The effect of oxygen on the recoil reactions of carbon-11 in hydrocarbons

The recoil reactions of carbon-11 produced by the c 12 (y, n)C11 reaction in benzene, cyclohexane, and n-hexane have been studied. Using gas chromatography for the analysis, the yields of carbon-11 labeled methane, ethane, ethylene, and acetylene were determined. The effect of radiation dose and oxygen scavenger on these yields was investigated

Marshall-Peierls sign rule for excited states of the frustrated J1-J2 Heisenberg antiferromagnet

We present analytical and numerical calculations for some exited states of the frustrated J1-J2 spin-1/2 Heisenberg model for linear chains and square lattices. We consider the lowest eigenstates in the subspaces determined by the eigenvalue M of the spin operator S_total^z. Because of the reduced number of Ising basis states in the subspaces with higher M we are able to diagonalize systems with up to N=144 spins. We find evidence that the Marshall-Peierls sign rule survives for a relatively large frustration parameter J2.Comment: 7 pages, LaTeX, 4 eps figures, to appear in Physica

Contribution of GABAergic Interneurons to the Development of Spontaneous Activity Patterns in Cultured Neocortical Networks

Periodic synchronized events are a hallmark feature of developing neuronal networks and are assumed to be crucial for the maturation of the neuronal circuitry. In the developing neocortex, the early network oscillations coincide with an excitatory action of the neurotransmitter gamma-aminobutyric acid (GABA). A relationship between the emerging inhibitory action of GABA and the gradual disappearance of early synchronized network activity has been previously suggested. Therefore we investigate the interplay between the action of GABA and spontaneous activity in cultured networks of the lateral or dorsal embryonic rat neocortex, which show considerable difference in the content of GABAergic neurons. Here we present the results of long-term monitoring of spontaneous electrical activity of cultured networks growing on microelectrode arrays and the time course of changes in GABA action using calcium imaging. All cultures studied displayed stereotyped synchronized burst events at the end of the first week in vitro. As the GABAA depolarizing action decreases, naturally or after bumetanide treatment, network activity in lateral cortex cultures changed from stereotypic bursting to more clustered and asynchronous activity patterns. Dorsal cortex cultures and cultures lacking GABAA-receptor mediated synaptic transmission, retained an immature synchronous firing pattern, but developed prominent intraburst oscillations (∼3–10 Hz). Large, mostly parvalbumin positive, GABAergic neurons dominate the GABAergic population in lateral cortex cultures. These large interneurons were virtually absent in dorsal cortex cultures. Based on these results, we suggest that the richly interconnected large GABAergic neurons contribute to desynchronize and temporally differentiate the spontaneous activity of cultured cortical networks

Energy intensity developments in 40 major economies: structural change or technology improvement?

This study analyzes energy intensity trends and drivers in 40 major economies using the WIOD database, a novel harmonized and consistent dataset of input-output table time series accompanied by environmental satellite data. We use logarithmic mean Divisia index decomposition to (1) study trends in global energy intensity between 1995 and 2007, (2) attribute efficiency changes to either changes in technology or changes in the structure of the economy, and (3) highlight sectoral and regional differences. We first show that heterogeneity within each sector across countries is high. These general trends within the sectors are dominated by large economies, first and foremost the United States. In most cases, heterogeneity is lower within each country across the different sectors. Regarding changes of energy intensity at the country level, improvements between 1995 and 2007 are largely attributable to technological change while structural change is less important in most countries. Notable exceptions are Japan, the United States, Australia, Taiwan, Mexico and Brazil where a change in the industry mix was the main driver behind the observed energy intensity reduction

A BGO detector for catalysis studies with positron emitters

A detector for measurement of the activity distribution of positron emitters in a catalyst reactor has been designed and built. The detector consists of two banks of each ten BGO scintillation crystals. The activity distribution is measured as a function of time and position along the reactor. The attainable position resolution along the reactor is 3 mm and the minimum sampling time for the measurement of an activity profile is 1 second. The detector has a high sensitivity and the flexibility to be used with catalyst reactors of different types and size