Asymptotics of the meta-atom: plane wave scattering by a single Helmholtz resonator.

Using a combination of multipole methods and the method of matched asymptotic expansions, we present a solution procedure for acoustic plane wave scattering by a single Helmholtz resonator in two dimensions. Closed-form representations for the multipole scattering coefficients of the resonator are derived, valid at low frequencies, with three fundamental configurations examined in detail: the thin-walled, moderately thick-walled and extremely thick-walled limits. Additionally, we examine the impact of dissipation for extremely thick-walled resonators, and also numerically evaluate the scattering, absorption and extinction cross-sections (efficiencies) for representative resonators in all three wall thickness regimes. In general, we observe strong enhancement in both the scattered fields and cross-sections at the Helmholtz resonance frequencies. As expected, dissipation is shown to shift the resonance frequency, reduce the amplitude of the field, and reduce the extinction efficiency at the fundamental Helmholtz resonance. Finally, we confirm results in the literature on Willis-like coupling effects for this resonator design, and connect these findings to earlier works by several of the authors on two-dimensional arrays of resonators, deducing that depolarizability effects (off-diagonal terms) for a single resonator do not ensure the existence of Willis coupling effects (bianisotropy) in bulk. This article is part of the theme issue 'Wave generation and transmission in multi-scale complex media and structured metamaterials (part 2)'.

Damage prediction via nonlinear ultrasound: A micro-mechanical approach.

Nonlinear constitutive mechanical parameters, predominantly governed by micro-damage, interact with ultrasound to generate harmonics that are not present in the excitation. In principle, this phenomenon therefore permits early stage damage identification if these higher harmonics can be measured. To understand the underlying mechanism of harmonic generation, a nonlinear micro-mechanical approach is proposed here, that relates a distribution of clapping micro-cracks to the measurable macroscopic acoustic nonlinearity by representing the crack as an effective inclusion with Landau type nonlinearity at small strain. The clapping mechanism inside each micro-crack is represented by a Taylor expansion of the stress-strain constitutive law, whereby nonlinear terms arise. The micro-cracks are considered distributed in a macroscopic medium and the effective nonlinearity parameter associated with compression is determined via a nonlinear Mori-Tanaka homogenization theory. Relationships are thus obtained between the measurable acoustic nonlinearity and the Landau-type nonlinearity. The framework developed therefore yields links with nonlinear ultrasound, where the dependency of measurable acoustic nonlinearity is, under certain hypotheses, formally related to the density of micro-cracks and the bulk material properties.

Obesity and the extent of liver damage among adult New Zealanders: findings from a national survey.

OBJECTIVE: Non-alcoholic fatty liver disease (NAFLD), defined as excessive fat accumulation in hepatocytes when no other pathologic causes are present, is an increasingly common obesity-related disorder. We sought to describe the prevalence of elevated liver enzymes, a marker of liver damage, among New Zealand adults, and high-risk subgroups including those with an elevated body mass index and those with pre-diabetes or diabetes, to gain a better understanding of the burden of liver disease. METHODS: A total of 4,721 New Zealanders aged 15+ years participated in a nationally representative nutrition survey. Liver enzymes, alanine transaminase (ALT) and gamma glutamyl transpeptidase (GGT) were measured in serum. Results were available for 3,035 participants, of whom 10.8% were Maori and 4.5% Pacific. RESULTS: Overall, the prevalence of elevated ALT and elevated GGT was 13.1% (95% confidence interval [CI]: 11.2 - 15.0) and 13.7% (95% CI: 12.0 - 15.4), respectively. Odds ratios for an elevated ALT or GGT markedly increased with increasing body mass index. Men with obesity had the highest elevated ALT prevalence (28.5%; 95% CI: 21.7-35.4), and women with diabetes had the highest elevated GGT prevalence (36.5%; 95% CI: 26.0-47.0). Adding alcohol consumption categories to each of the adjusted models did not meaningfully change any results, although for women, heavy alcohol consumption was associated with an elevated GGT (overall p = 0.03). CONCLUSIONS: Obesity-related liver disease is likely to increasingly burden the New Zealand health sector and contribute to health disparities unless effective obesity treatment and prevention measures are given high priority. © 2015 The Authors. Obesity Science & Practice published by John Wiley & Sons Ltd, World Obesity and The Obesity Society.

