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Appl. Sci., Volume 10, Issue 12 (June-2 2020) – 360 articles

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Cover Story (view full-size image) The nutritional and medicinal benefits of kiwifruit and persimmon have been known for years. [...] Read more.
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Open AccessArticle
NICE: Superpixel Segmentation Using Non-Iterative Clustering with Efficiency
Appl. Sci. 2020, 10(12), 4415; https://doi.org/10.3390/app10124415 - 26 Jun 2020
Viewed by 252
Abstract
Superpixels intuitively over-segment an image into small compact regions with homogeneity. Owing to its outstanding performance on region description, superpixels have been widely used in various computer vision tasks as the substitution for pixels. Therefore, efficient algorithms for generating superpixels are still important [...] Read more.
Superpixels intuitively over-segment an image into small compact regions with homogeneity. Owing to its outstanding performance on region description, superpixels have been widely used in various computer vision tasks as the substitution for pixels. Therefore, efficient algorithms for generating superpixels are still important for advanced visual tasks. In this work, two strategies are presented on conventional simple non-iterative clustering (SNIC) framework, aiming to improve the computational efficiency as well as segmentation performance. Firstly, inter-pixel correlation is introduced to eliminate the redundant inspection of neighboring elements. In addition, it strengthens the color identity in complicated texture regions, thus providing a desirable trade-off between runtime and accuracy. As a result, superpixel centroids are evolved more efficiently and accurately. For further accelerating the framework, a recursive batch processing strategy is proposed to eliminate unnecessary sorting operations. Therefore, a large number of neighboring elements can be assigned directly. Finally, the two strategies result in a novel synergetic non-iterative clustering with efficiency (NICE) method based on SNIC. Experimental results verify that it works 40% faster than conventional framework, while generating comparable superpixels for several quantitative metrics—sometimes even better. Full article
(This article belongs to the Special Issue Advanced Intelligent Imaging Technology 2020)
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Open AccessArticle
The Influence of Surfactants, Dynamic and Thermal Factors on Liquid Convection after a Droplet Fall on Another Drop
Appl. Sci. 2020, 10(12), 4414; https://doi.org/10.3390/app10124414 - 26 Jun 2020
Viewed by 229
Abstract
The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection [...] Read more.
The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection is considered. The particle motion is realized by a complex curvilinear trajectory. The fall of droplet with and without surfactant additives is considered. Estimates of the influence of the thermal factor (thermocapillary forces) and the dynamic factor (inertia forces) on convection are given. The scientific novelty of the work is the investigation of the simultaneous influence of several factors that is carried out for the first time. It is shown that in the presence of a temperature jump for the time of about 0.01–0.1 s thermocapillary convection leads to a 7–8 times increase in the mass transfer rate in drop. The relative influence of inertial forces is found to be no more than 5%. The fall of drops with surfactant additives (water + surfactant) reduces the velocity jump inside the sessile drop 2–4 times, compared with the water drop without surfactant. Thermocapillary convection leads to the formation of a stable vortex in the drop. The dynamic factor and surfactant additive lead to the vortex breakdown into many small vortices, which results in the suppression of convection. The obtained results are of great scientific and practical importance for heat transfer enhancement and for the control of heating and evaporation rates. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)
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Open AccessArticle
Harmony Search Optimization of Nozzle Movement for Additive Manufacturing of Concrete Structures and Concrete Elements
Appl. Sci. 2020, 10(12), 4413; https://doi.org/10.3390/app10124413 - 26 Jun 2020
Viewed by 332
Abstract
There are several ways of using three-dimensional printing techniques in the construction industry. One method that seems quite feasible is the concreting of walls and structural components starting at the bottom and progressing up in layers according to the principles of additive manufacturing. [...] Read more.
There are several ways of using three-dimensional printing techniques in the construction industry. One method that seems quite feasible is the concreting of walls and structural components starting at the bottom and progressing up in layers according to the principles of additive manufacturing. The goal of this study is to optimize the movements of a nozzle at one level that will result in this operation. This study considers that the movements of the nozzle can be of two types: rectangular only (i.e., only in x and y directions) or more freely, including moving in diagonal directions. Applications are performed on four hypothetical flats (with 7, 8, 14, and 31 walls, respectively) and a structural component with 17 members. It is shown that as the number of walls and members increase, the problem of optimizing the movements of the nozzle becomes increasingly difficult due to exponentially increasing path combinations. A comparison is presented in terms of the ratio of movements of the nozzle without concreting to total distances traveled. The optimization process is conducted using the Harmony Search algorithm with a special coding and encoding system. Full article
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Open AccessArticle
Agglomerative Clustering and Residual-VLAD Encoding for Human Action Recognition
Appl. Sci. 2020, 10(12), 4412; https://doi.org/10.3390/app10124412 - 26 Jun 2020
Viewed by 243
Abstract
Human action recognition has gathered significant attention in recent years due to its high demand in various application domains. In this work, we propose a novel codebook generation and hybrid encoding scheme for classification of action videos. The proposed scheme develops a discriminative [...] Read more.
Human action recognition has gathered significant attention in recent years due to its high demand in various application domains. In this work, we propose a novel codebook generation and hybrid encoding scheme for classification of action videos. The proposed scheme develops a discriminative codebook and a hybrid feature vector by encoding the features extracted from CNNs (convolutional neural networks). We explore different CNN architectures for extracting spatio-temporal features. We employ an agglomerative clustering approach for codebook generation, which intends to combine the advantages of global and class-specific codebooks. We propose a Residual Vector of Locally Aggregated Descriptors (R-VLAD) and fuse it with locality-based coding to form a hybrid feature vector. It provides a compact representation along with high order statistics. We evaluated our work on two publicly available standard benchmark datasets HMDB-51 and UCF-101. The proposed method achieves 72.6% and 96.2% on HMDB51 and UCF101, respectively. We conclude that the proposed scheme is able to boost recognition accuracy for human action recognition. Full article
(This article belongs to the Section Computing and Artificial Intelligence)
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Open AccessArticle
Approaches for Detailed Investigations on Transient Flow and Spray Characteristics during High Pressure Fuel Injection
Appl. Sci. 2020, 10(12), 4410; https://doi.org/10.3390/app10124410 - 26 Jun 2020
Viewed by 198
Abstract
High pressure injection systems have essential roles in realizing highly controllable fuel injections in internal combustion engines. The primary atomization processes in the near field of the spray, and even inside the injector, determine the subsequent spray development with a considerable impact on [...] Read more.
