Showing papers by "Michigan Technological University published in 1996"

Imaging Through Turbulence

Abstract: Introduction Overview of the Problem Area Historical Overview of Imaging Through Turbulence Overview of the Book Background: Fourier and Statistical Optics Fourier Optics Statistical Optics Turbulence Effects on Imaging Systems Index of Refraction Fluctuations in the Atmosphere Statistics of Index of Refraction Fluctuations Wave Propagation through Random Media First-Order Turbulence Effects on Incoherent Imaging Modal Expansions of Phase Perturbation Phase Screen Generation Speckle Imaging Techniques Introduction Overview of Speckle Imaging Speckle Interferometry Fourier Phase Estimation Techniques Image Reconstruction for Speckle Imaging Conclusion Adaptive Optical Imaging Systems Introduction Factors that Degrade AOI Systems Performance Adaptive Optical System Components and Models AOI System Performance Modeling Summary Hybrid Imaging Techniques Introduction Deconvolution from Wavefront Sensing Methods Involving Adaptive Optics Conclusion Index

Improving data locality with loop transformations

Abstract: In the past decade, processor speed has become significantly faster than memory speed. Small, fast cache memories are designed to overcome this discrepancy, but they are only effective when programs exhibit data locality. In the this article, we present compiler optimizations to improve data locality based on a simple yet accurate cost model. The model computes both temporal and spatial reuse of cache lines to find desirable loop organizations. The cost model drives the application of compound transformations consisting of loop permutation, loop fusion, loop distribution, and loop reversal. To validate our optimization strategy, we implemented our algorithms and ran experiments on a large collection of scientific programs and kernels. Experiments illustrate that for kernels our model and algorithm can select and achieve the best loop structure for a nest. For over 30 complete applications, we executed the original and transformed versions and simulated cache hit rates. We collected statistics about the inherent characteristics of these programs and our ability to improve their data locality. To our knowledge, these studies are the first of such breadth and depth. We found performance improvements were difficult to achieve bacause benchmark programs typically have high hit rates even for small data caches; however, our optimizations significanty improved several programs.

Numerical modeling of cellular/dendritic array growth: spacing and structure predictions

Abstract: A numerical model of cellular and dendritic growth has been developed that can predict cellular and dendritic spacings, undercoolings, and the transition between structures. Fully self-consistent solutions are produced for axisymmetric interface shapes. An important feature of the model is that the spacing selection mechanism has been treated. A small, stable range of spacings is predicted for both cells and dendrites, and these agree well with experiment at both low and high velocities. By suitable nondimensionalization, relatively simple analytic expressions can be used to fit the numerical results. These expressions provide an insight into the cellular and dendritic growth processes and are useful for comparing theory with experiment.

