Surface roughness reduction and diffraction efficiency optimisation for e-beam written phase masks

We report the control of surface relief grating parameters and roughness for phase masks produced using e-beam lithography (EBL) and reactive ion etching (RIE). The relationships between processing conditions, grating parameters, surface roughness and the diffraction efficiency of the zeroth and the two first order transmitted beams are discussed.

Surface roughness reduction and diffraction efficiency optimisation for e-beam written phase masks

We report the control of surface relief grating parameters and roughness for phase masks produced using e-beam lithography (EBL) and reactive ion etching (RIE). The relationships between processing conditions, grating parameters, surface roughness and the diffraction efficiency of the zeroth and the two first order transmitted beams are discussed.

Surface roughness after excimer laser ablation using a PMMA model:profilometry and effects on vision

PURPOSE: To show that the limited quality of surfaces produced by one model of excimer laser systems can degrade visual performance with a polymethylmethacrylate (PMMA) model. METHODS: A range of lenses of different powers was ablated in PMMA sheets using five DOS-based Nidek EC-5000 laser systems (Nidek Technologies, Gamagori, Japan) from different clinics. Surface quality was objectively assessed using profilometry. Contrast sensitivity and visual acuity were measured through the lenses when their powers were neutralized with suitable spectacle trial lenses. RESULTS: Average surface roughness was found to increase with lens power, roughness values being higher for negative lenses than for positive lenses. Losses in visual contrast sensitivity and acuity measured in two subjects were found to follow a similar pattern. Findings are similar to those previously published with other excimer laser systems. CONCLUSIONS: Levels of surface roughness produced by some laser systems may be sufficient to degrade visual performance under some circumstances.

Novel spatial scanning technique for surface roughness measurement

We present the first spatial scanning system using wavelength-spatial transformation of chromatic dispersion device. Optical probe used in fiber optic interferometer for surface measurement is demonstrated by using diffraction grating and wavelength scanning technique.

A geometrical model for surface roughness prediction when face milling Al 7075-T7351 with square insert tools

Surface quality is important in engineering and a vital aspect of it is surface roughness, since it plays an important role in wear resistance, ductility, tensile, and fatigue strength for machined parts. This paper reports on a research study on the development of a geometrical model for surface roughness prediction when face milling with square inserts. The model is based on a geometrical analysis of the recreation of the tool trail left on the machined surface. The model has been validated with experimental data obtained for high speed milling of aluminum alloy (Al 7075-T7351) when using a wide range of cutting speed, feed per tooth, axial depth of cut and different values of tool nose radius (0.8. mm and 2.5. mm), using the Taguchi method as the design of experiments. The experimental roughness was obtained by measuring the surface roughness of the milled surfaces with a non-contact profilometer. The developed model can be used for any combination of material workpiece and tool, when tool flank wear is not considered and is suitable for using any tool diameter with any number of teeth and tool nose radius. The results show that the developed model achieved an excellent performance with almost 98% accuracy in terms of predicting the surface roughness when compared to the experimental data. © 2014 The Society of Manufacturing Engineers.

Integrated optimisation of surface roughness and tool performance when face milling 416 SS

Tool life is an important factor to be considered during the optimisation of a machining process since cutting parameters can be adjusted to optimise tool changing, reducing cost and time of production. Also the performance of a tool is directly linked to the generated surface roughness and this is important in cases where there are strict surface quality requirements. The prediction of tool life and the resulting surface roughness in milling operations has attracted considerable research efforts. The research reported herein is focused on defining the influence of milling cutting parameters such as cutting speed, feed rate and axial depth of cut, on three major tool performance parameters namely, tool life, material removal and surface roughness. The research is seeking to define methods that will allow the selection of optimal parameters for best tool performance when face milling 416 stainless steel bars. For this study the Taguchi method was applied in a special design of an orthogonal array that allows studying the entire parameter space with only a number of experiments representing savings in cost and time of experiments. The findings were that the cutting speed has the most influence on tool life and surface roughness and very limited influence on material removal. By last tool life can be judged either from tool life or volume of material removal.

Artificial neural networks for surface roughness prediction when face milling Al 7075-T7351

In this work, different artificial neural networks (ANN) are developed for the prediction of surface roughness (R a) values in Al alloy 7075-T7351 after face milling machining process. The radial base (RBNN), feed forward (FFNN), and generalized regression (GRNN) networks were selected, and the data used for training these networks were derived from experiments conducted using a high-speed milling machine. The Taguchi design of experiment was applied to reduce the time and cost of the experiments. From this study, the performance of each ANN used in this research was measured with the mean square error percentage and it was observed that FFNN achieved the best results. Also the Pearson correlation coefficient was calculated to analyze the correlation between the five inputs (cutting speed, feed per tooth, axial depth of cut, chip°s width, and chip°s thickness) selected for the network with the selected output (surface roughness). Results showed a strong correlation between the chip thickness and the surface roughness followed by the cutting speed. © ASM International.

