Shape-formed ceramic superconductors by slip-casting

In order to rigorously test emerging applications using prototypes and pilot designs, high temperature superconductor (HTS) materials must be fabricated into a variety of shapes in an economical manner. We have developed a simple, economical, ceramic slip-casting approach to form complex shaped monolithic HTS articles for which high bulk density has been achieved. The sintered articles exhibit good Meissner signal and consist of phase-pure HTSC phase. A low transport critical current density is observed and is explained on the basis of densification and grain growth. © 1995 The Metallurgical of Society of AIME.

Base-induced decomposition of alkyl hydroperoxides in the gas phase. Part 3. Kinetics and dynamics in HO-+CH3OOH, C2H5OOH, and tert-C4H9OOH reactions

The E-CO(2) elimination reactions of alkyl hydroperoxides proceed via abstraction of an (x-hydrogen by a base: X- + (RRHCOOH)-R-1-H-2 -> HX + (RRC)-R-1-C-2=O + HO-. Efficiencies and product distributions for the reactions of the hydroxide anion with methyl, ethyl, and tert-butyl hydroperoxides are studied in the gas phase. On the basis of experiments using three isotopic analogues, HO- + CH3OOH, HO- + CD3OOH, and H18O- + CH3OOH. the overall intrinsic reaction efficiency is determined to be 80% or greater. The E(CO)2 decomposition is facile for these methylperoxide reactions, and predominates over competing proton transfer at the hydroperoxide moiety. The CH3CH2OOH reaction displays a similar E(CO)2 reactivity, whereas proton transfer and the formation of HOO- are the exclusive pathways observed for (CH3)(3)COOH, which has no (x-hydrogen. All results are consistent with the E-CO(2) mechanism, transition state structure, and reaction energy diagrams calculated using the hybrid density functional B3LYP approach. Isotope labeling for HO- + CH3OOH also reveals some interaction between H2O and HO- within the E(CO)2 product complex [H2O center dot center dot center dot CH2=O center dot center dot center dot HO-]. There is little evidence, however. for the formation of the most exothermic products H2O + CH2(OH)O-, which would arise from nuclephilic condensation of CH2=O and HO-. The results suggest that the product dynamics are not totally statistical but are rather direct after the E-CO(2) transition state. The larger HO- + CH3CH2OOH system displays more statistical behavior during complex dissociation.

Stoichiometry, crystallinity, and nano-scale surface morphology of the graded calcium phosphate-based bio-ceramic interlayer on Ti-Al-V

A plasma-assisted concurrent Rf sputtering technique for fabrication of biocompatible, functionally graded CaP-based interlayer on Ti-6Al-4V orthopedic alloy is reported. Each layer in the coating is designed to meet a specific functionality. The adherent to the metal layer features elevated content of Ti and supports excellent ceramic-metal interfacial stability. The middle layer features nanocrystalline structure and mimics natural bone apatites. The technique allows one to reproduce Ca/P ratios intrinsic to major natural calcium phosphates. Surface morphology of the outer, a few to few tens of nanometers thick, layer, has been tailored to fit the requirements for the bio-molecule/protein attachment factors. Various material and surface characterization techniques confirm that the optimal surface morphology of the outer layer is achieved for the process conditions yielding nanocrystalline structure of the middle layer. Preliminary cell culturing tests confirm the link between the tailored nano-scale surface morphology, parameters of the middle nanostructured layer, and overall biocompatibility of the coating.

The influence of atmospheric conditions on the leakage current of ceramic insulators on the Colombian Caribbean coast

The contamination of electrical insulators is one of the major contributors to the risk of operation outages in electrical substations, especially in coastal zones with high salinity levels and atmospheric pollution. By using the measurement of leakage-currents, which is one of the main indicators of contamination in insulators, this work seeks to the determine the correlation with climatic variables, such as ambient temperature, relative humidity, solar irradiance, atmospheric pressure, and wind speed and direction. The results obtained provide an input to the behaviour of the leakage current under atmospheric conditions that are particular to the Caribbean coast of Colombia. Spearman’s rank correlation coefficients and principal component analysis are utilised to determine the significant relationships among the different variables under consideration. The necessary information for the study was obtained via historical databases of both atmospheric variables and the leakage current measured in over a period of one year in a 220-kV potential transformer insulator. We identified the influencing factors of temperature, humidity, radiation, wind speed and direction on the magnitude of the leakage current as the most relevant.

