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Potential Range (potential + range)
Selected AbstractsResidence time and potential range: crucial considerations in modelling plant invasionsDIVERSITY AND DISTRIBUTIONS, Issue 1 2007John R. U. Wilson ABSTRACT A prime aim of invasion biology is to predict which species will become invasive, but retrospective analyses have so far failed to develop robust generalizations. This is because many biological, environmental, and anthropogenic factors interact to determine the distribution of invasive species. However, in this paper we also argue that many analyses of invasiveness have been flawed by not considering several fundamental issues: (1) the range size of an invasive species depends on how much time it has had to spread (its residence time); (2) the range size and spread rate are mediated by the total extent of suitable (i.e. potentially invasible) habitat; and (3) the range size and spread rate depend on the frequency and intensity of introductions (propagule pressure), the position of founder populations in relation to the potential range, and the spatial distribution of the potential range. We explored these considerations using a large set of invasive alien plant species in South Africa for which accurate distribution data and other relevant information were available. Species introduced earlier and those with larger potential ranges had larger current range sizes, but we found no significant effect of the spatial distribution of potential ranges on current range sizes, and data on propagule pressure were largely unavailable. However, crucially, we showed that: (1) including residence time and potential range always significantly increases the explanatory power of the models; and (2) residence time and potential range can affect which factors emerge as significant determinants of invasiveness. Therefore, analyses not including potential range and residence time can come to misleading conclusions. When these factors were taken into account, we found that nitrogen-fixing plants and plants invading arid regions have spread faster than other species, but these results were phylogenetically constrained. We also show that, when analysed in the context of residence time and potential range, variation in range size among invasive species is implicitly due to variation in spread rates, and, that by explicitly assuming a particular model of spread, it is possible to estimate changes in the rates of plant invasions through time. We believe that invasion biology can develop generalizations that are useful for management, but only in the context of a suitable null model. [source] Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol-Gel Thin Film Electrode Derived from 3-Aminopropyl Trimethoxy SilaneELECTROANALYSIS, Issue 22 2007K. Thenmozhi Abstract An organically modified sol-gel electrode using 3-aminopropyltrimethoxy silane for covalent immobilization of a redox mediator namely toluidine blue has been reported. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2,V to ,0.6,V exhibited stable voltammetric behavior in aqueous supporting electrolyte with a formal potential of ,0.265,V vs. SCE, corresponding to immobilized toluidine blue. The electrocatalytic activity of the modified electrode when tested towards nitrite ion exhibited a favorable response with the electrocatalytic reduction of nitrite occurring at a reduced potential of ,0.34,V. A good linear working range from 2.94×10,6,M to 2.11×10,3,M with a detection limit of 1.76×10,6,M and quantification limit of 5.87×10,6,M was obtained for nitrite determination. The stable and quick response (4,s) of the modified electrode towards nitrite under hydrodynamic conditions shows the feasibility of using the present sensor in flow systems. Significant improvements in the operational stability by overcoming the leachability problem and repeatability with a relative standard deviation of 1.8% of the TB thin film sensor have been obtained by the strategy of immobilization of the mediator in the sol-gel matrix. [source] Redox Active Two-Component Films of Palladium and Covalently Linked Zinc Porphyrin,Fullerene DyadELECTROANALYSIS, Issue 9 2006Marta Plonska Abstract Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C60 covalently linked to zinc meso -tetraphenyloporphyrin, ZnPC60, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnPC60/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties. [source] Electrochemical Impedance Characterization of Nafion-Coated Carbon Film Resistor Electrodes for ElectroanalysisELECTROANALYSIS, Issue 7 2005Carla Gouveia-Caridade Abstract Carbon film disk electrodes with Nafion coatings have been characterized by electrochemical impedance spectroscopy (EIS) with a view to a better understanding of their advantages and limitations in electroanalysis, particularly in anodic stripping voltammetry of metal ions. After initial examination by cyclic voltammetry, spectra were recorded over the full potential range in acetate buffer solution at the bare electrodes, electrodes electrochemically pretreated in acid solution, and Nafion-coated pretreated electrodes in the presence and absence of dissolved oxygen. EIS equivalent circuit analysis clearly demonstrated the changes between these electrode assemblies. In order to simulate anodic stripping voltammetry conditions, spectra were also obtained in the presence of cadmium and lead ions in solution at Nafion-coated electrodes, both after metal ion deposition and following re-oxidation. Permanent changes to the structure of the Nafion film occurred, which has implications for use of these electrode assemblies in anodic stripping voltammetry at relatively high trace metal ion concentrations. [source] Characteristics of Subtractive Anodic Stripping Voltammetry of Lead, Cadmium and Thallium at Silver-Gold Alloy ElectrodesELECTROANALYSIS, Issue 17 2003Y. Bonfil Abstract Silver-gold alloy electrodes have been studied for the purpose of the quantitative determination of heavy metals by subtractive anodic stripping voltammetry, (SASV). The results have been compared with those obtained with the silver and gold electrodes. The 50/50 a/o Ag/Au alloy electrode is the most suitable for quantifying thallium in the presence of lead and cadmium. The separation of its peak from those