Relative Density Estimates Research Articles

Sound sees more: A comparison of imaging sonars and optical cameras for estimating fish densities at artificial reefs

Imaging sonars are increasingly being utilised in fish surveys in conjunction with or as substitutes for optical instruments. To justify the use of imaging sonars, we must first describe their application, limitations, and efficacy compared to optics. This study compared quantitative data of fish assemblages obtained using imaging sonars operating at four frequencies (0.75, 1.2, 2.1, and 3 MHz) with simultaneous optical camera footage at two artificial reefs. Fish densities were on average three times higher for sonar than optics. Greater detection by the sonar was attributed to site-attached fishes that were camouflaged against the artificial reefs or the adjacent seabed, which could be discriminated by imaging sonar, but not using optics. This suggests that differences in habitat and fish assemblage composition could influence the relative performance and density estimates of imaging sonar versus optics. Several limitations of imaging sonar were identified that need to be accounted for in future survey designs, including: discriminating fishes from benthic growth; an inability to detect fishes within complex habitat structures; and seabed and side-lobe interferences that truncate survey volume. Overall, this study demonstrates the value of imaging sonar for quantifying fish communities and describes limitations and recommendations for their deployment in future surveys.

An Approach to Improving Homogeneous Cross-Project Defect Prediction by Jensen-Shannon Divergence and Relative Density

Homogeneous cross-project defect prediction (HCPDP) aims to apply a binary classification model built on source projects to a target project with the same metrics. However, there is still room for improvement in the performance of the existing HCPDP models. This study has proposed a novel approach, including one-to-one and many-to-one predictions. First, we apply the Jensen-Shannon divergence to select the most similar source project automatically. Second, relative density estimation is introduced to choose the suitable instance of the selected source project. Third, one-to-one and many-to-one prediction models are trained by the selected instances. Finally, two benchmark datasets are used to evaluate the proposed approach. Compared to the state-of-the-art methods, the experimental results demonstrated that the proposed approach could improve the prediction performance in the F1-score, AUC, and G-mean metrics and exhibit strong adaptability to the traditional classifiers.

Training data selection for imbalanced cross-project defect prediction

Machine learning methods have been applied in software engineering to effectively predict software defects. Researchers proposed cross-project defect prediction (CPDP) for cases in which few or no data are available. CPDP uses the labeled data of a source project to construct a prediction model for the target project. However, the prediction performance remains inferior because the training data selection for the source project is ineffective. In this paper, the Jensen-Shannon divergence is first applied to automatically select the source project most similar to the target project. Subsequently, a grouped synthetic minority oversampling technique (SMOTE) is applied to improve the class imbalance of the projects. Finally, relative density estimation is performed to select the data for the source project. The experimental results demonstrate that the proposed method improves the prediction performance and exhibits high adaptability to different classifiers.

Recruitment of Natural Enemies of the Invasive Sugarcane Aphid Vary Spatially and Temporally in Sorghum Fields in the Southern Great Plains of the USA

Sorghum (Sorghum bicolor (L.) Moench) is an important summer grain crop in the U.S. Southern Great Plains because it is one of the few crops that consistently produces acceptable yields in the harsh summer weather that characterizes the region. Damaging infestations of the sugarcane aphid, Melanaphis sacchari (Zehntner), occur commonly in sorghum throughout Texas and Oklahoma, two of the leading sorghum producing states. Grain sorghum fields were sampled at two locations in Texas and three locations in Oklahoma. Fields were sampled approximately weekly by examining two leaves on each of 54 plants and counting all sugarcane aphids and aphid natural enemies on each leaf. Sampling began at an early growth stage and continued until the crop either matured or was treated with insecticide to suppress the sugarcane aphid infestation. For a total of 123 fields in 2017 and 2018, aphids, Aphelinus nigritus Howard mummies, adult coccinellids, larval coccinellids, larval lacewings, and larval dipterans were counted, and relative density estimates were determined. When natural enemy and sugarcane aphid count data were aggregated at the scale of geographic locations and multiple years, there was no evidence for a numerical response by natural enemies to sugarcane aphid density. When fields were compared within locations, a numerical response was consistently observed. A natural enemy importance index was developed that incorporated cumulative degree days of first occurrence of a natural enemy taxa in a field, the average density of the natural enemy in a field, and natural enemy voracity. Factorial analyses of variance indicated that cumulative degree days at first occurrence and average relative density differed significantly among natural enemy taxa and locations, as did natural enemy importance. Averaged across locations larval coccinellids had the largest importance index, I = 1.47, and A. nigritus had the smallest, I = 0.61. Among locations, the Texas Coastal Plains had the largest importance index, I = 1.27 whereas the Oklahoma Panhandle had the smallest, I = 1.02. Results suggest that differences occur in the biological control contributions of various natural enemies and in biological control efficacy among locations.

