Control of ionic polymer metal composites Richardson, R.C.; Levesley, M.C.; Brown, M.D. ...
IEEE/ASME transactions on mechatronics,
06/2003, Letnik:
8, Številka:
2
Journal Article
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Robotic devices are traditionally actuated by hydraulic systems or electric motors. However, with the desire to make robotic systems more compact and versatile, new actuator technologies are ...required. In this paper, the control of ionic polymer metal composite actuators is investigated from a practical perspective. The actuator characteristics are examined through the unblocked maximum displacement and blocked force output. An open-loop position control and closed-loop position proportional-integral-derivative (PID) control are then applied to a strip of actuators. Finally, the performance of the polymer is investigated when implementing an impedance controller (force/position control).
Our recent measurements of long‐term fluid flux rates and output fluid chemistry at seep sites on Hydrate Ridge, Cascadia, suggest that the mechanisms driving fluid flow in gas hydrate bearing ...forearc settings may be significantly more complex than previously thought. Temporal changes in the polarity and magnitude of flow and in seep fluid chemistry were observed. The nature of flow appears to generate a strong response in the chemosynthetic seep community ecology. We document here: 1) the frequency and range of temporal variability in flow rates, 2) the relatively rapid changes in outflow composition, 3) strong outflow of seawater‐like fluids, 4) the association of Calyptogena (sp) clams with oscillatory and inflow settings, and 5) microbial mat communities associated with strong advection of altered fluids. These results suggest that a reappraisal may be required of the nature of the hydrologic system and its effect on related processes such as benthic seep community ecology and biogeochemical cycles.
Sorsby's fundus dystrophy (SFD) is an autosomal dominant degenerative disease of the retina, caused by mutations in exon 5 of the gene for tissue inhibitor of metalloproteinases-3 (TIMP-3). The ...mechanism by which these mutations give rise to the disease phenotype is unknown. In an attempt to identify common properties of these molecules that might underlie the disease phenotype, a range of SFD mutants were expressed from human retinal pigment epithelial (RPE) cells. This showed that resistance to turnover, resulting from intermolecular disulfide bond formation, was a common property of all the SFD mutants examined, providing a possible explanation for the increased deposition of the protein observed in eyes from SFD patients. In contrast, SFD mutants varied in their ability to inhibit cell-surface activation of matrix metalloproteinase-2 (MMP-2), a potent mediator of angiogenesis, ranging from being fully active to totally inactive. These data show that increased deposition of active TIMP-3, rather than dysregulation of metalloproteinase inhibition, is likely to be the primary, initiating event in SFD.
Clinicians must not simply decide that a patient with symptoms and a positive diagnostic test has a reason for a specific treatment, and likewise clinicians must not decide that a patient with ...symptoms and a negative test does not have a clinically important problem. We must also consider the sensitivity, specificity and predictive value of the diagnostic test and the individual characteristics of the patient. Treatment outcome depends on many factors. Point of service decisions vs population based decisions are obviously different. Each patient presents to the treating practitioner on a given day, at a given time, and it is this picture upon which a plan of care is formulated.
Severe plaque-type psoriasis has been successfully treated with orally administered cyclosporine, but there has been no comparative, controlled evaluation of various dosages and their efficacy and ...side effects.
In a 16-week, double-blind trial, we randomly assigned 85 patients with severe psoriasis to receive 3, 5, or 7.5 mg of cyclosporine per kilogram of body weight per day or a placebo consisting of the vehicle for the drug. After eight weeks the dose could be adjusted to improve safety or efficacy while maintaining blinding.
The psoriasis improved in a dose-dependent fashion. After eight weeks of fixed-dose therapy, 36, 65, and 80 percent of the patients receiving 3, 5, and 7.5 mg of cyclosporine per kilogram per day, respectively, were rated as being clear or almost clear of psoriasis; each group had significant improvement (P less than 0.0001) as compared with the group receiving vehicle, in which none of the patients were rated as clear or almost clear. The patients who received 5 mg per kilogram were the least likely to require dosage adjustments because of side effects or a lack of efficacy. The glomerular filtration rate, measured in a subgroup of 34 patients receiving cyclosporine, decreased by a median of 16 percent. Higher doses of cyclosporine had greater adverse effects on systolic blood pressure, glomerular filtration rate, and serum levels of creatinine, uric acid, bilirubin, and cholesterol. Delayed-type hypersensitivity reactions to skin-test antigens were reduced by cyclosporine administration. Cyclosporine appears to become concentrated in skin.