Analysis of ancient pottery and ceramic objects using X-ray fluorescence spectrometry

Archaeology has been called 'the science of the artefact' and nothing demonstrates this point better than the current interest displayed in provenance studies of archaeological objects. In theory, every vessel carries a chemical compositional pattern or 'fingerprint' identical with the clay from which it was made and this relationship is basic to provenance studies. The reasoning behind provenance or sourcing studies is to probe into this past and attempt to re-create prehistory by obtaining information on exchange and social interaction. This paper discusses the use of XRF spectrometry for the analysis of ancient pottery and ceramics to examine whether it is possible to predict prehictoric cultural exchanges.

Effectiveness of a puppet show on iodine knowledge, attitudes and behaviour of elementary students and the indirect effects on their parents and households in Ho Chi Minh City : a pilot study

Deficiencies in iodine levels have been shown to seriously affect a child’s intellectual development and learning capacity.1 In South-East Asia, iodine deficiency remains a major public health concern. Approximately 30% of the region’s population of 503.6 million have insufficient iodine intake, and only 61% of households have access to iodized salt.1 For this reason, it is necessary to initiate effective, community-based health promotion activities that are targeted toward populations of various ages. A puppet show is one imaginative and entertaining method of health education that has been advocated for use in communicating positive health behaviours to children.2e5 The authors undertook a literature review and found no studies assessing the effectiveness of a puppet show to teach an iodine education programme...

The impact of cataract surgery on vision-related quality of life for bilateral cataract patients in Ho Chi Minh City, Vietnam : a prospective study

Background To determine the impact of cataract surgery on vision-related quality of life (VRQOL) and examine the association between objective visual measures and change in VRQOL after surgery among bilateral cataract patients in Ho Chi Minh City, Vietnam. Methods A cohort of older patients with bilateral cataract was assessed one week before and one to three months after first eye or both eye cataract surgery. Visual measures including visual acuity, contrast sensitivity and stereopsis were obtained. Vision-related quality of life was assessed using the NEI VFQ-25. Descriptive analyses and a generalized linear estimating equation (GEE) analysis were undertaken to measure change in VRQOL after surgery. Results Four hundred and thirteen patients were assessed before cataract surgery and 247 completed the follow-up assessment one to three months after first or both eye cataract surgery. Overall, VRQOL significantly improved after cataract surgery (p < 0.001) particularly after both eye surgeries. Binocular contrast sensitivity (p < 0.001) and stereopsis (p < 0.001) were also associated with change in VRQOL after cataract surgery. Visual acuity was not associated with VRQOL. Conclusions Cataract surgery significantly improved VRQOL among bilateral cataract patients in Vietnam. Contrast sensitivity as well as stereopsis, rather than visual acuity significantly affected VRQOL after cataract surgery.

Prevalence and visual risk factors for falls in bilateral cataract patients in Ho Chi Minh City, Vietnam

Purpose To determine the prevalence of falls in the 12 months prior to cataract surgery and examine the associations between visual and other risk factors and falls among older bilateral cataract patients in Vietnam. Methods Data collected from 413 patients in the week before scheduled cataract surgery included a questionnaire and three objective visual tests. Results The outcome of interest was self-reported falls in the previous 12 months. A total of 13% (n = 53) of bilateral cataract patients reported 60 falls within the previous 12 months. After adjusting for age, sex, race, employment status, comorbidities, medication usage, refractive management, living status and the three objective visual tests in the worse eye, women (odds ratio, OR, 4.64, 95% confidence interval, CI, 1.85–11.66), and those who lived alone (OR 4.51, 95% CI 1.44–14.14) were at increased risk of a fall. Those who reported a comorbidity were at decreased risk of a fall (OR 0.43, 95% CI 0.19–0.95). Contrast sensitivity (OR 0.31, 95% CI 0.10–0.95) was the only significant visual test associated with a fall. These results were similar for the better eye, except the presence of a comorbidity was not significant (OR 0.45, 95% CI 0.20–1.02). Again, contrast sensitivity was the only significant visual factor associated with a fall (OR 0.15, 95% CI 0.04–0.53). Conclusion Bilateral cataract patients in Vietnam are potentially at high risk of falls and in need of falls prevention interventions. It may also be important for ophthalmologists and health professionals to consider contrast sensitivity measures when prioritizing cataract patients for surgery and assessing their risk of falls.

