Showing papers by "University of Illinois at Urbana–Champaign published in 1982"

Mathematical foundations of elasticity

Abstract: [Preface] This book treats parts of the mathematical foundations of three-dimensional elasticity using modern differential geometry and functional analysis. It is intended for mathematicians, engineers, and physicists who wish to see this classical subject in a modern setting and to see some examples of what newer mathematical tools have to contribute.

Mechanics of Transformation‐Toughening in Brittle Materials

Abstract: Particles which undergo a stress-induced martensitic transformation are known to toughen certain brittle materials. The enhanced toughness can be considered to originate from the residual strain fields which develop following transformation and tend to limit the crack opening. The increased toughness can estimated from the crack-tip stress-intensity change induced by the transformation of a volume of material near the crack tip. It is found that the initial zone, prior to crackgrowth, provides no change in stress intensity. As the crack grows, the zone (associated with a positive transformation strain) induces a stress-intensity reduction that rises to a maximum level after some crack propagation. The influence of particle-size distribution on the stress-intensity reduction is also discussed.

Radio wave scintillations in the ionosphere

Abstract: The phenomenon of scintillation of radio waves propagating through the ionosphere is reviewed in this paper. The emphasis is on propagational aspects, including both theoretical and experimental results. The review opens with a discussion of the motivation for stochastic formulation of the problem. Based on measurements from in-situ, radar, and propagation experiments, ionospheric irregularities ate found to be characterized, in general, by a power-law spectrum. While earlier measurements indicated a spectral index of about 4, there is recent evidence showing that the index may vary with the strength of the irregularity and possibly a two-component spectrum may exist with different spectral indices for large and small structures. Several scintillation theories including the Phase Screen, Rytov, and Parabolic Equation Method (PEM) are discussed next. Statistical parameters of the signal such as the average signal, scintillation index, rms phase fluctuations, correlation functions, power spectra, distributions, etc., are investigated. Effects of multiple scattering are discussed. Experimental results concerning irregularity structures and signal statics are presented. These results are compared with theoretical predictions. The agreements are shown to be satisfactory in a large measure. Next, the temporal behavior of a transionospheric radio signal is studied in terms of a two-frequency mutual coherence function and the temporal moments. Results including numerical simulations are discussed. Finally, some future efforts in ionospheric scintillation studies in the areas of transionospheric communication and space- and geophysics are recommended.

Theory and Analysis of Threshold Characters

Abstract: Summary This paper deals with theory, methods and problems in the analysis of categorical data in animal breed/ng when a threshold model is postulated foi an underlying normal distribution of phenotypes Linear and nonlinear statistical models potentially useful for estimating parameters of the underlying and outward distributions are reviewed and extended Methods for evaluating the genetic value of candidates for selection from single or multiple populations are discussed comparatively

Systematics of multilayer adsorption phenomena on attractive substrates

Abstract: This paper presents a systematic classification of multilayer-adsorption phenomena on attractive substrates, with emphasis on the buildup of thick films. The approach is based on statistical mechanics and includes adsorption-desorption effects and the interrelation of bulk and surface behavior. The surface phase diagram depends qualitatively on the relative strengths and ranges of adatom-adatom and adatom-substrate attractions. When the adatom-substrate attraction dominates (strong substrate), the film builds up uniformly, as the bulk adatom density increases, and the excess surface density diverges at coexistence (complete wetting). The buildup proceeds via an infinite sequence of discrete layer transitions (layering) at low temperatures (below the roughening temperature ${T}_{R}$ and smoothly at higher temperatures, as originally noted by de Oliveira and Griffiths. Substrates of intermediate strength are characterized by a wetting temperature ${T}_{W}$ above which wetting at coexistence is approached. The relative values of ${T}_{W}$ and ${T}_{R}$ define three subregions: When ${T}_{W}l{T}_{R}$ layering occurs, with an infinite sequence of transitions between ${T}_{W}$ and ${T}_{R}$ when ${T}_{R}\ensuremath{\lesssim}{T}_{W}$, layer transitions have coalesced into a single thick-film\char22{}thin-film transition (prewetting); when ${T}_{R}\ensuremath{\ll}{T}_{W}$, prewetting may disappear, leaving only a critical-wetting transition on the coexistence axis. For still weaker substrates, wetting is incomplete at all temperatures; however, a variety of drying phenomena may occur on the high-density side of bulk coexistence. Specific calculations are given for a lattice-gas model at $T=0$ and in the mean-field approximation. Conclusions are informed, in addition, by certain exact results and symmetries. The last section includes a critical discussion of the relation of the lattice-gas model to the real world and a brief review of relevant experimental data.

