Thesis (Ed.D.)--Boston University / The influx of international graduate students in science and engineering to the U.S. has changed since the terrorist attacks of September 11, 2001. The implementation of the Student and Exchange Visitor Information System (SEVIS) and related F-1 visa policies have required a higher level of scrutiny of the student visa procedures, and introduced strict student monitoring policies and measures. In addition, the SEVIS monitoring and compliance system has altered the operation of international student service offices, affected the students they serve, and the operation of the universities enrolling international students. This study investigated the effects of SEVIS on graduate programs in science and engineering and their students. Information was gathered from respondents from the 60 universities having the highest population of intemational students in these fields, according to NSF. Respondents included department administrators, admissions officials, and SEVIS professionals. Data V111 were collected from 75 on-line survey respondents and in 21 semi-structured interviews. The results of this study suggest that many international students are negatively affected by SEVIS, impacting their ability to remain in-status and to understand how the system works. To counter this, department administrators, SEVIS professionals, and student advisors have increased their level of support for these students, providing them guidance on how to remain in-status and how to improve their social and academic experience in the United States. As a result, relatively few international students are deported for falling out-of-status in SEVIS. The data also made clear that program administrators and admissions officials have little knowledge about SEVIS, F -1 visa policies, and their influence on international enrollments. Finally, this study provided evidence of an increased workload for international student advisors and SEVIS professionals. Universities have had to hire additional staff, increase their information technology investment in linking home-grown student service systems with SEVIS, and proactively anticipate any hurdles that international students may have and resolve them as expeditiously as possible. / 2031-01-01

Taluppfattning är ett tänkande och en färdighet som utvecklas med hjälp av erfarenhet och kunskap. Taluppfattning är grunden till all matematik och nödvändigt kunnande för elevens fortsatta matematiska progression. Studiens syfte är att undersöka hur fyra lärare på en skola arbetar för att stärka och utveckla varje elevs talförståelse. Vidare är syftet att synliggöra vilka metoder lärarna använder när en elev har svårt att förstå och använda tal. I undersökningen används kvalitativa intervjuer av semistrukturerad karaktär och informanterna är lärare som undervisar i matematik i årskurs F-2. I analysen används Gelman och Gallistels fem räkneprinciper som ramverk och resultatet sätts även i relation till John Deweys lärteori. Studiens resultat visar att lärarna har mycket god kännedom om talförståelsens betydande roll för elevens fortsatta matematiklärande. De låter arbetet med taluppfattning ta tid samt använder varierade undervisningsmetoder ofta med konkret material som stöd.

La tuberculose est une maladie infectieuse extrêmement contagieuse qui dans sa forme simple peut être soignée et guérie. Cependant, des formes multirésistantes aux traitements classiques ont récemment fait leur apparition et le développement de nouvelles molécules constitue donc un enjeu majeur de santé publique. Le 3,3-diméthyl-1,2-dihydro-3H-benzofuro[3,2-f][1]benzopyrane est un produit possédant une activité antituberculeuse marquée, y compris sur des lignées résistantes. L’objectif des travaux réalisés ici est la recherche de composés de puissance accrue et l’élucidation du mécanisme d’action de cette série. Dans une première partie, des modifications structurales portant sur le cycle A sont présentées. Les résultats des tests biologiques ont permis de sélectionner des composés qui possèdent un index de sélectivité favorable entre l’activité antituberculeuse et la toxicité. Un composé de structure linéaire a également montré un profil d’activité intéressant. Les études de mécanisme d’action ont mis en évidence que les composés synthétisés affectent les synthèses des époxy-mycolates ainsi que celle des α-mycolates de la paroi cellulaire. Dans une deuxième partie l’influence des groupements en position 3 du 3,3-diméthyl-1,2-dihydro-3H-benzofuro[3,2-f][1]benzopyrane a été étudiée. Des composés possédants des chaines de longueur croissante en cette position ont été synthétisés. L’activité antituberculeuse des premiers produits obtenus, a été mesurée et a montré une importante influence du type de chaine introduit sur l’activité biologique. Les études présentées dans ce travail ont donc permis d’une part de préciser la cible cellulaire de ces molécules et d’autre part de sélectionner des composés peu cytotoxiques. / Tuberculosis is a highly contagious infectious disease which can be treated and cured in its simple form. However, multidrug resistant forms towards classic treatments have recently appeared and the development of new drugs is a major challenge for public health. The 3,3-dimethyl-1,2-dihydro-3H-benzofuro[3,2-f][1]benzopyran have a significant anti-TB activity, including resistant lines. The goal of this work is the research of more active compounds and the elucidation of the mechanism of action of this series. In a first part, modifications are introduced on A ring. The results of biological tests were permitted to select compounds that have a favorable selectivity index between tuberculosis activity and toxicity. A linear compound has also showed an interesting activity. Studies on mycolates biosynthesis revealed that the synthesized compounds affect the synthesis of epoxy-mycolates and α-mycolates of the cell wall. In the second part of this work the influence of groups introduced at position 3 of 3,3-dimethyl-1 ,2-dihydro-3H-benzofuro[3,2-f][1]benzopyran was studied. Compounds possessing different length chains at this position have been synthesized. Anti-TB activity of the first products obtained was measured and showed a significant influence of the type of chain introduced. The studies presented in this work permitted to define the cellular target of these compounds and on the other hand to select the compounds with lowest cytotoxicity.

