Showing papers by "University of Missouri published in 1997"

Corporate Social Performance And Organizational Attractiveness To Prospective Employees

Abstract: Drawing on propositions from social identity theory and signaling theory, we hypothesized that firms' corporate social performance (CSP) is related positively to their reputations and to their attractiveness as employers. Results indicate that independent ratings of CSP are related to firms' reputations and attractiveness as employers, suggesting that a firm's CSP may provide a competitive advantage in attracting applicants. Such results add to the growing literature suggesting that CSP may provide firms with competitive advantages.

Aux/IAA proteins repress expression of reporter genes containing natural and highly active synthetic auxin response elements.

Abstract: A highly active synthetic auxin response element (AuxRE), referred to as DR5, was created by performing site-directed mutations in a natural composite AuxRE found in the soybean GH3 promoter. DR5 consisted of tandem direct repeats of 11 bp that included the auxin-responsive TGTCTC element. The DR5 AuxRE showed greater auxin responsiveness than a natural composite AuxRE and the GH3 promoter when assayed by transient expression in carrot protoplasts or in stably transformed Arabidopsis seedlings, and it provides a useful reporter gene for studying auxin-responsive transcription in wild-type plants and mutants. An auxin response transcription factor, ARF1, bound with specificity to the DR5 AuxRE in vitro and interacted with Aux/IAA proteins in a yeast two-hybrid system. Cotransfection experiments with natural and synthetic AuxRE reporter genes and effector genes encoding Aux/IAA proteins showed that overexpression of Aux/IAA proteins in carrot protoplasts resulted in specific repression of TGTCTC AuxRE reporter gene expression.

A chiral spherical molecular assembly held together by 60 hydrogen bonds

Abstract: Spontaneous self-assembly processes that lead to discretespherical molecular structures are common in nature. Sphericalviruses1 (such ashepatitis B) and fullerenes2 are well-known examples inwhich non-covalent and covalent forces,respectively, direct the assembly of smaller subunits intolarger superstructures. A common feature of theseshell-like architectures is their ability to encapsulateneutral and/or charged guests whose size, shape and chemicalexteriors complement those of the host's innersurface3,4. Their interiors can often beregarded as a new phase of matter5, capable of controlling the flowof reactants, transients and products, and of catalysingreactions of both chemical and biological relevance. Suchproperties have inspired the recent emergence ofmonomolecular5,6,7 and supramolecular dimeric molecularcapsules8,9, many of which have been basedon the head-to-head alignment of bowl-shapedpolyaromatic macrocycles such as calix[4]arenes5,7,9. But true structural mimicry offrameworks akin to viruses and fullerenes, which are based onthe self-assembly of n > 3 subunits,and where surface curvature is supplied by edge sharing of regularpolygons, has remained elusive. Here we present anexample of such a system: a chiral spherical molecular assemblyheld together by 60 hydrogen bonds (1) (Fig. 1). We demonstrate the ability of 1, which consists of six calix[4]resorcinarenes 2 and eight water molecules, to self-assemble and maintain its structure in apolar media and to encapsulate guest species within a well-defined cavity that possesses an internal volume of about 1,375 A3. Single crystal X-ray analysis shows that its topology resembles that of a spherical virus1 and conforms to the structure of a snub cube, one of the 13 Archimedean solids10.

ARF1, a Transcription Factor That Binds to Auxin Response Elements

Abstract: The plant hormone auxin regulates plant physiology by modulating the interaction of transcription factors with auxin response elements (AuxREs) of the affected genes. A transcription factor, Auxin Response Factor 1 (ARF1), that binds to the sequence TGTCTC in AuxREs was cloned from Arabidopsis by using a yeast one-hybrid system. ARF1 has an amino-terminal DNA-binding domain related to the carboxyl terminus of the maize transactivator Viviparous-1. Sequence requirements for ARF1 binding in vitro are identical to those that confer auxin responsiveness in vivo. The carboxyl terminus of ARF1 contains two motifs found in the Aux/IAA class of proteins and appears to mediate protein-protein interactions.

