Revisiting Slotted ALOHA: Density Adaptation in FANETs

Unmanned aerial vehicles have been widely used in many areas of life. They communicate with each other or infrastructure to provide ubiquitous coverage or assist cellular and sensor networks. They construct flying ad hoc networks. One of the most significant problems in such networks is communication among them over a shared medium. Using random channel access techniques is a useful solution. Another important problem is that the variations in the density of these networks impact the quality of service and introduce many challenges. This paper presents a novel density-aware technique for flying ad hoc networks. We propose Density-aware Slotted ALOHA Protocol that utilizes slotted ALOHA with a dynamic random access probability determined using network density in a distributed fashion. Compared to the literature, this paper concentrates on proposing a three-dimensional, easily traceable model and stabilize the channel utilization performance of slotted ALOHA with an optimized channel access probability to its maximum theoretical level, 1/e, where e is the Euler’s number. Monte-Carlo simulation results validate the proposed approach leveraging aggregate interference density estimator under the simple path-loss model. We compare our protocol with two existing protocols, which are Slotted ALOHA and Stabilized Slotted ALOHA. Comparison results show that the proposed protocol has 36.78% channel utilization performance; on the other hand, the other protocols have 24.74% and 30.32% channel utilization performances, respectively. Considering the stable results and accuracy, this model is practicable in highly dynamic networks even if the network is sparse or dense under higher mobility and reasonable non-uniform deployments.

     

Anomaly localization in regular textures based on deep convolutional generative adversarial networks

Applied Intelligence - Pixel-level anomaly localization is a challenging problem due to the lack of abnormal training samples. The existing adversarial network methods attempt to segment anomalies...     

Workability of hybrid fiber reinforced self-compacting concrete

Compared to fiber reinforced concrete (FRC), self-compacting concrete (SCC) is a relatively new type of concrete with high flowability and good cohesiveness. It offers very attractive economical and technical benefits, which can be further extended when combined with FRC. In this article two different types of steel fibers were used, in combination, and the effects of fiber inclusion on the workability of hybrid fiber reinforced self-compacting concrete (HFR-SCC) is studied. The effects of fibers are quantified based on the fiber volume, length, and aspect ratios of the fibers. It was concluded that in addition to the above-mentioned quantifiable three properties, other properties of fibers such as shape and surface roughness are also found to be important but they cannot be quantified at this stage.     

FREE-FORM SURFACE MACHINING AND COMPARING FEEDRATE SCHEDULING STRATEGIES

This article presents mathematical models of cutting forces and surface-form errors for machining of free-form surfaces. Besides the predictive models of cutting forces and surface deflections, a newly developed force based feedrate scheduling (FFS) technique is compared with material removal rate (MRR) based feedrate scheduling method that was used in feedrate optimization packages. With the experimental validations in free-form surfaces, it is shown that the mechanic models predict the forces and surface-form errors quite well. Moreover, by modifying the CNC programs with the new FFS technique, cycle times of the free-form parts can be decreased significantly.     

TOOL PATH SELECTION STRATEGIES FOR COMPLEX SCULPTURED SURFACE MACHINING

High performance machining of complex free form surfaces is very critical in many different industries. In this research, an advanced mathematical model of cutting forces that is based on the kinematics and mechanics of the 3D sculptured surface machining is integrated with CAM packages in order to predict the complex tool-workpiece engagements and machining forces for any tool path. Machined 3D free form topographies and distributions of errors between the desired CAD and machined surfaces are also predicted in advance. Now, an evaluation of different tool path strategies for 3D complex sculptured surfaces can be made. Theoretical simulations of forces and surface topographies for different tool paths are presented and compared with experimental measurements.     

