47,442 research outputs found
Small unmanned airborne systems to support oil and gas pipeline monitoring and mapping
Acknowledgments We thank Johan Havelaar, Aeryon Labs Inc., AeronVironment Inc. and Aeronautics Inc. for kindly permitting the use of materials in Fig. 1.Peer reviewedPublisher PD
Telescope to Observe Planetary Systems (TOPS): a high throughput 1.2-m visible telescope with a small inner working angle
The Telescope to Observe Planetary Systems (TOPS) is a proposed space mission
to image in the visible (0.4-0.9 micron) planetary systems of nearby stars
simultaneously in 16 spectral bands (resolution R~20). For the ~10 most
favorable stars, it will have the sensitivity to discover 2 R_E rocky planets
within habitable zones and characterize their surfaces or atmospheres through
spectrophotometry. Many more massive planets and debris discs will be imaged
and characterized for the first time. With a 1.2m visible telescope, the
proposed mission achieves its power by exploiting the most efficient and robust
coronagraphic and wavefront control techniques. The Phase-Induced Amplitude
Apodization (PIAA) coronagraph used by TOPS allows planet detection at 2
lambda/d with nearly 100% throughput and preserves the telescope angular
resolution. An efficient focal plane wavefront sensing scheme accurately
measures wavefront aberrations which are fed back to the telescope active
primary mirror. Fine wavefront control is also performed independently in each
of 4 spectral channels, resulting in a system that is robust to wavefront
chromaticity.Comment: 12 pages, SPIE conference proceeding, May 2006, Orlando, Florid
Review of small-angle coronagraphic techniques in the wake of ground-based second-generation adaptive optics systems
Small-angle coronagraphy is technically and scientifically appealing because
it enables the use of smaller telescopes, allows covering wider wavelength
ranges, and potentially increases the yield and completeness of circumstellar
environment - exoplanets and disks - detection and characterization campaigns.
However, opening up this new parameter space is challenging. Here we will
review the four posts of high contrast imaging and their intricate interactions
at very small angles (within the first 4 resolution elements from the star).
The four posts are: choice of coronagraph, optimized wavefront control,
observing strategy, and post-processing methods. After detailing each of the
four foundations, we will present the lessons learned from the 10+ years of
operations of zeroth and first-generation adaptive optics systems. We will then
tentatively show how informative the current integration of second-generation
adaptive optics system is, and which lessons can already be drawn from this
fresh experience. Then, we will review the current state of the art, by
presenting world record contrasts obtained in the framework of technological
demonstrations for space-based exoplanet imaging and characterization mission
concepts. Finally, we will conclude by emphasizing the importance of the
cross-breeding between techniques developed for both ground-based and
space-based projects, which is relevant for future high contrast imaging
instruments and facilities in space or on the ground.Comment: 21 pages, 7 figure
Laser Ultrasound Inspection Based on Wavelet Transform and Data Clustering for Defect Estimation in Metallic Samples
Laser-generated ultrasound is a modern non-destructive testing technique. It has been investigated over recent years as an alternative to classical ultrasonic methods, mainly in industrial maintenance and quality control procedures. In this study, the detection and reconstruction of internal defects in a metallic sample is performed by means of a time-frequency analysis of ultrasonic waves generated by a laser-induced thermal mechanism. In the proposed methodology, we used wavelet transform due to its multi-resolution time frequency characteristics. In order to isolate and estimate the corresponding time of flight of eventual ultrasonic echoes related to internal defects, a density-based spatial clustering was applied to the resulting time frequency maps. Using the laser scan beam’s position, the ultrasonic transducer’s location and the echoes’ arrival times were determined, the estimation of the defect’s position was carried out afterwards. Finally, clustering algorithms were applied to the resulting geometric solutions from the set of the laser scan points which was proposed to obtain a two-dimensional projection of the defect outline over the scan plane. The study demonstrates that the proposed method of wavelet transform ultrasonic imaging can be effectively applied to detect and size internal defects without any reference information, which represents a valuable outcome for various applications in the industry. View Full-TextPeer ReviewedPostprint (published version
A microchip optomechanical accelerometer
The monitoring of accelerations is essential for a variety of applications
ranging from inertial navigation to consumer electronics. The basic operation
principle of an accelerometer is to measure the displacement of a flexibly
mounted test mass; sensitive displacement measurement can be realized using
capacitive, piezo-electric, tunnel-current, or optical methods. While optical
readout provides superior displacement resolution and resilience to
electromagnetic interference, current optical accelerometers either do not
allow for chip-scale integration or require bulky test masses. Here we
