47 research outputs found
Phase diagram of the excitonic insulator
Motivated by recent experiments, which give strong evidence for an excitonic
insulating phase in , we developed a scheme to
quantitatively construct, for generic two-band models, the phase diagram of an
excitonic insulator. As a first application of our approach, we calculated the
phase diagram for an effective mass two-band model with long-range Coulomb
interaction. The shielded potential approximation is used to derive a
generalized gap equation controlling for positive (negative) energy gaps the
transition from a semi-conducting (semi-metallic) phase to an insulating phase.
Numerical results,obtained within the quasi-static approximation, show a
steeple-like phase diagram in contrast to long-standing expectations.Comment: 2 pages, 1 figure, SCES'05, accepted for publication in Physica
Influence of the substrate lattice structure on the formation of Quantum Well States in thin In and Pb films on silicon
The substrate lattice structure may have a considerable influence on the
formation of quantum well states in a metal overlayer material. Here we study
three model systems using angle resolved photoemission and low energy electron
diffraction: indium films on Si(111) and indium and lead on Si(100). Data are
compared with theoretical predictions based on density functional theory. We
find that the interaction between the substrate and the overlayer strongly
influences the formation of quantum well states; indium layers only exhibit
well defined quantum well states when the layer relaxes from an initial
face-centered cubic to the bulk body-centered tetragonal lattice structure. For
Pb layers on Si(100) a change in growth orientation inhibits the formations of
quantum well states in films thicker than 2 ML.Comment: 16 pages, 7 figure
Quality assurance of the Brewer UV measurements in Finland
International audienceThe quality assurance of the two Brewer spectrophotometers of the Finnish Meteorological Institute is discussed in this paper. The complete data processing chain from raw signal to high quality spectra is presented. The quality assurance includes daily maintenance, laboratory characterizations, calculation of long term spectral responsivity, data processing and quality assessment. The cosine correction of the measurements is based on a new method, and included in the data processing software. The results showed that the actual cosine correction factor of the Finnish Brewers can vary between 1.08?1.13 and 1.08?1.12, respectively, depending on the sky radiance distribution and wavelength. The temperature characterization showed a linear temperature dependence between the internal temperature and the photon counts per cycle, and a temperature correction was used for correcting the measurements. The long term spectral responsivity was calculated using time series of several lamps using two slightly different methods. The long term spectral responsivity was scaled to the irradiance scale of the Helsinki University of Technology (HUT) for the whole measurement time periods 1990?2006 and 1995?2006 for Sodankylä and Jokioinen, respectively. Both Brewers have participated in many international spectroradiometer comparisons, and have shown good stability. The differences between the Brewers and the portable reference spectroradiometer QASUME have been within 5% during 2002?2007
Quality assurance of the Brewer spectral UV measurements in Finland
The quality assurance of the two Brewer spectrophotometers of the Finnish Meteorological Institute is discussed in this paper. The complete data processing chain from raw signal to high quality spectra is presented. The quality assurance includes daily maintenance, laboratory characterizations, calculation of long-term spectral responsivity, data processing and quality assessment. The cosine correction of the measurements is based on a new method, and is included in the data processing software. The results showed that the actual cosine correction factor of the two Finnish Brewers can vary between 1.08–1.13 and 1.08–1.12, respectively, depending on the sky radiance distribution and wavelength. The temperature characterization showed a linear temperature dependence between the instruments' internal temperature and the photon counts per cycle, and a temperature correction was used for correcting the measurements. The long-term spectral responsivity was calculated using the time series of several lamps using two slightly different methods. The long-term spectral responsivity was scaled to the irradiance scale of the Helsinki University of Technology (HUT) for the whole of the measurement time-periods 1990–2006 and 1995–2006 for Sodankylä and Jokioinen, respectively. Both Brewers have participated in many international spectroradiometer comparisons, and have shown good stability. The differences between the Brewers and the portable reference spectroradiometer QASUME have been within 5% during 2002–2007
Intercomparison of erythemal broadband radiometers calibrated by seven UV calibration facilities in Europe and the USA
International audienceA bi-lateral intercomparison of erythemal broadband radiometers was performed between seven UV calibration facilities. The owners calibrations were compared relative to the characterisation and calibration performed at PMOD/WRC in Davos, Switzerland. The calibration consisted in the determination of the spectral and angular response of the radiometer, followed by an absolute calibration performed outdoors relative to a spectroradiometer which provided the absolute reference. The characterization of the detectors in the respective laboratories are in good agreement: The determination of the angular responses have deviations below ±4% and the spectral responses agree within ±20%. A "blind" intercomparison of the erythemally weighted irradiances derived by the respective institutes and PMOD/WRC showed consistent measurements to within ±2% for the majority of institutes. One institute showed slightly larger deviation of 10%. The differences found between the different instrument calibrations are all within the combined uncertainty of the calibration
An Ontological Approach to Inform HMI Designs for Minimizing Driver Distractions with ADAS
ADAS (Advanced Driver Assistance Systems) are in-vehicle systems designed to enhance driving
safety and efficiency as well as comfort for drivers in the driving process. Recent studies have
noticed that when Human Machine Interface (HMI) is not designed properly, an ADAS can cause
distraction which would affect its usage and even lead to safety issues. Current understanding of
these issues is limited to the context-dependent nature of such systems. This paper reports the
development of a holistic conceptualisation of how drivers interact with ADAS and how such
interaction could lead to potential distraction. This is done taking an ontological approach to
contextualise the potential distraction, driving tasks and user interactions centred on the use of
ADAS. Example scenarios are also given to demonstrate how the developed ontology can be used
to deduce rules for identifying distraction from ADAS and informing future designs