Time-Dependent Density Functional Theory Investigation of the Ground and Excited States of Coumarins 102, 152, 153, and 343

We present calculations of various properties of the ground and excited electronic states of coumarins 102, 152, 153, and 343. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT), we examine the excitation energies to the S1 and S2 states, the ground and excited-state dipole moments, and the lowest ionization potentials of these coumarins. In the case of C153, we locate two distinct S0 minima due to differing conformations of the julolidyl ring structure and compare properties for the syn and anti conformers. For C343, we examine the possibility of proton transfers in the ground and S1 states of the system. We find that (1) DFT tends to overestimate the ground-state dipole moments in these systems, (2) excellent agreement is obtained between TDDFT and experimental vertical excitation energies, (3) TDDFT and CIS yield similar estimates of the dipole moment change between the S0 and S1 states, both of which are in the range of previous experimental estimates, (4) in each case, the S2 state is at least 0.5 eV above the S1 state for the ground-state geometry, and (5) proton transfer is not likely in the ground state of C343 but is only 0.18 eV higher in energy in the S1 state. We also compare the DFT/TDDFT results with RHF/CIS, MP2, and INDO S/CI results. We find good agreement between MP2 and experimental ground-state dipole moments and good agreement between INDO S/CI and TDDFT gas-phase excitation energies

An English Major’s Revelation: Dominican’s Big History Summer Institute

Perhaps English majors are predisposed to appreciate Big History. After all, the epic of our universe is just that: an epic. The longest story ever told. My introduction to Big History came in my last year as an undergraduate at Dominican University of California, when I was given the unique opportunity to provide staff support for the world’s first general education program with Big History as its content

Crop Response to Low-Dose Dicamba

The introduction of dicamba-resistant (DR) soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) followed by a label allowing over-the-top applications of dicamba in the 2017 provided growers an additional option for broadleaf weed control. Because non-DR soybean is sensitive to low concentrations of dicamba, postemergence dicamba applications present growers choosing to plant non-DR soybean with concerns of damage from off-target movement through physical drift and volatilization of the herbicide as well as tank-contamination from prior dicamba application. Consequences of low-dose dicamba exposure on sensitive vegetative and reproductive soybean have been well researched, but little is known regarding the interaction between low-dose dicamba exposure and commonly applied contact herbicides. There is also limited research assessing repercussions caused by dicamba exposure during reproductive development in corn (Zea mays L.) and rice (Oryza sativa L.), two common cereal crops in Arkansas in proximity to soybean and cotton. Experiments included evaluating the potential for dicamba to elicit a hormetic response to sensitive soybean, determining if contact herbicides exacerbated off-target dicamba symptomology, and evaluating potential for low-dose dicamba exposure on reproductive corn and rice to reduce grain yield. Low doses of dicamba did not improve soybean grain yield, which indicates a hormetic response is unlikely. Contact herbicides such as glufosinate and acifluorfen applied in close proximity to a low dose of dicamba increased visible auxin symptomology to soybean at 21 and 28 days after treatment (DAT) compared to dicamba alone, but no effect on grain yield occurred. Soybean was injured more when dicamba exposure followed a glufosinate application than when dicamba preceded glufosinate or was applied in a mixture with glufosinate, with yield reductions resulting when the contact herbicide was applied 7 to 10 days after a V3 dicamba exposure. Visible injury to corn from dicamba was negligible (0%), but rice treated with dicamba at 56 and 560 g ae ha-1 demonstrated auxin symptomology which led to reductions in grain yield. Corn grain yield could only be reduced from dicamba at 560 g ae ha-1. In conclusion, dicamba tank-contamination and possibly off-target movement pose a greater threat to sensitive soybean regarding visible symptomology and yield as opposed to corn and rice, and it is unlikely that soybean exposure to low-dose dicamba will improve grain yields

Evidence of the virtual Anderson transition in a narrow impurity band of p-GaAs/AlGaAs quantum wells: ϵ4\epsilon_4 conductivity and electric breakdown at low temperatures

In highly doped uncompensated p-type layers within the central part of GaAs/AlGaAs quantum wells at low temperatures we observed an activated behavior of the conductivity with low activation energies (1-3) meV which can not be ascribed to standard mechanisms. We attribute this behavior to the delocalization of hole states near the maximum of the narrow impurity band in the sense of the Anderson transition. Low temperature conduction $\epsilon_4$ is supported by an activation of minority carriers - electrons (resulting from a weak compensation by back-ground defects) - from the Fermi level to the band of delocalized states mentioned above. The corresponding behavior can be specified as virtual Anderson transition. Low temperature transport ($<4$ K) exhibits also strong nonlinearity of a breakdown type characterized in particular by S-shaped I-V curve. The nonlinearity is observed in unexpectedly low fields ($<10$ V/cm). Such a behavior can be explained by a simple model implying an impact ionization of the localized states of the minority carriers mentioned above to the band of Anderson-delocalized states.Comment: 9 pages, 6 fi

