344 research outputs found
Mitigation Emission Strategy Based on Resonances from a Power Inverter System in Electric Vehicles
Large dv/dt and di/dt outputs of power devices in the DC-fed motor power inverter can generate conducted and/or radiated emissions through parasitics that interfere with low voltage electric systems in electric vehicles (EVs) and nearby vehicles. The electromagnetic interference (EMI) filters, ferrite chokes, and shielding added in the product process based on the black box approach can reduce the emission levels in a specific frequency range. However, these countermeasures may also introduce an unexpected increase in EMI noises in other frequency ranges due to added capacitances and inductances in filters resonating with elements of the power inverter, and even increase the weight and dimension of the power inverter system in EVs with limited space. In order to predict the interaction between the mitigation techniques and power inverter geometry, an accurate model of the system is needed. A power inverter system was modeled based on series of two-port network measurements to study the impact of EMI generated by power devices on radiated emission of AC cables. Parallel resonances within the circuit can cause peaks in the S21 (transmission coefficient between the phase-node-to-chassis voltage and the center-conductor-to-shield voltage of the AC cable connecting to the motor) and Z11 (input impedance at Port 1 between the Insulated gate bipolar transistor (IGBT) phase node and chassis) at those resonance frequencies and result in enlarged noise voltage peaks at Port 1. The magnitude of S21 between two ports was reduced to decrease the amount of energy coupled from the noise source between the phase node and chassis to the end of the AC cable by lowering the corresponding quality factor. The equivalent circuits were built by analyzing current-following paths at three critical resonance frequencies. Interference voltage peaks can be suppressed by mitigating the resonances. The capacitances and inductances generating the parallel resonances and responsible elements were determined by the calculation through the equivalent circuits. A combination of mitigation strategies including adding common-mode (CM) ferrite chokes through the Y-caps and the AC bus bar was designed to mitigate the resonances at 6 MHz, 11 MHz, and 26 MHz related to the CM conducted emission by IGBT switching and the radiated emission of the AC cable. The values of Z11 decreased respectively by 15 dB at 6 MHz, 0.4 dB at 11 MHz, and 11.5 dB at 26 MHz and the values of S21 decreased respectively by 8.6 dB at 6 MHz, 7 dB at 11 MHz, and 6.3 dB at 26 MHz. An equivalent model of the power inverter system for real-time simulation in time domain was built to validate the mitigation strategy in simulation software PSPICE
When high similarity copycats lose and moderate similarity copycats gain: The impact of comparative evaluation
Copycats imitate features of leading brands to free ride on their equity. The prevailing belief is that the more similar copycats are to the leader brand, the more positive their evaluation is, and thus the more they free ride. Three studies demonstrate when the reverse holds true: Moderate-similarity copycats are actually evaluated more positively than high-similarity copycats when evaluation takes place comparatively, such as when the leader brand is present rather than absent. The results demonstrate that blatant copycats can be less and subtle copycats can be more perilous than is commonly believed. This finding has implications for marketing theory and practice and trademark law
Elongation dynamics of amyloid fibrils: a rugged energy landscape picture
Protein amyloid fibrils are a form of linear protein aggregates that are
implicated in many neurodegenerative diseases. Here, we study the dynamics of
amyloid fibril elongation by performing Langevin dynamic simulations on a
coarse-grained model of peptides. Our simulation results suggest that the
elongation process is dominated by a series of local minimum due to frustration
in monomer-fibril interactions. This rugged energy landscape picture indicates
that the amount of recycling of monomers at the fibrils' ends before being
fibrilized is substantially reduced in comparison to the conventional two-step
elongation model. This picture, along with other predictions discussed, can be
tested with current experimental techniques
FUSE search for 10^5-10^6 K gas in the rich clusters of galaxies Abell 2029 and Abell 3112
Recent Chandra and XMM X-ray observations of rich clusters of galaxies have
shown that the amount of hot gas which is cooling below ~1 keV is generally
more modest than previous estimates. Yet, the real level of the cooling flows,
if any, remains to be clarified by making observations sensitive to different
temperature ranges. As a follow-up of the FUSE observations reporting a
positive detection of the OVI doublet at 1032, 1038 Angstrom in the cluster of
galaxies Abell 2597, which provided the first direct evidence for ~3x10^5 K gas
in a cluster of galaxies, we have carried out sensitive spectroscopy of two
rich clusters, Abell 2029 and Abell 3112 (z~0.07) located behind low HI
columns. In neither of these clusters could we detect the OVI doublet, yielding
fairly stringent limits of ~27 Msun yr-1 (Abell 2029) and ~25 Msun yr-1 (Abell
3112) to the cooling flow rates using the 10^5-10^6 K gas as a tracer. The
non-detections support the emerging picture that the cooling-flow rates are
much more modest than deduced from earlier X-ray observations.Comment: Astronomy & Astrophysics, in pres
Coming down from the trees: is terrestrial activity in Bornean orangutans natural or disturbance driven?
