Aerodynamic properties of turbulent combustion fields

Flow fields involving turbulent flames in premixed gases under a variety of conditions are modeled by the use of a numerical technique based on the random vortex method to solve the Navier-Stokes equations and a flame propagation algorithm to trace the motion of the front and implement the Huygens principle, both due to Chorin. A successive over-relaxation hybrid method is applied to solve the Euler equation for flows in an arbitrarily shaped domain. The method of images, conformal transformation, and the integral-equation technique are also used to treat flows in special cases, according to their particular requirements. Salient features of turbulent flame propagation in premixed gases are interpreted by relating them to the aerodynamic properties of the flow field. Included among them is the well-known cellular structure of flames stabilized by bluff bodies, as well as the formation of the characteristic tulip shape of flames propagating in ducts. In its rudimentary form, the mechanism of propagation of a turbulent flame is shown to consist of: (1) rotary motion of eddies at the flame front, (2) self-advancement of the front at an appropriate normal burning speed, and (3) dynamic effects of expansion due to exothermicity of the combustion reaction. An idealized model is used to illustrate these fundamental mechanisms and to investigate basic aerodynamic features of flames in premixed gases. The case of a confined flame stabilized behind a rearward-facing step is given particular care and attention. Solutions are shown to be in satisfactory agreement with experimental results, especially with respect to global properties such as the average velocity profiles and reattachment length

The multi-lingual database system

In the past, the design and implementation of a database system has followed a rather conventional approach. First, a specific data model for the database system is chosen. Second, a corresponding model-based data language is then specified. The result of this traditional approach to the database-system development is a mono-lingual database system where the user sees and uses the database system with a specific data model and its model-based data language. The conventional practice for the database-system design and implementation mandates that a database system must be restricted tot a single data model and a specific model-based data language. This paper introduces a new and unconventional approach to the design and implementation of a database system, the multi-lingual database system (MLDS). The multi-lingual database system is a single database system that can execute many transactions written respectively in different data languages and support many databases structured correspondingly in various data models. For example, this multi-lingual database system can run DL/I transactions on IMS databases, CODASYL-DML transactions on network database, SQL transactions on relational databases and Daplex transactions on entity-relationship databases, where the system appears to the user like a heterogeneous collection of database systems. Thus, a multi-lingual database system allows the old transactions and existing databases to be migrated to the new environment, the experienced user to continue to utilize certain favorite features of existing data languages and data models, the new user to explore the strong features of the various data languages and data models, the hardware upgrade to be focused on a single system instead of a heterogeneous collection of database systems, and the database application to cover wider types of transactions and different modes of interactionssupported in part by the Foundation Research Program of the Naval Postgraduate School with funds provided by the Chief of Naval Researchhttp://archive.org/details/multilingualdata00demuN0001486WR4E001NAApproved for public release; distribution is unlimited

Explicit Space-Time Codes Achieving The Diversity-Multiplexing Gain Tradeoff

A recent result of Zheng and Tse states that over a quasi-static channel, there exists a fundamental tradeoff, referred to as the diversity-multiplexing gain (D-MG) tradeoff, between the spatial multiplexing gain and the diversity gain that can be simultaneously achieved by a space-time (ST) block code. This tradeoff is precisely known in the case of i.i.d. Rayleigh-fading, for T>= n_t+n_r-1 where T is the number of time slots over which coding takes place and n_t,n_r are the number of transmit and receive antennas respectively. For T < n_t+n_r-1, only upper and lower bounds on the D-MG tradeoff are available. In this paper, we present a complete solution to the problem of explicitly constructing D-MG optimal ST codes, i.e., codes that achieve the D-MG tradeoff for any number of receive antennas. We do this by showing that for the square minimum-delay case when T=n_t=n, cyclic-division-algebra (CDA) based ST codes having the non-vanishing determinant property are D-MG optimal. While constructions of such codes were previously known for restricted values of n, we provide here a construction for such codes that is valid for all n. For the rectangular, T > n_t case, we present two general techniques for building D-MG-optimal rectangular ST codes from their square counterparts. A byproduct of our results establishes that the D-MG tradeoff for all T>= n_t is the same as that previously known to hold for T >= n_t + n_r -1.Comment: Revised submission to IEEE Transactions on Information Theor