of lead and cadmium is 200,mV, which is about twice the separation obtained on the pure metal electrodes and is also better than on mercury. The silver electrode is suitable for the simultaneous determination of thallium, lead and cadmium. The peaks of lead and cadmium overlap on the 50/50 alloy. Pure silver or pure gold can be used for simultaneous quantification of these two metals. The use of gold for quantifying lead and cadmium is more limited because the peak potential of cadmium is shifted in the negative direction as its concentration increases and at [Cd2+]>200,nM, the two peaks merge. SASV enables correction for background currents and is of utmost importance for obtaining well-defined peaks. The peaks of lead, cadmium and thallium appear over a relatively narrow potential range (ca. 200,mV) on all the electrodes presented in this work. For this reason, the quantifying of a peak is based on the derivative at the inflection point of only one of its branches (ascending or descending). All SASV measurements were carried out without removal of oxygen. [source] A novel reactor for exploring the effect of water content on biofilter degradation ratesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2003Milinda A. Ranasinghe A novel batch recycle reactor was developed to investigate the effect of water content changes on the biological degradation rate of gas phase contaminants in low water content systems, such as biofilters. The reactor tightly controlled the water content of the unsaturated packing material using the principle of a suction cell. Matric potential in the compost was controlled between ,6 and ,36 cm H2O. A soil water retention curve relating matric potential to gravimetric water content was generated for the compost. Periodic dry weight analyses of reactor samples, together with the water retention curve, verified moisture content control. Runs were performed with toluene as the contaminant using unamended compost at a constant temperature of 30°C. Degradation results indicated a linear, biologically limited degradation region, followed by a non-linear region at lower concentrations. Elimination capacities were calculated for the linear region for different matric potentials along both the wetting and drying curves, and both changes in the water content and direction of approach affected the removal rates in the linear region. The elimination capacity ranged from 155 g/m3 hr to 24 g/m3 hr for toluene over the matric potential range investigated. Repeatability studies indicated that moisture content was most likely the parameter that influenced changes in performance. [source] Changes in Quality of Life in Epilepsy: How Large Must They Be to Be Real?EPILEPSIA, Issue 1 2001Samuel Wiebe Summary: ,Purpose: The study goal was to assess the magnitude of change in generic and epilepsy-specific health-related quality-of-life (HRQOL) instruments needed to exclude chance or error at various levels of certainty in patients with medically refractory epilepsy. Methods: Forty patients with temporal lobe epilepsy and clearly defined criteria of clinical stability received HRQOL measurements twice, 3 months apart, using the Quality of Life in Epilepsy Inventory-89 and -31 (QOLIE-89 and QOLIE-31), Liverpool Impact of Epilepsy, adverse drug events, seizure severity scales, and the Generic Health Utilities Index (HUI-III). Standard error of measurement and test-retest reliability were obtained for all scales and for QOLIE-89 subscales. Using the Reliable Change Index described by Jacobson and Truax, we assessed the magnitude of change required by HRQOL instruments to be 90 and 95% certain that real change has occurred, as opposed to change due to chance or measurement error. Results: Clinical features, point estimates and distribution of HRQOL measures, and test-retest reliability (all > 0.70) were similar to those previously reported. Score changes of ±13 points in QOLIE-89, ±15 in QOLIE-31, ±6.3 in Liverpool seizure severity,ictal, ±11 in Liverpool adverse drug events, ±0.25 in HUI-III, and ±9.5 in impact of epilepsy exclude chance or measurement error with 90% certainty. These correspond, respectively, to 13, 15, 17, 18, 25, and 32% of the potential range of change of each instrument. Conclusions: Threshold values for real change varied considerably among HRQOL tools but were relatively small for QOLIE-89, QOLIE-31, Liverpool Seizure Severity, and adverse drug events. In some instruments, even relatively large changes cannot rule out chance or measurement error. The relation between the Reliable Change Index and other measures of change and its distinction from measures of minimum clinically important change are discussed. [source] REVIEW: Consilient research approaches in studying gene × environment interactions in alcohol researchADDICTION BIOLOGY, Issue 2 2010Kenneth J. Sher ABSTRACT This review article discusses the importance of identifying gene-environment interactions for understanding the etiology and course of alcohol use disorders and related conditions. A number of critical challenges are discussed, including the fact that there is no organizing typology for classifying different types of environmental exposures, many key human environmental risk factors for alcohol dependence have no clear equivalents in other species, much of the genetic variance of alcohol dependence in human is not ,alcohol specific', and the potential range of gene-environment interactions that could be considered is so vast that maintaining statistical control of Type 1 errors is a daunting task. Despite these and other challenges, there appears to be a number of promising approaches that could be taken in order to achieve consilience and ecologically valid translation between human alcohol dependence and animal models. Foremost among these is to distinguish environmental exposures that are thought to have enduring effects on alcohol use motivation (and self-regulation) from situational environmental exposures that facilitate the expression of such motivations but do not, by themselves, have enduring effects. In order to enhance consilience, various domains of human approach motivation should be considered so that relevant environmental exposures can be sampled, as well as the appropriate species to study them in (i.e. where such motivations are