Microscopic studies of semi-coke from different macerals after treatment of the coal in K/THF/naphthalene

The effect of K/THF/N (potassium in tetrahydrofuran plus naphthalene) on coke structure is illustrated.     

Analysis on profile accuracy for ultrasonic machining of alumina ceramics

Ultrasonic machining (USM) is a mechanical material removal process which has great potential for machining hard and brittle materials such as ceramics, semiconductors, glasses, etc. The accuracy of the job profile generated by USM can be improved by optimal control of the process parameters. This paper presents the study on the influences of ultrasonic machining process parameters such as abrasive grit size, slurry concentration, power rating, tool feed rate and slurry flow rate on generated hexagonal hole profile. The angular deviations at corner angles, dimensional deviations across flat surfaces and dimensional deviation across corners of the hexagonal hole profile have been studied. Based on experimental results, the influences of abrasive grit size, slurry concentration, power rating and tool feed rate were analysed. From the analysis of parametric influences based on various test results, the best parametric combination was found as grit number of 600, slurry concentration of 30 %, power rating of 50 % and feed rate of 1.08 mm/min for achieving better profile accuracy during machining of Al₂O₃ ceramics. The experimental investigations carried out for determining the influence of USM process parameters will provide effective guideline to select parametric settings for achieving desired job profile accuracy on non-circular holes during ultrasonic drilling of alumina.     

Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.     

Surface characteristics of ECMed titanium work samples for biomedical applications

Electrochemical machining (ECM) process has great potential on account of the versatility of its applications. ECM is being widely used in the manufacturing industry because hard metals can be machined regardless of the mechanical property of a work piece. Titanium is broadly used in a number of fields such as aerospace, power generation, automotive, chemical including petrochemical, and sporting goods. Apart from these applications, it has tremendous prospective in dental, medical industries, and biomedical engineering. The biological performance of titanium implant depends on their surface topography and form accuracy that includes various surface parameters. ECM is one of the alternative machining processes that can be applied to the machining of titanium implant for biomedical applications. The aim of this paper is to present experimental result of surface characteristics obtained on titanium samples, utilizing developed cross-flow electrolyte supply system in electrochemical machining. It is observed that electrolyte flow velocity and voltage between electrodes are some of the influencing parameters, which affect the surface characteristics. Titanium oxide layer has been generated on the machined surface, which facilitates the improvement of the corrosion and chemical resistance of titanium implant. Effects of electrolyte flow velocity and voltage during electrochemical machining process for generation of various surface characteristics have been successfully studied through experimentation. In the present work, the obtained surface roughness values on the titanium sample machined by ECM were in the range of 2.4 to 2.93???m, which is within acceptable value for the implants. Effects of electrolyte flow velocity and voltage on the material removal rate and machining accuracy in the form of overcut are also presented in the paper.     

Analysing factors affecting delays in Indian construction projects

Construction projects in India are experiencing widespread delays. Due to a dramatic shift in the capacity and volume of the Indian construction sector over the last decade, the need of a systematic analysis of the reasons of delays and developing a clear understanding among the industry professionals are highly crucial. Using a selected set of 45 attributes, this research first identified the key factors impacting delay in Indian construction industry and then established the relationship between the critical attributes for developing prediction models for assessing the impacts of these factors on delay. A questionnaire and personal interviews have formed the basis of this research. Factor analysis and regression modelling were used to examine the significance of the delay factors. From the factor analysis, most critical factors of construction delay were identified as (1) lack of commitment; (2) inefficient site management; (3) poor site coordination; (4) improper planning; (5) lack of clarity in project scope; (6) lack of communication; and (7) substandard contract. Regression model indicates slow decision from owner, poor labour productivity, architects' reluctance for change and rework due to mistakes in construction are the reasons that affect the overall delay of the project significantly. These findings are expected to be significant contributions to Indian construction industry in controlling the time overruns in construction contracts.     

In vitro cytotoxicity and ion release of multi-ion doped hydroxyapatite

Multi-ion doped hydroxyapatite (HA) is gaining more attention due to its potential in enhancing multifunctional biological, structural, and mechanical properties for orthopedic and dental applications. In this study, HA doped with multiple cations (Sr⁺², Zn⁺², Ag⁺) and anion (F⁻) was prepared by high-energy ball milling. Sintered HA samples were evaluated for their in vitro cytocompatibility, ion release, and bioactivity. The composition of multi-ion doped HA was optimized using Design of experiments (DOE). Our analysis showed that the contribution of each dopant on cell proliferation changes with culture duration. During first 3 days, F⁻ exhibited strongest influence and during 7-day proliferation Sr⁺² and Ag⁺ had maximum influence. Binary ion doping found to have strong interaction on cell proliferation, while the ternary and quaternary ion doping did not show any interactions. In general, up to twofold increase in the cell viability was achieved with ternary and quaternary ion doping consisting of Sr⁺², Zn⁺², Ag⁺ and F⁻. Although large number of compositions has been identified to exhibit better in vitro cell viability than pure HA, for enhanced long-term cytocompatibility the compositions of multi-ion doped HA would be 2.5Sr-2.5Zn-2.5Ag, 2.5Sr-5Zn-2.5Ag, and 5Sr-2.5Zn-2.5Ag with up to 5 wt% F.     

