97 research outputs found
Resonant Visible Light Modulation with Graphene
Fast modulation and switching of light at visible and near-infrared (vis-NIR)
frequencies is of utmost importance for optical signal processing and sensing
technologies. No fundamental limit appears to prevent us from designing
wavelength-sized devices capable of controlling the light phase and intensity
at gigaherts (and even terahertz) speeds in those spectral ranges. However,
this problem remains largely unsolved, despite recent advances in the use of
quantum wells and phase-change materials for that purpose. Here, we explore an
alternative solution based upon the remarkable electro-optical properties of
graphene. In particular, we predict unity-order changes in the transmission and
absorption of vis-NIR light produced upon electrical doping of graphene sheets
coupled to realistically engineered optical cavities. The light intensity is
enhanced at the graphene plane, and so is its absorption, which can be switched
and modulated via Pauli blocking through varying the level of doping.
Specifically, we explore dielectric planar cavities operating under either
tunneling or Fabry-Perot resonant transmission conditions, as well as Mie modes
in silicon nanospheres and lattice resonances in metal particle arrays. Our
simulations reveal absolute variations in transmission exceeding 90% as well as
an extinction ratio >15 dB with small insertion losses using feasible material
parameters, thus supporting the application of graphene in fast electro-optics
at vis-NIR frequencies.Comment: 17 pages, 13 figures, 54 reference
Recommended from our members
Use of a novel rover-mounted fluorescence imager and fluorescent probes to detect biological material in the Atacama Desert in daylight
We deployed our fluorescence imaging system which detects fluorescence signals from sparse microorganisms and biofilms on Carnegie Mellon University’s autonomous rover Zoë. The results of the 2004 Atacama Desert field season, in Chile, are discussed
Recommended from our members
Implementation of a daylight fluorescence imaging system to autonomously detect biomarkers of extant life in the Atacama Desert
We have integrated a biomarker detection system with a rover for the search for sparse life in extreme environments. The system incorporated a pulsed fluorescence imager, a reagent sprayer, and a surface scraping device for remote detection of fluorescence signals
Enhanced Light–Matter Interactions in Graphene-Covered Gold Nanovoid Arrays
The combination of graphene with noble-metal nanostructures is currently
being explored for strong light-graphene interaction enhanced by plasmons. We
introduce a novel hybrid graphene-metal system for studying light-matter
interactions with gold-void nanostructures exhibiting resonances in the visible
range. Strong coupling of graphene layers to the plasmon modes of the nanovoid
arrays results in significant frequency shifts of the underlying plasmon
resonances, enabling more than 30% absolute light absorption in a single layer
of graphene and up to 700-fold enhancement of the Raman response of the
graphene. These new perspectives enable us to verify the presence of graphene
on gold-void arrays and the enhancement even allows us to accurately quantify
the number of layers. Experimental observations are further supported by
numerical simulations and perturbation-theory analysis. The graphene gold-void
platform is beneficial for sensing of molecules and placing R6G dye molecules
on top of the graphene, we observe a strong enhancement of the R6G Raman
fingerprints. These results pave the way toward advanced substrates for
surface-enhanced Raman scattering (SERS) with potential for unambiguous
single-molecule detection on the atomically well-defined layer of graphene.Comment: 17 pages including 5 figure
A review of the optical properties of alloys and intermetallics for plasmonics
Alternative materials are required to enhance the efficacy of plasmonic
devices. We discuss the optical properties of a number of alloys, doped metals,
intermetallics, silicides, metallic glasses and high pressure materials. We
conclude that due to the probability of low frequency interband transitions,
materials with partially occupied d-states perform poorly as plasmonic
materials, ruling out many alloys, intermetallics and silicides as viable. The
increased probability of electron-electron and electron-phonon scattering rules
out many doped and glassy metals.Comment: 26 pages, 10 figures, 3 table
Protocol for a systematic review of screening tools for fear of recurrent illness in common life threatening diseases
