Graphene on Paper: A Simple, Low-Cost Chemical Sensing Platform

Graphene layers have been transferred directly on to paper without any intermediate layers to yield G-paper. Resistive gas sensors have been fabricated using strips of G-paper. These sensors achieved a remarkable lower limit of detection of similar to 300 parts per trillion (ppt) for NO2, which is comparable to or better than those from other paper-based sensors. Ultraviolet exposure was found to dramatically reduce the recovery time and improve response times. G-paper sensors are also found to be robust against minor strain, which was also found to increase sensitivity. G-paper is expected to enable a simple and inexpensive low-cost flexible graphene platform

Low-Wear High-Friction Behavior of Copper Matrix Composites Dispersed With an In Situ Polymer Derived Ceramic

We show that copper-matrix composites that contain 20 vol. % of an in situ processed, polymer-derived, ceramic phase constituted from Si-C-N have unusual friction-and-wear properties. They show negligible wear despite a coefficient of friction (COF) that approaches 0.7. This behavior is ascribed to the lamellar structure of the composite such that the interlamellar regions are infused with nanoscale dispersion of ceramic particles. There is significant hardening of the composite just adjacent to the wear surface by severe plastic deformation.

Studies on the effects of varying secondary gas properties in a low entrainment ratio supersonic ejector

A dilution cum purge ejector for application in fuel cells represents a domain of ejector operation involving low entrainment ratio with differing secondary and primary gas; which is hardly investigated and a cohesive design framework is not readily available. We comprehensively study a constant area ejector using analytical, experimental and numerical tools at low entrainment ratio (0.004-0.065) with Air, Helium and Argon as secondary gas while the primary gas is Air. For the first time, limits of operating parameters used in control volume method to design the ejector are found to be highly dependent on the secondary molecular weight. The entrainment ratio in the ejector (low for Helium and high for Argon) is affected by the molecular weight and the static pressure within the ejector (low for Air and high for Argon & Helium) by the gamma of the secondary gas. Sufficient suction pressure (0.3-0.55 bar) is generated by the ejector thereby preventing any backflow of secondary gas at all primary stagnation pressures (1.5, 2.2 and 3.1 bar). Numerical results agree well with experimental results. The ejector is shown to completely dilute and purge the secondary flow, meeting all key design requirements. (C) 2014 Elsevier Ltd. All rights reserved.

Co-liposomes of redox-active alkyl-ferrocene modified low MW branched PEI and DOPE for efficacious gene delivery in serum

Herein, we present six new lipopolymers based on low molecular weight, branched polyethylenimine (BPEI 800 Da) which are hydrophobically modified using ferrocene terminated alkyl tails of variable lengths. The effects of degree of grafting, spacer length and the redox state of ferrocene in the lipopolymers on the self assembly properties were investigated in detail by TEM, AFM, DLS and zeta potential measurements. The assemblies displayed an oxidation induced increase in the size of the aggregates. The co-liposomes comprising the lipopolymer and a helper lipid, 1,2-dioleoyl phosphatidyl ethanolamine (DOPE), showed excellent gene (pDNA) delivery capability in a serum containing environment in two cancer cell lines (HeLa and U251 cells). Optimized formulations showed remarkably higher transfection activity than BPEI (25 kDa) and were also significantly better than a commercial transfection reagent, Lipofectamine 2000 as evidenced from both the luciferase activity and GFP expression analysis. Oxidation of ferrocene in the lipopolymers led to drastically reduced levels of gene transfection which was substantiated by reduced cellular internalization of fluorescently labelled pDNA as detected using confocal microscopy and flow cytometry. Moreover, the transfection inactive oxidized lipopolyplexes could be turned transfection active by exposure to ascorbic acid (AA) in cell culture medium during transfection. Endocytosis inhibition experiments showed that gene expression mediated by reduced formulations involved both clathrin and caveolae mediated pathways while the oxidized formulations were routed via the caveolae. Cytotoxicity assays revealed no obvious toxicity for the lipopolyplexes in the range of optimized transfection levels in both the cell lines studied. Overall, we have exploited the redox activity of ferrocene in branched PEI-based efficient polymeric gene carriers whose differential transfection activities could be harnessed for spatial or temporal cellular transfections.

Energy Efficient Memory Decoder Design for Ultra-Low Voltage Systems

This paper presents a low energy memory decoder architecture for ultra-low-voltage systems containing multiple voltage domains. Due to limitations in scalability of memory supply voltages, these systems typically contain a core operating at subthreshold voltages and memories operating at a higher voltage. This difference in voltage provides a timing slack on the memory path as the core supply is scaled. The paper analyzes the feasibility and trade-offs in utilizing this timing slack to operate a greater section of memory decoder circuitry at the lower supply. A 256x16-bit SRAM interface has been designed in UMC 65nm low-leakage process to evaluate the above technique with the core and memory operating at 280 mV and 500 mV respectively. The technique provides a reduction of up to 20% in energy/cycle of the row decoder without any penalty in area and system-delay.

