A method for monitoring head media spacing change in a hard disk drive using an embedded contact sensor

Growth in the demand for higher capacity hard disk drives has pushed the requirement for head-media spacing to sub-nanometer levels. The drop in operational clearance makes a head-disk interface more susceptible to potential head-wear and contamination related issues. Such degradation processes are often accompanied by a noticeable shift in the head-disk clearance. Hence monitoring an interface for a spacing change can be helpful in early detection of its imminent failure. In this paper, we present a method to detect the change in head-disk spacing using an embedded contact sensor (ECS). This technique involves the analysis of ECS dynamic response for an interface that is subjected to heater induced spacing modulations. As the head moves closer to the disk surface, the magnitude of the ECS frequency components can be used to determine the ‘characteristic spacing’ which can be used as a metric to detect any physical change for a given interface.

     

Importance Sampling-Based Unscented Kalman Filter for Film-Grain Noise Removal

Photographic film contains film-grain noise that translates to multiplicative, non-Gaussian noise in the exposure domain. A method based on the unscented Kalman filter can suppress this noise while simultaneously preserving edge information.     

Cation distributions and magnetism of Al-substituted CoFe2O4 - NiFe2O4 solid solutions synthesized by sol-gel auto-combustion method

Aluminium substituted cobalt-nickel ferrite nanoparticles were synthesized by citrate gel auto-combustion method followed by annealing at 1000?°C for 1?h in air. Scanning electron micrographs of all the samples show crystalline particles of irregular morphology with a small variation in particle sizes (~ 110–160?nm). From the analysis of the X-ray diffraction results we observed that the unit cell parameter decreases linearly with increase in aluminium concentration due to the smaller ionic radius of the Al³⁺ ions substituting the other cations such as Co²⁺, Ni²⁺ and Fe³⁺ ions in the compounds. The room temperature Mössbauer spectra of the samples show Zeeman split sextet patterns corresponding to the tetrahedral (Th) and octahedral (Oh) interstitial iron (Fe³⁺) cations. The observed magnetic hyperfine field (B_hf) decreases with increase in Al-concentration due to the distribution of diamagnetic Al³⁺ in the environment of ⁵⁷Fe probe atoms. The saturation magnetization measured by Vibrating Sample Magnetometer (VSM) shows a similar trend like that of B_hf. The distributions of the cations obtained from the Rietveld refinement and Mössbauer spectroscopy results indicate an increase in Fe³⁺(Th)/Fe³⁺(Oh) occupancy-ratio on increasing Al³⁺ concentration, and Ni²⁺ cations prefer the octahedral site, whereas Co²⁺ and Al³⁺ ions redistribute themselves in tetrahedral and octahedral sites, in the ratio 2:3.     

Precursor-mediated dissociation of n-butane on a PdO(1 0 1) thin film

We investigated the molecular adsorption and dissociation of n-butane on a PdO(1 0 1) thin film using temperature-programmed reaction spectroscopy (TPRS) experiments and density functional theory (DFT) calculations. At low coverage, n-butane adsorbs on PdO(1 0 1) in a molecular state that is more strongly bound than n-butane physisorbed on Pd(1 1 1). This molecularly adsorbed state of n-butane on PdO(1 0 1) corresponds to a σ-complex that forms on the rows of coordinatively unsaturated (cus) Pd atoms of the oxide surface. TPRS results show that a fraction of the n-butane layer undergoes C–H bond cleavage below 215 K and that the resulting fragments are completely oxidized by the surface upon continued heating. The evolution of product yields with the n-butane coverage as well as site blocking experiments provide strong evidence that the n-butane σ-complex serves as the precursor to initial C–H bond cleavage of n-butane on PdO(1 0 1). DFT calculations confirm the formation of an n-butane σ-complex on PdO(1 0 1). In the preferred bonding geometry, the n-butane molecule aligns parallel to a cus-Pd row and adopts a so-called η¹(2H) configuration with two coordinate H–Pd bonds per molecule. Our DFT calculations also show that σ-complex formation weakens C–H bonds, causing bond elongation and vibrational mode softening. For methane, we predict that coordination with a cus-Pd atom lowers the barrier for C–H bond cleavage on PdO(1 0 1) by more than 100 kJ/mol. These results demonstrate that dative bonding between alkane molecules and cus-Pd atoms serves to electronically activate C–H bonds on PdO(1 0 1) and suggest that adsorbed σ-complexes play a general role as precursors in alkane activation on transition metal oxide surfaces.     