In vitro and in vivo release of cefuroxime axetil from bioactive glass as an implantable delivery system in experimental osteomyelitis

The aim of this study was to evaluate the characterisation, in vitro and in vivo biocompatibility and antimicrobial activity of bioactive glass (BG) impregnated with an antibiotic. The BG was prepared by normal glass melting procedures as a controlled release device to treat experimental osteomyelitis. The study design was for prospective in vivo experimental study. Two sets of porous bioactive glass ceramic blocks (9 mm × 4 mm × 4 mm and 20 mm × 9 mm × 9 mm) were fabricated using bioactive glass powder and subsequently antibiotic cefuroxime axetil (CFA) (55 and 125 mg on an average) was impregnated in these two sets of blocks, respectively. Osteomyelitis was produced in the right tibia of the rabbits according to the model of Norden. After thorough in vitro characterization of the porous blocks [including X-ray diffraction (XRD), Fourier-transformed infra-red spectroscopy (FTIR), thorough chemical analysis by inductively coupled plasma-atomic emission spectra (ICP-AES) and field-emission scanning electron microscopy (FESEM)] and in vitro elution of the said drug, in vivo test was carried out with rabbit species split into two groups: (a) animals treated with CFA impregnated bioactive glass and (b) parenteral [intra muscular (IM)] administration of CFA. Histological, radiological and drug concentration in bone and serum (measured by HPLC) in both groups were carried out. HPLC technique was used for determination of concentration both in vitro and in vivo. Fabricated porous struts showed amorphous microstructure without formation of any crystallite. The elution of said drug was stopped after 6 days in vitro. Histological studies at 3 and 6 weeks revealed formation of well-developed lamellar bone and havarsian canal. Radiological evaluation pointed out disappearance of sequestrum and existence of newly formed bony specules. Concentration of cefuroxime axetil in bone and serum showed highest value on day 21 which reduced marginally by day 42 and these values were higher than minimum inhibitory concentration (MIC) against Staphylococcus aureus (known pathogen for chronic osteomyelitis). It could be concluded that the biodegradable antibiotic carrier system developed in this study proved to be an effective therapeutic approach toward an experimental model of osteomyelitis. Based particularly on the in vivo results of the study, this cefuroxime axetil incorporated bioactive glass blocks can be successfully used in clinical cases of osteomyelitis in veterinary as well as human orthopaedic surgery.     

Fabrication of stepped hole on zirconia bioceramics by ultrasonic machining

Zirconia (ZrO₂) is a highly biocompatible ceramic material providing fracture strength properties that allow application as dental implants in biomedical engineering. In this present research, experimental analysis has been made for generating stepped hole on zirconia bioceramics with desired quality using ultrasonic machining (USM) process. Four independent controllable input process parameters are abrasive grain diameter, power rating, concentration of abrasive slurry, and tool feed rate. Material removal rate (MRR), overcut of larger diameter (OLD) hole, and overcut of smaller diameter (OSD) hole of stepped hole are considered as the responses. Response surface methodology (RSM) is used for modeling the performance of USM process. Multiobjective optimization has been performed to maximize the MRR and minimize the OLD hole and OSD hole of stepped holes. All the responses are improved at the optimal parametric condition and verified by confirmation test. The present research opens up the application feasibility of USM process for stepped hole generation on bioceramics and its utilization in biomedical field.     

Ethernet PON (ePON): Design and Analysis of an Optical Access Network

With the expansion of services offered over the Internet, the last mile bottleneck problems continue to exacerbate. A passive optical network (PON) is a technology viewed by many as an attractive solution to this problem. In this study, we propose the design and analysis of a PON architecture which has an excellent performance-to-cost ratio. This architecture uses the time-division multiplexing (TDM) approach to deliver data encapsulated in Ethernet packets from a collection of optical network units (ONUs) to a central optical line terminal (OLT) over the PON access network. The OLT, in turn, is connected to the rest of the Internet. A simulation model is used to analyze the systems performance such as bounds on packets delay and queue occupancy. Then, we discuss the possibility of improving the bandwidth utilization by means of timeslot size adjustment, and by packet scheduling.     

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.