Reactivity of a N-Coordinated Germylene-Borane Complex: From Ge→B to Ge→Ga Coordination

Reactivity studies of the Ge^II→B complex L(Cl)Ge⋅BH₃ ( 1 ; L=2-Et₂NCH₂-4,6-tBu₂-C₆H₂) were performed to determine the effect on the Ge^II→B donation. N-coordinated compounds L(OtBu)Ge⋅BH₃ ( 2 ) and [LGe⋅BH₃]₂ ( 3 ) were prepared. The possible tuning of the Ge^II→B interaction was proved experimentally, yielding compounds 1-PPh₂-8-(LGe)-C₁₀H₆ ( 4 ) and L(Cl)Ge⋅GaCl₃ ( 5 ) without a Ge^II→B interaction. In 5 , an unprecedented Ge^II→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the Ge^II→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.     

Programming With Models: Writing Statistical Algorithms for General Model Structures With NIMBLE

We describe NIMBLE, a system for programming statistical algorithms for general model structures within R. NIMBLE is designed to meet three challenges: flexible model specification, a language for programming algorithms that can use different models, and a balance between high-level programmability and execution efficiency. For model specification, NIMBLE extends the BUGS language and creates model objects, which can manipulate variables, calculate log probability values, generate simulations, and query the relationships among variables. For algorithm programming, NIMBLE provides functions that operate with model objects using two stages of evaluation. The first stage allows specialization of a function to a particular model and/or nodes, such as creating a Metropolis-Hastings sampler for a particular block of nodes. The second stage allows repeated execution of computations using the results of the first stage. To achieve efficient second-stage computation, NIMBLE compiles models and functions via C++, using the Eigen library for linear algebra, and provides the user with an interface to compiled objects. The NIMBLE language represents a compilable domain-specific language (DSL) embedded within R. This article provides an overview of the design and rationale for NIMBLE along with illustrative examples including importance sampling, Markov chain Monte Carlo (MCMC) and Monte Carlo expectation maximization (MCEM). Supplementary materials for this article are available online.     

Probing the Local Reaction Environment During High Turnover Carbon Dioxide Reduction with Ag-Based Gas Diffusion Electrodes

Discerning the influence of electrochemical reactions on the electrode microenvironment is an unavoidable topic for electrochemical reactions that involve the production of OH⁻ and the consumption of water. That is particularly true for the carbon dioxide reduction reaction (CO₂RR), which together with the competing hydrogen evolution reaction (HER) exert changes in the local OH⁻ and H₂O activity that in turn can possibly affect activity, stability, and selectivity of the CO₂RR. We determine the local OH⁻ and H₂O activity in close proximity to a CO₂-converting Ag-based gas diffusion electrode (GDE) with product analysis using gas chromatography. A Pt nanosensor is positioned in the vicinity of the working GDE using shear-force-based scanning electrochemical microscopy (SECM) approach curves, which allows monitoring changes invoked by reactions proceeding within an otherwise inaccessible porous GDE by potentiodynamic measurements at the Pt-tip nanosensor. We show that high turnover HER/CO₂RR at a GDE lead to modulations of the alkalinity of the local electrolyte, that resemble a 16 m KOH solution, variations that are in turn linked to the reaction selectivity.     

Influence of surroundings on photorefractive effect in lithium niobate crystals

In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO₃ crystals on photorefractive effect induced in these crystals by Gaussian Ar⁺ laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO₃: Fe and LiNbO₃: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl₂). The space and time dependences of the refractive index changes induced by the Ar⁺ laser beam are observed by means of the Mach–Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction.     

Optical and microstructural properties of self-assembled InAs quantum structures in silicon

The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm^?1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs.     

1,2,4‐Triazole‐based N‐heterocyclic carbene complexes of gold(I): synthesis,characterization and biological activity

Two gold(I) complexes of the (NHC)AuX type bearing a triazole‐based N‐heterocyclic carbene (NHC) ligand (1‐tert‐butyl‐4‐(4‐methylphenyl)‐3‐phenyl‐1H‐1,2,4‐triazol‐4‐ium‐5‐ylidene) and various halide ligands (X = Br, I) were synthesized and characterized in solution using NMR spectroscopy as well as in the solid state using X‐ray diffraction techniques. The cytotoxic properties of both compounds and the precursor, (NHC)AuCl, were screened against a panel of human tumour cell lines including liver cancer (HepG2), cervical cancer (HeLa S3) and leukaemia (CCRF‐CEM, HL‐60) and compared to cisplatin and auranofin. It was found that the activities of the chloro and bromo derivatives were generally superior to that of cisplatin and slightly less effective compared to auranofin, except for HepG2 cells where auranofin was not as effective. In addition, the ability to induce membrane phosphatidyl serine externalization as a hallmark of apoptosis in CCRF‐CEM leukaemic cells was investigated. Copyright © 2016 John Wiley & Sons, Ltd.     

Driven dynamics and rotary echo of a qubit tunably coupled to a harmonic oscillator

We have investigated the driven dynamics of a superconducting flux qubit that is tunably coupled to a microwave resonator. We find that the qubit experiences an oscillating field mediated by off-resonant driving of the resonator, leading to strong modifications of the qubit Rabi frequency. This opens an additional noise channel, and we find that low-frequency noise in the coupling parameter causes a reduction of the coherence time during driven evolution. The noise can be mitigated with the rotary-echo pulse sequence, which, for driven systems, is analogous to the Hahn-echo sequence.     

On pressure separation algorithms (PSepA) for improving the accuracy of incompressible flow simulations

We investigate a special technique called ‘pressure separation algorithm’ (PSepA) (see Applied Mathematics and Computation 2005; 165 :275–290 for an introduction) that is able to significantly improve the accuracy of incompressible flow simulations for problems with large pressure gradients. In our numerical studies with the computational fluid dynamics package FEATFLOW ( www.featflow.de ), we mainly focus on low‐order Stokes elements with nonconforming finite element approximations for the velocity and piecewise constant pressure functions. However, preliminary numerical tests show that this advantageous behavior can also be obtained for higher‐order discretizations, for instance, with Q₂/P₁ finite elements. We analyze the application of this simple, but very efficient, algorithm to several stationary and nonstationary benchmark configurations in 2D and 3D (driven cavity and flow around obstacles), and we also demonstrate its effect to spurious velocities in multiphase flow simulations (‘static bubble’ configuration) if combined with edge‐oriented, resp., interior penalty finite element method stabilization techniques. Copyright © 2008 John Wiley & Sons, Ltd.