Catch-effort model used as a management tool in exploited populations: Wild boar as a case study

For sustainable management of exploited populations, it is required to have good knowledge on temporal trends in population density to adapt the harvest. In this regard, hunting statistics are often collected routinely by government agencies and associations. These data are used to assess demographic trends through the development of indices, which are in turn used to manage exploited populations in a sustainable way. However, these population indices depend on features of the hunting process (e.g. hunting effort, hunting conditions, probability of catch). In this study, we show how to use hunting logs to assess demographic trends in exploited populations while accounting for the components of the hunting process. In particular, we developed a catch-effort model to study how the hunting effort leads to mortality rate – hunting pressure – within a given habitat type and during a given period. We illustrated the usefulness of this approach using exploited wild boar (Sus scrofa) populations as a case study. We used a large hunting logs dataset to perform our study, with several hundreds of thousands hunting events for more than 10 years in two French departments in France, including information about the number of hunters, of wild boars culled and the date of the hunt. We showed that catchability is a key parameter to assess hunting pressure at a given time and place. This parameter varies both within the hunting season and between habitat types. Once this variation in catchability was accounted for, our catch-effort model allowed us to obtain estimates of relative densities of wild boar populations over the study period at the management unit scale. Thus, catch-effort models are powerful tools to assess population density and to understand the underlying hunting process. Our study offers straightforward and reproducible conceptual framework that can be applied routinely by wildlife managers on exploited populations and practitioners from hunting statistics logs.

Group IV humpback whales: their status from aerial and landbased surveys off Western Australia, 2005

Single platform aerial line transect and land-based surveys of Southern Hemisphere Group IV humpback whales were undertaken to provide absoluteabundance estimates of animals migrating northward along the western Australian coast during June–August 2005. The aerial survey was designedto cover the whole period of northward migration but the resulting estimates from that survey alone could only, at best, provide relative abundanceestimates as it was not possible to estimate g(0), the detection probability along the trackline, from the data. Owing to logistical constraints, theland-based survey was only possible for a much shorter period (two weeks during the expected peak of the migration in mid-July). This paperproposes three methods that utilise these complementary data in different ways to attempt to obtain absolute abundance estimates. The aerial linetransect data were used to estimate relative whale density (for each day), allowing absolute abundance from the land-based survey to be estimatedfor the short period of its duration. In turn, the land-based survey allowed estimation of g(0) for the aerial survey. Absolute estimates of abundancefor the aerial survey were obtained by combining the g(0) estimate with the relative density estimates, summing over the appropriate number ofdays. The most reliable estimate of northward migrating whales passing the land station for the period of the land-based survey only was 4,700(95% CI 2,700–14,000). The most reliable estimate for the number of whales passing through the aerial survey region for the duration of that survey(55 days from June through to August) was 10,300 (95% CI 6,700–24,500). This is a conservative estimate because the duration of the aerial surveywas almost certainly shorter than the period of the migration. Extrapolation beyond the end of this survey was considered unreliable, but abundancefrom the estimated start of the migration to the end of the survey (87 days from mid-April to August) was estimated to be 12,800 (95% CI 7,500–44,600). The estimated number of whales depends crucially on the assumed migration and period of migration. Results for different migrationparameters are also presented. The point estimates of abundance, whilst higher than those from a previous survey in 1999 (when adjusted for surveyduration) are not significantly so. The peak of the whales’ distribution was found at c.90m water depth.

