739 research outputs found
Experimental investigation of the edge states structure at fractional filling factors
We experimentally study electron transport between edge states in the
fractional quantum Hall effect regime. We find an anomalous increase of the
transport across the 2/3 incompressible fractional stripe in comparison with
theoretical predictions for the smooth edge potential profile. We interpret our
results as a first experimental demonstration of the intrinsic structure of the
incompressible stripes arising at the sample edge in the fractional quantum
Hall effect regime.Comment: 5 pages, 5 figures included. Submitted to JETP Letter
A Very Intense Neutrino Super Beam Experiment for Leptonic CP Violation Discovery based on the European Spallation Source Linac: A Snowmass 2013 White Paper
Very intense neutrino beams and large neutrino detectors will be needed in
order to enable the discovery of CP violation in the leptonic sector. We
propose to use the proton linac of the European Spallation Source currently
under construction in Lund, Sweden to deliver, in parallel with the spallation
neutron production, a very intense, cost effective and high performance
neutrino beam. The baseline program for the European Spallation Source linac is
that it will be fully operational at 5 MW average power by 2022, producing 2
GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade
the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron
production and 14 pulses/s for neutrino production. Furthermore, because of the
high current required in the pulsed neutrino horn, the length of the pulses
used for neutrino production needs to be compressed to a few s with the
aid of an accumulator ring. A long baseline experiment using this Super Beam
and a megaton underground Water Cherenkov detector located in existing mines
300-600 km from Lund will make it possible to discover leptonic CP violation at
5 significance level in up to 50% of the leptonic Dirac CP-violating
phase range. This experiment could also determine the neutrino mass hierarchy
at a significance level of more than 3 if this issue will not already
have been settled by other experiments by then. The mass hierarchy performance
could be increased by combining the neutrino beam results with those obtained
from atmospheric neutrinos detected by the same large volume detector. This
detector will also be used to measure the proton lifetime, detect cosmological
neutrinos and neutrinos from supernova explosions. Results on the sensitivity
to leptonic CP violation and the neutrino mass hierarchy are presented.Comment: 28 page
Concave Plasmonic Particles: Broad-Band Geometrical Tunability in the Near Infra-Red
Optical resonances spanning the Near and Short Infra-Red spectral regime were
exhibited experimentally by arrays of plasmonic nano-particles with concave
cross-section. The concavity of the particle was shown to be the key ingredient
for enabling the broad band tunability of the resonance frequency, even for
particles with dimensional aspect ratios of order unity. The atypical
flexibility of setting the resonance wavelength is shown to stem from a unique
interplay of local geometry with surface charge distributions
The OPERA experiment Target Tracker
The main task of the Target Tracker detector of the long baseline neutrino
oscillation OPERA experiment is to locate in which of the target elementary
constituents, the lead/emulsion bricks, the neutrino interactions have occurred
and also to give calorimetric information about each event. The technology used
consists in walls of two planes of plastic scintillator strips, one per
transverse direction. Wavelength shifting fibres collect the light signal
emitted by the scintillator strips and guide it to both ends where it is read
by multi-anode photomultiplier tubes. All the elements used in the construction
of this detector and its main characteristics are described.Comment: 25 pages, submitted to Nuclear Instrument and Method
The BL Lac objects OQ 530 and S5 0716+714. Simultaneous observations in the X-rays, radio, optical and TeV bands
We present the results of the BeppoSAX observations of two BL Lacs, OQ 530
and S5 0716+714, as part of a ToO program for the simultaneous observation at
radio, optical, X-ray and TeV energies. Both sources are detected in the LECS
and MECS, with S5 0716+714 visible also in the PDS band, up to about 60 keV.
The X-ray spectra of both sources are better fitted by a double power-law
model, with a steep soft X-ray component flattening at harder energies, with
breaks at 0.3 and 1.5 keV, respectively. The concave shape of the spectra in
both objects is consistent with soft X-rays being produced by the synchrotron
and harder X-rays by the inverse Compton processes. Also the X-ray variability
properties confirm this scenario, in particular for S5 0716+714 our observation
shows variations by about a factor 3 over one hour below 3 keV and no
variability above. Their simultaneous broad band energy spectral distributions
can be successfully interpreted within the frame of a homogeneous synchrotron
and inverse Compton model, including a possible contribution from an external
source of seed photons with the different spectral states of S5 0716+714 being
reproduced by changing the injected power. The resulting parameters are fully
consistent with the two sources being intermediate objects within the
"sequence" scenario proposed for blazars.Comment: 10 pages, 8 figures, accepted by A&
Error-dependent modulation of speech-induced auditory suppression for pitch-shifted voice feedback
<p>Abstract</p> <p>Background</p> <p>The motor-driven predictions about expected sensory feedback (efference copies) have been proposed to play an important role in recognition of sensory consequences of self-produced motor actions. In the auditory system, this effect was suggested to result in suppression of sensory neural responses to self-produced voices that are predicted by the efference copies during vocal production in comparison with passive listening to the playback of the identical self-vocalizations. In the present study, event-related potentials (ERPs) were recorded in response to upward pitch shift stimuli (PSS) with five different magnitudes (0, +50, +100, +200 and +400 cents) at voice onset during active vocal production and passive listening to the playback.</p> <p>Results</p> <p>Results indicated that the suppression of the N1 component during vocal production was largest for unaltered voice feedback (PSS: 0 cents), became smaller as the magnitude of PSS increased to 200 cents, and was almost completely eliminated in response to 400 cents stimuli.</p> <p>Conclusions</p> <p>Findings of the present study suggest that the brain utilizes the motor predictions (efference copies) to determine the source of incoming stimuli and maximally suppresses the auditory responses to unaltered feedback of self-vocalizations. The reduction of suppression for 50, 100 and 200 cents and its elimination for 400 cents pitch-shifted voice auditory feedback support the idea that motor-driven suppression of voice feedback leads to distinctly different sensory neural processing of self vs. non-self vocalizations. This characteristic may enable the audio-vocal system to more effectively detect and correct for unexpected errors in the feedback of self-produced voice pitch compared with externally-generated sounds.</p
Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling
A planar slab of negative index material works as a superlens with
sub-diffraction-limited imaging resolution, since propagating waves are focused
and, moreover, evanescent waves are reconstructed in the image plane. Here, we
demonstrate a superlens for electric evanescent fields with low losses using
perovskites in the mid-infrared regime. The combination of near-field
microscopy with a tunable free-electron laser allows us to address precisely
the polariton modes, which are critical for super-resolution imaging. We
spectrally study the lateral and vertical distributions of evanescent waves
around the image plane of such a lens, and achieve imaging resolution of
wavelength/14 at the superlensing wavelength. Interestingly, at certain
distances between the probe and sample surface, we observe a maximum of these
evanescent fields. Comparisons with numerical simulations indicate that this
maximum originates from an enhanced coupling between probe and object, which
might be applicable for multifunctional circuits, infrared spectroscopy, and
thermal sensors.Comment: 20 pages, 6 figures, published as open access article in Nature
Communications (see http://www.nature.com/ncomms/
Microwave Assisted Synthesis of Py-Im Polyamides
Microwave synthesis was utilized to rapidly build Py-Im polyamides in high yields and purity using Boc-protection chemistry on Kaiser oxime resin. A representative polyamide targeting the 5′-WGWWCW-3′ (W = A or T) subset of the consensus Androgen and Glucocorticoid Response Elements was synthesized in 56% yield after 20 linear steps and HPLC purification. It was confirmed by Mosher amide derivatization of the polyamide that a chiral α-amino acid does not racemize after several additional coupling steps
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