8,617 research outputs found
Understanding Algorithm Performance on an Oversubscribed Scheduling Application
The best performing algorithms for a particular oversubscribed scheduling
application, Air Force Satellite Control Network (AFSCN) scheduling, appear to
have little in common. Yet, through careful experimentation and modeling of
performance in real problem instances, we can relate characteristics of the
best algorithms to characteristics of the application. In particular, we find
that plateaus dominate the search spaces (thus favoring algorithms that make
larger changes to solutions) and that some randomization in exploration is
critical to good performance (due to the lack of gradient information on the
plateaus). Based on our explanations of algorithm performance, we develop a new
algorithm that combines characteristics of the best performers; the new
algorithms performance is better than the previous best. We show how hypothesis
driven experimentation and search modeling can both explain algorithm
performance and motivate the design of a new algorithm
Volume-reflecting dielectric heat shield
White, volume-reflecting dielectric material absorbs essentially none of the incident radiant energy, and continues to reflect even though in severe environment its surface is melted and is being vaporized. Process of overall reflectance in dielectric material, involving internal refractions and reflections, is similar to process of reflection in paints
Kappa-symmetry for coincident D-branes
A kappa-symmetric action for coincident D-branes is presented. It is valid in
the approximation that the additional fermionic variables, used to incorporate
the non-abelian degrees of freedom, are treated classically. The action is
written as a Bernstein-Leites integral on the supermanifold obtained from the
bosonic worldvolume by adjoining the extra fermions. The integrand is a very
simple extension of the usual Green-Schwarz action for a single brane; all
symmetries, except for kappa, are manifest, and the proof of kappa-symmetry is
very similar to the abelian case.Comment: 18 pages. References adde
An exploration into the client at the heart of therapy : a qualitative perspective
Over 50 years ago Eysenck challenged the existing base of research into psychotherapy. Since that time, a large number of investigations have been conducted to verify the efficacy of therapy. Recently however, an increasing number of studies have cast new doubts on this research base. Instead of therapy being a function of the therapist, it is now becoming ever more apparent that the client plays a prime role in the therapeutic process. The qualitative studies presented in this paper provide some examples of research that demonstrates that clients are actively involved in their therapy, even making counselling work despite their counsellor. These studies suggest that clients may not experience therapy as beneficially as traditional outcome studies indicate. This raises a new challenge to researchers to more fully explore the client's experience of therapy, a challenge to which qualitative methods of inquiry would appear well suited
Identifying the challenges and facilitators of implementing a COPD care bundle.
BACKGROUND: Care bundles have been shown to improve outcomes, reduce hospital readmissions and reduce length of hospital stay; therefore increasing the speed of uptake and delivery of care bundles should be a priority in order to deliver more timely improvements and consistent high-quality care. Previous studies have detailed the difficulties of obtaining full compliance to bundle elements but few have described the underlying reasons for this. In order to improve future implementation this paper investigates the challenges encountered by clinical teams implementing a chronic obstructive pulmonary disease (COPD) care bundle and describes actions taken to overcome these challenges. METHODS: An initial retrospective documentary analysis of data from seven clinical implementation teams was undertaken to review the challenges faced by the clinical teams. Three focus groups with healthcare professionals and managers explored solutions to these challenges developed during the project. RESULTS: Documentary analysis identified 28 challenges which directly impacted implementation of the COPD care bundle within five themes; staffing, infrastructure, process, use of improvement methodology and patient and public involvement. Focus groups revealed that the five most significant challenges for all groups were: staff too busy, staff shortages, lack of staff engagement, added workload of the bundle and patient coding issues. The participants shared facilitating factors used to overcome issues including: shifting perceptions to improve engagement, further education sessions to increase staff participation and gaining buy-in from managers through payment frameworks. CONCLUSIONS: Maximising the impact of a care bundle relies on its successful and timely implementation. Teams implementing the COPD care bundle encountered challenges that were common to all teams and sites. Understanding and learning from the challenges faced by previous endeavours and identifying the facilitators to overcoming these barriers provides an opportunity to mitigate issues that waste time and resources, and ensures that training can be tailored to the anticipated challenges
Acoustic noise radiated by PWM-controlled induction machine drives
This paper investigates the acoustic noise radiated from two nominally identical induction motors when fed from sinusoidal, and asymmetric regular sampling subharmonic and space-vector pulsewidth modulation (PWM) converters. The theory for analyzing the noise spectrum is developed further to account for the interaction between the motor and the drive. It is shown that manufacturing tolerances can result in significant differences in the noise level emitted from nominally identical motors, and that mechanical resonances can result in extremely high noise emissions. Such resonances can be induced by stator and rotor slot air-gap field harmonics due to the fundamental component of current, and by the interaction between the airgap field harmonics produced by the fundamental and the PWM harmonic currents. The significance of the effect of PWM strategy on the noise is closely related to the mechanical resonance with vibration mode order zero, while the PWM strategy will be critical only if the dominant cause of the emitted noise is the interaction of the fundamental air-gap field and PWM harmonic
On the covariance of the Dirac-Born-Infeld-Myers action
A covariant version of the non-abelian Dirac-Born-Infeld-Myers action is
presented. The non-abelian degrees of freedom are incorporated by adjoining to
the (bosonic) worldvolume of the brane a number of anticommuting fermionic
directions corresponding to boundary fermions in the string picture. The
proposed action treats these variables as classical but can be given a matrix
interpretation if a suitable quantisation prescription is adopted. After
gauge-fixing and quantisation of the fermions, the action is shown to be in
agreement with the Myers action derived from T-duality. It is also shown that
the requirement of covariance in the above sense leads to a modified WZ term
which also agrees with the one proposed by Myers.Comment: 18 pages. Minor alterations to the text; references adde
The Effect of Visual Distinctiveness on Multiple Object Tracking Performance
Observers often need to attentively track moving objects. In everyday life, such objects are often visually distinctive. Previous studies have shown that tracking accuracy is increased when the targets contain a visual feature (e.g. a colour) not possessed by the distractors. Conversely, a gain in tracking accuracy was not observed when the targets differed from the distractors by only a conjunction of features (Makovski & Jiang, Visual Cognition, 17(1/2), 180). In this study we confirm that some conjunction targets have relatively little effect on tracking accuracy, but show that other conjunction targets can significantly aid tracking. For example, tracking accuracy is relatively high when the targets are small red squares and half the distractors are large red squares while the remaining distractors are small green squares. This seems to occur because the targets have a set of features (small and red) not shared by any one distractor. Attending to these features directs attention more to the targets than the distractors, thereby making the targets easier to track. Existing theories of attentive tracking cannot explain these results
Radiation reaction and renormalization in classical electrodynamics of point particle in any dimension
The effective equations of motion for a point charged particle taking account
of radiation reaction are considered in various space-time dimensions. The
divergencies steaming from the pointness of the particle are studied and the
effective renormalization procedure is proposed encompassing uniformly the
cases of all even dimensions. It is shown that in any dimension the classical
electrodynamics is a renormalizable theory if not multiplicatively beyond d=4.
For the cases of three and six dimensions the covariant analogs of the
Lorentz-Dirac equation are explicitly derived.Comment: minor changes in concluding section, misprints corrected, LaTeX2e, 15
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