Efficient QR Decomposition Using Low Complexity Column-wise Givens Rotation (CGR)

QR decomposition (QRD) is a widely used Numerical Linear Algebra (NLA) kernel with applications ranging from SONAR beamforming to wireless MIMO receivers. In this paper, we propose a novel Givens Rotation (GR) based QRD (GR QRD) where we reduce the computational complexity of GR and exploit higher degree of parallelism. This low complexity Column-wise GR (CGR) can annihilate multiple elements of a column of a matrix simultaneously. The algorithm is first realized on a Two-Dimensional (2 D) systolic array and then implemented on REDEFINE which is a Coarse Grained run-time Reconfigurable Architecture (CGRA). We benchmark the proposed implementation against state-of-the-art implementations to report better throughput, convergence and scalability.

Operand Isolation Circuits with Reduced Overhead for Low Power Data-Path Design

Dynamic power dissipation due to redundant switching is an important metric in data-path design. This paper focuses on the use of ingenious operand isolation circuits for low power design. Operand isolation attempts to reduce switching by clamping or latching the output of a first level of combinational circuit. This paper presents a novel method using power supply switching wherein both PMOS and NMOS stacks of a circuit are connected to the same power supply. Thus, the output gets clamped or latched to the power supply value with minimal leakage. The proposed circuits make use of only two transistors to clamp the entire Multiple Input Multiple Output (MIMO) block. Also, the latch-based designs have higher drive strength in comparison to the existing methods. Simulation results have shown considerable area reduction in comparison to the existing techniques without increasing timing overhead.

A Time-based Low Voltage Body Temperature Monitoring Unit

A neonatal temperature monitoring system operating in subthreshold regime that utilizes time mode signal processing is presented. Resistance deviations in a thermistor due to temperature variations are converted to delay variations that are subsequently quantized by a Delay measurement unit (DMU). The DMU does away with the need for any analog circuitry and is synthesizable entirely from digital logic. An FPGA implementation of the system demonstrates the viability of employing time mode signal processing, and measured results show that temperature resolution better than 0.1 degrees C can be achieved using this approach.

Low temperature giant magnetocaloric effect in multiferroic GdMnO3 single crystals

Magnetocaloric (MC) properties of GdMnO3 single crystals are investigated using magnetic and magneto-thermal measurements. GdMnO3 exhibits a giant MC effect (isothermal change in magnetic entropy (-Delta S-M) similar to 31 J (kg K)(-1) at 7 K and adiabatic change in temperature similar to 10 K at 19 K for magnetic field variation 0-80 kOe). Complex interactions between 3d and 4f magnetic sublattices influence MC properties. The rare-earth antiferromagnetic ordering induces an inverse MC effect (positive Delta S-M) along `a' and `c' axes whereas it's not seen along the `b' axis, revealing complex anisotropic magnetic ordering. The antiferromagnetic ordering possibly changes to ferromagnetic ordering at higher fields.

A unique strategy towards high dielectric constant and low loss with multiwall carbon nanotubes anchored onto graphene oxide sheets

Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C-C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT-GO hybrid was then melt mixed with 50/50 polyamide6-maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6-mABS) blend to design materials with high dielectric constant (30) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT-GO hybrid was selectively localized in the PA6 phase of the blend. The 30 scales with the concentration of MWNT-GO in the blends, which interestingly showed a very low dielectric loss (< 0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT-GO in the blends, demonstrating their reinforcing capability as well.

Reduced Hornbill Abundance Associated with Low Seed Arrival and Altered Recruitment in a Hunted and Logged Tropical Forest

Logging and hunting are two key direct threats to the survival of wildlife in the tropics, and also disrupt important ecosystem processes. We investigated the impacts of these two factors on the different stages of the seed dispersal cycle, including abundance of plants and their dispersers and dispersal of seeds and recruitment, in a tropical forest in north-east India. We focused on hornbills, which are important seed dispersers in these forests, and their food tree species. We compared abundances of hornbill food tree species in a site with high logging and hunting pressures (heavily disturbed) with a site that had no logging and relatively low levels of hunting (less disturbed) to understand logging impacts on hornbill food tree abundance. We compared hornbill abundances across these two sites. We, then, compared the scatter-dispersed seed arrival of five large-seeded tree species and the recruitment of four of those species. Abundances of hornbill food trees that are preferentially targeted by logging were two times higher in the less disturbed site as compared to the heavily disturbed site while that of hornbills was 22 times higher. The arrival of scatter-dispersed seeds was seven times higher in the less disturbed site. Abundances of recruits of two tree species were significantly higher in the less disturbed site. For another species, abundances of younger recruits were significantly lower while that of older recruits were higher in the heavily disturbed site. Our findings suggest that logging reduces food plant abundance for an important frugivore-seed disperser group, while hunting diminishes disperser abundances, with an associated reduction in seed arrival and altered recruitment of animal-dispersed tree species in the disturbed site. Based on our results, we present a conceptual model depicting the relationships and pathways between vertebrate-dispersed trees, their dispersers, and the impacts of hunting and logging on these pathways.

