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338 result(s) for "Cowden, C."
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Does evolutionary history determine specificity in broad ecological interactions?
1. Most species engage in broad interactions, in which they interact with multiple partner species. The evolutionary processes that generate such generalized interactions remain unknown, partly due to the difficulty in comparing their breadth. 2. We argue that the interaction specificity of species involved in broad interactions evolves in three ways: (a) assemblage specialization, in which a species specializes on particular host species that contribute unique resources, yielding specialization on the entire host assemblage; (b) apparent generalism, in which a species specializes on one or few host species that contribute unique resources, but also associates with other host species that contribute functionally redundant resources; and (c) true generalism, in which a species associates with multiple hosts that overlap functionally, and that are geographically interchangeable based on opportunity for encounter, leading to frequent host switching. 3. We performed a phylogenetically controlled analysis of data on mycorrhizal fungal associations for approximately 25% of the orchid subfamily Cypripedioideae to determine whether these plants have specialized on their mycorrhizal fungal communities, or whether they are true generalists. We also assessed the impact of environmental factors on these associations. 4. Our results suggested strong support for apparent generalism, suggesting strong specialization on particular, dominant fungi and weak specialization on others. Large orchid clades associated with dominant fungal species, notably Tulasnella cystidiophora for genus Cypripedium, and T. cystidiophora and T. calospora for genus Paphiopedilum. Significant phylogenetic signal in fungal species richness per plant species, but not in the fungal phylogenetic diversity per plant species nor in the composition of fungal assemblages across orchid species suggested that plant phylogeny is an important determinant of fungal association. Mixed linear models showed that environment influenced specificity across plant species, and that observed differences were strongly driven by differences in sampling effort. 5. Synthesis. We found evidence of specialization of plant species on dominant fungal species, and to a lesser extent on their close relatives. The strong dominance of particular fungal species in these associations suggests important ecological roles for them, while environmental gradients in specificity suggest strong environmental filtering of these interactions.
Object Reconstruction in Non-Pointing Geometry
The Combined Forward Calorimeter (CFC) option for the Phase II upgrades covers the endcap region (1.5 < |η| < 4) and its design calls for embedded clear and rad- hard scintillation fibers in an absorber matrix. The object construction using complementary features of Cherenkov and scintillating signals coupled with fast timing information results in some unique capabilities for high efficiency particle identification, precision energy measurement, background suppression and triggering. These topics along with possible pile-up mitigation techniques at the HL-LHC will be discussed in detail.
DSB:Ce3+ scintillation glass for future
One of the main challenges for detectors at future high-energy collider experiments is the high precision measurement of hadron and jet energy and momentum. One possibility to achieve this is the dual-readout technique, which allows recording simultaneously scintillation and Cherenkov light in an active medium in order to extract the electromagnetic fraction of the total shower energy on an event- by-event basis. Making use of this approach in the high luminosity LHC, however, puts stringent requirements on the active materials in terms of radiation hardness. Consequently, the R&D carried out on suitable scintillating materials focuses on the detector performance as well as on radiation tolerance. Among the different scintillating materials under study, scintillating glasses can be a suitable solution due to their relatively simple and cost effective production. Recently a new type of inorganic scintillating glass: Cerium doped DSB has been developed by Radiation Instruments and New Components LLC in Minsk for oil logging industry. This material can be produced either in form of bulk or fiber shape with diameter 0.3-2mm and length up to 2000 mm. It is obtained by standard glass production technology at temperature 1400°C with successive thermal annealing treatment at relatively low temperature. The production of large quantities is relatively easy and the production costs are significantly lower compared to crystal fibers. Therefore, this material is considered as an alternative and complementary solution to crystal fibers in view of a production at industrial scale, as required for a large dual readout calorimeter. In this paper, the first results on optical, scintillation properties as well as the radiation damage behaviour obtained on different samples made with different raw materials and various cerium concentrations will be presented.
Detection of Clustering Instabilities for Sequential Recombination Algorithms
We explore clustering stability of sequential recombination jet reconstruction algorithms. Events are reconstructed many times, using random variations of kinematic properties of the jet fragmentation process. Sensitivity of different algorithms to initial conditions are quantified by introducing probabilistic assignment of initial particles to jets (fuzzy clustering). A criterion detecting unstable configurations (bifurcation points) is proposed, based on the overall fuzziness of the event.
