Lower-limb exoskeletons could improve the mobility of people with disabilities, older adults, workers, first responders, and military personnel. Despite recent advances, few products are commercially ...available and exoskeleton research is still often limited by hardware constraints. Many promising multi-joint assistance strategies, especially those with high-torque and high-power components, have yet to be tested because they are beyond the capabilities of current devices. To study these untested assistance strategies, we present a hip–knee–ankle exoskeleton emulator that can apply high torques and powers that match or exceed those observed in uphill running. The system has powerful off-board motors that actuate a 13.5 kg exoskeleton end effector worn by the user. It can apply up to 200 Nm of torque in hip flexion, hip extension, and ankle plantarflexion, 250 Nm of torque in knee extension, and 140 Nm of torque in knee flexion, with over 4.5 kW of power at each joint and a closed-loop torque bandwidth of at least 18 Hz in each direction of actuation. The exoskeleton is compliant in unactuated directions, adjustable for a wide range of users and comfortable during walking and running. When paired with human-in-the-loop optimization, we expect that this system will identify new assistance strategies to improve human mobility. A complete computer-aided design (CAD) model of the exoskeleton and a bill of materials are included and available for download.
With aging, the brain undergoes several structural changes. These changes reflect the normal aging process and are therefore not necessarily pathologic. In fact, better understanding of these normal ...changes is an important cornerstone to also disentangle pathologic changes. Several studies have investigated normal brain aging, both cross-sectional and longitudinal, and focused on a broad range of magnetic resonance imaging (MRI) markers. This study aims to comprise the different aspects in brain aging, by performing a comprehensive longitudinal assessment of brain aging, providing trajectories of volumetric (global and lobar; subcortical and cortical), microstructural, and focal (presence of microbleeds, lacunar or cortical infarcts) brain imaging markers in aging and the sequence in which these markers change in aging. Trajectories were calculated on 10,755 MRI scans that were acquired between 2005 and 2016 among 5286 persons aged 45 years and older from the population-based Rotterdam Study. The average number of MRI scans per participant was 2 scans (ranging from 1 to 4 scans), with a mean interval between MRI scans of 3.3 years (ranging from 0.2 to 9.5 years) and an average follow-up time of 5.2 years (ranging from 0.3 to 9.8 years). We found that trajectories of the different volumetric, microstructural, and focal markers show nonlinear curves, with accelerating change with advancing age. We found earlier acceleration of change in global and lobar volumetric and microstructural markers in men compared with women. For subcortical and cortical volumes, results show a mix of more linear and nonlinear trajectories, either increasing, decreasing, or stable over age for the subcortical and cortical volume and thickness. Differences between men and women are visible in several parcellations; however, the direction of these differences is mixed. The presence of focal markers show a nonlinear increase with age, with men having a higher probability for cortical or lacunar infarcts. The data presented in this study provide insight into the normal aging process in the brain, and its variability.
•Retrospective view on the past two decades of medical image registration.•Classification of the field introduced in 1998 is still usable.•Main changes: intensity-based, nonlinear registration, ...generic software packages.•Urgent problems still: validation, clinical acceptance.
A retrospective view on the past two decades of the field of medical image registration is presented, guided by the article “A survey of medical image registration” (Maintz and Viergever, 1998). It shows that the classification of the field introduced in that article is still usable, although some modifications to do justice to advances in the field would be due. The main changes over the last twenty years are the shift from extrinsic to intrinsic registration, the primacy of intensity-based registration, the breakthrough of nonlinear registration, the progress of inter-subject registration, and the availability of generic image registration software packages. Two problems that were called urgent already 20 years ago, are even more urgent nowadays: Validation of registration methods, and translation of results of image registration research to clinical practice. It may be concluded that the field of medical image registration has evolved, but still is in need of further development in various aspects.
