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Subtle Variations (subtle + variation)
Selected AbstractsCan Contaminant Transport Models Predict Breakthrough?GROUND WATER MONITORING & REMEDIATION, Issue 4 2000Wei-Shyuan "Stone" Peng A solute breakthrough curve measured during a two-well tracer test was successfully predicted in 1986 using specialized contaminant transport models. Water was injected into a confined, unconsolidated sand aquifer and pumped out 125 feet (38.3 m) away at the same steady rate. The injected water was spiked with bromide for over three days; the outflow concentration was monitored for a month. Based on previous tests, the horizontal hydraulic conductivity of the thick aquifer varied by a factor of seven among 12 layers. Assuming stratified flow with small dispersivities, two research groups accurately predicted breakthrough with three-dimensional (12-layer) models using curvilinear elements following the arc-shaped flowlines in this test. Can contaminant transport models commonly used in industry, that use rectangular blocks, also reproduce this breakthrough curve? The two-well test was simulated with four MODFLOW-based models, MT3D (FD and HMOC options), MODFLOWT, MOC3D, and MODFLOW-SURFACT. Using the same 12 layers and small dispersivity used in the successful 1986 simulations, these models fit almost as accurately as the models using curvilinear blocks. Subtle variations in the curves illustrate differences among the codes. Sensitivities of the results to number and size of grid blocks, number of layers, boundary conditions, and values of dispersivity and porosity are briefly presented. The fit between calculated and measured breakthrough curves degenerated as the number of layers and/or grid blocks decreased, reflecting a loss of model predictive power as the level of characterization lessened. Therefore, the breakthrough curve for most field sites can be predicted only qualitatively due to limited characterization of the hydrogeology and contaminant source strength. [source] Geographical variation in predictive seedling emergence in a perennial desert grassJOURNAL OF ECOLOGY, Issue 1 2000Steven E. Smith Summary 1,Mechanisms that link germination and emergence to environmental cues associated with seedling success (predictive germination) would be expected to evolve when seedlings have a greater mortality risk than seeds, but may be less important in perennial plants than in annual plants. 2,We investigated variation in predictive seedling emergence among divergent populations of a short-lived perennial desert grass, Digitaria californica, from sites that differed in climatic and edaphic factors. This species is native to environments in which the amount and duration of adequate soil moisture may control germination and seedling establishment success. 3,We utilized a special irrigation system that permits application of a range of amounts of water within a single experiment in a glasshouse. Emergence data were subjected to probit and survival analyses to describe differences among the populations in response to applied water. 4,Significant variation in predictive emergence was shown to exist among populations of D. californica when measured as amount of water required for 50% emergence following 3 days of water application, or as time required to achieve this level of emergence. Both climatic and soil characteristics were important with populations that originated from sites with less summer precipitation, and soils with higher water-holding capacity tended to have lower water requirements for emergence. 5,The report demonstrates the existence of subtle variation in predictive emergence among populations of a perennial grass representing a relatively narrow range of ecological amplitude. It also establishes the usefulness of line-source irrigation and probit analysis procedures in studying seedling emergence behaviour. [source] Searching for the regulators of human gene expressionBIOESSAYS, Issue 10 2006Julian T. Forton Many common human traits are believed to be a composite reflection of multiple genetic and non-genetic factors and the genetic contribution is consequently often difficult to characterise. Recent advances suggest that subtle variation in the regulation of gene expression may contribute to complex human traits. In two reports,1,2 Cheung and colleagues scale up human genetics analysis to an impressive level in a genome-wide search for the regulators of gene expression. They perform linkage analysis on expression profiles for over 3,500 genes and then employ the HapMap resource3 to take positive findings through to association studies at the genome-wide level. This work gives new insights into the complexities of gene regulation and the plausibility of genome-wide study design. BioEssays 28: 968,972, 2006. © 2006 Wiley Periodicals, Inc. [source] Synthesis of Strained Tricyclic ,-Lactams by Intramolecular [2+2] Cycloaddition Reactions of 2-Azetidinone-Tethered Enallenols: Control of Regioselectivity by Selective Alkene SubstitutionCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2006Benito Alcaide Prof. Dr. Abstract A convenient metal-free methodology for the preparation of structurally novel, strained tricyclic ,-lactams containing a cyclobutane ring has been developed. The first examples accounting for the intramolecular [2+2] cycloaddition reactions in ,-lactams have been achieved by the thermolysis of 2-azetidinone-tethered enallenols, which have been prepared in aqueous media by regio- and diastereoselective indium-mediated