The effects of whole-body vibration on performance of a complex manual control task

This thesis investigates continuous manual control performance during exposure to z-axis whole-body vibration at frequencies between 0.5 and 10.0 Hz. The task involved first-order pursuit tracking with a simultaneous discrete target acquisition task. A major aim of the work was to determine the mechanisms underlying any vibration-induced impairment which occurred. The literature is first reviewed (Chapter 2) and a model is presented summarising the mechanisms by which vibration has been suggested to disrupt performance (Chapter 3). Six experiments are then reported. Experiment 1 (Chapter 5) measured vibration-induced activity at the head, hand and the output of the system dynamics. The results are discussed with reference to the mechanisms which could disrupt performance. Experiment 2 (Chapter 6) investigated performance during exposure to vibration at frequencies from 0.5 to 5.0 Hz. The magnitude of performance disruption was approximately constant at vibration frequencies below 2 Hz, and increased with the frequency of vibration to 5.0 Hz. Experiments 3 (Chapter 7) and 4 (Chapter 8) showed that the disruption at frequencies above 2.0 Hz could be attributed to visual impairment arising from relative translational movement between subjects' eyes and the display: collimating the display removed the impairment. Linear spectral analysis techniques were used to separate root-mean-square (rms) tracking error into components linearly and not linearly correlated with movements of the target. Changes in total rms error were mainly accompanied by changes in the linear components: closed-loop system transfer functions showed increased phase lags between movements of the target and the response of the controlled element. In experiment 5 (Chapter 9), three simple tasks were used to isolate non-visual mechanisms of disruption. The results suggested that whole-body vibration at 0.5 and 4.0 Hz could interfere with neuro-muscular processes. The results of experiment 5, and the increased phase lag observed in experiment 4, indicate changes in the way the task was performed during vibration: these are described as secondary vibration effects. Experiment 6 investigated whether the effect of vibration on the system studied would be time-dependent. One-octave-band random vibration centred on 4 Hz was presented at a magnitude considerably above the ISO 2631 (1985) 'fatigue-decreased-proficiency' limit for 180 minute vibration exposures. Performance declined with time, but vibration did not alter the time-dependence. The effect of duration was reduced when the task was performed over the entire duration on a second occasion. It is concluded that impairments in continuous tracking performance during whole-body vibration exposure were mainly caused by interference with visual and neuro-muscular processes. The results also show secondary effects which may represent adaptive change in performance during vibration. The behavioural model developed in Chapter 3 is used to summarise the mechanisms which were shown to be important, and to indicate other effects which could occur. Some suggestions for further research are offered

Star clusters near and far; tracing star formation across cosmic time

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00690-x.Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e.\ detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.Peer reviewedFinal Accepted Versio

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362

Effects of duration and vibration on performance of a continuous manual control task

An experiment is described in which two independent groups of seated subjects performed a pursuit tracking task for 202·5 min on two separate occasions. For one group, the total duration included 180 min exposure to vertical z-axis, whole-body random vibration with a bandwidth of 1 octave centred on 4 Hz. The weighted acceleration magnitude was 1·4 ms−2 r. m. s., with a crest factor of 4·13. Using the procedures denned in British Standard 6841 (BSI 1987), the motion had a vibration dose value of 20 ms−1·75. The other group received no vibration exposure. Results showed that performance declined as function of duration, but that vibration exposure did not impair performance or interact with the effect of duration. Performance in the second sessions showed less effect of duration than in the first session. The effect of duration was associated with change in both linear and non-linear tracking behaviour. Closed loop system transfer functions showed both reduced moduli and increased phase lags with increasing exposure duration.</p

Review of the effects of translational whole-body vibration on continuous manual control performance

A review of the literature concerned with experimental studies of the effects of translational whole-body vibration on continuous manual control performance is presented. Results from studies of the effects of vibration variables (vibration frequency, magnitude, axis, random vibration and multi-axis vibration) are compared. Evidence of the influence of control system variables (physical characteristics of the control, control gain, system dynamics and display variables) is also provided. Studies of the effects of vibration duration on manual control performance are reviewed separately. A behavioural model is presented to summarize the mechanisms (including vibration breakthrough, visual impairment, neuro-muscular interference and central effects) by which whole-body vibration may interfere with the performance of continuous manual control tasks. The model emphasizes the adaptive ability of the human operator.</p

Plaque retention by self-ligating vs elastomeric orthodontic brackets: quantitative comparison of oral bacteria and detection with adenosine triphosphate-driven bioluminescence.

Item does not contain fulltextINTRODUCTION: Enamel decalcification is a common problem in orthodontics. The objectives of this randomized clinical study were to enumerate and compare plaque bacteria surrounding 2 bracket types, self-ligating (SL) vs elastomeric ligating (E), and to determine whether adenosine triphosphate (ATP)-driven bioluminescence could be used for rapid assessment of bacterial load in plaque. METHODS: Patients (ages, 11-17 years) were bonded with SL and E brackets in 14 maxillary and 12 mandibular arches by using a split-mouth design. Recall visits were at 1 and 5 weeks after bonding. Plaque specimens were assayed for oral bacteria and subjected to ATP-driven bioluminescence determinations with a luciferin-based assay. RESULTS: In most patients, teeth bonded with SL attachments had fewer bacteria in plaque than did teeth bonded with E brackets. At 1 and 5 weeks after bonding, the means for SL vs E brackets were statistically lower for total bacteria and oral streptococci (P <0.05). ATP bioluminescence values were statistically correlated to the total oral bacteria and oral streptococci, with correlation coefficients of 0.895 and 0.843, respectively. CONCLUSIONS: SL appliances promote reduced retention of oral bacteria, and ATP bioluminescence might be a useful tool in the rapid quantification of bacterial load and the assessment of oral hygiene during orthodontic treatment