Showing papers by "Argonne National Laboratory published in 1999"

Measuring Thermal Conductivity of Fluids Containing Oxide Nanoparticles

Abstract: Oxide nanofluids were produced and their thermal conductivities were measured by a transient hot-wire method. The experimental results show that these nanofluids, containing a small amount of nanoparticles, have substantially higher thermal conductivities than the same liquids without nanoparticles. Comparisons between experiments and the Hamilton and Crosser model show that the model can predict the thermal conductivity of nanofluids containing large agglomerated Al{sub 2}O{sub 3} particles. However, the model appears to be inadequate for nanofluids containing CuO particles. This suggests that not only particle shape but size is considered to be dominant in enhancing the thermal conductivity of nanofluids.

Thermal Conductivity of Nanoparticle -Fluid Mixture

Abstract: Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts

The use of gene clusters to infer functional coupling

Abstract: Previously, we presented evidence that it is possible to predict functional coupling between genes based on conservation of gene clusters between genomes. With the rapid increase in the availability of prokaryotic sequence data, it has become possible to verify and apply the technique. In this paper, we extend our characterization of the parameters that determine the utility of the approach, and we generalize the approach in a way that supports detection of common classes of functionally coupled genes (e.g., transport and signal transduction clusters). Now that the analysis includes over 30 complete or nearly complete genomes, it has become clear that this approach will play a significant role in supporting efforts to assign functionality to the remaining uncharacterized genes in sequenced genomes.

A new version of the RDP (Ribosomal Database Project)

Abstract: The Ribosomal Database Project (RDP-II), previously described by Maidak et al. [ Nucleic Acids Res. (1997), 25, 109-111], is now hosted by the Center for Microbial Ecology at Michigan State University. RDP-II is a curated database that offers ribosomal RNA (rRNA) nucleotide sequence data in aligned and unaligned forms, analysis services, and associated computer programs. During the past two years, data alignments have been updated and now include >9700 small subunit rRNA sequences. The recent development of an ObjectStore database will provide more rapid updating of data, better data accuracy and increased user access. RDP-II includes phylogenetically ordered alignments of rRNA sequences, derived phylogenetic trees, rRNA secondary structure diagrams, and various software programs for handling, analyzing and displaying alignments and trees. The data are available via anonymous ftp (ftp.cme.msu. edu) and WWW (http://www.cme.msu.edu/RDP). The WWW server provides ribosomal probe checking, approximate phylogenetic placement of user-submitted sequences, screening for possible chimeric rRNA sequences, automated alignment, and a suggested placement of an unknown sequence on an existing phylogenetic tree. Additional utilities also exist at RDP-II, including distance matrix, T-RFLP, and a Java-based viewer of the phylogenetic trees that can be used to create subtrees.

A distributed resource management architecture that supports advance reservations and co-allocation

Abstract: The realization of end-to-end quality of service (QoS) guarantees in emerging network-based applications requires mechanisms that support first dynamic discovery and then advance or immediate reservation of resources that will often be heterogeneous in type and implementation and independently controlled and administered. We propose the Globus Architecture for Reservation and Allocation (GARA) to address these four issues. GARA treats both reservations and computational elements such as processes, network flows, and memory blocks as first-class entities, allowing them to be created, monitored, and managed independently and uniformly. It simplifies management of heterogeneous resource types by defining uniform mechanisms for computers, networks, disk, memory, and other resources. Layering on these standard mechanisms, GARA enables the construction of application-level co-reservation and co-allocation libraries that applications can use to dynamically assemble collections of resources, guided by both application QoS requirements and the local administration policy of individual resources. We describe a prototype GARA implementation that supports three different resource type-parallel computers, individual CPU under control of the dynamic soft real-time scheduler, and integrated services networks, and provide performance results that quantify the costs of our techniques.