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Resumo Este artigo reconstrói a trajetória do trabalho como categoria conceitual internamente à tradição intelectual que se designa como teoria crítica da sociedade, em suas transformações ao longo ...do século XX e na passagem para o século XXI. O artigo demonstrará um movimento de pêndulo: partindo de uma formulação teórica nos primórdios da Escola de Frankfurt, passou-se a uma concepção puramente empírica na sociologia do trabalho nos anos 1980, associada ao diagnóstico do “fim da sociedade do trabalho”, diagnóstico que se revela hoje questionável à luz das novas relações de trabalho da Gig Economy. Com isso, chega-se hoje a um movimento em que o trabalho pode voltar a ocupar a centralidade do pensamento crítico, inclusive rearticulando um programa político. Este artigo remonta esse movimento, mostrando como a centralidade da categoria trabalho oscilou ao longo do tempo, de acordo com as transformações estruturais do capitalismo mundial.◊
Abstract This paper reconstructs the development of labor as a conceptual category within the intellectual tradition that calls itself critical theory of society, in its transformations throughout the 20th century and into the 21st century. The paper will demonstrate a pendulum movement: starting from a theoretical formulation in the early days of the Frankfurt School, it moves to a purely empirical conception in the sociology of labor in the 1980s, associated with the diagnosis of the “end of the labor society”, a diagnosis that is now questionable in light of the new labor relations of the Gig Economy. So, we shift today to a context in which labor can once again occupy a central position for critical theory, perhaps enabling a new political project. This article reconstructs this movement, showing how the centrality of the labor category has oscillated over time, according to structural transformations of world capitalism.
Resumen Este artículo reconstruye el desarrollo del trabajo como categoría conceptual en la tradición intelectual que se autodenomina teoría crítica de la sociedad, en sus transformaciones a lo largo del siglo XX e inicio del siglo XXI. El texto mostrará un movimiento pendular: partiendo de una formulación teórica en los inicios de la Escuela de Frankfurt, se pasa a una concepción puramente empírica en la sociología del trabajo en los años 80, asociada al diagnóstico del “fin de la sociedad del trabajo”, diagnóstico que hoy es cuestionable a la luz de las nuevas relaciones laborales de la economía Gig. Con eso, se llega hoy a un contexto en el que el trabajo puede volver a ocupar un lugar central para la teoría crítica, posibilitando quizás un nuevo proyecto político. Este artículo reconstruye este movimiento, mostrando cómo la centralidad de la categoría trabajo ha oscilado a lo largo del tiempo, de acuerdo con las transformaciones estructurales del capitalismo mundial.
Purpose
Support groups might help survivors of allogeneic hematopoietic cell transplantations (HCT) to cope with medical, psychological, and social challenges. The aim of this project was (1) to ...establish a facilitated post-HCT support group and (2) to assess the participation behaviour.
Methods
From 11/2013 until 7/2017, all adult patients who had received a HCT at our centre were invited to participate in a professionally facilitated support group. The format of the group was unstructured without any rules regarding regular attendance. The attendance was prospectively minuted by the facilitator. Reasons for non-attendance were assessed by a survey.
Results
During the observation period, 53 group meetings were scheduled. Nine meetings were cancelled because of low attendance. Altogether 23 different patients (F:
n
=10; M:
n
=13) and 10 spouses (F:
n
=9; M:
n
=1) participated. Median participation was 5 range 2–11. With respect to all HCT patients who had the theoretical opportunity to attend, the mean participation rate was 7%. Thirteen patients and four spouses attended more than one meeting. The median count of participations among those participants was 8 2-32. The median interval from the first until the last participation was 16 months. The main reason reported for non-participation was the effort to get to the venue of the support group.
Conclusions
To our knowledge, this is the first analysis on the attendance behaviour of the participants of a support group for HCT survivors. The results provide guidance for the organization of future support groups and indicate what participation rates can be expected and how they might be increased.
A popular technique for nonrigid registration of medical images is based on the maximization of their mutual information, in combination with a deformation field parameterized by cubic B-splines. The ...coordinate mapping that relates the two images is found using an iterative optimization procedure. This work compares the performance of eight optimization methods: gradient descent (with two different step size selection algorithms), quasi-Newton, nonlinear conjugate gradient, Kiefer-Wolfowitz, simultaneous perturbation, Robbins-Monro, and evolution strategy. Special attention is paid to computation time reduction by using fewer voxels to calculate the cost function and its derivatives. The optimization methods are tested on manually deformed CT images of the heart, on follow-up CT chest scans, and on MR scans of the prostate acquired using a BFFE, Tl, and T2 protocol. Registration accuracy is assessed by computing the overlap of segmented edges. Precision and convergence properties are studied by comparing deformation fields. The results show that the Robbins-Monro method is the best choice in most applications. With this approach, the computation time per iteration can be lowered approximately 500 times without affecting the rate of convergence by using a small subset of the image, randomly selected in every iteration, to compute the derivative of the mutual information. From the other methods the quasi-Newton and the nonlinear conjugate gradient method achieve a slightly higher precision, at the price of larger computation times.