ecologically relevant). Foremost among these are social environments, which are central to the initiation and escalation of human alcohol consumption. The value of twin studies, human laboratory studies and pharmacogenetic studies is also highlighted. [source] Ethanol and Acetaldehyde Adsorption on a Carbon-Supported Pt Catalyst: A Comparative DEMS StudyFUEL CELLS, Issue 1-2 2004H. Wang Abstract The adsorption of ethanol and acetaldehyde on carbon Vulcan supported Pt fuel cell catalyst and the electrochemical desorption of the adsorption products were studied, using electrochemical measurements and differential electrochemical mass spectrosmetry (DEMS), under continuous flow conditions. Faradaic current adsorption transients at different constant adsorption potentials, which also include CO adsorption for comparison, show pronounced effects of the adsorption potential and the nature of the reactant molecule. Acetaldehyde adsorption is much faster than ethanol adsorption at all potentials. Pronounced Had induced blocking effects for ethanol adsorption are observed at very cathodic adsorption potentials, < 0.16,V, while for acetaldehyde adsorption this effect is much less significant. Comparison of the adsorption charge for CO adsorption with the H-upd charge allows differentiation between H-displacement and double-layer charging effects. Continuous bulk oxidation is observed for both reactants at potentials > 0.31,V; for acetaldehyde adsorption, increasing bulk reduction is found at low potentials. Based on the electron yield per CO2 molecule formed and on the similarity with the CO stripping characteristics the dominant stable adsorbate is CO, coadsorbed with smaller amounts of (partly oxidized) hydrocarbon decomposition fragments, which are also oxidized at higher potentials (> 0.85,V) and which can be reductively desorbed as methane or, to a very small extent, as ethane. The presence of small amounts of adsorbed C2 species and the oxidative dissociation of these species in the main CO oxidation potential range is clearly demonstrated by increased methane desorption after a potential shift to 0.85,V. The data demonstrate that the Pt/Vulcan catalyst is very reactive for C-C bond breaking upon adsorption of these reactants. [source] Constraining the Sheffield dynamic global vegetation model using stream-flow measurements in the United KingdomGLOBAL CHANGE BIOLOGY, Issue 12 2005G. Picard Abstract The biospheric water and carbon cycles are intimately coupled, so simulating carbon fluxes by vegetation also requires modelling of the water fluxes, with each component influencing the other. Observations of river streamflow integrate information at the catchment scale and are widely available over a long period; they therefore provide an important source of information for validating or calibrating vegetation models. In this paper, we analyse the performance of the Sheffield dynamic global vegetation model (SDGVM) for predicting river streamflow and quantifying how this information helps to constrain carbon flux predictions. The SDGVM is run for 29 large catchments in the United Kingdom. Annual streamflow estimates are compared with long time-series observations. In 23 out of the 29 catchments, the bias between model and observations is less than 50 mm, equivalent to less than 10% of precipitation. In the remaining catchments, larger errors are because of combinations of unpredictable causes, in particular various human activities and measurement issues and, in two cases, unidentified causes. In one of the catchments, we assess to what extent a knowledge of annual streamflow can constrain model parameters and in turn constrain estimates of gross primary production (GPP). For this purpose, we assume the model parameters are uncertain and constrain them by the streamflow observations using the generalized likelihood uncertainty estimation method. Comparing the probability density function of GPP with and without constraint shows that streamflow effectively constrains GPP, mainly by setting a low probability to GPP values below about 1100 g C,1 m2 yr,1. In other words, streamflow observations allow the rejection of low values of GPP, so that the potential range of possible GPP values is almost halved. [source] Modelling the benefits of American Mink Mustela vison management options for terns in west ScotlandIBIS, Issue 2008NORMAN RATCLIFFE American Mink Mustela vison is a semi-aquatic predator that has invaded the west coast of Scotland and many of its associated islands. We developed a GIS model of their potential range based on their dispersal abilities and habitat use, which revealed that most islands in west Scotland are accessible to Mink, and that these host a large proportion of the region's Common Sterna hirundo and Arctic Terns S. paradisaea. Mink are predators on tern eggs and chicks, and statistical modelling of long-term productivity data demonstrated that unprotected sites within their range have an average productivity of 0.33 chicks per pair, whereas that at sites where Mink were trapped was 253% higher. We assessed the benefits of current Mink control projects for terns in the Western Isles and the remainder of west Scotland using a population modelling approach. This showed that both projects delivered considerable benefits for Common Terns, because a large proportion of their numbers were within the area of the control programmes and in sites that would be accessible to Mink if no control were in operation. For Arctic Terns, the benefits were less clear, as a larger proportion of their numbers were outside the control areas, and many of these were in sites isolated from, or unsuitable for, Mink. We discuss the implications of these findings for future strategic planning of Mink management in west Scotland. [source] Real Options Analysis: Where Are the Emperor's Clothes?JOURNAL OF APPLIED CORPORATE FINANCE, Issue 2 2005Adam Borison Once a topic of interest only to finance specialists, real options analysis now receives active, mainstream attention in business schools and industry. This article provides practitioners with a critical review of five well-established real options approaches that are extensively documented in the academic and professional literature. These approaches include the "classic approach" and "revised classic