Showing papers by "Oklahoma State University–Stillwater published in 2002"
TL;DR: These findings demonstrate the collective behavior of nanoparticles as well as a convenient, simple technique for production of one-dimensional semiconductor colloids suitable for subsequent processing into quantum-confined superstructures, materials, and devices.
Abstract: Nanoparticles of CdTe were found to spontaneously reorganize into crystalline nanowires upon controlled removal of the protective shell of organic stabilizer. The intermediate step in the nanowire formation was found to be pearl-necklace aggregates. Strong dipole-dipole interaction is believed to be the driving force of nanoparticle self-organization. The linear aggregates subsequently recrystallized into nanowires whose diameter was determined by the diameter of the nanoparticles. The produced nanowires have high aspect ratio, uniformity, and optical activity. These findings demonstrate the collective behavior of nanoparticles as well as a convenient, simple technique for production of one-dimensional semiconductor colloids suitable for subsequent processing into quantum-confined superstructures, materials, and devices.
1,728 citations
TL;DR: Fast algorithms for computing persistence and experimental evidence for their speed and utility are given for topological simplification within the framework of a filtration, which is the history of a growing complex.
Abstract: We formalize a notion of topological simplification within the framework of a filtration, which is the history of a growing complex. We classify a topological change that happens during growth as either a feature or noise depending on its lifetime or persistence within the filtration. We give fast algorithms for computing persistence and experimental evidence for their speed and utility.
1,671 citations
01 Jun 2002
TL;DR: The evolution of DSS technologies and issues related to DSS definition, application, and impact are discussed, and four powerful decision support tools, including data warehouses, OLAP, data mining, and Web-based DSS are presented.
Abstract: Since the early 1970s, decision support systems (DSS) technology and applications have evolved significantly. Many technological and organizational developments have exerted an impact on this evolution. DSS once utilized more limited database, modeling, and user interface functionality, but technological innovations have enabled far more powerful DSS functionality. DSS once supported individual decision-makers, but later DSS technologies were applied to workgroups or teams, especially virtual teams. The advent of the Web has enabled inter-organizational decision support systems, and has given rise to numerous new applications of existing technology as well as many new decision support technologies themselves. It seems likely that mobile tools, mobile e-services, and wireless Internet protocols will mark the next major set of developments in DSS. This paper discusses the evolution of DSS technologies and issues related to DSS definition, application, and impact. It then presents four powerful decision support tools, including data warehouses, OLAP, data mining, and Web-based DSS. Issues in the field of collaborative support systems and virtual teams are presented. This paper also describes the state of the art of optimization-based decision support and active decision support for the next millennium. Finally, some implications for the future of the field are discussed.
1,360 citations
10 Dec 2002
TL;DR: In this article, the authors describe a framework for cooperative control of a group of nonholonomic mobile robots that allows them to build complex systems from simple controllers and estimators, and guarantee stability and convergence in a wide range of tasks.
Abstract: We describe a framework for cooperative control of a group of nonholonomic mobile robots that allows us to build complex systems from simple controllers and estimators. The resultant modular approach is attractive because of the potential for reusability. Our approach to composition also guarantees stability and convergence in a wide range of tasks. There are two key features in our approach: 1) a paradigm for switching between simple decentralized controllers that allows for changes in formation; 2) the use of information from a single type of sensor, an omnidirectional camera, for all our controllers. We describe estimators that abstract the sensory information at different levels, enabling both decentralized and centralized cooperative control. Our results include numerical simulations and experiments using a testbed consisting of three nonholonomic robots.
1,068 citations
TL;DR: The free-standing SWNT/polyelectrolyte membranes delaminated from the substrate were found to be exceptionally strong with a tensile strength approaching that of hard ceramics.
Abstract: The mechanical failure of hybrid materials made from polymers and single-wall carbon nanotubes (SWNT) is primarily attributed to poor matrix–SWNT connectivity and severe phase segregation. Both problems can be successfully mitigated when the SWNT composite is made following the protocol of layer-by-layer assembly. This deposition technique prevents phase segregation of the polymer/SWNT binary system, and after subsequent crosslinking, the nanometre-scale uniform composite with SWNT loading as high as 50 wt% can be obtained. The free-standing SWNT/polyelectrolyte membranes delaminated from the substrate were found to be exceptionally strong with a tensile strength approaching that of hard ceramics. Because of the lightweight nature of SWNT composites, the prepared free-standing membranes can serve as components for a variety of long-lifetime devices.
