The micro-volumetric determination of lead with thionalide and its application to the analysis of tin-base and lead-base alloys

The authors have elaborated an exact micro-volumetric method for the determination of lead with thionalide. The method has been successfully applied to the determination of lead in tin-base and lead-base alloys, following the isolation of lead as lead sulphate and its redissolution in ammonium acetate.     

Coherent-state theory for the proton-neutron quasispin group

An extended coherent-state theory ^{1, 2}) is used to give a simple construction for the matrix elements of the proton-neutron sp(4) quasispin algebra. A very simple analytical expression is given for the matrix elements of the sp(4) generators valid for all cases where initial and final states are multiplicity-free with respect to the U(1) × SU(2) n, T subalgebra. In the more general case, involving multiplicity, the most natural orthonormal basis constructed by the coherent-state method leads to many-nucleon states in the seniority scheme which are approximately labelled by T_p, the isospin of the p nucleon pairs coupled to J = 0, T = 1.     

Aktivierungsanalytische Untersuchungen an standardisierten Eisenlegierungen. II

Zusammenfassung Der Gehalt an Kupfer, Arsen, Antimon und Lanthan wurde in den standardisierten Legierungen NBS-1138 (Cast Steel 1) und NBS-1140 (Ductile Iron 1) quantitativ bestimmt, und zwar sowohl zerstörungsfrei als auch nach einer schnellen Gruppentrennung auf extraktionschromatographischem Wege im System Tri-n-octylamin — Salzsäure. Für Kupfer lagen Zertifikatswerte für beide Legierungen vor, für Arsen nur für eine Legierung. Unter Berücksichtigung der angegebenen Unsicherheitsgrenzen zeigten unsere Analysenwerte gute Übereinstimmung mit den Zertifikaten. Zusätzlich, das heißt ohne Zertifikats werte, wurden von uns quantitativ Antimon und Lanthan in beiden Proben, Arsen in einer Probe bestimmt.

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Activation analytical studies of standardized iron alloys. II

Summary The content of copper, arsenic, antimony and lanthanum was quantitatively determined in the standardized alloys NBS-1138 (CaS + Steel 1) and NBS-1140 (Ductile Iron 1), and in fact without destruction and likewise after a rapid group separation by means of a rapid extraction Chromatographic method in the system tri-n-octylamine-hydrochloric acid. Certificated values for copper were available in the case of both alloys, but such values were available for arsenic only in one alloy. Our analytical values showed good agreement with the certificated values if the uncertainties are taken into account. In addition, i. e. with no certificated values, we quantitatively determined antimony and lanthanum in both samples, arsenic in one sample.

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Herrn Prof. Dr. Hans Nowotny zum 60. Geburtstag gewidmet.     

Diffusion Limited Aggregation on a Cylinder

We consider the DLA process on a cylinder . It is shown that this process “grows arms”, provided that the base graph G has small enough mixing time. Specifically, if the mixing time of G is at most , the time it takes the cluster to reach the m ^th layer of the cylinder is at most of order . In particular we get examples of infinite Cayley graphs of degree 5, for which the DLA cluster on these graphs has arbitrarily small density. In addition, we provide an upper bound on the rate at which the “arms” grow. This bound is valid for a large class of base graphs G, including discrete tori of dimension at least 3. It is also shown that for any base graph G, the density of the DLA process on a G-cylinder is related to the rate at which the arms of the cluster grow. This implies that for any vertex transitive G, the density of DLA on a G-cylinder is bounded by 2/3.     

Crystalline and amorphous nanostructures in porous silicon

We report ab initio molecular dynamic simulations of several supercells of crystalline porous silicon, that are first relaxed and then analyzed by their radial distribution functions (RDF). The porosities vary from 10% to 80% of the total volume of the supercell. The interatomic distance is determined by the position of the first peak of the RDF. We manipulated a maximum of 500 atoms of silicon and a minimum of 32. The interatomic distance of the model with a porosity of 10% was 2.35 Å, for those models with porosity from 11% to 50% was 2.45 Å and finally, 2.55 Å for those with a porosity greater than 50%. If the supercell backbone structure is small compared with the void of the supercell, then the interatomic distance between the silicon atoms run out of the crystalline value. Our results agree with experiment.     

Pore Space Microstructure Evolution of Regular Sphere Packings Undergoing Compaction and Cementation

We examine the pore space structure evolution of ordered uniform sphere packs: simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC), undergoing simple diagenetic processes that reduce their pore spaces. Focus is on the occurrence of pore space microstructure changes or transitions, which are followed through their characteristic or critical pore lengths (l _c). For almost all the cubic packings undergoing either compaction or cementation there are no singularities in l _c. This is a consequence of having a single pore shape controlling flow at all stages of the process. However, this is not so for the BCC packing under cementation, for which l _c is non-monotonic exhibiting a kink at ${\phi \approx 0.1452}$ , the porosity at which the pore shape controlling flow switches to a different form and position. These results for uniform compaction/cementation complement our previous works on pore networks under random shrinkage. Kinks in l _c as porosity decreases signal pore space microstructure transitions that anticipate sudden changes in the permeability?Cporosity relation as porosity decreases. The consequences are great; clearly l _c is not a constant unless the diagenetic process is mild. A l _c function of compaction/cementation advancement should be used above a transition and a different l _c function below. For the sphere packs here, once the diagenetic process has reduced the pore space substantially, a l _c function of compaction/cementation advancement is mandatory if we are to capture all significant flow features.