Micropaleontological Record of a Preserved, Late Pleistocene Bald Cypress Forest on the Northern Gulf of Mexico Inner Shelf

A cluster of previously buried Taxodium distichum stumps are exposed and preserved in growth position at the bottom of a trough on the inner Gulf of Mexico (GOM) continental shelf in 18 m water depth and 13 km offshore Orange Beach, AL. Radiocarbon ages from wood and optically stimulated luminescence (OSL) dating of sediments suggest a Marine Isotope Stage (MIS) 3 age, or older. This study builds on the previous work of Gonzalez (2018) and Obeclz (2017). Five biofacies were identified in vibracore collected in 2015 and 2016: 1) the Holocene Mississippi-Alabama-Florida (MAFLA) sand sheet, 2) a Holocene interbedded sand and mud facies, 3) a Pleistocene interbedded sand and mud facies, 4) a paleosol, and 5) a Pleistocene interbedded mud and peat facies associated with the in situ stump horizon. The seafloor, a transgressive ravinement surface, and a basal contact between undifferentiated Pleistocene terrestrial facies and an older, steeply dipping clinoform package are resolved from geophysical data. Foraminiferal assemblage analysis revealed the transitional layer of interbedded sand and mud above the floodplain facies was late Holocene in origin and was part of a lower shoreface or marine-dominated estuarine environment. Stratigraphy of the area suggests paleotopographic relief was established prior to 56 ±5 ka and persisted until Holocene transgression. Two major factors allowed for unusual preservation of the in situ stump horizon: (1) paleotopographic relief created enough accommodation for sediment infill to bury and preserve the forest, and (2) significant pulses of sea level rise during MIS 3–4 produced widespread, rapid floodplain aggradation within the incised complex

Characterisation and defect engineering of poly-Si passivating contacts in silicon solar cells

From a broader perspective, this thesis is concerned with the development of a novel polycrystalline silicon on oxide passivating contact technology (poly-Si/SiOx) for high efficiency silicon (Si) solar cells. A comprehensive understanding of various characteristics of poly-Si films provides a clearer picture of underlying mechanisms limiting the performance of the passivating contact. This thesis is divided into two broad categories: the characterisation and the defect-engineering by hydrogenation treatments of the technology. First, this thesis utilizes various advanced characterisation techniques available to the photovoltaic (PV) research community to study the structural, electrical, and optoelectronic properties of different poly-Si/SiOx passivating contacts. Using transmission electron microscopy (TEM), interfacial images of the poly-Si/SiOx/c-Si stack are revealed at a nanometre-scale. Atomic force microscopy (AFM) morphologies of the poly-Si surfaces demonstrate the difference in film surface morphologies of different depositing methods. Grazing incidence X-ray diffraction (GIXRD) spectra give an overview of the difference in crystallinity of the poly-Si films with various deposition conditions. Electrochemical capacitance-voltage (ECV) doping profiles show electrically active doping levels inside the poly-Si films after different diffusion processes to form the contact. Meanwhile, secondary ion mass spectrometry (SIMS) doping profiles present total doping concentrations inside the stack. The difference between ECV and SIMS profiles reflects inactive dopant concentrations. Quasi-steady state photoconductance (QSSPC) is a useful method to quantitatively evaluate the performance of the passivating contact by measuring the effective lifetime tau_eff, implied open circuit voltage iVoc, and recombination current density Jo. For the optoelectronics studies, photoluminescence spectroscopy (PLS) and Fourier transform infrared spectroscopy (FTIR) are used. The PL spectra reveal various combined features from the poly-Si film, SiOx interface, and c-Si substrate. The characteristic PL signal from a hydrogenated amorphous Si phase (a-Si:H) inside the poly-Si film can be used as a mean to trace the presence of hydrogen. Meanwhile, the sub-bandgap PL signal from the film is also used to demonstrate the passivation of nonradiative defects inside it. FTIR spectra are employed as a way to verify the presence of hydrogen by tracking the peak of the Si-H stretching modes. By combining the various methods mentioned, a comprehensive examination of the different properties of the poly-Si passivating contacts is performed, suggesting different routes to improve their performance. Second, the thesis investigates defect-engineering processes for the poly-Si passivating contacts by different hydrogenation treatments, such as forming gas annealing (FGA), and depositing hydrogen-rich dielectric layer(s) (silicon nitride (SiNx), or aluminum oxide (AlOx)) and post-annealing in FGA. Generally, after the hydrogenation treatments, the performance of the different poly-Si passivating contacts is all improved, regardless of the deposition conditions. The presence of hydrogen inside the poly-Si/SiOx passivating contacts can be detected by the characteristic luminescence peak from the hydrogenated amorphous phase (a-Si:H). It is found that only a hydrogenation treatment involving SiNx on poly-Si films formed by a plasma-enhanced chemical vapour deposition (PECVD) method gives the a-Si:H PL peak. Proposed mechanisms of the different hydrogenation methods are as follows: the two different capping layers, AlOx and SiNx, could cause different associations of hydrogen in the poly-Si films. The hydrogen from the AlOx film could be injected into the poly-Si film and form complexes with other species rather than passivate the dangling bonds of the a-Si phase. Meanwhile, the hydrogen atoms from the SiNx film both passivate the a-Si phase and form complexes

