Results 1 - 10 of 9787
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[en] This study describes a noise-minimization, matched filter technique to increase the signal-to-noise ratio in time series records of geological data. The method is applied to two field examples to illustrate the use of the filtering technique both with good quality data in terms of sample density and signal, and with data of less than optimum quality in terms of low signal amplitude and low sample density. A synthetic example illustrates the resolution capabilities against a known situation. The method effectively minimizes the white noise content of the time series. Signals are extracted which best reflect geologic events for (i) carbon isotope changes with time in the Pliocene-late Miocene and (ii) morphological changes in an evolving lineage of planktonic foraminifera. The matched filter method can also be used to distinguish high quality data of any type from a total data set containing poor data with respect to relative signal-to-noise content. (Author)
[en] The in-ice radio interferometric phased array technique for detection of high energy neutrinos looks for Askaryan emission from neutrinos interacting in large volumes of glacial ice, and is being developed as a way to achieve a low energy threshold and a large effective volume at high energies. The technique is based on coherently summing the impulsive Askaryan signal from multiple antennas, which increases the signal-to-noise ratio for weak signals. We report here on measurements and a simulation of thermal noise correlations between nearby antennas, beamforming of impulsive signals, and a measurement of the expected improvement in trigger efficiency through the phased array technique. We also discuss the noise environment observed with an analog phased array at Summit Station, Greenland, a possible site for an interferometric phased array for radio detection of high energy neutrinos.
[en] We classify all coded masks onto which cyclic difference sets can be wrapped periodically using a generalization of the Finger and Prince construction. In particular, we establish simple numerical criteria which determine whether any given mask can be wrapped periodically in this way and, for each mask which can, we provide explicit constructions which will produce at least one such wrapping. We show that all periodic wrappings currently reported in the literature are special cases of our explicit constructions, and we often provide simpler alternatives. Using these constructions we show that all Singer cyclic difference sets of practical size and open fraction can be wrapped exactly onto masks which are very nearly as compact and symmetrical as hexagons, without the need for pixel padding
[en] Optical coherence tomography (OCT) images are severely degraded by speckle noise. Existing methods for despeckling multiframe OCT data cannot deliver sufficient speckle suppression while preserving image details well. To address this problem, the spiking cortical model (SCM) based non-local means (NLM) method has been proposed in this letter. In the proposed method, the considered frame and two neighboring frames are input into three SCMs to generate the temporal series of pulse outputs. The normalized moment of inertia (NMI) of the considered patches in the pulse outputs is extracted to represent the rotational and scaling invariant features of the corresponding patches in each frame. The pixel similarity is computed based on the Euclidean distance between the NMI features and used as the weight. Each pixel in the considered frame is restored by the weighted averaging of all pixels in the pre-defined search window in the three frames. Experiments on the real multiframe OCT data of the pig eye demonstrate the advantage of the proposed method over the frame averaging method, the multiscale sparsity based tomographic denoising method, the wavelet-based method and the traditional NLM method in terms of visual inspection and objective metrics such as signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), equivalent number of looks (ENL) and cross-correlation (XCOR). (letter)
[en] Hybrid MR-linac systems can use fast dynamic MR sequences for tumor tracking and adapt the radiation treatment in real-time. For this the imaging latency must be as short as possible. This work describes how different acquisition parameters influence this latency. First, the latency was measured for Cartesian readouts with phase encode orderings linear, reverse-linear, and high-low. Second, the latency was measured for radial readouts with linear and golden angle profile orderings. To reduce the latency, a spatio-temporal (k-t) filter that suppresses the k-space center of earlier acquired spokes was implemented for the golden angle sequence. For Cartesian readouts a high-low ordering achieved a three times lower latency compared to a linear ordering with our sampling parameters. For radial readouts the filter was able to reduce the acquisition latency from half the acquisition time to a quarter of the acquisition time. The filter did not compromise the signal-to-noise ratio and the artifact power. (paper)
[en] This article presents the possibility of in-salt radio detection of high energy neutrinos, and shows the implications that a heterogeneous propagating medium has on both antenna behaviour, and on constructing the detector. Based on several factors (propagation effects signal to noise ratio, minimum necessary number of triggers, etc.) it was found that observations are limited at a 1022 eV energy threshold. This higher limit allows both neutrino characteristics, and internal structure of the dome to be simultaneously determined. A total number of 40 to 200 events per year is expected when typical sedimentary layers of about 5cm are considered for the internal salt dome structure.
