Direction Of Path Research Articles

Mixed Propagation Modes in Three Bragg Propagation Periods of Variable Chain Structures

In this article, we studied the characteristics of multi-mode propagation and electric field distribution for a single layered and multi-layered periodic infinite-length square chain structures. We also studied the characteristics of mode propagation in silver and dielectric circular-rod chain structures. This article examines three modes of propagation in three Bragg propagation periods of a square chain structure. Each mode exhibits different forms in each of the three propagation periods, including the propagation, leaky, and cut-off modes. We also consider multiple complex characteristics. For example, the directions of wave and energy propagation paths have two forms: syntropy and reverse (one-way and two-way). The leaky wave has a variety of distribution states, for instance, attenuation and divergence. By analyzing these new physical properties, we have established a solid foundation for better development and application of leaky antennas and other applications. The method in this article was designed and validated for general metal structure applications.

An immersive head-mounted display with a liquid lens

An optical design for an immersive head-mounted display (HMD) with a liquid lens is described. This design combines the liquid lens with an immersive HMD system to improve the image quality for myopic and hyperopic users. A penta-prism is also incorporated and used to change the direction of the optical path to improve any optical aberration caused by the gravity effect. This immersive head-mounted display has a field of view of 14.9 degrees, focal length of 47.78 mm, and f-number of 5.97 with an exit pupil diameter of 8 mm, eye relief of 15 mm. The value of the MTF is above 0.9 at 3.3 lp/mm.

Numerical simulation of distortion-induced fatigue crack growth using extended finite element method

Aiming to investigate the propagation behaviour of distortion-induced fatigue cracks in steel bridge web gaps, multi-scale numerical analysis models were built based on fracture mechanics theory and extended finite element method (XFEM), combining with the full-scale fatigue tests data. Propagation behaviours of representative fatigue cracks in vertical stiffener web gaps and horizontal gusset plate web gaps were analysed. Finite element models of welds connecting web, vertical stiffener and horizontal gusset plate were built, and the welding residual stresses of such details were analysed. Significant transverse welding residual tensile stresses exist at stiffener web weld toes for web gap details. Residual stress measurements were conducted, and the crack shape and the propagation direction path were basically the same with that in the numerical simulation, indicating that the numerical simulation results were relatively reliable. Furthermore, the welding residual stress fields were considered in the crack propagation analysis models. Representative fatigue cracks at web gaps are Mode I leading mixed-mode cracks of Modes I, II and III. Crack propagation considering welding residual stress has faster propagation rate and is more consistent with fatigue test results. The welding residual stress cannot be ignored for analysis and assessment of distortion-induced fatigue cracks in steel bridges.

Removing mesh bias in mixed‐mode cohesive fracture simulation with stress recovery and domain integral

SummaryTo remove mesh bias and provide an accurate crack path representation in mixed‐mode investigation, a novel stress recovery technique is proposed in conjunction with a domain integral and element splits. Based on a domain integral and stress recovery technique, a maximum strain energy release rate is estimated to determine a crack path direction. Then, for a given crack path direction, continuum elements are split, and a cohesive surface element is adaptively inserted. One notes that the proposed stress recovery technique provides a more accurate stress field than a standard stress evaluation procedure. The proposed computational framework is verified and validated by solving mode‐I and mixed‐mode examples. Computational results demonstrate that the domain integral with the stress recovery accurately evaluates a crack path, even with a lower‐quality mesh and under a biaxial stress state. Furthermore, the cohesive surface element approach, with the element split in conjunction with the stress recovery and the domain integral, predicts mixed‐mode fracture behaviors while removing mesh bias in the crack path representation. Additionally, the condition numbers of stiffness matrices are within the same order of magnitude during cohesive fracture simulation.

Low-level wind effects on the glide paths of the North Runway of HKIA: A wind tunnel study

To study the low-level wind effects of buildings on the glide paths of the North Runway at Hong Kong International Airport, wind tunnel testing was conducted in a boundary layer wind tunnel. Both terrain with buildings and terrain without buildings were considered in the wind tunnel tests. The wind speed and wind direction of the glide paths were measured by cobra probes. The effects of the buildings on the wind field characteristics, including the mean wind speed, turbulence intensity, mean crosswind speed, and mean headwind speed, were analysed. The results show that the buildings significantly affect the wind flow of glide path 25RA. The presence of the buildings increases the turbulence intensity and reduces the mean wind speed of glide path 25RA.

Preliminary Characterization of Novel LDPE-Based Wear-Resistant Composite Suitable for FDM 3D Printing.

