Tunneling spectroscopy of the elementary excitations in a one-dimensional wire     

Auslaender OM  Yacoby A  de Picciotto R  Baldwin KW  Pfeiffer LN  West KW 《Science (New York, N.Y.)》2002,295(5556):825-828

The collective excitation spectrum of interacting electrons in one dimension has been measured by controlling the energy and momentum of electrons tunneling between two closely spaced, parallel quantum wires in a GaAs/AlGaAs heterostructure while measuring the resulting conductance. The excitation spectrum deviates from the noninteracting spectrum, attesting to the importance of Coulomb interactions. An observed 30% enhancement of the excitation velocity relative to noninteracting electrons with the same density, a parameter determined experimentally, is consistent with theories on interacting electrons in one dimension. In short wires, 6 and 2 micrometers long, finite size effects, resulting from the breaking of translational invariance, are observed.  相似文献   

Scanning Single-Electron Transistor Microscopy: Imaging Individual Charges     

MJ Yoo  TA Fulton  HF Hess  RL Willett  LN Dunkleberger  RJ Chichester  LN Pfeiffer  KW West 《Science (New York, N.Y.)》1997,276(5312):579-582

A single-electron transistor scanning electrometer (SETSE)-a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron-has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/AlxGa1-xAs heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.  相似文献   

Cooperation and competition in the evolution of ATP-producing pathways     

Pfeiffer T  Schuster S  Bonhoeffer S 《Science (New York, N.Y.)》2001,292(5516):504-507

Heterotrophic organisms generally face a trade-off between rate and yield of adenosine triphosphate (ATP) production. This trade-off may result in an evolutionary dilemma, because cells with a higher rate but lower yield of ATP production may gain a selective advantage when competing for shared energy resources. Using an analysis of model simulations and biochemical observations, we show that ATP production with a low rate and high yield can be viewed as a form of cooperative resource use and may evolve in spatially structured environments. Furthermore, we argue that the high ATP yield of respiration may have facilitated the evolutionary transition from unicellular to undifferentiated multicellular organisms.  相似文献   

Two-dimensional x-ray waveguides and point sources     

Pfeiffer F  David C  Burghammer M  Riekel C  Salditt T 《Science (New York, N.Y.)》2002,297(5579):230-234

We show that resonant coupling of synchrotron beams into suitable nanostructures can be used for the generation of coherent x-ray point sources. A two-dimensionally confining x-ray waveguide structure has been fabricated by e-beam lithography. By shining a parallel undulator beam onto the structure, a discrete set of resonant modes can be excited in the dielectric cavity, depending on the two orthogonal coupling angles between the beam and the waveguide interfaces. The resonant excitation of the modes is evidenced from the characteristic set of coupling angles as well as the observed far-field pattern. The x-ray nanostructure may be used as coherent x-ray point sources with a beam cross section in the nanometer range.  相似文献   

Testosterone-Induced Incubation Patches of Phalarope Birds     

Johns JE  Pfeiffer EW 《Science (New York, N.Y.)》1963,140(3572):1225-1226

In order to determine the endocrine factors in the production of the incubation patch of phalarope birds (Steganopus tricolor and Lobipes lobatus), adults of both sexes have been maintained in captivity and injected with estradiol, testosterone, or prolactin, or with different combinations of these hormones. Only testosterone and prolactin in combination produced incubation patches in all birds, both male and female, in the two species.  相似文献   

Quasi-particle properties from tunneling in the v = 5/2 fractional quantum Hall state     

Radu IP  Miller JB  Marcus CM  Kastner MA  Pfeiffer LN  West KW 《Science (New York, N.Y.)》2008,320(5878):899-902

Quasi-particles with fractional charge and statistics, as well as modified Coulomb interactions, exist in a two-dimensional electron system in the fractional quantum Hall (FQH) regime. Theoretical models of the FQH state at filling fraction v = 5/2 make the further prediction that the wave function can encode the interchange of two quasi-particles, making this state relevant for topological quantum computing. We show that bias-dependent tunneling across a narrow constriction at v = 5/2 exhibits temperature scaling and, from fits to the theoretical scaling form, extract values for the effective charge and the interaction parameter of the quasi-particles. Ranges of values obtained are consistent with those predicted by certain models of the 5/2 state.  相似文献   

Metabolism of curcuminoids in tissue slices and subcellular fractions from rat liver     

Hoehle SI  Pfeiffer E  Sólyom AM  Metzler M 《Journal of agricultural and food chemistry》2006,54(3):756-764

Curcumin and its natural congeners are of current interest because of their putative anti-inflammatory and anticarcinogenic activities, but knowledge about their metabolic fate is scant. In the present study conducted with precision-cut liver slices from male and female Sprague-Dawley rats, five reductive but no oxidative metabolites of curcumin and its demethoxy and bis-demethoxy analogues were observed and identified by HPLC and GC-MS analysis, mostly by comparison with authentic reference compounds. The major reductive metabolites were the hexahydrocurcuminoids in both male and female rat liver slices, whereas male rats formed more octahydro than tetrahydro metabolites and female rats more tetrahydro- than octahydrocurcuminoids. Tetrahydro, hexahydro, and octahydro metabolites were predominantly present as glucuronides, but a significant proportion of sulfate conjugates was also observed. The lack of formation of oxidative metabolites of curcumin and the ready generation of reductive metabolites were confirmed using rat liver microsomes and cytosol, respectively. Results of enzymatic hydrolysis studies conducted under various conditions revealed that curcumin and demethoxycurcumin are chemically less stable than bis-demethoxycurcumin, whereas the reductive metabolites of all three curcuminoids are stable compounds. This is the first report on the metabolism of demethoxycurcumin and bis-demethoxycurcumin. In view of the chemical instability of the parent curcuminoids, it is proposed to use their major phase I metabolites, that is, the stable hexahydro products, as biomarkers for exposure in clinical studies.  相似文献   

Laws and regulations concerning the confidentiality of veterinarian-client communication     

Babcock SL  Pfeiffer C 《Journal of the American Veterinary Medical Association》2006,229(3):365-369

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Explanation and Elaboration Document for the STROBE‐Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology—Veterinary Extension          下载免费PDF全文

A.M. O'Connor  J.M. Sargeant  I.R. Dohoo  H.N. Erb  M. Cevallos  M. Egger  A.K. Ersbøll  S.W. Martin  L.R. Nielsen  D.L. Pearl  D.U. Pfeiffer  J. Sanchez  M.E. Torrence  H. Vigre  C. Waldner  M.P. Ward 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2016,30(6):1896-1928

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers, and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples, and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE‐Vet statement. Thus, this is a companion document to the STROBE‐Vet statement methods and process document (JVIM_14575 “Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology—Veterinary (STROBE‐Vet) Statement” undergoing proofing), which describes the checklist and how it was developed.  相似文献   

Multivariate analysis of risk factors for feline hyperthyroidism in New Zealand     

Olczak J  Jones BR  Pfeiffer DU  Squires RA  Morris RS  Markwell PJ 《New Zealand veterinary journal》2005,53(1):53-58

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