Dynamic Characterization of Periodic Lattice of Elastically-connected Bi-stable Elements under Seismic Excitation

Metamaterials are engineered materials, typically in periodic arrangements, which exhibit unconventional or extreme properties not found in nature. Understanding the dynamics of metamaterials enables the design of structures with specific functionalities. The dynamics of metamaterials in linear regime has been relatively well studied in recent years, however the unique phenomena arising from nonlinearities in metamaterials are yet to be explored. In this paper, we focus on an array of bi-stable elements connected by elastic springs under various forms of external excitations acting on the entire system. The general equations of motion are derived to handle any degree-of-freedom (DoF) systems of interest. The MATLAB-based code is developed using finite difference method to solve numerically the system of equations and is validated through the correlation studies with the analytical solutions in previously known linear systems. Numerical investigations are performed on 2-DoF and infinitely-long systems under various excitation levels with focuses on nonlinear responses. The predicted behaviors are experimentally verified from the dynamic testing, using 3D-printed lattice samples

Dynamic Behavior of a Clamped-Clamped Bi-Stable Laminate for Energy Harvesting

Multi-stable laminates have many applications in morphing structures, energy harvesting devices, and metamaterials due to the specific characteristics attributed to the exhibited stable states. Changes between stable states allow for large deflections, on-demand variation of the stiffness of compliant structures embedded within these elements, and control of effective dynamic properties in periodic lattices. These changes in state can be accessed via a snap-through instability triggered by introducing a well-defined activation energy. The resulting oscillations could enable broadband energy harvesting via piezoelectric transduction and resistive circuits. In this paper, a clamped-clamped bi-stable laminate is studied to understand the behavior of the laminate at each stable state and determine energy harvesting capabilities. An FEA model is created to determine the frequency and shapes of resonant modes. Certain modal shapes have significant deformations near the clamp which are necessary for piezoelectric elements to generate a voltage. Small amplitude low frequency vibrations are used to excite the laminate at each stable state using a shaker. The laminate is then excited so that inter-well oscillations become present. The resonant characteristics of each stable state determined by the simulations are similar to the experimentally observed responses with some variation. The laminate shows inter-well dynamics at particular resonant frequencies and for a range of frequencies in which both sable states have similar modal characteristics. At higher excitations and a range of frequencies is observed causing chaotic and inter-well oscillations. This shows that the laminate exhibits vibrational dynamics which are capable of enabling broadband energy harvesting devices

Modelling and Configuration Control of Wing-Shaped Bi-Stable Piezoelectric Composites Under Aerodynamic Loads

Bi-stable composites have been considered for morphing applications thanks to their ability to hold two statically stable shapes with no energy consumption. In this paper, the modelling of the dynamic response of cantilevered wing-shaped bi-stable composites is presented. To this end, an analytical model approximating the dynamic response about each statically stable shape of wing-shaped bi-stable composites is derived. Theoretical modal properties are obtained to attain or stabilise a desired configuration following a previously introduced resonant control strategy. The resonant control technique is evaluated for a wing-shaped bi-stable composite subject to aerodynamic loads. Wind tunnel experiments are conducted on a wing-shaped specimen showing the ability of the control strategy to stabilise or attain a desired stable shape under aerodynamic loads

Frost Formation in Evaporator Fins with Embedded Negative Stiffness Structures

Frosting in the evaporator leads to an increase in thermal resistance and reduced airflow, resulting in decreased performance. Traditional thermal defrosting strategies lead to significant energy penalties. Novel shape morphing evaporator fins embedded with multistable structures offer the opportunity for faster defrosting and large energy savings while keeping the capital cost low. This type of morphing fins enables a mechanical defrosting approach that is more effective for higher densities and thicknesses of frost. However, there is a need to better understand frost formation in these structures. In this study, we use a modeling and experimental approach to understand frosting on shape morphing fins. An experimental setup was developed that is capable of frost formation at different conditions and testing various defrosting strategies. Leveraging this, we formed frost at various conditions on both an angled shape morphing fin and a flat fin and performed comparisons between model predictions and measurements

Unidirectional Transition Waves in Bistable Lattices

We present a model system for strongly nonlinear transition waves generated in a periodic lattice of bistable members connected by magnetic links. The asymmetry of the on-site energy wells created by the bistable members produces a mechanical diode that supports only unidirectional transition wave propagation with constant wave velocity. We theoretically justify the cause of the unidirectionality of the transition wave and confirm these predictions by experiments and simulations. We further identify how the wave velocity and profile are uniquely linked to the double-well energy landscape, which serves as a blueprint for transition wave control

