Search results

The present paper aims at the multi-objective optimization of a reentrant hexagonal cell auxetic structure. In addition, a parametric analysis will be carried out to verify how each of the design factors impact each of the responses.

The multi-objective optimization of five different responses of an auxetic model was considered: mass, critical buckling load under compression effort, natural frequency, Poisson's ratio and failure load. The response surface methodology was applied, and a new meta-heuristic of optimization called the multi-objective Lichtenberg algorithm was applied to find the optimized configuration of the model. It was possible to increase the failure load by 26.75% in compression performance optimization. Furthermore, in the optimization of modal performance, it was possible to increase the natural frequency by 37.43%. Finally, all 5 responses analyzed simultaneously were optimized. In this case, it was possible to increase the critical buckling load by 42.55%, the failure load by 28.70% and reduce the mass and Poisson's ratio by 15.97 and 11%, respectively. This paper addresses something new in the scientific world to date when evaluating in a multi-objective optimization problem, the compression and modal performance of an auxetic reentrant model.

It was possible to find multi-objective optimized structures. It was possible to increase the critical buckling load by 42.82%, and the failure load in compression performance by 26.75%. Furthermore, in the optimization of modal performance, it was possible to increase the natural frequency by 37.43%, and decrease the mass by 15.97%. Finally, all 5 responses analyzed simultaneously were optimized. In this case, it was possible to increase the critical buckling load by 42.55%, increase the failure load by 28.70% and reduce the mass and Poisson's ratio by 15.97 and 11%, respectively.

There is no work in the literature to date that performed the optimization of 5 responses simultaneously of a reentrant hexagonal cell auxetic structure. This paper also presents an unprecedented statistical analysis in the literature that verifies how the design factors impact each of the responses.

The joint photographic experts group (JPEG) 2000 image compression system is being used for cultural heritage preservation. The authors are aware of over a dozen of big memory institutions worldwide using this format. This paper aims to review and explain choices for end users to help resolve trade-offs that these users are likely to encounter in practice.

The JPEG 2000 format is quite complex and therefore sometimes considered as a preservation risk. A lossy compression is governed by a number of parameters that control compression speed and rate-distortion trade-off. Their inappropriate adjustment may fairly easily lead to sub-optimal compression performance. This paper provides general guidelines for selecting the most appropriate parameters for a specific application.

This paper serves as a guide for the preservation of digital heritage in cultural heritage institutions, including libraries, archives and museums.

This paper serves as a guide for the preservation of digital heritage in cultural heritage institutions, including libraries, archives and museums.

The purpose of this paper is to analyze the effects of wearing compression pants of varying pressure levels on the wearer’s attention/concentration to investigate the appropriate level of compression for sport performance and confirm whether this methodology is feasible as a means of evaluating sportswear functionality.

After wearing compression pants of varying compression levels, spontaneous potentials were analyzed by calculating the spontaneous electroencephalography (EEG) indices: relative low beta (RLB) power spectrum ((12~15 Hz)/(4~50 Hz)), relative mid beta (RMB) power spectrum ((15~20 Hz)/(4~50 Hz)), and ratio of sensory motor rhythm to theta waves ((12~15 Hz)/(4~8 Hz)). The activation of brain waves was mapped and visualized from EEG data using BioScan-Map (BioBrain Inc., Daejeon, Korea).

The influence of pressure levels on brain waves was confirmed: RLB power, RMB power and RST varied by experimental clothing. CP3, the compression pants that applied moderate pressure (1.57±0.41 kPa), was associated with a relatively higher level of attention/concentration – i.e., the results confirmed that sports compression pants that apply approximately 1.0~2.0 kPa to the area between the thighs and shins are improve attention/concentration. It was further confirmed that EEG is a useful tool for evaluating the psychophysiological effects of functional apparel.

Unlike preceding studies that considered only alpha waves and the effects of clothing on comfort, this study investigated the influence of compression garments on attention/concentration.

This study aims to clarify the key factors among physical‐mechanical properties of fabrics in relation to the dynamic pressure performance of compression garment.

The physical‐mechanical properties of 16 different fabrics were measured using a KESF standard evaluation system and INSTRON tensile tester, and the garment pressure was measured by dynamic pressure measuring system. Grey correlation analysis is used to determine the correlation degree of fabric physical‐mechanical properties and dynamic pressure magnitude.