BUCKLING ANALYSIS OF THE INDUSTRIAL FACTORY MODEL BY FINITE ELEMENT METHOD

Buckling is a subject that has been discussed for a long time, however, it still be studied and developed due to its practicality. The following article introduces two methods that are used to solve the problems involving buckling of the beam, shell and solid with an I shape cross-section having different cases of boundary load. The theory which is used in this article is Euler's formula and Eurocode 3 standard. The analytical results by ANSYS commercial software are compared with the theoretical results and results from Eurocode 3 standard. The authors based on the reliability of the calculating results to simulate buckling of the industrial factory model with different cases of load conditions. The simulating results show a general view of buckling cases

TET3の年齢依存性エピジェネティック制御

この博士論文は内容の要約のみの公開（または一部非公開）になっています筑波大学 (University of Tsukuba)201

DoubleEcho: Mitigating Context-Manipulation Attacks in Copresence Verification

Copresence verification based on context can improve usability and strengthen security of many authentication and access control systems. By sensing and comparing their surroundings, two or more devices can tell whether they are copresent and use this information to make access control decisions. To the best of our knowledge, all context-based copresence verification mechanisms to date are susceptible to context-manipulation attacks. In such attacks, a distributed adversary replicates the same context at the (different) locations of the victim devices, and induces them to believe that they are copresent. In this paper we propose DoubleEcho, a context-based copresence verification technique that leverages acoustic Room Impulse Response (RIR) to mitigate context-manipulation attacks. In DoubleEcho, one device emits a wide-band audible chirp and all participating devices record reflections of the chirp from the surrounding environment. Since RIR is, by its very nature, dependent on the physical surroundings, it constitutes a unique location signature that is hard for an adversary to replicate. We evaluate DoubleEcho by collecting RIR data with various mobile devices and in a range of different locations. We show that DoubleEcho mitigates context-manipulation attacks whereas all other approaches to date are entirely vulnerable to such attacks. DoubleEcho detects copresence (or lack thereof) in roughly 2 seconds and works on commodity devices

