Using hop bines as reinforcements for lightweight polypropylene composites

Whole hop bines (HBs), the peeled outer bark (OB) of HBs, and fibers chemically extracted from hop bark (HFs) were used as reinforcements to make lightweight composites with polypropylene (PP) webs or fibers as the matrix materials. Using discarded HBs for composites not only increases the value of hop crops but also provides a green, sustainable, and biodegradable material for the composite industry. Lightweight composites are preferred, especially for automotive applications because of the potential energy savings. In this research, the effects of the processing parameters on the properties of PP composites reinforced with HBs were studied. The composites reinforced with OB without any chemical treatment showed better properties than the composites reinforced with HFs or HBs. Compared with jute–PP composites of the same density (0.47 g/cm³), composites reinforced with OB had 43% higher flexural strength, 46% higher impact resistance, 56% higher Young's modulus, similar modulus of elasticity, 33% lower tensile strength, and better sound‐absorption properties. OB–PP composites with optimized properties have the potential to be used in industrial applications such as support layers in automotive interiors, ceiling tiles, and office panels. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of poly(vinyl alcohol)/water glass (SiO2) nano‐hybrids via sol‐gel process

A new class of materials based on inorganic and organic species combined at a nanoscale level has received large attention recently. In this work the idea of producing hybrid materials with controllable properties is applied to obtain foams to be used as catalyst supporting. Hybrids were synthesized by reacting poly(vinyl alcohol) in acidic solution with water glass. The inorganic phase was also modified by incorporating a hexamethyldisiloxane as precursor. The hybrid aerogel powder was analyzed by scanning electron microscopy, TG‐DTA, Nitrogen adsorption–desorption, X‐ray diffraction and fourier transform infrared spectroscopy (FTIR) spectroscopy. The powder obtained had a higher porosity varying from 65 to 90% and the nanopore diameter ranged from 17 to 20 nm. The surface area and nanopore volume decreased as polymer content increased in the hybrids. The sharp decline in the weight observed at around 500°C accompanied an exothermic peak of the DTA curve. The sharp peak was observed around 211°C represents the DTA curve of Poly vinyl alcohol constituent in nano hybrids. The peak at 1638 cm^?1 in the FTIR indicated the formation of Si? O? PVA? O? Si bridge in aerogel powder. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Direct torque control of induction motor based on advanced discontinuous PWM algorithm for reduced current ripple

In recent years several discontinuous pulse width modulation (DPWM) methods are reported to improve the performance of AC drives at high modulation indices. It is proved that the performance of the popular PWM methods is modulation index dependent and no single DPWM method provides satisfactory performance over the entire high modulation range. Two popular existing DPWM methods renowned with the names DPWMMIN, DPWMMAX clamp each phase for 120° duration in every cycle of its fundamental voltage. It is observed that only the zero state is different in these two sequences. In this paper, it is proposed that, utilizing these two DPWM sequences and by changing the zero state at any spatial angle γ, where γ is between 0° and 60°, an infinite number of DPWM sequences including the existing DPWM methods and advanced DPWM (ADPWM) methods can be generated which are categorized as “continual clamping” and “split clamping” sequences. Using these ADPWM techniques an optimal split clamping sequence-based DTC of induction motor is proposed. With the proposed DTC method it is shown that steady state line current distortion at higher line side voltages is reduced significantly compared with the CDTC as well as conventional SVPWM (CSVPWM)-based DTC.     

Fabrication of copper–TiC–graphite hybrid metal matrix composites through microwave processing

The significant requirements such as wear resistance and better tribological properties in addition to good electrical conductivity necessitate the development of copper-based advanced metal matrix composites for electrical sliding contact applications. Though the addition of graphite to copper matrix induces self-lubricating property, the strength of the composite reduces. The improvement in the strength of the composite can be achieved by reinforcing harder ceramic particles such as SiC, TiC, and Al₂O₃. In this paper, the development of hybrid composite of copper metal matrix reinforced with TiC and graphite particles through microwave processing was investigated. The effects of TiC (5, 10, and 15 vol.%) and graphite (5 and 10 vol.%) reinforcements on physical and mechanical properties of microwave-sintered copper–TiC–graphite hybrid composites are discussed in detail. Micrographs show the uniform distribution of reinforcements in copper matrix. Microwave-sintered composites exhibited higher relative density, sintered density, and hardness compared with conventionally sintered ones.     

Temporal and spectral characteristics of aerosol optical depths in a semi-arid region of southern India

The spectral and temporal variations of aerosol optical depths (AOD) observed over Anantapur (a semi-arid region) located in the Southern part of India are investigated by analyzing the data obtained from a Multiwavelength Solar Radiometer (MWR) during January 2005-December 2006 (a total of 404 clear-sky observations) using the Langley technique. In this paper, we highlighted the studies on monthly, seasonal and spectral variations of aerosol optical depth and their implications. The results showed seasonal variation with higher values during pre-monsoon (March-May) and lower in the monsoon (June-November) season at all wavelengths. The pre-monsoon increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The post-monsoon (December-February) AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. Also during the post-monsoon, direction of winds in association with high or low pressure weather systems and the air brings more aerosol content to the region which is surrounded by a number of cement plants, lime kilns, slab polishing and brick making units. The quantity of AOD values in pre-monsoon is higher (low during post-monsoon) for wavelength, such as shortwave infrared (SWIR) or near infrared (NIR), which shows that coarse particles contribute more compare with the sub-micron particles. The composite aerosols near the surface follow suit with the share of the accumulation mode to the total mass concentration decreasing from ~ 70% to 30% from post-monsoon to pre-monsoon. Coarse mode particle loading observed to be high during pre-monsoon and accumulation mode particles observed to be high during post-monsoon. The backward trajectories at three representative altitudes with source point at the observing site indicate a possible transport from the outflow regions into Bay of Bengal, southern peninsular India and Arabian Sea. The temporal variations of AOD, Angstrom wavelength exponent and precipitable water content over Anantapur have also been compared with those reported from selected locations in India.     

