Evaluation of porosity and degree of saturation from seismic and electrical data

The characterisation of unsaturated intermediate and coarse-grained soils faces some practical difficulties because undisturbed sampling is not easy. Geophysical methods provide useful information as they can be applied on site for testing geo-materials in their natural state. Moreover their repeated application over time is effective and efficient for monitoring purposes. A procedure for evaluating porosity and degree of saturation on the basis of electrical resistivity and wave velocities measurements is proposed. The approach is based on an electro-seismic model that utilises Archie's law to describe the electrical behaviour of soils and a recent formulation of elastic wave propagation in unsaturated soils. The proposed procedure is applied to laboratory data, and shows promising result

One-electron bands, quantum Monte Carlo, and real superconductors

We use the doped Fullerenes as an example of how realistic systems can be described by simple models. Starting from the band structure we set up a tight-binding model that describes the t_{1u} conduction band. Adding correlation terms we arrive at a generalized Hubbard Hamiltonian that we treat using quantum Monte Carlo. To address the problem of superconductivity in the doped Fullerenes, we study the screening of a point charge. We find surprisingly efficient metallic screening even for strong correlations, almost up to the Mott transition, and discuss the implications on superconductivity, in particular the effect of the efficient screening on the Coulomb pseudopotential and the electron-phonon coupling.Comment: 9 pages LaTeX with 2 eps figures; Proceedings of the International Conference on Statistical Mechanics and Strongly Correlated Electrons in honor of Giovanni Paladin, Sept 27-29, 1999, Universita di Roma "La Sapienza"; additional material available at http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene

Limits on Phase Separation for Two-Dimensional Strongly Correlated Electrons

From calculations of the high temperature series for the free energy of the two-dimensional t-J model we construct series for ratios of the free energy per hole. The ratios can be extrapolated very accurately to low temperatures and used to investigate phase separation. Our results confirm that phase separation occurs only for J/t greater than 1.2. Also, the phase transition into the phase separated state has Tc of approximately 0.25J for large J/t.Comment: 4 pages, 6 figure

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

Issues and Observations on Applications of the Constrained-Path Monte Carlo Method to Many-Fermion Systems

We report several important observations that underscore the distinctions between the constrained-path Monte Carlo method and the continuum and lattice versions of the fixed-node method. The main distinctions stem from the differences in the state space in which the random walk occurs and in the manner in which the random walkers are constrained. One consequence is that in the constrained-path method the so-called mixed estimator for the energy is not an upper bound to the exact energy, as previously claimed. Several ways of producing an energy upper bound are given, and relevant methodological aspects are illustrated with simple examples.Comment: 28 pages, REVTEX, 5 ps figure

High number of circulating CD34+ cells in patients with myelophthisis.

Hematopoietic Stem Cells High number of circulating CD34+ cells in patients with myelophthisis Six patients with bone marrow micrometastases from solid cancers presented with increased numbers of circulating CD34+ cells; the CD34+ cell counts were very high in some cases. By contrast, no patient with metastatic cancer without bone marrow involvement showed raised numbers of circulating hemopoietic progenitors. haematologica 2005; 90:976-977 (http:/

Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography

In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi

Exact bounds on the ground-state energy of the infinite-U Hubbard model

We give upper and lower bounds for the ground-state energy of the infinite-U Hubbard model. In two dimensions, using these bounds we are able to rule out the possibility of phase separation between the undoped-insulating state and an hole-rich state.Comment: 2 pages, 1 figure, to appear in Phys. Rev.

Phase Separation Based on U(1) Slave-boson Functional Integral Approach to the t-J Model

We investigate the phase diagram of phase separation for the hole-doped two dimensional system of antiferromagnetically correlated electrons based on the U(1) slave-boson functional integral approach to the t-J model. We show that the phase separation occurs for all values of J/t, that is, whether $0 < J/t < 1$ or $J/t \geq 1$ with J, the Heisenberg coupling constant and t, the hopping strength. This is consistent with other numerical studies of hole-doped two dimensional antiferromagnets. The phase separation in the physically interesting J region, $0 < J/t \lesssim 0.4$ is examined by introducing hole-hole (holon-holon) repulsive interaction. We find from this study that with high repulsive interaction between holes the phase separation boundary tends to remain robust in this low $J$ region, while in the high J region, J/t > 0.4, the phase separation boundary tends to disappear.Comment: 4 pages, 2 figures, submitted to Phys. Rev.

What the water says as it runs

During the last two years, I have been examining the importance of vulnerability, memory and empowerment within my work as it relates to archival silence. The archive is presumed to be an objective record but what is chosen and discarded is an inherently political act. When there is archival silence, what then becomes missing from our collective histories? My exploration has spread across many forms of media, including sound, video, textiles, sculpture and writing . I have sought to understand the ways that these different mediums embody sentiment and concept, while establishing an open-ended record within which others can explore their own personal context. Archival silence is often perpetuated by discrimination and untold traumatic narratives. What then happens when we create records of these excluded or unspoken narratives, when we express vulnerability? Might we reach a point of collective empowerment? Through this work, I have found that negotiating between different mediums has allowed me to create a context for myself and explore deeply personal subjects, while simultaneously creating work and records that will resonate with those who pay close enough attention. I have done this by using video and sound recordings of places that are the architectures of my memory, building an installation that replicates a location very formative to me and my memory, and – perhaps most importantly – writing that presents my memory fragments as they are retrieved. These architectures are intentionally abstracted through a spectrum of mediums, creating a container into which the audience is enabled to project their own memories and identities. My personal record reaches towards justice by presenting vulnerable stories with which others may be able to identify. If this work does anything, I hope that it prompts my viewers to reflect on their own experiences, and to orient themselves to a future in which they don’t feel as though sharing a difficult experience is impossible. Through that process, I believe that we can move our record keeping towards justice