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Comparison of dc and microwave resistivity in polycrystalline La0.7−xYxCa0.3MnO3 samples: Influence of Y at grain boundaries (2000)

Yates, K. A. ; Cohen, L. F. ; Watine, C. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 88 (2000), S. 4703-4708

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: A series of polycrystalline La0.7−xYxCa0.3MnO3 samples were studied, where x=0, 0.07, 0.1, 0.15, and 0.2. Measurement of the dc resistivity, microwave surface resistance, ac susceptibility, and dc magnetization were made. As expected, the magnetic state becomes more frustrated as Y is added. It is found that the dc resistivity is approximately two orders of magnitude larger than the 9 GHz resistivity for all samples, however, both increase with Y doping by the same multiplicative factor. From circumstantial evidence and estimation of the grain boundary response time, it is found that the microwave measurement short circuits the grain boundaries. We assume that the dc resistivity is dominated by grain boundary properties and the microwave resistivity reflects intragranular behavior. Analysis of the electrical transport at dc and microwave frequencies is carried out and a phenomenological model proposed which agrees well with observation. The model implies that the influence of Y is modified by the underlying static disorder in which it is placed. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1289522

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Aberrant T-Cell Receptor Signalling of Interferon-γ- and Tumour Necrosis Factor-α-Producing Cytotoxic CD8+ Vδ1/Vβ16 T Cells in a Patient with Chronic Neutropenia (2003)

Bank, I. ; Cohen, L. ; Kneller, A. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Scandinavian journal of immunology 58 (2003), S. 0

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ISSN: 1365-3083

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: We previously found that the peripheral blood (PB) mononuclear cells (MCs) (PBMCs) of a patient with chronic neutropenia contained an expanded population of cytotoxic CD8+ T cells using a variable (V) region δ1 gene product in the T-cell receptor-α (TCR-α) polypeptide [Vδ1-constant(C)α+ T cells]. Sequencing of polymerase chain reaction (PCR) amplification products have now revealed a productive Vδ1/joining (J)αIGRJa03/Cα rearrangement of the TCR-α gene, predominantly associated with a Vβ16/Dβ2.1/Jβ2.1/Cβ2 TCR-β gene, in these cells. Furthermore, we detected a markedly deficient proliferative response of the patient PBMCs to triggering with monoclonal antibodies (MoAbs) to the CD3 molecule, contrasting with a substantial response to the Vβ3, 12, 14, 15, 17 and 20-specific staphylococcal enterotoxin B (SEB) superantigen, suggesting defective TCR-mediated activation of the Vδ1+/Vβ16+ clone. Moreover, whereas triggering of Vδ1– T cells cultured with interleukin-2 (IL-2) by MoAb to the CD3 molecule enhanced proliferation, Vδ1-Cα+ T cells were inhibited by MoAbs to either CD3 or Vδ1. Vδ1-Cα+ T-cell clones spontaneously secrete interferon-γ (IFN-γ) and were further induced to release tumour necrosis factor (TNF-α) when triggered by anti-CD3 plus phorbol ester. Aberrant signalling by the clonotypic TCR together with the functional properties of the CD8+ Vδ1+/Vβ16+ clone may thus contribute to the immunohaematological abnormalities observed in this patient.