Household food insecurity, diet, and weight status in a disadvantaged district of Ho Chi Minh City, Vietnam: A cross-sectional study

Background Food security exists when all people, at all times, have physical, economic and socially acceptable access to safe, sufficient, and adequately nutritious food in order to meet their dietary needs for an active and healthy life. For high income countries and those experiencing the nutrition transition, food security is not only about the quantity of available food but also the nutritional quality as related to over- and under-nutrition. Vietnam is currently undergoing this nutrition transition, and as a result the relationship between food insecurity, socio-demographic factors and weight status is complex. The primary objective of this study was to therefore measure the prevalence of household food insecurity in a disadvantaged urban district in Ho Chi Minh City (HCMC) in Vietnam using a more comprehensive tool. This study also aims to examine the relationships between food insecurity and socio-demographic factors, weight status, and food intakes. Methods A cross-sectional study was conducted using multi-stage sampling. Adults who were mainly responsible for cooking were interviewed in 250 households. Data was collected on socioeconomic and demographic factors using previously validated tools. Food security was assessed using the Latin American and Caribbean Household Food Security Scale (ELCSA) tool and households were categorized as food secure or mildly, moderately or severely food insecure. Questions regarding food intake were based on routinely used and validated questions in HCMC, weight status was self-reported. Results Cronbach’s alpha coefficient was 0.87, showing the ELCSA had a good internal reliability. Approximately 34.4% of households were food insecure. Food insecurity was inversely related to total household income (OR = 0.09, 95% CI = 0.04 - 0.22) and fruit intakes (OR = 2.2, 95% CI 1.31 - 4.22). There was no association between weight and food security status. Conclusions Despite rapid industrialization and modernization, food insecurity remains an important public health issue in large urban areas of HCMC, suggesting that strategies to address food insecurity should be implemented in urban settings, and not just rural locations. Fruit consumption among food insecure households may be compromised because of financial difficulties, which may lead to poorer health outcomes particularly related to non-communicable disease prevention and management.

Nanopatterning by solid-state dewetting on reconstructed ceramic surfaces

We demonstrate ordered array formation of Au nanoparticles by controlled solid-state dewetting of a metal film on stepped alumina substrates. In situ transmission electron microscopy studies reveal that the dewetting process starts with nucleation of ordered dry regions on the substrate. The chemical potential difference between concave and convex surface regions induces anisotropic metal diffusion leading to the formation of nanowires in the valleys. The nanowires fragment due to Rayleigh instability forming arrays of metal nanoparticles on the substrate. The length scale of reconstruction relative to the starting film thickness is an important parameter in controlling the spatial order of the nanoparticles.

Indentation strength of a piezoelectric ceramic: Experiments and simulations

The spherical indentation strength of a lead zirconate titanate (PZT) piezoelectric ceramic was investigated under poled and unpoled conditions and with different electrical boundary conditions (arising through the use of insulating or conducting indenters). Experimental results show that the indentation strength of the poled PZT is higher than that of the unpoled PZT. The strength of a poled PZT under a conducting indenter is higher than that under an insulating indenter. Poling direction (with respect to the direction of indentation loading) did not significantly affect the strength of material. Complementary finite element analysis (FEA) of spherical indentation of an elastic, linearly coupled piezoelectric half-space is conducted for rationalizing the experimental observations. Simulations show marked dependency of the contact stress on the boundary conditions. In particular, contact stress redistribution in the Coupled problem leads to a change in the fracture initiation, from Hertzian cracking in the unpoled material to Subsurface damage initiation in poled PZT. These observations help explain the experimental ranking of strength the PZT in different material conditions or under different boundary conditions.