Effect of Silicon on Mechanical and Wear Properties of Aluminium-Alloyed Gray Cast Iron

Influence of Si on mechanical and wear properties of Al-alloyed gray cast iron has been investigated in this work. The Si content is varied from 1.27 to 2.1% in five different alloys with nearly 2% Al additions. Alloy with 2.1% Si and 1.9% Al shows maximum ferrite matrix with highest flake volume (17.3%). It also has the lowest hardness and strength. Rest of the alloys with Si content equal to or less than 1.7% and 2% Al content shows maximum pearlite matrix with higher hardness and strength. They have also shown a tendency for oxide formation and reduced wear during sliding probably due to higher friction heat and lower heat dissipation tendency due to lower flake volume and Al addition which reduces thermal conductivity of the matrix. The same oxide layer was not evident in alloy with 2.1% Si and 1.9% Al alloy having the highest flake volume (17.3%).     

Optimal designs for constant‐heating‐rate differential scanning calorimetry experiments for polymerization kinetics: nth‐order kinetics

Optimal designs have been constructed for differential scanning calorimetry (DSC) experiments conducted under constant‐heating‐rate conditions for materials that are a priori assumed to follow nth‐order kinetics. Two different operating scenarios are considered, including single‐scan and multiscan DSC experiments for eight different kinetic parameter combinations representing a range of typical polymeric curing reactions. The resulting designs are studied to determine which kinetic model parameters are influential in determining the optimal design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of insoluble dietary fibre addition on technological,sensory, and structural properties of durum wheat spaghetti

Insoluble fibres are important in human health and disease prevention and can be incorporated into food. High fibre pasta prepared with bran is typically inferior quality compared to durum pasta. This study compared spaghetti prepared from durum semolina substituted with various amounts of either durum bran or germ (pollard) dried at high temperature. Pasta was evaluated for cooking properties, texture, sensory, fibre content, antioxidant status (AO) and in vitro starch digestibility to determine the dose producing acceptable quality. Pollard at 10% substitution had minimal impact on quality with higher AO and fibre. Above 30%, pasta had undesirable colour, sensory properties and higher starch digestion. Although bran substituted pasta had undesirable sensory and technological properties, especially at 30% incorporation, it does provide more dietary fibre and antioxidants than regular pasta and does not affect starch digestibility. Interestingly, a significant amount of AO was retained in the cooked pasta. The study illustrates the value of structural analysis to explain observed technological properties of the product with fibre inclusion.     

Prediction of the performance of a solid oxide fuel cell fuelled with biosyngas: Influence of different steam-reforming reaction kinetic parameters

SOFCs are often designed to operate with specific fuels, quite often natural gas. CFD modeling is often used to arrive at efficient and safe SOFC designs. Therefore, when an SOFC is fed with different fuels, i.e., biosyngas, CFD can be used as a tool to predict whether the cell and stack will be safe and operate efficiently, and thus can give suggestions for the operation strategies for SOFCs. For that reason, a combined mass and heat transport model of an SOFC (single channel) has been developed for an anode-supported SOFC fed with biosyngas with special attention to the reaction kinetics of the direct internal reforming (DIR) reaction together with the water–gas shift reaction. An SOFC design jointly developed by ECN and Delft University of Technology is employed for the calculations. This work aims to predict the influence of different reforming reaction kinetic parameters on the cell performance by using an anode-supported intermediate temperature DIR planar solid oxide fuel single channel model, under co-flow operation. The DIR reaction of methane, the water–gas shift reaction and the electrochemical oxidation of hydrogen are being considered. As different reaction kinetic models are available in literature and employing them in CFD calculations will yield different results, a comparative analysis is carried out. Several cases were studied with a variety of DIR and water gas shift reaction kinetic parameters available from literature. For the different cases considered, the modeling results show differences in the current density distribution and temperature profile in the channel and in gas concentration profile along the channel. These differences are presented and discussed in detail. Predictions of the behaviors of internal reforming reaction in the reaction zone, and the possibilities of unwanted side reactions such as carbon deposition and Ni oxidation are given with constructive suggestions for future lab experiments.     

Anode recirculation behavior of a solid oxide fuel cell system: A safety analysis and a performance optimization

Anode recirculation, which is generally driven by an ejector, is commonly used in solid oxide fuel cell (SOFC) systems that operate with natural gas. Alternative fuels such as gasification syngas from biomass have been proposed for potential use in the SOFC systems because of the fuel flexibility of SOFCs and the sustainability of biomass resources. Because the ejector was initially designed to use natural gas, its recirculation behavior when using alternative fuels is not well understood. The aim of this research work is to study anode recirculation behavior and analyze its effect on safety issues regarding carbon deposition and nickel oxidation and the performance of an SOFC system fed with gasification syngas under steady state operation. We developed a detailed model including a recirculation model and an SOFC stack model for this study, which was well validated by experimental data. The results show that the entrainment ratio with the gasification syngas is much smaller than that with the natural gas, and the gasification syngas does not have the tendency toward carbon deposition or nickel oxidation under the operating conditions studied. In addition, the recirculation affects the performance of the SOFC, especially the net electrical efficiency, which could be promoted by 160%.