A representation-free description of the Kasevich-Chu interferometer: a resolution of the redshift controversy

Motivated by a recent claim by Muller et al (2010 Nature 463 926-9) that an atom interferometer can serve as an atom clock to measure the gravitational redshift with an unprecedented accuracy, we provide a representation-free description of the Kasevich-Chu interferometer based on operator algebra. We use this framework to show that the operator product determining the number of atoms at the exit ports of the interferometer is a c-number phase factor whose phase is the sum of only two phases: one is due to the acceleration of the phases of the laser pulses and the other one is due to the acceleration of the atom. This formulation brings out most clearly that this interferometer is an accelerometer or a gravimeter. Moreover, we point out that in different representations of quantum mechanics such as the position or the momentum representation the phase shift appears as though it originates from different physical phenomena. Due to this representation dependence conclusions concerning an enhanced accuracy derived in a specific representation are unfounded.

Understanding and validating accelerometry as a measure of physical activity in children with intellectual disabilities

Background Physical activity in children with intellectual disabilities is a neglected area of study, which is most apparent in relation to physical activity measurement research. Although objective measures, specifically accelerometers, are widely used in research involving children with intellectual disabilities, existing research is based on measurement methods and data interpretation techniques generalised from typically developing children. However, due to physiological and biomechanical differences between these populations, questions have been raised in the existing literature on the validity of generalising data interpretation techniques from typically developing children to children with intellectual disabilities. Therefore, there is a need to conduct population-specific measurement research for children with intellectual disabilities and develop valid methods to interpret accelerometer data, which will increase our understanding of physical activity in this population. Methods Study 1: A systematic review was initially conducted to increase the knowledge base on how accelerometers were used within existing physical activity research involving children with intellectual disabilities and to identify important areas for future research. A systematic search strategy was used to identify relevant articles which used accelerometry-based monitors to quantify activity levels in ambulatory children with intellectual disabilities. Based on best practice guidelines, a novel form was developed to extract data based on 17 research components of accelerometer use. Accelerometer use in relation to best practice guidelines was calculated using percentage scores on a study-by-study and component-by-component basis. Study 2: To investigate the effect of data interpretation methods on the estimation of physical activity intensity in children with intellectual disabilities, a secondary data analysis was conducted. Nine existing sets of child-specific ActiGraph intensity cut points were applied to accelerometer data collected from 10 children with intellectual disabilities during an activity session. Four one-way repeated measures ANOVAs were used to examine differences in estimated time spent in sedentary, moderate, vigorous, and moderate to vigorous intensity activity. Post-hoc pairwise comparisons with Bonferroni adjustments were additionally used to identify where significant differences occurred. Study 3: The feasibility on a laboratory-based calibration protocol developed for typically developing children was investigated in children with intellectual disabilities. Specifically, the feasibility of activities, measurements, and recruitment was investigated. Five children with intellectual disabilities and five typically developing children participated in 14 treadmill-based and free-living activities. In addition, resting energy expenditure was measured and a treadmill-based graded exercise test was used to assess cardiorespiratory fitness. Breath-by-breath respiratory gas exchange and accelerometry were continually measured during all activities. Feasibility was assessed using observations, activity