Low Complexity Power and Scheduling Policies for Wireless Networks to Provide Quality of Service

We consider optimal power allocation policies for a single server, multiuser system. The power is consumed in transmission of data only. The transmission channel may experience multipath fading. We obtain very efficient, low computational complexity algorithms which minimize power and ensure stability of the data queues. We also obtain policies when the users may have mean delay constraints. If the power required is a linear function of rate then we exploit linearity and obtain linear programs with low complexity.

EXPERIENCE OF OPERATING OPEN TOP BIOMASS GASIFIER USING A LOW DENSITY FUEL-COCONUT FRONDS

Use of fuel other than woody generally has been limited to rice husk and other residues are rarely tried as a fuel in a gasification system. With the availability of woody biomass in most countries like India, alternates fuels are being explored for sustainable supply of fuel. Use of agro residues has been explored after briquetting. There are few feedstock's like coconut fronts, maize cobs, etc, that might require lesser preprocessing steps compared to briquetting. The paper presents a detailed investigation into using coconut fronds as a fuel in an open top down draft gasification system. The fuel has ash content of 7% and was dried to moisture levels of 12 %. The average bulk density was found to be 230 kg/m3 with a fuel size particle of an average size 40 mm as compared to 350 kg/m3 for a standard wood pieces. A typical dry coconut fronds weighs about 2.5kgs and on an average 6 m long and 90 % of the frond is the petiole which is generally used as a fuel. The focus was also to compare the overall process with respect to operating with a typical woody biomass like subabul whose ash content is 1 %. The open top gasification system consists of a reactor, cooling and cleaning system along with water treatment. The performance parameters studied were the gas composition, tar and particulates in the clean gas, water quality and reactor pressure drop apart from other standard data collection of fuel flow rate, etc. The average gas composition was found to be CO 15 1.0 % H-2 16 +/- 1% CH4 0.5 +/- 0.1 % CO2 12.0 +/- 1.0 % and rest N2 compared to CO 19 +/- 1.0 % H-2 17 +/- 1.0 %, CH4 1 +/- 0.2 %, CO2 12 +/- 1.0 % and rest N2. The tar and particulate content in the clean gas has been found to be about 10 and 12 mg/m3 in both cases. The presence of high ash content material increased the pressure drop with coconut frond compared to woody biomass.

Low-frequency dc bus ripple cancellation in single phase pulse-width modulation inverters

This study presents a topology for a single-phase pulse-width modulation (PWM) converter which achieves low-frequency ripple reduction in the dc bus even when there are grid frequency variations. A hybrid filter is introduced to absorb the low-frequency current ripple in the dc bus. The control strategy for the proposed filter does not require the measurement of the dc bus ripple current. The design criteria for selecting the filter components are also presented in this study. The effectiveness of the proposed circuit has been tested and validated experimentally. A smaller dc-link capacitor is sufficient to keep the low-frequency bus ripple to an acceptable range in the proposed topology.

New single-source precursor for bismuth sulfide and its use as low-cost counter electrode material for dye-sensitized solar cells

One new homoleptic Bi(dtc)(3)] (1) (dtc = 4-hydroxypiperdine dithiocarbamate) has been synthesized and characterized by microanalysis, IR, UV-Vis, H-1 and C-13 spectroscopy and X-ray crystallography. The photoluminescence spectrum for the compound in DMSO solution was recorded. The crystal structure of 1 displayed distorted octahedral geometry around the Bi(III) center bonded through sulfur atoms of the dithiocarbamate ligands. TGA indicates that the compound decomposes to a Bi and Bi-S phase system. The Bi and Bi-S obtained from decomposition of the compound have been characterized by pXRD, EDAX and SEM. Solvothermal decomposition of 1 in the absence and presence of two different capping agents yielded three morphologically different Bi2S3 systems which were deployed as counter-electrode in dye-sensitized solar cells (DSSCs). (C) 2015 Elsevier B.V. All rights reserved.