Relation of work–family conflict to health outcomes: A four-year longitudinal study of employed parents

Abstract: Cross-sectional research provides consistent evidence that work-family conflict is positively associated with a host of adverse health-related outcomes. The authors extend past research by examining the longitudinal relarions of work → family and family → work conflict to self-report (depressive symptomatology, physical health, and heavy alcohol use) and objective cardiovascular (incidence of hypertension) health outcomes. Survey data were obrained from a random community sample of 267 employed parents during 1989 (baseline) and 1993 (follow-up). Ordinary least squares and logistic regression analyses revealed rhar family → work conflict was longitudinally related to elevated levels of depression and poor physical health, and to the incidence of hypertension. In contrast, work → family conflict was longitudinally related to elevated levels of heavy alcohol consumption.

A role for oestrogens in the male reproductive system

Abstract: Oestrogen is considered to be the 'female' hormone, whereas testosterone is considered the 'male' hormone. However, both hormones are present in both sexes. Thus sexual distinctions are not qualitative differences, but rather result from quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen, and as high as 250 pg ml(-1) in rete testis fluids, which is higher than serum oestradiol in the female. It is well known that male reproductive tissues express oestrogen receptors, but the role of oestrogen in male reproduction has remained unclear. Here we provide evidence of a physiological role for oestrogen in male reproductive organs. We show that oestrogen regulates the reabsorption of luminal fluid in the head of the epididymis. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility. This finding raises further concern over the potential direct effects of environmental oestrogens on male reproduction and reported declines in human sperm counts.

Relative binding affinity-serum modified access (RBA-SMA) assay predicts the relative in vivo bioactivity of the xenoestrogens bisphenol A and octylphenol

Abstract: We have developed a relative binding affinity-serum modified access (RBA-SMA) assay to determine the effect of serum on the access of xenoestrogens to estrogen receptors within intact cultured MCF-7 human breast cancer cells. We used this assay to predict low dose activity of two xenoestrogens in mice. In serum-free medium, bisphenol A, a component of polycarbonates and of resins used to line metal food cans, showed a lower relative binding affinity (RBA; 0.006%) than octylphenol (0.072%) and nonylphenol (0.026%), which are used as surfactants in many commercial products (all RBAs are relative to estradiol, which is equal to 100%). In 100% serum from adult men, bisphenol A showed a higher RBA (0.01%) than in serum-free medium and thus enhanced access to estrogen receptors relative to estradiol. In contrast, octylphenol showed a 22-fold decrease in RBA (0.0029%) and nonylphenol showed a 5-fold decrease in RBA (0.0039%) when measured in adult serum. This indicates that, relative to estradiol, serum had less of an inhibitory effect on the cell uptake and binding in MCF-7 cells of bisphenol A, while serum had a greater inhibitory effect on octylphenol and nonylphenol relative to estradiol. Extrapolation of these relative activities in adult serum predicted that the estrogenic bioactivity of bisphenol A would be over 500-fold greater than that of octylphenol in fetal mouse serum. Bisphenol A and octylphenol were fed to pregnant mice at 2 and 20 micrograms/kg/day. Exposure of male mouse fetuses to either dose of bisphenol A, but to neither dose of octylphenol, significantly increased their adult prostate weight relative to control males, which is consistent with the higher predicted bioactivity of bisphenol A than octylphenol in the RBA-SMA assay. In addition, our findings show for the first time that fetal exposure to environmentally relevant parts-per-billion (ppb) doses of bisphenol A, in the range currently being consumed by people, can alter the adult reproductive system in mice.

Prospective study of blunt aortic injury: Multicenter trial of the American Association for the Surgery of Trauma

Abstract: Background: Blunt aortic injury is a major cause of death from blunt trauma. Evolution of diagnostic techniques and methods of operative repair have altered the management and posed new questions in recent years. Methods: This study was a prospectively conducted multicenter trial involving 50 trauma centers in North America under the direction of the Multi-institutional Trial Committee of the American Association for the Surgery of Trauma. Results: There were 274 blunt aortic injury cases studied over 2.5 years, of which 81% were caused by automobile crashes. Chest computed tomography and transesophageal echocardiography were applied in 88 and 30 cases, respectively, and were 75 and 80% diagnostic, respectively. Two hundred seven stable patients underwent planned thoracotomy and repair. Clamp and sew technique was used in 73 (35%) and bypass techniques in 134 (65%). Overall mortality was 31%, with 63% of deaths being attributable to aortic rupture; mortality was not affected by method of repair. Paraplegia occurred postoperatively in 8.7%. Logistic regression analysis demonstrated clamp and sew (p = 0.002) and aortic cross clamp time of 30 minutes (p = 0.01) to be associated with development of postoperative paraplegia. Conclusions: Rupture after hospital admission remains a major problem. Although newer diagnostic techniques are being applied, at this time aortography remains the diagnostic standard. Aortic cross clamp time beyond 30 minutes was associated with paraplegia; bypass techniques, which provide distal aortic perfusion, produced significantly lower paraplegia rates than the clamp and sew approach.