completion rates, and respiratory data. Study 4: Thirty-six children with intellectual disabilities participated in a semi-structured school-based physical activity session to calibrate accelerometry for the estimation of physical activity intensity. Participants wore a hip-mounted ActiGraph wGT3X+ accelerometer, with direct observation (SOFIT) used as the criterion measure. Receiver operating characteristic curve analyses were conducted to determine the optimal accelerometer cut points for sedentary, moderate, and vigorous intensity physical activity. Study 5: To cross-validate the calibrated cut points and compare classification accuracy with existing cut points developed in typically developing children, a sub-sample of 14 children with intellectual disabilities who participated in the school-based sessions, as described in Study 4, were included in this study. To examine the validity, classification agreement was investigated between the criterion measure of SOFIT and each set of cut points using sensitivity, specificity, total agreement, and Cohen’s kappa scores. Results Study 1: Ten full text articles were included in this review. The percentage of review criteria met ranged from 12%−47%. Various methods of accelerometer use were reported, with most use decisions not based on population-specific research. A lack of measurement research, specifically the calibration/validation of accelerometers for children with intellectual disabilities, is limiting the ability of researchers to make appropriate and valid accelerometer use decisions. Study 2: The choice of cut points had significant and clinically meaningful effects on the estimation of physical activity intensity and sedentary behaviour. For the 71-minute session, estimations for time spent in each intensity between cut points ranged from: sedentary = 9.50 (± 4.97) to 31.90 (± 6.77) minutes; moderate = 8.10 (± 4.07) to 40.40 (± 5.74) minutes; vigorous = 0.00 (± .00) to 17.40 (± 6.54) minutes; and moderate to vigorous = 8.80 (± 4.64) to 46.50 (± 6.02) minutes. Study 3: All typically developing participants and one participant with intellectual disabilities completed the protocol. No participant met the maximal criteria for the graded exercise test or attained a steady state during the resting measurements. Limitations were identified with the usability of respiratory gas exchange equipment and the validity of measurements. The school-based recruitment strategy was not effective, with a participation rate of 6%. Therefore, a laboratory-based calibration protocol was not feasible for children with intellectual disabilities. Study 4: The optimal vertical axis cut points (cpm) were ≤ 507 (sedentary), 1008−2300 (moderate), and ≥ 2301 (vigorous). Sensitivity scores ranged from 81−88%, specificity 81−85%, and AUC .87−.94. The optimal vector magnitude cut points (cpm) were ≤ 1863 (sedentary), ≥ 2610 (moderate) and ≥ 4215 (vigorous). Sensitivity scores ranged from 80−86%, specificity 77−82%, and AUC .86−.92. Therefore, the vertical axis cut points provide a higher level of accuracy in comparison to the vector magnitude cut points. Study 5: Substantial to excellent classification agreement was found for the calibrated cut points. The calibrated sedentary cut point (ĸ =.66) provided comparable classification agreement with existing cut points (ĸ =.55−.67). However, the existing moderate and vigorous cut points demonstrated low sensitivity (0.33−33.33% and 1.33−53.00%, respectively) and disproportionately high specificity (75.44−.98.12% and 94.61−100.00%, respectively), indicating that cut points developed in typically developing children are too high to accurately classify physical activity intensity in children with intellectual disabilities. Conclusions The studies reported in this thesis are the first to calibrate and validate accelerometry for the estimation of physical activity intensity in children with intellectual disabilities. In comparison with typically developing children, children with intellectual disabilities require lower cut points for the classification of moderate and vigorous intensity activity. Therefore, generalising existing cut points to children with intellectual disabilities will underestimate physical activity and introduce systematic measurement error, which could be a contributing factor to the low levels of physical activity reported for children with intellectual disabilities in previous research.