Estimating the dynamic effective mass density of random composites.

The effective mass density of an inhomogeneous medium is discussed. Random configurations of circular cylindrical scatterers are considered, in various physical contexts: fluid cylinders in another fluid, elastic cylinders in a fluid or in another solid, and movable rigid cylinders in a fluid. In each case, time-harmonic waves are scattered, and an expression for the effective wavenumber due to Linton and Martin [J. Acoust. Soc. Am. 117, 3413-3423 (2005)] is used to derive the effective density in the low frequency limit, correct to second order in the area fraction occupied by the scatterers. Expressions are recovered that agree with either the Ament formula or the effective static mass density, depending upon the physical context.

Waist-to-height ratios in relation to BMI z-scores in three ethnic groups from a representative sample of New Zealand children aged 5-14 years.

Waist-to-height ratio (WHtR) is purported to offer a simpler index of health risk than body mass index (BMI) in children as it requires no adjustment for age or sex. Little is known regarding the usefulness of WHtR in different ethnic groups. The aim of this study was to compare the WHtR cutpoints associated with BMI definitions of overweight and obesity in a nationally representative sample of New Zealand children. Height, weight and waist circumference were measured in 3006 children (51.5% male) aged 5-14 years (n=1107 Maori, n=985 Pacific and n=924 New Zealand European and Others (NZEO)). A WHtR >0.5 was more common in Pacific (43.4%) and Maori (33.1%) children than in NZEO children (20.8%, P<0.001), with 25.6% of children overall being above this cutoff. Although ethnicity influenced the relationship between BMI and WHtR (P<0.01), differences were clinically insignificant as illustrated by the similarity in WHtR values for a given BMI (WHtR of 0.47 in Maori, 0.46 in Pacific and 0.48 in European boys at the 85th BMI percentile). The present results suggest that having WHtR values >0.5 should be equally useful in evaluating cardiovascular health risks in groups of Maori, Pacific and NZEO children.

Predicting iron status in low birthweight infants.

OBJECTIVE: To determine the iron status of a selected group of low birthweight infants at approximately 9 months of age, and examine the feasibility of predicting iron status by examining the history of supplementary iron intake. METHODS: All live low birthweight infants recorded in the Dunedin Hospital Queen Mary Maternity Unit birth register who reached 9 months of age between November 1995 and September 1996 were eligible to participate. Infants were categorized into 'high' or 'low' iron intake groups depending on their consumption of infant formula or medicinal iron for one month prior to the study, and their iron status compared. RESULTS: Eighty-one infants of 73 mothers, with an average age of 10 months (range 8-13 months), participated. Thirty-three per cent (n = 27) were iron deficient: 19% (n = 15) had latent iron deficiency and 15% (n = 12) had iron deficiency anaemia. Those with a 'low' iron intake were 13-fold more likely to be iron deficient than infants with a 'high' iron intake (95% confidence interval: 4.4-41.5). Screening for iron deficiency using categories based on supplementary iron intake had a positive predictive value of 66% and a negative predictive value of 88%. CONCLUSIONS: The risk of iron deficiency was considerably greater for infants who had not received supplementary iron daily over the course of the previous month. Current preventative methods for avoiding poor iron status in this group of high risk infants are not effective. Screening for iron deficiency in low birthweight infants on the basis of iron intake from infant formula or medicinal iron provides a useful method for identifying infants whose iron status should be investigated.

Methodology of the 1997 New Zealand National Nutrition Survey.

