100,385 research outputs found
Occupancy, spatial variance, and the abundance of species
A notable and consistent ecological observation known for
a long time is that spatial variance in the abundance of a
species increases with its mean abundance and that this relationship typically conforms well to a simple
power law (Taylor 1961). Indeed, such models can be
used at a spectrum of spatial scales to describe spatial
variance in the abundance of a single species at different
times or in different regions and of different species across the same set of areas (Taylor et al. 1978; Taylor and Woiwod 1982)
Estimating species abundance from occurrence
The number of individuals, or the abundance, of a species
in an area is a fundamental ecological parameter and a
critical consideration when making management and conservation decisions (Andrewartha and Birch 1954; Krebs
1978; Gaston 1994; Caughley and Gunn 1996). However,
unless the scale is very fine or localized (e.g., in a measurable habitat or a forest stand), abundance is not readily determined. At coarse or regional scales for many species, information on commonness and rarity is, at best, limited to a map of their presence or absence from recording units in a specified time frame. Various species data at large scales are increasingly documented in this presence/absence forma
A concentrator for static magnetic field
We propose a compact passive device as a super-concentrator to create an
extremely high uniform static magnetic field over 50T in a large
two-dimensional free space from a weak background magnetic field. Such an
amazing thing becomes possible for the first time, thanks to space-folded
transformation and metamaterials for static magnetic fields. Finite element
method (FEM) is utilized to verify the performance of the proposed device
Transforming magnets
Based on the form-invariant of Maxwell's equations under coordinate
transformations, we extend the theory of transformation optics to
transformation magneto-statics, which can design magnets through coordinate
transformations. Some novel DC magnetic field illusions created by magnets
(e.g. shirking magnets, cancelling magnets and overlapping magnets) are
designed and verified by numerical simulations. Our research will open a new
door to designing magnets and controlling DC magnetic fields
Reply To "Comment on 'Quantum String Seal Is Insecure' "
In Phys. Rev. A. 76, 056301 (2007), He claimed that the proof in my earlier
paper [Phys. Rev. A 75, 012327 (2007)] is insufficient to conclude the
insecurity of all quantum string seals because my measurement strategy cannot
obtain non-trivial information on the sealed string and escape detection at the
same time. Here, I clarify that our disagreement comes from our adoption of two
different criteria on the minimum amount of information a quantum string seal
can reveal to members of the public. I also point out that He did not follow my
measurement strategy correctly.Comment: 2 page
A dual catalytic strategy for carbon-phosphorus cross-coupling via gold and photoredox catalysis.
A new method for the P-arylation of aryldiazonium salts with H-phosphonates via dual gold and photoredox catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives, and offers an efficient approach to arylphosphonates. The reaction is proposed to proceed through a photoredox-promoted generation of an electrophilic arylgold(III) intermediate that undergoes coupling with the H-phosphonate nucleophile
Quark Recombination and Heavy Quark Diffusion in Hot Nuclear Matter
We discuss resonance recombination for quarks and show that it is compatible
with quark and hadron distributions in local thermal equilibrium. We then
calculate realistic heavy quark phase space distributions in heavy ion
collisions using Langevin simulations with non-perturbative T-matrix
interactions in hydrodynamic backgrounds. We hadronize the heavy quarks on the
critical hypersurface given by hydrodynamics after constructing a criterion for
the relative recombination and fragmentation contributions. We discuss the
influence of recombination and flow on the resulting heavy meson and single
electron R_AA and elliptic flow. We will also comment on the effect of
diffusion of open heavy flavor mesons in the hadronic phase.Comment: Contribution to Quark Matter 2011, submitted to J.Phys.G; 4 pages, 5
figure
Cocommutative Calabi-Yau Hopf algebras and deformations
The Calabi-Yau property of cocommutative Hopf algebras is discussed by using
the homological integral, a recently introduced tool for studying infinite
dimensional AS-Gorenstein Hopf algebras. It is shown that the skew-group
algebra of a universal enveloping algebra of a finite dimensional Lie algebra
\g with a finite subgroup of automorphisms of \g is Calabi-Yau if and
only if the universal enveloping algebra itself is Calabi-Yau and is a
subgroup of the special linear group SL(\g). The Noetherian cocommutative
Calabi-Yau Hopf algebras of dimension not larger than 3 are described. The
Calabi-Yau property of Sridharan enveloping algebras of finite dimensional Lie
algebras is also discussed. We obtain some equivalent conditions for a
Sridharan enveloping algebra to be Calabi-Yau, and then partly answer a
question proposed by Berger. We list all the nonisomorphic 3-dimensional
Calabi-Yau Sridharan enveloping algebras
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