By employing magnetization and small angle neutron scattering (SANS) measurements, we have investigated the behavior of the skyrmion lattice (SKL) and the helical order in MnSi0.992Ga0.008. Our results indicate that the order of the SKL is sensitive to the orientation of an applied magnetic field with respect to the crystal lattice and small variations in the sequence of temperature and applied magnetic field changes. The disorder caused by the substitution of the heavier element Ga for Si is sufficient to reduce the pinning of the SKL to the underlying crystalline lattice. This reduces the propensity for the SKL to be aligned with the crystal lattice. This tendency is most evident when the applied field is not well oriented with respect to the high symmetry axes of the crystal resulting in disorder in the long range SKL while maintaining sharp radial order. We have also investigated the effect of substituting heavier elements into MnSi on the reorientation process of the helical domains with field cycling in MnSi0.992Ga0.008 and Mn0.985Ir0.015Si. A comparison of the reorientation process in these materials with field reduction indicates that the substitution of heavier elements on either Mn or Si sites creates a higher energy barrier for the reorientation of the helical order and for the formation of domains.

Ordering and incomplete factorization issues for matrices arising from the TRANAIR CFD code. A locally reened rectangular grid nite element method: Application to computational uid dynamics and computational physics. A comparison of domain decomposition techniques for elliptic partial diierential equations and their parallel implementation. Inexact Newton's method solutions to the incompressible Navier-Stokes and energy equations using standard and matrix-free implementations. 16 eration counts and/or memory consumption. However, the plethora of parameters can be exploited, in principle, to produce optimal tradeoos in space and time for a given problem class. Though parametric tuning is important to performance, conservative robust choices are not diicult. methods for the unsteady compressible Navier-Stokes equations on unstructured meshes. A comparison of some domain decomposition and ILU preconditioned iterative methods for nonsymmetric elliptic problems. 15 Table 8: Wall-clock performance and relative parallel eeciency for unstructured Euler code on an Intel Paragon. We have shown that steady aerodynamics problems in two diierent formulations (full potential and Euler) can be eeectively solved, and cost-eeectively solved in parallel, by NKS methods. The NK technique has been compared with V-cycle multigrid on Euler and Navier-Stokes problems without parallelizing the preconditioning in 14, 20]. For a subsonic unstructured grid example, NK trails multigrid in execution time by a factor of only about 1.5. This penalty can be accepted when it is realized that the NK method has the advantage of doing all of its computation without generation of a family of coarse unstructured grids (which is diicult for three-dimensional unstructured grids). This work has been extended to three-dimensional problems in 20]. Large-scale time-dependent problems suuering from multiple scales often require parallel implicit algorithms. The KS technique has been shown eeective in the unsteady Navier-Stokes context in 3]. In 3], two of the same parameters explored herein (level of ll in the local ILU factorizations and subdomain overlap) are varied to produce a Schwarz precondi-tioner whose strength can be adjusted to adapt to the varying time-evolving ill-conditioning of the linear system arising at each implicit time step. A variety of CFD applications are (or have inner) nonlinear elliptically-dominated problems amenable to solution by NKS algorithms, which are characterized by low storage requirements (for an implicit method) and locally concentrated data dependencies with small overlaps between the preconditioner blocks. The addition of a global coarse grid in the Schwarz preconditioner is often eeective, where architecturally convenient. A deterrent to the widespread adoption of NKS …

Characteristics of nocturnal bird migration are poorly understood for many regions of the United States. This information will be critical in areas where wind power projects are proposed. We used portable marine radar to conduct a nocturnal bird migration study at multiple sites along the Allegheny Front, West Virginia, on 45 nights during autumn 2003, to document migration characteristics at a proposed wind power project. Nocturnal passage rates were highly variable among nights, ranging from 8 to 852 targets/km/hour, with a seasonal mean of 241 +/- 33 targets/km/hour at the primary (central) study site and 199 targets/km/hour for the entire proposed development. Mean flight altitudes also were highly variable among nights, ranging from 214 to 769 m above ground level (agl), with a mean flight altitude of 410 +/- 2 m agl. Flight directions indicated that most migrants crossed, rather than followed, the Allegheny Front ridgeline. We believe portable marine radars, when coupled with a rigorous study design, can collect important baseline information on avian migration and address site specific questions posed at proposed developments. Concurrent collection of low-altitude migration and avian fatality data could help elucidate which metrics are most useful for predicting avian fatalities at wind power developments.

