Natural Trajectories Research Articles

Faster-than-natural spacecraft circumnavigation via way points

Circumnavigation relative motion is considered for applications such as inspecting a space object for damage, or characterizing space debris before engaging a remediation operation. Faster-than-natural circumnavigation is a guidance method in which the deputy spacecraft is advanced ahead of the natural Keplerian relative motion. A state transition matrix method of generating a discrete way point guidance solution is proposed for faster-than natural circumnavigation. The state transition matrix methodology is applied to both circular and elliptical chief orbits. For the circular chief case, natural relative trajectories are planar in nature. With the faster-than-natural circumnavigation, this work illustrates how the required relative trajectories become three-dimensional curves. This methodology allows for closed-form impulsive control solutions and the associated fuel cost. Numerical simulations illustrate and validate the proposed method.

Identifying clinical measures that most accurately reflect the progression of disability in Parkinson disease

IntroductionThe temporal relationship between disease and disability progression in Parkinson disease (PD) is not well understood. Our objective was to describe the natural, multidimensional trajectory of disability in persons with PD over a two-year period. MethodsWe conducted a multi-center, prospective cohort study involving four institutions. Data were collected at baseline and at 6-month intervals over 2 years using standardized clinical tests representing three World Health Organization defined disability domains: impairment, activity limitation, and participation restriction. Unadjusted mixed effects growth models characterized trajectories of disability in the three disability domains. The data set was analyzed using restricted maximum likelihood (REML) estimation. Standardized estimates of change were also computed using Cohen's d for each measure. ResultsOf the 266 enrolled participants, we analysed data from individuals who participated in at least 3 assessments (n = 207, 79%). Rates of disability progression over the 2-year period differed across domains. Moderate effects were detected for motor impairment (d = .28) and walking-related activity limitation (gait-related balance (d = .31); gait speed (d = .30)). Marginal effects were noted for upper extremity-related activity limitation (d = .11) and health-related quality of life participation restriction (d = .08). ConclusionsThe natural trajectory of walking-related activity limitation was the most potent indicator of evolving disability, suggesting that routine assessment of walking and periodic rehabilitation is likely to be warranted for many persons with PD. Natural trajectories of disability provide important comparison data for future intervention studies.

Natural motion trajectory enhances the coding of speed in primate extrastriate cortex.

The ability to estimate the speed of an object irrespective of size or texture is a crucial function of the visual system. However, previous studies have suggested that the neuronal coding of speed in the middle temporal area (MT, a key cortical area for motion analysis in primates) is ambiguous, with most neurons changing their speed tuning depending on the spatial frequency (SF) of a visual pattern. Here we demonstrate that the ability of MT neurons to encode speed is markedly improved when stimuli follow a trajectory across the visual field, prior to entering their receptive fields. We also show that this effect is much less marked in the primary visual area. These results indicate that MT neurons build up on computations performed at earlier levels of the visual system to provide accurate coding of speed in natural situations, and provide additional evidence that nonlinear pooling underlie motion processing.

Evaluation of the effects of the Arm Light Exoskeleton on movement execution and muscle activities: a pilot study on healthy subjects.

BackgroundExoskeletons for lower and upper extremities have been introduced in neurorehabilitation because they can guide the patient’s limb following its anatomy, covering many degrees of freedom and most of its natural workspace, and allowing the control of the articular joints. The aims of this study were to evaluate the possible use of a novel exoskeleton, the Arm Light Exoskeleton (ALEx), for robot-aided neurorehabilitation and to investigate the effects of some rehabilitative strategies adopted in robot-assisted training.MethodsWe studied movement execution and muscle activities of 16 upper limb muscles in six healthy subjects, focusing on end-effector and joint kinematics, muscle synergies, and spinal maps. The subjects performed three dimensional point-to-point reaching movements, without and with the exoskeleton in different assistive modalities and control strategies.ResultsThe results showed that ALEx supported the upper limb in all modalities and control strategies: it reduced the muscular activity of the shoulder’s abductors and it increased the activity of the elbow flexors. The different assistive modalities favored kinematics and muscle coordination similar to natural movements, but the muscle activity during the movements assisted by the exoskeleton was reduced with respect to the movements actively performed by the subjects. Moreover, natural trajectories recorded from the movements actively performed by the subjects seemed to promote an activity of muscles and spinal circuitries more similar to the natural one.ConclusionsThe preliminary analysis on healthy subjects supported the use of ALEx for post-stroke upper limb robotic assisted rehabilitation, and it provided clues on the effects of different rehabilitative strategies on movement and muscle coordination.

