Miami University

About: Miami University is a education organization based out in Oxford, Ohio, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 9949 authors who have published 19598 publications receiving 568410 citations. The organization is also known as: Miami of Ohio & Miami-Ohio.

On the impossibility of dimension reduction in l1

Abstract: The Johnson--Lindenstrauss lemma shows that any n points in Euclidean space (i.e., ℝn with distances measured under the e2 norm) may be mapped down to O((log n)/e2) dimensions such that no pairwise distance is distorted by more than a (1 p e) factor. Determining whether such dimension reduction is possible in e1 has been an intriguing open question. We show strong lower bounds for general dimension reduction in e1. We give an explicit family of n points in e1 such that any embedding with constant distortion D requires nΩ(1/D2) dimensions. This proves that there is no analog of the Johnson--Lindenstrauss lemma for e1; in fact, embedding with any constant distortion requires nΩ(1) dimensions. Further, embedding the points into e1 with (1pe) distortion requires nh−O(e log(1/e)) dimensions. Our proof establishes this lower bound for shortest path metrics of series-parallel graphs. We make extensive use of linear programming and duality in devising our bounds. We expect that the tools and techniques we develop will be useful for future investigations of embeddings into e1.

Differences in Entrepreneurial Opportunities: The Role of Tacitness and Codification in Opportunity Identification*

Abstract: The role of opportunities in the entrepreneurial process remains relatively underdeveloped. To address this issue, we develop a definition of an entrepreneurial opportunity and draw upon a distinction from the domain of knowledge management to suggest a continuum of entrepreneurial opportunities ranging from codified to tacit. Though both traditional and contemporary research has examined how individual differences relate to the identification of opportunities, we focus instead on the importance of differences in the opportunities themselves. Specifically, we examine how relative differences in the degree of opportunity tacitness relate to the process of opportunity identification. We find that relatively more codified opportunities are more likely to be discovered through systematic search, whereas more tacit opportunities are more likely to be identified due to prior experience. These findings contribute to an increased understanding of the role of the opportunity in entrepreneurship research and have important implications for economic theories of entrepreneurship, entrepreneurial learning, entrepreneurial networks, and entrepreneurial education.

Substance Use and PTSD Symptoms Impact the Likelihood of Rape and Revictimization in College Women

Abstract: The present study utilized a mixed retrospective and prospective design with an 8-month follow-up period to test a model of revictimization that included multiple childhood (i.e., child sexual, physical, and emotional abuse) and situational variables (i.e., substance use, sexual behavior) for predicting rape among 276 college women. It was of particular interest to determine whether traumatic responses (e.g., posttraumatic symptomatology or risky behavior) increased vulnerability for revictimization. During the 8-month follow-up period, 9% of participants were raped; 88% of assaults involved substance use by the victim. Posttraumatic stress disorder (PTSD) symptomatology predicted rape, substance use, and sexual behavior. Substance use, but not sexual behavior, mediated the relation between PTSD symptomatology and rape during the follow-up period. Sexual behavior indirectly impacted risk for rape via substance use. Results suggest that college women with PTSD symptomatology may be at greater risk for rape if they use substances to reduce distress.

Phytochromes A and B Mediate Red-Light-Induced Positive Phototropism in Roots

Abstract: The interaction of tropisms is important in determining the final growth form of the plant body. In roots, gravitropism is the predominant tropistic response, but phototropism also plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism that is mediated by the phototropin family of photoreceptors. In contrast, red light induces a positive phototropism in Arabidopsis roots. Because this red-light-induced response is weak relative to both gravitropism and negative phototropism, we used a novel device to study phototropism without the complications of a counteracting gravitational stimulus. This device is based on a computer-controlled system using real-time image analysis of root growth and a feedback-regulated rotatable stage. Our data show that this system is useful to study root phototropism in response to red light, because in wild-type roots, the maximal curvature detected with this apparatus is 30 degrees to 40 degrees, compared with 5 degrees to 10 degrees without the feedback system. In positive root phototropism, sensing of red light occurs in the root itself and is not dependent on shoot-derived signals resulting from light perception. Phytochrome (Phy)A and phyB were severely impaired in red-light-induced phototropism, whereas the phyD and phyE mutants were normal in this response. Thus, PHYA and PHYB play a key role in mediating red-light-dependent positive phototropism in roots. Although phytochrome has been shown to mediate phototropism in some lower plant groups, this is one of the few reports indicating a phytochrome-dependent phototropism in flowering plants.