Search Results (12)

When a gravity current encounters a barrier, it is reflected as a moving hydraulic jump or bore. These reflected flows, which play a significant role in estuarine mixing and sediment transport, are often simplified in theoretical models as purely advective processes with no mixing and dilution effects. This study explores the dynamics of gravity currents fully blocked by various inclined barriers, focusing on the resulting mixing behavior. Using an image analysis technique based on light attenuation to capture instantaneous density fields, we reveal how the presence of a barrier influences the current even before impact. By applying the Thorpe scale to assess turbulent mixing, we show that a barrier’s geometry significantly affects mixing intensity. Notably, this study finds that barriers can increase the local turbulent mixing compared to horizontal surfaces. Full article

Thorpe analysis is a commonly used method to study turbulence, an important research object in the field of atmospheric science. However, using Thorpe analysis to retrieve turbulence parameters from radiosonde data can reduce inversion accuracy due to instrument noise. Therefore, this paper presents a new wavelet denoising method to determine the optimal decomposition layer based on adaptative Monte Carlo simulation, and the denoising effect of this method is tested by simulation data and real detection data. Numerical experiments shows that the stability and accuracy of the proposed new method are better than those of the previous methods. Full article

Unmanned underwater vehicles (UUVs) are becoming increasingly important for a variety of applications, including ocean exploration, mine detection, and military surveillance. This paper aims to provide a comprehensive examination of the technologies that enable the operation of UUVs. We begin by introducing various types of unmanned vehicles capable of functioning in diverse environments. Subsequently, we delve into the underlying technologies necessary for unmanned vehicles operating in underwater environments. These technologies encompass communication, propulsion, dive systems, control systems, sensing, localization, energy resources, and supply. We also address general technical approaches and research contributions within this domain. Furthermore, we present a comprehensive overview of related work, survey methodologies employed, research inquiries, statistical trends, relevant keywords, and supporting articles that substantiate both broad and specific assertions. Expanding on this, we provide a detailed and coherent explanation of the operational framework of UUVs and their corresponding supporting technologies, with an emphasis on technical descriptions. We then evaluate the existing gaps in the performance of supporting technologies and explore the recent challenges associated with implementing the Thorp model for the distribution of shared resources, specifically in communication and energy domains. We also address the joint design of operations involving unmanned surface vehicles (USVs), unmanned aerial vehicles (UAVs), and UUVs, which necessitate collaborative research endeavors to accomplish mission objectives. This analysis highlights the need for future research efforts in these areas. Finally, we outline several critical research questions that warrant exploration in future studies. Full article

Nanoporous materials show a promising combination of mechanical properties in terms of their relative density; while there are numerous studies based on metallic nanoporous materials, here we focus on amorphous carbon with a bicontinuous nanoporous structure as an alternative to control the mechanical properties for the function of filament composition.Using atomistic simulations, we study the mechanical response of nanoporous amorphous carbon with 50% porosity, with sp${}^3$ content ranging from 10% to 50%. Our results show an unusually high strength between 10 and 20 GPa as a function of the $\%s{p}^3$ content. We present an analytical analysis derived from the Gibson–Ashby model for porous solids, and from the He and Thorpe theory for covalent solids to describe Young’s modulus and yield strength scaling laws extremely well, revealing also that the high strength is mainly due to the presence of sp${}^3$ bonding. Alternatively, we also find two distinct fracture modes: for low $\%s{p}^3$ samples, we observe a ductile-type behavior, while high $\%s{p}^3$ leads to brittle-type behavior due to high high shear strain clusters driving the carbon bond breaking that finally promotes the filament fracture. All in all, nanoporous amorphous carbon with bicontinuous structure is presented as a lightweight material with a tunable elasto-plastic response in terms of porosity and sp${}^3$ bonding, resulting in a material with a broad range of possible combinations of mechanical properties. Full article