Olivine LiCoPO4 as 4.8 V Electrode Material for Lithium Batteries

Abstract: Reversible extraction and insertion of lithium from and into olivine at vs. lithium have shown that this material is a good candidate for a high‐voltage lithium‐ion battery. Electrochemical extraction was limited to 0.42 lithium per formula unit, with a charge capacity of and a discharge capacity of . In this case. the material retains its structural integrity with a slight contraction of the unit cell upon cycling. The crystallinity of the electrode during charge and discharge processes was not affected, as deduced from the sharpness of the X‐ray diffraction peaks of the cycled cathode material. ©2000 The Electrochemical Society

Nonlinear Predictive Control and Moving Horizon Estimation — An Introductory Overview

Abstract: In the past decade model predictive control (MPC) has become a preferred control strategy for a large number of processes. The main reasons for this preference include the ability to handle constraints in an optimal way and the flexible formulation in the time domain. Linear MPC schemes, i.e. MPC schemes for which the prediction is based on a linear description of the plant, are by now routinely used in a number of industrial sectors and the underlying control theoretic problems, like stability, are well studied. Nonlinear model predictive control (NMPC), i.e. MPC based on a nonlinear plant description, has only emerged in the past decade and the number of reported industrial applications is still fairly low. Because of its additional ability to take process nonlinearities into account, expectations on this control methodology are high.

Data sieving and collective I/O in ROMIO

Abstract: The I/O access patterns of parallel programs often consist of accesses to a large number of small, noncontiguous pieces of data. If an application's I/O needs are met by making many small, distinct I/O requests, however, the I/O performance degrades drastically. To avoid this problem, MPI-IO allows users to access a noncontiguous data set with a single I/O function call. This feature provides MPI-IO implementations an opportunity to optimize data access. We describe how our MPI-IO implementation, ROMIO, delivers high performance in the presence of noncontiguous requests. We explain in detail the two key optimizations ROMIO performs: data sieving for noncontiguous requests from one process and collective I/O for noncontiguous requests from multiple processes. We describe how one can implement these optimizations portably on multiple machines and file systems, control their memory requirements, and also achieve high performance. We demonstrate the performance and portability with performance results for three applications-an astrophysics-application template (DIST3D) the NAS BTIO benchmark, and an unstructured code (UNSTRUC)-on five different parallel machines: HP Exemplar IBM SP, Intel Paragon, NEC SX-4, and SGI Origin2000.

Soft core hyperon - nucleon potentials

Abstract: A new Nijmegen soft-core OBE potential model is presented for the low-energy $\mathrm{YN}$ interactions. Besides the results for the fit to the scattering data, which largely defines the model, we also present some applications to hypernuclear systems using the G-matrix method. The potentials are generated by the exchange of nonets of pseudoscalar, vector, and scalar mesons. As is standard in the Nijmegen soft-core models, we also include the $J=0$ contributions from the tensor ${f}_{2}{,f}_{2}^{\ensuremath{'}}{,a}_{2},$ and pomeron Regge trajectories, and use Gaussian form factors to guarantee that the potentials have a soft behavior near the origin. An important innovation with respect to the original soft-core potential is the assignment of the cutoff masses for the baryon-baryon-meson (BBM) vertices in accordance with broken $\mathrm{SU}{(3)}_{F},$ which serves to connect the $\mathrm{NN}$ and the $\mathrm{YN}$ channels. As a novel feature, we allow for medium strong breaking of the coupling constants, using the ${}^{3}{P}_{0}$ model with a Gell-Mann--Okubo hypercharge breaking for the BBM coupling. Charge-symmetry breaking in the $\ensuremath{\Lambda}p$ and $\ensuremath{\Lambda}n$ channels is included as well. We present six hyperon-nucleon potentials which describe the available $\mathrm{YN}$ cross section data equally well, but which exhibit some differences on a more detailed level. The differences are constructed such that the models encompass a range of scattering lengths in the $\ensuremath{\Sigma}N$ and $\ensuremath{\Lambda}N$ channels. In all cases, we obtained ${\ensuremath{\chi}}^{2}{/N}_{\mathrm{data}}\ensuremath{\approx}0.55$ for 35 $\mathrm{YN}$ data. In particular, we were able to fit the precise experimental datum ${r}_{R}=0.468\ifmmode\pm\else\textpm\fi{}0.010$ for the inelastic capture ratio at rest. For the scalar-meson mixing angle we obtained values ${\ensuremath{\theta}}_{S}=37\ifmmode^\circ\else\textdegree\fi{}--40\ifmmode^\circ\else\textdegree\fi{},$ which points to almost ideal mixing angles for the scalar $q\overline{q}$ states. The G-matrix results indicate that the remarkably different spin-spin terms of the six potentials appear specifically in the energy spectra of $\ensuremath{\Lambda}$ hypernuclei.

