Coherent two-dimensional nanoscopy     

Aeschlimann M  Brixner T  Fischer A  Kramer C  Melchior P  Pfeiffer W  Schneider C  Strüber C  Tuchscherer P  Voronine DV 《Science (New York, N.Y.)》2011,333(6050):1723-1726

We introduce a spectroscopic method that determines nonlinear quantum mechanical response functions beyond the optical diffraction limit and allows direct imaging of nanoscale coherence. In established coherent two-dimensional (2D) spectroscopy, four-wave-mixing responses are measured using three ingoing waves and one outgoing wave; thus, the method is diffraction-limited in spatial resolution. In coherent 2D nanoscopy, we use four ingoing waves and detect the final state via photoemission electron microscopy, which has 50-nanometer spatial resolution. We recorded local nanospectra from a corrugated silver surface and observed subwavelength 2D line shape variations. Plasmonic phase coherence of localized excitations persisted for about 100 femtoseconds and exhibited coherent beats. The observations are best explained by a model in which coupled oscillators lead to Fano-like resonances in the hybridized dark- and bright-mode response.  相似文献   

Analyzing the effect of stepping stones on target patch colonisation in structured landscapes for Eurasian lynx     

Stephanie Kramer-Schadt  Tobias S. Kaiser  Karin Frank  Thorsten Wiegand 《Landscape Ecology》2011,26(4):501-513

With habitat loss and fragmentation having become two of the major threats to the viability of species, the question of how to manage landscapes for species conservation has attracted much attention. In this context, the planning of stepping stones has been proposed to increase connectivity in fragmented landscapes. We present a simulation study with a neutral landscape approach to assess the effects of stepping stones on colonization success. To that end, we used a spatially explicit, calibrated population model of the European lynx (Lynx lynx) coupled with structured landscapes, in which we could control the landscape parameters of dispersal habitat coverage and contagion, as well as the number and size of stepping stones available for breeding. In general, we found that colonization success increased with increasing habitat coverage but decreased with increasing habitat contagion, while the introduction of stepping stones had significant effects in critical situations. Especially at low to medium dispersal habitat coverage and high disperser mortality, stepping stones had a positive effect on colonization success when they were large enough to produce new dispersers, but negative effects when they were small and located in a way that dispersers would be distracted from more suitable breeding habitat patches. The latter clearly constituted a shading effect and argues for a thorough consideration of the trade-offs related to stepping stone size and location when implementing stepping stones as a conservation measure, especially when the number of individuals of conservation concern is low.  相似文献   

Canine pericardial mesothelioma.     

S P McDonough  N J MacLachlan  A H Tobias 《Veterinary pathology》1992,29(3):256-260

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Aneurysmal dilatation of the right auricle in two dogs     

Schwarz T  Willis R  Summerfield NJ  Doust R 《Journal of the American Veterinary Medical Association》2005,226(9):1512-5, 1500

An 8-year-old sexually intact male Golden Retriever with a history of collapse during exercise underwent an examination during which tachydysrhythmia was identified. At another institution, a 12.5-year-old spayed female Lhasa Apso was referred because of a cough and for evaluation of a heart murmur. In the Golden Retriever, radiographic examination revealed bulging of the craniodorsal aspect of the cardiac silhouette and echocardiography revealed right atrial dilatation. In the Lhasa Apso, a cranial mediastinal mass was suspected on the basis of radiographic findings, but no abnormalities were detected echocardiographically. In both dogs, nonselective angiography and contrast-enhanced computed tomography revealed a markedly enlarged, thin-walled right auricle. Exploratory thoracotomy in the Golden Retriever revealed a defect in the pericardium through which the right auricle and part of the atrium had herniated. In dogs, a right auricular aneurysm should be considered in differential diagnoses of a cranial mediastinal mass (detected radiographically) adjacent to the cardiac silhouette.  相似文献   