PRECISION MEDICINE - The Golden Gate for Detection, Treatment and Prevention of Alzheimer's Disease.

During this decade, breakthrough conceptual shifts have commenced to emerge in the field of Alzheimer's disease (AD) recognizing risk factors and the non-linear dynamic continuum of complex pathophysiologies amongst a wide dimensional spectrum of multi-factorial brain proteinopathies/neurodegenerative diseases. As is the case in most fields of medicine, substantial advancements in detecting, treating and preventing AD will likely evolve from the generation and implementation of a systematic precision medicine strategy. This approach will likely be based on the success found from more advanced research fields, such as oncology. Precision medicine will require integration and transfertilization across fragmented specialities of medicine and direct reintegration of Neuroscience, Neurology and Psychiatry into a continuum of medical sciences away from the silo approach. Precision medicine is biomarker-guided medicine on systems-levels that takes into account methodological advancements and discoveries of the comprehensive pathophysiological profiles of complex multi-factorial neurodegenerative diseases, such as late-onset sporadic AD. This will allow identifying and characterizing the disease processes at the asymptomatic preclinical stage, where pathophysiological and topographical abnormalities precede overt clinical symptoms by many years to decades. In this respect, the uncharted territory of the AD preclinical stage has become a major research challenge as the field postulates that early biomarker guided customized interventions may offer the best chance of therapeutic success. Clarification and practical operationalization is needed for comprehensive dissection and classification of interacting and converging disease mechanisms, description of genomic and epigenetic drivers, natural history trajectories through space and time, surrogate biomarkers and indicators of risk and progression, as well as considerations about the regulatory, ethical, political and societal consequences of early detection at asymptomatic stages. In this scenario, the integrated roles of genome sequencing, investigations of comprehensive fluid-based biomarkers and multimodal neuroimaging will be of key importance for the identification of distinct molecular mechanisms and signaling pathways in subsets of asymptomatic people at greatest risk for progression to clinical milestones due to those specific pathways. The precision medicine strategy facilitates a paradigm shift in Neuroscience and AD research and development away from the classical "one-size-fits-all" approach in drug discovery towards biomarker guided "molecularly" tailored therapy for truly effective treatment and prevention options. After the long and winding decade of failed therapy trials progress towards the holistic systems-based strategy of precision medicine may finally turn into the new age of scientific and medical success curbing the global AD epidemic.

マルチボディダイナミクスによるテレスコピックブーム型介護リフトの開発と最適設計

Recently a number of nursing care equipments to aid lift and transfer for aged person have been developed. Especially, rotational boom type care lifts are widely used because of its simplicity and usefulness. However, this type of lifts give mental and physical burden to cared person since while lifting up human body becomes unnatural posture. Hence, in this paper, we propose a telescopic boom type care lift in order to approximate lift-up motion to a natural human standing-up trajectory. By using a multibody dynamics approach, we show that the proposed mechanism can achieve nearly natural standing-up motion and is able to reduce required force to lift-up than conventional type lift. Then, we develop a prototype telescopic boom type care lift and verify its effectiveness through experiments. Finally, we also consider the optimal design problem of the proposed care lift to further reduce mental and physical burden.

A spectral series approach to high-dimensional nonparametric regression

A key question in modern statistics is how to make fast and reliable inferences for complex, high-dimensional data. While there has been much interest in sparse techniques, current methods do not generalize well to data with nonlinear structure. In this work, we present an orthogonal series estimator for predictors that are complex aggregate objects, such as natural images, galaxy spectra, trajectories, and movies. Our series approach ties together ideas from kernel machine learning, and Fourier methods. We expand the unknown regression on the data in terms of the eigenfunctions of a kernel-based operator, and we take advantage of orthogonality of the basis with respect to the underlying data distribution, P, to speed up computations and tuning of parameters. If the kernel is appropriately chosen, then the eigenfunctions adapt to the intrinsic geometry and dimension of the data. We provide theoretical guarantees for a radial kernel with varying bandwidth, and we relate smoothness of the regression function with respect to P to sparsity in the eigenbasis. Finally, using simulated and real-world data, we systematically compare the performance of the spectral series approach with classical kernel smoothing, k-nearest neighbors regression, kernel ridge regression, and state-of-the-art manifold and local regression methods.

