The Restriction Principle and Commuting Families of Toeplitz Operators on the Unit Ball

On the unit ball B^n we consider the weighted Bergman spaces H_\lambda and their Toeplitz operators with bounded symbols. It is known from our previous work that if a closed subgroup H of \widetilde{\SU(n,1)} has a multiplicity-free restriction for the holomorphic discrete series of \widetilde{\SU(n,1)}, then the family of Toeplitz operators with H-invariant symbols pairwise commute. In this work we consider the case of maximal abelian subgroups of \widetilde{\SU(n,1)} and provide a detailed proof of the pairwise commutativity of the corresponding Toeplitz operators. To achieve this we explicitly develop the restriction principle for each (conjugacy class of) maximal abelian subgroup and obtain the corresponding Segal-Bargmann transform. In particular, we obtain a multiplicity one result for the restriction of the holomorphic discrete series to all maximal abelian subgroups. We also observe that the Segal-Bargman transform is (up to a unitary transformation) a convolution operator against a function that we write down explicitly for each case. This can be used to obtain the explicit simultaneous diagonalization of Toeplitz operators whose symbols are invariant by one of these maximal abelian subgroups

Vanishing Cosmological Constant in Modified Gauss-Bonnet Gravity with Conformal Anomaly

We consider dark energy cosmology in a de Sitter universe filled with quantum conformal matter. Our model represents a Gauss-Bonnet model of gravity with contributions from quantum effects. To the General Relativity action an arbitrary function of the GB invariant, f(G), is added, and taking into account quantum effects from matter the cosmological constant is studied. For the considered model the conditions for a vanishing cosmological constant are considered. Creation of a de Sitter universe by quantum effects in a GB modified gravity is discussed.Comment: 8 pages latex, 1 figure. To appear in Int. J. Mod. Phys.

Tachyon fields with effects of quantum matter in an Anti-de Sitter Universe

We consider an Anti-de Sitter universe filled by quantum conformal matter with the contribution from the usual tachyon and a perfect fluid. The model represents the combination of a trace-anomaly annihilated and a tachyon driven Anti-de Sitter universe. The influence exerted by the quantum effects and by the tachyon on the AdS space is studied. The radius corresponding to this universe is calculated and the effect of the tachyon potential is discussed, in particular, concerning to the possibility to get an accelerated scale factor for the proposed model (implying an accelerated expansion of the AdS type of universe). Fulfillment of the cosmological energy conditions in the model is also investigatedComment: 14 Latex pages, no figure

Exploring Commercial Counter-UAS Operations: A Case Study of the 2017 Dominican Republic Festival Presidente

The proliferation of commercial off-the-shelf unmanned aircraft technology has resulted in a growing number of illicit or hazardous UAS activities, highlighting the growing need for effective counter-UAS mitigations. The purpose of this exploratory research is to develop a better understanding of the existing tactics, techniques, procedures involved in counter-UAS operations. Using a critical paradigm approach, the authors conducted a qualitative, unstructured interview with counter-UAS professionals. The authors sought to identify mission planning considerations, counter-UAS engagement tasks, and unanticipated conditions associated with performing a commercial [non-military] counter-UAS mission. The authors codified 11 key mission planning tasks and a 22-step engagement process by which one organization effected counter-UAS operations at a contracted, international event. The authors conclude that the study’s findings underscore existing vulnerabilities to UAS threats and the accompanying need for additional research in this field of UAS security

Simulated Galactic methanol maser distribution to constrain Milky Way parameters

Using trigonometric parallaxes and proper motions of masers associated with massive young stars, the Bar and Spiral Structure Legacy (BeSSeL) survey has reported the most accurate values of the Galactic parameters so far. The determination of these parameters with high accuracy has a widespread impact on Galactic and extragalactic measurements. This research is aimed at establishing the confidence with which such parameters can be determined. This is relevant for the data published in the context of the BeSSeL survey collaboration, but also for future observations, in particular from the Southern Hemisphere. In addition, some astrophysical properties of the masers can be constrained, notably the luminosity function. We have simulated the population of maser-bearing young stars associated with Galactic spiral structure, generating several samples and comparing them with the observed samples used in the BeSSeL survey. Consequently, we checked the determination of Galactic parameters for observational biases introduced by the sample selection. Galactic parameters obtained by the BeSSeL survey do not seem to be biased by the sample selection used. In fact, the published error estimates appear to be conservative for most of the parameters. We show that future BeSSeL data and future observations with Southern arrays will improve the Galactic parameters estimates and smoothly reduce their mutual correlation. Moreover, by modeling future parallax data with larger distance and, thus, greater relative uncertainties for a larger numbers of sources, we found that parallax-distance biasing is an important issue. Hence, using fractional parallax uncertainty in the weighting of the motion data is imperative. Finally, the luminosity function for 6.7 GHz methanol masers was determined, allowing us to estimate the number of Galactic methanol masers.Comment: Accepted for publication in A&A. Language edition include

Testing collinear factorization and nuclear parton distributions with pA collisions at the LHC

Global perturbative QCD analyses, based on large data sets from electron-proton and hadron collider experiments, provide tight constraints on the parton distribution function (PDF) in the proton. The extension of these analyses to nuclear parton distributions (nPDF) has attracted much interest in recent years. nPDFs are needed as benchmarks for the characterization of hot QCD matter in nucleus-nucleus collisions, and attract further interest since they may show novel signatures of non- linear density-dependent QCD evolution. However, it is not known from first principles whether the factorization of long-range phenomena into process-independent parton distribution, which underlies global PDF extractions for the proton, extends to nuclear effects. As a consequence, assessing the reliability of nPDFs for benchmark calculations goes beyond testing the numerical accuracy of their extraction and requires phenomenological tests of the factorization assumption. Here we argue that a proton-nucleus collision program at the LHC would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits.Comment: 4 pages, 5 figure

Overview of the JET results in support to ITER

The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at βN ~ 1.8 and n/nGW ~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D–T campaign and 14 MeV neutron calibration strategy are reviewed.European Commission (EUROfusion 633053

Vegetation Response to Grazing Pressure in the Puna Flat, NW Argentina

Puna grasslands are located at a high‐altitude flat plateau in the Northwest of Argentina. It is an arid territory (100 to 300 mm rainfall/year) at 3,000 to 4,000 m a.s.l. The vegetation is scarce, where Andean pastoralist communities produce meat and wool, specialized in llama (Lama glama) and sheep‐breeding, although they do breed multi‐species herds that may also include goats and cattle. There are erosion processes in the Puna, where shepherds and their animals could be synergetic factors with natural very hard climatic conditions. In this work we assess the effect of ovine and lama grazing on the plant communities in the Puna grasslands. Considering that stockyards are used in a very complex way along the year, having differences between those used in winter or in summer, or used for many months or only one month, etc. we built up a Grazing Pressure Index taking in account all these factors in each sampling point. We sampled 28 paired transects (14 in sites with high grazing pressure, and 14 in sites with low grazing pressure) in 2 different ecological sites (grassy grassland and shrubby steppe). Focusing our work on the community functionality, we analysed Plant Functional Types (PTF) measuring their cover, richness and diversity. Our results do not show significant differences on PFT cover, richness or diversity between sites at different grazing pressures. It could be the result of a low grazing pressure or a long grazing pressure history that had configured the TFP associations