Characterization of an orphan Ra–Be neutron source

Journal of Radioanalytical and Nuclear Chemistry - An orphan radium-beryllium (Ra–Be) neutron source (Nuclear Chicago Corporation) detected inside a scrap metal shipping container, was seized...     

Modular Synthesis of a Dual Metal–Dual Semiconductor Nano‐Heterostructure

Reported is the design and modular synthesis of a dual metal–dual semiconductor heterostructure with control over the dimensions and placement of its individual components. Analogous to molecular synthesis, colloidal synthesis is now evolving into a series of sequential synthetic procedures with separately optimized steps. We detail the challenges and parameters that must be considered when assembling such a multicomponent nanoparticle, and their solutions. This multicomponent nanosystem, Ru‐CdSe@CdS‐Pt, was designed to achieve charge carrier separation and directional transfer across different interfaces toward two separate redox catalysts. This heterostructure may potentially serve as a nanometric closed circuit photoelectrochemical cell.     

Algorithms for the Split Variational Inequality Problem

We propose a prototypical Split Inverse Problem (SIP) and a new variational problem, called the Split Variational Inequality Problem (SVIP), which is a SIP. It entails finding a solution of one inverse problem (e.g., a Variational Inequality Problem (VIP)), the image of which under a given bounded linear transformation is a solution of another inverse problem such as a VIP. We construct iterative algorithms that solve such problems, under reasonable conditions, in Hilbert space and then discuss special cases, some of which are new even in Euclidean space.     

Isotope abundance analysis for improved sample identification with tandem mass spectrometry

Tandem mass spectrometry (MS/MS) is widely used for trace level sample analysis in complex mixtures. However, sample identification in MS/MS is challenging and not as trustworthy as with electron ionization (EI) mass spectral libraries. This paper presents a novel method for the combination of isotope abundance analysis (IAA) and EI‐MS/MS for improved sample identification even at trace level in complex matrices. Accordingly, the first quadrupole is scanned in a narrow range around the molecular ion group of isotopomers such as M⁺, [M+1]⁺ and [M+2]⁺, Q2 serves for collision‐induced dissociation to produce product ions while Q3 transfers the major sample product ions with low resolution, thus encompassing and uniformly transmitting all the product ion isotopomers. IAA can then be used to derive elemental formula information from the cleansed experimental data. IAA‐MS/MS was experimentally tested with perfluorotributylamine and a very good matching factor of 995 (out of 1000) was obtained for IAA on m/z 502, 503 and 504 (fragment ion isotopomers) while Q3 transmitted the m/z 264 product ion with a mass window of 6 m/z units. The IAA‐MS/MS method was further tested with the pesticide diazinon on its molecular ions m/z 304, 305 and 306 while Q3 was locked on its m/z 179 product ion with a mass window of 6 m/z units. Again, very good matching factors were obtained, even for 40 pg diazinon on‐column during its GC/MS analysis (match = 981). IAA‐MS/MS combines the traditional benefits of MS/MS in the removal of matrix interferences with the IAA power of elemental analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Pulsed flow modulation two-dimensional comprehensive gas chromatography-tandem mass spectrometry with supersonic molecular beams

Pulsed flow modulation (PFM) two-dimensional comprehensive gas chromatography (GC x GC) was combined with quadrupole-based mass spectrometry (MS) via a supersonic molecular beam (SMB) interface using a triple-quadrupole system as the base platform, which enabled tandem mass spectrometry (MS-MS). PFM is a simple GC x GC modulator that does not consume cryogenic gases while providing tunable second GC x GC column injection time for enabling the use of quadrupole-based mass spectrometry regardless its limited scanning speed. The 20-ml/min second column flow rate involved with PFM is handled, splitless, by the SMB interface without affecting the sensitivity. The combinations of PFM GC x GC-MS with SMB and PFM GC x GC-MS-MS with SMB were explored with the analysis of diazinon and permethrin in coriander. PFM GC x GC-MS with SMB is characterized by enhanced molecular ion and tailing-free fast ion source response time. It enables universal pesticide analysis with full scan and data analysis with reconstructed single ion monitoring on the enhanced molecular ion and another prominent high mass fragment ion. The elimination of the third fragment ion used in standard three ions method results in significantly reduced matrix interference. GC x GC-MS with SMB improves the GC separation, and thereby our ability for sample identification using libraries. GC-MS-MS with SMB provides better reduction (elimination) of matrix interference than GC x GC-MS. However, it is a target method, which is not always applicable. GC x GC-MS-MS does not seem to further reduce matrix interferences over GC-MS-MS and unlike GC x GC-MS, it is incompatible with library identification, but it is beneficial to have both GC x GC and MS-MS capabilities in the same system.     

