9,094 research outputs found
Approximate solutions in space mission design
In this paper, we address multi-objective space mission design problems. From a practical point of view, it is often the case that,during the preliminary phase of the design of a space mission, the solutions that are actually considered are not 'optimal' (in the Pareto sense)but belong to the basin of attraction of optimal ones (i.e. they are nearly
optimal). This choice is motivated either by additional requirements that the decision maker has to take into account or, more often, by robustness considerations. For this, we suggest a novel MOEA which is a modification of the well-known NSGA-II algorithm equipped with a recently
proposed archiving strategy which aims at storing the set of approximate solutions of a given MOP. Using this algorithm we will examine some space trajectory design problems and demonstrate the benefit of the novel approach
Heart rate variability in relation to cognition and behavior in neurodegenerative diseases: A systematic review and meta-analysis
Neurodegenerative diseases, which frequently present with neuropsychiatric symptoms related to prefrontal cortical dysfunction, can alter the integrity of the neural networks involved in central autonomic nervous system regulation, which is proposed to be indexed by heart rate variability (HRV). We systematically reviewed the characteristics, methodology and outcomes of 27 studies of HRV in relation to measures of cognition and behavior in neurodegenerative conditions, and assessed the strength of this relationship, cross-sectionally, across 18 studies. A significant, moderate effect was observed (r = 0.25), such that higher HRV was related to better cognitive and behavioral scores, which was not influenced by mean age or cognitive status. There was no evidence of small-study effects but we could not rule out publication bias, and other factors may have contributed to heterogeneity between studies. Our findings support the proposal that HRV may be a marker of self-regulatory processes in neurodegenerative conditions, and further research on this association is needed in relation to neuropsychiatric symptoms and alongside neuroimaging methods
The Sources of b-Quarks at the Tevatron and their Correlations
The leading-log order QCD hard scattering Monte-Carlo models of HERWIG,
ISAJET, and PYTHIA are used to study the sources of b-quarks at the Tevatron.
The reactions responsible for producing b and bbar quarks are separated into
three categories; flavor creation, flavor excitation, and
parton-shower/fragmentation. Flavor creation corresponds to the production of a
b-bbar pair by gluon fusion or by annihilation of light quarks, while flavor
excitation corresponds to a b or bbar quark being knocked out of the
initial-state by a gluon or a light quark or antiquark. The third source occurs
when a b-bbar pair is produced within a parton shower or during the
fragmentation process of a gluon or a light quark or antiquark (includes gluon
splitting). The QCD Monte-Carlo models indicate that all three sources of
b-quarks are important at the Tevatron and when combined they qualitatively
describe the inclusive cross-section data. Correlations between the b and bbar
quark are very different for the three sources and can be used to isolate the
individual contributions.Comment: RevTex4, 14 pages, 20 figures, submitted to Phys. Rev.
Resonant Formation of Molecules in Deuterium: An Atomic Beam Measurement of Muon Catalyzed dt Fusion
Resonant formation of molecules in collisions of muonic tritium
() on D was investigated using a beam of atoms,
demonstrating a new direct approach in muon catalyzed fusion studies. Strong
epithermal resonances in formation were directly revealed for the
first time. From the time-of-flight analysis of fusion
events, a formation rate consistent with times the theoretical prediction was obtained. For the largest
peak at a resonance energy of eV, this corresponds to a rate
of s, more than an order of magnitude larger
than those at low energies.Comment: To appear in Phys. Rev. Let
The convergence of the ab-initio many-body expansion for the cohesive energy of solid mercury
A many-body expansion for mercury clusters of the form E = \sum_{i<j}\Delta
\epsilon_{ij} + \sum_{i<j<k}\Delta \epsilon_{ijk} + ... \quad, does not
converge smoothly with increasing cluster size towards the solid state. Even
for smaller cluster sizes (up to n=6), where van der Waals forces still
dominate, one observes bad convergence behaviour. For solid mercury the
convergence of the many-body expansion can dramatically be improved by an
