736 research outputs found
Endomorphism fields of abelian varieties
We give a sharp divisibility bound, in terms of g, for the degree of the
field extension required to realize the endomorphisms of an abelian variety of
dimension g over an arbitrary number field; this refines a result of
Silverberg. This follows from a stronger result giving the same bound for the
order of the component group of the Sato-Tate group of the abelian variety,
which had been proved for abelian surfaces by Fite-Kedlaya-Rotger-Sutherland.
The proof uses Minkowski's reduction method, but with some care required in the
extremal cases when p equals 2 or a Fermat prime.Comment: 10 pages; v2: refereed versio
Body size trends in response to climate and urbanization in the widespread North American deer mouse, Peromyscus maniculatus
© 2020, The Author(s). Body size decline is hypothesized to be a key response to climate warming, including warming driven by urban heat islands. However, urbanization may also generate selective gradients for body size increases in smaller endotherms via habitat fragmentation. Here we utilize a densely sampled, multi-source dataset to examine how climate and urbanization affect body size of Peromyscus maniculatus (PEMA), an abundant rodent found across North America. We predicted PEMA would conform to Bergmannâs Rule, e.g. larger individuals in colder climates, spatially and temporally. Hypotheses regarding body size in relation to urbanization are less clear; however, with increased food resources due to greater anthropogenic activity, we expected an increase in PEMA size. Spatial mixed-models showed that PEMA conform to Bergmannâs Rule and that PEMA were shorter in more urbanized areas. With the inclusion of decade in mixed-models, we found PEMA mass, but not length, is decreasing over time irrespective of climate or population density. We also unexpectedly found that, over time, smaller-bodied populations of PEMA are getting larger, while larger-bodied populations are getting smaller. Our work highlights the importance of using dense spatiotemporal datasets, and modeling frameworks that account for bias, to better disentangle broad-scale climatic and urbanization effects on body size
Bounding the dimensions of rational cohomology groups
Let be an algebraically closed field of characteristic , and let
be a simple simply-connected algebraic group over that is defined and
split over the prime field . In this paper we investigate
situations where the dimension of a rational cohomology group for can be
bounded by a constant times the dimension of the coefficient module. We then
demonstrate how our results can be applied to obtain effective bounds on the
first cohomology of the symmetric group. We also show how, for finite Chevalley
groups, our methods permit significant improvements over previous estimates for
the dimensions of second cohomology groups.Comment: 13 page
Stability, Change, and Correlates of the Peer Relationships of Young Children With Mild Developmental Delays
Recommended from our members
Increasing phenological asynchrony between spring green-up and arrival of migratory birds
Consistent with a warming climate, birds are shifting the timing of their migrations, but it remains unclear to what extent these shifts have kept pace with the changing environment. Because bird migration is primarily cued by annually consistent physiological responses to photoperiod, but conditions at their breeding grounds depend on annually variable climate, bird arrival and climate-driven spring events would diverge. We combined satellite and citizen science data to estimate rates of change in phenological interval between spring green-up and migratory arrival for 48 breeding passerine species across North America. Both arrival and green-up changed over time, usually in the same direction (earlier or later). Although birds adjusted their arrival dates, 9 of 48 species did not keep pace with rapidly changing green-up and across all species the interval between arrival and green-up increased by over half a day per year. As green-up became earlier in the east, arrival of eastern breeding species increasingly lagged behind green-up, whereas in the westâwhere green-up typically became laterâbirds arrived increasingly earlier relative to green-up. Our results highlight that phenologies of species and trophic levels can shift at different rates, potentially leading to phenological mismatches with negative fitness consequences
On Sylow normalizers of finite groups
Electronic version of an article published as Journal of Algebra and Its Applications
Vol. 13, No. 3 (2014) 1350116 (20 pages). DOI 10.1142/S0219498813501168. © [copyright World Scientific Publishing Company] http://www.worldscientific.com/[EN] The paper considers the influence of Sylow normalizers, i.e. normalizers of Sylow subgroups, on the structure of finite groups. In the universe of finite soluble groups it is known that classes of groups with nilpotent Hall subgroups for given sets of primes are exactly the subgroup- closed saturated formations satisfying the following property: a group belongs to the class if and only if its Sylow normalizers do so. The paper analyzes the extension of this research to the universe of all finite groups.The second and third authors have been supported by Proyecto MTM2010-19938C03-02, Ministerio de Econom ia y Competitividad, Spain. The first author would like to thank the Universitat de Valencia and the Universitat Politecnica de Valencia for their warm hospitality during the preparation of this paper. He has been also supported by RFBR Project 13-01-00469.Kazarin, L.; MartĂnez Pastor, A.; Perez Ramos, MD. (2014). On Sylow normalizers of finite groups. Journal of Algebra and Its Applications. 13(3):1-20. https://doi.org/10.1142/S0219498813501168S12013
Pilot-scale production and physicochemical characterisation of spray-dried nanoparticulated whey protein powders
Spray-dried whey protein isolate (WPI) powders were prepared at pilot-scale from solutions without heat (WPIUH), heated (WPIH) or heated with calcium (WPIHCa), which were analysed and compared with a control sample (WPIC). WPIC, WPIUH, WPIH and WPIHCa solutions had whey protein denaturation levels of 0.0, 3.2, 64.4 and 74.4%, respectively. Computerised tomography scanning showed that 52.6, 84.0, 74.5 and 41.9% of WPIC, WPIUH, WPIH and WPIHCa powder particles had diameters of â€30 ”m. WPIHCa and WPIH powders were cohesive, while WPIC and WPIUH powders were easy flowing. Marked differences in microstructure were observed between WPIH and WPIHCa. There were no measured differences in wall friction, bulk density or colour