approach" (as proposed by Martha Amram and Nalin Kulatilaka), the "subjective approach" (as proposed by Tim Luehrman), the "MAD Approach" (as proposed by Tom Copeland and Vladimir Antikarov), and the "integrated approach" (as proposed by James Smith and Robert Nau). The article discusses the assumptions, mechanics, and potential range of applications of each approach, along with the results when applied to a simple case involving development of a natural gas field. While the approaches share a focus on investment flexibility and shareholder value, they rely on fundamentally different assumptions, use significantly different techniques, and can produce dramatically different results. Consequently, a great deal of thought must go into selecting and applying them in practice. The revised classic approach appears to be best suited to cases dominated either by "market" risk or "private" risk alone, and where approximate results are acceptable and resources are limited. The integrated approach is best suited to cases with a mix of market and technological risks, and where accuracy and a management roadmap are critical. [source] Construction of a novel sensor based on electropolymerization of carmine for voltammetric determination of 4-nitrophenolJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007Chunya Li Abstract 4-Nitrophenol (4-NP) has been determined with voltammetric technique based on a novel sensor fabricated by electropolymerization of carmine on a glassy carbon electrode (GCE). An obvious reduction peak located at about ,0.700 V and a couple of redox peaks that were not well-defined were observed in the potential range of ,1.00 to 0.600 V. Compared with its voltammetric behavior on a bare GCE, the reduction peak potential shifted positively and the peak current increased significantly. All experimental parameters were optimized and linear sweep voltammetry was proposed for its determination. In the optimal conditions, the reduction peak current was proportional to the 4-NP concentration over the concentration range from 5.00 × 10,8 to 1.00 × 10,5 mol L,1, and the detection limit was 1.00 × 10,8 mol L,1 after 200 s of accumulation. The high sensitivity and selectivity of the sensor was demonstrated by its practical application for the determination of trace amounts of 4-NP in lake water. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3271,3277, 2007 [source] Predicting the distribution of Sasquatch in western North America: anything goes with ecological niche modellingJOURNAL OF BIOGEOGRAPHY, Issue 9 2009J. D. Lozier Abstract The availability of user-friendly software and publicly available biodiversity databases has led to a rapid increase in the use of ecological niche modelling to predict species distributions. A potential source of error in publicly available data that may affect the accuracy of ecological niche models (ENMs), and one that is difficult to correct for, is incorrect (or incomplete) taxonomy. Here we remind researchers of the need for careful evaluation of database records prior to use in modelling, especially when the presence of cryptic species is suspected or many records are based on indirect evidence. To draw attention to this potential problem, we construct ENMs for the North American Sasquatch (i.e. Bigfoot). Specifically, we use a large database of georeferenced putative sightings and footprints for Sasquatch in western North America, demonstrating how convincing environmentally predicted distributions of a taxon's potential range can be generated from questionable site-occurrence data. We compare the distribution of Bigfoot with an ENM for the black bear, Ursus americanus, and suggest that many sightings of this cryptozoid may be cases of mistaken identity. [source] ORIGINAL ARTICLE: Towards an understanding of the Holocene distribution of Fagus sylvatica L.JOURNAL OF BIOGEOGRAPHY, Issue 1 2007Thomas Giesecke Abstract Aim, Understanding the driving forces and mechanisms of changes in past plant distribution and abundance will help assess the biological consequences of future climate change scenarios. The aim of this paper is to investigate whether modelled patterns of climate parameters 6000 years ago can account for the European distribution of Fagus sylvatica at that time. Consideration is also given to the role of non-climatic parameters as driving forces of the Holocene spread and population expansion of F. sylvatica. Location, Europe. Methods, European distributions were simulated using a physiologically-based bioclimatic model (STASH) driven by three different atmospheric general circulation model (AGCM) outputs for 6000 years ago. Results, The three simulations generally showed F. sylvatica to have potentially been as widespread 6000 years ago as it is today, which gives a profound mismatch with pollen-based reconstructions of the F. sylvatica distribution at that time. The results indicate that drier conditions during the growing season 6000 years ago could have caused a restriction of the range in the south. Poorer growth conditions with consequently reduced competitive ability were modelled for large parts of France. Main conclusions, Consideration of the entire European range of F. sylvatica showed that no single driving force could account for the observed distributional limits 6000 years ago, or the pattern of spread during the Holocene. Climatic factors, particularly drought during the growing season, are the likely major determinants of the potential range. Climatic factors are regionally moderated by competition, disturbance effects and the intrinsically slow rate of population increase of F. sylvatica. Dynamic vegetation modelling is needed to account for potentially important competitive interactions and their relationship with changing climate. We identify uncertainties in the climate and pollen data, as well as the bioclimatic model, which suggest that the current study does not identify whether or not climate determined the distribution of F. sylvatica 6000 years ago. Pollen data are better suited for comparison with relative abundance gradients rather than absolute distributional limits. These uncertainties from a study of the past, where we have information about plant distribution and abundance, argue for extreme caution in making forecasts for the future using equilibrium