Expanded Byrne model for evaluating seismic compression

Seismic compression is the accrual of contractive volumetric strain in unsaturated or partially saturated sandy soils during earthquake shaking and has caused significant distress to overlying and nearby structures. The phenomenon can be well characterized by load-dependent, interaction macro-level fatigue theories. Toward this end, the Byrne cyclic shear-volumetric strain coupling model is expanded and calibrated for evaluating seismic compression for several soil types. In addition, the model was transformed to allow it to be implemented in a “simplified” manner, in addition to the original “non-simplified” formulation. Both implementation approaches are used to analyze a site in Japan impacted by the 2007, Mw6.6 Niigata-ken Chuetsu-oki earthquake. The results from the analyses are in general accord with the post-earthquake field observations and highlight the sensitivity of predicted magnitude of the seismic compression to the input variables used and modeling assumptions (e.g. relative density of the soil, magnitude of the volumetric threshold strain, orientation of the ground motions, settlement of soils below the ground water table, and accounting for multidirectional shaking). Although additional studies are needed to further validate the findings presented herein, estimation of relative density and threshold shear strain of the soil and ground motion orientation individually have moderate-to-significant influence on the computed magnitude of seismic compression, but they have a significant influence when taken in combination. Also, the seismic compression models can seemingly be used to predict the settlement in fully saturated sand when the excess pore water pressures are limited. Finally, accounting for multidirectional shaking has a significant influence on the computed magnitude of seismic compression.

Change in Piñon-Juniper Woodland Cover Since Euro-American Settlement: Expansion Versus Contraction Associated with Soil Properties

Woodland and forest ecosystems across western North America have experienced increased density and expansion since the early 1900s, including in the widely distributed piñon-juniper vegetation type of the western United States. Fire suppression and grazing are often cited as the main drivers of these historic changes and have led to extensive tree-reduction treatments across the region. However, much of the scientific literature on piñon-juniper expansion dates back only to the early 1900s, which is generally half a century after Euro-American settlement. Yet US General Land Office (GLO) surveys provide valuable insight into the historical extent and density of woodland and forest ecosystems as surveyors would note where on the landscape they entered and exited woodlands or forests and provided qualitative estimates of relative tree density. This study uses these GLO surveys to establish piñon-juniper woodland extent in the late 19th century at the incipient stages of Euro-American settlement in southeastern Colorado and compares these data with 2017 aerial imagery of woodland cover. We found substantial amounts of woodland contraction, as well as expansion: ≈61% of historically dense woodland is now savanna or open (treeless), whereas ≈57% of historically open areas are now savannas or woodlands. The highest rates of expansion occurred on shallow, rocky soil types with low soil available water capacity, which support little herbaceous vegetation and were consequently less likely to be affected by fire suppression or grazing. Meanwhile, the significant contractions in woodland extent occurred on deeper, upland soils with higher soil available water capacity, which were likely where early settlement and tree cutting was most prevalent. Our results provide mixed support for the widespread assumption of woodland expansion since Euro-American settlement in southeast Colorado and suggest that the expansion that has occurred in our study area is unlikely a result of past grazing or fire suppression.

Low-dose megavoltage cone-beam computed tomography using a novel multi-layer imager (MLI).

The feasibility of low-dose megavoltage cone-beam acquisition (MVCBCT) using a novel, high detective quantum efficiency (DQE) multi-layer imager (MLI) was investigated. The aim of this work was to reconstruct MVCBCT images using the MLI at different total dose levels, and assess Hounsfield Unit (HU) accuracy, noise and contrast-to-noise ratio (CNR) for low-dose megavoltage cone-beam acquisition. The MLI has four stacked layers; each layer contains a combination of copper filter/converter, gadolinium oxysulfide (GOS) scintillator and a-Si detector array. In total, 720 projections of a CATPHAN® phantom were acquired over 360° at 2.5, 6, and 6MV flattening filter free (FFF) beam energies on a Varian TrueBeam LINAC. The dose per projection was 0.01, 0.0167, and 0.05MU for 2.5, 6, and 6MV FFF, respectively. MVCBCT images were reconstructed with varying numbers of projections to provide a range of doses for evaluation. Hounsfield Unit uniformity, accuracy, noise and CNR were estimated. Improvements were quantified relative to the standard AS1200 single-layer imager. Average HU uniformity for the MLI reconstructions was within a range of 95%-99% for all of the energies studied. Relative electron density estimation from HU values was within 0.4%±1.8% from nominal values. The CNR for MVCBCT based on MLI projections was 2-4× greater than from AS1200 projections. The 2.5MV beam acquisition with the MLI exhibited the lowest noise and the best balance between CNR and dose for low-dose reconstructions. Megavoltage cone-beam acquisition imaging with a novel MLI prototype mounted on a clinical linear accelerator demonstrated substantial improvement over the standard AS1200 EPID. Further optimization of MVCBCT reconstruction, particularly for 2.5MV acquisitions, will improve image metrics. Overall, the MLI improves CNR at substantially lower doses than currently required by conventional detectors. This new high DQE detector could provide high-quality MVCBCT at clinically acceptable doses.

