1,060 research outputs found
Control strategies for integration of electric motor assist and functional electrical stimulation in paraplegic cycling: Utility for exercise testing and mobile cycling
AIM: The aim of this study was to investigate feedback
control strategies for integration of electric motor assist and functional electrical stimulation (FES) for paraplegic cycling, with particular focus on development of a testbed for exercise testing in FES cycling, in which both cycling cadence and workrate are simultaneously well controlled and contemporary physiological measures of exercise performance derived. A second aim was
to investigate the possible benefits of the approach for mobile, recreational cycling.
METHODS: A recumbent tricycle with an auxiliary electric motor is used, which is adapted for paraplegic users, and instrumented for stimulation control. We propose a novel integrated control strategy which simultaneously provides feedback control of leg power output (via automatic adjustment of stimulation intensity) and cycling cadence (via electric motor control). Both loops are
designed using system identification and analytical (model-based) feedback design methods. Ventilatory and pulmonary gas exchange response profiles are derived using a portable system for real-time breath-by-breath acquisition.
RESULTS:We provide indicative results from one paraplegic subject in which a series of feedback-control tests illustrate accurate control of cycling cadence, leg power control, and external disturbance rejection. We also provide physiological response profiles from a submaximal exercise step test and a maximal incremental exercise test, as facilitated by the control strategy.
CONCLUSION: The integrated control strategy is effective in facilitating
exercise testing under conditions of well-controlled cadence
and power output. Our control approach significantly extends the
achievable workrate range and enhances exercise-test sensitivity
for FES cycling, thus allowing a more stringent characterization
of physiological response profiles and estimation of key parameters
of aerobic function.We further conclude that the control approach
can significantly improve the overall performance of mobile recreational
cycling
Higher-order total variation bounds for expectations of periodic functions and simple integer recourse approximations
Higher-order total variation bounds for expectations of periodic functions and simple integer recourse approximations
Convex approximations for totally unimodular integer recourse models:A uniform error bound
We consider a class of convex approximations for totally unimodular (TU) integer recourse models and derive a uniform error bound by exploiting properties of the total variation of the probability density functions involved. For simple integer recourse models this error bound is tight and improves the existing one by a factor 2, whereas for TU integer recourse models this is the first nontrivial error bound available. The bound ensures that the performance of the approximations is good as long as the total variations of the densities of all random variables in the model are small enough
Yield conditions for deformation of amorphous polymer glasses
Shear yielding of glassy polymers is usually described in terms of the
pressure-dependent Tresca or von Mises yield criteria. We test these criteria
against molecular dynamics simulations of deformation in amorphous polymer
glasses under triaxial loading conditions that are difficult to realize in
experiments. Difficulties and ambiguities in extending several standard
definitions of the yield point to triaxial loads are described. Two
definitions, the maximum and offset octahedral stresses, are then used to
evaluate the yield stress for a wide range of model parameters. In all cases,
the onset of shear is consistent with the pressure-modified von Mises
criterion, and the pressure coefficient is nearly independent of many
parameters. Under triaxial tensile loading, the mode of failure changes to
cavitation.Comment: 9 pages, 8 figures, revte
A method for mapping corn using the US Geological Survey 1992 National Land Cover Dataset
Novel point mutation in the extracellular domain of the granulocyte colony-stimulating factor (G-CSF) receptor in a case of severe congenital neutropenia hyporesponsive to G-CSF treatment
Severe congenital neutropenia (SCN) is a heterogeneous condition
characterized by a drastic reduction in circulating neutrophils and a
maturation arrest of myeloid progenitor cells in the bone marrow. Usually
this condition can be successfully treated with granulocyte
colony-stimulating factor (G-CSF). Here we describe the identification of
a novel point mutation in the extracellular domain of the G-CSF receptor
(G-CSF-R) in an SCN patient who failed to respond to G-CSF treatment. When
this mutant G-CSF-R was expressed in myeloid cells, it was defective in
both proliferation and survival signaling. This correlated with diminished
activation of the receptor complex as determined by signal transducer and
activator of transcription (STAT) activation, although activation of STAT5