models. [source] Model-based uncertainty in species range predictionJOURNAL OF BIOGEOGRAPHY, Issue 10 2006Richard G. Pearson Abstract Aim, Many attempts to predict the potential range of species rely on environmental niche (or ,bioclimate envelope') modelling, yet the effects of using different niche-based methodologies require further investigation. Here we investigate the impact that the choice of model can have on predictions, identify key reasons why model output may differ and discuss the implications that model uncertainty has for policy-guiding applications. Location, The Western Cape of South Africa. Methods, We applied nine of the most widely used modelling techniques to model potential distributions under current and predicted future climate for four species (including two subspecies) of Proteaceae. Each model was built using an identical set of five input variables and distribution data for 3996 sampled sites. We compare model predictions by testing agreement between observed and simulated distributions for the present day (using the area under the receiver operating characteristic curve (AUC) and kappa statistics) and by assessing consistency in predictions of range size changes under future climate (using cluster analysis). Results, Our analyses show significant differences between predictions from different models, with predicted changes in range size by 2030 differing in both magnitude and direction (e.g. from 92% loss to 322% gain). We explain differences with reference to two characteristics of the modelling techniques: data input requirements (presence/absence vs. presence-only approaches) and assumptions made by each algorithm when extrapolating beyond the range of data used to build the model. The effects of these factors should be carefully considered when using this modelling approach to predict species ranges. Main conclusions, We highlight an important source of uncertainty in assessments of the impacts of climate change on biodiversity and emphasize that model predictions should be interpreted in policy-guiding applications along with a full appreciation of uncertainty. [source] Ehealth: Market Potential and Business StrategiesJOURNAL OF COMPUTER-MEDIATED COMMUNICATION, Issue 4 2001Pamela Whitten Due to the economic and social priorities afforded health services in the United States, research on new delivery modalities such as the Internet is gaining in popularity. Claims of the Internet's potential range from a promise to revolutionize the fundamental way health care is delivered to a tool for empowering patients through enhanced interaction with providers (Rice, 2001). Even though a great amount of attention has been given to e-health activity, the preponderance of publications to date has focused on the Internet as a source of health information. However important this form of e-health is, this type of service simply does not face the same constraints that must be addressed by those actually delivering health care services or tightly regulated pharmaceutical products. In this paper, we examine e-health by focusing explicitly on the delivery of health care products and services. Our examination of e-health activity is guided by two broad research questions. First, we ask what the potential is for the development of online health care services by examining its potential in major health care service and product sectors. Second, based upon case studies of two online health service firms, we seek to understand the emerging strategies of firms that are attempting to enter the health care market with an entirely online approach. Our examination of current e-health trends, as well as our two case studies, demonstrates the tremendous potential for health-related commercial activity on the Internet. However, our examination of the barriers facing ehealth from the US health system also pointed out the almost insurmountable challenges. We therefore conclude that a "click and mortar" model may perhaps be the optimal strategy for e-health. [source] Forecasting plant migration rates: managing uncertainty for risk assessmentJOURNAL OF ECOLOGY, Issue 3 2003S. I. Higgins Summary 1Anthropogenic changes in the global climate are shifting the potential ranges of many plant species. 2Changing climates will allow some species the opportunity to expand their range, others may experience a contraction in their potential range, while the current and future ranges of some species may not overlap. Our capacity to generalize about the threat these range shifts pose to plant diversity is limited by many sources of uncertainty. 3In this paper we summarize sources of uncertainty for migration forecasts and suggest a research protocol for making forecasts in the context of uncertainty. [source] Modeling distributions of disjunct populations of the Sierra Madre SparrowJOURNAL OF FIELD ORNITHOLOGY, Issue 3 2008Octavio R. Rojas-Soto ABSTRACT Sierra Madre Sparrows (Xenospiza baileyi) are among the least known of all bird species in Mexico. Recent surveys have discovered previously unknown populations and the current known distribution of Sierra Madre Sparrows consists of two populations separated by >800 km. We used available distributional information to develop ecological niche models that (1) predict much of the distribution potential of the species, (2) establish that the broad disjunction separating the two populations has ecological correlates that appear to be important to the distributional of these sparrows, and (3) illustrate the extremely restricted ecological distribution of the species. We used two sets of climatic and topographic variables, with one including all 22 variables available and the second with only six variables that were positively related to quality of distributional models. Although indications of differences between the two sets of populations were found based on the full 22-dimensional environmental dataset, such a highly dimensional analysis is vulnerable to over-fitting; models based on the reduced dataset indicated that the two populations occur in areas with similar ecological conditions. Our models also suggest that southern population of Sierra Madre Sparrows covers most of their potential range in that region. The potential range of the northern population, however, extends beyond known points of occurrence. To clarify