Two new marine sediment standard reference materials (SRMs) for the determination of organic contaminants

Two new marine sediment standard reference materials (SRMs), SRM 1941b Organics in Marine Sediment and SRM 1944 New York/New Jersey Waterway Sediment, have been recently issued by the National Institute of Standards and Technology (NIST) for the determination of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, and chlorinated pesticides. Both sediment SRMs were analyzed using multiple analytical methods including gas chromatography/mass spectrometry (GC/MS) on columns with different selectivity, reversed-phase liquid chromatography with fluorescence detection (for PAHs only), and GC with electron capture detection (for PCBs and pesticides only). SRM 1941b has certified concentrations for 24 PAHs, 29 PCB congeners, and 7 pesticides, and SRM 1944 has certified concentrations for 24 PAHs, 29 PCB congeners, and 4 pesticides. Reference concentrations are also provided for an additional 58 (SRM 1941b) and 39 (SRM 1944) PAHs, PCB congeners, and pesticides. SRM 1944, which was collected from multiple sites within New York/New Jersey coastal waterways, has contaminant concentrations that are generally a factor of 10–20 greater than SRM 1941b, which was collected in the Baltimore (Maryland) harbor. These two SRMs represent the most extensively characterized marine sediment certified reference materials available for the determination of organic contaminants.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Dynamics of effort allocation and evolution of trust: an agent-based model

Trust is a dynamic and complex phenomenon and understanding the factors which affect its formation, evolution and disappearance is a critical research issue. It has been shown that trust plays a key role in how human and social capital develop, how economies grow and how societies progress. In this paper, we present an agent-based model of the relations between a dynamic effort allocation system, an evolving trust framework and a reputation module to study how changes in micro-level rent-seeking traits and decisions can shape the emergence of trust across the simulated environment. According to our results, variations in trust are correlated more with the returns to being productive, rather than rent-seeking. In line with previous studies, our model shows that higher than average levels of risk-taking by agents lead to further trust and gains during an interaction, though taken to an extreme, both trust and gain can decline as a result of reckless decisions. We also report on the formation of trust clusters in our model as an emergent phenomenon.     

Laser and fluorescence properties of dye-doped sol-gel silica from 400 nm to 800 nm

Lasing and fluorescence properties of ten dyes covering the spectral range from 400 nm to 800 nm were studied in a silica matrix prepared by the sol-gel technique. The dye-doped sol-gel silica samples fluoresced strongly under laser excitation. Many of the samples were also induced to superradiate. In comparison to dyes in alcohol solvents, significant red-shifting was observed in the sol-gel silica fluorescence spectra. Plausible causes of the red-shift are discussed.     

A Rigourous Demonstration of the Validity of Boltzmann’s Scenario for the Spatial Homogenization of a Freely Expanding Gas and the Equilibration of the Kac Ring

Boltzmann provided a scenario to explain why individual macroscopic systems composed of a large number N of microscopic constituents are inevitably (i.e., with overwhelming probability) observed to approach a unique macroscopic state of thermodynamic equilibrium, and why after having done so, they are then observed to remain in that state, apparently forever. We provide here rigourous new results that mathematically prove the basic features of Boltzmann’s scenario for two classical models: a simple boundary-free model for the spatial homogenization of a non-interacting gas of point particles, and the well-known Kac ring model. Our results, based on concentration inequalities that go back to Hoeffding, and which focus on the typical behavior of individual macroscopic systems, improve upon previous results by providing estimates, exponential in N, of probabilities and time scales involved.     

Quantum and stochastic aspects of low-temperature trapping and reaction dynamics

We discuss theoretical work on motion-limited trapping kinetics at very low temperatures where theories based upon strictly diffusive models break down due to quantum mechanical effects. In addition, we present numerical results which confirm earlier asymptotic predictions regarding the survival probability for one-dimensional chains, and discuss the important role fluctuations and selfaveraging (or the lack thereof) play in the analysis of finite systems.     

Equilibration,Generalized Equipartition,and Diffusion in Dynamical Lorentz Gases

We demonstrate approach to thermal equilibrium in the fully Hamiltonian evolution of a dynamical Lorentz gas, by which we mean an ensemble of particles moving through a d-dimensional array of fixed soft scatterers that each possess an internal harmonic or anharmonic degree of freedom to which moving particles locally couple. We analytically predict, and numerically confirm, that the momentum distribution of the moving particles approaches a Maxwell-Boltzmann distribution at a certain temperature T, provided that they are initially fast and the scatterers are in a sufficiently energetic but otherwise arbitrary stationary state of their free dynamics—they need not be in a state of thermal equilibrium. The temperature T to which the particles equilibrate obeys a generalized equipartition relation, in which the associated thermal energy k _B T is equal to an appropriately defined average of the scatterers’ kinetic energy. In the equilibrated state, particle motion is diffusive.     

Asymmetric synthesis of cyclopropanes and dihydrofurans based on phosphine oxide chemistry

The asymmetric synthesis of gamma-azido trans-cyclopropyl ketones is accomplished via a short, simple and efficient sequence. The cyclopropanation step is achieved by an intramolecular nucleophilic ring closure, with a diphenylphosphinate leaving group, to give trans-cyclopropane exclusively. beta-Keto-diphenylphosphine oxides cyclise to form optically active dihydrofurans. All possible diastereoisomers of dihydrofurans can be prepared selectively starting from the same olefin.