Parallel Surface Research Articles

Parallel pore and surface diffusion of levulinic acid in basic polymeric adsorbents

The equilibrium and kinetics of levulinic acid (LA) adsorption on two basic polymeric adsorbents, 335 (highly porous gel) and D315 (macroreticular), were investigated. Experimental adsorption rates in batch stirred vessels under a variety of operating conditions were described successfully by the parallel pore and surface diffusion model taking into account external mass transfer and nonlinear Toth isotherm. The film-pore diffusion model was matched with the rate data and the resulting apparent pore diffusivities were strongly concentration-dependent and approached to a constant value for 335 adsorbent. Thus, the constant value was taken as the accurate pore diffusivity, while the pore diffusivity in D315 was estimated from the particle porosity. The surface diffusivities decreased with increasing initial bulk concentration for both adsorbents. The inverse concentration dependence was correlated reasonably well to the change of isosteric heat of adsorption as amount adsorbed.

Corrosion-induced copper runoff from naturally and pre-patinated copper in a marine environment

Corrosion-induced copper runoff has been monitored for copper sheet, naturally patinated copper and pre-patinated copper, with and without surface treatments, in a marine environment during one year. The study comprises solution measurements on total copper runoff rates, sulphates and chlorides released from the patina, and parallel surface analytical studies on patina formation, combined with electrochemical impedance measurements on changes in barrier properties during exposure. Bioassay tests and model predictions were applied to elucidate copper bioavailability at the immediate release situation. The runoff rate of copper was significantly lower compared to the corrosion rate throughout the exposure period. At comparable rain quantities, copper runoff rates were significantly lower at the marine site compared to similar data obtained in an urban environment. The bioavailable concentration of released copper was significantly lower compared to the total copper concentration.

Nitridation of niobium films by rapid thermal processing: different behaviour of films on oxydized silicon and monocrystalline sapphire substrates

By electron beam evaporation and RF magnetron sputtering 500 nm thick niobium films were deposited on thermally oxidized Si-(100)-wafers and by RF magnetron sputtering on monocrystalline sapphire-(1-102)-wafers. Investigations by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the substrate used: films deposited on SiO2 exhibited an even surface with small crystallites, films on sapphire showed parallel surface structures with relatively large and well-shaped crystallites pointing at regular crystal growth influenced by the substrate. These differences in film morphology were also reflected in different reflection intensities of the films in XRD patterns, indicating that the films deposited on sapphire were strongly textured. In a first set of experiments nitridation in molecular nitrogen and ammonia was investigated. In a second set of experiments, it was tried to form oxynitrides of niobium by annealing the nitrided films in molecular oxygen. Particularly by X-ray-diffraction the formation of different nitride and oxide phases in dependence of the reaction temperature was examined. Further, elemental depth profiles were recorded by secondary ion mass spectrometry (SIMS) to track the position of the phases formed in the film.

Radiotracer measurements of protein mass transfer: Kinetics in ion exchange media

We describe a method to measure protein mass transfer kinetics in ion exchange adsorbents for preparative chromatography based on the use of radioactively labeled protein. The method was developed and evaluated using lysozyme as a test protein with the three commercial strong-acid cation exchangers SP-Sepharose-FF, SP-Sepharose-XL, and S-HyperD. Iodination with 125I was used to label the protein, which was added in trace amounts (approximately 0.1%) to an unlabeled protein solution. The solution was recirculated through a shallow bed of the adsorbent particles and the radioactivity accumulated in the bed measured with a gamma-counter as a function of time. Radiotracer-based kinetics measurements were found to be in good agreement with results obtained with a conventional shallow-bed technique, provided that freshly labeled protein solutions were used. The method has advantages in terms of simplicity, ability to deal with adsorption from complex mixtures, and the potential for measurements under tracer diffusion conditions. Kinetics results obtained for the three different stationary phases were generally consistent with previous studies. Protein mass transfer can be described by a pore diffusion model with a nearly salt-independent pore diffusivity for SP-Sepharose-FF and by a homogeneous diffusion model with a saltindependent adsorbed phase diffusivity for S-HyperD. However, it appears that a more complex model, accounting for parallel pore and surface diffusion, is needed to describe protein mass transfer in SP-Sepharose-XL. The modeling results were found to be correlated with the apparent pore sizes determined by inverse SEC.

