A study of the global distribution of sulfate aerosols with a 2D model including microphysics

Summary The global distribution of sulfate aerosols in the troposphere and lower stratosphere has been calculated using a two-dimensional model. The chemistry includes the main families (NO _x , NO _y , HO _x ) plus the sulfur compounds, while the heterogeneous processes are modelled with a microphysics code which takes into account nucleation, condensation and coagulation. The results are compared with experimental data wherever available. A too low concentration of sulfuric acid is predicted by the model in the troposphere and this is explained by too large a flux of condensation nuclei and partly by the absence of sulfate production from methane sulfuric acid (MSA) in our scheme. Aerosol concentration and size distribution are comparable to observations; however the calculations show a more complex meridional structure than observed, while the size distribution is somewhat shifted toward smaller sizes. This fact is also attributed to the presence of a large number of nuclei and to the absence of any mechanism for evaporation of aerosol particles back to the core. We have also perturbed the anthropogenic fluxes of SO₂, CS₂ and the OCS ground mixing ratios to asses the sensitivity of the aerosol concentration: we have found very little changes in the aerosol distribution because H₂SO₄ chemistry is dominated by heterogeneous processes.     

A multi-component reaction (MCR) approach to the synthesis of highly diverse polymers with polypeptide-like features

A new strategy for the combinatorial synthesis of new materials has been developed through the consecutive application of an Ugi 4CC reaction and a ring-opening metathesis polymerization (ROMP) reaction. Norbornenyl aldehydes and carboxylic acids could be used in the Ugi MCR to give highly diverse monomers that were converted to the corresponding polymers by exposure to the second-generation Grubbs' catalyst. These polymers have structural features reminiscent of polypeptides and the process could be extended to the preparation of chiral materials.     

The charge exchange of slow highly charged ions at surfaces unraveled with freestanding 2D materials

The property of a variable charge state makes ions unique to other types of radiation a material surface can be exposed to. As a consequence of charge exchange between ions and surfaces, energy is transferred to the surface and material damage may be triggered. Furthermore, a changing charge state of the ion alters its slowing down process in solids and has important implications when back-scattered ions are to be measured for material analysis purposes. Over the last decades extensive research was devoted to the understanding of ion charge exchange with solids. Here I review recent progress in this field with special emphasize on slow ions in high charge states. This class of ions allows a detailed analysis of charge exchange in experiments, which employ also ultra-thin solid targets and therefore give experimental access to electronic processes on the femtosecond timescale. In this review I will discuss general properties of charge exchange and present typical experimental techniques. I will also discuss current developments in the modelling and simulation of ion-surface interaction. Recent findings using freestanding 2D materials are discussed as well as results from spectroscopy of emitted secondary particles. The paper concludes with a unified picture of ion charge exchange at surfaces and presents possible applications based on the understanding of the underlying physics.     

A covariant approach to gauged 2D self-dual fields

We obtain a non-Abelian version of a theory involving vector and tensor gauge fields interacting via a massive topological coupling, besides the nonminimun one. The new fact is that the non-Abelian theory is not reducible and Stuckelberg fields are introduced in order to make compatible gauge invariance, nontrivial physical degrees of freedom and the limit of the Abelian case.     

A new approach to the charged current induced weak one-pion production

The weak one-pion production mechanism is analyzed in terms of resonant and non-resonant contributions coming from the πN invariant-mass region extended from threshold to 1.6 GeV/c². Together with the P₃₃, contributing to the $\text{I =}\text{3}\text{2}$ amplitude, the first $\text{I =}\text{1}\text{2}$ resonances (S₁₁, P₁₁, D₁₃) are also added to the background treated in the Born approximation. Form factors are explicitly extracted from PCAC and from existing fits to electroproduction data, so that the “free” parameters are essentially reduced to the axial masses of the resonances. In the calculation of the cross sections the resonance-background interference is explicitly worked out and its important rôle is stressed. The emerging picture is compared with the available data, which are in this way extensively reviewed, at low, intermediate and high energy. Good agreement is found, and in particular the experimentally observed increasing $\text{I =}\text{1}\text{2}$ contribution is justified by the model in terms of an increasing rôle of the 1.4 ? M_Nπ ? 1.6 GeV/c² invariant-mass region.     

