We are surrounded by soft materials in a variety of physical and chemical states, which can be easily deformed under external stimuli. When subjected to sufficiently large compression, electric voltage, gravity or impact, soft materials may undergo mechanical instabilities of various types. The instability modes can be either linear or nonlinear, depending on the form of perturbation when the instability set in. When the material is a pressurized dielectric elastomeric film under high voltage, snap-through instability is linear with finite change of volume, while the bulge-out mode is nonlinear with a localized deformation. In terms of surface instability, wrinkles are linear instability mode with undulations finite in space with infinitesimal strain deviating from the smooth state, while creases are localized nonlinear modes with large strain deviating from smooth state. If a soft material is subjected to high speed impact, both the viscoelastic behaviors of the material and inertial effect are involved, and the mechanical instability is coupled with the wave propagation, finally leading to highly nonlinear instability mode.

We start with the instability analysis of a pressurized dielectric elastomeric film subjected to high voltage. By adopting ideal dielectric elastomer (DE) constitutive model, we show that linear perturbation analysis can capture the shape bifurcation in a spherical DE balloon. However, nonlinear bulge-out shape with a highly localized deformation appears as constraints of the boundaries of the film is applied. A competition between the surface instability modes between the wrinkle and crease is studied in both experiment and theoretical analysis under a deformation mode called eversion, and crease is shown to form prior to wrinkle with lower critical strain to set in. A transition between the wrinkle and crease instability happens when gravity becomes important. We measure the dynamics of soft elastomeric blocks with stiff surface films subjected to high-speed impact, and observe wrinkles forming along with, and riding upon, waves propagating through the system.

Aging is intimately related to health and disease. The incidence of major fatal pathological conditions, including cancer, is strongly associated with aging. The finding that aging is malleable by genetic or pharmacological perturbations has offered enormous hope for transforming our understanding and treatment of aging and age-related diseases. Yet few valid longevity drugs have been developed or translated for treating age-related diseases as target identification and a mechanistic understanding of their activity is largely missing.

Metabolism plays a pivotal role in aging. Metabolic interventions, such as dietary restriction, significantly modulate aging and aging-related symptoms. Recently, emerging evidences has shown that metabolites can directly modulate aging as well. Studies of these endogenous “elixirs” provide insights on the biological regulatory networks acted upon by the metabolites as well as potential therapeutic interventions for aging and aging-related symptoms.

Our lab aims to discover novel longevity metabolites and explore their applications in aging-related symptoms. Here we present several novel longevity metabolites, which are α-ketoglutarate (α-KG), 2-hydroxyglutarate (2-HG), and α-ketobutyrate (α-KB). By combining target identification, epistasis, metabolomics, and bioenergetics analyses, we successfully uncover the molecular mechanisms of the longevity effects of these compounds. Specifically, we, for the first time, showed that α-KG and 2-HG extend lifespan of C. elegans by inhibiting ATP synthase and TOR, while α-KB delays aging through interruption of pyruvate oxidation and activation of AMPK. Interestingly, we discover an unexpected growth inhibitory effects of α-KG and 2-HG on tumor cells through targeting ATP synthase, and find that α-KG may confer beneficial effects for tumor treatment. In brief, our results identify novel potent longevity compounds and reveal their underlying mechanisms. More importantly, our work suggests a potential translational application of longevity metabolites in aging-related symptoms and provides novel directions for metabolic therapy.

tRNA-derived small RNAs (tsRNAs) are a type of widely existed small non-coding RNA with their mechanisms of action little explored. tsRNAs are sophisticatedly modified, creating a challenge to study their biological function because synthetic tsRNAs may not mimic their structure and interacting potential. Here, we show examples how endogenous tsRNAs with extensive RNA modifications can have cellular functions different from synthetic ones that without modifications. By adding site-specific RNA modifications to engineer synthetic tsRNAs, we mimic the endogenous tsRNAs structure conformation and recapitulate the functional effects of endogenous tsRNAs. In addition, we applied a LC-MS based de novo RNA sequencing method (MLC-seq) to profile RNA modification of endogenous tRNAs or tsRNAs. Our efforts may guide future understanding and designing of modified tsRNAs for precise gene regulation with a comprehensive tsRNA modification profile identified.

