Quantum contact interactions

The existence of several exotic phenomena, such as duality and spectral anholonomy is pointed out in one-dimensional quantum wire with a single defect. The topological structure in the spectral space which is behind these phenomena is identified.Comment: A lecture presented at the 2nd Winter Institute on Foundations of Quantum Theory and Quantum Optics (WINST02), Jan. 2-11, 2002, S.N.Bose Institute, Calcutta, India: 8 pages latex with Indian Acad. Sci. style fil

Moebius Structure of the Spectral Space of Schroedinger Operators with Point Interaction

The Schroedinger operator with point interaction in one dimension has a U(2) family of self-adjoint extensions. We study the spectrum of the operator and show that (i) the spectrum is uniquely determined by the eigenvalues of the matrix U belonging to U(2) that characterizes the extension, and that (ii) the space of distinct spectra is given by the orbifold T^2/Z_2 which is a Moebius strip with boundary. We employ a parametrization of U(2) that admits a direct physical interpretation and furnishes a coherent framework to realize the spectral duality and anholonomy recently found. This allows us to find that (iii) physically distinct point interactions form a three-parameter quotient space of the U(2) family.Comment: 16 pages, 2 figure

A general approximation of quantum graph vertex couplings by scaled Schroedinger operators on thin branched manifolds

We demonstrate that any self-adjoint coupling in a quantum graph vertex can be approximated by a family of magnetic Schroedinger operators on a tubular network built over the graph. If such a manifold has a boundary, Neumann conditions are imposed at it. The procedure involves a local change of graph topology in the vicinity of the vertex; the approximation scheme constructed on the graph is subsequently `lifted' to the manifold. For the corresponding operator a norm-resolvent convergence is proved, with the natural identification map, as the tube diameters tend to zero.Comment: 19 pages, one figure; introduction amended and some references added, to appear in CM

Improvement of Fire Hydrant Design to Enhance Water Main Flushing

AbstractFlushing is a good practice to avoid problems related to sediment, bio-film growth, and corrosion. Artificial sediment was removed from fire hydrant with pilot scale water distribution main. The sediment removal in fire hydrant and main was carefully compared with different flow rate with velocity ranged from 0.3 to 3.0 m/s and the depth of fire hydrant from 0.5 m to 1.3m. The drain capability of fire hydrant decreased as the flow rate increased. Sediment with higher density was hard to remove from water main. The length effect of upward fire hydrant was relatively minor. Downward drain showed better efficiency for both sand and actual sediment

Spectral properties on a circle with a singularity

We investigate the spectral and symmetry properties of a quantum particle moving on a circle with a pointlike singularity (or point interaction). We find that, within the U(2) family of the quantum mechanically allowed distinct singularities, a U(1) equivalence (of duality-type) exists, and accordingly the space of distinct spectra is U(1) x [SU(2)/U(1)], topologically a filled torus. We explore the relationship of special subfamilies of the U(2) family to corresponding symmetries, and identify the singularities that admit an N = 2 supersymmetry. Subfamilies that are distinguished in the spectral properties or the WKB exactness are also pointed out. The spectral and symmetry properties are also studied in the context of the circle with two singularities, which provides a useful scheme to discuss the symmetry properties on a general basis.Comment: TeX, 26 pages. v2: one reference added and two update

Productivity change in Nigerian seaports after reform: a Malmquist productivity index decomposition approach

During the 1990s, Nigerian seaports were considered inefficient, unsafe due to massive cargo theft (wharf rat phenomenon) and one of the most expensive port systems in the world. This resulted in long turnaround times for ships and increased container dwell times. As a result, port operations were transferred to the private sector through concession contracts. This paper employs a Malmquist productivity index (MPI) technique to benchmark pre-and post-reform total factor productivity growth of the six major Nigeria seaports (Apapa, Calabar, Onne, Port Harcourt, TinCan Island and Warri) for the period 2000–2011 which represents six years before (2000–2005) and six years after (2006–2011) the reform. The results indicate progress in technical efficiency of the ports after reform but deterioration in technological progress. Overall productivity growth was higher in the pre-concession period compared to the post-concession period. The source of pre-concession period productivity growth was technological progress while the change in productivity of the post-concession period is generated by an increase in scale efficiency. This suggests that concessionaires have not brought in the much anticipated investment in modern technology to drive port efficiency. The ports of Calabar and Apapa experienced the highest productivity growth while lowest result was Onne

An approximation to δ′\delta' couplings on graphs

We discuss a general parametrization for vertices of quantum graphs and show, in particular, how the $\delta'_s$ and $\delta'$ coupling at an $n$ edge vertex can be approximated by means of $n+1$ couplings of the $\delta$ type provided the latter are properly scaled.Comment: 10 pages, LaTeX, 1 figure added, to be published in J. of Phys.