Regular and chaotic dynamics of a 4-DOF mechanical system with dry friction

In this paper the model of four degree-of-freedom mechanical sliding system with dry friction is considered. One of the components of the mentioned system rides on driving belt, which is driven at constant velocity. This model corresponds to a row of carriage laying on a guideway, which moves at constant velocity with respect to the guideway as a foundation. From a mathematical point of view the analyzed problem is governed by four second order differential equations of motion, and numerical analysis is performed in Mathematica software. Some interesting behaviors are detected and reported using Phase Portraits, Poincaré Maps and Lyapunov Exponents. Moreover, Power Spectral Densities obtained by the Fast Fourier Transform technique are reported. The presented results show different behaviors of the system, including periodic, quasi-periodic and chaotic orbits

Numerical model of the human upper extremity and its analysis related to forward fall

Praca przedstawia model numeryczny kończyny górnej człowieka przydatny do analizy ryzyka złamania kości kończyny podczas upadku do przodu. W odróżnieniu od innych modeli spotykanych w literaturze, proponowany w tej pracy model uwzględnia wszystkie trzy główne kości kończyny górnej połączone powierzchniami stawowymi w stawie łokciowym i nadgarstkowym przy zastosowaniu kontaktu typu bonded jako jeden złożony układ biomechaniczny. Analizę dynamiczną przeprowadzono dla różnych konfiguracji kości przedramienia, wykorzystując dwa kryteria wytrzymałościowe do oceny potencjalnych miejsc złamań kości kończyny.The paper presents numerical model of the human upper extremity useful for the analysis of the upper extremity bones fracture risk during the falling process in a forward direction. Unlike previous models met in literature, the proposed in this paper model considers all three main upper extremity bones connected in the elbow and wrist joints by the bonded type contact as one complex biomechanical system. Transient analysis has been carried out for different forearm configurations by using two strength criteria to estimate possible sites of upper extremity bone fractures

Cyclic phosphatidic acid and its analogues can regulate ERK1/2 activity via LPA receptors

Cyclic phosphatidic acid (1-acyl-sn-glycerol-2,3 cyclic phosphate, cPA) and lysophosphatidic acid (LPA) are bioactive lipid mediators belonging to the small glycerophospholipids. Recent studies have shown that these compounds possess contrasting biological activities: LPA induces tumor cell proliferation and motility, while cPA suppresses metastasis and invasion of cancer cells. There are known at least eight LPA receptors involved in LPA signaling, however selective receptors of cPA are still unknown

Serum lipids in adults with late age-related macular degeneration: a case-control study

Abstract Background Lipids are implicated in the pathogenesis of age-related macular degeneration (AMD). The relationship between systemic lipids and AMD has not been well characterized. The objective was to investigate the relationship between serum lipids and AMD in older adults using a lipidomic approach. Methods In a case-control study, 240 adults, aged ≥66 years, a third each having geographic atrophy, neovascular AMD, or no signs of AMD, were selected from a population-based sample of participants in the Age Gene/Environment Susceptibility-Reykjavik Study. The exposure was serum lipids and risk factors for AMD. The outcome was late AMD, assessed through fundus images taken through dilated pupils using a 45-degree digital camera and grading for neovascular AMD and geographic atrophy using the modified Wisconsin Age-Related Maculopathy Grading System. Results Of 177 serum lipid species measured, there were no significant differences in serum lipids between controls and those with geographic atrophy or neovascular AMD, respectively. Adults with neovascular AMD had higher total serum lysophosphatidylcholine (LPC) (P = 0.004) and serum LPC 18:0 (P = 0.0002) compared to those with geographic atrophy. Conclusion Late AMD was not characterized by alterations in systemic lipids compared with normal controls. These findings suggest that there may be differences in the LPC pathway between adults with neovascular AMD and geographic atrophy