Small nickel metal particles in Ni---Al2O3 metal-ceramic composites

Magnetic measurements have been used in combination with transmission electron microscopy to investigate small nickel metal particles in metal-ceramic composites. Estimates of the average number of atoms in the particles are given for nonmagnetic samples with low Ni content.

EPR studies on donor doped BaTiO3 grain boundary layer ceramic dielectrics

Donor doped BaTiO3 ceramics become insulating5 under controlled conditions with effective dielectric constants >10. The changes in EPR signals indicate that a certain fraction of the donor doped BaTiO3 is cubic even at room temperature and that the cubic fraction increases with the donor content. X-ray powder diffraction data support the EPR results. The coexistence of both the phases over a range of temperature is characteristic of diffused phase transition. The effect of grain size variation on EPR signal intensities indicate that the boundary layers surrounding the grains may constitute the cubic phase as a result of higher Ba-vacancies and donor contents at the grain boundary layer than in the bulk. Since the acceptor states arising from the Ba-vacancies and the impurities are activated in the cubic phase, they capture electrons from the conduction band, rendering the cubic phase electrically more insulating than the semiconductive tetragonal grain interiors. Thus, the cubic grain boundary layers act as effective dielectric media where the field tends to concentrate.

Validating adult and paediatric nutrition screening and assessment tools in Vietnamese language in two acute hospital in Ho Chi Minh City, Vietnam

Despite being commonly prevalent in acute care hospitals worldwide, malnutrition often goes unidentified and untreated due to a lack in the implementation of a nutrition care pathway. The aim of this study was to validate nutrition screening and assessment tools in Vietnamese language. After converting into Vietnamese, Malnutrition Screening Tool (MST) and Subjective Global Assessment (SGA) were used to identify malnutrition in the adult setting; and the Paediatric Nutrition Screening Tool (PNST) and paediatric Subjective Global Nutritional Assessment (SGNA) were used in the paediatric setting in two acute care hospitals in Vietnam. This cross-sectional observational study sampled 123 adults (median age 78 years [39–96 years], 63% males) and 105 children (median age 20 months [2–100 months], 66% males). In adults, nutrition risk and malnutrition were identified in 29% and 45% of the cohort respectively. Nutrition risk and malnutrition were identified in 71% and 43% of the paediatric cohort respectively. The sensitivity and specificity of the screening tools were: 62% and 99% for the MST compared to the SGA; 89% and 42% for the PNST compared to the SGNA. This study provides a stepping stone to the potential use of evidence-based nutrition screening and assessment tools in Vietnamese language within the adult and paediatric Vietnamese acute care setting. Further work is required into integrating a complete nutrition care pathway within the acute care setting in Vietnamese hospitals.

Tribological properties of γ-Y2Si2O7 ceramic against AISI 52100 steel and Si3N4 ceramic counterparts

Reciprocating ball-on-flat dry sliding friction and wear experiments have been conducted on singlephase γ-Y2Si2O7 ceramic flats in contact with AISI 52100 bearing steel and Si3N4 ceramic balls at 5-15N normal loads in an ambient environment. The kinetic friction coefficients of γ-Y2Si2O7 varied in the range over 0.53-0.63 against AISI 52100 steel and between 0.51-0.56 against Si3N4 ceramic. We found thatwear occurred predominantly during the running-in period and it almost ceased at the steady friction stage. The wear rates of γ-Y2Si2O7 were in the order of 10-4mm3/(N m). Besides, wear debris strongly influenced the friction and wear processes. The strong chemical affinity between γ-Y2Si2O7 and AISI 52100 balls led to a thick transfer layer formed on both contact surfaces of the flat and counterpart ball, which changed the direct sliding between the ball and the flat into a shearing within the transfer layer. For the γ-Y2Si2O7/Si3N4 pair, a thin silica hydrate lubricant tribofilm presented above the compressed debris entrapped in the worn track and contact ball surface. This transfer layer and the tribofilm separated the sliding couple from direct contact and contributed to the low friction coefficient and wear rate.