High pressure injection systems have essential roles in realizing highly controllable fuel injections in internal combustion engines. The primary atomization processes in the near field of the spray, and even inside the injector, determine the subsequent spray development with a considerable impact on the combustion and pollutant formation. Therefore, the processes should be understood as much as possible; for instance, to develop mathematical and numerical models. However, the experimental difficulties are extremely high, especially near the injector nozzle or inside the nozzle, due to the very small geometrical scales, the highly concentrated optical dense spray processes and the high speed and drastic transient nature of the spray. In this study, several unique and partly recently developed techniques are applied for detailed measurements on the flow inside the nozzle and the spray development very near the nozzle. As far as possible, the same three-hole injector for high pressure diesel injection is used to utilize and compare different measurement approaches. In a comprehensive section, the approach is taken to discuss the measurement results in comparison. It is possible to combine the observations within and outside the injector and to discuss the entire spray development processes for high pressure diesel sprays. This allows one to confirm theories and to provide detailed and, in parts, even quantitative data for the validation of numerical models. Full article
(This article belongs to the Special Issue Progress in Spray Science and Technology)
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Open AccessArticle
Handover Management for D2D Communication in 5G Networks
Appl. Sci. 2020, 10(12), 4409; https://doi.org/10.3390/app10124409 - 26 Jun 2020
Viewed by 192
Abstract
This study addresses the handover management issue for Device-to-Device communication in fifth-generation (5G) networks. The Third Generation Partnership Project (3GPP) drafted a standard for proximity services (ProSe), also named device-to-device (D2D) communication, which is a promising technology in offering higher throughput and lower [...] Read more.
This study addresses the handover management issue for Device-to-Device communication in fifth-generation (5G) networks. The Third Generation Partnership Project (3GPP) drafted a standard for proximity services (ProSe), also named device-to-device (D2D) communication, which is a promising technology in offering higher throughput and lower latency services to end users. Handover is an essential issue in wireless mobile networks due to the mobility of user equipment (UE). Specifically, we need to transfer an ongoing connection from an old E-UTRAN Node B (eNB) to a new one, so that the UE can retain its connectivity. In the data plane, both parties of a D2D pair can communicate directly with each other without the involvement of the base station. However, in the control plane, devices must be connected to the eNB for tasks such as power control and resource allocation. In the current standard of handover scheme, the number of unnecessary handovers would be increased by the effect of shadowing fading on two devices. More important, the handover mechanism for D2D pairs is not standardized yet. LTE-A only considers the handover procedure of a single user. Therefore, when a D2D pair moves across cell boundaries, the control channels of the two UEs may connect to different base stations and result in increased latency due to the exchange of D2D related control messages. Hence, we propose a handover management scheme for D2D communication to let both parties of a D2D pair handover to the same destination eNB at the same time. By doing so, the number of unnecessary handovers, as well as the handover latency, can be reduced. In the proposed method, we predict the destination eNB of D2D users based on their movements and the received signal characteristics. Subsequently, we make a handover decision for each D2D pair by jointly factoring in the signal quality and connection stability. Expected improvement can be attained, as revealed in the simulation. Unnecessary handover can be avoided. Consequently, both UEs of a D2D pair reside in the same cell and, therefore, result in increased throughput and decreased delay. Full article
(This article belongs to the Section Electrical, Electronics and Communications Engineering)
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Open AccessArticle
Hybrid Framework for Simulating Building Collapse and Ruin Scenarios Using Finite Element Method and Physics Engine
Appl. Sci. 2020, 10(12), 4408; https://doi.org/10.3390/app10124408 - 26 Jun 2020
Viewed by 217
Abstract
Reliable and high-fidelity virtual ruin scenarios for collapsed buildings are essential for post-earthquake emergency search and rescue training. However, the existing research on the distribution of ruins caused by building collapse is insufficient for supporting post-earthquake rescue training. Therefore, this paper proposes a [...] Read more.
Reliable and high-fidelity virtual ruin scenarios for collapsed buildings are essential for post-earthquake emergency search and rescue training. However, the existing research on the distribution of ruins caused by building collapse is insufficient for supporting post-earthquake rescue training. Therefore, this paper proposes a hybrid framework for simulating building collapse and ruin scenarios, using a finite element (FE) model and a physics engine. Based on this framework, the following methods are proposed: (1) geometric model conversion from the FE model to the physics engine; (2) determination of the initial moment of collapse; and (3) data mapping of the FE simulation results. In addition, a corresponding program, Finite Element Method to Rigid Body Dynamics (FEM2RBD), is developed for the hybrid framework. The proposed framework simulates the entire process of building collapse and the distribution of ruins. The accuracy of the framework is validated using a shaking table test of a three-story reinforced concrete frame. The collapse process and ruin scenario of a real-world library building is simulated as a case study. The results show that the proposed framework combines the advantages of the FE model during the small-deformation stage with the advantages of physics engines during the large-deformation stage. The proposed framework can be valuable in simulating building collapse and ruin scenarios for post-earthquake rescue training. Full article
(This article belongs to the Special Issue Structural Reliability of RC Frame Buildings)
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Open AccessArticle
Analysis on Steering Performance of Active Steering Bogie According to Steering Angle Control on Curved Section
Appl. Sci. 2020, 10(12), 4407; https://doi.org/10.3390/app10124407 - 26 Jun 2020
Viewed by 195
Abstract
In this paper, prior to the commercialization of a developed active steering bogie, we want to analyze steering performance experimentally according to steering angle level with the aim of obtaining steering performance data to derive practical design specifications for a steering system. In [...] Read more.
