2,819 research outputs found
Chandra Observations of the X-Ray Jet of 3C273
We report results from Chandra observations of the X-ray jet of 3C~273 during
the calibration phase in 2000 January. The zeroeth-order images and spectra
from two 40-ks exposures with the HETG and LETG+ACIS-S show a complex X-ray
structure. The brightest optical knots are detected and resolved in the 0.2-8
keV energy band. The X-ray morphology tracks well the optical. However, while
the X-ray brightness decreases along the jet, the outer parts of the jet tend
to be increasingly bright with increasing wavelength. The spectral energy
distributions of four selected regions can best be explained by inverse Compton
scattering of (beamed) cosmic microwave background photons. The model
parameters are compatible with equipartition and a moderate Doppler factor,
which is consistent with the one-sidedness of the jet. Alternative models
either imply implausible physical conditions and energetics (the synchrotron
self-Compton model) or are sufficiently ad hoc to be unconstrained by the
present data (synchrotron radiation from a spatially or temporally distinct
particle population).Comment: 3 figures; Figure 1 in color. Accepted for publication by ApJ Letter
Radio/X-ray Offsets of Large Scale Jets Caused by Synchrotron Time Lags
In the internal shock scenario, we argue that electrons in most kpc (or even
larger) scale jets can be accelerated to energies high enough to emit
synchrotron X-rays, if shocks exist on these scales. These high energy
electrons emit synchrotron radiation at high frequencies and cool as they
propagate downstream along the jet, emitting at progressively lower frequencies
and resulting in time lags and hence radio/X-ray (and optical/X-ray if the
optical knot is detectable) offsets at bright knots, with the centroids of
X-ray knots being closer to the core. Taking into account strong effects of jet
expansion, the behaviour of radio/X-ray and optical/X-ray offsets at bright
knots in M87, Cen A, 3C 66B, 3C 31, 3C 273, and PKS 1127-145 is consistent with
that of synchrotron time lags due to radiative losses. This suggests that the
large scale X-ray and optical jets in these sources are due to synchrotron
emission.Comment: 4 pages, Accepted for publication in ApJ Letter
Innovative product design conceptualization with oil-less two-stroke engine as a case study
University of Technology, Sydney. Faculty of Engineering.Innovative Product Design Conceptualization with Oil-Less Two-Stroke Engine as a Case Study
Innovative product design is a creative process, involving extensive skills and knowledge, numerous stakeholders with often conflicting interests, and a variety of trade-off decisions. The multitude of different variables to be considered together with the complex nature of engineering design confronts designers with a difficult challenge.
The objective of this thesis is to establish a methodology that will help to formalise and enhance innovative conceptual product design. To achieve this, an oil-less two-stroke engine concept has been taken as a case study in order to elaborate, demonstrate, and validate the proposed Innovative Conceptual Design framework. The methodology aims to yield design process insight and transparency, and embodies two major phases: the Pre-Development activities, including the identification of need and product definition, and the Conceptualization Loop, which comprises the determination of attributes, concept generation, concept evaluation, and concept decision.
In this present research, the Determination of Critical Design Issues together with Early Empirical Design are identified as two essential aspects of successful conceptual design. Early detection of potential design problems is vital for making intelligent and rapid concept decisions before significant development resources are committed. This approach also allows critical design issues to be tackled first in order to avoid going down blind alleys, and helps to control risk and cost.
The thesis presents the authorâs view of conceptual design as involving a continuous focus on four major pillars of design, namely the Time Focus, the Innovation Focus, the Cost Focus, and the Simplicity Focus, the âTICS Focusesâ. On the basis of this perception the discrete design activities during the entire design process aim to develop an innovative, inexpensive, and simple product that is introduced to the marketplace in a timely manner. This may require the designer to make a number of compromises, which can be facilitated by the early detection of design problems by means of Early Empirical Design.