966 citations
TL;DR: The Metacognitive Awareness of Reading Strategies Inventory (MAPS) as mentioned in this paper is a self-report instrument designed to assess adolescents' metacognitive awareness and perceived use of reading strategies while reading academic or school-related materials.
Abstract: This article describes the development and validation of a new self-report instrument, the Metacognitive Awareness of Reading Strategies Inventory, which is designed to assess adolescent and adult readers' metacognitive awareness and perceived use of reading strategies while reading academic or school-related materials. There were 3 strategy subscales or factors: Global Reading Strategies, Problem-Solving Strategies, and Support Reading Strategies. The reliability and factorial validity of the scale were demonstrated. After a brief review of the literature, the development and validation of the instrument are described, and its psychometric properties are discussed. In addition, directions for administering and scoring the instrument are provided, and suggestions for interpreting the results obtained are offered. Finally, the scales' implications for reading research and instruction are discussed.
893 citations
TL;DR: In this article, the authors extend earlier research on the relationship between corporate social and financial performance and use the Community Reinvestment Act ratings as a social performance measure to support the hypothesis that the link between social and monetary performance is positive.
Abstract: The purpose of this investigation is to extend earlier research on the relationship between corporate social and financial performance. The unique contribution of the study is the empirical analysis of a sample of companies from the banking industry and the use of Community Reinvestment Act ratings as a social performance measure. The empirical analysis solidly supports the hypothesis that the link between social and financial performance is positive.
881 citations
TL;DR: A reliability generalization study for Spielberger's State-Trait Anxiety Inventory (STAI) was conducted by as mentioned in this paper, where a total of 816 research articles utilizing the STAI between 1990 and 2000 were reviewed and compared.
Abstract: A reliability generalization study for Spielberger’s State-Trait Anxiety Inventory (STAI) was conducted. A total of 816 research articles utilizing the STAI between 1990 and 2000 were reviewed and ...
855 citations
TL;DR: In this article, the validity of using in-season estimates of grain yield (INSEY) and a response index (RI) to modulate N at 1-m 2 spatial resolution was evaluated.
Abstract: In 2001, N fertilizer prices nearly doubled as a result of increased natural gas prices This was further troubling when considering that the world N use efficiency (NUE) in cereal grain production averages only 33% Methods to improve NUE in winter wheat (Triticum aestivum L) have not included high spatial-resolution management based on sensed plant growth properties nor on midseason prediction of grain yield Our objective was to determine the validity of using inseason estimates of grain yield (INSEY) and a response index (RI) to modulate N at 1-m 2 spatial resolution Four winter wheat field experiments were conducted that evaluated prescribed midseason N applications compared with uniform rates that simulated farmer practices Our methods recognize that each 1-m 2 area in wheat fields needs to be sensed and managed independently and that the need for fertilizer N is temporally dependent Averaged over locations, NUE was improved by >15% when N fertilization was based on optically sensed INSEY, determined for each 1-m 2 area, and a RI compared with traditional practices at uniform N rates
706 citations
TL;DR: The discrete non-Abelian symmetry, valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses.
Abstract: The discrete non-Abelian symmetry $A_4$, valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mass splittings and mixing angles (one of which is necessarily maximal and the other large) are then induced radiatively in the context of softly broken supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter $U_{e3}$ is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and $\tau \to \mu \gamma$ should be in the experimentally accessible range.
577 citations
TL;DR: DCL1 shows similarity to the Dicer group of genes, which are required for RNA silencing in Drosophila and Caenorhabditis and is important for development in eukaryotes.
TL;DR: The immunocomplexes can be considered as a prototype of NP superstructures based on biospecific ligands, while the competitive FRET inhibition can be used in an immunoassay protocol.
Abstract: Complementary bioconjugates based on antibody−antigen interactions were synthesized from luminescent CdTe nanoparticles (NPs). Antigen (bovine serum albumin) was conjugated to red-emitting CdTe NPs, while green-emitting NPs were attached to the corresponding anti-BSA antibody (IgG). The NP bioconjugates were characterized by native and SDS−PAGE electrophoresis, gel-permeation HPLC, and circular dichroism. Antigen−antibody binding affinity was evaluated by enzyme-linked immunosorbent assay (ELISA). The formation of BSA−IgG immunocomplex resulted in the Forster resonance energy transfer (FRET) between the two different NPs: the luminescence of green-emitting NPs was quenched whereas the emission of the red-emitting NPs was enhanced. The luminescence recovered when the immunocomplex was exposed to an unlabeled antigen. The immunocomplexes can be considered as a prototype of NP superstructures based on biospecific ligands, while the competitive FRET inhibition can be used in an immunoassay protocol.
