1,900 research outputs found
Counting maximal arithmetic subgroups
We study the growth rate of the number of maximal arithmetic subgroups of bounded covolumes in a semisimple Lie group using an extension of the method developed by Borel and Prasad
Strategies for Engaging Scientists in Collaborative Processes
Scientists are often reluctant to get involved in collaborative efforts to address natural resource issues because of potential professional repercussions. As agents for change, Extension professionals can help to bring scientists into these problem-solving efforts. In this article, collaborative and scientific processes are compared and contrasted to provide one way for Extension professionals to communicate the role of scientists in collaborative problem solving. Extension activities can be instrumental in efforts to move scientists from experts outside of the problem-solving process to scientists as key players and full partners in the process
Evaluating the ecological realism of plant species distribution models with ecological indicator values
Species distribution models (SDMs) are routinely applied to assess current as well as future species distributions, for example to assess impacts of future environmental change on biodiversity or to underpin conservation planning. It has been repeatedly emphasized that SDMs should be evaluated based not only on their goodness of fit to the data, but also on the realism of the modelled ecological responses. However, possibilities for the latter are hampered by limited knowledge on the true responses as well as a lack of quantitative evaluation methods. Here we compared modelled niche optima obtained from European-scale SDMs of 1,476 terrestrial vascular plant species with empirical ecological indicator values indicating the preferences of plant species for key environmental conditions. For each plant species we first fitted an ensemble SDM including three modeling techniques (GLM, GAM and BRT) and extracted niche optima for climate, soil, land use and nitrogen deposition variables with a large explanatory power for the occurrence of that species. We then compared these SDM-derived niche optima with the ecological indicator values by means of bivariate correlation analysis. We found weak to moderate correlations in the expected direction between the SDM-derived niche optima and ecological indicator values. The strongest correlation occurred between the modelled optima for growing degree days and the ecological indicator values for temperature. Correlations were weaker for SDM-derived niche optima with a more distal relationship to ecological indicator values (notably precipitation and soil moisture). Further, correlations were consistently highest for BRT, followed by GLM and GAM. Our method gives insight into the ecological realism of modelled niche optima and projected core habitats and can be used to improve SDMs by making a more informed selection of environmental variables and modeling techniques
Direct Visualization of Single Nuclear Pore Complex Proteins Using Genetically-Encoded Probes for DNA-PAINT
The nuclear pore complex (NPC) is one of the largest and most complex protein assemblies in the cell and, among other functions, serves as the gatekeeper of nucleocytoplasmic transport. Unraveling its molecular architecture and functioning has been an active research topic for decades with recent cryogenic electron microscopy and super-resolution studies advancing our understanding of the architecture of the NPC complex. However, the specific and direct visualization of single copies of NPC proteins is thus far elusive. Herein, we combine genetically-encoded self-labeling enzymes such as SNAP-tag and HaloTag with DNA-PAINT microscopy. We resolve single copies of nucleoporins in the human Y-complex in three dimensions with a precision of circa 3 nm, enabling studies of multicomponent complexes on the level of single proteins in cells using optical fluorescence microscopy
Determining cellular CTCF and cohesin abundances to constrain 3D genome models.