AIMS: To describe the development and use of the methodologies in the 1997 New Zealand National Nutrition Survey (NNS97). METHODS: NNS97 was a voluntary cross-sectional population survey conducted over a twelve month period on 4,636 non-institutionalized urban and rural New Zealand residents aged fifteen years and older. Survey data were collected in the participants' home and included: a self-administered qualitative food frequency questionnaire, including questions on food preparation habits; a three-pass 24-hour diet recall; interviewer-administered questions on diet supplement use, barriers to dietary change and participant perception of household food security; physical measurements including weight, height, three circumferences, two skinfolds and elbow breadth; blood pressure; and a blood sample to determine cholesterol and iron status. RESULTS: New methodologies developed for NNS97 included a computer based interview system, probability analyses for estimating prevalence of inadequate intake of selected nutrients, determination of iron status by both dietary and biochemical assessment, assessments of dietary supplement use and food security. A full range of quality control procedures at each stage of the data collection were also initiated. CONCLUSION: NNS97 has improved on previous New Zealand national nutrition survey methodologies, particularly with direct data capture and rigorous quality control procedures used in the collection of survey data.

Dietary iron intakes and biochemical iron status of 15-49 year old women in New Zealand: is there a cause for concern?

AIM: To assess dietary iron intakes and biochemical iron status of a nationally representative sample of nonpregnant 15-49 year old women (n=1,751) in New Zealand. METHODS: A cross-sectional national survey was conducted in 1996/97. Women were selected via a multistage stratified cluster sampling procedure with increased sampling of Maori and Pacific women. Dietary iron intakes were estimated using a 24-hour diet recall. Biochemical iron status was assessed on a non-fasting venipuncture blood sample (n=1,047) via haemoglobin, mean cell volume, erythrocyte zinc protoporphyrin, transferrin receptors and serum ferritin. RESULTS: Average daily dietary iron intakes ranged from 9.6 mg/day among Pacific women to 10.5 mg/day among Maori women; 41% of 20-49 year olds and 45% of adolescents were at risk of low dietary iron intakes. The estimated percentage of 15-49 year old women with iron deficiency anaemia ranged from 1.4-5.5%, and for iron deficiency without anaemia from 0.7-12.6% depending on the age group and criteria used. CONCLUSIONS: The overall estimated prevalence of suboptimal biochemical iron status among 15-49 year old women in New Zealand ranged from 7-13%, which compared favourably with premenopausal women living in other western countries. This situation is, however, a public health concern given the potential negative functional consequences associated with even mild iron deficiency.

Attaining optimal bone status: lessons from the 1997 National Nutrition Survey.

AIMS: To examine the adequacy of calcium intake in relation to current recommendations, demographic differences in calcium intake and dietary sources in the New Zealand population. METHODS: 24-hour diet recall and qualitative food frequency data from the 1997 New Zealand National Nutrition Survey (NNS97) were used. RESULTS: No age-gender subgroups had median intakes meeting the latest (1998) US recommendations. Women's median intakes failed to meet even the considerably lower 1990 Australian recommendations. 20% of New Zealanders and one in four women had intakes below the UK Estimated Average Requirements for calcium. Intakes below the UK Lower Reference Nutrient Intake (the level at which the risk of deficiency is virtually 100%) were common (15-20%) among women aged 15-18 years, those living in the most deprived areas or Maori. Milk and milk products were the major sources of the nation's calcium intake. CONCLUSION: Although other factors such as genetics, hormonal status, vitamin D status and exercise influence skeletal health, adequate calcium intakes are important in minimizing bone loss. A reduction in the proportion of New Zealanders with inadequate calcium intakes will most readily be achieved if more people meet the milk products Dietary Guideline (minimum of two servings daily). Health professionals can play an important role in raising perceptions of the benefits of adequate calcium intakes, promoting the milk products Dietary Guideline, and emphasising that lower fat diets can include adequate calcium through use of reduced fat milk products.

Food security: is New Zealand a land of plenty?