Recyclable nanocomposite foams of Poly(vinyl alcohol), clay and cellulose nanofibrils – Mechanical properties and flame retardancy

Foam-like clay-nanocellulose hybrids are of great interest as load-bearing structural foams with excellent fire retardancy, due to unique effects from clay on thermal cellulose degradation. For the first time, the fire retardancy of clay-nanocellulose foams are studied in detail, in particular the effect of a third polymer phase, poly(vinyl alcohol). The composition with optimum mechanical properties and fire retardancy is identified and analyzed. Foams are prepared by freeze-drying and the compositions are varied systematically. Thermogravimetric analysis is performed on foam degradation. Mechanical properties from compression tests and fire retardancy data from cone calorimetry are reported, together with cellular structures from SEM and relative density estimates for the foams. Self-extinguishing foams are obtained with superior flame retardancy to commercial polymer foams. Addition of poly(vinyl alcohol) is beneficial for mechanical properties of clay-nanocellulose foams, but impedes the fire retardancy by reducing clay-cellulose synergies and cellulose charring during degradation.

Estimating absolute indoor density of Aedes aegypti using removal sampling

BackgroundQuantification of adult Aedes aegypti abundance indoors has relied on estimates of relative density (e.g. number of adults per unit of sampling or time), most commonly using traps or timed collections using aspirators. The lack of estimates of the sensitivity of collections and lack of a numerical association between relative and the absolute density of adult Ae. aegypti represent a significant gap in vector surveillance. Here, we describe the use of sequential removal sampling to estimate absolute numbers of indoor resting Ae. aegypti and to calculate calibration coefficients for timed Prokopack aspirator collections in the city of Merida, Yucatan State, Mexico. The study was performed in 200 houses that were selected based on recent occurrence of Aedes-borne viral illness in residents. Removal sampling occurred in 10-minute sampling rounds performed sequentially until no Ae. aegypti adult was collected for 3 hours or over 2 consecutive 10-minute periods.ResultsA total of 3439 Ae. aegypti were collected. The sensitivity of detection of positive houses in the first sampling round was 82.5% for any adult Ae. aegypti, 78.5% for females, 75.5% for males and 73.3% for blood-fed females. The total number of Ae. aegypti per house was on average ~5 times higher than numbers collected for the first sampling round. There was a positive linear relationship between the relative density of Ae. aegypti collected during the first 10-min round and the absolute density for all adult metrics. Coefficients from the linear regression were used to calibrate numbers from 10-min collections into estimates of absolute indoor Ae. aegypti density for all adults, females and males.ConclusionsExhaustive removal sampling represents a promising method for quantification of absolute indoor Ae. aegypti density, leading to improved entomological estimates of mosquito distribution, a key measure in the assessments of the risk pathogen transmission, disease modeling and the evaluation of vector control interventions.

Estimating in situ relative density and friction angle of nearshore sand from portable free-fall penetrometer tests

The friction angle of sand in the nearshore zone of Cannon Beach, Yakutat, Alaska, was estimated from the deceleration measured by a portable free-fall penetrometer (PFFP) at 72 test locations. A correlation between the relative density and PFFP’s maximum deceleration was developed from controlled PFFP deployments into sand of different relative densities. Two approaches were tested: (i) a correlation between relative density and friction angle and (ii) bearing capacity theory. For the former, laboratory vacuum triaxial tests were performed to adjust an existing correlation between relative density and friction angle for the tested nearshore sediments. In situ peak friction angles were then determined using this adjusted correlation and estimates of relative densities. The resulting in situ relative density and friction angle varied between 32%–88% and 44°–56°, respectively. Two bearing capacity–based methods suitable for shallow penetrations were tested. For this approach, equivalents of static cone resistance were determined from the measured decelerations considering the strain rate effect. A range of empirical strain rate coefficients K = 0.1–1.5 were tested. A K value between 0.2 and 0.4 yielded matching results between the two approaches. The estimated friction angles agreed well with expected values and may be applied to problems of sediment transport or early site assessment.