In essence, the suggested conceptual design framework supports design engineers in making issues and problems obvious in the early, least-costly phases of product development. This is the key to accelerating the overall design process and avoiding product failures
Electronic properties of Fabre charge-transfer salts under various temperature and pressure conditions
Using density functional theory, we determine parameters of tight-binding
Hamiltonians for a variety of Fabre charge transfer salts, focusing in
particular on the effects of temperature and pressure. Besides relying on
previously published crystal structures, we experimentally determine two new
sets of structures; (TMTTF)SbF at different temperatures and
(TMTTF)PF at various pressures. We find that a few trends in the
electronic behavior can be connected to the complex phase diagram shown by
these materials. Decreasing temperature and increasing pressure cause the
systems to become more two-dimensional. We analyze the importance of
correlations by considering an extended Hubbard model parameterized using
Wannier orbital overlaps and show that while charge order is strongly activated
by the inter-site Coulomb interaction, the magnetic order is only weakly
enhanced. Both orders are suppressed when the effective pressure is increased.Comment: 12 pages, 16 figure
Na2V3O7, a frustrated nanotubular system with spin-1/2 diamond rings
Following the recent discussion on the puzzling nature of the interactions in
the nanotubular system Na2V3O7, we present a detailed ab-initio microscopic
analysis of its electronic and magnetic properties. By means of a non-trivial
downfolding study we propose an effective model in terms of tubes of nine-site
rings with the geometry of a spin-diamond necklace with frustrated inter-ring
interactions. We show that this model provides a quantitative account of the
observed magnetic behavior.Comment: 5 pages, 5 figures. Phys. Rev. Lett. (in press
Large-Scale Regular Morphological Patterns in the Radio Jet of NGC 6251
We report on large-scale, regular morphological patterns found in the radio
jet of the nearby radio galaxy NGC 6251. Investigating morphological properties
of this radio jet from the nucleus to a radial distance of 300 arcsec
( 140 kpc) mapped at 1662 MHz and 4885 MHz by Perley, Bridle, &
Willis, we find three chains, each of which consists of five radio knots. We
also find that eight radio knots in the first two chains consist of three small
sub-knots (the triple-knotty substructures). We discuss the observational
properties of these regular morphological patterns.Comment: 8 figures, 15 pages, accepted for publication in A
Proton acceleration beyond 100 EeV by an oblique shock wave in the jet of 3C 273
We estimate the highest energy of proton diffusively accelerated by shock in
knot A1 of the jet in luminous nearby quasar 3C 273. Referring to the recent
polarization measurements using very long baseline interferometry (VLBI), we
consider the shock propagation across magnetic field lines, namely,
configuration of the oblique shock. For larger inclination of the field lines,
the effects of particle reflection at the shock front are more pronounced, to
significantly increase acceleration efficiency. The quasiperpendicular shock
turns out to be needed for safely achieving the proton acceleration to the
energy above 100 EeV (10^20 eV) in a parameter domain reflecting conceivable
energy restrictions.Comment: 12 pages, 2 figures, accepted for publication in Astrophysical
Journal Letter
Synthetic Observations of Simulated Radio Galaxies I: Radio and X-ray Analysis
We present an extensive synthetic observational analysis of numerically-
simulated radio galaxies designed to explore the effectiveness of conventional
observational analyses at recovering physical source properties. These are the
first numerical simulations with sufficient physical detail to allow such a
study. The present paper focuses on extraction of magnetic field properties
from nonthermal intensity information. Synchrotron and inverse-Compton
intensities provided meaningful information about distributions and strengths
of magnetic fields, although considerable care was called for. Correlations
between radio and X-ray surface brightness correctly revealed useful dynamical
relationships between particles and fields. Magnetic field strength estimates
derived from the ratio of X-ray to radio intensity were mostly within about a
factor of two of the RMS field strength along a given line of sight. When
emissions along a given line of sight were dominated by regions close to the
minimum energy/equipartition condition, the field strengths derived from the
standard power-law-spectrum minimum energy calculation were also reasonably
close to actual field strengths, except when spectral aging was evident.
Otherwise, biases in the minimum- energy magnetic field estimation mirrored
actual differences from equipartition. The ratio of the inverse-Compton
magnetic field to the minimum-energy magnetic field provided a rough measure of
the actual total energy in particles and fields in most instances, within an
order of magnitude. This may provide a practical limit to the accuracy with
which one may be able to establish the internal energy density or pressure of
optically thin synchrotron sources.Comment: 43 pages, 14 figures; accepted for publication in ApJ, v601 n2
February 1, 200
Comparison of Powertrain System Configurations for Electric Passenger Vehicles
Copyright © 2015 SAE International. Electric vehicles (EV) are considered a practical alternative to conventional and hybrid electric passenger vehicles, with higher overall powertrain efficiencies by omitting the internal combustion engine. As a consequence of lower energy density in the battery energy storage as compared to fossil fuels powered vehicles, EVs have limited driving range, leading to a range phobia and limited consumer acceptance. Particularly for larger luxury EVs, electric motors with a single reduction gear typically do not achieve the diverse range of function needs that are present in multi-speed conventional vehicles, most notably acceleration performance and top speed requirements. Subsequently, multi-speed EV powertrains have been suggested for these applications. Through the utilization of multiple gear ratios a more diverse range of functional needs can be realized without increasing the practical size of the electric motor. The major limitation of multi-speed EV powertrains is that the increased transmission complexity introduces additional losses to the vehicle. Through a number of simulations this paper studies the integration of multispeed transmission with EV platforms. Particularly, it investigates the performance improvements of both B and E class vehicle platforms realized through utilization of two and three speed transmissions. Also the potential application of hybrid energy storage systems (i.e. batteries combined with super-capacitors) is studied. Results demonstrate that there can be significant benefits attained for both small and large passenger vehicles through the application of multi-speed transmissions. However, optimization of these ratios must be considered in the analysis
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