4,967 research outputs found
High Resolution Current & Bathymetry Determined by Nautical X-Band Radar in Shallow Waters
The wave and current monitoring system WaMoS
II is a remote sensing system based on a nautical X-Band radar generally used for navigation and ship traffic control. It has been used in recent years to monitor sea state information from moored platforms, coastal sites and moving vessels. A nautical radar can scan the sea surface over a large area (~ 10km2 ) with a high spatial (~7.5m) and temporal resolution (~2s). Directionalwave spectra and standard sea state parameters such as significant wave height, peak wave period and direction can be derived by analyzing the sea surface image sequences. Using the temporal and spatial evolution of the sea surface wave images it is also possible to determine high resolution current and bathymetry information.
In the paper a brief introduction into the measuring principle of WaMoS II is given and results of a high resolution current and bathymetric mapping technique for shallow water areas (<20m) are presented. For validation these results are compared with model data and in-situ measurements
Realization of the purely spatial Einstein-Podolsky-Rosen paradox in full-field images of spontaneous parametric down conversion
We demonstrate Einstein-Podolsky-Rosen (EPR) entanglement by detecting purely
spatial quantum correlations in the near and far fields of spontaneous
parametric down-conversion generated in a type-2 beta barium borate crystal.
Full-field imaging is performed in the photon-counting regime with an
electron-multiplying CCD camera. The data are used without any postselection,
and we obtain a violation of Heisenberg inequalities with inferred quantities
taking into account all the biphoton pairs in both the near and far fields by
integration on the entire two-dimensional transverse planes. This ensures a
rigorous demonstration of the EPR paradox in its original position momentum
form
Early CRT monitoring using time-domain optical coherence tomography does not add to visual acuity for predicting visual loss in patients with central retinal vein occlusion treated with intravitreal ranibizumab:A secondary analysis of trial data
Our primary purpose was to assess the clinical (predictive) validity of central retinal thickness (CRT) and best corrected visual acuity (BCVA) at 1 week and 1 month after starting treatment with ranibizumab for central retinal vein occlusion. The authors also assessed detectability of response to treatment
Stress Tensor from the Trace Anomaly in Reissner-Nordstrom Spacetimes
The effective action associated with the trace anomaly provides a general
algorithm for approximating the expectation value of the stress tensor of
conformal matter fields in arbitrary curved spacetimes. In static, spherically
symmetric spacetimes, the algorithm involves solving a fourth order linear
differential equation in the radial coordinate r for the two scalar auxiliary
fields appearing in the anomaly action, and its corresponding stress tensor. By
appropriate choice of the homogeneous solutions of the auxiliary field
equations, we show that it is possible to obtain finite stress tensors on all
Reissner-Nordstrom event horizons, including the extreme Q=M case. We compare
these finite results to previous analytic approximation methods, which yield
invariably an infinite stress-energy on charged black hole horizons, as well as
with detailed numerical calculations that indicate the contrary. The
approximation scheme based on the auxiliary field effective action reproduces
all physically allowed behaviors of the quantum stress tensor, in a variety of
quantum states, for fields of any spin, in the vicinity of the entire family (0
le Q le M) of RN horizons.Comment: 43 pages, 12 figure
Classical communication cost of quantum steering
Quantum steering is observed when performing appropriate local measurements
on an entangled state. Here we discuss the possibility of simulating
classically this effect, using classical communication instead of entanglement.
We show that infinite communication is necessary for exactly simulating
steering for any pure entangled state, as well as for a class of mixed
entangled states. Moreover, we discuss the communication cost of steering for
general entangled states, as well as approximate simulation. Our findings
reveal striking differences between Bell nonlocality and steering, and provide
a natural way of measuring the strength of the latter.Comment: 7 pages, 1 figure. See also arXiv:1603.xxxxx for related work by S.
Nagy and T. V\'ertes
A temporal waterline approach to mapping intertidal areas using X-band marine radar
Mapping the morphology of intertidal areas is a logistically challenging, time consuming and expensive task due to their large expanse and difficulties associated with access. A technique is presented here that uses standard marine navigational radar operating at X-band frequency. The method uses a series of time-exposure radar images over the course of a two-week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images, thereby building up a morphological map of the target intertidal area. This “Temporal Waterline” method is applied to a dataset acquired from Hilbre Island at the mouth of the Dee Estuary, UK, spanning March 2006 to January 2007. The radar gathered data with a radial range of 4 km and the resulting elevation maps describe the intertidal regions of that area. The results are compared with airborne LiDAR data surveyed over the same area and within the radar survey time period. The residual differences show good agreement across large areas of beach and sandbanks, with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water. This paper presents the theoretical framework of the method and demonstrates its stability and accuracy. The Temporal Waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines
Hierarchy of steering criteria based on moments for all bipartite quantum systems
Einstein-Podolsky-Rosen steering is a manifestation of quantum correlations exhibited by quantum systems that allows for entanglement certification when one of the subsystems is not characterized. Detecting the steerability of quantum states is essential to assess their suitability for quantum information protocols with partially trusted devices. We provide a hierarchy of sufficient conditions for the steerability of bipartite quantum states of any dimension, including continuous variable states. Previously known steering criteria are recovered as special cases of our approach. The proposed method allows us to derive optimal steering witnesses for arbitrary families of quantum states and provides a systematic framework to analytically derive nonlinear steering criteria. We discuss relevant examples and, in particular, provide an optimal steering witness for a lossy single-photon Bell state; the witness can be implemented just by linear optics and homodyne detection and detects steering with a higher loss tolerance than any other known method. Our approach is readily applicable to multipartite steering detection and to the characterization of joint measurability
Optical-fiber source of polarization-entangled photon pairs in the 1550nm telecom band
We present a fiber based source of polarization-entangled photon pairs that
is well suited for quantum communication applications in the 1550nm band of
standard fiber-optic telecommunications. Polarization entanglement is created
by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed
orthogonally-polarized pump pulses and subsequently removing the time
distinguishability by passing the parametrically scattered signal-idler photon
pairs through a piece of birefringent fiber. Coincidence detection of the
signal-idler photons yields biphoton interference with visibility greater than
90%, while no interference is observed in direct detection of either the signal
or the idler photons. All four Bell states can be prepared with our setup and
we demonstrate violations of CHSH form of Bell's inequalities by up to 10
standard deviations of measurement uncertainty.Comment: 12 pages, 4 figures, to be submitted to Phys. Rev. Lett. See also
paper QTuB4 in QELS'03 Technical Digest (OSA, Washington, D.C., 2003). This
is a more complete versio
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