465 research outputs found
Modeling and Detection of Ice Particle Accretion in Aircraft Engine Compression Systems
The accretion of ice particles in the core of commercial aircraft engines has been an ongoing aviation safety challenge. While no accidents have resulted from this phenomenon to date, numerous engine power loss events ranging from uneventful recoveries to forced landings have been recorded. As a first step to enabling mitigation strategies during ice accretion, a detection scheme must be developed that is capable of being implemented on board modern engines. In this paper, a simple detection scheme is developed and tested using a realistic engine simulation with approximate ice accretion models based on data from a compressor design tool. These accretion models are implemented as modified Low Pressure Compressor maps and have the capability to shift engine performance based on a specified level of ice blockage. Based on results from this model, it is possible to detect the accretion of ice in the engine core by observing shifts in the typical sensed engine outputs. Results are presented in which, for a 0.1 percent false positive rate, a true positive detection rate of 98 percent is achieved
History repeats? : the rise of the new middle classes in the developing world
1.
Although the ability to detect chemical cues is widespread in many organisms, it is surprising how
little is known about the role of chemical communication in avian life histories. Nowadays, growing
evidence suggests that birds can use olfaction in several contexts. However, we still do not know the
role of bird olfaction in one of the most important determinants of survival, predator detection.
2.
Blue tits,
Cyanistes caeruleus
L., were exposed to chemical cues of: (i) mustelid (predator), (ii) quail
(odorous control); or (iii) water (odourless control) inside the nest-box where they were provisioning
8-day-old nestlings.
3.
We show that blue tits were able to detect the chemical cues and showed antipredatory behaviours
to cope with the risk of predation. Birds delayed their entry to the nest-box, and they perched on the
hole of the nest-box and refused to enter more times when they found predator scent than control
scents inside the nest-box. In addition, birds decreased the time spent inside the predator-scented
nest-box when feeding nestlings.
4.
The discovery of the ability of birds to use chemical cues of predators to accurately assess predation
may help to understand many aspects of bird life histories that have been neglected until now.Peer reviewe
The Ising-Kondo lattice with transverse field: an f-moment Hamiltonian for URu2Si2?
We study the phase diagram of the Ising-Kondo lattice with transverse
magnetic field as a possible model for the weak-moment heavy-fermion compound
URu2Si2, in terms of two low-lying f singlets in which the uranium moment is
coupled by on-site exchange to the conduction electron spins. In the mean-field
approximation for an extended range of parameters, we show that the conduction
electron magnetization responds logarithmically to f-moment formation, that the
ordered moment in the antiferromagnetic state is anomalously small, and that
the Neel temperature is of the order observed. The model gives a qualitatively
correct temperature-dependence, but not magnitude, of the specific heat. The
majority of the specific heat jump at the Neel temperature arises from the
formation of a spin gap in the conduction electron spectrum. We also discuss
the single-impurity version of the model and speculate on ways to increase the
specific heat coefficient. In the limits of small bandwidth and of small
Ising-Kondo coupling, we find that the model corresponds to anisotropic
Heisenberg and Hubbard models respectively.Comment: 20 pages RevTeX including 5 figures (1 in LaTeX, 4 in uuencoded EPS),
Received by Phys. Rev. B 19 April 199
Systematic review of economic evaluations and cost analyses of guideline implementation strategies
Objectives To appraise the quality of economic studies undertaken as part of evaluations of guideline implementation strategies; determine their resources use; and recommend methods to improve future studies. Methods Systematic review of economic studies undertaken alongside robust study designs of clinical guideline implementation strategies published (1966-1998). Studies assessed against the BMJ economic evaluations guidelines for each stage of the guideline process (guideline development, implementation and treatment). Results 235 studies were identified, 63 reported some information on cost. Only 3 studies provided evidence that their guideline was effective and efficient. 38 reported the treatment costs only, 12 implementation and treatment costs, 11 implementation costs alone, and two guideline development, implementation and treatment costs. No study gave reasonably complete information on costs. Conclusions Very few satisfactory economic evaluations of guideline implementation strategies have been performed. Current evaluations have numerous methodological defects and rarely consider all relevant costs and benefits. Future evaluations should focus on evaluating the implementation of evidence based guidelines. Keywords: Cost-effectiveness analysis, physician (or health care professional) behaviour, practice guidelines, quality improvement, systematic review.Peer reviewedAuthor versio
Confined granular packings: structure, stress, and forces
The structure and stresses of static granular packs in cylindrical containers
are studied using large-scale discrete element molecular dynamics simulations
in three dimensions. We generate packings by both pouring and sedimentation and
examine how the final state depends on the method of construction. The vertical
stress becomes depth-independent for deep piles and we compare these stress
depth-profiles to the classical Janssen theory. The majority of the tangential
forces for particle-wall contacts are found to be close to the Coulomb failure
criterion, in agreement with the theory of Janssen, while particle-particle
contacts in the bulk are far from the Coulomb criterion. In addition, we show
that a linear hydrostatic-like region at the top of the packings unexplained by
the Janssen theory arises because most of the particle-wall tangential forces
in this region are far from the Coulomb yield criterion. The distributions of
particle-particle and particle-wall contact forces exhibit
exponential-like decay at large forces in agreement with previous studies.Comment: 11 pages, 11 figures, submitted to PRE (v2) added new references,
fixed typo
Funding for preventative Children’s Services and rates of children becoming looked after : a natural experiment using longitudinal area-level data in England
Background
Children in care face adverse health outcomes, throughout the life-course, relative to the general population. In England, over the last decade, the rate of children entering care has increased. The rate of change differs markedly for older and younger children, who may also experience different preventative services. These services have been subject to inequitable spending reductions due to fiscal policies trailing the 2008 recession.