Robust clustering methods: a unified view

Abstract: Clustering methods need to be robust if they are to be useful in practice. In this paper, we analyze several popular robust clustering methods and show that they have much in common. We also establish a connection between fuzzy set theory and robust statistics, and point out the similarities between robust clustering methods and statistical methods such as the weighted least-squares technique, the M estimator, the minimum volume ellipsoid algorithm, cooperative robust estimation, minimization of probability of randomness, and the epsilon contamination model. By gleaning the common principles upon which the methods proposed in the literature are based, we arrive at a unified view of robust clustering methods. We define several general concepts that are useful in robust clustering, state the robust clustering problem in terms of the defined concepts, and propose generic algorithms and guidelines for clustering noisy data. We also discuss why the generalized Hough transform is a suboptimal solution to the robust clustering problem.

Agency conflict and corporate strategy: the effect of divestment on corporate value

Abstract: Among the various stakeholders of a firm, senior managers are the most likely targets for private and public political pressures. Other stakeholder groups are less visible and may be perceived as less influential in corporate strategy formulation and implementation. In some situations, consequently, senior executives may adopt corporate strategies in response to political pressures even if these strategies may be costly to shareholders. In this study, a special case is examined: the effect of divestment of South African business units on firm value. Using data from 1984 through 1990, we examine the impact that announcements of divestments have upon the stock return behavior of publicly traded firms. Our results indicate that significant and negative excess returns accrue to shares of companies announcing divestments of South African operations. These results are supportive of the premise that noneconomic pressures may influence managerial strategies rather than value-enhancement goals. © 1997 by John Wiley & Sons, Ltd.

Prostate enlargement in mice due to fetal exposure to low doses of estradiol or diethylstilbestrol and opposite effects at high doses

Abstract: On the basis of results of studies using high doses of estrogens, exposure to estrogen during fetal life is known to inhibit prostate development. However, it is recognized in endocrinology that low concentrations of a hormone can stimulate a tissue, while high concentrations can have the opposite effect. We report here that a 50% increase in free-serum estradiol in male mouse fetuses (released by a maternal Silastic estradiol implant) induced a 40% increase in the number of developing prostatic glands during fetal life; subsequently, in adulthood, the number of prostatic androgen receptors per cell was permanently increased by 2-fold, and the prostate was enlarged by 30% (due to hyperplasia) relative to untreated males. However, as the free serum estradiol concentration in male fetuses was increased from 2- to 8-fold, adult prostate weight decreased relative to males exposed to the 50% increase in estradiol. As a model for fetal exposure to man-made estrogens, pregnant mice were fed diethylstilbestrol (DES) from gestation days 11 to 17. Relative to controls, DES doses of 0.02, 0.2, and 2.0 ng per g of body weight per day increased adult prostate weight, whereas a 200-ng-per-g dose decreased adult prostate weight in male offspring. Our findings suggest that a small increase in estrogen may modulate the action of androgen in regulating prostate differentiation, resulting in a permanent increase in prostatic androgen receptors and prostate size. For both estradiol and DES, prostate weight first increased then decreased with dose, resulting in an inverted-U dose-response relationship.

Clinical Significance of Mitral Regurgitation After Acute Myocardial Infarction

Abstract: Background Mitral regurgitation (MR) may complicate acute myocardial infarction (MI). However, it is not known whether mild MR is an independent predictor of post-MI outcome. Methods and Results The study cohort consisted of 727 Survival and Ventricular Enlargement Study patients who underwent cardiac catheterization, including left ventriculography, up to 16 days after MI. Left ventriculograms were analyzed for diastolic and systolic volumes, global left ventricular sphericity, extent of wall motion abnormality, and endocardial curvature. The presence of MR was related to the risk of developing a cardiovascular event during 3.5 years of follow-up. MR was present in 141 patients (19.4%). Severe (3+) MR was present in only 2 patients. Patients with MR were more likely to have a persistently occluded infarct artery (MR versus no MR, 27.3% versus 15.2%; P=.001). Although the ejection fractions were similar, MR patients had larger end-systolic and end-diastolic volumes and more spherical ventricles than patie...

