Non-Gaussianity in String Cosmology: A Case Study

We study non-gaussianity effects, using the $\delta N$ formalism, in a multi-field inflationary model consisting of K\"ahler moduli derived from type IIB string compactification in the large volume limit. The analytical work in this paper mostly follows the separable potential method developed by Vernizzi and Wands. The numerical analysis is then used in computing non-gaussianity beyond slow-roll regime. The possibility of the curvaton scenario is also discussed. We give the condition for the existence of the curvaton and calculate the non-guassianity generated by the curvaton decay in the large volume limit.Comment: 25 page

Multi-Field Inflation from String Theory

We construct a multi-field inflationary model consisting of multiple K\"ahler moduli derived from type IIB string compactification in the large volume limit. The model consists of both heavy and light fields, with the former being frozen during the inflationary period and the latter acting as the inflaton(s). We study the evolution of all the fields during and after inflation until the preheating era when all the fields oscillate around their vacuum expectation values. Our numerical analysis shows that the curvature perturbations have an almost scale invariant power spectrum with $n_s \simeq 0.96$.Comment: 25 pages, 17 figure

Evolution of Endosperm Starch Synthesis Pathway genes in the Context of Rice: Oryza sativa) Domestication

The evolution of metabolic pathways is a fundamental but poorly understood aspect of evolutionary change. The rice endosperm starch biosynthetic pathway is one of the most thoroughly characterized biosynthesis pathways in plants, and starch is a trait that has evolved in response to strong selection during rice domestication and subsequent crop improvement. In this study, I have examined six key genes in the rice endosperm starch biosynthesis pathway to investigate the evolution of this pathway before rice domestication and during rice domestication. Oryza rufipogon is the wild ancestor of cultivated rice: Oryza sativa). Oryza sativa has five variety groups: aus, indica, tropical japonica, temperate japonica and aromatic. I have sequenced five genes: shrunken2, Sh2; brittle2, Bt2; waxy, Wx; starch synthase IIa, SsIIa; starch branching enzyme IIb, SbeIIb; and isoamylase1, Iso1) in 70 O. rufipogon accessions, 99 cultivated rice accessions: aus, 10; indica, 34; tropical japonica, 26; temperate japonica, 21; aromatic rice, 8) and two accessions of two closely related species, O. barthii, O. meridionalis. The published sequence data for Wx in rice are included in the analysis as well. The difficulty of detecting selection is often caused by the complex demographic history of a species. Genome-wide sequence data in a species would mainly reflect its demographic history. I have compared the pattern of nucleotide variation at each starch gene with published genome-wide sequence data and with a standard neutral model for detecting selection. Results show no evidence of deviations from neutrality at these six starch genes in O. rufipogon and no evidence of deviations from neutrality at four starch genes in O. sativa. Evidence of selection is observed at Wx in tropical japonica and temperate japonica, and at Wx and SbeIIb in aromatic rice. Starch quality is one of the most important agronomic traits in rice. Starch synthase IIa: SsIIa) has been mapped as a gene which contributes to the starch quality variation in cultivated rice, O. sativa. Within the gene, three nonsysnonymous mutations in the exon 8 region were shown to affect its enzyme activity in Escherichia coli. In order to identify the mutation in SsIIa exon 8 region that is responsible for starch quality variation in rice, I have sequenced SSIIa exon 8 region and recorded the alkali spreading score in 57 O. rufipogon accessions and 151 cultivated rice accessions: aus, 8; indica, 51; tropical japonica, 55; temperate japonica, 29; aromatic, 8). Starch alkali spreading score is used to quantify rice endosperm starch quality and has been shown to be significantly associated with SsIIa enzyme activity in rice. Both a general linear model and nested clade analysis were used to detect an association between the three nonsynonymous mutations in SSIIa exon 8 and the alkali spreading score. In order to avoid the effect of population structure on the association analysis, both association analyses are conducted within each rice variety group. Among the previously identified nonsynonymous mutations, my results show strong evidence of association at one nonsynonymous mutation: SNP3, see Fig 2 of Chapter 2), and evidence of no association at another nonsynonymous mutation. Tests of association for the other nonsynonymous mutation are inconclusive with current samples and will require further investigation. This dissertation reveals the relative role of evolutionary forces in shaping the variation pattern of six starch genes in O. sativa and its wild ancestor, O. rufipogon. It also reveals an association between a nonsynonymous mutation in SSIIa exon 8 and rice endosperm starch quality

Aspects of String Compactification

This dissertation addresses some interesting problems in string compactification relevant to phenomenology, especially cosmological models derived from string theory Most attention is drawn to stabilizing the moduli and discussing the cosmology solutions given the effective potential obtained from string theory. We first discuss compactification of type IIB string theory in the presence of flux. With the moduli stabilized, we obtain the effective potential in the large volume limit. We then focus on getting the vacua of the potential and solving the cosmology equations. Finally we compare the solutions with observations in cosmology

Syntactic Complexity in Reading Comprehension: An Eye-Tracking Study of Text Processing Among Bilinguals and Monolinguals