In this paper, prior to the commercialization of a developed active steering bogie, we want to analyze steering performance experimentally according to steering angle level with the aim of obtaining steering performance data to derive practical design specifications for a steering system. In other words, the maximum steering performance can be obtained by controlling the steering angle at the 100% level of the target steering angle, but it is necessary to establish the practical control range in consideration of the steering system cost increase, size increase, and consumer steering performance requirements and commercialize. The steering control test using the active steering bogie was conducted in the section of the steep curve with a radius of curvature of R300, and steering performance such as bogie angle, wheel lateral force, and derailment coefficient were analyzed according to the steering angle level. As the steering angle level increased, the bogie indicated that it was aligned with the radial steering position, and steering performance such as wheel lateral force and derailment coefficient was improved. The steering control at 100% level of the target steering angle can achieve the highest performance of 83.6% reduction in wheel lateral force, but it can be reduced to about one-half of the conventional bogie at 25% level control and about one-third at 50% level. Considering cost rise by adopting the active steering system, this result can be used as a very important design indicator to compromise steering performance and cost rise issues in the design stage of the steering system from a viewpoint of commercialization. Therefore, it is expected that the results of the steering performance experiment according to the steering angle level in this paper will be used as very useful data for commercialization. Full article
(This article belongs to the Section Acoustics and Vibrations)
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Open AccessArticle
Response Characteristics of Cross Tunnel Lining under Dynamic Train Load
Appl. Sci. 2020, 10(12), 4406; https://doi.org/10.3390/app10124406 - 26 Jun 2020
Viewed by 192
Abstract
The crossing area is a vulnerable component of the interchange high-speed railway tunnel because of the high-static stress level and the long-term dynamic train load in the operation period. Although attention has been paid to this problem, the response characteristics of high-speed railway [...] Read more.
The crossing area is a vulnerable component of the interchange high-speed railway tunnel because of the high-static stress level and the long-term dynamic train load in the operation period. Although attention has been paid to this problem, the response characteristics of high-speed railway tunnel lining at the cross position under the dynamic train load may still need further research as very little investigation is available on this issue at present. In this paper, the initial stress state and dynamic response characteristics of tunnel lining were studied using the three-dimensional finite element method. Furthermore, the damage evolutionary characteristics of the tunnel inverted arch under dynamic and initial static loads were researched using a set of self-developed indoor fatigue test devices. The size of the test box is 400 × 300 × 250 mm (length × width × height). Numerical simulation results indicate that the displacement and stress levels of tunnel lining are very high at the cross position. The stress increment of tunnel lining due to the dynamic train load is more likely to induce a break in the tunnel lining at this position. The indoor fatigue tests reveal that the change of structural strain increment amplitude and strain ratio is obvious when the dynamic load stress level is higher. It is better for dynamic stress levels not to exceed 0.6 times of structural tensile strength to avoid the tunnel lining being damaged in the long-time service period. The initial static load has an influence on the tunnel inverted arch, and the static stress level should be lower than 0.65 times of structural tensile strength to ensure the tunnel has long-time serviceability. This paper provides a reference for the future design of new cross tunnels and the operation safety evaluation and disease regulation of existing high-speed railway tunnels. Full article
(This article belongs to the Special Issue Dynamics of Building Structures)
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Open AccessEditorial
Sustainable Energy Systems: Optimization and Efficiency
Appl. Sci. 2020, 10(12), 4405; https://doi.org/10.3390/app10124405 - 26 Jun 2020
Viewed by 229
Abstract
The world population is growing at a very high rate, which also entails a massive increase in energy consumption, and also, therefore, in its production, which is gradually and steadily increasing. Energy and the environment are essential to achieving sustainable development, and constitute [...] Read more.
The world population is growing at a very high rate, which also entails a massive increase in energy consumption, and also, therefore, in its production, which is gradually and steadily increasing. Energy and the environment are essential to achieving sustainable development, and constitute a fundamental part of human activity. If we consider energy efficiency as the use of an appliance, process or installation for which we try to produce more energy, but with less energy consumption than the average for these appliances, processes or installations, then achieving a higher energy efficiency is imperative. Energy efficiency is a cornerstone policy on the road to stopping climate change and to achieving sustainable societies, along with the development of renewable energy and an environmentally friendly transport policy. In this Special Issue, 11 selected and peer-reviewed articles have been contributed, on a wide range of topics under the umbrella of sustainable energy systems. The published articles encompass distinct areas of interest. One area addresses distributed generation, which addresses such topics as the optimal planning of distributed generation, protection of blind areas in distribution networks, multi-objective optimization in distributed generation, energy management of virtual power plants in distributed generation, and the impact of demand-response programs on a home microgrid, as well as concentrating solar power into a highly renewable, penetrated power system. The second section of the Special Issue addresses a wide range of topics, from parametric studies of 2 MW gas engines or data centers, to combustion characteristics of a non-premixed oxy-flame, to new techniques of PV Tracking, to applications of nanofluids in the thermal performance enhancement of parabolic trough solar collectors. Full article
(This article belongs to the Special Issue Sustainable Energy Systems: Optimization and Efficiency)
Open AccessArticle
Temperature and Pressure Dependence of the Infrared Spectrum of 1-Ethyl-3-Methylimidazolium Trifluoromethanesulfonate Ionic Liquid
Appl. Sci. 2020, 10(12), 4404; https://doi.org/10.3390/app10124404 - 26 Jun 2020
Viewed by 195
Abstract
The infrared absorption spectrum of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI–TfO) was investigated at ambient pressure and variable temperatures between 120 and 330 K, or at room temperature and variable pressures up to 10 GPa. Upon cooling, the ionic liquid crystallizes; on the contrary, upon compression [...] Read more.
