11,548 research outputs found
Doppler Spectrum Estimation by Ramanujan Fourier Transforms
The Doppler spectrum estimation of a weather radar signal in a classic way
can be made by two methods, temporal one based in the autocorrelation of the
successful signals, whereas the other one uses the estimation of the power
spectral density PSD by using Fourier transforms. We introduces a new tool of
signal processing based on Ramanujan sums cq(n), adapted to the analysis of
arithmetical sequences with several resonances p/q. These sums are almost
periodic according to time n of resonances and aperiodic according to the order
q of resonances. New results will be supplied by the use of Ramanujan Fourier
Transform (RFT) for the estimation of the Doppler spectrum for the weather
radar signal
A Few Photons Among Many: Unmixing Signal and Noise for Photon-Efficient Active Imaging
Conventional LIDAR systems require hundreds or thousands of photon detections
to form accurate depth and reflectivity images. Recent photon-efficient
computational imaging methods are remarkably effective with only 1.0 to 3.0
detected photons per pixel, but they are not demonstrated at
signal-to-background ratio (SBR) below 1.0 because their imaging accuracies
degrade significantly in the presence of high background noise. We introduce a
new approach to depth and reflectivity estimation that focuses on unmixing
contributions from signal and noise sources. At each pixel in an image,
short-duration range gates are adaptively determined and applied to remove
detections likely to be due to noise. For pixels with too few detections to
perform this censoring accurately, we borrow data from neighboring pixels to
improve depth estimates, where the neighborhood formation is also adaptive to
scene content. Algorithm performance is demonstrated on experimental data at
varying levels of noise. Results show improved performance of both reflectivity
and depth estimates over state-of-the-art methods, especially at low
signal-to-background ratios. In particular, accurate imaging is demonstrated
with SBR as low as 0.04. This validation of a photon-efficient, noise-tolerant
method demonstrates the viability of rapid, long-range, and low-power LIDAR
imaging
Acoustical Ranging Techniques in Embedded Wireless Sensor Networked Devices
Location sensing provides endless opportunities for a wide range of applications in GPS-obstructed environments;
where, typically, there is a need for higher degree of accuracy. In this article, we focus on robust range
estimation, an important prerequisite for fine-grained localization. Motivated by the promise of acoustic in
delivering high ranging accuracy, we present the design, implementation and evaluation of acoustic (both
ultrasound and audible) ranging systems.We distill the limitations of acoustic ranging; and present efficient
signal designs and detection algorithms to overcome the challenges of coverage, range, accuracy/resolution,
tolerance to Dopplerâs effect, and audible intensity. We evaluate our proposed techniques experimentally on
TWEET, a low-power platform purpose-built for acoustic ranging applications. Our experiments demonstrate
an operational range of 20 m (outdoor) and an average accuracy 2 cm in the ultrasound domain. Finally,
we present the design of an audible-range acoustic tracking service that encompasses the benefits of a near-inaudible
acoustic broadband chirp and approximately two times increase in Doppler tolerance to achieve better performance
A Compressed Sampling and Dictionary Learning Framework for WDM-Based Distributed Fiber Sensing
We propose a compressed sampling and dictionary learning framework for
fiber-optic sensing using wavelength-tunable lasers. A redundant dictionary is
generated from a model for the reflected sensor signal. Imperfect prior
knowledge is considered in terms of uncertain local and global parameters. To
estimate a sparse representation and the dictionary parameters, we present an
alternating minimization algorithm that is equipped with a pre-processing
routine to handle dictionary coherence. The support of the obtained sparse
signal indicates the reflection delays, which can be used to measure
impairments along the sensing fiber. The performance is evaluated by
simulations and experimental data for a fiber sensor system with common core
architecture.Comment: Accepted for publication in Journal of the Optical Society of America
A [ \copyright\ 2017 Optical Society of America.]. One print or electronic
copy may be made for personal use only. Systematic reproduction and
distribution, duplication of any material in this paper for a fee or for
commercial purposes, or modifications of the content of this paper are
prohibite
Quantum state estimation with unknown measurements
Improved measurement techniques are central to technological development and
foundational scientific exploration. Quantum optics relies upon detectors
sensitive to non-classical features of light, enabling precise tests of
physical laws and quantum-enhanced technologies such as precision measurement
and secure communications. Accurate detector response calibration for
quantum-scale inputs is key to future research and development in these cognate
areas. To address this requirement quantum detector tomography (QDT) has been