the distribution of Sierra Madre Sparrows and evaluate their status and conservation opportunities, detailed searches for additional populations in areas identified by the model are needed. SINOPSIS El gorrión serrano (Xenospiza baileyi) se encuentra entre las especies menos conocidas de México. En un estudio reciente se descubrieron nuevas poblaciones, por lo que la distribución actual de esta ave está conformada por dos meta-poblaciones separadas por más de 800 km. Utilizamos la información disponible sobre su distribución para desarrollar modelos del nicho ecológico que: 1) predigan la mayor parte de la distribución potencial de la especie, 2) establezcan que la amplia separación de las dos poblaciones está correlacionada con condiciones ecológicas que parecen ser importantes para la distribución de la especie y 3) ilustren la extrema restricción ecológica que caracteriza la distribución de la especie. Para generar los modelos, utilizamos dos conjuntos de variables climatológicas y topográficas. Uno con 22 variables y el otro con las seis variables que estaban positivamente correlacionadas con la calidad de los modelos de distribución. Aunque se encontraron indicios de diferencias ecológicas entre las dos poblaciones con base en las 22 variables ambientales estudiadas, el análisis con tantas dimensiones es sensible a un efecto de sobre-ajuste. Los modelos producidos con el subconjunto de seis variables indicaron que las dos poblaciones se encuentran en áreas con condiciones ecológicas similares. Nuestros modelos sugieres que la población del sur ocupa la mayor parte de su área de distribución potencial en la región. No obstante, la distribución potencial de la población del norte es mucho más amplia que su distribución conocida. Es necesario realizar búsquedas minuciosas del gorrión serrano en los sitios identificados por el modelo propuesto para definir adecuadamente su distribución, evaluar su estatus y buscar oportunidades para su conservación. [source] Inferring the past to predict the future: climate modelling predictions and phylogeography for the freshwater gastropod Radix balthica (Pulmonata, Basommatophora)MOLECULAR ECOLOGY, Issue 3 2009M. CORDELLIER Abstract Understanding the impact of past climatic events on species may facilitate predictions of how species will respond to future climate change. To this end, we sampled populations of the common pond snail Radix balthica over the entire species range (northwestern Europe). Using a recently developed analytical framework that employs ecological niche modelling to obtain hypotheses that are subsequently tested with statistical phylogeography, we inferred the range dynamics of R. balthica over time. A Maxent modelling for present-day conditions was performed to infer the climate envelope for the species, and the modelled niche was used to hindcast climatically suitable range at the last glacial maximum (LGM) c. 21 000 years ago. Ecological niche modelling predicted two suitable areas at the LGM within the present species range. Phylogeographic model selection on a COI mitochondrial DNA data set confirmed that R. balthica most likely spread from these two disjunct refuges after the LGM. The match observed between the potential range of the species at the LGM given its present climatic requirements and the phylogeographically inferred refugial areas was a clear argument in favour of niche conservatism in R. balthica, thus allowing to predict the future range. The subsequent projection of the potential range under a global change scenario predicts a moderate pole-ward shift of the northern range limits, but a dramatic loss of areas currently occupied in France, western Great Britain and southern Germany. [source] Sulfide anion interaction with Cu(1 0 0) and Cu modified Au(1 0 0): An electrochemical STM studyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010Christian Schlaup Abstract We describe the formation of thin copper sulfide semiconductor films under electrochemical conditions. In a first step we investigated the fundamental interaction of the Cu(1 0 0) surface with a sulfide anions containing electrolyte. Beside the classical p(2,×,2)-S and c(2,×,6)-S adlayer phases we found the formation of a closer packed "pseudo- c(2,×,2)"-S phase accompanied by an expansion of the topmost copper layer. For a further investigation of this "pseudo- c(2,×,2)"-S phase, we switched from the bulk Cu(1 0 0) electrode to a copper monolayer on a Au(1 0 0) electrode, which can be easily prepard using copper underpotential deposition. Since such a copper monolayer is pseudomorphic to the Au(1 0 0) surface and therefore expanded by 12.5% with respect to the bulk Cu(1 0 0)-plane, exclusively a commensurate c(2,×,2)-S structure is instantaneously formed and remains stable over a wide potential range. [source] Preparation of lithium indium oxide via a rheological phase route and its electrochemical characteristics in LiOH and Li2SO4 solutionsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Guo-Qing Zhang Abstract Submicrometer-sized lithium indium oxide (LiInO2) powder via a rheological phase method using trilithium citrate tetra hydrate (C6H5Li3O7,·,4H2O) and indium oxide (In2O3) has been prepared in this work for the first time. The optimal pyrolyzing temperature range to prepare crystalline LiInO2 is between 650 and 900,°C, which was confirmed by thermal gravimetric and differential thermogravimetric analysis of the precursor and X-ray diffraction analysis. The pure phase LiInO2 sample obtained has a uniform particle morphology and submicrosize, which was observed by scanning electron microscopy. The electrochemical studies show that a new pair of cathodic and anodic peaks at 0.23 and 0.38,V (vs. saturated calomel electrode) was obviously observed from the cyclic voltammetry curve of LiInO2 in 1,M LiOH solution, indicating a battery characteristic of the material in this electrolyte. While in 1,M Li2SO4 solution, the sample presents a supercapacitive characteristic within the same potential range. The reasons for different electrochemical behaviors in these two electrolytes can be attributed to the fact that the reaction of lithium ion insertion/extraction into/out of a LiInO2 electrode takes place in the bulk material in LiOH electrolyte solution, whereas it takes place on the