Theoretical reaction mechanistic studies on energetic nanomaterials and Li-CO2 battery via multi-scale molecular simulation

Department of Chemical EngineeringIn recent years, the development of energy systems with improved efficiency has become an important issue in the industrial manufacturing field due to the depletion of traditional energy fuels and ever-increasing commercial demands. Amid this sweeping trend, nanomaterials, which can exert different novel properties to those in conventional macroscopic materials, can be utilized for various energy applications. Nanomaterials play a major role in energy release and energy source. For application in energy release and energy sources, nanomaterials need to release high thermal energy from a relatively low energy level of external shocks or need to exert a high specific capacity and power density, respectively. In other words, nanomaterials for energy applications are required to have high energy density. To enhance their energy density, several nanomaterial candidates have been considered and synthesized. However, there are several difficulties in testing all the candidates due to time constraints and economic issues. Thus, for a more efficient development of the target nanomaterial, a process to screen the candidates is necessary, and reaction mechanistic studies can be conducted as additional processes to advance real experiments. These studies facilitate maximization of energy density in nanomaterials from investigation of thermodynamically and kinetically efficient reaction pathway and comparison of energy surfaces among reaction intermediates. Moreover, theoretical methods can prove to be helpful for reaction mechanistic studies. In this doctoral dissertation, reaction mechanistic studies in energy applications of nanomaterials have been conducted via multi-scale molecular simulation technique, which can prove to be a powerful tool to understand the physico-chemical phenomena for the reaction mechanistic studies of nanomaterials in energy applications. In Chapter 2, we theoretically tracked the reaction process of Ni-Al nanoalloys. Molecular dynamics simulations had been applied to investigate the characteristics depending on molar ratio of Ni and Al, the bilayer thickness of nanolayer, and ignition temperature. It was found that the variation of stoichiometry between Ni and Al had marginal effects on the overall process of reaction coordinates, however, the reaction rate and intermixing regions were different in each system. In addition, quantitative analysis on the reaction kinetics and thermodynamics were performed under different reaction and structural conditions. In this theoretical study, the reaction characteristics of Ni-Al nanolayers were quantified with systematic calculations. Therefore, it was expected to contribute to fabricate more advanced Ni-Al nanolayer products. In Chapter 3, we investigated the explosion characteristics of a nanobomb. In a nanobomb, nitromethane is constantly protected from the external environment due to stable mechanical and thermal properties of carbon nanotube (CNT) and is confined with the built-up pressure. After injection of thermal energy into confined nitromethane (NM) at various densities, the nanobomb was completely decomposed along the bursting process. The results show that the explosion time was reduced at a higher density and initial temperature. While NM was being decomposed into intermediates, Stone-Wales (SW) defects or high-order rings were randomly constructed at both the cap and side wall of CNT. Subsequently, carbon atoms at defect sites were functionalized by the reaction intermediates, where nanoholes were generated and burst at the end of bursting phenomena. Next, physicochemical modification of CNT was considered to improve the performance of the nanobomb. Chirality, nitrogen-doping, and monovacancy defect were introduced into CNT. All types of modifications on CNT brought time reduction in bursting of nanobomb although there was similarity on overall bursting mechanism. Among modifications on CNT, monovacancy defect exhibited the most striking effects on the enhancement of bursting. This suggests that chemical reactivity increased drastically around the defect sites. To intensively study the reason for this difference, SW defect formation energy and the adsorption energies of radical products on CNT were calculated for each modification. Both the formations of SW defects and bindings of the products were more favorable on monovacancy defect and nitrogen-doping site than the sites in pristine CNT. Furthermore, two heating methods were examined (e.g. electric spark and electromagnetic induction) as the additional external shocks on nanobomb. Bursting of nanobomb with electromagnetic induction occurs much rapidly due to oscillating frequency under a continuous electric field. Additionally, synergistic effects on the bursting of nanobombs with NM-detonating molecule mixed inside CNT were investigated. Detonating molecule candidates were initially filtered by comparing detonation velocity and pressure derived from Kamlet???Jacobs (K???J) equations. When bulk mixtures which contain NM and detonating molecules were constructed and decomposed at high temperatures, HMX or RDX showed a faster decomposition rate than that of NM and supported acceleration in NM decomposition rate. Furthermore, nanobombs in which HMX or RDX is confined with NM in CNT were heated by thermal energy from CNT, and their decomposition processes were compared with pure NM nanobomb. After the confined molecules were heated, detonating molecules were decomposed prior to NM and contributed to enhanced decomposition of NM. Eventually, CNT with the detonating molecule burst by continuous functionalization of reaction intermediates in much short time than pure NM nanobomb. We believe that our theoretical explorations to improve the explosion performance of nanobomb enable much feasible manipulation of nanostructured HEMs. In Chapter 4, reaction pathways in quinary molten-salt electrolyte-based Li???CO2 battery with Ru catalyst were theoretically estimated, in which nitrate-based molten salt and Ru catalyst were introduced. This led to a significantly improved performance compared to previous Li???CO2 batteries. Additionally, the number of battery cycles that can be operated was increased, but the reasonable electrochemical reaction behind its charge and discharge process was still veiled. From DFT calculation, three plausible reaction pathways in charge processes depending on operation temperature of battery cell were derived. For the discharge process, each free energy diagram with and without Ru surface was compared to probe the catalytic role of Ru nanoparticle. Consequently, Ru surface strongly reduced the energy in thermodynamic barrier of discharge process, and this was because movement of electrons from CO2??? to Ru surface energetically stabilized CO2???. We believe that mechanistic understanding of electrochemical reactions in charge and discharge processes will provide significant information for further development of Li???CO2 battery cell.clos

