Tailoring energy absorption capacity of CNT forests through application of electric field

This study examines the effect of electric field on energy absorption capacity of carbon nanotube forests (CNTFs), comprising of vertically aligned multiwalled carbon nanotubes, under both quasistatic (strain rate, (epsilon) over dot = 10(-3) s(-1)) and dynamic ((epsilon) over dot = similar to 10(3) s(-1)) loading conditions. Under quasistatic condition, the CNTFs were cyclically loaded and unloaded while electric field was applied along the length of carbon nanotube (CNT) either throughout the loading cycle or explicitly during either the loading or the unloading segment. The energy absorbed per cycle by CNTF increased monotonically with electric field when the field was applied only during the loading segment: A 7 fold increase in the energy absorption capacity was registered at an electric field of 1 kV/m whereas no significant change in it was noted for other schemes of electro-mechanical loading. The energy absorption capacity of CNTF under dynamic loading condition also increased monotonically with electric field; however, relative to the quasistatic condition, less pronounced effect was observed. This intriguing strain rate dependent effect of electric field on energy absorption capacity of CNTF is explained in terms of electric field induced strengthening of CNTF, originating from the time dependent electric field induced polarization of CNT. (C) 2015 Elsevier Ltd. All rights reserved.

Tailored nitrogen dioxide sensing response of three-dimensional graphene foam

Ultralight and macroporous three-dimensional reduced graphene oxide (rGO) foams are prepared by lyophilization (freeze-drying) technique to avoid a conventional template method. This method allows tailoring the porosity of the foams by varying the weight percentages of graphene oxide dispersions in water. Three different rGO foams of 0.2, 0.5 and 1.0 wt% are used for NO2 sensing. Sensing response from the tailored structure of rGO is found to be directly related to the density. A maximum of 20% sensing response is observed for a higher porosity of the structure, better than the known results so far on graphene foams in the literature. (C) 2015 Elsevier B.V. All rights reserved.

Synthesis of ZnO nanorods on a flexible Phynox alloy substrate: influence of growth temperature on their properties

A novel flexible alloy substrate (Phynox, 50 mm thick) was used for the synthesis of zinc oxide (ZnO) nanorods via a low-temperature solution growth method. The growth of ZnO nanorods was observed over a low temperature range of 60-90 degrees C for a growth duration of 4 hours. The as-synthesized nanorods were characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) for their morphology, crystallinity, microstructure and composition. The as-grown ZnO nanorods were observed to be relatively vertical to the substrate. However, the morphology of the ZnO nanorods in terms of their length, diameter and aspect ratio was found to vary with the growth temperature. The morphological variation was mainly due to the effects of the various relative growth rates observed at the different growth temperatures. The growth temperature influenced ZnO nanorods were also analyzed for their wetting (either hydrophobic or hydrophilic) properties. After carrying out multiple wetting behaviour analyses, it has been found that the as-synthesized ZnO nanorods are hydrophobic in nature. The ZnO nanorods have potential application possibilities in self-cleaning devices, sensors and actuators as well as energy harvesters such as nanogenerators.

Thermal Modeling of Organic Light-Emitting Diode Display Panels

Power densities required to operate active-matrix organic-light-emitting diode (AMOLED) based displays for high luminance applications, lead to temperature rise due to self heating. Temperature rise leads to significant degradation and consequent reduction in life time. In this work numerical techniques based computational fluid dynamics (CFD) is used to determine the temperature rise and its distribution for an AMOLED based display for a given power density and size. Passive cooling option in form of protruded rectangular fins is implemented to reduce the display temperature.

Ascorbate Protects Neurons against Oxidative Stress: A Raman Microspectroscopic Study

Oxidative stress due to excessive accumulation of reactive oxygen or nitrogen species in the brain as seen in certain neurodegenerative diseases can have deleterious effects on neurons. Hydrogen peroxide, endogenously generated in neurons under normal physiological conditions, can produce an excess of hydroxyl radical via a Fenton mediated mechanism. This may induce acute oxidative injury if not scavenged or removed effectively by antioxidants. There are several biochemical assay methods to estimate oxidative injury in cells; however, they do not provide information on the biochemical changes as the cells get damaged progressively under oxidative stress. Raman microspectroscopy offers the possibility of real time monitoring of the chemical composition of live cells undergoing oxidative stress under physiological conditions. In the present study, a hippocampal neuron coculture was used to observe the acute impact of hydroxyl radicals generated by hydrogen peroxide in the presence of Fe2+ (Fenton reaction). Raman peaks related to nucleic acids (725, 782, 1092, 1320, 1340, 1420, and 1576 cm(-1)) showed time-dependent changes over the experimental period (60 mm), indicating the breakdown of the phosphodiester backbone as well as nuclear bases. Interestingly, ascorbic acid (a potent antioxidant) when cotreated with Fenton reactants showed protection of cells as inferred from the Raman spectra, presumably by scavenging hydroxyl radicals. Little or no change in the Raman spectra was observed for untreated control cells and for cells exposed to Fe2+ only, H2O2 only, and ascorbate only. A live dead assay study also supported the current observations. Hence, Raman microspectroscopy has the potential to be an excellent noninvasive tool for early detection of oxidative stress that is seen in neurodegenerative diseases.

