Plane flame furnace combustion tests on JPL desulfurized coal

The combustion characteristics of three raw bituminous (PSOC-282 and 276) and subbituminous (PSOC-230) coals, the raw coals partially desulfurized (ca -60%) by JPL chlorinolysis, and the chlorinated coals more completely desulfurized (ca -75%) by JPL hydrodesulfurization were determined. The extent to which the combustion characteristics of the untreated coals were altered upon JPL sulfur removal was examined. Combustion conditions typical of utility boilers were simulated in the plane flame furnace. Upon decreasing the parent coal voltaile matter generically by 80% and the sulfur by 75% via the JPL desulfurization process, ignition time was delayed 70 fold, burning velocity was retarded 1.5 fold, and burnout time was prolonged 1.4 fold. Total flame residence time increased 2.3 fold. The JPL desulfurization process appears to show significant promise for producing technologically combustible and clean burning (low SO3) fuels

Functional renormalization group analysis of Dzyaloshinsky Moriya and Heisenberg spin interactions on the kagome lattice

We investigate the effects of Dzyaloshinsky-Moriya (DM) interactions on the frustrated $J_1$-$J_2$ kagome-Heisenberg model using the pseudo-fermion functional-renormalization-group (PFFRG) technique. In order to treat the off-diagonal nature of DM interactions, we develop an extended PFFRG scheme. We benchmark this approach in parameter regimes that have previously been studied with other methods and find good agreement of the magnetic phase diagram. Particularly, finite DM interactions are found to stabilize all types of non-collinear magnetic orders of the $J_1$-$J_2$ Heisenberg model ($\mathbf{q}=0$, $\sqrt{3}\times\sqrt{3}$, and cuboc orders) and shrink the extents of magnetically disordered phases. We discuss our results in the light of the mineral {\it herbertsmithite} which has been experimentally predicted to host a quantum spin liquid at low temperatures. Our PFFRG data indicates that this material lies in close proximity to a quantum critical point. In parts of the experimentally relevant parameter regime for {\it herbertsmithite}, the spin-correlation profile is found to be in good qualitative agreement with recent inelastic-neutron-scattering data

Effects of two loop contributions in the pseudofermion functional renormalization group method for quantum spin systems

We implement an extension of the pseudofermion functional renormalization group method for quantum spin systems that takes into account two loop diagrammatic contributions. An efficient numerical treatment of the additional terms is achieved within a nested graph construction which recombines different one loop interaction channels. In order to be fully self consistent with respect to self energy corrections, we also include certain three loop terms of Katanin type. We first apply this formalism to the antiferromagnetic J1 amp; 8722;J2 Heisenberg model on the square lattice and benchmark our results against the previous one loop plus Katanin approach. Even though the renormalization group RG equations undergo significant modifications when including the two loop terms, the magnetic phase diagram, comprising N el ordered and collinear ordered phases separated by a magnetically disordered regime, remains remarkably unchanged. Only the boundary position between the disordered and the collinear phases is found to be moderately affected by two loop terms. On the other hand, critical RG scales, which we associate with critical temperatures Tc, are reduced by a factor of 2 indicating that the two loop diagrams play a significant role in enforcing the Mermin Wagner theorem. Improved estimates for critical temperatures are also obtained for the Heisenberg ferromagnet on the three dimensional simple cubic lattice where errors in Tc are reduced by 34 . These findings have important implications for the quantum phase diagrams calculated within the previous one loop plus Katanin approach which turn out to be already well converge

