Synthesis, characterization, and nonlinear optical properties of donor–acceptor conjugated polymers and polymer/Ag nanocomposites

Two new donor–acceptor (D–A) conjugated polymers P1 and P2 containing 3,4-didodecyloxythiophene and 1,3,4-oxadiazole units are synthesized via Wittig reaction methodology. Cyclic voltammetry studies reveal that the polymers are both p and n dopable, and possess low-lying LUMO energy levels (?3.34?eV for P1 and ?3.46?eV for P2) and high-lying HOMO energy levels (?5.34?eV for P1 and ?5.27?eV for P2). The optical band gap of the polymers is in the range of 2.25–2.29?eV, calculated from the onset absorption edge. The polymers emit orange to yellow light in the film state when irradiated with a UV light. The synthesized polymers are used to prepare polymer nanocomposites with different wt% of silver nanoparticles. The polymer nanocomposites are characterized by UV–Vis absorption spectroscopy, field emission scanning electron microscopy, and thermogravimetric analysis. Both polymers and polymer/Ag nanocomposites show good thermal stability with onset decomposition temperature around 300?°C under nitrogen atmosphere. The nonlinear optical properties of polymers and polymer/Ag nanocomposites are measured by Z-scan technique. Both polymers and polymer nanocomposites show a good optical limiting behavior. Nearly five times enhancement in the nonlinear optical properties is observed for polymer/Ag nanocomposites. The value of effective two-photon absorption coefficient (β) is in the order of 10^?10–10^?11?m/W. These results indicate that the synthesized polymers (P1 and P2) and their Ag nanocomposites are expected to be good candidates for application in photonic devices.     

Highly conductive and porous activated reduced graphene oxide films for high-power supercapacitors

We present a novel method to prepare highly conductive, free-standing, and flexible porous carbon thin films by chemical activation of reduced graphene oxide paper. These flexible carbon thin films possess a very high specific surface area of 2400 m(2) g(-1) with a high in-plane electrical conductivity of 5880 S m(-1). This is the highest specific surface area for a free-standing carbon film reported to date. A two-electrode supercapacitor using these carbon films as electrodes demonstrated an excellent high-frequency response, an extremely low equivalent series resistance on the order of 0.1 ohm, and a high-power delivery of about 500 kW kg(-1). While higher frequency and power values for graphene materials have been reported, these are the highest values achieved while simultaneously maintaining excellent specific capacitances and energy densities of 120 F g(-1) and 26 W h kg(-1), respectively. In addition, these free-standing thin films provide a route to simplify the electrode-manufacturing process by eliminating conducting additives and binders. The synthetic process is also compatible with existing industrial level KOH activation processes and roll-to-roll thin-film fabrication technologies.     

Properties of pulse plated SnSe films

In this work, the pulse electrodeposition technique has been employed for the first time to deposit SnSe films from a bath containing Analar grade 50?mM tin chloride (SnCl₄) and 5?mM SeO₂. The XRD profile of SnSe thin films deposited at different duty cycles indicate the peaks corresponding to SnSe. Atomic force microscopy studies indicated that the surface roughness increased from 0.5 to 1.5?nm with duty cycle. The transmission spectra exhibited interference fringes. The value of refractive index at 780?nm was 2.1, this value decreased to 1.95 with decrease of duty cycle. The room temperature resistivity increased from 0.1 to 10?Ωcm with decrease of duty cycle. Photo electrochemical cell studies were made using the films deposited at different duty cycles. For duty cycles greater than 15% photo output was observed. For a film deposited at 50% duty cycle, an open circuit voltage of 0.55?V and a short circuit current density of 5.0?mA?cm^?2 at 60 mW?cm^?2 illumination. Capacitance voltage measurements indicated V_fb?=?0.67?V (SCE) and p type, carrier density?=?6.98?×?10¹⁶?cm^?3.     

Reduced graphene oxide/tin oxide composite as an enhanced anode material for lithium ion batteries prepared by homogenous coprecipitation

Reduced graphene oxide/tin oxide composite is prepared by homogenous coprecipitation. Characterizations show that tin oxide particles are anchored uniformly on the surface of reduced graphene oxide platelets. As an anode material for Li ion batteries, it has 2140 mAh g⁻¹ and 1080 mAh g⁻¹ capacities for the first discharge and charge, respectively, which is more than the theoretical capacity of tin oxide, and has good capacity retention with a capacity of 649 mAh g⁻¹ after 30 cycles. The simple synthesis method can be readily adapted to prepare other composites containing reduced graphene oxide as a conducting additive that, in addition to supporting metal oxide nanoparticles, can also provide additional Li binding sites to, perhaps, further enhance capacity.     

Effects of<Emphasis Type="Italic"> B</Emphasis>-fields in the Proton Detection Channel of an IEC Device

Proton detection in an IEC device is a complicated task because, unlike the neutron detector, it has to be shielded from X-rays and electrons. Owing to the fusion proton’s short range in matter the proton detectors are placed in the vacuum environment of the device. Also, the proton detectors are vulnerable to damage if exposed to excess light or electrons. The detector is shielded from the light using a Pb shield and, to reduce the electrons reaching the lead shield, a B-field is used. However the B-fields also influence the protons reaching the detector, and hence a good design for the magnet placement is required. In the present paper we investigate the effects of various B-field configurations on the proton detection.     

