47,387 research outputs found
Recommended from our members
Who are Rural Students? How Definitions of Rurality Affect Research on College Completion
Given a revived national discourse about rural populations, more educational research on rural students is necessary, including ways that rural students transition to college and the success (or lack thereof) that they experience once there. However, the National Center for Education Statistics (NCES) has changed the definition of rurality used in each iterative dataset over the last few decades, casting doubt on the consistency of what is meant by the term rural. The purpose of this study is to: (a) communicate to the educational research audience various ways of defining rural students, and specifically how NCES has changed their definition of rurality over their last three major data collections; (b) demonstrate how conclusions about rural students’ and their college degree completion may differ based on these alternate NCES definitions; and (c) discuss how this specific example using NCES data relates to the wider landscape of research on rural students. Results show that conclusions about college degree completion change depending on the definition of rurality used for analysis. Therefore, the education research community should consider the options for defining rural students, report transparently about the choices made, consider the sensitivity of results to the definition of rurality, and ultimately build a more robust body of literature concerning rural students’ college success. Gaining definitional clarity will be beneficial, particularly for those who wish to translate their research into practical action for the benefit of rural students
Finite Dimensional Statistical Inference
In this paper, we derive the explicit series expansion of the eigenvalue
distribution of various models, namely the case of non-central Wishart
distributions, as well as correlated zero mean Wishart distributions. The tools
used extend those of the free probability framework, which have been quite
successful for high dimensional statistical inference (when the size of the
matrices tends to infinity), also known as free deconvolution. This
contribution focuses on the finite Gaussian case and proposes algorithmic
methods to compute the moments. Cases where asymptotic results fail to apply
are also discussed.Comment: 14 pages, 13 figures. Submitted to IEEE Transactions on Information
Theor
Impact of Home Field Advantage: Analyzed Across Three Professional Sports
We examined the impact of home-field advantage in the NFL, NBA, and MLB. We defined home-field advantage as winning more than 50% of the home games. Additionally, we took into consideration how season length could act as a moderator and influence the impact of home-field advantage. We collected data from the 2015 NBA and MLB seasons and the 2015 and 2016 NFL seasons to determine statistical significance. In total, we got data from 4,141 games to analyze. We found that there is statistical significance that the home team has a better chance of winning than the away team across the NFL, NBA, and MLB. We also found that season length has a significant impact on home team winning percentage
Quantifying the Biases of Spectroscopically Selected Gravitational Lenses
Spectroscopic selection has been the most productive technique for the
selection of galaxy-scale strong gravitational lens systems with known
redshifts. Statistically significant samples of strong lenses provide a
powerful method for measuring the mass-density parameters of the lensing
population, but results can only be generalized to the parent population if the
lensing selection biases are sufficiently understood. We perform controlled
Monte Carlo simulations of spectroscopic lens surveys in order to quantify the
bias of lenses relative to parent galaxies in velocity dispersion, mass axis
ratio, and mass density profile. For parameters typical of the SLACS and BELLS
surveys, we find: (1) no significant mass axis ratio detection bias of lenses
relative to parent galaxies; (2) a very small detection bias toward shallow
mass density profiles, which is likely negligible compared to other sources of
uncertainty in this parameter; (3) a detection bias towards smaller Einstein
radius for systems drawn from parent populations with group- and cluster-scale
lensing masses; and (4) a lens-modeling bias towards larger velocity
dispersions for systems drawn from parent samples with sub-arcsecond mean
Einstein radii. This last finding indicates that the incorporation of
velocity-dispersion upper limits of \textit{non-lenses} is an important
ingredient for unbiased analyses of spectroscopically selected lens samples. In
general we find that the completeness of spectroscopic lens surveys in the
plane of Einstein radius and mass-density profile power-law index is quite
uniform, up to a sharp drop in the region of large Einstein radius and steep
mass density profile, and hence that such surveys are ideally suited to the
study of massive field galaxies.Comment: Accepted for publication in Astrophys. J., June 7, 2012. In press. 9
pages, 5 figures, 1 tabl
Extending Quantum Coherence in Diamond
We experimentally demonstrate over two orders of magnitude increase in the
coherence time of nitrogen vacancy centres in diamond by implementing
decoupling techniques. We show that equal pulse spacing decoupling performs
just as well as non-periodic Uhrig decoupling and has the additional benefit
that it allows us to take advantage of "revivals" in the echo (due to the
coherent nature of the bath) to explore the longest coherence times. At short
times, we can extend the coherence of particular quantum states out from
T_2*=2.7 us out to an effective T_2 > 340 us. For preserving arbitrary states
we show the experimental importance of using pulse sequences, that through
judicious choice of the phase of the pulses, compensate the imperfections of
individual pulses for all input states. At longer times we use these
compensated sequences to enhance the echo revivals and show a coherence time of
over 1.6 ms in ultra-pure natural abundance 13C diamond.Comment: 7 pages, 7 figures; minor syntax/typo. changes and updated reference
Risk evaluations and condom use decisions of homeless youth: a multi-level qualitative investigation.
