24 research outputs found
Spin fluctuations in CuGeO probed by light scattering
We have measured temperature dependence of low-frequency Raman spectra in
CuGeO, and have observed the quasi-elastic scattering in the
polarization above the spin-Peierls transition temperature. We attribute it to
the fluctuations of energy density in the spin system. The magnetic specific
heat and an inverse of the magnetic correlation length can be derived from the
quasi-elastic scattering. The inverse of the magnetic correlation length is
proportional to at high temperatures. We compare the
specific heat with a competing- model. This model cannot explain
quantitatively both the specific heat and the magnetic susceptibility with the
same parameters. The origin of this discrepancy is discussed.Comment: 17 pages, REVTeX, 5 Postscript figures; in press in PR
The Role of Interdiffusion and Spatial Confinement in the Formation of Resonant Raman Spectra of Ge/Si(100) Heterostructures with Quantum-Dot Arrays
The phonon modes of self-assembled Ge/Si quantum dots grown by molecular-beam
epitaxy in an apparatus integrated with a chamber of the scanning tunneling
microscope into a single high-vacuum system are investigated using Raman
spectroscopy. It is revealed that the Ge-Ge and Si-Ge vibrational modes are
considerably enhanced upon excitation of excitons between the valence band
and the conduction band (the E1 and E1 +
transitions). This makes it possible to observe the Raman spectrum of very
small amounts of germanium, such as one layer of quantum dots with a germanium
layer thickness of 10 \r{A}. The enhancement of these modes suggests a strong
electron-phonon interaction of the vibrational modes with the E1 and E1 +
excitons in the quantum dot. It is demonstrated that the frequency
of the Ge-Ge mode decreases by 10 cm^-1 with a decrease in the thickness of the
Ge layer from 10 to 6 \r{A} due to the spatial-confinement effect. The optimum
thickness of the Ge layer, for which the size dispersion of quantum dots is
minimum, is determined.Comment: 14 pages, 9 figure
Moving From Partnership to Collective Accountability and Sustainable Change: Applying a Systems-Change Model to Foundations’ Evolving Roles
· In a time of scarce resources and significant needs, funders may seek to maximize the impact of their grantmaking through collaboration. While many foundations move well from identifying a problem to building broader awareness and forging key partnerships, they typically flounder in trying to move beyond collaboration to a sense of mutual responsibility or collective accountability for the greater good, which is a precondition for sustainable systems change.
· This article discusses three complex initiatives that made sustainable changes in integrated behavioral health and primary care. Using a conceptual framework based on the Building Blocks of Systems Change model, this article focuses on achieving collective accountability and sustainable systems change, highlights common challenges, and presents guidelines for funders.
· While the article details how various policy approaches and tools drove cultural transformation in these three funding regions, the conceptual framework and lessons learned apply to a broad range of environments and intended outcomes. These lessons can be used to move initiatives to collective accountability and systems change, so that the change becomes the new “normal,” independent of external funding or expectations