1,465 research outputs found
The H.E.S.S. multi-messenger program
Based on fundamental particle physics processes like the production and
subsequent decay of pions in interactions of high-energy particles, close
connections exist between the acceleration sites of high-energy cosmic rays and
the emission of high-energy gamma rays and high-energy neutrinos. In most cases
these connections provide both spatial and temporal correlations of the
different emitted particles. The combination of the complementary information
provided by these messengers allows to lift ambiguities in the interpretation
of the data and enables novel and highly sensitive analyses. In this
contribution the H.E.S.S. multi-messenger program is introduced and described.
The current core of this newly installed program is the combination of
high-energy neutrinos and high-energy gamma rays. The search for gamma-ray
emission following gravitational wave triggers is also discussed. Furthermore,
the existing program for following triggers in the electromagnetic regime was
extended by the search for gamma-ray emission from Fast Radio Bursts (FRBs). An
overview over current and planned analyses is given and recent results are
presented.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Percutaneous pulmonary valve implantation alters electrophysiologic substrate
BACKGROUND: Percutaneous pulmonary valve implantation (PPVI) is firstâline therapy for some congenital heart disease patients with right ventricular outflow tract dysfunction. The hemodynamics improvements after PPVI are well documented, but little is known about its effects on the electrophysiologic substrate. The objective of this study is to assess the shortâ and mediumâterm electrophysiologic substrate changes and elucidate postprocedure arrhythmias. METHODS AND RESULTS: A retrospective chart review of patients undergoing PPVI from May 2010 to April 2015 was performed. AÂ total of 106 patients underwent PPVI; most commonly these patients had tetralogy of Fallot (n=59, 55%) and pulmonary insufficiency (n=60, 57%). The median followâup time was 28Â months (7â63Â months). PreâPPVI, 25 patients (24%) had documented arrhythmias: nonsustained ventricular tachycardia (NSVT) (n=9, 8%), frequent premature ventricular contractions (PVCs) (n=6, 6%), and atrial fibrillation/flutter (AF/AFL) (n=10, 9%). PostâPPVI, arrhythmias resolved in 4 patients who had NSVT (44%) and 5 patients who had PVCs (83%). New arrhythmias were seen in 16 patients (15%): 7 NSVT, 8 PVCs, and 1 AF/AFL. There was resolution at mediumâterm followâup in 6 (86%) patients with newâonset NSVT and 7 (88%) patients with newâonset PVCs. There was no difference in QRS duration preâPPVI, postâPPVI, and at mediumâterm followâup (P=0.6). The median corrected QT lengthened immediately postâPPVI but shortened significantly at midterm followâup (P<0.01). CONCLUSIONS: PPVI reduced the prevalence of NSVT. The majority of postimplant arrhythmias resolve by 6Â months of followâup
Zur Funktion der Serin-Threonin-Proteinphosphatase 1 in der vaskulären glatten Muskulatur
Die reversible Phosphorylierung ist ein verbreiteter Mechanismus der Regulation zellulärer Prozesse. Der Grad der Phosphorylierung reflektiert die relative Aktivität phosphorylierender Proteinkinasen und dephosphorylierender Proteinphosphatasen (PP). Bei der Kontraktion der glatten Muskulatur der GefäĂe ist die PP1 von zentraler Bedeutung, da sie den Phosphorylierungsgrad der regulatorischen leichten Kette des Myosins (MLC20) mitbestimmt. Ziel der Untersuchungen war es, durch eine ErhĂśhung bzw. Erniedrigung der zellulären PP-Aktivität den Phosphorylierungsgrad der MLC20 zu variieren. Hierzu wurde die PP-Aktivität einerseits in intakten und gehäuteten GefäĂpräparationen durch den Einsatz exogener PP-Hemmstoffe erniedrigt und andererseits die PP1alpha mittels des Baculovirussystems als rekombinantes Protein hergestellt. Des weiteren konnte ein rekombinanter Adenovirus generiert werden, der die Expression des endogenen Inhibitors 2 der PP1 in intakten Zellen und Geweben ermĂśglichte
In situâDirected Growth of Organic Nanofibers and Nanoflakes: Electrical and Morphological Properties
Organic nanostructures made from organic molecules such as para-hexaphenylene (p-6P) could form nanoscale components in future electronic and optoelectronic devices. However, the integration of such fragile nanostructures with the necessary interface circuitry such as metal electrodes for electrical connection continues to be a significant hindrance toward their large-scale implementation. Here, we demonstrate in situâdirected growth of such organic nanostructures between pre-fabricated contacts, which are sourceâdrain gold electrodes on a transistor platform (bottom-gate) on silicon dioxide patterned by a combination of optical lithography and electron beam lithography. The dimensions of the gold electrodes strongly influence the morphology of the resulting structures leading to notably different electrical properties. The ability to control such nanofiber or nanoflake growth opens the possibility for large-scale optoelectronic device fabrication
Mott transition in one dimension: Benchmarking dynamical cluster approaches
The variational cluster approach (VCA) is applied to the one-dimensional
Hubbard model at zero temperature using clusters (chains) of up to ten sites
with full diagonalization and the Lanczos method as cluster solver. Within the
framework of the self-energy-functional theory (SFT), different cluster
reference systems with and without bath degrees of freedom, in different
topologies and with different sets of variational parameters are considered.
