Reduced mixing generates oscillations and chaos in the oceanic deep chlorophyll maximum

Deep chlorophyll maxima (DCMs) are widespread in large parts of the world's oceans. These deep layers of high chlorophyll concentration reflect a compromise of phytoplankton growth exposed to two opposing resource gradients: light supplied from above and nutrients supplied from below. It is often argued that DCMs are stable features. Here we show, however, that reduced vertical mixing can generate oscillations and chaos in phytoplankton biomass and species composition of DCMs. These fluctuations are caused by a difference in the timescales of two processes: (1) rapid export of sinking plankton, withdrawing nutrients from the euphotic zone and (2) a slow upward flux of nutrients fuelling new phytoplankton production. Climate models predict that global warming will reduce vertical mixing in the oceans. Our model indicates that reduced mixing will generate more variability in DCMs, thereby enhancing variability in oceanic primary production and in carbon export into the ocean interior.     

Brain homeostasis: VEGF receptor 1 and 2—two unequal brothers in mind

Vascular endothelial growth factors (VEGFs), initially thought to act specifically on the vascular system, exert trophic effects on neural cells during development and adulthood. Therefore, the VEGF system serves as a promising therapeutic target for brain pathologies, but its simultaneous action on vascular cells paves the way for harmful side effects. To circumvent these deleterious effects, many studies have aimed to clarify whether VEGFs directly affect neural cells or if the effects are mediated secondarily via other cell types, like vascular cells. A great number of reports have shown the expression and function of VEGF receptors (VEGFRs), mainly VEGFR-1 and -2, in neural cells, where VEGFR-2 has been described as the major mediator of VEGF-A signals. This review aims to summarize and compare the divergent roles of VEGFR-1 and -2 during CNS development and homeostasis.     

Mineral lick use by GPS radio-collared mountain goats in southeastern British Columbia

In most populations of mountain goats ( Oreamnos americanus ), mineral lick use is an essential part of the ecology of the species. In many areas, the distribution and use of licks in the landscape is poorly known, rendering planning for resource development difficult. We examined lick use by 28 GPS radio-collared mountain goats in 2 study areas in southeastern British Columbia during 2004–2005. Viewing collar-location movements on digital orthophotos, we assumed goat use of 6 previously known and 10 suspected mineral licks. Field visits verified that 9 of the 10 suspected sites were mineral licks. Thirteen of the 15 licks used by collared goats were within forests with commercial harvesting potential. All but 3 of the licks were ≤600 m from the closest logging block, and 5 licks were <100 m away. Number of annual visits to licks by individual goats ranged from 0 to 9. Goats often moved considerable distances (up to 17.3 km) to visit licks. Most visits by males occurred between early May and late June (median 9 June), and most visits by females occurred between early June and mid-July (median 21 June). Mean time spent at licks on each visit was 1.5 days for females and 1.6 days for males. Most of the licks were characterized by numerous cavities dug under trees (which we term “lick trees”). Using GPS collars, we were able to collect data on lower-elevation mineral licks not previously known to researchers.     

Production of Biodegradable Copolyesters and Terpolyesters of Polyhydroxyalkanoates by Alcaligenes latus DSM 1124

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Encoding of conditioned fear in central amygdala inhibitory circuits

The central amygdala (CEA), a nucleus predominantly composed of GABAergic inhibitory neurons, is essential for fear conditioning. How the acquisition and expression of conditioned fear are encoded within CEA inhibitory circuits is not understood. Using in vivo electrophysiological, optogenetic and pharmacological approaches in mice, we show that neuronal activity in the lateral subdivision of the central amygdala (CEl) is required for fear acquisition, whereas conditioned fear responses are driven by output neurons in the medial subdivision (CEm). Functional circuit analysis revealed that inhibitory CEA microcircuits are highly organized and that cell-type-specific plasticity of phasic and tonic activity in the CEl to CEm pathway may gate fear expression and regulate fear generalization. Our results define the functional architecture of CEA microcircuits and their role in the acquisition and regulation of conditioned fear behaviour.     

纳米复合Li2SO4质子传导膜H2S中温燃料电池

开发了一种制备纳米复合Li_2SO_4质子传导电解质和膜电极组装(MEA)的工艺.与传统的丝网涂布工艺不同,新的制备工艺是将阳极、阴极催化剂与纳米复合电解质同时一次压制成MEA.这就使得MEA的设计具有某些结构上的特点,由于膜厚减少和电极与电解质之间的接触良好,可以降低电解质与电极之间的欧姆电阻,提高其机械和导电性能,增加膜的质子传导性以及改善电池的性能.用电子扫描电镜(SEM)和电化学阻抗分析技术对电解质薄膜进行了表征,结果表明,纳米复合材料改善了MEA的总体性能.由于膜的致密性和不透气性,不会发生气体穿透过膜的现象.MEA在H_2S环境中很稳定.电池结构为H_2S,(MoS_2/NiS Ag 电解质量 淀粉) /Li_2SO_4 Al_2O_3/(NiO Ag 电解质量 淀粉),空气、MEA厚为0.8mm、电解质组成为65% Li_2SO_4 35% Al_2O_3的单电池在680℃时产生最大功率密度为130mW/cm~2,相应的电流密度为200mW/cm~2.     

复合Li2SO4质子传导膜的制备及电化学性能

制备了以Li2SO4为基体、Al2O3为填充物的复合质子传导膜.采用电化学阻抗波谱分析法(EIS)研究了掺杂不同组分(Li2WO4或Na2SO4)以及掺杂不同比例时制备的不同厚度的复合质子传导膜的离子(电)传导率.分析结果表明,在Li2SO4中掺杂一定比例的Li2WO4或Na2SO4均可提高膜的离子传导率,Li2WO4对复合膜性能的影响优于Na2SO4.扫描电镜(SEM)分析显示,掺杂Li2WO4的复合膜结构更加致密和紧凑.实验结果表明,由Li2SO4、Li2WO4和Al2O3制备的复合膜的适宜组成为75%Li2SO4/Li2WO4混合物(Li2SO4与Li2WO4摩尔比为9: 1) 25%Al2O3,其离子传导率在600,650,700和750 ℃时分别高达0.16,0.38,0.46和0.52 S/cm,适宜的膜厚为0.8 mm.文中还研究了以H2S为燃料、复合Mo-Ni-S为阳极、复合Li2SO4为质子传导膜、复合NiO为阴极、空气为氧化剂的单电池的电化学性能,发现Li2SO4 Li2WO4 Al2O3复合膜的电化学性能较优.     

Genetic dissection of an amygdala microcircuit that gates conditioned fear

The role of different amygdala nuclei (neuroanatomical subdivisions) in processing Pavlovian conditioned fear has been studied extensively, but the function of the heterogeneous neuronal subtypes within these nuclei remains poorly understood. Here we use molecular genetic approaches to map the functional connectivity of a subpopulation of GABA-containing neurons, located in the lateral subdivision of the central amygdala (CEl), which express protein kinase C-δ (PKC-δ). Channelrhodopsin-2-assisted circuit mapping in amygdala slices and cell-specific viral tracing indicate that PKC-δ(+) neurons inhibit output neurons in the medial central amygdala (CEm), and also make reciprocal inhibitory synapses with PKC-δ(-) neurons in CEl. Electrical silencing of PKC-δ(+) neurons in vivo suggests that they correspond to physiologically identified units that are inhibited by the conditioned stimulus, called CEl(off) units. This correspondence, together with behavioural data, defines an inhibitory microcircuit in CEl that gates CEm output to control the level of conditioned freezing.