<div> <div> <div> <p>The Effective Fragment Potential (EFP) is a quantum-mechanical based model potential for accurate calculations of non-covalent interactions between molecules. It can be coupled with ab initio methods in so-called QM/EFP models to explore the electronic properties of extended molecular systems by providing rigorous description of surrounding environments. The current EFP formulation is, however, not well suited for large-scale simulations due to its inherent limitation of representing effective fragments as rigid structures. The process of utilizing EFP method for the molecular systems with flexible degrees of freedom entails multiple sets of parameter calculations requiring intensive computational resources. This work presents development of the EFP method for describing flexible molecular systems, so-called Flexible EFP. To validate the applicability of the Flexible EFP method, extensive benchmark studies on the amino acid interactions, binding energies, and electronic properties of flavin chromophore of the cryptochrome protein have been demonstrated. In addition to methodological developments, excitonic properties of the Fenna-Matthews-Olson (FMO) photosynthetic pigment-protein complex are explored. In biological systems where intermolecular interactions span a broad range from non-polar to polar and ionic forces, EFP is superior to the classical force fields. In the present study, we demonstrate excellent performance of the QM/EFP model for predicting excitonic interactions and spectral characteristics of the FMO wildtype complex. We characterize the key factors for accurate modeling of electronic properties of bacteriochlrophyll a (BChl a) photosynthetic pigments and suggest a robust computational protocol that can be applied for modeling other photosynthetic systems. Developed computational procedures were also successfully utilized to elucidate photostability and triplet dynamics in the FMO complex and spectroscopic effects of single-point mutagenesis in FMO. A combination of polarizable EFP molecular dynamics and QM/EFP vibrational frequency calculations were also applied to understanding and interpreting structures and Raman spectroscopy of tert-butyl alcohol solutions. </p> </div> </div> </div>

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One learning problem is that public understanding of science is limited. Many people blame at least part of the problem on the predominant lecture approach for students' lack of science understanding. Current research indicates that more active instructional approaches can improve student learning in introductory undergraduate biology courses. Active learning may be difficult to implement because methods and strategies, ranging from in-class collaborative problem-solving to out of class multimedia presentations, are diverse, and sometimes difficult to implement. Merrill's First Principles of Instruction (hereafter referred to as "First Principles" or "First Principles of Instruction") provides a framework for implementing active learning strategies. This study used First Principles of Instruction as a framework for organizing multiple active learning strategies in a web-based module in an introductory biology course. Participants in this exploratory study were university students in Life Sciences 1350, an introductory biology course for nonscience majors. Students were randomly assigned to use either the module using First Principles of Instruction (hereafter called the First Principles module) or the module using a more traditional web-based approach (hereafter called the traditional module) as supplementary instruction. The First Principles module implemented several active learning strategies and used a progression of whole problems and several demonstration and application activities to teach the topic of "microevolution," defined as the study of how populations evolve and change over time. The traditional module implemented a more traditional web-based approach, providing information and explanations about microevolution with limited examples. This exploratory study's results showed that the learning gain from pretest to posttest at the remember level was significant for the traditional group at alpha = .05 and was significant for the First Principles group at alpha = .1. In addition the pretest to posttest gain at problem solving for the First Principles group was significant at alpha = .05. When students rated their confidence in solving future problems, those in the First Principles group were significantly more likely to predict future success at alpha = .1.

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<p dir="ltr">Porous silicon (po-Si) is a unique form of silicon (Si) that features tunable nanopores distributed throughout its bulk structure. While crystalline Si (c-Si) already boasts technological advantages, po-Si offers an additional key aspect with its large surface area relative to its small volume, making it highly conducive to surface chemistry. In this research, our focus centers on the design of a synaptic device based on po-Si, exploring its potential for neuromorphic hardware applications.</p><p><br></p><p dir="ltr">To begin, we delve into the analysis of several electrical properties of po-Si using density functional theory (ab initio/first principles) calculations. Notably, we discover the presence of intra-pore dangling states within the bandgap region of po-Si. Although po-Si is known for its higher bandgap compared to c-Si, resulting in low carrier density and increased resistance, the existence of these dangling states significantly impacts its electronic transport.</p><p><br></p><p dir="ltr">Additionally, we investigate the electric-field driven modulation of dangling bonds through controlled intra-pore Si-H bond dissociation. This modulation enables precise control over the density of dangling states, facilitating the tunability of po-Si conductance. Theoretically evaluating the current-voltage characteristics of our proposed po-Si based synaptic devices, we determine the potential range of obtainable conductivity.</p><p><br></p><p dir="ltr">Finally, we evaluate the performance by integrating porous silicon nanoelectronics devices into neural networks. These devices exhibit superior synaptic plasticity, faster response times, and reduced power consumption compared to other synapses. The research indicates that poroussilicon devices are highly effective in neuromorphic systems, paving the way for more efficient and scalable neural networks. These advancements have significant practical and cost-effective implications for a wide range of applications, including pattern recognition, machine learning, and artificial intelligence.</p><p><br></p><p dir="ltr">Overall, our analyses reveal that the integration of po-Si based synaptic devices into the neural fabric offers a path towards achieving significantly denser and more energy-efficient neuromorphic hardware. With its tunable properties, large surface area, and potential for controlled conductance, po-Si emerges as a promising candidate for the development of advanced silicon based nano-electronic devices tailored for neuromorphic computing. As we delve deeper into the potentials of po-Si, the era of cognitive computing, inspired by the elegance of bio-mimetic neural networks, edges closer to becoming a reality.<br><br></p>

