942 research outputs found
Skew in ovarian activation depends on domicile size in phyllode-glueing thrips
Costs and benefits of group living are a fundamental topic in behavioural ecology. Resource availability affects individuals’ breeding prospects alone and in groups, as well as how reproduction is distributed within groups (“reproductive skew”). Here, we provide correlational evidence in facultatively social thrips that breeding resources are associated with (1) whether solitary or social living is favoured, and (2) the degree of ovarian skew. Dunatothrips aneurae (Thysanoptera, Phlaeothripidae) cooperatively build silk “domiciles” on Australian Acacias, feeding exclusively from internal phyllode surfaces. Per capita productivity scaled differently with group size depending on domicile volume - females in small domiciles did better alone than in groups, whereas in large domiciles single and group-nesting females did equally well. Ovarian dissections revealed that in small domiciles some females were nonreproductive, indicating ovarian (i.e. reproductive) skew. Skew increased as domicile size decreased and group size increased. Breeders had smaller oocyte volume in smaller domiciles, especially those containing nonreproductives. These findings suggest group formation and reproductive skew in D. aneurae may be influenced by reproductive competition for breeding resources. Nonreproductive females in small domiciles may be reproductively suppressed, subfertile, or accumulating resources to reproduce
Washington Park Main Street Plan
There is an immense variety of privately owned businesses. They will be stakeholders because their businesses are located there, but they will also be assets in themselves in drawing people to the area. There is basically everything anyone could possible want or need in this area. There are two gas stations, a Family Dollar, a liquor store, a few sit down restaurants, numerous places where one can get a quick bite to eat, a frame shop, a clothing store, a pawn shop, a store with fresh produce (which is hard to find in urban areas), a store that sells sports uniforms, a frame shop, a lawyerʼs office, an animal hospital, two Laundromats, a record shop, a health food store, two cell phone stores, an automotive shop, and a karate school with an afterschool program. With such variety, it will draw people to the area and then give them other reasons to keep coming back
Quantum dots in magnetic fields: thermal response of broken symmetry phases
We investigate the thermal properties of circular semiconductor quantum dots
in high magnetic fields using finite temperature Hartree-Fock techniques. We
demonstrate that for a given magnetic field strength quantum dots undergo
various shape phase transitions as a function of temperature, and we outline
possible observable consequences.Comment: In Press, Phys. Rev. B (2001
Compilation of extended recursion in call-by-value functional languages
This paper formalizes and proves correct a compilation scheme for
mutually-recursive definitions in call-by-value functional languages. This
scheme supports a wider range of recursive definitions than previous methods.
We formalize our technique as a translation scheme to a lambda-calculus
featuring in-place update of memory blocks, and prove the translation to be
correct.Comment: 62 pages, uses pi
Influence of Gap Extrema on the Tunneling Conductance Near an Impurity in an Anisotropic Superconductor
Changes: figures added in postscript form, Eq. (7) and various typos
corrected. We examine the effect of an impurity on the nearby tunneling
conductance in an anisotropically-gapped superconductor. The variation of the
conductance has pronounced spatial dependence which depends strongly on the
Fermi surface location of gap extrema. In particular, different gap symmetries
produce profoundly different spatial features in the conductance. These effects
may be detectable with an STM measurement on the surface of a high-temperature
superconductor.Comment: 12 pages (revtex) + 3 figures (included - postscript), NSF-ITP-93-8
Emergent Electroweak Symmetry Breaking with Composite W, Z Bosons
We present a model of electroweak symmetry breaking in a warped extra
dimension where electroweak symmetry is broken at the UV (or Planck) scale. An
underlying conformal symmetry is broken at the IR (or TeV) scale generating
masses for the electroweak gauge bosons without invoking a Higgs mechanism. By
the AdS/CFT correspondence the W,Z bosons are identified as composite states of
a strongly-coupled gauge theory, suggesting that electroweak symmetry breaking
is an emergent phenomenon at the IR scale. The model satisfies electroweak
precision tests with reasonable fits to the S and T parameter. In particular
the T parameter is sufficiently suppressed since the model naturally admits a
custodial SU(2) symmetry. The composite nature of the W,Z-bosons provide a
novel possibility of unitarizing WW scattering via form factor suppression.
Constraints from LEP and the Tevatron as well as discovery opportunities at the
LHC are discussed for these composite electroweak gauge bosons.Comment: 39 pages, 4 figure
A microscopic model for d-wave charge carrier pairing and non-Fermi-liquid behavior in a purely repulsive 2D electron system
We investigate a microscopic model for strongly correlated electrons with
both on-site and nearest neighbor Coulomb repulsion on a 2D square lattice.
