On Solving Quickest Time Problems in Time-Dependent, Dynamic Networks

In this paper, a pseudopolynomial time algorithm is presented for solving the integral time-dependent quickest flow problem (TDQFP) and its multiple source and sink counterparts: the time-dependent evacuation and quickest transshipment problems. A more widely known, though less general version, is the quickest flow problem (QFP). The QFP has historically been defined on a dynamic network, where time is divided into discrete units, flow moves through the network over time, travel times determine how long each unit of flow spends traversing an arc, and capacities restrict the rate of flow on an arc. The goal of the QFP is to determine the paths along which to send a given supply from a single source to a single sink such that the last unit of flow arrives at the sink in the minimum time. The main contribution of this paper is the time-dependent quickest flow (TDQFP) algorithm which solves the TDQFP, i.e. it solves the integral QFP, as defined above, on a time-dependent dynamic network, where the arc travel times, arc and node capacities, and supply at the source vary with time. Furthermore, this algorithm solves the time-dependent minimum time dynamic flow problem, whose objective is to determine the paths that lead to the minimum total time spent completing all shipments from source to sink. An optimal solution to the latter problem is guaranteed to be optimal for the TDQFP. By adding a small number of nodes and arcs to the existing network, we show how the algorithm can be used to solve both the time-dependent evacuation and the time-dependent quickest transshipment problems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of the out-of-plane emission of protons and light fragments in symmetric heavy-ion collisions

Midrapidity protons from²⁰⁹Bi+²⁰⁹Bi collisions were measured with the Kaon Spectrometer at SIS at incident energies of E _Lab /A=400, 700 and 1000 MeV. Additionally, light fragments were analysed at 400 MeV. We have investigated the azimuthal emission pattern of the particles relative to the reaction plane as function of transverse momentum, bombarding energy and impact parameter. We observe an enhanced emission of particles perpendicular to the reaction plane at all bombarding energies. The ratio of the number of particles emitted out-of-plane/in-plane increases strongly with the particles transverse momentum. The anisotropy decreases with increasing beam energy. Composite particles show a much stronger effect than protons.     

Energy-selective charging of type-II GaSb/GaAs quantum dots

The hole confinement in type-II self-organized GaSb/GaAs quantum dots (QDs) was investigated by combining optical excitation and time-resolved capacitance spectroscopy. The experimental results indicate energy-selective charging even for type-II QDs. With increasing excitation energy the apparent hole activation energy decreases, which is attributed to light absorption in sub-ensembles of QDs with decreasing hole localization. The large localization energy of about 450 meV and the possibility of optical-multiplexing makes type-II GaSb/GaAs QDs a potential material system for QD memory concepts.     

Absolute fluorescence quantum yields for vapour-phase benzene and naphthalene,and comments on the non-radiative processes

Optic—acoustic measurements have been employed in the determination of absolute quantum yields for benzene and naphthalene. Heat yields are measured by a method using oxygen quenching of both triplet and singlet states. For vibrationally relaxed excited singlet states the fluorescence quantum yields, φ^B_f, are 0.16 ± 0.02 and 0.79 ± 0.02 for benzene and naphthalene respectively. For 0.07 torr naphthalene at room temperature with 248 nm excitation, φ_f = 0.35 ± 0.03 and the quantum yield of internal conversion is less than 0.05. The decay of the highly vibrationally excited triplet state is dominated by vibrational relaxation for 0.07 torr naphthalene, but for benzene, even at high pressures, strong competition comes from an indirect coupling process to the ground state.     

The cathodic stripping voltammetry of certain thiols in acetate medium

The cathodic stripping voltammetry of six thiols by deposition at a hanging mercury drop electrode (+0.05 V vs. SCE) from acetate-buffered solution (pH 4.76) and scanning to —0.8 V is described. Peak potentials are reported. The peak height—concentration relationships are reasonably linear in the range 0.4–1.2 μM. The compounds tested are 2-mercaptopyridine, 2-mercapto-3-pyridinol, 2-mercaptopyridine-N-oxide, mercaptosuccinic acid, 2-mercaptopyrimidine and cysteine hydrochloride.