Analytical solutions for transient temperature distribution in a geothermal reservoir due to cold water injection

An analytical solution to describe the transient temperature distribution in a geothermal reservoir in response to injection of cold water is presented. The reservoir is composed of a confined aquifer, sandwiched between rocks of different thermo-geological properties. The heat transport processes considered are advection, longitudinal conduction in the geothermal aquifer, and the conductive heat transfer to the underlying and overlying rocks of different geological properties. The one-dimensional heat transfer equation has been solved using the Laplace transform with the assumption of constant density and thermal properties of both rock and fluid. Two simple solutions are derived afterwards, first neglecting the longitudinal conductive heat transport and then heat transport to confining rocks. Results show that heat loss to the confining rock layers plays a vital role in slowing down the cooling of the reservoir. The influence of some parameters, e.g. the volumetric injection rate, the longitudinal thermal conductivity and the porosity of the porous media, on the transient heat transport phenomenon is judged by observing the variation of the transient temperature distribution with different values of the parameters. The effects of injection rate and thermal conductivity have been found to be profound on the results.

Self Catalytic Growth of Indium Oxide (In2O3) Nanowires by Resistive Thermal Evaporation

Self catalytic growth of Indium Oxide (In2O3) nanowires (NWs) have been grown by resistive thermal evaporation of Indium (In) in the presence of oxygen without use of any additional metal catalyst. Nanowires growth took place at low substrate temperature of 370-420 degrees C at an applied current of 180-200 A to the evaporation boat. Morphology, microstructures, and compositional studies of the grown nanowires were performed by employing field emission scanning electron microscopy (FESEM), X-Ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) respectively. Nanowires were uniformly grown over the entire Si substrate and each of the nanowire is capped with a catalyst particle at their end. X-ray diffraction study reveals the crystalline nature of the grown nanowires. Transmission electron microscopy study on the nanowires further confirmed the single crystalline nature of the nanowires. Energy dispersive X-ray analysis on the nanowires and capped nanoparticle confirmed that Indium act as catalyst for In2O3 nanowires growth. A self catalytic Vapor-Liquid-Solid (VLS) growth mechanism was responsible for the growth of In2O3 nanowires. Effect of oxygen partial pressure variation and variation of applied currents to the evaporation boat on the nanowires growth was systematically studied. These studies concluded that at oxygen partial pressure in the range of 4 x 10(-4), 6 x 10(-4) mbar at applied currents to the evaporation boat of 180-200 A were the best conditions for good nanowires growth. Finally, we observed another mode of VLS growth along with the standard VLS growth mode for In2O3 nanowires similar to the growth mechanism reported for GaAs nanowires.

Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250-400 degrees C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (similar to 10-15 nm) and micron long ITO NWs growth was observed in a temperature window of 300-400 degrees C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300-400 degrees C have shown similar to 2-6% reflection and similar to 70-85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.

Novel spherical hierarchical structures of GdOOH and Eu:GdOOH: rapid microwave-assisted synthesis through self-assembly, thermal conversion to oxides, and optical studies

We report a novel, rapid, and low-temperature method for the synthesis of undoped and Eu-doped GdOOH spherical hierarchical structures, without using any structure-directing agents, through the microwave irradiation route. The as-prepared product consists of nearly monodisperse microspheres measuring about 1.3 mu m in diameter. Electron microscopy reveals that each microsphere is an assembly of two-dimensional nanoflakes (about 30 nm thin) which, in turn, result from the assembly of crystallites measuring about 9 nm in diameter. Thus, a three-level hierarchy can be seen in the formation of the GdOOH microspheres: from nanoparticles to 2D nanoflakes to 3D spherical structures. When doped with Eu3+ ions, the GdOOH microspheres show a strong red emission, making them promising candidates as phosphors. Finally, thermal conversion at modest temperatures leads to the formation of corresponding oxide structures with enhanced luminescence, while retaining the spherical morphology of their oxyhydroxide precursor.

Self-assembled dipeptide nanotubes constituted by flexible beta-phenylalanine and conformationally constrained alpha,beta-dehydrophenylalanine residues as drug delivery system

Peptide based self assembled nanostructures have attracted growing interest in recent years due to their numerous potential applications particularly in biomedical sciences. Di-peptide Phe-Phe was shown previously to self-assemble into nanotube like structures. In this work, we studied the affect of peptide backbone length and conformational flexibility on the self assembly process by using two dipeptides based on the Phe-Phe backbone (beta Phe-Phe and beta Phe-Delta Phe): one containing a flexible beta Phe amino acid, and the other containing both a flexible bPhe as well as a backbone constraining Alpha Phe (alpha,beta-dehydrophenylalanine) amino acid. Electron microscopy and X-ray diffraction experiments revealed that these new di-peptides can self-assemble into nanotubes having different properties than the native Phe-Phe nanotubes. These nanotubes were stable over a broad range of temperatures and the introduction of non-natural amino acids provided them with stability against the action of nonspecific proteases. Moreover, these dipeptides showed no cytotoxicity towards HeLa and L929 cells, and were able to encapsulate small drug molecules. We further showed that anticancerous drug mitoxantrone was more efficient in killing HeLa and B6F10 cells when entrapped in nanotubes as compared to free mitoxantrone. Therefore, these beta-phenylalanine and alpha, beta-dehydrophenylalanine containing dipeptide nanotubes may be useful in the development of biocompatible and proteolytically stable drug delivery vehicles.