The crystal structure of a T cell receptor in complex with peptide and MHC class II

Abstract: The crystal structure of a complex involving the D10 T cell receptor (TCR), 16-residue foreign peptide antigen, and the I-Ak self major histocompatibility complex (MHC) class II molecule is reported at 3.2 angstrom resolution. The D10 TCR is oriented in an orthogonal mode relative to its peptide-MHC (pMHC) ligand, necessitated by the amino-terminal extension of peptide residues projecting from the MHC class II antigen-binding groove as part of a mini beta sheet. Consequently, the disposition of D10 complementarity-determining region loops is altered relative to that of most pMHCI-specific TCRs; the latter TCRs assume a diagonal orientation, although with substantial variability. Peptide recognition, which involves P-1 to P8 residues, is dominated by the Valpha domain, which also binds to the class II MHC beta1 helix. That docking is limited to one segment of MHC-bound peptide offers an explanation for epitope recognition and altered peptide ligand effects, suggests a structural basis for alloreactivity, and illustrates how bacterial superantigens can span the TCR-pMHCII surface.

Structural Fatigue in Spinel Electrodes in High Voltage ( 4 V ) Li / Li x Mn2 O 4 Cells

Abstract: Evidence of structural fatigue has been detected at the surface of discharged Li{sub x}[Mn{sub 2}]O{sub 4} spinel electrodes in (4 V) Li/Li{sub x}[Mn{sub 2}]O{sub 4} cells. Under nonequilibrium conditions, domains of tetragonal Li{sub 2}[Mn{sub 2}]O{sub 4} coexist with cubic Li[Mn{sub 2}]O{sub 4}, even at 500mV above the thermodynamic voltage expected for the onset of the tetragonal phase. The presence of Li{sub 2}[Mn{sub 2}]O{sub 4} on the particle surface may contribute to some of the capacity fade observed during cycling of Li/Li{sub x}[Mn{sub 2}]O{sub 4} cells.

On implementing MPI-IO portably and with high performance

Abstract: We discuss the issues involved in implementing MPI-IO portably on multiple machines and file systems and also achieving high performance. One way to implement MPI-IO portably is to implement it on top of the basic Unix I/O functions (open, lseek, read, write, and close), which are themselves portable. We argue that this approach has limitations in both functionality and performance. We instead advocate an implementation approach that combines a large portion of portable code and a small portion of code that is optimized separately for different machines and file systems. We have used such an approach to develop a high-performance, portable MPI-IO implementation, called ROMIO. In addition to basic I/O functionality, we consider the issues of supporting other MPI-IO features, such as 64-bit file sizes, noncontiguous accesses, collective I/O, asynchronous I/O, consistency and atomicity semantics, user-supplied hints, shared file pointers, portable data representation, and file preallocation. We describe how we implemented each of these features on various machines and file systems. The machines we consider are the HP Exemplar, IBM SP, Intel Paragon, NEC SX-4, SGI Origin2000, and networks of workstations; and the file systems we consider are HP HFS, IBM PIOFS, Intel PFS, NEC SFS, SGI XFS, NFS, and any general Unix file system (UFS). We also present our thoughts on how a file system can be designed to better support MPI-IO. We provide a list of features desired from a file system that would help in implementing MPI-IO correctly and with high performance.

Development of Solid‐Oxide Fuel Cells That Operate at 500°C

Abstract: Solid‐oxide fuel cells based on doped ceria electrolytes and operating at 500°C are shown to be feasible. The operating regime of doped ceria electrolytes is discussed. It is shown that the ionic conductivity of ceria‐based fuel cells is sufficiently high for operation with hydrogen fuel at low temperatures. The major challenges of fabricating a thin electrolyte by a conventional method and the development of high‐performance cathodes capable of operating at 500–600°C are addressed. Cells based on thin‐film ceria electrolytes also exhibited good open‐circuit voltages between 0.97 and 1 V. Cathode materials with high performance have been developed from pyrochlores, perovskites, and cermets of silver and doped bismuth oxide. The advantages and disadvantages of different cathode materials are discussed. The maximum power density obtained at 500°C was . © 1999 The Electrochemical Society. All rights reserved.

