546 research outputs found
First direct observation of the Van Hove singularity in the tunneling spectra of cuprates
In two-dimensional lattices the electronic levels are unevenly spaced, and
the density of states (DOS) displays a logarithmic divergence known as the Van
Hove singularity (VHS). This is the case in particular for the layered cuprate
superconductors. The scanning tunneling microscope (STM) probes the DOS, and is
therefore the ideal tool to observe the VHS. No STM study of cuprate
superconductors has reported such an observation so far giving rise to a debate
about the possibility of observing directly the normal state DOS in the
tunneling spectra. In this study, we show for the first time that the VHS is
unambiguously observed in STM measurements performed on the cuprate Bi-2201.
Beside closing the debate, our analysis proves the presence of the pseudogap in
the overdoped side of the phase diagram of Bi-2201 and discredits the scenario
of the pseudogap phase crossing the superconducting dome.Comment: 4 pages, 4 figure
TIME-RELATED QUALITY DIMENSIONS OF URBAN REMOTELY SENSED BIG DATA
Abstract. Our rapidly changing world requires new sources of image based information. The quickly changing urban areas, the maintenance and management of smart cities cannot only rely on traditional techniques based on remotely sensed data, but also new and progressive techniques must be involved. Among these technologies the volunteer based solutions are getting higher importance, like crowd-sourced image evaluations, mapping by satellite based positioning techniques or even observations done by unskilled people. Location based intelligence has become an everyday practice of our life. It is quite enough to mention the weather forecast and traffic monitoring applications, where everybody can act as an observer and acquired data – despite their heterogeneity in quality – provide great value. Such value intuitively increases when data are of better quality. In the age of visualization, real-time imaging, big data and crowd-sourced spatial data have revolutionary transformed our general applications. Most important factors of location based decisions are the time-related quality parameters of the used data. In this paper several time-related data quality dimensions and terms are defined. The paper analyses the time sensitive data characteristics of image-based crowd-sourced big data, presents quality challenges and perspectives of the users. The data quality analyses focus not only on the dimensions, but are also extended to quality related elements, metrics. The paper discusses the connection of data acquisition and processing techniques, considering even the big data aspects. The paper contains not only theoretical sections, strong practice-oriented examples on detecting quality problems are also covered. Some illustrative examples are the OpenStreetMap (OSM), where the development of urbanization and the increasing process of involving volunteers can be studied. This framework is continuing the previous activities of the Remote Sensing Data Quality Working Group (ICWGIII/IVb) of the ISPRS in the topic focusing on the temporal variety of our urban environment.</p
Direct simulation of ion beam induced stressing and amorphization of silicon
Using molecular dynamics (MD) simulation, we investigate the mechanical
response of silicon to high dose ion-irradiation. We employ a realistic and
efficient model to directly simulate ion beam induced amorphization. Structural
properties of the amorphized sample are compared with experimental data and
results of other simulation studies. We find the behavior of the irradiated
material is related to the rate at which it can relax. Depending upon the
ability to deform, we observe either the generation of a high compressive
stress and subsequent expansion of the material, or generation of tensile
stress and densification. We note that statistical material properties, such as
radial distribution functions are not sufficient to differentiate between
different densities of amorphous samples. For any reasonable deformation rate,
we observe an expansion of the target upon amorphization in agreement with
experimental observations. This is in contrast to simulations of quenching
which usually result in denser structures relative to crystalline Si. We
conclude that although there is substantial agreement between experimental
measurements and most simulation results, the amorphous structures being
investigated may have fundamental differences; the difference in density can be
attributed to local defects within the amorphous network. Finally we show that
annealing simulations of our amorphized samples can lead to a reduction of high
energy local defects without a large scale rearrangement of the amorphous
network. This supports the proposal that defects in amorphous silicon are
analogous to those in crystalline silicon.Comment: 13 pages, 12 figure
The onset of the vortex-like Nernst signal above Tc in La_{2-x}Sr_xCuO_4 and Bi_2Sr_{2-y}La_yCuO_6
The diffusion of vortices down a thermal gradient produces a Josephson signal
which is detected as the vortex Nernst effect. In a recent report, Xu et al.,
Nature 406, 486 (2000), an enhanced Nernst signal identified with vortex-like
excitations was observed in a series of La_{2-x}Sr_xCuO_4 (LSCO) crystals at
temperatures 50-100 K above T_c. To pin down the onset temperature T_{\nu} of
the vortex-like signal in the lightly doped regime (0.03 < x < 0.07), we have
re-analyzed in detail the carrier contribution to the Nernst signal. By
supplementing new Nernst measurements with thermopower and Hall-angle data, we
isolate the off-diagonal Peltier conductivity \alpha_{xy} and show that its
profile provides an objective determination of T_{\nu}. With the new results,
we revise the phase diagram for the fluctuation regime in LSCO to accomodate
the lightly doped regime. In the cuprate Bi_2Sr_{2-y}La_yCuO_6, we find that
the carrier contribution is virtually negligible for y in the range 0.4-0.6.
