359 research outputs found
Collapse of generalized Euler and surface quasi-geostrophic point-vortices
Point vortex models are presented for the generalized Euler equations, which
are characterized by a fractional Laplacian relation between the active scalar
and the streamfunction. Special focus is given to the case of the surface
quasi-geostrophic (SQG) equations, for which the existence of finite-time
singularities is still a matter of debate. Point vortex trajectories are
expressed using Nambu dynamics. The formulation is based on a noncanonical
bracket and allows for a geometrical interpretation of trajectories as
intersections of level sets of the Hamiltonian and Casimir. Within this
setting, we focus on the collapse of solutions for the three point vortex
model. In particular, we show that for SQG the collapse can be either
self-similar or non-self-similar. Self-similarity occurs only when the
Hamiltonian is zero, while non-self-similarity appears for non-zero values of
the same. For both cases, collapse is allowed for any choice of circulations
within a permitted interval. These results differ strikingly from the classical
point vortex model, where collapse is self-similar for any value of the
Hamiltonian, but the vortex circulations must satisfy a strict relationship.
Results may also shed a light on the formation of singularities in the SQG
partial differential equations, where the singularity is thought to be reached
only in a self-similar way
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Strengthening multi-stakeholder cooperation in the international investment regime: The Brazilian model
The rule of law and dispute avoidance and settlement may not be enough to turn FDI into a means to the realization of the SDGs. Multi-stakeholder dialogue and cooperation should also be a central aspect of any institutional design. In this regard, the Brazilian model, at least in theory, scores better than most existing treaties and reform proposals
Measuring a Light Neutralino Mass at the ILC: Testing the MSSM Neutralino Cold Dark Matter Model
The LEP experiments give a lower bound on the neutralino mass of about 46 GeV
which, however, relies on a supersymmetric grand unification relation. Dropping
this assumption, the experimental lower bound on the neutralino mass vanishes
completely. Recent analyses suggest, however, that in the minimal
supersymmetric standard model (MSSM), a light neutralino dark matter candidate
has a lower bound on its mass of about 7 GeV. In light of this, we investigate
the mass sensitivity at the ILC for very light neutralinos. We study slepton
pair production, followed by the decay of the sleptons to a lepton and the
lightest neutralino. We find that the mass measurement accuracy for a few-GeV
neutralino is around 2 GeV, or even less if the relevant slepton is
sufficiently light. We thus conclude that the ILC can help verify or falsify
the MSSM neutralino cold dark matter model even for very light neutralinos.Comment: 7 pages, 1 figure; references adde
Multi-lepton Signatures of a Hidden Sector in Rare B Decays
We explore the sensitivity of flavour changing b -> s transitions to a
(sub-)GeV hidden sector with generic couplings to the Standard Model through
the Higgs, vector and axion portals. The underlying two-body decays of B
mesons, B -> X_s S and B0 -> SS, where S denotes a generic new GeV-scale
particle, may significantly enhance the yield of monochromatic lepton pairs in
the final state via prompt decays of S to a dilepton pair. Existing
measurements of the charged lepton spectrum in neutral-current semileptonic B
decays provide bounds on the parameters of the light sector that are
significantly more stringent than the requirements of naturalness. New search
modes, such as B -> X_s + n(l+l-) and B0 -> n(l+l-) with n > 1 can provide
additional sensitivity to scenarios in which both the Higgs and vector portals
are active, and are accessible to (super-)B factories and hadron colliders.Comment: 12 pages, 2 figures; v2: reference added, minor correction
Posttransplant lymphoproliferative disorders in neuronal xenotransplanted macaques
Posttransplant lymphoproliferative disorders (PTLDs) are a heterogeneous group of lymphoid proliferations that occur in the setting of depressed T-cell function due to immunosuppressive therapy used following solid organ transplantation, hematopoietic stem cell transplantation, and also xenotransplantation. In the present study, 28 immunosuppressed parkinsonian Macaca fascicularis were intracerebrally injected with wild-type or CTLA4-Ig transgenic porcine xenografts to identify a suitable strategy to enable long-term cell survival, maturation, and differentiation. Nine of 28 (32%) immunosuppressed primates developed masses compatible with PTLD, located mainly in the gastrointestinal tract and/or nasal cavity. The masses were classified as monomorphic PTLD according to the World Health Organization