441 research outputs found
Exploiting nonlinearity for the design of linear oscillators: Application to an inherently strong nonlinear X-shaped-spring suspension
No full textThis paper proposes a paradigm shift in the perspective of designing nonlinear oscillators, i.e., the exploitation of nonlinearity to achieve a linear behaviour to good engineering purposes. An elastic suspension with four inclined springs is studied, which has an inherently strong geometric nonlinear stiffness characteristic. Such a configuration has attracted remarkable research efforts in last couple of years, because, compared to other classical nonlinear spring configurations, it has more design parameters, which can be wisely selected to attain a tailored force–displacement characteristic. A particular relationship among these parameters is found so that the overall characteristic becomes exactly linear. Compared to the use of classical linear springs mounted along the direction of motion, the proposed configuration with inclined springs has the potential to allow more freedom in the dimensioning of an engineering device. Also, while the equivalent spring obtained is linear, the equivalent damping is not, and this has the potential advantage of practically realising a linear elastic behaviour with the benefit of geometrical nonlinear damping. Experiments are performed for validation on a prototype device, and results confirm the linear behaviour predicted by the theoretical analysis
Performance of a vibration isolator with sigmoidal force-deflection curve
No full textThis paper presents a theoretical insight on the performance of a vibration isolator consisting of a combination of linear mechanical springs arranged to achieve a specific form of geometric nonlinearity. In particular, positive and negative stiffness nonlinearities are combined to achieve a sigmoidal shape of the force-deflection curve, which is proven to be beneficial for vibration isolation purposes when the amplitude of vibration is relatively large. Such behaviour is fundamentally different from that of the classical quasi-zero-stiffness isolator, which presents a low dynamic stiffness at the equilibrium configuration and is thus effective for relatively low amplitude of vibration. The analytical findings are validated by numerical simulations, providing useful guidelines for the design of such isolators
Realization and characterization of fiber-pumped room temperature Tm:YAG and Tm-Ho:YAG lasers at 2 umwavelength
No full textColchicine inhibition of ADH effect on frog skin permeability.
No full textADH and AMPc enhance both thiourea unidirectional fluxes in frog skin. This effect is completely abolished by colchicine pretreatment. The ADH increase of thiourea discharge with or without colchicine led us to suppose that colchicine does not directly affect ADH action on outer membrane permeability, but exerts its effects on a site which is limiting for the ADH action on transepithelial permeability
Frequency stabilization of an external cavity diode laser against HI molecule at 1.541 um
No full textSkin prick test digital imaging system with manual, semiautomatic, and automatic wheal edge detection and area measurement
No full textA novel biomedical instrument for supporting the physician in Skin Prick Testanalysis was designed, developed, characterized, and is now ready for clinical trials. SkinPrick Test is the gold standard front-end analysis for diagnosis of allergies in human subjects.The forearm skin is punctured with different allergens and the resulting reaction wheals areanalyzed and compared to standard reaction, with larger areas corresponding to strongerallergy to the specific allergen. The wheals inspection and allergy diagnosis are performed,visually and subjectively, by the Medical Doctor. This procedure is laborious and somehowunreliable, being subject to variability both intra- and inter-operator because the doctorsubjectivity in detecting and measuring the wheals is significant. Registration of the examresult is rarely available in a digital format, useful for data saving, transmission, retrieval andcomparative analyses. Many of the above criticalities of the actual Prick Test manual practiceare addressed and resolved by the proposed biomedical instrumentation that makes use ofdigital image-processing and data storage. In this work, we present a prototype of whealmeasurement system, designed, developed and characterized to specifically measure geometry and areas of the allergic reaction wheals in Prick Test clinical exams. After softwaredevelopments from previous version of the instrument, the wheal-meter now allows manual,semi-automatic, automatic, and fully-automatic operating conditions always providing digitalexams output
Amplitude and frequency noise sensitivities of optical frequency discriminators based on Fabry-Perot interferometers and the FM technique
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