Microsaccades are at the interface between basic oculomotor phenomena and complex processes of cognitive functioning, and they also have been a challenge for subtle experimentation and adequate statistical analysis. In the second part of the special thematic issue (for the first part see Martinez-Conde, Engbert, & Groner, 2020) the authors present a series of articles which demonstrate that microsaccades are still an interesting and rewarding area of scientific research the forefront of research in many areas of sensory, perceptual, and cognitive processes. In their article “Pupillary and microsaccadic responses to cognitive effort and emotional arousal during complex decision making” Krejtz, Żurawska, Duchowski, & Wichary (2020) investigate pupillary and microsaccadic responses to information processing during multi-attribute decision making under affective priming. The participants were randomly assigned into three affective priming conditions (neutral, aversive, and erotic) and instructed to make discriminative decisions. As hypothesized by the authors, the results showed microsaccadic rate inhibition and pupillary dilation, depending on cognitive effort prior to decision and moderated by affective priming. Aversive priming increased pupillary and microsaccadic responses to information processing effort. The results indicate that pupillary response is more influenced by affective priming than microsaccadic rate. The results are discussed in the light of neuropsychological mechanisms of pupillary and microsaccadic behavior. In the article “Microsaccadic rate signatures correlate under monocular and binocular stimulation conditions” Essig, Leube, Rifai, & Wahl (2020) investigate microsaccades with respect to their directional distribution and rate under monocular and binocular conditions. In both stimulation conditions participants fixated a Gabor patch presented randomly in orientation of 45° or 135° over a wide range of spatial frequencies. Microsaccades were mostly horizontally oriented regardless of the spatial frequency of the grating. This outcome was consistent between both stimulation conditions. This study found that the microsaccadic rate signature curve correlates between both stimulation conditions, therefore extending the use of microsaccades to clinical applications, since parameters as contrast sensitivity, have frequently been measured monocularly in the clinical studies. The study “Microsaccades during high speed continuous visual search” by Martin, Davis, Riesenhuber, & Thorpe (2020) provides an analysis of the microsaccades occurring during visual search, targeting to small faces pasted either into cluttered background photos or into a simple gray background. Participants were instructed to target singular 3-degree upright or inverted faces in changing scenes. As soon as the participant’s gaze reached the target face, a new face was displayed in a different random location. Regardless of the experimental context (e.g., background scene, no background scene), or target eccentricity (from 4 to 20 degrees of visual angle), The authors found that the microsaccade rate dropped to near zero levels within 12 ms. There were almost never any microsaccades after stimulus onset and before the first saccade to the face. In about 20% of the trials, there was a single microsaccade that occurred almost immediately after the preceding saccade’s offset. The authors argue that a single feedforward pass through the visual hierarchy of processing a stimulus is needed to effectuate prolonged continuous visual search and provide evidence that microsaccades can serve perceptual functions like correcting saccades or effectuating task-oriented goals during continuous visual search. While many studies have characterized the eye movements during visual fixation, including microsaccades, in most cases only horizontal and vertical components have been recorded and analyzed. Little is known about the torsional component of microsaccades. In the study “Torsional component of microsaccades during fixation and quick phases during optokinetic stimulation” Sadeghpour & Otero-Millan (2020) recorded eye movements around the three axes of rotation during fixation and torsional optokinetic stimulus. The authors found that the average amplitude of the torsional component of microsaccades during fixation was 0.34 ± 0.07 degrees with velocities following a main sequence with a slope comparable to the horizontal and vertical components. The size of the torsional displacement during microsaccades was correlated with the horizontal but not the vertical component. In the presence of an optokinetic stimulus a nystagmus was induced producing more frequent and larger torsional quick phases compared to microsaccades produced during fixation of a stationary stimulus. The torsional component and the vertical vergence component of quick phases increased with higher velocities. In previous research, microsaccades have been interpreted as psychophysiological indicators of task load. So far, it is still under debate how different types of task demands are influencing microsaccade rate. In their article “The interplay between task difficulty and microsaccade rate: Evidence for the critical role of visual load” Schneider et al. (1921) examined the relation between visual load, mental load and microsaccade rate. The participants carried out a continuous performance task (n-back) in which visual task load (letters vs. abstract figures) and mental task load (1-back to 4-back) were manipulated as within-subjects variables. Eye tracking data, performance data as well as subjective workload were recorded. Data analysis revealed an increased level of microsaccade rate for stimuli of high visual demand (i.e., abstract figures), while mental demand (n-back-level) did not modulate microsaccade rate. The authors concluded that microsaccade rate reflects visual load of a task rather than its mental load. This conclusion is in accordance with the proposition of Krueger et al. (2019) “Microsaccades distinguish looking from seeing”, linking sensory with cognitive phenomena. The present special thematic issue adds several new interesting facets to the research landscape around microsaccades. They still remain an attractive focus of interdisciplinary research and transdisciplinary applications. Thus, as already noted in the first part of this special thematic issue, research on microsaccades will not only endure, but keep evolving as the knowledge base expands. Full article