New Directions In Database-Systems Research and Development

Prepared for: Chief of Naval Research Arlington, VA 22217In this paper, three new directions in database-systems research and development are indicated. One new direction is the emergence of the multilingual database systems where a single database system can execute many transactions written respectively in different data languages and support many databases structured correspondingly in various data models. Thus, a multi-lingual database system allows the old transactions and existing databases to be migrated to the new system, the user to explore the strong features of the various data languages and data models in the same system, the hardware upgrade to be focused on a single system instead of a heterogeneous collection of database systems, and the database application to cover wider types of transactions and interaction in the same environment. One other new direction is the emphasis of the multi-backend database systems where the database system is configured with a number of microprocessor-based processing units and their disk subsystems. These processing units and disk subsystems are called database backends. The unique characteristics of the backends are that the number of the backends is variable, the system software in all of the backends is identical, and the multiplicity of the backends is proportional to the performance and capacity of the system. Thus, for the first time, a multi-backend database system enables the user to relate the amount of hardware used (i.e., the number of the backends) to the degree of performance gain and capacity growth of the system. The third new direction is the possibility of the multi-host database systems where a single database system can communicate with a variable number and heterogeneous collection of mainframes in several different data languages and allow the mainframes to share the common database store and access. This paper attempts to articulate the background, benefits, requirements and architectures of these new types of database system, namely, the multi-lingua the multi-backend, and the multi-host database systems.DoD STARS Program and from the Office of Naval Research.Approved for public release; distribution is unlimited

Trajectory-Based Dynamic Map Labeling

In this paper we introduce trajectory-based labeling, a new variant of dynamic map labeling, where a movement trajectory for the map viewport is given. We define a general labeling model and study the active range maximization problem in this model. The problem is NP-complete and W[1]-hard. In the restricted, yet practically relevant case that no more than k labels can be active at any time, we give polynomial-time algorithms. For the general case we present a practical ILP formulation with an experimental evaluation as well as approximation algorithms.Comment: 19 pages, 7 figures, extended version of a paper to appear at ISAAC 201

Near-IR studies of recurrent nova V745 Scorpii during its 2014 outburst

The recurrent nova (RN) V745 Scorpii underwent its third known outburst on 2014 February 6. Infrared monitoring of the eruption on an almost daily basis, starting from 1.3d after discovery, shows the emergence of a powerful blast wave generated by the high velocity nova ejecta exceeding 4000 kms$^{-1}$ plowing into its surrounding environment. The temperature of the shocked gas is raised to a high value exceeding 10$^{8}$K immediately after outburst commencement. The energetics of the outburst clearly surpass those of similar symbiotic systems like RS Oph and V407 Cyg which have giant secondaries. The shock does not show a free-expansion stage but rather shows a decelerative Sedov-Taylor phase from the beginning. Such strong shockfronts are known to be sites for $\gamma$ ray generation. V745 Sco is the latest nova, apart from five other known novae, to show $\gamma$ ray emission. It may be an important testbed to resolve the crucial question whether all novae are generically $\gamma$ ray emitters by virtue of having a circumbinary reservoir of material that is shocked by the ejecta rather than $\gamma$ ray generation being restricted to only symbiotic systems with a shocked red giant (RG) wind. The lack of a free-expansion stage favors V745 Sco to have a density enhancement around the white dwarf (WD), above that contributed by a RG wind. Our analysis also suggests that the WD in V745 Sco is very massive and a potential progenitor for a future SN Ia explosion.Comment: To appear in ApJ (Letters

A benchmarking methodology for the centralized-database computer with expandable and parallel database processors and stores

In this paper a benchmarking methodology for a new kind of database computers is introduced. The emergence in the research community and in the commercial world of this kind of database computer (known as the multiple-backed database computers), were each computer system is configured with two or more identical processors and their associated stores for concurrent execution of transactions and for parallel processing of a centralized database spread over separate stores, is evident. The motivation and characterization of the multiple-backend database computer are first given. The need and lack of a methodology for benchmarking the new computer with a variable number of backends for the same database or with a fixed number of backends for different capacities are also evident. The measures (benchmarks) of the new computer are articulated and established and the design of the methodology for conducting the measurements is then given. Because of the novelty of the database computer architecture, the benchmarking methodology is rather elaborate and somewhat complicated. To aid our understanding of the methodology, a concrete sample is given herein. This sample also illustrates the use of the methodology. Meanwhile, a CAD system which computerizes the benchmarking methodology for systematically assisting the design of test databases and test-transaction mixes, for automatically tallying the design data and workloads, and for completely generating the test databases and test-transaction mixes is being implementedPrepared for: Chief of Naval Research Arlington, VAhttp://archive.org/details/benchmarkingmeth00demu61153N; RRO14-0 8-01 N0001485WR24046NAApproved for public release; distribution is unlimited