The evidence for an extended temperature interval with vortex-like excitations
is even stronger in this system. Finally, we discuss how T_{\nu} relates to the
pseudogap temperature T* and the implications of strong fluctuations between
the pseudogap state and the d-wave superconducting state.Comment: 10 pages, 10 figure
IMPROVING DATA QUALITY AND MANAGEMENT FOR REMOTE SENSING ANALYSIS: USE-CASES AND EMERGING RESEARCH QUESTIONS
During the last decades satellite remote sensing has become an emerging technology producing big data for various application fields every day. However, data quality checking as well as the long-time management of data and models are still issues to be improved. They are indispensable to guarantee smooth data integration and the reproducibility of data analysis such as carried out by machine learning models. In this paper we clarify the emerging need of improving data quality and the management of data and models in a geospatial database management system before and during data analysis. In different use cases various processes of data preparation and quality checking, integration of data across different scales and references systems, efficient data and model management, and advanced data analysis are presented in detail. Motivated by these use cases we then discuss emerging research questions concerning data preparation and data quality checking, data management, model management and data integration. Finally conclusions drawn from the paper are presented and an outlook on future research work is given
Electronic structure of the trilayer cuprate superconductor BiSrCaCuO
The low-energy electronic structure of the trilayer cuprate superconductor
BiSrCaCuO near optimal doping is investigated by
angle-resolved photoemission spectroscopy. The normal state quasiparticle
dispersion and Fermi surface, and the superconducting d-wave gap and coherence
peak are observed and compared with those of single and bilayer systems. We
find that both the superconducting gap magnitude and the relative
coherence-peak intensity scale linearly with for various optimally doped
materials. This suggests that the higher of the trilayer system should be
attributed to parameters that simultaneously enhance phase stiffness and
pairing strength.Comment: 5 pages, 5 figre
The Mast Cell Degranulator Compound 48/80 Directly Activates Neurons
Background
Compound 48/80 is widely used in animal and tissue models as a “selective” mast cell activator. With this study we demonstrate that compound 48/80 also directly activates enteric neurons and visceral afferents.
Methodology/Principal Findings
We used in vivo recordings from extrinsic intestinal afferents together with Ca++ imaging from primary cultures of DRG and nodose neurons. Enteric neuronal activation was examined by Ca++ and voltage sensitive dye imaging in isolated gut preparations and primary cultures of enteric neurons. Intraluminal application of compound 48/80 evoked marked afferent firing which desensitized on subsequent administration. In egg albumen-sensitized animals, intraluminal antigen evoked a similar pattern of afferent activation which also desensitized on subsequent exposure to antigen. In cross-desensitization experiments prior administration of compound 48/80 failed to influence the mast cell mediated response. Application of 1 and 10 µg/ml compound 48/80 evoked spike discharge and Ca++ transients in enteric neurons. The same nerve activating effect was observed in primary cultures of DRG and nodose ganglion cells. Enteric neuron cultures were devoid of mast cells confirmed by negative staining for c-kit or toluidine blue. In addition, in cultured enteric neurons the excitatory action of compound 48/80 was preserved in the presence of histamine H1 and H2 antagonists. The mast cell stabilizer cromolyn attenuated compound 48/80 and nicotine evoked Ca++ transients in mast cell-free enteric neuron cultures.
Conclusions/Significance
The results showed direct excitatory action of compound 48/80 on enteric neurons and visceral afferents. Therefore, functional changes measured in tissue or animal models may involve a mast cell independent effect of compound 48/80 and cromolyn
Particle density fluctuations
Event-by-event fluctuations in the multiplicities of charged particles and
photons at SPS energies are discussed. Fluctuations are studied by controlling
the centrality of the reaction and rapidity acceptance of the detectors.
Results are also presented on the event-by-event study of correlations between
the multiplicity of charged particles and photons to search for DCC-like
signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc
Azimuthal Anisotropy of Photon and Charged Particle Emission in Pb+Pb Collisions at 158 A GeV/c
The azimuthal distributions of photons and charged particles with respect to
the event plane are investigated as a function of centrality in Pb + Pb
collisions at 158 A GeV/c in the WA98 experiment at the CERN SPS. The
anisotropy of the azimuthal distributions is characterized using a Fourier
analysis. For both the photon and charged particle distributions the first two
Fourier coefficients are observed to decrease with increasing centrality. The
observed anisotropies of the photon distributions compare well with the
expectations from the charged particle measurements for all centralities.Comment: 8 pages and 6 figures. The manuscript has undergone a major revision.
The unwanted correlations were enhanced in the random subdivision method used
in the earlier version. The present version uses the more established method
of division into subevents separated in rapidity to minimise short range
correlations. The observed results for charged particles are in agreement
with results from the other experiments. The observed anisotropy in photons
is explained using flow results of pions and the correlations arising due to
the decay of the neutral pion
Central Pb+Pb Collisions at 158 A GeV/c Studied by Pion-Pion Interferometry
Two-particle correlations have been measured for identified negative pions
from central 158 AGeV Pb+Pb collisions and fitted radii of about 7 fm in all
dimensions have been obtained. A multi-dimensional study of the radii as a
function of kT is presented, including a full correction for the resolution
effects of the apparatus. The cross term Rout-long of the standard fit in the
Longitudinally CoMoving System (LCMS) and the vl parameter of the generalised
Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a
boost invariant expansion. The shapes of the correlation functions in Qinv and
Qspace have been analyzed in detail. They are not Gaussian but better
represented by exponentials. As a consequence, fitting Gaussians to these
correlation functions may produce different radii depending on the acceptance
of the experimental setup used for the measurement.Comment: 13 pages including 10 figure
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