Objective
To assess the impact of cuts to prevention on rates of preschool children and adolescents entering care between 2012 and 2019.
Participants and Setting
Children aged 1–4 and 16–17 years, across 150 English upper-tier local authorities.
Methods
Our outcomes were annual rates of children entering care, aged 1–4 and 16–17. Our exposures were Children’s Services prevention spend per child under 5, and per child over 12. Regression models were used to quantify, within areas, associations between trends in prevention spend and trends in rates of children entering care, controlling for employment and child poverty rates.
Results
We found no association between changes in prevention spend per child under 5 and changes in care entry for 1–4-year-olds. However, spending reductions per child over 12 were associated with rising rates of 16–17-year-olds entering care. Every £10 per child decrease in prevention spend was associated with an estimated additional 1.9 per 100,000 children aged 16–17 entering care the following year (95% CI 0.7 to 2.9), equivalent to 1 in 25 care entries in this age group between 2012 and 2019.
Conclusion
This study offers evidence that rising rates of older children entering care has partly been driven by cuts to prevention services catering to their needs. Policies to tackle adverse trends should promote reinvestment in youth services, placing ordinary help on a robust statutory footing
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Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets: artificial and historic records
A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011-2001 design spectrum to a parametrically defined evolutionary power spectrum (EPS). Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned design spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response spectrum is in a close agreement with the considered design spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signals’ response spectra with the GB 50011-2001 design spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice
Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder
We have studied how 2- and 3- dimensional systems made up of particles
interacting with finite range, repulsive potentials jam (i.e., develop a yield
stress in a disordered state) at zero temperature and applied stress. For each
configuration, there is a unique jamming threshold, , at which
particles can no longer avoid each other and the bulk and shear moduli
simultaneously become non-zero. The distribution of values becomes
narrower as the system size increases, so that essentially all configurations
jam at the same in the thermodynamic limit. This packing fraction
corresponds to the previously measured value for random close-packing. In fact,
our results provide a well-defined meaning for "random close-packing" in terms
of the fraction of all phase space with inherent structures that jam. The
jamming threshold, Point J, occurring at zero temperature and applied stress
and at the random close-packing density, has properties reminiscent of an
ordinary critical point. As Point J is approached from higher packing
fractions, power-law scaling is found for many quantities. Moreover, near Point
J, certain quantities no longer self-average, suggesting the existence of a
length scale that diverges at J. However, Point J also differs from an ordinary
critical point: the scaling exponents do not depend on dimension but do depend
on the interparticle potential. Finally, as Point J is approached from high
packing fractions, the density of vibrational states develops a large excess of
low-frequency modes. All of these results suggest that Point J may control
behavior in its vicinity-perhaps even at the glass transition.Comment: 21 pages, 20 figure
Memory enhancing drugs and Alzheimer’s Disease: Enhancing the self or preventing the loss of it?
In this paper we analyse some ethical and philosophical questions related to the development of memory enhancing drugs (MEDs) and anti-dementia drugs. The world of memory enhancement is coloured by utopian thinking and by the desire for quicker, sharper, and more reliable memories. Dementia is characterized by decline, fragility, vulnerability, a loss of the most important cognitive functions and even a loss of self. While MEDs are being developed for self-improvement, in Alzheimer’s Disease (AD) the self is being lost. Despite this it is precisely those patients with AD and other forms of dementia that provide the subjects for scientific research on memory improvement. Biomedical research in the field of MEDs and anti-dementia drugs appears to provide a strong impetus for rethinking what we mean by ‘memory’, ‘enhancement’, ‘therapy’, and ‘self’. We conclude (1) that the enhancement of memory is still in its infancy, (2) that current MEDs and anti-dementia drugs are at best partially and minimally effective under specific conditions, (3) that ‘memory᾿and ‘enhancement᾿are ambiguous terms, (4) that there is no clear-cut distinction between enhancement and therapy, and (5) that the research into MEDs and anti-dementia drugs encourages a reductionistic view of the human mind and of the self
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