Industry influences on strategy reformulation

Abstract: This paper emphasizes the contribution of ‘borrowed experience’ to strategy reformulation. The industry group is described as a particularly important arena in which niche-related problems and solutions are identified and tested. Industry-wide mistakes in environmental interpretation and strategic response provide interesting evidence of the importance of this contribution to organizational decision making. An industry oriented view of strategy reformulation requires two kinds of research which are rarely conducted today. We need to know more about the pool of strategic concepts which a group of organizations holds in common at any given time. Spender's study of fork-lift truck rental companies is reviewed as an example of this kind of work. A second kind of needed research involves change in strategic concepts over time. A study of the perceived import threat to the appliance industry from 1950 to 1975 is summarized as an example of this second kind of research.

Composites of aluminium alloys: fabrication and wear behaviour

Abstract: In this paper processes for fabrication of aluminium-alloy composites containing paniculate non-metals, the net shape forming of these composites, their microstructures, their friction and wear behaviours and their mechanical properties are described. Composites of two wrought (2014 and 2024) and one cast (201) aluminium alloys containing 2 to 30 wt% of Al2O3 and SiC particles in the size range of 1 to 142μm were prepared. The non-metallic particles were added to a partially-solid vigorously-agitated matrix alloy. The particles were then retained in the matrix until interface interaction, for example, the formation of MgAl2O4 spinel in the case of Al2O3 particles, were faciliated. These composites were solidified and subsequently reheated to above their liquidus temperature and formed under high pressure in a closed-die forging type of apparatus. Composites with particulate additions of size larger than 5μm possessed homogeneous structures; particles of size 1μm, however, tended to cluster. The wear behaviour of the composites was studied using a pin-on-disc type machine. It was shown that composites containing large amounts of non-metals, ≈ 20 wt%, exhibit excellent wear resistance whilst those with small to moderate amounts of non-metals possess tensile properties comparable to the matrix alloy. Increasing the amount of particulate additions results in reduced ductility. Finally, a method was investigated of producing components with high weight-fractions of non-metals near their surface.

Luteinizing Hormone-Releasing Hormone Release during the Rat Estrous Cycle and after Ovariectomy, as Estimated with Push-Pull Cannulae

Abstract: A push-pull perfusion (PPP) system was used to carry out the first examination of LHRH release from the mediobasal hypothalami (MBH) of conscious, freely moving rats during stages of the estrous (E) cycle and after ovariectomy (Ovx). Female rats received push-pull cannula (PPC) implants into the MBH and then were allowed to recover for 2–10 weeks before PPP experiments. During that time, E cycles were determined by daily inspection of vaginal smears. After exhibiting two consecutive E cycles, rats were fitted with indwelling jugular catheters between 0830–1030 h and subjected to PPP of the MBH and hourly bleeding for more than 6 h. LHRH and LH levels were determined by RIA in perfusates and plasma, respectively. PPP and bleeding sessions were performed on the afternoon of proestrus (Pro; n – 10), diestrous day I (DI; n – 5), diestrous day II (DII; n – 5), estrus (E; n – 5), or more than 28 days after Ovx (n – 5). LHRH output was detectable in at least some samples in all rats whose PPC tips resided within...

Ascorbic Acid and Vitamin A Activity in Selected Vegetables from Different Geographical Areas of the United States

Abstract: Reduced ascorbic acid (RAA) and Vitamin A (carotenoid) contents of six vegetables obtained from six cities in the United States at two seasons of the year were determined. Mean RAA content (mg/lOOg) of cabbage was 45.2, carrots 7.8, celery 6.0, corn 6.5, onions 8.4, and tomatoes 15.3. Vitamin C in cooked cabbage was 22.1, corn 6.2, and onions 5.7 mg/100g. Mean vitamin A activity (I.U.) of car- rots was 15,228, cabbage 114, celery 133, corn 219, and tomatoes 750. In cooked cabbage and corn, vitamin A content was 89 and 217 I.U., respectively. The RAA and vitamin A content of vege- tables from the six geographical areas varied significantly. Vitamin concentrations were generally lower than tabulated values. Reten- tion of RAA in cooked cabbage was 52%; in onions, 58%; and in corn, 98%. Vitamin A retention in cooked cabbage was 82%, and in cooked corn was 98%. cities, at two different seasons. The vegetables were obtained from six different areas in the United States: West (Seattle and Denver), Midwest (St. Louis and Minneapolis), and East (Boston and Atlanta), at two different times of the year. The source of the vegetables, including the gowing area (when known), and the months they were obtained, are given in Table 1. Produce typical of that being sold in each area was shipped directly to the University of Illinois via air freight to Champaign-Urbana, IL, stored at 4"C, and pre- pared for analysis within 48 hr of shipment. Tomatoes in some cases were held at room temperature (24°C) to ripen. The times and conditions during shipping were similar to what is encountered in transport from warehouses to market outlets. Sampling procedures All vegetables were analyzed raw, and cabbage, corn and onions were also cooked and analyzed. The vegetables were trimmed, peeled if necessary, washed in deionized distilled (DD) water, and blotted dry. Approximately 15-20 kg of each vegetable were sliced (carrots, celery, onions) or cut in eighths (tomatoes, cabbage). The samples for cooking and analyses were drawn from these com- posites. Approximately 7.5-10 kg of each vegetable were cooked by the methods given below. The cooked vegetables were combined and samples drawn from the composite for nutrient assay. Corn was husked, rinsed and blotted dry, and then cut from the cob for the raw samples. Corn was cooked on the cob and the kernels removed for the cooked samples. All cutting implements used were stainless steel, and care was taken to avoid contamination with minerals. Duplicate or triplicate determinations were performed for every nutrient for each raw or cooked vegetable at each sampling period from all of the geographical areas. Cooking methods