On the role of surface roughness in the aerodynamic performance and energy conversion of horizontal wind turbine blades:a review

Summary: Renewable energy is one of the main pillars of sustainable development, especially in developing economies. Increasing energy demand and the limitation of fossil fuel reserves make the use of renewable energy essential for sustainable development. Wind energy is considered to be one of the most important resources of renewable energy. In North African countries, such as Egypt, wind energy has an enormous potential; however, it faces quite a number of technical challenges related to the performance of wind turbines in the Saharan environment. Seasonal sand storms affect the performance of wind turbines in many ways, one of which is increasing the wind turbine aerodynamic resistance through the increase of blade surface roughness. The power loss because of blade surface deterioration is significant in wind turbines. The surface roughness of wind turbine blades deteriorates because of several environmental conditions such as ice or sand. This paper is the first review on the topic of surface roughness effects on the performance of horizontal-axis wind turbines. The review covers the numerical simulation and experimental studies as well as discussing the present research trends to develop a roadmap for better understanding and improvement of wind turbine performance in deleterious environments.

Cellular interactions with hydrogels

An efficient means of evaluating potential biomaterials is to use the in vitro fibroblast cell culture model. However, the chemistry which influences cell adhesion on polymer substrates is poorly understood. The work in this thesis aims to rationalise several theories of current opinion and introduce new chemical techniques that may predict cellular behaviour. The keratoprosthesis is a typical example of the need to be able to manipulate cell adhesion of materials since both adhesive and non adhesive sections are needed for proper integration and optical function. Calcein AM/ethidium homodimer-1 and DAPI assays were carried out using 3T3 and EKl.BR cells. Poly(HEMA) was found to be the most cell adhesive hydrogel tested. The reactivity of monomers and the resulting sequence distribution were found to affect surface properties and this may explain the poor levels of cell adhesion seen on NVP/MMA copolymers. Surface free energy is shown to be dependent on the polar and non polar groups present along the backbone chain of the polymers. Dehydrated and hydrated contact angle measurements show the effect of rotation of surface groups around the backbone chain. This effect is most apparent on hydrogels containing methacrylic acid. Dynamic contact angle measurements confirm sequence distribution irregularities and demonstrate the mobility of surface groups. Incorporation of NVI or DEAEMA into the hydrogels does not affect the mobility of the surface groups despite their bulkiness. Foetal calf serum was used for the first time as a test solution in an attempt to mimic a biological environment during surface experiments. A Vroman effect may be present, and may involve different surface proteins for each material tested. This interdisciplinary study combines surface characterisation and biological testing to further the knowledge of the biomaterial/host interface. Surface chemistry techniques appear to be insufficiently sensitive to predict cellular behaviour. The degree of ionisation of hydrogels containing ionic groups depends on the nature of the functional groups as well as the concentration and this is an important parameter to consider when comparing charged materials.

Ordered mixing of drugs with particulate excipients

A novel direct compression tableting excipient has been made by recrystallisation of lactose. The particles produced had high porosity, high specific surface area and high surface roughness. The resistance to segregation of ordered mixes formed between a model drug; potassium chloride and the excipients recrystallised lactose, spray crystallised maltose-dextrose (Emdexl and a direct compacting sugar (Dipac) was studied using a vibrational segregation model. The highly porous excipients, Emdex and recrystallised lactose formed ordered mixes which did not segregate even at high accelerations and low frequencies whereas the relatively smooth excipient, Dipac, displayed marked segregation in most vibration conditions. The vibrations were related to practical conditions measured in pharmaceutical process machinery. The time required to form an ordered mix was inversely related to the stability of the mix when subjected to vibration. An ultracentrifuge technique was developed to determine the interparticle adhesion forces holding drug and excipient particles together as ordered units. Excipient powders such as Emdex and recrystallised lactose, which formed non-segregating ordered mixes, had high interparticle adhesion forces. Other ordered mixes that segregated when subjected to different vibration conditions were found to have large quantities of weekly-bound drug particles; such mixes included those with Dipac as the carrier excipient as well as those containing a high concentration of drug. The electrostatic properties of different drug and excipient powders were studied using a Faraday well and an electrometer. Excipient powders such as Emdex and recrystallised lactose which formed stable ordered mixes also had a widely different surface charge in comparison with drug particles, whereas Dipac had a similar surface charge to the drug particles and formed unstable ordered mixes. A specially constructed triboelectric charging apparatus based on an air cyclone was developed to increase the affinity of drug particles for different excipient particles. Using triboelectrification to increase the interparticle adhesion forces, the segregation tendencies of unstable ordered mixes were greatly reduced. The stability of ordered mixes is shown to be related to both the surface physical characteristics and the surface electrical properties of the constituent carrier (excipientl particles.

