3,880 research outputs found
A night out with the nerds (review of: "Theatre of Science", a performance by Simon Singh and Richard Wiseman at the Soho Theatre, London)
Note about a second "evidence" for a WIMP annual modulation
This note, with its five questions, is intended to contribute to a
clarification about a claimed "evidence" by the DAMA group of an annual
modulation of the counting rate of a Dark Matter NaI(Tl) detector as due to a
neutralino (SUSY-LSP) Dark Matter candidate.Comment: LaTex, 3 pages, 2 figure
Impact of local stacking on the graphene-impurity interaction: theory and experiments
We investigate the graphene-impurity interaction problem by combining
experimental - scanning tunneling microscopy (STM) and spectroscopy (STS) - and
theoretical - Anderson impurity model and density functional theory (DFT)
calculations - techniques. We use graphene on the SiC(000-1)(2x2)_C
reconstruction as a model system. The SiC substrate reconstruction is based on
silicon adatoms. Graphene mainly interacts with the dangling bonds of these
adatoms which act as impurities. Graphene grown on SiC(000-1)(2x2)_C shows
domains with various orientations relative to the substrate so that very
different local graphene/Si adatom stacking configurations can be probed on a
given grain. The position and width of the adatom (impurity) state can be
analyzed by STM/STS and related to its local environment owing to the high bias
electronic transparency of graphene. The experimental results are compared to
Anderson's model predictions and complemented by DFT calculations for some
specific local environments. We conclude that the adatom resonance shows a
smaller width and a larger shift toward the Dirac point for an adatom at the
center of a graphene hexagon than for an adatom just on top of a C graphene
atom.Comment: 13 pages, 6 figures, Accepted for publication in Phys. Rev.
Why Nature and Science are both negative. Or: Is it better to reward or punish?
Machiavelli felt that punishments were more effective than rewards. However, Machiavelli's explanation is unconvincing: "...the bond of love is one which people, base creatures that they are, break when it is to their advantage; but fear is strengthened by a dread of punishment which never fails". This conclusion is paradoxical because rewards and punishments with equal fitness ratios will seem equal to recipients, which should quickly evolve to perceive these ratios. In natural selection, it is the proportional, rather than the absolute fitness that is important
A compact design for the Josephson mixer: the lumped element circuit
We present a compact and efficient design in terms of gain, bandwidth and
dynamical range for the Josephson mixer, the superconducting circuit performing
three-wave mixing at microwave frequencies. In an all lumped-element based
circuit with galvanically coupled ports, we demonstrate non degenerate
amplification for microwave signals over a bandwidth up to 50 MHz for a power
gain of 20 dB. The quantum efficiency of the mixer is shown to be about 70
and its saturation power reaches dBm.Comment: 5 pages, 4 figure
Quasiparticle Chirality in Epitaxial Graphene Probed at the Nanometer Scale
Graphene exhibits unconventional two-dimensional electronic properties
resulting from the symmetry of its quasiparticles, which leads to the concepts
of pseudospin and electronic chirality. Here we report that scanning tunneling
microscopy can be used to probe these unique symmetry properties at the
nanometer scale. They are reflected in the quantum interference pattern
resulting from elastic scattering off impurities, and they can be directly read
from its fast Fourier transform. Our data, complemented by theoretical
calculations, demonstrate that the pseudospin and the electronic chirality in
epitaxial graphene on SiC(0001) correspond to the ones predicted for ideal
graphene.Comment: 4 pages, 3 figures, minor change
A Calibrated Time Domain Envelope Measurement System for the Behavioral Modeling of Power Amplifiers
This paper presents a set-up which enables the generation and the calibrated time domain measurements of complex envelopes of modulated signals at both ports of non linear microwave power amplifiers. The architecture of the characterization tool is given. Examples of error corrected time domain envelopes at the input / output RF ports of a 36 dBm output power – 30dB power gain L-band SSPA are shown. Futhermore, the use of this characterization tool and a suitable processing of measurement data are applied to a novel measurement based behavioral modeling approach of non linear devices accounting for memory effects
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