EDGAR ALLEN     

Gardner WU 《Science (New York, N.Y.)》1943,97(2521):368-369

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Laser ablation and the production of polymer films     

Blanchet GB  Fincher CR  Jackson CL  Shah SI  Gardner KH 《Science (New York, N.Y.)》1993,262(5134):719-721

The formation of high-quality thin films of polytetrafluoroethylene (PTFE) is important in many applications ranging from material reinforcement to molecular electronics. Laser ablation, a technique widely used to deposit a variety of inorganic materials, can also be used as a simple and highly versatile method for forming thin polymer films. The data presented show that PTFE films can be produced on various supports by the evaporation of a solid PTFE target with a pulsed ultraviolet laser. The composition of the ablation plume suggests that PTFE ablation and subsequent film formation occur by way of a laser-induced pyrolitic decomposition with subsequent repolymerization. The polymer films produced by this method are composed of amorphous and highly crystalline regions, the latter being predominantly in a chain-folded configuration with the molecular axis aligned parallel to the substrate surface.  相似文献   

Freedom and rules: the acquisition and reprogramming of a bird's learned song     

Gardner TJ  Naef F  Nottebohm F 《Science (New York, N.Y.)》2005,308(5724):1046-1049

Canary song is hierarchically structured: Short stereotyped syllables are repeated to form phrases, which in turn are arranged to form songs. This structure occurs even in the songs of young isolates, which suggests that innate rules govern canary song development. However, juveniles that had never heard normal song imitated abnormal synthetic songs with great accuracy, even when the tutor songs lacked phrasing. As the birds matured, imitated songs were reprogrammed to form typical canary phrasing. Thus, imitation and innate song constraints are separate processes that can be segregated in time: freedom in youth, rules in adulthood.  相似文献   

Removal of meteoric iron on polar mesospheric clouds     

Plane JM  Murray BJ  Chu X  Gardner CS 《Science (New York, N.Y.)》2004,304(5669):426-428

Polar mesospheric clouds are thin layers of nanometer-sized ice particles that occur at altitudes between 82 and 87 kilometers in the high-latitude summer mesosphere. These clouds overlap in altitude with the layer of iron (Fe) atoms that is produced by the ablation of meteoroids entering the atmosphere. Simultaneous observations of the Fe layer and the clouds, made by lidar during midsummer at the South Pole, demonstrate that essentially complete removal of Fe atoms can occur inside the clouds. Laboratory experiments and atmospheric modeling show that this phenomenon is explained by the efficient uptake of Fe on the ice particle surface.  相似文献   

Structural basis of a phototropin light switch     

Harper SM  Neil LC  Gardner KH 《Science (New York, N.Y.)》2003,301(5639):1541-1544

Phototropins are light-activated kinases important for plant responses to blue light. Light initiates signaling in these proteins by generating a covalent protein-flavin mononucleotide (FMN) adduct within sensory Per-ARNT-Sim (PAS) domains. We characterized the light-dependent changes of a phototropin PAS domain by solution nuclear magnetic resonance spectroscopy and found that an alpha helix located outside the canonical domain plays a key role in this activation process. Although this helix associates with the PAS core in the dark, photoinduced changes in the domain structure disrupt this interaction. We propose that this mechanism couples light-dependent bond formation to kinase activation and identifies a signaling pathway conserved among PAS domains.  相似文献   

COLORED PHOTOGRAPHS OF PLANT DISEASE SPECIMENS     

Gardner MW  Link GK 《Science (New York, N.Y.)》1920,51(1327):556-558

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Early signs of language in child and chimpanzee     

Gardner RA  Gardner BT 《Science (New York, N.Y.)》1975,187(4178):752-753

In a sequel to Project Washoe, chimpanzees are being taught American Sign Language from birth by humans who are fluent in the language, including persons who are themselves deaf or whose parents were deaf. The first two subjects began to use signs when they were 3 months old, and these early results indicate that the new conditions are significantly superior to the conditions of Project Washoe. More valid comparisons can now be made between the acquisition of language by children and by chimpanzees.  相似文献   

The Arabidopsis circadian clock incorporates a cADPR-based feedback loop     

Dodd AN  Gardner MJ  Hotta CT  Hubbard KE  Dalchau N  Love J  Assie JM  Robertson FC  Jakobsen MK  Gonçalves J  Sanders D  Webb AA 《Science (New York, N.Y.)》2007,318(5857):1789-1792

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Relapse to cocaine-seeking after hippocampal theta burst stimulation     

Vorel SR  Liu X  Hayes RJ  Spector JA  Gardner EL 《Science (New York, N.Y.)》2001,292(5519):1175-1178

Treatment efforts for cocaine addiction are hampered by high relapse rates. To map brain areas underlying relapse, we used electrical brain stimulation and intracranial injection of pharmacological compounds after extinction of cocaine self-administration behavior in rats. Electrical stimulation of the hippocampus containing glutamatergic fibers, but not the medial forebrain bundle containing dopaminergic fibers, elicited cocaine-seeking behavior dependent on glutamate in the ventral tegmental area. This suggests a role for glutamatergic neurotransmission in relapse to cocaine abuse. The medial forebrain bundle electrodes supported intense electrical self-stimulation. These findings suggest a dissociation of neural systems subserving positive reinforcement (self-stimulation) and incentive motivation (relapse).  相似文献   

Transfer of Agrobacterium DNA to Plants Requires a T-DNA Border But Not the virE Locus     

Gardner RC  Knauf VC 《Science (New York, N.Y.)》1986,231(4739):725-727

Agrobacterium tumefaciens induces tumors in plants by transferring and integrating oncogenes (T-DNA) into the chromosomes of host plant cells. Agrobacterium strains were used to transfer complementary DNA copies of a potato spindle tuber viroid (PSTV) to plant cells at a wound site on tomato plant stems. Subsequently, infectious viroid RNA was found in the leaves of these plants, indicating systemic PSTV infection. This process utilized the T-DNA transfer mechanisms of Agrobacterium since PSTV infection required most virulence genes (vir) as well as one of the DNA sequences that flank either side of the Agrobacterium T-DNA. However, transfer still occurred from virE mutants of Agrobacterium, strains that fail to induce tumors even though a completely functional T-DNA is present. The virE gene seems to be directly involved in the integration of foreign DNA into plant chromosomes.  相似文献