Development and Optimal Design of a Telescopic Boom Lift for Nursing Care Using a Multibody Dynamics Approach

Recently a number of nursing care equipments to aid lift and transfer for aged person have been developed. Especially, rotational boom type care lifts are widely used due to its simplicity and usefulness. However, this type of lifts sometimes provide a feeling of uneasiness since while lift-up human body center moves backward than the position of the heel. Hence, in this paper, we propose a telescopic boom type care lift in order to approximate lift-up motion to a natural human standing-up trajectory. By using a multibody dynamics approach, we show that the proposed mechanism can achieve nearly natural standing-up motion and is able to reduce required force to lift-up than conventional type lift. Then, we develop a prototype telescopic boom type care lift and verify its effectiveness through experiments. Finally, we also consider the optimal design problem of the proposed care lift structure.

A Theory of the Evolution of Social Power: Natural Trajectories of Interpersonal Influence Systems along Issue Sequences

This article reports new advancements in the theory of influence system evolution in small deliberative groups, and a novel set of empirical findings on such evolution. The theory elaborates the specification of the single-issue opinion dynamics of such groups, which has been the focus of theory development in the field of opinion dynamics, to include group dynamics that occur along a sequence of issues. The theory predicts an evolution of influence centralities along issue sequences based on elementary reflected appraisal mechanisms that modify influence network structure and flows of influence in the group. The new empirical findings, which are also reported in this article, present a remarkable suite of issue-sequence effects on influence network structure consistent with theoretical predictions.

Dying within dying: Ethical dilemmas of treating terminally ill patients with acute life-threatening illnesses.

Sir, With the advent of palliative care, severely ill patients with terminal illnesses are often treated in accordance with their autonomy and with dignity, compassion, and comfort.[1] However, this most often happens if the patient is dying from the said terminal illness such as renal or heart failure or cancer.[2] Such patients may choose to die at home or even in palliative care wards. It is a comforting feeling for physicians and families that nonbeneficial life-sustaining and often agonizing care is not being delivered against a patient's wishes. There are pathways, protocols, and advance care plans for identifying and allowing such patients to complete their journey at the end of life.[3] However, an alarming number of patients with terminal illnesses fall through the cracks of this optimal situation.[4] Patients may receive care that is not in keeping with their natural trajectory of illness or wishes if they are admitted with an acute potentially “reversible” pathology while having a background terminal illness such as developing pneumonia, suffering myocardial infarctions, or be involved in trauma.[5] The rising costs of admitting and treating terminally ill patients with acute illness with modern day technology is unsustainable. The aim of this letter is to provide a brief review of the literature on the ethical difficulties that physicians and families face when decision-making in a terminally ill patient (at times with an advance care plan in place) is thrown off balance by a sudden acute illness. The question here is “should physicians feel morally obliged to treat an acute illness when the patient is already far along his or her end of life journey?” The thematic analysis of these papers revealed the following subtopics: Family communication, reiteration of diagnosis, burden of critical treatment, and goal setting. There was general agreement that terminally ill patients should have continuity of care and preferably be referred to the same center familiar with their terminal diagnosis and end of life goals. In an aging world with limited critical care resources, there are many demands on acute care settings such as Intensive Care Units. Patients who may not benefit from aggressive life-sustaining care perhaps should not be offered such treatment options such as life-saving surgery, if in fact it is merely prolonging their ultimate fate, unless it can add to alleviating suffering. Instead, effort and resources should be used in trying to match their goals and values, including palliation and providing mindful dignity and comfort. Often symptom control to provide relief is the driving force behind acute admissions in terminally ill patients; however, it seems that frank and consistent communication with patients and families may allay the ethical conflicts that usually arise when a patient presents in extremis while already dying from a separate illness including old age. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Atopia Awaits! A Critical Sociological Analysis of Marx’s Political Imaginary

Marx’s (1844) estranged labor manuscript maps processes that stultify spontaneous human relations under the division of labor in the regime of capital accumulation. For Marx, negating absolutes would put ‘Man’ back on its natural trajectory toward positive freedom. Such evacuation of mediating ‘substances’ results in either frivolity or pragmatic barbarism rather than positive freedom. Marx’s political imaginary rejected philosophical mysticism but overlooked finer points of Hegel’s dialectic that contribute to an immanent critique of Marxist political ideology. Missing from Marx’s thought is the logic of post-capitalist mediation and a trace of the subjective modalities that correspond with the objective forms of alienation. Lacking an adequate psychology, Marx did not see that he had constructed a communism that mirrored the subjective spirit of bourgeois society. We draw upon philosophical, sociological, and psychoanalytic currents to remap the genome of Marxist political philosophy with a Whitmanesque imaginary congenial to free, poetic social mediation.