Origins of Mass
Newtonian mechanics posited mass as a primary quality of matter, incapable of
further elucidation. We now see Newtonian mass as an emergent property. Most of
the mass of standard matter, by far, arises dynamically, from back-reaction of
the color gluon fields of quantum chromodynamics (QCD). The equations for
massless particles support extra symmetries - specifically scale, chiral, and
gauge symmetries. The consistency of the standard model relies on a high degree
of underlying gauge and chiral symmetry, so the observed non-zero masses of
many elementary particles ( and bosons, quarks, and leptons) requires
spontaneous symmetry breaking. Superconductivity is a prototype for spontaneous
symmetry breaking and for mass-generation, since photons acquire mass inside
superconductors. A conceptually similar but more intricate form of
all-pervasive (i.e. cosmic) superconductivity, in the context of the
electroweak standard model, gives us a successful, economical account of
and boson masses. It also allows a phenomenologically successful, though
profligate, accommodation of quark and lepton masses. The new cosmic
superconductivity, when implemented in a straightforward, minimal way, suggests
the existence of a remarkable new particle, the so-called Higgs particle. The
mass of the Higgs particle itself is not explained in the theory, but appears
as a free parameter. Earlier results suggested, and recent observations at the
Large Hadron Collider (LHC) may indicate, the actual existence of the Higgs
particle, with mass GeV. In addition to consolidating our
understanding of the origin of mass, a Higgs particle with
GeV could provide an important clue to the future, as it is consistent with
expectations from supersymmetry.Comment: Invited review for the Central European Journal of Physics. This is
the supplement to my 2011 Solvay Conference talk promised there. It is
adapted from an invited talk given at the Atlanta APS meeting, April 2012. 33
pages, 6 figures. v2: Added update section bringing in the CERN discovery
announcemen
Research applications of primary biodiversity databases in the digital age.
Our world is in the midst of unprecedented change-climate shifts and sustained, widespread habitat degradation have led to dramatic declines in biodiversity rivaling historical extinction events. At the same time, new approaches to publishing and integrating previously disconnected data resources promise to help provide the evidence needed for more efficient and effective conservation and management. Stakeholders have invested considerable resources to contribute to online databases of species occurrences. However, estimates suggest that only 10% of biocollections are available in digital form. The biocollections community must therefore continue to promote digitization efforts, which in part requires demonstrating compelling applications of the data. Our overarching goal is therefore to determine trends in use of mobilized species occurrence data since 2010, as online systems have grown and now provide over one billion records. To do this, we characterized 501 papers that use openly accessible biodiversity databases. Our standardized tagging protocol was based on key topics of interest, including: database(s) used, taxa addressed, general uses of data, other data types linked to species occurrence data, and data quality issues addressed. We found that the most common uses of online biodiversity databases have been to estimate species distribution and richness, to outline data compilation and publication, and to assist in developing species checklists or describing new species. Only 69% of papers in our dataset addressed one or more aspects of data quality, which is low considering common errors and biases known to exist in opportunistic datasets. Globally, we find that biodiversity databases are still in the initial stages of data compilation. Novel and integrative applications are restricted to certain taxonomic groups and regions with higher numbers of quality records. Continued data digitization, publication, enhancement, and quality control efforts are necessary to make biodiversity science more efficient and relevant in our fast-changing environment
For common community phylogenetic analyses, go ahead and use synthesis phylogenies
Should we build our own phylogenetic trees based on gene sequence data, or can we simply use available synthesis phylogenies? This is a fundamental question that any study involving a phylogenetic framework must face at the beginning of the project. Building a phylogeny from gene sequence data (purposeâbuilt phylogeny) requires more effort, expertise, and cost than subsetting an already available phylogeny (synthesisâbased phylogeny). However, we still lack a comparison of how these two approaches to building phylogenetic trees influence common community phylogenetic analyses such as comparing community phylogenetic diversity and estimating trait phylogenetic signal. Here, we generated three purposeâbuilt phylogenies and their corresponding synthesisâbased trees (two from Phylomatic and one from the Open Tree of Life, OTL). We simulated 1,000 communities and 12,000 continuous traits along each purposeâbuilt phylogeny. We then compared the effects of different trees on estimates of phylogenetic diversity (alpha and beta) and phylogenetic signal (Pagelâs λ and Blombergâs K). Synthesisâbased phylogenies generally yielded higher estimates of phylogenetic diversity when compared to purposeâbuilt phylogenies. However, resulting measures of phylogenetic diversity from both types of phylogenies were highly correlated (Spearmanâs Ï > 0.8 in most cases). Mean pairwise distance (both alpha and beta) is the index that is most robust to the differences in tree construction that we tested. Measures of phylogenetic diversity based on the OTL showed the highest correlation with measures based on the purposeâbuilt phylogenies. Trait phylogenetic signal estimated with synthesisâbased phylogenies, especially from the OTL, was also highly correlated with estimates of Blombergâs K or close to Pagelâs λ from purposeâbuilt phylogenies when traits were simulated under Brownian motion. For commonly employed community phylogenetic analyses, our results justify taking advantage of recently developed and continuously improving synthesis trees, especially the Open Tree of Life.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151322/1/ecy2788_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151322/2/ecy2788.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151322/3/ecy2788-sup-0001-AppendixS1.pd
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