4,139 research outputs found
Respiration rates of soil invertebrates from temperate and tropical zones as measured by infrared gas analysis.
The aim of our investigation was to measure the amount of carbon that is directly contributed by the soil fauna. Therefore a devide to measure the small amounts of CO2 released by soil invertebrates was developed. A commercially available portable photosynthesis measuring system, based on an infrared gas analyzer (IRGA) and designed to quantifity the CO2 uktake to single plant leaves, was modified in such a way that the CO2 production of soil invertebrates could be measured
Decrumpling membranes by quantum effects
The phase diagram of an incompressible fluid membrane subject to quantum and
thermal fluctuations is calculated exactly in a large number of dimensions of
configuration space. At zero temperature, a crumpling transition is found at a
critical bending rigidity . For membranes of fixed lateral
size, a crumpling transition occurs at nonzero temperatures in an auxiliary
mean field approximation. As the lateral size L of the membrane becomes large,
the flat regime shrinks with .Comment: 9 pages, 4 figure
Ferromagnetism and superconductivity in P-doped CeFeAsO
We report on superconductivity in CeFeAs1-xPxO and the possible coexistence
with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with
ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering
temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K
and does not shift to lower temperatures with further increase of the P
concentration. Therefore, a quantum-critical-point scenario with T^N_Fe -> 0K
which is widely discussed for the iron based superconductors can be excluded
for this alloy series. Surprisingly, thermal expansion and X-ray powder
diffraction indicate the absence of an orthorhombic distortion despite clear
evidence for short range AFM Fe-ordering from muon-spin-rotation measurements.
Furthermore, we discovered the formation of a sharp electron spin resonance
signal unambiguously connected with the emergence of FM ordering.Comment: 5 pages, 4 figures, published in Phys. Rev. B (Rapid Communication,
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Review of SIS Experimental Results on Strangeness
>A review of meson emission in heavy ion collisions at incident energies
around 1 -- 2 GeV is presented. It is shown how the shape of the
spectra and the various particle yields vary with system size, with centrality
and with incident energy. A statistical model assuming thermal and chemical
equilibrium and exact strangeness conservation (i.e. strangeness conservation
per collision) explains most of the observed features.
Emphasis is put onto the study of and emission. In the framework
of this statistical model it is shown that the experimentally observed equality
of and rates at threshold corrected energies is due to a crossing of two excitation functions. Furthermore,
the independence of the to ratio on the number of participating
nucleons observed between 1 and 10 GeV is consistent with this model.
The observed flow effects are beyond the scope of this model.Comment: 10 pages, 9 figures, Strangeness 2000, V International Conference on
Strangeness in Quark Matter, July, 2000, Berkeley, Californi
Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain
Background
This paper describes the metabolic engineering of Escherichia coli for the anaerobic fermentation of glucose to acetoin. Acetoin has well-established applications in industrial food production and was suggested to be a platform chemical for a bio-based economy. However, the biotechnological production is often hampered by the simultaneous formation of several end products in the absence of an electron acceptor. Moreover, typical production strains are often potentially pathogenic. The goal of this study was to overcome these limitations by establishing an electrode-assisted fermentation process in E. coli. Here, the surplus of electrons released in the production process is transferred to an electrode as anoxic and non-depletable electron acceptor.
Results
In a first step, the central metabolism was steered towards the production of pyruvate from glucose by deletion of genes encoding for enzymes of central reactions of the anaerobic carbon metabolism (ÎfrdA-D ÎadhE ÎldhA Îptaâack). Thereafter, the genes for the acetolactate synthase (alsS) and the acetolactate decarboxylase (alsD) were expressed in this strain from a plasmid. Addition of nitrate as electron acceptor led to an anaerobic acetoin production with a yield of up to 0.9 mol acetoin per mol of glucose consumed (90% of the theoretical maximum). In a second step, the electron acceptor nitrate was replaced by a carbon electrode. This interaction necessitated the further expression of c-type cytochromes from Shewanella oneidensis and the addition of the soluble redox shuttle methylene blue. The interaction with the non-depletable electron acceptor led to an acetoin formation with a yield of 79% of the theoretical maximum (0.79 mol acetoin per mol glucose).
Conclusion
Electrode-assisted fermentations are a new strategy to produce substances of biotechnological value that are more oxidized than the substrates. Here, we show for the first time a process in which the commonly used chassis strain E. coli was tailored for an electrode-assisted fermentation approach branching off from the central metabolite pyruvate. At this early stage, we see promising results regarding carbon and electron recovery and will use further strain development to increase the anaerobic metabolic turnover rate
How Many Cooks Spoil the Soup?
In this work, we study the following basic question: "How much parallelism
does a distributed task permit?" Our definition of parallelism (or symmetry)
here is not in terms of speed, but in terms of identical roles that processes
have at the same time in the execution. We initiate this study in population
protocols, a very simple model that not only allows for a straightforward
definition of what a role is, but also encloses the challenge of isolating the
properties that are due to the protocol from those that are due to the
adversary scheduler, who controls the interactions between the processes. We
(i) give a partial characterization of the set of predicates on input
assignments that can be stably computed with maximum symmetry, i.e.,
, where is the minimum multiplicity of a state in
the initial configuration, and (ii) we turn our attention to the remaining
predicates and prove a strong impossibility result for the parity predicate:
the inherent symmetry of any protocol that stably computes it is upper bounded
by a constant that depends on the size of the protocol.Comment: 19 page
Theory of Exciton Migration and Field-Induced Dissociation in Conjugated Polymers
The interplay of migration, recombination, and dissociation of excitons in
disordered media is studied theoretically in the low temperature regime. An
exact expression for the photoluminescence spectrum is obtained. The theory is
applied to describe the electric field-induced photoluminescence-quenching
experiments by Kersting et al. [Phys. Rev. Lett. 73, 1440 (1994)] and Deussen
et al. [Synth. Met. 73, 123 (1995)] on conjugated polymer systems. Good
agreement with experiment is obtained using an on-chain dissociation mechanism,
which implies a separation of the electron-hole pair along the polymer chain.Comment: 4 pages, RevTeX, 2 Postscript figure
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