was more affected than STAT3. Interestingly, the mutant receptor showed
normal affinity for ligand, but a reduced number of ligand binding sites
compared with the wild-type receptor. This suggests that the mutation in
the extracellular domain affects ligand-receptor complex formation with
severe consequences for intracellular signal transduction. Together these
data add to our understanding of the mechanisms of cytokine receptor
signaling, emphasize the role of GCSFR mutations in the etiology of SCN,
and implicate such mutations in G-CSF hyporesponsiveness
Bomb-<sup>14</sup>C analysis of ecosystem respiration reveals that peatland vegetation facilitates release of old carbon
The largest terrestrial-to-atmosphere carbon flux is respired CO<sub>2</sub>. However, the partitioning of soil and plant sources, understanding of contributory mechanisms, and their response to climate change are uncertain. A plant removal experiment was established within a peatland located in the UK uplands to quantify respiration derived from recently fixed plant carbon and that derived from decomposition of soil organic matter, using natural abundance <sup>13</sup>C and bomb-<sup>14</sup>C as tracers. Soil and plant respiration sources were found respectively to contribute ~ 36% and between 41-54% of the total ecosystem CO<sub>2</sub> flux. Respired CO<sub>2</sub> produced in the clipped (‘soil’) plots had a mean age of ~ 15 years since fixation from the atmosphere, whereas the <sup>14</sup>C content of ecosystem CO<sub>2</sub> was statistically indistinguishable from the contemporary atmosphere. Results of carbon mass balance modelling showed that, in addition to respiration from bulk soil and plant respired CO<sub>2</sub>, a third, much older source of CO<sub>2</sub> existed. This source, which we suggest is CO<sub>2</sub> derived from the catotelm constituted between ~ 10 and 23% of total ecosystem respiration and had a mean radiocarbon age of between several hundred to ~ 2000 years before present (BP). These findings show that plant-mediated transport of CO<sub>2</sub> produced in the catotelm may form a considerable component of peatland ecosystem respiration. The implication of this discovery is that current assumptions in terrestrial carbon models need to be re-evaluated to consider the climate sensitivity of this third source of peatland CO<sub>2</sub>
The Functional, Metabolic, and Anabolic Responses to Exercise Training in Renal Transplant and Hemodialysis Patients
BACKGROUND.: Exercise intolerance is common in hemodialysis (HD) and renal transplant (RTx) patients and is related to muscle weakness. Its pathogenesis may vary between these groups leading to a different response to exercise. The aim of the study was to compare intrinsic muscular parameters between HD and RTx patients and controls, and to assess the response to exercise training on exercise capacity and muscular structure and function in these groups. METHODS.: Quadriceps function (isokinetic dynamometry), body composition (dual-energy x-ray absorptiometry), and vastus lateralis muscle biopsies were analyzed before and after a 12-week lasting training-program in 35 RTx patients, 16 HD patients, and 21 healthy controls. RESULTS.: At baseline, myosin heavy chain (MyHC) isoform composition and enzyme activities were not different between the groups. VO2peak and muscle strength improved significantly and comparably over the training-period in RTx, HD patients and controls (ptime<0.05). The proportion of MyHC type I isoforms decreased (ptime<0.001) and type IIa MyHC isoforms increased (ptime<0.05). The 3-hydroxyacyl-CoA-dehydrogenase activity increased (ptime=0.052). Intrinsic muscular changes were not significantly different between groups. In the HD group, changes in lean body mass were significantly related to changes in muscle insulin-like growth factor (IGF)-II and IGF binding protein-3. CONCLUSIONS.: Abnormalities in metabolic enzyme activities or muscle fiber redistribution do not appear to be involved in muscle dysfunction in RTx and HD patients. Exercise training has comparable beneficial effects on functional and intrinsic muscular parameters in RTx patients, HD patients, and controls. In HD patients, the anabolic response to exercise training is related to changes in the muscle IGF system
Simulations of the Static Friction Due to Adsorbed Molecules
The static friction between crystalline surfaces separated by a molecularly
thin layer of adsorbed molecules is calculated using molecular dynamics
simulations. These molecules naturally lead to a finite static friction that is
consistent with macroscopic friction laws. Crystalline alignment, sliding
direction, and the number of adsorbed molecules are not controlled in most
experiments and are shown to have little effect on the friction. Temperature,
molecular geometry and interaction potentials can have larger effects on
friction. The observed trends in friction can be understood in terms of a
simple hard sphere model.Comment: 13 pages, 13 figure
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