27,923 research outputs found
Eigenstructure Assignment Based Controllers Applied to Flexible Spacecraft
The objective of this paper is to evaluate the behaviour of a controller designed using a parametric Eigenstructure Assignment method and to evaluate its suitability for use in flexible spacecraft. The challenge of this objective lies in obtaining a suitable controller that is specifically designated to alleviate the deflections and vibrations suffered by external appendages in flexible spacecraft while performing attitude manoeuvres. One of the main problems in these vehicles is the mechanical cross-coupling that exists between the rigid and flexible parts of the spacecraft. Spacecraft with fine attitude pointing requirements need precise control of the mechanical coupling to avoid undesired attitude misalignment. In designing an attitude controller, it is necessary to consider the possible vibration of the solar panels and how it may influence the performance of the rest of the vehicle. The nonlinear mathematical model of a flexible spacecraft is considered a close approximation to the real system. During the process of controller evaluation, the design process has also been taken into account as a factor in assessing the robustness of the system
Numerical analysis of the Iosipescu specimen for composite materials
A finite element analysis of the Iosipescu shear tests for unidirectional and cross-ply composites is presented. It is shown that an iterative analysis procedure must be used to model the fixture-specimen kinematics. The correction factors which are needed to compensate for the nonuniformity of stress distribution in calculating shear modulus are shown to be dependent on the material orthotropic ratio and the finite element loading models. Test section strain distributions representative of typical graphite-epoxy specimens are also presented
An easy-to-use diagnostic system development shell
The Diagnostic System Development Shell (DSDS), an expert system development shell for diagnostic systems, is described. The major objective of building the DSDS is to create a very easy to use and friendly environment for knowledge engineers and end-users. The DSDS is written in OPS5 and CommonLisp. It runs on a VAX/VMS system. A set of domain independent, generalized rules is built in the DSDS, so the users need not be concerned about building the rules. The facts are explicitly represented in a unified format. A powerful check facility which helps the user to check the errors in the created knowledge bases is provided. A judgement facility and other useful facilities are also available. A diagnostic system based on the DSDS system is question driven and can call or be called by other knowledge based systems written in OPS5 and CommonLisp. A prototype diagnostic system for diagnosing a Philips constant potential X-ray system has been built using the DSDS
The Optimal Inhomogeneity for Superconductivity: Finite Size Studies
We report the results of exact diagonalization studies of Hubbard models on a
square lattice with periodic boundary conditions and various
degrees and patterns of inhomogeneity, which are represented by inequivalent
hopping integrals and . We focus primarily on two patterns, the
checkerboard and the striped cases, for a large range of values of the on-site
repulsion and doped hole concentration, . We present evidence that
superconductivity is strongest for of order the bandwidth, and intermediate
inhomogeneity, . The maximum value of the ``pair-binding
energy'' we have found with purely repulsive interactions is for the checkerboard Hubbard model with and .
Moreover, for near optimal values, our results are insensitive to changes in
boundary conditions, suggesting that the correlation length is sufficiently
short that finite size effects are already unimportant.Comment: 8 pages, 9 figures; minor revisions; more references adde
Unconventional Spin Density Waves in Dipolar Fermi Gases
The conventional spin density wave (SDW) phase (Overhauser, 1962), as found
in antiferromagnetic metal for example (Fawcett 1988), can be described as a
condensate of particle-hole pairs with zero angular momentum, ,
analogous to a condensate of particle-particle pairs in conventional
superconductors. While many unconventional superconductors with Cooper pairs of
finite have been discovered, their counterparts, density waves with
non-zero angular momenta, have only been hypothesized in two-dimensional
electron systems (Nayak, 2000). Using an unbiased functional renormalization
group analysis, we here show that spin-triplet particle-hole condensates with
emerge generically in dipolar Fermi gases of atoms (Lu, Burdick, and
Lev, 2012) or molecules (Ospelkaus et al., 2008; Wu et al.) on optical lattice.
The order parameter of these exotic SDWs is a vector quantity in spin space,
and, moreover, is defined on lattice bonds rather than on lattice sites. We
determine the rich quantum phase diagram of dipolar fermions at half-filling as
a function of the dipolar orientation, and discuss how these SDWs arise amidst
competition with superfluid and charge density wave phases.Comment: 5 pages, 3 figure
Living with the user: Design drama for dementia care through responsive scripted experiences in the home
Participation in forms of drama and narrative can provoke empathy and creativity in user-centred design processes. In this paper, we expand upon existing methods to explore the potential for responsive scripted experiences that are delivered through the combination of sensors and output devices placed in a home. The approach is being developed in the context of Dementia care, where the capacity for rich user participation in design activities is limited. In this case, a system can act as a proxy for a person with Dementia, allowing designers to gain experiences and insight as to what it is like to provide care for, and live with, this person. We describe the rationale behind the approach, a prototype system architecture, and our current work to explore the creation of scripted experiences for design, played out though UbiComp technologies.This research is funded by the Arts and Humanities Research Council UK, (AH/K00266X/1) and Horizon Digital Economy Research (RCUK grant EP/G065802/1)
Money Walks: A Human-Centric Study on the Economics of Personal Mobile Data
In the context of a myriad of mobile apps which collect personally
identifiable information (PII) and a prospective market place of personal data,
we investigate a user-centric monetary valuation of mobile PII. During a 6-week
long user study in a living lab deployment with 60 participants, we collected
their daily valuations of 4 categories of mobile PII (communication, e.g.
phonecalls made/received, applications, e.g. time spent on different apps,
location and media, photos taken) at three levels of complexity (individual
data points, aggregated statistics and processed, i.e. meaningful
interpretations of the data). In order to obtain honest valuations, we employ a
reverse second price auction mechanism. Our findings show that the most
sensitive and valued category of personal information is location. We report
statistically significant associations between actual mobile usage, personal
dispositions, and bidding behavior. Finally, we outline key implications for
the design of mobile services and future markets of personal data.Comment: 15 pages, 2 figures. To appear in ACM International Joint Conference
on Pervasive and Ubiquitous Computing (Ubicomp 2014
A variational study of the random-field XY model
A disorder-dependent Gaussian variational approach is applied to the
-dimensional ferromagnetic XY model in a random field. The randomness yields
a non extensive contribution to the variational free energy, implying a random
mass term in correlation functions. The Imry-Ma low temperature result,
concerning the existence () or absence () of long-range order is
obtained in a transparent way. The physical picture which emerges below
is that of a marginally stable mixture of domains. We also calculate within
this variational scheme, disorder dependent correlation functions, as well as
the probability distribution of the Imry-Ma domain size.Comment: 14 pages, latex fil
Using cultural probes to inform the design of assistive technologies
This paper discusses the practical implications of applying cultural probes to drive the design of assistive technologies. Specifically we describe a study in which a probe was deployed with home-based carers of people with dementia in order to capture critical data and gain insights of integrating the technologies into this sensitive and socially complex design space. To represent and utilise the insights gained from the cultural probes, we created narratives based on the probe data to enhance the design of assistive technologies.This work was supported by the Arts and Humanities Research Council (AH/K00266X/1) and RCUK through the Horizon Digital Economy Research grant (EP/G065802/1)
Connection Between Wave Functions in the Dirac and Foldy-Wouthuysen Representations
The connection between wave functions in the Dirac and Foldy-Wouthuysen
representations is found. When the Foldy-Wouthuysen transformation is exact,
upper spinors in two representations differ only by constant factors, and lower
spinors in the Foldy-Wouthuysen representation are equal to zero.Comment: 7 page
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