Levitation effect and its relationship with the underlying potential energy landscape

Positions of potential energy minima for spherical monatomic sorbates in zeolite NaY have been identified for different sizes of the sorbate. It is found that for small sorbates (sigma less than or equal to 4.96 Angstrom) there are only six adsorption sites per alpha-cage, which are located close to the inner surface of the alpha-cage. For larger sorbates, additional sites of comparable energies appear close to the 12-ring window which forms the bottleneck for intercage diffusion. Minimum energy paths between these sites have been computed. These suggest that the barriers for both intracage and intercage site-to-site migrations are comparable and decrease with increase in sorbate size. Earlier simulation studies on the diffusion of monatomic sorbates in zeolites indicated that there is a dramatic change in the nature of dependence of D on sorbate size around 4.96 Angstrom, for zeolite NaY. Therefore, the present results suggest that the dependence of D on sorbate size and the changes in the potential energy landscape are correlated. The sorbate-zeolite system is characterized by a flatter potential energy landscape when the sorbate size is large. (C) 1999 American Institute of Physics. [S0021-9606(99)51110-0].

Photoelectron spectroscopic study of CdS nanocrystallites

Nanocrystallites of semiconductors, especially those belonging to II-VI and III-V groups, show size-dependent optical and electrical properties. In this paper we report on x-ray photoemission results of CdS nanocrystallites of two different sizes and compare these results with bulk CdS. The S 2p and 2s core levels of the nanocrystallites reveal three different types of sulfur, unlike bulk CdS, which shows only one kind of sulfur species. Details of the spectroscopic results provide estimates of the size of the nanocrystallites, while also indicating the origin of the stability of such small clusters. [S0163-1829(99)03811-4].

DEPTH: a web server to compute depth and predict small-molecule binding cavities in proteins

Depth measures the extent of atom/residue burial within a protein. It correlates with properties such as protein stability, hydrogen exchange rate, protein-protein interaction hot spots, post-translational modification sites and sequence variability. Our server, DEPTH, accurately computes depth and solvent-accessible surface area (SASA) values. We show that depth can be used to predict small molecule ligand binding cavities in proteins. Often, some of the residues lining a ligand binding cavity are both deep and solvent exposed. Using the depth-SASA pair values for a residue, its likelihood to form part of a small molecule binding cavity is estimated. The parameters of the method were calibrated over a training set of 900 high-resolution X-ray crystal structures of single-domain proteins bound to small molecules (molecular weight < 1.5 KDa). The prediction accuracy of DEPTH is comparable to that of other geometry-based prediction methods including LIGSITE, SURFNET and Pocket-Finder (all with Matthew's correlation coefficient of similar to 0.4) over a testing set of 225 single and multi-chain protein structures. Users have the option of tuning several parameters to detect cavities of different sizes, for example, geometrically flat binding sites. The input to the server is a protein 3D structure in PDB format. The users have the option of tuning the values of four parameters associated with the computation of residue depth and the prediction of binding cavities. The computed depths, SASA and binding cavity predictions are displayed in 2D plots and mapped onto 3D representations of the protein structure using Jmol. Links are provided to download the outputs. Our server is useful for all structural analysis based on residue depth and SASA, such as guiding site-directed mutagenesis experiments and small molecule docking exercises, in the context of protein functional annotation and drug discovery.

Continued self-similar breakup of drops in viscous continuous phase in agitated vessels

Drop breakup inviscous liquids in agitated vessels occurs in elongational flow around impeller blade edges. The drop size distributions measured over extended periods for impellers of different sizes show that breakup process continues up to 15-20 h, before a steady state is reached. The size distributions evolve in a self-similar way till the steady state is reached. The scaled size distributions vary with impeller size and impeller speed, in contrast with the near universal scaling known for drop breakup in turbulent flows. The steady state size of the largest drop follows inverse scaling with impeller tip velocity. The breadth of the scaled size distributions also shows a monotonic relationship with impeller tip velocity only. (C) 2011 Elsevier Ltd. All rights reserved.

