Methyldicarboxylatostibane und -bismutane

Methyldicarboxylatostibanes and -bismuthanes These compounds are received either by reacting of Methyldibromostibanes and -bismuthanes with Sodium-carboxylates or by reacting Diethoximethylstibane and -bismuthane with the free acids.     

Hypervalent iodine chemistry in synthesis: scope and new directions

The impressive development of hypervalent iodine chemistry in recent years is reflected by the number of publications in this area. Although the synthesis of the first hypervalent iodine compound dates back more than 100 years, the investigation of the reactivities of these compounds and their efficient use as metal-free reagents in organic synthesis is still ongoing. This contribution summarizes recent achievements and highlights key findings and developments that will influence future research and lead to novel applications of hypervalent iodine reagents in synthesis.     

Molecular and cluster structures in 18O

We have studied the multi-nucleon transfer reaction ¹²C ( ⁷Li ,p) at E _lab = 44 MeV, populating states in the oxygen isotope ¹⁸O . The experiments were performed at the Tandem accelerator of the Maier-Leibniz Laboratory in Munich using the high-resolution Q3D magnetic spectrograph. States were populated up to an excitation energy of 21.2MeV with an overall energy resolution of 45keV, and 30 new states of ¹⁸O have been identified. The structure of the rotational bands observed is discussed in terms of cluster bands with the underlying cluster structures: ¹⁴C$ $\displaystyle \otimes$ $\displaystyle \alpha$ $and 12C ? 2n ? $ \alpha$ . Because of the broken intrinsic reflection symmetry in these structures the corresponding rotational bands appear as parity doublets.     

Random telegraph signals with time dependent capture and emission probabilities: Analytical and numerical results

In this work, we study the noise spectra of random telegraph signals (RTS) with time dependent capture and emission probabilities. The capture and emission probabilities are made time dependent by cyclo-stationary excitation. Rigorous analytical calculations are performed to derive the model equations, and Monte Carlo simulations are performed to explore the noise behavior and validate the analytical model. Two study cases are explored: input signals modeled by periodic square wave and sinusoidal waves. We present clear situations where the integrated noise power is smaller than stationary case for a suitable choice of parameters in both cyclo-stationary inputs studied.     

Molecular dynamics simulation of the interaction between a mixed dislocation and a stacking fault tetrahedron

A high number-density of nanometer-sized stacking fault tetrahedra are commonly found during irradiation of low stacking fault energy metals. The stacking fault tetrahedra act as obstacles to dislocation motion leading to increased yield strength and decreased ductility. Thus, an improved understanding of the interaction between gliding dislocations and stacking fault tetrahedra are critical to reliably predict the mechanical properties of irradiated materials. Many studies have investigated the interaction of a screw or edge dislocation with a stacking fault tetrahedron (SFT). However, atomistic studies of a mixed dislocation interaction with an SFT are not available, even though mixed dislocations are the most common. In this paper, molecular dynamics simulation results of the interaction between a mixed dislocation and an SFT in face-centered cubic copper are presented. The interaction results in shearing, partial absorption, destabilization or simple bypass of the SFT, depending on the interaction geometry. However, the SFT was not completely annihilated, absorbed or collapsed during a single interaction with a mixed dislocation. These observations, combined with simulation results of edge or screw dislocations, suggest that defect-free channel formation in irradiated copper is not likely by a single dislocation sweeping or destruction process, but rather by a complex mix of multiple shearing, partial absorption and defect cluster transportation that ultimately reduces the size of stacking fault tetrahedra within a localized region.     

Study of defect evolution by TEM with in situ ion irradiation and coordinated modeling

The paper describes a novel transmission electron microscopy (TEM) experiment with in situ ion irradiation designed to improve and validate a computer model. TEM thin foils of molybdenum were irradiated in situ by 1?MeV Kr ions up to ～0.045 displacements per atom (dpa) at 80°C at three dose rates ?5?×?10^?6, 5?×?10^?5, and 5?×?10^?4?dpa/s – at the Argonne IVEM-Tandem Facility. The low-dose experiments produced visible defect structure in dislocation loops, allowing accurate, quantitative measurements of defect number density and size distribution. Weak beam dark-field plane-view images were used to obtain defect density and size distribution as functions of foil thickness, dose, and dose rate. Diffraction contrast electron tomography was performed to image defect clusters through the foil thickness and measure their depth distribution. A spatially dependent cluster dynamic model was developed explicitly to model the damage by 1?MeV Kr ion irradiation in an Mo thin foil with temporal and spatial dependence of defect distribution. The set of quantitative data of visible defects was used to improve and validate the computer model. It was shown that the thin foil thickness is an important variable in determining the defect distribution. This additional spatial dimension allowed direct comparison between the model and experiments of defect structures. The defect loss to the surfaces in an irradiated thin foil was modeled successfully. TEM with in situ ion irradiation of Mo thin foils was also explicitly designed to compare with neutron irradiation data of the identical material that will be used to validate the model developed for thin foils.     

In-situ transmission electron microscopy observations and molecular dynamics simulations of dislocation-defect interactions in ion-irradiated copper

An in-situ transmission electron microscopy straining technique has been used to investigate the dynamics of dislocation-defect interactions in ion-irradiated copper and the subsequent formation of defect-free channels. Defect removal frequently required interaction with multiple dislocations, although screw dislocations were more efficient at annihilating defects than edge dislocations were. The defect pinning strength was determined from the dislocation curvature prior to breakaway and exhibited values ranging from 15 to 175 MPa. Pre-existing dislocations percolated through the defect field but did not show long-range motion, indicating that they are not responsible for creating the defect-free channels and have a limited contribution to the total plasticity. Defect-free channels were associated with the movement of many dislocations, which originated from grain boundaries or regions of high stress concentration such as at a crack tip. These experimental results are compared with atomistic simulations of the interaction of partial dislocations with defects in copper and a dispersed-barrier-hardening crystal plasticity model to correlate the observations to bulk mechanical properties.     

Development of an OPO system at 1.57 μm for integrated path DIAL measurement of atmospheric carbon dioxide

Active remote sensing is a promising technique to close the gaps that exist in global measurement of atmospheric carbon dioxide sources, sinks and fluxes. Several approaches are currently under development. Here, an experimental setup of an integrated path differential absorption lidar (IPDA) is presented, operating at 1.57 μm using direct detection. An injection seeded KTP-OPO system pumped by a Nd:YAG laser serves as the transmitter. The seed laser is actively stabilized by means of a CO₂ reference cell. The line-narrowed OPO radiation yields a high spectral purity, which is measured by means of a long path absorption cell. First measurements of diurnal variations of the atmospheric CO₂ mixing ratio using a topographic target were performed and show good agreement compared to simultaneously taken measurements of an in situ device. A further result is that the required power reference measurement of each laser pulse in combination with the spatial beam quality is a critical point of this method. The system described can serve as a testbed for further investigations of special features of the IPDA technique. PACS  42.65.Yj; 42.68.Wt; 92.60.hg