The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple hexagonal w phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the b phase, thwarts its transformation to w, and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other w forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether w can transform to a -phase in the crystal bulk or if it occurs only at high-energy regions such as grain boundaries. Furthermore, what is the nature of the a phase embryo? (iv) Although previous computational results discovered a new wa transformation mechanism in pure Ti with activation energy lower than the classical Silcock pathway, it is at odds with the a / b / w orientation relationship seen in experiments. First principles calculations based on density functional theory provide an accurate approach to study such nanoscale behavior with full atomistic resolution, allowing investigation of the complex structural and chemical effects inherent in the alloyed state. In the present work, a model Ti-Mo system is investigated to resolve these fundamental questions. Particular attention is paid to how Mo- (i) influences the bonding in Ti, (ii) distorts the local structure in the Ti lattice, (iii) impacts the point and interfacial defect formation and migration energies, and (iv) affects the mechanism and energetics of b w and wa transformations. Our results are correlated with appropriate experimental results of our collaborators and those in open literature. The modification of Ti bonding by Mo solutes and the attendant distortion of the lattice hold the key to answering the diverse questions listed above. The solutes enhance electron charge density in the <111> directions and, consequently, stiffen the lattice against the displacements necessary for b w transformation. However, Ti atoms uncoordinated by Mo remain relatively mobile, and locally displace towards w lattice positions. This effect was further studied in a metastable Ti-8.3 at.% Mo system with an alternate cell geometry which allows for either b w or $\betaa transformation, and it was found that after minimization Ti atoms possessed either a or w coordination environments. The creation of this microstructure is attributed to both the disruption of uniform b w transformation by the Mo atoms and the overlap of Ti-Mo bond contractions facilitating atomic displacements to the relatively stable a or w structures in Mo-free regions. The vacancy migration behavior in such a microstructure was then explored. Additionally, several minimized configurations were created with planar interfaces between Mo-stabilized b region and its adjacent a- or w- phases, and it was found that the positioning of Mo at the interface strongly dictates the structure of the adjacent Mo depleted region.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第25556号 / エネ博第484号 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)准教授 蜂谷 寛, 教授 佐川 尚, 教授 野平 俊之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Silicon nanowires (SiNWs) and the copper chalcogenides, namely copper sulfide (Cu2S) and selenide Cu2Se, have diverse applications in renewable energy technology. For example, SiNWs which have direct band gaps unlike bulk Si, have the potential to radically reduce the cost of Si based photovoltaic cells. However, they degrade quickly under ambient conditions. Various surface passivations have therefore been investigated for enhancing their stability but it is not yet well understood how they affect the electronic structure of SiNWs at a fundamental level. Here, we will explore, from first-principles simulation, how fluorine, methyl and hydrogen surface passivations alter the electronic structures of [111] and [110] SiNWs via strain and quantum confinement. We also show how electronic charge states in [111] and [110] SiNWs can be effectively modelled by simple quantum wells. In addition, we address the issue of why [111] SiNWs are less influenced by their surface passivation than [110] SiNWs. Like SiNWs, Cu2S and Cu2Se also make excellent photovoltaic cells. However, they are most well known for their exceptional thermoelectric performance. This is by virtue of their even more unique solid-liquid hybrid nature which combines the low thermal conductivity and good electrical characteristics required for a high thermoelectric efficiency. We use first-principles molecular dynamics simulations to show that Cu diffusion rates in Cu2S and Cu2Se can be as high as 10-5cm2s-1. We also relate their phonon power spectra to their low thermal conductivities. Furthermore, we evaluate the thermoelectric properties of Cu2S and Cu2Se using a combination of Boltzmann transport theory and first-principles electronic structure calculations. Our results show that both Cu2S and Cu2Se are capable of maintaining high Seebeck coefficients in excess of 200μVK-1 for hole concentrations as high as 3x1020cm-3.