2,748 research outputs found
A comparison of conjunctival bacterial populations of contact lens wearers vs. non-contact lens wearers
Conjunctival swab samples were taken from each eye of 42 contact lens wearers and 60 subjects who don\u27t wear. contacts. From the questionaire that each subject filled out, it was found that the majority of the subjects were male students between the ages of 23-30. Concerning the contact lens wearers\u27 habits and hygiene, they responded that the majority had worn their lenses 3 years or more and currently wore their lenses above 14 hours per day. The bulk of the wearers either often or always washed their hands before handling their lenses, used separate solutions, and stored their lenses wet. From the samples that were taken, a lower incidence of bacterial growth was found among the contact lens group (although the difference was found to be statistically insignificant for = 0.025 and Z = 1.96). The conclusion from this study was that if proper contact lens hygiene and care was maintained, there would be no increase in bacterial conjunctival flora in the contact lens wearer
Scaling law and stability for a noisy quantum system
We show that a scaling law exists for the near resonant dynamics of cold
kicked atoms in the presence of a randomly fluctuating pulse amplitude.
Analysis of a quasi-classical phase-space representation of the quantum system
with noise allows a new scaling law to be deduced. The scaling law and
associated stability are confirmed by comparison with quantum simulations and
experimental data.Comment: Published in Physical Review E (Rapid Comm.
Highly confined low-loss plasmons in graphene-boron nitride heterostructures
Graphene plasmons were predicted to possess ultra-strong field confinement
and very low damping at the same time, enabling new classes of devices for deep
subwavelength metamaterials, single-photon nonlinearities, extraordinarily
strong light-matter interactions and nano-optoelectronic switches. While all of
these great prospects require low damping, thus far strong plasmon damping was
observed, with both impurity scattering and many-body effects in graphene
proposed as possible explanations. With the advent of van der Waals
heterostructures, new methods have been developed to integrate graphene with
other atomically flat materials. In this letter we exploit near-field
microscopy to image propagating plasmons in high quality graphene encapsulated
between two films of hexagonal boron nitride (h-BN). We determine dispersion
and particularly plasmon damping in real space. We find unprecedented low
plasmon damping combined with strong field confinement, and identify the main
damping channels as intrinsic thermal phonons in the graphene and dielectric
losses in the h-BN. The observation and in-depth understanding of low plasmon
damping is the key for the development of graphene nano-photonic and
nano-optoelectronic devices
Infrared Instrumentation and Astronomy
Contains research objectives and summary of research on five research projects.Joint Services Electronics Program (Contract DAAB07-76-C-1400)M.I.T. Sloan Fund for Basic ResearchNational Aeronautics and Space Administration (Contract NAS5-23731)National Aeronautics and Space Administration (Grant NGR 22-009-526
Tuning quantum non-local effects in graphene plasmonics
The response of an electron system to electromagnetic fields with sharp
spatial variations is strongly dependent on quantum electronic properties, even
in ambient conditions, but difficult to access experimentally. We use
propagating graphene plasmons, together with an engineered dielectric-metallic
environment, to probe the graphene electron liquid and unveil its detailed
electronic response at short wavelengths.The near-field imaging experiments
reveal a parameter-free match with the full theoretical quantum description of
the massless Dirac electron gas, in which we identify three types of quantum
effects as keys to understanding the experimental response of graphene to
short-ranged terahertz electric fields. The first type is of single-particle
nature and is related to shape deformations of the Fermi surface during a
plasmon oscillations. The second and third types are a many-body effect
controlled by the inertia and compressibility of the interacting electron
liquid in graphene. We demonstrate how, in principle, our experimental approach
can determine the full spatiotemporal response of an electron system.Comment: 8 pages, 4 figure
Nuclear Charge Radius of Be
The nuclear charge radius of Be was precisely determined using the
technique of collinear laser spectroscopy on the transition in the Be ion. The mean square charge radius increases
from Be to Be by \delta ^{10,12} = 0.69(5) \fm^{2}
compared to \delta ^{10,11} = 0.49(5) \fm^{2} for the
one-neutron halo isotope Be. Calculations in the fermionic molecular
dynamics approach show a strong sensitivity of the charge radius to the
structure of Be. The experimental charge radius is consistent with a
breakdown of the N=8 shell closure.Comment: 5 pages, 3 figure
Electrical detection of hyperbolic phonon-polaritons in heterostructures of graphene and boron nitride
Light properties in the mid-infrared can be controlled at a deep
subwavelength scale using hyperbolic phonons-polaritons (HPPs) of hexagonal
boron nitride (h-BN). While propagating as waveguided modes HPPs can
concentrate the electric field in a chosen nano-volume. Such a behavior is at
the heart of many applications including subdiffraction imaging and sensing.
Here, we employ HPPs in heterostructures of h-BN and graphene as new
nano-optoelectronic platform by uniting the benefits of efficient hot-carrier
photoconversion in graphene and the hyperbolic nature of h-BN. We demonstrate
electrical detection of HPPs by guiding them towards a graphene pn-junction. We
shine a laser beam onto a gap in metal gates underneath the heterostructure,
where the light is converted into HPPs. The HPPs then propagate as confined
rays heating up the graphene leading to a strong photocurrent. This concept is
exploited to boost the external responsivity of mid-infrared photodetectors,
overcoming the limitation of graphene pn-junction detectors due to their small
active area and weak absorption. Moreover this type of detector exhibits
tunable frequency selectivity due to the HPPs, which combined with its high
responsivity paves the way for efficient high-resolution mid-infrared imaging
Infrared Instrumentation and Astronomy
Contains reports on five research projects.Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Aeronautics and Space Administration (Grant NGR 22-009-526)National Aeronautics and Space Administration (Grant NSG-7328)National Aeronautics and Space Administration (Contract NAS5-24096
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