The orangutan is the world's largest arboreal mammal, and images of the red ape moving through the tropical forest canopy symbolise its typical arboreal behaviour. Records of terrestrial behaviour are scarce and often associated with habitat disturbance. We conducted a large-scale species-level analysis of ground-based camera-trapping data to evaluate the extent to which Bornean orangutans Pongo pygmaeus come down from the trees to travel terrestrially, and whether they are indeed forced to the ground primarily by anthropogenic forest disturbances. Although the degree of forest disturbance and canopy gap size influenced terrestriality, orangutans were recorded on the ground as frequently in heavily degraded habitats as in primary forests. Furthermore, all age-sex classes were recorded on the ground (flanged males more often). This suggests that terrestrial locomotion is part of the Bornean orangutan's natural behavioural repertoire to a much greater extent than previously thought, and is only modified by habitat disturbance. The capacity of orangutans to come down from the trees may increase their ability to cope with at least smaller-scale forest fragmentation, and to cross moderately open spaces in mosaic landscapes, although the extent of this versatility remains to be investigated
Adiabatic scaling relations of galaxy clusters
The aim of the present work is to show that, contrary to popular belief,
galaxy clusters are **not** expected to be self-similar, even when the only
energy sources available are gravity and shock-wave heating. In particular, we
investigate the scaling relations between mass, luminosity and temperature of
galaxy groups and clusters in the absence of radiative processes. Theoretical
expectations are derived from a polytropic model of the intracluster medium and
compared with the results of high-resolution adiabatic gasdynamical
simulations. It is shown that, in addition to the well-known relation between
the mass and concentration of the dark matter halo, the effective polytropic
index of the gas also varies systematically with cluster mass, and therefore
neither the dark matter nor the gas profiles are exactly self-similar. It is
remarkable, though, that the effects of concentration and polytropic index tend
to cancel each other, leading to scaling relations whose logarithmic slopes
roughly match the predictions of the most basic self-similar models. We provide
a phenomenological fit to the relation between polytropic index and
concentration, as well as a self-consistent scheme to derive the non-linear
scaling relations expected for any cosmology and the best-fit normalizations of
the M-T, L-T and F-T relations appropriate for a Lambda-CDM universe. The
predicted scaling relations reproduce observational data reasonably well for
massive clusters, where the effects of cooling and star formation are expected
to play a minor role.Comment: 12 pages, 5 figures, accepted by MNRA
Performance of Landsat-8 and Sentinel-2 Surface Reflectance Products for River Remote Sensing Retrievals of Chlorophyll-A and Turbidity
Rivers and other freshwater systems play a crucial role in ecosystems, industry, transportation and agriculture. Despite the more than 40 years of inland water observations made possible by optical remote sensing, a standardized reflectance product for inland waters is yet forthcoming. The aim of this work is to compare the standard USGS land surface reflectance product to two Landsat-8 and Sentinel-2 aquatic remote sensing reflectance products over the Amazon, Columbia and Mississippi rivers. Landsat-8 reflectance products from all three routines are then evaluated for their comparative performance in retrieving chlorophyll-a and turbidity in reference to shipborne, underway in situ validation measurements. The land surface product shows the best agreement (4 percent Mean Absolute Percent Difference) with field measurements of radiometry collected on the Amazon River and generates 36 percent higher reflectance values in the visible bands compared to aquatic methods (ACOLITE (Atmospheric Correction for OLI (Operational Land Imager) 'lite') and SeaDAS (Sea-viewing Wide Field-of-View Sensor (SeaWiFS) Data Analysis System)) with larger differences between land and aquatic products observed in Sentinel-2 (0.01 per steraradian) compared to Landsat-8 (0.001 per steraradian). Choice of atmospheric correction routine can bias Landsat-8 retrievals of chlorophyll-a and turbidity by as much as 59 percent and 35 percent respectively. Using a more restrictive time window for matching in situ and satellite imagery can reduce differences by 531 percent depending on correction technique. This work highlights the challenges of satellite retrievals over rivers and underscores the need for future optical and biogeochemical research aimed at improving our understanding of the absorbing and scattering properties of river water and their relationships to remote sensing reflectance
