Large Mesh Research Articles

Assessing airflow unsteadiness in the human respiratory tract under different expiration conditions

To enhance the understanding of airflow characteristics in the human respiratory system, the expiratory airflow in a human respiratory tract model was simulated using large eddy simulation and dynamic mesh under different expiration conditions aligned with clinically measured data. The airflow unsteadiness was quantitatively assessed using power spectral density (PSD) and spectral entropy (SE). The following findings were obtained: (1) The airflow is highly turbulent in the mouth-pharynx region during expiration, with its dynamic characteristics being influenced by both the transient expiration flow pattern at mouth piece and the glottis motion. (2) PSD analysis reveals that the expiratory airflow is very unsteady, exhibiting a broad-band attenuation spectrum in the pharynx-trachea region. When only transient expiration or glottis motion is considered, the PSD spectrum changes slightly. When both are ignored, however, the change is significant, with the peak frequency reduced to 10% of the real expiration condition. (3) SE analysis indicates that the airflow transitions into turbulence in the trachea, and there may be multiple transitions in the region of soft palate. The transient expiration or glottis motion alone increases turbulence intensity by 2%–15%, while ignoring both reduces turbulence intensity by 10%–20%. This study implies that turbulence characteristics can be significantly different under different expiratory conditions, and therefore it is necessary to determine the expiratory flow characteristics using clinically measured expiratory data.

The Escape Intensity and Its Influencing Factors in Antarctic Krill (Euphausia superba) Passing through Large Mesh at the Front End of a Commercial Trawl

The purpose of this study was to comprehend the escape intensity and its influencing factors in Antarctic krill (Euphausia superba) that escaped through large mesh located at the front end of commercial trawl nets. Two pocket nets were employed to collect escaped krill that passed through the mesh opening in the first section (400 mm mesh size, without liner) and second section (16 mm mesh size liner) of the trawl body. The results show that krill escape primarily took place in the first section of the trawl body. Meanwhile, there was almost no krill escape observed in the second section of the trawl body, primarily attributable to the presence of a 16 mm mesh size liner. In terms of body length composition, the average PSI (percentage similarity index) was 67.31 (95% CI: 61.86–72.87) for krill from the pocket net on the larger mesh part and the codend. In addition, the PSI was significantly different (p < 0.05) between the day (60.96, 95% CI: 55.68–66.71) and night (83.62, 95% CI: 76.80–89.46). The escape intensity of krill ranged from 20.83 to 213.13 g·m−2 per ton per hour in the area at the front end of trawl body, with a mean value of 76.52 (95% CI: 55.22–101.09) g·m−2 per ton per hour during the daytime, and 144.66 (95% CI: 110.44–180.03) g·m−2 per ton per hour at night. These results indicate that krill can see and avoid contacting the netting easily during the day, particularly for larger individuals. This provides insight into the design of krill trawls, specifically on the arrangement of liners, which should be integrated from the front part of the trawl body.

Applicability evaluation of innovative simplified methods of slatted floor in pig houses – A CFD study

The slatted floor system is often used in pig housing. Computational Fluid Dynamics (CFD) is a valuable technique for determining the airflow and gas dispersion within the pit headspace through the slatted floor. However, there is a practical issue related to modeling the thousands of small slot openings in real livestock buildings for CFD simulation. It is unpractical to simulate the slatted floor with geometry details due to the large mesh number and the limited computer capacity. In this study, several methods to simplify the model of the slatted floor were explored to reduce the computational cost. The study was based on CFD analysis supported by experimental validation. The slatted floor was modeled in four ways: direct geometry method (DGM), porous-region method (POM), and profiled-porous-region method (including PPOM-cell (PPOM-C) and PPOM-floor (PPOM-F)). To assess the feasibility of the simplification, the four modeling approaches were compared with the experimental data. The results showed that it’s feasible to model the slatted floor as POM or PPOM. The accuracy of POM was high, but it was greatly affected by the calculation of the resistance coefficient. PPOM-C has greatly reduced the amount of calculation, which could be used to simplify the large-scale pig house model whose flow fields and gas emissions below the slatted floor could be ignored. The simulation result of PPOM-F was the closest to DGM, however, due to the large number of meshes and complex setup, it was not suitable for practical simulation.

