High-performance anion-exchange chromatography–mass spectrometry method for determination of levoglucosan, mannosan, and galactosan in atmospheric fine particulate matter

Biomass burning has a strong influence on the atmospheric aerosol composition through particulate organic, inorganic, and soot emissions. When biomass burns, cellulose and hemicelluloses degrade, producing monosaccharide anhydrides (MAs) such as levoglucosan, mannosan, and galactosan. Therefore, these compounds have been commonly used as tracers for biomass burning. In this study, a fast water-based method was developed for the routine analysis of MAs, based on high-performance anion-exchange chromatography with electrospray ionization mass spectrometry detection. This method combines simple sample preparation, fast separation, and the advantages of the selective detection with MS. Analysis run was optimized to the maximum separation of levoglucosan, mannosan, and galactosan with 15-min analysis. The validation results indicated that the method showed good applicability for determination of MA isomer concentrations in ambient samples. The limit of detection was 100 pg for levoglucosan and 50 pg for mannosan and galactosan. Wide determination ranges enabled the analysis of samples of different concentration levels. The method showed good precision, both for standard solutions (3.9–5.9% RSD) and for fine particle samples (4.3–8.5% RSD). Co-elution of internal standard (carbon-13-labeled levoglucosan) and sugar alcohols with levoglucosan decreased the sensitivity of levoglucosan determination. The method was used to determine the MA concentrations in ambient fine particle samples from urban background (Helsinki) and rural background (Hyytiälä) in Finland. The average levoglucosan, mannosan, and galactosan concentrations were 77, 8.8, and 4.2 ng?m^?3 in Helsinki (winter 2008–2009) and 17, 2.3, and 1.4 ng?m^?3 in Hyytiälä (spring 2007), respectively. The interrelation of the three MA isomers was fairly constant in the ambient fine particle samples.     

Are the structures of twist grain boundaries in silicon ordered at 0 K?

Contrary to previous simulation results on the existence of amorphous intergranular films at high-angle twist grain boundaries (GBs) in elemental solids such as silicon, recent experimental results imply structural order in some high-angle boundaries. With a novel protocol for simulating twist GBs, which allows the number of atoms at the boundary to vary, we have found new low-energy ordered structures. We give a detailed exposition of the results for the simplest boundary. The validity of our results is confirmed by first-principles calculations.     

An adjustment scheme for nonlinear pricing problem with two buyers

We examine a contracting problem with asymmetric information in a monopoly pricing setting. Traditionally, the problem is modeled as a one-period Bayesian game, where the incomplete information about the buyers’ preferences is handled with some subjective probability distribution. Here we suggest an iterative online method to solve the problem. We show that, when the buyers behave myopically, the seller can learn the optimal tariff by selling the product repeatedly. In a practical modification of the method, the seller offers linear tariffs and adjusts them until optimality is reached. The adjustment can be seen as gradient adjustment, and it can be done with limited information and so that it benefits both the seller and the buyers. Our method uses special features of the problem and it is easily implementable.     

Markov Chains on Graded Posets

We consider two types of discrete-time Markov chains where the state space is a graded poset and the transitions are taken along the covering relations in the poset. The first type of Markov chain goes only in one direction, either up or down in the poset (an up chain or down chain). The second type toggles between two adjacent rank levels (an up-and-down chain). We introduce two compatibility concepts between the up-directed transition probabilities (an up rule) and the down-directed (a down rule), and we relate these to compatibility between up-and-down chains. This framework is used to prove a conjecture about a limit shape for a process on Young’s lattice. Finally, we settle the questions whether the reverse of an up chain is a down chain for some down rule and whether there exists an up or down chain at all if the rank function is not bounded.     

Enumeration of 2-(9, 3, λ) Designs and Their Resolutions

We consider 2-(9, 3, ) designs, which are known to exist for all 1, andenumerate such designs for = 5 and their resolutions for 3 5, the smallestopen cases. The number of nonisomorphic such structures obtained is 5 862 121 434, 426, 149 041, and 203 047732, respectively. The designs are obtained by an orderly algorithm, and the resolutions by two approaches:either by starting from the enumerated designs and applying a clique-finding algorithm on two levels or by anorderly algorithm.     

Classification of resolvable balanced incomplete block designs — the unitals on 28 points

Approaches for classifying resolvable balanced incomplete block designs (RBIBDs) are surveyed. The main approaches can roughly be divided into two types: those building up a design parallel class by parallel class and those proceeding point by point. With an algorithm of the latter type — and by refining ideas dating back to 1917 and the doctoral thesis by Pieter Mulder — it is shown that the list of seven known resolutions of 2-(28, 4, 1) designs is complete; these objects are also known as the resolutions of unitals on 28 points. This research was supported in part by the Academy of Finland, Grants No. 107493, 110196, and 117499.     

Instability of matchings in decentralized markets with various preference structures

In any two-sided matching market, a stable matching can be found by a central agency using the deferred acceptance procedure of Gale and Shapley. But if the market is decentralized and information is incomplete then stability of the ensuing matching is not to be expected. Despite the prevalence of such matching situations, and the importance of stability, little theory exists concerning instability. We discuss various measures of instability and analyze how they interact with the structure of the underlying preferences. Our main result is that even the outcome of decentralized matching with incomplete information can be expected to be “almost stable” under reasonable assumptions.     

Congestion and cascades in payment systems

We develop a parsimonious model of the interbank payment system. The model incorporates an endogenous instruction arrival process, a scale-free topology of payments between banks, a fixed total liquidity which limits banks’ capacity to process arriving instructions, and a global market that distributes liquidity. We find that at low liquidity the system becomes congested and payment settlement loses correlation with payment instruction arrival, becoming coupled across the network. The onset of congestion is evidently related to the relative values of three characteristic times: the time for banks’ net position to return to 0, the time for a bank to exhaust its liquidity endowment, and the liquidity market relaxation time. In the congested regime settlement takes place in cascades having a characteristic length scale. A global liquidity market substantially attenuates congestion, requiring only a small fraction of the payment-induced liquidity flow to achieve strong beneficial effects.     

Intelligent minority game with genetic crossover strategies

We have developed a novel game theoretical model of N interacting agents playing a minority game such that they change their strategies intelligently or adaptively depending on their temporal performances. The strategy changes are done by generating new strategies through one-point genetic crossover mechanism. The performances of agents are found to change dramatically (from losing to winning or otherwise) and the game moves rapidly to an efficient state, in which fluctuations in the number of agents performing a particular action, characterized by the variance , reaches a low value.Received: 2 June 2003, Published online: 11 August 2003PACS: 87.23.Ge Dynamics of social systems - 02.50.Le Decision theory and game theory - 87.23.Kg Dynamics of evolution