Preroughening transitions in a model for Si and Ge (001) type crystal surfaces

The uniaxial structure of Si and Ge (001) facets leads to nontrivial topological properties of steps and hence to interesting equilibrium phase transitions. The disordered flat phase and the preroughening transition can be stabilized without the need for step-step interactions. A model describing this is studied numerically by transfer matrix type finite-size-scaling of interface free energies. Its phase diagram contains a flat, rough, and disordered flat phase, separated by roughening and preroughening transition lines. Our estimate for the location of the multicritical point where the preroughening line merges with the roughening line, predicts that Si and Ge (001) undergo preroughening induced simultaneous deconstruction transitions.Comment: 13 pages, RevTex, 7 Postscript Figures, submitted to J. Phys.

Reconstructed Rough Growing Interfaces; Ridgeline Trapping of Domain Walls

We investigate whether surface reconstruction order exists in stationary growing states, at all length scales or only below a crossover length, $l_{\rm rec}$. The later would be similar to surface roughness in growing crystal surfaces; below the equilibrium roughening temperature they evolve in a layer-by-layer mode within a crossover length scale $l_{\rm R}$, but are always rough at large length scales. We investigate this issue in the context of KPZ type dynamics and a checker board type reconstruction, using the restricted solid-on-solid model with negative mono-atomic step energies. This is a topology where surface reconstruction order is compatible with surface roughness and where a so-called reconstructed rough phase exists in equilibrium. We find that during growth, reconstruction order is absent in the thermodynamic limit, but exists below a crossover length $l_{\rm rec}>l_{\rm R}$, and that this local order fluctuates critically. Domain walls become trapped at the ridge lines of the rough surface, and thus the reconstruction order fluctuations are slaved to the KPZ dynamics

Evaluating the effectiveness of emergency relief of the Central Emergency Response Fund after natural disasters

Natural disasters are increasingly common and emergency relief is often provided to help the affected countries recover. The United Nations started the Central Emergency Response Fund (CERF) in 2005 that allows for fast allocation of money to providers of humanitarian aid. This thesis evaluates this fund with respect to natural disasters, since its effectiveness can have implications for future emergency relief allocations. The following question is answered: To what extent can the grants provided by the Central Emergency Response Fund decrease the output growth volatility caused by natural disasters? A panel database is constructed and dynamic panel models are estimated by applying the Generalised Method of Moments. Results show that when CERF funding is provided after a natural disaster, the expected effect on output growth volatility of the natural disaster is neutralised and close to zero. This implies that CERF funding is effective, however, reports on the functioning of CERF report possible improvements concerning the allocation. Furthermore, alternative estimation methods might provide consistent results