Extended nonlinear analytical models of compliant parallelogram mechanisms: third-order models

This paper proposes extended nonlinear analytical models, third-order models, of compliant parallelogram mechanisms. These models are capable of capturing the accurate effects from the very large axial force within the transverse motion range of 10% of the beam length through incorporating the terms associated with the high-order (up to third-order) axial force. Firstly, the free-body diagram method is employed to derive the nonlinear analytical model for a basic compliant parallelogram mechanism based on load-displacement relations of a single beam, geometry compatibility conditions, and load-equilibrium conditions. The procedures for the forward solutions and inverse solutions are described. Nonlinear analytical models for guided compliant multi-beam parallelogram mechanisms are then obtained. A case study of the compound compliant parallelogram mechanism, composed of two basic compliant parallelogram mechanisms in symmetry, is further implemented. This work intends to estimate the internal axial force change, the transverse force change, and the transverse stiffness change with the transverse motion using the proposed third-order model in comparison with the first-order model proposed in the prior art. In addition, FEA (finite element analysis) results validate the accuracy of the third-order model for a typical example. It is shown that in the case study the slenderness ratio affects the result discrepancy between the third-order model and the first-order model significantly, and the third-order model can illustrate a non-monotonic transverse stiffness curve if the beam is thin enough.

Dentofacial parameters associated with the unilateral palatally impacted canine

Aims To investigate the relationship between unilateral PIC and specific dentofacial parameters. Materials and methods A sample of 216 subjects, with 108 subjects in the retrospective and prospective samples respectively. Dental parameters: The following dental parameters were assessed: Inter-canine and intermolar width; palatal depth and palatal area; anterior Bolton tooth-size discrepancy (TSD); maxillary arch shape and ratio and maxillary central and lateral incisor shape and ratio. Facial parameters: Three-dimensional (3D) images were taken for subjects in the prospective sample only, and were used to assess the following facial parameters: Face shape; face ratio and 3D distances and angles. Results Dental parameters: Inter-canine width was significantly smaller in the test group compared to the control group in the retrospective (p= 0.0002) and prospective (p= 0.0018) samples respectively. Anterior Bolton TSD was significantly higher in the prospective test group compared to controls (p= 0.0070). Arch ratio was significantly smaller in the test group than the control group for the retrospective sample (p= 0.0029), whereas no significant difference was recorded in the prospective sample (p= 0.1017). Arch shape distribution was significantly different in the retrospective sample (p= 0.009). Tooth shape distribution was significantly different for the maxillary right central incisor in the retrospective sample (p= 0.030). Tooth ratio showed no significant difference for both samples. Facial parameters: Basal width was significantly smaller in the test compared to the control group (p= 0.0001). No significant difference was found in all other 3D distances and angles measured. Conclusion Inter-canine width was significantly smaller in unilateral PIC subjects compared to controls. Anterior Bolton TSD was significantly higher in prospective unilateral PIC compared to controls. Maxillary arch ratio was significantly smaller in retrospective subjects. Square/tapered tooth shape was significantly more common in the retrospective group. Basal width was significantly smaller in subjects with unilateral PIC than controls.

Enhanced Volatile Organic Compounds emissions and organic aerosol mass increase the oligomer content of atmospheric aerosols

Secondary organic aerosol (SOA) accounts for a dominant fraction of the submicron atmospheric particle mass, but knowledge of the formation, composition and climate effects of SOA is incomplete and limits our understanding of overall aerosol effects in the atmosphere. Organic oligomers were discovered as dominant components in SOA over a decade ago in laboratory experiments and have since been proposed to play a dominant role in many aerosol processes. However, it remains unclear whether oligomers are relevant under ambient atmospheric conditions because they are often not clearly observed in field samples. Here we resolve this long-standing discrepancy by showing that elevated SOA mass is one of the key drivers of oligomer formation in the ambient atmosphere and laboratory experiments. We show for the first time that a specific organic compound class in aerosols, oligomers, is strongly correlated with cloud condensation nuclei (CCN) activities of SOA particles. These findings might have important implications for future climate scenarios where increased temperatures cause higher biogenic volatile organic compound (VOC) emissions, which in turn lead to higher SOA mass formation and significant changes in SOA composition. Such processes would need to be considered in climate models for a realistic representation of future aerosol-climate-biosphere feedbacks.