988 resultados para INTERFACE MATRIX
Resumo:
Titanium dioxide thin films were deposited by RF reactive magnetron sputtering technique on p-type silicon(100) substrates held at temperatures in the range 303-673 K. The influence of substrate temperature on the core level binding energies, chemical bonding configuration, crystallographic structure and dielectric properties was investigated. X-ray photoelectron spectroscopy studies and Fourier transform infrared transmittance data confirmed the formation of stoichiometric films with anatase phase at a substrate temperature of 673 K. The films formed at 303 K were nanocrystalline with amorphous matrix while those deposited at 673 K were transformed in to crystalline phase and growth of grains in pyramidal like structure as confirmed by X-ray diffraction and atomic force microscopy respectively. Metal-oxide-semiconductor capacitors were fabricated with the configuration of Al/TiO2/Si structures. The current voltage, capacitance voltage and conductance voltage characteristics were studied to understand the electrical conduction and dielectric properties of the MOS devices. The leakage current density (at gate voltage of 2 V) decreased from 2.2 x 10(-6) to 1.7 x 10(-7) A/cm(2), the interface trap density decreased from 1.2 x 10(13) to 2.1 x 10(12) cm(-2) eV(-1) and the dielectric constant increased from 14 to 36 with increase of substrate temperature from 303 to 673 K.
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We propose an architecture for dramatically enhancing the stress bearing and energy absorption capacities of a polymer based composite. Different weight fractions of iron oxide nano-particles (NPs) are mixed in a poly(dimethylesiloxane) (PDMS) matrix either uniformly or into several vertically aligned cylindrical pillars. These composites are compressed up to a strain of 60% at a strain rate of 0.01 s(-1) following which they are fully unloaded at the same rate. Load bearing and energy absorption capacities of the composite with uniform distribution of NPs increase by similar to 50% upon addition of 5 wt% of NPs; however, these properties monotonically decrease with further addition of NPs so much so that the load bearing capacity of the composite becomes 1/6th of PDMS upon addition of 20 wt% of NPs. On the contrary, stress at a strain of 60% and energy absorption capacity of the composites with pillar configuration monotonically increase with the weight fraction of NPs in the pillars wherein the load bearing capacity becomes 1.5 times of PDMS when the pillars consisted of 20 wt% of NPs. In situ mechanical testing of composites with pillars reveals outward bending of the pillars wherein the pillars and the PDMS in between two pillars, located along a radius, are significantly compressed. Reasoning based on effects of compressive hydrostatic stress and shape of fillers is developed to explain the observed anomalous strengthening of the composite with pillar architecture.
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Mechanical properties of single-walled carbon nanohoms (SWNH) and SWNH plus few-layer graphene (EG)-reinforced poly(vinyl alcohol) (PVA) matrix composites have been measured using the nanoindentation technique. The elastic modulus (E) and hardness (H) of PVA were found to improve by similar to 315% and similar to 135%, respectively, upon the addition of just 0.4 wt % SWNH. These properties were found to be comparable to those obtained upon the addition of 0.2 wt % single-walled nanotubes (SWNT) to PVA. Furthermore, upon binary addition of 0.2 wt % EG and 0.4 wt % SWNH to PVA, benefits in the form of similar to 400% and similar to 330% synergy in E and H, respectively, were observed, along with an increased resistance to viscoelastic deformation. The reasons for these improvements are discussed in terms of the dimensionality of nanocarbon, the effectiveness of nanocarbon and polymer matrix interaction, and the influence of nanocarbon on the degree of crystallinity of the polymer. The results from SWNH reinforcement in this study demonstrate the scope for a novel and, in contrast to SWNT composites, a commercially feasible opportunity for strengthening polymer matrices.