AIM: To explore the concept of food security (when there is enough, appropriate and acceptable food available) in the adult New Zealand population using the National Nutrition Survey (NNS97). METHODS: The stepwise development of indicators of food security included a literature search and focus groups with low income women and men. Key issues surrounding the procurement and provision of food were determined and eight indicator statements prepared for inclusion in NNS97, to be addressed by each participant on behalf of their household. RESULTS: Prevalence was significantly higher (p<0.05) for females compared to males for the majority of indicator statements among New Zealand European & Others and Maori. New Zealand European & Others reported the most food security; Pacific people reported the least and Maori fell between the two. There was a significant increasing linear trend of food security with age (p<0.001), after adjusting for gender. "Food runs out in my/our household due to lack of money" was cited more often by female compared to male New Zealand European & Others in NZDep96 quartiles III and IV. CONCLUSION: The issue of 'not having enough food' may be more prevalent in New Zealand than US or Australia. Among New Zealand European & Others the higher prevalence of insufficient food due to lack of money among females from NZDep96 quartiles III and IV suggests that males may be protected from this by their female partners. Food security needs to be improved among young adults, women, Maori and Pacific people in order to prevent longer term nutritional health consequences.

Validation of a short food frequency questionnaire to assess consumption of cereal foods, fruit and vegetables in Chinese Singaporeans.

OBJECTIVE: To assess the ability of a 16-item food frequency questionnaire (FFQ) to measure consumption of cereal foods, fruit and vegetables in Chinese Singaporeans. DESIGN: Subjects completed the questionnaire twice, at the beginning and end of a six-week period during which they also provided three 24 h diet recalls. Estimates of intake from the questionnaire were compared with those from diet recalls. SUBJECTS: Subjects were recruited from a range of occupational groups through random sampling across divisions in the headquarters of the Singapore Ministry of Health. Of the 81 subjects initially recruited, three failed to complete the diet recalls, one was excluded due to changes in diet, and seven did not return the second questionnaire. RESULTS: Mean difference in food group consumption estimated by the two methods did not differ significantly from zero for fruit (0.00 serving, s.d.=0.54, 95% CI= -0.13, +0.12, P=0.95) or vegetables (-0.05, s.d.=0.29, 95% CI= -0.12, +0.02, P=0.13). For cereal foods, the mean difference was small, but significantly different from zero only in women (-0.32 servings, s.d. = 0.92, 95% CI = -0.59, -0.06, P=0.02). At an individual level, cereal food intake as measured by the FFQ may be 37% below or 59% above the diet recall values; and values for total fruit and vegetables may be half or double the recall values. Among subjects whose intake was classified into the lowest quartiles by diet recalls, 78% and 94% respectively, fell into the lowest two questionnaire quartiles for cereal foods, and total fruit and vegetables. The ability of the questionnaire to predict those having inadequate intake based on recall data was more than 90% for the three food groups. CONCLUSION: The short questionnaire cannot replace the three-day recalls in intake assessment for individuals, but it could be used to screen for low consumers in intervention programmes, to assess mean food group intake in population groups, and to rank individuals into broad categories of food group intake.

The nutritional health of New Zealand vegetarian and non-vegetarian Seventh-day Adventists: selected vitamin, mineral and lipid levels.

AIM: To determine whether adult non-vegetarian Seventh-day Adventists differ in selected nutrition related health aspects from adult vegetarian Seventh-day Adventists. METHODS: One hundred and forty-one Seventh-day Adventist church members responded to a general health questionnaire. Forty-seven sex and age matched subjects (23 non-vegetarians and 24 vegetarians) were selected for further investigation. Blood lipids, serum vitamin B12, folate, haemoglobin and ferritin levels were measured along with stature, weight and blood pressure. A quantitative 7-day diet record was also completed. RESULTS: Body mass index was similar between the non-vegetarian and vegetarian groups but diastolic blood pressure was higher for non-vegetarian than vegetarian males. Even though the dietary vitamin B12 intake was significantly lower (p < 0.01) in the vegetarian group both vegetarians and non-vegetarians recorded similar serum vitamin B12 levels. The vegetarian and non-vegetarian groups had similar haemoglobin concentrations. While dietary iron intake was higher in the female vegetarian group, though predominantly in the non-haem form, the difference was not significant. Low serum ferritin levels were found in both female dietary groups even though the vegetarian group had a significantly (p < 0.05) higher vitamin C intake. Blood lipid levels were similar in the two diet groups even though the vegetarian group had a lower percentage energy contribution from total and saturated fat (p < 0.01) and consumed significantly less cholesterol. CONCLUSION: Both non-vegetarian and vegetarian Seventh-day Adventists appear likely to enjoy a lower risk of nutrition related chronic degenerative disease than the average New Zealander and have a satisfactory iron and vitamin B12 status.

