257 research outputs found
Suns-V characteristics of high performance kesterite solar cells
Low open circuit voltage () has been recognized as the number one
problem in the current generation of CuZnSn(Se,S) (CZTSSe) solar
cells. We report high light intensity and low temperature Suns-
measurement in high performance CZTSSe devices. The Suns- curves
exhibit bending at high light intensity, which points to several prospective
limiting mechanisms that could impact the , even at 1 sun for
lower performing samples. These V limiting mechanisms include low bulk
conductivity (because of low hole density or low mobility), bulk or interface
defects including tail states, and a non-ohmic back contact for low carrier
density CZTSSe. The non-ohmic back contact problem can be detected by
Suns- measurements with different monochromatic illumination. These
limiting factors may also contribute to an artificially lower -
diode ideality factor.Comment: 9 pages, 9 figures, 1 supplementary materia
Effective mass suppression in a ferromagnetic two-dimensional electron liquid
We present numerical calculations of the electron effective mass in an
interacting, ferromagnetic, two-dimensional electron system. We consider
quantum interaction effects associated with the charge-density fluctuation
induced many-body vertex corrections. Our theory, which is free of adjustable
parameters, reveals that the effective mass is suppressed (relative to its band
value) in the strong coupling limit, in good agreement with the results of
recent experimental measurements.Comment: 5 pages, 4 figures, To appear in Phys. Rev.
Observation of fractional quantum Hall effect at even-denominator 1/2 and 1/4 fillings in asymmetric wide quantum wells
We report the observation of developing fractional quantum Hall states at
Landau level filling factors and 1/4 in electron systems confined
to wide GaAs quantum wells with significantly charge
distributions. The very large electric subband separation and the highly
asymmetric charge distribution at which we observe these quantum Hall states,
together with the fact that they disappear when the charge distribution is made
symmetric, suggest that these are one-component states, possibly described by
the Moore-Read Pfaffian wavefunction.Comment: submitted for publicatio
Screening of suitable cationic dopants for solar absorber material CZTS/Se: A first principles study
The earth abundant and non-toxic solar absorber material kesterite Cu2ZnSn(S/Se)(4) has been studied to achieve high power conversion efficiency beyond various limitations, such as secondary phases, antisite defects, band gap adjustment and microstructure. To alleviate these hurdles, we employed screening based approach to find suitable cationic dopant that can promote the current density and the theoretical maximum upper limit of the energy conversion efficiency (P(%)) of CZTS/Se solar devices. For this task, the hybrid functional (Heyd, Scuseria and Ernzerhof, HSE06) were used to study the electronic and optical properties of cation (Al, Sb, Ga, Ba) doped CZTS/Se. Our in-depth investigation reveals that the Sb atom is suitable dopant of CZTS/CZTSe and also it has comparable bulk modulus as of pure material. The optical absorption coefficient of Sb doped CZTS/Se is considerably larger than the pure materials because of easy formation of visible range exciton due to the presence of defect state below the Fermi level, which leads to an increase in the current density and P(%). Our results demonstrate that the lower formation energy, preferable energy gap and excellent optical absorption of the Sb doped CZTS/Se make it potential component for relatively high efficient solar cells
Effects of processing conditions on the formation of Acrylamide and 5-hydroxymethyl-2-furfural in cereal-based products
Large tunable valley splitting in edge-free graphene quantum dots on boron nitride
Coherent manipulation of binary degrees of freedom is at the heart of modern
quantum technologies. Graphene offers two binary degrees: the electron spin and
the valley. Efficient spin control has been demonstrated in many solid state
systems, while exploitation of the valley has only recently been started, yet
without control on the single electron level. Here, we show that van-der Waals
stacking of graphene onto hexagonal boron nitride offers a natural platform for
valley control. We use a graphene quantum dot induced by the tip of a scanning
tunneling microscope and demonstrate valley splitting that is tunable from -5
to +10 meV (including valley inversion) by sub-10-nm displacements of the
quantum dot position. This boosts the range of controlled valley splitting by
about one order of magnitude. The tunable inversion of spin and valley states
should enable coherent superposition of these degrees of freedom as a first
step towards graphene-based qubits
CCD UBV photometric and Gaia astrometric study of eight open clusters- ASCC 115, Collinder 421, NGC 6793, NGC 7031, NGC 7039, NGC 7086, Roslund 1 and Stock 21
In this study, we carried out CCD UBV photometry of eight open clusters, ASCC
115, Collinder 421, NGC 6793, NGC 7031, NGC 7039, NGC 7086, Roslund 1, Stock
21, and determined their reddening, metallicity, distance, age, and mass
functions. We used new Gaia Data Release 2 (DR2) astrometric data to separate
cluster member stars from the field stars and obtain precise structural and
astrophysical parameters. To identify cluster member stars we utilized an
unsupervised membership assignment code (UPMASK), which is based on the
photometric and astrometric data. The density distributions for the open
clusters show good fits with the empirical King model except for Roslund 1 and
Stock 21 not having central concentration. The colour excesses and
metallicities were derived separately using U-B vs B-V two-colour diagrams.