Electrical Engineering: Principles and Applications

Abstract: (NOTE: Each chapter concludes with Summary and Problems.) I. CIRCUITS. 1. Introduction. Overview of Electrical Engineering. Circuits, Currents, and Voltages. Power and Energy. Kirchhoff's Current Law. Kirchhoff's Voltage Law. Introduction to Circuit Elements. Introduction to Circuits. 2. Resistive Circuits. Resistances in Series and Parallel. Network Analysis by Using Series and Parallel Equivalents. Voltage-Divider and Current-Divider Circuits. Node-Voltage Analysis. Mesh-Current Analysis. Thevenin and Norton Equivalent Circuits. Superposition Principle. Wheatstone Bridge. 3. Inductance and Capacitance. Capacitance. Capacitances in Series and Parallel. Physical Characteristics of Capacitors. Inductance. Inductances in Series and Parallel. Practical Inductors. Mutual Inductance. 4. Transients. First-Order RC Circuits. DC Steady State. RL Circuits. RC and RL Circuits with General Sources. Second-Order Circuits. 5. Steady-State Sinusoidal Analysis. Sinusoidal Currents and Voltages. Phasors. Complex Impedances. Circuit Analysis with Phasors and Complex Impedances. Power in AC Circuits. Thevenin and Norton Equivalent Circuits. Balanced Three-Phase Circuits. 6. Frequency Response, Bode Plots, and Resonance. Fourier Analysis, Filters, and Transfer Functions. First-Order Lowpass Filters. Decibels, the Cascade Connection, and Logarithmic Frequency Scales. Bode Plots. First-Order Highpass Filters. Series Resonance. Parallel Resonance. Ideal and Second-Order Filters. Digital Signal Processing. II. DIGITAL SYSTEMS. 7. Logic Circuits. Basic Logic Circuit Concepts. Representation of Numerical Data in Binary Form. Combinatorial Logic Circuits. Synthesis of Logic Circuits. Minimization of Logic Circuits. Sequential Logic Circuits. 8. Microcomputers. Computer Organization. Memory Types. Digital Process Control. The Motorola 68HC11/12. The Instruction Set and Addressing Modes for the 68HC11. Assembly-Language Programming. 9. Computer-Based Instrumentation Systems. Measurement Concepts and Sensors. Signal Conditioning. Analog-to-Digital Conversion. LabVIEWaA A . III. ELECTRONICS. 10. Diodes. Basic Diode Concepts. Load-Line Analysis of Diode Circuits. Zener-Diode Voltage-Regulator Circuits. Ideal-Diode Model. Piecewise-Linear Diode Models. Rectifier Circuits. Wave-Shaping Circuits. Linear Small-Signal Equivalent Circuits. 11. Amplifiers: Specifications and External Characteristics. Basic Amplifier Concepts. Cascaded Amplifiers. Power Supplies and Efficiency. Additional Amplifier Models. Importance of Amplifier Impedances in Various Applications. Ideal Amplifiers. Frequency Response. Linear Waveform Distortion. Pulse Response. Transfer Characteristic and Nonlinear Distortion. Differential Amplifiers. Offset Voltage, Bias Current, and Offset Current. 12. Field-Effect Transistors. NMOS and PMOS Transistors. Load-Line Analysis of a Simple NMOS Amplifier. Bias Circuits. Small-Signal Equivalent Circuits. Common-Source Amplifiers. Source Followers. CMOS Logic Gates. 13. Bipolar Junction Transistors. Current and Voltage Relationships. Common-Emitter Characteristics. Load-Line Analysis of a Common-Emitter Amplifier. pnp Bipolar Junction Transistor. Large-Signal DC Circuit Models. Large-Signal DC Analysis of BJT Circuits. Small-Signal Equivalent Circuits. Common-Emitter Amplifiers. Emitter-Followers. 14. Operational Amplifiers. Ideal Operational Amplifiers. Summing-Point Constraint. Inverting Amplifiers. Noninverting Amplifiers. Design of Simple Amplifiers. Op-Amp Imperfections in the Linear Range of Operation. Nonlinear Limitations. DC Imperfections. Differential and Instrumentation Amplifiers. Integrators and Differentiators. Active Filters. IV. ELECTROMECHANICS. 15. Magnetic Circuits and Transformers. Magnetic Fields. Magnetic Circuits. Inductance and Mutual Inductance. Magnetic Materials. Ideal Transformers. Real Transformers. 16. DC Machines. Overview of Motors. Principles of DC Machines. Rotating DC Machines. Shunt-Connected and Separately Excited DC Motors. Series-Connected DC Motors. Speed Control of DC Motors. 17. AC Machines. Three-Phase Induction Motors. Equivalent Circuit and Performance Calculations for Induction Motors. Synchronous Machines. Single-Phase Motors. Stepper Motors. Appendix A: Complex Numbers. Appendix B: Nominal Values and the Color Code for Resistors. Appendix C: Preparing for the Fundamentals of Engineering Exam. Appendix D: Computer-Aided Circuit Analysis. Index.