Health Monitoring Of Composite Structures Based On Acoustic Wave Sensing Using Fiber Optic Sensors

Structural Health Monitoring has gained wide acceptance in the recent past as a means to monitor a structure and provide an early warning of an unsafe condition using real-time data. Utilization of structurally integrated, distributed sensors to monitor the health of a structure through accurate interpretation of sensor signals and real-time data processing can greatly reduce the inspection burden. The rapid improvement of the Fiber Optic Sensor technology for strain, vibration, ultrasonic and acoustic emission measurements in recent times makes it feasible alternative to the traditional strain gauges, PVDF and conventional Piezoelectric sensors used for Non Destructive Evaluation (NDE) and Structural Health Monitoring (SHM). Optical fiber-based sensors offer advantages over conventional strain gauges, and PZT devices in terms of size, ease of embedment, immunity from electromagnetic interference (EMI) and potential for multiplexing a number of sensors. The objective of this paper is to demonstrate the acoustic wave sensing using Extrinsic Fabry-Perot Interferometric (EFPI) sensor on a GFRP composite laminates. For this purpose experiments have been carried out initially for strain measurement with Fiber Optic Sensors on GFRP laminates with intentionally introduced holes of different sizes as defects. The results obtained from these experiments are presented in this paper. Numerical modeling has been carried out to obtain the relationship between the defect size and strain.

Tension-Softening Properties for Concrete-Concrete Interfaces

The tension-softening parameters for different concrete-concrete interfaces are determined using the bimaterial cracked hinge model. Beams of different sizes having a jointed interface between two different strengths of concrete are tested under three-point bending (TPB). The load versus crack mouth opening displacement (CMOD) results are used to obtain the stress-crack opening relation through an inverse analysis. In addition, the fracture energy, tensile strength, and modulus of elasticity are also computed from the inverse analysis. The fracture properties are used in the nonlinear fracture mechanics analysis of a concrete patch-repaired beam to determine its load-carrying capacity when repaired with concrete of different strengths.

Modeling of seepage flow through layered solis

A two-dimensional finite difference model, which solves mixed type of Richards' equation, whose non-linearity is dealt with modified Picard's iteration and strongly implicit procedure to solve the resulting equations, is presented. Modeling of seepage flow through heterogeneous soils, which is common in the field is addressed in the present study. The present model can be applied to both unsaturated and saturated soils and can handle very dry initial condition and steep wetting fronts. The model is validated by comparing experimental results reported in the literature. Newness of this two dimensional model is its application on layered soils with transient seepage face development, which has not been reported in the literature. Application of the two dimensional model for studying unconfined drainage due to sudden drop of water table at seepage face in layered soils is demonstrated. In the present work different sizes of rectangular flow domain with different types of layering are chosen. Sensitivity of seepage height due to problem dimension of layered system is studied. The effect of aspect ratio on seepage face development in case of the flow through layered soil media is demonstrated. The model is also applied to random heterogeneous soils in which the randomness of the model parameters is generated using the turning band technique. The results are discussed in terms of phreatic surface and seepage height development and also flux across the seepage face. Such accurate modeling of seepage face development and quantification of flux moving across the seepage face becomes important while modeling transport problems in variably saturated media.

Ultrasonic Guided Wave Characterization and Damage Detection in Foam-core Sandwich Panel using PWAS and LDV

Lamb wave type guided wave propagation in foam core sandwich structures and detectability of damages using spectral analysis method are reported in this paper. An experimental study supported by theoretical evaluation of the guided wave characteristics is presented here that shows the applicability of Lamb wave type guided ultrasonic wave for detection of damage in foam core sandwich structures. Sandwich beam specimens were fabricated with 10 mm thick foam core and 0.3 mm thick aluminum face sheets. Thin piezoelectric patch actuators and sensors are used to excite and sense guided wave. Group velocity dispersion curves and frequency response of sensed signal are obtained experimentally. The nature of damping present in the sandwich panel is monitored by measuring the sensor signal amplitude at various different distances measured from the center of the linear phased array. Delaminations of increasing width are created and detected experimentally by pitch-catch interrogation with guided waves and wavelet transform of the sensed signal. Signal amplitudes are analyzed for various different sizes of damages to differentiate the damage size/severity. A sandwich panel is also fabricated with a planer dimension of 600 mm x 400 mm. Release film delamination is introduced during fabrication. Non-contact Laser Doppler Vibrometer (LDV) is used to scan the panel while exciting with a surface bonded piezoelectric actuator. Presence of damage is confirmed by the reflected wave fringe pattern obtained from the LDV scan. With this approach it is possible to locate and monitor the damages by tracking the wave packets scattered from the damages.

