Association between PM 2.5 in Minnesota and Influencing Factors: Tree Space Area, Road Pollution, and Rainfall

The purpose of this paper is trying to use air monitoring data of Particulate Matter (PM 2.5) from 19 monitoring sites in Minnesota, to determine the correlations between PM 2.5 and the influencing factors, such as road traffic, tree space area, and rainfall. The study will be based on pollutant data which were from Environment Protection Agency (EPA) and Minnesota Pollution Control Agency (MPCA), then through regression analysis and Pearson correlation analysis to determine the correlations of all variables. The correlation analysis results between PM 2.5 concentration and three variables (tree space area, traffic volume, and rainfall) showed that tree space area ratio had a negative, traffic volume had a positive and rainfall had a negative, correlation with PM 2.5 in Minnesota urban. The air traffic volume had a positive correlation with PM 2.5 in airport areas. In this study, GIS system is a useful tool for geostatistical analysis. It can be used for Normalized Difference Vegetation Index (NDVI) analysis, raster data geoprocessing, and kriging spatial analysis

Few-photon single ionization of cold rubidium in the over-the-barrier regime

Photoionization of the rubidium (Rb) atoms cooled in a magneto-optical trap, characterized by the coexistence of the ground 5$S_{1/2}$ and the excited 5$P_{3/2}$ states, is investigated experimentally and theoretically with the 400 nm femtosecond laser pulses at intensities of $I=3\times10^9$ W/cm$^2$ - $4.5\times10^{12}$ W/cm$^2$. Recoil-ion momentum distribution (RIMD) of Rb$^+$ exhibits rich ring-like structures and their energies correspond to one-photon ionization of the 5$P_{3/2}$ state, two-photon and three-photon ionizations of the 5$S_{1/2}$ state, respectively. With the increasing of $I$, we find that experimental signals near zero-momentum (NZM) in RIMDs resulted from the 5$P_{3/2}$ state enhance dramatically and its peaked Rb$^+$ momenta dwindle obviously while that from the 5$S_{1/2}$ state is maintained. Meanwhile, the ion-yield ratio of the 5$S_{1/2}$ over the 5$P_{3/2}$ states varies from $I$ to $I^{1.5}$ as $I$ increases. These features indicate a transition from perturbative ionization to strong-perturbative ionization for the 5$P_{3/2}$ state. Numerical simulations by solving the time-dependent Schr\"odinger equation (TDSE) can qualitatively explain the measurements of RIMD, photoion angular distributions, as well as ion-yield ratio. However, some discrepancies still exist, especially for the NZM dip, which could stem from the electron-electron correlation that is neglected in the present TDSE simulations since we have adopted the single-active-electron approximation

Ellipticity-dependent sequential over-barrier ionization of cold rubidium

We perform high-resolution measurements of momentum distribution on Rb$^{n+}$ recoil ions up to charge state $n=4$, where laser-cooled rubidium atoms are ionized by femtosecond elliptically polarized lasers with the pulse duration of 35 fs and the intensity of 3.3$\times$10$^{15}$ W/cm$^2$ in the over-barrier ionization (OBI) regime. The momentum distributions of the recoil ions are found to exhibit multi-band structures as the ellipticity varies from the linear to circular polarizations. The origin of these band structures can be explained quantitatively by the classical OBI model and dedicated classical trajectory Monte Carlo simulations with Heisenberg potential. Specifically, with back analysis of the classical trajectories, we reveal the ionization time and the OBI geometry of the sequentially released electrons, disentangling the mechanisms behind the tilted angle of the band structures. These results indicate that the classical treatment can describe the strong-field multiple ionization processes of alkali atoms

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Gold nanoparticles-modified titanium dioxide photoelectrode by screenprinting techniques