Synthesis and nonlinear optical properties of Lead Telluride nanorods

Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (γ) are in the order of 10⁻²² m³ W⁻² and for femtosecond excitation it is in the order of 10⁻²⁹ m³ W⁻². The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications.     

Minimally invasive injectable short nanofibers of poly(glycerol sebacate) for cardiac tissue engineering

Myocardial tissue lacks the ability to appreciably regenerate itself following myocardial infarction (MI) which ultimately results in heart failure. Current therapies can only retard the progression of disease and hence tissue engineering strategies are required to facilitate the engineering of a suitable biomaterial to repair MI. The aim of this study was to investigate the in?vitro properties of an injectable biomaterial for the regeneration of infarcted myocardium. Fabrication of core/shell fibers was by co-axial electrospinning, with poly(glycerol sebacate) (PGS) as core material and poly-l-lactic acid (PLLA) as shell material. The PLLA was removed by treatment of the PGS/PLLA core/shell fibers with DCM:hexane (2:1) to obtain PGS short fibers. These PGS short fibers offer the advantage of providing a minimally invasive injectable technique for the regeneration of infarcted myocardium. The scaffolds were characterized by SEM, FTIR and contact angle and cell-scaffold interactions using cardiomyocytes. The results showed that the cardiac marker proteins actinin, troponin, myosin heavy chain and connexin 43 were expressed more on short PGS fibers compared to PLLA nanofibers. We hypothesized that the injection of cells along with short PGS fibers would increase cell transplant retention and survival within the infarct, compared to the standard cell injection system.     

Structures and performances of simultaneous ultrasound and alkali treated oil palm empty fruit bunch fiber reinforced poly(lactic acid) composites

In this study composites were produced using extrusion followed by injection molding with alkali and ultrasound treated oil palm empty fruit bunch (EFB) fibers with poly(lactic acid). The fiber content, alkali solution concentration, exposing time and treatment temperature were optimized. The optimized EFB fibers were treated with hyper branched polyester solution. The composites were characterized by tensile testing, impact testing, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and Fourier transformation infra-red spectroscopy. A significant increase in mechanical and interfacial properties was found for composites due to simultaneous alkali and ultrasound treatment.     

Epitaxial Ni?Mn?Ga Films for Magnetic Shape Memory Alloy Microactuators

Active materials such as piezoelectrics are established in the field of microsystems application despite their low achievable strains which often require the integration of additional gear mechanisms. The ongoing search for new active materials has focused on magnetic shape memory (MSM) alloys such as Ni? Mn? Ga since they combine macroscopic strains of up to 10% with a cycling frequency well above the frequencies of conventional thermal shape memory alloys. The present review focuses on preparation and analysis of Ni? Mn? Ga films that can eventually be integrated in microsystems. Single crystal like films are prepared by epitaxial growth on suitable substrate materials. Since the magnetically induced reorientation of variants is blocked by a rigid substrate, we present different methods for releasing films from the substrates. We show that the sacrificial layer technology is the most promising approach. Further processing of the freestanding film requires a microtechnology which is adjusted to the film laminate structure. The properties of the freestanding films are compared with films on a rigid substrate. Although we observe stress‐induced twin boundary motion, the twinning stress is too high to be overcome by an external magnetic field. Therefore, it is necessary to develop suitable training methods to reduce the twinning stress below 2 MPa to enable the activation of the material by means of an external magnetic field.     

3D nanoporous nanowire current collectors for thin film microbatteries

Conventional thin film batteries are fabricated based on planar current collector designs where the high contact resistance between the current collector and electrodes impedes overall battery performance. Hence, current collectors based on 3D architectures and nanoscale roughness has been proposed to dramatically increase the electrode-current collector surface contact areas and hence significantly reduce interfacial resistance. The nanorod-based current collector configuration is one of several 3D designs which has shown high potential for the development of high energy and high power microbatteries in this regard. Herein we fabricate a nanoporous nanorod based current collector, which provides increased surface area for electrode deposition arising from the porosity of each nanorods, yet keeping an ordered spacing between nanorods for the deposition of subsequent electrolyte and electrode layers. The new nanostructured 3D current collector is demonstrated with a polyaniline (PANI)-based electrode system and is shown to deliver improved rate capability characteristics compared to planar configurations. We have been able to achieve stable capacities of ~32 μAh/cm(2) up to 75 cycles of charge/discharge even at a current rate of ~0.04 mA/cm(2) and have observed good rate capability even at high current rates of ~0.8 mA/cm(2).