Guided wave based detection of damage in honeycomb core sandwich structures

We report on the Lamb wave type guided wave propagation in honeycomb core sandwich structures. An experimental study supported by theoretical evaluation of the guided wave characteristics is presented that proves the potential of Lamb wave type guided wave for detection of damage in sandwich structures. A sandwich panel is fabricated with planar dimension of 600 mm x 600 mm, having a core thickness of 7 mm, cell size of 5 mm and 0.1 mm thick aluminum face sheets. Thin piezoelectric patch actuators and sensors are used to excite and sense a frequency band limited guided wave with a central frequency. A linear phased array of piezoelectric patch actuators is used to achieve higher signal strength and directivity. Group velocity dispersion curves and corresponding frequency response of sensed signal are obtained experimentally. Linearity between the excitation signal amplitude and the corresponding sensed signal amplitude is found for certain range of parameters. The nature of damping present in the sandwich panel is monitored by measuring the sensor signal amplitude at various different distances measured from the center of the linear phased array. Indentation and low velocity impact induced damages of increasing diameter covering several honeycomb cells are created. Crushing of honeycomb core with rupture of face sheet is observed while introducing the damage. The damages are then detected experimentally by pitch-catch interrogation with guided waves and wavelet transform of the sensed signal. Signal amplitudes are analyzed for various different sizes of damages to differentiate the damage size/severity. Monotonic changes in the sensor signal amplitude due to increase in the damage size has been established successfully. With this approach it is possible to locate and monitor the damages with the help of phased array and by tracking the wave packets scattered from the damages. (C) 2012 Elsevier Ltd. All rights reserved.

Structural and phase dependent thermo and photoluminescent properties of Dy(OH)(3) and Dy2O3 nanorods

Hexagonal Dy(OH)(3) and cubic Dy2O3 nanorods were prepared by hydrothermal method. Dy(OH)(3) nanorods was directly obtained at 180 degrees C for 20 h after hydrothermal treatment whereas subsequently heat treatment at 750 degrees C for 2 h gives pure cubic Dy2O3. SEM micrographs reveal that needle shaped rods with different sizes were observed in both the phases. TEM results also confirm this. The TL response of hexagonal Dy(OH)(3) and cubic Dy2O3 nanorods have been analyzed for gamma-irradiation over a wide range of exposures (1-5 kGy). TL glow peak intensity increases with gamma dose in both the phases. The activation energy (E), order of kinetics (6), and frequency factor (s) for both the phases have been determined using Chen's peak shape method. The simple glow curve shape, structure and linear response to gamma-irradiation over a large span of exposures makes the cubic Dy2O3 as a useful dosimetric material to estimate high exposures of gamma-rays. (c) 2012 Elsevier Ltd. All rights reserved.

Spherical and rod-like Gd2O3:Eu3+ nanophosphors-Structural and luminescent properties

A comparative study of spherical and rod-like nanocrystalline GdO:Eu (GdEuO) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of GdO:Eu. Upon calcinations at 800C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH):Eu phase and it converts to pure cubic phase of GdO:Eu on calcination at 600C for 3 h. TEM micrographs of hydrothermally prepared cubic GdO:Eu phase shows nanorods with a diameter of 15 nm and length varying from 50 to 150 nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50-250 nm. Dominant red emission (612 nm) was observed in cubic GdO:Eu which has been assigned to transition. However, in hexagonal Gd(OH):Eu, emission peaks at 614 and 621 nm were observed. The strong red emission of cubic GdO:Eu nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap () was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.

