59 research outputs found
Revisiting the Tradespace Exploration Paradigm: Structuring the Exploration Process
A number of case applications of tradespace exploration have further extended the types of analyses and knowledge insights that can be gained about tradeoffs between design choices and perceived utility and cost of alternatives. These extensions include application beyond its heritage aerospace domain to the transportation domain, comparing distinct concepts on a common tradespace, considering the impact of changing needs and contexts over time, evaluation of alternatives in a “light effort” manner. In parallel with these case applications, a formalization of the tradespace exploration process has emerged, using a question-driven approach to ensure the knowledge generated is practical and useful to decision makers. These questions are introduced and applied to three example space systems in order to illustrate insights gained in answering the questions. The insights include identifying “good” designs, the strengths and weakness of selected alternatives across a tradespace, limiting constraints and requirements that could allow for less expensive solutions. Additionally, advanced insights include understanding the sensitivities of designs to changes in contexts and needs, and consideration of the differential impact of uncertainty across a set of alternatives with potential opportunities for risk mitigation.Massachusetts Institute of Technology. Engineering Systems Division (Systems Engineering Advancement Research Initiative (SEAri)
Conductance oscillations of a spin-orbit stripe with polarized contacts
We investigate the linear conductance of a stripe of spin-orbit interaction
in a 2D electron gas; that is, a 2D region of length along the transport
direction and infinite in the transverse one in which a spin-orbit interaction
of Rashba type is present. Polarization in the contacts is described by means
of Zeeman fields. Our model predicts two types of conductance oscillations:
Ramsauer oscillations in the minority spin transmission, when both spins can
propagate, and Fano oscillations when only one spin propagates. The latter are
due to the spin-orbit coupling with quasibound states of the non propagating
spin. In the case of polarized contacts in antiparallel configuration Fano-like
oscillations of the conductance are still made possible by the spin orbit
coupling, even though no spin component is bound by the contacts. To describe
these behaviors we propose a simplified model based on an ansatz wave function.
In general, we find that the contribution for vanishing transverse momentum
dominates and defines the conductance oscillations. Regarding the oscillations
with Rashba coupling intensity, our model confirms the spin transistor
behavior, but only for high degrees of polarization. Including a position
dependent effective mass yields additional oscillations due to the mass jumps
at the interfaces.Comment: 8.5 pages, 9 figure
Universality, the QCD critical/tricritical point and the quark number susceptibility
The quark number susceptibility near the QCD critical end-point (CEP), the
tricritical point (TCP) and the O(4) critical line at finite temperature and
quark chemical potential is investigated. Based on the universality argument
and numerical model calculations we propose a possibility that the hidden
tricritical point strongly affects the critical phenomena around the critical
end-point. We made a semi-quantitative study of the quark number susceptibility
near CEP/TCP for several quark masses on the basis of the
Cornwall-Jackiw-Tomboulis (CJT) potential for QCD in the improved-ladder
approximation. The results show that the susceptibility is enhanced in a wide
region around CEP inside which the critical exponent gradually changes from
that of CEP to that of TCP, indicating a crossover of different universality
classes.Comment: 18 pages, 10 figure
Modelling of strain effects in manganite films
Thickness dependence and strain effects in films of
perovskites are analyzed in the colossal magnetoresistance regime. The
calculations are based on a generalization of a variational approach previously
proposed for the study of manganite bulk. It is found that a reduction in the
thickness of the film causes a decrease of critical temperature and
magnetization, and an increase of resistivity at low temperatures. The strain
is introduced through the modifications of in-plane and out-of-plane electron
hopping amplitudes due to substrate-induced distortions of the film unit cell.
The strain effects on the transition temperature and transport properties are
in good agreement with experimental data only if the dependence of the hopping
matrix elements on the bond angle is properly taken into account.
Finally variations of the electron-phonon coupling linked to the presence of
strain turn out important in influencing the balance of coexisting phases in
the filmComment: 7 figures. To be published on Physical Review
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Organic acids in the rhizosphere and phytoavailability of sewage sludge-borne trace elements
Dust in Supernovae and Supernova Remnants II: Processing and survival
Observations have recently shown that supernovae are efficient dust factories, as predicted for a long time by theoretical models. The rapid evolution of their stellar progenitors combined with their efficiency in precipitating refractory elements from the gas phase into dust grains make supernovae the major potential suppliers of dust in the early Universe, where more conventional sources like Asymptotic Giant Branch (AGB) stars did not have time to evolve. However, dust yields inferred from observations of young supernovae or derived from models do not reflect the net amount of supernova-condensed dust able to be expelled from the remnants and reach the interstellar medium. The cavity where the dust is formed and initially resides is crossed by the high velocity reverse shock which is generated by the pressure of the circumstellar material shocked by the expanding supernova blast wave. Depending on grain composition and initial size, processing by the reverse shock may lead to substantial dust erosion and even complete destruction. The goal of this review is to present the state of the art about processing and survival of dust inside supernova remnants, in terms of theoretical modelling and comparison to observations
EP-1535: Planning quality Variations : for IMRT lung cancer based on treatment plan database
How should I treat multiple coronary aneurysms with severe stenoses?
BACKGROUND: A 46-year-old male, with a history of old myocardial infarction in the first diagonal branch (D1) treated with balloon angioplasty three years before, was admitted to our institution because of chest pain on effort. He underwent coronary angiography which revealed multiple coronary aneurysms in the left anterior descending artery (LAD) and the D1 with severe stenoses in the LAD, D1, and the obtuse marginal branch. INVESTIGATION: Coronary angiography, fractional flow reserve, scintigraphy, coronary computed tomography. DIAGNOSIS: Multiple coronary aneurysms with severe stenoses. MANAGEMENT: Percutaneous coil embolisation and stenting
The Nutritional Value and Microbial Content of Dried Face Fly Pupae (Musca autumnalis (De Geer)) When Fed to Chicks
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