2,459 research outputs found
Diffusion equation and spin drag in spin-polarized transport
We study the role of electron-electron interactions for spin polarized
transport using the Boltzmann equation and derive a set of coupled transport
equations. For spin polarized transport the electron-electron interactions are
important, because they tend to equilibrate the momentum of the two spin
species. This ``spin drag'' effect enhances the resistivity of the system. The
enhancement is stronger the lower the dimension and should be measurable in for
example a two dimensional electron gas with ferromagnetic contacts. We also
include spin flip scattering which has two effects: it equilibrates the spin
density imbalance and, provided it has a non s-wave component, also the current
imbalance.Comment: 9 pages, 1 figur
Localized plasmons in graphene-coated nanospheres
We present an analytical derivation of the electromagnetic response of a
spherical object coated by a conductive film, here exemplified by a graphene
coating. Applying the framework of Mie-Lorenz theory augmented to account for a
conductive boundary condition, we derive the multipole scattering coefficients,
modified essentially through the inclusion of an additive correction in
numerator and denominator. By reductionist means, starting from the retarded
response, we offer simple results in the quasistatic regime by analyzing the
multipolar polarizability and associated dispersion equation for the localized
plasmons. We consider graphene coatings of both dielectric and conducting
spheres, where in the former case the graphene coating introduces the plasmons
and in the latter case modifies in interesting ways the existing ones. Finally,
we discuss our analytical results in the context of extinction cross-section
and local density of states. Recent demonstrations of fabricated spherical
graphene nanostructures make our study directly relevant to experiments.Comment: 9 pages, 5 figures, 1 tabl
The Tolerance of Shewanella woodyi for Electric Potentials and Heavy Metals as Biofilms
Shewanella woodyi is a bioluminescent marine organism that is known to be metal tolerant and modulate the intensity of its luminescence with electrochemical potential. The viability of S. woodyi as a bioreporter for the toxic heavy metal zinc, copper, and silver was analyzed. Biofilms of S. woodyi was grown on marine broth agar plates and then exposed to various concentrations of each metal ion to evaluate biofilm response to the metal ions that were generated from an operating short circuited electrode containing either Zn, Cu, or Ag metal. The ability of the bacteria to tolerate the heavy metals and continue to luminesce was evaluated at designated distances from the electrode by ICP-OES. The possibility of an electricidal effect was determined to be insignificant near the electrodes. So, even though S. woodyi showed unprecedented tolerance for Zn(II), it would ultimately be a marginal living bioreporter without genetic modification
Generalized nonlocal optical response in nanoplasmonics
Metallic nanostructures exhibit a multitude of optical resonances associated
with localized surface plasmon excitations. Recent observations of plasmonic
phenomena at the sub-nanometer to atomic scale have stimulated the development
of various sophisticated theoretical approaches for their description. Here
instead we present a comparatively simple semiclassical generalized nonlocal
optical response (GNOR) theory that unifies quantum-pressure convection effects
and induced-charge diffusion kinetics, with a concomitant complex-valued GNOR
parameter. Our theory explains surprisingly well both the frequency shifts and
size-dependent damping in individual metallic nanoparticles (MNPs) as well as
the observed broadening of the cross-over regime from bonding-dipole plasmons
to charge-transfer plasmons in MNP dimers, thus unraveling a classical
broadening mechanism that even dominates the widely anticipated
short-circuiting by quantum tunneling. We anticipate that the GNOR theory can
be successfully applied in plasmonics to a wide class of conducting media,
including doped semiconductors and low-dimensional materials such as graphene.Comment: 7 pages, including 3 figures. Supplementary information is available
upon request to author
Kerr nonlinearity and plasmonic bistability in graphene nanoribbons
We theoretically examine the role of Kerr nonlinearities for graphene
plasmonics in nanostructures, specifically in nanoribbons. The nonlinear Kerr
interaction is included semiclassically in the intraband approximation. The
resulting electromagnetic problem is solved numerically by self-consistent
iteration with linear steps using a real-space discretization. We derive a
simple approximation for the resonance shifts in general graphene
nanostructures, and obtain excellent agreement with numerics for moderately
high field strengths. Near plasmonic resonances the nonlinearities are strongly
enhanced due to field enhancement, and the total nonlinearity is significantly
affected by the field inhomogeneity of the plasmonic excitation. Finally, we
discuss the emergence of a plasmonic bistability which exists for frequencies
redshifted relative to the linear resonance. Our results offer new insights
into the role of nonlinear interaction in nanostructured graphene and paves the
way for experimental investigation.Comment: 5 pages, 3 figures, and additional supplemental materia
Classical and Quantum Plasmonics in Graphene Nanodisks: the Role of Edge States
Edge states are ubiquitous for many condensed matter systems with
multicomponent wave functions. For example, edge states play a crucial role in
transport in zigzag graphene nanoribbons. Here, we report microscopic
calculations of quantum plasmonics in doped graphene nanodisks with zigzag
edges. We express the nanodisk conductivity as a sum of the
conventional bulk conductivity ,
and a novel term , corresponding
