Magnon-magnon interactions in the Spin-Peierls compound CuGeO_3

In a magnetic substance the gap in the Raman spectrum, Delta_R, is approximatively twice the value of the neutron scattering gap, Delta_S, if the the magnetic excitations (magnons) are only weakly interacting. But for CuGeO_3 the experimentally observed ratio Delta_R/Delta_S is approximatively 1.49-1.78, indicating attractive magnon-magnon interactions in the quasi-1D Spin-Peierls compound CuGe_3. We present numerical estimates for Delta_R/Delta_S from exact diagonalization studies for finite chains and find agreement with experiment for intermediate values of the frustration parameter alpha. An analysis of the numerical Raman intensity leads us to postulate a continuum of two-magnon bound states in the Spin-Peierls phase. We discuss in detail the numerical method used, the dependence of the results on the model parameters and a novel matrix-element effect due to the dimerization of the Raman-operator in the Spin-Peierls phase.Comment: submitted to PRB, Phys. Rev. B, in pres

Two-magnon Raman scattering in insulating cuprates: Modifications of the effective Raman operator

Calculations of Raman scattering intensities in spin 1/2 square-lattice Heisenberg model, using the Fleury-Loudon-Elliott theory, have so far been unable to describe the broad line shape and asymmetry of the two magnon peak found experimentally in the cuprate materials. Even more notably, the polarization selection rules are violated with respect to the Fleury-Loudon-Elliott theory. There is comparable scattering in $B_{1g}$ and $A_{1g}$ geometries, whereas the theory would predict scattering in only $B_{1g}$ geometry. We review various suggestions for this discrepency and suggest that at least part of the problem can be addressed by modifying the effective Raman Hamiltonian, allowing for two-magnon states with arbitrary total momentum. Such an approach based on the Sawatzsky-Lorenzana theory of optical absorption assumes an important role of phonons as momentum sinks. It leaves the low energy physics of the Heisenberg model unchanged but substantially alters the Raman line-shape and selection rules, bringing the results closer to experiments.Comment: 7 pages, 6 figures, revtex. Contains some minor revisions from previous versio

Diagnosis Of Mycosis Fungoides: A Comparative Immunohistochemical Study Of T-cell Markers Using A Novel Anti-cd7 Antibody