Production of Charginos, Neutralinos, and Sleptons at Hadron Colliders

Abstract: We analyze the production of charginos, neutralinos, and sleptons at the hadron colliders Tevatron and LHC in the direct channels p{ovr p}/pp{r_arrow}{tilde {chi}}{sub i}{tilde {chi}}{sub j}+X and {tilde {ell}}{ell}d{sup {prime}}+X . The cross sections for these reactions are given in next-to-leading order supersymmetric QCD. By including the higher-order corrections, the predictions become theoretically stable, being nearly independent of the factorization and renormalization scales. Since the corrections increase the cross sections, the discovery range for these particles is extended in the refined analysis. {copyright} {ital 1999} {ital The American Physical Society }

Li x Cu6Sn5 ( 0 < x < 13 ) : An Intermetallic Insertion Electrode for Rechargeable Lithium Batteries

Abstract: It has been discovered that lithium can be inserted into the intermetallic compound in a two‐phase reaction to yield the product . This finding has important implications for designing new intermetallic insertion electrodes (anodes) for rechargeable lithium batteries. The theoretical capacity of derived from the eta‐phase, , with a structure is for , which corresponds to a fully lithiated composition ; this capacity is close to the theoretical capacity of lithiated graphite . The reaction occurs at approximately vs. lithium metal. The best cycling efficiency is obtained when the end voltage is restricted to above the potential of lithium metal. A mechanism is proposed for the insertion of lithium into . ©1999 The Electrochemical Society

Improving Optical and Charge Separation Properties of Nanocrystalline TiO2 by Surface Modification with Vitamin C

Abstract: The structural and electrochemical properties of nanoparticles were found to be different from those of the corresponding bulk semiconductors. Due to the specific binding of modifiers to “corner defects”, the optical properties of small titania particles were red shifted 1.6 eV compared to unmodified nanocrystallites. It was found using electron paramagnetic resonance (EPR) that, as with organic charge transfer superconductors, these novel nanocrystallites operate with a charge-transfer mechanism, and exhibit semiconducting properties through both constituents (large band gap semiconductor and organic modifier). The EPR spectra were consistent with hole trapping on the surface modifier and electron trapping on shallow interstitial and partially delocalized Ti sites. These systems have an important feature in that charge pairs are instantaneously separated into two phasesthe holes on the donating organic modifier and the electrons in the conduction band of TiO2.

Complete Sequence of a 184-Kilobase Catabolic Plasmid from Sphingomonas aromaticivorans F199

Abstract: Sphingomonas aromaticivorans F199 was isolated from sediments collected 410 m below the land surface near Allendale, S.C., in 1988 (4, 21). It was established that this bacterium possessed the novel ability to degrade a variety of aromatic compounds including toluene, all isomers of xylene, p-cresol, naphthalene, biphenyl, dibenzothiophene, fluorene, salicylate, and benzoate (20, 22). In recent years, there have been many reports of other Sphingomonas strains that are capable of degrading aromatic compounds (12, 17, 30, 36, 40, 44, 45, 62–65, 68–70, 88, 91). Studies of Sphingomonas strains suggest that members of this genus are well adapted for the degradation of high-molecular-weight polycyclic aromatic hydrocarbons and other aromatic contaminants. The inability to detect Sphingomonas biodegradative genes via hybridization with catabolic genes from phylogenetically distinct bacteria suggested that biodegradative genes from Sphingomonas sp. evolved independently from phylogenetically distinct bacteria such as those within the genus Pseudomonas (46, 47). Some Sphingomonas strains are further distinguished in that the genes necessary for degradation of one type of aromatic compound are distributed into multiple operons that also possess genes for the degradation of other aromatic compounds (107). This unusual gene arrangement suggests that a highly complex regulatory network is responsible for the expression of aromatic degradative pathways in some Sphingomonas spp. S. aromaticivorans F199 was shown to possess two plasmids (20, 22), which are designated pNL1 (∼180 kbp) and pNL2 (∼480 kbp). We reported earlier that catechol meta ring cleavage activity, a central step in the catabolism of aromatic rings, was associated with the smaller plasmid, pNL1 (86), and we described a physical map for this plasmid. To further probe the catabolic functions and accessory genes encoded on pNL1, we undertook the complete sequencing and annotation of this plasmid. This approach has allowed a thorough genetic analysis of pNL1-associated catabolic genes, a comparison of these genes with analogous chromosomally located ones in S. yanoikuyae B1, and the development of hypotheses regarding functions of pNL1-encoded genes.