The infrared absorption spectrum of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI–TfO) was investigated at ambient pressure and variable temperatures between 120 and 330 K, or at room temperature and variable pressures up to 10 GPa. Upon cooling, the ionic liquid crystallizes; on the contrary, upon compression no evidence of crystallization can be obtained from the infrared spectra. Moreover, Density Functional Theory (DFT) calculations were applied to gain a better description of the ionic couple. The ωB97X-D functional, including not only the empirical dispersion corrections but also the presence of a polar solvent, gives a good agreement with the infrared spectrum and suggests that TfO resides above the plane of the imidazolium, with the shorter distance between the O atom of the anion and the C2 atom of the imidazolium ring equal to 2.23 Å. Full article
(This article belongs to the Special Issue Ionic Liquids: Properties and Applications)
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Open AccessArticle
Quasi-Static Characteristics and Vibration Responses Analysis of Helical Geared Rotor System with Random Cumulative Pitch Deviations
Appl. Sci. 2020, 10(12), 4403; https://doi.org/10.3390/app10124403 - 26 Jun 2020
Viewed by 187
Abstract
As one of the long period gear errors, the effects of random cumulative pitch deviations on mesh excitations and vibration responses of a helical geared rotor system (HGRS) are investigated. The long-period mesh stiffness (LPMS), static transmission error (STE), as well as composite [...] Read more.
As one of the long period gear errors, the effects of random cumulative pitch deviations on mesh excitations and vibration responses of a helical geared rotor system (HGRS) are investigated. The long-period mesh stiffness (LPMS), static transmission error (STE), as well as composite mesh error (CMS), and load distributions of helical gears are calculated using an enhanced loaded tooth contact analysis (LTCA) model. A dynamic model with multi degrees of freedom (DOF) is employed to predict the vibration responses of HGRS. Mesh excitations and vibration responses analysis of unmodified HGRS are conducted in consideration of random cumulative pitch deviations. The results indicate that random cumulative pitch deviations have significant effects on mesh excitations and vibration responses of HGRS. The curve shapes of STE and CMS become irregular when the random characteristic of cumulative pitch deviations is considered, and the appearance of partial contact loss in some mesh cycles leads to decreased LPMS when load torque is relatively low. Vibration modulation phenomenon can be observed in dynamic responses of HGRS. In relatively light load conditions, the amplitudes of sideband frequencies become larger than that of mesh frequency and its harmonics (MFIHs) because of relatively high contact ratio. The influences of random cumulative pitch deviations on the vibration responses of modified HGRS are also discussed. Full article
(This article belongs to the Section Mechanical Engineering)
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Open AccessArticle
A New Semi-Analytical Method for Elasto-Plastic Analysis of a Deep Circular Tunnel Reinforced by Fully Grouted Passive Bolts
Appl. Sci. 2020, 10(12), 4402; https://doi.org/10.3390/app10124402 - 26 Jun 2020
Viewed by 179
Abstract
The use of fully grouted passive bolts as a reinforcement technique has been widely applied to improve the stability of tunnels. To analyze the behaviors of passive bolts and rock mass in a deep circular tunnel, a new semi-analytical solution is presented in [...] Read more.
The use of fully grouted passive bolts as a reinforcement technique has been widely applied to improve the stability of tunnels. To analyze the behaviors of passive bolts and rock mass in a deep circular tunnel, a new semi-analytical solution is presented in this work based on the finite difference method. The rock mass was assumed to experience elastic–brittle–plastic behavior, and the linear Mohr–Coulomb criterion and the nonlinear generalized Hoek–Brown criterion were employed to govern the yielding of the rock mass. The interaction and decoupling between the rock mass and bolts were considered by using the spring–slider model. To simplify the analysis process, a bolted tunnel was divided into a bolted region and an unbolted region, while the contact stress at the bolted–unbolted interface and the rigid displacement of the bolts were obtained using two boundary conditions in combination with the bisection method. Comparisons show that the results obtained using the proposed solution agree well with those from the commercial numerical software and the in situ test. Finally, parametric analyses were performed to examine the effects of various reinforcement parameters on the tunnel’s stability. The proposed solution provided a fast but accurate estimation of the behavior of a reinforced deep circular tunnel for preliminary design purposes. Full article
(This article belongs to the Section Civil Engineering)
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Open AccessArticle
The Elastic Wave Propagation in Rectangular Waveguide Structure: Determination of Dispersion Curves and Their Application in Nondestructive Techniques
Appl. Sci. 2020, 10(12), 4401; https://doi.org/10.3390/app10124401 - 26 Jun 2020
Viewed by 279
Abstract
The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in [...] Read more.
The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in damage detection, in this case, knowing the interaction between the wave propagation and the geometry of the waveguides is mandatory. In the present work, the wave propagation in rectangular steel rod is presented. In this study, the section dimensions were fixed as 5 × 15 [mm], a typical element of the flexible riser structural amour commonly used in the offshore oil industry. The studies here presented were restricted to [0, 100 KHz] frequencies. This frequency interval is in the range of commercial waveguide equipment commonly applied in ducts in NDT applications. The computation of the dispersion curves is performed by using three different methodologies: (i) analytical solutions, (ii) a method that combines analytical approaches with finite element methods (SAFE), and (iii) experimental method that extracted information from the rod using laser vibrometers and piezoelectric actuators. Finally, two applications based on the dispersion curves determined in the rectangular waveguide are presented to illustrate the possibilities of the curve dispersion knowledge related to the specific geometry in the development and application linked to NDT. The first application consists on showing the possibilities of the techniques that use a fiber grating Bragg cell (FGB) to measure the wave displacement and the second application involves the simulation of pre-fissured prismatic waveguide aimed at searching to induce three characteristic acoustic events. The model was built combining the finite element method and a version of the discrete element method. Full article
(This article belongs to the Special Issue Nondestructive Testing (NDT): Volume II)
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Open AccessArticle
End-to-End Automated Guided Modular Vehicle
Appl. Sci. 2020, 10(12), 4400; https://doi.org/10.3390/app10124400 - 26 Jun 2020
Viewed by 332
Abstract
Autonomous Vehicles (AVs) have caught people’s attention in recent years, not only from an academic or developmental viewpoint but also because of the wide range of applications that these vehicles may entail, such as intelligent mobility and logistics, as well as for industrial [...] Read more.
