Stochastic gain in population dynamics

We introduce an extension of the usual replicator dynamics to adaptive learning rates. We show that a population with a dynamic learning rate can gain an increased average payoff in transient phases and can also exploit external noise, leading the system away from the Nash equilibrium, in a resonancelike fashion. The payoff versus noise curve resembles the signal to noise ratio curve in stochastic resonance. Seen in this broad context, we introduce another mechanism that exploits fluctuations in order to improve properties of the system. Such a mechanism could be of particular interest in economic systems.     

Functional MRI using intravascular contrast agents: detrending of the relative cerebrovascular (rCBV) time course

In pharmacological fMRI experiments in animal models, blood pool contrast agents may be used to map cerebral blood volume change as a surrogate for neural activation. When the background signal drift due to contrast agent washout is non-negligible over the duration of the signal changes of interest, time-course detrending is essential for accurate interpretation of the experiment. Detrending approaches based on estimation of the background signal from a baseline period of the time course prior to pharmacological (or functional) challenge were evaluated with the aim of identifying a robust method of estimating the contrast agent washout contribution to the background signal drift. For fMRI studies in the rat, it was found that a constrained fit of a mono-exponential washout model was more accurate than a constant background approximation and unconstrained fits for experiments investigating the functional response to rapid pharmacological challenges such as cocaine and amphetamine. Moreover, the constrained fitting approach allows shorter baseline periods than unconstrained extrapolation, reducing the required duration of the experiment.     

Asymptotics of Determinants of Bessel Operators

 For aL ^∞ (ℝ₊)∩L ¹ (ℝ₊) the truncated Bessel operator B _τ (a) is the integral operator acting on L ² [0,τ] with the kernel

Activation parameters for the reactive intermediates relevant to carbonylation catalysts based on cobalt carbonyls

Time-resolved spectroscopic techniques have been used to prepare and to interrogate transient species that are models for reactive intermediates in cobalt-catalyzed hydroformylation. Flash photolysis of acetylcobalt carbonyl complexes of the type RC(O)Co(CO)3(PR'3) (A; R = CH3, CD3, or C2H5; R' = Ph or nBu) leads to CO photodissociation to give the "unsaturated" intermediate [RC(O)Co(CO)2(PR'3)] (I), which decays by two competitive pathways, alkyl migration to the cobalt to give RCo(CO)3PR'3 (M) and reaction with CO to re-form A. With the perdeuterioacetyl complex (R = CD3, R' = Ph), rate constants both of CO trapping (kco) and of methyl migration (kM) were just slightly smaller than those of the perprotio analogue (kh/kd = 1.04 +/- 0.01 and 1.07 +/- 0.09, respectively). Thus, any stabilization of the "vacant" coordination site of I by agostic interactions with the acetyl methyl group appears to be kinetically insignificant, consistent with the previous conclusion (Inorg. Chem. 2000, 39, 3098-3106) that this site is stabilized by an eta 2-coordinated carbonyl. Changing the phosphine ligand has a greater influence on the kinetics of I. The species generated by the flash photolysis of the trialkyl phosphine complex CH3C(O)Co-(CO)3(P(nBu3)) exhibited a much larger kM than was the case for the PPh3 analogue, although there was little difference in the kco values. Similarly, kM proved to be sensitive to the nature of R as demonstrated by the slower alkyl migration (at 298 K) for the intermediate formed by CO photodissociation from the propionyl complex C2H5C(O)Co(CO)3PPh3 relative to the acetyl analogue. Nonetheless, all these intermediates displayed analogous time-resolved infrared spectra and general kinetics behavior in benzene solution (implying common mechanisms for decay), so it is concluded that all are present as the eta 2-chelated acyl structure under these conditions.     

Hierarchical Nanoporous Structures by Self‐Assembled Hybrid Materials Based on Block Copolymers

Hierarchical nanoporous structures are fabricated by adsorption of micelles of diblock copolymer‐templated Au‐nanoparticles onto a hydrophilic solid substrate. Gold nanoparticles are prepared using micelles (19 nm) of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) as nanoreactors. Deposition of thin films of the micellar solution, modified with a non‐selective solvent (THF), on hydrophilic surfaces leads to the formation of hierarchical nanoporous morphologies. The thin films exhibit two different pore diameters and a total pore density of 15 × 10⁸ holes per cm². The structure was analyzed in terms of topography and chemical composition using AFM, TEM and XPS measurements. The PS‐b‐P4VP template was subsequently removed by oxygen plasma etching, to leave behind metallic nanopores that mimic the original thin film morphology.

     

Effects of Spiro-Cyclohexane Substitution of Nitroxyl Biradicals on Dynamic Nuclear Polarization

Spiro-substituted nitroxyl biradicals are widely used as reagents for dynamic nuclear polarization (DNP), which is especially important for biopolymer research. The main criterion for their applicability as polarizing agents is the value of the spin–spin exchange interaction parameter (J), which can vary considerably when different couplers are employed that link the radical moieties. This paper describes a study on biradicals, with a ferrocene-1,1′-diyl-substituted 1,3-diazetidine-2,4-diimine coupler, that have never been used before as DNP agents. We observed a substantial difference in the temperature dependence between Electron Paramagnetic Resonance (EPR) spectra of biradicals carrying either methyl or spirocyclohexane substituents and explain the difference using Density Functional Theory (DFT) calculation results. It was shown that the replacement of methyl groups by spirocycles near the N-O group leads to an increase in the contribution of conformers having J ≈ 0. The DNP gain observed for the biradicals with methyl substituents is three times higher than that for the spiro-substituted nitroxyl biradicals and is inversely proportional to the contribution of biradicals manifesting the negligible exchange interaction. The effects of nucleophiles and substituents in the nitroxide biradicals on the ring-opening reaction of 1,3-diazetidine and the influence of the ring opening on the exchange interaction were also investigated. It was found that in contrast to the methyl-substituted nitroxide biradical (where we observed the ring-opening reaction upon the addition of amines), the ring opening does not occur in the spiro-substituted biradical owing to a steric barrier created by the bulky cyclohexyl substituents.     

Sequencing and scheduling for filling lines in dairy production

We consider an integrated sequencing and scheduling problem arising at filling lines in dairy industry. Even when a processing sequence is decided, still a scheduling problem has to be solved for the sequence. This incorporates typical side constraints as they occur also in other sequencing problems in practice. Previously, we proposed a framework for general sequencing and scheduling problems: A genetic algorithm is utilized for the sequencing, incorporating a problem specific algorithm for the fixed-sequence scheduling. In this paper, we investigate how this approach performs for filling lines. Based on insights into structural properties of the problem, we propose different scheduling algorithms. In cooperation with Sachsenmilch GmbH, the algorithm was implemented for their bottleneck filling line, and evaluated in an extensive computational study. For the real data from production, our algorithm computes almost optimal solutions. However, as a surprising result, our simple greedy algorithms outperform the more elaborate ones in many aspects, showing interesting directions for future research.