Damaged fuels originated from the accident at the Fukushima-Daiichi Nuclear Power Station, and the spent nuclear fuels from commercial light water reactors (LWRs) in Japan are considered to be disposed of in deep geological repository. For a prospective repository, as part of generic performance assessment, a criticality safety assessment (CSA) should be performed to ensure that the repository system including the engineered barriers and host geological formations remains sub-critical for tens of thousands to millions of years. For various repository concepts, CSA is considered to include three major stages in chronological order: (1) the stage before package failure, (2) the stage after package failure, while fissile nuclides remain within the engineered barrier system (EBS) and in the near-field region, and (3) the stage in which fissile nuclides originated from multiple packages are deposited in far-field host rocks. Defining the model for neutronics calculations plays a central role in CSAs, where conservative assumptions are usually made to cope with various uncertainties and to simplify the model. The aim of this dissertation is to develop neutronics models for different stages in the criticality safety study, and provide basic understandings for the long-term criticality safety for the disposal of spent nuclear fuel in geologic repository.

In the near-field analysis, a neutronics model has been developed for a system consisting of a canister containing fuel debris from Fukushima reactors and the surrounding buffer, in a water-saturated deep geological repository. The fuel debris has been modeled as a hexagonal lattice of spherical fuel particles. Following key observations have been concluded from the numerical results: (a) the calculated neutron multiplicity (keff) is sensitively dependent on assumptions related to moderation, (b) the carbon steel canister plays an important role in reducing the potential for criticality, (c) the maximum keff of the canister-buffer system could be achieved after a fraction of fissile nuclides been released from the canister, and (d) under several assumptions, the maximum keff of the canister-buffer system could be principally determined by the dimension and composition of the canister, not by the initial fuel loading. Based on the preliminary results and findings, a parametric study has been made to identify the optimized lattice parameters for criticality. And the critical mass of damaged fuels for a single canister has been calculated. If this critical mass is used as the maximum canister mass loadings, roughly a thousand canisters are needed to contain the damaged fuels from the three damaged cores. For the LWR spent fuels, a parametric study has been performed to examine spent fuels with different designs and burnup histories. The numerical results indicate that, under the conditions assumed, for all UO2 spent fuels and most of the MOX spent fuels, the single canister model will always be subcritical.

The far-field study has been focusing on neutronic analysis to examine the criticality conditions for uranium depositions in geological formations which result from geological disposal of damaged fuels from Fukushima reactors. Neutronics models are used to evaluate the keff and critical mass for various combinations of host rock and geometries. The present study has revealed that the planar fracture geometry applied in the previous criticality safety assessment for geological disposal would not necessarily yield conservative results against the homogeneous uranium deposition. It has been found that various far-field critical configurations are conceivable for given conditions of materials and geological formations. Prior to knowing the site location, some important points for selecting a site for criticality safety can be suggested. These include: (a) iron existing in the host rock reduces the likelihood of criticality significantly; (b) low host rock porosity is preferred for criticality safety; (c) the conservatism could change when comparing heterogeneous geometries for different fracture apertures; and (d) the importance of the mass of the deposition increases when it is smaller.

As part of the improvement for the models developed in the far-field analysis, preliminary works on uranium depositions in randomly fractured rocks have been presented. The randomly fractured geometry could fundamentally influence the far-field criticality, because the system’s keff value sensitively depends on the fracture aperture and the depositions at fracture intersections. No previous work has been made to study the effect of random geometry in the context of the long-term criticality safety in a geologic repository. Different numerical schemes have been developed and compared for the direct sampling of uranium depositions in randomly fractured rocks using MCNP. A general literature review of existing methods for neutron transport problems with random processes has been made. And the analytical Feinberg-Galanin-Horning (FGH) method has been derived and tested for a numerical example.

This report documents the outcomes of the February 6, 2007 workshop. It presents the most valued system characteristics of the Bronco Express EDAPTS system through the use of scored operational scenarios. The operational scenarios included in this report are down selected from those described in the initial release (V3.0) of the Operations Description report. The Advisory Panel members considered only scenarios with medium or high priority to be worthy of final consideration as deployable elements. These selected scenarios will allow the researchers to have an overall understanding of how the system will need to function in daily activities, better characterize the benefits that will be realized, and define any limitations that will have to be accommodated when the system is actually implemented.

This report is intended to communicate overall quantitative and qualitative EDAPTS system characteristics to users, developers, integrators, dispatchers, administrative staff and others. It is considered as the foundation for prioritizing customer needs and wants. It will be used to establish the baseline for the system requirements definition in the design process.