Showing papers by "Iowa State University published in 1984"
TL;DR: In this article, the percentiles of the distributions for time series that have unit roots at the seasonal lag are computed by Monte Carlo integration for finite samples and by analytic techniques and Monte-Carlo integration for the limit case.
Abstract: Regression estimators of coefficients in seasonal autoregressive models are described. The percentiles of the distributions for time series that have unit roots at the seasonal lag are computed by Monte Carlo integration for finite samples and by analytic techniques and Monte Carlo integration for the limit case. The tabled distributions may be used to test the hypothesis that a time series has a seasonal unit root.
635 citations
TL;DR: In this paper, the authors present a model of adoption behavior and explain differences econometrically in farmers' decisions to adopt reduced-tillage practices and in the efficiency of farmers' adoption decisions.
Abstract: This paper presents a model of adoption behavior and explains differences econometrically in farmers' decisions to adopt reduced‐tillage practices and in the efficiency of farmers' adoption decisions. The empirical results, obtained from microdata, show that the probability of adopting reduced tillage in corn enterprises differs widely across farms and depends on soil characteristics, cropping systems, and size of farming operation. The results also show that farmers' schooling enhances the efficiency of the adoption decision.
611 citations
01 Jan 1984
TL;DR: In this paper, the authors consider ways to combine sets of data for the purpose of estimation that may violate a basic assumption of the linear regression model, and they focus on models with parameters that vary in some systematic and/or random way across partitions of the sample data, even from observation to observation.
Abstract: In this and the following chapter we consider ways to combine sets of data for the purpose of estimation that may violate a basic assumption of the linear regression model. Specifically, we will study cases when it cannot be assumed that the structural parameters are identical for all observations in a sample of data. Frequently these problems occur when a data set consists of series of observations over time on cross-sectional units. Many of the topics discussed in this chapter can or do apply directly to the pooling of time series and cross-sectional data, but the primary discussion of that topic is contained in Chapter 15. In this chapter we focus on models with parameters that vary in some systematic and/or random way across partitions of the sample data, even from observation to observation.
608 citations
01 Jan 1984
TL;DR: Starch granules range in size from sub-micron elongated granules of chloroplasts to the relatively huge oval granule of potato and canna as discussed by the authors, and these differences in size and shape make it possible to recognize most of the ordinary food and commercial starches.
Abstract: Publisher Summary
Starch granules range in size from sub-micron elongated granules of chloroplasts to the relatively huge oval granules of potato and canna. Semi-compound granules originate as two or more distinct granules, which then fuse together. Pseudo-compound granules, such as pea starch granules, start out as individual granules, which then develop several large cracks while remaining a single entity. These differences in size and shape make it possible to recognize most of the ordinary food and commercial starches. Starch granules contain small amounts of non-carbohydrate components—lipids, proteins, phosphate, and ash—that affect the behavior of starch in various applications. The tiny starch granules of chloroplasts are important as a temporary carbohydrate reserve and show diurnal synthesis and degradation. Native starch granules show growth rings when observed by optical microscopy, scanning electron microscopy of eroded granules, and transmission electron microscopy of thin sections, especially after chemical treatment. Starches that show prominent growth rings, such as potato starch, require high or saturating water levels for ring visibility.
517 citations
TL;DR: In this article, the true values of the variance ratios are replaced by estimated values, and the mean squared errors of the estimators of the fixed and random effects increase in size.
Abstract: Best linear unbiased estimators of the fixed and random effects of mixed linear models are available when the true values of the variance ratios are known. If the true values are replaced by estimated values, the mean squared errors of the estimators of the fixed and random effects increase in size. The magnitude of this increase is investigated, and a general approximation is proposed. The performance of this approximation is investigated in the context of (a) the estimation of the effects of the balanced one-way random model and (b) the estimation of treatment contrasts for balanced incomplete block designs.
483 citations
TL;DR: In this article, a quasi-static model for ultrasonic transmission and reflection at imperfect interfaces is developed, where the interface is represented by a distributed spring determined by the change in static compliance of the medium with respect to one with a perfect interface, and a distributed mass, representing excess mass at the interface.
