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Objective.Our goal was to determine the conditions for which a more precise calculation of the electric potential than the quasi-static approximation may be needed in models of electrical neurostimulation, particularly for signals with kilohertz-frequency components.Approach.We conducted a comprehensive quantitative study of the differences in nerve fiber activation and conduction block when using the quasi-static and Helmholtz approximations for the electric potential in a model of electrical neurostimulation.Main results.We first show that the potentials generated by sources of unbalanced pulses exhibit different transients as compared to those of charge-balanced pulses, and this is disregarded by the quasi-static assumption. Secondly, relative errors for current-distance curves were below 3%, while for strength-duration curves these ranged between 1%-17%, but could be improved to less than 3% across the range of pulse duration by providing a corrected quasi-static conductivity. Third, we extended our analysis to trains of pulses and reported a 'congruence area' below 700 Hz, where the fidelity of fiber responses is maximal for supra-threshold stimulation. Further examination of waveforms and polarities revealed similar fidelities in the congruence area, but significant differences were observed beyond this area. However, the spike-train distance revealed differences in activation patterns when comparing the response generated by each model. Finally, in simulations of conduction-block, we found that block thresholds exhibited errors above 20% for repetition rates above 10 kHz. Yet, employing a corrected value of the conductivity improved the agreement between models, with errors no greater than 8%.Significance.Our results emphasize that the quasi-static approximation cannot be naively extended to electrical stimulation with high-frequency components, and notable differences can be observed in activation patterns. As well, we introduce a methodology to obtain more precise model responses using the quasi-static approach, retaining its simplicity, which can be a valuable resource in computational neuroengineering.
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Fibras Nervosas , Estimulação Elétrica/métodos , Condutividade ElétricaRESUMO
2,4-Dinitroanisole (DNAN) is an insensitive munitions compound expected to replace 2,4,6-trinitrotoluene (TNT). The product of DNAN's reduction in the environment is 2,4-diaminoanisole (DAAN), a toxic and carcinogenic aromatic amine. DAAN is known to become irreversibly incorporated into soil natural organic matter (NOM) after DNAN's reduction. Herein, we investigate the reactions between DAAN and NOM under anoxic conditions, using 1,4-benzoquinone (BQ) and methoxybenzoquinone (MBQ) as model humic moieties of NOM. A new method stopped the fast reactions between DAAN and quinones, capturing the fleeting intermediates. We observed that DAAN incorporation into NOM (represented by BQ and MBQ models) is quinone-dependent and occurs via Michael addition, imine (Schiff-base) formation, and azo bond formation. After dimers are formed, incorporation reactions continue, resulting in trimers and tetramers. After 20 days, 56.4% of dissolved organic carbon from a mixture of DAAN (1 mM) and MBQ (3 mM) had precipitated, indicating an extensive polymerization, with DAAN becoming incorporated into high-molecular-weight humic-like compounds. The present work suggests a new approach for DNAN environmental remediation, in which DNAN anaerobic transformation can be coupled to the formation of non-extractable bound DAAN residues in soil organic matter. This process does not require aerobic conditions nor a specific catalyst.
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Monadelpha L.J.Gillespie & Card.-McTeag., gen. nov., is described as a new member of Euphorbiaceae tribe Plukenetieae subtribe Tragiinae, to accommodate Tragia guayanensis, a species known from western Amazonas, Venezuela and, newly reported here, from Amazonas, Brazil. The genus is unique in the subtribe for having 5-colpate pollen and staminate flowers with filaments entirely connate into an elongate, cylindrical staminal column terminated by a tight cluster of anthers. Phylogenetic analyses based on nuclear rDNA ITS and sampling 156 accessions across the diversity of Tragiinae (all 12 genera and 77 of ~195 species) also support Monadelpha as a distinct lineage that is separate from Tragia. A revised key to the genera of Tragiinae in South America and Central America is provided.
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OBJECTIVE: This study describes secular trends in physical stature, Cormic Index (CI), and body mass index (BMI) of adult Makushi Amerindians born between 1910 and 1980, compares the stature of these Makushi adults to Makushi adults measured in 1921, and provides contextual data to inform the findings. METHODS: Pearson's correlation was used to assess the relationship between year of birth and physical stature, BMI, and CI for 231 females and 113 males, 20 to 90 years of age measured in 2000 to 2001. Wilcoxon's test was used to compare physical stature of Makushi adults measured in 2000 to 2001 with that of 40 Makushi adults measured in 1921. RESULTS: Among Makushi measured in 2000 to 2001, females and males born more recently were taller and had a lower CI but did not differ in BMI relative to their elders. Makushi measured in 2000 to 2001 are significantly taller than those Maksuhi measured in 1921. CONCLUSION: The increased physical stature of and decreased CI in more recently born Makushi may be explained by a more favorable early life environment possibly due to public health measures and dietary changes. As well, trends in stature may be linked to genetic admixture with African-Guyanese migrating into the region during this time.