electrode/electrolyte interface for Li2SO4 electrolyte case. [source] Monitoring of Anti Cancer Drug Letrozole by Fast Fourier Transform Continuous Cyclic Voltammetry at Gold MicroelectrodeCHINESE JOURNAL OF CHEMISTRY, Issue 7 2010Parviz Norouzi Abstract A continuous cyclic voltammetric study of letrozole at gold microelectrode was carried out. The drug in phosphate buffer (pH 2.0) is adsorbed at ,200 mV, giving rise to change in the current of well-defined oxidation peak of gold in the flow injection system. The proposed detection method has some of advantages, the greatest of which are as follows: first, it is no more necessary to remove oxygen from the analyte solution and second, this is a very fast and appropriate technique for determination of the drug compound in a wide variety of chromatographic analysis methods. Signal-to-noise ratio has significantly increased by application of discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as sweep rate, eluent pH, and accumulation time and potential were optimized. The linear concentration range was of 1.0×10,7,1.0×10,10 mol/L (r=0.9975) with a limit of detection and quantitation 0.08 nmol/L and 0.15 nmol/L, respectively. The method has the requisite accuracy, sensitivity, precision and selectivity to assay letrozol in tablets. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the letrozol were considered. [source] Synthesis and Electrochemical Properties of Semicrystalline Gyroidal Mesoporous MnO2CHINESE JOURNAL OF CHEMISTRY, Issue 7 2006Qin Zhou Abstract Mesoporous silica KIT-6 has novel three-dimensional gyroidal channel structure, space group of Ia-3d, and ordered tunable pores up to 10 nm. In this paper, such mesostructured silica was employed as hard template to prepare semicrystalline gyroidal mesoporous MnO2. The structure was investigated by XRD, TEM and HRTEM, and found to be of high quality Ia- 3d symmetry, in good accordance with the template structure. The material has a BET surface of 118 m2·g -1 and pore volume of 0.35 cm3·g,1 after eliminating template. Mesoporous MnO2 has shown good electrochemical property as supercapacitor material in 1 mol·L,1 Na2SO4 and 1 mol·L,1 LiClO4 solutions, but interesting pseudocapacitance behavior was observed in the case of 6 mol·L,1 KOH. It was found that mesoporous MnO2 performed stable reversible electrochemical behavior with capacitance of 220 F·g,1 in a potential range of ,0.1,0.55 V vs. Hg/HgO in alkaline solution, demonstrating that it is a promising novel electrode material for the fabrication of electrochemical capacitors. [source] Studies on Charging Processes and Capacitances of Oxidized Polyethylenedioxythiophene FilmsCHINESE JOURNAL OF CHEMISTRY, Issue 7 2005She Ping-Ping Abstract In this paper, the chronoamperometry was used to study the charging processes of polyethylenedioxythiophene (PEDOT) modified electrodes in the potential range where PEDOT was in the oxidized state. The results show that the charging behaviors of the PEDOT films are well agreed with the exhausted finite diffusion model. The dependence of the capacitance values of the films on potential and concentration of solution was also studied in this potential range. [source] Residence time and potential range: crucial considerations in modelling plant invasionsDIVERSITY AND DISTRIBUTIONS, Issue 1 2007John R. U. Wilson ABSTRACT A prime aim of invasion biology is to predict which species will become invasive, but retrospective analyses have so far failed to develop robust generalizations. This is because many biological, environmental, and anthropogenic factors interact to determine the distribution of invasive species. However, in this paper we also argue that many analyses of invasiveness have been flawed by not considering several fundamental issues: (1) the range size of an invasive species depends on how much time it has had to spread (its residence time); (2) the range size and spread rate are mediated by the total extent of suitable (i.e. potentially invasible) habitat; and (3) the range size and spread rate depend on the frequency and intensity of introductions (propagule pressure), the position of founder populations in relation to the potential range, and the spatial distribution of the potential range. We explored these considerations using a large set of invasive alien plant species in South Africa for which accurate distribution data and other relevant information were available. Species introduced earlier and those with larger potential ranges had larger current range sizes, but we found no significant effect of the spatial distribution of potential ranges on current range sizes, and data on propagule pressure were largely unavailable. However, crucially, we showed that: (1) including residence time and potential range always significantly increases the explanatory power of the models; and (2) residence time and potential range can affect which factors emerge as significant determinants of invasiveness. Therefore, analyses not including potential range and residence time can come to misleading conclusions. When these factors were taken into account, we found that nitrogen-fixing plants and plants invading arid regions have spread faster than other species, but these results were phylogenetically constrained. We also show that, when analysed in the context of residence time and potential range, variation in range size among invasive species is implicitly due to variation in spread rates, and, that by explicitly assuming a particular model of spread, it is possible to estimate changes in the rates of plant invasions through time. We believe that invasion biology can develop generalizations that are useful for management, but only in the context of a suitable null model. [source] Relating streamflow characteristics to specialized insectivores in the Tennessee River Valley: a regional approach,ECOHYDROLOGY, Issue 4 2008Rodney R. Knight Abstract Analysis of hydrologic time series and fish community data across the Tennessee River Valley identified three hydrologic metrics essential to habitat suitability and food availability for insectivorous fish communities in streams of the Tennessee River Valley: constancy (flow stability or temporal invariance), frequency of moderate flooding (frequency of habitat disturbance), and rate of streamflow recession. Initial