CuBr-Ne-HBr laser with a high repetition frequency of the lasing pulses at a reduced energy deposition in the discharge

Experimental and computer studies of the CuBr laser with periodic-pulse pumping are performed with and without addition of HBr. The analysis based on the numerical simulation reveals how additions improve the lasing characteristics of this laser at both typical (10 to 20 kHz) and higher (up to 100 kHz) excitation pulse repetition frequencies during the operation with a low energy deposition in the discharge. This allows the lasing pulse repetition frequency to be increased in the experiment to 750 kHz, which does not seem to be a limit as yet.     

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

Top‐down mass spectrometry of intact phosphorylated β‐casein: Correlation between the precursor charge state and internal fragments

Phosphorylated proteins play essential roles in many cellular processes, and identification and characterization of the relevant phosphoproteins can help to understand underlying mechanisms. Herein, we report a collision‐induced dissociation top‐down approach for characterizing phosphoproteins on a quadrupole time‐of‐flight mass spectrometer. β‐casein, a protein with two major isoforms and five phosphorylatable serine residues, was used as a model. Peaks corresponding to intact β‐casein ions with charged states up to 36⁺ were detected. Tandem mass spectrometry was performed on β‐casein ions of different charge states (12⁺, and 15⁺ to 28⁺) in order to determine the effects of charge state on dissociation of this protein. Most of the abundant fragments corresponded to y, b ions, and internal fragments caused by cleavage of the N‐terminal amide bond adjacent to proline residues (Xxx‐Pro). The abundance of internal fragments increased with the charge state of the protein precursor ion; these internal fragments predominantly arose from one or two Xxx‐Pro cleavage events and were difficult to accurately assign. The presence of abundant sodium adducts of β‐casein further complicated the spectra. Our results suggest that when interpreting top‐down mass spectra of phosphoproteins and other proteins, researchers should consider the potential formation of internal fragments and sodium adducts for reliable characterization.     

A Pseudo MS<Superscript>3</Superscript> Approach for Identification of Disulfide-Bonded Proteins: Uncommon Product Ions and Database Search

It has previously been reported that disulfide and backbone bonds of native intact proteins can be concurrently cleaved using electrospray ionization (ESI) and collision-induced dissociation (CID) tandem mass spectrometry (MS/MS). However, the cleavages of disulfide bonds result in different cysteine modifications in product ions, making it difficult to identify the disulfide-bonded proteins via database search. To solve this identification problem, we have developed a pseudo MS³ approach by combining nozzle-skimmer dissociation (NSD) and CID on a quadrupole time-of-flight (Q-TOF) mass spectrometer using chicken lysozyme as a model. Although many of the product ions were similar to those typically seen in MS/MS spectra of enzymatically derived peptides, additional uncommon product ions were detected including c_i-1 ions (the i^th residue being aspartic acid, arginine, lysine and dehydroalanine) as well as those from a scrambled sequence. The formation of these uncommon types of product ions, likely caused by the lack of mobile protons, were proposed to involve bond rearrangements via a six-membered ring transition state and/or salt bridge(s). A search of 20 pseudo MS³ spectra against the Gallus gallus (chicken) database using Batch-Tag, a program originally designed for bottom up MS/MS analysis, identified chicken lysozyme as the only hit with the expectation values less than 0.02 for 12 of the spectra. The pseudo MS³ approach may help to identify disulfide-bonded proteins and determine the associated post-translational modifications (PTMs); the confidence in the identification may be improved by incorporating the fragmentation characteristics into currently available search programs.     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.