Showing papers by "North Carolina State University published in 1989"

Survival analysis in telemetry studies: the staggered entry design

Abstract: The estimation of survival distributions for radio-tagged animals is important to wildlife ecologists. Allowance must be made for animals being lost (or censored) due to radio failure, radio loss, or emigration of the animal from the study area. The Kaplan-Meier procedure (Kaplan and Meier 1958), widely used in medical studies subject to censoring, can be applied to this problem. We developed a simple modification of the Kaplan-Meier procedure that allows for new animals to be added after the study has begun. We present 2 examples using telemetry data collected from northern bobwhite quail (Colinus virginianus) to show the simplicity and utility of the Kaplan-Meier procedure and its modifications. The log rank test used to compare 2 survival distributions can also be modified to allow for additions during the study. Simple computer programs that can be run on a personal computer are available from the authors. J. WILDL. MANAGE. 53(1):7-15 Radio-tagged animals are used to study survival. Present techniques for analyzing data from these studies assume that each survival event (typically an animal surviving a day) is independent and has a constant probability over all animals and all periods (Trent and Rongstad 1974, Bart and Robson 1982, Heisey and Fuller 1985). We believe these assumptions are often unrealistic and restrictive. White (1983) generalized discrete approaches using the same framework as that of band return models (Brownie et al. 1985) and he developed a flexible computer program (SURVIV) for use with his approach. Heisey and Fuller (1985) generalized the Trent and Rongstad (1974) approach to allow mortality from different causes (e.g., predation, starvation) and developed a microcomputer program called MICROMORT. Typically an animal's exact survival time (at least to within 1-2 days) is known unless that survival time is right censored (i.e., only known to be greater than some value). Pollock (1984) and Pollock et al. (1989) suggested a useful approach based on continuous survival models allowing right censoring that is widely used in medicine and engineering (Kalbfleisch and Prentice 1980, Cox and Oakes 1984) and provided examples of the Kaplan-Meier procedure. The Kaplan-Meier procedure does not require specification of a particular parametric continuous distribution; e.g., the exponential or Weibull. Related ecological papers using survival methods include Muenchow (1986), Pyke and Thompson (1986), Kurzejeski et al. (1987), and White et al. (1987). We present a simple description of the Kaplan-Meier procedure with an example using northern bobwhite quail survival data collected by PDC. We then generalize the Kaplan-Meier procedure to allow gradual (or staggered) entry of animals into the study. The calculations are illustrated with an example from the quail data. Finally, we present the log-rank test for comparison of survival distributions (modified for staggered entry of animals) with an example. We also present a discussion of model assumptions and directions for future research. We thank J. D. Nichols and W. L. Link for helpful comments on an earlier draft of this paper. We acknowledge G. C. White and D. M. Heisey for their helpful reviews that improved the final version. THE KAPLAN-MEIER OR PRODUCT LIMIT PROCEDURE The Kaplan-Meier or product limit estimator was developed by Kaplan and Meier (1958) and is d scussed by Cox and Oakes (1984:48) and Kalbfleisch and Prentice (1980:13). The survival function (S[t]) is the probability of an arbitrary animal in a population surviving t units of time from the beginning of the study. A nonparametric estimator of the survival function can be obtained by restricting ourselves to the discrete time points when deaths occur a1, a2, ..., ag. We define r, . . . , rg to be the numbers of an-

Multisensor integration and fusion in intelligent systems

Abstract: The issues involved in integrating multiple sensors into the operation of a system are presented in the context of the type of information these sensors can uniquely provide. A survey is provided of the variety of approaches to the problem of multisensor integration and fusion that have appeared in the literature in recent years ranging from general paradigms, frameworks, and methods for integrating and fusing multisensory information to existing multisensor systems used in different areas of application. General multisensor fusion methods, sensor selection strategies, and world models are examined, along with approaches to the integration and fusion of information from combinations of different types of sensors. Short descriptions of the role of multisensor integration and fusion in the operation of a number of existing mobile robots are provided, together with proposed high-level multisensory representations suitable for mobile robot navigation and control. Existing multisensor systems for industrial and other applications are considered. >