Adsorption of long flexible polymer chains at planar surfaces: scaling analysis and criticalexponents

The process of adsorption on a planar repulsive, ‘marginal’ and attractivewall of long flexible polymer chains with excluded volume interactions in theframework of the renormalization group field-theoretical approach, directly ind = 3 dimensions up to two-loop order, for the semi-infinite|ϕ|4 n-vector model in the limit n → 0 is investigated. We perform Padé and Padé–Borel resummation of the series obtained forthe surface critical exponents, characterizing the process of adsorption of long flexiblepolymer chains at the surface. The polymer linear dimensions parallel and perpendicular tothe surface and the corresponding partition functions, as well as the behaviour of themonomer density profiles and the fraction of adsorbed monomers at the surface and in theinterior, are studied. The field-theoretical results obtained at fixed dimensionsd = 3 are in good agreement with recent Monte Carlo calculations.

Parallel remeshing of unstructured volume grids for CFD applications

AbstractThis paper presents a new approach towards the parallel local remeshing of unstructured tetrahedral grids on distributed memory parallel computers based on the message passing paradigm (MPI). The overall remeshing approach consisting of the parallel determination of the regions to be remeshed and the parallel local surface and volume remeshing is described in detail. An application of the remeshing algorithms in a time‐accurate simulation of bodies in relative motion demonstrates the capabilities of the approach. Copyright © 2006 John Wiley & Sons, Ltd.

AE Sensor Calibration for Out-of-Plane and In-Plane Displacement Sensitivity

This paper proposes a method for both the out-of-plane and in-plane displacement sensitivity calibration of an acoustic emission (AE) sensor. In the method, a laser homodyne interferometer is used to measure the out-of-plane and in-plane displacement of the surface of a large test block excited by a repeatable source transducer. The out-of-plane displacement is measured by aligning the laser beam perpendicular to the surface with time gating of the receive waveform used to isolate only the direct arrival of the longitudinal wave produced by the piston source transducer. For the in-plane displacement measurement, the laser beam is aligned parallel to the surface to intersect a small optically reflective step with the time waveform being gated to measure only the direct shear arrival produced using a normal incidence shear wave source transducer. In each case, the interferometer measurement is followed by coupling the sensor under test to the measurement surface, which is then exposed to the same acoustic field and the sensor output signal measured. This substitution method allows the sensor sensitivity to be obtained in terms of volts per unit displacement for both the out-of-plane and in-plane surface displacement. The method allows a comprehensive description of an AE sensor response to different planes of displacement and offers the potential for a traceable sensor calibration to units of length.

Characterization of the surface tension and viscosity effects on the formation of nano-liter droplet arrays by an instant protein micro stamper**Partially based on the following paper presented at the μTAS'02 Conference: Lin Shih-Chang, Tsai Yi-Chin, Tseng Fan-Gang, Huang Haimei and Chieng Ching-Chang 2002 Protein microarray patterned by a surface-tension-driven stamping system with discrete dispensing channels μTAS2002 (Nara, Japan, 3–7 Nov.

Rapid and parallel protein micro/nano array formation provides a powerful tool for protein chip fabrication and protein preservation. This paper presents the characterization of the surface tension and viscosity effects on the formation of nano-liter droplet arrays by a novel instant micro stamper, which can simultaneously immobilize hundreds of proteins on a chip. Capillary force is the major driving mechanism of the micro stamper, flowing protein solutions through the chip channel for array-registration and droplet-size control. Three important properties have been characterized in this paper, including uniformity of the parallel printing process, surface wettability and solution viscosity effect on micro droplet size and the dynamic sequence of micro droplet formation. Experimental results demonstrated the uniformity of the parallel stamping process for protein micro arrays from area to area and chip to chip. The effects of surface wettability of bioassay chips and solution viscosity on droplet-size variation have been investigated in detail by experiments and simulations. Both simulation and experimental results demonstrate that the spot size increases with increasing surface wettability and decreasing solution viscosity, and they showed similar tends. The dynamic process of droplet formation has also been observed and analyzed by high-speed images, demonstrating that the footprint reduction rate, formation time and necking of the printed micro droplet are lower on the more hydrophobic surface. This is due to the rapid shrinkage of the droplet footprint area on a hydrophobic surface, resulting in smaller droplet formation. The droplet size can shrink up to 50% when the contact angle of the bioassay chip surface increases from 30° to 80°. On the other hand, the variation of solution viscosity from 1.02 to 10.08 cp makes the droplet size shrink to 70%.

