Stripe phases in the two-dimensional Falicov-Kimball model

The observation of charge stripe order in the doped nickelate and cuprate materials has motivated much theoretical effort to understand the underlying mechanism of the stripe phase. Numerical studies of the Hubbard model show two possibilities: (i) stripe order arises from a tendency toward phase separation and its competition with the long-range Coulomb interaction or (ii) stripe order inherently arises as a compromise between itinerancy and magnetic interactions. Here we determine the restricted phase diagrams of the two-dimensional Falicov-Kimball model and see that it displays rich behavior illustrating both possibilities in different regions of the phase diagram.Comment: (5 pages, 3 figures

The Length of an SLE - Monte Carlo Studies

The scaling limits of a variety of critical two-dimensional lattice models are equal to the Schramm-Loewner evolution (SLE) for a suitable value of the parameter kappa. These lattice models have a natural parametrization of their random curves given by the length of the curve. This parametrization (with suitable scaling) should provide a natural parametrization for the curves in the scaling limit. We conjecture that this parametrization is also given by a type of fractal variation along the curve, and present Monte Carlo simulations to support this conjecture. Then we show by simulations that if this fractal variation is used to parametrize the SLE, then the parametrized curves have the same distribution as the curves in the scaling limit of the lattice models with their natural parametrization.Comment: 18 pages, 10 figures. Version 2 replaced the use of "nu" for the "growth exponent" by 1/d_H, where d_H is the Hausdorff dimension. Various minor errors were also correcte

Charge-ordered ferromagnetic phase in manganites

A mechanism for charge-ordered ferromagnetic phase in manganites is proposed. The mechanism is based on the double exchange in the presence of diagonal disorder. It is modeled by a combination of the Ising double-exchange and the Falicov-Kimball model. Within the dynamical mean-field theory the charge and spin correlation function are explicitely calculated. It is shown that the system exhibits two successive phase transitions. The first one is the ferromagnetic phase transition, and the second one is a charge ordering. As a result a charge-ordered ferromagnetic phase is stabilized at low temperature.Comment: To appear in Phys. Rev.

The overlap operator as a continued fraction

We use a continued fraction expansion of the sign-function in order to obtain a five dimensional formulation of the overlap lattice Dirac operator. Within this formulation the inverse of the overlap operator can be calculated by a single Krylov space method where nested conjugate gradient procedures are avoided. We show that the five dimensional linear system can be made well conditioned using equivalence transformations on the continued fractions. This is of significant importance when dynamical overlap fermions are simulated.Comment: 3 pages, 1 figure, talk presented by U. Wenger at Lattice2001(chiral

Green characters in Cabernet Sauvignon

The intensity rating of green character attributes of five commercial Cabernet Sauvignon wines from the Margaret River appellation were determined according to the Standards Association of Australia method 2542.2.3 (1988), using an expert panel of five judges, comprising winemakers and wine judges

A new look at C*-simplicity and the unique trace property of a group

We characterize when the reduced C*-algebra of a group has unique tracial state, respectively, is simple, in terms of Dixmier-type properties of the group C*-algebra. We also give a simple proof of the recent result by Breuillard, Kalantar, Kennedy and Ozawa that the reduced C*-algebra of a group has unique tracial state if and only if the amenable radical of the group is trivial.Comment: 8 page

Phase separation due to quantum mechanical correlations

Can phase separation be induced by strong electron correlations? We present a theorem that affirmatively answers this question in the Falicov-Kimball model away from half-filling, for any dimension. In the ground state the itinerant electrons are spatially separated from the classical particles.Comment: 4 pages, 1 figure. Note: text and figure unchanged, title was misspelle

Charge-density-wave order parameter of the Falicov-Kimball model in infinite dimensions

In the large-U limit, the Falicov-Kimball model maps onto an effective Ising model, with an order parameter described by a BCS-like mean-field theory in infinite dimensions. In the small-U limit, van Dongen and Vollhardt showed that the order parameter assumes a strange non-BCS-like shape with a sharp reduction near T approx T_c/2. Here we numerically investigate the crossover between these two regimes and qualitatively determine the order parameter for a variety of different values of U. We find the overall behavior of the order parameter as a function of temperature to be quite anomalous.Comment: (5 pages, 3 figures, typeset with ReVTeX4

Sand Gradation in Seasonal Rivers and Their Suitability for Construction of Sand Dams in Kitui South, Kenya

This study was undertaken in Kitui South in Kitui County in the south eastern parts of Kenya. The main objective of the study was to develop a spatial model that can be used for selection of suitable sites for sand dam in Kitui South. The study also assessed the spatial variation of sand grain sizes and how these determines the suitability of sites for the sand dams. Data analysis was done using three approaches. The first approach involved the use of the Remote Sensing (RS) technique where data was preprocessed and analyzed using Erdas Imagine software and Geographical Information Systems (GIS) for spatial modelling. The distribution of sand particle-sizes was based on sieve analysis on the sand samples collected from seasonal rivers in the study area. The seasonal rivers that were investigated in this study included Mwila, Kakya, Wiitu, Nguni, Ngunyumu, Muvuko, Kanzilu, Masaa, Katiliku, Ngulungu, Nzeeu, Koma and Katitika. Statistical analysis was done to establish the relationships between the various spatial components affecting sand particle distribution. The results from the spatial model which integrated all factors shows that 16% of the studied sites along the seasonal rivers in Kitui South were fairly suitable for construction of sand dams while 79% were classified as suitable and 5% are categorized as very suitable. Several sites in the central and the entire eastern parts of Mutha Ward were found not suitable for sand dam construction due to poor conditions such as the lack of suitable sand particles, lack of bedrock exposure on the riverbeds, flat terrain, very shallow stream banks, and weak soils on the riverbanks. Suitable sites for sand dams were found on the western and central areas of Kitui South where production and high accumulation of coarse sands was observed along the seasonal rivers. The areas near Mutomo hills and the rocky areas in Ikanga wards were found to be characterized with few excellent sites for sand dams. The optimum accumulation of different grades of sand in the seasonal rivers was found on streams with slope of between 1.5 and 6% that were dominated with0 to 40% coarse sands, 0 to 30% fine gravels, 0 to 20% fine sands, and 20 to 80% medium sands. The accumulation of fine gravels was found to be closely related to the distribution of D30, D60 and D90sand particle-sizes (0.4-4mm) while accumulation of coarse sands showed good relationship with the distribution of the medium size sand (0.2-0.4mm). The accumulation of medium sands was equally high when the occurrence of coarse sands was minimal. Different grades of sand were found to be strongly influenced by the changes in the elevation of the stream especially with regard to the accumulation of the medium sands (r= 0.76) and coarse sands(r=0.75). Out of 80 investigated sites, 59% of them were dominated with uniform sands (Cu<3), 30% were intermediate sands and only 11% were well-graded sands (Cu>5). The study also found that86% of the sites along the seasonal streams were dominated with medium sands while 10% were dominated with fine sands and the rest (4%) dominated by coarse and gravelly sands. From the results this study concludes that 59% of the 80 sites that were investigated in this study have a high potential for providing suitable sites for sand dams in Kitui South. Keywords: Sand Dams; Particle Size Distribution; Hydrology; Water Management; Kitui South, Keny