3,400 research outputs found
Low-field diffusion magneto-thermopower of a high mobility two-dimensional electron gas
The low magnetic field diffusion thermopower of a high mobility
GaAs-heterostructure has been measured directly on an electrostatically defined
micron-scale Hall-bar structure at low temperature (T = 1.6 K) in the low
magnetic field regime (B < 1.2 T) where delocalized quantum Hall states do not
influence the measurements. The sample design allowed the determination of the
field dependence of the thermopower both parallel and perpendicular to the
temperature gradient, denoted respectively by Sxx (longitudinal thermopower)
and Syx (Nernst-Ettinghausen coefficient). The experimental data show clear
oscillations in Sxx and Syx due to the formation of Landau levels for 0.3 T < B
< 1.2 T and reveal that Syx is approximately 120 times larger than Sxx at a
magnetic field of 1 T, which agrees well with the theoretical prediction.Comment: 4 pages, 4 figure
PUBLIC PRIVATE PARTNERSHIP AS MEANS OF OVERCOMING ENTRY BARRIERS FOR PRIVATE INVESTORS TO A MARKET OFINFRASTRUCTURE PROJECTS
The definition of Public Private Partnership is given in the article. The major entry barriers for private investors are concerned. Influence of Public Private Partnership development process is analyzed
PUBLIC PRIVATE PARTNERSHIP AS MEANS OF OVERCOMING ENTRY BARRIERS FOR PRIVATE INVESTORS TO A MARKET OFINFRASTRUCTURE PROJECTS
The definition of Public Private Partnership is given in the article. The major entry barriers for private investors are concerned. Influence of Public Private Partnership development process is analyzed
Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra
With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arcti
A smoothing monotonic convergent optimal control algorithm for NMR pulse sequence design
The past decade has demonstrated increasing interests in using optimal
control based methods within coherent quantum controllable systems. The
versatility of such methods has been demonstrated with particular elegance
within nuclear magnetic resonance (NMR) where natural separation between
coherent and dissipative spin dynamics processes has enabled coherent quantum
control over long periods of time to shape the experiment to almost ideal
adoption to the spin system and external manipulations. This has led to new
design principles as well as powerful new experimental methods within magnetic
resonance imaging, liquid-state and solid-state NMR spectroscopy. For this
development to continue and expand, it is crucially important to constantly
improve the underlying numerical algorithms to provide numerical solutions
which are optimally compatible with implementation on current instrumentation
and at same time are numerically stable and offer fast monotonic convergence
towards the target. Addressing such aims, we here present a smoothing
monotonically convergent algorithm for pulse sequence design in magnetic
resonance which with improved optimization stability lead to smooth pulse
sequence easier to implement experimentally and potentially understand within
the analytical framework of modern NMR spectroscopy
Monitoring synaptic transmission in primary neuronal cultures using local extracellular stimulation
Various techniques have been applied for the functional analysis of synaptic transmission in Cultured neurons. Here, we describe a method of studying synaptic transmission in neurons cultured at high-density from different brain regions such as the cortex, striatum and spinal cord. We use postsynaptic whole-cell recordings to monitor synaptic Currents triggered by presynaptic action potentials that are induced by brief stimulations with a nearby extracellular bipolar electrode. Pharmacologically isolated excitatory or inhibitory postsynaptic currents can be reliably induced, with amplitudes, synaptic charge transfers, and short-term plasticity properties that are reproducible from culture to culture. We show that the size and kinetics of pharmacologically isolated inhibitory postsynaptic Currents triggered by single action potentials or stimulus trains depend on the Ca2+ concentration, temperature and stimulation frequency. This method can be applied to study synaptic transmission in wildtype neurons infected with lentiviruses encoding various components of presynaptic release machinery, or in neurons from genetically modified mice, for example neurons carrying floxed genes in which gene expression can be acutely ablated by expression of Cre recombinase. The preparation described in this paper should be useful for analysis of synaptic transmission in inter-neuronal synapses formed by different types of neurons. (c) 2006 Elsevier B.V. All rights reserved
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