recently introduced. However, the QDT approach becomes increasingly challenging
as the complexity of the detector response and input space grows. Here we
present the first experimental implementation of a versatile alternative
characterization technique to address many-outcome quantum detectors by
limiting the input calibration region. To demonstrate the applicability of this
approach the calibrated detector is subsequently used to estimate non-classical
photon number states.Comment: 7 pages, 3 figure
Quantum-inspired computational imaging
Computational imaging combines measurement and computational methods with the aim of forming images even when the measurement conditions are weak, few in number, or highly indirect. The recent surge in quantum-inspired imaging sensors, together with a new wave of algorithms allowing on-chip, scalable and robust data processing, has induced an increase of activity with notable results in the domain of low-light flux imaging and sensing. We provide an overview of the major challenges encountered in low-illumination (e.g., ultrafast) imaging and how these problems have recently been addressed for imaging applications in extreme conditions. These methods provide examples of the future imaging solutions to be developed, for which the best results are expected to arise from an efficient codesign of the sensors and data analysis tools.Y.A. acknowledges support from the UK Royal Academy of Engineering under the Research Fellowship Scheme (RF201617/16/31). S.McL. acknowledges financial support from the UK Engineering and Physical Sciences Research Council (grant EP/J015180/1). V.G. acknowledges support from the U.S. Defense Advanced Research Projects Agency (DARPA) InPho program through U.S. Army Research Office award W911NF-10-1-0404, the U.S. DARPA REVEAL program through contract HR0011-16-C-0030, and U.S. National Science Foundation through grants 1161413 and 1422034. A.H. acknowledges support from U.S. Army Research Office award W911NF-15-1-0479, U.S. Department of the Air Force grant FA8650-15-D-1845, and U.S. Department of Energy National Nuclear Security Administration grant DE-NA0002534. D.F. acknowledges financial support from the UK Engineering and Physical Sciences Research Council (grants EP/M006514/1 and EP/M01326X/1). (RF201617/16/31 - UK Royal Academy of Engineering; EP/J015180/1 - UK Engineering and Physical Sciences Research Council; EP/M006514/1 - UK Engineering and Physical Sciences Research Council; EP/M01326X/1 - UK Engineering and Physical Sciences Research Council; W911NF-10-1-0404 - U.S. Defense Advanced Research Projects Agency (DARPA) InPho program through U.S. Army Research Office; HR0011-16-C-0030 - U.S. DARPA REVEAL program; 1161413 - U.S. National Science Foundation; 1422034 - U.S. National Science Foundation; W911NF-15-1-0479 - U.S. Army Research Office; FA8650-15-D-1845 - U.S. Department of the Air Force; DE-NA0002534 - U.S. Department of Energy National Nuclear Security Administration)Accepted manuscrip
Diagnostic accuracy of 3.0-T magnetic resonance T1 and T2 mapping and T2-weighted dark-blood imaging for the infarct-related coronary artery in Non-ST-segment elevation myocardial infarction
Background: Patients with recent nonâSTâsegment elevation myocardial infarction commonly have heterogeneous characteristics that may be challenging to assess clinically.
Methods and Results: We prospectively studied the diagnostic accuracy of 2 novel (T1, T2 mapping) and 1 established (T2âweighted short tau inversion recovery [T2WâSTIR]) magnetic resonance imaging methods for imaging the ischemic area at risk and myocardial salvage in 73 patients with nonâSTâsegment elevation myocardial infarction (mean age 57±10 years, 78% male) at 3.0âT magnetic resonance imaging within 6.5±3.5 days of invasive management. The infarctârelated territory was identified independently using a combination of angiographic, ECG, and clinical findings. The presence and extent of infarction was assessed with late gadolinium enhancement imaging (gadobutrol, 0.1 mmol/kg). The extent of acutely injured myocardium was independently assessed with native T1, T2, and T2WâSTIR methods. The mean infarct size was 5.9±8.0% of left ventricular mass. The infarct zone T1 and T2 times were 1323±68 and 57±5 ms, respectively. The diagnostic accuracies of T1 and T2 mapping for identification of the infarctârelated artery were similar (P=0.125), and both were superior to T2WâSTIR (P<0.001). The extent of myocardial injury (percentage of left ventricular volume) estimated with T1 (15.8±10.6%) and T2 maps (16.0±11.8%) was similar (P=0.838) and moderately well correlated (r=0.82, P<0.001). Mean extent of acute injury estimated with T2WâSTIR (7.8±11.6%) was lower than that estimated with T1 (P<0.001) or T2 maps (P<0.001).
Conclusions: In patients with nonâSTâsegment elevation myocardial infarction, T1 and T2 magnetic resonance imaging mapping have higher diagnostic performance than T2WâSTIR for identifying the infarctârelated artery. Compared with conventional STIR, T1 and T2 maps have superior value to inform diagnosis and revascularization planning in nonâSTâsegment elevation myocardial infarction.
Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02073422
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