Analysis of fluid flow in centrifugal casting

Centrifugal casting process is a fast process with melt, cast and moulds being opaque. It is almost impossible to observe the melt behavior during casting. Cold modeling experiments were conducted using horizontal transparent moulds and transparent fluids of different viscosities to study the effect of different process variables on the flow pattern. Effects of the thickness of fluid cylinder, viscosity of the fluid, diameter of the mould, and rotational speed of the mould on the formation of complete hollow fluid cylinder are investigated. The influence of rotational speed has been studied in aluminum casting. The cylinders are cast at different rotational speed with varying thickness. It is observed that the speed required to form uniform cylinder increases with the increase in thickness of a fluid cylinder. As rotational speed is increased the hardness of the cast cylinder also increases. The flow patterns seen in cold modeling experiments and actual castings agree reasonably well.     

A Cost-Effective Ultrasonic Sensor-Based Driver-Assistance System for Congested Traffic Conditions

In urban areas, congested traffic results in a large number of accidents at low speeds. This paper describes an accurate and fast driver-assistance system (DAS) that detects obstacles and warns the driver in advance of possible collisions in such a congested traffic environment. A laboratory prototype of the system is built and tested by simulating different weather conditions in the laboratory. The proposed DAS is also suitable as a parking-assistance system. Ultrasonic sensors are used to detect obstacles in this paper because they have several advantages over other types of sensors in short-range object detection. Multiple sensors are needed to get a full-field view because of the limited lateral detectable range of ultrasonic sensors. Furthermore, crosstalk is a common problem when multiple ultrasonic sensors are used. A simple microcontroller-based method to reduce crosstalk between sensors is described, which is achieved by firing each transducer by a pseudorandom number of pulses so that the echo of each transducer can uniquely be identified. Existing DASs need more time to reliably detect the objects, making them unsuitable for DASs, where time is a critical factor. A method to reduce the obstacle detection time of the system is also proposed. The cost of this high-performance system is expected to be very reasonable. All the practical implementation details are included. Extensive experimentation has been carried out, and the results confirm the speed and reliability of the presented system.     

Effect of Trace Additions (Be,Cr, Mn and Co) on the Mechanical Properties and Fracture Toughness of Fe-containing Al-7Si-0.3Mg Alloy

Abstract

The detrimental effect of iron impurity on the mechanical properties and fracture toughness of Al-7Si-0.3Mg alloy has been widely reported. It is also quite evident that Fe forms the intermetallic compound β-FeSiAl₅, which exists as needles/plates in the interdendritic regions, thereby lowering the mechanical properties. However, very little is known about the methods of counteracting this detrimental effect. The present study has shown that trace additions of Be, Cr, Mn and Co, individually or combined, tie up the iron to form new phases with altered morphology which significantly influence the mechanical properties. Among the trace additions, Be is found to be most effective in neutralising the detrimental effect of Fe on tensile properties. Hardness, tensile and yield strengths, ductility, dynamic fracture toughness (K_d and, K_jd remain constant with an increase in Fe from 0.1 to 0.93% where Be additions are present. Be additions in combination with Mn and/or Cr are also found to nullify the detrimental effect of Fe. However, Be and Mn, when added together, seem to be most effective in providing better tensile properties, than does a Be addition alone or with other additions. The probable reason for good mechanical properties, even in the case of higher-Fe-containing alloys containing a Be addition can be explained as follows: The Be-Fe phases are present inside the α-Al dendrites and act as a preferential site for crack nucleation rather than the Si particles. However, these nucleated cracks are arrested when they approach the α-Al dendrites.     

Designing fault-tolerant real-time computer systems with diversified bus architecture for nuclear power plants

Fault-tolerant real-time computer (FT-RTC) systems are widely used to perform safe operation of nuclear power plants (NPP) and safe shutdown in the event of any untoward situation. Design requirements for such systems need high reliability, availability, computational ability for measurement via sensors, control action via actuators, data communication and human interface via keyboard or display. All these attributes of FT-RTC systems are required to be implemented using best known methods such as redundant system design using diversified bus architecture to avoid common cause failure, fail-safe design to avoid unsafe failure and diagnostic features to validate system operation. In this context, the system designer must select efficient as well as highly reliable diversified bus architecture in order to realize fault-tolerant system design. This paper presents a comparative study between CompactPCI bus and Versa Module Eurocard (VME) bus architecture for designing FT-RTC systems with switch over logic system (SOLS) for NPP.     

Edge doping of graphene sheets

We present a direct comparison between two fundamental methods of chemically doping the 2-dimensional graphene sheet: (1) passivation of dangling σ-bonds resulting from a vacancy defect and (2) charge transfer from adsorption on the pristine basal plane. Using electron beam lithography and the negative tone resist hydrogen silsesquioxane, we are able to observe the doping contribution from the passivation of such defects that naturally reside along the edge of graphene sheets, and directly compare them to the doping limitations of basal plane adsorption methods. We demonstrate that the passivation of the edge is over three orders of magnitude more efficient for chemical doping than adsorption, in terms of conducting carriers donated per available C-atom. Moreover, as large-area graphene sheets are tailored into nanoscale devices, and the portion of C-atoms that occupy the edge increases, we demonstrate that edge decoration becomes a more pronounced method of chemical doping, exhibiting a scaling law that will induce vast carrier densities and dominance over adsorption techniques in the nanoscale.