755 research outputs found
A New Concept for a Laser-Based Ultrasonic Phased Array Receiver Using Photo-emf Detection
The virtues of laser-based ultrasound [1], LBU, in general, and phased-array generation and detection in particular, have been appreciated for many years. The ability to improve the spatial resolution of an imaging system, coupled with the potential reduction in local laser intensity at a given location on a component to avoid surface damage while still realizing enhanced performance, represent but two motivating factors that have driven the community to seek methods by which to realize phased-array processing. There has been much activity in demonstrating that phased-array generation of ultrasound can lead to an enhanced directivity of the ultrasound as well as to a decrease (or, increase) in the bandwidth of the generated ultrasound (if desired), be it in the bulk or along the surface of components. Examples of such phased-array generationtechniques (either in the thermoelastic or ablative regimes) include illumination of several discrete spots or locus of points with pulsed lasers [1] on the surface of a workpiece (simultaneously or sequentially), be it a line, an annular ring, or a plurality of spots — or illumination of a scanning pattern of lines along the surface of a sample, the so-called phase-velocity scanning technique [2]. By extension of the phased-array generation concept, one is led to consider the notion of laser-based, phased-array detectionof ultrasound [3]. By reciprocity, this can lead to a receiver of higher resolution relative to a single location for the optical sensing of the ultrasound, as well as to a reduction in the local laser fluence required to achieve a given spatial performance. Moreover, one can, in principle, combine the two modes of phased-array excitation and detection to realize even greater resolution capabilities, which one may refer to as “product processing.” In this case, one has, in essence, a focusing transmitter and an imaging detector, both functioning in concert
Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes
We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline Gdx Zn 1−xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films
The International Mass Loading Service
The International Mass Loading Service computes four loadings: a) atmospheric
pressure loading; b) land water storage loading; c) oceanic tidal loading; and
d) non-tidal oceanic loading. The service provides to users the mass loading
time series in three forms: 1) pre-computed time series for a list of 849 space
geodesy stations; 2) pre-computed time series on the global 1deg x 1deg grid;
and 3) on-demand Internet service for a list of stations and a time range
specified by the user. The loading displacements are provided for the time
period from 1979.01.01 through present, updated on an hourly basis, and have
latencies 8-20 hours.Comment: 8 pages, 3 figures, to appear in the Proceedings of the Reference
Frames for Applications in Geosciences Simposium, held in Luxemboug in
October 201
Removing orientation-induced localization biases in single-molecule microscopy using a broadband metasurface mask
Nanoscale localization of single molecules is a crucial function in several advanced microscopy techniques, including single-molecule tracking and wide-field super-resolution imaging. Until now, a central consideration of such techniques is how to optimize the precision of molecular localization. However, as these methods continue to push towards the nanometre size scale, an increasingly important concern is the localization accuracy. In particular, single fluorescent molecules emit with an anisotropic radiation pattern of an oscillating electric dipole, which can cause significant localization biases using common estimators. Here we present the theory and experimental demonstration of a solution to this problem based on azimuthal filtering in the Fourier plane of the microscope. We do so using a high-efficiency dielectric metasurface polarization/phase device composed of nanoposts with subwavelength spacing. The method is demonstrated both on fluorophores embedded in a polymer matrix and in dL5 protein complexes that bind malachite green
Retrograde Interference in Perceptual Learning of a Peripheral Hyperacuity Task
Consolidation, a process that stabilizes memory trace after initial acquisition, has been studied for over a century. A number of studies have shown that a skill or memory must be consolidated after acquisition so that it becomes resistant to interference from new information. Previous research found that training on a peripheral 3-dot hyperacuity task could retrogradely interfere with earlier training on the same task but with a mirrored stimulus configuration. However, a recent study failed to replicate this finding. Here we address the controversy by replicating both patterns of results, however, under different experimental settings. We find that retrograde interference occurs when eye-movements are tightly controlled, using a gaze-contingent display, where the peripheral stimuli were only presented when subjects maintained fixation. On the other hand, no retrograde interference was found in a group of subjects who performed the task without this fixation control. Our results provide a plausible explanation of why divergent results were found for retrograde interference in perceptual learning on the 3-dot hyperacuity task and confirm that retrograde interference can occur in this type of low-level perceptual learning. Furthermore, our results demonstrate the importance of eye-movement controls in studies of perceptual learning in the peripheral visual field
Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
We present a review of the interplay between the evolution of circumstellar
disks and the formation of planets, both from the perspective of theoretical
models and dedicated observations. Based on this, we identify and discuss
fundamental questions concerning the formation and evolution of circumstellar
disks and planets which can be addressed in the near future with optical and
infrared long-baseline interferometers. Furthermore, the importance of
complementary observations with long-baseline (sub)millimeter interferometers
and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics
Review"; The final publication is available at http://www.springerlink.co
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
Study of decays to the final state and evidence for the decay
A study of decays is performed for the first time
using data corresponding to an integrated luminosity of 3.0
collected by the LHCb experiment in collisions at centre-of-mass energies
of and TeV. Evidence for the decay
is reported with a significance of 4.0 standard deviations, resulting in the
measurement of
to
be .
Here denotes a branching fraction while and
are the production cross-sections for and mesons.
An indication of weak annihilation is found for the region
, with a significance of
2.4 standard deviations.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-022.html,
link to supplemental material inserted in the reference
- …