On Solving the Transportation Problem

The Hitchcock transportation problem is perhaps one of the ‘most solved’ linear programming problems in existence. We shall propose yet another computation for the problem....¹The current computational status of the transportation problem is reviewed, and the claims of three papers that recently appeared in this journal are put into perspective.     

Investigación toxicológica de microcantidades de barbitúricos

Resumen Se ha estudiado la investigación cualitativa de microcantidades de barbitúricos en materiales biológicos. Se propone una técnica basada en la extracción de estos compuestos con metanol, purificación del extracto por ascenso capilarimétrico en papel de filtro y reconocimiento mediante la reacción deParri yKoppanyi. Se consideran las interferencias y las condiciones particulares del trabajo sobre vísceras, sangre y orina. El límite de identificacíon de la técnica llega a 10g y representa un método económico en cuanto a tiempo y material.

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Summary A study was made of the qualitative detection of micro amounts of barbiturates in biological materials. A procedure is suggested based on extraction of these compounds with methanol, followed by purification of the extract by ascending paper chromatography, and identification with the aid of theParri andKoppanyi reaction. The interferences and the special conditions of applying the test to viscera, blood, and urine were studied. The identification limits of the procedure is 10g. The method saves time and material.

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Zusammenfassung Der qualitative Nachweis von Mikromengen von Barbituraten in biologischem Material wurde studiert. Zu diesem Zweck wird eine Arbeitstechnik vorgeschlagen, die auf der Extraktion dieser Verbindungen mit Methanol, der nachfolgenden Reinigung des Extraktes durch aufsteigende Papierchromatographie und Identifizierung mit Hilfe der Reaktion nachParri undKoppanyi beruht. Störende Einflüsse und die besonderen Bedingungen der Anwendung der Methode auf Eingeweide, Blut und Harn wurden untersucht. Die Erfassungsgrenze des beschriebenen Verfahrens erreicht 10 g. Es ermöglicht Zeit- und Materialersparnis.

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Résumé Etude de l'identification qualitative de microquantités de barbituriques dans les milieux biologiques. A cette fin on recommande une technique opératoire qui comporte une extraction de ces composés dans le méthanol, une purification consécutive de l'extrait par chromatographie ascendante sur papier et une identification par la réaction deParri etKoppanyi. On a étudié les influences gênantes ainsi que les conditions particulières d'emploi de la méthode pour les viscères, le sang et l'urine. Sa limite de sensibilité est de 10g; elle permet d'épargner du temps et du matériel.

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Presentado al III Congreso Panamericano de Farmacia y Bioquímica, Sao Paulo, Brasil, XII, 1954.     

On energy bounds derived from the conjugate eigenvalue problem

An upper bound for E₀, which has been derived from the conjugate eigenvalue problem by Hall, is discussed. It is emphasized that the bound is only guaranteed when V is negative-definite. An alternative bound is presented which is free from this restriction, and the underlying iterative procedure is given. Hall's result is generalized to admit internuclear distances, and the theory is illustrated by a one-dimensional system with delta-function potentials. Some disadvantages of the approach are mentioned.     

Mining combinatorial data in protein sequences and structures

Combinatorial searches of structural and physical chemical properties involving the components of libraries of dipeptide, tripeptide and tetra peptide fragments were carried out in the Protein Data Bank and the SwissProt databases. The properties investigated are structural propensities, co localization of peptide fragments in protein sequences, interactions between peptide fragments in close structural proximity and the participation of physical chemical profiles in the distribution of structural motifs among peptide fragments. The results obtained for each combinatorial search in the study are classified according to the structural motifs alpha-helix, beta-sheet, reverse turn I and reverse turn II. The application of combinatorial data mined in protein databases to the design of new peptide libraries is discussed. The present findings have implications for the study of protein structure which are also discussed.     

Synthesis and properties of palladium(II) complexes with sulfur ligands

Complexes of L-2 thiolhistidine (th) and 2-mercaptoimidazole (miz) with Pd(II) were synthesized, Pd(th)₄(NO₃)₂ and Pd(miz)₄Cl₂, and their structure determined by FTIR, UV/VIS, NMR, mass spectroscopy, and X-ray crystallography. For comparison, a Pd(II) complex with thiourea (tu), Pd(tu)₄Cl₂, was prepared. This compound has been reported in the literature. Spectral evidence indicates a single coordination site between the Pd(II) and S for all complexes. A Pd-S stretch band was identified for all complexes. NMR spectra provided evidence for deshielding effects in the complexes from that of its ligands. Charge transfer bands were identified in the UV/VIS spectra for the new complexes as well. The crystal structure for Pd(miz)₄Cl₂ was determined. Unit cell data was found to be:a=8.102(3)Å,b=8.300(3)Å,c=8.304(3)Å. The crystal system is triclinic and the space group isP ¯1.     

Ionic liquid crystals with 1,2,3-triazole + tolane core and a pendant imidazolium unit: mesophases from one- to three-dimensional molecular organisation by the variation of alkoxy chains number and spacer length

Ionic liquid crystals (ILCs) are a class of materials that present a large and varied form of applicability and whose properties can change dramatically with small modifications in their molecular structure. It is, therefore, of great importance to improve the knowledge about the property–molecular structure relationship. In this study, we present the synthesis and characterisation of 7 new rod- and wedge-shaped ILCs, whose liquid crystalline behaviour variation is related to the variations in the number of alkoxy chains and/or in the spacer chain length. All compounds have a rigid core constituted by a tolane group and a 1,2,3-triazole heterocycle, which is connected to a pendant 1-methylimidazolium through a alkyl spacer chain. The mesomorphic properties were studied by DSC, thermogravimetric analysis, polarising optical microscopy, wide angle X-ray diffraction and SAXS with synchrotron radiation. The increase in the number of long alkoxy chains changed the molecular self-assembly from bilayered SmA₂ and SmC₂ to hexagonal columnar, passing through oblique columnar, bicontinuous cubic and hexagonal close-packed mesophase. On the other hand, the increase in the alkyl spacer chain length has an especially significant effect for the compounds with two terminal alkoxy chains, where a Col_o/Col_h – Cub_v – HCP phase sequences were observed.     

Toward developing accelerated stress tests for proton exchange membrane electrolyzers

Proton exchange membrane water electrolysis is technically the most suitable technology for the production of green hydrogen on a large scale. Although it is still more expensive than hydrogen produced from fossil sources, it has already been commercialized. Novel components with cost-effective materials and efficient manufacturing processes are being rapidly developed. However, these components must endure durability tests that can guarantee a lifetime of at least 50,000 operation hours. Consequently, there is an urgent need to develop accelerated stress test protocols based on a deep understanding of degradation mechanisms of stack components. Recent reports show that the main degradation mechanisms are associated to anode catalyst dissolution, membrane chemical decomposition, and formation of semiconducting oxides on the metal components. These mechanisms can be accelerated by stressors such as high current density, dynamic operation, and shutdown modes. On the basis of these reports and knowledge of the operational requirements for large-scale proton exchange membrane water electrolysis, we propose an accelerated stress test protocol for the fast evaluation of newly developed cost efficient and durable components.