A monitorização da carga de treino através da análise tempo-movimento e da perceção subjetiva do esforço, PSE, no futebol

O objetivo do presente estudo foi verificar se existe variação dos parâmetros que caraterizam a atividade motora de jogadores de futebol em treino, obtidos através do Viper Software STATSports, ao longo de vários microciclos (MCs) integrando o período preparatório (PP) e o início do período competitivo (PC), assim como, averiguar a associação existente entre a variação destes parâmetros, MC a MC, e a Perceção Subjetiva do Esforço Sessão (PSE-sessão) respetiva, e verificar, ainda, se existe correlação entre estes parâmetros e a PSE, em cada MC do período considerado. A amostra do estudo foi constituída por 13 jogadores (idade: 25 ± 1,78 anos) de futebol do sexo masculino a competir no escalão de Séniores da Associação Futebol de Setúbal. A recolha de dados ocorreu durante o PP (4 semanas) e o PC (4 semanas). Os jogadores incluídos no estudo cumpriram o único critério definido: a realização total das sessões de treino previstas. Os instrumentos utilizados durante o processo foram o sistema Viper (Viper Software v.1.2, STATSports), integrando um GPS 10 Hz, acelerómetro 100 Hz, cardiofrequencímetro e a escala de PSE adaptada por Foster. Verificou-se elevada variabilidade no comportamento dos parâmetros no PP, mas não nos 3 últimos MCs já integrados no PC. Verificamos forte associação entre os parâmetros Distância Explosiva (r=0,762), Nº Esforços de Elevada Carga Metabólica (r=0,714), Nº Acelerações (r=0,714), Nº Desacelerações (r=0,762) e a PSE-sessão (p˂0,05). O parâmetro com maior potencial preditor de elevados valores da PSE-sessão é a Distância Explosiva (p˂0,001). Por fim, não encontramos uma associação regular entre os parâmetros e a PSE-sessão em cada MC. Os valores de PSE-sessão apresentados durante o estudo são semelhantes a valores apresentados em outros estudos no futebol profissional. Conclui-se que no PP ocorreu a variabilidade de todos os parâmetros e estabilização no PC da Distância Total, Distância de Elevada Carga Metabólica, Distâcia Explosiva, Nº Esforços de Elevada Carga Metabólica e PSE-sessão. A PSE-sessão depende dos parâmetros Distância Explosiva, Nº Esforços de Elevada Carga Metabólica, Nº Acelerações e Nº Desacelerações, i.e., as ações de elevada exigência metabólica e neuromuscular explicam a relação existente entre os parâmetros de carga e a PSE-sessão como indicador global de carga interna. A utilização do sistema Viper possibilita a recolha de parâmetros que descrevem as exigências fisícas a que os jogadores estão sujeitos e fornece informação fundamental para o planeamento do treino em conjunto com a recolha sistemática da PSE-sessão.

Validade simultânea do questionário internacional de actividade física através da medição objectiva da actividade física por actigrafia proporcional

Este estudo faz parte de um esforço a nível internacional com o objectivo de validar o Questionário Internacional de Actividade Física (IPAQ) proposto pela Organização Mundial de Saúde, no sentido de encontrar um instrumento que possa ser utilizado a nível mundial para determinar o nível de actividade física das populações. O propósito desta investigação foi analisar a validade da forma curta e longa do IPAQ, versão portuguesa. Utilizou-se o modelo auto-administrativo e o período de referência de uma semana habitual. Para validar este instrumento foi proposta a utilização do acelerómetro Computer Science and Application (CSA), modelo 7164. Os monitores CSA foram usados durante sete dias consecutivos como uma medida directa para validar o IPAQ curto e longo. A amostra utilizada neste estudo foi constituída por 152 pessoas (52 homens e 100 mulheres). O processo de validação foi realizado por oposição das medidas do questionário IPAQ com a utilização dos CSA durante um período de uma semana. Os resultados preliminares sugerem que existe uma correlação (r = 0,33, p <0,01) entre a média de impulsos registados pelos CSA e o questionário curto e uma correlação mais fraca (r = 0,095, p <0,01) entre a média de impulsos registados pelos CSA e o questionário longo. Os resultados evidenciam também que existe uma correlação (r = 0,45, p <0,01) entre a forma longa e curta do IPAQ. Deste modo, conclui-se que a forma curta e longa do IPAQ são aceitáveis. Os resultados são similares a outros estudos com objectivos idênticos, em que se utilizou o mesmo instrumento de medição da actividade física e os mesmos procedimentos.

Patterns of sedentary behavior : insights from observational and experimental studies on body composition and energy expenditure