Considerable scholarly attention has been directed to the adverse health effects caused by residential segregation. We aimed to visualize the state-of-the-art residential segregation and health research to provide a reference for follow-up studies. Employing the CiteSpace software, we uncovered popular themes, research hotspots, and frontiers based on an analysis of 1211 English-language publications, including articles and reviews retrieved from the Web of Science Core Collection database from 1998 to 2022. The results revealed: (1) The Social Science & Medicine journal has published the most studies. Roland J. Thorpe, Thomas A. LaVeist, Darrell J. Gaskin, David R. Williams, and others are the leading scholars in residential segregation and health research. The University of Michigan, Columbia University, Harvard University, the Johns Hopkins School of Public Health, and the University of North Carolina play the most important role in current research. The U.S. is the main publishing country with significant academic influence. (2) Structural racism, COVID-19, mortality, multilevel modelling, and environmental justice are the top five topic clusters. (3) The research frontier of residential segregation and health has significantly shifted from focusing on community, poverty, infant mortality, and social class to residential environmental exposure, structural racism, and health care. We recommend strengthening comparative research on the health-related effects of residential segregation on minority groups in different socio-economic and cultural contexts. Full article

Thermal microstructure profiling is an established technique for investigating turbulent mixing and stratification in lakes and oceans. However, it provides only quasi-instantaneous, 1-D snapshots. Other approaches to measuring these phenomena exist, but each has logistic and/or quality weaknesses. Hence, turbulent mixing and stratification processes remain greatly under-sampled. This paper contributes to addressing this problem by presenting a novel analysis of thermal microstructure profiles, focusing on their multi-scale stratification structure. Profiles taken in two small lakes using a Self-Contained Automated Micro-Profiler (SCAMP) were analysed. For each profile, buoyancy frequency (N), Thorpe scales (L_T), and the coefficient of vertical turbulent diffusivity (K_Z) were determined. To characterize the multi-scale stratification, profiles of d²T/dz² at a spectrum of scales were calculated and the number of turning points in them counted. Plotting these counts against the scale gave pseudo-spectra, which were characterized by the index D of their power law regression lines. Scale-dependent correlations of D with N, L_T and K_Z were found, and suggest that this approach may be useful for providing alternative estimates of the efficiency of turbulent mixing and measures of longer-term averages of K_Z than current methods provide. Testing these potential uses will require comparison of field measurements of D with time-integrated K_Z values and numerical simulations. Full article

In this article, Thorpe analysis, which often retrieves the characteristics of mixing in the free atmosphere from balloon sounding data, is applied to the data of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC). We find that the COSMIC data can well retrieve the strongest mixed layer in the troposphere (SMLT) altitude, and can reveal the basic variation trend of the SMLT thickness and Thorpe scale $L_T$ . We use COSMIC data to reveal the global spatial and temporal distribution of the SMLT from 2007 to 2015 and analyze the fluctuation period of the SMLT altitude with Hilbert–Huang transform (HHT), we find that the variation of the SMLT altitude is influenced by the dual effects of terrain and solar radiation. Full article

Based on a new type of sensor mounted on a near-space balloon released in Hami, Xinjiang, the Thorpe method was used to analyze turbulence. The method was applied for the first time to northwest China (the mid-latitude region), and almost no radiosonde data above 40 km have been used to study turbulence hitherto. The feasibility of analyzing turbulence characteristics using radiosonde data based on the Beidou positioning system by the Thorpe method was thus verified. The distribution characteristics of turbulence scale, turbulence intensity, and turbulence kinetic energy dissipation rate, and the turbulence diffusion coefficient, were analyzed and discussed. The relationship between turbulence fraction, turbulence intensity, and stratified instability was also investigated. The results show that over 35 km, the influence of instrument noise on turbulence detection is significantly enhanced, which lead to an overestimation of turbulence in that region. The turbulence fraction was defined to reflect the degree of turbulence internal mixing, which is closely related to atmospheric instability. It was found that when the turbulence fraction reached 60%–80%, the turbulence reached its strongest intensity, and when the turbulence fraction exceeded 80%, the turbulence could not be maintained and began to decay. Full article

