Modeling and evaluation of moisture diffusion in polymer composite materials

Fiber-reinforced polymer composites have extensive applications due to their high specific strength, improved product performance, low maintenance and design flexibility. However, moisture absorbed by polymer composites during the service life plays a detrimental role in both the integrity and durability of composite structure. It is essential to understand the moisture diffusion behavior and induced damage in polymer matrix composites under varying hygrothermal conditions. In Part I, the moisture diffusion characteristics in hybrid composites using moisture concentration-dependent diffusion method have been investigated. Also, a multi-stage diffusion model was proposed to explain the deviation of moisture diffusion behavior for sandwich composites from classical Fick\u27s law using a time-dependent diffusivity scheme. User-defined subroutines were developed to implement these methods into commercial finite element code. To validate the simulation results, an open-edge moisture diffusion experiment was conducted for sandwich composites composed of woven E-glass fiber-reinforced polyurethane (PU) face sheets and a closed-cell rigid PU foam core. In Part II, the behavior of moisture diffusion and its effects on the mechanical properties of carbon/bismaleimide composites exposed to seawater conditioning at elevated temperatures were investigated. The degradation of mechanical properties due to hygrothermal aging was assessed by conducting short beam shear test and flexural test at three immersion time points. In Part III, the effect of moisture on mechanical performance of PU sandwich composites was investigated. Mechanical property degradation due to moisture absorption was evaluated by conducting compression test of the foam core, flexural test of the laminates, and double cantilever beam Mode-I interfacial fracture test of sandwich composites --Abstract, page iv

Signatures of Self-Interacting Dark Matter in the Matter Power Spectrum and the CMB

We consider a self-interacting dark matter model in which the massive dark photon mediating the self-interaction decays to light dark fermions to avoid over-closing the universe. We find that if the model is constrained to explain the dark matter halos inferred for spiral galaxies and galaxy clusters simultaneously, there is a strong indication that dark matter is produced asymmetrically in the early universe. It also implies the presence of dark radiation, late kinetic decoupling for dark matter, and a suppressed linear power spectrum due to dark acoustic damping. The Lyman-$\alpha$ forest power spectrum measurements put a strong upper limit on the damping scale and the model has little room to reduce the abundances of satellite galaxies. Future observations in the matter power spectrum and the CMB, in tandem with the impact of self-interactions in galactic halos, makes it possible to measure the gauge coupling and masses of the dark sector particles even when signals in conventional dark matter searches are absent.Comment: 5 pages, 7 figures, published version in PL

Essays in Macroeconomics

University of Minnesota Ph.D. dissertation.June 2015. Major: Economics. Advisor: Jose-Victor Rios-Rull. 1 computer file (PDF); vii, 190 pages.This dissertation includes three chapters. The first two chapters are co-authored with Naoki Takayama. The first chapter presents a model of business cycles driven by shocks to agents' beliefs about economic fundamentals. Agents are hit both by common and idiosyncratic shocks. Common shocks act as confidence shocks, which cause economy-wide optimism or pessimism and consequently, aggregate fluctuations in real variables. Idiosyncratic shocks generate dispersed information, which prevents agents from perfectly inferring the state of the economy. Crucially, asymmetric information induces the infinite regress problem, that is, agents need to forecast the forecasts of others. We develop a method that can solve the infinite regress problem without approximation. Even though agents face a complicated learning problem, the equilibrium policy can be represented by a small number of state variables. Theoretically, we prove that the persistence of aggregate output is increasing in the degree of information frictions and strategic complementarity, and there is a hump-shaped relationship between the variance of output and the variance of the confidence shock. Quantitatively, our model with confidence shocks can match a number of the key business cycle moments. The second chapter develops a general method of solving rational expectations models with higher order beliefs. Higher order beliefs are crucial in an environment with dispersed information and strategic complementarity, and the equilibrium policy depends on infinite higher order beliefs. It is generally believed that solving this type of equilibrium policy requires an infinite number of state variables (Townsend, 1983). This paper proves that the equilibrium policy rule can always be represented by a finite number of state variables if the signals observed by agents follow an ARMA process, in which case we obtain a general solution formula. We also prove that when the signals contain endogenous variables, a finite-state-variable representation of the equilibrium may not exist. For this case, we develop a tractable algorithm that can approximate the solution arbitrarily well. The key innovation in our method is to use the factorization identity and Wiener filter to solve signal extraction problems conditional on infinite observables. This method can be used in a wide range of applications. We demonstrate its strong practicability by solving several classical models featuring higher order beliefs. The third chapter is co-authored with Jose-Victor Rios-Rull. We build a variation of the neoclassical growth model in which both wealth shocks (in the sense of wealth destruction) and financial shocks to households generate recessions. The model features three mild departures from the standard model: (1) adjustment costs make it difficult to expand the tradable goods sector by reallocating factors of production from nontradables to tradables; (2) there is a mild form of labor market frictions (Nash bargaining wage setting with Mortensen-Pissarides labor markets); (3) goods markets for nontradables require active search from households wherein increases in consumption expenditures increase measured productivity. These departures provide a novel quantitative theory to explain recessions like those in southern Europe without relying on technology shocks

