100,779 research outputs found
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Handwritten biographical information on Paulina T. McClung Merritt
No full textA handwritten biography of Paulina T. McClung Merritt by an unknown author, 1892.
Heterogeneous and tissue-specific regulation of effector T cell responses by IFN-gamma during Plasmodium berghei ANKA infection.
No full textIFN-γ and T cells are both required for the development of experimental cerebral malaria during Plasmodium berghei ANKA infection. Surprisingly, however, the role of IFN-γ in shaping the effector CD4(+) and CD8(+) T cell response during this infection has not been examined in detail. To address this, we have compared the effector T cell responses in wild-type and IFN-γ(-/-) mice during P. berghei ANKA infection. The expansion of splenic CD4(+) and CD8(+) T cells during P. berghei ANKA infection was unaffected by the absence of IFN-γ, but the contraction phase of the T cell response was significantly attenuated. Splenic T cell activation and effector function were essentially normal in IFN-γ(-/-) mice; however, the migration to, and accumulation of, effector CD4(+) and CD8(+) T cells in the lung, liver, and brain was altered in IFN-γ(-/-) mice. Interestingly, activation and accumulation of T cells in various nonlymphoid organs was differently affected by lack of IFN-γ, suggesting that IFN-γ influences T cell effector function to varying levels in different anatomical locations. Importantly, control of splenic T cell numbers during P. berghei ANKA infection depended on active IFN-γ-dependent environmental signals--leading to T cell apoptosis--rather than upon intrinsic alterations in T cell programming. To our knowledge, this is the first study to fully investigate the role of IFN-γ in modulating T cell function during P. berghei ANKA infection and reveals that IFN-γ is required for efficient contraction of the pool of activated T cells
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Magnetotransport in variable-coupling one-dimensional ballistic constrictions
No full textA scheme to produce closely spaced high-quality one-dimensional electronic channels is presented. It is based on standard nanolithography fabrication applied to a single, wide quantum well AlGaAs/GaAs heterostructure where the spatial separation of the wire modes is given by Coulomb repulsion. The lack of a composition-induced barrier in the double layer leads to electron mobility of 5x10(6) cm(2)/Vs in the starting double two-dimensional system. This in turn yields high-quality one-dimensional channels following nanolithography, as shown by our detailed analysis of the magnetotransport properties of the system. Variable coupling is achieved by split-gate polarization and external magnetic-field intensity and orientation. The relevance for the implementation of coherent nanodevices of this fabrication approach is discussed. (C) 2002 American Institute of Physics
Pelevin’s Trinity in the novel “t”: author – protagonist – reader
No full textThe article attempts to interpret Pelevin's artistic strategy in the novel "T" by exploring its subject organization and addressing the key problems of the author, the protagonist, and the reader as they are seen by the researcher. The article analyzes the peculiarities of constructing the narrative reality in the novel "T", and goes on to discuss Pelevin's philosophic models of the development of the humankind, and the emergence of his new anthropology
Measuring industry-science links through inventor-author relations: A profiling method
No full textIn this pilot study we examine the performance of text-based profiling in recovering a set of validated inventor-author links. In a first step we match patents and publications solely based on their similarity in content. Next, we compare inventor and author names on the highest ranked matches for the occurrence of name matches. Finally, we compare these candidate matches with the names listed in a validated set of inventor-author names. Our text-based profile methodology performs significantly better than a random matching of patents and publications, suggesting that text-based profiling is a valuable complementary tool to the name searches used in previous studies.innovation; industry-science links; text-based profiling;
Review: Spin photocurrents in quantum wells