Autonomous Vehicles (AVs) have caught people’s attention in recent years, not only from an academic or developmental viewpoint but also because of the wide range of applications that these vehicles may entail, such as intelligent mobility and logistics, as well as for industrial purposes, among others. The open literature contains a variety of works related to the subject. They employ a diversity of techniques ranging from probabilistic to ones based on Artificial Intelligence. The increase in computing capacity, well known to many, has opened plentiful opportunities for the algorithmic processing needed by these applications, making way for the development of autonomous navigation, in many cases with astounding results. The following paper presents a low-cost but high-performance minimal sensor open architecture implemented in a modular vehicle. It was developed in a short period of time, surpassing many of the currently available solutions found in the literature. Diverse experiments were carried out in the controlled and circumscribed environment of an autonomous circuit that demonstrates the efficiency of the applicability of the developed solution. Full article
(This article belongs to the Special Issue Intelligent Transportation Systems: Beyond Intelligent Vehicles)
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Open AccessArticle
A Strain-Transfer Model of Surface-Bonded Sapphire-Derived Fiber Bragg Grating Sensors
Appl. Sci. 2020, 10(12), 4399; https://doi.org/10.3390/app10124399 - 26 Jun 2020
Viewed by 171
Abstract
An improved strain-transfer model was developed for surface-bonded sapphire-derived fiber Bragg grating sensors. In the model, the core and cladding of the fiber are separated into individual layers, unlike in conventional treatment that regards the fiber as a unitive structure. The separation is [...] Read more.
An improved strain-transfer model was developed for surface-bonded sapphire-derived fiber Bragg grating sensors. In the model, the core and cladding of the fiber are separated into individual layers, unlike in conventional treatment that regards the fiber as a unitive structure. The separation is because large shear deformation occurs in the cladding when the core of the sapphire-derived fiber is heavily doped with alumina, a material with a high Young’s modulus. Thus, the model was established to have four layers, namely, a core, a cladding, an adhesive, and a host material. A three-layer model could also be obtained from the regressed four-layer model when the core’s radius increased to that of the cladding, which treated the fiber as if it were still homogeneous material. The accuracy of both the four- and three-layer models was verified using a finite-element model and a tensile-strain experiment. Experiment results indicated that a larger core diameter and a higher alumina content resulted in a lower average strain-transfer rate. Error percentages were less than 1.8% when the four- and three-layer models were used to predict the transfer rates of sensors with high and low alumina content, respectively. Full article
(This article belongs to the Section Optics and Lasers)
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Open AccessFeature PaperArticle
Use of Biofuel Industry Wastes as Alternative Nutrient Sources for DHA-Yielding Schizochytrium limacinum Production
Appl. Sci. 2020, 10(12), 4398; https://doi.org/10.3390/app10124398 - 26 Jun 2020
Viewed by 324
Abstract
The simultaneous use of crude glycerol and effluent from anaerobic digestate, both wastes derived from the biofuel industry, were tested in the frame of circular economy concept, as potential low-cost nutrient sources for the cultivation of rich in docosahexaenoic acid (DHA) oil microalgae [...] Read more.
The simultaneous use of crude glycerol and effluent from anaerobic digestate, both wastes derived from the biofuel industry, were tested in the frame of circular economy concept, as potential low-cost nutrient sources for the cultivation of rich in docosahexaenoic acid (DHA) oil microalgae strain Schizochytrium limacinum SR21. Initially, the optimal carbon and nitrogen concentration levels for high S. limacinum biomass and lipids production were determined, in a culture media containing conventional, high cost, organic nitrogen sources (yeast extract and peptone), micronutrients and crude glycerol at varying concentrations. Then, the effect of a culture media composed of crude glycerol (as carbon source) and effluent digestate at varying proportions on biomass productivity, lipid accumulation, proximate composition, carbon assimilation and fatty acid content were determined. It was shown that the biomass and total lipid content increased considerably with varying effluent concentrations reaching 49.2 g L−1 at 48% (v/v) of effluent concentration, while the lipid yield at the same effluent concentration reached 10.15 g L−1, compared to 17.0 g L−1 dry biomass and 10.2 g L−1 lipid yield when yeast extract and peptone medium with micronutrients was used. Compared to the control treatment, the above production was obtained with 48% less inorganic salts, which are needed for the preparation of the artificial sea water. It was shown that Schizochytrium limacinum SR21 was able to remediate 40% of the total organic carbon content of the biofuel wastes, while DHA productivity remained at low levels with saturated fatty acids comprising the main fraction of total fatty acid content. The results of the present study suggest that the simultaneous use of two waste streams from the biofuel industry can serve as potential nutrient sources for the growth of Schizochytrium limacinum SR21, replacing the high cost organic nutrients and up to one half the required artificial sea water salts, but upregulation of DHA productivity through optimization of the abiotic environment is necessary for industrial application, including aqua feed production. Full article
(This article belongs to the Special Issue Algal Biomass, Biofuels and Bioproducts)
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Open AccessArticle
Precise Channel Estimation Approach for a mmWave MIMO System
Appl. Sci. 2020, 10(12), 4397; https://doi.org/10.3390/app10124397 - 26 Jun 2020
Viewed by 224
Abstract
Channel estimation is a formidable challenge in mmWave Multiple Input Multiple Output (MIMO) systems due to the large number of antennas. Therefore, compressed sensing (CS) techniques are used to exploit channel sparsity at mmWave frequencies to calculate fewer dominant paths in mmWave channels. [...] Read more.
Channel estimation is a formidable challenge in mmWave Multiple Input Multiple Output (MIMO) systems due to the large number of antennas. Therefore, compressed sensing (CS) techniques are used to exploit channel sparsity at mmWave frequencies to calculate fewer dominant paths in mmWave channels. However, conventional CS techniques require a higher training overhead for efficient recovery. In this paper, an efficient extended alternation direction method of multipliers (Ex-ADMM) is proposed for mmWave channel estimation. In the proposed scheme, a joint optimization problem is formulated to exploit low rank and channel sparsity individually in the antenna domain. Moreover, a relaxation factor is introduced which improves the proposed algorithm’s convergence. Simulation experiments illustrate that the proposed algorithm converges at lower Normalized Mean Squared Error (NMSE) with improved spectral efficiency. The proposed algorithm also ameliorates NMSE performance at low, mid and high Signal to Noise (SNR) ranges. Full article
(This article belongs to the Section Electrical, Electronics and Communications Engineering)
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Open AccessArticle
Efficient Multifocal Structured Illumination Microscopy Utilizing a Spatial Light Modulator
Appl. Sci. 2020, 10(12), 4396; https://doi.org/10.3390/app10124396 - 26 Jun 2020
Viewed by 213
Abstract
We demonstrated an efficient system for multifocal structured illumination microscopy (MSIM) utilizing a spatial light modulator (SLM). Nine phase profiles of chessboard phase plates loaded on the SLM in sequence are used to generate nine multifocal arrays on the focal plane. Subsequently, nine [...] Read more.