TL;DR: This paper examined empirical and theoretical work in three eras (infancy, toddlerhood, and early childhood) and for each era describe the structure of dyadic synchrony in interactions involving children and their caregivers and offer speculation about its developmental function for the child.
TL;DR: In this paper, the surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively, were found to have preferential adsorption of the flat particles on polyelectrolyte films.
Abstract: Gold nanoparticles (NPs) were prepared by reduction with salicylic acid in aqueous solution. The resulting dispersions were found to contain a mixture of flat triangular/hexagonal and smaller close-to-spherical NPs. As expected from theoretical considerations, such nanocolloids display two clearly differentiated surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively. Layer-by-layer (LBL) assembly was used to deposit thin films of the Au colloids. UV−visible data indicate preferential adsorption of the flat particles on polyelectrolyte films. Importantly, a new band developed at 650 nm as the number of the Au NPs bilayers increased. This finding indicates that there exists a strong interaction between the NPs in adjacent layers, resulting in the surface plasmon absorption at a new wavelength. The insertion of extra polyelectrolyte or montmorillonite layers between the Au bilayers was shown to gradually reduce the interlayer interaction and r...
TL;DR: In this paper, the authors investigated the antecedents and consequences of relationship quality in the context of hotel management and found that greater service providers' relational and customer orientation resulted in higher relationship quality.
TL;DR: The results confirm that Don production plays a significant role in the spread of FHB within a spike, and are the first report that DON production is not necessary for initial infection by the fungus.
Abstract: Fusarium graminearum is a major pathogen that causes fusarium head blight (FHB) in wheat and produces deoxynivalenol (DON) in infected grain. In previous studies, the trichodiene synthase gene (Tri5) in the fungal strain GZ3639 was disrupted to produce the DON-nonproducing strain GZT40. In this report, the virulence of strains GZ3639 and GZT40 was tested on wheat cultivars with various resistance levels by using methods of spray inoculation and injection inoculation with fungal conidia. Under field and greenhouse conditions, strain GZ3639 produced significantly more disease symptoms and reduced more yield than strain GZT40 in all wheat cultivars tested. Conidia of strain GZT40 germinated and infected inoculated spikelets, but disease symptoms were limited to inoculated spikelets without spread to uninoculated spikelets. When strain GZT40 was inoculated using the spray method, multiple initial infection sites in a spike resulted in higher levels of disease symptoms than in spikes inoculated by a single injection. Greenhouse tests confirmed that strain GZT40 did not produce DON in the infected kernels following either inoculation method. The results confirm that DON production plays a significant role in the spread of FHB within a spike, and are the first report that DON production is not necessary for initial infection by the fungus.
TL;DR: In this article, the dynamics of a large class of N = 1 quiver theories, geometrically realized by type IIB D-brane probes wrapping cycles of local Calabi-Yau three-folds, are studied.
TL;DR: This work proposes several strategies for utilizing external data (such as might be obtained using GIS) to aid in the completion of species lists, and demonstrates the potential of these approaches using simulation and case studies from Oklahoma.
Abstract: A substantial body of literature has accumulated on the topic of the estimation of species richness by extrapolation. However, most of these methods rely on an objective sampling of nature. This condition is difficult to meet and seldom achieved for large regions. Furthermore, scientists conducting biological surveys often already have preliminary but subjectively gathered species lists, and would like to assess the completeness of such lists, and/or to find a way to perfect them. We propose several strategies for utilizing external data (such as might be obtained using GIS) to aid in the completion of species lists. These include: (i) using existing species lists to develop predictive models; (ii) using the uniqueness of the environment as a guide to find underrepresented species; (iii) using spectral heterogeneity to locate environmentally heterogeneous regions; (iv) combining surveys with statistical model-building in an iterative manner. We demonstrate the potential of these approaches using simulation and case studies from Oklahoma. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors examined the moderating effects of age and partner trust on the relationship between control mechanisms and perceptions of performance in 129 US-based international joint ventures (IJVs).