demonstrate an optomechanical accelerometer that employs ultra-sensitive
all-optical displacement read-out using a planar photonic crystal cavity
monolithically integrated with a nano-tethered test mass of high mechanical
Q-factor. This device architecture allows for full on-chip integration and
achieves a broadband acceleration resolution of 10 \mu g/rt-Hz, a bandwidth
greater than 20 kHz, and a dynamic range of 50 dB with sub-milliwatt optical
power requirements. Moreover, the nano-gram test masses used here allow for
optomechanical back-action in the form of cooling or the optical spring effect,
setting the stage for a new class of motional sensors.Comment: 16 pages, 9 figure
SPHERE: the exoplanet imager for the Very Large Telescope
Observations of circumstellar environments to look for the direct signal of
exoplanets and the scattered light from disks has significant instrumental
implications. In the past 15 years, major developments in adaptive optics,
coronagraphy, optical manufacturing, wavefront sensing and data processing,
together with a consistent global system analysis have enabled a new generation
of high-contrast imagers and spectrographs on large ground-based telescopes
with much better performance. One of the most productive is the
Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE)
designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE
includes an extreme adaptive optics system, a highly stable common path
interface, several types of coronagraphs and three science instruments. Two of
them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager
and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared
(NIR) range in a single observation for efficient young planet search. The
third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to
look for the reflected light of exoplanets and the light scattered by debris
disks. This suite of three science instruments enables to study circumstellar
environments at unprecedented angular resolution both in the visible and the
near-infrared. In this work, we present the complete instrument and its on-sky
performance after 4 years of operations at the VLT.Comment: Final version accepted for publication in A&
Emerging technologies for the non-invasive characterization of physical-mechanical properties of tablets
The density, porosity, breaking force, viscoelastic properties, and the presence or absence of any structural defects or irregularities are important physical-mechanical quality attributes of popular solid dosage forms like tablets. The irregularities associated with these attributes may influence the drug product functionality. Thus, an accurate and efficient characterization of these properties is critical for successful development and manufacturing of a robust tablets. These properties are mainly analyzed and monitored with traditional pharmacopeial and non-pharmacopeial methods. Such methods are associated with several challenges such as lack of spatial resolution, efficiency, or sample-sparing attributes. Recent advances in technology, design, instrumentation, and software have led to the emergence of newer techniques for non-invasive characterization of physical-mechanical properties of tablets. These techniques include near infrared spectroscopy, Raman spectroscopy, X-ray microtomography, nuclear magnetic resonance (NMR) imaging, terahertz pulsed imaging, laser-induced breakdown spectroscopy, and various acoustic- and thermal-based techniques. Such state-of-the-art techniques are currently applied at various stages of development and manufacturing of tablets at industrial scale. Each technique has specific advantages or challenges with respect to operational efficiency and cost, compared to traditional analytical methods. Currently, most of these techniques are used as secondary analytical tools to support the traditional methods in characterizing or monitoring tablet quality attributes. Therefore, further development in the instrumentation and software, and studies on the applications are necessary for their adoption in routine analysis and monitoring of tablet physical-mechanical properties
LANDSAT TM image data quality analysis for energy-related applications
This project represents a no-cost agreement between National Aeronautic Space Administration Goddard Space Flight Center (NASA GSFC) and the Pacific Northwest Laboratory (PNL). PNL is a Department of Energy (DOE) national laboratory operted by Battelle Memorial Institute at its Pacific Northwest Laboratories in Richland, Washington. The objective of this investigation is to evaluate LANDSAT's thematic mapper (TM) data quality and utility characteristics from an energy research and technological perspective. Of main interest is the extent to which repetitive TM data might support DOE efforts relating to siting, developing, and monitoring energy-related facilities, and to basic geoscientific research. The investigation utilizes existing staff and facility capabilities, and ongoing programmatic activities at PNL and other DOE national laboratories to cooperatively assess the potential usefulness of the improved experimental TM data. The investigation involves: (1) both LANDSAT 4 and 5 TM data, (2) qualitative and quantitative use consideration, and 3) NASA P (corrected) and A (uncorrected) CCT analysis for a variety of sites of DOE interest. Initial results were presented at the LANDSAT Investigator's Workshops and at specialized LANDSAT TM sessions at various conferences
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