to a coupling between the edge and bulk states. We show that the edge states
give rise to a red-shift and broadening of the plasmon resonance, and that they
often significantly impact the absorption efficiency. We further develop
simplified models, incorporating nonlocal response within a hydrodynamical
approach, which allow a semiquantitative description of plasmonics in the
ultrasmall size regime. However, the polarization dependence is only given by
fully microscopic models. The approach developed here should have many
applications in other systems supporting edge states.Comment: 5 pages, 4 figure
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Frequency Of Development Of Connective Tissue Disease In Statin-Users Versus Nonusers
Statins have pleiotropic properties that may affect the development of connective tissue diseases (CTD). The objective of this study was to compare the risk of CTD diagnoses in statin users and nonusers. This study was a propensity score-matched analysis of adult patients (30 to 85 years old) in the San Antonio military medical community. The study was divided into baseline (October 1, 2003 to September 30, 2005), and follow-up (October 1, 2005 to March 5, 2010) periods. Statin users received a statin prescription during fiscal year 2005. Nonusers did not receive a statin at any time during the study. The outcome measure was the occurrence of 3 diagnosis codes of the International Classification of Diseases, 9th Revision, Clinical Modification consistent with CTD. We described co-morbidities during the baseline period using the Charlson Comorbidity Index. We created a propensity score based on 41 variables. We then matched statin users and nonusers 1:1, using a caliper of 0.001. Of 46,488 patients who met study criteria (13,640 statin users and 32,848 nonusers), we matched 6,956 pairs of statin users and nonusers. Matched groups were similar in terms of patient age, gender, incidence of co-morbidities, total Charlson Comorbidity Index, health care use, and medication use. The odds ratio for CTD was lower in statin users than nonusers (odds ratio: 0.80; 95% confidence interval: 0.64 to 0.99; p = 0.05). Secondary analysis and sensitivity analysis confirmed these results. In conclusion, statin use was associated with a lower risk of CTD. Published by Elsevier Inc.Pharmac
Børn og voksnes kropslighed i daginstitutioner: Refleksion og viden om kroppens betydning i dagtilbuddet med særlig vægt på socialt udsatte børn
Denne artikel er udarbejdet i tilknytning til forskningsprojektet ”Handlekompetencer i pædagogisk arbejde med socialt udsatte børn og unge – indsats og effekt” (HPA-projektet), som er gennemført ved DPU og er finansieret af Det Strategiske Program for Velfærdsforskning (Socialministeriet) i perioden oktober 2005 frem til maj 2009.Projektets sigte er at udvikle metoder, der giver pædagoger mulighed for at udvikle deres pædagogiske handlekompetencer, så de kan fremme udsatte børns handlemuligheder og livschancer
Plasmonic eigenmodes in individual and bow-tie graphene nanotriangles
Serving as a new two-dimensional plasmonic material, graphene has stimulated
an intensive study of its optical properties which benefit from the unique
electronic band structure of the underlying honeycomb lattice of carbon atoms.
In classical electrodynamics, nanostructured graphene is commonly modeled by
the computationally demanding problem of a three-dimensional conducting film of
atomic-scale thickness. Here, we propose an efficient alternative
two-dimensional electrostatic approach where all the calculation procedures are
restricted to the plane of the graphene sheet. To explore possible quantum
effects, we perform tight-binding calculations, adopting a random-phase
approximation. We investigate the multiple plasmon modes in triangles of
graphene, treating the optical response classically as well as quantum
mechanically in the case of both armchair and zigzag edge termination of the
underlying atomic lattice. Compared to the classical plasmonic spectrum which
is "blind" to the edge termination, we find that the quantum plasmon
frequencies exhibit blueshifts in the case of armchair edge termination, while
redshifts are found for zigzag edges. Furthermore, we find spectral features in
the zigzag case which are associated with electronic edge states not present
for armchair termination. Merging pairs of such triangles into dimers, the
plasmon hybridization leads to energy splitting in accordance with
plasmon-hybridization theory, with a lower energy for the antisymmetric modes
and a smaller splitting for modes with less confinement to the gap region. The
hybridization appears strongest in classical calculations while the splitting
is lower for armchair edges and even more reduced for zigzag edges. Our various
results illustrate a surprising phenomenon: Even 20 nm large graphene
structures clearly exhibit quantum plasmonic features due to atomic-scale
details in the edge termination.Comment: 27 pages including 7 figures. Supplementary information available
upon request to author
Fish, Marine n−3 Fatty Acids, and Atrial Fibrillation – Experimental Data and Clinical Effects
Marine n−3 polyunsaturated fatty acids (PUFA) may have beneficial effects in relation to atrial fibrillation (AF) with promising data from experimental animal studies, however, results from studies in humans have been inconsistent. This review evaluates the mechanisms of action of marine n−3 PUFA in relation to AF based on experimental data and provides a status on the evidence obtained from observational studies and interventional trials. In conclusion, there is growing evidence for an effect of marine n−3 PUFA in prevention and treatment of AF. However, further studies are needed to establish which patients are more likely to benefit from n−3 PUFA, the timing of treatment, and dosages
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