We demonstrated an efficient system for multifocal structured illumination microscopy (MSIM) utilizing a spatial light modulator (SLM). Nine phase profiles of chessboard phase plates loaded on the SLM in sequence are used to generate nine multifocal arrays on the focal plane. Subsequently, nine raw multifocal images are acquired. Finally, by extracting the parameters of the illumination patterns from the raw images precisely, a final super-resolved image is reconstructed by performing the standard reconstruction procedure of structured illumination microscopy (SIM). Our MSIM system realized nearly a 1.5-fold enhancement in spatial resolution compared with wide-field (WF) microscopy. The feasibility of the present system is validated on experiments and the results show its great performances along with good compatibility. Full article
(This article belongs to the Section Optics and Lasers)
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Open AccessArticle
Retinex Based Image Enhancement via General Dictionary Convolutional Sparse Coding
Appl. Sci. 2020, 10(12), 4395; https://doi.org/10.3390/app10124395 - 26 Jun 2020
Viewed by 191
Abstract
Retinex theory represents the human visual system by showing the relative reflectance of an object under various illumination conditions. A feature of this human visual system is color constancy, and the Retinex theory is designed in consideration of this feature. The Retinex algorithms [...] Read more.
Retinex theory represents the human visual system by showing the relative reflectance of an object under various illumination conditions. A feature of this human visual system is color constancy, and the Retinex theory is designed in consideration of this feature. The Retinex algorithms have been popularly used to effectively decompose the illumination and reflectance of an object. The main aim of this paper is to study image enhancement using convolution sparse coding and sparse representations of the reflectance component in the Retinex model over a learned dictionary. To realize this, we use the convolutional sparse coding model to represent the reflectance component in detail. In addition, we propose that the reflectance component can be reconstructed using a trained general dictionary by using convolutional sparse coding from a large dataset. We use singular value decomposition in limited memory to construct a best reflectance dictionary. This allows the reflectance component to provide improved visual quality over conventional methods, as shown in the experimental results. Consequently, we can reduce the difference in perception between humans and machines through the proposed Retinex-based image enhancement. Full article
(This article belongs to the Section Computing and Artificial Intelligence)
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Open AccessArticle
Appraisal of the Spatial Resolution of 2D Electrical Resistivity Tomography for Geotechnical Investigation
Appl. Sci. 2020, 10(12), 4394; https://doi.org/10.3390/app10124394 - 26 Jun 2020
Viewed by 192
Abstract
In the past decade, the 2D electrical resistivity tomography (ERT) has been extensively used in the investigation and monitoring of geotechnical engineering and environment engineering, but there are many uncertainties hidden behind its vivid color earth-resistivity profiles. In order to use the 2D [...] Read more.
In the past decade, the 2D electrical resistivity tomography (ERT) has been extensively used in the investigation and monitoring of geotechnical engineering and environment engineering, but there are many uncertainties hidden behind its vivid color earth-resistivity profiles. In order to use the 2D ERT in the scale of geotechnical engineering effectively, the accuracy and spatial resolution capability of measurements must be enhanced, or at least these uncertainties should be mastered to avoid overreading the measurement results. There were seven common geological models built in this study to discuss the variance in spatial analysis capability of 2D electrical resistivity profiles under different geologic conditions. The findings show that the resolution capability of 2D electrical resistivity profiles was influenced by depth, and in different strata, it may be influenced by the resistivity ratio, layer depth, covering depth, interlayer thickness, tilt angle, medium size, and noise intensity. Generally speaking, the relatively low resistance stratum had better resolution capability; if the relatively high resistance stratum was located under the relatively low resistance stratum, its resolution capability declined. In different strata, the resolution capability may be degraded under the effect of different factors. In addition, any noise in the course of measurement resulted in a random jump of the electrical resistivity profile, which worsened as the noise increased. These circumstances should be paid special attention to avoid misrecognition of electrical resistivity profile images. Full article
(This article belongs to the Section Civil Engineering)
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Open AccessArticle
Experimental Study on the Performance of GFRP–GFRP Slip-Critical Connections with and without Stainless-Steel Cover Plates
Appl. Sci. 2020, 10(12), 4393; https://doi.org/10.3390/app10124393 - 26 Jun 2020
Viewed by 184
Abstract
Composite structures have become increasingly popular in civil engineering due to many advantages, such as light weight, excellent corrosion resistance and high productivity. However, they still lack the strength, stiffness, and convenience of constructions of fastener connections in steel structures. The most popular [...] Read more.
Composite structures have become increasingly popular in civil engineering due to many advantages, such as light weight, excellent corrosion resistance and high productivity. However, they still lack the strength, stiffness, and convenience of constructions of fastener connections in steel structures. The most popular fastener connections in steel structures are slip-critical connections, and the major factors that influence their strength are the slip factors between faying surfaces and the clamping force due to the prevailing torque. This paper therefore examined the effect that changing the following parameters had on the slip factor: (1) replacing glass fiber reinforced plastic (GFRP) cover plates with stainless-steel cover plates; (2) adopting different surface treatments for GFRP-connecting plates and stainless-steel cover plates, respectively; and (3) applying different prevailing torques to the high-strength bolts. The impact on the long-term effects of the creep property in composite elements under the pressure of high-strength bolts was also studied with pre-tension force relaxation tests. It is shown that a high-efficiency fastener connection can be obtained by using stainless-steel cover plates with a grit-blasting surface treatment, with the maximum slip factor reaching 0.45, while the effects of the creep property are negligible. Full article
(This article belongs to the Special Issue Progress of Fiber-Reinforced Composites: Design and Applications)
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Open AccessArticle
A Textile-Based Microfluidic Platform for the Detection of Cytostatic Drug Concentration in Sweat Samples
Appl. Sci. 2020, 10(12), 4392; https://doi.org/10.3390/app10124392 - 26 Jun 2020
Viewed by 190
Abstract
This work presents a new multilayered microfluidic platform, manufactured using a rapid and cost-effective xurography technique, for the detection of drug concentrations in sweat. Textile fabrics made of cotton and polyester were used as a component of the platform, and they were positioned [...] Read more.