For Chinese students, studying in a country with different cultural components and language structures is challenging. Compared to English, the Chinese prefers shorter and simple sentence structure and allows for two sentences to be stated side by side. Different sentence structures in Chinese may influence native-Chinese readers’ understanding of English sentences and even a whole text. This exploratory study examined whether there were any differences between English monolingual and Chinese-English children while reading varied English texts with simple or complex structures at different reading difficulty levels. This study explored the differences across texts and readers, as well as the possible effect of first-language transfer on text comprehension behavior. Behavioral and eye-tracking data, including accuracy of true/false questions, reading speed, and first fixation duration were analyzed. For true/false questions, both groups answered the questions with sufficient accuracy, indicating basic understanding of the brief passages. For reading speed and first fixation duration, as expected, monolinguals read faster with shorter fixations than bilinguals across all passages and monolinguals revealed faster reading speed for easy passages than for hard passages. However, no difference was found between easy and hard passage reading for bilinguals, which was surprising, suggesting that vocabulary difficulty may not have influenced reading speed. Additionally, the findings that no differences for reading difficulty or syntactic complexity between or within each group in first fixation duration were unexpected. To examine whether participants’ offline behavioral test scores (i.e., language, reading and cognitive capacity) influenced the relationship between first fixation duration and syntactic complexity or reading difficulty, the offline behavioral test scores were added into analysis. According to the results, monolinguals performed expectedly with stronger influence of reading and cognitive capacities on complex structure passages. However, bilinguals appeared to attend to the simple structure passages as expected, but not complex passages. Results suggest that English complex structures may have been too difficult for bilinguals to apply reading knowledge or cognitive ability for text processing or bilinguals were less responsive to the syntactic complexity due to their first-language transfer

Impacts of Rice Field Winter Planting on Soil Organic Carbon and Carbon Management Index

To tackle with the problem of prevailing farmland abandonment in winter, 5 treatments includes Chinese milk vetch-double cropping rice (CRR), rape-double cropping rice (RRR), garlic-double cropping rice (GRR), winter crop multiple cropping rotation (ROT), winter fallow control (WRR) were set up. By measuring soil total organic carbon, active organic carbon and its components and calculating the soil carbon pool management index in 0~15 cm and 15~30 cm soil layers in the early and late rice ripening stage. The effects of different winter planting patterns on the changes of soil organic carbon and carbon pool management index were discussed. In order to provide theoretical basis for the optimization and adjustment of winter planting pattern of double cropping rice field in the middle reaches of Yangtze River. The results showed that soil total organic carbon, active organic carbon and its components in different winter cropping patterns were increased, and ROT and CRR treatments were more beneficial to the accumulation of soil total organic carbon, active organic carbon and its components as well as the improvement of soil carbon pool management index, which should be preferred in the adjustment of cropping patterns

Effects of Returning Straw and Milk Vetch on Rice Growth and Greenhouse Gas Emissions

The effects of different nitrogen application levels on rice yield and greenhouse gas (NO2, CH4) emissions from rice fields under the combined action of straw and milk vetch. Two treatments were set up in the main area of this experiment: R0 (no straw returned to the field, 0); R1 (amount of straw returned to the field under normal conditions, 6000 kg·hm-2). Before turning the straw back into the field, use a circular knife to cut the straw into 10~13 cm.And 3 kinds of nitrogen application treatments in the sub-district: N1 (no nitrogen application, 0), N2 (nitrogen application, 15 kg·hm-2), N3 (nitrogen application, 30 kg·hm-2), two-factor cross-combination,and a non-nitrogen control CK, total of 7 treatments. The results showed that in 2017, early rice R1N2 treatment increased the most obvious yield, which was 32.44% higher than CK, and late rice R1N1 treatment increased the most significantly, which was 17.91% higher than CK. CH4 emission is positively correlated with the straw returned to the field. N2O is the opposite. The N2O emission flux was highest in the treatment of R1N3, and the CH4 emission flux was the highest in the treatment of R1N2

A Review of Research on Agroecosystem Services Based on Bibliometric Analysis

Agricultural ecosystem is one of the most important ecosystems in the world, which provides multiple ecosystem services such as grain production, climate regulation, water conservation and biodiversity. The degradation of ecosystem services has become an important factor that severely restricts the sustainable development of agriculture. Agroecosystem services have become the core and hot topic of ecological research. In recent years, countries and related institutions have been increasing their research on agricultural ecosystem service. Based on Web of Science(WoS) and China Knowledge Resource Integrated (CNKI) databases, the development characteristics and trends of agroecosystem services research were analyzed by bibliometric methods. The results show that: (1) The number of papers on agroecosystem services is increasing, which shows that the research on it is developing. (2) Developed countries are the main research forces in the field of ecosystem services, and the developed countries in Europe and the United States occupy the absolute leading position; China Agricultural University and the University of California in the United States are the main research institutions. (3) At present, eight research hotspots in this field are the study of ecosystem services mechanism, protection management and sustainability, sustainable development, biodiversity, land use and landscape change, value assessment, climate change, sustainable development of agriculture, ecological compensation. From the overall distribution of research hotspots in each period, the international research focuses more on the interdependence between ecosystem services and ecosystem services and human well-being, while the research in China focuses more on ecosystem services assessment. (4) In recent years, there is a big gap between China and foreign countries in the field of ecosystem services research. It is necessary to strengthen cooperation with research institutions in developed countries in Europe and the United States, and further improve the research content, research vision and research method