The mechanical behaviors (e.g. tensile, shearing, and bending) and physical characteristics are different in elastic fabrics with varied content of elastic fiber, kinds of yarn, et al. Grey correlation analysis is a valid method to analyze the indices of a system, quantize them and put them in order. All the degrees of Grey correlation are more than 0.6. The degree of grey correlation between tensile force (F), shearing rigidity (G) and bending rigidity (B) are higher than others, hence it is conducted that these would significantly effect on garment pressure. The quantitative regression equations between pressure magnitude at extension of 50 percent and the individual key parameters (mean values in wale and course directions) of tested samples are illustrated.

The other parameters (e.g. fabric structure, yarn fineness, and pre‐tension, et al.) should be taken into account. Further, an integrative mathematic model would be established, which could predict the garment pressure directly from the physical‐mechanical properties of fabric.

The present study indicates that pressure magnitude of elastic fabric is an integrative action performed by physical‐mechanical properties. The developed illustrative equations and method offer a rational and practical tool for assessing pressure functional performance of elastic fabric in the stages of design and product development.

For privacy protection, federated learning based on data separation allows machine learning models to be trained on remote devices or in isolated data devices. However, due to the limited resources such as bandwidth and power of local devices, communication in federated learning can be much slower than in local computing. This study aims to improve communication efficiency by reducing the number of communication rounds and the size of information transmitted in each round.

This paper allows each user node to perform multiple local trainings, then upload the local model parameters to a central server. The central server updates the global model parameters by weighted averaging the parameter information. Based on this aggregation, user nodes first cluster the parameter information to be uploaded and then replace each value with the mean value of its cluster. Considering the asymmetry of the federated learning framework, adaptively select the optimal number of clusters required to compress the model information.

While maintaining the loss convergence rate similar to that of federated averaging, the test accuracy did not decrease significantly.

By compressing uplink traffic, the work can improve communication efficiency on dynamic networks with limited resources.

The purpose of this paper is to characterize mechanical properties (tensile, compressive and flexural) for the three-dimensional printing (3DP) process, using various common recommended infiltrate materials and post-processing conditions.

A literature review is conducted to assess the information available related to the mechanical properties, as well as the experimental methodologies which have been used when investigating the 3D printing process characteristics. Test samples are designed, and a methodology to measure infiltrate depths is presented. A full factorial experiment is conducted to collect the tensile, compressive and bending forces for a set of infiltrates and build orientations. The impact of the infiltrate type and depth with respect to the observed strength characteristics is evaluated.

For most brittle materials, the ultimate compression strength is much larger than the ultimate tensile strength, which is shown in this work. Unique stress–strain curves are generated from the infiltrate and build orientation conditions; however, the compressive strength trends are more consistent in behavior compared to the tensile and flexural results. This comprehensive study shows that infiltrates can significantly improve the mechanical characteristics, but performance degradation can also occur, which occurred with the Epsom salts infiltrates.

More experimental research needs to be performed to develop predictive models for design and fabrication optimization. The material-infiltrate performance characteristics vary per build orientation; hence, experimental testing should be performed on intermediate angles, and a double angle experiment set should also be conducted. By conducting multiple test scenarios, it is now understood that this base material-infiltrate combination does not react similar to other materials, and any performance characteristics cannot be easily predicted from just one study.

These results provide a foundation for a process design and post-processing configuration database, and downstream design and optimization models. This research illustrates that there is no “best” solution when considering material costs, processing options, safety issues and strength considerations. This research also shows that specific testing is required for new machine–material–infiltrate combinations to calibrate a performance model.

There is limited published data with respect to the strength characteristics that can be achieved using the 3DP process. No published data with respect to stress–strain curves are available. This research presents tensile, compressive and flexural strength and strain behaviors for a wide variety of infiltrates, and post-processing conditions. A simple, unique process is presented to measure infiltrate depths. The observed behaviors are non-linear and unpredictable.

The purpose of this paper is to find out the use of compressive sensing (CS) algorithm for wireless sensor networks (WSNs). As energy-efficient algorithms are required for WSNs, CS is very much useful as less than 25 per cent of the entire input data alone is required to be transmitted, and reconstruction at the receiver with this reduced data set is of good quality. But, the usefulness of the algorithm with suitable modulation schemes is not analyzed so far in the literature. Hence, this work concentrated on the algorithm performance with different modulation schemes and different channel conditions.

Compressive sensing encoding is performed by using suitable transform on the input signal. Here, DCT and DWT are used to generate the sparse signal. Random measurement matrix is used to generate the compressed output, which is reconstructed using the Basis Pursuit (BP) method. Also, an analysis for the energy-efficient modulation scheme is performed by modulating the compressed output using QPSK/BPSK/QAM and transmitted by considering the Gaussian and Rayleigh Channels. Energy required per bit transmission is modeled and computed for different schemes.

