The production of activated carbon from coconut shell treated with phosphoric acid (H
3PO
4) was optimized using the response surface methodology (RSM). Fifteen combinations of the three variables ...namely; impregnation ratio (1, 1.5, and 2); activation time (10, 20, and 30
min); and activation temperature (400, 450, and 500
°C) were optimized based on the responses evaluated (yield, bulk density, average pore diameter, small pore diameter, and number of pores in a unit area). Pore diameters were directly measured from scanning electron microscope (SEM) images. Individual second-order response surface models were developed and contour plots were generated for the optimization analysis. The optimum range identified for impregnation ratio was from 1.345 to 2, while for the activation time was from 14.9 to 23.9
min. For the activation temperature it was from 394 to 416
°C. The optimum points are 1.725, 19.5
min, and 416
°C, respectively. The models were able to predict well the values of the responses when the optimum variable parameters were validated as proven by the generally acceptable values of the residual percentages. Direct characterization of the pores using the SEM was found to be a good technique to actually see the pores and get actual measurements. Additionally, RSM has also proven to be a good tool in optimization analysis to get not only optimum production condition points but ranges, which are crucial for the flexibility of the production process, as well.
This study examines the influence of temperature of sub-zero treatment on the wear behaviour of AISI D2 steel. A series of dry sliding wear studies have been made under constant normal load at ...varying sliding velocities. Emphasis has been laid to understand the operative modes and mechanisms of wear by the estimation of specific wear rates and detailed characterizations of the worn surfaces, wear debris and subsurfaces with the help of scanning electron microscope (SEM) examinations coupled with energy dispersive X-ray (EDX) microanalyses. The obtained results unambiguously infer that lower the temperature of sub-zero treatment higher is the improvement in wear resistance. Wear resistance can increase by 1.5–125 times depending on sliding velocity while hardness increases only by 4.2% at the lowest temperature of sub-zero treatment (77K) compared to the conventionally treated specimens. These results corroborate well with the reduction in retained austenite content associated with simultaneous increase in the amount of secondary carbide particles with lowering of sub-zero treatment temperature. The operative modes and mechanisms of wear are identified as either mild oxidative or severe delaminative, which depends on the temperature of sub-zero treatment and the sliding velocity of the wear test.
This study aims to reveal the underlying mechanisms responsible for the enhancement of wear resistance of AISI D2 steel by deep cryogenic treatment (DCT) through in-depth microstructural analyses, ...and thereby attempt to correlate microstructure with wear behaviour of DCT specimens with reference to that of conventional heat treatment (CHT) and cold treatment (CT). Microstructural characterizations of the differently treated specimens have been done by image analyses of optical and SEM photographs, XRD, and EDX analyses, whereas wear behaviour has been characterized by wear rate, wear resistance, and analyses of worn surfaces, wear debris and subsurfaces. The results indicate that DCT markedly enhances the wear resistance of the selected steel compared to CHT and CT. Formation of white layer and its subsequent delamination have been identified as the operative wear mechanisms; the extent of these phenomena and the consequent wear rate is dependent on the type of treatment that determines the microstructures. The wear behaviour can be unambiguously correlated with the modifications in the precipitation behaviour of secondary carbides and reduction in the retained austenite content of the microstructure, which are the governing mechanisms for the improved of wear resistance of tool steels by DCT.
Aim
To describe two patients with X‐linked hypophosphatemia presenting with spontaneous signs of pulpal necrosis in multiple intact teeth. The presentation and management are discussed, along with ...the diagnostic and endodontic treatment challenges.
Summary
Two young male patients with X‐linked hypophosphatemia were referred to the Department of Restorative Dentistry at the Edinburgh Dental Institute, UK for management of dental infection. Both patients were referred due to their unusual clinical presentation and abnormal root canal morphology. They subsequently presented on multiple occasions with pain or sinus tracts over a 3‐ and 5‐year period whilst under care. Clinical examination revealed intact teeth with buccal swellings, draining buccal sinuses and negative responses to pulp sensibility testing. Radiographic examination, generally consisting of periapical radiographs, revealed intact teeth with a range of unusual morphological features including large pulp chambers, wide canals, short roots and open apices, all with associated periapical radiolucencies. Due to the unusual morphology, some teeth required apexification with a mineral trioxide aggregate plug. Patient 1 underwent root canal treatment on teeth 21 and 43 over a 3‐year period. Patient 2 underwent root canal treatment on 10 permanent teeth over a 5‐year period. At follow‐up, both patients were asymptomatic and clinically the teeth had no signs of infection or periapical inflammation. Radiographic examination confirmed complete resolution of the apical radiolucencies on 11 out of 12 teeth. Favourable outcomes have been demonstrated up to a follow‐up of 4.5 years.
Key learning points
Patients with X‐linked hypophosphatemia may present with ‘spontaneous’ signs of pulp necrosis in multiple teeth in the absence of caries and trauma posing a diagnostic challenge.
Abnormal morphological features, including wide canals and open apices, may present challenges during root canal treatment.
Outcomes demonstrate that an appropriate root canal treatment protocol, including the application of apexification procedures, may be implemented to successfully manage such cases.
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•Single phase codoped cobalt ferrite nanoparticles using co-precipitation route.•Doping causes formation of mixed spinel ferrite phase.•UV–vis spectroscopy suggests blue and red shift ...for doped samples.•Both grain and grain boundary contributed in electrical conductivity.•Doped samples showed enhanced dielectric and resistive properties.