Fine root respiration in northern hardwood forests in relation to temperature and nitrogen availability

Abstract: We examined fine-root (< 2.0 mm diameter) respiration throughout one growing season in four northern hardwood stands dominated by sugar maple (Acer saccharum Marsh.), located along soil temperature and nitrogen (N) availability gradients. In each stand, we fertilized three 50 x 50 m plots with 30 kg NO(3) (-)-N ha(-1) year(-1) and an additional three plots received no N and served as controls. We predicted that root respiration rates would increase with increasing soil temperature and N availability. We reasoned that respiration would be greater for trees using NO(3) (-) as an N source than for trees using NH(4) (+) as an N source because of the greater carbon (C) costs associated with NO(3) (-) versus NH(4) (+) uptake and assimilation. Within stands, seasonal patterns of fine-root respiration rates followed temporal changes in soil temperature, ranging from a low of 2.1 micro mol O(2) kg(-1) s(-1) at 6 degrees C to a high of 7.0 micro mol O(2) kg(-1) s(-1) at 18 degrees C. Differences in respiration rates among stands at a given soil temperature were related to variability in total net N mineralized (48-90 micro g N g(-1)) throughout the growing season and associated changes in mean root tissue N concentration (1.18-1.36 mol N kg(-1)). The hypothesized increases in respiration in response to NO(3) (-) fertilization were not observed. The best-fit model describing patterns within and among stands had root respiration rates increasing exponentially with soil temperature and increasing linearly with increasing tissue N concentration: R = 1.347Ne(0.072T) (r(2) = 0.63, P < 0.01), where R is root respiration rate ( micro mol O(2) kg(-1) s(-1)), N is root tissue N concentration (mol N kg(-1)), and T is soil temperature ( degrees C). We conclude that, in northern hardwood forests dominated by sugar maple, root respiration is responsive to changes in both soil temperature and N availability, and that both factors should be considered in models of forest C dynamics.

The Effect of Fuel and Engine Design on Diesel Exhaust Particle Size Distributions

Abstract: The objective of this research was to obtain diesel particle size distributions from a 1988 and a 1991 diesel engine using three different fuels and two exhaust control technologies (a ceramic particle trap and an oxidation catalytic converter). The particle size distributions from both engines were used to develop models to estimate the composition of the individual size particles. Nucleation theory of the H{sub 2}O and H{sub 2}SO{sub 4} vapor is used to predict when nuclei-mode particles will form in the dilution tunnel. Combining the theory with the experimental data, the conditions necessary in the dilution tunnel for particle formation are predicted. The paper also contains a discussion on the differences between the 1988 and 1991 engine`s particle size distributions. The results indicated that nuclei mode particles (0.0075--0.046 {micro}m) are formed in the dilution tunnel and consist of more than 80% H{sub 2}O-H{sub 2}SO{sub 4} particles when using the 1988 engine and 0.29 wt% sulfur fuel. Nucleation theory indicated that H{sub 2}O-H{sub 2}SO{sub 4} particles may form during dilution at 0.03 wt% fuel sulfur levels and above. The 1991 engine was designed for lower particulate emissions than the 1988 engine and the 1991 engine`s accumulation mode particles (0.046-1.0 {micro}m) weremore » reduced more than 80% by volume compared to the 1988 engine using the same low sulfur fuel. The particle size composition model indicated that using low sulfur fuel and the 1991 engine, the nuclei mode contained more than 45% of the total solid particles and over 85% of the soluble organic fraction.« less

The influence of mass transfer characteristics and porous media heterogeneity on nonaqueous phase dissolution