Superior Place Learning of C57BL/6 vs. DBA/2 Mice Following Prior Cued Learning in the Water Maze Depends on Prefrontal Cortical Subregions

The participation of the prefrontal cortex (PFC), hippocampus, and dorsal striatum in switching the learning task from cued to place learning were examined in C57BL/6 and DBA/2 mice, by assessing changed levels of phosphorylated CREB (pCREB). Mice of both strains first received cued training in a water maze for 4 days (4 trials per day), and were then assigned to one of four groups, one with no place training, and three with different durations of place training (2, 4, or 8 days). Both strains showed equal performance in cued training. After the switch to place training, C57BL/6 mice with 2 or 4 days of training performed significantly better than DBA/2 mice, but their superiority disappeared during the second half of an 8 days-place training period. The pCREB levels of these mice were measured 30 min after place training and compared with those of mice that received only cued training. Changes in pCREB levels of C57BL/6 mice were greater in the hippocampal CA3, hippocampal dentate gyrus, orbitofrontal and medial PFC than those of DBA/2 mice, when mice of both received the switched place training for 2 days. We further investigated the roles of orbitofrontal and medial PFC among these brain regions showing strain differences, by destroying each region using selective neurotoxins. C57BL/6 mice with orbitofrontal lesions were slower to acquire the place learning and continued to use the cued search acquired during the cued training phase. These findings indicate that mouse orbitofrontal cortex (OFC) pCREB is associated with behavioral flexibility such as the ability to switch a learning task

Evaluation of therapeutic effects of natural killer (NK) cell-based immunotherapy in mice using in vivo apoptosis bioimaging with a caspase-3 sensor

Natural killer (NK) cellâ based immunotherapy is a promising strategy for cancer treatment, and caspaseâ 3 is an important effector molecule in NK cellâ mediated apoptosis in cancers. Here, we evaluated the antitumor effects of NK cellâ based immunotherapy by serial noninvasive imaging of apoptosis using a caspaseâ 3 sensor in mice with human glioma xenografts. Human glioma cells expressing both a caspaseâ 3 sensor as a surrogate marker for caspaseâ 3 activation and Renilla luciferase (Rluc) as a surrogate marker for cell viability were established and referred to as D54â CR cells. Human NK92 cells were used as effector cells. Treatment with NK92 cells resulted in a timeâ and effector numberâ dependent increase in bioluminescence imaging (BLI) activity of the caspaseâ 3 sensor in D54â CR cells in vitro. Caspaseâ 3 activation by NK92 treatment was blocked by Zâ VAD treatment in D54â CR cells. Transfusion of NK92 cells induced an increase of the BLI signal by caspaseâ 3 activation in a doseâ and timeâ dependent manner in D54â CR tumorâ bearing mice but not in PBSâ treated mice. Accordingly, sequential BLI with the Rluc reporter gene revealed marked retardation of tumor growth in the NK92â treatment group but not in the PBSâ treatment group. These data suggest that noninvasive imaging of apoptosis with a caspaseâ 3 sensor can be used as an effective tool for evaluation of therapeutic efficacy as well as for optimization of NK cellâ based immunotherapy.â Lee, H. W., Singh, T. D., Lee, S.â W., Ha, J.â H., Rehemtulla, A., Ahn, B.â C., Jeon, Y.â H., Lee, J. Evaluation of therapeutic effects of natural killer (NK) cellâ based immunotherapy in mice using in vivo apoptosis bioimaging with a caspaseâ 3 sensor. FASEB J. 28, 2932â 2941 (2014). www.fasebj.orgPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154541/1/fsb2fj13243014.pd

Continuous-wave upconversion lasing with a sub-10 W cm(-2) threshold enabled by atomic disorder in the host matrix

