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Abstract:Tropical forests play an important role in regulating the global climate and the carbon cycle. With the changing temperature and moisture along the elevation gradient, the Luquillo Experimental Forest in Northeastern Puerto Rico provides a natural approach to understand tropical forest ecosystems under climate change. In this study, we conducted a soil translocation experiment along an elevation gradient with decreasing temperature but increasing moisture to study the impacts of climate change on soil organic carbon (SOC) and soil respiration. As the results showed, both soil carbon and the respiration rate were impacted by microclimate changes. The soils translocated from low elevation to high elevation showed an increased respiration rate with decreased SOC content at the end of the experiment, which indicated that the increased soil moisture and altered soil microbes might affect respiration rates. The soils translocated from high elevation to low elevation also showed an increased respiration rate with reduced SOC at the end of the experiment, indicating that increased temperature at low elevation enhanced decomposition rates. Temperature and initial soil source quality impacted soil respiration significantly. With the predicted warming climate in the Caribbean, these tropical soils at high elevations are at risk of releasing sequestered carbon into the atmosphere.

Design and modeling of a bi-laminate, Galfenol-driven composite beam is presented in which the elasticity of the adhesive layer is considered. The optimal thickness ratio necessary to maximize the tip deflection is found by minimization of the internal energy of the beam. Model simulations show that use of a substrate material with high modulus leads to larger tip deflections. Stainless steel was therefore utilized as substrate in the experiments. In order to reduce eddy currents, a laminated silicon steel frame was employed to magnetize the beam. A dynamic model is proposed by coupling the structural dynamics of the beam and adhesive layer with the magnetostriction generated by the Galfenol layer. The latter is described with a linear piezomagnetic law with uniform magnetic field distribution along the length of the beam. Galerkin discretization combined with Newmark numerical integration are employed to approximate the dynamic response of the beam. The model is shown to describe both the transient and steady-state response of the composite beam tip displacement under harmonic excitation between 10 and 320 Hz. The RMS error between model and data range between 1.44% at 10 Hz and 6.34% at 320 Hz, when the same set of model parameters (optimized at quasistatic frequency) is utilized.

Noncircular bevel gear is applied to intersecting axes, realizing given function of transmission ratio. Currently, researches are focused mainly on gear with involute tooth profile and straight tooth lengthwise, while that with free-form tooth profile and curvilinear tooth lengthwise are seldom touched upon. Based on screw theory and equal arc-length mapping method, this paper proposes a generally applicable generating method for noncircular bevel gear with free-form tooth profile and curvilinear tooth lengthwise, covering instant screw axis, conjugate pitch surface, as well as the generator with free-form tooth profile and curvilinear tooth lengthwise. Further, the correctness of the proposed method is verified through illustrations of computerized design.

This article presents a fully coupled, nonlinear model for the dynamic response of Galfenol-driven unimorph actuators in a cantilever configuration. The hysteretic magnetomechanical behavior of Galfenol is modeled using a discrete energy-averaged model, and the structural behavior of the unimorph is modeled using the finite element method. The weak form equations that describe bending of the unimorph are obtained using the principle of virtual work. Since the local strain and stress are nonlinearly coupled with both the vertical and horizontal displacements, a nonlinear solver is developed to approximate the coupled finite element equations. The nonlinear solver is verified against the analytical solution and experimental data for the case of a passive beam. The analytical solution is obtained using beam theory for free and harmonic responses. The analytical model and experimental data verify that the nonlinear solver correctly quantifies the first natural frequency of the composite beam. The numerical simulations match the analytical solutions for both free and harmonic responses. Finally, the dynamic response of the nonlinear magnetoelastic model is investigated and experimentally validated from 0.1 to 500 Hz, the range in which the model is accurate without the need for adjustable parameters.