One mesh does not fit all: A dual compartment codend provides flexible selectivity opportunities to manage mixed fisheries

Fisheries management is moving from a single-species to an ecosystem-based approach to better balance the technical, biological, and economic aspects of the many mixed-species fisheries in the world. Most mixed fisheries are conducted with trawl gears, which have a hereditary challenge of providing a species and size selectivity that meets the development in management objectives of reducing unwanted catch. When fishing on sympatric species, a codend that allows separation of species into different compartments during towing can provide separated catch fractions with contrasting selectivity opportunities. In a case study, we quantified the processes of vertical separation and length-based selectivity for a dual compartment codend having an upper, large mesh compartment intended for cod (Gadus morhua) and a lower, small mesh compartment intended for Nephrops (Nephrops norvegicus). This allowed identification of which processes to improve to reduce unwanted catch. The gear concept delivered a complex selectivity profile while enabling high flexibility to adjust selectivity, also at sea, and provides a tool for the industry to ensure better compliance with increasing management ambitions. An unusual selectivity curve for cod resulted from the contrast in mesh size between the two compartments. Cod and Nephrops smaller than and just above the minimum conservation reference size (MCRS) were efficiently released through the 120 mm square meshes in the upper and the 60 mm square meshes in the lower compartment, respectively. Cod (47%) had a low probability of escaping when caught in the lower compartment, and Nephrops (9%) were lost when caught in the upper compartment. A compartment in the dual compartment codend may easily be changed at sea to adjust the selectivity according to the mix of species encountered, available quota portfolio, and management regime.

Incisional hernia repair following pancreatic surgery—open vs laparoscopic approach

IntroductionFor pancreatic procedures, transverse and midline or combined approaches are used. Having an increased morbidity after pancreatic surgery, these patients have an increased risk of developing an incisional hernia. In the following, we will analyze how the results of incisional hernia surgery after pancreatic surgery are presented in the Herniamed Registry.MethodsHospitals and surgeons from Germany, Austria and Switzerland can voluntarily enter all routinely performed hernia operations prospectively into the Herniamed Registry. All patients sign a special informed consent declaration that they agree to the documentation of their treatment in the Herniamed Registry. Perioperative complications (intraoperative complications, postoperative complications, complication-related reoperations and general complications) are recorded up to 30 days after surgery. After 1, 5, and 10 years, patients and primary care physicians are contacted and asked about any pain at rest, pain on exertion, chronic pain requiring treatment or recurrence. This retrospective analysis of prospectively collected data compares the outcomes of minimally invasive vs open techniques in incisional hernia repair after pancreatic surgery.ResultsRelative to the total number of all incisional hernia patients in the Herniamed Registry, the proportion after pancreatic surgery with 1-year follow-up was 0.64% (n = 461) patients. 95% of previous pancreatic surgeries were open. Minimally invasive incisional hernia repair was performed in 17.1% and open repair in 82.9% of cases. 23.2% of the defects were larger than 10 cm and 32.8% were located laterally or were a combination of lateral and medial defects. Among the few differences between the collectives, a significantly higher rate of defect closure (58.1% vs 25.3%; p < 0.001) and drainage (72.8% vs 13.9%; p < 0.001) was found in the open repairs, and larger meshes were seen in the minimally invasive procedures (340.6 cm2 vs 259.6 cm2; p < 0.001). No difference deemed a risk factor for chronic postoperative pain was seen in the rate of preoperative pain between the open and minimally invasive procedures (Appendix Table 4) No significant differences were found in either the perioperative complications or at 1-year follow-up.ConclusionsIncisional hernias after complex pancreatic surgery can be repaired safely and with a low recurrence rate in both open and minimally invasive techniques.

Efficient multi-fidelity computation of blood coagulation under flow.