Abstract: A quasi-static model for the ultrasonic transmission and reflection at imperfect interfaces is developed. The interface is represented by a distributed spring, determined by the change in static compliance of the medium with respect to one with a perfect interface, and a distributed mass, representing excess mass at the interface. Comparison of the model predictions to exact solutions for two simple cases illustrates its accuracy at low frequencies. The spring stiffnesses can be derived from existing solutions for the elastic displacement of materials containing cracks and inclusions under static load. Results for a variety of cases are reviewed. Applications of the model to study the characteristics of partially contacting surfaces in several problem areas of current interest are discussed.
373 citations
TL;DR: In this article, a theoretical model based on the Hunt model is developed, and it is found that the theory adequately explains the variation in primary spacing, λ 1, with the growth rate,V.
Abstract: The primary spacing data of Part I are compared to the existing theoretical models of Hunt and of Kurz and Fisher, and a significant disagreement is found. A theoretical model based on the Hunt model is developed, and it is found that the theory adequately explains the variation in primary spacing, λ1, with the growth rate,V. A maximum in λ1,vs V is predicted and the velocity at which the maximum occurs matches with the result obtained experimentally. It is shown that the maximum in λ1 corresponds to the dendrite-to-cell transition, and cellular structures are found to grow with much smaller spacings than dendritic structures under identical growth conditions.
355 citations
TL;DR: A structure for retrograded amylose is proposed in which there are crystalline, double-helical regions that are 10 nm long, interspersed with amorphous regions, which are hydrolyzed by acid and by alpha amylases, leaving the crystalline regions intact.
320 citations
TL;DR: This paper disproves a conjecture made by Even and Yacobi (1980) that would imply nonexistence of public-key cryptosystems with NP-hard cracking problems and raises a new conjecture that implies that NP-complete sets cannot be accepted by Turing machines that have at most one accepting computation for each input word.
Abstract: A “promise problem” is a formulation of partial decision problem. Complexity issues about promise problems arise from considerations about cracking problems for public-key cryptosystems. Using a notion of Turing reducibility between promise problems, this paper disproves a conjecture made by Even and Yacobi (1980) , that would imply nonexistence of public-key cryptosystems with NP-hard cracking problems. In its place a new conjecture is raised having the same consequence. In addition, the new conjecture implies that NP-complete sets cannot be accepted by Turing machines that have at most one accepting computation for each input word.
309 citations
TL;DR: Plasma vitamin A levels in the plasma are not good indicators of vitamin A status, except in cases of deficiency or excess.
Abstract: Of the total body reserve of vitamin A, the liver is the major repository (greater than or equal to 90%); plasma contains only 1% of the total amount. Although the median liver concentration in well-nourished American adults is approximately 100 micrograms/g, a minimally adequate concentration is suggested to be 20 micrograms/g. Physiologic, nutritional, clinical, and genetic factors affect plasma retinol levels by a variety of mechanisms. Of total body carotenoids, most are associated with adipose tissue (greater than 80%), and a lesser amount is associated with liver (10%). Vitamin A concentrations in the liver are low at birth but then rise to adult levels at 1-4 years of age. Liver carotenoid concentrations are not proportional to liver vitamin A reserves. Total liver retinol is proportional to dietary retinol but not in a purely linear fashion. When liver reserves exceed 30 micrograms/g, the excretion of vitamin A metabolites in bile is much increased. Plasma vitamin A is homeostatically controlled over the physiologic range of liver vitamin A concentrations, e.g., 20-300 micrograms/g. Below 20 micrograms/g liver, plasma vitamin A values tend to fall; above 300 micrograms/g liver, plasma values tend to increase. At very high intakes, plasma vitamin A values can be greater than or equal to 300 micrograms/dl. In such cases most of the plasma vitamin A is in the form of retinyl ester. Thus, except in cases of deficiency or excess, vitamin A levels in the plasma are not good indicators of vitamin A status. Other methods of evaluating vitamin A status include relative dose response, analysis of liver autopsy or biopsy samples, isotope-dilution approach, and pseudoequilibrium approach. The first two of these methods have proven to be very useful in specific circumstances, whereas the others are under development.
261 citations
TL;DR: In this article, a scaling law is shown to exist between the secondary dendrite arm spacing, λ2, near the tip and the Dendrite tip radius, p, which is λ 2/ρ = 2.2 ± 0.3.