Low-density polyethylene (LDPE) composites reinforced with finely powdered waste glass were identified as a potential material for 3D printed structures for use in low-duty frictional applications. A recently published 3D printing model was used to calculate the limits in the filament feed rate and printing speed. Tribological tests (pin-on-disc method) of the printed composites were performed for different print-path directions. Differential scanning calorimetry (DSC) was performed on the samples and the composites showed a higher crystallinity compared with LDPE, which partially explains the higher elastic modulus of the composites determined during static tensile tests. Using a fine glass powder as reinforcement improved the wear resistance of LDPE by 50% due to the formation of a sliding film on the sample’s surface. An evident effect of friction direction vs. the printed path direction on wear was found; which was likely related to differences in the removal of friction products from the friction area for different print-path directions. The LDPE composites with fine waste glass particles are promising materials for low-duty frictional applications and should be the subject of further research.

Numerical simulation of thermal and stress field of single track cladding in wide-beam laser cladding

This research established half of the finite element model to investigate the thermal and stress field evolution of single track cladding deposited by the wide-beam laser. The proposed FE model is validated by the molten pool temperature measured by a pyrometer. And the characteristic of the cladding shows good agreement with the temperature profile. Based on the temperature data, the molten pool length, width, and depth are calculated. Meanwhile, the effect of process parameters including laser power and scanning speed on the molten pool dimensions, temperature gradient G, cooling rate e, solidification rate R, and G/R are discussed. Three experiments under different process parameters are conducted to verify the simulation results. Furthermore, the thermal stress distribution of the cladding in different direction and different path are discussed. The results indicate that laser power and scanning speed have a significant influence on the thermal and stress field evolution.

An Integrated Causal Path Identification Method

Finding causality merely from observed data is a fundamental problem in science. The most basic form of this causal problem is to determine whether X leads to Y or Y leads to X in the case of joint observation of two variables X, Y. In statistics, path analysis is used to describe the direct dependence between a set of variables. But in fact, we usually do not know the causal order between variables. However, ignoring the direction of the causal path will prevent researchers from analyzing or using causal models. In this study, we propose a method for estimating causality based on observed data. First, observed variables are cleaned and valid variables are retained. Then, a direct linear non-Gaussian acyclic graph models (DirectLiNGAM) estimates the causal order K between variables. The third step is to estimate the adjacency matrix B of the causal relationship based on K. Next, since B is not convenient for model interpretation, we use adaptive lasso to prune the causal path and variables. Further, a causal path graph and a recursive model are established. Finally, we test and debug the recursive model, obtain a causal model with good fit, and estimate the direct, indirect and total effects between causal variables. This paper overcomes the randomness assigning causal order to variables. This study is different from the researcher’s understanding of his own model by generating some form of simulation data. The simplest and relatively unsmooth statistical learning method used in this study has obvious advantages in the field of interpretable machine learning.

Mapping spatial patterns of groundwater discharge in a deep lake using high-resolution temperature sensors

ABSTRACTIdentifying groundwater discharge zones to lakes is important because the groundwater system can contribute a significant flux of water and solutes and potentially influence lake chemistry and ecology. We present a new instrument, Temperature Mapper (TM), to map groundwater discharge zones in lakes via temperature anomalies along the lake bottom, tested in Lake Constance at 2 former sand and gravel extraction sites. TM is essentially a 4 m wide sled with an array of 19 high-resolution sensors attached to an aluminum lattice towed along the lake bed behind a boat. It is able to map spatial temperature patterns representing groundwater discharge zones at a resolution of 20 cm laterally and 2.5 m in path direction. We conducted 2 field campaigns in February 2016 and February 2017, during which TM identified several temperature anomalies interpreted as groundwater discharging zones. Radon-222 was also analyzed at selected locations as an independent indicator of groundwater discharge. Overall, when comparing the different methods and different years, we observed similar spatial patterns of preferential groundwater discharge. TM offers a useful qualitative tool to identify and map potential groundwater discharge zones in lakes or coastal areas that can then be further studied by more quantitative, small-scale methods such as chemical tracers or seepage meters.

Correlation analysis and causal analysis in the era of big data

Based on the essence of correlation analysis, this paper studies the difference and relation between correlation analysis and causal analysis. It points out that in the era of big data, correlation analysis and causal analysis are different aspects of the analysis of things. They are neither antagonistic nor mutually replaceable but a dependency. Big data provides better and more powerful functions for correlation analysis. Correlation analysis provides direction and verification path for causal analysis. Causal analysis provides deep support for correlation analysis. Studying the application methods of correlation analysis and causal analysis under the condition of big data.

