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Sensitivity analysis modelling for microscale multiphysics robust engineering design
Sensitivity Analysis (SA) plays an important role in the development of any practical engineering model. It can help to reveal the sources and mechanisms of variability that provide the key to understanding system uncertainty. SA can also be used to calibrate simulation models for closer agreement with experimental results. Robust Engineering Design (RED) seeks to exploit such knowledge in the search for design solutions that are optimal in terms of performance in the face of variability.
Microscale and multiphysics problems present challenges to modelling due to their complexity, which puts increased demands on computational methods. For example, in developing a model of a piezoelectric actuator, the process of calibration is prolonged by the number of parameters that are difficult to verify with the physical device.
In the approach presented in this paper, normalised sensitivity coefficients are determined directly and accurately using the governing finite element model formulation, offering an efficient means of identifying parameters that affect the output of the model, leading to increased accuracy and knowledge of system performance in the face of variability
Equilibrium spin pulsars unite neutron star populations
Many pulsars are formed with a binary companion from which they can accrete
matter. Torque exerted by accreting matter can cause the pulsar spin to
increase or decrease, and over long times, an equilibrium spin rate is
achieved. Application of accretion theory to these systems provides a probe of
the pulsar magnetic field. We compare the large number of recent torque
measurements of accreting pulsars with a high-mass companion to the standard
model for how accretion affects the pulsar spin period. We find that many long
spin period (P > 100 s) pulsars must possess either extremely weak (B < 10^10
G) or extremely strong (B > 10^14 G) magnetic fields. We argue that the
strong-field solution is more compelling, in which case these pulsars are near
spin equilibrium. Our results provide evidence for a fundamental link between
pulsars with the slowest spin periods and strong magnetic fields around
high-mass companions and pulsars with the fastest spin periods and weak fields
around low-mass companions. The strong magnetic fields also connect our pulsars
to magnetars and strong-field isolated radio/X-ray pulsars. The strong field
and old age of our sources suggests their magnetic field penetrates into the
superconducting core of the neutron star.Comment: 6 pages, 4 figures; to appear in MNRA
On the accretion mode of the intermediate polar V1025 Centauri
The long white-dwarf spin periods in the magnetic cataclysmic variables EX
Hya and V1025 Cen imply that if the systems possess accretion discs then they
cannot be in equilibrium. It has been suggested that instead they are discless
accretors in which the spin-up torques resulting from accretion are balanced by
the ejection of part of the accretion flow back towards the secondary. We
present phase-resolved spectroscopy of V1025 Cen aimed at deducing the nature
of the accretion flow, and compare this with simulations of a discless
accretor. We find that both the conventional disc-fed model and the
discless-accretor model have strengths and weaknesses, and that further work is
needed before we can decide which applies to V1025 Cen.Comment: 9 pages, 8 figures, To appear in MNRAS, includes low-res figures to
reduce siz
-optimal saturated designs: a simulation study
In this work we focus on saturated -optimal designs. Using recent results,
we identify -optimal designs with the solutions of an optimization problem
with linear constraints. We introduce new objective functions based on the
geometric structure of the design and we compare them with the classical
-efficiency criterion. We perform a simulation study. In all the test cases
we observe that designs with high values of -efficiency have also high
values of the new objective functions.Comment: 8 pages. Preliminary version submitted to the 7th IWS Proceeding
Informed citizen and empowered citizen in health: results from an European survey
Background: The knowledge about the relationship between health-related activities on the Internet (i.e. informed citizens) and individuals? control over their own experiences of health or illness (i.e. empowered citizens) is valuable but scarce. In this paper, we investigate the correlation between four ways of using the Internet for information on health or illness and citizens attitudes and behaviours toward health professionals and health systems and establish the profile of empowered eHealth citizens in Europe. Methods: Data was collected during April and May 2007 (N = 7022), through computer-assisted telephone interviews (CATI). Respondents from Denmark, Germany, Greece, Latvia, Norway, Poland and Portugal participated in the survey. The profiles were generated using logistic regressions and are based on: a) socio-demographic and health information, b) the level of use of health-related online services, c) the level of use of the Internet to get health information to decide whether to consult a health professional, prepare for a medical appointment and assess its outcome, and d) the impact of online health information on citizens? attitudes and behavior towards health professionals and health systems. Results: Citizens using the Internet to decide whether to consult a health professional or to get a second opinion are likely to be frequent visitors of health sites, active participants of online health forums and recurrent buyers of medicines and other health related products online, while only infrequent epatients, visiting doctors they have never met face-to-face. Participation in online health communities seems to be related with more inquisitive and autonomous patients. Conclusions: The profiles of empowered eHealth citizens in Europe are situational and country dependent. The number of Europeans using the Internet to get health information to help them deal with a consultation is raising and having access to online health information seems to be associated with growing number of inquisitive and self-reliant patients. Doctors are increasingly likely to experience consultations with knowledgeable and empowered patients, who will challenge them in various ways
R-Mode Oscillations and Spindown of Young Rotating Magnetic Neutron Stars
Recent work has shown that a young, rapidly rotating neutron star loses
angular momentum to gravitational waves generated by unstable r-mode
oscillations. We study the spin evolution of a young, magnetic neutron star
including both the effects of gravitational radiation and magnetic braking
(modeled as magnetic dipole radiation). Our phenomenological description of
nonlinear r-modes is similar to, but distinct from, that of Owen et al. (1998)
in that our treatment is consistent with the principle of adiabatic invariance
in the limit when direct driving and damping of the mode are absent. We show
that, while magnetic braking tends to increase the r-mode amplitude by spinning
down the neutron star, it nevertheless reduces the efficiency of gravitational
wave emission from the star. For B >= 10^14 (\nus/300 Hz)^2 G, where \nus is
the spin frequency, the spindown rate and the gravitational waveforms are
significantly modified by the effect of magnetic braking. We also estimate the
growth rate of the r-mode due to electromagnetic (fast magnetosonic) wave
emission and due to Alfven wave emission in the neutron star magnetosphere. The
Alfven wave driving of the r-mode becomes more important than the gravitational
radiation driving when B >= 10^13 (\nus/150 Hz)^3 G; the electromagnetic wave
driving of the r-mode is much weaker. Finally, we study the properties of local
Rossby-Alfven waves inside the neutron star and show that the fractional change
of the r-mode frequency due to the magnetic field is of order 0.5 (B/10^16 G)^2
(\nus/100 Hz)^-2.Comment: 18 pages, 4 figures; ApJ, accepted (v544: Nov 20, 2000); added two
footnotes and more discussion of mode driving by Alfven wave
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