Spray-produced coral-shaped assemblies of MnS nanocrystal clusters

A novel spray-based technique enables the production of high-quality, free, uncoated semiconductor nanocrystals. Their collection, following spray droplet desolvation during flight, could result in unusual structures. We report on spray-produced ordered clusters (approximately 50 nm diameter) of MnS nanocrystals with grain size range of 1-2 nm and their assembly into micron-sized coral-shaped fractal aggregates. Ballistic cluster-particle aggregation, with the introduction of physical interaction between particles, is suggested as a model for the assemblies' growth.     

<Emphasis Type="Italic">l</Emphasis><Subscript>1</Subscript>-<Emphasis Type="Italic">l</Emphasis><Subscript>2</Subscript> regularization of split feasibility problems

Numerous problems in signal processing and imaging, statistical learning and data mining, or computer vision can be formulated as optimization problems which consist in minimizing a sum of convex functions, not necessarily differentiable, possibly composed with linear operators and that in turn can be transformed to split feasibility problems (SFP); see for example Censor and Elfving (Numer. Algorithms 8, 221–239 1994). Each function is typically either a data fidelity term or a regularization term enforcing some properties on the solution; see for example Chaux et al. (SIAM J. Imag. Sci. 2, 730–762 2009) and references therein. In this paper, we are interested in split feasibility problems which can be seen as a general form of Q-Lasso introduced in Alghamdi et al. (2013) that extended the well-known Lasso of Tibshirani (J. R. Stat. Soc. Ser. B 58, 267–288 1996). Q is a closed convex subset of a Euclidean m-space, for some integer m ≥ 1, that can be interpreted as the set of errors within given tolerance level when linear measurements are taken to recover a signal/image via the Lasso. Inspired by recent works by Lou and Yan (2016), Xu (IEEE Trans. Neural Netw. Learn. Syst. 23, 1013–1027 2012), we are interested in a nonconvex regularization of SFP and propose three split algorithms for solving this general case. The first one is based on the DC (difference of convex) algorithm (DCA) introduced by Pham Dinh Tao, the second one is nothing else than the celebrate forward-backward algorithm, and the third one uses a method introduced by Mine and Fukushima. It is worth mentioning that the SFP model a number of applied problems arising from signal/image processing and specially optimization problems for intensity-modulated radiation therapy (IMRT) treatment planning; see for example Censor et al. (Phys. Med. Biol. 51, 2353–2365, 2006).     

On the evolution of recombination in haploids and diploids: I. Deterministic models

In population genetic theory, most analytical and numerical studies of the evolution of recombination have focused on diploid genetics. In studies of the foundations and applications of genetic algorithms (GA's), however, the bit-strings are usually treated as haploid genotypes. In this paper and its companion paper (Bergman et al., 1995), we compare results for the evolutionary dynamics of modifiers of recombination in haploids with results derived for diploids. In this paper, we study the evolution of an allele that controls the rate of recombination between two loci subject to directional selection. It is shown analytically that the fate of a recombination modifier in both haploids and diploids is determined in a complicated way by the sign of the epistasis (interaction in fitness) between the loci, the sign of the initial linkage disequilibrium, and the amount of recombination between the modifier and the genes under selection. This theory is deterministic in that the population is regarded as infinite and no sampling occurs to produce offspring from parents. In the companion paper (Bergman et al., Complexity, 1(2) 1995), we expand upon this work by addressing epistatic interactions among several loci in finite populations.     

A spray-based method for the production of semiconductor nanocrystals

We present a spray based-method for the formation and production of semiconductor nanocrystals that provides an attractive alternative to the commonly used epitaxial and colloidal procedures. According to this spray-based method, mainly thermospray, solutions of semiconductor salts are first sprayed into monodispersed droplets, which subsequently become solid nanocrystals by solvent evaporation. A semiconductor nanocrystal is produced from a single spray droplet upon the full vaporization of the solvent. The average diameter and size distribution of the final nanocrystals are controlled and determined by the solute concentration of the sprayed solution and by the droplet size, hence by the spray production parameters. The spray-produced nanocrystals are collected on any selected solid support. Representative results, shown in this letter, reveal the formation of CdS nanocrystals in the size range of 3 to 6 nanometers and with a size distribution of as low as five percent. A further structural analysis of these nanocrystals showed that they were formed in the zinc blend phase with a high degree of crystallinity.