Keeping these parameters as constants, we simultaneously calculated distance
moduli and ages of the clusters from V vs B-V and V vs U-B colour-magnitude
diagrams using PARSEC theoretical isochrones. Taking into account Gaia DR2
proper motion components and parallaxes of the member stars, we also calculated
mean proper motions and distances for the clusters. Distances derived both from
isochrone fitting to colour-magnitude diagrams of the clusters and Gaia DR2
trigonometric parallaxes are compatible with each other. Slopes of the mass
functions of the eight open clusters are in good agreement with Salpeter (1955)
value of 1.35.Comment: 24 pages, 12 figures and 7 tables, accepted for publication in
Astrophysics and Space Scienc
Brain function assessment in different conscious states
Background: The study of brain functioning is a major challenge in neuroscience fields as human brain has a dynamic and ever changing information processing. Case is worsened with conditions where brain undergoes major changes in so-called different conscious states. Even though the exact definition of consciousness is a hard one, there are certain conditions where the descriptions have reached a consensus. The sleep and the anesthesia are different conditions which are separable from each other and also from wakefulness. The aim of our group has been to tackle the issue of brain functioning with setting up similar research conditions for these three conscious states.Methods: In order to achieve this goal we have designed an auditory stimulation battery with changing conditions to be recorded during a 40 channel EEG polygraph (Nuamps) session. The stimuli (modified mismatch, auditory evoked etc.) have been administered both in the operation room and the sleep lab via Embedded Interactive Stimulus Unit which was developed in our lab. The overall study has provided some results for three domains of consciousness. In order to be able to monitor the changes we have incorporated Bispectral Index Monitoring to both sleep and anesthesia conditions.Results: The first stage results have provided a basic understanding in these altered states such that auditory stimuli have been successfully processed in both light and deep sleep stages. The anesthesia provides a sudden change in brain responsiveness; therefore a dosage dependent anesthetic administration has proved to be useful. The auditory processing was exemplified targeting N1 wave, with a thorough analysis from spectrogram to sLORETA. The frequency components were observed to be shifting throughout the stages. The propofol administration and the deeper sleep stages both resulted in the decreasing of N1 component. The sLORETA revealed similar activity at BA7 in sleep (BIS 70) and target propofol concentration of 1.2 Όg/mL.Conclusions: The current study utilized similar stimulation and recording system and incorporated BIS dependent values to validate a common approach to sleep and anesthesia. Accordingly the brain has a complex behavior pattern, dynamically changing its responsiveness in accordance with stimulations and states. © 2010 Ozgoren et al; licensee BioMed Central Ltd
Policies in Hard Times: Assessing the Impact of Financial Crises on Structural Reforms
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A Scaleable and License Free 5G Internet of Radio Light Architecture for Services in Train Stations
In this paper we present a 5G Internet Radio-
Light (IoRL) architecture for underground train stations that
can be readily deployed because it utilizes unlicensed visible light
and millimeter wave part of the spectrum, which does not require
Mobile Network Operator (MNO) permission to deploy and
which is used to provide travelers with accurate location,
interaction, access to Internet and Cloud based Services, such as
high resolution video on a Tablet PC. The paper describes the
train station use cases and the IoRL architecture.European Commissio
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