Achieving a quantitative and predictive understanding of 3D genome architecture remains a major challenge, as it requires quantitative measurements of the key proteins involved. Here, we report the quantification of CTCF and cohesin, two causal regulators of topologically associating domains (TADs) in mammalian cells. Extending our previous imaging studies (Hansen et al., 2017), we estimate bounds on the density of putatively DNA loop-extruding cohesin complexes and CTCF binding site occupancy. Furthermore, co-immunoprecipitation studies of an endogenously tagged subunit (Rad21) suggest the presence of cohesin dimers and/or oligomers. Finally, based on our cell lines with accurately measured protein abundances, we report a method to conveniently determine the number of molecules of any Halo-tagged protein in the cell. We anticipate that our results and the established tool for measuring cellular protein abundances will advance a more quantitative understanding of 3D genome organization, and facilitate protein quantification, key to comprehend diverse biological processes
Nuclear pore assembly proceeds by an inside-out extrusion of the nuclear envelope
The nuclear pore complex (NPC) mediates nucleocytoplasmic transport through the
nuclear envelope. How the NPC assembles into this double membrane boundary has remained
enigmatic. Here, we captured temporally staged assembly intermediates by correlating live cell
imaging with high-resolution electron tomography and super-resolution microscopy. Intermediates
were dome-shaped evaginations of the inner nuclear membrane (INM), that grew in diameter and
depth until they fused with the flat outer nuclear membrane. Live and super-resolved fluorescence
microscopy revealed the molecular maturation of the intermediates, which initially contained the
nuclear and cytoplasmic ring component Nup107, and only later the cytoplasmic filament
component Nup358. EM particle averaging showed that the evagination base was surrounded by
an 8-fold rotationally symmetric ring structure from the beginning and that a growing mushroomshaped
density was continuously associated with the deforming membrane. Quantitative structural
analysis revealed that interphase NPC assembly proceeds by an asymmetric inside-out extrusion of
the INM
Using species attributes to characterize late-glacial and early-Holocene environments at KrÄkenes, western Norway
Aim: We aim to use species attributes such as distributions and indicator values to reconstruct past biomes, environment, and temperatures from detailed plantâmacrofossil data covering the late glacial to the early Holocene (ca. 14â9 ka). Location: KrĂ„kenes, western Norway. Methods: We applied attributes for presentâday geographical distribution, optimal July and January temperatures, and Ellenberg indicator values for plants in the macrofossil dataâset. We used assemblage weighted means (AWM) to reconstruct past biomes, changes in light (L), nitrogen (N), moisture (F), and soil reaction (R), and temperatures. We compared the temperature reconstructions with previous chironomidâinferred temperatures. Results: After the start of the Holocene around 11.5 ka, the Arcticâmontane biome, which was stable during the lateâglacial period, shifted successively into the Boreoâarctic montane, Wideâboreal, Boreoâmontane, Boreoâtemperate, and Wideâtemperate biomes by ca. 9.0 ka. Circumpolar and Eurasian floristic elements characteristic of the lateâglacial decreased and the Eurosiberian element became prominent. Light demand (L), soil moisture (F), nitrogen (N), and soil reaction (R) show different, but complementary responses. Lightâdemanding plants decreased with time. Soil moisture was relatively stable until it increased during organic soil development during the early Holocene. Soil nitrogen increased during the early Holocene. Soil reaction (pH) decreased during the AllerĂžd, but increased during the Younger Dryas. It decreased markedly after the start of the Holocene, reaching low but stable levels in the early Holocene. Mean July and January temperatures show similar patterns to the chironomidâinferred mean July temperature trends at KrĂ„kenes, but chironomids show larger fluctuations and interesting differences in timing. Conclusion: Assigning attributes to macrofossil species is a useful new approach in palaeoecology. It can demonstrate changes in biomes, ecological conditions, and temperatures. The lateâglacial to earlyâHolocene transition may form an analogue for changes observed in the modern arctic and in mountains, with melting glaciers, permafrost thaw, and shrub encroachment into tundra.publishedVersio
Testing Hardy nonlocality proof with genuine energy-time entanglement
We show two experimental realizations of Hardy ladder test of quantum
nonlocality using energy-time correlated photons, following the scheme proposed
by A. Cabello \emph{et al.} [Phys. Rev. Lett. \textbf{102}, 040401 (2009)].
Unlike, previous energy-time Bell experiments, these tests require precise
tailored nonmaximally entangled states. One of them is equivalent to the
two-setting two-outcome Bell test requiring a minimum detection efficiency. The
reported experiments are still affected by the locality and detection
loopholes, but are free of the post-selection loophole of previous energy-time
and time-bin Bell tests.Comment: 5 pages, revtex4, 6 figure
Averages of Fourier coefficients of Siegel modular forms and representation of binary quadratic forms by quadratic forms in four variables
Let be a a negative discriminant and let vary over a set of
representatives of the integral equivalence classes of integral binary
quadratic forms of discriminant . We prove an asymptotic formula for for the average over of the number of representations of by an
integral positive definite quaternary quadratic form and obtain results on
averages of Fourier coefficients of linear combinations of Siegel theta series.
We also find an asymptotic bound from below on the number of binary forms of
fixed discriminant which are represented by a given quaternary form. In
particular, we can show that for growing a positive proportion of the
binary quadratic forms of discriminant is represented by the given
quaternary quadratic form.Comment: v5: Some typos correcte
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