Analysis and trends of photo-trapping in Mexico: text mining in R

This paper gathers published studies that used photo-trapping as the primary or supplementary method to obtain data on mammal and bird species in Mexico. The aim is to determine temporal trends, scientific journals, species, research groups, regions, and key topics investigated using this technology. A secondary objective of this paper was to illustrate the usefulness of text mining tools to analyze and summarize relatively large amounts of information. Papers about photo-trapping in Mexico published in specialized journals and books from 1998 to 2017 were compiled from Google Scholar and processed with various packages in R. A total of 188 papers about photo-trapping in Mexico were compiled, with 88.2 % published in 50 journals over the past seven years. The main journals were Therya, Revista Mexicana de Biodiversidad, Acta Zoologica Mexicana (New Series) and Revista de Biologia Tropical. The articles identified were written by 406 co-authors, 28 of whom contributed with 32.4 % of the papers published. A total of 40 species were reported in the title and abstract of these papers; the most frequent species were Panthera onca, Leopardus pardalis, Puma concolor, Tapirus bairdii, Tayassu pecari, Odocoileus virginianus , and Cuniculus paca . Oaxaca, Campeche, Sonora, Chiapas, Guanajuato, and Puebla were the main states where studies were conducted; in particular, most of them were carried out within Biosphere Reserves. Major research topics comprised records that broaden the distribution range, estimates of relative abundance and density, analysis of activity patterns, ecological interactions between species, and use of photo-trapping data as supplementary information to elaborate inventories of species. The analysis of text mining clearly indicates a trend towards an increasing use of photo-trapping in Mexico. Felines, ungulates and various species of the order Carnivora are main subjects of study. Photo-trapping has been used to explore a number of aspects of the biology of animal species. A large number of studies have been carried out in southeastern Mexico. The use of text mining techniques is a practical approach to analyze large volumes of data.

Caterpillars Count! A Citizen Science Project for Monitoring Foliage Arthropod Abundance and Phenology

Caterpillars Count! is a citizen science project that allows participants to collect data on the seasonal timing, or phenology, of foliage arthropods that are important food resources for forest birds. This project has the potential to address questions about the impacts of climate change on birds over biogeographic scales. Here, we provide a description of the project’s two survey protocols, evaluate the impact of survey methodology on results, compare findings made by citizen scientist participants versus trained scientists, and identify the minimum levels of sampling frequency and intensity needed to accurately capture phenological dynamics. We find that beat sheet surveys and visual surveys yield similar relative and absolute density estimates of different arthropod groups, with beat sheet surveys recording a higher frequency of beetles and visual surveys recording a higher frequency of flies. Citizen scientists generated density estimates within 6% of estimates obtained by trained scientists regardless of survey method. However, patterns of phenology were more consistent between citizen scientists and trained scientists when using beat sheet surveys than visual surveys. By subsampling our survey data, we found that conducting 30 foliage surveys on a weekly basis led to 95% of peak caterpillar date estimates to fall within one week of the “true” peak. We demonstrate the utility of Caterpillars Count! for generating a valuable dataset for ecological research, and call for future studies to evaluate how training and resource materials impact data quality and participant learning gains.

Spatial Dynamics of Olive Ridley Turtles (Lepidochelys olivacea) Density in the Tropical Sea Water of India