Simulation result shows that the use of CS algorithm for data compression tremendously reduces the number of transmission bits and, hence, enhances the transmission and bandwidth efficiency in WSN. Results show that DWT is a much suitable transform to be used for sparse measurement generation. In comparison with DCT, DWT is computationally simple and takes very less time, which is expected in real-time application. The reconstruction result shows that about 25 per cent of the data sample is sufficient to recover the original image, perhaps which is the most surprising result. An extensive analysis of various modulation schemes based on the energy model shows that QPSK is in the AWGN channel, and QAM modulation in the Rayleigh channel is a much suitable modulation scheme to be used in WSN for further reduction of energy consumption.

Compressive sensing is recently gaining importance for quantization, compression and noise removal in images. In this paper, this technique was used along with modulation schemes to analyze the suitability of the algorithm for WSN.

This paper aims to look into employee perceptions of politics and fairness in a work setting where a new merit pay system had recently been implemented.

The results are based on employee survey responses from three governmental organizations (n=367) that had implemented analogous merit pay systems.

Hierarchical moderated regression results indicated that perceptions of politics and fairness distinctively and interactively predicted whether the pay system was perceived effective in achieving its objectives. The results suggest that some forms of politics in performance appraisals (e.g. compression) might be perceived less detrimental than others (e.g. favoritism). In a high politics environment, the pay system effectiveness varied as a function of the level of distributive justice. Voice in the pay system development only mattered in a situation where there was a low level of organizational politics.

One of the main limitations of this study is its reliance on cross‐sectional data. Future research should complement employee perceptions about pay system effectiveness with objective data from the organizations studied. Research on the effect of contextual factors, such as national culture on the motives, in and reactions to, organizational politics, is desired.

The result suggests that the adopted merit pay systems were not ineffective or detrimental per se, but that the effectiveness varied as a function of the established political and fairness climates at different levels of the organization.

This study contributes to the discussion on what are the conditions under which politics and fairness are antithetical, and when they are interactively associated with outcomes.

Selective laser melting (SLM) is an additive manufacturing process suitable for fabricating metal porous scaffolds. The unit cell topology is a significant factor that determines the mechanical property of porous scaffolds. Therefore, the purpose of this paper is to evaluate the effects of unit cell topology on the compression properties of porous Cobalt–chromium (Co-Cr) scaffolds fabricated by SLM using finite element (FE) and experimental measurement methods.

The Co-Cr alloy porous scaffolds constructed in four different topologies, i.e. cubic close packed (CCP), face-centered cubic (FCC), body-centered cubic (BCC) and spherical hollow cubic (SHC), were designed and fabricated via SLM process. FE simulations and compression tests were performed to evaluate the effects of unit cell topology on the compression properties of SLM-processed porous scaffolds.

The Mises stress predicted by FE simulations showed that different unit cell topologies resulted in distinct stress distributions on the bearing struts of scaffolds, whereas the unit cell size directly determined the stress value. Comparisons on the stress results for four topologies showed that the FCC unit cell has the minimum stress concentration due to its inclined bearing struts and horizontal arms. Simulations and experiments both indicated that the compression modulus and strengths of FCC, BCC, SHC, CCP scaffolds with the same cell size presented in a descending order. These distinct compression behaviors were correlated with the corresponding mechanics response on bearing struts. Two failure mechanisms, cracking and collapse, were found through the results of compression tests, and the influence of topological designs on the failure was analyzed and discussed. Finally, the cell initial response of the SLM-processed Co-Cr scaffold was tested through the in vitro cell culture experiment.

A focus and concern on the compression properties of SLM-processed porous scaffolds was presented from a new perspective of unit cell topology. It provides some new knowledge to the structure optimization of porous scaffolds for load-bearing bone implants.

The purpose of this paper is to study extensive enlargement and safety of flight data recorder memory.

The study involves the moving the memory of flight data recorders from an internal embedded device to a cloud.

The implementation has made the embedded memory device of flight data recorder effectively unlimited, and, hence, much more information can be stored.

The possibility of a flight data recorder to be damaged or lost in a crash is not so high, but the implementation can be very helpful in cases such as aerial disappearances.

The implication is larger and protected memory for flight data recorders.

Finding reasons for crashes is faster, and immediate actions can be taken to find remedy to the failures.

The use of internet and cellphones in airplanes is nothing special at present. It is suggested to take this technology for flight data recorders as well.