incremental procedure within an embedded cluster approach. Here one adds the
coupled cluster many-body electron correlation contributions of the embedded
cluster to the bulk HF energy. In this way we obtain a cohesive energy (not
corrected for zero-point vibration) of 0.79 eV in perfect agreement with the
experimental value.Comment: 10 pages, 3 figures, accepted PR
Desertification
IPCC SPECIAL REPORT ON CLIMATE CHANGE AND LAND (SRCCL)
Chapter 3: Climate Change and Land: An IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystem
Preclinical detection of PrP\u3csup\u3eSc\u3c/sup\u3e in nictitating membrane lymphoid tissue of sheep
SHEEP scrapie is the prototype of a heterogeneous group of transmissible spongiform encephalopathies (TSES) which occur in humans, cattle, cats, mink and cervids. TSEs are characterised by the deposition of prion proteins (Prp-Scrapie or PrpSc) in the central nervous system of affected individuals (Prusiner 1982). PrPSc and infectivity have also been detected in the lymphoreticular system of sheep well before symptoms occur (Hadlow and others 1982, Race and others 1992). Detection of PrpSc in lymphoid tissue, such as tonsils or peripheral lymph nodes, has been proposed as a preclinical diagnostic test for scrapie (Ikegami and others 1991, Schreuder and others 1996). This short communication reports the use of a non-invasive diagnostic assay based on biopsy of lymphoid nodules in the nictitating membrane of sheep. The nictitating membrane or third eyelid (palpebra tertia) of ruminant animals consists of a cartilaginous sheet with superficial lymphoid follicles and a seromucinous secretory gland beneath the conjunctiva of the bulbar surface (Slatter and Mills 1981). The lymphoid nodules are easily biopsied under local anaesthesia. Sheep were pretreated by topical administration of proparacaine hydrochloride (Ophthetic; Allergan) and the nictitating membrane was everted with disposable 1 x 2-toothed, 5½-inch forceps (Sklar 78055-1). Typically two clusters of lymphoid tissue were visualised above the more pale glandular tissue. A biopsy of one cluster of lymphoid tissue was collected using disposable Metzenbaum scissors (Sklar 30455) and a second set of forceps. Biopsied tissue was fixed in formalin and paraffin embedded using conventional methods. Sections typically contained four to seven lymphoid follicles
P(3HB) Based Magnetic Nanocomposites: Smart Materials for Bone Tissue Engineering
The objective of this work was to investigate the potential application of Poly(3-hydroxybutyrate)/magnetic nanoparticles, P(3HB)/MNP, and Poly(3-hydroxybutyrate)/ferrofluid (P(3HB)/FF) nanocomposites as a smart material for bone tissue repair. The composite films, produced using conventional solvent casting technique, exhibited a good uniform dispersion of magnetic nanoparticles and ferrofluid and their aggregates within the P(3HB) matrix. The result of the static test performed on the samples showed that there was a 277% and 327% increase in Young's modulus of the composite due to the incorporation of MNP and ferrofluid, respectively. The storage modulus of the P(3HB)MNP and P(3HB)/FF was found to have increased to 186% and 103%, respectively, when compared to neat P(3HB). The introduction of MNP and ferrofluid positively increased the crystallinity of the composite scaffolds which has been suggested to be useful in bone regeneration. The total amount of protein absorbed by the P(3HB)/MNP and P(3HB)/FF composite scaffolds also increased by 91% and 83%, respectively, with respect to neat P(3HB). Cell attachment and proliferation were found to be optimal on the P(HB)/MNP and P(3HB)/FF composites compared to the tissue culture plate (TCP) and neat P(3HB), indicating a highly compatible surface for the adhesion and proliferation of the MG-63 cells. Overall, this work confirmed the potential of using P(3HB)/MNP and P(3HB)/FF composite scaffolds in bone tissue engineering
Measurement of the Resonant Molecular Formation Rate in Solid HD
Measurements of muon-catalyzed dt fusion () in solid
HD have been performed. The theory describing the energy dependent resonant
molecular formation rate for the reaction + HD is
compared to experimental results in a pure solid HD target. Constraints on the
rates are inferred through the use of a Monte Carlo model developed
specifically for the experiment. From the time-of- flight analysis of fusion
events in 16 and 37 targets, an average formation rate
consistent with 0.897(0.046) (0.166) times the
theoretical prediction was obtained.Comment: 4 pages, 5 figure
- …