Dynamical properties of low dimensional CuGeO3 and NaV2O5 systems

Properties of low-dimensional spin-Peierls systems are described by using a one dimensional S=1/2 antiferromagnetic Heisenberg chain linearly coupled to a single phonon mode of wave vector pi (whose contribution is expected to be dominant). By exact diagonalizations of small rings with up to 24 sites supplemented by a finite size scaling analysis, static and dynamical properties are investigated. Numerical evidences are given for a spontaneous discrete symmetry breaking towards a spin gapped phase with a frozen lattice dimerization. Special emphasis is put on the comparative study of the two inorganic spin-Peierls compounds CuGeO3 and NaV2O5 and the model parameters are determined from a fit of the experimental spin gaps. We predict that the spin-phonon coupling is 2 or 3 times larger in NaV2O5 than in CuGeO3. Inelastic neutron scattering spectra are calculated and similar results are found in the single phonon mode approximation and in the model including a static dimerization. In particular, the magnon S=1 branch is clearly separated from the continuum of triplet excitations by a finite gap.Comment: 10 pages, RevTex, revised version submitted to Euro. Phys. Rev.

Affording Health Care and Education on the Minimum Wage

The current value of the federal minimum wage -- $7.25 per hour -- is often compared to the cost of living, the average wage in the economy, or the productivity of the average worker. By all of these benchmarks, the current federal minimum is well below its historical levels. But the current minimum wage looks even worse when compared to two kinds of purchases strongly associated with a middle-class standard of living or the ability to move up to the middle class: health insurance and a college degree

Size and Characteristics of States? Union Workforces

Unionization rates -- and the gender and racial composition of unionized workers -- vary widely across the 50 states and the District of Columbia. The figures and tables in this issue brief, based on our analysis of the Current Population Survey, give an overview of the size and basic demographics of the unionized workforce in each state. Throughout, we define a unionized worker as anyone who is a member of a union or represented by a collective bargaining agreement

Threshold Effect and Financial Intermediation in Economic Development

This paper analyzes the theoretical finance-growth nexus. Using the Neoclassical growth framework, we raise a new issue where our finance-growth nexus has multiple stationary states with threshold effect. Threshold effect prevents the economy to reach long-run steady state equilibrium of capital and hence financial economists in developing countries should be aware of such an impediment. We show that the development of banking sector should be more supported than financial market, since banking sector is better than financial market in order to reduce threshold effect and ensure the existence and uniqueness of a higher long-run steady state equilibrium of capital stock.Threshold Effect; Financial Intermediation; Economic Growth; Developing Countries

Threshold Effect and Financial Intermediation in Economic Development

This paper reformulates the finance-growth nexus in the case of developing countries. Using the Neoclassical growth framework, our contribution is threefold. First, we show that entrepreneurship is a growth-enhancing factor in both financial intermediary equilibrium and financial market equilibrium. Second, we show that agent's saving is one of the determinants of the optimal proportion of long-term investment and hence, we characterize the role of bank as financial intermediary. Third, our model is characterized by the existence of multiple steady states equilibrium with threshold effect that impedes the economy to reach a long-run higher steady state equilibrium. Furthermore, we show that financial intermediary is better than financial market, in order to reduce threshold effect and to ensure the long-run steady state equilibrium of capital stock.Threshold Effect, Financial Intermediary, Economic Growth, Developing Countries

The Insertion of Small-scale Farmers into market auction, Can it really improve the Indonesian gurem farmers’ welfare? The perspective of the auction price formation and farmers’ motivation factors

The condition of small-scale farmers in Indonesia is getting worse that is caused by an unfair low price that reflects to the low level of revenue for their income. This happens either because the dependency on trader/middlemen for selling the produce and the low accessibility of farmers to the market. The existence of auction mechanisms created by the Indonesian government auctions is still dominated by traders/middlemen, so that the increasing of prices have not affected to the farmers. Alternatively, by linking directly farmers to the auction mechanism will be analyzed in a descriptive and a qualitative ways from the point of view of price formation in the auction and the farmers’ determining factors to participate in the auction. The analysis conducts policy recommendations for ongoing agricultural auction development with the direct participation of small-scale farmers in the mechanism.Small-scale Farmers, Auction mechanism, price formation, farmer’s motivation, International Development,

FluidFFT: common API (C++ and Python) for Fast Fourier Transform HPC libraries

The Python package fluidfft provides a common Python API for performing Fast Fourier Transforms (FFT) in sequential, in parallel and on GPU with different FFT libraries (FFTW, P3DFFT, PFFT, cuFFT). fluidfft is a comprehensive FFT framework which allows Python users to easily and efficiently perform FFT and the associated tasks, such as as computing linear operators and energy spectra. We describe the architecture of the package composed of C++ and Cython FFT classes, Python "operator" classes and Pythran functions. The package supplies utilities to easily test itself and benchmark the different FFT solutions for a particular case and on a particular machine. We present a performance scaling analysis on three different computing clusters and a microbenchmark showing that fluidfft is an interesting solution to write efficient Python applications using FFT

Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

The Impact of Rules of Origin On Trade Flows

Within any preferential trade agreement (PTA) origin rules exist in order to prevent third countries from taking advantage of the PTA concessions. The rules thus are there to preserve the existing external protection of countries within the PTA. However, depending on their formulation, they can also increase that level of external protection, resulting in trade suppression and trade diversion. This paper provides the first serious empirical examination of the possible impact of rules of origin on patterns of trade in the European context. The methodology employed is that of an augmented gravity model where we focus on the impact within the Pan-european system of cumulation. The results suggest that rules of origin do indeed restrict trade, that the cumulation of such rules could increase trade in the order of 50%, and that the impact is greater on intermediate than manufacturing trade.international trade, rules of origin, gravity model