Roundness and positioning deviation prediction in single point incremental forming using deep learning approaches

This article proposes a deep learning technique for the prevision of the geometric accuracy in single point incremental forming. Moreover, predicting geometric accuracy is one of the most crucial measures of part quality. Accordingly, roundness and positioning deviation are two indicators for measuring geometric accuracy and presenting two output variables. Two types of artificial intelligence learning approaches, that is, shallow learning and deep learning, are investigated and compared for forecasting geometrical accuracy in the single point incremental forming process. Therefore, the back-propagation neural network with one hidden layer is selected as the representative for shallow learning and deep belief network and stack autoencoder are chosen as the representatives for deep learning. Accurate prediction is closely related to the feature learning of single point incremental forming process parameters. The following six parameters were considered as input variables: sheet thickness, tool path direction, step depth, speed rate, feed rate, and wall angle. The results of these studies indicate that deep learning could be a powerful tool in the current search for geometric accuracy prediction in single point incremental forming. Otherwise, the deep learning approach shows the best performance prediction with shallow learning. In addition, the deep belief network model achieves superior performance accuracy for the prediction of roundness and position deviation in comparison with the stack autoencoder approach.

Multicomponent bioprinting of heterogeneous hydrogel constructs based on microfluidic printheads.

Multimaterial bioprinting provides a promising strategy to recapitulate complex heterogeneous architectures of native tissues in artificial tissue analogs in a controlled manner. However, most of the existing multimaterial bioprinting techniques relying on multiple printing nozzles and complicate control program make it difficult to flexibly change the material composition during the printing process. Here, we developed a multicomponent bioprinting strategy to produce heterogeneous constructs using a microfluidic printhead with multiple inlets and one outlet. The composition of the printed filaments can be flexibly changed by adjusting volumetric flow rate ratio. Heterogeneous hydrogel constructs were successfully printed to have predefined spatial gradients of inks or microparticles. A rotary microfluidic printhead was used to maintain the heterogeneous morphology of the printed filaments as the printing path direction changed. Multicellular concentric ring constructs with two kinds of cell types distribution in the printed filaments were fabricated by utilizing coaxial microfluidic printhead and rotary collecting substrate, which significantly improves the printing efficiency for multicomponent concentric structures. The presented approach is simple and promising to potentially print multicomponent heterogeneous constructs for the fabrication of artificial multicellular tissues.

Cross-link is a risk factor for rod fracture at pedicle subtraction osteotomy site: A finite element study

BackgroundWe aim to investigate using finite element model (FEM) whether the use of a cross-link is a risk factor for rod fracture at the pedicle subtraction osteotomy (PSO) site. MethodsThe geometry and dimensions of the FEM were obtained from a high-resolution computed tomography scan data of a 65 years old female patient with spinal sagittal imbalance. The intact model was modified to place PSO on the L4 spine. A cross-link was placed at the PSO site. A multisegment spinal fusion model from L1 to the pelvis was used to compare and analyze the peak von Mises stress (PVMS) values of the implants. A compressive follower load of 400 N was added to the validated intact lumbar spinal model in the follower load path direction. ResultsAfter PSO surgery, the PVMS of the rod was significantly increased during flexion and extension at the PSO site. With the cross-link at the PSO site, the PVMS of the rod was further significantly increased during flexion and extension. ConclusionThe cross-link at the PSO site increased the risk of rod facture, especially during flexion and extension stress.

A sequential path-planning methodology for wire and arc additive manufacturing based on a water-pouring rule

Path planning has a crucial influence on the process stability and densification of wire and arc additive manufacturing (WAAM). In this paper, a sequential path-planning method based on a water-pouring rule for WAAM is proposed to ensure the internal structural densification and also improve the path-planning response speed. The proposed path-planning method can transfer all the intersection areas of the path to the outer contour, thereby ensuring that the inner area is uniform and compact. The innovative method of sequentially generating paths decentralizes the computational cost of generating all paths at one time, improving the real-time and dynamic nature of path planning. This makes it possible to generate a compensation path in real time in a closed-loop WAAM system with higher forming accuracy. The proposed path-planning method can change the path direction of adjacent layer with only one arc extinguished in the whole process, thereby improving the forming stability and the deposition efficiency. The experiments verified the effectiveness of the proposed path-planning method. Compared with the traditional zigzag path-planning method, the proposed path-planning method performs better in terms of densification and deposition efficiency.

