2,119 research outputs found
The XV-15 tilt rotor research aircraft
The design characteristics of the XV-15 Tilt rotor research aircraft are presented. Particular attention is given to the following: control system; conversion system; and propulsion system. Flight test results are also reported
Very Large Hadron Collider R&D
This article discusses the present state of R&D for a post-LHC very large hadron collider (VLHC). Such a machine can be built with today's technology; the thrust of the R&D is to reduce the cost of the machine, through development of new ideas and utilization of new technologies. R&D issues in the areas of accelerator physics, magnets, and general accelerator technologies, will be reviewed. Finally, the outlook for future R&D will be presented. (35 refs)
Identification and verification of frequency-domain models for XV-15 tilt-rotor aircraft dynamics
Frequency-domain methods are used to extract the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight test data for the cruise condition (V = 170 knots). The frequency responses are numerically fitted with transfer-function forms to identify equivalent model characteristics. The associated handling quality parameters meet or exceed Level 2, Category A, requirements for fixed-wing military aircraft. Step response matching is used to verify the time-domain fidelity of the transfer-function models for the cruise and hover flight conditions. The transient responses of the model and aircraft are in close agreement in all cases, except for the normal acceleration response to elevator deflection in cruise. This discrepancy is probably due to the unmodeled rotor rpm dynamics. The utility of the frequency-domain approach for dynamics identification and analysis is clearly demonstrated
Reliability analysis of dynamic systems by translating temporal fault trees into Bayesian networks
Classical combinatorial fault trees can be used to assess combinations of failures but are unable to capture sequences of faults, which are important in complex dynamic systems. A number of proposed techniques extend fault tree analysis for dynamic systems. One of such technique, Pandora, introduces temporal gates to capture the sequencing of events and allows qualitative analysis of temporal fault trees. Pandora can be easily integrated in model-based design and analysis techniques. It is, therefore, useful to explore the possible avenues for quantitative analysis of Pandora temporal fault trees, and we identify Bayesian Networks as a possible framework for such analysis. We describe how Pandora fault trees can be translated to Bayesian Networks for dynamic dependability analysis and demonstrate the process on a simplified fuel system model. The conversion facilitates predictive reliability analysis of Pandora fault trees, but also opens the way for post-hoc diagnostic analysis of failures
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Estimate of the Pbar Yields for the CERN ACOL Project
For a check of the yield estimates expected for the new ACOL target station, calculations have been performed for the CERN parameters using the relatively, simple semi-analytical techniques outlined in pbar note 449. These calculations correspond to operation with a 15 cm long, 1 cm radius lithium lens at 750 T/m gradient, and a 6.5 cm tungsten production target. Comparison with the current calculated yield number for the AA with the present target station configuration (10**7 pbars per 10**13 protons, into dp/p = 1.5%) indicates an increase of a factor of 15 using the normal ACOL parameters (dp/p = 6%, a(transverse acceptance) = 240 pi mm-mrad). As explained in the report, the above lens parameters are not optimized, that is, increases in lens gradient and/or radius will result in an increase in yield, providing the corresponding changes in focal distance, beam line matching, etc. are made
Quality of life and well-being of carers of people with dementia: are there differences between working and nonworking carers? Results from the IDEAL program
The aim of this study was to identify the differences in quality of life (QoL) and well-being between working and nonworking dementia carers and the relative contribution of psychological characteristics, caregiving experience, and social support. Multiple regressions modeled the contribution of working status, caregiver experiences, and psychological and social resources to carer QoL (EQ-5D) and well-being (WHO-5). After controlling for age, gender, carer–dyad relationship, and severity of dementia, working status contributed significant variance to EQ-5D (2%) but not to WHO-5 scores. Independent of working status, higher self-esteem and reduced stress contributed to variance in both models. Self-efficacy, social support, and positive perceptions of caregiving additionally contributed to higher WHO-5 scores. Working status associated with higher EQ-5D QoL; this may reflect the sustained sense of independence associated with supported work opportunities for carers. Outside of working status, the findings support the importance of psychological and social factors as targets to improved mental health for dementia carers
Model independent determination of the shape function for inclusive B decays and of the structure functions in DIS
We present a method to compute, by numerical simulations of lattice QCD, the
inclusive semileptonic differential decay rates of heavy hadrons and the
structure functions which occur in deep inelastic scattering. The method is
based on first principles and does not require any model assumption. It allows
the prediction of the differential rate in B semileptonic decays for values of
the recoiling hadronic mass W ~ sqrt(M_B Lambda_QCD), which is in the relevant
region to extract |V_ub| from the end-point of the lepton spectrum in inclusive
decays.Comment: 16 pages, LaTeX fil
Quantification of temporal fault trees based on fuzzy set theory
© Springer International Publishing Switzerland 2014. Fault tree analysis (FTA) has been modified in different ways to make it capable of performing quantitative and qualitative safety analysis with temporal gates, thereby overcoming its limitation in capturing sequential failure behaviour. However, for many systems, it is often very difficult to have exact failure rates of components due to increased complexity of systems, scarcity of necessary statistical data etc. To overcome this problem, this paper presents a methodology based on fuzzy set theory to quantify temporal fault trees. This makes the imprecision in available failure data more explicit and helps to obtain a range of most probable values for the top event probability
Impact of the Wiggler Coherent Synchrotron Radiation Impedance on the Beam Instability
Coherent Synchrotron Radiation (CSR) can play an important role by not only
increasing the energy spread and emittance of a beam, but also leading to a
potential instability. Previous studies of the CSR induced longitudinal
instability were carried out for the CSR impedance due to dipole magnets.
However, many storage rings include long wigglers where a large fraction of the
synchrotron radiation is emitted. This includes high-luminosity factories such
as DAPHNE, PEP-II, KEK-B, and CESR-C as well as the damping rings of future
linear colliders. In this paper, the instability due to the CSR impedance from
a wiggler is studied assuming a large wiggler parameter . The primary
consideration is a low frequency microwave-like instability, which arises near
the pipe cut-off frequency. Detailed results are presented on the growth rate
and threshold for the damping rings of several linear collider designs.
Finally, the optimization of the relative fraction of damping due to the
wiggler systems is discussed for the damping rings.Comment: 10 pages, 7 figure
Deformed dimensional regularization for odd (and even) dimensional theories
I formulate a deformation of the dimensional-regularization technique that is
useful for theories where the common dimensional regularization does not apply.
The Dirac algebra is not dimensionally continued, to avoid inconsistencies with
the trace of an odd product of gamma matrices in odd dimensions. The
regularization is completed with an evanescent higher-derivative deformation,
which proves to be efficient in practical computations. This technique is
particularly convenient in three dimensions for Chern-Simons gauge fields,
two-component fermions and four-fermion models in the large N limit, eventually
coupled with quantum gravity. Differently from even dimensions, in odd
dimensions it is not always possible to have propagators with fully Lorentz
invariant denominators. The main features of the deformed technique are
illustrated in a set of sample calculations. The regularization is universal,
local, manifestly gauge-invariant and Lorentz invariant in the physical sector
of spacetime. In flat space power-like divergences are set to zero by default.
Infinitely many evanescent operators are automatically dropped.Comment: 27 pages, 3 figures; v2: expanded presentation of some arguments,
IJMP
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