Crystalline Ropes of Metallic Carbon Nanotubes   总被引：7，自引：0，他引：7  

A Thess  R Lee  P Nikolaev  H Dai  P Petit  J Robert  C Xu  YH Lee  SG Kim  AG Rinzler  DT Colbert  GE Scuseria  D Tomanek  JE Fischer  RE Smalley 《Science (New York, N.Y.)》1996,273(5274):483-487

Fullerene single-wall nanotubes (SWNTs) were produced in yields of more than 70 percent by condensation of a laser-vaporized carbon-nickel-cobalt mixture at 1200degreesC. X-ray diffraction and electron microscopy showed that these SWNTs are nearly uniform in diameter and that they self-organize into "ropes," which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice with a lattice constant of 17 angstroms. The x-ray form factor is consistent with that of uniformly charged cylinders 13.8 +/- 0.2 angstroms in diameter. The ropes were metallic, with a single-rope resistivity of <10(-4) ohm-centimeters at 300 kelvin. The uniformity of SWNT diameter is attributed to the efficient annealing of an initial fullerene tubelet kept open by a few metal atoms; the optimum diameter is determined by competition between the strain energy of curvature of the graphene sheet and the dangling-bond energy of the open edge, where growth occurs. These factors strongly favor the metallic (10,10) tube with C5v symmetry and an open edge stabilized by triple bonds.  相似文献   

The Rag GTPases bind raptor and mediate amino acid signaling to mTORC1   总被引：3，自引：0，他引：3  

Sancak Y  Peterson TR  Shaul YD  Lindquist RA  Thoreen CC  Bar-Peled L  Sabatini DM 《Science (New York, N.Y.)》2008,320(5882):1496-1501

The multiprotein mTORC1 protein kinase complex is the central component of a pathway that promotes growth in response to insulin, energy levels, and amino acids and is deregulated in common cancers. We find that the Rag proteins--a family of four related small guanosine triphosphatases (GTPases)--interact with mTORC1 in an amino acid-sensitive manner and are necessary for the activation of the mTORC1 pathway by amino acids. A Rag mutant that is constitutively bound to guanosine triphosphate interacted strongly with mTORC1, and its expression within cells made the mTORC1 pathway resistant to amino acid deprivation. Conversely, expression of a guanosine diphosphate-bound Rag mutant prevented stimulation of mTORC1 by amino acids. The Rag proteins do not directly stimulate the kinase activity of mTORC1, but, like amino acids, promote the intracellular localization of mTOR to a compartment that also contains its activator Rheb.  相似文献   

Coordinate regulation of beta-lactamase induction and peptidoglycan composition by the amp operon   总被引：5，自引：0，他引：5  

E Tuomanen  S Lindquist  S Sande  M Galleni  K Light  D Gage  S Normark 《Science (New York, N.Y.)》1991,251(4990):201-204

The amp operon, which is located on the Escherichia coli chromosome, modulates the induction of plasmid-borne beta-lactamase genes by extracellular beta-lactam antibiotics. This suggests that the gene products AmpD and AmpE may function in the transduction of external signals. beta-Lactam antibiotics are analogs of cell wall components that can be released during cell wall morphogenesis of enterobacteria. The amp operon was studied to determine its importance in signal transduction during cell wall morphogenesis. The peptidoglycan compositions of amp mutants were determined by high-performance liquid chromatography and fast atom bombardment mass spectrometry. When a chromosomal or plasmid-borne copy of ampD was present, the amount of pentapeptide-containing muropeptides in the cell wall increased upon addition of the cell wall constituent diaminopimelic acid to the growth medium. These results suggest that beta-lactamase induction and modulation of the composition of the cell wall share elements of a regulatory circuit that involves AmpD. Escherichia coli requires AmpD to respond to extracellular signaling amino acids, such as diaminopimelic acid, and this signal transduction system may regulate peptidoglycan composition in response to cell wall turnover products.  相似文献   

Neurotoxicity and neurodegeneration when PrP accumulates in the cytosol     

Ma J  Wollmann R  Lindquist S 《Science (New York, N.Y.)》2002,298(5599):1781-1785

Changes in prion protein (PrP) folding are associated with fatal neurodegenerative disorders, but the neurotoxic species is unknown. Like other proteins that traffic through the endoplasmic reticulum, misfolded PrP is retrograde transported to the cytosol for degradation by proteasomes. Accumulation of even small amounts of cytosolic PrP was strongly neurotoxic in cultured cells and transgenic mice. Mice developed normally but acquired severe ataxia, with cerebellar degeneration and gliosis. This establishes a mechanism for converting wild-type PrP to a highly neurotoxic species that is distinct from the self-propagating PrP(Sc) isoform and suggests a potential common framework for seemingly diverse PrP neurodegenerative disorders.  相似文献   

Suspected Lythrum hyssopifolia (lesser loosestrife) poisoning of cattle     

JN Tran  P‐J Yang  AG Morton  AA Todd  JG Boulton  AW Philbey 《Australian veterinary journal》2013,91(11):474-476

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Synthesis and testing of novel alternative oxidase (AOX) inhibitors with antifungal activity against Moniliophthora perniciosa (Stahel), the causal agent of witches' broom disease of cocoa,and other phytopathogens     

Mario RO Barsottini  Brbara A Pires  Maria L Vieira  Jos GC Pereira  Paulo CS Costa  Jaqueline Sanit  Alessandro Coradini  Fellipe Mello  Cidnei Marschalk  Eder M Silva  Daniele Paschoal  Antonio Figueira  Fbio HS Rodrigues  Artur T Cordeiro  Paulo CML Miranda  Paulo SL Oliveira  Maurício L Sfora  Marcelo F Carazzolle  Silvana A Rocco  Gonalo AG Pereira 《Pest management science》2019,75(5):1295-1303