The spatial dynamics and density of Olive Ridley sea turtles in the near shore water of the Gahirmatha rookery, Odisha, India was studied from 2007 to 2010 turtle breeding season. The study focused on off-shore dynamics, estimation of relative density of Olive Ridleys at their off-shore breeding ground, behaviour of Olive Ridley sea turtles in offshore water prior to their approach to the arribada beach. A total of 2256, 3116 and 5573 surfacing turtles were sighted that included mating pairs, groups of two and three in the tropical off water during seasonal breeding period of 2007–2008, 2008–2009 and 2009–2010. Congregations of turtle were found to be aggregated within 5 km distance from the shoreline at a depth range of 7–20 m. The mean ± SE SST was 25.8 ± 0.02 °C (range: 21–32 °C) and 27.1 ± 0.07 °C (range: 23–32.3 °C) for the periods of 2008–2009 and 2009–2010 breeding season. The estimated surface density of individual turtles in 2007–2008 was 42.2 turtles/Km2 (CV = 13.3%) followed by 47.3 turtles/Km2 (CV = 24.3%) in 2008–2009 and 78.3 turtles/Km2 (CV = 15.6%) in 2009–2010 breeding season. The result of this present work suggests that turtle movement in the offshore water of Gahirmatha are dynamics and move spatio-temporarily. Therefore, offshore conservation measures for Olive Ridleys at Gahirmatha rookery or elsewhere should be of area specific and area wise turtle congregation patches should be identified during their breeding season, and patrolling can be intensified in these areas to prevent any harmful fishing activities.

Determination of the specific gravity of eggs of equine strongylids, Parascaris spp., and Anoplocephala perfoliata

Given the ever-increasing levels of anthelmintic resistance in livestock parasites globally, it is recommended to use parasite fecal egg counts to make treatment decisions and to evaluate treatment efficacy. The consensus in equine parasitology is to use a flotation medium with a specific gravity (SG) of ≥ 1.20 to float the main parasite egg types of interest in egg counting techniques. However, the density of common equine endoparasite eggs has been sparsely investigated. Equine tapeworm eggs are known to be particularly difficult to determine and count in fecal samples. It is unknown whether this could be because of differences in egg density. The aim of this study was to provide estimates of relative densities for equine ascarid, strongyle, and tapeworm eggs. Six aqueous glucose-salt solutions with specific gravities ranging from 1.06 to 1.16 were made and placed from most to least dense into thirteen 15 mL centrifuge tubes. Concentrated aqueous suspensions of the three types of endoparasite eggs were placed on top of each tube. These tubes were then centrifuged at 800 g for 20 min and each layer of flotation solution was carefully pipetted and transferred to a McMaster egg counting slide. Egg type and count were recorded for each specific gravity layer. Each egg was assigned a specific gravity based on the specific gravity layer it was observed in. In a second trial of this study, five similar flotation media were made ranging from 1.02 to 1.10 and were used in four subsequent replicates. In total between the two trials, the mean egg SGs of Anoplocephala perfoliata (n = 3811), Parascaris spp. (n = 3478), and strongylid type eggs (n = 9291) were 1.0636 (95% confidence interval (CI): 1.0629–1.0642), 1.0903 (95% CI: 1.0897–1.0909), and 1.0453 (95% CI: 1.0448–1.0458), respectively. The three egg types were statistically different from each other (p < 0.0001). This is the first time that the specific gravity of equine strongylid and Anoplocephala perfoliata eggs has been determined. With a tapeworm egg density demonstrated to be between that of strongylids and Parascaris spp., the poor recovery of tapeworm eggs in equine fecal samples must have other explanations.

Comparison of two passive methods for sampling invasive round goby (Neogobius melanostomus) populations at different depths in artificial lakes

Sampling of benthic fish is complicated, especially in deep inland water bodies with a structured bottom. The catches were compared of rapidly spreading round goby (Neogobius melanostomus) using small fykes nets and benthic gillnets in three artificial lakes in The Netherlands over a two year period. Round gobies were captured at all depth layers in each sampled lake. Significantly larger individuals were captured in gillnets compared to fyke nets. Reference sampling in littoral areas captured a wide range in size of round gobies with beach seines. With fyke nets, the highest catches were usually achieved in the shallowest and deepest depth strata. Gillnets catch decreased at deeper layers. Both methods are passive sampling tools and did not provide the absolute catch per bottom area, however relative density estimates of round gobies at different depths or habitats are possible. Round gobies showed a significant size bias associated with capture method. Because it is important to understand the biology and ecology of invasive species like round goby, the combination of small fyke nets and gillnets appears to be a good solution to sample a variety of ranges in deep or/and structured benthic habitats.