A broad pore size distribution mesoporous SnO2 as anode for lithium-ion batteries

We demonstrate here that mesoporous tin dioxide (abbreviated M-SnO2) with a broad pore size distribution can be a prospective anode in lithium-ion batteries. M-SnO2 with pore size ranging between 2 and 7.5 nm was synthesized using a hydrothermal procedure involving two different surfactants of slightly different sizes, and characterized. The irreversible capacity loss that occurs during the first discharge and charge cycle is 890 mAh g(-1), which is smaller than the 1,010-mAh g(-1) loss recorded for mesoporous SnO2 (abbreviated S-SnO2) synthesized using a single surfactant. After 50 cycles, the discharge capacity of M-SnO2 (504 mAh g(-1)) is higher than that of S-SnO2 (401 mAh g(-1)) and solid nanoparticles of SnO2 (abbreviated nano-SnO2 < 4 mAh g(-1)) and nano-SnO2. Transmission electron microscopy revealed higher disorder in the pore arrangement in M-SnO2. This, in turn imparts lower stiffness to M-SnO2 (elastic modulus, E (R) a parts per thousand aEuro parts per thousand 14.5 GPa) vis-a-vis S-SnO2 (E (R) a parts per thousand aEuro parts per thousand 20.5 GPa), as obtained using the nanoindentation technique. Thus, the superior battery performance of M-SnO2 is attributed to its intrinsic material mechanical property. The fluidity of the internal microstructure of M-SnO2 resulted in a lower degree of aggregation of Sn particles compared to S-SnO2 and nano-SnO2 structural stabilization and long-term cyclability.

Time dependent superhydrophobicity of drag reducing surfaces

Air can be trapped on the crevices of specially textured hydrophobic surfaces immersed in water. This heterogenous state of wetting in which the water is in contact with both the solid surface and the entrapped air is not stable. Diffusion of air into the surrounding water leads to gradual reduction in the size and numbers of the air bubbles. The sustainability of the entrapped air on such surfaces is important for many underwater applications in which the surfaces have to remain submersed for longer time periods. In this paper we explore the suitability of different classes of surface textures towards the drag reduction application by evaluating the time required for the disappearance of the air bubbles under hydrostatic conditions. Different repetitive textures consisting of holes, pillars and ridges of different sizes have been generated in silicon, aluminium and brass by isotropic etching, wire EDM and chemical etching respectively. These surfaces were rendered hydrophobic with self-assembled layer of fluorooctyl trichlorosilane for silicon and aluminium surfaces and 1-dodecanethiol for brass surfaces. Using total internal reflection the air bubbles are visualized with the help of a microscope and time lapse photography. Irrespective of the texture, both the size and the number of air pockets were found to decrease with time gradually and eventually disappear. In an attempt to reverse the diffusion we explore the possibility of using electrolysis to generate gases at the textured surfaces. The gas bubbles are nucleated everywhere on the surface and as they grow they coalesce with each other and get pinned at the texture edges.

Study of the Formation of Nano-Networks in Colloidal Particles

The authors studied the formation of a wafer-scale network of connected colloidal beads by reactive ion etching. The dimensions of the connections have been studied as a function of etching time for colloidal beads of different sizes, and could be well controlled. The authors have found that the nano-network forms and disappears for the same time of etching independent of the diameter of the polystyrene beads. With recent interest of connected colloidal networks in various optical sensing applications, such as photonic crystals, as surface-enhanced Raman scattering substrates, the studies have potential uses in the development of wafer-scale nanophotonic sensors.

Adaptive constellation rotation scheme for two-user fading MAC with quantized fade state feedback

With no Channel State Information (CSI) at the users, transmission over the two-user Gaussian Multiple Access Channel with fading and finite constellation at the input, will have high error rates due to multiple access interference (MAI). However, perfect CSI at the users is an unrealistic assumption in the wireless scenario, as it would involve extremely large feedback overheads. In this paper we propose a scheme which removes the adverse effect of MAI using only quantized knowledge of fade state at the transmitters such that the associated overhead is nominal. One of the users rotates its constellation relative to the other without varying the transmit power to adapt to the existing channel conditions, in order to meet certain predetermined minimum Euclidean distance requirement in the equivalent constellation at the destination. The optimal rotation scheme is described for the case when both the users use symmetric M-PSK constellations at the input, where M = 2(gimel), gimel being a positive integer. The strategy is illustrated by considering the example where both the users use QPSK signal sets at the input. The case when the users use PSK constellations of different sizes is also considered. It is shown that the proposed scheme has considerable better error performance compared to the conventional non-adaptive scheme, at the cost of a feedback overhead of just log log(2) (M-2/8 - M/4 + 2)] + 1 bits, for the M-PSK case.