Self-organized public key management in MANETs with enhanced security and without certificate-chains

In the self-organized public key management approaches, public key verification is achieved through verification routes constituted by the transitive trust relationships among the network principals. Most of the existing approaches do not distinguish among different available verification routes. Moreover, to ensure stronger security, it is important to choose an appropriate metric to evaluate the strength of a route. Besides, all of the existing self-organized approaches use certificate-chains for achieving authentication, which are highly resource consuming. In this paper, we present a self-organized certificate-less on-demand public key management (CLPKM) protocol, which aims at providing the strongest verification routes for authentication purposes. It restricts the compromise probability for a verification route by restricting its length. Besides, we evaluate the strength of a verification route using its end-to-end trust value. The other important aspect of the protocol is that it uses a MAC function instead of RSA certificates to perform public key verifications. By doing this, the protocol saves considerable computation power, bandwidth and storage space. We have used an extended strand space model to analyze the correctness of the protocol. The analytical, simulation, and the testbed implementation results confirm the effectiveness of the proposed protocol. (c) 2014 Elsevier B.V. All rights reserved.

In vitro osteogenic cell proliferation, mineralization, and in vivo osseointegration of injection molded high-density polyethylene-based hybrid composites in rabbit animal model

The present work reports the biocompatibility property of injection molded HDPE-HA-Al2O3 hybrid composites. In vitro cytocompatibility results reveal that osteogenic cell viability and bone mineralization are favorably supported in a statistically significant manner on HDPE-20% HA-20% Al2O3 composite, in comparison to HDPE-40 wt.% HA or HDPE-40 wt.% Al2O3. The difference in cytocompatibility property is explained in terms of difference in substrate wettability/surface energy and importantly, both the cell proliferation at 7 days or bone mineralization at 21 days on HDPE-20% HA-20% Al2O3 composite are either comparable or better than sintered HA. The progressive healing of cylindrical femoral bone defects in rabbit animal model was assessed by implantation experiments over 1, 4 and 12 weeks. Based on the histological analysis as well as histomorphometrical evaluation, a better efficacy of HDPE-20% HA-20% Al2O3 over high-density polyethylene (HDPE) for bone regeneration and neobone formation at host bone-implant interface was established. Taken together, the present study unequivocally establishes that despite the presence of 20% Al2O3, HDPE-based hybrid composites are as biocompatible as HA in vitro or better than HDPE in vivo.

Dynamics of the reaction between the free end of a tethered self-avoiding polymer and a flat penetrable surface: A renormalization group study

The average time tau(r) for one end of a long, self-avoiding polymer to interact for the first time with a flat penetrable surface to which it is attached at the other end is shown here to scale essentially as the square of the chain's contour length N. This result is obtained within the framework of the Wilemski-Fixman approximation to diffusion-limited reactions, in which the reaction time is expressed as a time correlation function of a ``sink'' term. In the present work, this sink-sink correlation function is calculated using perturbation expansions in the excluded volume and the polymer-surface interactions, with renormalization group methods being used to resum the expansion into a power law form. The quadratic dependence of tau(r) on N mirrors the behavior of the average time tau(c) of a free random walk to cyclize, but contrasts with the cyclization time of a free self-avoiding walk (SAW), for which tau(r) similar to N-2.2. A simulation study by Cheng and Makarov J. Phys. Chem. B 114, 3321 (2010)] of the chain-end reaction time of an SAW on a flat impenetrable surface leads to the same N-2.2 behavior, which is surprising given the reduced conformational space a tethered polymer has to explore in order to react. (C) 2014 AIP Publishing LLC.

Reversible and irreversible pH induced conformational changes in self-assembled weak polyelectrolyte multilayers probed using etched fiber Bragg grating sensors

Polyelectrolytes are charged polymer species which electrostatically adsorb onto surfaces in a layer by layer fashion leading to the sequential assembly of multilayer structures. It is known that the morphology of weak polyelectrolyte structures is strongly influenced by environmental variables such as pH. We created a weak polyelectrolyte multilayer structure (similar to 100 nm thick) of cationic polymer poly-allylamine hydrochloride (PAH) and an anionic polymer poly-acrylic acid (PAA) on an etched clad fiber Bragg grating (EFBG) to study the pH induced conformational transitions in the polymer multilayers brought about by the variation in charge density of weak polyelectrolyte groups as a function of pH. The conformational changes of the polyelectrolyte multilayer structure lead to changes in optical density of the adsorbed film which reflects in the shift of the Bragg wavelength from the EFBG. Using the EFBG system we were able to probe reversible and irreversible pH induced transitions in the PAH/PAA weak polyelectrolyte system. (C) 2014 Elsevier B.V. All rights reserved.

