Polymer Nanocomposites Containing Carbon Nanofibers as Soft Printable Sensors Exhibiting Strain‐Reversible Piezoresistivity

Designed as flexible and extendable conductive print media for pervasive computing as strain sensors, nanocomposites composed of a plasticized thermoplastic or a cross‐linked elastomer and containing carbon nanofibers at concentrations just above the percolation threshold are observed to exhibit a uniquely strain‐reversible piezoresistive response upon application of quasi‐static tensile strain. At small strain levels, the electrical resistance of these nanocomposites reduces with increasing strain, indicative of negative piezoresistivity. Beyond a critical strain, however, the resistance reverses and increases with increasing strain, revealing the existence of a negative‐to‐positive piezoresistivity transition that is fully strain‐reversible and repeatable upon strain cycling. These characteristics imply that the nanocomposite morphologies are highly stable with little evidence of mechanical hysteresis. The mechanism underlying this transition is attributed to reorientation of high‐aspect‐ratio nanofibers (initially homogeneously dispersed) at low strains, followed by separation at high strains. While deposition of these nanocomposites as robust print coatings on textile fabric alters the percolation threshold, strain‐reversible piezoresistivity is retained, confirming that they are suitable as printable strain sensors.     

A decentralized discrete-time controller for dynamic routing

A decentralized controller for dynamic routing in multi-destination large-scale data communication networks is presented. A dynamic model, which can incorporate possibly time-varying different processing delays at different nodes, is developed to describe the network dynamics. A knowledge of these delays is, however, not required for the actual implementation of the controller. It is assumed that the rate of messages being sent out from one node to another (the control signals) are updated at discrete time instants, which is the usual case in practice. The proposed controller is decentralized in the sense that all on-line computations can be done locally at the individual nodes without any information transfer from the other nodes. The design of the controller involves a linear programming optimization problem, which can be solved off-line. The resulting controller has the property that it allows the maximum possible magnitude on each external message arrival rate of the system to occur, without violating any constraints on the system. It is also shown that the proposed controller guarantees stability and clears the queues of the system in the absence of external message arrivals. The controller also avoids any looping of messages and keeps the queue lengths bounded in the presence of external message arrival rates which do not exceed a certain maximum rate. Some simulation results are presented to illustrate the controller's performance in a number of practical cases.     

Effects of pattern coating and vacuum assistance on porosity of aluminium lost foam castings

Lost foam casting (LFC) process has several advantages when compared to conventional sand casting techniques however formation of large amount of gaseous products during foam pattern removal increases porosity fraction of castings, especially for low melting point A1 and Mg alloys. In this study pattern coating and vacuum assistance at the time of filling were investigated and their characterizations in constant casting conditions have been determined. Green sand moulding technique was carried out for all moulds because it is necessary to obtain sound castings by using expandable polystyrene (EPS) foam patterns without refractory coating. Simple prismatic shaped patterns were prepared from cutting pieces from an EPS isolation board. A well-known A380 Al-Si-Cu casting alloy was cast at 730°C. As expected, pattern coating reduce the gas permeability and increase porosity however metal penetration into sand grains and surface roughening occurs without coating. Slight vacuum were applied to moulds with vacuum casting machine until solidification. Vacuum assistance enhanced gas removal and it has clear effect on decreasing porosity.     

Optical dispersion and dielectric properties of rubrene organic semiconductor thin film

Rubrene thin film has been fabricated on a glass substrate by spin-coating at 300 K. The optical dispersion and dielectric properties of the film have been determined from the analysis of transmittance and reflectance measurements at normal incident of light between 200 and 700 nm. The optical transmittance of the film was estimated as of 80–85 % in the visible range. Optical absorption characteristics show that the absorption mechanism is due to the indirect transition. The transport and onset optical energy gaps were determined as 2.93 and 2.31 eV, respectively. Single term Sellmeier dispersion relation and Wemple–DiDomenico single oscillator model were used to determine the optical dispersion parameters. Several dispersion parameters such as lattice dielectric constant, optical dielectric constant at higher frequency, dispersion energy, oscillator energy, the ratio of carrier concentration to the effective mass, the average oscillator wavelength, and average oscillator strength were determined by analysis of refractive index dispersion. The loss factor, the electric modulus, the optical conductivity, the volume and surface energy loss functions, and the relaxation time were also evaluated from the optical dielectric constants analysis.     

Optical and electrical properties of new organic thin film

This paper describes a new organic thin film (OTF) (50 nm) which was deposited by spin coated at room temperature. OTF has been constructed from chemically synthesized poly(pentachlorophenyl methacrylate-co-glycidyl methacrylate). Optical properties of the obtained poly(pentachlorophenyl methacrylate-co-glycidyl methacrylate) in solution were tested by ultraviolet–visible absorption spectroscopy. The analysis of the optical absorption data revealed an existence of a direct and indirect transition optical band gap (E_g). The electrical properties of ITO/PEDOT:PSS/OTF/Al heterojunction structure has been investigated by forward and reverse bias current–voltage (I–V) measurements at room temperature. The main electrical parameters such as barrier height (Φ_Bo), ideality factor (n) and reverse saturation current (I_o) have been calculated by applying thermionic emission theory as 0.80 eV, 3.69, 1.86 × 10^?8 A respectively. Additionally, series resistance (R_s), Φ_Bo and n were calculated from the forward bias I–V data using the methods of Cheung and Cheung with Norde and showed that these methods can be applied successfully for this structure.     

Analysis of tweets about football: 2013 and 2018 leagues in Turkey

ABSTRACT

Football has recently developed into a unique sector with complex management and marketing functions, where novel communication technologies are employed. In this paper, we aim to contribute to the numerous fields involving emerging European sports marketing literature, social media analytics, and digital consumer behaviour. Our purpose is to explore Twitter use related with football by analysing real-time streamed data in offering a longitudinal perspective by focusing on 2013 and 2018 leagues in Turkey via the use of social media analytics framework. Retrieved dataset involved randomly selected publicly available 370 thousand and 6.8 million real-time tweets in 2013 and 2018 leagues, respectively. We report that majority of tweets about the football was posted within the three-hour window before the match independent of the match result and the importance of the result. Moreover, pre-match tweeting volume was almost a crystal ball signalling match winning. Our findings are valuable for sports managers and marketers where some key suggestions provided are to involve particular contexts of winning or losing in their after-match marketing plans, to value weekdays as much as the weekends, and to utilise the after-work prime time of social media engagement.     

Influence of orbital shaking on microstructure and mechanical properties of A380 aluminium alloy produced by lost foam casting

Using vibration for refining microstructure and improve mechanical properties of aluminium alloys castings are in the interest of researchers for many years. Within the framework of these studies mechanical, ultrasonic and electromagnetic vibration applications were carried out. Results of these processes can be summarized as grain refining and changing the dendritic structure into globular. Accordingly increasing in density and mechanical properties were reported. In this work, orbital shaking technique was used alternatively to conventional mechanical vibration in lost foam casting (LFC) of A380 aluminium alloy. In the experiment castings, effects of shaking movement and speed during pouring were investigated. First of all orbital shaking movement has not damage LFC parts and any shape disorder was not occurred. Optical microstructure observations show that, the increase in shaking speed, decrease secondary dendrite arm spacing (SDAS) and partial dendrite arm fractures were determined at 150 rpm shaking. Density and hardness of as cast specimens were increased with shaking and rising shaking speed as well.