177,150 research outputs found
Quantum-Aided modeling and design techniques for advanced wireless network architectures
No full textThe next generation of wireless communication systems will be characterized by ever-increasing computational demands and complex data processing requirements. Quantum computing and quantum communications, underpinned by the principles of quantum mechanics, promise to significantly enhance processing capabilities compared to conventional classical approaches. This paradigm shift presents novel challenges that demand sophisticated strategies to ensure a suitable integration. As a result, this thesis focuses on addressing these challenges from anarchitectural stand point, proposing and analyzing various strategies to incorporate quantum computing into future wireless communication systems. Moreover, this work delves into the entanglement distribution problem with the primary goal of optimizing the teleportation rate, a crucial aspect of quantum communication efficiency
Multiple Access Control Strategies for Nanoscale Communications and Networking
No full textNowadays, communication technologies are breaking the boundaries of common wireless and wired channels toward innovative areas, aiming to go beyond traditional mediums to novel channels to extend the opportunities and increase the range of communicating devices. In this framework, nanoscale and molecular communications represent an interesting subject of investigation
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Performance optimization in machining of aluminium alloys for mould production: HSM and EDM
No full textAluminium alloys offer many machining advantages such as excellent machinability and finish degree with high cutting speed, low cutting forces, outstanding tool life. Elevated thermal exchange and weight reduction compared to steels are additional characteristics that lead to increasing applications in the automotive and aerospace industry and in the field of mould production. Relatively recent Aluminium alloys derived by aeronautical uses offer very high strength and hardness: the gap with steels is thus reduced or even reversed in terms of specific properties. Two examples are Al 2219 and Al 7050. If the first examples of Aluminium moulds for plastic injection were limited to preproduction, the properties of these new alloys match the requirements of medium production volumes, which are also the main market demand.The research focuses on two distinct operations typical of the tooling phase: High Speed Milling (HSM) and Electro Discharge Machining (EDM). In both cases the machining performance is evaluated in specific tests through a multiscale approach: measurements of the macroscopic process outputs are merged with the investigation of mechanisms at a microscopic level. The methodology enhances optimization chances with respect to traditional practice.As to milling operation, several studies prove that Aluminium alloys allow the advantageous adoption of high cutting speed, ensuring time and cost savings together with excellent surface finish and low tool wear. Yet, the traditional laws between cutting parameters do not apply to the field of high-speed machining and the mechanisms of chip removal still need investigation. In order to appraise the machinability of Al 2219 and Al 7050 alloys, high speed milling tests using uncoated carbide tools are performed. The tests are carried out on Al 7075 as well, an alloy of common employment for preproduction moulds, to provide control data. Cutting speed ranges from 600 to 2200 m/min and feed per tooth between 0.075 and 0.18 mm/tooth. Correlations between cutting parameters and surface finish, tool wear and chip formation mechanisms are studied with the aid of SEM observation and EDX semi-quantitative analysis. The best surface finish is obtained for Al 7050 with high cutting speed and low feed. No tool wear is observed in the considered conditions. Microscope observation of tools and chip proves that surface finish is ruled by tool-chip adhesion and that alloys having almost the same chemical composition can provide substantially different results due to grain dimension and distribution.EDM is used for the machining of complex shapes and textures typical of plastic injection moulds. Aim of this research is to verify the EDMachinability of the Aluminum alloys previously studied with regard to HSM. Literature studies on the specific subject are very rare. EDM tests are planned and performed using electrolytic copper electrodes on Al 7050 and Al 2219, plus Al 7075 as a control. A benchmark is chosen whose geometry points out the typical problems of moulds machining and allows an easy and significant dimensional characterization, because of the presence of different geometrical features and relative orientations. Roughing, semifinishing and finishing cycles are conducted; then the effect of process parameters on dimensional tolerance, surface finish and electrode wear is studied. Moreover, the electrodes and the machined surfaces are observed through optical- and scanning electron microscope (OM, SEM) to verify the presence and composition of deposits on the electrodes surfaces, as well as the eroded surfaces morphology on the workpieces. No remarkable differences can be identified as to dimensional tolerances between the three alloys. A slight trend to give lower roughness values can be noticed for the alloy 7050. The results are coherent with the regular morphology observed on the machined surfaces of this alloy. The observation of the erosion mechanisms allows to affirm that, for the same process parameters and very similar finishing results, the morphology of the machined surface can be considerably different, for example as to cracks density
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Identification of the Manhattan bridge dynamic properties for fatigue assessment
No full textIn this paper, dynamic properties and results of the identification process on the Manhattan Bridge are described. Accelerations during ambient vibrations have been recorded using an advanced MEMSbased system,whose main features are the transmission of the data in digital formand the possibility of performing some system analyses directly on-board of the sensors, transmitting synthetic data only to the main computer. 28 MEMS accelerometers have been used and 4 different experimental setups adopted. Several modes of the main span are identified, with natural frequencies in the range 0.2-1.0 Hz. A FE model updating procedure is also performed by means of an improved Evolutionary Algorithm. After the updating procedure, numerical modal frequencies and mode shapes match well the experimental data. This work is part of a research that aims at investigating how real-time monitoring systems can be used to detect the occurrence of fatigue phenomena induced by vibrations and distortion modes in existing steel bridges
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