84 research outputs found
On the computational complexity of portal and push-pull block puzzles
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 49-53).We classify the computational complexity of two types of motion planning problems represented in games. Portal, a popular video game, is shown to be NP-hard or PSPACE-complete depending on the game mechanics allowed. Push-pull block puzzles are games, similar to Sokoban, which involve moving a 'robot' on a square grid with obstacles and blocks that can be pushed or pulled by the robot into adjacent squares. We prove that push-pull block puzzles in 3D and push-pull block puzzles in 2D with thin walls are NP-hard to solve. We also show certain 3D push-pull block puzzles are PSPACE-complete. This work follows in a long line of algorithms and complexity work on similar problems Wil91, DDO00, Hof00, DHH04, DH01, DO92, DHH02, Cul98, DZ96, Rit10]. The 2D push-pull block puzzle also shows up in a number of video games, thus implying other results, further continuing the work on understanding video games as in Vig12, ADGV14, For10, Cor04.by Jayson Lynch.M. Eng
Hyperlocal Career Pathway Programs in New Hampshire: Collaborating to Support Youth at the Secondary/Postsecondary Transition
No full textCollege costs and persistent workforce shortages have prompted educators, policymakers, and employers to shift the conversation on the transition from high school from a narrow “college for all” emphasis to a broader “postsecondary education” and “career pathways” perspective. The timing of this shift coincides with current and anticipated workforce needs; by 2032, New Hampshire will have 197,000 positions available across its top 80 occupations, with labor force growth projected to fill only 6,100 of those jobs.
Some commentators argue that broadening options to include career and technical education, certificates, and 2-year degrees is essential for realizing equity gains. Successfully building such pathways cannot be accomplished by educational institutions alone; it requires collaboration across public, nonprofit, and private sectors, as well as financial and policy incentives that reduce barriers and risks.
In this paper, author Jayson Seaman describes an innovative effort to address these challenges in New Hampshire, focusing on programs following a “hyperlocal” approach to career pathway development that simultaneously address specific, local industry, community, and individual needs. Their purpose is to increase the likelihood of social mobility by using career exposure and hands-on involvement to spur interest and motivation toward additional education and training in promising fields. The research reported here focused on programs that target youth approaching the secondary-postsecondary transition.
The study’s main findings show what it takes for career pathway sites to realize effective collaboration among partners and provide learners with a positive experience. The paper concludes with a discussion about areas of ongoing need both within and outside of individual pathway programs
Monte Carlo simulations of a physical cryptographic warhead verification protocol using nuclear resonance fluorescence
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Page 99 blank. Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 93-98).Future multilateral nuclear arms reduction efforts will require technologies for the verification of treaty compliance. In particular, warheads slated for dismantlement will need to be verified for authenticity without revealing any sensitive weapons design information to international inspectors. Recent efforts have investigated physical cryptographic verification protocols that attempt to solve this treaty verification problem by using physics processes rather than electronics to encrypt sensitive information. The physical cryptographic protocol simulated in this thesis exploits the isotope-specific nature of nuclear resonance fluorescence (NRF) measurements to provide a strong indicator of the authenticity of a warhead. To protect against sensitive information leakage, the NRF signal from the warhead is convoluted with that of an encrypting foil containing the same isotopes as the warhead but in unknown amounts. The convoluted spectrum from a candidate warhead is then statistically compared against that from an authenticated template warhead to determine whether the candidate itself is authentic. This work presents the initial Geant4 Monte Carlo simulations of the physical cryptographic warhead verification protocol. Using a 2.7 MeV endpoint bremsstrahlung beam, a template warhead is interrogated. Several hoax geometries are also compared against the template to show the protocol's robustness against cheating. Isotopic hoaxes in which weapons-grade plutonium is replaced with reactor-grade plutonium or depleted uranium are shown to be detectable in realistic measurement times. An optimized geometric hoax that mimics the areal densities and attenuations of the authentic template warhead along one axis can also be detected with a second measurement under a different projection. Results of the simulations as well as future research objectives will be presented and discussed.by Jayson Robert Vavrek.S.M
Development of an isotope-sensitive warhead verification technique using nuclear resonance fluorescence
