1,990 research outputs found
The abundance of galaxy clusters in MOND: Cosmological simulations with massive neutrinos
We present a new Particle-Mesh cosmological N-body code for accurately
solving the modified Poisson equation of the Quasi Linear formulation of MOND.
We generate initial conditions for the Angus (2009) cosmological model, which
is identical to LCDM except that the cold dark matter is switched for a single
species of thermal sterile neutrinos. We set the initial conditions at z=250
for a (512 Mpc/h)^3 box with 256^3 particles and we evolve them down to z=0. We
clearly demonstrate the necessity of MOND for developing the large scale
structure in a hot dark matter cosmology and contradict the naive expectation
that MOND cannot form galaxy clusters. We find that the correct order of
magnitude of X-ray clusters (with T_X > 4.5 keV) can be formed, but that we
overpredict the number of very rich clusters and seriously underpredict the
number of lower mass clusters. The latter is a shortcoming of the resolution of
our simulations, whereas we suggest that the over production of very rich
clusters might be prevented by incorporating a MOND acceleration constant that
varies with redshift and an expansion history that cannot be described by the
usual Friedmann models. We present evidence that suggests the density profiles
of our simulated clusters are compatible with those of observed X-ray clusters
in MOND. It remains to be seen if the low mass end of the cluster mass function
can be reproduced and if the high densities of dark matter in the central 20
kpc of groups and clusters of galaxies, measured in the MOND framework, can be
achieved. As a last test, we computed the relative velocity between pairs of
halos within 10 Mpc and find that pairs with velocities larger than 3000 km/s
like the bullet cluster, can form without difficulty.Comment: 9 pages, 7 figur
Dynamic Influence Networks for Rule-based Models
We introduce the Dynamic Influence Network (DIN), a novel visual analytics
technique for representing and analyzing rule-based models of protein-protein
interaction networks. Rule-based modeling has proved instrumental in developing
biological models that are concise, comprehensible, easily extensible, and that
mitigate the combinatorial complexity of multi-state and multi-component
biological molecules. Our technique visualizes the dynamics of these rules as
they evolve over time. Using the data produced by KaSim, an open source
stochastic simulator of rule-based models written in the Kappa language, DINs
provide a node-link diagram that represents the influence that each rule has on
the other rules. That is, rather than representing individual biological
components or types, we instead represent the rules about them (as nodes) and
the current influence of these rules (as links). Using our interactive DIN-Viz
software tool, researchers are able to query this dynamic network to find
meaningful patterns about biological processes, and to identify salient aspects
of complex rule-based models. To evaluate the effectiveness of our approach, we
investigate a simulation of a circadian clock model that illustrates the
oscillatory behavior of the KaiC protein phosphorylation cycle.Comment: Accepted to TVCG, in pres
Convergent adaptations: bitter manioc cultivation systems in fertile anthropogenic dark earths and floodplain soils in central Amazonia
Shifting cultivation in the humid tropics is incredibly diverse, yet research tends to focus on one type: long-fallow shifting cultivation. While it is a typical adaptation to the highly-weathered nutrient-poor soils of the Amazonian terra firme, fertile environments in the region offer opportunities for agricultural intensification. We hypothesized that Amazonian people have developed divergent bitter manioc cultivation systems as adaptations to the properties of different soils. We compared bitter manioc cultivation in two nutrient-rich and two nutrient-poor soils, along the middle Madeira River in Central Amazonia. We interviewed 249 farmers in 6 localities, sampled their manioc fields, and carried out genetic analysis of bitter manioc landraces. While cultivation in the two richer soils at different localities was characterized by fast-maturing, low-starch manioc landraces, with shorter cropping periods and shorter fallows, the predominant manioc landraces in these soils were generally not genetically similar. Rather, predominant landraces in each of these two fertile soils have emerged from separate selective trajectories which produced landraces that converged for fast-maturing low-starch traits adapted to intensified swidden systems in fertile soils. This contrasts with the more extensive cultivation systems found in the two poorer soils at different localities, characterized by the prevalence of slow-maturing high-starch landraces, longer cropping periods and longer fallows, typical of previous studies. Farmers plant different assemblages of bitter manioc landraces in different soils and the most popular landraces were shown to exhibit significantly different yields when planted in different soils. Farmers have selected different sets of landraces with different perceived agronomic characteristics, along with different fallow lengths, as adaptations to the specific properties of each agroecological micro-environment. These findings open up new avenues for research and debate concerning the origins, evolution, history and contemporary cultivation of bitter manioc in Amazonia and beyond
Principals’ Strategies for Successfully Closing the Achievement Gaps in their Schools
One of our greatest educational challenges is reducing the achievement gap between successful and less-successful students. The achievement gap is usually discussed in terms of dramatic differences in graduation rates and the academic achievement between white and minority students such as Hispanics (Waxman, Padrón, and Garcia, 2007). Research in this area typically looks at school districts and/or schools that do better than others in reducing the gaps between groups of students. There are fewer research studies, however, that focus on achievement gaps within schools and classrooms. These “within” school educational disparities often are greater than the differences between schools or school differences (Waxman et al., 2007)
Athletes, you’re doing weight training all wrong
First paragraph: To become stronger and develop more muscle, you must lift heavier weights over relatively few repetitions. At least, that has been the received wisdom among professional athletes. However, a new body of evidence suggests that it may be wrong. https://theconversation.com/athletes-youre-doing-weight-training-all-wrong-6279
Structure of Fear and Horror in "Benito Cereno," "Heart of Darkness," and "The Turn of the Screw"
Englis
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