A novel 2D vanadium(V)-isonicotinohydrazide coordination polymer, C15H16AgN4O8V: Synthesis, structure, catalytic activity and DFT calculation

A novel two-dimensional 3d-4d transition metal-based coordination polymer [VO(OCH₃)(OHCH₃)(L)Ag(NO₃)]_∞ (1) has been synthesized and characterized by single crystal X-ray diffraction and fluorescence spectroscopy (H₂L = (E)-N′-(2-hydroxybenzylidene)isonicotinohydrazide). The coordination sphere of each V center is octahedral and chelates to a tridentate ligand L, while the tetrahedral conformation of Ag center consists of two O and two N atoms. Infinite zigzag chains of Ag-tetrahedrals are formed. The hydrazinide L²⁻ ligands of octahedral-V centers link adjacent chains to form an undulated heterometal based 2D layer. DFT calculations on 1 reproduced the geometric parameters and the electronic absorptions were predicted. The coordination polymer 1 showed very selective heterogeneous catalytic activity with 77-89% conversion in oxidation of alkenes, cyclooctane and benzyl alcohol by H₂O₂.     

Computing logarithms digit-by-digit

In this work, we present an algorithm for computing logarithms of positive real numbers, that bears structural resemblance to the elementary school algorithm of long division. Using this algorithm, we can compute successive digits of a logarithm using a 4-operation pocket calculator. The algorithm makes no use of Taylor series or calculus, but rather exploits properties of the radix-d representation of a logarithm in base d. As such, the algorithm is accessible to anyone familiar with the elementary properties of exponents and logarithms.     

A numerical study of highly-diluted,burner-stabilised dimethyl ether flames

Recently, a new burner was designed by Zhang et al. (Proc. Combust. Inst. 34 [2013], 763–770) to enable the investigation of 1D, premixed flames at atmospheric pressure with a temperature in the burnt gases near 1500 K. It consists of a matrix burner plate with alternating fuel and oxidiser feeds that, because of small-scale nozzles, mix quite rapidly. Flames at high dilution and reduced temperatures such as realised here are of relevance for the understanding of low-temperature combustion strategies. In this work, we examine the burner with regard to the validity of the 1D assumption for the investigated flames. Experimental measurements are conducted and 1D and 3D simulations are performed in which the chemistry is described by a detailed chemistry approach based on a reduced reaction scheme derived from the mechanism of Fischer et al. (Int. J. Chem. Kinetics 32 [2000], 713–740). The experimental results are compared to 1D simulations with two different temperature treatments. First, the unburnt temperature is set to the measured temperature closest to the burner surface; second, the experimental temperature profile is prescribed in the whole simulation domain without solving the energy equation. The comparison shows that the 1D simulation predicts the experimental results reasonably well, if the experimentally obtained temperature profile is prescribed in the simulation domain. Differences are found in the mole fractions of methyl and formaldehyde. Further comparisons of the experimental data with 3D simulation results and comparisons of 3D and 1D simulation results indicate that the differences between measured and computed mole fractions of these species are not a result of the 3D nature of the experimental flame and might be attributed to the chemical mechanism. The conclusion is that the measurement data can be used for validation purposes with the 1D simulation setup shown here if the measured temperature profiles are prescribed in the 1D simulation domain.     

Reporting requirements for sulphur isotope measurements on environmental samples†

It is strongly encouraged that authors reporting sulphur isotope data for environmental samples provide detailed information regarding (1) the reproducibility of their extraction procedure for the sulphur compound of interest, (2) the measuring gas and mass spectrometer technique used, and (3) the δ³⁴S values assigned for the reference materials utilised in the study. This would greatly facilitate comparisons of sulphur isotope data generated in different laboratories world-wide.     