Abstract: Directional solidification experiments have been carried out in a succinonitrile-5.5 mol pct acetone system to characterize dendrite tip radius and interdendrite spacings as functions of growth rate and temperature gradient in the liquid. A maximum in primary dendrite spacing as a function of growth rate is observed, and this maximum is found to occur at the dendrite-cellular transition velocity. A scaling law is shown to exist between the secondary dendrite arm spacing, λ2, near the tip and the dendrite tip radius, p, which is λ2/ρ = 2.2 ± 0.3. Experimental results on ρ have been found to agree with the theoretical model based on the marginal stability criterion.
TL;DR: Repetitive stimulation of a dorsal root elicited a slow depolarization in about half of the dorsal horn neurons examined in the rat spinal cord slice preparation, which was markedly depressed or abolished in the presence of substance P, substance P antagonists and capsaicin.
TL;DR: This paper investigated three areas of maternal psychological functioning (emotional distress, authoritarian child-rearing values, negative perceptions of children) that might mediate the relationship between three separate dimensions of family demographic characteristics, conceptualized as chronic environmental stressors (i.e., financial, structural, and historical circumstances), and the emotionally affective behavior of mothers.
Abstract: This observational study of 74 families investigated 3 areas of maternal psychological functioning (emotional distress, authoritarian child-rearing values, negative perceptions of children) that might mediate the relationship between 3 separate dimensions of family demographic characteristics, conceptualized as chronic environmental stressors (i.e., financial, structural, and historical circumstances), and the emotionally affective behavior of mothers. Demographic conditions accounted for 52.9% of the variance in mothers' psychological characteristics and as much as 36.6% of the variance in positive and negative behaviors to children. The psychological characteristics explained as much as 15.1% of the variance in maternal behavior. Both chronic stress and the psychological variables had an independent influence on the general emotional tone of maternal behavior. The findings provide tentative support for the conclusion that the psychological characteristics examined here partially mediate the influence of some demographic or stressful life conditions on the positive and negative behaviors of mothers. Language: en
TL;DR: In this article, the elastic constants of single crystals of yttria-stabilized zirconia were determined through the temperature range 20/phi/ to 700/sup 0/C.
Abstract: Elastic constants of single crystals of yttria-stabilized zirconia were determined through the temperature range 20/phi/ to 700/sup 0/C. Crystals containing 8.1, 11.1, 12.1, 15.5, and 17.9 mol% Y/sub 2/O/sub 3/ were measured. The elastic constant C/sub 11/ was found to decrease and C/sub 12/ and C/sub 44/ to increase with increasing Y/sub 2/O/sub 3/ content; this appears to be due to decreasing coulombic interaction as Y/sup 3 +/ replaces Zr/sup 4 +/. Except for the 8.1 mol% Y/sub 2/O/sub 3/ crystal, the conventional elastic constants all showed normal monotonic decreases with increasing temperature. In the case of the 8.1 mol% Y/sub 2/O/sub 3/ crystal, measurements as a function of temperature were not reproducible, and it is likely that this composition at room temperature is below the composition limit of thermodynamic stability of the cubic fluorite phase.
TL;DR: This paper studies restrictions R on both the deterministic and also the nondeterministic polynomial time-bounded oracle machines such that the size of the set of strings queried by the oracle in computations of a machine on an input is bounded by aPolynomial in the length of the input.
Abstract: Consider the following open problems: (i) ${\text{P}} = ? {\text{ NP}}$ (ii) ${\text{NP}} = ? {\text{ co-NP}}$; (iii) ${\text{P}} = ? {\text{ PSPACE}}$; (iv) ${\text{NP}} = ? {\text{ PSPACE}}$. In this paper we study these four problems from a particular point of view. To illustrate our approach, consider the first problem. It is known that there exist recursive sets A and B such that ${\text{P}}(A) = {\text{NP}}(A)$ and ${\text{P}}(B)
e {\text{NP}}(B)$. We study restrictions R on both the deterministic and also the nondeterministic polynomial time-bounded oracle machines such that the following holds: ${\text{P}} = {\text{NP}}$ if and only if for every set A, ${\text{P}}_R (A) = {\text{NP}}_R (A)$. The restrictions are “quantitative” in the sense that the size of the set of strings queried by the oracle in computations of a machine on an input is bounded by a polynomial in the length of the input. We study several different ways of specifying such quantitative restrictions, each of which has the desire...
