Monitoring Changes In Density Research Articles

Comparison of methods for estimating density and population trends for low-density Asian bears

Populations of bears in Asia are vulnerable to extinction and effective monitoring is critical to measure and direct conservation efforts. Population abundance (local density) or growth (λ) are the most sensitive metrics to change. We discuss the value in implementing spatially explicit capture-recapture (SCR), the current gold standard for density estimation, and open population SCR (OPSCR) to monitor changes in density over time. We provide guidance for designing studies to provide estimates with sufficient power to detect changes. Because of the wide availability of camera traps and interest in their use, we consider six density estimation methods and their extensions developed for use with camera traps, with specific consideration of assumptions and applications for monitoring Asian bears. We conducted a power analysis to calculate the precision in estimates needed to detect changes in populations with reference to IUCN Red List criteria. We performed a systematic review of empirical studies implementing camera trap abundance estimation methods and considered sample sizes, effort, and model assumptions required to achieve adequate precision for population monitoring. We found SCR and OPSCR, reliant on “marked” individuals, are currently the only methods with enough power to reliably detect even moderate to major (20–80%) declines. Camera trap methods with unmarked individuals rarely achieved precision sufficient to detect even large declines (80–90%), although with some exceptions (e.g., situations with moderate population densities, large number of sampling sites, or inclusion of ancillary local telemetry data. We describe additional estimation options including line transects, direct observations, monitoring age-specific survival and reproductive rates, and hybrid/integrated methodologies that may have potential to work for some Asian bear populations. We conclude monitoring changes in abundance or density is possible for most Asian bear populations but will require collaboration among researchers over broad spatial extents and extensive financial investment to overcome biological and logistical constraints. We strongly encourage practitioners to consider study design and sampling effort required to meet objectives by conducting simulations, power analyses, and assumption checks prior to implementing monitoring efforts, and reporting standardized dispersion measures such as coefficients of variation to allow for assessment of precision. Our guidance is relevant to other low-density and wide-ranging species.

Muon radiography employing the DIRC principle for density change measurements under volcanoes and fluid reservoirs

Mapping the density distribution and monitoring density changes under volcanoes and geological reservoirs is a major challenge in geology and volcanology. Muon radiography has a high potential to advance this field, but often there are no inexpensive high-end detectors available that are suitable for field installations. A DIRC-type Cherenkov detector as a muon camera has a small dimension and is suited for such field applications (MagmaDIRC idea). In measuring directions and energies of the incoming muons one can turn the mass density integrals along the lines of flight into a radiography image, and by discarting low-energy muons with their blurred angular information one obtains sharper images. In particular one may detect the time variation of the mass density distributions situated above the horizon line in a volcanic edifice that occurs when magma is filling its plumbing system or when the level of a lava lake changes. Using numerical simulations, we discuss design aspects and the requirements of such a DIRC system. Two sites are identified for proof-of-principle field measurements. The required measurement times are estimated for the given site conditions and morphology based on the specifications of an operational DIRC system. The merits of DIRC sensors are contrasted to other muon radiography techniques.

Novel grid and sectoral analyses in monitoring corneal scars.

We aim to design two sampling methods, the grid and sectoral methods, to provide more precise detection of focal corneal scar changes with time following pterygium excision with the Pentacam imaging system. This is a retrospective study of our previous prospective observational case series. Thirty patients underwent primary pterygium excision with adjuvant topical mitomycin-C application were followed up and imaged with Pentacam system at postoperative weeks 1, 4, 12 and month 18. Grid and sectoral methods were used to sample density changes (in grayscale units, GSU) over the scarred areas as well as the clear pole of the same cornea. Using the grid method, the average corneal densities were 39.4, 37.1, 36.7 and 34.7GSU at postoperative 1, 4, 12weeks and 18months, respectively. On the other hand, using the sectoral method, the average corneal densities were 35.3, 33.3, 32.5 and 31.9GSU at postoperative 1, 4, 12weeks and 18months, respectively. Paired t tests achieved statistical significance when comparing all follow-up time points to first postoperative visit. A statistically significant effect of time on the average density was shown on ANOVA (p < 0.001) using both analyses over the scarred areas, but not over the clear pole of the same cornea (p > 0.05). Our novel approach to monitor corneal density changes using the grid or sectoral sampling methods seemingly enhances the power in monitoring density changes in corneal scars when compared to conventional total-diameter average densitometry.