It is recognized that sedentary behavior (SB) has deleterious effects on numerous health outcomes and it appears that physiological mechanisms underlying these harms are distinct from the ones explaining moderate-to-vigorous physical activity (MVPA) benefits. Sedentary behavior represents a large portion of human’s life and is increasing with technological development. A new current of opinion supports the idea that the manner SB is accumulated plays an important role. This dissertation presents six research studies conducted under the scope of SB. In the methodological area, the first study highlighted the magnitude of potential errors in estimating SB and its patterns from common alternative methods (accelerometer and heart rate monitor) compared to ActivPAL. This study presented the accelerometer as a valid method at a group level. Two studies (2 and 5) were performed in older adults (the most sedentary group in the population) to test the associations for SB patterns with abdominal obesity using accelerometry. The findings showed positive graded associations for prolonged sedentary bouts with abdominal obesity and showed that those who interrupted SB more frequently were less likely to present abdominal obesity. Therefore, public health recommendations regarding breaking up SB more often are expected to be relevant. The associations between sedentary patterns and abdominal obesity were independent of MVPA in older adults. However, the low MVPA in this group makes it unclear whether this independent relationship still exists if highly active persons are analysed. Study 3 inovates by examining the association of SB with body fatness in highly trained athletes and found SB to predict total fat mass and trunk fat mass, independently of age and weekly training time. Study 4 also brings novelty to this research field by quantifying the metabolic and energetic cost of the transition from sitting to standing and then sitting back down (a break), informing about the modest energetic costs (0.32 kcal·min−1). Finally, from a successful multicomponent pilot intervention to reduce and break up SB (study 6), an important behavioral resistance to make more sit/stand transitions despite successfully reducing sitting time (~ 1.85 hours·day-1) was found, which may be relevant to inform future behavioral modification programs. The present work provides observational and experimental evidence on the relation for SB patterns with body composition outcomes and energy regulation that may be relevant for public health interventions.

Auscultación cervical: alternativa no invasiva en el diagnóstico de disfagia en niños con problemas de neurodesarrollo

Los niños y las niñas con disfunciones neurológicas tienen frecuentemente disfagia, condición que les ocasiona infecciones respiratorias a repetición, desnutrición, mala calidad de vida; su oportuno diagnóstico permite decidir sobre la mejor intervención. La videofluoroscopia y de videoendoscopia son técnicas diagnósticas invasivas, costosas y por lo tanto difíciles de hacerlas, lo que ocasiona retardo en el diagnóstico e intervención. Hoy en día existen nuevas tecnologías médicas no invasivas que pueden ser muy eficaces, una de ellas es la auscultación cervical que escucha los sonidos de la deglución mediante un estetoscopio u otro dispositivo de medición como la colocación de un micrófono o un acelerómetro en la superficie del cuello. Este método tiene como principio que los sonidos y/o movimientos biológicos normales de la deglución son diferentes de los anormales. En este artículo se presenta una revisión de la pertinencia social del diagnóstico de la disfagia, de las aplicaciones clínicas de la auscultación cervical y los dispositivos usados para realizarla, como una base para establecer su potencial de uso para la detección de disfagia en niños con problemas de neurodesarrollo. Estas orientaciones teóricas permiten al médico tener actuaciones más acertadas en el diagnóstico integral de niños y niñas con disfunción neurológica

