254 research outputs found
Toward Realistic Intersecting D-Brane Models
We provide a pedagogical introduction to a recently studied class of
phenomenologically interesting string models, known as Intersecting D-Brane
Models. The gauge fields of the Standard-Model are localized on D-branes
wrapping certain compact cycles on an underlying geometry, whose intersections
can give rise to chiral fermions. We address the basic issues and also provide
an overview of the recent activity in this field. This article is intended to
serve non-experts with explanations of the fundamental aspects, and also to
provide some orientation for both experts and non-experts in this active field
of string phenomenology.Comment: 85 pages, 8 figures, Latex, Bibtex, v2: refs added, typos correcte
Bosonic excitation spectra of superconducting and extracted from scanning tunneling spectra
A detailed interpretation of scanning tunneling spectra obtained on
unconventional superconductors enables one to gain information on the pairing
boson. Decisive for this approach are inelastic tunneling events. Due to the
lack of momentum conservation in tunneling from or to the sharp tip, those are
enhanced in the geometry of a scanning tunneling microscope compared to planar
tunnel junctions. This work extends the method of obtaining the bosonic
excitation spectrum by deconvolution from tunneling spectra to nodal -wave
superconductors. In particular, scanning tunneling spectra of slightly
underdoped with a of
and optimally doped with a
of reveal a resonance mode in their bosonic excitation
spectrum at and
respectively. In both cases, the
overall shape of the bosonic excitation spectrum is indicative of predominant
spin scattering with a resonant mode at and
overdamped spin fluctuations for energies larger than . To perform the
deconvolution of the experimental data, we implemented an efficient iterative
algorithm that significantly enhances the reliability of our analysis
Discrete Path Planing Strategies for Coverage and Multi-Robot Rendezvous
This thesis addresses the problem of motion planning for autonomous robots, given a map and an estimate of the robot pose within it. The motion planning problem for a mobile robot can be defined as computing a trajectory in an environment from one pose to another while avoiding obstacles and optimizing some objective such as path length or travel time, subject to constraints like vehicle dynamics limitations. More complex planning problems such as multi-robot planning or complete coverage of an area can also be defined within a similar optimization structure. The computational complexity of path planning presents a considerable challenge for real-time execution with limited resources and various methods of simplifying the problem formulation by discretizing the solution space are grouped under the class of discrete planning methods. The approach suggests representing the environment as a roadmap graph and formulating shortest path problems to compute optimal robot trajectories on it. This thesis presents two main contributions under the framework of discrete planning.
The first contribution addresses complete coverage of an unknown environment by a single omnidirectional ground rover. The 2D occupancy grid map of the environment is first converted into a polygonal representation and decomposed into a set of convex sectors. Second, a coverage path is computed through the sectors using a hierarchical inter-sector and intra-sector optimization structure. It should be noted that both convex decomposition and optimal sector ordering are known NP-hard problems, which are solved using a greedy cut approximation algorithm and Travelling Salesman Problem (TSP) heuristics, respectively.
The second contribution presents multi-robot path-planning strategies for recharging autonomous robots performing a persistent task. The work considers the case of surveillance missions performed by a team of Unmanned Aerial Vehicles (UAVs). The goal is to plan minimum cost paths for a separate team of dedicated charging robots such that they rendezvous with and recharge all the UAVs as needed. To this end, planar UAV trajectories are discretized into sets of charging locations and a partitioned directed acyclic graph subject to timing constraints is defined over them. Solutions consist of paths through the graph for each of the charging robots. The rendezvous planning problem for a single recharge cycle is formulated as a Mixed Integer Linear Program (MILP), and an algorithmic approach, using a transformation to the TSP, is presented as a scalable heuristic alternative to the MILP. The solution is then extended to longer planning horizons using both a receding horizon and an optimal fixed horizon strategy.
Simulation results are presented for both contributions, which demonstrate solution quality and performance of the presented algorithms
Quantum physics needs complex numbers
Complex numbers, i.e., numbers with a real and an imaginary part, are
essential for mathematical analysis, while their role in other subjects, such
as electromagnetism or special relativity, is far less fundamental. Quantum
physics is the only physical theory where these numbers seem to play an
indispensible role, as the theory is explicitly formulated in terms of
operators acting on complex Hilbert spaces. The occurrence of complex numbers
within the quantum formalism has nonetheless puzzled countless physicists,
including the fathers of the theory, for whom a real version of quantum
physics, where states and observables are represented by real operators, seemed
much more natural. In fact, previous works showed that such "real quantum
physics" can reproduce the outcomes of any multipartite experiment, as long as
the parts share arbitrary real quantum states. Thus, are complex numbers really
needed for a quantum description of nature? Here, we show this to be case by
proving that real and complex quantum physics make different predictions in
network scenarios comprising independent quantum state sources. This allows us
to devise a Bell-type quantum experiment whose input-output correlations cannot
be approximated by any real quantum model. The successful realization of such
an experiment would disprove real quantum physics, in the same way as standard
Bell experiments disproved local physics.Comment: 17 pages. MATLAB codes available under reques
Human NOD2 Recognizes Structurally Unique Muramyl Dipeptides from Mycobacterium leprae.
