5,521 research outputs found
Direct-write, focused ion beam-deposited,7 K superconducting C-Ga-O nanowire
We have fabricated C-Ga-O nanowires by gallium focused ion beam-induced
deposition from the carbon-based precursor phenanthrene. The electrical
conductivity of the nanowires is weakly temperature dependent below 300 K, and
indicates a transition to a superconducting state below Tc = 7 K. We have
measured the temperature dependence of the upper critical field Hc2(T), and
estimate a zero temperature critical field of 8.8 T. The Tc of this material is
approximately 40% higher than that of any other direct write nanowire, such as
those based on C-W-Ga, expanding the possibility of fabricating direct-write
nanostructures that superconduct above liquid helium temperaturesComment: Accepted for AP
Electronic compressibility of layer polarized bilayer graphene
We report on a capacitance study of dual gated bilayer graphene. The measured
capacitance allows us to probe the electronic compressibility as a function of
carrier density, temperature, and applied perpendicular electrical displacement
D. As a band gap is induced with increasing D, the compressibility minimum at
charge neutrality becomes deeper but remains finite, suggesting the presence of
localized states within the energy gap. Temperature dependent capacitance
measurements show that compressibility is sensitive to the intrinsic band gap.
For large displacements, an additional peak appears in the compressibility as a
function of density, corresponding to the presence of a 1-dimensional van Hove
singularity (vHs) at the band edge arising from the quartic bilayer graphene
band structure. For D > 0, the additional peak is observed only for electrons,
while D < 0 the peak appears only for holes. This asymmetry that can be
understood in terms of the finite interlayer separation and may be useful as a
direct probe of the layer polarization
The architectures of media power: editing, the newsroom, and urban public space
This paper considers the relation of the newsroom and the city as a lens into the more general relation of production spaces and mediated publics. Leading theoretically from Lee and LiPuma’s (2002) notion of ‘cultures of circulation’, and drawing on an ethnography of the Toronto Star, the paper focuses on how media forms circulate and are enacted through particular practices and material settings. With its attention to the urban milieus and orientations of media organizations, this paper exhibits both affinities with but also differences to current interests in the urban architectures of media, which describe and theorize how media get ‘built into’ the urban experience more generally. In looking at editing practices situated in the newsroom, an emphasis is placed on the phenomenological appearance of media forms both as objects for material assembly as well as more abstracted subjects of reflexivity, anticipation and purposiveness. Although this is explored with detailed attention to the settings of the newsroom and the city, the paper seeks to also provide insight into the more general question of how publicness is material shaped and sited
Mojave remote sensing field experiment
The Mojave Remote Sensing Field Experiment (MFE), conducted in June 1988, involved acquisition of Thermal Infrared Multispectral Scanner (TIMS); C, L, and P-band polarimetric radar (AIRSAR) data; and simultaneous field observations at the Pisgah and Cima volcanic fields, and Lavic and Silver Lake Playas, Mojave Desert, California. A LANDSAT Thematic Mapper (TM) scene is also included in the MFE archive. TM-based reflectance and TIMS-based emissivity surface spectra were extracted for selected surfaces. Radiative transfer procedures were used to model the atmosphere and surface simultaneously, with the constraint that the spectra must be consistent with field-based spectral observations. AIRSAR data were calibrated to backscatter cross sections using corner reflectors deployed at target sites. Analyses of MFE data focus on extraction of reflectance, emissivity, and cross section for lava flows of various ages and degradation states. Results have relevance for the evolution of volcanic plains on Venus and Mars
Dynamic Spin Response for Heisenberg Ladders
We employ the recently proposed plaquette basis to investigate static and
dynamic properties of isotropic 2-leg Heisenberg spin ladders. Simple
non-interacting multi-plaquette states provide a remarkably accurate picture of
the energy/site and dynamic spin response of these systems. Insights afforded
by this simple picture suggest a very efficient truncation scheme for more
precise calculations. When the small truncation errors are accounted for using
recently developed Contractor Renormalization techniques, very accurate results
requiring a small fraction of the computational effort of exact calculations
are obtained. These methods allow us to determine the energy/site, gap, and
spin response of 2x16 ladders. The former two values are in good agreement with
density matrix renormalization group results. The spin response calculations
show that nearly all the strength is concentrated in the lowest triplet level
and that coherent many-body effects enhance the response/site by nearly a
factor of 1.6 over that found for 2x2 systems.Comment: 9 pages with two enclosed postscript figure
Mean-Field Theory for Spin Ladders Using Angular-Momentum Coupled Bases
We study properties of two-leg Heisenberg spin ladders in a mean-field
approximation using a variety of angular-momentum coupled bases. The mean-field
theory proposed by Gopalan, Rice, and Sigrist, which uses a rung basis, assumes
that the mean-field ground state consists of a condensate of spin-singlets
along the rungs of the ladder. We generalize this approach to larger
angular-momentum coupled bases which incorporate---by their mere definition---a
substantial fraction of the important short-range structure of these materials.
In these bases the mean-field ground-state remains a condensate of spin
singlet---but now with each involving a larger fraction of the spins in the
ladder. As expected, the ``purity'' of the ground-state, as judged by the
condensate fraction, increases with the size of the elementary block defining
the basis. Moreover, the coupling to quasiparticle excitations becomes weaker
as the size of the elementary block increases. Thus, the weak-coupling limit of
the theory becomes an accurate representation of the underlying mean-field
dynamics. We illustrate the method by computing static and dynamic properties
of two-leg ladders in the various angular-momentum coupled bases.Comment: 28 pages with 8 figure
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