MODELING OF TRANSFER PATH FOR DETERMINATION OF COMBUSTION AND NOISE METRICS ON DIESEL ENGINES

Determination of combustion metrics for a diesel engine has the potential of providing feedback for closed-loop combustion phasing control to meet current and upcoming emission and fuel consumption regulations. This thesis focused on the estimation of combustion metrics including start of combustion (SOC), crank angle location of 50% cumulative heat release (CA50), peak pressure crank angle location (PPCL), and peak pressure amplitude (PPA), peak apparent heat release rate crank angle location (PACL), mean absolute pressure error (MAPE), and peak apparent heat release rate amplitude (PAA). In-cylinder pressure has been used in the laboratory as the primary mechanism for characterization of combustion rates and more recently in-cylinder pressure has been used in series production vehicles for feedback control. However, the intrusive measurement with the in-cylinder pressure sensor is expensive and requires special mounting process and engine structure modification. As an alternative method, this work investigated block mounted accelerometers to estimate combustion metrics in a 9L I6 diesel engine. So the transfer path between the accelerometer signal and the in-cylinder pressure signal needs to be modeled. Depending on the transfer path, the in-cylinder pressure signal and the combustion metrics can be accurately estimated - recovered from accelerometer signals. The method and applicability for determining the transfer path is critical in utilizing an accelerometer(s) for feedback. Single-input single-output (SISO) frequency response function (FRF) is the most common transfer path model; however, it is shown here to have low robustness for varying engine operating conditions. This thesis examines mechanisms to improve the robustness of FRF for combustion metrics estimation. First, an adaptation process based on the particle swarm optimization algorithm was developed and added to the single-input single-output model. Second, a multiple-input single-output (MISO) FRF model coupled with principal component analysis and an offset compensation process was investigated and applied. Improvement of the FRF robustness was achieved based on these two approaches. Furthermore a neural network as a nonlinear model of the transfer path between the accelerometer signal and the apparent heat release rate was also investigated. Transfer path between the acoustical emissions and the in-cylinder pressure signal was also investigated in this dissertation on a high pressure common rail (HPCR) 1.9L TDI diesel engine. The acoustical emissions are an important factor in the powertrain development process. In this part of the research a transfer path was developed between the two and then used to predict the engine noise level with the measured in-cylinder pressure as the input. Three methods for transfer path modeling were applied and the method based on the cepstral smoothing technique led to the most accurate results with averaged estimation errors of 2 dBA and a root mean square error of 1.5dBA. Finally, a linear model for engine noise level estimation was proposed with the in-cylinder pressure signal and the engine speed as components.

iGrooving: A Generative Music Mobile Application for Runners

iGrooving is a generative music mobile application specifically designed for runners. The application’s foundation is a step-counter that is programmed using the iPhone’s built-in accelerometer. The runner’s steps generate the tempo of the performance by mapping each step to trigger a kick-drum sound file. Additionally, different sound files are triggered at specific step counts to generate the musical performance, allowing the runner a level of compositional autonomy. The sonic elements are chosen to promote a meditative aspect of running. iGrooving is conceived as a biofeedback-stimulated musical instrument and an environment for creating generative music processes with everyday technologies, inspiring us to rethink our everyday notions of musical performance as a shared experience. Isolation, dynamic changes, and music generation are detailed to show how iGrooving facilitates novel methods for music composition, performance and audience participation.

Exploring the relationship between patterns of physical activity, sedentary behaviour and cardiometabolic health in middle-aged Irish adults