Reactions of transition metal clusters with small molecules.

Abstract: Atoms and small molecules react with transition metal clusters in ways that are analogous to the physisorption and chemisorption reactions observed on the corresponding extended metal surface. However, often underlying these similarities are size-dependent variations in the reaction mechanisms and rates, the interpretation of which requires a detailed understanding of the structures of both the bare metal cluster substrates and the cluster-molecule complexes. Although polyatomic transition metal clusters cannot be characterized by the traditional methods of molecular spectroscopy, the combination of other physical and chemical probes can provide qualitative and semiquantitative structural information. These techniques, when combined with equilibrium geometries calculated using ab initio or semiempirical methods, provide a detailed picture of the structural origin of metal cluster reactivity and its variation with size.

Electronic Spectra and Their Relation to the ( π,π) Collective Mode in High- Tc Superconductors

Abstract: The photoemission line shape near (pi, 0) in Bi(2)Sr(2)CaCu(2)O(8+delta) below T(c) is characterized by a sharp peak, followed at higher energy by a dip and hump. We study the evolution of this line shape as a function of momentum, temperature, and doping. We find the hump scales with the peak and persists above T(c) in the pseudogap state. We present strong evidence that the peak-dip-hump structure arises from the interaction of electrons with a collective mode of wave vector (pi, pi). The inferred mode energy and its doping dependence agree well with a magnetic resonance observed by neutron scattering.

Soft-core baryon-baryon potentials for the complete baryon octet

Abstract: SU(3) symmetry relations on the recently constructed hyperon-nucleon potentials are used to develop potential models for all possible baryon-baryon interaction channels. The main focus is on the interaction channels with total strangeness $S=\ensuremath{-}2,$ $\ensuremath{-}3,$ and $\ensuremath{-}4,$ for which no experimental data exist yet. The potential models for these channels are based on SU(3) extensions of potential models for the $S=0$ and $S=\ensuremath{-}1$ sectors, which are fitted to experimental data. Although the SU(3) symmetry is not taken to be exact, the $S=0$ and $S=\ensuremath{-}1$ sectors still provide the necessary constraints to fix all free parameters. The potentials for the $S=\ensuremath{-}2,$ $\ensuremath{-}3,$ and $\ensuremath{-}4$ sectors, therefore, do not contain any additional free parameters, which makes them among the first models of this kind. Various properties of the potentials are illustrated by giving results for scattering lengths, bound states, and total cross sections.

GASS: a data movement and access service for wide area computing systems

Abstract: In wide area computing, programs frequently execute at sites that are distant from their data. Data access mechanisms are required that place limited functionality demands on an application or host system yet permit high-performance implementations. To address these requirements, we propose a data movement and access service called Global Access to Secondary Storage (GASS). This service defines a global name space via Uniform Resource Locators and allows applications to access remote files via standard I/O interfaces. High performance is achieved by incorporating default data movement strategies that are specialized for I/O patterns common in wide area applications and by providing support for programmer management of data movement. GASS forms part of the Globus toolkit, a set of services for high-performance distributed computing. GASS itself makes use of Globus services for security and communication, and other Globus components use GASS services for executable staging and real-time remote monitoring. Application experiences demonstrate that the library has practical utility.

Using Run-Time Predictions to Estimate Queue Wait Times and Improve Scheduler Performance

Abstract: On many computers, a request to run a job is not serviced immediately but instead is placed in a queue and serviced only when resources are released by preceding jobs. In this paper, we build on run-time prediction techniques that we developed in previous research to explore two problems. The first problem is to predict how long applications will wait in a queue until they receive resources. We develop run-time estimates that result in more accurate wait-time predictions than other run-time prediction techniques. The second problem we investigate is improving scheduling performance. We use run-time predictions to improve the performance of the least-work-first and backfill scheduling algorithms. We find that using our run-time predictor results in lower mean wait times for the workloads with higher offered loads and for the backfill scheduling algorithm.