Projective construction of two-dimensional symmetry-protected topological phases with U(1), SO(3), or SU(2) symmetries

We propose a general approach to construct symmetry protected topological (SPT) states i.e the short-range entangled states with symmetry) in 2D spin/boson systems on lattice. In our approach, we fractionalize spins/bosons into different fermions, which occupy nontrivial Chern bands. After the Gutzwiller projection of the free fermion state obtained by filling the Chern bands, we can obtain SPT states on lattice. In particular, we constructed a U(1) SPT state of a spin-1 model, a SO(3) SPT state of a boson system with spin-1 bosons and spinless bosons, and a SU(2) SPT state of a spin-1/2 boson system. By applying the "spin gauge field" which directly couples to the spin density and spin current of $S^z$ components, we also calculate the quantum spin Hall conductance in each SPT state. The projective ground states can be further studied numerically in the future by variational Monte Carlo etc.Comment: 7+ pages, accepted by Phys. Rev.

Public health and education spending in Ghana in 1992-98 : issues of equity and efficiency

Using primary data from the health and education ministries, and household survey data from the Ghana Statistical Service, the authors analyze equity, and efficiency issues in public spending on health, and education in Ghana in the 1990s. Public expenditures in the education sector, declined in the second half of the 1990s. Basic education enrollment has been stagnant, or declining in public schools, but increasing in private schools, resulting in a moderate increase in total enrollment. Regional disparities are significant, with lower public resource allocations, and lower enrollment ratios in the three poorest regions. The quality of basic education in public schools remains poor, while it has steadily improved in privateschools. Enrollments in higher levels are lagging behind those in basic education. Ghana ranks high among West African countries in health indicators, although its health expenditures tend to favor the non-poor. While more of the rural population have gained access to health services in recent years, many still have limited access, or none. Moreover, there is no link between the pattern of public expenditures - especially the pattern of immunization across Ghana - and health outcomes. To ensure that social services are efficiently, and equitably delivered in a fiscally constrained economy, the authors argue, public expenditures need to be linked to outcomes.Primary Education,Curriculum&Instruction,Teaching and Learning,Public Health Promotion,Health Monitoring&Evaluation,Primary Education,Teaching and Learning,Gender and Education,Health Monitoring&Evaluation,Curriculum&Instruction

Issues in comparing poverty trends over time in Cote de'Ivoire

Cote d'Ivoire conducted household surveys between 1985 and 1995, making it possible to trace changes in urban and rural poverty and changes in poverty among different socioeconomic groups. During the decade surveyed, the country experienced a major recession. Poverty increased substantially and continued unabated in the year after devaluation, in part because much of the increase in export crop prices, especially for cocoa, was taxed away. Between 1988 and 1993, urban poverty increased faster than rural poverty did, though mean expenditures in urban areas remained substantially above mean expenditures in rural areas. Food crop farmers apparently suffered more than export crop farmers. All in all these trends persisted after devaluation. However, the authors found that exploring poverty trends across regions and socioeconomic groups raised questions about the patterns of change and the reliability of the data and the methods used to derive poverty estimates. Secondary data cast some doubt on certain survey findings, suggesting that they may not have truly reflected real economic trends. The authors emphasized the need to draw reliable conclusions from time-series data in order to understand how policy reform affects poverty. They urged that far more attention be paid to comparability issues in designing and analyzing data and to developing better regional and temporal priceindices, if reliable time-series data are to be generated for Sub-Saharan Africa.Environmental Economics&Policies,Poverty Reduction Strategies,Economic Theory&Research,Crops&Crop Management Systems,Earth Sciences&GIS,Crops&Crop Management Systems,Environmental Economics&Policies,Economic Theory&Research,Poverty Assessment,Achieving Shared Growth

Efficiency improvement of the frequency-domain BEM for rapid transient elastodynamic analysis

The frequency-domain fast boundary element method (BEM) combined with the exponential window technique leads to an efficient yet simple method for elastodynamic analysis. In this paper, the efficiency of this method is further enhanced by three strategies. Firstly, we propose to use exponential window with large damping parameter to improve the conditioning of the BEM matrices. Secondly, the frequency domain windowing technique is introduced to alleviate the severe Gibbs oscillations in time-domain responses caused by large damping parameters. Thirdly, a solution extrapolation scheme is applied to obtain better initial guesses for solving the sequential linear systems in the frequency domain. Numerical results of three typical examples with the problem size up to 0.7 million unknowns clearly show that the first and third strategies can significantly reduce the computational time. The second strategy can effectively eliminate the Gibbs oscillations and result in accurate time-domain responses

Weak Decays of Doubly-Heavy Tetraquarks bcˉqqˉ{b\bar c}{q\bar q}

We study the weak decays of exotic tetraquark states ${b\bar c}{q\bar q}$ with two heavy quarks. Under the SU(3) symmetry for light quarks, these tetraquarks can be classified into an octet plus a singlet: $3\bigotimes\bar 3=1\bigoplus8$. We will concentrate on the octet tetraquarks with $J^{P}=0^{+}$, and study their weak decays, both semileptonic and nonleptonic. Hadron-level effective Hamiltonian is constructed according to the irreducible representations of the SU(3) group. Expanding the Hamiltonian, we obtain the decay amplitudes parameterized in terms of a few irreducible quantities. Based on these amplitudes, relations for decay widths are derived, which can be tested in future. We also give a list of golden channels that can be used to look for these states at various colliders.Comment: 14 pages,3 figure