Abstract: A two-dimensional multiphase flow and species transport model was developed and applied to the case of nonaqueous phase liquid (NAPL) emplacement and dissolution in both homogeneous and heterogeneous porous media systems. Simulations were performed to observe dissolution rate variations and the degree of NAPL-aqueous phase nonequilibrium as a function of two aqueous phase velocities and five forms of the NAPL-aqueous phase mass transfer formulation. An integrated form of the Damkohler number was introduced to analyze the degree of NAPL-aqueous phase nonequilibrium. Mass removal rates for homogeneous media were insensitive to the form of the NAPL-aqueous phase mass transfer formulation, yielding results similar to a local equilibrium approach for all but one mass transfer formulation. This latter formulation was most sensitive to NAPL saturation and yielded significant nonequilibrium behavior, which was manifested as a decrease in NAPL dissolution rates as the NAPL volume fraction decreased. Variations in mass elution rates between homogeneous and heterogeneous media were observed, with more significant variations found for variances in porous media properties than for horizontal correlation lengths. In heterogeneous media, decreases in dissolution rates were attributed to the existence of relatively immobile regions of NAPL with saturations greater than the residual saturation of the media, so-called NAPL pools. These results illustrate the importance of the statistical characteristics of heterogeneous porous media on NAPL distribution and dissolution processes.

Effects of elevated CO2 and light availability on the photosynthetic light response of trees of contrasting shade tolerance

Abstract: Photosynthetic light response curves (A/PPFD), leaf N concentration and content, and relative leaf absorbance (alpha(r)) were measured in 1-year-old seedlings of shade-intolerant Betula papyrifera Marsh., moderately shade-tolerant Quercus rubra L. and shade-tolerant Acer rubrum L. Seedlings were grown in full sun or 26% of full sun (shade) and in ambient (350 ppm) or elevated (714 ppm) CO(2) for 80 days. In the shade treatments, 80% of the daily PPFD on cloud-free days was provided by two 30-min sun patches at midday. In Q. rubra and A. rubrum, leaf N concentration and alpha(r) were significantly higher in seedlings in the shade treatments than in the sun treatments, and leaf N concentration was lower in seedlings in the ambient CO(2) treatments than in the elevated CO(2) treatments. Changes in alpha(r) and leaf N content suggest that reapportionment of leaf N into light harvesting machinery in response to shade and elevated CO(2) tended to increase with increasing shade tolerance of the plant. Shifts induced by elevated CO(2) in the A/PPFD relationship in sun plants were largest in B. papyrifera and least in A. rubrum: the reverse was true for shade plants. Elevated CO(2) resulted in increased light-saturated A in every species x light treatment combination, except in shaded B. papyrifera. The light compensation point (Gamma) decreased in response to shade in all species, and in response to elevated CO(2) in A. rubrum and Q. rubra. Acer rubrum had the greatest increases in apparent quantum yield (phi) in response to shade and elevated CO(2). To illustrate the effects of shifts in A, Gamma and phi on daily C gain, daily integrated C balance was calculated for individual sun and shade leaves. Ignoring possible stomatal effects, estimated daily (24 h) leaf C balance was 218 to 442% higher in the elevated CO(2) treatments than in the ambient CO(2) treatments in both sun and shade seedlings of Q. rubra and A. rubrum. These results suggest that the ability of species to acclimate photosynthetically to elevated CO(2) may, in part, be related to their ability to adapt to low irradiance. Such a relationship has implications for altered C balance and nitrogen use efficiency of understory seedlings.

Response of Spawning Lake Sturgeons to Change in Hydroelectric Facility Operation

Abstract: Spawning of lake sturgeon Acipenser fulvescens was documented from 1987 to 1992 below the Prickett hydroelectric facility on the Sturgeon River, a tributary to Portage Lake, Michigan. Lake sturgeons were captured at the spawning site with dip nets during periods of reduced flow. A change in the spawning characteristics of the population was noted that corresponded to a change in the operation of the hydroelectric facility. In 1987 and 1988 the facility operated in a peaking mode, which resulted in large daily fluctuations in river flows. The years 1989 and 1990 were years of transition, and in 1991 and 1992 the facility released near run-of-the-river (ROR) flows. Under near-ROR flows, which were more natural, adult lake sturgeons spent 4–6 weeks less at the spawning sites, 74% more fish were observed, weights were greater due to a 68% increase in number of females, and fish had increased reproductive readiness. The change in flow regime was the result of a Federal Energy Regulatory Commission rel...

