1,722,917 research outputs found
Increasing nitrogen deposition and peat decomposition in European bogs: from C sinks to C sources?
No full textHigh nitrogen availability reduces polyphenol content in Sphagnum peat
No full textPeat mosses of the genus Sphagnum constitute the bulk of living and dead biomass in bogs. These plants contain peculiar polyphenols which hamper litter peat decomposition through their inhibitory activity on microbial breakdown. In the light of the increasing availability of biologically active nitrogen in natural ecosystems, litter derived from Sphagnum mosses is an ideal substrate to test the potential effects of increased atmospheric nitrogen deposition on polyphenol content in litter peat. To this aim,
we measured total nitrogen and soluble polyphenol concentration in Sphagnum litter peat collected in 11 European bogs under a chronic gradient of atmospheric nitrogen deposition. Our results demonstrate that increasing nitrogen concentration in Sphagnum
litter, as a consequence of increased exogenous nitrogen availability, is accompanied by a decreasing concentration of polyphenols. This inverse relationship is consistent with reports that in Sphagnum mosses, polyphenol and protein biosynthesis compete for the
same precursor. Our observation of modified Sphagnum litter chemistry under chronic nitrogen eutrophication has implications in the context of the global carbon balance, because a lower content of decay-inhibiting polyphenols would accelerate litter peat
decomposition
Newton-method based iterative learning control for robot-assisted rehabilitation using FES
No full textPrecise control of useful movement is critical in providing effective upper limb stroke rehabilitation using functional electrical stimulation (FES). To address the lack of accuracy currently available in clinical practice, this paper develops a general framework based on iterative learning control, an advanced model-based approach that has been successfully employed in three clinical treatment trials. An upper limb model is first developed to encompass unconstrained movements of the upper arm, with, in line with clinical need, additional assistance incorporated via a general class of robotic support mechanism. An iterative learning scheme is then developed to enable a subset of joint angles to be controlled via stimulation of an arbitrary set of muscles. This scheme is the first ILC approach which explicitly addresses coupled multivariable nonlinear dynamics in rehabilitation, enforcing convergence over multiple repetitions of a reaching task. Experiments with six participants confirm practical utility and performance
Robust Control Design for Electrical Stimulation Electrode Arrays
No full textElectrical stimulation electrode arrays are an emerging technology that enables muscles to be artificiallyactivated to assist human motion for orthotic or therapeuticpurposes. This paper develops robust performance marginsquantifying feedback controller tracking performance in thepresence of disturbance and modeling mismatch. These are thenapplied to formulate control design procedures that address the practical difficulty of obtaining an accurate model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Chemotherapy for brain stem gliomas.
No full textAbstract
Approximately 80% of tumors arising in the brain stem are diffuse intrinsic lesions. Patients typically present with a short duration of symptoms and signs with significant neurological impairment. Imaging findings are typical, and biopsy is not usually necessary to make a diagnosis. Standard treatment consists of radiotherapy alone. Although the majority of patients will show a significant improvement in neurological status following such treatment, the prognosis is very poor. The median time to disease progression is of the order of 5-6 months, the median survival time less than 1 year, and survival at 2 years and beyond, less than 10%. Over the last 10-15 years, numerous studies have been undertaken in an attempt to develop more effective treatment for children with diffuse intrinsic brain stem tumors. Using a hyperfractionated (twice-daily) schedule, doses of radiotherapy as high as 78 Gy have been given without success. Other approaches use chemotherapy combined with radiotherapy in a variety of different ways, including up-front, concurrent, and adjuvant chemotherapy, and high-dose chemotherapy with rescue. The results of these studies using chemotherapy, as well as other approaches using other systemic agents, are reviewed in detail
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