Optimally Convergent Quantum Jump Expansion

A method for deriving accurate analytic approximations for Markovian open quantum systems was recently introduced in [F. Lucas and K. Hornberger, Phys. Rev. Lett. 110, 240401 (2013)]. Here, we present a detailed derivation of the underlying non-perturbative jump expansion, which involves an adaptive resummation to ensure optimal convergence. Applying this to a set of exemplary master equations, we find that the resummation typically leads to convergence within the lowest two to five orders. Besides facilitating analytic approximations, the optimal jump expansion thus provides a numerical scheme for the efficient simulation of open quantum systems.Comment: 13 pages, 3 figure

Adaptive Resummation of Markovian Quantum Dynamics

We introduce a method for obtaining analytic approximations to the evolution of Markovian open quantum systems. It is based on resumming a generalized Dyson series in a way that ensures optimal convergence even in the absence of a small parameter. The power of this approach is demonstrated by two benchmark examples: the spatial detection of a free particle and the Landau-Zener problem in the presence of dephasing. The derived approximations are asymptotically exact and exhibit errors on the per mil level over the entire parameter range.Comment: 5 pages, 2 figures - minor changes, typos correcte

Synchronization Through Uncorrelated Noise in Excitatory-Inhibitory Networks

© 2022 Rebscher, Obermayer and Metzner. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)Gamma rhythms play a major role in many different processes in the brain, such as attention, working memory, and sensory processing. While typically considered detrimental, counterintuitively noise can sometimes have beneficial effects on communication and information transfer. Recently, Meng and Riecke showed that synchronization of interacting networks of inhibitory neurons in the gamma band (i.e., gamma generated through an ING mechanism) increases while synchronization within these networks decreases when neurons are subject to uncorrelated noise. However, experimental and modeling studies point towardz an important role of the pyramidal-interneuronal network gamma (PING) mechanism in the cortex. Therefore, we investigated the effect of uncorrelated noise on the communication between excitatory-inhibitory networks producing gamma oscillations via a PING mechanism. Our results suggest that, at least in a certain range of noise strengths and natural frequency differences between the regions, synaptic noise can have a supporting role in facilitating inter-regional communication, similar to the ING case for a slightly larger parameter range. Furthermore, the noise-induced synchronization between networks is generated via a different mechanism than when synchronization is mediated by strong synaptic coupling. Noise-induced synchronization is achieved by lowering synchronization within networks which allows the respective other network to impose its own gamma rhythm resulting in synchronization between networks.Peer reviewedFinal Published versio

Interaction of aromatic isocyanates with n-acetyl-lcysteine under physiological conditions

Isocyanates are of toxicological relevance since they are considered to cause occupational asthma. The majority of polyurethanes is based on aromatic diisocyanates (e.g., TDI and MDI), they are used for foams, elastomers, adhesives and coatings. Therefore we studied reactions of p-tolylisocyanate (pTI), 2,4-toluene diisocyanate (TDI) and 4,4- methylenediphenyl diisocyanate (MDI) with N-acetyl-L-cysteine (AcCys) with different molar ratios in aqueous buffer solutions of pH 5.0 - 7.4. Type and amounts of products formed in these reactions were identified and quantified. Conjugates of AcCys and the aromatic isocyanates have been synthesized and characterized as reference materials. Conjugates and ureas were found to be the main products. The ratio of these two compounds varied with the ratio of AcCys to isocyanate. Approximately 90 % of pTI conjugate were found for the 10 : 1 ratio, approximately 40 % conjugate for the 10 : 5 and around 15 % for the 10 : 15 ratio. For TDI yields of conjugate were comparable. Ureas, apart from minor amounts of TDA-urea could not be determined quantitatively due to formation of oligomeric ureas with different end groups. Minor amounts of MDI-conjugates were found apart from high amounts of insoluble material, which proved to be unreacted MDI encapsulated by oligomeric ureas. The reaction of the -SH group with the isocyanate moiety is independent of the pH of the solution in the range studied. No diamine, i.e. 2,4-TDA or 4,4-MDA, could be detected in reactions of the diisocyanates 2,4-TDI or 4,4-MDI. Small amounts of p-toluidine (pTA) were found in the reaction of the mono isocyanate pTI when it was in excess with respect to AcCys. Reactions of the isocyanates with an aqueous buffer solution of pH 6.5 in the absence of AcCys gave ureas as main products, while significant amounts of unreacted diisocyanates remained encapsulated in the mixture. No 2,4-TDA or 4,4-MDA was detected under these conditions. Again small amounts of pTA were formed from the reaction of pTI with water

Pay What You Want as a Pricing Model for Open Access Publishing?

We analyze 'Pay What You Want' as a business model for Open Access publishing by discussing motives leading authors to make voluntary contributions, potential benefits for publishers and present results from a field experiment at one publisher. Data from the field experiment indicate authors' willingness to voluntarily contribute