Unidirectional Transition Waves in Bistable Lattices

We present a model system for strongly nonlinear transition waves generated in a periodic lattice of bistable members connected by magnetic links. The asymmetry of the on-site energy wells created by the bistable members produces a mechanical diode that supports only unidirectional transition wave propagation with constant wave velocity. We theoretically justify the cause of the unidirectionality of the transition wave and confirm these predictions by experiments and simulations. We further identify how the wave velocity and profile are uniquely linked to the double-well energy landscape, which serves as a blueprint for transition wave control

High plasma levels of soluble ST2 but not its ligand IL-33 is associated with severe forms of pediatric dengue

Q2Q1766-771Identification of early determinants of dengue disease progression, which could potentially enable individualized patient care are needed at present times. Soluble ST2 (sST2) has been recently reported to be elevated in the serum of children older than 2 years old and adults with dengue infection and it was correlated with secondary infections as well as with severe presentations of the disease. The mechanism by which secreted ST2 is linked to severe dengue and plasma leakage remains unclear. One possibility is that IL-33 ligand may be elevated, contributing to membrane bound ST2 as part of the immune activation in dengue infection. We determined plasma levels of sST2 and the ligand IL-33 in 66 children with acute secondary dengue infections clinically classified using the guidelines of the World Health Organization, 2009. Dengue infection showed significant increases in cytokines IL-12p70, IL-10, IL-8, IL-6, IL-1β and TNFα measured by flow cytometry based assay compared to uninfected individuals. In contrast, IL-33 levels remained unchanged between infected and uninfected individuals. The levels of sST2 positively correlated with values of IL-6 and IL-8 and inversely correlated with number of median value of platelet levels. In addition to circulating cytokine positive correlations we found that sST2 and isoenzyme creatine kinase-MB (CK-MB), a marker of myocardial muscle damage present in severe dengue cases were associated. Our pediatric study concluded that in dengue infections sST2 elevation does not involve concomitant changes of IL-33 ligand. We propose a study to assess its value as a predictor factor of disease severity

La vesícula extracelular TGF-β basal es un biomarcador predictivo de la respuesta a los inhibidores del punto de control inmunitario y de la supervivencia en el cáncer de pulmón no microcítico

Antecedentes: Los inhibidores de los puntos de control inmunitarios (ICI) son una estrategia terapéutica eficaz que mejora la supervivencia de los pacientes con cáncer de pulmón en comparación con los tratamientos convencionales. terapéutica eficaz que mejora la supervivencia de los pacientes con cáncer de pulmón en comparación con los tratamientos convencionales. Sin embargo, se necesitan biomarcadores predictivos novedosos para estratificar qué pacientes obtienen un beneficio clínico, ya que el histológico PD-L1, actualmente utilizado y altamente heterogéneo, ha mostrado una baja precisión. La biopsia líquida es el análisis de biomarcadores en fluidos corporales y representa una herramienta mínimamente invasiva que puede utilizarse para monitorizar la evolución del tumor y los efectos del tratamiento, reduciendo potencialmente los sesgos asociados a la heterogeneidad tumoral asociada a las biopsias de tejidos. En este contexto citoquinas, como el factor de crecimiento transformante-β (TGF-β), pueden encontrarse libres en circulación en la sangre y empaquetadas en vesículas extracelulares (VE), que tienen un tropismo de administración específico y pueden afectar a la interacción entre el tumor y el sistema inmunitario. El TGF-β es una citocina inmunosupresora que desempeña un papel crucial en el escape inmunitario de los tumores, la resistencia al tratamiento y la metástasis. Así pues, nuestro objetivo era evaluar el valor predictivo predictivo del TGF-β circulante y EV en pacientes con cáncer de pulmón no microcítico que reciben ICI.Background: Immune‐checkpoint inhibitors (ICIs) are an effective therapeutic strategy, improving the survival of patients with lung cancer compared with conventional treatments. However, novel predictive biomarkers are needed to stratify which patients derive clinical benefit because the currently used and highly heterogenic histological PD‐L1 has shown low accuracy. Liquid biopsy is the analysis of biomarkers in body fluids and represents a minimally invasive tool that can be used to monitor tumor evolution and treatment effects, potentially reducing biases associated with tumor heterogeneity associated with tissue biopsies. In this context, cytokines, such as transforming growth factor‐β (TGF‐β), can be found free in circulation in the blood and packaged into extracellular vesicles (EVs), which have a specific delivery tropism and can affect in tumor/immune system interaction. TGF‐β is an immunosuppressive cytokine that plays a crucial role in tumor immune escape, treatment resistance, and metastasis. Thus, we aimed to evaluate the predictive value of circulating and EV TGF‐β in patients with non–small‐cell lung cancer receiving ICIs