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Estatura , Índice de Massa Corporal , Indígenas Sul-Americanos/estatística & dados numéricos , Postura Sentada , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Guiana , Humanos , Masculino , Pessoa de Meia-Idade , Estações do Ano , Adulto JovemRESUMO
CONTEXT: Diets of subsistence-based Amazonian populations have been linked to local resources, but are changing with market penetration. OBJECTIVE: To review the available data on traditional Amazonian foods and diets and evaluate their implications for human biology as a step toward understanding nutrition transitions in the region. METHODS: This study used the Human Relations Area Files for information on the diets of Amerindian groups in the Amazon Basin from 1950 to the present, and used other published sources and the authors' own data. RESULTS: Data on food use was identified for only nine groups and dietary intake data for individuals in only three of the groups. A diet based on starchy staples (manioc and plantains) and fish, supplemented with a limited variety of other plant and animal foods, was found. Bitter manioc-based foods were associated with the consumption of cyanogens and fish with the consumption of mercury. Diets of adults appear to be adequate in energy and protein and low in fats. Children's diets were not well documented. CONCLUSION: Based on the limited available data, Amazonian diets are restricted in variety, but appear to be adequate in energy and protein for adults, but likely insufficiently nutrient-dense for children.
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Biologia , Alimentos , Brasil , Dieta , Poluentes Ambientais , Humanos , Carne , Estado NutricionalRESUMO
Adult stature variation is commonly attributed to differential stress-levels during development. However, due to selective mortality and heterogeneous frailty, a population's tall stature may be more indicative of high selective pressures than of positive life conditions. This article examines stature in a biocultural context and draws parallels between bioarchaeological and living populations to explore the multidimensionality of stature variation in the past. This study investigates: 1) stature differences between archaeological populations exposed to low or high stress (inferred from skeletal indicators); 2) similarities in growth retardation patterns between archaeological and living groups; and 3) the apportionment of variance in growth outcomes at the regional level in archaeological and living populations. Anatomical stature estimates were examined in relation to skeletal stress indicators (cribra orbitalia, porotic hyperostosis, linear enamel hypoplasia) in two medieval bioarchaeological populations. Stature and biocultural information were gathered for comparative living samples from South America. Results indicate 1) significant (P < 0.01) differences in stature between groups exposed to different levels of skeletal stress; 2) greater prevalence of stunting among living groups, with similar patterns in socially stratified archaeological and modern groups; and 3) a degree of regional variance in growth outcomes consistent with that observed for highly selected traits. The relationship between early stress and growth is confounded by several factors-including catch-up growth, cultural buffering, and social inequality. The interpretations of early life conditions based on the relationship between stress and stature should be advanced with caution.
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Antropologia Física , Arqueologia , Estatura/fisiologia , Adolescente , Adulto , Idoso , Feminino , História Medieval , Humanos , Indígenas Sul-Americanos/estatística & dados numéricos , Itália , Masculino , Pessoa de Meia-Idade , Polônia , Valores de Referência , Classe Social , América do Sul , Estresse Fisiológico , População Branca/estatística & dados numéricos , Adulto JovemRESUMO
Most childhood obesity research has classified participants by normative standards for Body Mass Index (BMI) through population percentiles or values corresponding to overweight adults (World Health Organization (WHO), Centers for Disease Control and Prevention (CDC) and the International Obesity Task Force (IOTF)). In 2006, criterion-referenced standards (FitnessGram®) were developed (revised in 2010) which directly associate BMI values with adverse health outcomes. This study assessed agreement between normative and criterion-referenced standards. Participants included 653 Mexican American 3rd to 5th graders living in the U.S.-Mexico border area who participated in a health promotion project. At baseline, agreement was compared between normative and criterion-referenced classifications. At follow-up, agreement between classifications on changes (e.g. from overweight to healthy weight) was assessed. According to FitnessGram® standards, 53.0% of participants were overweight or obese at baseline. Compared to FitnessGram®, the IOTF and CDC standards classified 15% fewer participants as obese/high risk. The WHO standards were closely related to FitnessGram® (kappa=.925) and showed significantly greater agreement with FitnessGram® than the CDC (kappa=.925 versus 0.722, p<.001) and IOTF standards (kappa=.925 versus .682, p<.001). Compared to the FitnessGram® (8.9%), the WHO and CDC (8.6%) were similar, but IOTF standards lower (6.5%) in how many children improved following the health program. Despite acceptable agreement between the different indices, several normative classifications may underestimate the proportion of children who are at risk for BMI-related adverse health consequences.
