Abstract. Osteoarthritis (OA) is a common age-related degenerative joint disease, which is caused by the breakdown of joint cartilage and the underlying bone. Carboxymethyl (CM)-chitosan is a soluble derivative of chitosan that has similar physicochemical properties to the extracellular proteoglycans identified in hyaline cartilage. Previous studies have demonstrated that CM-chitosan serves a protective role in a rabbit OA model. The aim of the present study was to investigate the effect of CM-chitosan on NO production and inflammation through its upregulation of interleukin (IL)-10, and the activation of the janus kinase (JAK)/signal transducer and activator of transcription (STAT)/suppressor of cytokine signaling (SOCS) signaling pathway. In the present study primary rat chondrocytes were induced to inflammation with 2 µg/ml lipopolysaccharide. The cells were subsequently subjected to increasing concentrations of CM-chitosan (50, 100 and 200 µg/ml) and the relative mRNA and protein expression of inducible nitric oxide synthase (iNOS), IL-10, JAK1, STAT3 and SOCS3 were measured by RT-qPCR and western blot analysis respectively. The results revealed that CM-chitosan attenuated inflammation by significantly reducing iNOS expression and upregulating the anti-inflammatory cytokine IL-10 in a dose-dependent manner (P<0.05). The expression of JAK1, STAT3 and SOCS3 were also significantly upregulated by CM-chitosan (all P<0.05).
Dry galloping of inclined cables has been shown to have a strong relation to the critical Reynolds number. This study concerns the occurrence of galloping of an elliptical cylinder at critical Reynolds numbers under normal wind and an assessment of the quasi-steady assumption on predicting these vibrations. A series of static and dynamic wind tunnel tests are carried out to measure the wind pressure on a static cylinder and displacement of a three-degree-freedom vibrating cylinder. The static aerodynamic force on the cylinder shows the occurrence of reattachment which lowers the drag coefficient and increases the lift coefficient at critical Reynolds numbers. This phenomenon gives the possibility of satisfying the across-wind galloping criterion by adversely changing the aerodynamic force with the angle of attack. Meanwhile, unsteady and steady amplitude galloping are observed in dynamic tests in a certain range of Reynolds number and angle of attack. The observations indicate that the galloping is across-wind dominated and strongly depends on the Reynolds number. Finally, quasi-steady predictions of galloping instability are compared with the observed galloping. Most of the observed occurrences of galloping are in the predicted unstable range, but several other cases for which galloping was predicted do not exhibit large vibrations. This implies that the quasi-steady assumption does not work well in predicting the galloping of elliptical cylinders at critical Reynolds numbers.
The excitation mechanism of vibrations of circular cylinders in the critical Reynolds number range remains unclear. These vibrations have been observed in wind tunnels many times but rarely in the field. The surface roughness of the cylinder might be a reason for this difference. Aiming to reveal the effect of surface roughness on the aerodynamic forces and vibrations in the critical Reynolds number range, seven circular cylinders with various value of surface roughness were covered with abrasive papers and tested in stationary and elastically mounted wind tunnel tests. The results show that the surface roughness significantly influences the aerodynamic forces in the critical Reynolds number range by reducing the range of transitions on boundary layers. These influences include suppressing the jumps in lift coefficients and other phenomena that relate to a bistable state occurring only for less rough cylinders. Therefore, sufficient surface roughness can mitigate the vibrations in the critical Reynolds number range by suppressing the bistable state in which the vibrations appear.
A novel aerodynamic measure, an arch mounted leeward of a circular cylinder, is proposed to reduce drag and mitigate vortex shedding for a circular cylinder. To confirm the validity of the proposed measure, the aerodynamic forces were measured through a force meter at the end of a cylinder, the wind pressure was measured at seven cross-sections of the cylinder, and elastically mounted cylinders were also tested. The results show that the arch significantly reduces drag and fluctuating lift by mitigating the vortex shedding in the subcritical Reynolds number range when the proper central angle is selected for the arch. The arch creates a higher base pressure at the leeward side and induces a pressure exchange and spanwise axial flow. This influence is extended along the length of the cylinder by the axial flow due to the strong correlation in the wake in the subcritical regime. Therefore, the arch lowers the base pressure and disrupts the formation of vortex shedding.
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