Algebraic approach to the geometry of the (super-) string model

We discuss the extension of constraint algebras to include subsidiary constraints within a larger algebra. The interplay between various mathematical aspects of this procedure is described. Tools from Lie algebra cohomology and differential geometry are used to gain new insights into BRS techniques for nonabelian constrained systems. We show that cohomology considerations restrict our formalism to non-semisimple constraint algebras, such as the (super-) string model; we illustrate the ideas by presenting concrete results for this case.     

SU2 ⊗ U1 gauge model of electroweak interaction with (V + A) strangeness-changing charged current

We construct a model of renormalizable electroweak interaction with (V+A) strangeness-changing charged current in the framework of the minimal spontaneously broken SU₂ ⊗ U₁ gauge theory, taking our motivation from the recently reported measurement of the electron asymmetry in polarizedΣ ⁻-hyperonβ-decay by Keller and co-workers. The model avoids strangeness-changing but admits charm-changing pieces in the neutral current. Several phenomenological consequences of the model are discussed together with a comparison with the standard model of electroweak interaction.     

Photoelectron spectroscopy verification of highly charged silver ions in the ethylenebis(biguanide)-silver(III) complex ion

Photoelectron spectroscopy has established that a highly charged silver ion exists in the ethylenebis(biguanide)silver(III) ion.     

Hamiltonian map approach to 1D Anderson model

A one-dimensional diagonal tight binding electronic system is analyzed with the Hamiltonian map approach to study analytically the inverse localization length of an infinite sample. Both the uncorrelated and the dichotomic correlated random potential sequences are considered in the evaluations of the inverse localization length. Analytical expressions for the invariant measure or the angle density distribution are the main motivation of this work in order to derive analytical results. The well-known uncorrelated weak disorder result of the inverse localization length is derived with a clear procedure. In addition, an analytical expression for high disorder is obtained near the band edge. It is found that the inverse localization length goes to 1 in this limit. Following the procedure used in the uncorrelated situation, an analytical expression for the inverse localization length is also obtained for the dichotomic correlated sequence in the small disorder situation.     

A laser system for the spectroscopy of highly charged bismuth ions

We present and characterize a laser system for the spectroscopy on highly charged ²⁰⁹Bi⁸²⁺ ions at a wavelength of 243.87?nm. For absolute frequency stabilization, the laser system is locked to a near-infra-red laser stabilized to a rubidium transition line using a transfer cavity based locking scheme. Tuning of the output frequency with high precision is achieved via a tunable rf offset lock. A?sample-and-hold technique gives an extended tuning range of several THz in the UV. This scheme is universally applicable to the stabilization of laser systems at wavelengths not directly accessible to atomic or molecular resonances. We determine the frequency accuracy of the laser system using Doppler-free absorption spectroscopy of Te₂ vapor at 488?nm. Scaled to the target wavelength of 244 nm, we achieve a frequency uncertainty of σ _{244 nm}=6.14?MHz (one standard deviation) over six days of operation.     

MC model of Auger spectra from highly charged ion beam surface interaction

Abstract

A Monte Carlo code is described which simulates angle resolved Auger electron energy spectra from highly charged ion surface interaction. The combined effect of the Doppler spread of laboratory emission energy and electron scattering by the solid, together with the broad inherent line width, is found to have considerable influence on the spectral lines. As a new feature, low or high energy shoulders can appear. By comparison between simulated and measured spectra information on the kinematic and electronic state of the projectile ions in the moment of electron emission can be extracted. The standard method of spectrum analysis, which is based on the assumption of direct escape of the electrons, is evaluated with respect to the simulated spectra.     