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Clustering techniques which can handle incomplete data have become increasingly important due to varied applications in marketing research, medical diagnosis and survey data analysis. Existing techniques cope up with missing values either by using data modification/imputation or by partial distance computation, often unreliable depending on the number of features available. In this paper, we propose a novel approach for clustering data with missing values, which performs the task by Symmetric Non-Negative Matrix Factorization (SNMF) of a complete pair-wise similarity matrix, computed from the given incomplete data. To accomplish this, we define a novel similarity measure based on Average Overlap similarity metric which can effectively handle missing values without modification of data. Further, the similarity measure is more reliable than partial distances and inherently possesses the properties required to perform SNMF. The experimental evaluation on real world datasets demonstrates that the proposed approach is efficient, scalable and shows significantly better performance compared to the existing techniques.
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The present paper analyzes the effects of plumes for heat transfer enhancement at solid-liquid interface taking both smooth and grooved surfaces. The experimental setup consists of a tank of dimensions 265 x 265 x 300 (height) containing water. The bottom surface was heated and free surface of the water was left open to the ambient. In the experiments, the bottom plate had either a smooth surface or a grooved surface. We used 90 V-grooved rough surfaces with two groove heights, 10mm and 3mm. The experiment was done with water layer depths of 90mm and 140mm, corresponding to values of aspect ratio(AR) equal to 2.9 and 1.8 respectively. Thymol blue, a pH sensitive dye, was used to visualize the flow near the heated plate. The measured heat transfer coefficients over the grooved surfaces were higher compared that over the smooth surface. The enhanced heat transport in the rough cavities cannot be ascribed to the increase in the contact area, rather it must be the local dynamics of the thermal boundary layer that changes the heat transport over the rough surface.
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This paper presents the Treadport Active Wind Tunnel (TPAWT)-a full-body immersive virtual environment for the Treadport locomotion interface designed for generating wind on a user from any frontal direction at speeds up to 20 kph. The goal is to simulate the experience of realistic wind while walking in an outdoor virtual environment. A recirculating-type wind tunnel was created around the pre-existing Treadport installation by adding a large fan, ducting, and enclosure walls. Two sheets of air in a non-intrusive design flow along the side screens of the back-projection CAVE-like visual display, where they impinge and mix at the front screen to redirect towards the user in a full-body cross-section. By varying the flow conditions of the air sheets, the direction and speed of wind at the user are controlled. Design challenges to fit the wind tunnel in the pre-existing facility, and to manage turbulence to achieve stable and steerable flow, were overcome. The controller performance for wind speed and direction is demonstrated experimentally.
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The genome of Leishmania major encodes a type II fatty acid biosynthesis pathway for which no structural or biochemical information exists. Here, for the first time, we have characterized the central player of the pathway, the acyl carrier protein (LmACP), using nuclear magnetic resonance (NMR). Structurally, the LmACP molecule is similar to other type II ACPs, comprising a four-helix bundle, enclosing a hydrophobic core. Dissimilarities in sequence, however, exist in helix II (recognition helix) of the protein. The enzymatic conversion of apo-LmACP into the holo form using type I (Escherichia coli AcpS) and type II (Sfp type) phosphopantetheinyl transferases (PPTs) is relatively slow. Mutagenesis studies underscore the importance of the residues present at the protein protein interaction interface of LmACP in modulating the activity of PPTs. Interestingly, the cognate PPT for this ACP, the L. major 4'-phosphopantetheinyl transferase (LmPPT), does not show any enzymatic activity toward it, though it readily converts other type I and type II ACPs into their holo forms. NMR chemical shift perturbation studies suggest a moderately tight complex between LmACP and its cognate PPT, suggesting inhibition. We surmise that the unique surface of LmACP might have evolved to complement its cognate enzyme (LmPPT), possibly for the purpose of regulation.
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Lanthanide ions are strong Lewis acids. Their complexation to a variety of ligands can further enhance their Lewis acidity allowing the hydrolysis of phosphoesters and even DNA. We show that the interaction of lanthanide ions with vesicles from zwitterionic phosphatidylcholine lipids gives supramolecular structures in which the metal ion is loosely coordinated to the surface. This assembly provides a high density of Lewis-acidic metal centres, which hydrolyze phosphodiesters with enhanced rates.