Nitrate Reductase Biochemistry Comes of Age.

Abstract: NR (EC 1.6.6.1-3) was first isolated and characterized more than 40 years ago, and each decade of study of this key enzyme of nitrate assimilation has been associated with a new understanding of its structure and function. Briefly, NR is a homodimeric enzyme (native form = A,) with each subunit containing a 100-kD polypeptide and one each of molybdate, Mo-pterin, Fe, heme, and FAD (Redinbaugh and Campbell, 1985). NR has two active sites, one where NADH donates electrons to FAD to begin the transport of electrons via the heme-Fe to the Mo / Mo-pterin in the second active site, where nitrate is reduced to nitrite. NR has two-site, ping-pong, steady-state kinetics, where the enzyme “pings and pongs” between oxidized and reduced forms, as NADH/NADC bind at the electron donor active site and nitrate/nitrite bind at the electron acceptor site. The most recent advances have resulted from the cloning of the NR gene (Campbell and Kinghorn, 1990; Solomonson and Barber, 1990; Rouze and Caboche, 1992). The deduced amino acid sequence of higher-plant NR showed that it contained about 900 residues with a predicted molecular size of approximately 100 kD. Although this size is a bit smaller than the NR polypeptide appears on SDS-PAGE gels (110-115 kD; Redinbaugh and Campbell, 1985), this may be explained by the runs of acidic residues near the N terminus of well-characterized and sequenced NR forms such as squash (Hyde et al., 1991). In this general review, I will focus on recent advances in NR biochemistry. I last reviewed this topic in a general way in 1988 (Campbell, 1988). Reviews by Solomonson and Barber (1990), Rouze and Caboche (1992), and Crawford (1995) provide more detailed accounts of various aspects of this topic than will be presented here. Recently, Kaiser and Huber (1994) reviewed posttranslational regulation of NR in an Update.

Mechanical deformation of dendrites by fluid flow

Abstract: It is generally accepted that liquid agitation during alloy solidification assists in crystal multiplication, as in dendrite fragmentation and the detachment of side arms in the mushy region of a casting. Even without deliberate stirring by electromagnetic or mechanical means, there is often vigorous interdendritic fluid flow promoted by natural thermosolutal convection. Interdendritic fluid flow rates in metals might be as high as 10 mm s{sup {minus}1}. It is the purpose of this article to examine whether such fluid flow can cause mechanical deformation of dendrites, sufficient to cause side arms to bend or break. Metals are so ductile at their melting points that applied forces could only be expected to cause bending, as opposed to fracture, although there are no reports of which the authors are aware of dendritic arms being mechanically bent in this way. The following estimates demonstrate why even bending is not to be expected. In this analysis, the authors shall estimate the stress at the root of a secondary dendrite arm of aluminum arising from the action of a flow of molten metal past the dendrite arm.

Analytical and empirical evaluation of software reuse metrics

Abstract: How much can be saved by using existing software components when developing new software systems? With the increasing adoption of reuse methods and technologies, this question becomes critical. However, directly tracking the actual cost savings due to reuse is difficult. A worthy goal would be to develop a method of measuring the savings indirectly by analyzing the code for reuse of components. The focus of the paper is to evaluate how well several published software reuse metrics measure the "time, money and quality" benefits of software reuse. We conduct this evaluation both analytically and empirically. On the analytic front, we introduce some properties that should arguably hold of any measure of "time, money and quality" benefit due to reuse. We assess several existing software reuse metrics using these properties. Empirically, we constructed a toolset (using GEN+S) to gather data on all published reuse metrics from CS+ code; then, using some productivity and quality data from "nearly replicated" student projects at the University of Maryland, we evaluate the relationship between the known metrics and the process data. Our empirical study sheds some light on the applicability of our different analytic properties, and has raised some practical issues to be addressed as we undertake broader study of reuse metrics in industrial projects.

