A form of regular variation and its application to the domain of attraction of the double exponential distribution

Probability Theory and Related Fields -     

Charge transport in self-organized pi-stacks of p-phenylene vinylene oligomers

We have studied the mobility of charge carriers along self-organizing pi-stacks of hydrogen-bonded phenylene vinylene oligomers in solution, by time-resolved microwave conductivity measurements. The value deduced for the mobility along the stacks is 3 x 10(-3) and 9 x 10(-3) cm2/(V s) for holes and electrons, respectively. Additionally, we have calculated the mobility along the pi-stacks using a hopping model based on parameters from density functional theory. The mobility values obtained from these calculations are in good agreement with the experimental values if it is assumed that there are relatively large twist angles between neighboring molecules in the stack. It is shown that a significantly higher mobility can be attained if the twist angle between neighboring oligomers is reduced.     

On the core of routing games

A repairman makes a round-trip along a set of customers. He starts in his home location, visits each customer exactly once, and returns home. The cost of his trip has to be shared by the customers. A cooperative cost game, calledrouting game, is associated with this allocation problem, and anO(n ²) algorithm is given which computes a core element of a routing game if the core is non-empty. The non-emptiness of the core depends on the tour which is traversed by the repairman. Several procedures are given to construct tours which guarantee the non-emptiness of the core.     

Improvement of photosynthetic CO2 fixation at high light intensity through reduction of chlorophyll antenna size

At elevated light intensities (greater than ∼200 μE/[m²·s]), the kinetic imbalance between the rate of photon excitation and thermally activated electron transport results in saturation of the rate of photosynthesis. Since maximum terrestrial solar radiation can reach 200 μE/(m²·s), a significant opportunity exists to improve photosynthetic efficiency at elevated light intensities by achieving a kinetic balance between photon excitation and electron transport, especially in designed large-scale photosynthetic reactors in which a low-cost and efficient biomass production system is desired. One such strategy is a reduction in chlorophyll (chl) antenna size in relation to the reaction center that it serves. In this article, we report recent progress in this area of research. Light-saturation studies for CO₂ fixation were performed on an antenna-deficient mutant of Chlamydomonas (DS521) and the wild type (DES15) with 700 ppm of CO₂ in air. The light-saturated rate for CO₂ assimilation in the mutant DS521 was about two times higher (187 μmol/[h·mg of chl]) than that of the wild type, DES15 (95 μmol/[h·mg of chl]). Significantly, a partial linearization of the light-saturation curve was also observed. These results confirmed that DS521 has a smaller relative chl antenna size and demonstrated that reduction of relative antenna size can improve the overall efficiency of photon utilization at higher light intensities. The antenna-deficient mutant DS521 can provide significant resistance to photoinhibition, in addition to improvement in the overall efficiency of CO₂ fixation at high light. The experimental data reported herein support the idea that reduction in chl antenna size could have significant implications for both fundamental understanding of photosynthesis and potential application to improve photosynthetic CO₂ fixation efficiency. The article was authored by a contractor of the U.S. government under contract no. DE-AC05-00OR22725. Accordingly, the U.S. government retains a nonexclusive, royaltyfree license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. government purposes.     

Unbiased computation of transition times by pathway recombination

In many systems, the time scales of the microscopic dynamics and macroscopic dynamics of interest are separated by many orders of magnitude. Examples abound, for instance, nucleation, protein folding, and chemical reactions. For these systems, direct simulation of phase space trajectories does not efficiently determine most physical quantities of interest. The past decade has seen the advent of methods circumventing brute force simulation. For most dynamical quantities, these methods all share the drawback of systematical errors. We present a novel method for generating ensembles of phase space trajectories. By sampling small pieces of these trajectories in different phase space domains and piecing them together in a smart way using equilibrium properties, we obtain physical quantities such as transition times. This method does not have any systematical error and is very efficient; the computational effort to calculate the first passage time across a free energy barrier does not increase with the height of the barrier. The strength of the method is shown in the Ising model. Accurate measurements of nucleation times span almost ten orders of magnitude and reveal corrections to classical nucleation theory.     

Photothermal Detection of Individual Gold Nanoparticles: Perspectives for High‐Throughput Screening

We use photothermal microscopy to detect and image individual gold nanoparticles that are either embedded in a polymer film or immobilized in an aqueous environment. Reducing the numerical aperture of the detection optics allows us to achieve a 200‐fold‐enlarged detection volume while still retaining sufficient detectivity. We characterize the capabilities of this approach for the detection of gold colloids with a diameter of 20 nm, with emphasis on practical aspects that are important for high‐throughput‐screening applications. The extended detection volume in combination with the stability of the photothermal signal are major advantages compared to fluorescence‐based approaches, which are limited by photoblinking and photobleaching. Careful consideration is given to the trade‐off between the maximum increase in local temperature that can be tolerated by a biological specimen and the minimum integration time needed to reliably determine whether a given volume contains a target species. We find that our approach has the potential to increase the detection‐limited flow rate (i.e. the limit given by the detection volume divided by the minimum detection time) by two to three orders of magnitude.     

High speed analysis of H2S and COS impurities in coal gas by capillary gas chromatography

There is a need for rapid, on-line, gas chromatographic analysis of trace levels of hydrogen sulfide and carbon oxysulfide in the oil-from-coal industry. In order to improve an existing method based on a polymer bed concentrator, a porous layer open tubular column, and a flame photometric detector, time-optimization of the various steps involved was attempted. Use of a redesigned concentrator, changed column operating conditions, and a photoionization detector reduced analysis times from 6.5 to 3 min and cycle times from 8 to 3 min. This could be achieved without compromising the 10 ppb detection limit required.