Variation in Local-Scale Edge Effects: Mechanisms and landscape Context

Abstract: Ecological processes neat" habitat edges often differ from processes away fromedges. Yet, the generality of "edge effects" has been hotly debated because results vary tremendously. To understand the factors responsible for this variation, we described nest predation and cowbird distribution patterns in forest edge and forest core habitats on 36 randomly selected plots in three states in the midwestern United States. We tested four hypotheses that may explain the variation and mechanisms responsible for edge effects - among the 36 plots: (1) the landscape context, (2) the local predator community, (3) the local bird (host-prey) community, and (4) the nest site microhabitat structure. We used artificial nests baited with quail and clay eggs to determine nest predation patterns and " predators and used point count surveys to determine cowbird and host abundance in forest edge and forest core habitats. Raccoons, Opossums, canids, and birds accounted for most predation of artificial nests. Neither local host abundance nor mean nest concealment of artificial nests significantly •influenced nest predation rates in habitat edge or in habitat core. Nest predation was sig- nificantly greater in highly fragmented landscapes than in unfragmented landscapes and was significantly higher in edge habitats than in core habitats. However, detection of edge effects varied, depending upon landscape type. Higher predation rates in edge habitats were detected in highly and moderately fragmented landscapes, but not in unfragmented land- , , s.capes. Both mammalian and avian predator groups contributed to higher predation rates along edges in highly and moderately fragmented landscapes. ,Cowbird abundance was significantly related to host abundance, but the effect of hosts varied depending upon habitat type. In edge habitats, cowbird abundance was negatively associated with host abundance in all three landscapes studied. By contrast, cowbird abun- dance was positively associated with host abundance in core habitats. Once the effects of host abundance were removed, cowbird abundance in core habitat was greater in highly fragmented landscapes than in moderately and unfragmented landscapes, but did not differ between the latter two. In edge habitat, cowbird abundance did not differ between land- scapes, but abundance in edges tended to be highest in the highly fragmented landscape and lowest in the unfragmented landscape. Cowbird abundance did not vary between edge and core habitat in any of the landscapes studied. We suggest that the first approximation to predicting the impact of agricultural or permanently managed edges on forest songbird reproductive success is to assess habitat characteristics at the landscape scale. Given geographic location, local factors such as host abundance and predator composition should be assessed.

Extracellular Matrix Remodeling in Heart Failure A Role for De Novo Angiotensin II Generation

Abstract: Heart failure is a major health problem worldwide. In the United States, it represents the number one hospital discharge diagnosis among elderly persons each year. It appears most commonly in patients with previous MI.1,2 The chronically failing heart of ischemic origin is characterized by iterations in tissue structure, particularly fibrous tissue formation, that appear in infarcted and noninfarcted myocardium of both right and left ventricles.3,4 In other words, fibrosis appears at the site of MI as well as remote from it. Fibrosis remote from the infarct site is considered “the major cause of ventricular remodeling” in ischemic cardiomyopathy.4 Such an adverse accumulation of extracellular matrix initially raises myocardial stiffness; its continued accumulation further increases stiffness and impairs contractile behavior.5–10 Elucidating cellular and molecular mechanisms responsible for accumulation of extracellular matrix is essential to designing cardioprotective and reparative strategies that could prevent or regress fibrosis, respectively, after infarction.11,12 ACE inhibition has proved effective in reducing mortal and morbid events, improving symptomatic status, and attenuating the progressive nature of cardiac failure in symptomatic patients with ventricular diastolic and/or systolic dysfunction in whom activation of the circulating RAAS is present.1,13,14 ACE inhibitor–mediated reductions in circulating Ang II and aldosterone no doubt contribute to this salutary response. This would include an attenuation of well-recognized endocrine properties of these hormones, such as altered sodium homeostasis and vascular tonicity, and their adverse influence on matrix structure of atria and ventricles.15–20 Collectively, these adverse responses to RAAS effector hormones contribute to the progressive nature of chronic cardiac failure, which includes recurring bouts of symptomatic failure1,2,21 and reentrant arrhythmias originating in either atria or ventricles.22,23 ACEIs have also proved effective in asymptomatic patients with equivalent levels of ventricular systolic dysfunction but in whom chronic RAAS activation is not present. …