Enablers and Consequences of Interfirm Co-Production

As contemporary firms increase their reliance on information technology (IT) and are increasingly turning their attention to jointly creating value with their primary stakeholders, there is a growing need to understand what enablers promote from interfirm value co-creation from co-production in supply chains, how the co-production can be realized and what value can be created through the co-production. We integrate systems theory and the relational view perspectives to develop an explanatory model to explain how co-production mediates the impacts of enablers on the reciprocal benefits created in the global supply chain context. Drawing upon systems theory, we identify three constructs: platform compatibility (i.e., compatibility), co-production (i.e., synergy), and collaborative governance (i.e., integration effort). We draw on the relational view to identify two activities: process alignment and resource sharing for co-production, conceptualize three basic types of reciprocal benefits: market, innovation and anshin value, and theorize co-production—the synergy of process alignment and resource sharing activities—as key to the realization of synergy, thereby contributing to the reciprocal benefits in the context of interfirm supply chain. Based on survey data collected from 464 senior management representatives from 230 high-tech manufacturing firms from within Taiwan and China, we found 1) collaborative governance has a positive effect on platform compatibility, 2) both collaborative governance and platform compatibility promote co-production, 3) guanxi has a positive effect on collaborative governance and has a positive moderating effect on collaborative governance and co-production, and 4) co-production positively affects reciprocal benefits. Our findings highlight 1) the important role of co-production in mediating the platform compatibility and collaborative governance effects on reciprocal benefits, and 2) the complementary role of guanxi in strengthening the collaborative governance effect on co-production. These results provide insights into how firms can co-create value through enhanced interfirm co-production

Eradication of unresectable liver metastasis through induction of tumour specific energy depletion.

Treatment of liver metastasis experiences slow progress owing to the severe side effects. In this study, we demonstrate a strategy capable of eliminating metastatic cancer cells in a selective manner. Nucleus-targeting W18O49 nanoparticles (WONPs) are conjugated to mitochondria-selective mesoporous silica nanoparticles (MSNs) containing photosensitizer (Ce6) through a Cathepsin B-cleavable peptide. In hepatocytes, upon the laser irradiation, the generated singlet oxygen species are consumed by WONPs, in turn leading to the loss of their photothermally heating capacity, thereby sparing hepatocyte from thermal damage induced by the laser illumination. By contrast, in cancer cells, the cleaved peptide linker allows WONPs and MSNs to respectively target nucleus and mitochondria, where the therapeutic powers could be unleashed, both photodynamically and photothermally. This ensures the energy production of cancer cells can be abolished. We further assess the underlying molecular mechanism at both gene and protein levels to better understand the therapeutic outcome

Evaluation of Juglans regia L., root for wound healing via antioxidant, antimicrobial and anti-inflammatory activity