Resumo:
Poly(vinyl butyral) - MMT clay nanocomposites were synthesized in situ with three different degrees of acetalization and with varying clay content for each vinyl butyral polymer ratio. The clay nano-platelet galleries were expanded, as determined by X-ray diffraction and TEM analysis. The glass transition temperature of the polymer nanocomposites were found to be similar to 56 degrees C and similar to 52 degrees C for the neat polymer and the 4% clay loaded samples, respectively. The 4 wt% clay loaded film showed higher strength and low strain to failure. The dynamic mechanical analysis also confirmed the improved stability of the matrix. The matrix with 0.5 butyral to alcohol ratio for 4 wt% clay exhibited good water vapor transmission compared to all other compositions. The encapsulated devices with 2.5 and 4 wt% clay loaded films increases the device life time and the efficiencies of these films were 50% higher than their encapsulated pristine polymer films. (C) 2015 Elsevier Ltd. All rights reserved.
Resumo:
Colloidal systems offer an effective medium to micro-engineer complex structures without involving sophisticated fabrication procedures. This article presents a deployment strategy of multiple droplets of different colloidal composition and utilizes the inherent capillary flow driven self assembly of nanoparticles to construct stacks of multiple materials on a given glass substrate. Here we used aqueous nano-crystalline titania and nano-amorphous silica solutions as the two materials. Initially, a pure nanotitania (nanosilica) droplet is deployed and allowed to dry partially. Subsequently, a second droplet of pure nanosilica (nanotitania) is deployed co-axially on the partially dried precipitate. The proposed deployment strategy allowed significant morphological differences when the deployment order of nanosilica and nanotitania were interchanged. Compositional analysis performed using EDX (Energy Dispersive X-ray spectroscopy) showed preferential deposition of nanosilica and nanotitania along the radial as well as the axial plane of the final deposit pattern. The underlying mechanism for such a phenomenon could be attributed to the contact line dynamics of a sessile double droplet. We also observe heteroaggregation of the nanosilica-nanotitania interaction along a narrow interface which resulted in nanotitania particles clustering into isolated islands embedded into a matrix of nanosilica particles. Overall, this work elucidates the evaporation driven dynamics of a mixed colloidal system which displays both macroscopic as well as microscopic phenomena. Such a system could be used to generate ordered arrays of functional materials with engineered micro to nano-scale properties.
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Fabricating supramolecular hydrogels with embedded metal nanostructures is important for the design of novel hybrid nanocomposite materials for diverse applications such as biosensing and chemosensing platforms, catalytic and antibacterial functional materials etc. Supramolecular self-assembly of bile acid-dipeptide conjugates has led to the formation of new supramolecular hydrogels. Gelation of these molecules depends strongly on the hydrophobic character of the bile acids. The possibility of in situ fabrication of Ag and Au NPs in these supramolecular hydrogels by incorporating Ag+ and Au3+ salts was investigated via photoreduction. Chemical reductions of Ag+ and Au3+ salts in the hydrogels were performed without adding any external stabilizing agents. In this report we have shown that the color, size and shape of silver nanoparticles formed by photoreduction depend on the amino acid residue of the side chain.
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The ambiguous behavior of metal-graphene interface has been addressed in this paper using density functional theory and nonequilibrium Green's function formalism. For the first time, the fundamental chemistry of metal-graphene interface, in particular role of sp-hybridized and sp(2)-hybridized carbon atoms, has been emphasized and discussed in detail in this paper. It was discovered that the sp-hybridized sites at the edge of a graphene monolayer contribute to 40% of current conduction when compared with sp(2)-hybridized atom sites in the graphene-metal overlap region. Moreover, we highlighted the insignificance of an additional metal layer, i.e., sandwiched contact, due to lacking sp-hybridized carbon sites. A fundamental way of defining the contact resistance, while keeping chemical bonding in mind, has been proposed. The bonding insight has been further used to propose the novel ways of interfacing metal with graphene, which results in a 40% reduction in contact resistance.