Definition of experiments to investigate fire suppressants in microgravity

Defined and justified here are the conceptual design and operation of a critical set of experiments expected to yield information on suppressants and on suppressant delivery systems under realistic spacecraft-fire conditions (smoldering). Specific experiment parameters are provided on the solid fuel (carbon), oxidants (habitable spacecraft atmospheres), fuel/oxidant supply, mixing mode, and rate (quiescent and finite; ventilated and replenishable), ignition mode, event, and reignition tendency, fire-zone size, fire conditions, lifetime, and consequences (toxicity), suppressants (CO2, H2O, N2) and suppressant delivery systems, and diagnostics. Candidate suppressants were identified after an analysis of how reduced gravity alters combustion, and how these alterations may influence the modes, mechanisms, and capacities of terrestrial agents to suppress unwanted combustion, or fire. Preferred spacecraft suppression concepts included the local, near-quiescent application of a gas, vapor, or mist that has thermophysical fire-suppression activity and is chemically inert under terrestrial (normal gravity) combustion conditions. The scale, number, and duration (about 1 hour) of the proposed low-gravity experiments were estimated using data not only on the limitations imposed by spacecraft-carrier (Shuttle or Space Station Freedom) accommodations, but also data on the details and experience of standardized smolder-suppression experiments at normal gravity. Deliberately incorporated into the conceptual design was sufficient interchangeability for the prototype experimental package to fly either on Shuttle now or Freedom later. This flexibility is provided by the design concept of up to 25 modular fuel canisters within a containment vessel, which permits both integration into existing low-gravity in-space combustion experiments and simultaneous testing of separate experiments to conserve utilities and time

Matrix measures and random walks

In this paper we study the connection between matrix measures and random walks with a tridiagonal block transition matrix. We derive sufficient conditions such that the blocks of the n-step transition matrix of the Markov chain can be represented as integrals with respect to a matrix valued spectral measure. Several stochastic properties of the processes are characterized by means of this matrix measure. In many cases this measure is supported in the interval [-1, 1]. The results are illustrated by several examples including random walks on a grid and the embedded chain of a queuing system. --Markov chain,block tridiagonal transition matrix,spectral measure,matrix measure,quasi birth and death processes,canonical moments

Control theory based airfoil design for potential flow and a finite volume discretization

This paper describes the implementation of optimization techniques based on control theory for airfoil design. In previous studies it was shown that control theory could be used to devise an effective optimization procedure for two-dimensional profiles in which the shape is determined by a conformal transformation from a unit circle, and the control is the mapping function. The goal of our present work is to develop a method which does not depend on conformal mapping, so that it can be extended to treat three-dimensional problems. Therefore, we have developed a method which can address arbitrary geometric shapes through the use of a finite volume method to discretize the potential flow equation. Here the control law serves to provide computationally inexpensive gradient information to a standard numerical optimization method. Results are presented, where both target speed distributions and minimum drag are used as objective functions

Characterization of quantum spin liquids and their spinon band structures via functional renormalization

We combine the pseudofermion functional renormalization group PFFRG method with a self consistent Fock like mean field scheme to calculate low energy effective theories for emergent spinon excitations in spin 1 2 quantum spin liquids. Using effective spin interactions from PFFRG as an input for the Fock equation and allowing for the most general types of free spinon Ansätze as classified by the projective symmetry group PSG method, we are able to systematically determine spinon band structures for spin liquid candidate systems beyond mean field theory. We apply this approach to the antiferromagnetic J1 amp; 8722;J2 Heisenberg model on the square lattice and to the antiferromagnetic nearest neighbor Heisenberg model on the kagome lattice. For the J1 amp; 8722;J2 model, we find that in the regime of maximal frustration a SU 2 pi flux state with Dirac spinons yields the largest mean field amplitudes. For the kagome model, we identify a gapless Z2 spin liquid with a small circular spinon Fermi surface and approximate Dirac cones at low but finite energie

Absence of ferromagnetism in V-implanted ZnO single crystals

The structural and magnetic properties of V doped ZnO are presented. V ions were introduced into hydrothermal ZnO single crystals by ion implantation with fluences of 1.2*10^16 to 6*10^16 cm^-2. Post-implantation annealing was performed in high vacuum from 823 K to 1023 K. The ZnO host material still partly remains in a crystalline state after irradiation, and is partly recovered by annealing. The V ions show a thermal mobility as revealed by depth profile Auger electron spectroscopy. Synchrotron radiation x-ray diffraction revealed no secondary phase formation which indicates the substitution of V onto Zn site. However in all samples no pronounced ferromagnetism was observed down to 5 K by a superconducting quantum interference device magnetometer.Comment: 13 pages, 4 figs, MMM conference 2007, accepted by J. Appl. Phy