304-311The burden of the management of problematic skin wounds characterized by a compromised skin barrier is growing rapidly. There is an urgent requirement for efficient mechanism-based treatments and more efficacious drug delivery systems. The present study was aimed to examine the wound healing potential of Juglans regia L. root (JR) in rats by incision and excision wound methods via the anti-inflammatory, antioxidant and antimicrobial activities. We have used tensile strength and biochemical parameters for studying the wound healing properties of JR by incision wound methodology. The anti-inflammatory effect was assessed by the measurement of paw edema in carrageenan-induced inflammation in rats. The wound contraction area, antioxidant status, and antimicrobial studies were exhausted excision wound methodology. There was a significant decrease in percent inhibition of paw edema (0.63 ± 0.03 to 0.33 ± 0.02 after 24 h) with an increase in JR concentration. Tensile strength and hydroxyproline level of different concentrations (1, 2.5, 5, and 10% w/w) of JR ointment treated groups were found significantly (P <0.001) comparable to the reference group. Moreover, JR showed significant antimicrobial and antioxidant properties, by its ability to increase antioxidant and antimicrobial levels. In conclusion, the overall results obtained in this study clarify that JR inhibits paw edema and accelerates cutaneous wound healing

Intelectin contributes to allergen-induced IL-25, IL-33, and TSLP expression and type 2 response in asthma and atopic dermatitis.

The epithelial and epidermal innate cytokines IL-25, IL-33, and thymic stromal lymphopoietin (TSLP) have pivotal roles in the initiation of allergic inflammation in asthma and atopic dermatitis (AD). However, the mechanism by which the expression of these innate cytokines is regulated remains unclear. Intelectin (ITLN) is expressed in airway epithelial cells and promotes allergic airway inflammation. We hypothesized that ITLN is required for allergen-induced IL-25, IL-33, and TSLP expression. In two asthma models, Itln knockdown reduced allergen-induced increases in Il-25, Il-33, and Tslp and development of type 2 response, eosinophilic inflammation, mucus overproduction, and airway hyperresponsiveness. Itln knockdown also inhibited house dust mite (HDM)-induced early upregulation of Il-25, Il-33, and Tslp in a model solely inducing airway sensitization. Using human airway epithelial cells, we demonstrated that HDM-induced increases in ITLN led to phosphorylation of epidermal growth factor receptor and extracellular-signal regulated kinase, which were required for induction of IL-25, IL-33, and TSLP expression. In two AD models, Itln knockdown suppressed expression of Il-33, Tslp, and Th2 cytokines and eosinophilic inflammation. In humans, ITLN1 expression was significantly increased in asthmatic airways and in lesional skin of AD. We conclude that ITLN contributes to allergen-induced Il-25, Il-33, and Tslp expression in asthma and AD

Programming hydrogel adhesion with engineered polymer network topology

Hydrogel adhesion that can be easily modulated in magnitude, space, and time is desirable in many emerging applications ranging from tissue engineering, and soft robotics, to wearable devices. In synthetic materials, these complex adhesion behaviors are often achieved individually with mechanisms and apparatus that are difficult to integrate. Here, we report a universal strategy to embody multifaceted adhesion programmability in synthetic hydrogels. By designing the surface network topology of a hydrogel, supramolecular linkages that result in contrasting adhesion behaviors are formed on the hydrogel interface. The incorporation of different topological linkages leads to dynamically tunable adhesion with high-resolution spatial programmability without alteration of bulk mechanics and chemistry. Further, the association of linkages enables stable and tunable adhesion kinetics that can be tailored to suit different applications. We rationalize the physics of chain slippage, rupture, and diffusion that underpins emergent programmable behaviors. We then incorporate the strategy into the designs of various devices such as smart wound patches, fluidic channels, drug-eluting devices, and reconfigurable soft robotics. Our study presents a simple and robust platform in which adhesion controllability in multiple aspects can be easily integrated into a single design of a hydrogel network