Influence of k-space trajectory corrections on proton density mapping with ultrashort echo time imaging: Application for imaging of short T2 components in white matter

PurposeTo evaluate the impact of MR gradient system imperfections and limitations for the quantitative mapping of short T2* signals performed by ultrashort echo time (UTE) acquisition approach. Materials and methodsThe measurement of short T2* signals from a phantom and a healthy volunteer study (8 subjects of average age 28 ± 4 years) were performed on a 3T scanner. The characteristics of the gradient system were obtained using calibration method performed directly on the measured subject or phantom. This information was used to calculate the actual sampling trajectory with the help of a parametric eddy current model. The actual sample positions were used to reconstruct corrected images and compared with uncorrected data. ResultsComparison of both approaches, i.e., without and with correction of k-space sampling trajectories revealed substantial improvement when correction was applied. The phantom experiments demonstrate substantial in-plane signal intensity variations for uncorrected sampling trajectories. In the case of the volunteer study, this led to significant differences in relative proton density (RPD) estimation between the uncorrected and corrected data (P = 0.0117 by Wilcoxon matched-pairs test) and provides for about ~15% higher values for short T2* components of white matter (WM) in the case of uncorrected images. ConclusionThe imperfection of the applied gradients could induce errors in k-space data sampling which further propagates into the fidelity of the UTE images and jeopardizes precision of quantification. However, the study proved that measurement of gradient errors together with correction of sample positions can contribute to increased accuracy and unbiased characterization of short T2* signals.

Seasonal food habits and prey selection of Amur tigers and Amur leopards in Northeast China

We analyzed the scats of Amur tigers and Amur leopards, and examined their annual and seasonal food habits in Northeast China to comprehend their coexistence. Wild boar had the highest annual and seasonal consumption frequencies by the tigers, while both roe deer and sika deer were mostly preyed by the leopards annually. The three species appeared to be the key preys in terms of high proportion of consumed biomass by the two felids. Our data also revealed numerous mid-sized carnivores and small mammals included in the two felids’ food list. We used the relative abundance and biomass density estimation in prey density estimation to calculate the prey preferences of tigers and leopards, and both methods confirmed that Amur tigers strongly preferred wild boar. However, preference estimations of Amur leopards were not consistant, or even opposite to one another from the two methods. The results of the study suggested that prey preference of predators is largely determined by body size of the prey species. Variation in diet composition of the two felids suggests that resource partitioning may contribute to their coexistence.

Evaluation of relative density and friction angle based on SPT-N values

This study is an attempt to evaluate relative density and friction angle of sands on the basis of SPT-N values. In order to develop the relationships among relative density (Dr), friction angle (ϕ) and SPT-N value, field and laboratory test results from sixty boreholes executed in sandy deposit were used. The field tests include the SPTs conducted in the boreholes and the determination of in-situ density at various depths in the boreholes using the pitcher sampler whereas the laboratory tests include routine classification, direct shear box, maximum and minimum density and specific gravity tests. The SPT-N values were observed to vary between 4 and 100 and the in-situ bulk density of undisturbed samples as recovered through pitcher sampler are in the range of 13.24 ~ 18.44 kN/m3. The soil samples are classified as poorly graded sand (SP), poorly graded sand with silt (SP-SM) and silty sand (SM) on the basis of Unified Soil Classification System. The values of minimum dry unit weight fall in the range of 12.22~14.95 kN/m3 and maximum dry unit weight varies in the range of 14.64~19.17 kN/m3 as obtained through vibratory table. Based on the test results, correlation analysis was performed to identify the parameters that affect relative density. The parameters include SPT-N value corrected for field procedures (N60), relative density (Dr), void ratio range (emax–emin), effective overburden stresses (σv’) and in-situ dry density (γdf). Based on the results of correlation analyses, it was observed that SPT-N values alone cannot be related to Dr. Therefore, multiple regression analysis was carried out using Statistical Package for the Social Sciences (SPSS) software and relation between relative density, corrected SPT-N value and effective overburden stress is being proposed. The variation between experimental and predicted values falls within ± 10% at 95% confidence interval. Validation of the proposed correlation was also performed by using an independent data set which indicated that the prediction by using the proposed correlation also falls within ± 10%. Further, comparison of the proposed correlation with other similar relationships already available in the literature was also performed. In addition to the above, correlation between ϕ and SPT-N60 has also been proposed. It has been observed that the experimental and predicted values of friction angle fall within ± 10% with 95% confidence interval. The proposed correlations may be very useful in the field of geotechnical engineering during feasibility/preliminary design stage for rapid estimation of relative density or friction angle based on the field SPT-N60 values.