Dielectric investigation of molecular dynamics of blends: III. Effect of molecular weight in TMPC/PS blends

Dielectric and calorimetric measurements have been carried out for tetramethyl polycarbonate/polystyrene (TMPC/PS) blends with different compositions. The effect of varying the molecular weight of the weakly polar component (PS) on the molecular dynamics of the polar segments of TMPC has been thoroughly studied over wide ranges of frequency (10⁻²−10⁵ Hz), temperature (50–220°C) and number average molecular weight, M̄_n, (6500–560 000 g mol⁻¹). All blends were found to be compatible regardless of the composition ratio and the molecular weight of PS. Some new and interesting experimental findings have been observed concerning the effect of molecular weight on the glass temperature and on the broadness of the glass transition and relaxation. Neither the kinetics nor the distribution of relaxation times of the local process observed in pure TMPC was affected by blending with PS, regardless of the composition ratio or the molecular weight of PS. It has been concluded that the mixing of the polymeric components to form a homogeneous single phase (compatible blend) does not take place on a segmental level but on a structural one. The size of this structural level has been suggested to have the same volume as the cooperative dipoles, which is assumed to be the minimum volume responsible for a uniform glass transition (10–15 nm). The molecular weight dependence of the relaxation characteristics of the glass process and temperature could be attributed to the variation in the size and packing of the structural units.     

Effect of γ-irradiation on the sheet resistance of two-dimensional island platinum films

Four sets (A, B, C, and D) of two-dimensional island platinum films were prepared via the thermal evaporation technique. The mass thicknesses of the films of the different sets are 1, 5, 10, and 20 Å, respectively. The sheet resistance of these films was found experimentally from knowing the d.c. resistance of the films. Before exposing the films to γ-rays, we monitored the increase in the sheet resistance in air with time (aging) till short-term stability for the films was achieved. The stabilized films were exposed to γ-rays such that the different doses are 100, 200, 300, 500, and 700 Gy using ¹³⁷Cs (0.662 MeV) radiation source with dose rate 0.5 Gy/min. It was found that; (i) the sheet resistance of the investigated films decreases with the increase in the dose, (ii) for any particular mass thickness, the value of the fractional change in sheet resistance increases with the increase in dose, (iii) for any particular dose the increase in the fractional change in sheet resistance becomes more pronounced with the increase in mass thickness. Qualitative interpretation for our results was given on the ground that γ-rays changed the shape of islands from spherical to prolate.     

Two phase biomass air-steam gasification model for fluidized bed reactors: Part II—model sensitivity

A sensitivity analysis was performed on the two phase biomass gasification model developed by Sadaka et al. (Biomass Bioenergy) to test its response to variations in three operating parameters (fluidization velocity, steam flow rate and biomass to steam ratio). The model performance criteria included bed temperature, gas compositions, higher heating value and gas production rate. The results showed that the model was sensitive to changes in all operating parameters. The temperatures of the reactor were more influenced by changes in the steam flow rate than those of fluidization velocity and biomass to steam ratio. The steam flow rate has the most effect on the mole fractions of CH₄, and CO₂ followed by the biomass to steam ratio and then the fluidization velocity. In the case of H₂, and CO the biomass to steam ratio has the most effect on their mole fractions followed by the steam flow rate and then fluidization velocity. The fluidization velocity has the most effect on the mole fraction of N₂. The biomass to steam ratio has the most effect on the gas higher heating value and the gas production rate.     

Mass production of CNTs using CVD multi-quartz tubes

Carbon nanotubes (CNTs) have become the backbone of modern industries, including lightweight and heavy-duty industrial applications. Chemical vapor deposition (CVD) is considered as the most common method used to synthesize high yield CNTs. This work aims to develop the traditional CVD for the mass production of more economical CNTs, meeting the growing CNT demands among consumers by increasing the number of three particular reactors. All reactors housing is connected by small channels to provide the heat exchange possibility between the chambers, thereby decreasing synthesis time and reducing heat losses inside the ceramic body of the furnace. The novel design is simple and cheap with a lower reacting time and heat loss compared with the traditional CVD design. Methane, hydrogen, argon, and catalyzed iron nanoparticles were used as a carbon source and catalyst during the synthesis process. In addition, CNTs were produced using only a single quartz tube for comparison. The produced samples were examined using XRD, TEM, SEM, FTIR, and TGA. The results showed that the yield of CNTs increases by 287 % compared with those synthesized with a single quartz tube. Moreover, the total synthesis time of CNTs decreases by 37 % because of decreased heat leakage.

     

Change detection in urban areas from remote sensing data: a multidimensional classification scheme

Change detection (CD) from remote sensing data is a very challenging research problem, especially when we analyse an urban scene. Urban scenes are composed of many different types of objects, both natural and man-made. The building class is one of the important and most complex classes to analyse, important because it is useful for so many applications and complex because it exhibits many changes due to human activity and natural catastrophes. For these reasons, we focus our study on building change detection (BCD). In this paper we propose a classification scheme for BCD research according to several important dimensions including objective, input data, temporal resolution, analysis unit, target output unit, building features, processing technique, change categories, and assessment of results. This classification scheme can guide practitioners in choosing appropriate change detection methods to achieve their goals as well as informing new research efforts. Based on this multidimensional characterisation of BCD, we offer a number of suggestions for further work to be done in this field.     

Optimal economic study of hybrid PV-wind-fuel cell system integrated to unreliable electric utility using hybrid search optimization technique

This study addresses the problem of power outages in distant districts by taking advantage of the available renewable energy resources in the surrounding environment. This was done by proposing connecting the utility to a hybrid system constituting from photovoltaic (PV), wind turbine (WT), and fuel cell (FC) systems where this hybrid system is considered as a backup system that works when the grid is unavailable. This hybrid system proposed is used for feeding the load to a tourist resort in Hurghada, Egypt.The design of the introduced system has taken into consideration the cost of purchasing electric energy and the profit from selling it to the utility network. Component scaling was implemented to improve the net present cost of the proposed system using two grouped meta-heuristic techniques, which are the Hybrid Firefly and Harmony Search optimization technique (HFA/HS) and compared to the particle swarm optimization (PSO) technique.Simulation results have shown that the optimal system for solving the grid unavailability consists of eighty PVs, two WTs, twenty FCs, forty-one electrolyzers, and one hundred eighteen hydrogen tanks. The results also showed that the volume of exchange with the grid has reached 4 GW of purchase and 3 GW of sale. It is manifest from the results that the suggested system is economically viable with an LCOE of 0.0628 $/kWh, which is less than the purchase of electricity from the grid for commercial users in Egypt, which is 0.1 $/kWh.