The innate immune system recognizes microbial pathogens via pattern recognition receptors. One such receptor, NOD2, via recognition of muramyl dipeptide (MDP), triggers a distinct network of innate immune responses, including the production of interleukin-32 (IL-32), which leads to the differentiation of monocytes into dendritic cells (DC). NOD2 has been implicated in the pathogenesis of human leprosy, yet it is not clear whether Mycobacterium leprae, which has a distinct MDP structure, can activate this pathway. We investigated the effect of MDP structure on the innate immune response, finding that infection of monocytes with M. leprae induces IL-32 and DC differentiation in a NOD2-dependent manner. The presence of the proximal l-Ala instead of Gly in the common configuration of the peptide side chain of M. leprae did not affect recognition by NOD2 or cytokine production. Furthermore, amidation of the d-Glu residue did not alter NOD2 activation. These data provide experimental evidence that NOD2 recognizes naturally occurring structural variants of MDP
Room for Improvement in Conducting and Reporting Non-Inferiority Randomized Controlled Trials on Drugs: A Systematic Review
BACKGROUND: A non-inferiority (NI) trial is intended to show that the effect of a new treatment is not worse than the comparator. We conducted a review to identify how NI trials were conducted and reported, and whether the standard requirements from the guidelines were followed. METHODOLOGY AND PRINCIPAL FINDINGS: From 300 randomly selected articles on NI trials registered in PubMed at 5 February 2009, we included 227 NI articles that referred to 232 trials. We excluded studies on bioequivalence, trials on healthy volunteers, non-drug trials, and articles of which the full-text version could not be retrieved. A large proportion of trials (34.0%) did not use blinding. The NI margin was reported in 97.8% of the trials, but only 45.7% of the trials reported the method to determine the margin. Most of the trials used either intention to treat (ITT) (34.9%) or per-protocol (PP) analysis (19.4%), while 41.8% of the trials used both methods. Less than 10% of the trials included a placebo arm to confirm the efficacy of the new drug and active comparator against placebo, and less than 5.0% were reporting the similarity of the current trial with the previous comparator's trials. In general, no difference was seen in the quality of reporting before and after the release of the CONSORT statement extension 2006 or between the high-impact and low-impact journals. CONCLUSION: The conduct and reporting of NI trials can be improved, particularly in terms of maximizing the use of blinding, the use of both ITT and PP analysis, reporting the similarity with the previous comparator's trials to guarantee a valid constancy assumption, and most importantly reporting the method to determine the NI margin
Timeliness of contact tracing among flight passengers for influenza A/H1N1 2009
<p>Abstract</p> <p>Background</p> <p>During the initial containment phase of influenza A/H1N1 2009, close contacts of cases were traced to provide antiviral prophylaxis within 48 h after exposure and to alert them on signs of disease for early diagnosis and treatment. Passengers seated on the same row, two rows in front or behind a patient infectious for influenza, during a flight of â„ 4 h were considered close contacts. This study evaluates the timeliness of flight-contact tracing (CT) as performed following national and international CT requests addressed to the Center of Infectious Disease Control (CIb/RIVM), and implemented by the Municipal Health Services of Schiphol Airport.</p> <p>Methods</p> <p>Elapsed days between date of flight arrival and the date passenger lists became available (contact details identified - CI) was used as proxy for timeliness of CT. In a retrospective study, dates of flight arrival, onset of illness, laboratory diagnosis, CT request and identification of contacts details through passenger lists, following CT requests to the RIVM for flights landed at Schiphol Airport were collected and analyzed.</p> <p>Results</p> <p>24 requests for CT were identified. Three of these were declined as over 4 days had elapsed since flight arrival. In 17 out of 21 requests, contact details were obtained within 7 days after arrival (81%). The average delay between arrival and CI was 3,9 days (range 2-7), mainly caused by delay in diagnosis of the index patient after arrival (2,6 days). In four flights (19%), contacts were not identified or only after > 7 days. CI involving Dutch airlines was faster than non-Dutch airlines (<it>P </it>< 0,05). Passenger locator cards did not improve timeliness of CI. In only three flights contact details were identified within 2 days after arrival.</p> <p>Conclusion</p> <p>CT for influenza A/H1N1 2009 among flight passengers was not successful for timely provision of prophylaxis. CT had little additional value for alerting passengers for disease symptoms, as this information already was provided during and after the flight. Public health authorities should take into account patient delays in seeking medical advise and laboratory confirmation in relation to maximum time to provide postexposure prophylaxis when deciding to install contact tracing measures. International standardization of CT guidelines is recommended.</p