TL;DR: In this article, the authors argue that buyers are either irrational or poorly in-formed relative to the differences in land productivity between poor and good farmland, and that willingness-to-pay rent on the part of tenant operators is correlated with the quality of the land.
Abstract: Arguments have long persisted that purchasers pay too much for poor land (i.e., less productive, more erosive) relative to the higher quality counterpart. In other words, purchasers are either irrational or poorly in- formed relative to the differences in land productivity between poor and good farmland. Similar arguments have been advanced concerning the willingness-to-pay rent on the part of tenant operators.
TL;DR: In this paper, a measure of agreement for partially ordered data is suggested that makes use of the k categories with the highest ranks, the ranks of the remaining categories being disregarded.
TL;DR: In this paper, the authors examined the breakup of a planar solid-liquid interface into a cellular or a dendritic interface under directional solidification conditions and provided experimental results on the effect of composition on the dendrite tip radius.
TL;DR: There is remarkable structure and sequence homology between Spm‐I8 and the transposable elements Tam1 and Tam2 of Antirrhinum majus at their termini, reflecting a possible evolutionary and/or functional relationship between transposons in different plant species.
Abstract: The waxy (Wx) locus of Zea mays was cloned from strains carrying the wild-type and wxm-8 mutant alleles. The receptor component of the Suppressor-Mutator (Spm) controlling element system in the wxm-8 allele was shown to be a 2 kb long insertion within the transcribed region of the Wx gene. The insertion, termed Spm-I8, is excised during somatic reversion events induced by the autonomous controlling element Enhancer (En), which is an equivalent to Spm. Integration of Spm-I8 into the Wx gene generates a 3-bp target site duplication. Spm-I8 has a 13 bp long inverted repeat at its termini. The ends of the element can be further folded to build a large double-stranded structure consisting of five perfectly matching double-stranded regions of 9–13 bp in length, interrupted by single-stranded loops. A comparison of the wild-type and wxm-8 alleles revealed two additional insertions 6 (insert-1) and 0.25 (insert-2) kb in length. No En-induced excision of insert-1 and insert-2 could be detected so far. There is remarkable structure and sequence homology between Spm-I8 and the transposable elements Tam1 and Tam2 of Antirrhinum majus at their termini, reflecting a possible evolutionary and/or functional relationship between transposons in different plant species.
TL;DR: This chapter discusses the neuronal secretory systems to critically examine the processes in the magnocellular neurons, and considers to what extent they are variations of Palade's model, and whether they display any unique characteristics, particularly in comparison with other types of neurons.
Abstract: Publisher Summary This chapter discusses the neuronal secretory systems to critically examine the processes in the magnocellular neurons, and considers to what extent they are variations of Palade's model, and whether they display any unique characteristics, particularly in comparison with other types of neurons. Vasopressin (VP) and oxytocin (OT) are designated as neurohypophysial hormones, for the hypothalamic neurohypophysial system (HNS), which was the first neuronal secretory system in which they are identified in profusion. The specific enzymes could vary the cleavage products of propressophysin and prooxyphysin in different central nervous system (CNS) sites. In addition, modifying influences are probably exerted by the different co-peptides and co-transmitters within VP and OT neurons. The rich efferent input from other neuronal systems, the feedback relays, and the selective coordination between neurosecretory cells contribute to the extended repertoire of the so-called neurohypophysial peptides. The diversity and versatility of the peptidergic neurosecretory cells that produce VP and OT reveal affinities with other neurons in the CNS.
TL;DR: This article found that most respondents did not judge all errors as equally grievous; rather, their judgments generated a hierarchy of errors, and that both the age and academic discipline of faculty members may be important factors in predicting their response to certain ESL student writing errors.
Abstract: This study is part of a larger project which examines faculty response to the written errors of students who are non-native speakers of English. The particular study described here was designed to determine which sentence-level errors are judged to be most serious by an academic community and to discover what factors may influence this judgment. A survey was conducted to measure how a cross-section of faculty at Iowa State University respond to certain common ESL writing errors. The 164 respondents ranked the relative gravity of 12 typical ESL written errors occurring in 24 sentences. Results indicate that most respondents did not judge all errors as equally grievous; rather, their judgments generate a hierarchy of errors. The study also suggests that both the age and academic discipline of faculty members may be important factors in predicting their response to certain ESL student writing errors.
