Cosmology with Weak Lensing Peaks

Recent studies have shown that the number counts of peaks in weak lensing (WL) surveys contain significant cosmological information. Motivated by this finding, in the first part of the thesis, we address two questions: (i) what is the physical origin of WL peaks; and (ii) how much information do the peaks contain beyond the traditional cosmological WL observable (the power spectrum). To investigate the first question, we use a suite of ray-tracing N-body simulations, in which we identify individual dark matter halos. We study the halos' contribution to the peaks. We find that high peaks are typically dominated by a single massive halo, while low peaks are created by galaxy shape noise, but with an important contribution from a line-of-sight projection of typically 4-8 halos. For the second question, we first compare the cosmological peak count distributions to those in a Gaussian random field. We find significant differences, both in the peak-count distributions themselves, as well as in how the distributions depend on cosmology, demonstrating that the peaks contain non-Gaussian information. To explicitly quantify the information content of the peaks beyond the power spectrum, we use the Fisher matrix method to forecast errors in the three-dimensional parameters space (σ_8, w, Ω_m). We find that when we combine the peaks and the power spectrum, the marginalized errors are a factor of about two smaller than from power spectrum alone. In the second part of the thesis, we address a major theoretical systematic error: the presence of baryons -- not included in the N-body simulations -- can affect the WL statistics (both peaks and power spectrum), and the inferred cosmological parameters. We apply a simplified model, which mimics the cooling and condensation of baryons at the centers of dark matter halos. In particular, we manually steepen the density profile of each dark matter halo identified in the N-body simulations, and repeat the ray-tracing procedure create WL maps in mock "baryonic'' universes. We then compare the peak count distributions and power spectra in these baryonic models to those from the pure DM models. We find that there is a large increase in the number of high peaks, but low peaks -- which contain most of the cosmological information -- are robust to baryons. Similarly, we find that the high--l power spectrum is increased, but the change in the low--l power spectrum is relatively modest. We then utilize a Monte Carlo approach to compute the joint, and in general, biased constraints on σ_8, w, Ω_m when the baryonic model is fit by the pure DM models. We find that: (i) constraints obtained from low peaks are nearly unbiased; (ii) high peaks yield large biases, but in different directions in parameter space than the biases from the power spectrum. Our first finding suggests it may be advantageous to use low peaks for analysis until the baryonic processes are better understood. However, our second finding suggests the possibility of "self-calibration'': simultaneously fitting astrophysical "nuisance'' parameters (describing lensing halo profiles) with cosmological parameters

Examining the Cross-cultural Experience of Eight Chinese International EFL Students Studying STEM Disciplines in Doctoral Programs at a Large Public Research University

Chinese international students’ difficulties in adjusting to the U.S. classrooms has long been overlooked. They have been stereotyped as not experiencing any problems as a result of their excellence at all levels of education, which also implies that they have been succeeding at handling cross-cultural issues. Research which focuses on Chinese international students are usually generated in the area of second language learning or pedagogical methods, Chinese international students’ cross-cultural experience has not been fully explored. The present study was hence conducted to fill the literature gap. Its results could lead to an improvement of Chinese international EFL students’ studying abroad experience, as well as provide directions for possible future studies. The study investigated the research question: how does a group of eight Chinese international EFL students studying STEM disciplines in doctoral programs at a large public research university make meaning of their cross-cultural classrooms/lab setting experiences? The study is a qualitative case study. Participants were recruited via purposeful snowball sampling. An interpersonal, semi-structured interview was used for data collection, and guidelines provided by Smith et al. (2009) were adopted for data analysis. The results show that all eight participants have been experiencing culture-shock since they arrived in the U.S., and they held many erroneous assumptions about studying in the U.S.. Their major difficulties were generated by adjusting to the U.S. classroom culture and using/understanding cultural English. Causes of their cross-cultural experience could be traced to differences between the Chinese and the U.S. curricula and pedagogical methods; and the teacher centered, textbook oriented teaching methods adopted in their Chinese schools for English teaching. Besides, since most of the participants were top students when they were in China, considering the demand for academic excellence in the Chinese culture, participants’ eagerness to maintain/obtain academic accomplishments severed the negative part of their cross-cultural experience. On the basis of my findings, I recommend re-examining (and corresponding change) of the curricula, avoiding the expert blind spot while teaching, and a change in schools in China regarding its English teaching method. However, because this is a qualitative case study, when facing a different group of students (other than my participants), these suggestions should be applied selectively