Nutrient intakes of Tongan and Tokelauan children living in New Zealand.

AIMS: To assess the adequacy of nutrient intakes of 10- to 13-year-old Tongan and Tokelauan children living in New Zealand and to compare these data with data from nonPacific Islands children of the same age. METHODS: A 24-hour diet record was used to assess the nutrient intakes of Tongan and Tokelauan school children (n = 162), aged 10- to 13-years, living in Auckland and Wellington. Nutrient intakes using the same methodology were compared with those from a nationally representative sample of nonPacific Islands, Form 1 children and also with Australian recommended dietary intakes for children aged 12- to 15-years. RESULTS: Data were collected from 162 (68 boys and 94 girls) of 220 children eligible to participate in the study (74%). Mean energy intakes for both the Tongan (8855 kJ for boys, 8610 kJ for girls) and the Tokelauan (9872 kJ for boys, 8826 kJ for girls) children were above the range of intake recommended by the World Health Organisation. The combined average energy intake of the two groups was higher than that of nonPacific Islands children for both boys and girls although not statistically significantly. Total fat intake was significantly higher (p < 0.05) for Tongan and Tokelauan boys, protein intake significantly higher for Tongan and Tokelauan boys (p < 0.01) and girls (p < 0.01), and carbohydrate intake significantly lower (p < 0.01) for Tongan and Tokelauan girls than for nonPacific Islands children. Compared with nonPacific Islands children micronutrient intakes were generally lower for Tongan and Tokelauan children with intakes of calcium, riboflavin, thiamin, niacin, folate and vitamin A being significantly lower for both sexes. Vitamin C was also significantly lower for girls (p < 0.05). Tongan and Tokelauan children obtain most of their nutrients from meat, bakery products, fast foods and dairy products. Fruit and vegetables were not significant contributors to nutrient intakes. CONCLUSIONS: Tongan and Tokelauan children living in New Zealand consume a diet that is larger in amount but lower in nutrient density compared to that of nonPacific Islands New Zealand children. Their relatively high dietary energy intakes allow them to meet the recommended intake requirements for most nutrients although if current intakes of fat and energy are maintained this may put them at risk of heart disease and other diseases later in life.

Nutrient intakes of women who are breastfeeding.

OBJECTIVE: A study was carried out in Dunedin, New Zealand, to assess the adequacy of dietary intakes of a group of healthy women who had been exclusively breast feeding for approximately 3 months. DESIGN: Demographic data and nutrient intakes as determined by two quantitative 24 h recalls within 2 weeks were collected from each woman. Dietary intakes were compared to Australian recommended nutrient intakes (RNIs) for lactating women. SUBJECTS: From 93 eligible women who were recruited, 73 completed the study, giving a 78% response rate. RESULTS: The mean (SD) energy intake of 8411 (2575) kJ (2007 kcal) was much lower than the recommended intake of 10,500 kJ. The majority of the women had intakes below two-thirds of the RNI for zinc, calcium, folate and vitamin A. Maternal age was significantly positively related to energy intakes (R2 = 14.2%), with women over thirty years having significantly higher energy intake (P = 0.01). CONCLUSIONS: Findings suggest that lactation may be maintained on lower levels of energy intake than currently recommended, although there is concern that zinc and calcium may not be consumed in adequate amounts. Recommended intakes need to be reassessed to determine if they are too high for some nutrients. Maternal age appears to be a significant factor determining energy and nutrient intakes in this population.