Clot formation is a crucial process that prevents bleeding, but can lead to severe disorders when imbalanced. This process is regulated by the coagulation cascade, a biochemical network that controls the enzyme thrombin, which converts soluble fibrinogen into the fibrin fibers that constitute clots. Coagulation cascade models are typically complex and involve dozens of partial differential equations (PDEs) representing various chemical species' transport, reaction kinetics, and diffusion. Solving these PDE systems computationally is challenging, due to their large size and multi-scale nature. We propose a multi-fidelity strategy to increase the efficiency of coagulation cascade simulations. Leveraging the slower dynamics of molecular diffusion, we transform the governing PDEs into ordinary differential equations (ODEs) representing the evolution of species concentrations versus blood residence time. We then Taylor-expand the ODE solution around the zero-diffusivity limit to obtain spatiotemporal maps of species concentrations in terms of the statistical moments of residence time, [Formula: see text], and provide the governing PDEs for [Formula: see text]. This strategy replaces a high-fidelity system of N PDEs representing the coagulation cascade of N chemical species by N ODEs and p PDEs governing the residence time statistical moments. The multi-fidelity order (p) allows balancing accuracy and computational cost providing a speedup of over N/p compared to high-fidelity models. Moreover, this cost becomes independent of the number of chemical species in the large computational meshes typical of the arterial and cardiac chamber simulations. Using a coagulation network with N = 9 and an idealized aneurysm geometry with a pulsatile flow as a benchmark, we demonstrate favorable accuracy for low-order models of p = 1 and p = 2. The thrombin concentration in these models departs from the high-fidelity solution by under 20% (p = 1) and 2% (p = 2) after 20 cardiac cycles. These multi-fidelity models could enable new coagulation analyses in complex flow scenarios and extensive reaction networks. Furthermore, it could be generalized to advance our understanding of other reacting systems affected by flow.

Migration and sedimentation of proppant and its influencing factors in a visual plate fracture model

Hydraulic fracturing technology is the main method used to form high-conductivity fracture networks in unconventional oil and gas reservoirs, and the effective filling of quartz sand proppant in the fracture network is key to its successful implementation. Conventional experiments on the evaluation of sand carrying migration are mainly based on the migration and sedimentation law of a single-mesh proppant in the main fracture; the results obtained are inconsistent with the field observations. To improve our understanding of the migration and sedimentation law of the proppant in the main and branch fractures, in this study, the influences of injection time, injection rate, fracturing fluid viscosity, and proppant combination type on the migration and sedimentation law of a proppant in single and branch fractures were analyzed based on the injection parameters of the sand-carrying fracturing fluid obtained using a similarity criterion through a visual large-scale parallel-plate fracture model system built indoors. The results showed that the rapid accumulation stage of the proppant in the fracture is during the injection time of 5–10 min; the injection rate affected the accumulation area and height of the proppant to a certain extent but had little effect on the final sand dike morphology. A low viscosity of the fracturing fluid was not conducive to the sedimentation of the proppant in the branch fractures; an excessively high fracturing fluid viscosity was not conducive to the sedimentation of the proppant in both the main and branch fractures. When the fracture morphology is single, the viscosity of the fracturing fluid is recommended to be between 30 and 60 mPa·s. When the fracture morphology is complex, the recommended value is between 40 and 50 mPa s. Taking the migration and sedimentation laws of the proppant in the main fracture as an example, the flow of fracturing fluid in the fracture after the formation of a stable sand dike could be divided into five regions: ① inlet scour zone; ② buffer zone; ③ sand dike stable transition zone; ④ sand dike stability zone; and ⑤ outlet scour zone. The higher the large mesh proppant ratio used in the fracturing fluid, the lower the total area ratio of the corresponding sand dike; however, the proppant sedimentation ratio in the branch fracture increases. This study enriches and improves the relevant theoretical research on the migration and sedimentation of proppants and has a certain effect on improving the success rate of the hydraulic fracturing technology applied to unconventional oil and gas reservoirs.

Assessment of the Performance of FireFOAM in Simulating a Real-Scale Fire Scenario Using High Resolution Data

An assessment of the performance of FireFOAM in simulating a large-scale compartment fire scenario is presented in this study, using the Edinburgh Tall Building Fire Test I (2017) as the basis for evaluation. Different mesh geometries and sizes are tested, and both theory-based and experiment-based validation approaches are employed. The theory-based validation revealed that the implemented finite volumes method is generally conservative, but unaccounted deviations of up to 20% for the heat release rate were observed due to errors in numerically modelling subgrid phenomena, particularly with tetrahedral meshes. In the experiment-based validation, the simulated data showed good agreement with experimental measurements for flow patterns inside the compartment, neutral plane height, and temperatures outside the ceiling jet. However, there were relatively large errors in incident radiation in the hot gas zone, thermal boundary layer transient temperatures, and compartment inflow/outflow velocities. Systematic errors were attributed to deficient heat transfer boundary conditions and under-estimated air entrainment. The study also identified ways to improve run-time efficiency by implementing parallel processing or reducing solid angles in FVDOM, although using large meshes (30 cm and 40 cm cell size) resulted in faster run-times at the cost of accuracy.

