Computational design of new scintillator chemistries and defect structures

The focus of this thesis is computationally designing inorganic scintillators previously predicted by informatics, which have not been validated computationally. Density Functional Theory (DFT) calculations were performed to (1) select garnet host lattices that are good scintillators, thereby down selecting from compounds previously identified via informatics, and (2) identify co-dopant chemistries in perovskites which enhance scintillator property. In this thesis, the property of focus is bandgap, which in general has an inverse correlation to light yield. The total energy code Cambridge Sequential Total Energy Package (CASTEP) was used for performing DFT calculations, taking advantage of its speed in modeling the electronic structure of the complex inorganic scintillators. From our calculations, Tb3Al2Ga3O12 was identified as forming a stable garnet structure and having a modeled direct bandgap corresponding with light yield better than other similar garnet host lattices. Further, from our calculations, we find four co-dopant chemistries which improve the bandgap from singly doped perovskites

Masses and decay constants of pions and kaons in mixed-action staggered chiral perturbation theory

Lattice QCD calculations with different staggered valence and sea quarks can be used to improve determinations of quark masses, Gasser-Leutwyler couplings, and other parameters relevant to phenomenology. We calculate the masses and decay constants of flavored pions and kaons through next-to-leading order in staggered-valence, staggered-sea mixed-action chiral perturbation theory. We present the results in the valence-valence and valence-sea sectors, for all tastes. As in unmixed theories, the taste-pseudoscalar, valence-valence mesons are exact Goldstone bosons in the chiral limit, at non-zero lattice spacing. The results reduce correctly when the valence and sea quark actions are identical, connect smoothly to the continuum limit, and provide a way to control light quark and gluon discretization errors in lattice calculations performed with different staggered actions for the valence and sea quarks.Comment: 8 pages, 9 figures, extended with more explanation. arXiv admin note: text overlap with arXiv:1311.626

Kaon mixing matrix elements from beyond-the-Standard-Model operators in staggered chiral perturbation theory

Models of new physics induce K-Kbar mixing operators having Dirac structures other than the "left-left" form of the Standard Model. We calculate the functional form of the corresponding B-parameters at next-to-leading order in both SU(3) and SU(2) staggered chiral perturbation theory (SChPT). Numerical results for these matrix elements are being generated using improved staggered fermions; our results can be used to extrapolate these matrix elements to the physical light and strange quark masses. The SU(3) SChPT results turn out to be much simpler than that for the Standard Model B_K operator, due to the absence of chiral suppression in the new operators. The SU(2) SChPT result is of similar simplicity to that for B_K. In fact, in the latter case, the chiral logarithms for two of the new B-parameters are identical to those for B_K, while those for the other two new B-parameters are of opposite sign. In addition to providing results for the 2+1 flavor theory in SU(3) SChPT and the 1+1+1 flavor theory in SU(2) SChPT, we present the corresponding continuum partially quenched results, as these are not available in the literature.Comment: 16 pages, 3 figures. Typos corrected--published versio

Built Environment Factors Influencing Walking to School Behaviors: A Comparison between a Small and Large US City

Citation: Kim HJ and Heinrich KM (2016) Built Environment Factors Influencing Walking to School Behaviors: A Comparison between a Small and Large US City. Front. Public Health 4:77. doi: 10.3389/fpubh.2016.00077A growing body of evidence supports the association between the built environment and children walking to school (WTS), but few studies have compared WTS behaviors in cities of different sizes. This case-comparison study utilized WTS data from fourth graders in the small city of Manhattan, KS, USA (N = 171, from all eight schools) and data from fourth graders in the large city of Austin, TX, USA (N = 671 from 19 stratified-sampled schools). The same survey instrument was used in both locations. After controlling for socioeconomic and demographic variables, built environment, neighborhood, and attitudinal differences were demonstrated by the odds ratios for WTS in the small city vs. the large city. WTS in the small city was more likely to be associated with walking paths/trails and sidewalk landscape buffers en route to school despite lower perceived neighborhood social cohesion, school bus availability, and parental concerns about crime, compared to WTS in the large city. Also, the small city lacked key pedestrian infrastructure elements that were present in the large city. This study highlights important differences related to WTS behaviors and, thus, provides key insights for encouraging WTS in cities of different sizes

Built Environment Factors Influencing Walking to School Behaviors: A Comparison between a Small and Large US City

Citation: Kim HJ and Heinrich KM (2016) Built Environment Factors Influencing Walking to School Behaviors: A Comparison between a Small and Large US City. Front. Public Health 4:77. doi: 10.3389/fpubh.2016.00077A growing body of evidence supports the association between the built environment and children walking to school (WTS), but few studies have compared WTS behaviors in cities of different sizes. This case-comparison study utilized WTS data from fourth graders in the small city of Manhattan, KS, USA (N = 171, from all eight schools) and data from fourth graders in the large city of Austin, TX, USA (N = 671 from 19 stratified-sampled schools). The same survey instrument was used in both locations. After controlling for socioeconomic and demographic variables, built environment, neighborhood, and attitudinal differences were demonstrated by the odds ratios for WTS in the small city vs. the large city. WTS in the small city was more likely to be associated with walking paths/trails and sidewalk landscape buffers en route to school despite lower perceived neighborhood social cohesion, school bus availability, and parental concerns about crime, compared to WTS in the large city. Also, the small city lacked key pedestrian infrastructure elements that were present in the large city. This study highlights important differences related to WTS behaviors and, thus, provides key insights for encouraging WTS in cities of different sizes