Preliminary feasibility analysis of a pressure modulator radiometer for remote sensing of tropospheric constituents

A pressure modulator radiometer operated in a nadir viewing mode from the top of a midlatitude summer model of the atmosphere was theoretically studied for monitoring the mean volumetric mixing ratio of carbon monoxide in the troposphere. The mechanical characteristics of the instrument on the Nimbus 7 stratospheric and mesospheric sounder experiment are assumed and CO is assumed to be the only infrared active constituent. A line by line radiative transfer computer program is used to simulate the upwelling radiation reaching the top of the atmosphere. The performance of the instrument is examined as a function of the mean pressure in and the length of the instrument gas correlation cell. Instrument sensitivity is described in terms of signal to noise ratio for a 10 percent change in CO mixing ratio. Sensitivity to mixing ratio changes is also studied. It is concluded that tropospheric monitoring requires a pressure modulator drive having a larger swept volume and producing higher compression ratios at higher mean cell pressures than the Nimbus 7 design

Adaptation and optimization of a line-by-line radiative transfer program for the STAR-100 (STARSMART)

A program to calculate upwelling infrared radiation was modified to operate efficiently on the STAR-100. The modified software processes specific test cases significantly faster than the initial STAR-100 code. For example, a midlatitude summer atmospheric model is executed in less than 2% of the time originally required on the STAR-100. Furthermore, the optimized program performs extra operations to save the calculated absorption coefficients. Some of the advantages and pitfalls of virtual memory and vector processing are discussed along with strategies used to avoid loss of accuracy and computing power. Results from the vectorized code, in terms of speed, cost, and relative error with respect to serial code solutions are encouraging

Equity Issues in Dual Enrollment Programs: Exploring African American Community College Students’ Perceptions of Dual Enrollment

Dual enrollment has been shown to increase post-secondary student success outcomes across a variety of measures such as retention, grade point average, and four-year attainment (Allen & Dadgar, 2012; Hoffman, 2012, Pretlow & Wathington, 2014). In Virginia, access to community colleges among students of color has increased from 32.3% in 2008 to 42.7% in 2018 (SCHEV, 2019-a). Despite these gains, far fewer African American students than White students participate in dual enrollment in Virginia, which has significant implications for their future success in post-secondary education. This study examined the experiences that influenced African American students’ choice to participate in dual enrollment, and the implications of these experiences. Using a phenomenological approach, this study sought to gain insight and understanding of the lived experiences of African American dual enrollment students. The findings from this study described African American high school students’ perceptions as they moved from awareness of dual enrollment to interest in dual enrollment to acting on a choice to dual enroll. The students’ experiences highlighted a lack of awareness and a belief that dual enrollment is more for White students. Despite this, the students identified the positive factors in participating, such as improving their GPA, getting a head start on college, and saving money. The students who were undecided about their post-secondary plans prior to participating in dual enrollment credit that experience with their decision to enroll in college

Advances in Hydroboration: Metal-Free Oxygen-Directed Hydroboration and Asymmetric Hydroboration with N-Tosyl-(R,R)-2,6-diisopropyl-1,4-borazinane.

