529 research outputs found
Real-Time Imaging of K atoms on Graphite: Interactions and Diffusion
Scanning tunneling microscopy (STM) at liquid helium temperature is used to
image potassium adsorbed on graphite at low coverage (~0.02 monolayer). Single
atoms appear as protrusions on STM topographs. A statistical analysis of the
position of the atoms demonstrates repulsion between adsorbates, which is
quantified by comparison with molecular dynamics simulations. This gives access
to the dipole moment of a single adsorbate, found to be 10.5 Debye. Time lapse
imaging shows that long range order is broken by thermally activated diffusion,
with a 32 meV barrier to hopping between graphite lattice sites
Conductance fluctuations in quasi-two-dimensional systems: a practical view
The universal conductance fluctuations of quasi-two-dimensional systems are
analyzed with experimental considerations in mind. The traditional statistical
metrics of these fluctuations (such as variance) are shown to have large
statistical errors in such systems. An alternative characteristic is
identified, the inflection point of the correlation function in magnetic field,
which is shown to be significantly more useful as an experimental metric and to
give a more robust measure of phase coherence.Comment: 9 pages, 7 figure
The Impact of a Campus-Based 4-H Summer Conference Program on Youth Thriving
In 2014 the Oregon 4-H program adopted a new program model to describe and evaluate the impact of 4-H on youths. The model is based on promoting thriving in young people, with an emphasis on high program quality. This article discusses the impact on thriving in 378 youth participants of the 4-H Summer Conference (4-HSC) program. The results of the study conducted provide preliminary support for the validity of the program model as well as the impact of the 4-HSC program on participants. Additionally, the study has implications for the use of program models in translating research into practice across Extension programs
Spin dependent quantum interference in non-local graphene spin valves
Spin dependent electron transport measurements on graphene are of high
importance to explore possible spintronic applications. Up to date all spin
transport experiments on graphene were done in a semi-classical regime,
disregarding quantum transport properties such as phase coherence and
interference. Here we show that in a quantum coherent graphene nanostructure
the non-local voltage is strongly modulated. Using non-local measurements, we
separate the signal in spin dependent and spin independent contributions. We
show that the spin dependent contribution is about two orders of magnitude
larger than the spin independent one, when corrected for the finite
polarization of the electrodes. The non-local spin signal is not only strongly
modulated but also changes polarity as a function of the applied gate voltage.
By locally tuning the carrier density in the constriction we show that the
constriction plays a major role in this effect and indicates that it can act as
a spin filter device. Our results show the potential of quantum coherent
graphene nanostructures for the use in future spintronic devices
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
Evolving information systems: meeting the ever-changing environment
To meet the demands of organizations and their ever-changing environment, information systems are required which are able to evolve to the same extent as organizations do. Such a system has to support changes in all time-and application-dependent aspects. In this paper, requirements and a conceptual framework for evolving information systems are presented. This framework includes an architecture for such systems and a revision of the traditional notion of update. Based on this evolutionary notion of update (recording, correction and forgetting) a state transition-oriented model on three levels of abstraction (event level, recording level, correction level) is introduced. Examples are provided to illustrate the conceptual framework for evolving information systems
On the Application of a Monolithic Array for Detecting Intensity-Correlated Photons Emitted by Different Source Types
It is not widely appreciated that many subtleties are involved in the
accurate measurement of intensity-correlated photons; even for the original
experiments of Hanbury Brown and Twiss (HBT). Using a monolithic 4x4 array of
single-photon avalanche diodes (SPADs), together with an off-chip algorithm for
processing streaming data, we investigate the difficulties of measuring
second-order photon correlations g2 in a wide variety of light fields that
exhibit dramatically different correlation statistics: a multimode He-Ne laser,
an incoherent intensity-modulated lamp-light source and a thermal light source.
Our off-chip algorithm treats multiple photon-arrivals at pixel-array pairs, in
any observation interval, with photon fluxes limited by detector saturation, in
such a way that a correctly normalized g2 function is guaranteed. The impact of
detector background correlations between SPAD pixels and afterpulsing effects
on second-order coherence measurements is discussed. These results demonstrate
that our monolithic SPAD array enables access to effects that are otherwise
impossible to measure with stand-alone detectors.Comment: 17 pages, 6 figure
Itch and skin rash from chocolate during fluoxetine and sertraline treatment: Case report
BACKGROUND: The skin contains a system for producing serotonin as well as serotonin receptors. Serotonin can also cause pruritus when injected into the skin. SSRI-drugs increase serotonin concentrations and are known to have pruritus and other dermal side effects. CASE PRESENTATION: A 46-year-old man consulted his doctor due to symptoms of depression. He did not suffer from any allergy but drinking red wine caused vasomotor rhinitis. Antidepressive treatment with fluoxetine 20 mg daily was initiated which was successful. After three weeks of treatment an itching rash appeared. An adverse drug reaction (ADR) induced by fluoxetine was suspected and fluoxetine treatment was discontinued. The symptoms disappeared with clemastine and betametasone treatment. Since the depressive symptoms returned sertraline medication was initiated. After approximately two weeks of sertraline treatment he noted an intense itching sensation in his scalp after eating a piece of chocolate cake. The itch spread to the arms, abdomen and legs and the patient treated himself with clemastine and the itch disappeared. He now realised that he had eaten a chocolate cake before this episode and remembered that before the first episode he had had a chocolate mousse dessert. He had never had any reaction from eating chocolate before and therefore reported this observation to his doctor. CONCLUSIONS: This case report suggests that there may be individuals that are very sensitive to increases in serotonin concentrations. Dermal side reactions to SSRI-drugs in these patients may be due to high activity in the serotonergic system at the dermal and epidermo-dermal junctional area rather than a hypersensitivity to the drug molecule itself
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