Positron Emission Intensity in the Decay of 86gY for Use in Dosimetry Studies

The β⁺-emitting radionuclide ^86gY (t_1/2 = 14.7 h) forms a matched-pair with the β⁻-emitting therapeutic radionuclide ⁹⁰Y (t_1/2 = 2.7 d) for theranostic application in medicine. This approach demands a precise knowledge of the positron emission probability of the PET nuclide which was until recently rather uncertain for ^86gY. In this work, an ^86gY source of high radionuclidic purity was prepared and a direct measurement of the positron emission intensity per 100 decay of the parent (hereafter “positron emission intensity”) was performed using high-resolution HPGe detector γ-ray spectroscopy. The electron capture intensity was also determined as an additional check by measuring the K_α and K_β X-rays of energies 14.1 and 15.8 keV, respectively, using a low energy HPGe detector. From those measurements, normalized values of 27.2 ± 2.0% for β⁺-emission and 72.8 ± 2.0% for EC were obtained. These results are in excellent agreement with values recently reported in the literature based on a detailed decay scheme study.     

Simultaneous Assessment of Kinetic,Site‐Specific,and Structural Aspects of Enzymatic Protein Phosphorylation

Protein phosphorylation is a widespread process forming the mechanistic basis of cellular signaling. Up to now, different aspects, for example, site‐specificity, kinetics, role of co‐factors, and structure–function relationships have been typically investigated by multiple techniques that are incompatible with one another. The approach introduced here maximizes the amount of information gained on protein (complex) phosphorylation while minimizing sample handling. Using high‐resolution native mass spectrometry on intact protein (assemblies) up to 150 kDa we track the sequential incorporation of phosphate groups and map their localization by peptide LC‐MS/MS. On two model systems, the protein kinase G and the interplay between Aurora kinase A and Bora, we demonstrate the simultaneous monitoring of various aspects of the phosphorylation process, namely the effect of different cofactors on PKG autophosphorylation and the interaction of AurA and Bora as both an enzyme–substrate pair and physical binding partners.     

Synthesis and Characterisation of Fluorescent Carbon Nanodots Produced in Ionic Liquids by Laser Ablation

Carbon nanodots (C‐dots) with an average size of 1.5 and 3.0 nm were produced by laser ablation in different imidazolium ionic liquids (ILs), namely, 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate (BMI.BF₄), 1‐n‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf₂) and 1‐n‐octyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (OMI.NTf₂). The mean size of the nanoparticles is influenced by the imidazolium alkyl side chain but not by the nature of the anion. However, by varying the anion (BF₄ vs. NTf₂) it was possible to detect a significant modification of the fluorescence properties. The C‐dots are much probably stabilised by an electrostatic layer of the IL and this interaction has played an important role with regard to the formation, stabilisation and photoluminescence properties of the nanodots. A tuneable broadband fluorescence emission from the colloidal suspension was observed under ultraviolet/visible excitation with fluorescence lifetimes fitted by a multi‐exponential decay with average values around 7 ns.     

Neutral kaon production inK + p and π+ p interactions at 250 GeV/c

The inclusive production of neutral kaons is studied inK ⁺ p and π⁺ p interactions at 250 GeV/c. Total and semi-inclusive cross sections and average kaon multiplicities are presented and compared with the data at lower energies. The longitudinal and transverse momentum distributions and their energy dependence are analyzed. The results are interpreted in the framework of recent parton models.     

Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State,Geometric Structure,and Catalytic Selectivity using Operando Spectroscopy

The direct electrochemical conversion of carbon dioxide (CO₂) into multi-carbon (C₂₊) products still faces fundamental and technological challenges. While facet-controlled and oxide-derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu₂O nanocubes during operation in low-current H-Cells and in high-current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C₂₊ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C₁ products. Operando XAS and time-resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu-seeds during the surprisingly slow reduction of bulk Cu₂O. The initially (100)-rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide-derived generation of under-coordinated lattice defects, can support the high C₂₊ product yields.     

Modeling light trapping and electronic transport of waffle-shaped crystalline thin-film Si solar cells

Monocrystalline Si films from the novel perforated-Si process are candidates for the fabrication of thin-film solar cells because their waffle shape enhances the optical absorption and hence permits the use of films with a thickness of only a few microns. We study the optics of waffle cells by three-dimensional Monte Carlo ray-tracing. A high photogeneration of 38 mA/cm² from a film of thickness W_f=4 μm is possible due to a detached Al-back surface reflector that has an effective reflectance of 99.7% at 1250 nm. Our analytical model for light trapping in thin films explains this high reflectance. Two-dimensional numerical transport modeling reveals the existence of an optimum texture period p≈2W_f that originates from a carrier collection efficiency that increases with texture period while the photogeneration decreases with period. For well-passivated cells the optimum thickness W_f is at least one fifth of the diffusion length L. Efficiencies of 17% to 18% are feasible with waffle films of 1 to 3 μm in thickness. We introduce an analytic model for the minority carrier transport that agrees with two-dimensional numerical modeling to within 10% and reduces the computation time by orders of magnitude. This analytic model is also applicable to conformal thin-film geometries differing from the waffle geometry. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999