Extraction of a weak climatic signal by an ecosystem

The complexity of ecosystems can cause subtle and chaotic responses to changes in external forcing. Although ecosystems may not normally behave chaotically, sensitivity to external influences associated with nonlinearity can lead to amplification of climatic signals. Strong correlations between an El Ni?o index and rainfall and maize yield in Zimbabwe have been demonstrated; the correlation with maize yield was stronger than that with rainfall. A second example is the 100,000-year ice-age cycle, which may arise from a weak cycle in radiation through its influence on the concentration of atmospheric CO2 (ref. 5). Such integration of a weak climatic signal has yet to be demonstrated in a realistic theoretical system. Here we use a particular climatic phenomenon-the observed association between plankton populations around the UK and the position of the Gulf Stream-as a probe to demonstrate how a detailed marine ecosystem model extracts a weak signal that is spread across different meteorological variables. Biological systems may therefore respond to climatic signals other than those that dominate the driving variables.     

Popper and Dingle on special relativity and the issue of symmetry

Karl Popper and Herbert Dingle engaged in a fascinating debate concerning the kind of theory the special theory of relativity is. One of the issues was whether applications of the theory could be made consistent with the principle of relativity, a cornerstone of the theory itself. The principle of relativity seems to imply some sort of symmetry in results obtained for similar experiments as observed in two different inertial reference frames. Peter Hayes has recently dealt with the Dingle–Popper debate on this matter, as well as other issues. The present paper seeks to clarify what kind of symmetry is appropriate in a situation discussed by Popper, Dingle, and Hayes.     

Ni2MnGa铁磁形状记忆材料

铁磁形状记忆合金 (FSMA)是在一定温度范围马氏体相稳定同时又具铁磁性的一类特殊的形状记忆合金。Ni2MnGa铁磁形状记忆合金近年来成为呈现磁场驱动大应变的新型驱动材料 ,这些应变来自磁场诱发马氏体孪晶的重排 ,而不是磁场对奥氏体至马氏体相变的作用。孪晶变体的重排在宏观上呈现为正或切应变 ,一非化学计量比Ni2 MnGa单晶于室温加 0 .4T磁场能产生6 %的应变 ,Ni Mn Ga单晶在高至 15 0Hz的交变磁场仍可得到 2 .5 %的应变。本文阐述了与这种磁控形状记忆效应相关的孪晶界迁动的磁学和晶体学理论。马氏体相的大磁晶各向异性能使磁化沿c轴方向有利 ,穿过孪晶界c轴刚好转动 90度 ,同时 ,这个孪晶界也构成了约 90度的畴界。在各向异性的情况下 ,孪晶界的迁动仅有相邻孪晶变体的Zeeman能差驱动 ,μ0 ΔMis·Hi。磁场和外应力对应变的影响通过对一简单的自由能表达式取极小值来表示 ,自由能表达式包括Zeeman能、磁晶各向异性能和外应力以及在某些情况下需考虑的内部弹性能 ,模型的所有参数可通过应力 应变曲线和磁化曲线测量得到。铁磁形状记忆合金的磁场诱发应变可类比传统热弹性形状记忆效应 ,与更为人们所熟知的磁致伸缩现象不同。     

The knockout mouse project

Mouse knockout technology provides a powerful means of elucidating gene function in vivo, and a publicly available genome-wide collection of mouse knockouts would be significantly enabling for biomedical discovery. To date, published knockouts exist for only about 10% of mouse genes. Furthermore, many of these are limited in utility because they have not been made or phenotyped in standardized ways, and many are not freely available to researchers. It is time to harness new technologies and efficiencies of production to mount a high-throughput international effort to produce and phenotype knockouts for all mouse genes, and place these resources into the public domain.     

