Two Particle States in a Box and the ss-Matrix in Multi-Channel Scattering

Using a quantum mechanical model, the exact energy eigenstates for two-particle two-channel scattering are studied in a cubic box with periodic boundary conditions. A relation between the exact energy eigenvalue in the box and the two-channel $S$-matrix elements in the continuum is obtained. This result can be viewed as a generalization of the well-known L\"uscher's formula which establishes a similar relation in elastic scattering.Comment: 4 pages, typeset with ws-ijmpa.cls. Talk presented at International Conference on QCD and Hadronic Physics, June 16-20, 2005, Beijing, China. One reference adde

Analysing web search logs to determine session boundaries for user-oriented learning

Incremental learning approaches based on user search activities provide a means of building adaptive information retrieval systems. To develop more effective user-oriented learning techniques for the Web, we need to be able to identify a meaningful session unit from which we can learn. Without this, we run a high risk of grouping together activities that are unrelated or perhaps not from the same user. We are interested in detecting boundaries of sequences between related activities (sessions) that would group the activities for a learning purpose. Session boundaries, in Reuters transaction logs, were detected automatically. The generated boundaries were compared with human judgements. The comparison confirmed that a meaningful session threshold for establishing these session boundaries was confined to a 11-15 minute range

Effects of current on vortex and transverse domain walls

By using the spin torque model in ferromagnets, we compare the response of vortex and transverse walls to the electrical current. For a defect-free sample and a small applied current, the steady state wall mobility is independent of the wall structure. In the presence of defects, the minimum current required to overcome the wall pinning potential is much smaller for the vortex wall than for the transverse wall. During the wall motion, the vortex wall tends to transform to the transverse wall. We construct a phase diagram for the wall mobility and the wall transformation driven by the current

Of McKay Correspondence, Non-linear Sigma-model and Conformal Field Theory

The ubiquitous ADE classification has induced many proposals of often mysterious correspondences both in mathematics and physics. The mathematics side includes quiver theory and the McKay Correspondence which relates finite group representation theory to Lie algebras as well as crepant resolutions of Gorenstein singularities. On the physics side, we have the graph-theoretic classification of the modular invariants of WZW models, as well as the relation between the string theory nonlinear $\sigma$-models and Landau-Ginzburg orbifolds. We here propose a unification scheme which naturally incorporates all these correspondences of the ADE type in two complex dimensions. An intricate web of inter-relations is constructed, providing a possible guideline to establish new directions of research or alternate pathways to the standing problems in higher dimensions.Comment: 35 pages, 4 figures; minor corrections, comments on toric geometry and references adde

Searching for radiative pumping lines of OH masers: II. The 53.3um absorption line towards 1612MHz OH maser sources

This paper analyzes the 53.3um line in the ISO LWS spectra towards a similar sample of OH/IR sources. We find 137 LWS spectra covering 53.3um and associated with 47 galactic OH/IR sources. Ten of these galactic OH/IR sources are found to show and another 5 ones tentatively show the 53.3um absorption while another 7 sources highly probably do not show this line. The source class is found to be correlated with the type of spectral profile: red supergiants (RSGs) and AGB stars tend to show strong blue-shifted filling emission in their 53.3um absorption line profiles while HII regions tend to show a weak red-shifted filling emission in the line profile. GC sources and megamasers do not show filling emission feature. It is argued that the filling emission might be the manifestation of an unresolved half emission half absorption profile of the 53.3um doublet. The 53.3 to 34.6um equivalent width (EW) ratio is close to unity for RSGs but much larger than unity for GC sources and megamasers while H II regions only show the 53.3um line. The pump rate defined as maser to IR photon flux ratio is approximately 5% for RSGs. The pump rates of GC sources are three order of magnitude smaller. Both the large 53.3 to 34.6um EW ratio and the small pump rate of the GC OH masers reflect that the two detected `pumping lines' in these sources are actually of interstellar origin. The pump rate of Arp 220 is 32%--much larger than that of RSGs, which indicates that the contribution of other pumping mechanisms to this megamaser is important.Comment: 34 pages, 12 figures, 4 table

Quantum bit string sealing

Though it was proven that secure quantum sealing of a single classical bit is impossible in principle, here we propose an unconditionally secure quantum sealing protocol which seals a classical bit string. Any reader can obtain each bit of the sealed string with an arbitrarily small error rate, while reading the string is detectable. The protocol is simple and easy to be implemented. The possibility of using this protocol to seal a single bit in practical is also discussed.Comment: Add a discussion on the possibility of sealing a single bit in practica