Coexistence of Crumpling and Flat Sheet Conformations in Two-Dimensional Polymer Networks: An Understanding of Aggrecan Self-Assembly.

We investigate the conformational properties of self-avoiding two-dimensional (2D) ideal polymer networks with tunable mesh sizes as a model of self-assembled structures formed by aggrecan. Polymer networks having few branching points and large enough mesh tend to crumple, resulting in a fractal dimension of d_{f}≈2.7. The flat sheet behavior (d_{f}=2) emerges in 2D polymer networks having more branching points at large length scales; however, it coexists with crumpling conformations at intermediate length scales, a feature found in scattering profiles of aggrecan solutions. Our findings bridge the long-standing gap between theories and simulations of polymer sheets.

Influence of Different Porosities of Titanium Meshes on Bone Neoformation: Pre-Clinical Animal Study with Microtomographic and Histomorphometric Evaluation.

The aim of this study was to evaluate the influence of different types of porosity of titanium meshes on the bone neoformation process in critical defects surgically created in rat calvaria, by means of microtomographic and histomorphometric analyses. Defects of 5 mm in diameter were created in the calvaria of 36 rats, and the animals were randomly treated and divided into the following groups (6 animals per group): NCOG (negative control, only blood clot), TEMG (Polytetrafluoroethylene-PTFE-membrane), SPTMG (small pore titanium mesh), SPMMG (small pore mesh + PTFE), LPTMG (large pore titanium mesh), and LPMMG (large pore mesh + PTFE). After 60 days, the animals were sacrificed, and the bone tissue formed was evaluated with micro-CT and histomorphometry. The data were compared using an ANOVA followed by the Tukey post-test (p ≤ 0.05). The microtomographic results showed that the SPTMG group presented the highest numerical value for bone volume/total volume (22.24 ± 8.97), with statistically significant differences for all the other groups except LPTMG. Considering the histomorphometric evaluation, groups with only porous titanium meshes showed higher values compared to the groups that used the PTFE membrane and the negative control. The SPTMG group presented higher values in the parameters of area (0.44 mm2 ± 0.06), extension (1.19 mm2 ± 0.12), and percentage (7.56 ± 1.45%) of neoformed bone. It was concluded that titanium mesh with smaller pores showed better results and that the association of PTFE membranes with titanium meshes did not improve the outcomes, suggesting a correlation between mesh porosity and underlying bone repair.

Experimental study on proppant-carrying migration and settlement of slickwater in narrow plate fractures based on PIV / PTV

Hydraulic fracturing is the primary method used for oilfield stimulation, and the migration and settlement pattern of proppant plays a crucial role in the formation of high conductivity propping fractures in the reservoir. This study summarizes two growth modes of sand dune: the ‘overall longitudinal growth’ mode and the ‘push growth along fracture length direction’ mode. To investigate these modes, a two-phase velocity test is conducted using PIV, and the exposure difference is utilized to separate the tracer and track the single-phase velocity. By analyzing the slickwater flow field and proppant velocity field, the micro-motion mechanism behind the two dune growth modes is quantitatively examined. The results indicate that mode 1 growth of the sand dune occurs when a pump with a large mesh number, high polymer viscosity, and large displacement is used. On the other hand, mode 2 growth is observed when a pump with a small mesh number, low polymer viscosity, and small displacement is employed. It is important to note that there is no clear boundary for the migration and sedimentation mode of proppant, as they can transition into each other under certain conditions. These modes only exist during specific stages of sand dune growth. In the case of the ‘backflow’ pattern, the settlement of proppant is primarily influenced by the vortex structure of slickwater. Conversely, in the ‘direct’ pattern, the proppant is propelled forward by the drag of the fluid and settles due to its own gravity. Once the proppant placement reaches equilibrium, the direction of proppant velocity follows a normal distribution within 0°. This approach establishes a connection between the overall placement of the sand dune and the microscopic movement of the proppant and slickwater. Optimizing construction parameters during fracturing construction can enhance the effectiveness of distal proppant placement in fractures.