Comparison of sample preparation methods for stable isotope analysis of dissolved sulphate in forested watersheds

Pretreatment methods for measuring stable sulphur (δ³⁴S) and oxygen (δ¹⁸O) isotope ratios of dissolved sulphate from watersheds have evolved throughout the last few decades. The current study evaluated if there are differences in the measured stable S and O isotope values of dissolved sulphate from forested watersheds when pretreated using three different methods: Method 1 (M1): adsorb sulphate on anion exchange resins and send directly to isotope facility; Method 2 (M2): adsorb sulphate on anion exchange resins, extract sulphate from anion exchange resins, and send the produced BaSO₄ to the isotope facility; and Method 3 (M3): directly precipitate BaSO₄ without anion exchange resins with the precipitates being sent to the isotope facility. We found an excellent agreement of the δ³⁴S_sulphate values among all the three methods. However, some differences were observed in the δ¹⁸O_sulphate values (M1 versus M2:?1.5 ‰; M1 versus M3:?1.2 ‰) associated with possible O contamination before isotope measurement. Several approaches are recommended to improve the pretreatment procedures for δ¹⁸O_sulphate analysis.     

The feasibility of assessing branched-chain amino acid metabolism in cellular models of prostate cancer with hyperpolarized [1-C]-ketoisocaproate

Recent advancements in the field of hyperpolarized ¹³C magnetic resonance spectroscopy (MRS) have yielded powerful techniques capable of real-time analysis of metabolic pathways. These non-invasive methods have increasingly shown application in impacting disease diagnosis and have further been employed in mechanistic studies of disease onset and progression. Our goals were to investigate branched-chain aminotransferase (BCAT) activity in prostate cancer with a novel molecular probe, hyperpolarized [1-¹³C]-2-ketoisocaproate ([1-¹³C]-KIC), and explore the potential of branched-chain amino acid (BCAA) metabolism to serve as a biomarker. Using traditional spectrophotometric assays, BCAT enzymatic activities were determined in vitro for various sources of prostate cancer (human, transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse and human cell lines). These preliminary studies indicated that low levels of BCAT activity were present in all models of prostate cancer but enzymatic levels are altered significantly in prostate cancer relative to healthy tissue. The MR spectroscopic studies were conducted with two cellular models (PC-3 and DU-145) that exhibited levels of BCAA metabolism comparable to the human disease state. Hyperpolarized [1-¹³C]-KIC was administered to prostate cancer cell lines, and the conversion of [1-¹³C]-KIC to the metabolic product, [1-¹³C]-leucine ([1-¹³C]-Leu), could be monitored via hyperpolarized ¹³C MRS.     

Application of double spin echo spiral chemical shift imaging to rapid metabolic mapping of hyperpolarized [1-¹³C]-pyruvate

Undersampled spiral CSI (spCSI) using a free induction decay (FID) acquisition allows sub-second metabolic imaging of hyperpolarized 13C. Phase correction of the FID acquisition can be difficult, especially with contributions from aliased out-of-phase peaks. This work extends the spCSI sequence by incorporating double spin echo radiofrequency (RF) pulses to eliminate the need for phase correction and obtain high quality spectra in magnitude mode. The sequence also provides an added benefit of attenuating signal from flowing spins, which can otherwise contaminate signal in the organ of interest. The refocusing pulses can potentially lead to a loss of hyperpolarized magnetization in dynamic imaging due to flow of spins through the fringe field of the RF coil, where the refocusing pulses fail to provide complete refocusing. Care must be taken for dynamic imaging to ensure that the spins remain within the B?-homogeneous sensitive volume of the RF coil.     

Wave attenuation in microcrystal copper at irradiation by a powerful electron beam

The numerical study of high-rate plasticity of Cu target with different grain sizes under the action of nanosecond relativistic high-current electron beam has been carried out in the paper. The model of microcrystal material plasticity includes dislocation kinetics and dynamics as well as the stress relief in the grain boundaries of the polycrystal. This model has only two adjustable parameters. The presented results demonstrate a strong dependence of the shock wave attenuation coefficient on the grain size. At the grain size of about 70 nm, the plasticity mechanism of the dislocation glide inside grains changes to plasticity mechanism along grain boundaries.