Ventricular dysfunction and the risk of stroke after myocardial infarction

Abstract: Background In patients who have had a myocardial infarction, the long-term risk of stroke and its relation to the extent of left ventricular dysfunction have not been determined. We studied whether a reduced left ventricular ejection fraction is associated with an increased risk of stroke after myocardial infarction and whether other factors such as older age and therapy with anticoagulants, thrombolytic agents, or captopril affect long-term rates of stroke. Methods We performed an observational analysis of prospectively collected data on 2231 patients who had left ventricular dysfunction after acute myocardial infarction who were enrolled in the Survival and Ventricular Enlargement trial. The mean follow-up was 42 months. Risk factors for stroke were assessed by both univariate and multivariate Cox proportional-hazards analysis. Results Among these patients, 103 (4.6 percent) had fatal or nonfatal strokes during the study (rate of stroke per year of follow-up, 1.5 percent). The estimated five-year rate o...

Sediment in Streams: Sources, Biological Effects, and Control

Abstract: (1997). Sediment in Streams: Sources, Biological Effects, and Control. Transactions of the American Fisheries Society: Vol. 126, No. 6, pp. 1048-1051.

The Evolution of Ribosomal DNA Divergent Paralogues and Phylogenetic Implications

Abstract: Although nuclear ribosomal DNA (rDNA) repeats evolve together through concerted evolution, some genomes contain a considerable diversity of paralogous rDNA. This diversity includes not only multiple functional loci but also putative pseudogenes and recombinants. We examined the occurrence of divergent paralogues and recombinants in Gossypium, Nicotiana, Tripsacum, Winteraceae, and Zea ribosomal internal transcribed spacer (ITS) sequences. Some of the divergent paralogues are probably rDNA pseudogenes, since they have low predicted secondary structure stability, high substitution rates, and many deamination-driven substitutions at methylation sites. Under standard PCR conditions, the low stability paralogues amplified well, while many high-stability paralogues amplified poorly. Under highly denaturing PCR conditions (i.e., with dimethylsulfoxide), both low- and high-stability paralogues amplified well. We also found recombination between divergent paralogues. For phylogenetics, divergent ribosomal paralogues can aid in reconstructing ancestral states and thus serve as good outgroups. Divergent paralogues can also provide companion rDNA phylogenies. However, phylogeneticists must discriminate among families of divergent paralogues and recombinants or suffer from muddled and inaccurate organismal phylogenies.

Estrogen inhibits the vascular injury response in estrogen receptor alpha-deficient mice.

Abstract: The atheroprotective effects of estrogen in women are well recognized, but the underlying mechanisms responsible are not well understood. Blood vessel cells express the classic estrogen receptor, ER alpha (ref. 2-6), and are directly affected by estrogen, which inhibits the development of atherosclerotic and injury-induced vascular lesions. We have generated mice in which the ER alpha gene is disrupted and have used a mouse model of carotid arterial injury to compare the effects of estrogen on wild-type and estrogen receptor-deficient mice. Increases in vascular medial area and smooth muscle cell proliferation were quantified following vascular injury in ovariectomized mice treated with vehicle or with physiologic levels of 17 beta-estradiol. Surprisingly, in both wild-type and estrogen receptor-deficient mice, 17 beta-estradiol markedly inhibited to the same degree all measures of vascular injury. These data demonstrate that estrogen inhibits vascular by a novel mechanism that is independent of the classic estrogen receptor, ER alpha.

Electronic structure and thermoelectric properties of bismuth telluride and bismuth selenide

Abstract: The electronic structures of the two thermoelectric materials and are studied using density-functional theory with the spin - orbit interaction included. The electron states in the gap region and the chemical bonding can be described in terms of interaction between the atomic p orbitals within the `quintuple' layer. For , we find both the valence-band maximum as well as the conduction-band minimum, each with a nearly isotropic effective mass, to occur at the zone centre in agreement with experimental results. For , we find that the six valleys for the valence-band maximum are located in the mirror planes of the Brillouin zone and they have a highly anisotropic effective mass, leading to an agreement between the de Haas - van Alphen data for the p-doped samples and the calculated Fermi surface. The calculated conduction band, however, has only two minima, instead of the six minima indicated from earlier experiments. The calculated Seebeck coefficients for both p-type and n-type materials are in agreement with the experiments.