Transient response of pavement structures under moving wheel loads using the ALE methodology

AbstractThe dynamic response of long structures (e.g., pavements) subjected to moving loads is generally difficult to simulate using conventional methods like the finite element method in the Lagrangian setting. This is because the entire length of the structure in the path of the moving load would need to be discretized, and in turn would require large meshes. Additionally, if improvement in quality of results through the use of finer mesh sizes is sought, the entire region of the mesh in the load path would require refinement. As a direct result, long simulation run‐times can be expected when using conventional methods. To overcome these drawbacks, and improve the efficiency of the finite element simulations, the Arbitrary Lagrangian Eulerian (ALE) approach can be used to simulate pavement structures, provided longitudinal homogeneity is assumed. This contribution uses an extension of the quasi‐static ALE framework to the transient domain, enabling the study of the dynamic response of pavement structures subjected to moving loads. In this work, some case studies are considered to highlight the capabilities of this dynamic ALE framework.

Mini- or less-open sublay (E/MILOS) operation vs open sublay and laparoscopic IPOM repair for the treatment of incisional hernias: a registry-based propensity score matched analysis of the 5-year results.

Open sublay and laparoscopic IPOM repair have specific disadvantages and risks. In recent years, this evidence led to a paradigm shift and induced the development of new minimally invasive techniques of sublay mesh repair. Pioneering this trend, we developed the endoscopically assisted mini- or less-open sublay (MILOS) concept. The operation is performed trans-hernially via a small incision with light-holding laparoscopic instruments either under direct, or endoscopic visualization. After dissection of an extra-peritoneal space of at least 8cm, port placement and CO2 insufflation, each MILOS operation can be continued endoscopically (EMILOS repair). All E/MILOS operations were prospectively documented in the Herniamed Registry with 1- and 5-year questionnaire follow-ups. Propensity score matching of incisional hernia operations comparing the results of the E/MILOS operation with the laparoscopic intraperitoneal onlay mesh operation (IPOM) and open sublay repair from all other institutions participating in the Herniamed Registry was performed. The results with perioperative complications and 1-year follow-up have been published previously. This paper reports on the 5-year results. The 5-year follow-up rate was 87.5% (538 of 615 patients with E/MILOS incisional hernia operations). Comparing E/MILOS repair with laparoscopic IPOM and open sublay operation, propensity score matching analysis was possible with 448 and 520 pairs of operations, respectively. Compared with laparoscopic IPOM incisional hernia operation, the E/MILOS repair is associated with significantly fewer general complications (P = 0.004), recurrences (P < 0.001), less pain on exertion (P < 0.001), and less chronic pain requiring treatment (P = 0.016) and tends to result in fewer postoperative complications (P = 0.052), and less pain at rest (P = 0.053). Matched pair analysis with open sublay repair revealed significantly fewer general complications (P < 0.001), postoperative complications (P < 0.001), recurrences (P = 0.002), less pain at rest (P = 0.004), less pain on exertion (P < 0.001), and less chronic pain requiring treatment (P = 0.014). A limitation of this analysis is a relative low 5-year follow-up rate for laparoscopic IPOM and open sublay. The E/MILOS technique allows minimally invasive trans-hernial repair of incisional hernias using large standard meshes with low morbidity and good long-term results. The technique combines the advantages of sub-lay repair and a mini- or less-invasive approach. ClinicalTrials.gov Identifier NCT03133000.

Even Faster Exact Exchange for Solids via Tensor Hypercontraction.

Hybrid density functional theory (DFT) remains intractable for large periodic systems due to the demanding computational cost of exact exchange. We apply the tensor hypercontraction (THC) (or interpolative separable density fitting) approximation to periodic hybrid DFT calculations with Gaussian-type orbitals using the Gaussian plane wave approach. This is done to lower the computational scaling with respect to the number of basis functions (N) and k-points (Nk) at a fixed system size. Additionally, we propose an algorithm to fit only occupied orbital products via THC (i.e., a set of points, NISDF) to further reduce computation time and memory usage. This algorithm has linear scaling cost with k-points, no explicit dependence of NISDF on basis set size, and overall cubic scaling with unit cell size. Significant speedups and reduced memory usage may be obtained for moderately sized k-point meshes, with additional gains for large k-point meshes. Adequate accuracy can be obtained using THC-oo-K for self-consistent calculations. We perform illustrative hybrid density function theory calculations on the benzene crystal in the basis set and thermodynamic limits to highlight the utility of this algorithm.

