Groupoid equivalence and the associated iterated crossed product

Given groupoids $G$ and $H$ and a $(G,H)$-equivalence $X$ we may form the transformation groupoid $G\ltimes X\rtimes H$. Given a separable groupoid dynamical system $(A,G\ltimes X\rtimes H,\omega)$ we may restrict $\omega$ to an action of $G\ltimes X$ on $A$ and form the crossed product $A\rtimes G\ltimes X$. We show that there is an action of $H$ on $A\rtimes G\ltimes X$ and that the iterated crossed product $(A\rtimes G\ltimes X)\rtimes H$ is naturally isomorphic to the crossed product $A\rtimes (G\ltimes X\rtimes H)$.Comment: 18 pages; changed typo in titl

Are There Differential Effects of Price and Policy on College Students' Drinking Intensity?

This paper investigates whether college students' response to alcohol price and policies differ according to their drinking intensity. Individual level data on drinking behavior, price paid per drink, and college alcohol policies come from the student and administrator components of the 1997 and 1999 waves of the Harvard School of Public Health (HSPH) College Alcohol Study (CAS). Students drinking behavior is classified on the basis of the number of drinks they typically consume on a drinking occasion, and the number of times they have been drunk during the 30 days prior to survey. A generalized ordered logit model is used to determine whether key variables impact differentially the odds of drinking and the odds of heavy drinking. We find that students who faced a higher money price for alcohol are less likely to make the transition from abstainer to moderate drinker and moderate drinker to heavy drinker, and this effect is equal across thresholds. Campus bans on the use of alcohol are a greater deterrent to moving from abstainer to moderate drinker than moderate drinker to heavy drinker.

Photophysical And Photochemical Factors Affecting Multi-photon Direct Laser Writing Using The Cross-linkable Epoxide Su-8

For the past decade, the epoxy based photoresist SU-8 has been used commercially and in the lab for fabricating micro- and nano-structures. Investigators have studied how processing parameters such as pre- and post-exposure bake temperatures affect the resolution and quality of SU-8 structures patterned using ultraviolet or x-ray lithography. Despite the advances in understanding the phenomena, not all of them have been explored, especially those that are specific to multi-photon direct laser writing (mpDLW). Unlike conventional exposure techniques, mpDLW is an inherently three-dimensional (3D) process that is activated by nonlinear absorption of light. This dissertation reports how several key processing parameters affect mpDLW using SU-8 including pre-exposure bake duration, focal depth, incident laser power, focal-point scan speed, and excitation wavelength. An examination of solvent content of films at various stages in the mpDLW by 1H-NMR shows that even moderate solvent content (over 1 wt-%) affects film viscosity and photoacid diffusion lengths, and can greatly affect the overall fidelity of small features. A study of micro-fabricated feature size versus writing depth in the material shows that even slight refractive index mismatch between SU-8 and the medium between it and the focusing objective introduces spherical aberration that distorts the focus, causing feature size to decrease or even increase in size with writing depth, depending on the average exposure power used. Proper adjustment of the average exposure power was demonstrated as a means to fabricate more uniform features with writing depth. Third, when varying the power and scan speed, it was observed that the feature-size scales with these two parameters in a manner that is consistent with a three-photon absorption mechanism at an excitation wavelength of 800 nm. When an iii excitation wavelength of 725 nm is used, the feature-size scaling becomes consistent with that of two photon absorption. This shows that the photoinitiators in the SU-8 can be activated by either two- or three-photon absorption over this wavelength range. Using an irradiance of ~2 TW cm-2 and elongated femtosecond pulses resulted in an observed fourth order power dependence. This observation is in agreement with the literature and suggests that the effective absorptive nonlinearity is also sensitive to pulse duration. These findings will be useful for creating accurate models of the process of mpDLW in SU-8. These models could be used to optimize the processing parameters and develop new processing methods and materials for high-resolution fabrication of robust 3D microstructures. Some of the findings were used to develop a method for fabricating functional microlenses on the tip of optical fibers. This approach opens a new route to functional integrated photonic devices

Black Business Owners Overcoming Barriers in Texas

Black entrepreneurs in the state of Texas reported that they did not achieve the same level of success as nonminority enterprises. Many Black entrepreneurs have obtained education from top tier institutions and have the managerial experiences, skills, and working knowledge that facilitate business success, but they are not able to sustain business growth. The purpose of this phenomenological study was to explore the lived experiences of Black Texan entrepreneurs. This research was established using the conceptual framework of human capital. The overarching research question concerned the lived experiences of Black Texas entrepreneurs who were not as successful in business as their counterparts. Data were collected in the form of semistructured face-to-face interviews with 14 Black participants, using the African American Chamber of Commerce to facilitate networking among Black entrepreneurs. NVivo 11 software was used for data codification and thematic reduction. Emergent themes included (a) feeling good about being in business, (b) resourcefulness in business, (c) network advertising systems, (d) education, (e) having alternative plans if business closes, (f) feeling independent, and (g) activeness in business. The implications for positive social change include the potential for advising researchers on barriers confronted by Black entrepreneurs and potential steps to overcome those barriers. Additionally, scholars have recognized the need for greater understanding of how businesses are structured and managed by Black business-owners because this knowledge is vital to creating business prosperity for Black entrepreneurs who have dreams of becoming business owners

Electricity sector emissions and expanding renewable energy in Colorado

Includes bibliographical references

Painted Snipe observations

Volume: XXII