Density Matrix Renormalisation Group Calculations for Two-Dimensional Lattices: An Application to the Spin-Half and Spin-One Square-Lattice Heisenberg Models

A new density matrix renormalisation group (DMRG) approach is presented for quantum systems of two spatial dimensions. In particular, it is shown that it is possible to create a multi-chain-type 2D DMRG approach which utilises previously determined system and environment blocks {\it at all points}. One firstly builds up effective quasi-1D system and environment blocks of width $L$ and these quasi-1D blocks are then used to as the initial building-blocks of a new 2D infinite-lattice algorithm. This algorithm is found to be competitive with those results of previous 2D DMRG algorithms and also of the best of other approximate methods. An illustration of this is given for the spin-half and spin-one Heisenberg models on the square lattice. The best results for the ground-state energies per bond of the spin-half and spin-one square-lattice Heisenberg antiferromagnets for the $N = 20 \times 20$ lattice using this treatment are given by $E_g/N_B = -0.3321$ and $E_g/N_B = -1.1525$, respectively.Comment: 7 Figures. Accepted for publication in Phys. Rev.

Local versus organic: a turn in consumer preferences and willingness-to-pay

Demand for local food in the United States has significantly increased over the last decade. In an attempt to understand the drivers of this demand and how they have changed over time, we investigate the literature on organic and local foods over the last few decades. We focus our review on studies that allow comparison of characteristics now associated with both local and organic food. We summarize the major findings of these studies and their implications for understanding drivers of local food demand. Prior to the late 1990s, most studies failed to consider factors now associated with local food, and the few that included these factors found very little support for them. In many cases, the lines between local and organic were blurred. Coincident with the development of federal organic food standards, studies began to find comparatively more support for local food as distinct and separate from organic food. Our review uncovers a distinct turn in the demand for local and organic food. Before the federal organic standards, organic food was linked to small farms, animal welfare, deep sustainability, community support, and many other factors that are not associated with most organic foods today. Based on our review, we argue that demand for local food arose largely in response to corporate cooptation of the organic food market and the arrival of “organic lite.” This important shift in consumer preferences away from organic and toward local food has broad implications for the environment and society. If these patterns of consumer preferences prove to be sustainable, producers, activists, and others should be aware of the implications that these trends have for the food system at large

Is J 133658.3-295105 a Radio Source at z >= 1.0 or at the Distance of M 83?

We present Gemini optical imaging and spectroscopy of the radio source J 133658.3-295105. This source has been suggested to be the core of an FR II radio source with two detected lobes. J 133658.3-295105 and its lobes are aligned with the optical nucleus of M 83 and with three other radio sources at the M 83 bulge outer region. These radio sources are neither supernova remnants nor H II regions. This curious configuration prompted us to try to determine the distance to J 133658.3-295105. We detected H_alpha emission redshifted by ~ 130 km s^-1 with respect to an M 83 H II region 2.5" east-southeast of the radio source. We do not detect other redshifted emission lines of an optical counterpart down to m_i = 22.2 +/- 0.8. Two different scenarios are proposed: the radio source is at z >= 2.5, a much larger distance than the previously proposed lower limit z >= 1.0, or the object was ejected by a gravitational recoil event from the M 83 nucleus. This nucleus is undergoing a strong dynamical evolution, judging from previous three-dimensional spectroscopy.Comment: 6 pages, 4 figure

Bioeconomic Modeling of the Invasive Aquatic Plants Hydrilla verticillata (hydrilla), Eichhornia crassipes (water hyacinth), and Pistia stratiotes (water lettuce) and their impacts on angler effort on Florida lakes

The invasive aquatic plants Hydrilla verticillata (hydrilla), Eichhornia crassipes (water hyacinth), and Pistia stratiotes (water lettuce) have the potential to negatively impact recreational use of Florida lakes if consistent, adequate control expenditures are not made. In the mid-1990's, Florida significantly reduced its spending on invasive aquatic plant control measures, which resulted in a significant increase in needed control expenditures in subsequent years. This paper attempts to formalize a relationship between coverage of these invasive aquatic plants and angler effort on Florida lakes using data on 38 lakes over 20 years. Estimated regression coefficients are used to simulate control alternatives, and expenditure cost-benefit comparisons are made.Hydrilla, water hyacinth, water lettuce, bioeconomic, invasive, control, Resource /Energy Economics and Policy,

The Einstein solid state spectrometer and monitor proportional counter survey of low mass x‐ray binaries

The HEAO‐2 Einstein solid state spectrometer (SSS; 0.5–4.5 keV) and monitor proportional counter (MPC; 1.2–20.0 keV) carried out an extensive survey of 50 low mass x‐ray binaries (LMXB). Simultaneous SSS plus MPC spectra, selected on the basis of their intensity, were fit with a set of simple and complex spectral models. For all the sources, including Eddington‐limited bulge sources, bursters, dippers, the soft spectrum black hole candidates, and a few transients in decline, the spectra could be fit acceptably with combinations of thermal bremsstrahlung and blackbody spectra or a Comptonized spectrum and a blackbody. The results rule out optically thick disk models for the bright (Z) sources and for the bursters power law models are unacceptable. The SSS can confirm only the strongest of previously reported low energy emission lines due to OVIII or Fe L transitions. The data does not support a unique physical interpretation. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87678/2/193_1.pd

Evaluating the Potential for Technology Adoption in Mitigating Invasive Species Damage and Risk: Application to Zebra Mussels

Research and Development/Tech Change/Emerging Technologies, Resource /Energy Economics and Policy,

Innocent III, Peter of Benevento and the history of Spain

En los primeros años del siglo XIII surgieron una serie de minorías que tuvieron un impacto significativo y duradero en la historia de ciertos reinos (Federico II en Sicilia; Enrique III en Inglaterra; Luis IX en Francia), pero ninguno tanto como el de Jaime I en Aragón. La supervivencia del joven Jaime y el posterior desarrollo de su reino fueron en gran medida posibles gracias a los esfuerzos del Papa Inocencio III y de su legado en España, el gran canonista Pedro de Benevento, la importancia de su intervención fue reconocida por Jaime en su autobiografía y por Rodrigo Jiménez de Rada. La forma de la intervención del Papa nos dice mucho acerca de las preocupaciones principales del papado en el momento en que su autoridad llegó a su máximo apogeo.The early years of the thirteenth century saw a series of minorities which would have significant and lasting results in the history of their particular realms (Frederick II in Sicily; Henry III in England; Louis IX in France) but none more so than that of James I in Aragon. James’s survival and the subsequent development of his kingdom were in no small measure down to the efforts of Pope Innocent III and his legate in Spain the great canonist, Peter of Benevento, the importance of whose intervention was acknowledged both by James in his autobiography and by Rodrigo Jiménez de Rada. The manner of papal intervention tells us much about the papacy’s major concerns at the moment when its authority was at its height.Ciencias ReligiosasDerech