1,344 research outputs found
Alternating Projections and Douglas-Rachford for Sparse Affine Feasibility
The problem of finding a vector with the fewest nonzero elements that
satisfies an underdetermined system of linear equations is an NP-complete
problem that is typically solved numerically via convex heuristics or
nicely-behaved nonconvex relaxations. In this work we consider elementary
methods based on projections for solving a sparse feasibility problem without
employing convex heuristics. In a recent paper Bauschke, Luke, Phan and Wang
(2014) showed that, locally, the fundamental method of alternating projections
must converge linearly to a solution to the sparse feasibility problem with an
affine constraint. In this paper we apply different analytical tools that allow
us to show global linear convergence of alternating projections under familiar
constraint qualifications. These analytical tools can also be applied to other
algorithms. This is demonstrated with the prominent Douglas-Rachford algorithm
where we establish local linear convergence of this method applied to the
sparse affine feasibility problem.Comment: 29 pages, 2 figures, 37 references. Much expanded version from last
submission. Title changed to reflect new development
Projection Methods in Sparse and Low Rank Feasibility
In this thesis, we give an analysis of fixed point algorithms involving projections onto closed, not necessarily convex, subsets of finite dimensional vector
spaces.
These methods are used in applications such as imaging science, signal processing, and inverse problems. The tools used in the analysis
place this work at the intersection of optimization and variational analysis. Based on the underlying optimization problems, this work is devided into two main parts. The first one is the compressed sensing problem. Because the problem
is NP-hard, we relax it to a feasibility problem with two sets, namely,
the set of vectors with at most s nonzero entries and, for a linear mapping M
the affine subspace B of vectors satisfying Mx=p for p given.
This problem will be referred to as the sparse-affine-feasibility problem. For the Douglas-Rachford algorithm, we give the proof of linear convergence to a fixed point in the case of a feasibility problem of two affine subspaces.
It allows us to conclude a result of local linear convergence of the Douglas-Rachford algorithm in the sparse affine feasibility problem.
Proceeding, we name sufficient conditions for the alternating projections algorithm to converge to the intersection of an affine subspace with lower level sets
of point symmetric, lower semicontinuous, subadditive functions.
This implies convergence of alternating projections to a solution of the sparse affine feasibility problem.
Together with a result of local linear convergence of the alternating projections algorithm, this allows us to deduce linear convergence after finitely many steps
for any initial point of a sequence of points generated by the alternating projections algorithm. The second part of this dissertation deals with the minimization of the rank of matrices satisfying a set of linear equations.
This problem will be called rank-constrained-affine-feasibility problem.
The motivation for the analysis of the rank minimization problem comes from the physical application of phase retrieval and a reformulation of the same as a
rank minimization problem. We show that, locally, the method of alternating projections must converge at linear rate to a solution of the rank
constrained affine feasibility problem
Indicators for managing human centred manufacturing
Establishing indicators for managing human factors (HF) aspects in the design of production systems remains a challenge. We address the problem in two dimensions â firstly, what aspects of HF are to be considered, and secondly, where in the development process HF is to be measured. In these dimensions a large number of HF metrics are possible in the perceptual, cognitive, physical and psychosocial domains of HF. The relevance of these measures to injury, productivity, quality and organizational strategy continue to be poorly understood. From this perspective we make propositions on the need for: 1) strategic HF metrics selection, 2) metrics application throughout the development process, 3) predictive âvirtualâ HF metrics approaches, 4) metrics based design guidelines, 5) connecting metrics with design choices and strategies, 6) integrating HF metrics within existing approaches, 7) continuous improvement of the metrics system, and 8) the need to evaluate metrics system quality
Human Factors: Spanning the Gap between OM & HRM
Purpose: This paper examines the claim that the application of human factors (HF) knowledge can improve both human well-being and operations system performance.
Methodology: A systematic review was conducted using a general and two specialist databases to identify empirical studies addressing both human effects and operations system effects in examining manufacturing operations system design aspects.
Findings: We found 45 empirical studies addressing both the human effects and system effects of operations system (re)design. Of those studies providing clear directional effects, 95% showed a convergence between human effects and system effects (+,+ or -,-), 5% showed a divergence of human and system effects (+,- or -,+). System effects included quality, productivity, implementation performance of new technologies, and also more âintangibleâ effects in terms of improved communication and co-operation. Human effects included employee health, attitudes, physical workload, and âquality of working lifeâ.