Vibrational dephasing and frequency shifts of polyatomic molecules in solution

Abstract: A theory for the effects of repulsive and spatially slowly varying attractive forces on the vibrational frequency and dephasing of polyatomic molecular liquids is developed. Thermodynamic state dependence of these features is of particular interest because of the competition between the two types of forces. Solvent shifts of vibrational lines are computed. Proper separation of the rapidly and slowly varying branches of the intermolecular potentials leads to a separation of time scales that allows the dephasing relaxation to be computed using a combination of binary collision and mean field ideas. The question of homogeneous vs inhomogeneous broadening of the isotropic Raman line is addressed. The theory is applied to several polyatomic fluids with special emphasis on the isothermal density dependence of the spectral features. Agreement with experiment is good. The slowly varying attractive forces are found to play a significant role in determining the Raman linewidth for all the systems studied. Comparison with previous theories is made.

Microbial removal of hazardous organic compounds

Abstract: An in-depth evaluation of the potential for microorganisms to remove anthropogenic organic compounds, mainly priority pollutants and related compounds, is presented. The evaluation indicates that use of properly selected populations of microbes, and the maintenance of environmental conditions most conducive to their metabolism, can be an important means of improving biological treatment of organic wastes. One major theme is that microorganisms not normally associated with biological waste treatment have potential advantages when the removal of anthropogenic compounds is the goal. An extensive summary of examples of anthropogenic compounds and microorganisms that can attack them is presented in tabular form. A second table lists the selective uses of microorganisms for removal of different anthropogenic compounds. (KRM)

Concurrent Error Detection in ALU's by Recomputing with Shifted Operands

Abstract: A new method of concurrent error detection in the Arithmetic and Logic Units (ALU's) is proposed. This method, called "Recomputing with Shifted Operands" (RESO), can detect errors in both the arithmetic and logic operations. RESO uses the principle of time redundancy in detecting the errors and achieves its error detection capability through the use of the already existing replicated hardware in the form of identical bit slices. It is shown that for most practical ALU implementations, including the carry-lookahead adders, the RESO technique will detect all errors caused by faults in a bit-slice or a specific subcircuit of the bit slice. The fault model used is more general than the commonly assumed stuck-at fault model. Our fault model assumes that the faults are confined to a small area of the circuit and that the precise nature of the faults is not known. This model is very appropriate for the VLSI circuits.

Photosynthetic acclimation to variability in the light environment of early and late successional plants.

Abstract: Fourteen plant species from early-, mid-, and late-successional habitats were grown for a period of 25 to 50 days in each of two light environments, i.e. full sunlight and in deep shade. The rate of photosynthesis for newly formed leaves was measured as a function of light intensity for plants from each light environment. Photosynthetic flexibility, measured as the difference in response between sun- and shade-grown plants, was determined for each of 5 parameters including dark respiration, quantum yield, light compensation, half-saturating irradiance for photosynthesis, and the photosynthetic rate at 1,400 μE m-2 s-1. We found photosynthetic flexibility to be high for early successional annuals, intermediate for midsuccessional species, and low for late successional species.

Error Probability for Direct-Sequence Spread-Spectrum Multiple-Access Communications--Part II: Approximations

Abstract: Approximations are obtained for the average probability of error in an asynchronous direct-sequence spread-spectrum multiple-access communications system. Both binary and quaternary systems are considered, and the chip waveforms are allowed to be arbitrary time-limited waveforms with time duration equal to the inverse of the chip rate. The approximation is based on the integration of the characteristic function of the multiple-access interference. The amount of computation required to evaluate this approximation grows only linearly with the product of the number of simultaneous transmitters and the number of chips per bit. The accuracy of the approximation is extremely good in most cases, but it can be improved, if necessary, by an application of a series expansion. Numerical results are presented for specific chip waveforms and signature sequences.