test scores. Male advantage in test scores, particularly at the top of the distribution, is concentrated in cities and in the schools with an advanced curriculum. In other high schools, especially in the countryside, gender differences in all parts of the distribution are small. We suggest several mechanisms based on selection and school effects that account for our findings
Cosmological constraints from the CMB and Ly-alpha forest revisited
The WMAP team has recently highlighted the usefulness of combining the
Ly-alpha forest constraints with those from the cosmic microwave background
(CMB). This combination is particularly powerful as a probe of the primordial
shape of the power spectrum. Converting between the Ly-alpha forest
observations and the linear mass power spectrum requires a careful treatment of
nuisance parameters and modeling with cosmological simulations. We point out
several issues which lead to an expansion of the errors, the two most important
being the range of cosmological parameters explored in simulations and the
treatment of the mean transmitted flux constraints. We employ a likelihood
calculator for the current Ly-alpha data set based on an extensive
6-dimensional grid of simulations. We show that the current uncertainties in
the mean transmission and the flux power spectrum define a degeneracy line in
the amplitude-slope plane. The CMB degeneracy due to the primordial power
spectrum shape follows a similar relation in this plane. This weakens the
statistical significance of the primordial power spectrum shape constraints
based on combined CMB+Ly-alpha forest analysis. Using the current data the
simplest n=1 scale invariant model with dn/dln k=0 and no tensors has a Delta
chi^2=4 compared to the best fitting model in which these 3 parameters are
free. Current data therefore do not require relaxing these parameters to
improve the fit.Comment: 7 pages, 2 figures, expanded, matches the accepted version in MNRA
Can sterile neutrinos be the dark matter?
We use the Ly-alpha forest power spectrum measured by the SDSS and
high-resolution spectroscopy observations in combination with cosmic microwave
background and galaxy clustering constraints to place limits on a sterile
neutrino as a dark matter candidate in the warm dark matter (WDM) scenario.
Such a neutrino would be created in the early universe through mixing with an
active neutrino and would suppress structure on scales smaller than its free
streaming scale. We ran a series of high-resolution hydrodynamic simulations
with varying neutrino mass to describe the effect of a sterile neutrino on the
Ly-alpha forest power spectrum. We find that the mass limit is m_s >14 keV at
95% c.l. (10keV at 99.9%), which is nearly an order of magnitude tighter
constraint than previously published limits and is above the upper limit
allowed by X-ray constraints, excluding this candidate as dark matter in this
model. The corresponding limit for a neutrino that decoupled early while in
thermal equilibrium is 2.5keV (95% c.l.).Comment: 4 pages, 2 figures, submitted to PR
Secular Orbital Dynamics of the Possibly Habitable Planet K2-18 b with and without the Proposed Inner Companion
The transiting planet K2-18 b is one of the best candidates for a relatively
nearby world harboring biological life. The long-term orbital evolution of this
planet is investigated using theoretical and purely numerical techniques for
two possible configurations: a single planet orbiting the host star, and a
two-planet system including the proposed inner planet close to the 4:1 mean
motion rationalization. The emphasis is made on the secular changes of
eccentricity and orbital inclination, which are important for the climate
stability of the planet. It is demonstrated that the secular orbital dynamics
of planet K2-18 b with an internal companion are accurately represented by the
periodic eccentricity and inclination exchange on the time scales of a few Kyr.
A single planet is not expected to experience fast orbital changes, with the
much weaker tidal and rotation-driven perturbations mostly reflecting in a slow
periastron and nodal precession. The tidal decay of the orbit is too
insignificant on the time scale of the stellar age. However, the conditions for
the habitability of a single K2-18 b planet are much improved if, like the
Earth, it rotates faster than the mean motion and its rotation angle is tilted
by a hypothetical moon. Milankovi{\'c}'s cycles of the habitable planet's
climate are discussed for both configurations.Comment: Published in Universe 2023, 9, 46
Sunyaev-Zeldovich effect in WMAP and its effect on cosmological parameters
We use multi-frequency information in first year WMAP data to search for the
Sunyaev-Zeldovich (SZ) effect. WMAP has sufficiently broad frequency coverage
to constrain SZ without the addition of higher frequency data: the SZ power
spectrum amplitude is expected to increase 50% from W to Q frequency band.
This, in combination with the low noise in WMAP, allows us to strongly
constrain the SZ contribution. We derive an optimal frequency combination of
WMAP cross-spectra to extract SZ in the presence of noise, CMB, and radio point
sources, which are marginalized over. We find that the SZ contribution is less
than 2% (95% c.l.) at the first acoustic peak in W band. Under the assumption
that the removed radio point sources are not correlated with SZ this limit
implies sigma_8<1.07 at 95% c.l. We investigate the effect on the cosmological
parameters of allowing an SZ component. We run Monte Carlo Markov Chains with
and without an SZ component and find that the addition of SZ does not affect
any of the cosmological conclusions. We conclude that SZ does not contaminate
the WMAP CMB or change cosmological parameters, refuting the recent claims that
they may be corrupted.Comment: 10 pages, 5 figures, 2 tables. Submitted to Phys. Rev.
Gyr-timescale destruction of high-eccentricity asteroids by spin and why 2006 HY51 has been spared
Asteroids and other small celestial bodies have markedly prolate shapes, and
the perturbative triaxial torques which are applied during pericenter passages
in highly eccentric orbits trigger and sustain a state of chaotic rotation.
Because the prograde spin rate around the principal axis of inertia is not
bounded from above, it can accidentally reach the threshold value corresponding
to rotational break-up. Previous investigations of this process were limited to
integrations of orbits because of the stiff equation of motion. We
present here a fast 1D simulation method to compute the evolution of this spin
rate over orbits. We apply the method to the most eccentric solar
system asteroid known, 2006 HY51 (with ), and find that for any
reasonably expected shape parameters, it can never be accelerated to break-up
speed. However, primordial solar system asteroids on more eccentric orbits may
have already broken up from this type of rotational fission. The method also
represents a promising opportunity to investigate the long-term evolution of
extremely eccentric triaxial exo-asteroids (), which are thought to
be common in white dwarf planetary systemsComment: Accepted in ApJ. The computer-heavier version of chaotic rotation
simulation with reparameterization is available as a Julia code at
https://github.com/agoldin/2006HY5
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