This exhibits a state in which electrons undergo a ``somersault'' in their
internal spin-space (spin-flux) as they traverse a closed loop in external
coordinate space. When this spin-1/2 antiferromagnetic (AFM) insulator is
doped, the ground state is a liquid of charged, bosonic meron-vortices, which
for topological reasons are created in vortex-antivortex pairs. The magnetic
exchange energy of the distorted AFM background leads to a logarithmic
vortex-antivortex attraction which overcomes the direct Coulomb repulsion
between holes localized on the vortex cores. This leads to the appearance of
pre-formed charged pairs. We use the Configuration Interaction (CI) Method to
study the quantum translational and rotational motion of various charged
magnetic solitons and soliton pairs. The CI method systematically describes
fluctuation and quantum tunneling corrections to the Hartree-Fock Approximation
(HFA). We find that the lowest energy charged meron-antimeron pairs exhibit
d-wave rotational symmetry, consistent with the symmetry of the cuprate
superconducting order parameter. For a single hole in the 2D AFM plane, we find
a precursor to spin-charge separation in which a conventional charged
spin-polaron dissociates into a singly charged meron-antimeron pair. This model
provides a unified microscopic basis for (i) non-Fermi-liquid transport
properties, (ii) d-wave preformed charged carrier pairs, (iii) mid-infrared
optical absorption, (iv) destruction of AFM long range order with doping and
other magnetic properties, and (v) certain aspects of angled resolved
photo-emission spectroscopy (ARPES).Comment: 14 pages, 17 figure
Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates
The low-energy excitations of the lightly doped cuprates were studied by
angle-resolved photoemission spectroscopy. A finite gap was measured over the
entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This
effect was observed to be generic to the normal states of numerous cuprates,
including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and
electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to
close with increasing carrier doping. We consider various scenarios to explain
our results, including the possible effects of chemical disorder, electronic
inhomogeneity, and a competing phase.Comment: To appear in Phys. Rev.
A numerical study of multi-soliton configurations in a doped antiferromagnetic Mott insulator
We evaluate from first principles the self-consistent Hartree-Fock energies
for multi-soliton configurations in a doped, spin-1/2, antiferromagnetic Mott
insulator on a two-dimensional square lattice. We find that nearest-neighbor
Coulomb repulsion stabilizes a regime of charged meron-antimeron vortex soliton
pairs over a region of doping from 0.05 to 0.4 holes per site for intermediate
coupling 3 < U/t <8. This stabilization is mediated through the generation of
``spin-flux'' in the mean-field antiferromagnetic (AFM) background. Holes
cloaked by a meron-vortex in the spin-flux AFM background are charged bosons.
Our static Hartree-Fock calculations provide an upper bound on the energy of a
finite density of charged vortices. This upper bound is lower than the energy
of the corresponding charged stripe configurations. A finite density of charge
carrying vortices is shown to produce a large number of unoccupied electronic
levels in the Mott-Hubbard charge transfer gap. These levels lead to
significant band tailing and a broad mid-infrared band in the optical
absorption spectrum as observed experimentally. At very low doping (below 0.05)
the doping charges create extremely tightly bound meron-antimeron pairs or even
isolated conventional spin-polarons, whereas for very high doping (above 0.4)
the spin background itself becomes unstable to formation of a conventional
Fermi liquid and the spin-flux mean-field is energetically unfavorable. Our
results point to the predominance of a quantum liquid of charged, bosonic,
vortex solitons at intermediate coupling and intermediate doping
concentrations.Comment: 12 pages, 25 figures; added references, modified/eliminated some
figure
Interplay of structural and electronic phase separation in single crystalline La(2)CuO(4.05) studied by neutron and Raman scattering
We report a neutron and Raman scattering study of a single-crystal of
La(2)CuO(4.05) prepared by high temperature electrochemical oxidation. Elastic
neutron scattering measurements show the presence of two phases, corresponding
to the two edges of the first miscibility gap, all the way up to 300 K. An
additional oxygen redistribution, driven by electronic energies, is identified
at 250 K in Raman scattering (RS) experiments by the simultaneous onset of
two-phonon and two-magnon scattering, which are fingerprints of the insulating
phase. Elastic neutron scattering measurements show directly an
antiferromagnetic ordering below a N\'eel temperature of T_N =210K. The opening
of the superconducting gap manifests itself as a redistribution of electronic
Raman scattering below the superconducting transition temperature, T_c = 24K. A
pronounced temperature-dependent suppression of the intensity of the (100)
magnetic Bragg peak has been detected below T_c. We ascribe this phenomenon to
a change of relative volume fraction of superconducting and antiferromagnetic
phases with decreasing temperature caused by a form of a superconducting
proximity effect.Comment: 9 pages, including 9 eps figures, submitted to PR
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