286 research outputs found
Economic and Theological Approaches to Debt Cancellation
Differences in economic and theological approaches to debt cancellation result from differences in disciplinary assumptions in respect of purpose, method, and argument. We argue that they provide alternative commentaries upon the need for debt cancellation, but that it is not possible to demonstrate the superiority of one over the other, so practitioners in one are likely to continue to find it difficult to respond meaningfully to arguments from the other.debt cancellation, conditionality, theology
Dynamics of colloidal particles in ice
We use X-ray Photon Correlation Spectroscopy (XPCS) to probe the dynamics of colloidal particles in polycrystalline ice. During freezing, the dendritic ice morphology and rejection of particles from the ice created regions of high-particle-density, where some of the colloids were forced into contact and formed disordered aggregates. We find that the particles in these high density regions underwent ballistic motion coupled with both stretched and compressed exponential decays of the intensity autocorrelation function, and that the particles’ characteristic velocity increased with temperature. We explain this behavior in terms of ice grain boundary migration
Islands, craters, and a moving surface step on a hexagonally reconstructed (100) noble metal surface
Deposition/removal of metal atoms on the hex reconstructed (100) surface of
Au, Pt and Ir should present intriguing aspects, since a new island implies hex
-> square deconstruction of the substrate, and a new crater the square -> hex
reconstruction of the uncovered layer. To obtain a microscopic understanding of
how islands/craters form in these conditions, we have conducted simulations of
island and crater growth on Au(100), whose atomistic behavior, including the
hex reconstruction on top of the square substrate, is well described by mean s
of classical many-body forces. By increasing/decreasing the Au coverage on
Au(100), we find that island/craters will not grow unless they exceed a
critical size of about 8-10 atoms. This value is close to that which explains
the nonlinear coverage dependence observed in molecular adsorption on the
closely related surface Pt (100). This threshold size is rationalized in terms
of a transverse step correlation length, measuring the spatial extent where
reconstruction of a given plane is disturbed by the nearby step.Comment: 11 pages, 5 figures, accepted for publication in Surface Science
(ECOSS-18
X-ray Near Field Speckle: Implementation and Critical Analysis
We have implemented the newly-introduced, coherence-based technique of x-ray
near-field speckle (XNFS) at 8-ID-I at the Advanced Photon Source. In the near
field regime of high-brilliance synchrotron x-rays scattered from a sample of
interest, it turns out, that, when the scattered radiation and the main beam
both impinge upon an x-ray area detector, the measured intensity shows
low-contrast speckles, resulting from interference between the incident and
scattered beams. We built a micrometer-resolution XNFS detector with a high
numerical aperture microscope objective and demonstrate its capability for
studying static structures and dynamics at longer length scales than
traditional far field x-ray scattering techniques. Specifically, we
characterized the structure and dynamics of dilute silica and polystyrene
colloidal samples. Our study reveals certain limitations of the XNFS technique,
which we discuss.Comment: 53 pages, 16 figure
Epitaxy and Step Structures on Semiconductor Surfaces
Contains reports on one research project and a list of publications.Joint Services Electronics Program Contract DAAL03-92-C-000
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