99 research outputs found
Matching commercial thrips predating phytoseids with the highly diversified climatic conditions of different strawberry production systems
Flower inhabiting thrips (Order: Thysanoptera) are a major threat to fruit quality in strawberry production around the world. As chemical control is often inefficient, alternative control measures are of broad and current interest. Their fast reproduction makes predatory mites highly suitable for thrips control in a crop with a relatively short cropping season like strawberry. However, climatic conditions of strawberry production can differ strongly depending on the production system (glasshouse, plastic tunnel, open field, etc.) and the time span of cultivation (depending mostly on planting date and the type of cultivar: summer-or everbearing). As predatory mites typically display a temperature-dependent life history and the current commercially available thrips predating phytoseids vary in geographic origin, one can assume that under certain climatic conditions some species will be more applicable than others. The goal of this study is to determine which species are suitable for which climatic conditions. Therefore all (Belgian) production systems and time spans are categorized into three climate types, simulated in the laboratory. The population build-up of seven predatory mite species (A. degenerans, A. montdorensis, A. andersoni, A. limonicus, A. swirskii, N. cucumeris and E. gallicus) were assessed for each of these climatic conditions. Under the coldest condition (A), the in West-Europe indigenous E. gallicus was the only species with a significant population build up. When moderate conditions (B) were simulated E. gallicus, N. cucumeris and A. limonicus were most successful. The warmest regime (C) was most adequate for E. gallicus and A. swirskii
Unstable magnetohydrodynamical continuous spectrum of accretion disks. A new route to magnetohydrodynamical turbulence in accretion disks
We present a detailed study of localised magnetohydrodynamical (MHD)
instabilities occuring in two--dimensional magnetized accretion disks. We model
axisymmetric MHD disk tori, and solve the equations governing a
two--dimensional magnetized accretion disk equilibrium and linear wave modes
about this equilibrium. We show the existence of novel MHD instabilities in
these two--dimensional equilibria which do not occur in an accretion disk in
the cylindrical limit. The disk equilibria are numerically computed by the
FINESSE code. The stability of accretion disks is investigated analytically as
well as numerically. We use the PHOENIX code to compute all the waves and
instabilities accessible to the computed disk equilibrium. We concentrate on
strongly magnetized disks and sub--Keplerian rotation in a large part of the
disk. These disk equilibria show that the thermal pressure of the disk can only
decrease outwards if there is a strong gravitational potential. Our theoretical
stability analysis shows that convective continuum instabilities can only
appear if the density contours coincide with the poloidal magnetic flux
contours. Our numerical results confirm and complement this theoretical
analysis. Furthermore, these results show that the influence of gravity can
either be stabilizing or destabilizing on this new kind of MHD instability. In
the likely case of a non--constant density, the height of the disk should
exceed a threshold before this type of instability can play a role. This
localised MHD instability provides an ideal, linear route to MHD turbulence in
strongly magnetized accretion disk tori.Comment: 20 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
Can Streamer Blobs prevent the Buildup of the Interplanetetary Magnetic Field?
Coronal Mass Ejections continuously drag closed magnetic field lines away
from the Sun, adding new flux to the interplanetary magnetic field (IMF). We
propose that the outward-moving blobs that have been observed in helmet
streamers are evidence of ongoing, small-scale reconnection in streamer current
sheets, which may play an important role in the prevention of an indefinite
buildup of the IMF. Reconnection between two open field lines from both sides
of a streamer current sheet creates a new closed field line, which becomes part
of the helmet, and a disconnected field line, which moves outward. The blobs
are formed by plasma from the streamer that is swept up in the trough of the
outward moving field line. We show that this mechanism is supported by
observations from SOHO/LASCO. Additionally, we propose a thorough statistical
study to quantify the contribution of blob formation to the reduction of the
IMF, and indicate how this mechanism may be verified by observations with
SOHO/UVCS and the proposed NASA STEREO and ESA Polar Orbiter missions.Comment: 7 pages, 2 figures; accepted by The Astrophysical Journal Letters;
uses AASTe
A Component Based Heuristic Search Method with Evolutionary Eliminations
Nurse rostering is a complex scheduling problem that affects hospital
personnel on a daily basis all over the world. This paper presents a new
component-based approach with evolutionary eliminations, for a nurse scheduling
problem arising at a major UK hospital. The main idea behind this technique is
to decompose a schedule into its components (i.e. the allocated shift pattern
of each nurse), and then to implement two evolutionary elimination strategies
mimicking natural selection and natural mutation process on these components
respectively to iteratively deliver better schedules. The worthiness of all
components in the schedule has to be continuously demonstrated in order for
them to remain there. This demonstration employs an evaluation function which
evaluates how well each component contributes towards the final objective. Two
elimination steps are then applied: the first elimination eliminates a number
of components that are deemed not worthy to stay in the current schedule; the
second elimination may also throw out, with a low level of probability, some
worthy components. The eliminated components are replenished with new ones
using a set of constructive heuristics using local optimality criteria.