carbonyl allenylation of 4-oxoazetidine-2-carbaldehydes. Notably, the regioselectivity of the cycloaddition can be tuned in the allene component just by a subtle variation in the substitution pattern of the alkene component. Se ha descubierto una metodología para la preparación de ,-lactamas tricíclicas tensionadas estructuralmente novedosas sin la intervención de metales. La pirólisis de alenoles-,-lactámicos, que se prepararon en medio acuoso mediante la alenilación carbonílica de 4-oxoazetidin-2-carbaldehidos, constituye el primer ejemplo de cicloadición intramolecular [2+2] en ,-lactamas. Mención especial merece la regioselectividad observada, pudiéndose controlar y modular con un simple cambio en la sustitución del alqueno. [source] Lessons learned from DNA repair defective syndromesEXPERIMENTAL DERMATOLOGY, Issue 6 2007Kai-Martin Thoms Abstract:, Genomic instability is the driving force behind cancer development. Human syndromes with DNA repair deficiencies comprise unique opportunities to study the clinical consequences of faulty genome maintenance leading to premature aging and premature cancer development. These syndromes include chromosomal breakage syndromes with defects in DNA damage signal transduction and double-strand break repair, mismatch repair defective syndromes as well as nucleotide excision repair defective syndromes. The same genes that are severely affected in these model diseases may harbour more subtle variations in the ,healthy' normal population leading to genomic instability, cancer development, and accelerated aging at later stages of life. Thus, studying those syndromes and the molecular mechanisms behind can significantly contribute to our understanding of (skin) cancerogenesis as well as to the development of novel individualized preventive and therapeutic anticancer strategies. The establishment of centers of excellence for studying rare genetic model diseases may be helpful in this direction. [source] Settling the "Dead Layer" Debate in Nanoscale CapacitorsADVANCED MATERIALS, Issue 48 2009Li-Wu Chang Permittivity peaks in single crystal thin film capacitors are strongly suppressed compared to bulk in the case of Pt/SrTiO3/Pt, but are relatively unaffected in Pt/BaTiO3/Pt structures. This is consistent with the recent suggestion that subtle variations in interfacial bonding between the dielectric and electrode are critical in determining the presence or absence of inherent dielectric "dead layers". [source] Women and attention deficit disorders: A great burden overlookedJOURNAL OF THE AMERICAN ACADEMY OF NURSE PRACTITIONERS, Issue 3 2007Assistant Professor2), CS (Postdoctoral Research Fellow, Roberta Waite EdD Abstract Purpose: To describe adult attention-deficit/hyperactivity disorder (ADHD) in relation to gender-based differences in symptom expression with particular emphasis on disparities concerning women, psychiatric comorbidities that affect assessment and detection, and evidenced-based treatment approaches for nurse practitioners (NPs). Data sources: Health sciences literature was reviewed using the following data-bases: Medline, Cumulative Index to Nursing and Allied Health Literature, PubMed, Proquest, Psych Info, Wiley Interscience, Cambridge Press, Science Direct, and Thomson Gale. Conclusions: Recognizing adult ADHD may be challenging; however, with increased understanding regarding the subtle variations in symptoms, use of screening instruments, and careful assessment techniques, NPs will be better able to recognize the characteristics of ADHD that are important to early detection, proper diagnosis, and effective treatment. Implications for practice: Additional research and improved clinician education may facilitate early detection and treatment of ADHD among adults of all ages and ethnic/racial backgrounds. [source] Robotic total station for microtopographic mapping: an example from the Northern Great PlainsARCHAEOLOGICAL PROSPECTION, Issue 2 2006Kenneth L. Kvamme Abstract Past human activities in cultural landscapes are often expressed by subtle variations in surface topography that reflect buried archaeological features. When seen from the air under low sunlight angles, resultant ,shadow marks' form a cornerstone of site detection in aerial archaeology. Past attempts to quantify and map such variations across large archaeological landscapes have resorted to aerial photogrammetry, electronic total stations, air- and ground-based lidar, and kinematic global positioning systems. The most commonly used surveying instrument is the total station, but its slow rate of data acquisition makes it poorly suited for collecting vast amounts of elevation data over large areas, although it is often used for that task. A robotic total station, examined here, is a relatively new technology that provides a rapid survey solution. It requires only a single person to operate the total station by radio linkage from a control pad affixed to a wheeled reflector rod. As the rod is rolled over the landscape it is automatically tracked, and measurements of surface topography may be acquired to subcentimetre accuracy continuously, at a rate of one measurement per second. A case study from the Double Ditch State Historic Site in the Great Plains of North Dakota, a fortified earthlodge village with culturally significant surface expressions, exemplifies this potential. The loci of prehistoric houses, borrow pits, fortification ditches, middens and defensive mounds are clearly revealed in the topographic mapping. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||