Power semiconductor device figure of merit for high-frequency applications

Abstract: A figure of merit (the Baliga high-frequency figure of merit) is derived for power semiconductor devices operating in high-frequency circuits. Using this figure of merit, it is predicted that the power losses incurred in the power device will increase as the square root of the operating frequency and approximately in proportion to the output power. By relating the device power dissipation to the intrinsic material parameters, it is shown that the power loss can be reduced by using semiconductors with larger mobility and critical electric field for breakdown. Examination of data in the literature indicates that significant performance improvement can be achieved by replacing silicon with gallium arsenide, silicon carbide, or semiconducting diamond. >

Effects of the nearest neighbors and the alloy matrix on SiH stretching vibrations in the amorphous SiO r :H (0<r<2) alloy system

Abstract: Hydrogenated silicon suboxides, ${\mathrm{SiO}}_{\mathrm{r}}$:H, for alloy range (0lrl2) have been deposited by remote plasma-enhanced chemical vapor deposition (remote PECVD) under conditions in which hydrogen is incorporated predominantly in monohydride or SiH bonding configurations. We have investigated both the SiH bond-stretching and bond-bending absorption bands by infrared (ir) absorption spectroscopy as a function of r, the alloy composition. In this paper, we have focused on the bond-stretching absorption bands, and have modeled the shape of the bond-stretching band as a function of the alloy composition. There are four distinct local environments for the SiH group in the sub- oxides; these can be written as HSi-${\mathrm{Si}}_{3\mathrm{\ensuremath{-}}\mathrm{n}}$${\mathrm{O}}_{\mathrm{n}}$, for n=0--3. A sum of Gaussian functions, one for each environment, is used to synthesize the absorption in the SiH stretching band. The peak positions of these Gaussians are calculated by an induction model which includes both local and matrix (or alloy) effects; the amplitude weightings are determined from a random statistical model for the local bonding environments of the Si-O groups in the ${\mathrm{SiO}}_{\mathrm{r}}$ alloy. We find that the frequency shifts caused by changes in the matrix, and associated with different values of r, are comparable to the shifts associated with the different local environments. The combination of these effects serves to diminish the discreteness of subband features in the absorption spectrum.

Sucrose Phosphate Synthase and Acid Invertase as Determinants of Sucrose Concentration in Developing Muskmelon (Cucumis melo L.) Fruits.

Abstract: Fruits of orange-fleshed and green-fleshed muskmelon (Cucumis melo L.) were harvested at different times throughout development to evaluate changes in metabolism which lead to sucrose accumulation, and to determine the basis of differences in fruit sucrose accumulation among genotypes. Concentrations of sucrose, raffinose saccharides, hexoses and starch, as well as activities of the sucrose metabolizing enzymes sucrose phosphate synthase (SPS) (EC 2.4.1.14), sucrose synthase (EC 2.4.1.13), and acid and neutral invertases (EC 3.2.1.26) were measured. Sucrose synthase and neutral invertase activities were relatively low (1.7 ± 0.3 micromole per hour per gram fresh weight and 2.2 ± 0.2, respectively) and changed little throughout fruit development. Acid invertase activity decreased during fruit development, (from as high as 40 micromoles per hour per gram fresh weight) in unripe fruit, to undetectable activity in mature, ripened fruits, while SPS activity in the fruit increased (from 7 micromoles per hour per gram fresh weight) to as high as 32 micromoles per hour per gram fresh weight. Genotypes which accumulated different amounts of sucrose had similar acid invertase activity but differed in SPS activity. Our results indicate that both acid invertase and SPS are determinants of sucrose accumulation in melon fruit. However, the decline in acid invertase appears to be a normal function of fruit maturation, and is not the primary factor which determines sucrose accumulation. Rather, the capacity for sucrose synthesis, reflected in the activity of SPS, appears to determine sucrose accumulation, which is an important component of fruit quality.