We estimate that from 500 million to possibly over 1 billion birds are killed annually in the United States due to anthropogenic sources including collisions with human-made structures such as vehicles, buildings and windows, power lines, communication towers, and wind turbines; electrocutions; oil spills and other contaminants; pesticides; cat predation; and commercial fishing by-catch. Many of the deaths from these sources would be considered unlawful take under federal laws such as the Endangered Species Act, Migratory Bird Treaty Act, and the Bald and Golden Eagle Protection Act. In this paper, we summarize this literature and provide the basis for the mortality projections for many of the apparent significant sources. Most of the mortality projections are based on small sample sizes, and on studies typically lacking adjustments for scavenging and searcher efficiency biases. Although the estimates for each source often range by an order of magnitude, the cumulative mortality from all these sources continues to be a concern.

thispaper, we shall use the nonlinear additive Schwarz algorithm as the preconditionerand focus on the performance of PIN for a compressible shock tubeproblem, which is known to be a dicult test case for inexact Newton typealgorithms.

Temperature-dependent transport and magnetic measurements on ${\mathrm{Sr}}_{2}{\mathrm{Y}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Co}}_{2}{\mathrm{O}}_{7}$ indicate that ferromagnetism appears along with a crossover between two forms of variable-range-hopping (VRH) conductivity on cooling. Efros-Shklovskii (ES)-type VRH conduction was found below approximately 30 K, transformed from Mott-type VRH at higher temperature. The magnitude of the Coulomb gap and the Mott-ES VRH crossover temperature are \ensuremath{\sim}57 K and \ensuremath{\sim}170 K, respectively. These are unusually large compared to those of nonmagnetic disordered materials. The peculiar electronic state for the ferromagnetic Coulomb gap is probably due to Coulomb correlations among $d$ electrons in the disordered system.

The thermoelectric properties of the pure and doped half-Heusler compounds FeVSb and FeNbSb are reported. The electrical resistivities are between 0.2 and 20 mΩ cm at room temperature. Thermoelectric power measurements indicate that FeVSb is an n-type material with moderate Seebeck coefficients near −70 μV/K at 300 K. The thermal conductivity at room temperature is large, approximately 0.1 W/cm K, and increases with decreasing temperature. Chemical substitutions, which have a dramatic effect on the transport properties, were performed in an effort to enhance the thermoelectric performance. Band-structure calculations are presented for the pure materials.

Electronic structure calculations predict Ag3AuTe2 to be a small-band-gap semiconductor. Polycrystalline samples of the pure and doped materials have been synthesized, and the physical properties are reported. Thermoelectric power measurements indicate that pure Ag3AuTe2 is a p-type material with a very large room-temperature Seebeck coefficient of 530 μV/K. The thermal conductivity is very low, and at room temperature, is lower than that of the best thermoelectrics. The transport properties were found to be very sensitive to chemical doping and nonstoichiometry. Although samples made with excess Ag resulted in improved thermoelectric performance at higher temperatures (>500 K), the large resistivity of these materials makes them noncompetitive with state-of-the-art thermoelectrics.

The thermoelectric properties near ambient temperature of half-Heusler alloys based on LnPdSb, where Ln=Ho, Er, and Dy are reported. The Seebeck coefficients are large, between 60 and 250 mu V/K, and the materials are p type. The resistivities are between 0.6 and 20 m Omega cm. Thermal conductivities are between approximately 5.0 and 3.5 W/mK at 300 K, and are smallest in intentionally disordered materials. The highest ambient temperature ZT obtained is 0.06. Band-structure calculations are presented for LuPdSb. It is suggested that half-Heusler alloys with 18 electrons per formula unit may represent a large class of thermoelectric materials. (C) 1999 American Institute of Physics. [S0003-6951(99)01710-6].