This work presents a new multilayered microfluidic platform, manufactured using a rapid and cost-effective xurography technique, for the detection of drug concentrations in sweat. Textile fabrics made of cotton and polyester were used as a component of the platform, and they were positioned in the middle of the microfluidic device. In order to obtain a highly conductive textile, the fabrics were in situ coated with different amounts of polyaniline and titanium dioxide nanocomposite. This portable microfluidic platform comprises at least three layers of optically transparent and flexible PVC foils which were stacked one on top of the other. Electrical contacts were provided from the edge of the textile material when a microfluidic variable resistor was actually created. The platform was tested in plain artificial sweat and in artificial sweat with a dissolved cytostatic test drug, cyclophosphamide, of different concentrations. The proposed microfluidic device decreased in resistance when the sweat was applied. In addition, it could successfully detect different concentrations of cytostatic medication in the sweat, which could make it a very useful tool for simple, reliable, and fast diagnostics. Full article
(This article belongs to the Section Electrical, Electronics and Communications Engineering)
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Open AccessArticle
Inspiration for Seismic Diffraction Modelling, Separation, and Velocity in Depth Imaging
Appl. Sci. 2020, 10(12), 4391; https://doi.org/10.3390/app10124391 - 26 Jun 2020
Viewed by 193
Abstract
Fractured imaging is an important target for oil and gas exploration, as these images are heterogeneous and have contain low-impedance contrast, which indicate the complexity in a geological structure. These small-scale discontinuities, such as fractures and faults, present themselves in seismic data in [...] Read more.
Fractured imaging is an important target for oil and gas exploration, as these images are heterogeneous and have contain low-impedance contrast, which indicate the complexity in a geological structure. These small-scale discontinuities, such as fractures and faults, present themselves in seismic data in the form of diffracted waves. Generally, seismic data contain both reflected and diffracted events because of the physical phenomena in the subsurface and due to the recording system. Seismic diffractions are produced once the acoustic impedance contrast appears, including faults, fractures, channels, rough edges of structures, and karst sections. In this study, a double square root (DSR) equation is used for modeling of the diffraction hyperbola with different velocities and depths of point diffraction to elaborate the diffraction hyperbolic pattern. Further, we study the diffraction separation methods and the effects of the velocity analysis methods (semblance vs. hybrid travel time) for velocity model building for imaging. As a proof of concept, we apply our research work on a steep dipping fault model, which demonstrates the possibility of separating seismic diffractions using dip frequency filtering (DFF) in the frequency–wavenumber (F-K) domain. The imaging is performed using two different velocity models, namely the semblance and hybrid travel time (HTT) analysis methods. The HTT method provides the optimum results for imaging of complex structures and imaging below shadow zones. Full article
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Open AccessArticle
Assessment of Angular Spectral Distributions of Laser Accelerated Particles for Simulation of Radiation Dose Map in Target Normal Sheath Acceleration Regime of High Power Laser-Thin Solid Target Interaction—Comparison with Experiments
Appl. Sci. 2020, 10(12), 4390; https://doi.org/10.3390/app10124390 - 26 Jun 2020
Viewed by 278
Abstract
An adequate simulation model has been used for the calculation of angular and energy distributions of electrons, protons, and photons emitted during a high-power laser, 5-µm thick Ag target interaction. Their energy spectra and fluencies have been calculated between 0 and 360 degrees [...] Read more.
An adequate simulation model has been used for the calculation of angular and energy distributions of electrons, protons, and photons emitted during a high-power laser, 5-µm thick Ag target interaction. Their energy spectra and fluencies have been calculated between 0 and 360 degrees around the interaction point with a step angle of five degrees. Thus, the contribution of each ionizing species to the total fluency value has been established. Considering the geometry of the experimental set-up, a map of the radiation dose inside the target vacuum chamber has been simulated, using the Geant4 General Particle Source code, and further compared with the experimental one. Maximum values of the measured dose of the order of tens of mGy per laser shot have been obtained in the direction normal to the target at about 30 cm from the interaction point. Full article
(This article belongs to the Special Issue Laser-Driven Accelerators, Radiations, and Their Applications)
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Open AccessFeature PaperArticle
Experimental Characterization of Plasmonic Sensors Based on Lab-Built Tapered Plastic Optical Fibers
Appl. Sci. 2020, 10(12), 4389; https://doi.org/10.3390/app10124389 - 26 Jun 2020
Viewed by 206
Abstract
In this work, we have compared several configurations of surface plasmon resonance (SPR) sensors based on D-shaped tapered plastic optical fibers (TPOFs). Particularly, the TPOFs used to obtain the SPR sensors are made by a lab-built system based on two motorized linear positioning [...] Read more.
In this work, we have compared several configurations of surface plasmon resonance (SPR) sensors based on D-shaped tapered plastic optical fibers (TPOFs). Particularly, the TPOFs used to obtain the SPR sensors are made by a lab-built system based on two motorized linear positioning stages and a heating plate. Preliminarily, a comparative analysis has been carried out between two different configurations, one with and one without a thin buffer layer deposited between the core of TPOFs and the gold film. After this preliminary step, we have used the simpler configuration, obtained without the buffer layer, to realize different SPR D-shaped TPOF sensors. This study could be of interest in SPR D-shaped multimode plastic optical fiber (POF) sensors because, without the tapers, the performances decrease when the POF’s diameter decreases, whereas the performances improve in SPR D-shaped tapered POF sensors, where the diameter decreases in the D-shaped sensing area. The performances of the SPR sensors based on different taper ratios have been analyzed and compared. The SPR-TPOF sensors have been tested using water–glycerin mixtures with refractive indices ranging from 1.332 to 1.381 RIU. According to the theory, the experimental results have demonstrated that, as the taper ratio increases, the sensitivity of the SPR sensor increases as well, while on the contrary the signal-to-noise ratio (SNR) decreases. Full article
(This article belongs to the Special Issue World of Biosensing)
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Open AccessEditorial
Recent Trends in DC and Hybrid Microgrids: Opportunities from Renewables Sources, Battery Energy Storages and Bi-Directional Converters
Appl. Sci. 2020, 10(12), 4388; https://doi.org/10.3390/app10124388 - 26 Jun 2020
Viewed by 211
Abstract
This editorial manuscript reviews the papers accepted for publication in the Special Issue “DC & Hybrid Microgrids” of Applied Sciences. This Special Issue, co-organized by the University of Pisa, Italy and Østfold University College in Norway, has collected nine papers from 25 [...] Read more.