Mycosis fungoides (MF) is the most common form of primary cutaneous T-cell lymphoma. In its early stage it may mimic benign dermatoses both on a clinical and histologic basis. MF usually expresses CD3 and CD4 (T-cell) markers. CD7 is expressed on about 90% of CD4 T cells and is often deficient on malignant T cells. Thus, CD7 may be useful in evaluating the nature of dermal lymphoid infiltrates. The aim of this study was to evaluate the usefulness of immunohistochemical detection of T-cell markers on paraffin-embedded sections, CD3 and CD7 (clone CBC.37), in the differential diagnosis of MF and benign dermatoses. Forty-two patients with diffuse dermal T-lymphocytic infiltrates were selected. Previous clinicopathologic correlation and follow-up had established the diagnosis of MF in 31 patients and benign dermatoses in 11. The mean value of stained cells in MF was 86.45% for CD3 and 53.09% for CD7 (P<0.001); in benign dermatoses it was 79.09% for CD3 and 73.63% for CD7 (P=0.669). CD7 immunolabeling was significantly lower in the MF group (P=0.048). A semiquantitative evaluation revealed a considerable loss of CD7 immunolabeling in comparison with CD3 in patients with MF. The authors conclude that CD7 study may represent a valuable tool in the distinction between inflammation and neoplasia in T-lymphoproliferative skin disorders. Copyright © 2006 by Lippincott Williams & Wilkins.143291295Willemze, R., Kerl, H., Sterry, W., EORTC classification for primary cutaneous lymphomas: A proposal from the Cutaneous Lymphoma Study Group of the European Organization for Research and Treatment of Cancer (1997) Blood, 90, pp. 354-371Diaz-Cascajo, C., Strong immunoexpression of the monoclonal antibody CD-30 in lymphocytic infiltrates of the skin not by itself evidence for diagnosing malignant lymphoma (2001) Am J Dermatopathol, 23, pp. 79-83Berti, E., Tomasini, D., Vermeer, M.H., Primary cutaneous CD8-positive epidermotropic cytotoxic T cell lymphomas. A distinct clinicopathological entity with an aggressive clinical behavior (1999) Am J Pathol, 155, pp. 483-492Burns, M.K., Chan, L.S., Cooper, K.D., Worringer-Kolopp disease (localized pagetoid reticulosis) or unilesional mycosis fungoides? (1995) Arch Dermatol, 131, pp. 325-329Izban, K.F., Hsi, E.D., Alkan, S., Immunohistochemical analysis of mycosis fungoides on paraffin-embedded tissue sections (1998) Mod Pathol, 11, pp. 978-982Hudson, A.R., Smoller, B.R., Immunohistochemistry in diagnostic dermatopathology (1999) Dermatol Clin, 17, pp. 667-689Nuckols, J.D., Shea, C.R., Horenstein, M.G., Quantitation of intraepidermal T-cell subsets in formalin-fixed, paraffin-embedded tissue helps in the diagnosis of mycosis fungoides (1999) J Cutan Pathol, 26, pp. 169-175Glusac, E.J., Shapiro, P.E., McNiff, J.M., Cutaneous T-cell lymphoma. Refinement in the application of controversial histologic criteria (1999) Dermatol Clin, 17, pp. 601-614Rijlaarsdam, J.U., Scheffer, E., Meijer, C.J.L.M., Cutaneous pseudo-T-cell lymphomas. A clinicopathologic study of 20 patients (1992) Cancer, 69, pp. 717-724Haeffner, A.C., Smoller, B.R., Zepter, K., Differentiation and clonality of lesional lymphocytes in small plaque parapsoriasis (1995) Arch Dermatol, 131, pp. 321-324Cotta, A.C., Cintra, M.L., De Souza, E.M., Reassessment of diagnostic criteria in cutaneous lymphocytic infiltrates (2004) Sao Paulo Med J, 122, pp. 161-165Al Saati, T., Alibaud, L., Lamant, L., A new monoclonal Anti-CD7 antibody reactive on paraffin sections (2001) Appl Immunohistochem Mol Morphol, 9, pp. 289-296Ackerman, A.B., (1997) Histologic Diagnosis of Inflammatory Skin Diseases. 2nd Ed., , Baltimore: Williams & Wilkins;LeBoit, P., Variants of mycosis fungoides and related cutaneous T-cell lymphomas (1991) Semin Diagn Pathol, 8, pp. 73-81Altemani, A.M., Bittencourt, A.L., Lana, A.M.A., Immunohistochemical characterization of the inflammatory infiltrate in placental Chagas disease: A qualitative and quantitative analysis (2000) Am J Trop Med Hyg, 62, pp. 319-324Ormsby, A., Bergfeld, W.F., Tubbs, R.R., Evaluation of a new paraffin-reactive CD7 T-cell deletion marker and a polymerase chain reaction-based T-cell receptor gene rearrangement assay: Implications for diagnosis of mycosis fungoides in community clinical practice (2001) J Am Acad Dermatol, 45, pp. 405-413Weisberger, J., Cornfield, D., Gorczyca, W., Down-regulation of pan-T-cell antigens, particularly CD7, in acute infectious mononucleosis (2003) Am J Clin Pathol, 120, pp. 49-55Murphy, M., Fullen, D., Carlson, A., Low CD7 expression in benign and malignant cutaneous lymphocytic infiltrates. Experience with an antibody reactive with paraffin-embedded tissue (2002) Am J Dermatopathol, 1, pp. 6-16Moll, M., Reinhold, U., Kukel, S., CD7-negative helper T cells accumulate in inflammatory skin lesions (1994) J Invest Dermatol, 102, pp. 328-332Harmon, C.B., Witzig, T.E., Katzmann, J.A., Detection of circulating T cells with CD4+CD7- Immunophenotype in patients with benign and malignant lymphoproliferative dermatoses (1996) J Am Acad Dermatol, 35, pp. 404-410Reinhold, U., Abken, H., Kukel, S., CD7-T cells represent a subset of normal human blood lymphocytes (1993) J Immunol, 150, pp. 2081-2089Wood, G.S., Hong, S.R., Sasaki, D.T., Leu-8/CD7 antigen expression by CD3+ T cells: Comparative analysis of skin and blood in MF/SS syndrome relative to normal blood values (1990) J Am Acad Dermatol, 22, pp. 602-60

Fermi LAT Observations of the Vela Pulsar.

e-Print: arXiv:0812.2960 [astro-ph] , Submitted to Astrophys.J