Collaboration on reference to objects that are not mutually known

In conversation, a person sometimes has to refer to an object that is not previously known to the other participant. We present a plan-based model of how agents collaborate on reference of this sort. In making a reference, an agent uses the most salient attributes of the referent. In understanding a reference, an agent determines his confidence in its adequacy as a means of identifying the referent. To collaborate, the agents use judgment, suggestion, and elaboration moves to refashion an inadequate referring expression.Comment: 6 pages, to appear in proceedings of COLING-94, LaTeX (now uses fullname.sty, fullname.bst

The first hill:The signature of Istanbul

Taha Toros Arşivi, Dosya No: 6-Sultanahmetİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

The first hill:The signature of Istanbul

Taha Toros Arşivi, Dosya Adı: İstanbul Genel Dokümanlarıİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

The Application of Combined Gas Chromatography-Mass Spectrometry to Compounds of Biological Interest: Steroid Analysis by the Use of Glass Open Tubular Gas Chromatographic Columns

Steroidal compounds are virtually ubiquitous in nature and frequently occur in complex mixtures as constituents of closely similar structure. Packed column gas chromatography-mass spectrometry (GC-MS) is an analytical technique of unique facility for the simultaneous separation and characterisation of complex mixtures of organic compounds. This thesis examines the additional facility provided by glass open tubular gas chromatographic columns of higher efficiency in the analysis by GC and GC-MS of complex mixtures of steroidal compounds derived from a number of natural sources. A method for the preparation of stable, efficient and reproducible glass open tubular gas chromatographic columns is described. The construction of chromatographic systems adapted to their somewhat more critical requirements is outlined. Particular attention is paid to the requirements for the interface of these columns to an LKB 9000 combined gas chromatograph-mass spectrometer. The performance of this system with emphasis on the nature of the advantage obtained over conventional packed columns is demonstrated by several model separations of mixtures of closely related standard steroidal compounds. Mixtures of sterols derived from yeast and marine sources frequently consist in mixtures of components differing in the degree and position of alkylation and unsaturation in the basic cholestanol structure. Correlation of gas chromatographic retention, on glass open tubular columns of OV-1 stationary phase, with sterol structure is described. Complementary data available in the literature are integrated into a scheme for the rationalisation of increments of Kovats retention index associated with particular alterations in sterol structure. This system and mass spectral correlations obtained by glass open tubular GC-MS is applied to the analysis of sterol mixtures derived from five species of marine invertebrate and two mutant strains of the yeast Candida albicans. Two other applications to sterol analysis are also described. A significant advantage is demonstrated over GC and GC-MS methods heretofore employed. Mixtures of hydroxy and ketosteroids may be derivatised as the alkyloxime-trimethylsilyl ether derivatives for GC and GC-MS analysis. The occurrence of syn- and anti-isomers in the alkyloximes of various ketosteroid structures is a complicating factor in their GC analysis, in particular at higher column efficiencies. Several alkyloximes of increasing hulk of the O-alkyl substituent were examined in this respect. The methyloxime is shown to provide the least complications for open tubular GC, though the "group separations" of hydroxy and ketosteroids provided by the higher alkyloximes may provide useful correlations. The utility of this approach is demonstrated in the analysis of mixtures of standard hydroxy and ketosteroids. Preliminary results obtained on a mixture of urinary steroid hormone metabolites of the human newborn by open tubular GC-MS of the isopentyloxime-trimethylsilyl ether derivatives are reported

Hypergraphic LP Relaxations for Steiner Trees

We investigate hypergraphic LP relaxations for the Steiner tree problem, primarily the partition LP relaxation introduced by Koenemann et al. [Math. Programming, 2009]. Specifically, we are interested in proving upper bounds on the integrality gap of this LP, and studying its relation to other linear relaxations. Our results are the following. Structural results: We extend the technique of uncrossing, usually applied to families of sets, to families of partitions. As a consequence we show that any basic feasible solution to the partition LP formulation has sparse support. Although the number of variables could be exponential, the number of positive variables is at most the number of terminals. Relations with other relaxations: We show the equivalence of the partition LP relaxation with other known hypergraphic relaxations. We also show that these hypergraphic relaxations are equivalent to the well studied bidirected cut relaxation, if the instance is quasibipartite. Integrality gap upper bounds: We show an upper bound of sqrt(3) ~ 1.729 on the integrality gap of these hypergraph relaxations in general graphs. In the special case of uniformly quasibipartite instances, we show an improved upper bound of 73/60 ~ 1.216. By our equivalence theorem, the latter result implies an improved upper bound for the bidirected cut relaxation as well.Comment: Revised full version; a shorter version will appear at IPCO 2010

Proton emission induced by polarized photons

The proton emission induced by polarized photons is studied in the energy range above the giant resonance region and below the pion emission threshold. Results for the 12C, 16O and 40Ca nuclei are presented. The sensitivity of various observables to final state interaction, meson exchange currents and short range correlations is analyzed. We found relevant effects due to the virtual excitation of the $\Delta$ resonance.Comment: 12 pages, 11 figures, 1 tabl

Spin evolution of spin-1 Bose-Einstein condensates

An analytical formula is obtained to describe the evolution of the average populations of spin components of spin-1 atomic gases. The formula is derived from the exact time-dependent solution of the Hamiltonian $H_{S}=c mathbf{S}^{2}$ without using approximation. Therefore it goes beyond the mean field theory and provides a general, accurate, and complete description for the whole process of non-dissipative evolution starting from various initial states. The numerical results directly given by the formula coincide qualitatively well with existing experimental data, and also with other theoretical results from solving dynamic differential equations. For some special cases of initial state, instead of undergoing strong oscillation as found previously, the evolution is found to go on very steadily in a very long duration.Comment: 7 pages, 3 figures

Surface reflectance and conversion efficiency dependence of technologies for mitigating global warming

A means of assessing the relative impact of different renewable energy technologies on global warming has been developed. All power plants emit thermal energy to the atmosphere. Fossil fuel power plants also emit CO2 which accumulates in the atmosphere and provides an indirect increase in global warming via the greenhouse effect. A fossil fuel power plant may operate for some time before the global warming due to its CO2 emission exceeds the warming due to its direct heat emission. When a renewable energy power plant is deployed instead of a fossil fuel power plant there may be a significant time delay before the direct global warming effect is less than the combined direct and indirect global warming effect from an equivalent output coal fired plant - the " business as usual" case. Simple expressions are derived to calculate global temperature change as a function of ground reflectance and conversion efficiency for various types of fossil fuelled and renewable energy power plants. These expressions are used to assess the global warming mitigation potential of some proposed Australian renewable energy projects. The application of the expressions is extended to evaluate the deployment in Australia of current and new geo-engineering and carbon sequestration solutions to mitigate global warming. Principal findings are that warming mitigation depends strongly on the solar to electric conversion efficiency of renewable technologies, geo-engineering projects may offer more economic mitigation than renewable energy projects and the mitigation potential of reforestation projects depends strongly on the location of the projects. © 2010 Elsevier Ltd