Guided Endodontics Modified for Treating Molars by Using an Intracoronal Guide Technique

The aim of this case report was to show the concept of guided endodontics in a maxillary first molar with limited interocclusal space. Guided endodontics involves merging cone-beam computed tomographic imaging and a surface scan of the tooth in order to create a guide to perform a drill path into the seemingly obliterated root canal. In the molar region, the interocclusal space is often too small to accommodate the guide, bur, and handpiece at once, and, therefore, a modified approach is presented. A 52-year-old man was referred because the dentist had failed to localize the distobuccal root canal of a maxillary molar (#3) associated with apical pathosis. After reopening and rubber dam placement, a glide path was established for both the palatal first mesiobuccal root canal and the second mesiobuccal using a size 10 hand file and coronal flaring. Further instrumentation to the working length was achieved by reciprocating file size 25. All 3 canals were temporarily filled with calcium hydroxide. For the distobuccal root canal, guided endodontics was chosen in order to avoid further impairment of the tooth because negotiation of the canal failed even with the use of the operating microscope. Following the merged data obtained from the cone-beam computed tomographic and surface scans, a translucent SICAT Optiguide (SICAT, Bonn, Germany) was constructed containing a sleeve representing the proper direction of a drill path in order to reach the distobuccal root canal. The access cavity was temporarily filled with a composite material made for light-curing. Before light curing, the Optiguide was replaced on the teeth, and a steel pin was pressed through the sleeve and the composite whereby the proper drill path direction was transferred into the composite. After polymerization and removal of the Optiguide and pin from the composite base sleeve, the guided drilling could be performed. This case report is the first on guided access preparation in a molar with pulp canal obliteration and limited interocclusal space. The demand for more interocclusal space was solved by transforming the virtual drill path into a composite-based intracoronal guide. The use of digital technology was essential.

Effectiveness analysis of three-dimensional printing assisted surgery for unstable pelvic fracture

To evaluate the effectiveness of three-dimensional (3D) printing assisted internal fixation for unstable pelvic fractures. The clinical data of 28 patients with unstable pelvic fractures admitted between March 2015 and December 2017 were retrospectively analyzed. The patients were divided into two groups according to different surgical methods. Eighteen cases in the control group were treated with traditional anterior and posterior open reduction and internal fixation with plate; 10 cases in the observation group were treated with 3D printing technology to make pelvic models and assist in shaping the subcutaneous steel plates of the anterior ring. Sacroiliac screw navigation template was designed and printed to assist posterior ring sacroiliac screw fixation. There was no significant difference between the two groups in gender composition, age, cause of injury, fracture type, and time interval from injury to surgery ( P>0.05). The operation time, intraoperative blood loss, intraoperative fluoroscopy times, incision length, waiting time for weight-bearing exercise, and fracture healing time were recorded and compared between the two groups. Majeed score was used to evaluate the function at last follow-up. At immediate after operation, the reduction was evaluated according to Matta imaging scoring criteria, and the success of sacroiliac joint screw implantation in the observation group was evaluated. The deviation of screw entry point and direction between postoperative screws and preoperative simulated screws were compared in the observation group. All the operation was successfully completed, and all patients were followed up 6-18 months (mean, 14.4 months). In the control group, 1 case had wound infection and 2 cases had deep vein thrombosis. No serious complication such as important blood vessels, and nerve injury and pulmonary embolism occurred in other patients in the two groups. No screw pulling out or steel plate breaking occurred. The operation time, intraoperative blood loss, fluoroscopy times, incision length, and waiting time for weight-bearing exercise of the control group were significantly more than those of the observation group ( P<0.05); there was no significant difference in fracture healing time between the two groups ( t=0.12, P=0.90). There was no significant difference in reduction quality between the two groups at immediate after operation ( Z=-1.05, P=0.30); Majeed score of the observation group was significantly better than that of the control group at last follow-up ( Z=-2.42, P=0.02). The success rate of sacroiliac joint screw implantation in the observation group reached category Ⅰ. In the observation group, the deviation angle of the direction of the screw path between the postoperative screw and the preoperative simulated screw implant was (0.09±0.22)°, and the deviation values of the entry points on the X, Y, and Z axes were (0.13±0.63), (0.14±0.58), (0.15±0.53) mm, respectively. There was no significant difference when compared with those before the operation (all values were 0) ( P>0.05). Computer design combined with 3D printing technology to make personalized pelvic model and navigation template applied to unstable pelvic fractures, is helpful to accurately place sacroiliac screw, reduce the operation time, intraoperative blood loss, and the fluoroscopy times, has good waiting time for weight-bearing exercise and function, and it is an optional surgical treatment for unstable fractures.