An alternative method of anthropometry of anterior cruciate ligament through 3-D digital image reconstruction
Accurate and flexible measurements of length, area, and volume are important in evaluation of the mechanical properties of soft tissue. Although a number of contact-based and non-contact techniques have been reported in the literature, due to a variety of reasons such as cost, complexity, and low accuracy, the research community has not adopted a standardized technique. In this paper, an alternative method of measuring the geometric parameters of cadaver anterior cruciate ligament (ACL) is presented. In this method, a 3-D scan of the ACL is constructed using a simple, commercially available, scanning system. The 3-D scan is then analyzed using the 3-D Doctor Software to extract important information regarding the length, cross-sectional area, and volume of the ACL. The accuracy and repeatability of measurements obtained by this method are acceptable and comparable to existing non-contact methods. The limitation of the method is that surface concavities cannot be detected. However, the non-contact optical method, described here, has inherent advantages over the existing methods: (1) it is inexpensive; (2) it allows the determination of area at any distance along the length of the tissue of interest; (3) all relevant information including minimum area is extracted from one single application of the method; (4) the volume can be calculated with a simple additional step of length measurement although, for accurate results, condylar blockage must be minimized by coring the ACL out. The entire process of scanning takes less than 30 min. This technique has the potential to become a standard method in anthropometry of soft tissue.
Searches for invisible decays of the Higgs boson in pp collisions at s = 7, 8, and 13 TeV
A bstract Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 fb −1 at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model production, yields an observed (expected) upper limit on the invisible branching fraction of 0.24 (0.23) at the 95% confidence level. The results are also interpreted in the context of Higgs-portal dark matter models.
Search for dark matter, extra dimensions, and unparticles in monojet events in proton–proton collisions at s=8TeV
Results are presented from a search for particle dark matter (DM), extra dimensions, and unparticles using events containing a jet and an imbalance in transverse momentum. The data were collected by the CMS detector in proton–proton collisions at the LHC and correspond to an integrated luminosity of 19.7 fb -1 at a centre-of-mass energy of 8 TeV . The number of observed events is found to be consistent with the standard model prediction. Limits are placed on the DM-nucleon scattering cross section as a function of the DM particle mass for spin-dependent and spin-independent interactions. Limits are also placed on the scale parameter M D in the Arkani-Hamed, Dimopoulos, and Dvali (ADD) model of large extra dimensions, and on the unparticle model parameter Λ U . The constraints on ADD models and unparticles are the most stringent limits in this channel and those on the DM-nucleon scattering cross section are an improvement over previous collider results.
Search for light bosons in decays of the 125 GeV Higgs boson in proton-proton collisions at s=8 TeV
A bstract A search is presented for decays beyond the standard model of the 125 GeV Higgs bosons to a pair of light bosons, based on models with extended scalar sectors. Light boson masses between 5 and 62.5 GeV are probed in final states containing four τ leptons, two muons and two b quarks, or two muons and two τ leptons. The results are from data in proton-proton collisions corresponding to an integrated luminosity of 19.7 fb −1 , accumulated by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV. No evidence for such exotic decays is found in the data. Upper limits are set on the product of the cross section and branching fraction for several signal processes. The results are also compared to predictions of two-Higgs-doublet models, including those with an additional scalar singlet.
Observation of Y(1S) pair production in proton-proton collisions at s=8 TeV
A bstract Pair production of Y(1S) mesons is observed at the LHC in proton-proton collisions at s = 8 TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb −1 . Both Y(1S) candidates are fully reconstructed via their decays to μ + μ − . The fiducial acceptance region is defined by an absolute Y(1S) rapidity smaller than 2.0. The fiducial cross section for the production of Y(1S) pairs, assuming that both mesons decay isotropically, is measured to be 68.8±12.7 (stat)±7.4 (syst)±2.8 ( ℬ ) pb, where the third uncertainty comes from the uncertainty in the branching fraction of Y(1S) decays to μ + μ − . Assuming instead that the Y(1S) mesons are produced with different polarizations leads to variations in the measured cross section in the range from −38% to +36%.
Search for a charged Higgs boson in pp collisions at s=8 TeV
A bstract A search for a charged Higgs boson is performed with a data sample corresponding to an integrated luminosity of 19.7 ± 0.5 fb −1 collected with the CMS detector in proton-proton collisions at s = 8 ,TeV. The charged Higgs boson is searched for in top quark decays for m H ± < m t − m b , and in the direct production pp → t(b)H ± for m H ± > m t − m b . The H ± → τ ± ν τ and H ± → tb decay modes in the final states τ h +jets, μτ h , ℓ +jets, and ℓℓ ’ ( ℓ =e, μ ) are considered in the search. No signal is observed and 95% confidence level upper limits are set on the charged Higgs boson production. A model-independent upper limit on the product branching fraction ℬ t → H ± b ℬ H ± → τ ± ν τ = 1.2 − 0.15 % is obtained in the mass range m H ± = 80–160 GeV, while the upper limit on the cross section times branching fraction σ pp → t b H ± ℬ H ± → τ ± ν τ = 0.38 − 0.025 pb is set in the mass range m H + = 180–600 GeV. Here, σ (pp → t(b)H ± ) stands for the cross section sum σ pp → t ¯ b H + + σ pp → t b ¯ H − . Assuming ℬ H ± → t b = 1 , an upper limit on σ (pp → t(b)H ± ) of 2.0–0.13 pb is set for m H ± = 180–600 GeV. The combination of all considered decay modes and final states is used to set exclusion limits in the m H ±−tan β parameter space in different MSSM benchmark scenarios.