Shocks in ion sputtering sharpen steep surface features   总被引：1，自引：0，他引：1  

Chen HH  Urquidez OA  Ichim S  Rodriquez LH  Brenner MP  Aziz MJ 《Science (New York, N.Y.)》2005,310(5746):294-297

We report a regime of ion beam sputtering that occurs for sufficiently steep slopes. High slopes propagate over large distances without dissipating the steepest features. Both the propagation velocity and the dynamically selected slope are universal, independent of the details of the initial shape of the surface. The resulting behavior can be understood as the propagation of a shock front that self-selects a stable slope, as has been previously observed in thin-film fluid flows. Experiments confirm predictions of the theory. An important implication of the propagative behavior at high surface slopes is that a pattern can be fabricated at a large length scale and, through uniform ion irradiation, reduced to a smaller length scale while preserving, or even sharpening, the sharpest features.  相似文献   

Mutations in dynein link motor neuron degeneration to defects in retrograde transport     

Hafezparast M  Klocke R  Ruhrberg C  Marquardt A  Ahmad-Annuar A  Bowen S  Lalli G  Witherden AS  Hummerich H  Nicholson S  Morgan PJ  Oozageer R  Priestley JV  Averill S  King VR  Ball S  Peters J  Toda T  Yamamoto A  Hiraoka Y  Augustin M  Korthaus D  Wattler S  Wabnitz P  Dickneite C  Lampel S  Boehme F  Peraus G  Popp A  Rudelius M  Schlegel J  Fuchs H  Hrabe de Angelis M  Schiavo G  Shima DT  Russ AP  Stumm G  Martin JE  Fisher EM 《Science (New York, N.Y.)》2003,300(5620):808-812

Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein.  相似文献   

Neuroscience. It takes more than two to Nogo     

Woolf CJ  Bloechlinger S 《Science (New York, N.Y.)》2002,297(5584):1132-1134

  相似文献   

Multi-university research teams: shifting impact, geography, and stratification in science   总被引：1，自引：0，他引：1  

Jones BF  Wuchty S  Uzzi B 《Science (New York, N.Y.)》2008,322(5905):1259-1262

This paper demonstrates that teamwork in science increasingly spans university boundaries, a dramatic shift in knowledge production that generalizes across virtually all fields of science, engineering, and social science. Moreover, elite universities play a dominant role in this shift. By examining 4.2 million papers published over three decades, we found that multi-university collaborations (i) are the fastest growing type of authorship structure, (ii) produce the highest-impact papers when they include a top-tier university, and (iii) are increasingly stratified by in-group university rank. Despite the rising frequency of research that crosses university boundaries, the intensification of social stratification in multi-university collaborations suggests a concentration of the production of scientific knowledge in fewer rather than more centers of high-impact science.  相似文献   

Fossilized nuclei and germination structures identify Ediacaran "animal embryos" as encysting protists   总被引：1，自引：0，他引：1  

Huldtgren T  Cunningham JA  Yin C  Stampanoni M  Marone F  Donoghue PC  Bengtson S 《Science (New York, N.Y.)》2011,334(6063):1696-1699

Globular fossils showing palintomic cell cleavage in the Ediacaran Doushantuo Formation, China, are widely regarded as embryos of early metazoans, although metazoan synapomorphies, tissue differentiation, and associated juveniles or adults are lacking. We demonstrate using synchrotron-based x-ray tomographic microscopy that the fossils have features incompatible with multicellular metazoan embryos. The developmental pattern is comparable with nonmetazoan holozoans, including germination stages that preclude postcleavage embryology characteristic of metazoans. We conclude that these fossils are neither animals nor embryos. They belong outside crown-group Metazoa, within total-group Holozoa (the sister clade to Fungi that includes Metazoa, Choanoflagellata, and Mesomycetozoea) or perhaps on even more distant branches in the eukaryote tree. They represent an evolutionary grade in which palintomic cleavage served the function of producing propagules for dispersion.  相似文献   

Increasing river discharge to the Arctic Ocean   总被引：10，自引：0，他引：10  

Peterson BJ  Holmes RM  McClelland JW  Vörösmarty CJ  Lammers RB  Shiklomanov AI  Shiklomanov IA  Rahmstorf S 《Science (New York, N.Y.)》2002,298(5601):2171-2173

Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average annual rate of increase was 2.0 +/- 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate.  相似文献   

Conditional dynamics of interacting quantum dots     

Robledo L  Elzerman J  Jundt G  Atatüre M  Högele A  Fält S  Imamoglu A 《Science (New York, N.Y.)》2008,320(5877):772-775

Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled-phase gate between two solid-state qubits.  相似文献   

Fluorometric detection of enzyme activity with synthetic supramolecular pores     

Das G  Talukdar P  Matile S 《Science (New York, N.Y.)》2002,298(5598):1600-1602

The reversible blockage of synthetic pores formed by rigid-rod beta barrels, either by substrates or products, was used to sense a variety of enzymatic reactions in high-throughput format with "naked-eye" fluorescent detection. Improvement of sensor sensitivity beyond three orders of magnitude by straightforward internal mutations underscores the functional plasticity of rigid-rod beta barrels. Such detectors of enzyme activity with the aforementioned characteristics are needed in areas as diverse as proteomics and environmentally benign organic synthesis.  相似文献   

Was there really an Archean phosphate crisis?     

Konhauser KO  Lalonde SV  Amskold L  Holland HD 《Science (New York, N.Y.)》2007,315(5816):1234

During the Archean, massive amounts of iron were deposited in the form of banded iron formations. It has been suggested that sedimenting particles of ferric oxyhydroxide may have stripped dissolved phosphate from the oceans, causing a reduction in phytoplankton productivity. However, that model does not take into account the high concentration of dissolved silica that was present in seawater at that time. We show experimentally that silica effectively competes with phosphate for sorption sites on ferrihydrite particles. Furthermore, coprecipitation of silica with ferrihydrite reduces particle reactivity toward phosphate. Hence, Archean oceans probably contained considerably more phosphate than previously predicted.  相似文献   

耐盐性Imt1基因表达载体的构建及其在酵母中的高效表达   总被引：2，自引：0，他引：2  

董云洲  沈波 《中国农业科学》1997,30(4):50-55

 将Imt1（Inositol O-methyltransferase，肌醇甲基转移酶）构建成酵母表达载体pBD#-3，在酵母双突变体gpd#+（-）(glycerol 3-phosphate-dehydrogenase,3-磷酸甘油脱氢酶)中高效表达，使gpd#+（-）突变株对氯化钠的耐性由2.5%提高到5.0%。生化分析表明，在每mg干酵母细胞内积累高达2.2nmol的Ononitol(芒柄醇)含量。Western blot分析证明了Imt1基因的表达。这一研究为植物耐盐基因工程开辟了一条新途径。  相似文献