Analysis of Plume Effects on Sonic Boom Signature for Isolated Nozzle Configurations

Computational fluid dynamics (CFD) analysis has been performed to study the plume effects on sonic boom signature for isolated nozzle configurations. The objectives of these analyses were to provide comparison to past work using modern CFD analysis tools, to investigate the differences of high aspect ratio nozzles to circular (axisymmetric) nozzles, and to report the effects of underexpanded nozzle operation on boom signature. CFD analysis was used to address the plume effects on sonic boom signature from a baseline exhaust nozzle. Near-field pressure signatures were collected for nozzle pressure ratios (NPRs) between 6 and 10. A computer code was used to extrapolate these signatures to a ground-observed sonic boom N-wave. Trends show that there is a reduction in sonic boom N-wave signature as NPR is increased from 6 to 10. The performance curve for this supersonic nozzle is flat, so there is not a significant loss in thrust coefficient as the NPR is increased. As a result, this benefit could be realized without significant loss of performance. Analyses were also collected for a high aspect ratio nozzle based on the baseline design for comparison. Pressure signatures were collected for nozzle pressure ratios from 8 to 12. Signatures were nearly twice as strong for the two-dimensional case, and trends also show a reduction in sonic boom signature as NPR is increased from 8 to 12. As low boom designs are developed and improved, there will be a need for understanding the interaction between the aircraft boat tail shocks and the exhaust nozzle plume. These CFD analyses will provide a baseline study for future analysis efforts

The mechanical behavior of cross-rolled beryllium sheet

In response to the failure of a conical section of the Insat C satellite during certification testing, the use of beryllium for payload structures, particularly in sheet product form, is being reevaluated. A test program was initiated to study the tensile, shear, and out-of-plane failure modes of beryllium cross-rolled sheet and to apply data to the development of an appropriate failure criterion. Tensile test results indicated that sanding the surface of beryllium sheet has no significant effect on yield strength but can produce a profound reduction in ultimate strength and results obtained by finite element analysis. Critical examination of these test results may contribute to the modification of a JSC policy for the use of beryllium in orbiter and payload structures

The Political Economy of Preferential Trade Agreements

This dissertation is comprised of three chapters on preferential trade agreements (PTAs). The first two chapters examine why countries sign PTAs with other countries, while the final chapter studies the effect of PTAs on imports. The first chapter provides direct empirical evidence that PTAs are consistent with the terms-of-trade theory. In other words, PTAs internalize the temptation to increase tariffs when countries possess importer market power. Using PTAs that occur between 2001-2015, I study the formation of PTAs and the structure of first year PTA tariff cuts. I first show the likelihood of a PTA increases when both countries have more importer market power. This suggests countries form PTAs in a way that internalizes the terms-of-trade externality by agreeing to mutual tariff decreases. Second, using recently available tariff data for 39 bilateral PTAs, I show high importer market power leads to tariff cuts that are 103 percent larger in magnitude when PTAs enter into force. Thus, countries target tariffs they have a strong temptation to raise in the absence of an agreement, as predicted by the terms-of-trade theory. These results provide a rationale for why PTAs are allowed under the World Trade Organization\u27s rules. The second chapter focuses on an alternative rationale for PTAs by examining the empirical relationship between trade agreements and domestic labor mobility. The domestic-commitment motive from Maggi and Rodriguez-Clare (2007) and standard trade models with labor frictions predict that trade liberalization should occur when labor is more mobile. I find support for this prediction. Using PTAs covering 56 countries in 2015, I show labor mobility is a strong predictor of trade liberalization. The probability of a PTA increases when the country pair\u27s average domestic labor market is less rigid. When the average labor mobility increases by 1 standard deviation from the mean, the probability of a PTA increases by 14-26 percent. These results are also consistent with results on the bound tariffs negotiated under the World Trade Organization, where less rigid labor markets are associated with lower bound tariffs. The final chapter, co-authored with Xiuming Dong, estimates the causal effect of phase-in tariffs on import growth for 11 PTAs signed by the United States between 2000-2007. The phase-in hypothesis from Baier and Bergstrand (2007) implies that products with longer periods of tariff cuts should experience slower and longer periods of import growth relative to unchanged tariffs. Using recently available PTA tariff data, we extend the work of Besedes et al. (2020) and utilize a triple-difference strategy to provide additional evidence that import growth is not consistent with the phase-in hypothesis. We show that phase-in tariffs do not necessarily yield additional import growth relative to already duty-free products. Our analysis documents the average effect of phase-in tariffs and PTA-specific trends