This is the authors' accepted version of an article published in Systematic Reviews, 2015.A myocardial infarction (MI) (‘heart attack’) can be intensely stressful, and the impact of this event can leave patients with clinically significant post-MI stress symptoms. Untreated stress can make heart disease worse. Few tools are available that screen for specific thoughts or beliefs that can trigger post-MI stress responses. In other life-threatening illnesses, fear of recurrence (FoR) of illness has been identified as a key stressor, and screening tools have been developed to identify this. The aim of this review is to identify FoR screening tools used in other common life-threatening diseases that report on the development of the tool, to assess if there are any that can be adapted for use in MI survivors so that those with high levels of FoR can be identified and helped
A Survey of Bayesian Statistical Approaches for Big Data
The modern era is characterised as an era of information or Big Data. This
has motivated a huge literature on new methods for extracting information and
insights from these data. A natural question is how these approaches differ
from those that were available prior to the advent of Big Data. We present a
review of published studies that present Bayesian statistical approaches
specifically for Big Data and discuss the reported and perceived benefits of
these approaches. We conclude by addressing the question of whether focusing
only on improving computational algorithms and infrastructure will be enough to
face the challenges of Big Data
Combining molecular and spin dynamics simulations with solid-state NMR: a case study of amphiphilic lysine-leucine repeat peptide aggregates
Interpreting dynamics in solid-state molecular systems requires characterization of the potentially heterogeneous environmental contexts of molecules. In particular, the analysis of solid-state NMR (ssNMR) data to elucidate molecular dynamics involves modeling the restriction to overall tumbling by neighbors, as well as the concentrations of water and buffer. In this exploration of the factors that influence motion, we utilize atomistic molecular dynamics (MD) trajectories of peptide aggregates with varying hydration to mimic an amorphous solid-state environment, and predict ssNMR relaxation rates. We also account for spin diffusion in multiply spin-labeled (up to 19 nuclei) residues, with several models of dipolar-coupling networks. The framework serves as a general approach to determine essential spin couplings affecting relaxation, benchmark MD force fields, and reveal the hydration-dependence of dynamics in a crowded environment. We demonstrate the methodology on a previously characterized amphiphilic 14-residue lysine-leucine repeat peptide, LKα14 (Ac-LKKLLKLLKKLLKL-c), which has an α-helical secondary structure and putatively forms leucine-burying tetramers in the solid state. We measure R1 relaxation rates of uniformly 13C-labeled, and site-specific 2H-labeled leucines in the hydrophobic core of LKα14 at multiple hydration levels. Studies of 9 and 18 tetramer bundles reveal that: (a) for the incoherent component of 13C relaxation, nearest-neighbor spin interactions dominate, while 1H-1H interactions have minimal impact; (b) AMBER ff14SB dihedral barriers for the leucine Cγ - Cδ bond (“methyl rotation barriers”) must be lowered by a factor of 0.7 to better match the 2H data; (c) proton-driven spin diffusion (PDSD) explains some of the discrepancy between experimental and simulated rates for the Cβ and Cα nuclei; and (d) 13C relaxation rates are mostly underestimated in the MD simulations at all hydrations, and the discrepancies identify likely motions missing in the 50 ns MD trajectories.<br/
Generation and characterization of thiol-deficient Mycobacterium tuberculosis mutants
Mycothiol (MSH) and ergothioneine (ERG) are thiols able to compensate for each other to protect mycobacteria against oxidative stress. Gamma-glutamylcysteine (GGC), another thiol and an intermediate in ERG biosynthesis has detoxification abilities. Five enzymes are involved in ERG biosynthesis, namely EgtA, EgtB, EgtC, EgtD and EgtE. The role of these enzymes in the production of ERG had been unclear. On the other hand, the enzyme MshA is known to be essential for MSH biosynthesis. In this manuscript, we describe the raw data of the generation and characterization of Mycobacterium tuberculosis (M.tb) mutants harbouring a deletion of the gene coding for each of these enzymes, and the raw data of the phenotypic characterization of the obtained thiol-deficient M.tb mutants. High throughput screening (HTS) of off-patent drugs and natural compounds revealed few compounds that displayed a higher activity against the thiol-deficient mutants relative to the wild-type strain. The mode of action of these drugs was further investigated. Raw data displaying these results are described here
- …