Short-Term Outcome of Laparoscopic Intraperitoneal Hernioplasty of Incisional Hernia in Khulna Medical College Hospital

Background: Herniorrhaphies that apply a large prosthetic mesh appear to have a lower failure rate, but extensive dissection of soft tissue contributes to an increased incidence of wound infections and wound-related complications. The method of laparoscopic incisional hernia repair was developed in the early 1990s. This technique is based on the same physical and surgical principles as the open underlay procedure. Therefore, this operation has increased in popularity promising shorter hospital stay, improved outcome and fewer complications than traditional open procedures. The aim of the study was to see the short-term outcome of laparoscopic intraperitoneal hernioplasty of incisional hernia in Khulna medical college hospital. Material &amp; Methods: This study was prospective single-cantered observational study carried out at the department of surgery; Khulna Medical College Hospital included 30 patients of incisional hernia those who underwent laparoscopic intraperitoneal on lay mesh (IPOM) technique using polypropylene mesh and the mesh was fixed with Tacker. The duration of the period from January, 2013 to June, 2013. Data was collected by researcher himself with face-to-face interview using a prepared structured questionnaires &amp; checklist and analyzed on SPSS 22. Results: The study was done on 30 patients among which 13 (43.3%) were male and 17 (56.6%) were female patients. Among them the maximum male and female came from 41-50 years age group. Among the 30 patients 16 belonged vertical incisional hernia, whereas 13 patients belonged transverse incisional hernia and the size of the defect of hernia in 27 were medium (defect is 5-10cm) and in 3 were small (defect is &lt;5cm). 21 patients underwent emergency surgery, whereas 9 patients underwent elective surgery for different diseases previously. Every patient in this study group had some predisposing factors to appear incisional hernia. Of them, 16 (53.33%) patients were suffering from Diabetes mellitus, 6 (20%) patients were suffering from chronic cough 2 (6%) patients from chronic retention of urine, 4(13.33%) from chronic constipation and 8 (26.67%) patients from immunocompromised condition due to diseases or drugs taken by them. In case of preoperative complication, only 1 (3.3%) patient each experienced omental haemorrhage, visceral haemorrhage, bowel injury and open conversion whereas 2 (6.6%) patients featured port site bleeding. As postoperative complication, the study shows that 4 (13.3%) patients developed paralytic ileus in followed by port site infection in 3(10%) patients. Conclusion: Laparoscopic hernioplasty is safe and convenient repair in short-term in our clinical setup. But to reach a precise conclusion a long-term case control study with conventional mesh hernioplasty in multiple centres should be done.

Tim Ingold and Object-Oriented Anthropology

Tim Ingold, while extending the radical undertaking of vitalism, with its Nietzschean matrix, puts the decentering undertaken by this philosophical tradition on a more solid foundation, opening up a new space of interobjective relations. Instead of an epistemic plunge into human categories, the goal is to move towards a broader ontological space, including other sites of meaning, such as chairs, spirits, animals, baskets, and many others. Unlike more classical anthropology, with its well-delimited Anthropos as an inevitable transcendental horizon, Ingold suggests a world where humans are not protagonists, but rather provisional negotiators within a large mesh of subjectless experiences. The model proposed in this essay distances itself from the plane of (neo)-Kantian speculation, converting its contours into something less orthodox by making room for a possible Object-Oriented Anthropology (O.O.A).

