Landuse and enviromental change in the Lake Chad Basin of Nigeria

The Lake Chad Basin is a major geographical region in the central part of the Sudan zone of Africa. The northern parts, however, extend into the Sahel and the southern parts of the Sahara desert. It consists of an extensive shallow depression of about 1.536.000 km2 (600.000 miles2) of which about 10% lies in Nigeria. The greater part is shared between the three countries of Cameroon, Chad and Niger. Climatically and agriculturally, the Chad Basin lies within the dry or semi-arid zone of Nigeria. It is a marginal area which has experienced severe droughts and considerable environmental changes in recent years. The natural environment, its use and misuse, and the threat of life posed by environmental pollution dominate discussions on environmental change. But in addition to the natural or physical environment, there are other equally important 'environments' which deserve some attention in view of the role that they play in generating economic growth and in ensuring sustainable development which is the central issue in our concern about the environment. These other environments are the cultural environment, the political environment and the economic environment, both internal and external. In the Chad Basin, all these other environments, along with the natural environment have been greatly influenced by its land locked location in the heart of Africa

VO2: A Novel View from Band Theory

New calculations for vanadium dioxide, one of the most controversely discussed materials for decades, reveal that band theory as based on density functional theory is well capable of correctly describing the electronic and magnetic properties of the metallic as well as both the insulating M1 and M2 phases. Considerable progress in the understanding of the physics of VO2 is achieved by the use of the recently developed hybrid functionals, which include part of the electron-electron interaction exactly and thereby improve on the weaknesses of semilocal exchange functionals as provided by the local density and generalized gradient approximations. Much better agreement with photoemission data as compared to previous calculations is found and a consistent description of the rutile-type early transition-metal dioxides is achieved.Comment: 5 pages, 4 figure

Strong coupling of a qubit to shot noise

We perform a nonperturbative analysis of a charge qubit in a double quantum dot structure coupled to its detector. We show that strong detector-dot interaction tends to slow down and halt coherent oscillations. The transitions to a classical and a low-temperature quantum overdamping (Zeno) regime are studied. In the latter, the physics of the dissipative phase transition competes with the effective shot noise.Comment: 5 pages, 4 figure

Effective Confinement as Origin of the Equivalence of Kinetic Temperature and Fluctuation-Dissipation Ratio in a Dense Shear Driven Suspension

We study response and velocity autocorrelation functions for a tagged particle in a shear driven suspension governed by underdamped stochastic dynamics. We follow the idea of an effective confinement in dense suspensions and exploit a time-scale separation between particle reorganization and vibrational motion. This allows us to approximately derive the fluctuation-dissipation theorem in a "hybrid" form involving the kinetic temperature as an effective temperature and an additive correction term. We show numerically that even in a moderately dense suspension the latter is negligible. We discuss similarities and differences with a simple toy model, a single trapped particle in shear flow

The Role of Surface Entropy in Statistical Emission of Massive Fragments from Equilibrated Nuclear Systems

Statistical fragment emission from excited nuclear systems is studied within the framework of a schematic Fermi-gas model combined with Weisskopf's detailed balance approach. The formalism considers thermal expansion of finite nuclear systems and pays special attention to the role of the diffuse surface region in the decay of hot equilibrated systems. It is found that with increasing excitation energy, effects of surface entropy lead to a systematic and significant reduction of effective emission barriers for fragments and, eventually, to the vanishing of these barriers. The formalism provides a natural explanation for the occurrence of negative nuclear heat capacities reported in the literature. It also accounts for the observed linearity of pseudo-Arrhenius plots of the logarithm of the fragment emission probability {\it versus} the inverse square-root of the excitation energy, but does not predict true Arrhenius behavior of these emission probabilities

Nonequilibrium stabilization of charge states in double quantum dots

We analyze the decoherence of charge states in double quantum dots due to cotunneling. The system is treated using the Bloch-Redfield generalized master equation for the Schrieffer-Wolff transformed Hamiltonian. We show that the decoherence, characterized through a relaxation $\tau_{r}$ and a dephasing time $\tau_{\phi}$, can be controlled through the external voltage and that the optimum point, where these times are maximum, is not necessarily in equilibrium. We outline the mechanism of this nonequilibrium-induced enhancement of lifetime and coherence. We discuss the relevance of our results for recent charge qubit experiments.Comment: 5 pages, 5 figure