Background and Study Rationale Being physically active is a major contributor to both physical and mental health. More specifically, being physically active lowers risk of coronary heart disease, high blood pressure, stroke, metabolic syndrome (MetS), diabetes, certain cancers and depression, and increases cognitive function and wellbeing. The physiological mechanisms that occur in response to physical activity and the impact of total physical activity and sedentary behaviour on cardiometabolic health have been extensively studied. In contrast, limited data evaluating the specific effects of daily and weekly patterns of physical behaviour on cardiometabolic health exist. Additionally, no other study has examined interrelated patterns and minute-by-minute accumulation of physical behaviour throughout the day across week days in middle-aged adults. Study Aims The overarching aims of this thesis are firstly to describe patterns of behaviour throughout the day and week, and secondly to explore associations between these patterns and cardiometabolic health in a middle-aged population. The specific objectives are to: 1 Compare agreement between the International Physical Activity Questionnaire-Short Form (IPAQ-SF) and GENEActiv accelerometer-derived moderate-to-vigorous (MVPA) activity and secondly to compare their associations with a range of cardiometabolic and inflammatory markers in middle-aged adults. 2 Determine a suitable monitoring frame needed to reliably capture weekly, accelerometer-measured, activity in our population. 3 Identify groups of participants who have similar weekly patterns of physical behaviour, and determine if underlying patterns of cardiometabolic profiles exist among these groups. 4 Explore the variation of physical behaviour throughout the day to identify whether daily patterns of physical behaviour vary by cardiometabolic health. Methods All results in this thesis are based on data from a subsample of the Mitchelstown Cohort; 475 (46.1% males; mean aged 59.7±5.5 years) middle-aged Irish adults. Subjective physical activity levels were assessed using the IPAQ-SF. Participants wore the wrist GENEActiv accelerometer for 7 consecutive days. Data was collected at 100Hz and summarised into a signal magnitude vector using 60s epochs. Each time interval was categorised based on validated cut-offs. Data on cardiometabolic and inflammatory markers was collected according to standard protocol. Cardiometabolic outcomes (obesity, diabetes, hypertension and MetS) were defined according to internationally recognised definitions by World Health Organisation (WHO) and Irish Diabetes Federation (IDF). Results The results of the first chapter suggest that the IPAQ-SF lacks the sensitivity to assess patterning of activity and guideline adherence and assessing the relationship with cardiometabolic and inflammatory markers. Furthermore, GENEActiv accelerometer-derived MVPA appears to be better at detecting relationships with cardiometabolic and inflammatory markers. The second chapter examined variations in day-to-day physical behaviour levels between- and within-subjects. The main findings were that Sunday differed from all other days in the week for sedentary behaviour and light activity and that a large within-subject variation across days of the week for vigorous activity exists. Our data indicate that six days of monitoring, four weekdays plus Saturday and Sunday, are required to reliably estimate weekly habitual activity in all activity intensities. In the next chapter, latent profile analysis of weekly, interrelated patterns of physical behaviour identified four distinct physical behaviour patterns; Sedentary Group (15.9%), Sedentary; Lower Activity Group (28%), Sedentary; Higher Activity Group (44.2%) and a Physically Active Group (11.9%). Overall the Sedentary Group had poorer outcomes, characterised by unfavourable cardiometabolic and inflammatory profiles. The remaining classes were characterised by healthier cardiometabolic profiles with lower sedentary behaviour levels. The final chapter, which aimed to compare daily cumulative patterns of minute-by-minute physical behaviour intensities across those with and without MetS, revealed significant differences in weekday and weekend day MVPA. In particular, those with MetS start accumulating MVPA later in the day and for a shorted day period. Conclusion In conclusion, the results of this thesis add to the evidence base regards an optimal monitoring period for physical behaviour measurement to accurately capture weekly physical behaviour patterns. In addition, the results highlight whether weekly and daily distribution of activity is associated with cardiometabolic health and inflammatory profiles. The key findings of this thesis demonstrate the importance of daily and weekly physical behaviour patterning of activity intensity in the context of cardiometabolic health risk. In addition, these findings highlight the importance of using physical behaviour patterns of free-living adults observed in a population-based study to inform and aid health promotion activity programmes and primary care prevention and treatment strategies and development of future tailored physical activity based interventions.

Baran: an interaction-centred user monitoring framework

User Quality of Experience (QoE) is a subjective entity and difficult to measure. One important aspect of it, User Experience (UX), corresponds to the sensory and emotional state of a user. For a user interacting through a User Interface (UI), precise information on how they are using the UI can contribute to understanding their UX, and thereby understanding their QoE. As well as a user’s use of the UI such as clicking, scrolling, touching, or selecting, other real-time digital information about the user such as from smart phone sensors (e.g. accelerometer, light level) and physiological sensors (e.g. heart rate, ECG, EEG) could contribute to understanding UX. Baran is a framework that is designed to capture, record, manage and analyse the User Digital Imprint (UDI) which, is the data structure containing all user context information. Baran simplifies the process of collecting experimental information in Human and Computer Interaction (HCI) studies, by recording comprehensive real-time data for any UI experiment, and making the data available as a standard UDI data structure. This paper presents an overview of the Baran framework, and provides an example of its use to record user interaction and perform some basic analysis of the interaction.

