The recent discovery of graphene has led to many advances in two-dimensional physics and devices. The graphene devices fabricated so far have relied on SiO(2) back gating. Electrochemical top gating ...is widely used for polymer transistors, and has also been successfully applied to carbon nanotubes. Here we demonstrate a top-gated graphene transistor that is able to reach doping levels of up to 5x1013 cm-2, which is much higher than those previously reported. Such high doping levels are possible because the nanometre-thick Debye layer in the solid polymer electrolyte gate provides a much higher gate capacitance than the commonly used SiO(2) back gate, which is usually about 300 nm thick. In situ Raman measurements monitor the doping. The G peak stiffens and sharpens for both electron and hole doping, but the 2D peak shows a different response to holes and electrons. The ratio of the intensities of the G and 2D peaks shows a strong dependence on doping, making it a sensitive parameter to monitor the doping.
Boron‐ and nitrogen‐doped graphenes are are prepared by the arc discharge between carbon electrodes or by the transformation of nanodiamond under appropriate atmospheres. Using a combination of ...experiment and theories based on first principles, systematic changes in the carrier‐concentration and electronic structure of the doped graphenes are demonstrated. Stiffening of the G‐band mode and intensification of the defect‐related D‐band in the Raman spectra are also observed.
Structural health monitoring (SHM) techniques have been studied for several years. An effective approach for SHM is to choose the parameters that are sensitive to the damage occurring in the ...structure but not sensitive to operational or environmental damages. This paper deals with a comparative study among the different vibration-based damage detection methods: fundamental modal examination, local diagnostic method, non-probabilistic methodology and the time series method. All these strategies contemplate different parameters of a structure to recognize damage. Out of the study made, time series analysis proves to more successfully in damage identification than the rest of the methods.
The magnetoelectric composites with chemical compositions (1−x) Ba0.5Sr0.5Zr0.5Ti0.5O3+(x) Ni0.12Mg0.18Cu0.2Zn0.5Fe2O4 (x=20, 40, 60 and 80wt%) was prepared by the conventional solid state reaction ...method. The presence of a biphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric dispersion is observed at lower frequencies due to interfacial polarization arising from the interface of the two phases. At higher frequencies, the dielectric constant is almost constant due to the inability of electric dipoles to follow the first variation of the alternating applied electric field. The dielectric loss shows maxima which are attributed when the hopping frequency of electrons between different ionic sites becomes nearly equal to the frequency of the applied field. The linearity in the log(σAC) vs. log(ω2) plots confirmed the small polaron hopping type of conduction mechanism. The composite materials are found to exhibit an excellent frequency dependence of magnetic properties. In the high frequency range, with increasing ferrite concentration the initial permeability increases and cut-off frequency decreases. An optimal magnetoelectric coupling responding voltage of about 600μVcm−1Oe−1 is obtained for x=20wt% at room temperature.
•XRD patterns confirmed the coexistence of ferroelectric and ferrimagnetic phases.•Dielectric dispersion observed at low frequencies due to interfacial polarization.•Linearity in logσac vs. logω2 is due to small polaron hopping mechanism.•Maximum ME voltage coefficient 600μVcm−1Oe−1 observed for 20% of ferrite.
Characterization of melting process in a Phase Change Material (PCM)-based heat sink with plate fin type thermal conductivity enhancers (TCEs) is numerically studied in this paper. Detailed ...parametric investigations are performed to find the effect of aspect ratio of enclosure and the applied heat flux on the thermal performance of the heat sinks. Various non-dimensional numbers, such as Nusselt number (
Nu), Rayleigh number (
Ra), Stefan number (
Ste) and Fourier number (
Fo) based on a characteristic length scale, are identified as important parameters. The half fin thickness and the fin height are varied to obtain a wide range of aspect ratios of an enclosure. It is found that a single correlation of
Nu with
Ra is not applicable for all aspect ratios of enclosure with melt convection taken into account. To find appropriate length scales, enclosures with different aspect ratios are divided into three categories,
viz. (a) shallow enclosure, (b) rectangular enclosure and (c) tall enclosure. Accordingly, an appropriate characteristic length scale is identified for each type of enclosure and correlation of
Nu with
Ra based on that characteristic length scale is developed.
The effectiveness of thermal conductivity enhancers (TCEs) in improving the overall thermal conductance of phase change materials (PCMs) used in cooling of electronics is investigated numerically. ...With respect to the distribution of TCE and PCM materials, the heat sink designs are classified into two types. The first type of heat sink has the PCM distributed uniformly in a porous TCE matrix, and the second kind has PCM with fins made of TCE material. A transient finite volume method is used to model the heat transfer; phase change and fluid flow in both cases. A generalized enthalpy based formulation and numerical model are used for simulating phase change processes in the two cases. The performance of heat sinks with various volume fractions of TCE for different configurations is studied with respect to the variation of heat source (or chip) temperature with time; melt fraction and dimensionless temperature difference within the PCM. Results illustrate significant effect of the thermal conductivity enhancer on the performance of heat sinks.