Cyclosporine therapy leads to a rapid and thorough clearing of psoriasis; an initial dose of 5 mg per kilogram per day seems to be appropriate. However, the safety of cyclosporine for the long-term treatment of psoriasis remains to be determined.
alpha-dystroglycan is a glycoprotein expressed on the surface of skeletal muscle fibres and other cell types. In muscle, alpha-dystroglycan provides a link between the myofibre cytoskeleton through ...its indirect binding to dystrophin, and the basal lamina through its binding to laminin-2, a protein of the extracellular matrix. The disruption of this linkage between the myofibre cytoskeleton and the extracellular matrix is a common feature of Duchenne and other muscular dystrophies, though the pathogenic mechanisms leading to muscle wasting remain unknown. By treating primary mouse muscle cultures with a monoclonal antibody which blocks alpha-dystroglycan binding to laminin, we show here the induction of a dystrophic phenotype in vitro. The phenotype is inducible in differentiated cultures only, is characterised by reduced myotube size, myofibril disorganisation, loss of contractile activity, reduced spontaneous clustering of acetylcholine receptors and is reversed by addition of excess exogenous laminin-2. Thus, alpha-dystroglycan may be part of a signalling pathway for the maturation and maintenance of skeletal myofibres. Detailed knowledge of this signalling pathway may provide insights into the molecular pathology of the various inherited muscular dystrophies, and identify valuable pharmacological targets and new therapeutic strategies.
Nonconservative excesses of dissolved metals in northern San Francisco Bay indicate that there are internal sources of metals within the bay. We quantified groundwater seepage and bioirrigation rates ...in this area to determine their roles in transporting dissolved metals from benthic sediments to surface waters. We deployed seepage meters and collected sediment, pore water, and bottom water samples at three sites. We determined seepage rates from seepage meters and modeled the transport of water through the sediment using pore water data to constrain rates of diffusion, advection, and bioirrigation. A groundwater flow model incorporating sediment physical properties and local topography constrains more regional seepage estimates. The seepage meters indicate upflow rates from 7 to 56 cm yr−1 in March and April 1999 with some large (≤50 cm yr−1) daily fluctuations that greatly exceed predictions based on sediment physical properties and tidally induced pore pressure variations. During this period, results from modeling pore water chemical data are consistent with a small bioirrigation rate (<1.5 × 10−7 s−1) relative to values determined for southern San Francisco Bay, and an average groundwater upwelling speed of 15 cm yr−1. The speed and direction of flow changed throughout the year, with best fits to the data ranging from 20 cm yr−1 upflow to 34 cm yr−1 downflow and averaging 4 cm yr−1 upflow. Confidence intervals (95%) are about ±10 cm yr−1 for this method, yet the range of acceptable seepage rates for temporally successive periods only overlap in one of four cases, suggesting that temporal variability can be discerned from potential artifacts. Groundwater flow modeling suggests that the seepage rates determined at our sites represent ∼45% of the average seepage rate for the area, applying one consolidation and permeability relationship to all sediments. If we apply these approximations to all of northern San Francisco Bay, benthic fluxes of dissolved metals to the surface waters could account for a relatively large amount (≤60%) of the unknown sources of dissolved cobalt and a relatively small amount (≤4%) of the unknown sources of dissolved silver, cadmium, copper, nickel, and zinc. More focused groundwater discharge or elevated metals concentrations are required to have a larger impact on trace element budgets in this setting.
Goose parvovirus is the etiological agent of Derzsy's disease, a fatal hepatitis of young geese. The virus infects geese and Muscovy ducks and can be propagated in the laboratory in primary embryonic ...goose fibroblasts. To date the virus has only been classified by morphological, biochemical, and culture characteristics as an autonomous parvovirus. We now report the cloning and partial sequencing of 3434 nucleotides of the vital genome. Three overlapping clones were obtained, encoding regions in the nonstructural and capsid coding region. The nucleotide sequence show little homology to other autonomous parvoviruses but 55% homology to the dependovirus AAV2. This homology to AAV2 was also confirmed at the amino acid level (nonstructural protein 55%, capsid coding region 51%). DNA cross hybridization studies indicate an even closer similarity of goose parvovirus to the yet unsequenced human dependoviruses AAV1 and AAV3 than to AAV2. These findings suggest that goose parvovirus may be genetically related to the dependovirus genus rather than to the other autonomous parvoviruses.
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