Cadmium Sulfide Nanocrystal Sensitized Vertically Aligned Titanium Dioxide Rods for Large Area Image Sensors on 3-D Substrates

We discuss here a semiconductors assembly comprising of titanium dioxide (TiO2) rods sensitized by cadmium sulfide (CdS) nanocrystals for potential applications in large area electronics on three dimensional (3-D) substrates. Vertically aligned TiO2 rods are grown on a substrate using a 150 degrees C process flow and then sensitized with CdS by SILAR method at room temperature. This structure forms an effective photoconductor as the photo-generated electrons are rapidly removed from the CdS via the TiO2 thereby permitting a hole rich CdS. Current-voltage characteristics are measured and models illustrate space charge limited photo-current as the mechanism of charge transport at moderate voltage bias. The stable assembly and high speed are achieved. The frequency response with a loading of 10 pF and 9 M Omega shows a half power frequency of 100 Hz. (C) 2015 The Electrochemical Society. All rights reserved.

A Mitigation Technique for Harmonic Downconversion in Wideband Spectrum Sensors

The down conversion of radio frequency components around the harmonics of the local oscillator (LO), and its impact on the accuracy of white space detection using integrated spectrum sensors, is studied. We propose an algorithm to mitigate the impact of harmonic downconversion by utilizing multiple parallel downconverters in the system architecture. The proposed algorithm is validated on a test-board using commercially available integrated circuits and a test-chip implemented in a 130-nm CMOS technology. The measured data show that the impact of the harmonic downconversion is closely related to the LO characteristics, and that much of it can be mitigated by the proposed technique.

Sulfurization of sputtered Ag-In precursors for AgInS2 solar cell absorber layers

Silver indium sulfide (AgInS2) thin films are deposited by sequential sputtering of metallic precursor Ag/In] followed by sulfurization. Effect of substrate temperature (Tsub) during sulfurization process on the film growth is studied by varying the substrate temperature from 350 to 500 degrees C. Films prepared above 350 degrees C showed a mixture of orthorhombic and tetragonal phases of AgInS2 with tetragonal phase being dominant. Better crystalline, nearly stoichiometric and p-type films are obtained at a substrate temperature of 500 degrees C. The characteristic A(1) mode of AgInS2 chalcopyrite structure is observed in the Raman spectra at 274 cm(-1) for the films prepared above 350 degrees C. The grain size of the film increases from 489 to 895 nm with the increase in substrate temperature. The binding energies of the constituent elements are determined using XPS. The band gap of AgInS2 films is in the range of 1.64-1.92 eV and the absorption coefficient is found to be >10(4) cm(-1). Preliminary studies on the AgInS2/ZnS solar cell showed an efficiency of 0.3%. (C) 2015 Elsevier B.V. All rights reserved.

Surface modification of titania aerogel films by oxygen plasma treatment for enhanced dye adsorption

Titania aerogels were synthesized by sol-gel route followed by ambient pressure subcritical drying technique. The aerogels synthesized in the present work possess a maximum surface area of 252 m(2)/g. The pore size distribution is between 2 and 30 nm which confirms their mesoporosity. The oxygen plasma treatment on titania aerogel thin films improved the surface area up to 273 m(2)/g and produced additional hydrophilic groups on the surface. It is confirmed by BET surface area, XPS and thermal analysis in conjunction with dye adsorption studies. After plasma treatment the dye adsorption capacity was increased 2.5 times higher than that of untreated aerogel film. The increased surface area and the hydrophilic groups generated on the titania aerogel surface during plasma treatment are responsible for enhanced dye adsorption. The overall nanoporous morphology of titania aerogel is preserved after plasma treatment. (C) 2015 Elsevier B.V. All rights reserved.

Temperature dependent compressive behavior of graphene mediated three-dimensional cellular assembly

Mechanical behavior of three-dimensional cellular assembly of graphene foam (GF) presented temperature dependent characteristics evaluated at both low temperature and room temperature conditions. Cellular structure of GF comprised of polydimethyl siloxane polymer as a flexible supporting material demonstrated 94% enhancement in the storage modulus as compared to polymer foam alone. Evaluation of frequency dependence revealed an increase in both storage modulus and tan delta with the increase in frequency. Moreover, strain rate independent highly reversible behavior is measured up to several compression cycles at larger strains. It is elucidated that the interaction between graphene and polymer plays a crucial role in thermo-mechanical stability of the cellular structure. (C) 2015 Elsevier Ltd. All rights reserved.