[en] Based on a high resolution and high signal-to-noise ratio (S/N) spectral analysis of 90 solar-type stars, we have established several new metallicity calibrations in the Teff range [5600, 6500] K based on red spectra with the wavelength range of 560-880 nm. The new metallicity calibrations are applied to determine the metallicity of solar analogs selected from Sloan Digital Sky Survey (SDSS) spectra. There is a good consistent result with the adopted value presented in SDSS-DR7 and a small scatter of 0.26 dex for stars with S/N > 50 being obtained. This study provides a new reliable way to derive the metallicity for solar-like stars with low resolution spectra. In particular, our calibrations are useful for finding metal-rich stars, which are missing in the SEGUE Stellar Parameter Pipeline.
[en] Complete text of publication follows. The detection and characterization of buried structures with GPR can be improved by using multi-offset (MO) methods in which the distance between the emitting and the receiving antennae varies. These methods can increase the resolution and continuity of the main events, making it possible a more complete and precise interpretation of them. Between the MO methods, the common midpoint method is the most commonly used in GPR. Other MO methods, such as the Synthetic Emitter Array (SEA) method are rarely investigated or applied. In this method the objective is to increase the directivity of the transmitted field, then increasing the amplitude on the target of interest and reducing the influence of the surroundings. The field impinging onto the target is synthesized from the superimposition of a number of individual records, which are obtained with a single source that is longitudinally displaced for each receiver position. The SEA method has proved to be efficient in characterizing different kinds of 2D archaeological and engineering structures, with a noticeable potential for similar kinds of ambient applications. In this work we show some results of the SEA method and compare it with the CMP method. We analyze the signal to noise ratio for a variety of targets, such us localized objects, extensive reflectors, and different combinations of them.
[en] We sought to investigate the optimum b value for resolving crossing fiber using high-angular resolution diffusion imaging (HARDI)-based multi-tensor tractography. The study tested the standard b values that are commonly used in the routine clinical setting. Ten normal volunteers (five men and five women) with a mean age of 26.3 years (range, 22-32 years) were scanned using a 1.5-T clinical magnetic resonance unit. Single-shot echo-planar imaging was used for diffusion-weighted imaging with a diffusion-sensitizing gradient in 32 orientations. The b values of 700, 1,400, 2,100, and 2,800 s/m2 were used. Data postprocessing was performed using multi-tensor methods. The depiction of the optic nerves, optic tracts, and decussation of superior cerebellar peduncles were assessed. The depictions of the nerve fibers were independent of the b values tested. The depiction of crossing fibers by HARDI-based multi-tensor tractography is not substantially influenced by b values ranging from 700 to 2,800 s/m2. Thus, the optimum b value within this range may be the lowest one considering the higher signal to noise ratio. (orig.)
[en] We report the discovery of the first new ultra-cool brown dwarf (BDs) found with the Wide-field Infrared Survey Explorer (WISE). The object's preliminary designation is WISEPC J045853.90+643451.9. Follow-up spectroscopy with the LUCIFER instrument on the Large Binocular Telescope indicates that it is a very late-type T dwarf with a spectral type approximately equal to T9. Fits to an IRTF/SpeX 0.8-2.5 μm spectrum to the model atmospheres of Marley and Saumon indicate an effective temperature of approximately 600 K as well as the presence of vertical mixing in its atmosphere. The new BD is easily detected by WISE, with a signal-to-noise ratio of ∼36 at 4.6 μm. Current estimates place it at a distance of 6-10 pc. This object represents the first in what will likely be hundreds of nearby BDs found by WISE that will be suitable for follow-up observations, including those with the James Webb Space Telescope. One of the two primary scientific goals of the WISE mission is to find the coolest, closest stars to our Sun; the discovery of this new BD proves that WISE is capable of fulfilling this objective.