Interaction of Pt and Rh nanoparticles with ceria supports: Ring opening of methylcyclobutane and CO hydrogenation after reduction at 373–723 K

The catalytic properties of a Pt (4%) and a Rh (2.5%) catalyst on a low-surface area ceria support were determined as a function of hydrogen reduction in the temperature range between 373 and 723 K and compared to those of silica-supported Rh (3%) subjected to equivalent treatments. Two reactions were studied: the ring opening of methylcyclobutane (MCB) as representative for structure-sensitive hydrocarbon reactions and the hydrogenation of CO as an example for C O bond activation. After reduction in the low- and mid-temperature range the rates of either reaction decrease significantly on ceria-supported Pt and Rh whereas they are hardly affected on Rh–silica. Annealing in vacuum at 723 K before the reduction step has a beneficial effect on the reaction rates but annealing after reduction leads to a general activity decrease. Accompanying ex situ high-resolution electron microscopy (HREM) investigations largely exclude particle decoration and formation of noble metal–Ce intermetallic bonds as possible effects of metal-support interaction at low and medium reduction temperatures. Taking also into account parallel surface science studies it is concluded that the observed activity decrease originates mainly from electronic perturbations at the interface between the metal nanoparticles and the increasingly reduced ceria support.

Movement of powder bed material during the selective laser sintering of bisphenol‐A polycarbonate

PurposeThe purpose of this paper is to report on a study of the movement of the powder bed material during selective laser sintering (SLS) of bisphenol‐A polycarbonate (PC) powder and its effect on the morphology of the sintered specimen.Design/methodology/approachTwo sintering experiments, i.e. single‐spot laser sintering and raster‐scan laser sintering, were carried out and the material movement mechanisms were investigated in situ and subsequently by scanning electron microscopy.FindingsDuring the raster‐scan laser sintering process, the movement of the powder was found to be primarily perpendicular to the scanning direction. When sintering at a high laser power, it significantly affected the surface morphology of the sintered specimens and parallel surface bands occurred along the scanning direction.Research limitations/implicationsExperiments were carried out on a modified laser engraving machine rather than a commercial SLS machine.Practical implicationsA schematic model of the material movement mechanism for each of the sintering strategies is presented.Originality/valueThe results further the understanding of the sintering behaviour of the powder bed.

On a maximum principle for minimal surfaces and their integrable discrete counterparts

A novel maximum principle for both classical and discrete minimal surfaces is recorded. In the discrete setting, the maximum principle is based on purely geometric notions of discrete Gaußian and mean curvatures and parallel discrete surfaces. As an additional confirmation of the validity of these notions, a discrete analogue of a classical theorem for linear Weingarten surfaces is obtained. Connections with the ‘parallel surface method’ utilized in condensed matter physics are discussed.

Adhesive contact modeling for sub-5-nm ultralow flying magnetic storage head-disk interfaces including roughness effects

As the slider flying height decreases to sub-5-nm to obtain extremely high-density magnetic recordings of the order of 1Tbit∕in.2, problems of adhesion can cause catastrophic behavior at the magnetic recording head-disk interface (HDI). In the earlier part of the paper, a number of interfacial adhesive models were implemented for simplified HDI configurations (i.e., two flat parallel surfaces and a sphere on a flat surface). With the use of realistic HDI properties, individual adhesive force models, such as van der Waals and electrostatic forces, can provide initial approximations to the adhesive forces present during sub-5-nm flying. In the second part of the paper, realistic roughness conditions applicable to actual HDI’s were modeled using an improved Derjaguin–Muller–Toporov-based elastic-plastic rough surface adhesion model. Specifically, the proposed adhesion model accounts for roughness, the presence of molecularly thin lubricant, and includes electrostatic forces. Using experimentally measured roughness values from ultralow flying HDI’s (root-mean-square roughness of 0.65–1.62 nm), it was found that while the contact force is negligible for an interface with low roughness, the adhesive force dominates such interface. Moreover, the effect of roughness promotes adhesion at higher separations than if a two flat parallel surface configuration is considered. Prior to the onset of contact, the total adhesive force for an interface with low roughness is comparable to a two flat parallel surface approximation. However, the simple flat parallel surface approximation fails to predict the realistic onset of contact due to the exclusion of roughness.