Comparación de la medida de actividad física mediante cuestionario Ipaq-L y acelerómetro ‘Mywellness Key’ en trabajadores

Objetivo: comparar la concordancia en las mediciones de actividad física en un grupo de trabajadores mediante el acelerómetro ‘Mywellness key’(Technogym, Gambettola, Italy), y un sistema indirecto, cuestionario ‘IPAQ-L’ (International Physical Activity Questionnaire, Long Version), y comprobar la relación entre ambas estimaciones. Sujetos: 59 trabajadores (41 mujeres y 18 hombres), con una edad media de 36 ± 7 años y un IMC de 23.96 ± 3.50. Material y métodos: la medición de los niveles de actividad física se realizó mediante el cuestionario IPAQ-L y acelerómetros ‘Mywellness key’ (Technogym, Gambettola, Italy). Todos los sujetos llevaron puesto el acelerómetro durante 7 días consecutivos (2 festivos y 5 laborables). Se empleó el coeficiente de correlaciones bivariadas de Pearson y el CCI (coeficiente de correlación intraclase) (p<.05). Resultados: los valores se correlacionaron positivamente en todo el grupo de manera significativa en los niveles de AF vigorosa (r = 0.93; CCI = 0.757; p<.001) y de AF Moderada (r=0.91; CCI = 0.951; p<.001). Conclusión: se encontró una muy buena correlación en actividades vigorosas y moderadas entre el acelerómetro ‘Mywellness key’ y el cuestionario IPAQ-L.

A practical MEMS gravimeter

The ability to measure tiny variations in the local gravitational acceleration allows – amongst other applications – the detection of hidden hydrocarbon reserves, magma build-up before volcanic eruptions, and subterranean tunnels. Several technologies are available that achieve the sensitivities required (tens of μGal/√Hz), and stabilities required (periods of days to weeks) for such applications: free-fall gravimeters, spring-based gravimeters, superconducting gravimeters, and atom interferometers. All of these devices can observe the Earth tides; the elastic deformation of the Earth’s crust as a result of tidal forces. This is a universally predictable gravitational signal that requires both high sensitivity and high stability over timescales of several days to measure. All present gravimeters, however, have limitations of excessive cost (£70 k) and high mass (<8 kg). In this thesis, the building of a microelectromechanical system (MEMS) gravimeter with a sensitivity of 40 μGal/√Hz in a package size of only a few cubic centimetres is discussed. MEMS accelerometers – found in most smart phones – can be mass-produced remarkably cheaply, but most are not sensitive enough, and none have been stable enough to be called a ‘gravimeter’. The remarkable stability and sensitivity of the device is demonstrated with a measurement of the Earth tides. Such a measurement has never been undertaken with a MEMS device, and proves the long term stability of the instrument compared to any other MEMS device, making it the first MEMS accelerometer that can be classed as a gravimeter. This heralds a transformative step in MEMS accelerometer technology. Due to their small size and low cost, MEMS gravimeters could create a new paradigm in gravity mapping: exploration surveys could be carried out with drones instead of low-flying aircraft; they could be used for distributed land surveys in exploration settings, for the monitoring of volcanoes; or built into multi-pixel density contrast imaging arrays.

Estado nutricional y etapas de cambio comportamental frente a la actividad física niños y adolescentes de Bogotá, Colombia: Estudio FUPRECOL

Objetivo: El propósito del estudio fue relacionar la etapa en el cambio en el comportamiento frente a la actividad física y el estado nutricional en escolares entre 9 y 17 años de Bogotá- Colombia, pertenecientes al estudio FUPRECOL. Método: Se trata de un estudio transversal, en 6.606 niños y adolescentes entre 9 y 17 años, pertenecientes a 24 instituciones educativas, de Bogotá-Colombia. Se aplicó de manera auto-diligenciada el cuestionario de cambio de comportamiento en función a la intensión de realizar actividad física (CCC-Fuprecol) y se midió el peso y la estatura para determinar el estado nutricional con el índice de masa corporal (IMC). Resultados: El porcentaje de respuesta fue 94% y se consideraron válidos 6,606 registros, siendo 58.3 % (n=3.850) niñas con un promedio de edad de 12,7±2,3 años. En la población general, el 5,3 % de los escolares se encontraban en etapa de pre-contemplación, 31,8 % en contemplación, el 26,7 % en acción y el 36,2 % en etapa de mantenimiento. Al comparar la etapa de cambio con el estado nutricional por IMC, los escolares clasificados en obesidad mostraron mayor frecuencia de respuesta en la etapa de pre-contemplación, mientras que los escolares con peso saludable acusaron mayores porcentajes en la etapa de mantenimiento. Conclusión: En escolares de Bogotá, Colombia, se encontró una relación estadísticamente significativa entre a la intensión de realizar actividad con el estado nutricional medido con el IMC. Fomentar la promoción de la actividad física y monitorear el estado nutricional, deberá ser una prioridad en las agendas y políticas públicas dentro del ámbito escolar.