Static and one-particle dynamical quantities are calculated for half-filling as
a function of U as well as for fixed U as a function of the chemical potential
to study the interaction- and filling-dependent metal-insulator (Mott)
transition. The recently developed Q-matrix technique is used to compute the
SFT grand potential. For benchmarking purposes we compare the VCA results with
exact results available from the Bethe ansatz, with essentially exact dynamical
DMRG data, with (cellular) dynamical mean-field theory and full diagonalization
of isolated Hubbard chains. Several issues are discussed including convergence
of the results with cluster size, the ability of cluster approaches to access
the critical regime of the Mott transition, efficiency in the optimization of
correlated-site vs. bath-site parameters and of multi-dimensional parameter
optimization. We also study the role of bath sites for the description of
excitation properties and as charge reservoirs for the description of filling
dependencies. The VCA turns out to be a computationally cheap method which is
competitive with established cluster approaches.Comment: 19 pages, 19 figures, v3 with minor corrections, extended discussio
Nonthermal Melting of NĂŠel Order in the Hubbard Model
Symmetry-broken states such as magnetic order and superconductivity are the hallmark of complex properties in solids. An intriguing new direction in condensed-matter physics is to manipulate these properties on the fastest possible time scales using ultrashort laser pulses. Theoretically, however, the collective many-particle dynamics that is responsible for the formation and melting of long-range order is associated with many open questions.Here, we combine two state-of-the-art numerical techniquesâtime-dependent density matrix renormalization group and nonequilibrium dynamical mean-field theoryâto create a model system that represents interacting electrons on a bipartite lattice in which electrons can tunnel between sites. We prepare this model such that particles on neighboring sites initially align their magnetic moments in an antiparallel manner (i.e., representing antiferromagnetic order). The particles can then move between lattice sites, which leads to the melting of the magnetic order. We theoretically show that the precise movement mechanism depends strongly on the interaction between the particles: For strong interactions, the system behaves like a collection of localized magnetic moments. For weak interactions, on the other hand, the dynamics reflects the existence of coherent quasiparticles, which are typically restricted to excitations close to the ground state. In our case, these quasiparticles prevail on short times even though the system is strongly excited.Our setup, which is well suited for experiments using cold atoms, has the ability to reveal the crossover between localized and itinerant behavior. In the future, similar studies of systems with several active orbitals may make it possible to better understand how complex solids can relax into entirely newâand possibly thermodynamically hiddenâphases
The H.E.S.S. II GRB Program
Gamma-ray bursts (GRBs) are some of the most energetic and exotic events in
the Universe, however their behaviour at the highest energies (>10 GeV) is
largely unknown. Although the Fermi-LAT space telescope has detected several
GRBs in this energy range, it is limited by the relatively small collection
area of the instrument. The H.E.S.S. experiment has now entered its second
phase by adding a fifth telescope of 600 m mirror area to the centre of
the array. This new telescope increases the energy range of the array, allowing
it to probe the sub-100 GeV range while maintaining the large collection area
of ground based gamma-ray observatories, essential to probing short-term
variability at these energies. We will present a description of the GRB
observation scheme used by the H.E.S.S. experiment, summarising the behaviour
and performance of the rapid GRB repointing system, the conditions under which
potential GRB repointings are made and the data analysis scheme used for these
observations.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Role of material properties and mesostructure on dynamic deformation and shear instability in Al-W granular composites
Dynamic experiments with Al-W granular/porous composites revealed
qualitatively different behavior with respect to shear localization depending
on bonding between Al particles. Two-dimensional numerical modeling was used to
explore the mesomechanics of the large strain dynamic deformation in Al-W
granular/porous composites and explain the experimentally observed differences
in shear localization between composites with various mesostructures.
Specifically, the bonding between the Al particles, the porosity, the roles of
the relative particle sizes of Al and W, the arrangements of the W particles,
and the material properties of Al were investigated using numerical
calculations. It was demonstrated in simulations that the bonding between the
"soft" Al particles facilitated shear localization as seen in the experiments.
Numerical calculations and experiments revealed that the mechanism of the shear
localization in granular composites is mainly due to the local high strain flow
of "soft" Al around the "rigid" W particles causing localized damage
accumulation and subsequent growth of the meso/macro shear bands/cracks. The
"rigid" W particles were the major geometrical factor determining the
initiation and propagation of "kinked" shear bands in the matrix of "soft" Al
particles, leaving some areas free of extensive plastic deformation as observed
in experiments and numerical calculations.Comment: 10 pages, 14 figures, submitted to Journal of Applied Physic
Optimization of an Alkylpolyglucoside-Based Dishwashing Detergent Formulation.
The aim of this work was to formulate and optimize the washing performance of an alkylpolyglucoside-based dishwashing detergent. The liquid detergent was formulated with five ingredients of commercial origin: anionic (linear sodium alkylbenzenesulfonate and sodium laurylethersulfate), nonionic (C12âC14 alkylpolyglucoside) and zwitterionic (a fatty acid amide derivative with a betaine structure) surfactants, and NaCl for viscosity control. In addition to the plate test, other properties were investigated including ââcloud pointââ, viscosity, and emulsion stability. Statistical analysis software was used to generate a central composite experimental design. Then, a second order design and analysis of experiments approach, known as the Response Surface Methodology, was set up to investigate the effects of the five components of the formulation on the studied properties in the region covering plausible component ranges. The method proved to be efficient for locating the domains of concentrations where the desired properties were met
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