Sunflower seed cake as reinforcing filler in thermoplastic composites

Dimensional stability, mechanical properties, and melting and crystallization behavior of polypropylene composites filled with sunflower seed cake (SSC) were investigated. Injection molded composites were prepared from the SSC flour and polypropylene with and without maleic anhydride‐grafted polypropylene (MAPP) at 30, 40, 50, and 60 wt % contents of the SSC flour. Twenty‐eight days thickness swelling and water absorption values of the specimens increased by 43 and 56% as the filler content increased from 30 to 60 wt %, respectively. The flexural modulus of the polypropylene composites increased from 3157 to 4363 MPa as the SSC flour increased from 30 to 60 wt %. The maximum flexural strength 38.4 MPa was observed for 40 wt % SSC flour filled specimens. However, further increment in the SCC flour decreased the flexural strength to 31.4 MPa. The tensile strength of the specimens decreased from 22.5 to 14 MPa while the tensile modulus increased from 3023 to 3677 MPa as the SSC flour increased from 30 to 60 wt %. The dimensional stability and mechanical properties of the composites were significantly improved by the incorporation of the coupling agent (MAPP). The effect of the MAPP addition was more pronounced for the strength than for the modulus. The melting temperature and degree of crystallinity of the neat polypropylene decreased with increasing content of the SSC flour. The degree of crystallinity of filled composites considerably increased with the incorporation of the MAPP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Physical,mechanical, and thermal properties of polypropylene composites filled with walnut shell flour

Injection molded specimens were prepared from the walnut shell flour and polypropylene with and without maleic anhydride-grafted polypropylene at 40, 50, and 60% (weight) contents of the walnut shell. The bending and tensile modulus of the composites significantly increased with increasing the filler content while the bending and tensile strengths significantly decreased. Water absorption and thickness swelling of the composites increased with increasing filler content. The MAPP improved the interfacial adhesion between walnut shell flour and polymer matrix. A 40/57/3 formulation of the walnut shell flour/polypropylene/MAPP can be used in outdoor applications requiring a high dimensional stability.     

Experimental characterization of helical swimming trajectories in circular channels

Trajectories of microorganisms and artificial helical swimmers in confinements are important in biology and for controlled swimming in medical applications. Numerical studies on the locomotion of model microorganisms and spherical particles are reported in the literature. Here, we report experimental results on the trajectories and velocities of artificial helical swimmers in circular channels. Trajectories are recorded by a digital camera and images are processed to obtain the radial position and the orientation of the swimmer. Tail length, channel diameter, rotation frequency and the rate of the Poiseuille flow are varied in the experiments. Experimental results demonstrate that confinement and flow affect the orientation of swimmer and the swimming performance. Swimmers follow stable helical trajectories in the forward direction when the tail pushes the swimmer. However, when the tail pulls the swimmer in the backward direction trajectories converge to a straight line in the narrow channel, whereas helical trajectories are observed for pullers as well in the wide channel.     

Mechanical and thermal properties of wood‐plastic composites reinforced with hexagonal boron nitride

Mechanical, thermal, and morphological properties of injection molded wood‐plastic composites (WPCs) prepared from poplar wood flour (50 wt%), thermoplastics (high density polyethlyne or polypropylene) with coupling agent (3 wt%), and hexagonal boron nitride (h‐BN) (2, 4, or 6 wt%) nanopowder were investigated. The flexural and tensile properties of WPCs significantly improved with increasing content of the h‐BN. Unlike the tensile and flexural properties, the notched izod impact strength of WPCs decreased with increasing content of h‐BN but it was higher than that of WPCs without the h‐BN. The WPCs containing h‐BN were stiffer than those without h‐BN. The tensile elongation at break values of WPCs increased with the addition of h‐BN. The differential scanning calorimetry (DSC) analysis showed that the crystallinity, melting enthalpy, and crystallization enthalpy of the WPCs increased with increasing content of the h‐BN. The increase in the crystallization peak temperature of WPCs indicated that h‐BN was the efficient nucleating agent for the thermoplastic composites to increase the crystallization rate. POLYM. COMPOS., 35:194–200, 2014. © 2013 Society of Plastics Engineers     

TOOL PATH SELECTION STRATEGIES FOR COMPLEX SCULPTURED SURFACE MACHINING

High performance machining of complex free form surfaces is very critical in many different industries. In this research, an advanced mathematical model of cutting forces that is based on the kinematics and mechanics of the 3D sculptured surface machining is integrated with CAM packages in order to predict the complex tool-workpiece engagements and machining forces for any tool path. Machined 3D free form topographies and distributions of errors between the desired CAD and machined surfaces are also predicted in advance. Now, an evaluation of different tool path strategies for 3D complex sculptured surfaces can be made. Theoretical simulations of forces and surface topographies for different tool paths are presented and compared with experimental measurements.