Cosmological AMR MHD with Enzo
In this work, we present MHDEnzo, the extension of the cosmological code Enzo
to include the effects magnetic fields through the ideal MHD approximation. We
use a higher order Godunov Riemann solver for the computation of interface
fluxes. We use two constrained transport methods to compute the electric field
from those interface fluxes, which simultaneously advances the induction
equation and maintains the divergence of the magnetic field. A third order
divergence free reconstruction technique is used to interpolate the magnetic
fields in the block structured AMR framework already extant in Enzo. This
reconstruction also preserves the divergence of the magnetic field to machine
precision. We use operator splitting to include gravity and cosmological
expansion. We then present a series of cosmological and non cosmological tests
problems to demonstrate the quality of solution resulting from this combination
of solvers.Comment: 56 pages, 26 figures, submitted to the Astrophysical Journal
Suppliment
Bubbles in Planetary Nebulae and Clusters of Galaxies: Jet Properties
I derive constraints on jet properties for inflating pairs of bubbles in
planetary nebulae and clusters of galaxies. This work is motivated by the
similarity in morphology and some non-dimensional quantities between
X-ray-deficient bubbles in clusters of galaxies and the optical-deficient
bubbles in planetary nebulae, which was pointed out in an earlier work. In the
present paper I find that for inflating fat bubbles, the opening angle of the
jets must be large, i.e., the half opening angle measured from the symemtry
axis of the jets should typically be larger than 40 degrees. Narrow jets will
form elongated lobes rather than fat bubbles. I emphasize the need to include
jets with large opening angle in simulating bubble inflation in both planetary
nebulae and (cooling flow) clusters of galaxies.Comment: submitted to AA; a second in a series of 3 paper
The MUSIC of Galaxy Clusters I: Baryon properties and Scaling Relations of the thermal Sunyaev-Zel'dovich Effect
We introduce the Marenostrum-MultiDark SImulations of galaxy Clusters (MUSIC)
Dataset, one of the largest sample of hydrodynamically simulated galaxy
clusters with more than 500 clusters and 2000 groups. The objects have been
selected from two large N-body simulations and have been resimulated at high
resolution using SPH together with relevant physical processes (cooling, UV
photoionization, star formation and different feedback processes). We focus on
the analysis of the baryon content (gas and star) of clusters in the MUSIC
dataset both as a function of aperture radius and redshift. The results from
our simulations are compared with the most recent observational estimates of
the gas fraction in galaxy clusters at different overdensity radii. When the
effects of cooling and stellar feedbacks are included, the MUSIC clusters show
a good agreement with the most recent observed gas fractions quoted in the
literature. A clear dependence of the gas fractions with the total cluster mass
is also evident. The impact of the aperture radius choice, when comparing
integrated quantities at different redshifts, is tested: the standard
definition of radius at a fixed overdensity with respect to critical density is
compared with a definition based on the redshift dependent overdensity with
respect to background density. We also present a detailed analysis of the
scaling relations of the thermal SZ (Sunyaev Zel'dovich) Effect derived from
MUSIC clusters. The integrated SZ brightness, Y, is related to the cluster
total mass, M, as well as, the M-Y counterpart, more suitable for observational
applications. Both laws are consistent with predictions from the self-similar
model, showing a very low scatter. The effects of the gas fraction on the Y-M
scaling and the presence of a possible redshift dependence on the Y-M scaling
relation are also explored.Comment: 22 pages, 25 figures, accepted for pubblication by MNRA
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