Genetic and Environmental Regulation of Dauer Larva Development

Abstract: I. INTRODUCTION Dauer larvae were first identified as a special larval stage of insect-parasitic nematodes. These larvae, which differed structurally from all other stages of the same species, were termed “dauerlarven” by Fuchs (1915). The dauer (enduring) stage of Caenorhabditis elegans is formed when environmental conditions are inadequate for successful reproduction. In abundant food, the animal develops continuously through the four larval stages (L1–L4) to the adult. Coincident with increased population density and limited food supply, development is arrested at the second molt, and the third-stage larva that is formed is structurally and behaviorally specialized for dispersal and long-term survival (Cassada and Russell 1975). Dauer larvae do not feed, but they can survive at least four to eight times the normal 2-week life span of C. elegans (Klass and Hirsh 1976). When favorable conditions are encountered, the dauer larva begins to feed and resumes development to the adult. Both entry into and exit from the dauer stage are developmental responses to specific chemosensory cues. These cues inform the larva whether there will be sufficient food available to support its reproduction. The environmental cues are first assessed and integrated throughout the L1 stage (Golden and Riddle 1984b). The primary cue is a Caenorhabditis-specific pheromone constitutively released by the nematodes (Golden and Riddle 1984c). The pheromone is very stable and hydrophobic and has chromatographic properties similar to those of hydroxylated fatty acids and bile acids. The concentration of pheromone reflects nematode population density. Temperature and food modulate the response to pheromone...

Visual Perception of Stochastic Resonance

Abstract: Stochastic resonance can be used as a measuring tool to quantify the ability of the human brain to interpret noise contaminated visual patterns. Here we report the results of a psychophysics experiment which show that the brain can consistently and quantitatively interpret detail in a stationary image obscured with time varying noise and that both the noise intensity and its temporal characteristics strongly determine the perceived image quality.

Fraudulently Misstated Financial Statements and Insider Trading: An Empirical Analysis

Abstract: This study investigates the relationship between insider trading and fraud. We find that in the presence of fraud, insiders reduce their holdings of company stock through high levels of selling activity as measured by either the number of transactions, the number of shares sold, or the dollar amount of shares sold. Moreover, we present evidence that a cascaded logit model, incorporating insider trading variables and firm-specific financial characteristics, differentiates companies with fraud from companies without fraud.

External Validity of “Trivial” Experiments: The Case of Laboratory Aggression:

Abstract: The external validity of artificial "trivial" laboratory settings is examined. Past views emphasizing generalizability of relations among conceptual variables are reviewed and affirmed. One major implication of typical challenges to the external validity of laboratory research is tested with aggression research: If laboratory research is low in external validity, then laboratory studies should fail to detect relations among variables that are correlated with aggression in "real-world" studies. Meta-analysis was used to examine 5 situational variables (provocation, violent media, alcohol, anonymity, hot temperature) and 3 individual difference variables (sex, Type A personality, trait aggressiveness) in real-world and laboratory aggression studies. Results strongly supported the extemal validity of trivial laboratory studies. Advice is given on how scholars might handle occasional descrepancies between laboratory and real-world findings.

Soybean disease loss estimates for the top 10 soybean producing countries in 1994

Abstract: Soybean disease loss estimates were compiled for the 1994 harvested crop from the 10 countries with the greatest soybean production. The objective was to document the major soybean disease problems in these countries and any recent changes in the severity of individual soybean diseases. Total yield losses caused by Heterodera glycines in these 10 countries were greater than those caused by any other disease. Next in order of importance were stem canker, brown spot, and charcoal rot. The total yield loss due to disease during 1994 in these countries was 14.99 million metric tons, valued at $3.31 billion. Methods used to estimate soybean disease losses were field surveys, plant disease diagnostic clinic samples, variety trial data, information from field workers and university extension staff, research plots, grower demonstrations, and private crop consultant reports. Yield loss estimates due to a particular disease varied by country. For example, yield losses due to rust were reported from China a...

Experimental and simulation studies of the coaxially fed U-slot rectangular patch antenna

Abstract: Experimental and simulation results are presented on the coaxially fed rectangular patch antenna with a U-shaped slot. Experimental results include impedance bandwidth, copolar- and crosspolar-pattern characteristics and gain measurements. Simulation results are obtained mainly through the development of a FDTD code. It is found that the U-slot patch on a foam substrate of about 0.08/spl lambda/ thick can be designed to attain 20-30% impedance as well as gain bandwidths without the need of parasitic patches on another layer or on the same layer. The far-field patterns have good copolar and crosspolar characteristics. By altering the patch width or feed position, the wideband characteristic can be changed into a dual-frequency characteristic. Simulation results are in good agreement with measurements.