Room temperature electrical spin injection into GaAs by an oxide spin injector

Spin injection, manipulation and detection are the integral parts of spintronics devices and have attracted tremendous attention in the last decade. It is necessary to judiciously choose the right combination of materials to have compatibility with the existing semiconductor technology. Conventional metallic magnets were the first choice for injecting spins into semiconductors in the past. So far there is no success in using a magnetic oxide material for spin injection, which is very important for the development of oxide based spintronics devices. Here we demonstrate the electrical spin injection from an oxide magnetic material Fe3O4, into GaAs with the help of tunnel barrier MgO at room temperature using 3-terminal Hanle measurement technique. A spin relaxation time tau similar to 0.9 ns for n-GaAs at 300 K is observed along with expected temperature dependence of t. Spin injection using Fe3O4/MgO system is further established by injecting spins into p-GaAs and a tau of similar to 0.32 ns is obtained at 300 K. Enhancement of spin injection efficiency is seen with barrier thickness. In the field of spin injection and detection, our work using an oxide magnetic material establishes a good platform for the development of room temperature oxide based spintronics devices.

Synthesis of self-light-scattering wrinkle structured ZnO photoanode by sol-gel method for dye-sensitized solar cells

A special morphological zinc oxide (ZnO) photoanode for dye-sensitized solar cell was fabricated by simple sol-gel drop casting technique. This film shows a wrinkled structure resembling the roots of banyan tree, which acts as an effective self scattering layer for harvesting more visible light and offers an easy transport path for photo-injected electrons. These ZnO electrode of low thickness (similar to 5 mu m) gained an enhanced short-circuit current density of 6.15 mA/cm(2), open-circuit voltage of 0.67 V, fill factor of 0.47 and overall conversion efficiency of 1.97 % under 1 sun illumination. This shows a high conversion efficiency and a superior performance than that of ZnO nanoparticle-based photoanode (eta similar to 1.13 %) of high thickness (similar to 8 mu m).

Self-assembly of Chloro-Bridged Arene-Ruthenium Based Rectangle: Synthesis, Structural Characterization and Sensing Study

Self-assembly of a chloro-bridged half-sandwich p-cymene ruthenium(II) complex Ru-2(mu-Cl-2)(eta(6)-p-cymene)(2)Cl-2] 1 with linear ditopic donor L; trans-1,2-bis(4-pyridyl) ethylene] in presence of 2 eq. AgNO3 in CH3CN yielded a chloro-bridged molecular rectangle 2. The rectangle 2 was isolated as nitrate salt in high yield (90 %) and characterized by infra-red, H-1 NMR spectroscopy including ESI-MS analyses. Molecular structure of 2 was determined by single crystal X-ray diffraction study The diffraction analysis shows that 2 adopts a tetranuclear rectangular geometry with the dimensions of 5.51 angstrom x 13.29 angstrom and forming an infinite supramolecular chain with large internal porosity arising through multiple pi-pi and CH-pi interactions between the adjacent rectangles. Furthermore, rectangle 2 is used as selective receptor for phenolic-nitroaromatic compounds such as picric acid, dinitrophenol and nitrophenol.

Effect of port gas injection on in-cylinder stratification in a CNG fuelled SI engine

The concept of barrel stratification of air-fuel mixture is evaluated for a port gas injection (PGI) single cylinder spark ignition (SI) internal combustion (IC) engine using a transient three-dimensional computational fluid dynamic (CFD) model. The gaseous fuel used in the study is compressed natural gas (CNG). It is observed that compared to the premixed gas carburettor case, a substantial amount of in-cylinder stratification can be achieved with port gas injection system. A detailed parametric study is reported to understand the effect of the various injection parameters such as injection location, injection orientation, start of injection (SOT) and its duration, and injection rate. Furthermore, the best injection timing is evaluated for various load and speed cases. It is observed that the best stratification pattern can be achieved at 50% engine load. The injection location is observed to have a profound effect on the in-cylinder stratification pattern, and injection towards the side of the spark plug is observed to give a rich fuel-air mixture near the spark plug. It is also shown that there exists an optimal injection pressure.

Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers

Low-density nanostructured foams are often limited in applications due to their low mechanical and thermal stabilities. Here we report an approach of building the structural units of three-dimensional (3D) foams using hybrid two-dimensional (2D) atomic layers made of stacked graphene oxide layers reinforced with conformal hexagonal boron nitride (h-BN) platelets. The ultra-low density (1/400 times density of graphite) 3D porous structures are scalably synthesized using solution processing method. A layered 3D foam structure forms due to presence of h-BN and significant improvements in the mechanical properties are observed for the hybrid foam structures, over a range of temperatures, compared with pristine graphene oxide or reduced graphene oxide foams. It is found that domains of h-BN layers on the graphene oxide framework help to reinforce the 2D structural units, providing the observed improvement in mechanical integrity of the 3D foam structure.