1,721,017 research outputs found
A Statistical Inference Approach to Gas Path Analysis of a Turbofan
No full textThe use of statistical inference to monitoring the condition of a turbofan subject to small unsteady changes of the operating conditions is investigated. The application of this approach to a Gas Path Analysis dynamic model of the machine allows for the solution of the typical nondeterministic problem of evaluating the degraded status of aircraft engines. The engine condition can be inferred in terms of probability density functions with a high level of confidence from the limited and possibly inaccurate data provided by the sensors usually available in aeronautical applications. The results illustrate the influence of different measurement choices and accuracy on the capability of the method of identifying the degradations or malfunctions of engine components
Monitoring and Fault Diagnosis of a Turbojet by Bayesian Inference
No full textThis paper is concerned with investigating the application of Bayesian inference to monitoring the condition of turbojet engines. In order to overcome the typical necessity of a large number. of measurements for a deterministic solution of the problem, a statistic approach to the identification of maifunctions or degradation of engine components has been developed by combining a Gas Path Analysis model of the engine with statistical inference. In this way it becomes possible to infer the engine condition with a high level of confidence from the limited data provided by the sensors usuaIly available in aeronautical applications. The database for testing the method is generated by the same engine mode1 used in the identification, with the addition of random noise and offset errors to simulate measurement uncertainties and sensor malfunctions. The performance of the identification procedure is analyzed for several choices of the available me-as urements and sensors accuracy. The results illustrate the influence of these factors on the capability of identifying degradations or malfunctions of engine components and sensors
Biological performance of two materials based on sulfated hyaluronic acid and polyurethane
No full textPolyurethane bound with sulfated hyaluronic acid was synthesized by two different chemical routes. Both the
materials obtained consist of a hydrophilic component, sulfated hyaluronic acid (HyalS3.5), and a hydrophobic
component, polyurethane (PU). In the material named Puhmdi, the HyalS3.5 was cross-linked to the PU chains
via hexamethylene diisocyanate (HMDI) while in that named Pubrac, the binding of HyalS3.5 to the PU chains
occurred only through a few carboxy groups via N,N'-dicyclohexylcarbodiimide (DCC) and bromoacetic acid.
The surface characteristics of the polymers were investigated by ATR FT-IR spectroscopy while the surface
morphology was analyzed by scanning electron microscopy.
There was a signi®cant difference between the surface characteristics of the ®lms in dry and hydrated
environments. In both materials the hydrophilic component (HyalS3.5) migrates from the bulk to the surface,
thus minimizing the surface free energy of the polymer when exposed to the hydrated environment. The
different biological behavior of the two materials was demonstrated with the thrombin time test and platelet
adhesion test. Pubrac inhibits the coagulation process while Puhmdi does not
Porous multi-layered composite hydrogel as cell substrate for in vitro culture of chondrocytes
No full textA porous multi-layered composite hydrogel (MSC), made of poly(vinyl alcohol) (PVA) and hydroxyapatite (HA), suitable as substitute for damaged cartilage, has been modified by the production of pores and its cytocompatibility and ability to prevent chondrocyte dedifferentiation in in vitro cell culture systems have been evaluated. Pores resulted homogeneously distributed on all the hydrogel surface and bulk. The material was not able to compromise cell viability, proliferation and structure of both NIH3T3 mouse fibroblasts and human chondrocytes (HC), supported HC colonization and showed a good ability to stimulate the production of hyaline extracellular matrix (ECM)
Fibrinogen-Catecholamine Interaction as Observed by NMR and Fourier Transform Infrared Spectroscopy
No full textIn this work, the interactions between the main catecholaminessepinephrine and norepinephrinesand fibrinogen
were investigated by NMR and Fourier transform infrared spectroscopies. The two hormones were found to interact
with fibrinogen and to affect the protein secondary structure to a different extent. In particular, the protein selectively
binds epinephrine at both the basal and stress concentrations, while it shows a weak nonspecific interaction with
norepinephrine. The interaction with the stress level of epinephrine leads to drastic protein conformational changes,
whereas norepinephrine does not affect fibrinogen secondary structure, even at stress concentration
Immobilisation of sulphatede hyaluronan for improved biocompatibility
No full textHyaluronan (Hyal) was modified by the insertion of sulphate to hydroxyl groups. A series of heparin-like compounds with controllable properties was obtained. The physicochemical and biological behaviours of all these sulphated hyaluronan acids (HyalSx) and their complexes with heavy metal ions (Cu2+ and Zn2+) were investigated. HyalS, derivatives showed a good anticoagulant activity and low platelet aggregation which increased with increasing degree of sulphation. Moreover HyalSx and their Cu2+ complexes were demonstrated to favour the growth of human endothelial cells. However, the utilisation of HyalSx as a material is hindered by its high solubility in physiological solution. Our approach to improve its stability was directed to the synthesis of new HyalSx-based hydrogels and on the preparation of new biocompatible polymeric surfaces obtained through covalent photoimmobilisation of HyalSx. The reaction of primary ovine chondrocytes and B10D2 endothelial cells was studied on both matrices in terms of cell number, F-actin and CD44 receptor immunostaining. Analysis of cell movement showed that the cells respond to HyalSx showing good adhesion and spreading. These results suggest that HyalSx containing materials could be used as biomaterials to aid cartilage repair and vessel endothelisation
Hyaluronan derivatives: chemical modification and biochemical applications
No full textSeven sulphated hyaluronic acid (HA) derivatives, with a general formula HyalS(x) (x = 1, 2, 2.5, 3, 3.5, 3.8, and 4), were synthesised. Coagulation tests performed on these compounds yielded promising results for HyalS(2.5) to HyalS(4). The relationship of the anticoagulant activity of HyalS to chain length was also evaluated. HyalS(x) cytotoxicity and cytocompatibility were assessed by a direct contact method using L929 fibroblasts and human endothelial cells. Tests of HyalS(x) susceptibility to enzymatic degradation showed that the introduction of sulphate along the hyaluronic acid chain renders the macromolecules resistant to enzymatic digestion. The interaction of HyalS(x) derivatives with platelets was determined by platelet aggregation, activation, and von Willebrand Factor-dependent agglutination. Moreover, the ability of HyalS to form complexes with metallic ions such as Cu(II) and Zn(II) was evaluated together with the ability of these complexes to favour cell adhesion and stimulate cell migration. Various HyalS derivatives were immobilised by different chemical routes on the surface of polymeric materials and the physico-chemical and biological characteristics of the modified materials were studied. Lastly the therapeutic potential of Hyal hydrogels generated by a cross-linking reaction and then sulphated to improve their haemocompatibility, were evaluated in an animal model of articular inflammation
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
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