A comparison of forest gap models : Model structure and behaviour

Abstract: Forest gap models share a common structure for simulating tree population dynamics, and many models contain the same or quite similar ecological factors. However, a wide variety of formulations are being used to implement this general structure. The comparison of models incorporating different formulations is important for model validation, for assessing the reliability of model projections obtained under scenarios of climatic change, and for the development of models with a wide range of applicability. This paper reviews qualitative and quantitative comparisons of the structure and behaviour of forest gap models.

Optimization of Long-Term Stability of Magnetic Fluids from Magnetite and Synthetic Polyelectrolytes

Abstract: Nanometer-sized suspensions of magnetite (Fe3O4) stabilized with polymeric surfactants, principally poly(methacrylic acid) (PMAA), were prepared by precipitation or sonication and studied by a variety of techniques. The long-term stability of the ferrofluids made with PMAA was optimal at pH 7 (close to the measured isoelectric point of the magnetite, 5.9) and improved at all pH values with increasing surfactant concentration. With extended times of sonication the molecular weight and polydispersity of the PMAA decreased, although magnetite in the ferrofluid was not oxidized (X-ray). Particle diameters of 9-38 nm were measured by saturation magnetization, electron microscopy, and dynamic light scattering. Centrifugation at 8,000 rpm removed the magnetite from the suspensions together with roughly one molecule of PMAA for each magnetite particle in the fluid, with the average number increasing with higher concentrations and average molecular weights of the polymer.

t-Covering Arrays: Upper Bounds and Poisson Approximations

Abstract: A k×n array with entries from the q-letter alphabet {0, 1, …, q − 1} is said to be t-covering if each k × t submatrix has (at least one set of) qt distinct rows. We use the Lovasz local lemma to obtain a general upper bound on the minimal number K = K(n, t, q) of rows for which a t-covering array exists; for t = 3 and q = 2, we are able to match the best-known such bound. Let Kλ = Kλ(n, t, q), (λ ≥ 2), denote the minimum number of rows that guarantees the existence of an array for which each set of t columns contains, amongst its rows, each of the qt possible ‘words’ of length t at least λ times. The Lovasz lemma yields an upper bound on Kλ that reveals how substantially fewer rows are needed to accomplish subsequent t-coverings (beyond the first). Finally, given a random k × n array, the Stein–Chen method is employed to obtain a Poisson approximation for the number of sets of t columns that are deficient, i.e. missing at least one word.

Root growth and physiology of potted and field-grown trembling aspen exposed to tropospheric ozone.

Abstract: We studied root growth and respiration of potted plants and field-grown aspen trees (Populus tremuloides Michx.) exposed to ambient or twice-ambient ozone. Root dry weight of potted plants decreased up to 45% after 12 weeks of ozone treatment, and root system respiration decreased by 27%. The ozone-induced decrease in root system respiration of potted plants was more closely correlated with decreased root dry weight than with specific root respiration, suggesting that aspen root metabolism was less affected by ozone than root growth. We used minirhizotrons to study the appearance and disappearance of roots in the field. Length of live roots of field-grown trees increased rapidly early in the season and peaked by midseason in association with a decrease in root production and an increase in root disappearance. In the twice-ambient ozone treatment, live root lengths were 17% less than those of controls, but the effect was not statistically significant. Seasonal soil CO(2) efflux of field-grown trees decreased significantly in the ozone treatments, but because differences in live root length were not significant and root dry weights were not available, the effect on CO(2) efflux could not be attributed directly to decreased root growth.

