10,856 research outputs found
Uncertainties for Pre- and Post-Launch Radiometric Calibration of Imaging Spectrometers for Multi-Sensor Applications
An important aspect to using imaging spectrometer data is the radiometric characterization and calibration of the sensors and validation of their data products and doing so with error budgets with known traceability. The radiometric accuracy of a given sensor is important for demonstrating the expected quality of data from the sensor. Known traceability allows data from multiple sensors to be directly comparable as will become more important in the near future with the expected launches of multiple imaging spectrometers from multiple countries, agencies, and commercial entities. The current work describes the state of pre- and post-launch radiometric absolute and relative uncertainties and their role in harmonising on-orbit data. Examples of prelaunch uncertainties based on the calibration of EnMAP and the calibration planned for the CLARREO Pathfinder Mission are presented highlighting recent work in the area of detector-based approaches using tunable laser sources. Post-launch calibration approaches for Pathfinder, EnMAP, CHIME, and DESIS including traditional vicarious calibration methods and the challenges of working with commercial data are presented. The vicarious calibration discussion relies on the example of the recently-available RadCalNet data to describe typical methods and challenges that will be faced when harmonising data between imaging spectrometers as well as with multispectral sensors
Determinations of upper critical field in continuous Ginzburg-Landau model
Novel procedures to determine the upper critical field have been
proposed within a continuous Ginzburg-Landau model. Unlike conventional
methods, where is obtained through the determination of the smallest
eigenvalue of an appropriate eigen equation, the square of the magnetic field
is treated as eigenvalue problems so that the upper critical field can be
directly deduced. The calculated from the two procedures are
consistent with each other and in reasonably good agreement with existing
theories and experiments. The profile of the order parameter associated with
is found to be Gaussian-like, further validating the methodology
proposed. The convergences of the two procedures are also studied.Comment: Revtex4, 8 pages, 4 figures, references modified, figures and table
embedde
Superluminal Propagation and Acausality of Nonlinear Massive Gravity
Massive gravity is an old idea: trading geometry for mass. Much effort has
been expended on establishing a healthy model, culminating in the current
ghost-free version. We summarize here our recent findings -- that it is still
untenable -- because it is locally acausal: CTC solutions can be constructed in
a small neighborhood of any event.Comment: Contribution to Conference in Honour of the 90th Birthday of Freeman
Dyson -- To Appear in Proceeding. v2: Explicit CTC example, and other
improvements, adde
An omnidirectional retroreflector based on the transmutation of dielectric singularities
In the field of transformation optics, metamaterials mimic the effect of
coordinate transformations on electromagnetic waves, creating the illusion that
the waves are propagating through a virtual space. Transforming space by
appropriately designed materials makes devices possible that have been deemed
impossible. In particular, transformation optics has led to the demonstration
of invisibility cloaking for microwaves, surface plasmons and infrared light.
Here we report the achievement of another "impossible task". We implement, for
microwaves, a device that would normally require a dielectric singularity, an
infinity in the refractive index. We transmute a singularity in virtual space
into a mere topological defect in a real metamaterial. In particular, we
demonstrate an omnidirectional retroreflector, a device for faithfully
reflecting images and for creating high visibility, from all directions. Our
method is robust, potentially broadband and similar techniques could be applied
for visible light
Anomalous thermopower and Nernst effect in : entropy-current loss in precursor state
The heavy-electron superconductor CeCoIn exhibits a puzzling precursor
state above its superconducting critical temperature at = 2.3 K. The
thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of
the electrons undergoes a steep decrease reaching 0 at .
Concurrently, the off-diagonal thermoelectric current is
enhanced. The delicate sensitivity of the zero-entropy state to field implies
phase coherence over large distances. The prominent anomalies in the
thermoelectric current contrast with the relatively weak effects in the
resistivity and magnetization.Comment: 5 figures, 4 page
Magnetization Behaviour of Nanocrystalline Permalloy Thin Films Prepared Using Oblique-angle Magnetron Sputtering Technique
In the current work, nanocrystalline Fe0.5Ni0.5 magnetic thin films were deposited on a Si(100) substrate using the oblique-angle sputtering technique with the oblique deposition angle ranging from 11.5 to 45°. Structure, static magnetic properties, and dynamic magnetic characteristics were evaluated as a function of the deposition angle. The results indicate that the nanocrystalline FCC phase of FeNi with (111) preferred orientation and the average crystallite size of 6.3-9.3 nm was deposited successfully. The measured value of the uniaxial anisotropy field shows an increment from 7.65 to 16.71 Oe as the oblique angle rises from 11.5 to 45°, which in turn leads to an increase in the ferromagnetic resonance frequency from 0.63 to 0.88 GHz
- …