Validación de criterio concurrente del sistema de observación de tiempo de instrucción de condición física – SOFIT- para la medición de la actividad física durante las clases de educación física en escolares de 1º A 9º de Bogotá, Colombia

Determinar la validez concurrente del Sistema de Observación de Tiempo de Instrucción de Condición Física (SOFIT) a través de acelerometría, como método para medir los niveles de actividad física (AF) de los escolares de 1º a 9º durante la clase de educación física en tres colegios públicos de Bogotá, Colombia. Estudio transversal entre Octubre de 2014 y Marzo de 2015. La medición se realizó en tres colegios públicos de Bogotá. Participaron 48 estudiantes (25 niñas; 23 niños), entre 5 y 17 años, seleccionados de acuerdo al protocolo de SOFIT. El resultado se categoriza en porcentaje de tiempo en comportamiento sedentario, AF moderada, AF vigorosa, y AF moderada a vigorosa. Se validó utilizando como patrón de oro la acelerometría en las mismas categorías. Se realizó diferencia de medias, regresión lineal y modelo de efectos fijos. La correlación entre SOFIT y acelerometría fue buena para AF moderada (rho=,958; p=0,000), AF vigorosa (rho=,937; p=0,000) y AF de moderada a vigorosa (rho=0,962; p=0,000). Al igual que utilizando un modelo de efectos fijos, AF moderada (β1=0,92; p=0,00), vigorosa (β1=0,94; p=0,00) y AF de moderada a vigorosa (β1=0,95; p=0,00), mostrando ausencia de diferencias significativas entre los dos métodos para la medición de los niveles de AF. El comportamiento sedentario correlacionó positivamente en Spearman (rho=,0965; p=0,000), El sistema SOFIT demostró ser válido para medir niveles de AF en clases de educación física, tras buena correlación y concordancia con acelerometría. SOFIT es un instrumento de fácil acceso y de bajo costo para la medición de la AF durante las clases de educación física en el contexto escolar y se recomienda su uso en futuros estudios.

Niveles de actividad física en los periodos de recreo de niños y adolescentes en un colegio distrital de Bogotá

Objetivo: determinar los niveles de actividad física (AF) de niños y adolescentes entre 10 y 17 años durante los periodos de recreo escolar en un colegio distrital de Bogotá. Método: estudio de corte transversal en un colegio distrital de la localidad de Puente Aranda en Bogotá. Fueron observados a través del sistema de observación de juego y de actividad en el tiempo libre en jóvenes (SOPLAY) los niveles y tipos de AF de niños y adolescentes en los periodos de recreo durante tres semanas, utilizando una condición de observación diferente para cada semana. Adicionalmente, las condiciones del contexto de las áreas recreo deportivas fueron evaluadas. Resultados: las prevalencias de escolares sedentarios fueron de 52,4 %, 77,3 % y 64,9 % durante la 1ª, 2ª y 3ª semana respectivamente. El sexo femenino fue más sedentario con el masculino (57 %, 82 % y 73 % vs 45 %, 70 % y 54 %) para cada semana observada. Se obtuvieron diferencias significativas (p<0,05) en los niveles de AF de los escolares. Conclusión: niños y adolescentes presentan elevadas prevalencias de sedentarismo siendo las actividades más frecuentes estar sentado, de pie o acostado durante los periodos de recreo. El sexo masculino mostró porcentajes superiores de participación en AF moderadas vigorosas. Las áreas recreo deportivas no contaban con condiciones del contexto relacionadas con disponibilidad de equipamiento para realizar AF ni existencia de actividades organizadas. Son necesarios programas e intervenciones eficaces que promuevan la AF en niños y adolescentes durante el recreo de la jornada escolar.