The thermoelectric properties of intermetallic compounds with the Y3Au3Sb4 structure type, of formula Ln3Au3Sb4 for Ln=Gd, Nd, Ho, and Sm, are reported. The highest Seebeck coefficients are on the order of 100–200 μV/K, indicating that the dominant carriers are holes, and increase with increasing temperature. Variation of the Au:Sb ratio significantly affects the resistivities and Seebeck coefficients. Materials with mixtures of lanthanides on the large atom site show improved Seebeck coefficients without degradation of the electrical resistivity. The thermal conductivities are very low, even for the stoichiometric materials, and decrease in materials with mixed lanthanides. Band-structure calculations show a complex multivalley character for both valence and conduction bands.

This report discusses design optimizationmethods, many of which are equivalent to classical optimal control methods [1, 2] in the sense that Newton's method is applied to the necessary conditions for optimality. In this context, many design methods are minor variants of the classical Lagrange-Newton method and can be understood by using the theory for Newton's method. In many application areas, variants of Newton's method have been used that have in common an augmented line search that ensures the satisfaction of certain of the nonlinear equations at each Newton iteration. This nonlinear elimination method has recently been analyzed by Lanzkron, Rose, and Wilkes [3] and is of signi cant value in boundary layer coupled CFD [4, 5, 6]. We rst review classical optimal control methods and then show how they can be extended to state equations derived from boundary value problems and to solution-adaptive grid methods. We then derive various proposed decomposition methods in this context and show a relationship between these methods and the inexact nonlinear elimination method. This report owes something to the spirit of [7] in the use of the relationship between methods for solving nonlinear systems of equations and optimization problems.

The thermoelectric properties near ambient temperature of half-Heusler alloys based on HoPdSb, DyPdSb, and ErPdSb are reported. The Seebeck coefficients are between 60 and 250 μV/K. The resistivities range between 0.6 and 20 mΩcm, and the majority carriers are p-type. Thermal conductivities are smallest in intentionally disordered materials. The highest ambient temperature ZT obtained is 0.06. Band structure calculations are presented, and are compared to those for ZrNiSn. It is suggested that half-Heusler alloys with 18 electrons per formula unit may represent a large class of thermoelectric materials. The thermoelectric properties of another family of cubic symmetry antimonides, based on Ho 3 Au 3 Sb 4 and Sm 3 Au 3 Sb 4 , are also reported.

We study parallel two-level overlapping Schwarz algorithms for solving nonlinear finite element problems, in particular, for the full potential equation of aerodynamics discretized in two dimensions with bilinear elements. The overall algorithm, Newton-Krylov-Schwarz (NKS), employs an inexact finite difference Newton method and a Krylov space iterative method, with a two-level overlapping Schwarz method as a preconditioner. We demonstrate that NKS, combined with a density upwinding continuation strategy for problems with weak shocks, is robust and economical for this class of mixed elliptic-hyperbolic nonlinear partial differential equations, with proper specification of several parameters. We study upwinding parameters, inner convergence tolerance, coarse grid density, subdomain overlap, and the level of fill-in in the incomplete factorization, and report their effect on numerical convergence rate, overall execution time, and parallel efficiency on a distributed-memory parallel computer.

The TRANAIR aerodynamics code is used as a testbed for developing advanced iterative methods that lend themselves to parallel or distributed computing. In the case of aerodynamics design optimization, a significant part of the computational cost is in the solution of large sparse nonsymmetric linear systems. We have implemented a two-level method for solving such linear systems and present preliminary computational results for problems in two space dimensions. We observe a lime-space trade-off mediated by parameters that govern the amount of fill-in in incomplete factorizations on each level. In both subsonic and transonic flow regimes, parameter choices exist that lead to substantial improvements in runtime for comparable memory requirements, relative to a single grid method.

The adaptive grid method implemented in the 3D general geometry CFD code TRANAIR is described. Adaptive gridding in TRANAIR has been used to help solve many industrial aerospace analysis and design problems. Grids are adapted to numerical solutions by refining and coarsening local rectangular finite elements according to values of error indicators computed for the elements. The underlying finite element method is summarized and details of the adaptive gridding approach are given. Emphasis is placed on several principles used in developing and applying the approach. In particular, many computational comparisons are presented to explain the reasoning behind the local error indicator and gridding strategy used.