The Need to Reconsider the Use of Condition Indices in Fishery Science

Abstract: Condition indices are used in fishery science as indicators of the weight-to-length relationship of a population or subgroup (e.g., strain, sex, or age category). This conversion of the two-dimensional weight-length relationship into a single statistic results in a loss of information and, in many cases, an inaccurate representation of that relationship. Fulton's condition factor (K) is based on the assumption that the slope of the weight-length relationship is 3.0. The relative condition factor (Kn) is based on the assumption that the slopes of all samples to be compared are equal to some specific value. Relative weight (W r ) is based on the assumption that the slope and the intercept of the weight-length relationship are the same as those in the “ideal” equation. Instead of providing simple, interpretable descriptions of the weight-length relationship in fish populations, all three of these commonly used condition indices have critical flaws that can result in incorrect conclusions. Relative w...

Production of a Broad Spectrum Antimicrobial Substance by Lactobacillus reuteri

Abstract: Lactobacillus reuteri resides in the gastrointestinal tract of humans, swine, poultry and other animals. Resting cells of this species convert glycerol into a potent, broad-spectrum antimicrobial substance termed reuterin. Reuterin is a low molecular weight, neutral, water soluble compound, capable of inhibiting growth of species representing all bacterial genera tested thus far, including: Escherichia, Salmonella, Shigella, Proteus, Pseudomonas, Clostridium and Staphylococcus. Also affected, but to a lesser degree, are lactic acid bacteria belonging to the genera Streptococcus, Pediococcus, Leuconostoc, and Lactobacillus. In this report we describe a method to screen lactobacilli for production of unique antimicrobial substances and the discovery of reuterin.

Chemical characterization of an antimicrobial substance produced by Lactobacillus reuteri.

Abstract: Lactobacillus reuteri converts glycerol into a potent cell growth inhibitor. This substance, termed reuterin, inhibits the growth of gram-positive and gram-negative bacteria as well as yeasts, fungi, and protozoa. Semipreparative chromatography was used to purify reuterin, and Fourier transform infrared spectroscopy and liquid chromatography-mass spectrometry were used to establish the molecular weight as well as the molecular functionality of the reuterin molecule. Nuclear magnetic resonance studies of purified reuterin carried out with deuterium oxide confirmed the presence of two three-carbon compounds, beta-hydroxypropionaldehyde and the corresponding hydrated acetal, and a six-carbon cyclic dimer of the aldehyde. Further nuclear magnetic resonance studies with deuterated methanol revealed that in this solvent the compound existed as a three-carbon compound in a methoxy form. Trimethylsilyl derivatives of reuterin were analyzed by gas chromatography-mass spectrometry, and a molecule was identified which had a molecular weight corresponding to a disilylated dimeric structure. On the basis of the above information, reuterin was determined to be an equilibrium mixture of monomeric, hydrated monomeric, and cyclic dimeric forms of beta-hydroxypropionaldehyde. This was subsequently confirmed by chemical synthesis.

Demand for Farm Output in a Complete System of Demand Functions

Abstract: Demand interrelationships for farm outputs that are theoretically consistent with consumer demand and marketing group behavior provide important linkages between retail and farm prices. A conceptual model, based on reduced-form specifications for retail and farm prices, is formulated and applied empirically to a set of eight disaggregated food commodities. This approach circumvents the need for retail quantities, which are frequently unavailable for disaggregated food commodities. The results are consistent with theory and generally indicate significant substitution between farm and marketing inputs. Except for poultry, derived demand elasticities are at least 40% larger compared to those derived assuming fixed proportions.

Quantifying food consumption and growth in insects

Abstract: Relative consumption rate is frequently calculated as weight of food consumed divided by mean body weight over the course of the feeding period. However, mean weight incorporates weight change, which is a function of digestive efficiency; relative consumption rate, therefore, is inherently dependent on physiological responses. In short-term (within one instar) experiments quantifying insect behavior, the maximum amount of food an insect can eat is not likely to vary directly with body weight. Under such circumstances, it is more appropriate to relate consumption to the weight of the insect at the beginning of the test, not to mean weight. The use of mean weights produces a similar bias in relative growth rate.