Muchos de los estudios sobre la obesidad infantil clasifican a los participantes por índices normativas para el índice de masa corporal (IMC) usando valores de percentil de población o valores correspondientes a adultos con sobrepeso (Organización Mundial de la Salud (WHO), Centros para el Control y Prevención de Enfermedades (CDC) y la Comisión International Sobre la Obesidad (OITF)). En 2006, índices con referencias a criterios (Fitness-Gram®) fueron creados asociando valores de IMC directamente a valores de impacto de salud adversos. Este estudio determino las equivalencias de los índices normativos y los con referencias a criterios. Los participantes incluyeron estudiantes (N=653), niveles 3°-5, viviendo en la frontera EEUU-México. Al inicio, se comparó la equivalencia entre el IMC basado en las clasificaciones normativas y los con referencias a criterios. La equivalencia entre las clasificaciones de los cambios fue evaluada. Según las normas Fitness-Gram®, 53.0% tenían sobrepeso o eran obesos aunque las normas OITF y CDC indicaron menos de 15% fueron clasificados con obesidad/alto riesgo. Las normas WHO fueron más cercanamente relacionadas con las de FitnessGram® (kappa=.925) y mostraron significativamente mayor equivalencia con las de FitnessGram® que a las del CDC (kappa= .925 V .722, p<.001) e IOTF (kappa=.925 V .669, p<.001). Los índices FitnessGram® (8.9%), WHO y CDC (8.6%) fueron similares en cuanto el número de niños que mejoraron siguiendo el programa, pero el índice IOTF fue menor (6.3%). Aunque había un acuerdo aceptable entre los índices diferentes, varios pueden subestimar la proporción a riesgo y las consecuencias adversas relacionadas al IMC.
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Criança , Feminino , Humanos , Masculino , Americanos Mexicanos/estatística & dados numéricos , Obesidade/epidemiologia , Índice de Massa Corporal , Estudos Transversais , Valores de ReferênciaRESUMO
We assess what monkeys see during electrical stimulation of primary visual cortex (area V1) and relate the findings to visual percepts evoked electrically from human V1. Discussed are: (1) the electrical, cytoarchitectonic, and visuo-behavioural factors that affect the ability of monkeys to detect currents in V1; (2) the methods used to ascertain what monkeys see when electrical stimulation is delivered to V1; (3) a corticofugal mechanism for the induction of visual percepts; and (4) the quantity of information transferred to V1 by electrical stimulation. Experiments are proposed that should advance our understanding of how electrical stimulation affects macaque and human V1. This work contributes to the development of a cortical visual prosthesis for the blind. We dedicate this work to the late Robert W. Doty.
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Estimulação Elétrica , Visão Ocular/fisiologia , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Animais , Humanos , Estimulação Luminosa , Detecção de Sinal Psicológico , Campos Visuais/fisiologiaRESUMO
Most childhood obesity research has classified participants by normative standards for Body Mass Index (BMI) through population percentiles or values corresponding to overweight adults (World Health Organization (WHO), Centers for Disease Control and Prevention (CDC) and the International Obesity Task Force (IOTF)). In 2006, criterion-referenced standards (FitnessGram) were developed (revised in 2010) which directly associate BMI values with adverse health outcomes. This study assessed agreement between normative and criterion-referenced standards. Participants included 653 Mexican American 3rd to 5th graders living in the U.S.-Mexico border area who participated in a health promotion project. At baseline, agreement was compared between normative and criterion-referenced classifications. At follow-up, agreement between classifications on changes (e.g., from overweight to healthy weight) was assessed. According to FitnessGram standards, 53.0% of participants were overweight or obese at baseline. Compared to FitnessGram, the IOTF and CDC standards classified 15% fewer participants as obese/high risk. The WHO standards were closely related to FitnessGram (kappa=.925) and showed significantly greater agreement with FitnessGram than the CDC (kappa=.925 versus 0.722, p < .001) and IOTF standards (kappa=.925 versus .682, p < .001). Compared to the FitnessGram (8.9%), the WHO and CDC (8.6%) were similar, but IOTF standards lower (6.5%) in how many children improved following the health program. Despite acceptable agreement between the different indices, several normative classifications may underestimate the proportion of children who are at risk for BMI-related adverse health consequences.
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Americanos Mexicanos/estatística & dados numéricos , Obesidade/epidemiologia , Índice de Massa Corporal , Criança , Estudos Transversais , Feminino , Humanos , Masculino , Valores de ReferênciaRESUMO
BACKGROUND: Amazonian Indians are in the midst of a rapid cultural transition. The developments affecting Amazonian Indians present an opportunity to address important public health problems through public and private initiatives, but to do so it is imperative to begin with information on the health status of these peoples and the underlying factors affecting it. However, relatively few such data are available for this vast region. AIM: This study describes the nutritional status of Makushi Amerindians of Guyana and considers several variables which might help to explain it. SUBJECTS AND METHODS: Data for 792 Makushi, 0-20 years of age from 11 villages are considered. Outcome variables considered are anthropometric markers of growth and nutritional status; specifically height-for-age, weight-for-height and body-mass index. Predictor variables explored are age, sex, relative isolation, number of siblings, season of birth, diet and morbidity. Fisher's exact test, chi-square, Pearson's correlation and multiple regression were used to assess possible relationships between these variables. RESULTS: Relative to other Amazonian Indians, the Makushi have a lower rate of linear-growth faltering and a higher rate of linear-growth faltering relative to non-Amerindian Guyanese. Males, older cohorts, those living in isolated villages or born in the wet season showed higher rates of growth faltering. CONCLUSION: Makushi nutritional status may be explained by sex, age, relative isolation, family size, season of birth, dietary intake and infectious disease.