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 93-99).Nearly three decades after the end of the Cold War, nuclear arms control remains a pressing global issue. Despite obligations under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) to make 'good-faith efforts' to disarm their nuclear arsenals, the United States and Russia still maintain thousands of nuclear warheads. Progress towards complete disarmament has been gradual due to a variety of socio-political barriers, but future efforts towards nuclear arms reduction will face an additional technological hurdle: no technology exists to verify that warheads slated for dismantlement are authentic without revealing any sensitive weapons design information in the process. Despite several decades of research, no technology has solved this apparent paradox between information security and confidence in a warhead verification measurement.Recent work by Kemp, Danagoulian, Macdonald, and Vavrek [1] has produced a novel physical cryptographic verification protocol that approaches this treaty verification problem by exploiting the isotope-specific nature of nuclear resonance fluorescence (NRF) measurements to verify the authenticity of a warhead. To protect sensitive information, the NRF signal from the warhead is convolved with that of an encryption foil that contains key warhead isotopes in amounts unknown to the inspector. The convolved spectrum from a candidate warhead is then statistically compared against that from an authenticated template warhead to determine whether the candidate itself is authentic. Since only the final, convolved spectra are observable, and the detailed foil construction is unknown to the inspector, sensitive information about the warhead is encrypted by physics rather than by software or electronics.In this thesis, we performed proof-of-concept NRF warhead verification experiments at the High Voltage Research Laboratory (HVRL) at MIT [2]. Using high-purity germanium (HPGe) detectors, we measured NRF spectra produced by the interrogation of proxy 'genuine' and 'hoax' objects by a 2.52 MeV endpoint bremsstrahlung beam. The observed differences in NRF intensities near 2.2 MeV indicate that the physical cryptographic protocol can distinguish between proxy genuine and hoax objects with high confidence. Extrapolations to thicker warheads and dedicated verification facilities indicate that realistic warhead verification measurements could be made on the order of hours. In support of these and future NRF experiments, we also improved and benchmarked the G4NRF code for the simulation of NRF in Geant4 [3]. We first constructed a high-accuracy semi-analytical model for the expected NRF count rate in both simple homogeneous and more complex heterogeneous geometries.We then performed Geant4+G4NRF simulations with these geometries, and found agreement in NRF rates predicted by the semi-analytical model and observed in the simulation at a level of ~1% in simple test cases and ~3% in the more realistic complex scenarios. These results improve upon the ~20% level of the initial G4NRF benchmarking study and establish a highly-accurate NRF framework for Geant [4]. Finally, we conducted a G4NRF validation study using the NRF data taken during the warhead verification experiments [4]. Agreement between the absolute NRF count rates observed in the data and predicted by extensive Geant4+G4NRF modeling validate the combined Geant4+G4NRF model to within ~20% in the 238U NRF transitions and 9% in 27Al, for an average 14% discrepancy across the entire study. Additionally, agreement between the model and data in relative NRF rates is found at the level of .5%.Such agreement in both relative and absolute analyses provides good predictive capability for the design and analysis of future NRF experiments using G4NRF, whether for warhead verification or other applications.by Jayson Robert Vavrek.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineerin
An Investigation into Vehicle Acceleration Characteristics on Freeway Loop Ramps
No full textFreeway loop ramps are the most restrictive common interchange ramp design, with sharp curves and low design speeds. Drivers utilizing these ramps can be forced to accelerate rapidly on entry ramps or decelerate rapidly on exit ramps. This thesis has several goals: to gain information about acceleration and deceleration on freeway loop ramps���both where it occurs and the magnitude of the speed change rate; to evaluate what ramp characteristics are most predictive of speed change rate and form models based off of these characteristics; to use the observed speed change rates to form a way to test for the adequacy of auxiliary lanes.
To accomplish these goals, the author uses a large dataset from the Strategic Highway Research Program 2 Naturalistic Driving Study (SHRP2 NDS). The dataset contains time-series vehicle dynamic data from nearly 2,000 vehicle trips on 20 freeway loop ramps in 5 states. The author supplemented this data set to be able to tie the dataset to physical locations and analyze the impact of various ramp characteristics on the speed change rates. The author uses two new terms, deceleration ratio and acceleration ratio to show where on the loop ramps deceleration and acceleration occur. Next, the actual deceleration rates and acceleration rates are shown and compared to the commonly used current rates. The author then models these rates using the most predictive ramp variables���radius of curve and speed limit of the adjacent freeway. Next, the author calls for updating the assumption of vehicle acceleration on ramps, suggesting that the rates of acceleration and deceleration may be closer than previously assumed and that acceleration may not be constant on loop ramps. Finally, the author introduces a method for determining the adequacy of auxiliary lanes on freeway loop ramps.