Abstract: This study empirically examines the moderating effects of age and partner trust on the relationship between control mechanisms and perceptions of performance in 129 US-based international joint ventures (IJVs). A reliance on formal control mechanisms and general managers’ perceptions of IJV performance were found to be positively related in younger IJVs, but this relationship became negative in more mature IJVs. In addition, social control mechanisms and perceptions of IJV performance were positively related, but only in the presence of affect-based trust between the parents.
TL;DR: The multilayer perceptron neural network is introduced and how it can be used for function approximation is described and several techniques for improving generalization are discussed.
Abstract: SUMMARY The purpose of this paper is to provide a quick overview of neural networks and to explain how they can be used in control systems. We introduce the multilayer perceptron neural network and describe how it can be used for function approximation. The backpropagation algorithm (including its variations) is the principal procedure for training multilayer perceptrons; it is briefly described here. Care must be taken, when training perceptron networks, to ensure that they do not overfit the training data and then fail to generalize well in new situations. Several techniques for improving generalization are discussed. The paper also presents three control architectures: model reference adaptive control, model predictive control, and feedback linearization control. These controllers demonstrate the variety of ways in which multilayer perceptron neural networks can be used as basic building blocks. We demonstrate the practical implementation of these controllers on three applications: a continuous stirred tank reactor, a robot arm, and a magnetic levitation system. Copyright # 2002 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors investigated the hopping self diffusion coefficient of an adatom on the (1, 0, 0) surface of nine FCC metals using Monte Carlo variational transition state theory and the Lennard-Jones (L-J) interactions.
17 Oct 2002
TL;DR: In this article, the historical development of the Darcy-Weisbach equation for pipe flow resistance is examined, and a concise examination of the evolution of the equation itself and its Darcy friction factor is presented from their inception to the present day.
Abstract: The historical development of the Darcy-Weisbach equation for pipe flow resistance is examined. A concise examination of the evolution of the equation itself and the Darcy friction factor is presented from their inception to the present day. The contributions of Chezy, Weisbach, Darcy, Poiseuille, Hagen, Prandtl, Blasius, von Karman, Nikuradse, Colebrook, White, Rouse and Moody are described.
TL;DR: In this paper, a plot of intergranular volume vs. depth was constructed using data from relatively uncemented reservoir sandstones from a variety of depths, ages, and geographic locations.
Abstract: To evaluate compaction as a factor in porosity evolution, a plot of intergranular volume vs. depth was constructed using data from relatively uncemented reservoir sandstones from a variety of depths, ages, and geographic locations. The resulting intergranular-volume-decline curve reveals that sands compact mechanically and intergranular volume declines rapidly, from about 40 to 42% at the surface, to about 28% at 1500 m. Between about 1500 and 2500 m, intergranular volume continues to decline slowly, until the framework stabilizes at around 26% (maximum potential porosity in the absence of cement or matrix). No further significant decrease in intergranular volume is observed to the depth limits of the data set at 6700 m. Comparison of intergranular volume and volume of quartz cement for different formations reveals no obvious balance between intergranular pressure solution (as monitored by intergranular volume) and quartz cementation. This indicates that grain-to-grain pressure solution and quartz cement precipitation do not proceed concomitantly on the thin-section scale. Moreover, grain compaction is limited (to about 26% intergranular volume) in rigid-grain sandstones, which suggests that the occurrence and distribution of deep porosity is a function of the volume of cement available to fill the intergranular pores. Therefore, deep, porous sandstones are relatively uncemented rather than undercompacted.
TL;DR: Evidence is presented for the coordination of hemolymph‐borne melanization with activation of the Toll pathway in the Drosophila host defence and it is shown that flies deficient for this serpin exhibit spontaneous melanization in larvae and adults.
Abstract: A prominent response during the Drosophila host defence is the induction of proteolytic cascades, some of which lead to localized melanization of pathogen surfaces, while others activate one of the major players in the systemic antimicrobial response, the Toll pathway. Despite the fact that gain-of-function mutations in the Toll receptor gene result in melanization, a clear link between Toll activation and the melanization reaction has not been firmly established. Here, we present evidence for the coordination of hemolymph-borne melanization with activation of the Toll pathway in the Drosophila host defence. The melanization reaction requires Toll pathway activation and depends on the removal of the Drosophila serine protease inhibitor Serpin27A. Flies deficient for this serpin exhibit spontaneous melanization in larvae and adults. Microbial challenge induces its removal from the hemolymph through Toll-dependent transcription of an acute phase immune reaction component.
