Can the provenance of the conflict minerals columbite and tantalite be ascertained by laser-induced breakdown spectroscopy?

Conflict minerals is a term applied to ores mined in conditions of armed conflict and human rights abuse. Niobium and tantalum are two rare metals whose primary natural occurrence is in the complex oxide minerals columbite and tantalite, the ore of which is commonly referred to as coltan. The illicit export of coltan ore from the Democratic Republic of the Congo is thought to be responsible for financing the ongoing civil conflicts in this region. Determining the chemical composition of an ore is one of the means of ascertaining its provenance. Laser-induced breakdown spectroscopy (LIBS) offers a means of rapidly distinguishing different geographic sources for a mineral because the LIBS plasma emission spectrum provides the complete chemical composition (i.e., “chemical fingerprint”) of any material in real time. To test this idea for columbite–tantalite, three sample sets were analyzed. Partial least squares discriminant analysis (PLSDA) allows correct sample-level geographic discrimination at a success rate exceeding 90%.     

Effect of Eshelby twist on core structure of screw dislocations in molybdenum: atomic structure and electron microscope image simulations

This paper addresses the question as to whether the core structure of screw dislocations in Mo in the bulk can be obtained from high-resolution electron microscopy (HREM) images of such dislocations viewed end-on in a thin foil. Atomistic simulations of the core structure of screw dislocations in elastically anisotropic Mo were carried out using bond order potentials. These simulations take account automatically of the effects of the surface relaxation displacements (anisotropic Eshelby twist). They show that the differential displacements of the atoms at the surface are different with components perpendicular to the Burgers vector about five times larger than those in the middle of the foil, the latter being characteristic of the bulk. Nye tensor plots show that the surface relaxation stresses strongly affect the incompatible distortions. HREM simulations of the computed structure reflect the displacements at the exit surface, modified by interband scattering and the microscope transfer function. Nye tensor plots obtained from the HREM images show that interband scattering also affects the incompatible distortions. It is concluded that it would be very difficult to obtain information on the core structure of screw dislocations in the bulk Mo from HREM images, even under ideal experimental conditions, and that quantitative comparisons between experimental and simulated images from assumed model structures would be essential.     

A bound connected with primitive matrices

Numerische Mathematik - LetA be a primitiven-square matrix, and letq 0(A) be the smallestq such thatA q ,A q +1 have a common nonzero entry. The following general bound forq 0(A) is proved: $$q_0...     

The use of ethylenediaminetetraacetic acid or nitrilo-triacetic acid as masking agents in the determination of palladium with dimethylglyoxime or quinaldic acid

The use of complexing agents to mask interference in the gravimetric determination of palladium has been studied. Ethylenediaminetetraacctic acid was used to complex interfering ions in the determination of palladium with dimethylglyoxime, and nitrilotriacetic acid has been employed as a masking agent in the determination of palladium with quinaldic acid. From 15 to 150 mg of palladium were determined. All the metals tested do not interfere with the exception of gold which s reduced by the complexing agents and has to be removed prior to the determination. The procedures are rapid, simple and accurate.     

Looking for the Origin of Allosteric Cooperativity in Metallopolymers

The basic concept of allosteric cooperativity used in biology, chemistry and physics states that any change in the intermolecular host–guest interactions operating in multisite receptors can be assigned to intersite interactions. Using lanthanide metals as guests and linear multi‐tridentate linear oligomers of variable lengths and geometries as hosts, this work shows that the quantitative modeling of metal loadings requires the consideration of a novel phenomenon originating from solvation processes. It stepwise modulates the intrinsic affinity of each isolated site in multisite receptors, and this without resorting to allosteric cooperativity. An easy‐to‐handle additive model predicts a negative power law dependence of the intrinsic affinity on the length of the linear metallopolymer. Applied to lanthanidopolymers, the latter common analysis overestimates cooperativity factors by more than two orders of magnitude.     

Multivariate statistical differentiation of renal cell carcinomas based on lipidomic analysis by ambient ionization imaging mass spectrometry

Desorption electrospray ionization (DESI) mass spectrometry (MS) was used in an imaging mode to interrogate the lipid profiles of thin tissue sections of 11 sample pairs of human papillary renal cell carcinoma (RCC) and adjacent normal tissue and nine sample pairs of clear cell RCC and adjacent normal tissue. DESI-MS images showing the spatial distributions of particular glycerophospholipids (GPs) and free fatty acids in the negative ion mode were compared to serial tissue sections stained with hematoxylin and eosin (H&E). Increased absolute intensities as well as changes in relative abundance were seen for particular compounds in the tumor regions of the samples. Multivariate statistical analysis using orthogonal projection to latent structures treated partial least square discriminate analysis (PLS-DA) was used for visualization and classification of the tissue pairs using the full mass spectra as predictors. PLS-DA successfully distinguished tumor from normal tissue for both papillary and clear cell RCC with misclassification rates obtained from the validation set of 14.3% and 7.8%, respectively. It was also used to distinguish papillary and clear cell RCC from each other and from the combined normal tissues with a reasonable misclassification rate of 23%, as determined from the validation set. Overall DESI-MS imaging combined with multivariate statistical analysis shows promise as a molecular pathology technique for diagnosing cancerous and normal tissue on the basis of GP profiles.     

Laser evaporation of some solid organosilicon polymers

Continuous wave (cw) CO₂ laser irradiation of some organosilicon polymers composed of -Me₂Si-, -Me₂SiMe₂SiCH₂-, RMeSi- and RMeSiMe₂SiCH₂CH₂- units (where R = methyl, adamantyl, phenyl and hydrogen) leads to the evaporation of the polymer and is dominated by the formation of a solid deposit that has a continuous structure. It is assumed that chemical changes occur prior to the transfer of ejected material to the gas phase and that these consist mainly of the formation of high molecular biradicals or 1,2-disilacyclobutane monomer that both re-polymerize spontaneously upon their deposition onto a nearby cold surface. The mechanism of these specific decompositions of the polymers is assessed on the basis of the IR spectra of the deposits and, for the minor gaseous products, identification by GC MS techniques.