BackgroundHomeless youth are at higher risk for sexually transmitted infections and unwanted pregnancy than non-homeless youth. However, little is known about how they evaluate risk within the context of their sexual relationships. It is important to understand homeless youths' condom use decisions in light of their sexual relationships because condom use decisions are influenced by relationship dynamics in addition to individual attitudes and event circumstances. It is also important to understand how relationship level factors, sexual event circumstances, and individual characteristics compare and intersect.MethodsTo explore these issues, we conducted semi-structured interviews with 37 homeless youth in Los Angeles County in 2011 concerning their recent sexual relationships and analyzed the data using systematic methods of team-based qualitative data analysis.ResultsWe identified themes of risk-related evaluations and decisions at the relationship/partner, event, and individual level. We also identified three different risk profiles that emerged from analyzing how different levels of risk intersected across individual respondents. The three profiles included 1) Risk Takers, who consistently engage in risk and have low concern about consequences of risk behavior, 2) Risk Avoiders, who consistently show high concern about protection and consistently avoid risk, and 3) Risk Reactors, those who are inconsistent in their concerns about risk and protection and mainly take risks in reaction to relationship and event circumstances.ConclusionsInterventions targeting homeless youth should reflect multiple levels of risk behavior and evaluation in order to address the diversity of risk profiles. Relationship/partner-, event-, and individual-level factors are all important but have different levels of importance for different homeless youth. Interventions should be tailored to address the most important factor contributing to homeless youth reproductive needs
Antiferromagnetic Spinor Condensates are Quantum Rotors
We establish a theoretical correspondence between spin-one antiferromagnetic
spinor condensates in an external magnetic field and quantum rotor models in an
external potential. We show that the rotor model provides a conceptually clear
picture of the possible phases and dynamical regimes of the antiferromagnetic
condensate. We also show that this mapping simplifies calculations of the
condensate's spectrum and wavefunctions. We use the rotor mapping to describe
the different dynamical regimes recently observed in Na condensates. We
also suggest a way to experimentally observe quantum mechanical effects
(collapse and revival) in spinor condensates.Comment: minor revisions. some typos correcte
Heavy and Light Quarks with Lattice Chiral Fermions
The feasibility of using lattice chiral fermions which are free of
errors for both the heavy and light quarks is examined. The fact that the
effective quark propagators in these fermions have the same form as that in the
continuum with the quark mass being only an additive parameter to a chirally
symmetric antihermitian Dirac operator is highlighted. This implies that there
is no distinction between the heavy and light quarks and no mass dependent
tuning of the action or operators as long as the discretization error is negligible. Using the overlap fermion, we find that the
(and ) errors in the dispersion relations of the pseudoscalar and
vector mesons and the renormalization of the axial-vector current and scalar
density are small. This suggests that the applicable range of may be
extended to with only 5% error, which is a factor of
larger than that of the improved Wilson action. We show that the generalized
Gell-Mann-Oakes-Renner relation with unequal masses can be utilized to
determine the finite errors in the renormalization of the matrix elements
for the heavy-light decay constants and semileptonic decay constants of the B/D
meson.Comment: final version to appear in Int. Jou. Mod. Phys.
The diamond Nitrogen-Vacancy center as a probe of random fluctuations in a nuclear spin ensemble
New schemes that exploit the unique properties of Nitrogen-Vacancy (NV)
centers in diamond are presently being explored as a platform for
high-resolution magnetic sensing. Here we focus on the ability of a NV center
to monitor an adjacent mesoscopic nuclear spin bath. For this purpose, we
conduct comparative experiments where the NV spin evolves under the influence
of surrounding 13C nuclei or, alternatively, in the presence of asynchronous AC
fields engineered to emulate bath fluctuations. Our study reveals substantial
differences that underscore the limitations of the semi-classical picture when
interpreting and predicting the outcome of experiments designed to probe small
nuclear spin ensembles. In particular, our study elucidates the NV center
response to bath fluctuations under common pulse sequences, and explores a
detection protocol designed to probe time correlations of the nuclear spin bath
dynamics. Further, we show that the presence of macroscopic nuclear spin order
is key to the emergence of semi-classical spin magnetometry.Comment: 30 pages, 4 figure
Antiphase dynamics in a multimode semiconductor laser with optical injection
A detailed experimental study of antiphase dynamics in a two-mode
semiconductor laser with optical injection is presented. The device is a
specially designed Fabry-Perot laser that supports two primary modes with a THz
frequency spacing. Injection in one of the primary modes of the device leads to
a rich variety of single and two-mode dynamical scenarios, which are reproduced
with remarkable accuracy by a four dimensional rate equation model. Numerical
bifurcation analysis reveals the importance of torus bifurcations in mediating
transitions to antiphase dynamics and of saddle-node of limit cycle
bifurcations in switching of the dynamics between single and two-mode regimes.Comment: 7 pages, 9 figure
- …