THE ANALYSIS OF FLUID DYNAMICS OF WAVE POWER STATION WITH WELLS TURBIN BY CFD

Natural energy such as wind, wave and other natural vibrations is one of the high potential renewable energy sources. The Wells turbine is based on the use of bidirectional turbines, which act as axial-flow self-rectifying turbines that employs a symmetrical blade profile and rotating unidirectionally in reciprocating airflows generated by the air chamber to extract energy from vibrations. These topics have been extensively studied both numerically and experimentally such as research on the parameters of the effects of structure, angle of attack, blade shape, etc. In this paper, numerical simulation is carried out using commercially available tool Fluent for fluid dynamics analysis and focus on oscillating predictions, with particular attention to the behavior of the flow. Based on the Numerical Wave Tank (NWT) model is simulated in a two dimensional used in this model, which is constructed mainly based on the spatially averaged Navier Stokes equation with the k-ε model for simulating the turbulence and modeled with Volume of Fluid (VOF). Axial-flow turbines system and future development as well as the proposed limitations will be discussed in detail

An enhanced nodal gradient finite element for non-linear heat transfer analysis

The present work is devoted to the analysis of non-linear heat transfer problems using the recent development of consective-interpolation procedure. Approximation of temperature is enhanced by taking into account both the nodal values and their averaged nodal gradients, which results in an improved finite element model. The novel formulation possesses many desirable properties including higher accuracy and higher-order continuity, without any change of the total number of degrees of freedom. The non-linear heat transfer problems equation is linearized and iteratively solved by the Newton-Raphson scheme. To show the accuracy and efficiency of the proposed method, several numerical examples are hence considered and analyzed

STUDENTS’ PERCEPTIONS OF ACTIVE LEARNING IN INTRODUCTION TO LITERATURE

There is a growing interest in active learning as a shift from traditional lecturing to improving student-centred learning in English. However, in the Vietnamese context of teaching and learning at tertiary levels, little research has examined students’ perceptions of active learning in approaching Introduction to Literature. This study is therefore aimed to look into this area of interest. Participants in this study were 94 students from junior and seniors majoring in high-quality programs at a university in the Mekong Delta. Data were collected from questionnaires. The findings show that students had positive perceptions of active learning in studying this course. Implications for teaching and learning this course are made.  Article visualizations

TYPES OF POLITENESS STRATEGIES AND DEGREES OF POLITENESS PERFORMED BY ENGLISH MAJOR STUDENTS IN REQUESTING FOR HELP

In social interaction, people need to pay attention to the face of others to maintain relationships and avoid losing their faces. To do this, people should use politeness strategies in communication. This study aims to investigate which type of politeness strategies are mostly used and the level of politeness shown by English major students in the High Quality Program in requesting help. This study is based on the theory of Brown and Levinson (1987). Based on the analysis of the data obtained from the questionnaire, negative politeness strategies were applied the most. This also performs a high degree of politeness. It shows that students majoring in English studies (High Quality Program) had an awareness of using politeness strategies in requesting help.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/edu_01/0704/a.php" alt="Hit counter" /></p&gt

Optimizing conditions to improve polyphenol content and screening antioxidant capacity with DNA protection activity of Perilla frutescens

Polyphenols are among the natural antioxidants that have been exploited in recent years for their safe and effective ability against oxidative stress. This project aimed to optimize 3 factor-conditions affecting total polyphenols extracted from Perilla frutescens (L.) Britt as well as DNA protection activity of polyphenols for applications in the fields of dietary supplements, pharmaceuticals, and health care. All extracts contained phenolic compounds and exhibited good antioxidant ability through a ferric reducing antioxidant power assay. The total polyphenolic compounds varied from 6.056 ± 0.08 to 9.630 ± 0.127 mg of gallic acid equivalents (GAE) per 1 g dry weight (dw). The highest phenolic content yield was extracted at 70°C for 60 minutes at a pH of 7.0. However, a sample with the highest polyphenol content had a lower residual DNA concentration than the extract (55°C, 60 min, and pH 6.0) with the greatest reducing power. The result of the DNA protection assay also indicated that the extraction concentration and pH condition had a significant effect on preventing DNA from being damaged by free radicals. The study found the conditions for improving polyphenol in the extraction of P. frutescens (L.) Britt with the aid of Box-Behnken Design. This research also proposed that P. frutescens (L.) Britt is a good source showing DNA protection and antioxidant activity for healthcare