A visual-numeric approach to clustering and anomaly detection for trajectory data

This paper proposes a novel application of Visual Assessment of Tendency (VAT)-based hierarchical clustering algorithms (VAT, iVAT, and clusiVAT) for trajectory analysis. We introduce a new clustering based anomaly detection framework named iVAT+ and clusiVAT+ and use it for trajectory anomaly detection. This approach is based on partitioning the VAT-generated Minimum Spanning Tree based on an efficient thresholding scheme. The trajectories are classified as normal or anomalous based on the number of paths in the clusters. On synthetic datasets with fixed and variable numbers of clusters and anomalies, we achieve 98 % classification accuracy. Our two-stage clusiVAT method is applied to 26,039 trajectories of vehicles and pedestrians from a parking lot scene from the real life MIT trajectories dataset. The first stage clusters the trajectories ignoring directionality. The second stage divides the clusters obtained from the first stage by considering trajectory direction. We show that our novel two-stage clusiVAT approach can produce natural and informative trajectory clusters on this real life dataset while finding representative anomalies.

Landscape trajectories and their effect on fragmentation for a Mediterranean semi-arid ecosystem in Central Chile

Changes in land use and land cover reflect anthropogenic effects in areas with a long history of human occupation, such as Mediterranean regions. To understand the landscape dynamics of a semi-arid Mediterranean ecosystem in Chile, we evaluated land-cover trajectories and their effects on landscape spatial patterns over a period of 36 years (1975–2011). We used landscape metrics combined with surveys of landowners to distinguish the main drivers of landscape change. General results indicated that changes in forest area followed both natural (64%) and human-induced (36%) trajectories. At the landscape level, fragmentation for all forest cover types increased, whereas at the class level, fragmentation of Native Forest decreased. The landscape changed from a homogeneous mosaic dominated by grazing and agriculture to a more heterogeneous environment, where natural cover had become more dominant. Thus, the use of a landscape ecology approach together with field information improved our understanding of the spatiotemporal dynamics in this landscape. This study is one of the first to assess landscape dynamics of the Mediterranean semi-arid region of Chile. This is important because it aids decision-making for biodiversity conservation in a global hotspot and land-use planning.

Foretelling plaque disruption: Is the journey to Ithaca reaching destination?

Plaque rupture with superimposed thrombus formation has long been identified as the predominant pathophysiologic hallmark of acute coronary syndromes and plaque progression [2]. Intensive research efforts over the last decades focused on the development of accurate prediction tools for those plaques which are more likely to undergo fibrous cap rupture in the future and trigger adverse vascular and clinical sequelae. The rationale underlying these complex, time-consuming andmultidisciplinary endeavors is that a prompt yet precise characterization of plaques at increased risk of triggering future coronary events would justify the adoption of either systemic or localized prophylactic measures to prevent catastrophic clinical manifestations. Advanced morphological and functional assessment of coronary lesions has provided incremental insights into the complex natural history trajectory of atherosclerosis and the factors which may contribute to the formation of high-risk plaque. Detailed vascular imaging has become feasible via the development and implementation of various imaging modalities such as coronary angiography, intravascular

Institutions, Labor Mobility, and Foreign Direct Investment in China and India

Why did China and India, despite their similar natural factor endowments and growth trajectories, attract different types of FDI? This article shows that microlevel institutions in China and India, particularly a set of regulations governing labor and land markets, shape their domestic labor mobility and consequently affect their FDI patterns and development paths. China’s high labor mobility motivates foreign firms to concentrate in labor-intensive manufacturing and exploit the benefits of scale economies. India’s low labor mobility motivates foreign firms to move away from unskilled-labor-intensive manufacturing and invest in the modern service sector where the demand for skilled labor is relatively high.

A Dynamic Localized Adjustable Force Field Method for Real-Time Assistive Non-Holonomic Mobile Robotics

Providing an assistive navigation system that augments rather than usurps user control of a powered wheelchair represents a significant technical challenge. This paper evaluates an assistive collision avoidance method for a powered wheelchair that allows the user to navigate safely whilst maintaining their overall governance of the platform motion. The paper shows that by shaping, switching and adjusting localized potential fields we are able to negotiate different obstacles by generating a more intuitively natural trajectory, one that does not deviate significantly from the operator in the loop desired-trajectory. It can also be seen that this method does not suffer from the local minima problem, or narrow corridor and proximity oscillation, which are common problems that occur when using potential fields. Furthermore this localized method enables the robotic platform to pass very close to obstacles, such as when negotiating a narrow passage or doorway.