Bounding elastic constants of an orthotropic polycrystal using measurements of the microstructure

Abstract: We show how information about the elastic stiffness and compliance of an orthotropic polycrystal may be obtained from measurements of the statistical properties of the microstructure We begin by discussing the statistical properties of the governing equations and the hierarchy that results when the equations are averaged Perturbation solutions are obtained in terms of low-order statistical information Using methods previously developed, we derive bounds for the elastic stiffnesses and compliances A hierarchy of bounds is derived using the statistical information obtained from measurement of the microstructure We discuss the methods used to obtain the correlation functions of the microstructure and provide a specific example, using data obtained from a copper sample

Methods for comparing a DNA sequence with a protein sequence

Abstract: We describe two methods for constructing an optimal global alignment of, and an optimal local alignment between, a DNA sequence and a protein sequence. The alignment model of the methods addresses the problems of frameshifts and introns in the DNA sequence. The methods require computer memory proportional to the sequence lengths, so they can rigorously process very huge sequences. The simplified versions of the methods were implemented as computer programs named NAP and LAP. The experimental results demonstrate that the programs are sensitive and powerful tools for finding genes by DNA-protein sequence homology.

Linear Solvation Energy Relationship of the Limiting Partition Coefficient of Organic Solutes between Water and Activated Carbon

Abstract: A linear solvation energy relationship has been found for 353 values of the limiting adsorption coefficients of diverse chemicals: log K = −0.37 + 0.0341Vi − 1.07β + D + 0.65P with R = 0.951, s = 0.51, n = 353, and F = 818.0, where Vi is the intrinsic molar volume; β is a measure of the hydrogen bond acceptor strength of the solute; D is an index parameter for the research group which includes the effects of the different types of carbon used, the temperature, and the length of time allowed for the adsorption equilibrium to be established; and P is an index parameter for the flatness of the molecule. P is defined to be unity if there is an aromatic system in the molecule or if there is a double bond or series of conjugated double bonds with no more that one non-hydrogen atom beyond the double bond and zero otherwise. A slightly better fit is obtained if the two-thirds power of Vi is used as a measure of the surface area in place of the volume term: log K = −1.75 + 0.227V2/3 − 1.10β + D + 0.60P with R = ...

Watercress Allelochemical Defends High‐Nitrogen Foliage Against Consumption: Effects on Freshwater Invertebrate Herbivores

Abstract: Watercress (Nasturtium officinale) is a spring-stream macrophyte that pos- sesses glucosinolates, which are hydrolyzed to feeding deterrent isothiocyanates when the enzyme myrosinase is released by tissue damage. Previous studies indicated that frequently associated aquatic shredders strongly prefer yellowed-senescent leaves over fresh-green foliage, because the latter releases much more isothiocyanate than senescent watercress. When the action of myrosinase was blocked by heating the tissue, the shredders' preference shifted to heated-green tissue, which contains much more nitrogen than that found in senescent tissue. Here we report a series of no-choice experiments on various tissue types designed to determine intermediate and long-term consumption rates and associated impacts on growth and survival of shredders associated with watercress. The amphipod Gammarus pseudo- limnaeus, the caddisflies Pycnopsyche sp., Hesperophylax designatus, and Limnephilus sp., and the snail Physella gyrina, all consumed much more senescent than fresh-green tissue. In long-term tests with G. pseudolimnaeus, H. designatus, and Limnephilus sp., growth was negative or zero on the defended fresh-green tissue and often highest on heated-green tissue. Reaction to glucosinolates differed among shredders. For the caddisflies, growth and survival were positively correlated with bulk tissue and nitrogen consumption, which were highest for heated-green tissue. However, amphipod survival was significantly lowered on heated- green watercress, although it was readily consumed. Therefore, consumption of high-glu- cosinolate tissue was detrimental to the amphipods but not to caddisflies. Our results indicate that the glucosinolate-myrosinase system defends live green wa- tercress against herbivory by an array of aquatic invertebrates. These generalist herbivores forgo eating high-quality fresh-green leaves because of plant defenses and instead settle for lower quality senescent leaves. When the defense system was experimentally shut down, these herbivores readily consumed young green tissue and frequently showed higher growth rates than those achieved on the senescent, but undefended, leaves they typically consume. Evidently, these shredders face a trade-off of high nitrogen and high defense vs. low nitrogen and low defense.

Characterization of fuel and aftertreatment device effects on diesel emissions.