TL;DR: It is demonstrated that either acetate or H2 alone can be sufficient to promote complete reductive dechlorination of chloroethenes to ethene and that syntrophic acetate-oxidizing population(s) were active in the enrichment cultures.
Abstract: A study to evaluate the dechlorination end points and the most promising electron donors to stimulate the reductive dechlorination process at the chloroethene-contaminated Bachman Road site in Oscoda, MI, was conducted. Aquifer materials were collected from inside the plume and used to establish microcosms under a variety of electron donor conditions using chlorinated ethenes as electron acceptors. All microcosms that received an electron donor showed dechlorination activity, but the end points depended on the sampling location, indicating a heterogeneous distribution of the dechlorinating populations in the aquifer. Interestingly, several microcosms that received acetate as the only electron donor completely dechlorinated PCE to ethene. All acetate-amended microcosms rapidly converted PCE to cis-DCE, whereas PCE dechlorination in H2-fed microcosms only occurred after a pronounced lag time and after acetate had accumulated by H2/CO2 acetogenic activity. The microcosm experiments were corroborated by defined co-culture experiments, which demonstrated that H2 sustained PCE to cis-DCE dechlorination by acetotrophic populations in the presence of H2/CO2 acetogens. In sediment-free nonmethanogenic enrichment cultures derived from ethene-producing microcosms, acetate alone supported complete reductive dechlorination of chloroethenes to ethene, although the addition of H2 resulted in higher cis-DCE and VC dechlorination rates. Measurements of H2 production and consumption suggested that syntrophic acetate-oxidizing population(s) were active in the enrichment cultures. These findings demonstrated that either acetate or H2 alone can be sufficient to promote complete
TL;DR: In this paper, the effects of long-term management practices on the level and distribution of soil P and enzyme activities involved in P transformations in soil were investigated, and it was found that manure-P is relatively more mobile than inorganic fertilizer-P.
Abstract: Studies were conducted to investigate the effects of long-term management practices on level and distribution of soil P and enzyme activities involved in P transformations in soil. Treatments included manure, P, NP, NPK, and NPK plus lime. Cattle manure was applied every 4 years at 269 kg N ha–1 for over a century and chemical fertilizers were applied every year at 67 kg N, 14.6 kg P, and 28 kg K ha–1 for over 69 years. Total soil P increase in soils ranged from 4.5 to 10.3 kg P ha–1 year–1 with the highest increase detected in the P-treated and the lowest in the manure-treated plot. Approximately 77–86% of the applied inorganic fertilizer-P in the past 69–71 years was recovered either in the harvested grain or remained in the top 30 cm of soil, while only 32% of the applied manure-P was recovered. Microbial biomass C and activities of alkaline phosphomonoesterase, phosphodiesterase, inorganic pyrophosphatase, and dehydrogenase were significantly higher in the soil treated with cattle manure. Acid phosphomonoesterase activity, however, was significantly higher in soils treated with chemical fertilizers. Results from this study suggested that manure-P is relatively more mobile than inorganic fertilizer-P. Long-term application of cattle manure promoted microbiological activities and P cycling, but did not result in P accumulation to levels close to those in inorganic P fertilizer-treated soils.
TL;DR: Alesch et al. as mentioned in this paper studied the long-term economic impacts of disasters on the private sector, focusing on short-term impacts, rather than the longer-term consequences of disaster victimization.
TL;DR: The National Beef Quality Audit-2005 assessed the current status of quality and consistency of US fed steers and heifers and provided a benchmark for future educational and research activities.