Prospective relationships between body weight and physical activity: an observational analysis from the NAVIGATOR study

ObjectivesWhile bidirectional relationships exist between body weight and physical activity, direction of causality remains uncertain and previous studies have been limited by self-reported activity or weight and small sample size....

Direct Power Control Based on Natural Switching Surface for Three-Phase PWM Rectifiers

In this letter, the natural trajectories of the output voltage and the inductor currents for three-phase pulse width modulation rectifiers are presented. On this basis, a novel direct power control (DPC) using the natural switching surface is proposed by combining DPC with the boundary control. Compared to the conventional DPC, the proposed control considers the output voltage when selecting the switching states. Therefore, the proposed control does not need an outer voltage control loop and can highly improve the dynamic performance of the dc output voltage. The experimental results on a 1.5-kW prototype confirm the correctness of the theoretical analysis. They verify the feasibility and the validity of the proposed control and show the excellent dynamic performance.

Planning in the continuous domain: A generalized belief space approach for autonomous navigation in unknown environments

We investigate the problem of planning under uncertainty, with application to mobile robotics. We propose a probabilistic framework in which the robot bases its decisions on the generalized belief, which is a probabilistic description of its own state and of external variables of interest. The approach naturally leads to a dual-layer architecture: an inner estimation layer, which performs inference to predict the outcome of possible decisions; and an outer decisional layer which is in charge of deciding the best action to undertake. Decision making is entrusted to a model predictive control (MPC) scheme. The formulation is valid for general cost functions and does not discretize the state or control space, enabling planning in continuous domain. Moreover, it allows to relax the assumption of maximum likelihood observations: predicted measurements are treated as random variables, and binary random variables are used to model the event that a measurement is actually taken by the robot. We successfully apply our approach to the problem of uncertainty-constrained exploration, in which the robot has to perform tasks in an unknown environment, while maintaining localization uncertainty within given bounds. We present an extensive numerical analysis of the proposed approach and compare it against related work. In practice, our planning approach produces smooth and natural trajectories and is able to impose soft upper bounds on the uncertainty. Finally, we exploit the results of this analysis to identify current limitations and show that the proposed framework can accommodate several desirable extensions.

Do physical activity levels in the cancer population recover without intervention? An observational study

Background: National UK directives expect physical activity (PA) to be included in cancer patients’ management due to recognition of its wide-ranging benefit. Local implementation is inconsistent and remains a challenge.Nationally, only 29% of females and 39% of males in England met American College of Sports Medicine (ACSM) exercise recommendations. Those receiving cancer treatments may be less likely to meet exercise recommendations at the completion of primary cancer treatment. Purpose: To evaluate PA levels in a representative sample of cancer survivors post primary treatment (end-of-treatment: EOT) and 4 months post EOT as part of determining their natural recovery trajectory to inform future development of services. Methods:A consecutive, representative sample of 76 survivors with breast, prostate, gynaecological, colorectal and lymphoma cancer (mean age 64.7 years, SD= 11.67) diagnosed and treated at a regional cancer centre in London, UK were measured between November 2012 and March 2013 at EOT. The short form International Physical Activity Questionnaire (IPAQ-SF) was our primary measure of patient self-reported PA levels. Patient demographics and characteristics represented secondary measures. Results: IPAQ-SF scores revealed 85% (n= 71) met exercise recommendations at EOT when translated to the ACSM recommendations.At 4months therewas no proportional difference (n= 53, 85%). There were no statistically significant associations between PA change and gender or tumour type. Overall, our results showed an unexpected over-reporting of recommended PA levels both at EOT and 4 months post EOT compared with the unimpaired population. Conclusion(s):Our results show that self reported PA levels do not change 4 months after EOT. The validity of the IPAQ-SF in translating PA with respect to exercise recommendations in cancer survivors is questionable. This may be secondary to erroneous reporting of low level activity included e.g. walking which may have inflated PA levels. There remains debate about operationalizing PA and other functional activities in this representative sample. Implications:Our data indicates that the use of the IPAQSF should be carefully considered in reportingPA levels in the context of recommended PA levels in the cancer population at the end of primary treatment. There is an urgent need for the professional community to reach consensus on what does and does not constitute PA in impaired populations.