Abstract: Heavy-duty diesel engines operated with a low-sulfur (LS)* fuel and either a particle trap or an oxidation catalytic converter (OCC) have been studied during steady-state operation (and during regeneration of the particle trap) to determine the effects of these devices on regulated and unregulated emissions, including the chemical and biological character of the exhaust. This study consisted of two phases, both of which were designed to determine the effects of fuel, particle control system, and engine type on (1) levels of regulated emissions such as oxides of nitrogen (NOx), total hydrocarbons (HC), and total particulate matter (TPM); (2) levels of unregulated emissions such as particle-associated soluble organic fraction (SOF), sulfate (SO4), solids (SOL), and the vapor-phase organic fraction collected on XAD-2 resin (XOC); (3) levels of selected mutagenic and carcinogenic polynuclear aromatic hydrocarbons (PAHs) in the particle-associated and vapor-phase organic fractions; (4) mutagenic activity associated with the same organic fractions; and (5) exhaust particle size distributions. Phase I involved a 1988 Cummins Engine Co. LTA 10-300 (L10) engine equipped with a ceramic particle trap having built-in regeneration controls. Phase II involved a 1991 prototype Cummings Engine Co. LTA 10-310 (LTA) engine equipped with an OCC. The 1991 LTA engine also contained a higher pressure fuel-injection system than the 1988 L10 engine and used an intake charge air-to-air aftercooling system, instead of the intake air-intercooler system on the 1988 engine.

Sulphur emissions to the stratosphere from explosive volcanic eruptions

Abstract: Two methods were used to quantify the flux of volcanic sulphur (as the equivalent mass of SO2) to the stratosphere over different timescales during the Holocene. A combination of satellite-based measurements of sulphur yields from recent explosive volcanic eruptions with an appropriate rate of explosive volcanism for the past 200 years constrains the medium-term (∼102 years) flux of volcanic sulphur to the stratosphere to be ∼1 Mt a–1, with lower and upper bounds of 0.3 and 3 Mt a–1. The short-term (∼10- to 20-year) flux due to small magnitude (1010–1012 kg) eruptions is of the order of 0.4 Mt a–1. At any time the instantaneous levels of sulphur in the stratosphere are dominated by the most recent (0–3 years) volcanic events. The flux calculations do not attempt to address this very short timescale variability. Although there are significant errors associated with the raw sulphur emission data on which this analysis is based, the approach presented is general and may be readily modified as the quantity and quality of the data improve. Data from a Greenland ice core support these conclusions. Integration of the sulphate signals from presumed volcanic sources recorded in the GISP2 core provides a minimum estimate of the 103–year volcanic SO2 flux to the stratosphere of 0.5–1 Mt a–1 over the past 9000 years. The short-term flux calculations do not account for the impact of rare, large events. The ice-core record does not fully account for the contribution from small, frequent events.

Cracks in gradient elastic bodies with surface energy

Abstract: In the present paper the effect of higher order gradients on the structure of line-crack tips is determined. In particular we introduce in the constitutive equations of the linear deformation of an elastic solid a volumetric energy term, which includes the contribution of the strain gradient, and a surface energy gradient dependent term and then determine the effect of these terms on the structure of the mode-III crack tip and the associated stress and strain fields. By making use of the solution in terms of Fourier transform of the equation of elastic equilibrium we solve the half-plane boundary value problems of: (a) specified tractions, and (b) prescribed displacements, along the crack surface, respectively.

Improving software pipelining with unroll-and-jam

Abstract: To take advantage of recent architectural improvements in microprocessors, advanced compiler optimizations such as software pipelining have been developed. Unfortunately, not all loops have enough parallelism in the innermost loop body to take advantage of all of the resources a machine provides. Unroll-and-jam is a transformation that can be used to increase the amount of parallelism in the innermost loop body by making better use of resources and limiting the effects of recurrences. We demonstrate how unroll-and-jam can significantly improve the initiation interval in a software-pipelined loop. Improvements in the initiation interval of greater than 40% are common, while dramatic improvements of a factor of 5 are possible.