Fast grain boundary diffusion and rate-limiting surface exchange reactions in polycrystalline materials

Analytical solutions to the diffusion equations for fast grain boundary diffusion in polycrystalline solids of finite thickness bounded by two parallel surface planes are presented. The grain boundary diffusion coefficient may be higher by several orders of magnitude than the bulk (volume) diffusion coefficient. The microstructure of the polycrystalline sample has been modeled by means of an isolated grain boundary as well as an array of parallel grain boundaries. The surface concentration has been assumed to vary continuously during the diffusion process, as the surface exchange reactions of the diffusing species are considered to be fairly slow and equilibrium between the surface and the constant diffusion source (gas phase) is not attained. Two different cases for surface diffusion at the interface polycrystalline sample/diffusion source are taken into account, viz. negligible and fast surface diffusion. The pertinent analytical solutions allow the calculation of two-dimensional diffusion profiles in thin films and average concentration profiles for semi-infinite diffusion systems. In addition, the time dependence of the total amount of diffusing species exchanged between the diffusion source and the solid sample has been calculated. The theoretical results are interpreted in terms of Harrison’s classification of diffusion regimes. The parallel grain boundary model enables the calculation of diffusion profiles for both type-A and type-B kinetics. In the case of type-A kinetics expressions for the effective diffusion coefficient as well as the effective surface exchange coefficient are proposed, which depend on the corresponding bulk values, the microstructure of the specimen, and the respective surface condition.

Induced Fit of an Epitope Peptide to a Monoclonal Antibody Probed with a Novel Parallel Surface Plasmon Resonance Assay

Class II major histocompatibility complex proteins bind peptides for presentation to T-cells as part of the immune response process. Monoclonal antibody MEM-265 recognizes the peptide-free conformation of the major histocompatibility complex class II protein HLA-DR1 through specific binding to an epitope contained between residues 50-67 of the beta-chain. In previous work using alanine scanning (1), we identified residues Leu-53, Asp-57, Tyr-60, Trp-61, Ser-63, and Leu-67 as essential for specific recognition by MEM-265. The spacing of these residues approximates a 3.5-residue repeat, suggesting that MEM-265 may recognize the epitope in an alpha-helical conformation. In the folded, peptide-loaded DR1 structure, the beta-chain residues 50-67 contain a kinked alpha-helical segment spanning Glu-52-Ser-63 (2). However, the conformation of this segment in the peptide-free form is unknown. We have used a new surface plasmon resonance approach in a SpotMatrix format to compare the kinetic rates and affinities for 18 alanine scanning mutants comprising epitope residues 50-67. In addition to the six essential residues described previously, we found two additional residues, Glu-52 and Gln-64, that contribute by enhancing MEM-265 binding. By contrast, mutation of either Gly-54 or Pro-56 to an alanine actually improved binding to MEM-265. In essentially all cases peptide substitutions that either improve or reduce MEM-265 recognition could be traced to differences in the dissociation rate (k off). The kinetic details of the present study support the presence of a structural component in the antigenic epitope recognized by MEM-265 in the peptide-free form of major histocompatibility complex II DR1 beta-chain.

Broaching of Ti-6-4 – Detection of Workpiece Surface Anomalies on Dovetail Slots through Process Monitoring

Surface anomalies induced by abusive broaching represent a concern for the safety of critical components of aero-engines. Using acoustic emission and force signals, the paper reports on process monitoring techniques to detect surface anomalies when abusively broaching dovetail slots in Ti-6-4. Parallel surface inspection helped in defining the correlation between the occurrence of uneven events in the output signals and the appearance/location of anomalies on the broached surfaces. The findings support the definition of process monitoring strategies to detect workpiece surface anomalies including surface deformation/ overheating, directed scoring and smearing of parent material.

RuO2-Based Dense Electrodes for ESB Electrolyte IT-SOFCs

In this work, we evaluated the performance of dense electrodes based on Ru oxides for Er 2 O 3 stabilized Bi 2 O 3 (ESB) electrolyte. To fabricate symmetric cells, RuO 2 thick films were deposited by screen printing on the parallel surface of dense ESB electrolyte pellets. A very dense layer of Er/Bi mthenate (EBR) was formed at the interface by in situ solid state reaction between the dense pellet (ESB) and the deposited RuO 2 . The reaction led to the formation at the electrode/electrolyte interface of a layer with pyrochlore structure. The electrochemical performance of the EBR/ESB/EBR symmetric cell was investigated using electrochemical impedance spectroscopy (EIS) measurements in air. The dense morphology of the electrodes allowed quantification of the triple phase boundary (TPB) length and its effect on the area specific resistance (ASR).