Biodiversity and ecosystem services science for a sustainable planet: the DIVERSITAS vision for 2012â20
DIVERSITAS, the international programme on biodiversity science, is releasing a strategic vision presenting scientific challenges for the next decade of research on biodiversity and ecosystem services: âBiodiversity and Ecosystem Services Science for a Sustainable Planetâ. This new vision is a response of the biodiversity and ecosystem services scientific community to the accelerating loss of the components of biodiversity, as well as to changes in the biodiversity science-policy landscape (establishment of a Biodiversity Observing Network â GEO BON, of an Intergovernmental science-policy Platform on Biodiversity and Ecosystem Services â IPBES, of the new Future Earth initiative; and release of the Strategic Plan for Biodiversity 2011â2020). This article presents the vision and its core scientific challenges.Fil: Larigauderie, Anne. DIVERSITAS. MusĂ©um National dâHistoire Naturelle; FranciaFil: Prieur Richard, Anne Helene. DIVERSITAS. MusĂ©um National dâHistoire Naturelle; FranciaFil: Mace, Georgina. Imperial College London. Center for Population Biology; Reino UnidoFil: Londsdale, Mark. CSIRO Ecosystem Sciences; AustraliaFil: Mooney, Harold A.. Stanford University. Department of Biological Sciences; Estados UnidosFil: Brussaard, Lijbert. Wageningen University, Soil Quality Department; PaĂses BajosFil: Cooper, David. Secretariat of the Convention on Biological Diversity; CanadĂĄFil: Wolfgang, Cramer. Institut MĂ©diterranĂ©en de BiodiversitĂ© et dâEcologie marine et continentale; FranciaFil: Daszak, Peter. EcoHealth Alliance. Wildlife Trust; Estados UnidosFil: Diaz, Sandra Myrna. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto Multidisciplinario de BiologĂa Vegetal. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Instituto Multidisciplinario de BiologĂa Vegetal; ArgentinaFil: Duraiappah, Anantha. International Human Dimensions Programme; AlemaniaFil: Elmqvist, Thomas. University of Stockholm. Department of Systems Ecology and Stockholm Resilience Center; SueciaFil: Faith, Daniel. The Australian Museum; AustraliaFil: Jackson, Louise. University of California; Estados UnidosFil: Krug, Cornelia. DIVERSITAS. MusĂ©um National dâHistoire Naturelle; FranciaFil: Leadley, Paul. UniversitĂ© Paris. Laboratoire Ecologie SystĂ©matique Evolution, Ecologie des Populations et CommunautĂ©s; FranciaFil: Le Prestre, Philippe. Laval University; CanadĂĄFil: Matsuda, Hiroyuki. Yokohama National University; JapĂłnFil: Palmer, Margaret. University of Maryland; Estados UnidosFil: Perrings, Charles. Arizona State University; Estados UnidosFil: Pulleman, Mirjam. Wageningen University; PaĂses BajosFil: Reyers, Belinda. Natural Resources and Environment; SudĂĄfricaFil: Rosa, Eugene A.. Washington State University; Estados UnidosFil: Scholes, Robert J.. Natural Resources and Environment; SudĂĄfricaFil: Spehn, Eva. Universidad de Basilea; SuizaFil: Turner II, B. L.. Arizona State University; Estados UnidosFil: Yahara, Tetsukazu. Kyushu University; JapĂł
Mass Hierarchies from MSSM Orientifold Compactifications
We investigate phenomenologically viable four- and five-stack MSSM D-brane
quivers which exhibit realistic fermion mass hierarchies. In our analysis, the
mass hierarchies arise either from higher order terms containing the VEV's of
SM singlets or from D-instanton effects, where the latter utilizes either
family splitting or a factorizable Yukawa matrix. Extending the systematic
bottom-up analysis of arXiv:0905.3379, we present the only four-stack quiver
with a semi-realistic Yukawa texture. Investigation of five-stack MSSM models
reveals many more quivers with analogous Yukawa textures, as well as a few
examples which exhibit three different mass scales for the up-quarks,
down-quarks, and electrons. Potential problems in this class of quivers are the
presence of U(1) instantons, which might lead to undesired effects, such as
R-parity violating couplings, and the presence of dimension 5 operators that
could lead to rapid proton decay. We present a five-stack setup which overcomes
all of these problems and exhibits three different mass scales for the
up-quarks, down-quarks and electrons.Comment: 31 page
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