3,026 research outputs found
Spectroscopic and redox properties of amine-unctionalized K_2[Os-^(II)(bpy)(CN)_4] complexes
We report the first examples of amine-functionalized K_2[Os^(II)(bpy)(CN)_4] (bpy = 2,2'-bipyridine) complexes. The tetracyanoosmate complexes were prepared by UV irradiation (λ = 254 nm) of K_4[Os^(II)(CN)_6] and primary amine-functionalized bpy ligands in acidic aqueous media. The aqueous solution pH dependences of the spectroscopic and redox properties of 4,4'- and 5,5'-substituted complexes have been investigated. The pendant amine functional groups and coordinated cyanide ligands are basic sites that can be sequentially protonated, thereby allowing systematic tuning of electrochemical and optical spectroscopic properties
A method to polarise antiprotons in storage rings and create polarised antineutrons
An intense circularely polarised photon beam interacts with a cooled
antiproton beam in a storage ring. Due to spin dependent absorption cross
sections for the reaction gamma+antiproton > pi- + antineutron a built-up of
polarisation of the stored antiprotons takes place. Figures-of-merit around 0.1
can be reached in principle over a wide range of antiproton energies. In this
process antineutrons with Polarisation > 70% emerge. The method is presented
for the case of 300 MeV/c cooled antiproton beam
A regional atmosphere-ocean climate system model (CCLMv5.0clm7-NEMOv3.3-NEMOv3.6) over Europe including three marginal seas: On its stability and performance
The frequency of extreme events has changed, having a direct impact on human lives. Regional climate models help us to predict these regional climate changes. This work presents an atmosphereâocean coupled regional climate system model (RCSM; with the atmospheric component COSMO-CLM and the ocean component NEMO) over the European domain, including three marginal seas: the Mediterranean, North, and Baltic Sea. To test the model, we evaluate a simulation of more than 100 years (1900â2009) with a spatial grid resolution of about 25âkm. The simulation was nested into a coupled global simulation with the model MPI-ESM in a low-resolution configuration, whose ocean temperature and salinity were nudged to the oceanâice component of the MPI-ESM forced with the NOAA 20th Century Reanalysis (20CR). The evaluation shows the robustness of the RCSM and discusses the added value by the coupled marginal seas over an atmosphere-only simulation. The coupled system is stable for the complete 20th century and provides a better representation of extreme temperatures compared to the atmosphere-only model. The produced long-term dataset will help us to better understand the processes leading to meteorological and climate extremes
The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Nucleon
The Gerasimov-Drell-Hearn sum rule is one of several dispersive sum rules
that connect the Compton scattering amplitudes to the inclusive photoproduction
cross sections of the target under investigation. Being based on such universal
principles as causality, unitarity, and gauge invariance, these sum rules
provide a unique testing ground to study the internal degrees of freedom that
hold the system together. The present article reviews these sum rules for the
spin-dependent cross sections of the nucleon by presenting an overview of
recent experiments and theoretical approaches. The generalization from real to
virtual photons provides a microscope of variable resolution: At small
virtuality of the photon, the data sample information about the long range
phenomena, which are described by effective degrees of freedom (Goldstone
bosons and collective resonances), whereas the primary degrees of freedom
(quarks and gluons) become visible at the larger virtualities. Through a rich
body of new data and several theoretical developments, a unified picture of
virtual Compton scattering emerges, which ranges from coherent to incoherent
processes, and from the generalized spin polarizabilities on the low-energy
side to higher twist effects in deep inelastic lepton scattering.Comment: 32 pages, 19 figures, review articl
High energy neutrinos from a slow jet model of core collapse supernovae
It has been hypothesized recently that core collapse supernovae are triggered
by mildly relativistic jets following observations of radio properties of these
explosions. Association of a jet, similar to a gamma-ray burst jet but only
slower, allows shock acceleration of particles to high energy and non-thermal
neutrino emission from a supernova. Detection of these high energy neutrinos in
upcoming kilometer scale Cherenkov detectors may be the only direct way to
probe inside these astrophysical phenomena as electromagnetic radiation is
thermal and contains little information. Calculation of high energy neutrino
signal from a simple and slow jet model buried inside the pre-supernova star is
reviewed here. The detection prospect of these neutrinos in water or ice
detector is also discussed in this brief review. Jetted core collapse
supernovae in nearby galaxies may provide the strongest high energy neutrino
signal from point sources.Comment: 17 pages, 5 figures, invited brief revie
Desymmetrization of an octahedral coordination complex inside a self-assembled exoskeleton.
The synthesis of a centrally functionalized, ribbon-shaped [6]polynorbornane ligand L that self-assembles with Pd(II) cations into a {Pd2 L4 } coordination cage is reported. The shape-persistent {Pd2 L4 } cage contains two axial cationic centers and an array of four equatorial H-bond donors pointing directly towards the center of the cavity. This precisely defined supramolecular environment is complementary to the geometry of classic octahedral complexes [M(XY)6 ] with six diatomic ligands. Very strong binding of [Pt(CN)6 ](2-) to the cage was observed, with the structure of the host-guest complex {[Pt(CN)6 ]@Pd2 L4 } supported by NMR spectroscopy, MS, and X-ray data. The self-assembled shell imprints its geometry on the encapsulated guest, and desymmetrization of the octahedral platinum species by the influence of the D4h -symmetric second coordination sphere was evidenced by IR spectroscopy. [Fe(CN)6 ](3-) and square-planar [Pt(CN)4 ](2-) were strongly bound. Smaller octahedral anions such as [SiF6 ](2-) , neutral carbonyl complexes ([M(CO)6 ]; M=Cr, Mo, W) and the linear [Ag(CN)2 ](-) anion were only weakly bound, showing that both size and charge match are key factors for high-affinity binding
Self-Consistent Field study of Polyelectrolyte Brushes
We formulate a self-consistent field theory for polyelectrolyte brushes in
the presence of counterions. We numerically solve the self-consistent field
equations and study the monomer density profile, the distribution of
counterions, and the total charge distribution. We study the scaling relations
for the brush height and compare them to the prediction of other theories. We
find a weak dependence of the brush height on the grafting density.We fit the
counterion distribution outside the brush by the Gouy-Chapman solution for a
virtual charged wall. We calculate the amount of counterions outside the brush
and find that it saturates as the charge of the polyelectrolytes increases
Delta Excitations in Neutrino-Nucleus Scattering
We derive the contribution of -h excitations to quasielastic
charged-current neutrino-nucleus scattering in the framework of relativistic
mean-field theory. We discuss the effect of production on the
determination of the axial mass in neutrino scattering experiments.Comment: 14 pages, revtex, 3 postscript figures (available upon request
Exclusive measurement of coherent eta photoproduction from the deuteron
Coherent photoproduction of eta mesons from the deuteron has been measured
from threshold up to incident photon energies of 750 MeV using the photon
spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI.
For the first time, differential coherent cross sections have been deduced from
the coincident detection of the eta meson and the recoil deuteron. A missing
energy analysis was used for the suppression of background events so that a
very clean identification of coherent eta-photoproduction was achieved. The
resulting cross sections agree with previous experimental results except for
angles around 90 deg in the photon-deuteron cm-system where they are smaller.
They are compared to various model calculations.Comment: 4 pages, 4 figure
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