Distributed ℋ 2 -Matrices for Boundary Element Methods

Standard discretization techniques for boundary integral equations, e.g., the Galerkin boundary element method, lead to large densely populated matrices that require fast and efficient compression techniques like the fast multipole method or hierarchical matrices. If the underlying mesh is very large, running the corresponding algorithms on a distributed computer is attractive, e.g., since distributed computers frequently are cost-effective and offer a high accumulated memory bandwidth. Compared to the closely related particle methods, for which distributed algorithms are well-established, the Galerkin discretization poses a challenge, since the supports of the basis functions influence the block structure of the matrix and therefore the flow of data in the corresponding algorithms. This article introduces distributed ℋ 2 -matrices, a class of hierarchical matrices that is closely related to fast multipole methods and particularly well-suited for distributed computing. While earlier efforts required the global tree structure of the ℋ 2 -matrix to be stored in every node of the distributed system, the new approach needs only local multilevel information that can be obtained via a simple distributed algorithm, allowing us to scale to significantly larger systems. Experiments show that this approach can handle very large meshes with more than 130 million triangles efficiently.

Abundance and composition of small floating plastics in the eastern and southern sectors of the Atlantic Ocean

We report the distribution of floating plastics in the eastern and southern sectors of the Atlantic Ocean based on 35 neuston net trawl samples collected during two research cruises in 2016 and 2017. Plastic particles (>200 μm) were found in 69% of net tows, with median densities of 1583 items·km−2 and 5.1 g·km−2. Most particles (80% of 158) were microplastics (<5 mm) of secondary origin (88%), followed by industrial pellets (5%), thin plastic films (4%) and lines/filaments (3%). Due to the large mesh size we used, textile fibers were not considered in this study. μFTIR analysis revealed that most particles found in the net were made of polyethylene (63%), followed by polypropylene (32%) and polystyrene (1%). A transect between 0 and 18°E along 35°S in the South Atlantic Ocean revealed higher densities farther west, supporting the accumulation of floating plastics in the South Atlantic gyre, mainly west of 10°E.

Calibration of fish biomass estimates from gillnets: Step towards broader application of gillnet data

Fish are an important component of aquatic ecosystems, thus representative and reliable assessments of their population variables are essential for a variety of ecological applications, management and conservation. Determining Fish Density per actual Spatial Unit (volume or area, FDSU) as a measure of absolute fish quantity is of particular interest. Gillnets are undoubtedly one of the most common and important methods for assessing fish populations in large lentic waters. However, direct calculating of FDSU from gillnet catches is impossible because of the passive nature of this method, and to date there is no reliable model for calculating FDSU from gillnet catches. This weakness largely limits the use of gillnet data for applications requiring FDSU estimates.The aim of this study was to calibrate gillnet catches using FDSU obtained by active methods (beach seine nets and hydroacoustics) to develop a tool for assessing FDSU from gillnet catches. To achieve this goal, we compared gillnet biomass to fish biomass estimated from the active methods, both of which cover similar spatiotemporal niches. This comparison was performed using a statistical approach based on the recognition of non-negligible random measurement error in both the explanatory (active methods) and response (gillnets) variables.We found a strong positive linear relationship between fish biomasses sampled with gillnets and with active methods. The slope of the fitted linear model was similar when comparing gillnets with the two active methods. The statistical method used allowed for the inclusion of error in the biomass estimates with gillnets and active methods, refining the credible intervals of the estimated relationship. The effect of gillnet effort on model accuracy was simulated to show how increased effort narrows the credible interval. Finally, comparison with previously published relationships revealed a large but explainable discrepancy between our model and previous models.Our study showed that conversion of gillnet biomass to biomass per actual spatial unit is possible. The effective sampling area of one square meter of gillnet was determined to be 8 m2 of waterbody surface area when European standard 12 mesh-sizes gillnets are used, and 5 m2 when four larger meshes are added to the European standard gillnets. Our model further stressed the impact of increased sampling effort on reducing estimation variability and shows that the model may be dependent on the fish community.

Investigation of ultrasonic welding of CF/PA66 using stainless steel mesh energy directors

This paper employs stainless steel mesh as energy director (ED) to join carbon fiber reinforced PA66 composite (CF/PA66). The effect of mesh size on the lap-shear failure load, cross-sectional microstructure, and fracture morphology is investigated. The results show that the mesh size has important impact on the weld formation and joint mechanical property. A small wire spacing leads to more pore defects in a joint; a large wire diameter increases the lack of fusion defects, and a large mesh area reduces the energy concentration effect. Mesh energy directors with large wire spacing, small wire diameter, and small area contribute to high joint strength. Under the appropriate welding energy and mesh size, the failure loads of joints are above 10000 N, and the failure model of these joints is workpiece fracture.