TL;DR: No one type of relationship, whether with a spouse, adult children, siblings, confidant friends, or organizational acquaintances, was able to satisfy all three of the psychological desires considered in the present study.
Abstract: A set of hypotheses is developed with regard to the way that lifecycle, cultural, and structural factors serve to delimit and specify the psychological desires satisfied through interaction with th...
01 Jan 1984
TL;DR: In this paper, a Kalman Filter model is used to estimate and predict clock phase, frequency and frequency drift. But the model is not suitable for the measurement of phase as a function of time rather than as a spectral density.
Abstract: A relationship was constructed between the Allan variance parameters (H sub z, H sub 1, H sub 0, H sub -1 and H sub -2) and a Kalman Filter model that would be used to estimate and predict clock phase, frequency and frequency drift. To start with the meaning of those Allan Variance parameters and how they are arrived at for a given frequency source is reviewed. Although a subset of these parameters is arrived at by measuring phase as a function of time rather than as a spectral density, they all represent phase noise spectral density coefficients, though not necessarily that of a rational spectral density. The phase noise spectral density is then transformed into a time domain covariance model which can then be used to derive the Kalman Filter model parameters. Simulation results of that covariance model are presented and compared to clock uncertainties predicted by Allan variance parameters. A two state Kalman Filter model is then derived and the significance of each state is explained.
01 Jan 1984
TL;DR: Comparison within ovules greatly exceeded that of unstained and nonspecifically stained clearings, and eliminated the need of special optics, i.e., Nomarski interference-contrast optics, for optimal viewing and photography.
Abstract: Nondissected ovaries of tuber-bearing Solatium sp. were stained with Mayer's hemalum, a positive stain for chromatin and nucleoli, and then optically cleared with methyl salicylate, a clearing agent. Clarity, resolution and contrast within the ovules dissected from ovaries were comparable to those of sectioned, paraffin embedded ovaries. Contrast within ovules greatly exceeded that of unstained and nonspecifically stained clearings, and eliminated the need of special optics, i.e, Nomarski interference-contrast optics, for optimal viewing and photography. Much less time and labor were required than for embedded specimens. Usefulness of the technique for cytogenetic and cytological research was verified by analyzing meiosis and other features of megasporogenesis and megagametogenesis in normal, and in two meiotic mutants, of Solatium. The results illustrate the usefulness of combined Mayer's hemalum staining and methyl salicylate clearing, and suggest additional stain-clearing agent combinations have potent...
TL;DR: Sulphur in agricultural soils occurs in organic and inorganic forms, with organic S accounting for > 95% of the total S in the United States and Canada as discussed by the authors.
Abstract: Sulphur in agricultural soils occurs in organic and inorganic forms, with organic S accounting for > 95% of the total S. Analysis of a wide range of soils shows that from 25 to 75% of the organic S in soils is HI-reducible, from 7 to 30% is C-bonded, and from 11 to 22% is unidentified S. Nitrogen is associated with S in soil organic matter in a ratio of about 8 : 1, although the extreme ratios may vary from 5: 1 to 13: 1. Laboratory studies showed that humus S is depleted faster than humus N. Mineralization of S in crop residues varied with type of crop residue and soil studied The amounts of S fertilizers (gypsum, elemental S, and sulfuric acid) used in the United States in 1981 and 1982 were 1.9 × 106 and 1.5 × 106 tons, respectively. Of the total amount used in 1982, 3, 5, 20, and 71% were used in the West North Central, Mountain, South Atlantic, and Pacific regions, respecitively. A survey of S deposition at about 100 sites in the United States and many other sites in Canada in 1980 showed that annual addition by precipitation in North America ranged from 0.5 to slightly above 10 kg/ha. The usual ranges of values in concentrations and spatial rates of N, P, and S in precipitation is well within the ranges of these elements in natural waters. Atmospheric sources are important components in meeting crops S requirements and should be considered in benefit-cost analyses relating to S emissions.