50 ECONOMIC FACTS AND FIGURES ABOUT KENTUCKY, 2020

50 ECONOMIC FACTS AND FIGURES ABOUT KENTUCKY, 202

Ages of Type Ia Supernovae Over Cosmic Time

We derive empirical models for galaxy mass assembly histories, and convolve these with theoretical delay time distribution (DTD) models for Type Ia supernovae (SNe Ia) to derive the distribution of progenitor ages for all SNe Ia occurring at a given epoch of cosmic time. In actively star-forming galaxies, the progression of the star formation rate is shallower than a $t^{-1}$ SN Ia DTD, so mean SN Ia ages peak at the DTD peak in all star-forming galaxies at all epochs of cosmic history. In passive galaxies which have ceased star formation through some quenching process, the SN Ia age distribution peaks at the quenching epoch, which in passive galaxies evolves in redshift to track the past epoch of major star formation. Our models reproduce the SN Ia rate evolution in redshift, the relationship between SN Ia stretch and host mass, and the distribution of SN Ia host masses in a manner qualitatively consistent with observations. Our model naturally predicts that low-mass galaxies tend to be actively star-forming while massive galaxies are generally passive, consistent with observations of galaxy "downsizing". Consequently, the mean ages of SNe Ia undergo a sharp transition from young ages at low host mass to old ages at high host mass, qualitatively similar to the transition of mean SN Ia Hubble residuals with host mass. The age discrepancy evolves with redshift in a manner currently not accounted for in SN Ia cosmology analyses. We thus suggest that SNe Ia selected only from actively star-forming galaxies will yield the most cosmologically uniform sample, due to the homogeneity of young SN Ia progenitor ages at all cosmological epochs.Comment: 15 pages, 15 figures, accepted for publication in MNRA

Narrow frequency-band laser with optical feedback

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 24).In this paper we discuss the construction of a narrow frequency-band laser with optical feedback. We use a distributed Bragg reflector (DBR) laser diode centered at the cesium D₂ transition wavelength, [gamma] = 852 nm. The linewidth of this diode is reduced by several orders of magnitude by means of optical feedback from an external cavity. The system is further stabilized by locking the path length between diode and cavity to optimize coupling between them. The absolute frequency of our laser is fixed by means of a delay line lock system that uses the beat note between our laser and a fixed reference laser to set our laser's frequency. We present both the theory behind these systems and data from our own setup. We then finally discuss potential uses of the narrow laser in atomic physics experiments, including detection of a single atom in an optical cavity.by Michael J. Childress.S.B

Going with the flow: Forecasting the impact of climate change on blue crabs

2014 S.C. Water Resources Conference - Informing Strategic Water Planning to Address Natural Resource, Community and Economic Challenge

Kentucky School Districts as Educational Bright Spots

Every year a select group of Kentucky school districts perform better than expected on measures of educational achievement. These measures include things like the percentage of elementary students who achieve proficiency or distinguished in reading, or the proportion of less‐advantaged middle school students who show a similar level of competency on the math assessment. There are wide differences in the learning environments, finances, and student outcomes among and within Kentucky’s 173 school districts. This is not surprising given that the largest school district in the state, Jefferson County, has 97,000 students and 165 schools, while the smallest, West Point Independent in Hardin County, has one school with 120 students. Since school districts are likely to reflect the underlying economic conditions of their surrounding communities, the socioeconomic characteristics of Kentucky’s school districts are as diverse as the state itself. Similarly, student outcomes are also widely distributed across the state’s 173 districts. From this broad range of student outcomes, family and community backgrounds, and school district characteristics, we identify districts that have performed better than expected—which we refer to as “bright spots.

Kentucky Public Schools as Educational Bright Spots (September 2020)

Understanding the reasons for better‐than‐expected performance across Kentucky\u27s 173 school districts, taking into account student outcomes, backgrounds, and school district characteristics. Building on the previous work with school districts and using school-level data, this paper discusses the estimated expected level of school-level performance using district-level fixed effects. From this broad range of student outcomes, family and community backgrounds, and school characteristics, we identify schools that have performed better than expected—which we refer to as “bright spots.

Modeling the Impact of Drought on South Carolina Blue Crabs Using a Spatially-Explicit Individual-Based Population Model

2010 S.C. Water Resources Conferences - Science and Policy Challenges for a Sustainable Futur

Kentucky\u27s Educational Performance & Points of Leverage

This issue brief explores the links between obstacles students face and educational outcomes