Vertex Structure of Master Corner Polyhedra

This paper focuses on vertices of the master corner polyhedra $P(G,g_0),$ the core of the group-theoretical approach to integer linear programming. We introduce two combinatorial operations that transform each vertex of $P(G,g_0)$ to adjacent ones. This implies that for any $P(G,g_0),$ there exists a subset of basic vertices, we call them support vertices, from which all others can be built. The class of support vertices is proved to be invariant under the automorphism group of $G,$ so this basis can be further reduced to a subset of pairwise non-equivalent support vertices. Among other results, we characterize irreducible points of the master corner polyhedra, establish relations between an integer point and the nontrivial facets that pass through it, construct complete subgraphs of the graph of $P(G,g_0),$ and show that these polyhedra are of diameter 2.Comment: 33 pages, 35 tables in the Appendi

Studies of cracking behavior in melt-processed YBCO bulk superconductors

An important phenomenon in bulk superconductors fabricated by top-seeded-melt growth (TSMG) is the formation of cracks due to the inherent brittleness of the YBa2Cu3O7-δ (Y-123) phase matrix. These form during the fabrication of the superconducting monolith and play an important role in the limitation of current flow. However, cracks may also form during cooling cycles of the sample to liquid nitrogen temperatures. In this investigation, macrocracks along the c-direction, in particular were analyzed microscopically before and after cooling. In addition we attempt to resolve the c-axis macrocrack formation pattern using the magnetoscan technique

Is U3Ni3Sn4 best described as near a quantum critical point?

Although most known non-Fermi liquid (NFL) materials are structurally or chemically disordered, the role of this disorder remains unclear. In particular, very few systems have been discovered that may be stoichiometric and well ordered. To test whether U3Ni3Sn4 belongs in this latter class, we present measurements of the x-ray absorption fine structure (XAFS) of polycrystalline and single-crystal U3Ni3Sn4 samples that are consistent with no measurable local structural disorder. We also present temperature-dependent specific heat data in applied magnetic fields as high as 8 T that show features that are inconsistent with the antiferromagnetic Griffiths' phase model, but do support the conclusion that a Fermi liquid/NFL crossover temperature increases with applied field. These results are inconsistent with theoretical explanations that require strong disorder effects, but do support the view that U3Ni3Sn4 is a stoichiometric, ordered material that exhibits NFL behavior, and is best described as being near an antiferromagnetic quantum critical point.Comment: 9 pages, 8 figures, in press with PR

Crystal Structure and Physical Properties of U3T3Sn4 (T = Ni, Cu) Single-Crystals

Heat capacity experiments, crystal structure determination and transmission electron microscopy have been carried out on U3Cu3Sn4 single-crystals. U3Cu3Sn4 was confirmed to be a heavy-fermion antiferromagnet (TN=13(1) K) with a low temperature electronic heat capacity coefficient gamma=390 mJ/molUK2. Low temperature heat capacity experiments on a U3Ni3Sn4 single-crystal indicate that below 0.4 K there is a crossover between the previously observed non-Fermi liquid behavior and a Fermi liquid state.Comment: 12 pages (incl. 2 tables & 4 figures), to appear in Physica

New nuclear three-body clusters \phi{NN}

Binding energies of three-body systems of the type \phi+2N are estimated. Due to the strong attraction between \phi-meson and nucleon, suggested in different approaches, bound states can appear in systems like \phi+np (singlet and triplet) and \phi+pp. This indicates the principal possibility of the formation of new nuclear clusters

Studies of cracking behavior in melt-processed YBCO bulk superconductors

An important phenomenon in bulk superconductors fabricated by top-seeded-melt growth (TSMG) is the formation of cracks due to the inherent brittleness of the YBa2Cu3O7-δ (Y-123) phase matrix. These form during the fabrication of the superconducting monolith and play an important role in the limitation of current flow. However, cracks may also form during cooling cycles of the sample to liquid nitrogen temperatures. In this investigation, macrocracks along the c-direction, in particular were analyzed microscopically before and after cooling. In addition we attempt to resolve the c-axis macrocrack formation pattern using the magnetoscan technique

PERFORMANCE OF THE CONTRACTUAL ARRANGEMENTS OF PUBLIC-PRIVATE PARTNERSHIPS: CASE OF RAILWAY CONCESSION IN TANZANIA.

This thesis analyzes dynamics of Public-Private Partnership contractual arrangements and focuses on uncovering reasons of the disintegration (renegotiation and/or cancellation) of such contracts. It looks in detail at a specific case of a contractual arrangement of concessioning of the Tanzania Railway Corporation (TRC), a backbone of the corridor that links the landlocked Rwanda, Burundi and Uganda, as well as the eastern DRC and the hinterland of Tanzania, to the port of Dar es Salaam. This research first concludes that such widely acknowledged causes as information incompleteness and asymmetry (contract-related explanations) and opportunistic behavior and strategic alliance-making (non-contractual explanations) cannot fully explain disintegration of a particular contractual arrangement. It then builds upon a case study to extend existing explanations of contract failure and renegotiation by drawing on organizational and alliance theories and explains which characteristics of the institutional context make the detrimental effects of particular causes possible

Structure and Physical Properties of SrNiRu\u3csub\u3e5\u3c/sub\u3eO\u3csub\u3e11\u3c/sub\u3e Single Crystals: An \u3cem\u3eR\u3c/em\u3e-Type Ferrite Based on Ordered Kagome Nets

Single crystals of the R-type ferrite SrNiRu5O11 were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on distorted kagome nets. The low-temperature dc magnetic susceptibilities (χ⊥ and χ∥, perpendicular and parallel to the c axis, respectively) diverge as T−0.3, and do not exhibit any indication of long-range magnetic order down to 4.5 K. The electrical resistivity varies as T1.6 below 40 K, which is typical of non-Fermi liquids, and may originate from a competition between residual magnetic interactions among Ni2+ (S = 1) spins and geometrical frustration on the two-dimensional kagome lattice of Ru3+ (S = ½) spins. The transverse magnetoresistivity ρxy at constant temperature T = 5 K for current (J) -magnetic field (H) configurations, J⊥H ∥ c axis and J ∥ H⊥c axis, reveals no anomalous contribution, which is consistent with the absence of magnetic order. Fits of the specific heat data below 10 K require a dominant, but unusual electronic term of the form Cel = γT1.2, which is expected for massless Dirac fermion states in topological insulators, or spin-liquid phases