The Instability of Charged Black Strings and p-Branes

We investigate the evolution of small perturbations around charged black strings and branes which are solutions of low energy string theory. We give the details of the analysis for the uncharged case which was summarized in a previous paper. We extend the analysis to the small charge case and give also an analysis for the generic case, following the behavior of unstable modes as the charge is modified. We study specifically a magnetically charged black 6-brane, but show how the instability is generic, and that charge does not in general stabilise black strings and p-branes.Comment: 41 pages plain TeX, 6 figures appended at end of file, DAMTP/R-94/7,LA-UR-93-447

Security, Conflict, and Reintegration in Mozambique: Case Studies of Land Access in the Postwar Period

In October 1992, the Peace Accord was signed in Mozambique. Many positive changes have taken place since then. and the countryside in postwar Mozambique is in a state of intense transformation. Nevertheless, the government has been largely silent on the issue of land tenure reform, while some of the recommendations regarding land-policy reform that have been proposed are simplistic, uninformed, and fail to reflect the present political reality in Mozambique. This report shows the need to initiate a comprehensive discussion on land policy reform, natural resource management, and decentralized control over resources. The discussion must address fundamental questions about what types of land rights will exist or, more specifically, what types of property rights will be permitted; who will have the power to distribute land rights; and how and by whom land disputes will be settled. At the heart of these questions lie profound issues relating to the role and nature of the state and other political institutions, the relationships of these institutions with the citizens, and the form and nature of governance in Mozambique. In this report we will raise several concerns with regard to land that we hope will help policymakers in Mozambique define the parameters of this discussion.Land Economics/Use,

Kaluza-Klein Black Holes with Squashed Horizons

We study geometrical structures of charged static black holes in the five-dimensional Einstein-Maxwell theory. The black holes we study have horizons in the form of squashed ${\rm S}^3$, and their asymptotic structure consists of a twisted ${\rm S}^1$ bundle over the four-dimensional flat spacetime at the spatial infinity. The spacetime we consider is fully five-dimensional in the vicinity of the black hole and four-dimensional with a compact extra dimension at infinity.Comment: 9pages. Final version to appear in Progress of Theoretical Physic

Microbial electrocatalysis with Geobacter sulfurreducens biofilm on stainless steel cathodes

Stainless steel and graphite electrodes were individually addressed and polarized at−0.60V vs. Ag/AgCl in reactors filled with a growth medium that contained 25mM fumarate as the electron acceptor and no electron donor, in order to force the microbial cells to use the electrode as electron source. When the reactor was inoculated with Geobacter sulfurreducens, the current increased and stabilized at average values around 0.75Am−2 for graphite and 20.5Am−2 for stainless steel. Cyclic voltammetry performed at the end of the experiment indicated that the reduction started at around −0.30V vs. Ag/AgCl on stainless steel. Removing the biofilm formed on the electrode surface made the current totally disappear, confirming that the G.sulfurreducens biofilm was fully responsible for the electrocatalysis of fumarate reduction. Similar current densities were recorded when the electrodes were polarized after being kept in open circuit for several days. The reasons for the bacteria presence and survival on non-connected stainless steel coupons were discussed. Chronoamperometry experiments performed at different potential values suggested that the biofilm-driven catalysis was controlled by electrochemical kinetics. The high current density obtained, quite close to the redox potential of the fumarate/succinate couple, presents stainless steel as a remarkable material to support biocathodes

Security of Tenure and Land Registration in Africa: Literature Review and Synthesis

In 1984, the Land Tenure Center embarked on a project to evaluate the experiences with land registration and tenure reform in Africa. The goal was to determine is African states been able to use tenure reform and land registration to provide greater security of tenure than was available through customary tenure systems. Donor agencies focused attention on the creation of individual freehold title, emphasizing the heightened security of holding, marketability, and access to credit under such tenure. National governments, on the other hand, were more concerned to see that land was used productively rather than merely accumulated for purposes of prestige or inheritance or as a hedge against inflation, and for this reason have tended to favor granting more circumscribed rights, such as leaseholds or rights of occupancy. This literature review and synthesis was prepared as part of an effort to increase very substantially our knowledge, especially on a quantitative level, of tenure and development relationships in Africa. The literature review is an attempt to gather in one place data about the diverse efforts at land registration and to describe briefly for each country the various registration programs that have taken place (if any), why they were undertaken, and what subsequent studies of these programs have found. Among other things, it will be seen that the intended benefits, and beneficiaries, of land registration have changed over the century or so since the first systems were put in place. In addition to these variations over time, there are also differences among Anglophone, Francophone, and Lusophone countries, differences that not only influenced the structure of registration systems established during the colonial era, but also continue to inform the kinds of registration systems adopted today.Land Economics/Use,

Inferring the eccentricity distribution

Standard maximum-likelihood estimators for binary-star and exoplanet eccentricities are biased high, in the sense that the estimated eccentricity tends to be larger than the true eccentricity. As with most non-trivial observables, a simple histogram of estimated eccentricities is not a good estimate of the true eccentricity distribution. Here we develop and test a hierarchical probabilistic method for performing the relevant meta-analysis, that is, inferring the true eccentricity distribution, taking as input the likelihood functions for the individual-star eccentricities, or samplings of the posterior probability distributions for the eccentricities (under a given, uninformative prior). The method is a simple implementation of a hierarchical Bayesian model; it can also be seen as a kind of heteroscedastic deconvolution. It can be applied to any quantity measured with finite precision--other orbital parameters, or indeed any astronomical measurements of any kind, including magnitudes, parallaxes, or photometric redshifts--so long as the measurements have been communicated as a likelihood function or a posterior sampling.Comment: Ap

Caged Black Holes: Black Holes in Compactified Spacetimes II - 5d Numerical Implementation

We describe the first convergent numerical method to determine static black hole solutions (with S^3 horizon) in 5d compactified spacetime. We obtain a family of solutions parametrized by the ratio of the black hole size and the size of the compact extra dimension. The solutions satisfy the demanding integrated first law. For small black holes our solutions approach the 5d Schwarzschild solution and agree very well with new theoretical predictions for the small corrections to thermodynamics and geometry. The existence of such black holes is thus established. We report on thermodynamical (temperature, entropy, mass and tension along the compact dimension) and geometrical measurements. Most interestingly, for large masses (close to the Gregory-Laflamme critical mass) the scheme destabilizes. We interpret this as evidence for an approach to a physical tachyonic instability. Using extrapolation we speculate that the system undergoes a first order phase transition.Comment: 42 pages, 19 eps figures; v2: 3 references added, version to appear in Phys.Rev.