A Robust Feedforward Model of the Olfactory System

Most natural odors have sparse molecular composition. This makes the principles of compressed sensing potentially relevant to the structure of the olfactory code. Yet, the largely feedforward organization of the olfactory system precludes reconstruction using standard compressed sensing algorithms. To resolve this problem, recent theoretical work has shown that signal reconstruction could take place as a result of a low dimensional dynamical system converging to one of its attractor states. However, the dynamical aspects of optimization slowed down odor recognition and were also found to be susceptible to noise. Here we describe a feedforward model of the olfactory system that achieves both strong compression and fast reconstruction that is also robust to noise. A key feature of the proposed model is a specific relationship between how odors are represented at the glomeruli stage, which corresponds to a compression, and the connections from glomeruli to third-order neurons (neurons in the olfactory cortex of vertebrates or Kenyon cells in the mushroom body of insects), which in the model corresponds to reconstruction. We show that should this specific relationship hold true, the reconstruction will be both fast and robust to noise, and in particular to the false activation of glomeruli. The predicted connectivity rate from glomeruli to third-order neurons can be tested experimentally.     

一种简单、快速、经济的mRNA分离方法

对oligo(dT)纤维素纯化poly(A)RNA的方法进行了改良.缩小了层析柱床的体积,使填料用量仅为常规量的1/50-1/100,即在移液器尖嘴中进行层析.与常规方法相比,它具有实验时间短、洗脱的mRNA可直接合成cDNA和得率较高等优点.     

Vascular Differentiation in the Shoot Apex of Matteuccia struthiopteris

Initial vascular differentiation is generally considered tooccur in procambium. In ferns, however, a provascular tissueimmediately subjacent to the promeristem has been suggestedas an initial stage within which the procambium is subsequentlyformed. In contrast to this interpretation, a zonation conceptapplied in ferns recognizes a promeristem consisting of severallayers of cells in which no differentiation takes place. Thisstudy demonstrates that the shoot apex of Matteuccia struthiopterishas one cell layer of promeristem. Immediately subjacent tothe promeristem is the provascular tissue surrounding a centralgroup of pith mother cells. The developmental continuity betweenthe provascular tissue and the mature vascular tissue, and betweenthe pith mother cells and the pith, through transitional stages,indicates that the initial differentiation of vascular tissueand pith takes place in this prestelar tissue. The continuityof vascular differentiation in the area confronting young leavesor incipient leaf positions is interrupted by the formationof leaf gap initials. Developing leaves thus begin to exertinfluence on the vascular system at the prestelar stage. Smallprotoxylem elements with helical cell wall thickening, and distinctiveprotophloem elements are present in the leaf traces, but endabruptly near the junction regions of leaf traces to the meristele.Copyright1994, 1999 Academic Press Initial vascular differentiation, provascular tissue, pith mother cells, shoot apex, Matteuccia struthiopteris     

Dual DNA unwinding activities of the Rothmund–Thomson syndrome protein,RECQ4

Human RECQ helicases have been linked to distinct clinical diseases with increased cancer rates and premature ageing. All RECQ proteins, except RECQ4, have been shown to be functional helicases. Mutations in RECQ4 lead to Rothmund–Thomson syndrome (RTS), and mouse models reveal that the conserved helicase motifs are required for avoidance of RTS. Furthermore, the amino (N) terminus of RECQ4 shares homology with yeast DNA replication initiation factor, Sld2, and is vital for embryonic development. Here, in contrast to previous reports, we show that RECQ4 exhibits DNA helicase activity. Importantly, two distinct regions of the protein, the conserved helicase motifs and the Sld2‐like N‐terminal domain, each independently promote ATP‐dependent DNA unwinding. Taken together, our data provide the first biochemical clues underlying the molecular function of RECQ4 in DNA replication and genome maintenance.     

Spatial Variation in Carbon and Nitrogen in Cultivated Soils in Henan Province,China: Potential Effect on Crop Yield

Improved management of soil carbon (C) and nitrogen (N) storage in agro-ecosystems represents an important strategy for ensuring food security and sustainable agricultural development in China. Accurate estimates of the distribution of soil C and N stores and their relationship to crop yield are crucial to developing appropriate cropland management policies. The current study examined the spatial variation of soil organic C (SOC), total soil N (TSN), and associated variables in the surface layer (0–40 cm) of soils from intensive agricultural systems in 19 counties within Henan Province, China, and compared these patterns with crop yield. Mean soil C and N concentrations were 14.9 g kg⁻¹ and 1.37 g kg⁻¹, respectively, whereas soil C and N stores were 4.1 kg m⁻² and 0.4 kg m⁻², respectively. Total crop production of each county was significantly, positively related to SOC, TSN, soil C and N store, and soil C and N stock. Soil C and N were positively correlated with soil bulk density but negatively correlated with soil porosity. These results indicate that variations in soil C could regulate crop yield in intensive agricultural systems, and that spatial patterns of C and N levels in soils may be regulated by both climatic factors and agro-ecosystem management. When developing suitable management programs, the importance of soil C and N stores and their effects on crop yield should be considered.     

Ultra‐High Surface Area Activated Porous Asphalt for CO2 Capture through Competitive Adsorption at High Pressures

This study reports an improved method for activating asphalt to produce ultra‐high surface area porous carbons. Pretreatment of asphalt (untreated Gilsonite, uGil ) at 400 °C for 3 h removes the more volatile organic compounds to form pretreated asphalt ( uGil‐P ) material with a larger fraction of higher molecular weight π‐conjugated asphaltenes. Subsequent activation of uGil‐P at 900 °C gives an ultra‐high surface area (4200 m² g^?1) porous carbon material ( uGil‐900 ) with a mixed micro and mesoporous structure. uGil‐900 shows enhanced room temperature CO₂ uptake capacity at 54 bar of 154 wt% (35 mmol g^?1). The CH₄ uptake capacity is 37.5 wt% (24 mmol g^?1) at 300 bar. These are relevant pressures in natural gas production. The room temperature working CO₂ uptake capacity for uGil‐900 is 19.1 mmol g^?1 (84 wt%) at 20 bar and 32.6 mmol g^?1 (143 wt%) at 50 bar. In order to further assess the reliability of uGil‐900 for CO₂ capture at elevated pressures, the authors study competitive sorption of CO₂ and CH₄ on uGil‐900 at pressures from 1 to 20 bar at 25 °C. CO₂/CH₄ displacement constants are measured at 2 to 40 bar, and found to increase significantly with pressure and surface area.     

城市绿地植物群落特征对亚微米颗粒物的影响

植物群落是构成城市绿地的基本单元之一,也是绿地发挥空气颗粒物调节功能的基础。亚微米级颗粒物,即PM1颗粒物对大气能见度、环境质量与人体健康等均存在严重的负面危害。为探究城市绿地植物群落对亚微米颗粒物水平的调节机制,本研究基于实地测量,针对不同类型植物群落内PM1颗粒物水平的差异,以及群落冠层结构对PM1浓度的影响开展定量研究。结果表明,植物群落对亚微米颗粒物具有一定的减滞效果。8种常见群落类型中,针阔-乔草型群落减滞PM1颗粒物的能力最优,阔叶-乔灌草群落次之,针叶-灌草型群落最弱,但不同类型植物群落内部的PM1浓度差异并不显著。植物群落的冠层结构同PM1颗粒物间存在明显的非线性响应关系,部分冠层指标存在关键的拐点阈值。当冠层郁闭度大于75%,疏透度小于55%左右时,植物群落减滞PM1颗粒物的效果最佳。