Computational results using 52 data instances demonstrate the applicability of
the proposed approach in solving real-world problems.Comment: 27 pages, 4 figure
1/f noise in magnetic Ni80Fe20 single layers and Ni80Fe20/Cu multilayers
We have investigated the room temperature 1/f noise of microstructured soft magnetic Ni80Fe20 films, showing the anisotropic magnetoresistance effect, and of Ni80Fe20/Cu magnetic multilayers, showing the giant magnetoresistance effect. We find that the 1/f noise in magnetic multilayers is considerably enhanced with respect to the noise of the single domain layer, which sets a limit on the usability of giant magnetoresistance materials for low-frequency applications
Local search for the surgery admission planning problem
We present a model for the surgery admission planning problem, and a meta-heuristic algorithm for solving it. The problem involves assigning operating rooms and dates to a set of elective surgeries, as well as scheduling the surgeries of each day and room. Simultaneously, a schedule is created for each surgeon to avoid double bookings. The presented algorithm uses simple Relocate and Two-Exchange neighbourhoods, governed by an iterated local search framework. The problem's search space associated with these move operators is analysed for three typical fitness surfaces, representing different compromises between patient waiting time, surgeon overtime, and waiting time for children in the morning on the day of surgery. The analysis shows that for the same problem instances, the different objectives give fitness surfaces with quite different characteristics. We present computational results for a set of benchmarks that are based on the admission planning problem in a chosen Norwegian hospital
Spatial concordance of DNA methylation classification in diffuse glioma
BACKGROUND:
Intratumoral heterogeneity is a hallmark of diffuse gliomas. DNA methylation profiling is an emerging approach in the clinical classification of brain tumors. The goal of this study is to investigate the effects of intratumoral heterogeneity on classification confidence.
METHODS:
We used neuronavigation to acquire 133 image-guided and spatially separated stereotactic biopsy samples from 16 adult patients with a diffuse glioma (7 IDH-wildtype and 2 IDH-mutant glioblastoma, 6 diffuse astrocytoma, IDH-mutant and 1 oligodendroglioma, IDH-mutant and 1p19q codeleted), which we characterized using DNA methylation arrays. Samples were obtained from regions with and without abnormalities on contrast-enhanced T1-weighted and fluid-attenuated inversion recovery MRI. Methylation profiles were analyzed to devise a 3-dimensional reconstruction of (epi)genetic heterogeneity. Tumor purity was assessed from clonal methylation sites.
RESULTS:
Molecular aberrations indicated that tumor was found outside imaging abnormalities, underlining the infiltrative nature of this tumor and the limitations of current routine imaging modalities. We demonstrate that tumor purity is highly variable between samples and explains a substantial part of apparent epigenetic spatial heterogeneity. We observed that DNA methylation subtypes are often, but not always, conserved in space taking tumor purity and prediction accuracy into account.
CONCLUSION:
Our results underscore the infiltrative nature of diffuse gliomas and suggest that DNA methylation subtypes are relatively concordant in this tumor type, although some heterogeneity exists
"You have to get wet to learn how to swim" applied to bridging the gap between research into personnel scheduling and its implementation in practice
Personnel scheduling problems have attracted research interests for several decades. They have been considerably changed over time, accommodating a variety of constraints related to legal and organisation requirements, part-time staff, flexible hours of staff, staff preferences, etc. This led to a myriad of approaches developed for solving personnel scheduling problems including optimisation, meta-heuristics, artificial intelligence, decision-support, and also hybrids of these approaches. However, this still does not imply that this research has a large impact on practice and that state-of-the art models and algorithms are widely in use in organisations. One can find a reasonably large number of software packages that aim to assist in personnel scheduling. A classification of this software based on its purpose will be proposed, accompanied with a discussion about the level of support that this software offers to schedulers. A general conclusion is that the available software, with some exceptions, does not benefit from the wealth of developed models and methods. The remaining of the paper will provide insights into some characteristics of real-world scheduling problems that, in the author’s opinion, have not been given a due attention in the personnel scheduling research community yet and which could contribute to the enhancement of the implementation of research results in practice. Concluding remarks are that in order to bridge the gap that still exists between research into personnel scheduling and practice, we need to engage more with schedulers in practice and also with software developers; one may say we need to get wet if we want to learn how to swim
Spatial concordance of DNA methylation classification in diffuse glioma.
BACKGROUND: Intratumoral heterogeneity is a hallmark of diffuse gliomas. DNA methylation profiling is an emerging approach in the clinical classification of brain tumors. The goal of this study is to investigate the effects of intratumoral heterogeneity on classification confidence.
METHODS: We used neuronavigation to acquire 133 image-guided and spatially separated stereotactic biopsy samples from 16 adult patients with a diffuse glioma (7 IDH-wildtype and 2 IDH-mutant glioblastoma, 6 diffuse astrocytoma, IDH-mutant and 1 oligodendroglioma, IDH-mutant and 1p19q codeleted), which we characterized using DNA methylation arrays. Samples were obtained from regions with and without abnormalities on contrast-enhanced T1-weighted and fluid-attenuated inversion recovery MRI. Methylation profiles were analyzed to devise a 3-dimensional reconstruction of (epi)genetic heterogeneity. Tumor purity was assessed from clonal methylation sites.
RESULTS: Molecular aberrations indicated that tumor was found outside imaging abnormalities, underlining the infiltrative nature of this tumor and the limitations of current routine imaging modalities. We demonstrate that tumor purity is highly variable between samples and explains a substantial part of apparent epigenetic spatial heterogeneity. We observed that DNA methylation subtypes are often, but not always, conserved in space taking tumor purity and prediction accuracy into account.
CONCLUSION: Our results underscore the infiltrative nature of diffuse gliomas and suggest that DNA methylation subtypes are relatively concordant in this tumor type, although some heterogeneity exists
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