Sparse representations classification (SRC) is a powerful technique for pixelwise classification of images and it is increasingly being used for a wide variety of image analysis tasks. The method ...uses sparse representation and learned redundant dictionaries to classify image pixels. In this empirical study we propose to further leverage the redundancy of the learned dictionaries to achieve a more accurate classifier. In conventional SRC, each image pixel is associated with a small patch surrounding it. Using these patches, a dictionary is trained for each class in a supervised fashion. Commonly, redundant/overcomplete dictionaries are trained and image patches are sparsely represented by a linear combination of only a few of the dictionary elements. Given a set of trained dictionaries, a new patch is sparse coded using each of them, and subsequently assigned to the class whose dictionary yields the minimum residual energy. We propose a generalization of this scheme. The method, which we call multiple sparse representations classification (mSRC), is based on the observation that an overcomplete, class specific dictionary is capable of generating multiple accurate and independent estimates of a patch belonging to the class. So instead of finding a single sparse representation of a patch for each dictionary, we find multiple, and the corresponding residual energies provides an enhanced statistic which is used to improve classification. We demonstrate the efficacy of mSRC for three example applications: pixelwise classification of texture images, lumen segmentation in carotid artery magnetic resonance imaging (MRI), and bifurcation point detection in carotid artery MRI. We compare our method with conventional SRC, K-nearest neighbor, and support vector machine classifiers. The results show that mSRC outperforms SRC and the other reference methods. In addition, we present an extensive evaluation of the effect of the main mSRC parameters: patch size, dictionary size, and sparsity level.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Resumo A produção teórica de Lélia Gonzalez se insere na tradição ensaística brasileira, rica em produzir interpretações sobre o Brasil e a América Latina. Em que pese a relevância e originalidade do ...pensamento da autora, ainda são relativamente incipientes os investimentos de pesquisa voltados à teoria social proposta pela pensadora brasileira. Neste artigo, busca-se identificar os fundamentos da teoria social produzida por Lélia Gonzalez, dando especial atenção a seus vínculos com o pensamento sociológico. O intuito é realçar a multidimensionalidade de sua abordagem, que mobiliza e dialoga criticamente com autoras(es) clássicas(os) das ciências sociais, apontando suas limitações em termos heurísticos, e articulando-se com investigações e reflexões que conferem aos conceitos de raça/cor e gênero lugar equiparável ao de classe na interpretação crítica do social.
Abstract The theorization of Lélia Gonzalez is part of a Brazilian essayistic tradition, with rich contributions towards the interpretation of Brazil and Latin America. Although she presents a relevant and original thought, research directed at her social theory is still comparably scarce. In this article we evidence the main traits of the social theory produced by Lélia Gonzalez, with special attention to her liaison to sociological thought. Our aim is to highlight a central aspect of this approach, the multidimensionality of her studies, that mobilize and critically dialogue with a number of classic authors from the social sciences, hereby pointing out their limitations in heuristic terms, as well as articulating this point of view with investigations and reflections that award the concepts of race/color and gender a place comparable to that of class in the critical interpretation of the social.
It is unknown whether white matter lesions (WML) develop abruptly in previously normal brain areas, or whether tissue changes are already present before WML become apparent on MRI. We therefore ...investigated whether development of WML is preceded by quantifiable changes in normal-appearing white matter (NAWM).
In 689 participants from the general population (mean age 67 years), we performed 2 MRI scans (including diffusion tensor imaging and Fluid Attenuation Inversion Recovery FLAIR sequences) 3.5 years apart using the same 1.5-T scanner. Using automated tissue segmentation, we identified NAWM at baseline. We assessed which NAWM regions converted into WML during follow-up and differentiated new WML into regions of WML growth and de novo WML. Fractional anisotropy, mean diffusivity, and FLAIR intensity of regions converting to WML and regions of persistent NAWM were compared using 3 approaches: a whole-brain analysis, a regionally matched approach, and a voxel-wise approach.
All 3 approaches showed that low fractional anisotropy, high mean diffusivity, and relatively high FLAIR intensity at baseline were associated with WML development during follow-up. Compared with persistent NAWM regions, NAWM regions converting to WML had significantly lower fractional anisotropy (0.337 vs 0.387; P<0.001), higher mean diffusivity (0.910 × 10(-3) mm(2)/s vs 0.729 × 10(-3) mm(2)/s; P<0.001), and relatively higher normalized FLAIR intensity (1.233 vs -0.340; P<0.001). This applied to both NAWM developing into growing and de novo WML.
White matter changes in NAWM are present and can be quantified on diffusion tensor imaging and FLAIR before WML develop. This suggests that WML develop gradually, and that visually appreciable WML are only the tip of the iceberg of white matter pathology.
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