A philosophy for CNS radiotracer design.

ConspectusDecades after its discovery, positron emission tomography (PET) remains the premier tool for imaging neurochemistry in living humans. Technological improvements in radiolabeling methods, camera design, and image analysis have kept PET in the forefront. In addition, the use of PET imaging has expanded because researchers have developed new radiotracers that visualize receptors, transporters, enzymes, and other molecular targets within the human brain.However, of the thousands of proteins in the central nervous system (CNS), researchers have successfully imaged fewer than 40 human proteins. To address the critical need for new radiotracers, this Account expounds on the decisions, strategies, and pitfalls of CNS radiotracer development based on our current experience in this area.We discuss the five key components of radiotracer development for human imaging: choosing a biomedical question, selection of a biological target, design of the radiotracer chemical structure, evaluation of candidate radiotracers, and analysis of preclinical imaging. It is particularly important to analyze the market of scientists or companies who might use a new radiotracer and carefully select a relevant biomedical question(s) for that audience. In the selection of a specific biological target, we emphasize how target localization and identity can constrain this process and discuss the optimal target density and affinity ratios needed for binding-based radiotracers. In addition, we discuss various PET test–retest variability requirements for monitoring changes in density, occupancy, or functionality for new radiotracers.In the synthesis of new radiotracer structures, high-throughput, modular syntheses have proved valuable, and these processes provide compounds with sites for late-stage radioisotope installation. As a result, researchers can manage the time constraints associated with the limited half-lives of isotopes. In order to evaluate brain uptake, a number of methods are available to predict bioavailability, blood–brain barrier (BBB) permeability, and the associated issues of nonspecific binding and metabolic stability. To evaluate the synthesized chemical library, researchers need to consider high-throughput affinity assays, the analysis of specific binding, and the importance of fast binding kinetics. Finally, we describe how we initially assess preclinical radiotracer imaging, using brain uptake, specific binding, and preliminary kinetic analysis to identify promising radiotracers that may be useful for human brain imaging. Although we discuss these five design components separately and linearly in this Account, in practice we develop new PET-based radiotracers using these design components nonlinearly and iteratively to develop new compounds in the most efficient way possible.

Time-lapse gravity inversion with an active time constraint

Traditional methods used to invert gravity data are generally based on smoothness as a regularizer and the time-lapse inversion of gravity data is traditionally based on sequential inversion. A smooth density model can be in contradiction with the known geology of the target and sequential time-lapse inversion may lead to the presence of artefacts in the sequence of tomograms due to the propagation of errors from the initial dataset and its associated tomogram. We propose a deterministic time-lapse algorithm to invert a sequence of gravity data combining two features: an image focusing technique and the use of a time-dependent regularizer using an Active Time Constrained (ATC) approach. These two features are included directly in the objective function to minimize. The ATC inversion of time-lapse gravity data is efficient in filtering out noise-contaminated data as long as the noise is not correlated over time. Our approach can also be used to incorporate prior information regarding the density model we want to retrieve. The forward solver is based on a commercial finite element solver with a high flexibility in meshing irregular domains, a feature that is important to include realistic topography from digital elevation maps, for instance, and to describe the density distribution of geological structures with complex geometries. We benchmark the accuracy of the forward modelling code using an analytical expression and test the effectiveness of the focusing algorithm. We show the advantage of our approach in the case of the water flooding of an oil reservoir in order to detect and monitor the position of the oil–water encroachment front. We also test the model against synthetic data describing the evolution of a hydrothermal system feed by a magmatic source and the collapse of a mine. In all these cases, the approach we follow is successful in monitoring density changes.