Influence of impact angles on penetration rates of CRAs exposed to a high velocity multiphase flow

A combined flow loop - jet impingement pilot plant has been used to determine mass loss rates in a mixed gas - saltwater - sand multiphase flow at impact velocities up to 70 m/s. Artificial brine with a salt content of 27 g/1 was used as liquid phase. Sand content, with grain size below 150 µ, was 2.7 g/l brine. CO at a pressure of 15 bar was used as gas phase. The impact angle between jet stream (nozzle) and sample surface was varied between 30 and 90°. Rectangular stainless steel disc samples with a size of 20 × 15 × 5 mm were used. They were mechanically ground and polished prior to testing. Damaged surfaces of specimens exposed to the high velocity multiphase flow were investigated by stereo microscopy, scanning electron microscopy (SEM) and an optical device for 3D surface measurements. Furthermore, samples were investigated by applying atomic force microscopy (AFM), magnetic force microscopy (MFM) and nanoindentation. Influence of impact velocity and impact angle on penetration rates (mass loss rates) of two CRAs (UNS S30400 and N08028) are presented. Moreover effects of chemical composition and mechanical properties are critically discussed. © 2008 by NACE International.

Chitosan-modified dry powder formulations for pulmonary gene delivery

Spray-drying is an effective process for preparing micron-dimensioned particles for pulmonary delivery. Previously, we have demonstrated enhanced dispersibility and fine particle fraction of spray-dried nonviral gene delivery formulations using amino acids or absorption enhancers as dispersibility-enhancing excipients. In this study, we investigate the use of the cationic polymer chitosan as a readily available and biocompatible dispersibility enhancer. Lactose-lipid:polycation:pDNA (LPD) powders were prepared by spray-drying and post-mixed with chitosan or spray-dried chitosan. In addition, the water-soluble chitosan derivative, trimethyl chitosan, was added to the lactose-LPD formulation before spray-drying. Spray-dried chitosan particles, displaying an irregular surface morphology and diameter of less than 2 mu m, readily adsorbed to lactose-LPD particles following mixing. In contrast with the smooth spherical surface of lactose-LPD particles, spray-dried trimethyl chitosan-lactose-LPD particles demonstrated increased surface roughness and a unimodal particle size distribution (mean diameter 3.4 mu m), compared with the multimodal distribution for unmodified lactose-LPD powders (mean diameter 23.7 mu m). The emitted dose and in vitro deposition of chitosan-modified powders was significantly greater than that of unmodified powders. Moreover, the inclusion of chitosan mediated an enhanced level of reporter gene expression. In summary, chitosan enhances the dispersibility and in vitro pulmonary deposition performance of spray-dried powders.

Electrografting of poly (carbazole-co-acrylamide) onto highly oriented pyroltic graphite. A cyclovoltammetric, atomic force microscopic and ellipsometric study

The electrocopolymerization of carbazole and acrylamide on highly oriented pyrolytic graphite (HOPG) from ACN solutions via cyclovoltammetry (CV) was studied in order to evaluate the possibility to deposit uniform and thin but pinhole-free and still reactive coatings onto graphite-like substrates. The morphology of the coatings was investigated using atomic force microscopy and the coating thicknesses and optical parameters were measured using ellipsometry. It was found that under the chosen conditions thin (coating thickness hf>180 nm) and relatively smooth (root mean square surface roughness RMS<150 nm) P(Cz-co-AAm)-coatings exhibiting a uniform globuoidal morphology can be deposited onto graphite. From a certain coating thickness (hf>50 nm) no pinholes could be detected. It was found that the thickness of the deposited coatings increases almost linearly with increasing number of CV-cycles while keeping all other experimental parameters (scan rate and comonomer concentration ratio) constant. No influence of the comonomer concentration ratio on the film thickness and coating appearance could be observed, however, at quite low initial concentrations. However, the CV-scanning rate has quite a significant influence on the thickness of the deposited coatings. Higher scan rates (100 mV/s) result in thin (hf≈22 nm) coatings whereas at lower scan rates (<50 mV/s) coatings with thicknesses of approximately 50 nm were obtained. The optical coating parameters (the refractive index n and extinction coefficient k) seem to be independent of the deposition parameters and therefore averaged values of n̄=1.54±0.03 and k̄=0.08±0.03 were obtained.