Peristaltic pump-based low range pressure sensor calibration system

Peristaltic pumps were normally used to pump liquids in several chemical and biological applications. In the present study, a peristaltic pump was used to pressurize the chamber (positive as well negative pressures) using atmospheric air. In the present paper, we discuss the development and performance study of an automatic pressurization system to calibrate low range (millibar) pressure sensors. The system includes a peristaltic pump, calibrated pressure sensor (master sensor), pressure chamber, and the control electronics. An in-house developed peristaltic pump was used to pressurize the chamber. A closed loop control system has been developed to detect and adjust the pressure leaks in the chamber. The complete system has been integrated into a portable product. The system performance has been studied for a step response and steady state errors. The system is portable, free from oil contaminants, and consumes less power compared to existing pressure calibration systems. The veracity of the system was verified by calibrating an unknown diaphragm based pressure sensor and the results obtained were satisfactory. (C) 2015 AIP Publishing LLC.

Ultra sensitive NO2 gas detection using the reduced graphene oxide coated etched fiber Bragg gratings

We report a simple and highly sensitive methodology for the room temperature NO2 gas sensing using reduced graphene oxide (RGO) coated clad etched fiber Bragg grating (eFBG). A significant shift (>10 pm) is observed in the reflected Bragg wavelength (lambda(B)) upon exposing RGO coated on the surface of eFBG to the NO2 gas molecules of concentration 0.5 ppm. The shift in Bragg wavelength is due to the change in the refractive index of RGO by charge transfer from the adsorbing NO2 molecules. The range of NO2 concentration is tested from 0.5 ppm to 3 ppm and the estimated time taken for 50% increase in Delta lambda(B) ranges from 20 min (for 0.5 ppm) to 6 min (for 3 ppm). (C) 2015 Elsevier B.V. All rights reserved.

Effect Of High Pressure On The Electrical Resistivity Of Ge-Te In Glasses

The variation in the electrical resistivity of the chalcogenide glasses Ge15Te85-x has been studied as a function of high pressure for pressures up to 8.5GPa. All the samples studied undergo a semi-conductor to metallic transition in a continuous manner at pressures between 1.5-2.5GPa. The transition pressure at which the samples turn metallic increases with increase in percentage of Indium. This increase is a direct consequence of the increase in network rigidity with the addition of Indium. At a constant pressure of 0.5GPa, the normalized resistivity shows some signature of the existence of the intermediate phase. Samples recovered after a pressure cycle remain amorphous suggesting that the semi-conductor to metallic transition arises from a reduction of the band gap due to pressure or the movement of the Fermi level into the conduction or valence band.

A Method for Delineation of Bone Surfaces in Photoacoustic Computed Tomography of the Finger

Photoacoustic (PA) imaging of interphalangeal peripheral joints is of interest in the context of using the synovial membrane as a surrogate marker of rheumatoid arthritis. Previous work has shown that ultrasound (US) produced by absorption of light at the epidermis reflects on the bone surfaces within the finger. When the reflected signals are backprojected in the region of interest, artifacts are produced, confounding interpretation of the images. In this work, we present an approach where the PA signals known to originate from the epidermis are treated as virtual US transmitters, and a separate reconstruction is performed as in US reflection imaging. This allows us to identify the bone surfaces. Furthermore, the identification of the joint space is important as this provides a landmark to localize a region-of-interest in seeking the inflamed synovial membrane. The ability to delineate bone surfaces allows us to identify not only the artifacts but also the interphalangeal joint space without recourse to new US hardware or a new measurement. We test the approach on phantoms and on a healthy human finger.

Molecular profiling of sepsis in mice using Fourier Transform Infrared Microspectroscopy

Sepsis is a life threatening condition resulting from a high burden of infection. It is a major health care problem and associated with inflammation, organ dysfunction and significant mortality. However, proper understanding and delineating the changes that occur during this complex condition remains a challenge. A comparative study involving intra-peritoneal injection of BALB/c mice with Salmonella Typhimurium (infection), lipopolysaccharide (endotoxic shock) or thioglycollate (sterile peritonitis) was performed. The changes in organs and sera were profiled using immunological assays and Fourier Transform Infrared (FTIR) micro-spectroscopy. There is a rapid rise in inflammatory cytokines accompanied with lowering of temperature, respiratory rate and glucose amounts in mice injected with S. Typhimurium or lipopolysaccharide. FTIR identifies distinct changes in liver and sera: decrease in glycogen and protein/lipid ratio and increase in DNA and cholesteryl esters. These changes were distinct from the pattern observed in mice treated with thioglycollate and the differences in the data obtained between the three models are discussed. The combination of FTIR spectroscopy and other biomarkers will be valuable in monitoring molecular changes during sepsis. GRAPHICS] Intra-peritoneal infection with high dose of Salmonella Typhimurium leads to rapid increase in inflammatory cytokines, e.g. Tnf alpha (A). FTIR analysis of liver (B) and sera (C) identifies several metabolic changes: glycogen, protein/lipid, cholesteryl esters and DNA.