Dissociative ionization of the H2O molecule bombarded by swift singly charged and slow highly charged ions

Fragment ion energy spectra of the water molecule have been measured in conventional crossed-beam experiments by the impact of 46 keV/u energy, singly charged ions (SCIs) and 4.3 keV/u energy, highly charged ions (HCIs). Double differential cross sections have been determined and a comparative analysis has been performed. We found that the fragmentation spectra for SCIs and HCIs are very similar, indicating that both collisions lead to the same fragmentation channels. This suggests that the Coulomb explosion of the water molecule is dominantly determined by the charge state of the transient molecular ions, and it is almost independent from the primary ionization mechanism. Differences were observed not only between the SCI and HCI impact-induced fragmentation cross sections, but between those obtained by the 60 keV N⁶⁺ and 70 keV O⁷⁺ projectiles. The differences were attributed to the selectivity of the electron capture process for HCIs. Multiple target ionization cross sections have been deduced from the fragment ion spectra. We found contributions of up to fivefold ionization for SCIs and up to sixfold ionization for HCIs.     

Analysis of charged device model (CDM) ESD in MEMS

The effect of charge injection due to CDM ESD in capacitive MEMS structures is analyzed. The results show that as feature size is reduced, ESD injected charge produces a change for the stiction effect which is inversely proportional to the square of the plate area and a change in the dielectric layer breakdown which is inversely proportional to the plate area. An electric field model is developed to examine charge and voltage modes in MEMS. A charge injection test method is proposed to determine the susceptibility of MEMS to CDM ESD.     

The $$SO(3,1) \times U(1)$$-gauge invariant approach to charged bosons in relativistic magnetars

Using a perturbative method, we investigate solutions of the Klein–Gordon equations for a charged massive field in the background of a magnetar, both in the interior solution and outside the star. A special attention is given to cases where the variables can be separated and the wave function is expressed in terms of the Heun’s general or confluent functions. By imposing various conditions on the parameters, one gets the energy quantization law and simple polynomial forms of the Heun’s functions, which can be used in computing first-order transition amplitudes.     

D* D_1(2420) and D D'*(2600) interactions and the charged charmonium-like state Z(4430)

The D* D_1(2420) and DD '*(2600) interactions are studied in a one-boson-exchange model. Isovector bound state solutions with spin parity J~P= 1~+are found from the D* D_1(2420) interaction, which may be related to the observed charged charmonium-like state Z(4430). There is no bound state solution found from the DD '*(2600)interaction.     

A simple approach to the synthesis of highly functionalized pyrrole derivatives

The reaction of dibenzoylacetylene and enaminocarbonyl compounds leads to 3-alkylidene-2,3-dihydro-1H-pyrrol-2-ol derivatives in nearly quantitative yields. The reaction of this heterocyclic system with alcohols in the presence of a catalytic amount of HCl produces highly functionalized pyrroles in good yields.     

Regge approach to charged pion photoproduction at invariant energies above 2 GeV

A Regge model with absorptive corrections is employed in a global analysis of the world data on positive and negative pion photoproduction for photon energies from 3 to 8GeV. In this region resonance contributions are expected to be negligible so that the available experimental information on differential cross-sections and single polarization observables at - t ⩽ 2 GeV^2 allows us to determine the non-resonant part of the reaction amplitude reliably. The model amplitude is then used to predict observables for photon energies below 3GeV. Differences between our predictions and data in this energy region are systematically examined as possible signals for the presence of excited baryons. We find that the data available for the polarized photon asymmetry show promising resonance signatures at invariant energies around 2GeV. With regard to differential cross-sections the analysis of negative pion photoproduction data, obtained recently at JLab, indicates likewise the presence of resonance structures around 2GeV.     

Defect mediated desorption of the KBr(001) surface induced by single highly charged ion impact

The individual impacts of slow (300 eV/amu) highly charged Xe ions induce nanometer sized pitlike structures on the KBr (001) surface. The volume of these structures shows a strong dependence on the ions potential energy. Total potential sputter yields from atomically flat (001) terraces are determined by imaging single ion impact sites. The dependence of the sputter yield on the ions initial charge state combined with structure formation at low and high-fluence irradiations indicates that agglomeration of defects into complex centers plays a major role in the desorption process induced by the potential energy.