Microscale lasers efficiently deliver coherent photons into small volumes for intracellular biosensors and all-photonic microprocessors. Such technologies have given rise to a compelling pursuit of ever-smaller and ever-more-efficient microlasers. Upconversion microlasers have great potential owing to their large anti-Stokes shifts but have lagged behind other microlasers due to their high pump power requirement for population inversion of multiphoton-excited states. Here, we demonstrate continuous-wave upconversion lasing at an ultralow lasing threshold (4.7Wcm(-2)) by adopting monolithic whispering-gallery-mode microspheres synthesized by laser-induced liquefaction of upconversion nanoparticles and subsequent rapid quenching ("liquid-quenching"). Liquid-quenching completely integrates upconversion nanoparticles to provide high pump-to-gain interaction with low intracavity losses for efficient lasing. Atomic-scale disorder in the liquid-quenched host matrix suppresses phonon-assisted energy back transfer to achieve efficient population inversion. Narrow laser lines were spectrally tuned by up to 3.56nm by injection pump power and operation temperature adjustments. Our low-threshold, wavelength-tunable, and continuous-wave upconversion microlaser with a narrow linewidth represents the anti-Stokes-shift microlaser that is competitive against state-of-the-art Stokes-shift microlasers, which paves the way for high-resolution atomic spectroscopy, biomedical quantitative phase imaging, and high-speed optical communication via wavelength-division-multiplexing. Upconversion microlasers present a lot of advantages but also require high pumping powers. Here the authors present a high-performing microlaser based on anti-Stokes-shift in upconversion nanoparticles synthesized using a technique of liquid quenching

An accurate method for quantifying and analyzing copy number variation in porcine KIT by an oligonucleotide ligation assay

<p>Abstract</p> <p>Background</p> <p>Aside from single nucleotide polymorphisms, copy number variations (CNVs) are the most important factors in susceptibility to genetic disorders because they affect expression levels of genes. In previous studies, pyrosequencing, mini-sequencing, real-time PCR, invader assays and other techniques have been used to detect CNVs. However, the higher the copy number in a genome, the more difficult it is to resolve the copies, so a more accurate method for measuring CNVs and assigning genotype is needed.</p> <p>Results</p> <p>PCR followed by a quantitative oligonucleotide ligation assay (qOLA) was developed for quantifying CNVs. The accuracy and precision of the assay were evaluated for porcine <it>KIT</it>, which was selected as a model locus. Overall, the root mean squares of bias and standard deviation of qOLA were 2.09 and 0.45, respectively. These values are less than half of those in the published pyrosequencing assay for analyzing CNV in porcine <it>KIT</it>. Using a combined method of qOLA and another pyrosequencing for quantitative analysis of <it>KIT </it>copies with spliced forms, we confirmed the segregation of <it>KIT </it>alleles in 145 F₁animals with pedigree information and verified the correct assignment of genotypes. In a diagnostic test on 100 randomly sampled commercial pigs, there was perfect agreement between the genotypes obtained by grouping observations on a scatter plot and by clustering using the nearest centroid sorting method implemented in PROC FASTCLUS of the SAS package. In a test on 159 Large White pigs, there were only two discrepancies between genotypes assigned by the two clustering methods (98.7% agreement), confirming that the quantitative ligation assay established here makes genotyping possible through the accurate measurement of high <it>KIT </it>copy numbers (>4 per diploid genome). Moreover, the assay is sensitive enough for use on DNA from hair follicles, indicating that DNA from various sources could be used.</p> <p>Conclusion</p> <p>We have established a high resolution quantification method using an oligonucleotide ligation assay to measure CNVs, and verified the reliability of genotype assignment for random animal samples using the nearest centroid sorting method. This new method will make it more practical to determine <it>KIT </it>CNV and to genotype the complicated <it>Dominant White/KIT </it>locus in pigs. This procedure could have wide applications for studying gene or segment CNVs in other species.</p

Low-temperature formation of epitaxial graphene on 6H-SiC induced by continuous electron beam irradiation

It is observed that epitaxial graphene forms on the surface of a 6H-SiC substrate by irradiating electron beam directly on the sample surface in high vacuum at relatively low temperature (similar to 670 degrees C). The symmetric shape and full width at half maximum of 2D peak in the Raman spectra indicate that the formed epitaxial graphene is turbostratic. The gradual change of the Raman spectra with electron beam irradiation time increasing suggests that randomly distributed small grains of epitaxial graphene form first and grow laterally to cover the entire irradiated area. The sheet resistance of epitaxial graphene film is measured to be similar to 6.7 k Omega/sq.open4

Enhanced Crystallinity of Epitaxial Graphene Grown on Hexagonal SiC Surface with Molybdenum Plate Capping

The crystallinity of epitaxial graphene (EG) grown on a Hexagonal-SiC substrate is found to be enhanced greatly by capping the substrate with a molybdenum plate (Mo-plate) during vacuum annealing. The crystallinity enhancement of EG layer grown with Mo-plate capping is confirmed by the significant change of measured Raman spectra, compared to the spectra for no capping. Mo-plate capping is considered to induce heat accumulation on SiC surface by thermal radiation mirroring and raise Si partial pressure near surface by confining the sublimated Si atoms between SiC substrate and Mo-plate, which would be the essential contributors of crystallinity enhancementclose0