Characterization of diamond thin films: Diamond phase identification, surface morphology, and defect structures

Abstract: Thin carbon films grown from a low pressure methane-hydrogen gas mixture by microwave plasma enhanced CVD have been examined by Auger electron spectroscopy, secondary ion mass spectrometry, electron and x-ray diffraction, electron energy loss spectroscopy, and electron microscopy. They were determined to be similar to natural diamond in terms of composition, structure, and bonding. The surface morphology of the diamond films was a function of position on the sample surface and the methane concentration in the feedgas. Well-faceted diamond crystals were observed near the center of the sample whereas a less faceted, cauliflower texture was observed near the edge of the sample, presumably due to variations in temperature across the surface of the sample. Regarding methane concentration effects, threefold {111} faceted diamond crystals were predominant on a film grown at 0.3% CH4 in H2 while fourfold {100} facets were observed on films grown in 1.0% and 2.0% CH4 in H2. Transmission electron microscopy of the diamond films has shown that the majority of diamond crystals have a very high defect density comprised of {111} twins, {111} stacking faults, and dislocations. In addition, cross-sectional TEM has revealed a 50 A epitaxial layer of β3–SiC at the diamond-silicon interface of a film grown with 0.3% CH4 in H2 while no such layer was observed on a diamond film grown in 2.0% CH4 in H2.

Time of Desiccation Effects on Plant Composition and Subsequent Nitrogen Release from Several Winter Annual Cover Crops

Abstract: (...)Averaged over 2 yr the late desiccation treatment resulted in increases in cover crop dry matter of 39, 41, and 61% for rye, crimson clover, and hairy vetch, respectively. Corresponding increases in total N content of the respective cover crops were 14, 23, and 41%. Significant differences in cellulose, hemicellulose, and lignin contents were found among cover crop residues between desiccation times (...)

Zinc methionine for ruminants: relative bioavailability of zinc in lambs and effects of growth and performance of growing heifers.

Abstract: Studies were conducted to evaluate zinc methionine (ZnMet) as a source of Zn for ruminants. Experiment 1 compared the availability of Zn in ZnMet and zinc oxide (ZnO) in lambs fed a semi-purified diet deficient in Zn. Based on growth rate and animal performance, plasma Zn and plasma alkaline phosphatase activity, no differences in Zn availability were detected between the two Zn sources. Apparent absorption of Zn also was similar, but Zn retention was higher (P less than .01) in lambs fed ZnMet because of a tendency for lower urinary Zn excretion (P less than .19) in this group. Zinc absorption and retention by lambs were similar for the two Zn sources in Exp. 2 when 20 mg Zn/kg was added to an orchardgrass hay-based diet containing 30 mg Zn/kg. In Exp. 3, lambs were dosed orally with 300 mg of Zn as ZnO or ZnMet, and the increase in plasma Zn following dosing was monitored. The increase in plasma Zn above predosing values was similar at 6 h but was higher at 12 (P less than .10) and 24 h (P less than .05) postdosing in lambs given ZnMet. Thirty-six Hereford x Simmental heifers (271 kg) were used in Exp. 4 to determine the influence of supplementing Zn (25 mg/kg) as ZnO or ZnMet of growth performance and Zn status. Heifers were fed a corn silage-based diet that contained 23.1 mg Zn/kg during the 126-d study. Zinc supplementation to the basal diet increased (P less than .05) gain and feed/gain during the first 56 d, but not for the entire 126-d study.(ABSTRACT TRUNCATED AT 250 WORDS)

Accretionary tectonics of Burma and the three-dimensional geometry of the Burma subduction zone

Abstract: The geometry of the Burma Wadati-Benioff zone (WBZ) has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well-located hypocenters. The dip of this surface, which passes through the middle of the WBZ, varies from about 50° in the north near the eastern Himalayan syntaxis to about 30° in the Bay of Bengal area. The eastern edge of the Indo-Burman ranges closely follows the map projection of the 60 km depth contour of the WBZ. The curvature of the Indo-Burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the Indian plate and the leading edge of the overriding Burma platelet. Shallow earthquakes beneath the Indo-Burman ranges are primarily confined to the underthrusting Indian plate. Their focal mechanisms indicate strike-slip faulting and north-south shortening parallel to the eastern margin of the Indian plate.

