Dynamics of resource production and utilisation in two-component biosphere-human and terrestrial carbon systems

This paper analyses simple models for "production-utilisation" systems, reduced to two state variables for producers and utilisers, respectively. Two modes are distinguished: in "harvester" systems the resource utilisation involves active seeking on the part of the utilisers, while in "processor" systems, utilisers function as passive material processors. An idealised model of biosphere-human interactions provides an example of a harvester system, and a model of plant and soil carbon dynamics exemplifies a processor system. The biosphere-human interaction model exhibits a number of features in accord with experience, including a tendency towards oscillatory behaviour which in some circumstances results in limit cycles. The plant-soil carbon model is used to study the effect of random forcing of production (for example by weather and climate fluctuations), showing that with appropriate parameter choices the model can flip between active-biosphere and dormant-biosphere equilibria under the influence of random forcing. This externally-driven transition between locally stable states is fundamentally different from Lorenzian chaos. A behavioural difference between two-component processor and harvester systems is that harvester systems have a capacity for oscillatory behaviour while processor systems do not

Observation of Feshbach resonances between two different atomic species

We have observed three Feshbach resonances in collisions between lithium-6 and sodium-23 atoms. The resonances were identified as narrow loss features when the magnetic field was varied. The molecular states causing these resonances have been identified, and additional lithium-sodium resonances are predicted. These resonances will allow the study of degenerate Bose-Fermi mixtures with adjustable interactions, and could be used to generate ultracold heteronuclear molecules

Formation Time of a Fermion Pair Condensate

The formation time of a condensate of fermionic atom pairs close to a Feshbach resonance was studied. This was done using a phase-shift method in which the delayed response of the many-body system to a modulation of the interaction strength was recorded. The observable was the fraction of condensed molecules in the cloud after a rapid magnetic field ramp across the Feshbach resonance. The measured response time was slow compared to the rapid ramp, which provides final proof that the molecular condensates reflect the presence of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure

Observation of Bose-Einstein Condensation of Molecules

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation.Comment: 4 pages, 3 figure

Characterization of a 450-km Baseline GPS Carrier-Phase Link using an Optical Fiber Link

A GPS carrier-phase frequency transfer link along a baseline of 450 km has been established and is characterized by comparing it to a phase-stabilized optical fiber link of 920 km length, established between the two endpoints, the Max-Planck-Institut f\"ur Quantenoptik in Garching and the Physikalisch-Technische Bundesanstalt in Braunschweig. The characterization is accomplished by comparing two active hydrogen masers operated at both institutes. The masers serve as local oscillators and cancel out when the double differences are calculated, such that they do not constitute a limitation for the GPS link characterization. We achieve a frequency instability of 3 x 10^(-13) in 30 s and 5 x 10^(-16) for long averaging times. Frequency comparison results obtained via both links show no deviation larger than the statistical uncertainty of 6 x 10^(-16). These results can be interpreted as a successful cross-check of the measurement uncertainty of a truly remote end fiber link.Comment: 14 pages, 6 figure

Evidence for Regulation ofECM3Expression by Methylation of Histone H3 Lysine 4 and Intergenic Transcription inSaccharomyces cerevisiae

Transcription of nonprotein-coding DNA is widespread in eukaryotes and plays important regulatory roles for many genes, including genes that are misregulated in cancer cells. Its pervasiveness presents the potential for a wealth of diverse regulatory roles for noncoding transcription. We previously showed that the act of transcribing noncoding DNA (ncDNA) across the promoter of the protein-coding SER3 gene in Saccharomyces cerevisiae positions nucleosomes over the upstream activating sequences, leading to strong repression of SER3 transcription. To explore the possibility of other regulatory roles for ncDNA transcription, we selected six candidate S. cerevisiae genes that express ncRNAs over their promoters and analyzed the regulation of one of these genes, ECM3, in detail. Because noncoding transcription can lead to changes in the local chromatin landscape that impinge on the expression of nearby coding genes, we surveyed the effects of various chromatin regulators on the expression of ECM3. These analyses identified roles for the Paf1 complex in positively regulating ECM3 transcription through methylation of histone H3 at lysine 4 (K4) and for Paf1 in controlling the pattern of intergenic transcription at this locus. By deleting a putative promoter for the noncoding transcription unit that lies upstream of ECM3, we provide evidence for a positive correlation between intergenic transcription and ECM3 expression. Our results are consistent with a model in which cotranscriptional methylation of histone H3 K4, mediated by the Paf1 complex and noncoding transcription, leads to activation of ECM3 transcription