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Association with TGF‐β1 Gene Polymorphisms and Reproductive Performance of Large White Pig     

YP Wu  AG Wang  N Li  JL Fu  XB Zhao 《Reproduction in domestic animals》2010,45(6):1028-1032

As a multifunctional cytokine, transforming growth factor‐beta1 (TGF‐β1) was detected in the utero‐placental interface during early pregnancy in the pig and believed to enhance trophoblast attachment to the endometrium. In this experiment, we selected TGF‐β1 as the candidate gene affecting litter size in pigs. Four polymorphic loci of TGF‐β1 gene were found by PCR‐SSCP (single‐strand conformation polymorphism) in Large white sows (n = 567): C→T mutation at 33nt in the intron 4; G→A mutation at 179nt in the intron 6; C→T mutation at 1043nt in the intron 6; GG→AA linkage mutations at 2490nt and 2494nt respectively. We haplotyped these SNPs as: CGCAA (denote as P) and TATGG (denote as K). The effects of three haplotypic combinations (HCs) of PP, PK and KK on litter sizes were investigated by a linear model. It was found that for the first parity litters, the least squares mean for total number born (TNB) of KK was 1.02 piglets/litter, higher than that of PK (p < 0.05), 0.49 piglets/litter higher than that of PP (p > 0.1). There were no significant differences between HCs on the second parity. The result indicated that KK HCs was significantly associated with pig litter size.  相似文献   

Epigenetics in the extreme: prions and the inheritance of environmentally acquired traits     

Halfmann R  Lindquist S 《Science (New York, N.Y.)》2010,330(6004):629-632

Prions are an unusual form of epigenetics: Their stable inheritance and complex phenotypes come about through protein folding rather than nucleic acid-associated changes. With intimate ties to protein homeostasis and a remarkable sensitivity to stress, prions are a robust mechanism that links environmental extremes with the acquisition and inheritance of new traits.  相似文献   

Emerging pests and diseases of South‐east Asian cassava: a comprehensive evaluation of geographic priorities,management options and research needs          下载免费PDF全文

Ignazio Graziosi  Nami Minato  Elizabeth Alvarez  Dung Tien Ngo  Trinh Xuan Hoat  Tin Maung Aye  Juan Manuel Pardo  Prapit Wongtiem  Kris AG Wyckhuys 《Pest management science》2016,72(6):1071-1089

Cassava is a major staple, bio‐energy and industrial crop in many parts of the developing world. In Southeast Asia, cassava is grown on >4 million ha by nearly 8 million (small‐scale) farming households, under (climatic, biophysical) conditions that often prove unsuitable for many other crops. While SE Asian cassava has been virtually free of phytosanitary constraints for most of its history, a complex of invasive arthropod pests and plant diseases has recently come to affect local crops. We describe results from a region‐wide monitoring effort in the 2014 dry season, covering 429 fields across five countries. We present geographic distribution and field‐level incidence of the most prominent pest and disease invaders, introduce readily‐available management options and research needs. Monitoring work reveals that several exotic mealybug and (red) mite species have effectively colonised SE Asia's main cassava‐growing areas, occurring in respectively 70% and 54% of fields, at average field‐level incidence of 27 ± 2% and 16 ± 2%. Cassava witches broom (CWB), a systemic phytoplasma disease, was reported from 64% of plots, at incidence levels of 32 ± 2%. Although all main pests and diseases are non‐natives, we hypothesise that accelerating intensification of cropping systems, increased climate change and variability, and deficient crop husbandry are aggravating both organism activity and crop susceptibility. Future efforts need to consolidate local capacity to tackle current (and future) pest invaders, boost detection capacity, devise locally‐appropriate integrated pest management (IPM) tactics, and transfer key concepts and technologies to SE Asia's cassava growers. Urgent action is needed to mobilise regional as well as international scientific support, to effectively tackle this phytosanitary emergency and thus safeguard the sustainability and profitability of one of Asia's key agricultural commodities. © 2016 Society of Chemical Industry  相似文献   

An integrated approach to control glyphosate‐resistant Ambrosia trifida with tillage and herbicides in glyphosate‐resistant maize          下载免费PDF全文

Z A Ganie  J L Lindquist  M Jugulam  G R Kruger  D B Marx  A J Jhala 《Weed Research》2017,57(2):112-122

Glyphosate‐resistant Ambrosia trifida is a competitive and difficult‐to‐control annual broad‐leaved weed in several agronomic crops in the Midwestern United States and Ontario, Canada. The objectives of this study were to compare treatments for control of glyphosate‐resistant A. trifida with tillage followed by pre‐emergence (PRE) and/or post‐emergence (POST) herbicides in glyphosate‐resistant maize and to determine the impact of A. trifida escapes on maize yield. Field experiments were conducted in 2013 and 2014 in grower fields infested with glyphosate‐resistant A. trifida. Tillage prior to maize sowing resulted in 80–85% control compared with no tillage. Tillage followed by PRE application of saflufenacil plus dimethenamid‐P with or without atrazine resulted in 99% control compared with ≤86 and 96% control with PRE herbicides alone at 7 and 21 days after application respectively. Tillage or POST‐only herbicides resulted in 4–14 A. trifida plants m^?2, whereas a PRE and POST programme had <3 plants m^?2. Maize yield was greatest (13.1–14.2 tonnes ha^?1) with tillage followed by PRE and POST herbicide programme. The relationship between maize yield and late‐season density of A. trifida escapes showed a 50% maize yield reduction irrespective of control measures when A. trifida density was 8.4 plants m^?2. It was concluded that the combination of tillage with PRE and/or POST herbicides reduced A. trifida density and biomass accumulation early in the season and provided an integrated approach for effective management.  相似文献