15,842 research outputs found
The Scythe Statistical Library: An Open Source C++ Library for Statistical Computation
The Scythe Statistical Library is an open source C++ library for statistical computation. It includes a suite of matrix manipulation functions, a suite of pseudo-random number generators, and a suite of numerical optimization routines. Programs written using Scythe are generally much faster than those written in commonly used interpreted languages, such as R and \proglang{MATLAB}; and can be compiled on any system with the GNU GCC compiler (and perhaps with other C++ compilers). One of the primary design goals of the Scythe developers has been ease of use for non-expert C++ programmers. Ease of use is provided through three primary mechanisms: (1) operator and function over-loading, (2) numerous pre-fabricated utility functions, and (3) clear documentation and example programs. Additionally, Scythe is quite flexible and entirely extensible because the source code is available to all users under the GNU General Public License.
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DNA Methylation Analysis Validates Organoids as a Viable Model for Studying Human Intestinal Aging.
Background & aimsThe epithelia of the intestine and colon turn over rapidly and are maintained by adult stem cells at the base of crypts. Although the small intestine and colon have distinct, well-characterized physiological functions, it remains unclear if there are fundamental regional differences in stem cell behavior or region-dependent degenerative changes during aging. Mesenchyme-free organoids provide useful tools for investigating intestinal stem cell biology in vitro and have started to be used for investigating age-related changes in stem cell function. However, it is unknown whether organoids maintain hallmarks of age in the absence of an aging niche. We tested whether stem cell-enriched organoids preserved the DNA methylation-based aging profiles associated with the tissues and crypts from which they were derived.MethodsTo address this, we used standard human methylation arrays and the human epigenetic clock as a biomarker of age to analyze in vitro-derived, 3-dimensional, stem cell-enriched intestinal organoids.ResultsWe found that human stem cell-enriched organoids maintained segmental differences in methylation patterns and that age, as measured by the epigenetic clock, also was maintained in vitro. Surprisingly, we found that stem cell-enriched organoids derived from the small intestine showed striking epigenetic age reduction relative to organoids derived from colon.ConclusionsOur data validate the use of organoids as a model for studying human intestinal aging and introduce methods that can be used when modeling aging or age-onset diseases in vitro
Collisional Formation and Modeling of Asteroid Families
In the last decade, thanks to the development of sophisticated numerical
codes, major breakthroughs have been achieved in our understanding of the
formation of asteroid families by catastrophic disruption of large parent
bodies. In this review, we describe numerical simulations of asteroid
collisions that reproduced the main properties of families, accounting for both
the fragmentation of an asteroid at the time of impact and the subsequent
gravitational interactions of the generated fragments. The simulations
demonstrate that the catastrophic disruption of bodies larger than a few
hundred meters in diameter leads to the formation of large aggregates due to
gravitational reaccumulation of smaller fragments, which helps explain the
presence of large members within asteroid families. Thus, for the first time,
numerical simulations successfully reproduced the sizes and ejection velocities
of members of representative families. Moreover, the simulations provide
constraints on the family dynamical histories and on the possible internal
structure of family members and their parent bodies.Comment: Chapter to appear in the (University of Arizona Press) Space Science
Series Book: Asteroids I
Pion Photoproduction Amplitude Relations in the 1/N_c Expansion
We derive expressions for pion photoproduction amplitudes in the 1/N_c
expansion of QCD, and obtain linear relations directly from this expansion that
relate electromagnetic multipole amplitudes at all energies. The leading-order
relations in 1/N_c compare favorably with available data, while the
next-to-leading order relations seem to provide only a small improvement.
However, when resonance parameters are compared directly, the agreement at
O(1/N_c) or O(1/N_c^2) is impressive.Comment: 19 pages, ReVTeX, 50 eps files combine into 5 compound figure
Apple-Polishers, Ass-Kissers and Suck-Ups: Towards a Sociology of Ingratiation
In this paper we use one form of communicative action, “brownnosing”, as a social lens for understanding power relations in both formal, organizational contexts and interpersonal relationships. We investigate this phenomenon by assessing processes of ingratiation at school and work settings. We do so using data collected from over one hundred student respondents to ascertain the meanings, uses, and outcomes of brownnosing. The study finds that members of the “millennial generation” develop skills in both the act of brownnosing and the detection of this form of communication as they participate in a variety of contexts, including family, school, work, and interpersonal relationships. Utilizing power-dependence models for analysis, our data suggest that brownnosing, as an organizational resource, commonly reflects the structural arrangements of both school and the workplace. We draw upon organizational and exchange theories in the interpretation of the data
A Tool in the Kit: Uses of Bullshitting among Millennial Workers
This study explores the nature, use, and social organization of one form of communicative action that is common in everyday life -- bullshitting. We use this form of communication to assess the ways in which dimensions of community, power and status are created in interaction. Abiding by the canons of ethnographic content analysis, we gathered data from over one hundred student respondents to ascertain the behaviors, utterances, and stories that people define as bullshitting. The study finds that members of the millennial generation hone skills both in the telling and detection of this form of communication as they participate in a variety of contexts, including school, work, and interpersonal relationships. Special attention is given to the ways in which bullshitting is used as a cultural resource for agentive action. Dramaturgical and organizational theories are drawn upon in theorizing the data
Theoretical uncertainty in baryon oscillations
We discuss the systematic uncertainties in the recovery of dark energy
properties from the use of baryon acoustic oscillations as a standard ruler. We
demonstrate that while unknown relativistic components in the universe prior to
recombination would alter the sound speed, the inferences for dark energy from
low-redshift surveys are unchanged so long as the microwave background
anisotropies can measure the redshift of matter-radiation equality, which they
can do to sufficient accuracy. The mismeasurement of the radiation and matter
densities themselves (as opposed to their ratio) would manifest as an incorrect
prediction for the Hubble constant at low redshift. In addition, these
anomalies do produce subtle but detectable features in the microwave
anisotropies.Comment: 4 pages, REVTeX, 1 figure. Submitted to PR
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