Resumo:
High-kappa TiO2 thin films have been fabricated from a facile, combined sol-gel spin - coating technique on p and n type silicon substrate. XRD and Raman studies headed the existence of anatase phase of TiO2 with a small grain size of 18 nm. The refractive index `n' quantified from ellipsometry is 2.41. AFM studies suggest a high quality, pore free films with a fairly small surface roughness of 6 angstrom. The presence of Ti in its tetravalent state is confirmed by XPS analysis. The defect parameters observed at the interface of Si/TiO2 were studied by capacitance - voltage (C - V) and deep level transient spectroscopy (DLTS). The flat - band voltage (V-FB) and the density of slow interface states estimated are -0.9, -0.44 V and 5.24x10(10), 1.03x10(11) cm(-2); for the NMOS and PMOS capacitors, respectively. The activation energies, interface state densities and capture cross -sections measured by DLTS are E-V + 0.30, E-C - 0.21 eV; 8.73x10(11), 6.41x10(11) eV(-1) cm(-2) and 5.8x10(-23), 8.11x10(-23) cm(2) for the NMOS and PMOS structures, respectively. A low value of interface state density in both P-and N-MOS structures makes it a suitable alternate dielectric layer for CMOS applications. And also very low value of capture cross section for both the carriers due to the amphoteric nature of defect indicates that the traps are not aggressive recombination centers and possibly can not contribute to the device operation to a large extent. (C) 2015 Author(s).
Resumo:
Bacterial biofilms display a collective lifestyle, wherein the cells secrete extracellular polymeric substances (EPS) that helps in adhesion, aggregation, stability, and to protect the bacteria from antimicrobials. We asked whether the BPS could act as a public good for the biofilm and observed that infiltration of cells that do not produce matrix components weakened the biofilm of Salmonella enterica serovar Typhimurium. PS production was costly for the producing cells, as indicated by a significant reduction in the fitness of wild type (WT) cells during competitive planktonic growth relative to the non-producers. Infiltration frequency of non-producers in the biofilm showed a concomitant decrease in overall productivity. It was apparent in the confocal images that the non producing cells benefit from the BPS produced by the Wild Type (WT) to stay in the biofilm. The biofilm containing non-producing cells were more significantly susceptible to sodium hypochlorite and ciprofloxacin treatment than the WT biofilm. Biofilm infiltrated with non-producers delayed the pathogenesis, as tested in a murine model. The cell types were spatially assorted, with non producers being edged out in the biofilm. However, cellulose was found to act as a barrier to keep the non-producers away from the WT microcolony. Our results show that the infiltration of non-cooperating cell types can substantially weaken the biofilm making it vulnerable to antibacterials and delay their pathogenesis. Cellulose, a component of BPS, was shown to play a pivotal role of acting as the main public good, and to edge-out the non-producers away from the cooperating microcolony.
Resumo:
A low Schottky barrier height (SBH) at source/drain contact is essential for achieving high drive current in atomic layer MoS(2-)channel-based field effect transistors. Approaches such as choosing metals with appropriate work functions and chemical doping are employed previously to improve the carrier injection from the contact electrodes to the channel and to mitigate the SBH between the MoS2 and metal. Recent experiments demonstrate significant SBH reduction when graphene layer is inserted between metal slab (Ti and Ni) and MoS2. However, the physical or chemical origin of this phenomenon is not yet clearly understood. In this work, density functional theory simulations are performed, employing pseudopotentials with very high basis sets to get insights of the charge transfer between metal and monolayer MoS2 through the inserted graphene layer. Our atomistic simulations on 16 different interfaces involving five different metals (Ti, Ag, Ru, Au, and Pt) reveal that (i) such a decrease in SBH is not consistent among various metals, rather an increase in SBH is observed in case of Au and Pt; (ii) unlike MoS2-metal interface, the projected dispersion of MoS2 remains preserved in any MoS2-graphene- metal system with shift in the bands on the energy axis. (iii) A proper choice of metal (e.g., Ru) may exhibit ohmic nature in a graphene-inserted MoS2-metal contact. These understandings would provide a direction in developing high-performance transistors involving heteroatomic layers as contact electrodes. (c) 2016 AIP Publishing LLC.