838 research outputs found
Energy efficient engine flight propulsion system: Aircraft/engine integration evaluation
Results of aircraft/engine integration studies conducted on an advanced flight propulsion system are reported. Economic evaluations of the preliminary design are included and indicate that program goals will be met. Installed sfc, DOC, noise, and emissions were evaluated. Aircraft installation considerations and growth were reviewed
COBE ground segment gyro calibration
Discussed here is the calibration of the scale factors and rate biases for the Cosmic Background Explorer (COBE) spacecraft gyroscopes, with the emphasis on the adaptation for COBE of an algorithm previously developed for the Solar Maximum Mission. Detailed choice of parameters, convergence, verification, and use of the algorithm in an environment where the reference attitudes are determined form the Sun, Earth, and star observations (via the Diffuse Infrared Background Experiment (DIRBE) are considered. Results of some recent experiments are given. These include tests where the gyro rate data are corrected for the effect of the gyro baseplate temperature on the spacecraft electronics
MATRIX Results II and Reference Report
As populations increase, especially in urban areas, the number of people affected by natural hazards is growing, as many regions of the world subject to multiple hazards. Although the volume of geophysical, sociological and economic knowledge is expanding, so are the losses from natural catastrophes. The slow transfer of appropriate knowledge from theory to practice may be due to the difficulties inherent in the communication process from science to policy-making, including perceptions by stakeholders from disaster mitigation practice regarding the usability of any developed tools. As scientific evidence shows, decision-makers are faced with the challenge of not only mitigating against single hazards and risks, but also multiple risks, which must include the consideration of their interrelations. As the multi-hazard and risk concept is a relatively young area of natural risk governance, there are only a few multi-risk models and the experience of practitioners as to how to use these models is limited. To our knowledge, scientific literature on stakeholders' perceptions of multi-risk models is lacking. In this document, we identify the perceptions of two decision-making tools, which involve multi-hazard and multi-risk. The first one is a generic, multi-risk framework based on the sequential Monte Carlo method to allow for a straightforward and flexible implementation of hazard interactions which may occur in a complex system. The second is a decision-making tool that integrates directly input from stakeholders by attributing weights to different components and constructing risk ratings. Based on the feedback from stakeholders, we found that interest in multi-risk assessment is high, but that its application remains hampered by the complexity of the processes involved
On the terms violating the custodial symmetry in multi-Higgs-doublet models
We prove that a generic multi-Higgs-doublet model (NHDM) generally must
contain terms in the potential that violate the custodial symmetry. This is
done by showing that the O(4) violating terms of the NHDM potential cannot be
excluded by imposing a symmetry on the NHDM Lagrangian. Hence we expect
higher-order corrections to necessarily introduce such terms. We also note, in
the case of custodially symmetric Higgs-quark couplings, that vacuum alignment
will lead to up-down mass degeneration; this is not true if the vacua are not
aligned.Comment: 16 pages, 1 figure. Title and abstract are modified, conclusions
remain the same. Section on Yukawa couplings is extended. Published versio
A Study of Quantum Error Correction by Geometric Algebra and Liquid-State NMR Spectroscopy
Quantum error correcting codes enable the information contained in a quantum
state to be protected from decoherence due to external perturbations. Applied
to NMR, quantum coding does not alter normal relaxation, but rather converts
the state of a ``data'' spin into multiple quantum coherences involving
additional ancilla spins. These multiple quantum coherences relax at differing
rates, thus permitting the original state of the data to be approximately
reconstructed by mixing them together in an appropriate fashion. This paper
describes the operation of a simple, three-bit quantum code in the product
operator formalism, and uses geometric algebra methods to obtain the
error-corrected decay curve in the presence of arbitrary correlations in the
external random fields. These predictions are confirmed in both the totally
correlated and uncorrelated cases by liquid-state NMR experiments on
13C-labeled alanine, using gradient-diffusion methods to implement these
idealized decoherence models. Quantum error correction in weakly polarized
systems requires that the ancilla spins be prepared in a pseudo-pure state
relative to the data spin, which entails a loss of signal that exceeds any
potential gain through error correction. Nevertheless, this study shows that
quantum coding can be used to validate theoretical decoherence mechanisms, and
to provide detailed information on correlations in the underlying NMR
relaxation dynamics.Comment: 33 pages plus 6 figures, LaTeX article class with amsmath & graphicx
package
Actuator Saturation in Individual Blade Control of Rotorcraft
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97053/1/AIAA2012-1477.pd
A Seesaw Mechanism in the Higgs Sector
In this letter we revisit the seesaw Higgs mechanism. We show how a seesaw
mechanism in a two Higgs doublets model can trigger the electroweak symmetry
breaking if at least one of the eigenvalues of the squared mass matrix is
negative. We then consider two special cases of interest. In the decoupling
scenario, there is only one scalar degree of freedom in the low energy regime.
In the degenerate scenario, all five degrees of freedom are in the low energy
regime and will lead to observables effects at the LHC. Furthermore, in that
scenario, it is possible to impose a discrete symmetry between the doublets
that makes the extra neutral degrees of freedom stable. These are thus viable
dark matter candidates. We find an interesting relation between the electroweak
symmetry breaking mechanism and dark matter.Comment: 10 page
Phase structure and phase transitions of the SU(2) x O(N) symmetric scalar field theory
Radiatively induced SU(2) symmetry breaking is shown to be a genuine feature
of SU(2) x O(N) globally symmetric renormalisable field theories in the large N
limit, describing interaction of a complex SU(2) doublet, O(N)-singlet field
with an SU(2) singlet, O(N) vector. Symmetry breaking solutions are found even
when all fields have positive renormalised squared mass. The emerging novel
mechanism of symmetry breaking can reproduce with a choice of N~300 the
standard range of the electroweak condensate and the Higgs mass occurring in
the extended Higgs dynamics of an SU(2) symmetric Gauge+Higgs model.Comment: 6 pages, 3 figures; the role of the cut-off in the effective theory
is discussed, references added; to appear in Europhys. Let
Adaptation in integrated assessment modeling: where do we stand?
Adaptation is an important element on the climate change policy agenda. Integrated assessment models, which are key tools to assess climate change policies, have begun to address adaptation, either by including it implicitly in damage cost estimates, or by making it an explicit control variable. We analyze how modelers have chosen to describe adaptation within an integrated framework, and suggest many ways they could improve the treatment of adaptation by considering more of its bottom-up characteristics. Until this happens, we suggest, models may be too optimistic about the net benefits adaptation can provide, and therefore may underestimate the amount of mitigation they judge to be socially optimal. Under some conditions, better modeling of adaptation costs and benefits could have important implications for defining mitigation targets. © Springer Science+Business Media B.V. 2009
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