Nocturnal line transect sampling of wild boar (Sus scrofa) in a Mediterranean forest: long-term comparison with capture–mark–resight population estimates

Although accurate estimates of wild boar (Sus scrofa) populations are crucial for any effective resource management or pest control programme, this species is well-known to be difficult to monitor. We conducted a 10-year study in a fenced Mediterranean forest (Rome, Italy) to evaluate nocturnal line transect sampling performances. We focused on its accuracy in monitoring changes in density, which was independently estimated by capture–mark–resight (CMR) performed on counts at feeding sites. We carried out night surveys in the autumn of 2001–2010, using portable infrared cameras to detect animals. We sampled on foot to cover the whole study area and the different habitat types evenly. However, to ensure safe working conditions during night and to limit disturbance, we placed transects along paths and forest roads. Therefore, we investigated the potential impact of our convenience sampling on the detection process, using radiolocations of wild boars to assess their distribution with respect to selected transects. We found that our survey design should not have biased our estimates and that densities and coefficients of variations from line transect sampling were consistent with CMR results. Although labour-intensive, we believe that our approach can improve wild boar monitoring effectively, even in concealing habitats, providing decision makers with accurate estimates (and quantified confidence limits) which can help to develop the most appropriate management programme. Moreover, the current low price of new-generation infrared cameras can also increase strongly the cost-effectiveness of this method.

Monitoring land cover and land use using NOAA-AVHRR data in the Husteca Potosina, Mexico

The Huasteca Potosina region, Mexico, is of great economic importance at local, state and national level. In recent decades it has experienced strong ecological transformations by human activity. Currently the natural vegetation and the agricultural areas are more fragile with respect to hydrometeorological phenomena and plagues. The natural vegetation and land use cover show yearly and seasonal changes that can be measured by means of remote sensing techniques, in particular those changes occurring during the growing period (rainy season). The objective of this study was to identify the land-cover and land-use changes and to monitor density changes and crop health, using vegetation indices derived from the visible and infrared bands of the Advanced Very High Resolution Radiometer (AVHRR) of the National Oceanic and Atmospheric Administration (NOAA) satellite. This study is part of an ample interdisciplinary investigation, the ultimate goal of which is to identify the vulnerability of natural vegetation to hydrometeorological phenomena and plagues by means of remote sensing, GIS, multivariate analysis and a climatic model.

Freezing and Pressure-Driven Flow of Solid Helium in Vycor

The recent torsional oscillator results of Kim and Chan suggest a supersolid phase transition in solid 4He confined in Vycor. We have used a capacitive technique to directly monitor density changes for helium confined in Vycor at low temperature and have used a piezoelectrically driven diaphragm to study the pressure-induced flow of solid helium into the Vycor pores. Our measurements showed no indication of a mass redistribution in the Vycor that could mimic supersolid decoupling and put an upper limit of about 0.003 microm/s on any pressure-induced supersolid flow in the pores of Vycor.

Development and Validation of Spectroscopic Methods for Monitoring Density Changes in Pressurized Gaseous and Supercritical Fluid Systems

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionDevelopment and Validation of Spectroscopic Methods for Monitoring Density Changes in Pressurized Gaseous and Supercritical Fluid SystemsMarc A. Blatchford and Scott L. WallenCite this: Anal. Chem. 2002, 74, 21, 5693Publication Date (Web):September 25, 2002Publication History Published online25 September 2002Published inissue 1 November 2002https://doi.org/10.1021/ac020502qCopyright © 2002 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views202Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (10 KB) Get e-Alerts Get e-Alerts

Development and validation of spectroscopic methods for monitoring density changes in pressurized gaseous and supercritical fluid systems.