Abstract: The National Beef Quality Audit-2005 assessed the current status of quality and consistency of US fed steers and heifers Hide colors or breed type were black (563%), red (186%), Holstein (79%), gray (60%), yellow (49%), brown (30%), white (23%), and brindle (10%) Identification method and fre- quency were lot visual tags (632%), individual visual tags (387%), metal-clip tags (118%), electronic tags (35%), bar-coded tags (03%), by other means (25%), and without identification (97%) Brand frequencies were no (613%), 1 (351%), and 2 or more (36%), and brands were located on the butt (265%), side (74%), and shoulder (12%) There were 223% of cattle with- out horns, and the majority of those with horns (522%) were between 254 and 127 cm in length Percentages of animals with mud or manure on specific body loca- tions were none (258%), legs (614%), belly (559%), side (226%), and top-line (100%) Permanent incisor number and occurrence were zero (822%), 1 (52%), 2 (99%), 3 (04%), 4 (12%), 5 (01%), 6 (03%), 7 (00%), and 8 (07%) Most carcasses (648%) were not bruised, 258% had one bruise, and 94% had multiple bruises Bruise location and incidence were round (106%), loin (326%), rib (195%), chuck (270%), and brisket, flank, and plate (103%) Condemnation item and incidence were liver (247%), lungs (115%), tripe (116%), heads (60%), tongues (97%), and carcasses (00%) Car- cass evaluation revealed these traits and frequencies: steer (637%), heifer (362%), bullock (005%), and cow (004%) sex classes; dark-cutters (19%); A (971%), B (17%), and C or older (12%) overall maturities; and native (909%), dairy-type (83%), and Bos indicus (08%) estimated breed types Mean USDA yield grade (YG) traits were USDA YG (29), HCW (3599 kg), adjusted fat thickness (13 cm), LM area (864 cm 2 ), and KPH (23%) The USDA YG were YG 1 (165%), YG 2 (363%), YG 3 (331%), YG 4 (118%), and YG 5 (23%) Mean USDA quality grade traits were USDA quality grade (Select 90 ), marbling score (Small 32 ), over- all maturity (A 64 ), lean maturity (A 57 ), and skeletal ma- turity (A 68 ) Marbling score distribution was Slightly Abundant or greater (27%), Moderate (43%), Modest (144%), Small (345%), Slight (412%), and Traces or less (29%) This information helps the beef industry measure progress and provides a benchmark for future educational and research activities
TL;DR: The study explores data quality problems with existing systems, and identifies critical success factors that impact data quality, which resulted in the development of a framework for understanding data quality issues in implementing an ERP and application in a case study in two large Australian organisations.
Abstract: Data quality is a critical issue during the implementation of an enterprise resource planning (ERP) system. Data quality problems can have a significant impact on an organisation’s information system. Therefore, it is essential to understand data quality issues to ensure success in implementing ERP systems. This paper uses SAP as an example of an ERP system and describes a study, which explores data quality problems with existing systems, and identifies critical success factors that impact data quality. The study resulted in the development of a framework for understanding data quality issues in implementing an ERP, and application of this framework in a case study in two large Australian organisations. The findings of the study suggest that the importance of data quality needs to be widely understood in implementing an ERP, as well as providing recommendations that may be useful to practitioners.
TL;DR: In this article, the authors provide an introduction to those characteristics that will facilitate interpretation of the occasionally problematic nature of phosphate U-Th-Pb dating results, and provide a greater understanding of their structure, stability and kinetic properties than does zircon.
Abstract: ### Introduction
The dominant occurrence of phosphate minerals in crystalline rocks is as accessory phases, most notably apatite, monazite, and xenotime. Because these minerals tend, to varying degrees, to partition U and Th into their structures they can often contain the majority of those elements in a rock. These three phases, again to varying degrees, tend not to incorporate significant amounts of Pb during crystallization and thus were early candidates for utilization as U-Th-Pb geochronometers.
The ideal U-Th-Pb geochronometer would be a phase that is stable over all possible environmental conditions and is quantitatively retentive of parent and daughter isotopes. In fact, the silicate zircon comes reasonably close to meeting these criteria. Zircon has a broad stability field, is refractory under a wide variety of geologic environments (e.g., weathering, sedimentary transport, anatexis, and metamorphism), and can be highly retentive of daughter products in the U-Th-Pb decay system. However, the limit of zircon as an ideal chronometer lies only in its limited resistance to auto-irradiation damage that can render it metamict. The phosphate minerals apatite, monazite and xenotime have a more restricted range of stability and, to varying degrees, are incompletely retentive of Pb under crustal conditions, but they are resilient to radiation damage. Thus interpretation of results from these geochronometers requires a greater understanding of their structure, stability, and kinetic properties than does zircon. This chapter is aimed at providing the reader with an introduction to those characteristics that will facilitate interpretation of the occasionally problematic nature of phosphate U-Th-Pb dating results.
### The U-Th-Pb dating system
#### U and Th decay.
Nuclei approaching one hundred protons are unstable because the strong nuclear force, which acts to hold neutrons and protons together, is about 100 times greater than electromagnetic repulsion. Both uranium (92 protons) and thorium (90 protons) decay by emission of a 4He nucleus (or α particle), which lowers the …