classification. Immunohistochemistry and polymerase chain reaction (PCR) analyses revealed that the PTLDs were associated with macaca lymphocryptovirus as confirmed by double-labeling immunohistochemistry for CD20 and Epstein-Barr nuclear antigen 2 (EBNA-2), where the viral protein was located within the CD20+ neoplastic B cells. In sera from 3 distinct phases of the experimental life of the primates, testing by quantitative PCR revealed a progression of the viral load that paralleled the PTLD progression and no evidence of zoonotic transmission of porcine lymphotropic herpesvirus through xenoneuronal grafts. These data suggest that monitoring the variation of macaca lymphocryptovirus DNA in primates could be used as a possible early diagnostic tool for PTLD progression, allowing preemptive treatment such as immunosuppression therapy reduction
Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools
Thermal tetrachloroethene (PCE) remediation by steam injection in a sandy aquifer led to the release of dissolved organic carbon (DOC) from aquifer sediments resulting in more reduced redox conditions, accelerated PCE biodegradation, and changes in microbial populations. These changes were documented by comparing data collected prior to the remediation event and eight years later. Based on the premise that dual C-Cl isotope slopes reflect ongoing degradation pathways, the slopes associated with PCE and TCE suggest the predominance of biotic reductive dechlorination near the source area. PCEwas the predominant chlorinated ethene near the source area prior to thermal treatment. After thermal treatment, cDCE became predominant. The biotic contribution to these changes was supported by the presence of Dehalococcoides sp. DNA (Dhc) and Dhc targeted rRNA close to the source area. In contrast, dual C-Cl isotope analysis together with the almost absent VC 13C depletion in comparison to cDCE 13C depletion suggested that cDCE was subject to abiotic degradation due to the presence of pyrite, possible surface-bound iron (II) or reduced iron sulphides in the downgradient part of the plume. This interpretation is supported by the relative lack of Dhc in the downgradient part of the plume. The results of this study show that thermal remediation can enhance the biodegradation of chlorinated ethenes, and that this effect can be traced to the mobilisation of DOC due to steaminjection. This, in turn, results in more reduced redox conditions which favor active reductive dechlorination and/or may lead to a series of redox reactions which may consecutively trigger biotically induced abiotic degradation. Finally, this study illustrates the valuable complementary application of compound-specific isotopic analysis combined with molecular biology tools to evaluate which biogeochemical processes are taking place in an aquifer contaminated with chlorinated ethenes
Radioscopic and ultrasonic data fusion via the evidence theory
A data fusion method, based on the the Dempster-Shafer evidence theory, is presented that aims at improving the reliability of
taking a decision by simultaneously exploiting complementary information from two different sources . Within this framework,
both discrete and continuous hypotheses are studied in a systematic manner. The data fusion method is applied to problems of
improving the reliability of Non Destructive Testing (NDT) using real-time x-ray (RX) radioscopy and ultrasounds (US). It is illustrated
with the aid of radioscopic and ultrasonic data corresponding to the same test objects . The results of detection, identification and
quantification of defects are discussed and compared in detail, in both monomodality and multimodality.Cet article propose une méthode de fusion, basée sur la théorie de l'évidence, qui vise à améliorer la fiabilité d'une prise de décision en exploitant simultanément des informations complémentaires issues de deux sources différentes. Dans ce cadre, les hypothèses aussi bien discrètes que continues sont traitées de manière systématique. La méthode de fusion est appliquée au problème d'amélioration de la fiabilité du contrôle non destructif (CND) utilisant la radioscopie numérique par rayons X (RX) et les ultrasons (US). Elle est illustrée à l'aide des données radioscopiques et ultrasonores correspondant aux mêmes pièces test. Les résultats de la détection, de l'identification et de la quantification des défauts dans le cas de la monomodalité et de la multimodalité sont discutés et comparés en détail
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加强国际投资体系中的多方合作:巴西模式
The rule of law and dispute avoidance and settlement may not be enough to turn FDI into a means to the realization of the SDGs. Multi-stakeholder dialogue and cooperation should also be a central aspect of any institutional design. In this regard, the Brazilian model, at least in theory, scores better than most existing treaties and reform proposals
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