The further development of new processes utilizing liquid or supercritical CO2 as a solvent will benefit from the rational design of new CO2-philes. Understanding solvation structures and mechanisms of these molecules is an important part of this process. In such studies, determining the change in density as a function of the measured thermodynamic conditions (pressure and temperature) provides an excellent means of directly monitoring the solution conditions in the detection volume for a given technique. By integrating spectroscopic peaks, changes in area can be used to determine changes in analyte concentration in the detection volume, and thus, it should be possible to monitor the system density in situ. In the present study, we examine the utility of Raman and NMR spectroscopy as a means of following changes in solution density conditions and validate this approach in pure fluids and gases (N2 and CO2) and supercritical fluid mixtures (acetaldehyde vapor in N2). In addition, we present the design of a simple, inexpensive cell for conducting Raman and NMR measurements under moderate pressure conditions.

Monitoreo del desarrollo de cultivos de temporal en la Mesa Central, Guanajuato, México, usando imágenes NOAA AVHRR

El análisis de los índices de vegetación derivados de las bandas visible e infrarrojo por el Radiómetro Avanzado de Muy Alta Resolución (AVHRR) de los satélites NOAA, es una herramienta útil para monitorear cambios en la densidad y vigor de los cultivos a lo largo de un ciclo agrícola. Este trabajo es un ejemplo del uso de las técnicas de detección en áreas cultivadas. La zona estudiada corresponde a la provincia fisiagráfica del estado de Guanajuato denominada Mesa Central, la cual, en general, posee características físicas, tales como topografía y suelos homogéneos y presencia de una marcada época de precipitación. Dentro de los cultivos que sustentan estas áreas, sobresalen las superficies sembradas de maíz y frijol, cuyo periodo de siembra - cosecha durante el ciclo productivo 1996 fue de agosta - noviembre. Paralelamente se recopilaron datos de campo como temperaturas, precipitaciones diarias y la situación meteorológica prevaleciente en diversos niveles de la atmósfera. Se digitizaron las áreas cultivadas y los suelos bajo el sistema ILWIS. Se obtuvieron además los datos de época de siembra, variedades utilizadas, fecha del periodo vegetativo, reproductivo y madurez. Se presentan los resultados de las relaciones entre los valores de Índice de Vegetación de Diferencia Normalizada (NDVI) obtenidos de los compuestos de imágenes de satélite en diferentes fechas, con diversos aspectos físicos como precipitación, siniestros climáticos e igualmente con el periodo vegetativo.

Monitoring of density changes in low-permittivity liquids by microwave-permittivity measurements with an open-ended probe

An open-ended co-axial probe was designed for monitoring density changes in low-permittivity fluids. The design was based on the Marcuvitz equation for the probe admittance and was tested with measurements on liquids of known permittivities at room temperature and atmospheric pressure. A simple calibration procedure and a bilinear calibration procedure were tested. Only the bilinear procedure was sufficiently accurate for monitoring density changes. The reproducibility of the measured high-frequency permittivity was found to be 0.005 at room temperature and atmospheric pressure. From measurements on mixtures of reference chemicals it was found that density differences of could be measured. The system was also used to measure the permittivity and density changes in the temperature range 20 - C and the pressure range 1 - 150 bar for n-decane, n-heptane and a petroleum-gas condensate. At temperatures above room temperature the reflection coefficients of liquids under test were corrected with a linear model. This accounted for changes in the measurement system. The results agreed with the temperature-induced density changes given in the literature. The small pressure-induced density changes could not be detected. This indicated that the probe can be used to monitor temperature-induced density changes in low-permittivity liquids when a bilinear calibration procedure and a linear temperature correction are used.

Improvement in core density of BSCCO/Ag tapes by cold isostatic pressing

Cold isostatic pressing was used to overcome the limitation of BSCCO core density after drawing and flat rolling. Cold isostatic pressing up to 2.5 GPa has been applied to as-rolled and pre-annealed Pb-doped single and multifilamentary BSCCO/Ag tapes. Microhardness profiles of core cross sections have been used for monitoring density changes. The self-field transport current densities of only sintered BSCCO/Ag tapes, one time isostatically pressed, and one time uniaxially pressed, are compared.