Atresia ani in the dog: a retrospective study     

Vianna ML  Tobias KM 《Journal of the American Animal Hospital Association》2005,41(5):317-322

Congenital anomalies of the rectum and anus are rare in dogs. The most frequently reported anomaly is atresia ani. Four types of atresia ani have been reported, including congenital anal stenosis (Type I); imperforate anus alone (Type II) or combined with more cranial termination of the rectum as a blind pouch (Type III); and discontinuity of the proximal rectum with normal anal and terminal rectal development (Type IV). An increased incidence was found in females and in several breeds, including miniature or toy poodles and Boston terriers. Surgical repair is the treatment of choice, but postoperative complications can occur, including fecal incontinence and colonic atony secondary to prolonged preoperative distension.  相似文献   

Optical spectroscopy of individual single-walled carbon nanotubes of defined chiral structure     

Sfeir MY  Beetz T  Wang F  Huang L  Huang XM  Huang M  Hone J  O'Brien S  Misewich JA  Heinz TF  Wu L  Zhu Y  Brus LE 《Science (New York, N.Y.)》2006,312(5773):554-556

We simultaneously determined the physical structure and optical transition energies of individual single-walled carbon nanotubes by combining electron diffraction with Rayleigh scattering spectroscopy. These results test fundamental features of the excited electronic states of carbon nanotubes. We directly verified the systematic changes in transition energies of semiconducting nanotubes as a function of their chirality and observed predicted energy splittings of optical transitions in metallic nanotubes.  相似文献   

Plant science. Auxin transport, but in which direction?     

Sieberer T  Leyser O 《Science (New York, N.Y.)》2006,312(5775):858-860

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Bruchpilot promotes active zone assembly, Ca2+ channel clustering, and vesicle release   总被引：1，自引：0，他引：1  

Kittel RJ  Wichmann C  Rasse TM  Fouquet W  Schmidt M  Schmid A  Wagh DA  Pawlu C  Kellner RR  Willig KI  Hell SW  Buchner E  Heckmann M  Sigrist SJ 《Science (New York, N.Y.)》2006,312(5776):1051-1054

The molecular organization of presynaptic active zones during calcium influx-triggered neurotransmitter release is the focus of intense investigation. The Drosophila coiled-coil domain protein Bruchpilot (BRP) was observed in donut-shaped structures centered at active zones of neuromuscular synapses by using subdiffraction resolution STED (stimulated emission depletion) fluorescence microscopy. At brp mutant active zones, electron-dense projections (T-bars) were entirely lost, Ca2+ channels were reduced in density, evoked vesicle release was depressed, and short-term plasticity was altered. BRP-like proteins seem to establish proximity between Ca2+ channels and vesicles to allow efficient transmitter release and patterned synaptic plasticity.  相似文献   

Diagnostic imaging: from art to science?     

Schwarz T 《The Journal of small animal practice》2006,47(11):641-642

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Generation of gut-homing IgA-secreting B cells by intestinal dendritic cells     

Mora JR  Iwata M  Eksteen B  Song SY  Junt T  Senman B  Otipoby KL  Yokota A  Takeuchi H  Ricciardi-Castagnoli P  Rajewsky K  Adams DH  von Andrian UH 《Science (New York, N.Y.)》2006,314(5802):1157-1160

Normal intestinal mucosa contains abundant immunoglobulin A (IgA)-secreting cells, which are generated from B cells in gut-associated lymphoid tissues (GALT). We show that dendritic cells (DC) from GALT induce T cell-independent expression of IgA and gut-homing receptors on B cells. GALT-DC-derived retinoic acid (RA) alone conferred gut tropism but could not promote IgA secretion. However, RA potently synergized with GALT-DC-derived interleukin-6 (IL-6) or IL-5 to induce IgA secretion. Consequently, mice deficient in the RA precursor vitamin A lacked IgA-secreting cells in the small intestine. Thus, GALT-DC shape mucosal immunity by modulating B cell migration and effector activity through synergistically acting mediators.  相似文献