No full textSpin photocurrents generated by homogeneous optical excitation with circularly polarized radiation in quantum wells (QWs) are reviewed. The absorption of circularly polarized light results in optical spin orientation due to the transfer of the angular momentum of photons to electrons of a two-dimensional electron gas. It is shown that in QWs belonging to one of the gyrotropic crystal classes a non-equilibrium spin polarization of uniformly distributed electrons causes a directed motion of electrons in the plane of the QW. A characteristic feature of this electric current, which occurs in unbiased samples, is that it reverses its direction upon changing the radiation helicity from left-handed to right-handed and vice versa. Two microscopic mechanisms are responsible for the occurrence of an electric current linked to a uniform spin polarization in a QW: the spin polarization-induced circular photogalvanic effect and the spin-galvanic effect. In both effects the current flow is driven by an asymmetric distribution of spin-polarized carriers in k-space of systems with lifted spin degeneracy due to k-linear terms in the Hamiltonian. Spin photocurrents provide methods to investigate spin relaxation and to reach a conclusion as regards the in-plane symmetry of QWs. The effect can also be utilized to develop fast detectors for determining the degree of circular polarization of a radiation beam. Furthermore, spin photocurrents under infrared excitation were used to demonstrate and investigate monopolar spin orientation of free carriers
Electronic transport in hybrid heterostructures and universal control of spin-orbit interaction in quantum wells
No full textIn recent years, the control of charge and spin in semiconductors has experienced outstanding progress. The extended spin coherence times established in high quality materials together with the advance in elaborate fabrication methods enable coherent spin control, ultimately leading to new spintronic devices. In this thesis, we investigate various aspects of quantum transport with respect to potential spintronic applications in two different kind of 2-dimensional electron gases (2DEGs) in GaAs/AlGaAs crystals.
First, we try to combine the advantages of optically active InAs quantum dots (QDs) and the versatile possibilities of gate tunable 2DEGs in a novel hybrid heterostructure. We have characterized a series of hybrid wafers with different spacings between the inverted 2DEG and Stranski-Krastanov grown self-assembled InAs QDs. Depending on this distance and actual QD nucleation – verified with atomic force microscopy on the wafer surface – the 2DEG mobility is reduced due to scattering induced by the QDs and the InAs wetting layer. For a tunnel barrier of 45 nm, the 2DEG exhibits mobilities exceeding 500′000 cm2/(Vs) despite the presence of InAs QDs, while coherent tunneling between 2DEG and QDs is still permitted. Using a top down approach, lateral quantum point contact gates are aligned precisely to a single, specifically chosen InAs QD. The 1D conductance is not sensitive to QD charging events, but is dominated by a disorder potential, even suppressing quantization.
In the second part of the thesis, we study the control of spin-orbit (SO) interaction. This relativistic coupling of the electron spin to its momentum can be used for coherent spin manipulation, but at the same time also causes spin relaxation. Theory predicts a special symmetry, protecting spin from relaxation in diffusive transport, when the two main contributions of SO interaction in GaAs quantum wells (QW) – the Rashba and the Dresselhaus effect – are of equal strength. We demonstrate broad, independent control of all relevant SO fields, allowing us to tune into this regime. By electrically locking the Rashba and Dresselhaus SO fields via top and back gate, we achieve spin protection for a wide range of voltages on a single QW. We use quantum corrections to 2D conductivity as a sensitive probe of SO coupling. The combination of transport data and numerical calculations allows us to quantify the relevant SO coefficients
Wave turbulence of a rotating array of quantized vortices in the T → 0 temperature limit
No full textThe dynamics of quantized vortices in the zero temperature limit is currently of great interest, particularly in the case of the Fermi superfluid He-B. Here we study wave turbulence, generated by the librating motion of a rotating cylindrical container filled with He-B, in the limit of vanishing viscous forces at temperatures . The polarization of the quantized vortices with respect to the axis of rotation is measured using non-invasive NMR techniques. We observe a decrease of the polarization when the librating motion is started, and a two-stage relaxation process when the modulation of the rotation velocity is stopped. The first relaxation process is associated with the dissipation of large-scale flow stored in inertial waves and the solid body rotation of the vortex array. From the decay of these energy reservoirs we determine the rate of energy dissipation of large-scale flow. The later second process is related to the relaxation of Kelvin waves on individual vortices. This process is monitored by the recovery of the polarization. The existence of a Kelvin wave cascade at the lowest temperatures is currently a central open question. We supply some evidence for the cascade
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