Asthma is the leading chronic illness in children in the United States. Since children in the U.S. spend a majority of their time indoors there is an increased need to understand key sources of daily asthma triggers in the home. Bacterial endotoxin, dust mite allergens and β-D-glucan have been shown to be potent inducers of asthma attacks, and high levels of these allergens in homes can trigger attacks in those with asthma. We aim to better understand the risks to those with asthma that might be associated with evaporative cooler (EC) use in low-income homes. ECs are often promoted because of their low energy consumption and decreased environmental impact compared to central air conditioning (AC). Because of their lower cost, ECs are more widely used in low-income homes. ECs use evaporation to cool the air, which leads to higher indoor relative humidity. This may create an ecological niche for house dust mites in semi-arid climates where they are normally absent. EC sump water also provides an ideal environment for bacteria and fungi to grow, possibly resulting in EC loading the air with more potential asthma triggers than central air conditioning. We sampled low-income homes around Utah county with central air and evaporative cooling and tested them for the presence of dust mite allergens, β-D-glucan and endotoxin. There were significantly higher levels of endotoxins and β-(1→3)-D-glucans in the EC homes compared to the AC homes, with increased odds of dust mite allergen prevalence but not at clinically significant levels. These findings suggest that in semi-arid environments, endotoxin and β-(1→3)-D-glucan levels in homes with evaporative coolers are more elevated than dust mite allergens.

As the demand for wireless electronics is increasing, more and more gadgets are connected wirelessly and devices are being improved constantly. The need of the new research and development for advance electronics with high performances is the priority. The data transfer rates are improved for faster communication and better efficiency is to reduce the battery consumption in handheld devices. This thesis presents three single-stage power amplifiers (PAs): class-AB, class-F and inverse class-F (class-F-1) at 28 GHz. The PAs have identical input networks: input matching, base DC feed, and base stabilizing networks. At the load side, there is a different load network for each PA. Class-AB PA load network has a single inductor with a parasitic capacitor to create a resonance at 28GHz. Class-F PA load network is composed of a parallel network (one LC tank in series with an inductor) and a series network (one 3f0-resonance LC tank in series with a capacitor) to create a multi-resonance load network. Class-F-1 load network is composed of a parallel network (two LC tank in series with an inductor) and a series network (one 2f0-resonance LC tank in series with a capacitor) to have a multi-resonance network. The main purpose of using multi-resonance load networks in class-F and class-F-1 is to shape the collector currents and voltages in order to achieve the highest efficiency possible. The chosen bias point is VCE=2.3V and ICE~12mA. As the results, class-AB PA achieves the peak PAE of 44%, 15 dBm OP-1dB, >19 dBm Psat , and 10 dB Gp. Class-F PA achieves the peak PAE of 46%, 14.5 dBm OP-1dB, ~18 dBm Psat , and 10 dB Gp. Class-F-1 PA achieves the peak PAE of 45%, 15.1 dBm OP-1dB, >18 dBm Psat , and 10 dB Gp.. In order to compare the linearity performances among three PA classes, a two-tone signal and a modulated signal with different modulation schemes (QPSK, 16QAM, 64QAM, and 256QAM) are applied to the PAs to produce IM3, ACPR, and EVM. After the analysis and comparison on efficiency and linearity, class-F PA gives the highest efficiency but has the worst linearity while class-AB has the best linearity but has the worst efficiency among three. Class-F-1 PA results lies in the middle of two other classes in term of efficiency and linearity. / Master of Science

An F-1 academic visa is required for foreign students studying at academic institutions in the United States. While requirements for acquiring the F-1 visa are a matter of federal policy, some of the principles regulating orientations, host families, and home-stays do not align with best practices found at the university level, which include quality student orientations and thorough trainings with a vetting process for host families and home-stays. This lack of regulation may place visiting students at risk in terms of personal safety and wellbeing and have negative impacts for program credibility and lost revenue. Using Stone's regime theory as the foundation, the purpose of this multiple case study of orientations and home-stay experiences of F-1 visa students under the Student and Exchange Visitor Program, was to explore from the perspective of program participants, ways to increase safety and quality assurance of these programs. Data were collected through in-depth interviews with six former student participants. These data were inductively coded and subjected to a thematic analysis procedure. A key theme of this study is that participants perceived that additional training to host families including vetting and monitoring processes and student orientations in acculturation and communication would enhance the experiences of F-1 visa holders. The implications for positive social change include recommendations to schools and study abroad organizations to implement policy changes regarding the requirements for students and host families, sponsors, and home-stay monitoring and orientation components for students and host families to promote more effective and safer home-stays for F-1 high school students.

This works demonstrates the feasibility of the inverse-Class-F harmonic tuning approach for mm-wave silicon PAs. This research addresses the challenges and limitations of the high efficiency inverse-Class-F PAs for mm-wave silicon technology. This work proposes different load networks to mitigate the challenges which are verified with implementations at different mm-wave frequencies with the highest power efficiency performances reported so far: PAE= 50% @ 24 GHz, PAE = 43% @ 41 GHz, and PAE = 23% @ 94 GHz. The design methodology and detailed analysis of the proposed load networks presented and verified with implementation and measured results. / Ph. D.