Energy densification via hydrothermal carbonization

A process called hydrothermal carbonization (HTC), also known as wet torrefaction involves treatment of raw biomass in hot, pressurized water. HTC of woody biomass has been shown to significantly increase the energy density of the feedstock, producing a biochar, similar to coal, having up to 40% higher calorific energy content. Feedstocks investigated include Tahoe chips, Pinion/Juniper chips, Rice hulls, and Corn Stover pellets pre-treated at 215 °C, 255 °C, and 295 °C. Chemical analyses were conducted on the gaseous, aqueous, and solid HTC products. Energy contents of the solid biochar products were measured by calorimetry, and mass balances were determined

The Doped Two Chain Hubbard Model

The properties of the two-chain Hubbard Model doped away from half-filling are investigated. The charge gap is found to vanish, but a finite spin gap exists over a range of interchain hopping strength $t_\perp$. In this range, there are modified $d_{x^2-y^2}$--like pairing correlations whose strength is correlated with the size of the spin gap. It is found that the pair field correlations are enhanced by the onsite Coulomb interaction U.Comment: 10 pages and 5 postscript figures, RevTeX 3.0, UCI-CMTHE-94-0

Competition Between Charge-Density Waves and Superconductivity in Striped Systems

Switching on interchain coupling in a system of one-dimensional strongly interacting chains often leads to an ordered state. Quite generally, there is a competition between an insulating charge-density-wave and a superconducting state. In the case of repulsive interactions, charge-density wave usually wins over superconductivity. Here, we show that a suitable modulation in the form of a period 4 bond-centered stripe can reverse this balance even in the repulsive case and produce a superconducting state with relatively high temperature.Comment: Proceedings of SCES 04, 2 page

On the dimerized phase in the cross-coupled antiferromagnetic spin ladder

We revisit the phase diagram of the frustrated s=1/2 spin ladder with antiferromagnetic rung and diagonal couplings. In particular, we reexamine the evidence for the columnar dimer phase, which has been predicted from analytic treatment of the model and has been claimed to be found in numerical calculations. By considering longer chains and by keeping more states than in previous work using the density-matrix renormalization group, we show that the numerical evidence presented previously for the existence of the dimerized phase is not unambiguous in view of the present more careful analysis. While we cannot completely rule out the possibility of a dimerized phase in the cross-coupled ladder, we do set limits on the maximum possible value of the dimer order parameter that are much smaller than those found previously.Comment: 6 pages, 7 figure

Quantum information analysis of the phase diagram of the half-filled extended Hubbard model

We examine the phase diagram of the half-filled one-dimensional extended Hubbard model using quantum information entropies within the density-matrix renormalization group. It is well known that there is a charge-density-wave phase at large nearest-neighbor and small on-site Coloumb repulsion and a spin-density-wave at small nearest-neighbor and large on-site Coloumb repulsion. At intermediate Coulomb interaction strength, we find an additional narrow region of a bond-order phase between these two phases. The phase transition line for the transition out of the charge-density-wave phase changes from first-order at strong coupling to second-order in a parameter regime where all three phases are present. We present evidence that the additional phase-transition line between the spin-density-wave and bond-order phases is infinite order. While these results are in agreement with recent numerical work, our study provides an independent, unbiased means of determining the phase boundaries by using quantum information analysis, yields values for the location of some of the phase boundaries that differ from those previously found, and provides insight into the limitations of numerical methods in determining phase boundaries, especially those of infinite-order transitions.Comment: 8 pages, 7 figure

CrocoPat 2.1 Introduction and Reference Manual

CrocoPat is an efficient, powerful and easy-to-use tool for manipulating relations of arbitrary arity, including directed graphs. This manual provides an introduction to and a reference for CrocoPat and its programming language RML. It includes several application examples, in particular from the analysis of structural models of software systems.Comment: 19 pages + cover, 2 eps figures, uses llncs.cls and cs_techrpt_cover.sty, for downloading the source code, binaries, and RML examples, see http://www.software-systemtechnik.de/CrocoPat

Electromagnetic induction heating as a driver of volcanic activity on massive rocky planets

Aims. We investigate possible driving mechanisms of volcanic activity on rocky super-Earths with masses exceeding 3-4 Mearth. Due to high gravity and pressures in the mantles of these planets, melting in deep mantle layers can be suppressed, even if the energy releae due to tidal heating and radioactive decay is substantial. Here we investigate whether a newly identified heating mechanism, namely induction heating by the star's magnetic field, can drive volcanic activity on these planets due to its unique heating pattern in the very upper part of the mantle. In this region the pressure is not yet high enough to preclude the melt formation. Methods. Using the super-Earth HD 3167b as an example, we calculate induction heating in the planet's interiors assuming an electrical conductivity profile typical of a hot rocky planet and a moderate stellar magnetic field typical of an old inactive star. Then we use a mantle convection code (CHIC) to simulate the evolution of volcanic outgassing with time. Results. We show that although in most cases volcanic outgassing on HD 3167b is not very significant in the absence of induction heating, including this heating mechanism changes the picture and leads to a substantial increase in the outgassing from the planet's mantle. This result shows that induction heating combined with a high surface temperature is capable of driving volcanism on massive super-Earths, which has important observational implications.Comment: Five pages, three figures, accepted for publication in A&A letter