Conditionally Unbiased Bounded-Influence Estimation in General Regression Models, with Applications to Generalized Linear Models

Abstract: In this article robust estimation in generalized linear models for the dependence of a response y on an explanatory variable x is studied. A subclass of the class of M estimators is defined by imposing the restriction that the score function must be conditionally unbiased, given x. Within this class of conditionally Fisher-consistent estimators, optimal bounded-influence estimators of regression parameters are identified, and their asymptotic properties are studied. The estimators studied in this article and the efficient bounded-influence estimators studied by Stefanski, Carroll, and Ruppert (1986) depend on an auxiliary centering constant and nuisance matrix. The centering constant can be given explicitly for the conditionally Fisher-consistent estimators, and thus they are easier to compute than the estimators studied by Stefanski et al. (1986). In addition, estimation of the nuisance matrix has no effect on the asymptotic distribution of the conditionally Fisher-consistent estimators; the sam...

Nitrogen isotope fractionation by oceanic zooplankton

Abstract: The ratio of 15 N: 14 N for particulate matter suspended in oceanic, surface waters is high after recent nitrate depletion and low in the stable, oligotrophic ocean. We hypothesize that zooplankters and other pelagic heterotrophs produce 15 N-depleted ammonium and 15 N-enriched particulate matter that are, respectively, recycled in and exported from the euphotic zone and thus cause the low values of 15 N: 14 N in oligotrophic seas. Heretofore, this pattern was attributed to nitrogen-fixation by the phytoplankton. We measured the ratio of 15 N: 14 N in the bodies and excreted ammonium of zooplankters from the northwest Pacific Ocean and compared these values to the ratio of 15 N: 14 N for subeuphotic, dissolved nitrate. We report that oceanic zooplankton excrete ammonium that is isotopically light relative to their bodies and subeuphotic nitrate. These results are consistent with our hypothesis and the view that the phytoplankton of oligotrophic seas is nourished primarily by nitrogen recycled within the euphotic zone. Nitrate injected into the euphotic zone may be manifest and hence detected by an increase of the ratio 15 N: 14 N for the particulate matter suspended therein.

Estimation and analysis of survival distributions for radio-tagged animals.

Abstract: We present results on the estimation of survival distributions for an important problem in animal ecology. The problem involves estimation of survival distributions using radio-tagged animals. It requires allowance for censored observations due to radio failure, emigration from the study area, and animals surviving past the end of the study period. We show that survival analysis techniques already used in medical and engineering studies may be applied to this problem. Emphasis is placed on the model assumptions and the need for further research. An example to illustrate the strengths and weaknesses of this approach is presented.

Performance of multiprocessor interconnection networks

Abstract: A tutorial is provided on the performance evaluation of multiprocessor interconnection networks, to guide system designers in their design process. A classification of parallel/distributed systems is followed by a classification of multiprocessor interconnection networks. Basic terminology for performance evaluation is presented. The performance of crossbar interconnection networks, multistage interconnection networks, and multiple-bus systems is then addressed, and a comparison is made along them. >

Biochemical Mechanism for Regulation of Sucrose Accumulation in Leaves during Photosynthesis

