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RISS 인기검색어
- 검색키워드
- 저자 : Gonzalez-Gutierrez, Arturo (검색결과 2 건)
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Minimum-length corridors: Complexity and approximations
Gonzalez-Gutierrez, Arturo University of California, Santa Barbara 2007 해외박사(DDOD)
The Minimum-Length Corridor (MLC) problem and some of its variants are studied. Given a rectangular boundary partitioned into rectilinear polygons (rooms), the MLC problem is to find a corridor of least total length. A corridor is a set of connected line segments, each of which must lie along the line segments that form the rectangular boundary and/or the boundary of the rooms, and must include at least one point from every room and from the rectangular boundary. The NP-completeness of the decision version of the MLC problem even when it is restricted to a rectangular boundary partitioned into rectangles is established. We call this restricted version the MLC-R problem. In virtue of these results, we present a parameterized algorithm Alg(S) for the MLC-R problem, where S is a selector function. For certain selector functions, Alg( S) results in the first provably polynomial time approximation algorithm for the MLC-R problem with a constant approximation ratio. Algorithm Alg(S) restricts the solution space by limiting in each room the possible vertices, from which at least one must be part of the corridor. The resulting problem, which remains NP-complete, is solved by relaxing the set of feasible solutions. Then the solution is rounded and solves the original problem instance. This approach is adapted to the rectangular group-TSP, resulting in a constant ratio approximation algorithm. The approximation scheme can also be applied to the MLCk problem, i.e., the MLC problem when every room is a rectilinear c-gon, for c ≥ k, but the approximation ratio depends on k. A polynomial time constant ratio approximation algorithm for the group-TSP for a rectangular boundary partitioned into rectilinear c-gons, as in the MLCk problem when k is a constant, is presented. An application for the MLC problem is when laying optical fiber in metropolitan areas and every block (or set of blocks) is connected through its own gateway. The objective is to find a minimum-length corridor connecting all the gateways in the area. Corridor problems also have applications in VLSI and floorplanning when laying wires for clock signals or power, and wires for electrical networks, or optical fibers for data communications.
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Binational cooperation for high school ELL immigrant students: The LUCHA program at UT Austin
Gutierrez-Gonzalez, Beatriz Irene The University of Texas at Austin 2009 해외박사(DDOD)
This dissertation is a qualitative case study of a program where binational program established by the University of Texas to lower the Hispanic high school dropout rate in the United States. The Language Learners at the University of Texas at Austin Center for Hispanic Achievement (LUCHA) program is the focus of this dissertation. The LUCHA program serves immigrant Hispanic students who account for 34% of the 45% Hispanic dropout rate reported by NCES. The theoretical framework employed included the theories of cultural and social capital and the theory of caring to answer the following questions: (1) What challenges had to be met in order to initiate and develop the LUCHA program, a binational education program to combat the high dropout rate among Latino immigrants?, and (2) What can be learned from the implementation and practice of the LUCHA program in school districts with almost identical, homogenous population, and different levels of success with the program. Data was collected in Mexico and the United States and included participants involved in the program at different levels ranging form political involvement in Mexico to immigrant students in South Texas Valley school districts where the program started operations in 2006. The researcher was a participant in this study. The innovative ideas developed and instituted to reduce the Hispanic dropout rate included equipping schools with essential/core and English as a Second Language courses produced in Mexico, validating prior high school credits students had from Mexico through a transcript analysis service, obtaining Mexican transcripts for immigrant students who could not deliver them to schools, and diagnostic tests produced in Mexico for immigrant students with interrupted schooling. These services and their delivery were modified and adapted to meet the changing needs and graduation requirements of students and the educational bureaucracy in the U.S. This study brings to light the skills sets, assumptions, and characteristics of people needed to create binational agreements of cooperation. This research suggests that the perception of caring (Noddings, 1984) of educational agents in schools and school districts influences the level of success of the program in schools with almost identical populations.
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