The work described herein addresses two unresolved issues in the hydroboration literature: 1) The regioselective hydroboration of 1,2-disubstituted olefins, and 2) the asymmetric hydroboration of prochiral olefins. Metal-free oxygen-directed hydroboration of 1,2-disubstituted olefins in homoallylic alcohols, lithium alkoxides, and ethers has been achieved using triflic acid-activated dimethylsulfide•borane conditions building on previous work in the Vedejs group involving homoallylic amine-directed hydroboration. Optimization provided a pre-activation approach to generate TfOBH2 that provides 1,3-diols from alcohols and alkoxides with excellent regioselectivity (>20:1) upon oxidative workup. An in situ approach to TfOBH2 provides optimal results in the case of homoallylic ethers, including allyl ethers, which afford monoprotected 1,3-diols upon oxidative workup. The originally envisioned mechanistic pathway for these transformations, in which the generation of a TfOBH2-oxygen complex enables intramolecular SN2-like boron-alkene complexation, can account for the regioselectivity, and the observation that homoallylic alcohols are preferentially hydroborated in the presence of excess cyclohexene is consistent with this mechanism. However, diastereoselectivity remains elusive, indicating that the mechanism of oxygen-directed hydroboration (ODHB) is not straightforward. Mechanistic studies have provided little insight into the pathway(s) leading to the regioselective, yet non-diastereoselective transformations. Oxygen-directed hydroboration remains an enigmatic phenomenon, in general. N-Tosyl-(R,R)-2,6-diisopropyl-1,4-borazinane, the first C2-symmetric borane incorporated into a 2,6-disubstituted-six-membered boracycle, has been generated in pursuit of an asymmetric hydroborating reagent that is capable of achieving excellent enantioselectivity on all four types of prochiral alkenes. Masamune’s (R,R)-2,5-dimethylborolane is the single most versatile asymmetric hydroborating agent in the literature, and serves as both inspiration and measuring stick for this work. The synthesis of N tosyl-(R,R)-2,6-diisopropyl-1,4-borazinane is streamlined compared with the preparation of Masamune’s borolane, thanks to diastereoselective boracycle formation, successful resolution of trans-borazinane enantiomers via alanine complexation/crystallization, and a one-pot hydroboration procedure from the diastereo-enriched alanine complex. On the other hand, N tosyl-(R,R)-2,6-diisopropyl-1,4-borazinane only achieves good enantioselectivity (86% ee) with cis-1,2-disubstituted (Type II) alkenes. This is more reminiscent of Brown’s diisopinocampheylborane than of Masamune’s borolane, which provides superior enantioselectivity with cis- and trans-1,2-disubstitued (Type II and III) and trisubstituted (Type IV) alkenes.Ph.D.ChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78851/1/rarig_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/78851/2/rarig_1.pd

Ammonium tris­(tetra­ethyl­ammonium) hexa­cosa­oxidoocta­molybdate

The structure of the title compound, NH4(C8H20N)3[Mo8O26], is built up by discrete cations and anions, with two formula units in the asymmetric unit. The β-octa­molybdate anions are linked to the ammonium cations via N—H⋯O hydrogen bonding involving terminal oxide groups and to the tetra­ethyl­ammonium cations via weak C—H⋯O inter­actions

Essays on local matching

The standard two-sided matching model with search frictions is extended to allow for geographic dispersion. The encounter technology is biased towards local meetings, so that agents are more likely to meet other agents who are closer to themselves than those who are far away. Steady state equilibria exist and result in otherwise identical agents receiving different equilibrium payoffs. This inequality occurs because offer distributions are specific to location, making agents\u27 reservation strategies depend not only on their own type but also on the location from which they are searching. Applications to the labor and marriage markets are explored

Regulatory effects on the ecology of organizational mortality of home health agencies in Massachusetts

Changes in the regulatory environment and in resource availability are thought to have had differential impact on home health agencies of different types over the period since Medicare and Medicaid were implemented in 1966. This study uses survival analysis methods including the proportional hazards model to examine an administrative data base of annual survey data for 199 agencies that reported to the Massachusetts Department of Public Health between 1975 and 1986 to examine the following: (1) to see if the major regulatory change imposing the Medicare uniform cost report on all home health agencies resulted in greater hazard rates in the period 1977-1980, (2) to see if organizational mortality rates were higher for public agencies than for free-standing non-profit agencies, and (3) to see if organizational characteristics such as size and scope of services, or locational characteristics such as rurality or poverty level accounted for differences. Results indicate that hazard of failure is inversely proportional to size, and that when size and other variables are controlled, the crude differences in the failure rates of public and non-profit agencies are greatly reduced. Data on proprietary and hospital-based agencies were insufficient for comparative analysis. Hazard ratios indicated that small agencies faced hazard of failure about three times that of larger agencies, controlling for other variables. Failure rates increased in the four year period between passage and actual implementation of the uniform cost report requirement. However, time dependence of the hazard rates appeared insufficient to require inclusion in the modelling process. The period of observation was too short and the population of agencies too small to assess the mortality rate impact of resource constraints in the middle 1980s. Empirical evidence was consistent with the hypotheses that small agencies were at risk during the period when regulatory changes imposed a major administrative requirement and constrained reimbursement options. Rural location, broader scope of services and more specialists had protective effects on agencies. Hypothesized protective effects of variables thought to be associated with community support were found to be of borderline significance, but these possible associations require further study. The proportional hazard regression method provided a useful tool for analyzing an administrative data base with time series data on health care organizations