This editorial manuscript reviews the papers accepted for publication in the Special Issue “DC & Hybrid Microgrids” of Applied Sciences. This Special Issue, co-organized by the University of Pisa, Italy and Østfold University College in Norway, has collected nine papers from 25 submitted, with authors from Asia, North America and Europe. The published articles provide an overview of the most recent research advances in direct current (DC) and hybrid microgrids, exploiting the opportunities offered by the use of renewable energy sources, battery energy storage systems, power converters, innovative control and energy management strategies. Full article
(This article belongs to the Special Issue DC & Hybrid Micro-Grids)
Open AccessArticle
Design and Implementation of an IoT-Oriented Strain Smart Sensor with Exploratory Capabilities on Energy Harvesting and Magnetorheological Elastomer Transducers
Appl. Sci. 2020, 10(12), 4387; https://doi.org/10.3390/app10124387 - 26 Jun 2020
Viewed by 213
Abstract
This work designed and implemented a new low-cost, Internet of Things-oriented, wireless smart sensor prototype to measure mechanical strain. The research effort explores the use of smart materials as transducers, e.g., a magnetorheological elastomer as an electrical-resistance sensor, and a cantilever beam with [...] Read more.
This work designed and implemented a new low-cost, Internet of Things-oriented, wireless smart sensor prototype to measure mechanical strain. The research effort explores the use of smart materials as transducers, e.g., a magnetorheological elastomer as an electrical-resistance sensor, and a cantilever beam with piezoelectric sensors to harvest energy from vibrations. The study includes subsequent and validated results with a magnetorheological elastomer transducer that contained multiwall carbon nanotubes with iron particles, generated voltage tests from an energy-harvesting system that functions with an array of piezoelectric sensors embedded in a rubber-based cantilever beam, wireless communication to send data from the sensor’s central processing unit towards a website that displays and stores the handled data, and an integrated manufactured prototype. Experiments showed that electrical-resistivity variation versus measured strain, and the voltage-generation capability from vibrations have the potential to be employed in smart sensors that could be integrated into commercial solutions to measure strain in automotive and aircraft systems, and civil structures. The reported experiments included cloud-computing capabilities towards a potential Internet of Things application of the smart sensor in the context of monitoring automotive-chassis vibrations and airfoil damage for further analysis and diagnostics, and in general structural-health-monitoring applications. Full article
(This article belongs to the Special Issue New Sensors for Nondestructive Evaluation)
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Open AccessArticle
A Polarity Capturing Sphere for Word to Vector Representation
Appl. Sci. 2020, 10(12), 4386; https://doi.org/10.3390/app10124386 - 26 Jun 2020
Viewed by 234
Abstract
Embedding words from a dictionary as vectors in a space has become an active research field, due to its many uses in several natural language processing applications. Distances between the vectors should reflect the relatedness between the corresponding words. The problem with existing [...] Read more.
Embedding words from a dictionary as vectors in a space has become an active research field, due to its many uses in several natural language processing applications. Distances between the vectors should reflect the relatedness between the corresponding words. The problem with existing word embedding methods is that they often fail to distinguish between synonymous, antonymous, and unrelated word pairs. Meanwhile, polarity detection is crucial for applications such as sentiment analysis. In this work we propose an embedding approach that is designed to capture the polarity issue. The approach is based on embedding the word vectors into a sphere, whereby the dot product between any vectors represents the similarity. Vectors corresponding to synonymous words would be close to each other on the sphere, while a word and its antonym would lie at opposite poles of the sphere. The approach used to design the vectors is a simple relaxation algorithm. The proposed word embedding is successful in distinguishing between synonyms, antonyms, and unrelated word pairs. It achieves results that are better than those of some of the state-of-the-art techniques and competes well with the others. Full article
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Open AccessArticle
Three-Dimensional Analysis of Root Anatomy and Root Canal Curvature in Mandibular Incisors Using Micro-Computed Tomography with Novel Software
Appl. Sci. 2020, 10(12), 4385; https://doi.org/10.3390/app10124385 - 26 Jun 2020
Viewed by 375
Abstract
Root canal treatment of mandibular incisor is difficult because of the narrow pulp space and apical curvature. The aim of this study was to measure the anatomical indicators of the mandibular incisors in Koreans using micro-computed tomography (MCT) with novel software (Kappa 2). [...] Read more.
Root canal treatment of mandibular incisor is difficult because of the narrow pulp space and apical curvature. The aim of this study was to measure the anatomical indicators of the mandibular incisors in Koreans using micro-computed tomography (MCT) with novel software (Kappa 2). The MCT-scanned data from 27 mandibular incisors were reconstructed and analyzed. For each canal, 3-dimensional (3D) surface models were re-sliced at 0.1 mm intervals perpendicular to the central axis of the root canal. Root canal width, dentine thickness, and direction and degree of root canal curvatures were measured automatically on each slice. Measurements were analyzed statistically with Bhapkar test, Friedman test, and Wilcoxon signed rank test. Labial and lingual dentine thicknesses were significantly larger than mesial and distal thicknesses (p < 0.001). The thinnest dentine was mainly located on the mesio-lingual side of the canals in the apical third. The mean narrowest and widest canal width in the apical sixth were 0.22 mm and 0.40 mm, respectively. The canal curvature abruptly increased in the apical 0.5-mm portion. MCT with novel software provided useful anatomical information for root canal instrumentation. Full article
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