In this paper three unlike coordinating contracts namely (i) joint rebate contract (ii) wholesale price discount contract and (iii) cost sharing contract are proposed for two echelon supply chain ...coordination perspective under stock and price induced demand. It is found analytically that the manufacturer׳s and the retailer׳s preferences among three contractual forms are not always aligned. By applying bargaining theory, it is established that stock elasticity plays an important role to select coordination contract and a threshold value stock elasticity is also determined, below which cost sharing contract is not feasible. It is also found that the retailer with higher bargaining power always prefers wholesale price discount contract among considered three contracts. Results are illustrated analytically as well as numerically.
Iron (Fe) toxicity is a major abiotic stress which severely reduces rice yield in many countries of the world. Genetic variation for this stress tolerance exists in rice germplasms. Mapping of ...gene(s)/QTL controlling the stress tolerance and transfer of the traits into high yielding rice varieties are essential for improvement against the stress. A panel population of 119 genotypes from 352 germplasm lines was constituted for detecting the candidate gene(s)/QTL through association mapping. STRUCTURE, GenAlEx and Darwin softwares were used to classify the population. The marker-trait association was detected by considering both the Generalized Linear Model (GLM) and Mixed Linear Model (MLM) analyses. Wide genetic variation was observed among the genotypes present in the panel population for the stress tolerance. Linkage disequilibrium was detected in the population for iron toxicity tolerance. The population was categorized into three genetic structure groups. Marker-trait association study considering both the Generalized Linear Model (GLM) and Mixed Linear Model (MLM) showed significant association of leaf browning index (LBI) with markers RM471, RM3, RM590 and RM243. Three novel QTL controlling Fe-toxicity tolerance were detected and designated as qFeTox4.3, qFeTox6.1 and qFeTox10.1. A QTL reported earlier in the marker interval of C955-C885 on chromosome 1 is validated using this panel population. The present study showed that QTL controlling Fe-toxicity tolerance to be co-localized with the QTL for Fe-biofortification of rice grain indicating involvement of common pathway for Fe toxicity tolerance and Fe content in rice grain. Fe-toxicity tolerance QTL qFeTox6.1 was co-localized with grain Fe-biofortification QTLs qFe6.1 and qFe6.2 on chromosome 6, whereas qFeTox10.1 was co-localized with qFe10.1 on chromosome 10. The Fe-toxicity tolerance QTL detected from this mapping study will be useful in marker-assisted breeding programs.
•Microstructure and corrosion performance are compared for two structural steels.•Microstructure evolution shows primarily ferrite-pearlite in both the steels.•Steels show higher corrosion rate in 1% ...HCl solution than in 3.5% NaCl solution.•The corrosion products show the presence of oxide, hydroxide and oxy-hydroxides.•The corroded surface reveals morphologies like flowery, cotton balls and rosette.
A comparison on microstructure and corrosion performance has been made between the two structural steels used in old railway girder bridge (Sample A) and modern grades of weathering structural steel (Sample B). The microstructures, viewed under optical microscope and scanning electron microscope (SEM), show mainly ferrite-pearlite phase constituents in both the steels, A and B. The phase fraction analysis shows higher amount of pearlite in steel A compared to that of steel B. The grain size of steel A is larger than that of steel B under identical processing condition. The immersion corrosion test in 3.5% NaCl shows that the corrosion rate of steel A increases with time, while the same for steel B decreases with time. On the other hand, corrosion test in 1% HCl shows that the corrosion rate of both steel A and B is higher as compared to that of NaCl which always decreases with time. The XRD analysis of corrosion products show the presence of many oxides, hydroxide and oxy-hydroxide like Lepidocrocite (γ-FeOOH), Goethite (α-FeOOH), Akaganeite (β-FeOOH), Magnetite (Fe3O4) and Maghemite (γ-Fe2O3) in both the steels. The SEM images of corroded surfaces reveal different morphologies like flowery, cotton balls and rosette etc. which indicate that the corrosion products primarily contain Lepidocrocite (γ-FeOOH), Goethite (α-FeOOH) and Akaganeite (β-FeOOH).
Electrocyclic reactions are characterized by the concerted formation and cleavage of both σ and π bonds through a cyclic structure. This structure is known as a pericyclic transition state for ...thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule α-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated π bonds. The σ bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.
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