Two-gram DTA as a thermal compatibility tool

A useful alternative to the standard techniques described by the North American Treaty Organization STANAG 4147 for determining thermal compatibilities of an energetic with other materials could be a simple 2-gram scale Differential Thermal Analysis (2gDTA). The 2gDTA system consists of samples introduced into standard size test tubes inserted into a controlled aluminum-heating block. Relatively inexpensive thermocouples are used for both temperature control and data collection. Cost of the entire system is much less than any commercial DSC. Since valuable instrumentation need not be protected, the 2gDTA allows thermal decomposition reactions to proceed to complete runaway, mimicking the true worst-case scenario.     

An efficient and numerically correct algorithm for the 2D convex hull problem

An efficient and numerically correct program called FastHull for computing the convex hulls of finite point sets in the plane is presented. It is based on the Akl-Toussaint algorithm and the MergeHull algorithm. Numerical correctness of the FastHull procedure is ensured by using special routines for interval arithmetic and multiple precision arithmetic. The FastHull algorithm guaranteesO(N logN) running time in the worst case and has linear time performance for many kinds of input patterns. It appears that the FastHull algorithm runs faster than any currently known 2D convex hull algorithm for many input point patterns.     

High-Throughput Proteomics Enabled by a Photocleavable Surfactant

Mass spectrometry (MS)-based proteomics provides unprecedented opportunities for understanding the structure and function of proteins in complex biological systems; however, protein solubility and sample preparation before MS remain a bottleneck preventing high-throughput proteomics. Herein, we report a high-throughput bottom-up proteomic method enabled by a newly developed MS-compatible photocleavable surfactant, 4-hexylphenylazosulfonate (Azo) that facilitates robust protein extraction, rapid enzymatic digestion (30 min compared to overnight), and subsequent MS-analysis following UV degradation. Moreover, we developed an Azo-aided bottom-up method for analysis of integral membrane proteins, which are key drug targets and are generally underrepresented in global proteomic studies. Furthermore, we demonstrated the ability of Azo to serve as an “all-in-one” MS-compatible surfactant for both top-down and bottom-up proteomics, with streamlined workflows for high-throughput proteomics amenable to clinical applications.     

On the relationship between critical tensile stress and fracture toughness in mild steel

An analysis is presented which relates the critical value of tensile stress (σ_f) for unstable cleavage fracture to the fracture toughness (K_Ic) for a high-nitrogen mild steel under plane strain conditions. The correlation is based on (i) the model for cleavage cracking developed by E. Smith and (ii) accurate plastic-elastic solutions for the stress distributions ahead of a sharp crack derived by J. R. Rice and co-workers. Unstable fracture is found to be consistent with the attainment of a stress intensification close to the tip such that the maximum principal stress σ_yy exceeds σ_f over a characteristic distance, determined as twice the grain size. The model is seen to predict the experimentally determined variation of K_Ic with temperature over the range -150 to -75°C from a knowledge of the yield stress and hardening properties. It is further shown that the onset of fibrous fracture ahead of the tip can be deduced from the position of the maximum achievable stress intensification. The relationship between the model for fracture ahead of a sharp crack, and that ahead of a rounded notch, is discussed in detail.     

A measure of independence for a multivariate normal distribution and some connections with factor analysis

This paper gives results for the population value of a measure of the goodness-of-fit of a general multivariate normal distribution to the simpler hypothesis of independent normal variables. The measure was introduced by Rudas, Clogg and Lindsay in 1994, who gave the value for the bivariate normal distribution. Connections with factor analysis are briefly discussed.     

Preparation of a family of hexanuclear rhenium cluster complexes containing 5-(phenyl)tetrazol-2-yl ligands and alkylation of 5-substituted tetrazolate ligands

The preparation of two new families of hexanuclear rhenium cluster complexes containing benzonitrile and phenyl-substituted tetrazolate ligands is described. Specifically, we report the preparation of a series of cluster complexes with the formula [Re(6)Se(8)(PEt(3))(5)L](2+) where L = benzonitrile, p-aminobenzonitrile, p-methoxybenzonitrile, p-acetylbenzonitrile, or p-nitrobenzonitrile. All of these complexes undergo a [2 + 3] cycloaddition with N(3)(-) to generate the corresponding [Re(6)Se(8)(PEt(3))(5)(5-(p-X-phenyl)tetrazol-2-yl)](+) (or [Re(6)Se(8)(PEt(3))(5)(2,5-p-X-phenyltetrazolate)](+)) cluster complexes, where X = NH(2), OMe, H, COCH(3), or NO(2). Crystal structure data are reported for three compounds: [Re(6)Se(8)(PEt(3))(5)(p-acetylbenzonitrile)](BF(4))(2)?MeCN, [Re(6)Se(8)(PEt(3))(5)(2,5-phenyltetrazolate)](BF(4))?CH(2)Cl(2), and [Re(6)Se(8)(PEt(3))(5)(2,5-p-aminophenyltetrazolate)](BF(4)). Treatment of [Re(6)Se(8)(PEt(3))(5)(2,5-phenyltetrazolate)](BF(4)) with HBF(4) in CD(3)CN at 100 °C leads to protonation of the tetrazolate ring and formation of [Re(6)Se(8)(PEt(3))(5)(CD(3)CN)](2+). Surprisingly, alkylation of the phenyl and methyl tetrazolate complexes ([Re(6)Se(8)(PEt(3))(5)(2,5-N(4)CPh)](BF(4)) and [Re(6)Se(8)(PEt(3))(5)(1,5-N(4)CMe)](BF(4))) with methyl iodide and benzyl bromide, leads to the formation of mixtures of 1,5- and 2,5-disubstituted tetrazoles.     

A Quadrupole mass spectrometer for resolution of low mass isotopes

The qualitative and quantitative identification of low mass isotopes in the mass range 1–6 u poses certain difficulties when attempting to achieve the required resolution with an instrument suitable for deployment within a process environment. Certain adjacent species present in the process sample (HT and D₂) require a resolution greater than 930 to achieve an accurate measurement. We demonstrate here through simulation techniques that this level of performance required is unachievable using commercially available instruments. Using previously reported simulation techniques, this article demonstrates how the required performance for resolving the low mass isotopes can be achieved by a quadrupole mass spectrometer (QMS), which incorporates a quadrupole mass filter (QMF) constructed from hyperbolic electrodes and operated in zone 3 of the Mathieu stability diagram.     

A small angle neutron scattering and electrochemical impedance spectroscopy study of the nanostructure of the iron chalcogenide glass ion-selective electrode

This paper presents a preliminary structural and interfacial study of the iron chalcogenide glass [i.e., Fe_x(Ge₂₈Sb₁₂Se₆₀)_100−x] ion-selective electrode (ISE) using small angle neutron scattering (SANS) and electrochemical impedance spectroscopy (EIS). SANS detected variations in the neutron scattering as a function of iron content in the chalcogenide glass. Furthermore, a change in the chalcogenide glass structure was observed at elevated iron dopant levels. Conversely, EIS was used to show that the iron chalcogenide membrane comprises various time constants, and the interfacial charge transfer reaction depends on the membrane iron content. Equivalent circuit modeling revealed that the charge transfer resistance decreases at elevated iron levels, and this may be related to the presence of iron defects in the glass. It is proposed that the iron chalcogenide membrane comprises an iron nanostructural network embedded in the amorphous matrix, and this directly influences the electrical conductivity and concomitant electrochemical reactivity of the glass.