Diet and dental caries in preschool children.

A study was carried out in two New Zealand cities with a fluoridated water supply, to look at the dietary habits of preschool children and to investigate whether any dietary factors or other variables are associated with dental decay in the deciduous teeth of these children. From a final study of 355 (a 59% response rate), demographic data, a dental examination, a series of three 24 h recalls over a period of 1 year, and a food frequency questionnaire to cover the same 1 year interval were collected. The sample included 93 children with dental decay and 262 caries-free children, matched for age, sex and sociodemographic variables. The energy and nutrient intakes of the preschool children were sufficient to support normal growth. The main sources of dietary energy in the diets of this study group came from bakery and dairy products. Boys had slightly higher mean intakes of most nutrients than girls. No significant differences were found in the food patterns or intakes of macronutrients between the children of this study group with caries and those without. There was an inverse relationship between social background and dental health, with increasing social advantage being associated with decreasing dental health problems. Syrup medicines and, in particular, antibiotic syrups independently increased the risk that a child would have a number of carious lesions, especially if taken frequently.

Nutrient intake of Dunedin women during pregnancy.

AIM: To assess the adequacy of dietary intake of women during the three trimesters of pregnancy. METHOD: Dietary intakes of 63 primiparous and 32 multiparous healthy pregnant Dunedin women were obtained by 3 day weighed records at about 12 weeks, 24 weeks, and 36 weeks of gestation. Energy and nutrient intakes were derived using the University of Otago food composition database. RESULTS: Mean energy and nutrient intakes differed remarkably little between primiparous and multiparous women; data were combined for analysis. Energy intakes at first and second trimesters were similar to that for non pregnant women in the National Heart Foundation 1977 survey but greater than in the LINZ 1989 survey. Energy and carbohydrate intakes had increased at third trimester; across the trimesters carbohydrate accounted for 44-46% energy intake, fat for 39% and protein for 15%. Protein intakes at the 10th centile were almost the same as the recommended low risk intake of 51 g/d set by WHO/FAO: No vitamin or mineral showed a trend in intake through the trimesters. Vitamin and mineral intakes were in general greater for the pregnant women than for nonpregnant women in both 1977 and 1989 studies. By comparison with recommended intakes for NZ, Australia, USA and UK, intakes for folate, vitamin B-6, iron and possibly zinc and thiamin were potentially inadequate. Over 10% were heavy smokers and 20% were light smokers; nutrient intakes were less for the smokers than for the nonsmokers, as were birth weights; energy intakes for smokers had not increased at the third trimester. CONCLUSION: An improvement in quality of diet is needed during pregnancy and in prenatal period; smoking should continue to be strongly discouraged.

Experimental production of respiratory tract disease in cebus monkeys after intratracheal or intranasal infection with influenza A/Victoria/3/75 or influenza A/New Jersey/76 virus.

A total of 28 cebus monkeys were inoculated intratracheally or intranasally with 10(6) 50% tissue culture infective doses of A/New Jersey/76 virus or 10(7) 50% tissue culture infective doses of A/Victoria/75 virus, and 8 additional monkeys received sterile allantoic fluid. Each of the animals became infected as evidenced by a serological response and/or shedding of the virus. Of the 10 animals inoculated intratracheally with A/Victoria/75 virus, 8 developed a systemic illness, and pulmonary infiltration was detected by X-ray in 7 of the 8. Administration of A/New Jersey/76 virus intratracheally to 10 monkeys produced a mild systemic illness in 2 animals and an upper respiratory tract illness in 6, but no illness developed in the remaining 2 monkeys; none of the animals developed X-ray evidence of lower respiratory tract disease. Intranasal administration of either virus failed to induce any illness or produced, at most, mild illness confined to the upper respiratory tract. These studies demonstrate that cebus monkeys are susceptible to respiratory tract infection with influenza A viruses and that the development of pulmonary disease is reflected in the appearance of easily recognizable radiological changes.