Equation of state of fully ionized electron-ion plasmas

Thermodynamic quantities of Coulomb plasmas consisting of point-like ions immersed in a compressible, polarizable electron background are calculated for ion charges Z=1 to 26 and for a wide domain of plasma parameters ranging from the Debye-Hueckel limit to the crystallization point and from the region of nondegenerate to fully degenerate nonrelativistic or relativistic electrons. The calculations are based on the linear-response theory for the electron-ion interaction, including the local-field corrections in the electronic dielectric function. The thermodynamic quantities are calculated in the framework of the N-body hypernetted-chain equations and fitted by analytic expressions. We present also accurate analytic approximations for the free energy of the ideal electron gas at arbitrary degeneracy and relativity and for the excess free energy of the one-component plasma of ions (OCP) derived from Monte Carlo simulations. The extension to multi-ionic mixtures is discussed within the framework of the linear mixing rule. These formulae provide a completely analytic, accurate description of the thermodynamic quantities of fully ionized electron-ion Coulomb plasmas, a useful tool for various applications from liquid state theory to dense stellar matter.Comment: 13 pages, 2 tables, 7 figures, REVTeX using epsf.sty. To be published in Phys. Rev. E, vol. 58 (1998

Variational quantum Monte Carlo study of two-dimensional Wigner crystals: exchange, correlation, and magnetic field effects

The two-dimensional Wigner crystals are studied with the variational quantum Monte Carlo method. The close relationship between the ground-state wavefunction and the collective excitations in the system is illustrated, and used to guide the construction of the ground-state wavefunction of the strongly correlated solid. Exchange, correlation, and magnetic field effects all give rise to distinct physical phenomena. In the absence of any external magnetic field, interesting spin-orderings are observed in the ground-state of the electron crystal in various two-dimensional lattices. In particular, two-dimensional bipartite lattices are shown not to lead necessarily to an antiferromagnetic ground-state. In the quantum Hall effect regime, a strong magnetic field introduces new energy and length scales. The magnetic field quenches the kinetic energy and poses constraints on how the electrons may correlate with each other. Care is taken to ensure the appropriate translational properties of the wavefunction when the system is in a uniform magnetic field. We have examined the exchange, intra-Landau-level correlation as well as Landau-level-mixing effects with various variational wavefunctions. We also determine their dependences on the experimental parameters such as the carrier effective mass at a modulation-doped semiconductor heterojunction. Our results, when combined with some recent calculations for the energy of the fractional quantum Hall liquid including Landau-level-mixing, show quantitatively that in going from $n$-doping to $p$-doping in $GaAS/AlGaAS$ heterojunction systems, the crossover filling factor from the fractional quantum Hall liquid to the Wigner crystal changes from filling factor $\nu \sim 1/5$ to $\nu \sim 1/3$. This lends strong support to the claim that theComment: LaTex file, 14 figures available from [email protected]

Differential livelihood adaptation to social-ecological change in coastal Bangladesh

Social-ecological changes, brought about by the rapid growth of the aquaculture industry and the increased occurrence of climatic stressors, have significantly affected the livelihoods of coastal communities in Asian mega-deltas. This paper explores the livelihood adaptation responses of households of different wealth classes, the heterogeneous adaptation opportunities, barriers and limits (OBLs) faced by these households and the dynamic ways in which these factors interact to enhance or impede adaptive capacities. A mixed methods approach was used to collect empirical evidence from two villages in coastal Bangladesh. Findings reveal that households’ adaptive capacities largely depend on their wealth status, which not only determine their availability of productive resources, but also empower them to navigate social-ecological change in desirable ways. Households operate within a shared response space, which is shaped by the broader socio-economic and political landscape, as well as their previous decisions that can lock them in to particular pathways. While an adaptive response may be effective for one social group, it may cause negative externalities that can undermine the adaptation options and outcomes of another group. Adaptation OBLs interact in complex ways; the extent to which these OBLs affect different households depend on the specific livelihood activities being considered and the differential values and interests they hold. To ensure more equitable and environmentally sustainable livelihoods in future, policies and programs should aim to expand households’ adaptation space by accounting for the heterogeneous needs and complex interdependencies between response processes of different groups

Structure and thermoelectric properties of EuTi(O,N)3 ± δ

After partial substitution of nitrogen for oxygen in EuTiO3, the crystal structure, thermoelectric properties, morphology, and electronic structure of the products were analyzed and compared with pristine EuTiO3. The space group of EuTi(O,N)3 ±  δ was orthorhombic Pnma due to the tilt and rotation of the anion octahedra, compared to cubic Pm3¯m of EuTiO3 (at room temperature). The thermoelectric properties of oxynitride polycrystalline bodies sintered in three different ways were investigated in the temperature range of 300 K < T < 950 K. The Seebeck coefficients (S) of the oxynitrides were lower compared with the oxide, and the electrical resistivities (ρ) were increased about one order of magnitude. The activation energies (E A) indicated a larger band gap of EuTi(O,N)3 ±  δ when compared to the pristine EuTiO3 (∼1.3 eV compared to 0.98 eV). A morphological characterization by transmission electron microscopy and scanning electron microscopy illustrated intrinsic nanopores within the individual particles and weak grain-interconnections indicating poor intergrain electron transport. Ab initio calculations of the electronic structures confirmed a larger band gap of the distorted crystal structure of the oxynitride and showed a decrease of the density of states at the Fermi level, explaining the reduction of the measured S

Brackish Water Shrimp Farming and the Growth of Aquatic Monocultures in Coastal Bangladesh

One of the most significant changes in marine and coastal environments since the mid–twentieth century has been the growth of coastal shrimp aquaculture in many tropical and sub–tropical regions of the world. This chapter, which draws on the author’s own archival and field research and the published works of other students of the global shrimp market, examines the growth of brackish water shrimp production from the 1970s to the present in Bangladesh’s coastal belt and its social and ecological impacts. It shows that for most of this period shrimp production was encouraged by the Bangladesh Government to expand in a fragmented and uncoordinated way with varying environmental, economic and social consequences. These included higher levels of soil salinity, increased risk of flooding, loss of agricultural land, a decline in biodiversity, contraction of various traditional occupational activities, growth in new non-agricultural work, a shift to diversified employment strategies among households, higher incomes for shrimp farmers and land renters and economic and social dislocation for others. Government, business and international aid agencies supported the expansion of mono–cultural forms of shrimp production integrated into global trading networks at the expense of local resource extraction activities such as artisanal fishing and forestry