Spatial variability assessment of Nile alluvial soils using electrical resistivity technique

Spatial information about soils generally results from local observations which are destructive and time consuming. Geophysical techniques could help soil mapping since they are non-destructive and fast. Electrical resistivity is interesting for soil studies due to a wide range of values and as it depends on soil characteristics. This work aims to study soil spatial variability using electrical resistivity. GPS defined grid points of 40X40 m were installed in the experimental western farm (EWF) in the Faculty of Agriculture of Cairo University in Giza. Electrical resistivity was measured at 40 points using 4-electrodes Wenner array in a line perpendicular to the path direction. Soil resistivity data from 2-depths profiling mode was considered to produce two apparent resistivity maps and geostatistically tested. Soil resistivity taxa were sampled and analyzed for soil moisture, EC and bulk density. Krigged soil resistivity maps were produced for depths (i.e. 30 and 60 cm). Kriging and Semivariogram interpretation was conducted, and the spatial dependency of top and subsoil resistivity were moderate (48.4% and 68.6% respectively). Highly significant negative correlations were recorded in the topsoil between apparent or true resistivity and soil moisture, EC or bulk density. The obtained models were used to produce conjugated moisture and EC maps and geostatistically investigated. The spatial dependency of the top and subsoil moisture or salinity were moderate. Soil moisture and EC are the most significant factors for controlling soil electrical resistivity. The method used opens the way to the development of semi-automatic soil mapping from electrical resistivity data.

Effects of scanning path and overlapping rate on residual stress of 316L stainless steel blade subjected to massive laser shock peening treatment with square spots

The effects of different scanning paths and overlapping rates on the residual stresses distribution in a 316L stainless steel blade subjected to massive laser shock peening treatment with square spots were investigated. Special attention was paid to the surface and in-depth residual stress distributions at 30%, 50% and 70% overlapping rates. Results showed that there were similar residual stress profiles for two scanning paths at 30% overlapping rate. At 50% overlapping rate, the induced surface compressive residual stresses along the width direction (Path 1) was larger than those along the length direction (Path 2), but the latter was more uniform than that of the former. When the overlapping rate increased to 70%, the former was more uniform and larger than the latter. Simulated residual stress profiles were in an agreement with the measured data in all cases. The calculated residual stresses by finite element model analysis were smaller compared with the measured residual stresses.

Analysis of Delay-Tolerant Routing Protocols using the Impact of Mobility Models

Intermittently connected mobile networks are sparsely connected wireless ad-hoc networks where there is no end-to-end path from a source device to a destination. Generally, these paths do not exist. Hence, these devices use intermittent path using the concept of the store-and-forward mechanism to successfully do the communication. These networks are featured by long delay, dissimilar data rates, and larger error rates. Hence, we see the analysis of several delay-tolerant routing protocols, e.g., epidemic, spray-and-wait, prophet, maxprop, rapid, and spray-and-focus using opportunistic network environment simulator. At first, the investigations of the above considered routing protocols are done across three mobility models namely random direction, random walk, and shortest path map based movement mobility model for node impact only. Then, we evaluate these routing protocols against the impact of message copy, buffer, and time-to-live using shortest path map considering the result of node impact. We use three metrics and the result shows that spray-and-focus deserves good performance for showing higher delivery, lower latency, and lower overhead among all routing techniques while epidemic the poor.

Microcrack interaction with circular inclusion and interfacial zone

A geometrically simplified plane elasticity problem of a finite small crack emanating from a thin interfacial zone surrounding the circular inclusion situated in the finite bounded domain is investigated. The crack is arbitrarily oriented and modelled using the distribution dislocation technique. This model represents the inner solution of the studied problem. The corresponding fundamental solution is based on the application of Muskhelishvili complex potentials in the form of the Laurent series. The coefficients of the series are evaluated from the compatibility conditions along the interfaces of the inclusion, the interfacial zone and the enclosing matrix. The fundamental solution is also used in the solution of the boundary integral method approximating the stress and strain relations of the so-called outer solution. The asymptotic analysis at the point of the crack initiation combines the inner and the outer solution and results in the evaluation of the stress intensity factors of the crack tip, which lies in the matrix. The topological derivative is subsequently used to approximate the energy release rate field associated with the perturbing crack in the matrix. The extreme values of the energy release rate allow one to assess the crack path direction of the initiated microcrack.