6,113 research outputs found
PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications
In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be
largely employed in Wide Area Monitoring, Protection and Control (WAMPAC)
applications. However, a standard approach towards ROCOF measurements is still
missing. In this paper, we investigate the feasibility of Phasor Measurement
Units (PMUs) deployment in ROCOF-based applications, with a specific focus on
Under-Frequency Load-Shedding (UFLS). For this analysis, we select three
state-of-the-art window-based synchrophasor estimation algorithms and compare
different signal models, ROCOF estimation techniques and window lengths in
datasets inspired by real-world acquisitions. In this sense, we are able to
carry out a sensitivity analysis of the behavior of a PMU-based UFLS control
scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters,
as long as the harmonic and inter-harmonic distortion within the measurement
pass-bandwidth is scarce. In the presence of transient events, the
synchrophasor model looses its appropriateness as the signal energy spreads
over the entire spectrum and cannot be approximated as a sequence of
narrow-band components. Finally, we validate the actual feasibility of
PMU-based UFLS in a real-time simulated scenario where we compare two different
ROCOF estimation techniques with a frequency-based control scheme and we show
their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE
Transactions on Instrumentation and Measurement (acceptance date: 9 March
2019
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
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&
A compact and robust method for full Stokes spectropolarimetry
We present an approach to spectropolarimetry which requires neither moving
parts nor time dependent modulation, and which offers the prospect of achieving
high sensitivity. The technique applies equally well, in principle, in the
optical, UV or IR. The concept, which is one of those generically known as
channeled polarimetry, is to encode the polarization information at each
wavelength along the spatial dimension of a 2D data array using static, robust
optical components. A single two-dimensional data frame contains the full
polarization information and can be configured to measure either two or all of
the Stokes polarization parameters. By acquiring full polarimetric information
in a single observation, we simplify polarimetry of transient sources and in
situations where the instrument and target are in relative motion. The
robustness and simplicity of the approach, coupled to its potential for high
sensitivity, and applicability over a wide wavelength range, is likely to prove
useful for applications in challenging environments such as space.Comment: 36 pages, 11 figures, 3 tables; accepted for publication in Applied
Optic
Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy
The Supernova / Acceleration Probe (SNAP) is a proposed space-based
experiment designed to study the dark energy and alternative explanations of
the acceleration of the Universe's expansion by performing a series of
complementary systematics-controlled measurements. We describe a
self-consistent reference mission design for building a Type Ia supernova
Hubble diagram and for performing a wide-area weak gravitational lensing study.
A 2-m wide-field telescope feeds a focal plane consisting of a 0.7
square-degree imager tiled with equal areas of optical CCDs and near infrared
sensors, and a high-efficiency low-resolution integral field spectrograph. The
SNAP mission will obtain high-signal-to-noise calibrated light-curves and
spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A
wide-field survey covering one thousand square degrees resolves ~100 galaxies
per square arcminute. If we assume we live in a cosmological-constant-dominated
Universe, the matter density, dark energy density, and flatness of space can
all be measured with SNAP supernova and weak-lensing measurements to a
systematics-limited accuracy of 1%. For a flat universe, the
density-to-pressure ratio of dark energy can be similarly measured to 5% for
the present value w0 and ~0.1 for the time variation w'. The large survey area,
depth, spatial resolution, time-sampling, and nine-band optical to NIR
photometry will support additional independent and/or complementary dark-energy
measurement approaches as well as a broad range of auxiliary science programs.
(Abridged)Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.go
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