Gelsolin inhibition of fast axonal transport indicates a requirement for actin microfilaments

The actions of actin-based microfilaments in cell motility suggest a possible role in the mechanism of fast axonal transport, but the pharmacological data evaluating their role in this process are equivocal. Moreover, microfilaments are difficult to preserve and identify in ultrastructural studies, so the organization and function of axonal actin has remained uncertain. We have now evaluated the role of actin microfilaments in intracellular transport of membranous organelles using video-enhanced contrast microscopy and gelsolin to analyse fast axonal transport directly in isolated axoplasm from the squid giant axon. With this preparation it is possible to perfuse axoplasm with large molecules that do not cross the plasmalemma, while controlling cation levels. The 90,000-molecular weight protein gelsolin depolymerizes actin microfilaments in micromolar Ca2+, but not in the absence of Ca2+. Axonal transport of membranous organelles has previously been shown to be unaffected by levels of Ca2+ up to 10 microM. In the presence of EGTA, gelsolin has no effect on the movement of membranous organelles, but in the presence of 10 microM Ca2+ it completely blocks transport of all membranous organelles. No changes in the organization of the axoplasm were detected. These results and results using other probes for actin are consistent with the hypothesis that actin-based microfilaments are involved in the movement of membranous organelles in the axon.     

ANALYSIS AND COMPUTATIONAL ALGORITHM FOR QUEUES WITH STATE-DEPENDENT VACATIONS Ⅱ:M(n)/G/1/K

We study a single-server queueing system with state-dependent arrivals and general service-distribution.or simply M(n)/G/1/K.where the server follows an N policy and takes multiple vacationswhen the system is empty.We provide a recursive algorithm using the supplementary variable tech-nique to munerically compute the stationary queue length distribution of the system.The only inputrequirements are the Laplace-Stieltjes transforms of the service time distribution and the vacation timedistribution.and the state-dependent arrival rate.The computational complexity of the algorithm isO(K~3).     

Gene network shaping of inherent noise spectra

Recent work demonstrates that stochastic fluctuations in molecular populations have consequences for gene regulation. Previous experiments focused on noise sources or noise propagation through gene networks by measuring noise magnitudes. However, in theoretical analysis, we showed that noise frequency content is determined by the underlying gene circuits, leading to a mapping between gene circuit structure and the noise frequency range. An intriguing prediction from our previous studies was that negative autoregulation shifts noise to higher frequencies where it is more easily filtered out by gene networks--a property that may contribute to the prevalence of autoregulation motifs (for example, found in the regulation of approximately 40% of Escherichia coli genes). Here we measure noise frequency content in growing cultures of E. coli, and verify the link between gene circuit structure and noise spectra by demonstrating the negative autoregulation-mediated spectral shift. We further demonstrate that noise spectral measurements provide mechanistic insights into gene regulation, as perturbations of gene circuit parameters are discernible in the measured noise frequency ranges. These results suggest that noise spectral measurements could facilitate the discovery of novel regulatory relationships.     

A family of structural genes for human lymphoblastoid (leukocyte-type) interferon

Amino acid sequences of tryptic and chymotryptic peptides from human lymphoblastoid interferon (IFN-alpha) have been determined. The results show that IFN-alpha consists of a family of proteins with at least five different, but homologous, primary structures. There appears to be little, if any, glycosylation of the major components of IFN-alpha.     

Translocation of vesicles from squid axoplasm on flagellar microtubules

Directed intracellular particle movement is a fundamental process characteristic of all cells. During fast axonal transport, membranous organelles move at rapid rates, from 1 to 5 micron s-1, in either the orthograde or retrograde direction along the neurone and can traverse distances as long as 1 m (for reviews, see refs 1-3). Recent studies indicate that this extreme example of intracellular motility can occur along single microtubules, but the molecules generating the motile force have not been identified or localized. It is not known whether the force-transducing 'motor' is associated with the moving particle or with the microtubule lattice. To distinguish between these hypotheses and to characterize the membrane-cytoskeletal interactions that occur during vesicle translocations, we have developed a reconstituted model for microtubule-based motility. We isolated axoplasmic vesicles from the giant axon of the squid Loligo pealei as described previously. The vesicles (35-475 nm in diameter) were then added to axonemes of Arbacia punctulata spermatozoa that served as a source of microtubules. Axonemes were used because the tubulin subunit lattice of the A-subfibre of a given outer doublet is the same as the subunit lattice of neuronal microtubules along which motility occurs. Moreover, all the microtubules of a single axoneme show the same structural polarity, indicating that the axoneme represents an oriented microtubule substrate. Here we demonstrate that vesicle motility is ATP-dependent, that it is not mediated by the flagellar force-transducing molecule dynein and that the direction of movement is not specified by microtubule polarity.