12 research outputs found
Plasmon dispersion in semimetallic armchair graphene nanoribbons
The dispersion relations for plasmons in intrinsic and extrinsic semimetallic
armchair graphene nanoribbons (acGNR) are calculated in the random phase
approximation using the orthogonal p_z-orbital tight binding method. Our model
predicts new plasmons for acGNR of odd atomic widths N=5,11,17,... Our model
further predicts plasmons in acGNR of even atomic width N=2,8,14,... related to
those found using a Dirac continuum model, but with different quantitative
dispersion characteristics. We find that the dispersion of all plasmons in
semimetallic acGNR depends strongly on the localization of the p_z electronic
wavefunctions. We also find that overlap integrals for acGNR behave in a more
complex way than predicted by the Dirac continuum model, suggesting that these
plasmons will experience a small damping for all q not equal to 0. Plasmons in
extrinsic semimetallic acGNR with the chemical potential in the lowest
(highest) conduction (valence) band are found to have dispersion
characteristics nearly identical to their intrinsic counterparts, with
negligible differencs in dispersion arising from the slight differences in
overlap integrals for the interband and intraband transitions.Comment: 8 pages, 9 figure
Experimental constraints of using slow-light in sodium vapor for light-drag enhanced relative rotation sensing
Abstract We report on experimental observation of electromagnetically induced transparency and slow-light (v g % c/607) in atomic sodium vapor, as a potential medium for a recently proposed experiment on slow-light enhanced relative rotation sensing [Shahriar, et al. Phys. Rev. Lett. (submitted for publication), http://arxiv.org/abs/quant-ph/0505192.]. We have performed an interferometric measurement of the index variation associated with a two-photon resonance to estimate the dispersion characteristics of the medium that are relevant to the slow-light based rotation sensing scheme. We also show that the presence of counter-propagating pump beams in an optical Sagnac loop produces a backward optical phase conjugation beam that can generate spurious signals, which may complicate the measurement of small rotations in the slow-light enhanced gyroscope. We identify techniques for overcoming this constraint. Conclusions reached from the results presented here will pave the way for designing and carrying out an experiment that will demonstrate the slow-light induced enhancement of rotation sensing
Demographic, clinical and antibody characteristics of patients with digital ulcers in systemic sclerosis: data from the DUO Registry
OBJECTIVES: The Digital Ulcers Outcome (DUO) Registry was designed to describe the clinical and antibody characteristics, disease course and outcomes of patients with digital ulcers associated with systemic sclerosis (SSc).
METHODS: The DUO Registry is a European, prospective, multicentre, observational, registry of SSc patients with ongoing digital ulcer disease, irrespective of treatment regimen. Data collected included demographics, SSc duration, SSc subset, internal organ manifestations, autoantibodies, previous and ongoing interventions and complications related to digital ulcers.
RESULTS: Up to 19 November 2010 a total of 2439 patients had enrolled into the registry. Most were classified as either limited cutaneous SSc (lcSSc; 52.2%) or diffuse cutaneous SSc (dcSSc; 36.9%). Digital ulcers developed earlier in patients with dcSSc compared with lcSSc. Almost all patients (95.7%) tested positive for antinuclear antibodies, 45.2% for anti-scleroderma-70 and 43.6% for anticentromere antibodies (ACA). The first digital ulcer in the anti-scleroderma-70-positive patient cohort occurred approximately 5 years earlier than the ACA-positive patient group.
CONCLUSIONS: This study provides data from a large cohort of SSc patients with a history of digital ulcers. The early occurrence and high frequency of digital ulcer complications are especially seen in patients with dcSSc and/or anti-scleroderma-70 antibodies