Metastable group II sulphides grown by MBE: surface morphology and crystal structure

Many group II sulphides semiconductors have the rocksalt structure as their stable crystal structure. In the case of MgS and MnS, it has been demonstrated that these compounds can be grown in the metastable zinc-blende structure using a simple MBE growth procedure that can increase the thickness of these metastable layers to over 130 nm. In this paper, we review the growth method and features which arise during the growth of both MgS and MnS, namely the development parallel surface ridges and the loss of the zinc-blende crystal structure.

Magnetic resonance imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most common primary hepatic malignancy, usually develops in patients with cirrhosis, growing sequentially from low-grade dysplastic nodules to frank malignant HCC. Its recognition is critical because curative treatment and prognosis require early diagnosis. Survival in patients with HCC relates directly to the number, size, and extent of lesions at diagnosis. Imaging of HCC is complicated because the tumor has a varied imaging appearance and frequently coexists with other cirrhotic nodules. Magnetic resonance imaging (MRI), the best available diagnostic technique, offers good contrast resolution and diagnostic sensitivity ranging from 33% to 77%. The main difficulty is not in diagnosing large tumors, but rather small tumors (<2 cm), because of considerable overlap on imaging between benign (regenerative), borderline (dysplastic), and malignant nodules. Increasing degrees of histological malignancy are associated with increasing arterialization and loss of portal blood supply; therefore, recognition of HCC requires dynamic imaging with gadolinium-enhanced T1-weighted sequence. Typically, HCC is a focal lesion with high signal intensity on T2-weighted images, variable signal intensity on T1-weighted images, intense arterial phase enhancement after gadolinium injection, and isointensity or hypointensity at the portal venous phase. The sensitivity of MRI for detecting small lesions is low, and improvement is still needed. Newer contrast agents, higher field strength (3 Tesla) imaging, and perfusion and diffusion MRI techniques possibly will provide greater sensitivity and specificity for detecting small HCCs in the future.

Bulk and boundary critical behavior at Lifshitz points

Lifshitz points are multicritical points at which a disordered phase, a homogeneous ordered phase, and a modulated ordered phase meet. Their bulk universality classes are described by natural generalizations of the standard $\phi^4$ model. Analyzing these models systematically via modern field-theoretic renormalization group methods has been a long-standing challenge ever since their introduction in the middle of the 1970s. We survey the recent progress made in this direction, discussing results obtained via dimensionality expansions, how they compare with Monte Carlo results, and open problems. These advances opened the way towards systematic studies of boundary critical behavior at $m$-axial Lifshitz points. The possible boundary critical behavior depends on whether the surface plane is perpendicular to one of the $m$ modulation axes or parallel to all of them. We show that the semi-infinite field theories representing the corresponding surface universality classes in these two cases of perpendicular and parallel surface orientation differ crucially in their Hamiltonian's boundary terms and the implied boundary conditions, and explain recent results along with our current understanding of this matter.

MIXED-CONVECTIVE COOLING OF AN ISOTHERMAL HOT SURFACE BY CONFINED SLOT JET IMPINGEMENT

The flow and heat transfer characteristics in the cooling of a heated surface by impinging slot jets have been investigated numerically. Computations are done for vertically downward-directed two-dimensional slot jets impinging on a hot isothermal surface at the bottom and confined by a parallel adiabatic surface on top. Some computations are also performed where the jet is vertically upward, with an impingement plate at the top. The principal objective of this study is to investigate the associated heat transfer process in the mixed-convective regime. The computed flow patterns and isotherms for various domain aspect ratios (4–10) and for a range of jet exit Reynolds numbers (100–500) and Richardson numbers (0–10) are analyzed to understand the mixed-convection heat transfer phenomena. The local and average Nusselt numbers and skin friction coefficients at the hot surface for various conditions are presented. It is observed that for a given domain aspect ratio and Richardson number, the average Nusselt number at the hot surface increases with increasing jet exit Reynolds number. On the other hand, for a given aspect ratio and Reynolds number, the average Nusselt number does not change significantly with Richardson number, indicating that the buoyancy effects are not very significant in the overall heat transfer process for the range of jet Reynolds number considered in this study. Also, for the same problem configuration, the average Nusselt number does not change significantly when the jet is moving upward or downward.