Research limitations/im
Without uniform indicators, firms are unable to deal with work health issues
Repetitive strain, stress and burnout go largely unreported, write Cory Searcy, Shane Dixon and Patrick Neuman
Ergonomics Contributions to Company Strategies
Managers usually associate ergonomics with occupational health and safety and related legislation, not with business performance. In many companies, these decision makers seem not to be positively motivated to apply ergonomics for reasons of improving health and safety. In order to strengthen the position of ergonomics and ergonomists in the business and management world, we discuss company strategies and business goals to which ergonomics could contribute. Conceptual models are presented and examples are given to illustrate: 1) the present situation in which ergonomics is not part of regular planning and control cycles in organizations to ensure business performance, and 2) the desired situation in which ergonomics is an integrated part of strategy formulation and implementation. In order to realize the desired situation, considerable changes must take place within the ergonomics research, education and practice community by moving from a health ergonomics paradigm to a business ergonomics paradigm, without losing the health and safety goals
Mitigating Bias in Organizational Development and Use of Artificial Intelligence
We theorize why some artificial intelligence (AI) algorithms unexpectedly treat protected classes unfairly. We hypothesize that mechanisms by which AI assumes agencies, rights, and responsibilities of its stakeholders can affect AI bias by increasing complexity and irreducible uncertainties: e.g., AIâs learning method, anthropomorphism level, stakeholder utility optimization approach, and acquisition mode (make, buy, collaborate). In a sample of 726 agentic AI, we find that unsupervised and hybrid learning methods increase the likelihood of AI bias, whereas âstrictâ supervised learning reduces it. Highly anthropomorphic AI increases the likelihood of AI bias. Using AI to optimize one stakeholderâs utility increases AI bias risk, whereas jointly optimizing the utilities of multiple stakeholders reduces it. User organizations that co-create AI with developer organizations instead of developing it in-house or acquiring it off-the-shelf reduce AI bias risk. The proposed theory and the findings advance our understanding of responsible development and use of agentic AI
MBE Growth of Al/InAs and Nb/InAs Superconducting Hybrid Nanowire Structures
We report on \textit{in situ} growth of crystalline Al and Nb shells on InAs
nanowires. The nanowires are grown on Si(111) substrates by molecular beam
epitaxy (MBE) without foreign catalysts in the vapor-solid mode. The metal
shells are deposited by electron-beam evaporation in a metal MBE. High quality
supercondonductor/semiconductor hybrid structures such as Al/InAs and Nb/InAs
are of interest for ongoing research in the fields of gateable Josephson
junctions and quantum information related research. Systematic investigations
of the deposition parameters suitable for metal shell growth are conducted. In
case of Al, the substrate temperature, the growth rate and the shell thickness
are considered. The substrate temperature as well as the angle of the impinging
deposition flux are explored for Nb shells. The core-shell hybrid structures
are characterized by electron microscopy and x-ray spectroscopy. Our results
show that the substrate temperature is a crucial parameter in order to enable
the deposition of smooth Al layers. Contrary, Nb films are less dependent on
substrate temperature but strongly affected by the deposition angle. At a
temperature of 200{\deg}C Nb reacts with InAs, dissolving the nanowire crystal.
Our investigations result in smooth metal shells exhibiting an impurity and
defect free, crystalline superconductor/InAs interface. Additionally, we find
that the superconductor crystal structure is not affected by stacking faults
present in the InAs nanowires.Comment: 8 pages, 10 figures, 1 tabl
Forsvarsanskaffelser; unntaksretten etter EĂS-avtalen artikkel 123 i lys av EU-direktiv 2009/81/EC
I 2009 innfĂžrte EU et nytt forsvars- og sikkerhetsdirektiv, direktiv 2009/81/EC. Forsvars- og sikkerhetsdirektivet er basert pĂ„ det alminnelige innkjĂžpsdirektivet, direktiv 2004/18/EC, men innfĂžrer nye regler som skal vĂŠre sĂŠrlig tilpasset Forsvarets behov ved offentlige anskaffelser av materiell og tjenester. SpĂžrsmĂ„let er i hvilken utstrekning EĂS-avtalen artikkel 123 kan anvendes etter implementeringen av direktivet i Norge
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