33,805 research outputs found
The absolute radiometric calibration of the advanced very high resolution radiometer
An increasing number of remote sensing investigations require radiometrically calibrated imagery from NOAA Advanced Very High Resolution Radiation (AVHRR) sensors. Although a prelaunch calibration is done for these sensors, there is no capability for monitoring any changes in the in-flight absolute calibration for the visible and near infrared spectral channels. Hence, the possibility of using the reflectance-based method developed at White Sands for in-orbit calibration of LANDSAT Thematic Mapper (TM) and SPOT Haute Resolution Visible (HVR) data to calibrate the AVHRR sensor was investigated. Three diffrent approaches were considered: Method 1 - ground and atmospheric measurements and reference to another calibrated satellite sensor; Method 2 - ground and atmospheric measurements with no reference to another sensor; and Method 3 - no ground and atmospheric measurements but reference to another satellite sensor. The purpose is to describe an investigation on the use of Method 2 to calibrate NOAA-9 AVHRR channels 1 and 2 with the help of ground and atmospheric measurements at Rogers (dry) Lake, Edwards Air Force Base (EAFB) in the Mojave desert of California
The absolute radiometric calibration of the advanced very high resolution radiometer
The need for independent, redundant absolute radiometric calibration methods is discussed with reference to the Thematic Mapper. Uncertainty requirements for absolute calibration of between 0.5 and 4 percent are defined based on the accuracy of reflectance retrievals at an agricultural site. It is shown that even very approximate atmospheric corrections can reduce the error in reflectance retrieval to 0.02 over the reflectance range 0 to 0.4
The absolute radiometric calibration of the advanced very high resolution radiometer
The measurement conditions are described for an intensive field campaign at White Sands Missile Range for the calibration of the AVHRRs on NOAA-9, NOAA-10 and NOAA-11, LANDSAT-4 TM and SPOT. Three different methods for calibration of AVHRRs by reference to a ground surface site are reported, and results from these methods are compared. Significant degradations in NOAA-9 and NOAA-10 AVHRR responsivities occurred since prelaunch calibrations were completed. As of February 1988, degradations in NOAA-9 AVHRR responsivities were on the order of 37 percent in channel and 41 percent in channel 2, and for the NOAA-10 AVHRR these degradations were 42 and 59 percent in channels 1 and 2, respectively
Angle-resolved photoemission studies of the superconducting gap symmetry in Fe-based superconductors
The superconducting gap is the fundamental parameter that characterizes the
superconducting state, and its symmetry is a direct consequence of the
mechanism responsible for Cooper pairing. Here we discuss about angle-resolved
photoemission spectroscopy measurements of the superconducting gap in the
Fe-based high-temperature superconductors. We show that the superconducting gap
is Fermi surface dependent and nodeless with small anisotropy, or more
precisely, a function of momentum. We show that while this observation is
inconsistent with weak coupling approaches for superconductivity in these
materials, it is well supported by strong coupling models and global
superconducting gaps. We also suggest that the strong anisotropies measured by
other probes sensitive to the residual density of states are not related to the
pairing interaction itself, but rather emerge naturally from the smaller
lifetime of the superconducting Cooper pairs that is a direct consequence of
the momentum dependent interband scattering inherent to these materials.Comment: 7 pages, 5 figure
Recurrent Coronal Jets Induced by Repetitively Accumulated Electric Currents
Three extreme-ultraviolet (EUV) jets recurred in about one hour on 2010
September 17 in the following magnetic polarity of active region 11106. The EUV
jets were observed by the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory (SDO). The Helioseismic and Magnetic Imager (HMI) on board
SDO measured the vector magnetic field, from which we derive the magnetic flux
evolution, the photospheric velocity field, and the vertical electric current
evolution. The magnetic configuration before the jets is derived by the
nonlinear force-free field (NLFFF) extrapolation.
We derive that the jets are above a pair of parasitic magnetic bipoles which
are continuously driven by photospheric diverging flows. The interaction drove
the build up of electric currents that we indeed observed as elongated patterns
at the photospheric level. For the first time, the high temporal cadence of HMI
allows to follow the evolution of such small currents. In the jet region, we
found that the integrated absolute current peaks repetitively in phase with the
171 A flux evolution. The current build up and its decay are both fast, about
10 minutes each, and the current maximum precedes the 171 A by also about 10
minutes. Then, HMI temporal cadence is marginally fast enough to detect such
changes.