Maternal immune activation causes age- and region-specific changes in brain cytokines in offspring throughout development

Maternal infection is a risk factor for autism spectrum disorder (ASD) and schizophrenia (SZ). Indeed, modeling this risk factor in mice through maternal immune activation (MIA) causes ASD- and SZ-like neuropathologies and behaviors in the offspring. Although MIA upregulates pro-inflammatory cytokines in the fetal brain, whether MIA leads to long-lasting changes in brain cytokines during postnatal development remains unknown. Here, we tested this possibility by measuring protein levels of 23 cytokines in the blood and three brain regions from offspring of poly(I:C)- and saline-injected mice at five postnatal ages using multiplex arrays. Most cytokines examined are present in sera and brains throughout development. MIA induces changes in the levels of many cytokines in the brains and sera of offspring in a region- and age-specific manner. These MIA-induced changes follow a few, unexpected and distinct patterns. In frontal and cingulate cortices, several, mostly pro-inflammatory, cytokines are elevated at birth, followed by decreases during periods of synaptogenesis and plasticity, and increases again in the adult. Cytokines are also altered in postnatal hippocampus, but in a pattern distinct from the other regions. The MIA-induced changes in brain cytokines do not correlate with changes in serum cytokines from the same animals. Finally, these MIA-induced cytokine changes are not accompanied by breaches in the blood–brain barrier, immune cell infiltration or increases in microglial density. Together, these data indicate that MIA leads to long-lasting, region-specific changes in brain cytokines in offspring—similar to those reported for ASD and SZ—that may alter CNS development and behavior

Robust grasping under object pose uncertainty

This paper presents a decision-theoretic approach to problems that require accurate placement of a robot relative to an object of known shape, such as grasping for assembly or tool use. The decision process is applied to a robot hand with tactile sensors, to localize the object on a table and ultimately achieve a target placement by selecting among a parameterized set of grasping and information-gathering trajectories. The process is demonstrated in simulation and on a real robot. This work has been previously presented in Hsiao et al. (Workshop on Algorithmic Foundations of Robotics (WAFR), 2008; Robotics Science and Systems (RSS), 2010) and Hsiao (Relatively robust grasping, Ph.D. thesis, Massachusetts Institute of Technology, 2009).National Science Foundation (U.S.) (Grant 0712012

Abundance Profiles and Kinematics of Damped Lyman-alpha Absorbing Galaxies at z < 0.65

We present a spectroscopic study of six damped Lya absorption (DLA) systems at z<0.65, based on moderate-to-high resolution spectra of the galaxies responsible for the absorbers. Combining known metallicity measurements of the absorbers with known optical properties of the absorbing galaxies, we confirm that the low metal content of the DLA population can arise naturally as a combination of gas cross-section selection and metallicity gradients commonly observed in local disk galaxies. We also study the Tully-Fisher relation of the DLA-selected galaxies and find little detectable evidence for evolution in the disk population between z=0 and z~0.5. Additional results of our analysis are as follows. (1) The DLA galaxies exhibit a range of spectral properties, from post-starburst, to normal disks, and to starburst systems, supporting the idea that DLA galaxies are drawn from the typical field population. (2) Large rotating HI disks of radius 30 h^{-1} kpc and of dynamic mass M_dyn > 10^{11} h^{-1} M_sun appear to be common at intermediate redshifts. (3) Using an ensemble of six galaxy-DLA pairs, we derive an abundance profile that is characterized by a radial gradient of -0.041 +/- 0.012 dex per kiloparsec (or equivalently a scale length of 10.6 h^{-1} kpc) from galactic center to 30 h^{-1} kpc radius. (4) Adopting known N(HI) profiles of nearby galaxies and the best-fit radial gradient, we further derive an N(HI)-weighted mean metallicity _weighted = -0.50 +/- 0.07 for the DLA population over 100 random lines of sight, consistent with _weighted = -0.64 (-0.86, +0.40) observed for z~1 DLA systems from Prochaska et al. Our analysis demonstrates that the low metal content of DLA systems does not rule out the possibility that the DLA population trace the field galaxy population.Comment: 57 pages, 17 figures, to appear in the ApJ 20 February 2005 issue; a pdf version of the paper with full-resolution figures is available at http://falcon.mit.edu/~hchen/public/tmp/dlachem.pd