Over the recent years, the discussion over environmental issues has been heated, especially due to the abnormal weather conditions and disasters which were being linked to greenhouse gases and global warming as the main causes. However the root of the problem is human use of non-renewable resources and the use of clean energy such as hydrogen has to be encouraged in order to solve the problem. There have been active research ongoing ever since a paper on photo electrolysis had been released in 1972 by Fukushima and Honda and the efficiency of the current water splitting process can still be further improved on so that its adoption will be more cost effective. For this experiment, Titanium Dioxide (TiO2) photoelectrode and spherical gold nanoparticles will be focused on and screen printing methodology will be used for the fabrication stage of modified TiO2 photo-electrodes. In the experiment, the two independent variables will be the particle sizes of the nanoparticles to be used and the amount of nanoparticles to be used. The dependent variables to be observed will be photocurrent density, reflectance and photocurrent conversion efficiency (PCE). The common controlled variables for the two independent variables include the apparatus to be used for the experiment, the intensity of the light source, the amount of TiO2 to be added, mixture stirring rate, curing temperature and curing time. An additional controlled variable for the first independent variable is the amount of nanoparticles used while that for the second independent variable is the particle size of the nanoparticles. The experimental results have been promising as it showed improvement to the efficiency of the TiO2 photo-electrode when sufficient amount of gold nanoparticles has been added and the larger the diameter of the nanoparticles is, the better the performance of the photo-electrode will be. On the contrary, if the amount of the 50 nanometres (nm) gold nanoparticles is at 1520 microliters (uL), the performance of the photo-electrode will decrease instead. This discovery will lead to further works to be done in the future where research towards the addition of noble nanoparticles such as silver or gold nanoparticles to metal oxides photo-electrodes can be focused on and perhaps lead to other significant improvements to the efficiency level of the water splitting process, promoting the use of clean energy to companies will therefore be easier.Bachelor of Engineering (Mechanical Engineering

Dark modes governed by translational-symmetry-protected bound states in the continuum in symmetric dimer lattices

Creating nonradiating dark modes is key to achieving high-Q resonance in dielectric open cavities. The concept of photonic bound states in the continuum (BIC) offers an efficient method to suppress radiative loss through symmetry engineering. Structural reflection symmetry (RS) has been widely utilized to construct BICs in asymmetric metasurfaces. In this paper, we show that the radiation channel of translational-symmetry (TS) protected BIC in 1D symmetric dimer lattice could be unlocked by dimer spacing perturbation. A semi-analytical coupled mode analysis reveals that the total radiation suppression of the TS-BIC is due to the elimination of the first Fourier harmonic component in the lattice parameters. TS-BIC mechanism could also be applied in a 2D symmetric dimer lattice, and BICs protected by TS are robust to RS breaking, and vice versa, providing a promising way to independently control the quality factor of two interacting BIC resonances. Our results suggest a new degree of freedom to engineer BICs as well as their interactions in dimer lattices tailored by different symmetries, and could provide new insight for realizing practical applications requiring high-Q resonances

Fabrication of Crystalline Si Thin Films for Photovoltaics

Crystalline Si (c‐Si) thin films have been widely studied for their application to solar cells and flexible electronics. However, their application at large scale is limited by their fabrication process. As reviewed in this paper, many approaches have been studied, but only some of them have been made into large‐scale industrial production. The standard wire sawing of Si ingots cannot be scaled down to produce thin c‐Si wafers and films due to the brittle nature of c‐Si material, the resulting significant thickness variations, and the waste of material. Therefore, techniques based on the kerf‐less processes including “top‐down” and “bottom‐up” approaches have been developed in recent decades. In this review, photovoltaic applications of thin c‐Si wafers with thicknesses ranging from 50 μm down to 1 μm are presented first. Then, methods to fabricate c‐Si thin films based on both approaches are detailed, including slim‐cut, “smart‐cut,” epi‐free, as well as various growth processes such as molecular beam epitaxy, liquid phase epitaxy, ion beam, and chemical vapor deposition processes at a wide range of growth temperatures, from 1000 °C down to 150 °C. The advantages and disadvantages of these methods are presented and compared