In this thesis, the author finds that much of the acceleration on entrance loop ramps and deceleration on exit loop ramps occurs outside of the loop ramp proper���on either the freeway or the auxiliary lanes���and notes the importance of adequate auxiliary lanes. The author finds that deceleration rates on exit loop ramps may be lower than previously thought and recommends that a lower rate be used for design purposes. The author finds that using the ���normal��� acceleration rate of 3.6 ft/sec^2, many of the studied ramps do not provide adequate room for vehicles to reach the freeway speed limit before they are forced to merge onto the freeway
ICT in Education Reform in Cambodia: Problems, Politics, and Policies Impacting Implementation
No full textThis article serves as a critique of an ICT in education reform in the nation of Cambodia. Although an ICT in education policy was adopted by the Cambodian Ministry of Education, tangible, quantifiable, and measured progress of this reform has, to date, been limited in nature. Hence, to understand the limitations of this reform, the author uses Kingdon's multiple streams model to investigate streams of policy, problems, and politics. This model allowed the author to explore existing data, events, and experiences in a robust manner. The current research is an analysis of policy papers, government documents, IGO briefs, personal experiences, and other nations' experiences with similar ICT in education reform movements. It was determined that failure to fully address the political stream has caused stress on the adoption process of this reform and has, in effect, slowed its progress. (c) 2008 by The Massachusetts Institute of Technology.
Adopting a Grounded Theory Approach to Cultural-Historical Research: Conflicting Methodologies or Complementary Methods?
No full textGrounded theory has long been regarded as a valuable way to conduct social and educational research. However, recent constructivist and postmodern insights are challenging long-standing assumptions, most notably by suggesting that grounded theory can be flexibly integrated with existing theories. This move hinges on repositioning grounded theory from a methodology with positivist underpinnings to an approach that can be used within different theoretical frameworks. In this article the author reviews this recent transformation of grounded theory, engages in the project of repositioning it as an approach by using cultural historical activity theory as a test case, and outlines several practical methods implied by the joint use of grounded theory as an approach and activity theory as a methodology. One implication is the adoption of a dialectic, as opposed to a constructivist or objectivist, stance toward grounded theory inquiry, a stance that helps move past the problem of emergence versus forcing
“Turning of the Wheel”: A Perennialist’s Answer to 1970s Curricular Debates
No full textThis paper utilizes archival sources and publications to underscore Harry S. Broudy’s responses to 1970s curricular shifting providing a window into Curriculum Reconceptualist debates of the 1970s whilst offering Broudy, Smith, Burnett’s (1964) curriculum study as an informative curriculum precursor. Ultimately, the author argues the Democracy and Excellence in American Secondary Education offers a valuable antecedent to numerous curriculum debates of the era
Cancer preventive effects of tocopherols in dietary carcinogen-induced colon and prostate carcinogenesis models
No full textColorectal and prostate cancers are leading causes of morbidity and mortality in the United States and worldwide. While immense progress has been made in reducing incidence and death of these cancers in the past few decades, they remain major public health issues, highlighting the need for better understanding, prevention and intervention of these diseases. One major strategy to address these issues is research into more relevant animal cancer models and potent chemopreventive agents. The purpose of this dissertation research was to characterize a novel colon carcinogenesis model induced by the meat-derived carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), with colitis from Dextran Sodium Sulfate (DSS) and determine the effects of different tocopherol forms of vitamin E on the colon carcinogenesis model as well as a PhIP-induced prostate carcinogenesis model. The rapid induction of PhIP/DSS-induced colon carcinogenesis in the CYP1A-humanized mice was determined to be caused by active Ctnnb1/β-catenin mutations in residual epithelial cells, which when promoted by colitis, developed into precancerous lesion, high-grade dysplasia, and finally adenocarcinoma. These features resembled human colitis-associated colon cancer. In the PhIP/DSS-induced colon carcinogenesis model, dietary supplementation with d-T and g-T, but not a-T, significantly attenuated colon tumor formation and inhibited oxidative and nitrosative stress as well as pro-inflammatory markers. Additional studies indicate the potent inhibitory effects of d-T and g-T was mainly due to protection against early cellular and DNA damage caused by the PhIP carcinogen. In the PhIP-induced prostate carcinogenesis model, dietary supplementation with g-TmT and d-T effectively reduced the formation and severity of mouse PIN lesions as well as p-Akt expression, whereas g-T and a-T were less effective. Further studies suggest the chemopreventive effects of the tocopherols involved the reduction in cellular oxidative and nitrosative stress and inhibition of the PI3K/Akt signaling pathway that regulate cell survival and proliferation. Together, the findings from this research demonstrate the relevance of PhIP dietary carcinogen-induced and DSS colitis-promoted colon carcinogenesis model and the superior cancer preventive activities of d-T and g-T compared to the classic a-T.Ph.D.Includes bibliographical referencesby Jayson Xiao-Chen Che
- …