Effect of Mn and Ni codoping on structure, optical and electrical properties of cobalt ferrite nanoparticles prepared by coprecipitation route have been investigated in detail. DSC-TGA, XRD and HRTEM studies have been explored to confirm the phase purity and structure. Most possible cation distribution as estimated by Rietveld analysis suggests the formation ofmixed spinel ferrite phase by the migration of Co2+ ions from B site to A site and hence Fe3+ ions from A site to B site in different amounts due to the doping of Mn and Ni ions. UV–vis study reveals a red shift for Mn and Mn-Ni co-doped samples while a blue shift was observed in case of Ni doping. Conductivity spectra follows the double power law and the modulus spectroscopy study indicates the coexistence of two incomplete relaxation processes in the system that arises due to the co-contribution from both grain and grain boundary which were thoroughly confirmed by complex impedance analysis. Improvement in the dielectric properties in the materials due to doping could be beneficial for device applications.
Drowsiness refers to the state of being sleepy or the state of minimal concentration. It is characterised by a decrease in a person's memory capacity and brain information processing speed. These ...conditions cause hazards in the real-time working environment such as driving, monitoring power generation and patient health etc. These hazards can be sidestepped by introducing the automatic drowsiness detection system. This Letter suggested the electroencephalogram (EEG)-based automatic drowsiness detection method. The clustering variational mode decomposition (CVMD) explores the non-stationary behaviour of EEG for drowsiness detection. In CVMD optimum allocation sampling analyses non-homogenous EEG signals and converts those into homogeneous EEG clusters. These clusters are then decomposed into band-limited modes. The oscillatory mode characteristics are extracted in terms of several features. These features are fed as input into the least-squares support vector machine classifier. The proposed method provides better drowsiness detection performance in comparison with the different methods using the same data set.
•Partial oxidation of seven fuels are reviewed.•Catalysts for CPOX reactions of each fuel are discussed.•Noble metals more stable than nickel for all CPOX reactions.•Methods of kinetic modelling are ...highlighted.•High molecular weight fuels require more rigorous reaction kinetics.
Synthesis gas production is a technology that dates to the 1950s. Recently, the conversion of hydrocarbons to syngas has played an important role in various applications from gas-to-liquid (GTL) processes to fuel cell applications. However, the current industrial production method is only profitable when large quantities of syngas are produced and generates high amounts of CO2 as a by-product. With the growing demands for smaller-scale and mobile syngas production technology, the catalytic partial oxidation of hydrocarbons has become a promising alternative to the conventional methane steam reforming technology. With the infrastructure for production and distribution of many commercial fuels already in place, numerous studies have been done on conversion of these fuels into syngas. This paper reviews the research that has been done in the past decade on the catalytic partial oxidation of conventional fuels and biofuels. The challenges faced in catalyst development are described as well as solutions that have been proposed to address those challenges. Advances in kinetic modelling of catalytic partial oxidation are presented, and techniques used to develop such models have also been highlighted. Finally, research gaps have been identified and recommendations have been given for further investigations to address current challenges.
In this article, we study linear complementarity problem with hidden Z-matrix. We extend the results of Fiedler and Pták for the linear system in complementarity problem using game theoretic ...approach. We establish a result related to singular hidden Z-matrix. We show that for a non-degenerate feasible basis, linear complementarity problem with hidden Z-matrix has unique non-degenerate solution under some assumptions. The purpose of this paper is to study some properties of hidden Z-matrix.
The wear properties, hardness values and the microstructural characteristics of AISI D2 steel cryotreated at 77
K for different soaking durations (0–132
h) have been examined to find out the ...optimized soaking time in cryogenic processing for maximization of its wear resistance. Examination of the structure–property relations of differently treated specimens indicates that the best wear resistance is obtained for specimens cryogenically processed for 36
h. This result has been substantiated using the nature of the associated variations of different microstructural features, hardness values, topography of worn surfaces and characteristics of wear debris.
Aim
To investigate the prevalence of periradicular periodontitis (PRP) using cone‐beam computed tomography (CBCT) scans in a retrospective cross‐sectional epidemiological study in a Scottish ...subpopulation.
Methodology
Of the 319 CBCT scans performed at Dundee Dental Hospital between November 2009 and July 2012, 245 dentate scans of patients over 18 years of age were included and 3595 teeth examined. Odds ratios were calculated, and the association between root filling and posts with PRP was determined.
Results
Radiological signs of PRP were detected in 209 teeth (5.8%) in 96 patients (male = 53, female = 43) of which 145 (69.4%) were measurable and 64 (30.6%) appeared as periapical widening. Most lesions were seen in the 46–55‐year age group and in maxillary anterior teeth (35.4%); 47.4% (n = 81) of the total root filled teeth (n = 171) had PRP. Of the root filled teeth with lesions, approximately half (50.6%) had an inadequate root filling. Teeth with crowns, but not root filled, accounted for 17.7% of PRP. Periapical changes were detected on a high proportion of teeth with post‐retained crowns (70.7%). The presence of a root filling was significantly associated with PRP (z = 17.689 P < 0.0001; odds ratio 16.36 < 23.17 < 32.83, 95% CI) and the presence of a post (z = 10.901 P < 0.0001; odds ratio 21.36 < 41.8021 < 81.78, 95% CI).
Conclusions
The prevalence of PRP in a Scottish subpopulation was 5.8%. The presence of a root filling or a post‐retained crown was significantly associated with the presence of PRP as determined by CBCT scans. The prevalence of periradicular disease in root filled teeth remains high in the Scottish population.
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