Abstract: It is not known why some species accumulate high concentrations of sucrose in leaves during photosynthesis while others do not. To determine the possible basis, we have studied 10 species, known to differ in the accumulation of sucrose, in terms of activities of sucrose hydrolyzing enzymes. In general, acid invertase activity decreased as leaves expanded; however, activities remaining in mature, fully expanded leaves ranged from low ( 100 micromoles per gram fresh weight per hour). In contrast, sucrose synthase activities were low and relatively similar among the species (4-10 micromoles per gram fresh weight per hour). Importantly, leaf sucrose concentration, measured at midafternoon, was negatively correlated with acid invertase activity. We propose that sucrose accumulation in vacuoles of species such as soybean and tobacco is prevented by acid invertase-mediated hydrolysis. Initial attempts were made to characterize the relatively high activity of acid invertase from mature soybean leaves. Two apparent forms of the enzyme were resolved by Mono Q chromatography. The two forms had similar affinity for substrate (apparent Km [sucrose] = 3 millimolar) and did not interconvert upon rechromatography. It appeared that the loss of whole leaf invertase activity during expansion was largely the result of changes in one of the enzyme forms. Overall, the results provide a mechanism to explain why some species do not accumulate sucrose in their leaves. Some futile cycling between sucrose and hexose sugars is postulated to occur in these species, and thus, the energy cost of sucrose production may be higher than is generally thought.

Kanban controlled pull systems: an analytic approach

Abstract: Three problem areas exist in designing and implementing a kanban controlled JIT system: the identification of flow lines problem, the flow line loading problem and the operational control problem. This paper addresses the operational control problem. A general N-stage serial production system is modeled as a discrete time Markov process. Capacity constraints, stochastic machine reliability and demand variability are included. The model is illustrated by a 3-stage system, describing the effects of the number of kanbans, the machine reliability, the demand variability and safety stock requirements on the performance of a kanban controlled pull system.

Proliferation of Maize (Zea mays L.) Roots in Response to Localized Supply of Nitrate

Abstract: Maize (Zea mays L) plants with two primary nodal root axes were grown for 8 d in flowing nutrient culture with each axis independently supplied with NO3- Dry matter accumulation by roots was similar whether 10 mol m-3 NO3- was supplied to one or both axes When NO3- was supplied to only one axis, however, accumulation of dry matter within the root system was significantly greater in the axis supplied with NO3- The increased dry matter accumulation by the +N-treated axis was attributable entirely to increased density and growth of lateral branches and not to a difference in growth of the primary axis Proliferation of lateral branches for the +N axis was associated with the capacity for in situ reduction and utilization of a portion of the absorbed NO3-, especially in the apical region where lateral primordia are initiated Although reduced nitrogen was translocated to the -N axis, concentrations in the -N axis remained significantly lower than in the +N axis The concentration of reduced nitrogen, as well as in vitro NO3- reductase activity, was greater in apical than in more basal regions of the +N axis The enhanced proliferation of lateral branches in the +N axis was accompanied by an increase in total respiration rate of the axis Part of the increased respiration was attributable to increased mass of roots The specific respiration rate (micromoles CO2 evolved per hour per gram root dry weight) was also greater for the +N than for the -N axis If respiration rate is taken as representative of sink demand, stimulation of initiation and growth of laterals by in situ utilization of a localized exogenous supply of NO3- establishes an increased sink demand through enhanced metabolic activity and the increased partitioning of assimilates to the +N axis responds to the difference in sink demand between +N and -N axes

A Hedonic Study of the Effects of Erosion Control and Drainage on Farmland Values

Abstract: Valuing farmland improvements is important for individual farmers and policy makers. This paper demonstrates the use of a hedonic land value study to determine the value of erosion control and drainage using data from North Carolina. Land values are significantly affected by both potential erosivity and drainage requirements. This study's estimates are compared with estimates derived from a variety of other types of studies.

Unbiased estimation of a nonlinear function a normal mean with application to measurement err oorf models

Abstract: Let W be a normal random variable with mean μand known variance σ2. Conditions on the function f(·) are given under which there exists an unbiased estimator, f(W), of f(μ) for all real μ. In particular it is shown that f(·) must be an entire function over the complex plane. Infinite series solutions for F(·) are obtained which are shown to be valid under growth conditions of the derivatives, fk( ·), of f(·). Approximate solutions are given for the cases in which no exact solution exists. The theory is applied to nonlinear measurement-error models as a means of finding unbiased score functions when measurement error is normally distributed. Relative efficiencies comparing the proposed method to the use of conditional scores (Stefanski and Carroll, 1987) are given for the Poisson regression model with canonical link.