67,819 research outputs found
Are Stars with Planets Polluted?
We compare the metallicities of stars with radial velocity planets to the
metallicity of a sample of field dwarfs. We confirm recent work indicating that
the stars-with-planet sample as a whole is iron rich. However, the lowest mass
stars tend to be iron poor, with several having [Fe/H]<-0.2, demonstrating that
high metallicity is not required for the formation of short period Jupiter-mass
planets. We show that the average [Fe/H] increases with increasing stellar mass
(for masses below 1.25 solar masses) in both samples, but that the increase is
much more rapid in the stars-with-planet sample. The variation of metallicity
with stellar age also differs between the two samples. We examine possible
selection effects related to variations in the sensitivity of radial velocity
surveys with stellar mass and metallicity, and identify a color cutoff
(B-V>0.48) that contributes to but does not explain the mass-metallicity trend
in the stars-with-planets sample. We use Monte Carlo models to show that adding
an average of 6.5 Earth masses of iron to each star can explain both the
mass-metallicity and the age-metallicity relations of the stars-with-planets
sample. However, for at least one star, HD 38529, there is good evidence that
the bulk metallicity is high. We conclude that the observed metallicities and
metallicity trends are the result of the interaction of three effects;
accretion of about 6 Earth masses of iron rich material, selection effects, and
in some cases, high intrinsic metallicity.Comment: 19 pages 11 figure
Climate Change, Food Security, and Agrobioversity: Toward a Just, Resilient, and Sustainable Food System
Racial Intelligence Testing and the Mexican People
In the 1920s and 1930s the Mexican school age population increasingly participated in the educational system of the US. Meanwhile, many first experiences of these children with the state came in the form of educational research. The intelligence testing movement had a brief history before then, one which was gathering much momentum and greatly encouraged by corporate foundations and the cooperation of university administrations. The rapid immigration in the 1920s and settlement of Mexicans into colonias of the Southwest coincided with the rise of academic research and publications on racial intelligence as well as with the combination of mass compulsory education and intelligence testing tracking and curriculum differentation [differentiation]
Measuring the Muon Content of Air Showers with IceTop
IceTop, the surface component of the IceCube detector, has been used to
measure the energy spectrum of cosmic ray primaries in the range between 1.58
PeV and 1.26 EeV. It can also be used to study the low energy muons in air
showers by looking at large distances (> 300m) from the shower axis. We will
show the muon lateral distribution function at large lateral distances as
measured with IceTop and discuss the implications of this measurement. We also
discuss the prospects for low energy muon studies with IceTop.Comment: 5 pages, 9 figures, presented at the 18th meeting of the
International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI
2014
EDUCATIONAL REFORM IN LOS ANGELES AND ITS EFFECT UPON THE MEXICAN COMMUNITY, 1900-1930
The theme of equal educational opportunity was a major concern of the urban Chicano Movement in the late sixties. Chicanos accused the entire school system of racism and insensitivity towards the Chicano community. Schools, declared the activists, used institutionalized techniques such as intelligence tests and a tracking system to insure that disproportional numbers of Chicano children would be placed in vocational education courses or in classes for the mentally retarded
An n-sided polygonal model to calculate the impact of cyber security events
This paper presents a model to represent graphically the impact of cyber
events (e.g., attacks, countermeasures) in a polygonal systems of n-sides. The
approach considers information about all entities composing an information
system (e.g., users, IP addresses, communication protocols, physical and
logical resources, etc.). Every axis is composed of entities that contribute to
the execution of the security event. Each entity has an associated weighting
factor that measures its contribution using a multi-criteria methodology named
CARVER. The graphical representation of cyber events is depicted as straight
lines (one dimension) or polygons (two or more dimensions). Geometrical
operations are used to compute the size (i.e, length, perimeter, surface area)
and thus the impact of each event. As a result, it is possible to identify and
compare the magnitude of cyber events. A case study with multiple security
events is presented as an illustration on how the model is built and computed.Comment: 16 pages, 5 figures, 2 tables, 11th International Conference on Risks
and Security of Internet and Systems, (CRiSIS 2016), Roscoff, France,
September 201
- …