The photospheric current pattern of the jets is found associated to the
quasi-separatrix layers deduced from the magnetic extrapolation. From previous
theoretical results, the observed diverging flows are expected to build
continuously such currents. We conclude that magnetic reconnection occurs
periodically, in the current layer created between the emerging bipoles and the
large scale active region field. It induced the observed recurrent coronal jets
and the decrease of the vertical electric current magnitude.Comment: 10 pages, 7 figures, accepted for publication in A&
H-Alpha and Hard X-Ray Observations of a Two-Ribbon Flare Associated with a Filament Eruption
We perform a multi-wavelength study of a two-ribbon flare on 2002 September
29 and its associated filament eruption, observed simultaneously in the H-alpha
line by a ground-based imaging spectrograph and in hard X-rays by RHESSI. The
flare ribbons contain several H-alpha bright kernels that show different
evolutional behaviors. In particular, we find two kernels that may be the
footpoints of a loop. A single hard X-ray source appears to cover these two
kernels and to move across the magnetic neutral line. We explain this as a
result of the merging of two footpoint sources that show gradually asymmetric
emission owing to an asymmetric magnetic topology of the newly reconnected
loops. In one of the H-alpha kernels, we detect a continuum enhancement at the
visible wavelength. By checking its spatial and temporal relationship with the
hard X-ray emission, we ascribe it as being caused by electron beam
precipitation. In addition, we derive the line-of-sight velocity of the
filament plasma based on the Doppler shift of the filament-caused absorption in
the H-alpha blue wing. The filament shows rapid acceleration during the
impulsive phase. These observational features are in principal consistent with
the general scenario of the canonical two-ribbon flare model.Comment: 15 pages, 5 figures, accepted for publication in Ap
Metal-free activation of H<sub>2</sub>O<sub>2</sub> by g-C<sub>3</sub>N<sub>4</sub> under visible light irradiation for the degradation of organic pollutants
Zero-Shot Deep Domain Adaptation
Domain adaptation is an important tool to transfer knowledge about a task
(e.g. classification) learned in a source domain to a second, or target domain.
Current approaches assume that task-relevant target-domain data is available
during training. We demonstrate how to perform domain adaptation when no such
task-relevant target-domain data is available. To tackle this issue, we propose
zero-shot deep domain adaptation (ZDDA), which uses privileged information from
task-irrelevant dual-domain pairs. ZDDA learns a source-domain representation
which is not only tailored for the task of interest but also close to the
target-domain representation. Therefore, the source-domain task of interest
solution (e.g. a classifier for classification tasks) which is jointly trained
with the source-domain representation can be applicable to both the source and
target representations. Using the MNIST, Fashion-MNIST, NIST, EMNIST, and SUN
RGB-D datasets, we show that ZDDA can perform domain adaptation in
classification tasks without access to task-relevant target-domain training
data. We also extend ZDDA to perform sensor fusion in the SUN RGB-D scene
classification task by simulating task-relevant target-domain representations
with task-relevant source-domain data. To the best of our knowledge, ZDDA is
the first domain adaptation and sensor fusion method which requires no
task-relevant target-domain data. The underlying principle is not particular to
computer vision data, but should be extensible to other domains.Comment: This paper is accepted to the European Conference on Computer Vision
(ECCV), 201
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Structure – Property relationships for nanofluids
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Nanofluids refer to dilute liquid suspensions of nanoparticles in commonly used heat transfer liquids. They triggered much excitement since mid 1990s mainly owing to the claims of anomalous enhancement of thermal conductivity even at very low nanoparticle concentrations. There have been
numerous attempts to interpret the mechanism(s) that drive the displayed enhancement. A long debate within the research community supported by experimental and theoretical evidence has highlighted the nanoparticle
structuring as the dominant underlying mechanism. On the other hand the viscosity increase as a result of nanoparticle structuring raises concerns about their suitability for certain applications. This paper mainly discusses the structure – property relationship for nanofluids in microscopically static conditions
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