380,833 research outputs found
On-line PD detection and localization in cross-bonded HV cable systems
This paper addresses the detection and localization of partial discharge (PD) in crossbonded (CB) high voltage (HV) cables. A great deal has been published in recent years on PD based cable insulation condition monitoring, diagnostics and localization in medium voltage (MV) and high voltage (HV) cables. The topic of pulse propagation and PD source localization in CB HV cable systems has yet to be significantly investigated. The main challenge to PD monitoring of CB HV cables is as a result of the interconnectedness of the sheaths of the three single phase cables. The cross-bonding of the sheaths makes it difficult to localize which of the three phases a PD signal has emanated from. Co-axial cables are used to connect cable sheaths to cable link boxes, for ease of installation and protection against moisture. A second challenge is, therefore, the coupling effect when a PD pulse propagates in HV cable joints and the co-axial cables, making PD detection and localization more complex. The paper presents experimental investigations into PD pulse coupling between the cable center conductor and the sheath and the behavior of PD pulse propagation in CB HV cables. It proposes a model to describe PD pulse propagation in a CB HV cable system to allow monitoring and localization, and also presents the knowledge rules required for PD localization in CB HV cable systems
Chemical abundances and ages of the bulge stars in APOGEE high-velocity peaks
A cold high-velocity (HV, 200 km/s) peak was first reported in several
Galactic bulge fields based on the APOGEE commissioning observations. Both the
existence and the nature of the high-velocity peak are still under debate. Here
we revisit this feature with the latest APOGEE DR13 data. We find that most of
the low latitude bulge fields display a skewed Gaussian distribution with a HV
shoulder. However, only 3 out of 53 fields show distinct high-velocity peaks
around 200 km/s. The velocity distribution can be well described by
Gauss-Hermite polynomials, except the three fields showing clear HV peaks. We
find that the correlation between the skewness parameter () and the mean
velocity (), instead of a distinctive HV peak, is a strong indicator
of the bar. It was recently suggested that the HV peak is composed of
preferentially young stars. We choose three fields showing clear HV peaks to
test this hypothesis using the metallicity, [/M] and [C/N] as age
proxies. We find that both young and old stars show HV features. The similarity
between the chemical abundances of stars in the HV peaks and the main component
indicates that they are not systematically different in terms of chemical
abundance or age. In contrast, there are clear differences in chemical space
between stars in the Sagittarius dwarf and the bulge stars. The strong HV peaks
off-plane are still to be explained properly, and could be different in nature.Comment: 13 pages, 10 figures, published in ApJ. Updated to match the final
ApJ published version. Minor revisions to the text and Figure
An Underappreciated Radiation Hazard from High Voltage Electrodes in Vacuum
The use of high voltage (HV) electrodes in vacuum is commonplace in physics
laboratories. In such systems, it has long been known that electron emission
from an HV cathode can lead to bremsstrahlung X-rays; indeed, this is the basic
principle behind the operation of standard X-ray sources. However, in
laboratory setups where X-ray production is not the goal and no electron source
is deliberately introduced, field-emitted electrons accelerated by HV can
produce X-rays as an unintended hazardous byproduct. Both the level of hazard
and the safe operating regimes for HV vacuum electrode systems are not widely
appreciated, at least in university laboratories. A reinforced awareness of the
radiation hazards associated with vacuum HV setups would be beneficial. We
present a case study of a HV vacuum electrode device operated in a university
atomic physics laboratory. We describe the characterisation of the observed
X-ray radiation, its relation to the observed leakage current in the device,
the steps taken to contain and mitigate the radiation hazard, and suggest
safety guidelines.Comment: Submitted to Health Physic
A New Vehicle Localization Scheme Based on Combined Optical Camera Communication and Photogrammetry
The demand for autonomous vehicles is increasing gradually owing to their
enormous potential benefits. However, several challenges, such as vehicle
localization, are involved in the development of autonomous vehicles. A simple
and secure algorithm for vehicle positioning is proposed herein without
massively modifying the existing transportation infrastructure. For vehicle
localization, vehicles on the road are classified into two categories: host
vehicles (HVs) are the ones used to estimate other vehicles' positions and
forwarding vehicles (FVs) are the ones that move in front of the HVs. The FV
transmits modulated data from the tail (or back) light, and the camera of the
HV receives that signal using optical camera communication (OCC). In addition,
the streetlight (SL) data are considered to ensure the position accuracy of the
HV. Determining the HV position minimizes the relative position variation
between the HV and FV. Using photogrammetry, the distance between FV or SL and
the camera of the HV is calculated by measuring the occupied image area on the
image sensor. Comparing the change in distance between HV and SLs with the
change in distance between HV and FV, the positions of FVs are determined. The
performance of the proposed technique is analyzed, and the results indicate a
significant improvement in performance. The experimental distance measurement
validated the feasibility of the proposed scheme
Optical Signatures of Circumstellar Interaction in Type IIP Supernovae
We propose new diagnostics for circumstellar interaction in Type IIP
supernovae by the detection of high velocity (HV) absorption features in Halpha
and He I 10830 A lines during the photospheric stage. To demonstrate the
method, we compute the ionization and excitation of H and He in supernova
ejecta taking into account time-dependent effects and X-ray irradiation. We
find that the interaction with a typical red supergiant wind should result in
the enhanced excitation of the outer layers of unshocked ejecta and the
emergence of corresponding HV absorption, i.e. a depression in the blue
absorption wing of Halpha and a pronounced absorption of He I 10830 A at a
radial velocity of about -10,000 km/s. We identify HV absorption in Halpha and
He I 10830 A lines of SN 1999em and in Halpha of SN 2004dj as being due to this
effect. The derived mass loss rate is close to 10^{-6} Msun/yr for both
supernovae, assuming a wind velocity 10 km/s. We argue that, in addition to the
HV absorption formed in the unshocked ejecta, spectra of SN 2004dj and SN
1999em show a HV notch feature that is formed in the cool dense shell (CDS)
modified by the Rayleigh-Taylor instability. The CDS results from both shock
breakout and radiative cooling of gas that has passed through the reverse shock
wave. The notch becomes dominant in the HV absorption during the late
photospheric phase, ~60 d. The wind density deduced from the velocity of the
CDS is consistent with the wind density found from the HV absorption produced
by unshocked ejecta.Comment: 38 pages, 12 figures, ApJ, in pres
Is wave-particle objectivity compatible with determinism and locality?
Wave-particle duality, superposition and entanglement are among the most
counterintuitive features of quantum theory. Their clash with our classical
expectations motivated hidden-variable (HV) theories. With the emergence of
quantum technologies we can test experimentally the predictions of quantum
theory {\em versus} HV theories and put strong restrictions on their key
assumptions. Here we study an entanglement-assisted version of the quantum
delayed-choice experiment and show that the extension of HV to the controlling
devices only exacerbates the contradiction. We compare HV theories that satisfy
the conditions of objectivity (a property of photons being either particles or
waves, but not both), determinism, and local independence of hidden variables
with quantum mechanics. Any two of the above conditions are compatible with it.
The conflict becomes manifest when all three conditions are imposed and
persists for any non-zero value of entanglement. We propose an experiment to
test our conclusions.Comment: A published version. The logic is similar to the original version,
but many changes were introduce
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