datasets included 1100 fish community sites and 300 streamgages. Reduction of these datasets to sites with coexisting data yielded 33 sites with streamflow and fish community data for analysis. Identification of critical hydrologic metrics was completed using a multivariate correlation procedure that maximizes the rank correlation between the hydrologic metrics and fish community resemblance matrices. Quantile regression was used to define thresholds of potential ranges of insectivore scores for given values of the hydrologic metrics. Increased values of constancy and insectivore scores were positively correlated. Constancy of streamflow maintains wetted perimeter, which is important for providing habitat for fish spawning and increased surface area for invertebrate colonization and reproduction. Site scores for insectivorous fish increased as the frequency of moderate flooding (3 times the median annual streamflow) decreased, suggesting that insectivorous fish communities respond positively to less frequent disturbance and a more stable habitat. Increased streamflow recession rates were associated with decreased insectivore scores. Increased streamflow recession can strand fish in pools and other areas that are disconnected from flowing water and remove invertebrates as food sources that were suspended during high-streamflow events. Copyright © 2008 John Wiley & Sons, Ltd. [source] Palladium Sub-Nanoparticle Decorated ,Bamboo' Multi-Walled Carbon Nanotubes Exhibit Electrochemical Metastability: Voltammetric Sensing in Otherwise Inaccessible pH RangesELECTROANALYSIS, Issue 24 2006Xiaobo Ji Abstract A generic approach for the detection of electroactive species in potential ranges that would normally be inhibited due to the stripping of the electrocatalytic material is presented. We demonstrate, via the example of the electrochemical oxidation of hydrazine, that palladium nanoparticle (< 1,nm) decorated bamboo multi-walled carbon nanotubes exhibit a metastability such that they allow the sensing of hydrazine in the pH range where palladium metal would normally be voltammetrically stripped (oxidized) from the surface of convectional electrodes. [source] Divanadium(V) and Trapped Valence Linear Tetravanadium(IV,V,V,IV) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Anindita Sarkar Abstract In an acetonitrile/water mixture, reactions of the N,N,-bis(diacetyl)hydrazine (H2diah), bis(acetylacetonato)oxidovanadium(IV) [VO(acac)2] and monodentate N -coordinating heterocycles (hc) in a 1:2:2 mol ratio provide yellow divanadium(V) complexes of formula [(hc)O2V(,-diah)VO2(hc)] (1, hc = imidazole; 2, hc = pyrazole; 3, hc = 3,5-dimethyl pyrazole). On the other hand, in the same solvent mixture reactions of the same reagents in a 1:4:2 mol ratio produce green linear tetravanadium(IV,V,V,IV) complexes of formula [(acac)2OV(,-O)VO(hc)(,-diah)(hc)OV(,-O)VO(acac)2] (4, hc = imidazole; 5, hc = pyrazole; 6, hc = 3,5-dimethyl pyrazole). The complexes 1,6 have been characterized by elemental analysis, magnetic susceptibility, and various spectroscopic and electrochemical measurements. The X-ray crystal structures of 1, 3 and 6 have been determined. In all three structures, the diazine ligand diah2, is in trans configuration. Metal-centred bond parameters are consistent with the localized electronic structure of the two trans -bent {OV(,-O)VO}3+ cores present in 6. The pentavalent metal centres in 1, 3 and 6 are in a distorted trigonal-bipyramidal N2O3 coordination environment, while the terminal tetravalent metal centres in 6 are in a distorted octahedral O6 coordination sphere. The eight-line EPR spectra of the tetravanadium species (4,6) in dimethyl sulfoxide at ambient temperature indicate the rare valence localized electronic structure in the fluid phase. All the complexes are redox active and display metal-centred electron transfer processes in dimethyl sulfoxide solution. A reduction within ,0.78 to ,0.94 V (vs. Ag/AgCl) is observed for the divanadium(V) species 1,3, while a reduction and an oxidation are observed in the potential ranges ,0.82 to ,0.90 V and 0.96 to 1.12 V (vs. Ag/AgCl), respectively, for the tetravanadium species 4,6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Macroecology meets macroevolution: evolutionary niche dynamics in the seaweed HalimedaGLOBAL ECOLOGY, Issue 4 2009Heroen Verbruggen ABSTRACT Aim Because of their broad distribution in geographical and ecological dimensions, seaweeds (marine macroalgae) offer great potential as models for marine biogeographical inquiry and exploration of the interface between macroecology and macroevolution. This study aims to characterize evolutionary niche dynamics in the common green seaweed genus Halimeda, use the observed insights to gain understanding of the biogeographical history of the genus and predict habitats that can be targeted for the discovery of species of special biogeographical interest. Location Tropical and subtropical coastal waters. Methods The evolutionary history of the genus is characterized using molecular phylogenetics and relaxed molecular clock analysis. Niche modelling is carried out with maximum entropy techniques and uses macroecological data derived from global satellite imagery. Evolutionary niche dynamics are inferred through application of ancestral character state estimation. Results A nearly comprehensive molecular phylogeny of the genus was inferred from a six-locus dataset. Macroecological niche models showed that species distribution ranges are considerably smaller than their potential ranges. We show strong phylogenetic signal in various macroecological niche features. Main conclusions The evolution of Halimeda is characterized by conservatism for tropical, nutrient-depleted habitats, yet one section of the genus managed to invade colder habitats multiple times independently. Niche models indicate that the restricted geographical ranges of Halimeda species are not due to habitat unsuitability, strengthening the case for dispersal limitation. Niche models identified hotspots of habitat suitability of Caribbean species in the eastern Pacific Ocean. We propose that these hotspots be targeted for discovery of new species separated from their Caribbean siblings since the Pliocene rise of the Central American Isthmus. [source] | ||||||||||||||||||||||