Neutron experiments have indicated that the structure factor S (q, co) for the two cuprates YBa2Cu307 q and La~Sr Cu04 has a different q dependence. Commensurate peaks at (~/a, m/a) are observed in the former case, whereas clearly incommensurate peaks are seen in the latter, for metallic hole concentrations. We attribute this contrasting q dependence to differences in the Fermi-surface geometry, obtained in band-structure approaches, and (for the YBaCuO system) also corroborated by photoemission experiments. Using a large Coulomb-U, Fermi-liquid-based scheme, we present results for the q, co and temperature dependence of the neutron cross section as well as for the temperature dependence of the NMR relaxation, in both cuprate families at various hole concentrations. When antiferromagnetic quasiparticle interactions of moderate strength are included, these calculations compare favorably with experiment.It should be stressed that the Fermi-surface shape must be accurately represented in both systems in order to produce this good agreement with the neutron data. We conclude that the close correspondence found, thus far, between band-structure-derived spin dynamics and the detailed fermiology of both cuprates provides support for Fermi-liquid-based schemes. Furthermore, this correspondence suggests important constraints which should be included in theoretical schemes ranging from the marginal and nearly antiferromagnetic Fermi liquid to more exotic scenarios for the normal state. Within this context, it is extremely important to determine the characteristic energy scales of the Fermi liquid. Comparison of our calculations with the measured energy scales of the spin dynamics indicates that these are sufficiently low so that one can reconcile deviations from canonical behavior above T, with a Fermi-liquid ground state. Explicit effects of these low-energy scales are discussed in the context of the quasiparticle lifetime as a function of frequency and temperature. Our detailed studies also yield predictions for future experiments which will help to test futher the validity of this approach.
We show that it is possible to reconcile NMR and neutron scattering experiments on both La2−xSrxCuO4 and YBa2Cu3O6+x, by making use of the Millis-Monien-Pines mean field phenomenological expression for the dynamic spin-spin response function, and reexamining the standard Shastry-Mila-Rice hyperfine Hamiltonian for NMR experiments.
MEIS2 has an important role in development and organogenesis, and is implicated in the pathogenesis of human cancer. The molecular basis of MEIS2 action in tumorigenesis is not clear. Here, we show that MEIS2 is highly expressed in human neuroblastoma cell lines and is required for neuroblastoma cell survival and proliferation. Depletion of MEIS2 in neuroblastoma cells leads to M-phase arrest and mitotic catastrophe, whereas ectopic expression of MEIS2 markedly enhances neuroblastoma cell proliferation, anchorage-independent growth, and tumorigenicity. Gene expression profiling reveals an essential role of MEIS2 in maintaining the expression of a large number of late cell-cycle genes, including those required for DNA replication, G2-M checkpoint control and M-phase progression. Importantly, we identify MEIS2 as a transcription activator of the MuvB-BMYB-FOXM1 complex that functions as a master regulator of cell-cycle gene expression. Further, we show that FOXM1 is a direct target gene of MEIS2 and is required for MEIS2 to upregulate mitotic genes. These findings link a developmentally important gene to the control of cell proliferation and suggest that high MEIS2 expression is a molecular mechanism for high expression of mitotic genes that is frequently observed in cancers of poor prognosis.
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