Inkjet Printing of Polarized Yeast Cells

The motivation is to applying engineering knowledge to develop 3D bio-printing in inkjet printer (first stage--monolayer). To achieve the goal, there are three problems to solve. First, we have to figure out regulation of growth of target cells; inability to regulate the location and pattern of growing cells make us even unable to build 3D printer in the direct way. Second problem is how to protect of yeast cells from high temperature and viscous force when printing. The third issue is how to modify the inkjet printer especially the feeding system in order to implement printing on other materials rather than paper. We obtain inspiration that building a synthetic polarization system that include positive feedback and mutual inhibition can generate artificial PIP3 and CDC42 poles in living cells. We program the proper genetic circuit inside yeast that leading polarization in specific spatial position. After building the exogenous polarization network, we found we cannot solve the upward/downward overlap of yeast cells for any ways that difficult to form single layer. The attempt solution of protecting cells is adding certain amount of sugars and salts into medium; as a result viscosity of medium, heat conductivity will decrease meanwhile the medium would not be toxic to yeast cells. The experimental results demonstrate glucose tends to decrease the surface tension of cells that help distribute cells monolayer in the physical way. Result shows yeast cells are growing well in the pattern that being set before printing, meanwhile, they are distributed in monolayer at a high possibility just as expected, the validity supports polarization could be a feasible way in 3D tissue printing

Difficulties of Chinese Students with Their Academic English: Evidence from a China-United States University Program

This study was conducted with four Chinese international students who were enrolled in a China-United States university program. It examined their difficulties in academic English through interviews, and the data were sorted into four categories: listening, speaking, reading, and writing

The study of influence factors in x-ray computed tomography using simulation approach.

XCT simulation scanning was used throughout the study because simulation scanning has the flexibility in changing scanning parameters as well as improving the efficiency. The research investigated the effect of voltage, scattering-contamination and multi-sampling on the quality of 2D image projection. For The study tested factors of scattering-contamination, multi-sampling and cone-beam angle on dimensional measurement error with the numerical geometry samples including spheres, cubes, cylinders and tubes. For cylinders and tubes, the measurement of outer diameter leaded more deviation than inner diameter. Scattering contamination had limited influencing (up to 1/35 of the voxel size) to the measurement result but scattering contamination can amplify the operator factor in the geometry determination step. 3X3 multi-sampling detector could optimise the measurement result when measuring the diameter of the cylinder. On the other hand, the effectiveness of the application of multi-sampling is related to the geometry features for measure, and the effect is independent to the scattering-contamination. When measuring circles on the tube, the cone-beam angle had only slight influence (up to 1/131 of voxel size) on the measurement error.PhD in Manufacturin

De novo Drug Design using Reinforcement Learning with Multiple GPT Agents

De novo drug design is a pivotal issue in pharmacology and a new area of focus in AI for science research. A central challenge in this field is to generate molecules with specific properties while also producing a wide range of diverse candidates. Although advanced technologies such as transformer models and reinforcement learning have been applied in drug design, their potential has not been fully realized. Therefore, we propose MolRL-MGPT, a reinforcement learning algorithm with multiple GPT agents for drug molecular generation. To promote molecular diversity, we encourage the agents to collaborate in searching for desirable molecules in diverse directions. Our algorithm has shown promising results on the GuacaMol benchmark and exhibits efficacy in designing inhibitors against SARS-CoV-2 protein targets. The codes are available at: https://github.com/HXYfighter/MolRL-MGPT.Comment: Accepted by NeurIPS 202

Cosmological Information in Weak Lensing Peaks

Recent studies have shown that the number counts of convergence peaks N(kappa) in weak lensing (WL) maps, expected from large forthcoming surveys, can be a useful probe of cosmology. We follow up on this finding, and use a suite of WL convergence maps, obtained from ray-tracing N-body simulations, to study (i) the physical origin of WL peaks with different heights, and (ii) whether the peaks contain information beyond the convergence power spectrum P_ell. In agreement with earlier work, we find that high peaks (with amplitudes >~ 3.5 sigma, where sigma is the r.m.s. of the convergence kappa) are typically dominated by a single massive halo. In contrast, medium-height peaks (~0.5-1.5 sigma) cannot be attributed to a single collapsed dark matter halo, and are instead created by the projection of multiple (typically, 4-8) halos along the line of sight, and by random galaxy shape noise. Nevertheless, these peaks dominate the sensitivity to the cosmological parameters w, sigma_8, and Omega_m. We find that the peak height distribution and its dependence on cosmology differ significantly from predictions in a Gaussian random field. We directly compute the marginalized errors on w, sigma_8, and Omega_m from the N(kappa) + P_ell combination, including redshift tomography with source galaxies at z_s=1 and z_s=2. We find that the N(kappa) + P_ell combination has approximately twice the cosmological sensitivity compared to P_ell alone. These results demonstrate that N(kappa) contains non-Gaussian information complementary to the power spectrum.Comment: 24 pages, 12 figures, 14 tables. Accepted for publication in PRD (version before proofs