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  1. Abstract

    We present a two-species population model in a well-mixed environment where the dynamics involves, in addition to birth and death, changes due to environmental factors and inter-species interactions. The novel dynamical components are motivated by two common mechanisms for developing antibiotic resistance in bacteria: plasmidtransformation, where external genetic material in the form of a plasmid is transferred inside a host cell; andconjugationby which one cell transfers genetic material to another by direct cell-to-cell contact. Through analytical and numerical methods, we identify the effects of transformation and conjugation individually. With transformation only, the two-species system will evolve towards one species’more »extinction, or a stable co-existence in the long-time limit. With conjugation only, we discover interesting oscillations for the system. Further, we quantify the combined effects of transformation and conjugation, and chart the regimes of stable co-existence, a result with ecological implications.

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  2. With support from NSF Scholarships in Science, Technology, Engineering, and Mathematics (S-STEM), the Culturally Adaptive Pathway to Success (CAPS) program aims to build an inclusive pathway to accelerate the graduation for academically talented, low-income students in Engineering and Computer Science majors at [University Name], which traditionally serves the underrepresented and educationally disadvantaged minority students in the [City Name area]. CAPS focuses on progressively developing social and career competence in our students via three integrated interventions: (1) Mentor+, a relationally informed advising strategy that encourages students to see their academic work in relation to their families and communities; (2) peer cohorts,more »providing social support structure for students and enhancing their sense of belonging in engineering and computer science classrooms and beyond; and (3) professional development from faculty who have been trained in difference-education theory, so that they can support students with varying levels of understanding of the antecedents of college success. To ensure success of these interventions, the CAPS program places great emphasis on developing culturally responsive advisement methods and training faculty mentors to facilitate creating a culture of culturally adaptive advising. This paper presents the CAPS progress in the past two project years. In particular, we will share several changes that we have made after the first project year to improve several key components of the program - recruitment, cohort building, and mentor training. The program strengthened the recruitment by actively involving scholars and faculties in reaching out to students and successfully recruited more scholars for the second cohort (16 scholars) than the first cohort (12 scholars). Also, the program has initiated new activities for peer-mentoring and cohort gathering within each major. As continuous development of the mentor training, the program has added a training session focusing on various aspects of intersectionality as it relates to individual’s social identities, and how mentors can use these knowledge to better interact with mentees. In addition to these changes, we will also report findings on how the program impacted on scholars’ academic growth and mentors’ understanding about the culturally adaptive advisement to answer the CAPS research questions (a) how these interventions affect the development of social belonging and engineering identity of CAPS scholars, and (b) the impact of Mentor+ on academic resilience and progress to degree. The program conducted qualitative data collection and analysis via focus group meetings and interviews as well as quantitative data collection and analysis using academic records and surveys. Our findings will help enhance the CAPS program and establish a sustainable Scholars Support Program at the university, which can be implemented with scholarships funded by other sources, and which can be transferred to similar culturally diverse institutions to increase success for students who have socio-economic challenges.« less
  3. The financial disadvantage of many students in the College of Engineering, Computer Science, and Technology (ECST) at California State University, Los Angeles, is often in parallel with inadequate academic preparation through K-12 education and limited family guidance. Hence, many students, including those who are academically-talented, experience significant challenges in achieving their academic goals. In 2018, the College of ECST received an award from NSF SSTEM program to establish a Culturally Adaptive Pathway to Success (CAPS) program that aims to build an inclusive pathway to accelerate the graduation for academically talented, lowincome students in Engineering and Computer Science majors. CAPS focusesmore »on progressively developing students’ social and career competence via three integrated interventions: (1) Mentor+, relationally informed advising that encourages students to see their academic work in relation to their families and communities; (2) peer cohorts, providing social support structure for students and enhancing their sense of belongings in engineering and computer science classrooms and beyond; and (3) professional development with difference-education, illuminating the hidden curricula that may disadvantage first-generation and low income students. This paper presents our progress and core program activities during the first year of the CAPS program, including the recruitment process and mentor training program. In Fall 18, group and individual mentoring sessions have taken place following the culturally responsive mentoring strategy. In addition to program activities, the paper will also share the data collected through focus groups and report the lessons learned during the first-year implementation phase.« less
  4. Metamodeling has been a topic of longstanding interest in stochastic simulation because of the usefulness of metamodels for optimization, sensitivity, and real- or near-real-time decision making. Experiment design is the foundation of classical metamodeling: an effective experiment design uncovers the spatial relationships among the design/decision variables and the simulation response; therefore, more design points, providing better coverage of space, is almost always better. However, metamodeling based on likelihood ratios (LRs) turns the design question on its head: each design point provides an unbiased prediction of the response at any other location in space, but perhaps with such inflated variance asmore »to be counterproductive. Thus, the question becomes more which design points to employ for prediction and less where to place them. In this paper we take the first comprehensive look at LR metamodeling, categorizing both the various types of LR metamodels and the contexts in which they might be employed.« less
  5. An extruded AZ31B (Mg-3Al-1Zn-0.5Mn) magnesium alloy with a twin volume fraction of 60% was subjected to fully reversed strain-controlled tension-compression along the extrusion direction at strain amplitudes ranging from 0.23% to 0.45%. Dislocation slips were the dominant plastic deformation mechanisms without involving persistent twinning-detwinning. At an identical strain amplitude, the fatigue life of the pre-twinned alloy was much lower than that of the as-extruded alloy. Fatigue cracks were mainly initiated on the prismatic or prismatic-basal slip bands in the parent grains. The material volume reduction of the parent grains in the pre-twinned alloy enhanced fatigue damage. Twin cracks were notmore »observed.« less