The question of how games should be taught is still a controversial subject. There has been a growing number of studies on teaching games and coaching sports since the first publication of Bunker and Thorpe on Teaching Games for Understanding (TGfU). In this sense, the present systematic review and meta-analysis aimed to systematically review the scientific literature about the effects of technical and tactical approach interventions on skill execution and decision making, and to examine the influence of the teacher/coach management style. A systematic literature search was carried out in accordance with PRISMA guidelines in Web of Science (WOS), PubMed (Medline), Scopus, and SportDiscus electronic databases. A total of seven and six studies were deemed to meet the inclusion criteria for decision making and skill execution, respectively. Meta-analysis results showed that tactical interventions achieved significant improvements in decision making (effect size = 0.89 with 95% confidence interval (CI) from 0.12 to 1.65), but they did not show significant improvements in skill execution (effect size = 0.89 with 95% CI from −0.45 to 2.23) compared to technical approaches. However, the heterogeneity of interventions was large and the quality of evidence was low according to GRADE. In conclusion, tactical approaches are recommended to teach games and sports in order to develop technique, understanding, tactical knowledge, and decision making, which are demanded in game play. These findings could be useful for teachers and coaches to improve these aspects of their players and students. Full article

This article addresses the properties of stably-stratified and unstable layers in the free troposphere. Thorpe’s method of analysis has been applied to potential temperature (PT) profiles obtained from the raw measurements of operational radiosondes. In principle, this method distinguishes stably stratified and unstable regions. The background static stability, quantified by the square Brunt-Väisälä frequency estimated on the sorted PT profiles (stable everywhere), is observed to be significantly smaller in the unstable regions, likely due to turbulent mixing. The vertical power spectral densities (PSDs) of temperature fluctuations are shown to be proportional to $m^{-p}$ , where p is in the average $2.8\pm 0.2$ in the stably stratified regions, and is $1.7\pm 0.3$ in the unstable regions, for wavenumbers m in the range $[{10}^{-2},{10}^{-1}]$ m ${}^{-1}$ . Such findings validate the Thorpe analysis when applied to radiosondes. Also, the distribution of thicknesses h of unstable layers is observed to approximately follow a power law, varying as $h^{-r}$ with $r\approx 2.1\pm 0.1$ . PT profiles for the entire troposphere have also been analyzed as the sum of a sorted profile and an anomaly profile. The PSDs of the sorted PT profiles are scaled as $m^{-3}$ down to a few meters on the vertical scale. Simple stochastic models based on random walks with increments having the property of flicker noise are shown to reproduce the spectral properties of the sorted PT profiles, i.e., of the vertical stratification of the free atmosphere. Full article

In recent years, Thorpe analysis has been used to retrieve the characteristics of turbulence in free atmosphere from balloon-borne sensor data. However, previous studies have mainly focused on the mid-high latitude region, and this method is still rarely applied at heights above 30 km, especially above 35 km. Therefore, seven sets of upper air (>35 km) sounding data from the Changsha Sounding Station (28°12′ N, 113°05′ E), China are analyzed with Thorpe analysis in this article. It is noted that, in the troposphere, Thorpe analysis can better retrieve the turbulence distribution and the corresponding turbulence parameters. Also, because of the thicker troposphere at low latitudes, the values of the Thorpe scale $L_T$ and turbulent energy dissipation rate $\epsilon$ remain greater in a larger height range. In the stratosphere below the height of 35 km, the obtained $\epsilon$ is higher, and Thorpe analysis can only be used to analyze the characteristics of large-scale turbulence. In the stratosphere at a height of 35–40 km, because of the interference of sensor noise, Thorpe analysis can only help to retrieve the rough distribution position of large-scale turbulence, while it can hardly help with the calculation of the turbulence parameters. Full article