Simulations of the angular dependence of the dipole-dipole interaction among Rydberg atoms

The dipole-dipole interaction between two Rydberg atoms depends on the relative orientation of the atoms and on the change in the magnetic quantum number. We simulate the effect of this anisotropy on the energy transport in an amorphous many atom system subject to a homogeneous applied electric field. We consider two experimentally feasible geometries and find that the effects should be measurable in current generation imaging experiments. In both geometries atoms of $p$ character are localized to a small region of space which is immersed in a larger region that is filled with atoms of $s$ character. Energy transfer due to the dipole-dipole interaction can lead to a spread of $p$ character into the region initially occupied by $s$ atoms. Over long timescales the energy transport is confined to the volume near the border of the $p$ region which is suggestive of Anderson localization. We calculate a correlation length of 6.3~$\mu$m for one particular geometry.Comment: 6 pages, 5 figures, revised draf

The "Unfriending" Problem: The Consequences of Homophily in Friendship Retention for Causal Estimates of Social Influence

An increasing number of scholars are using longitudinal social network data to try to obtain estimates of peer or social influence effects. These data may provide additional statistical leverage, but they can introduce new inferential problems. In particular, while the confounding effects of homophily in friendship formation are widely appreciated, homophily in friendship retention may also confound causal estimates of social influence in longitudinal network data. We provide evidence for this claim in a Monte Carlo analysis of the statistical model used by Christakis, Fowler, and their colleagues in numerous articles estimating "contagion" effects in social networks. Our results indicate that homophily in friendship retention induces significant upward bias and decreased coverage levels in the Christakis and Fowler model if there is non-negligible friendship attrition over time.Comment: 26 pages, 4 figure

Teaching and learning innovation and invention

Each quarter at Rochester Institute of Technology (RIT), our course on innovation and invention gathers undergraduate and graduate students from as many disciplines as possible and attempts to do something none of us (including the instructors) knows how to do. Our methodology, modeled after business startups more than traditional academic courses, produces interesting inventions and remarkable learning experiences. We will report on the first four offerings of this course at RIT, and speculate on why it works as well as it does. Class begins by presenting students with a stimulating but vague challenge that can engage all the participants (e.g., “build a multi-person multimedia computer that surrounds people”) and then mapping and connecting students’ interests and expertise. Sub-projects form, develop, die and/or expand, through student collaboration and peer problem solving, as the class pushes toward an ultimate deliverable in which all participants can feel ownership and pride. Relatively unstructured and unpredictable multidisciplinary problem solving experiences can complement traditionally structured and predictable intra-disciplinary curricula. By collaborating across disciplines, students can deepen their understanding and broaden the application of hard-won discipline-specific knowledge and expertise. They can also learn to enjoy and endure the fine art of improvisational innovation and invention

Pornography: A Concealed Behavior with Serious Consequences

Objectives: The purpose of the current study was to a) estimate prevalence of pornography use and addiction in Rhode Island young adults; b) identify sociodemographic disparities; and c) determine if use and addiction was associated with mental illness. Methods: Data from n=1022 participants of the Rhode Island Young Adult Survey were used. Pornography use and addiction were assessed. Sociodemographic variables included age, social status, sex, gender, sexual orientation and race/ethnicity. Depression, anxiety, and suicide ideation were also measured. Results: 54% indicated pornography use; 6.2% met the criteria for addiction. Odds of pornography use were 5 times higher (95%CI=3.18,7.71), and addiction 13.4 times higher (95%CI=5.71,31.4) among heterosexual cis-males. Pornography addiction was associated with increased odds of depression (OR=1.92, 95%CI=1.04,3.49) and suicide ideation (OR=2.34, 95%CI=1.24,4.43). Conclusions: Pornography use is highly prevalent, and addiction may be associated with mental illness. New screenings, media literacy training, and developing new therapeutic interventions should be considered

“Fabricación y tratamiento térmico de aleaciones de bronce al aluminio”.

Proyecto de Graduación (Licenciatura en Ingeniería en Materiales) Instituto Tecnológico de Costa Rica. Escuela de Ciencia e Ingeniería de los Materiales, 2011Este proyecto, fue desarrollado en el Centro de Investigación y Extensión en Ingeniería de los Materiales (CIEM) de la Escuela de Ciencia e Ingeniería de los Materiales. En el año 2008, se exportaron en desperdicios y desechos 15,9 millones de dólares estadounidenses (US$) de cobre; 14,4 millones de US$ de aluminio y 29,5 millones de US$ hierro o acero. Como alternativa para el aprovechamiento de estos desechos, se propone la fabricación de aleaciones de bronce al aluminio, tratables térmicamente, con alta resistencia a la corrosión y a la cavitación, entre otras propiedades. Se fabricó dos aleaciones, una con 84,6% Cu; 11,2% Al y 2,9% Fe. Otra con 83,1% Cu; 10,3% Al; 5,67% Fe, que fueron sometidas a temples desde 950°C hasta los 20°C y desde los 950°C hasta los -196°C. Así como, Se realizó revenidos a 550, 600, 650 y 700°C por dos horas. La dureza, por lo general, subió luego de los temples. Se descartó la influencia del temple criogénico sobre la dureza o la microestructura. Los temples provocaron la formación de la microestructura acicular martensítica (β’ sobre base α). Los revenidos a 550, 600 y 650°C, ablandaron las probetas dela aleación Cu-11%Al-3%Fe, mientras la microestructura cambiaba a granos más grandes de forma redondeada constituidos por solución sólida α y fase de composición variable α+γ2. Luego del revenido a 700°C, la dureza se incrementó, posiblemente, por una cantidad muy alta del compuesto intermetálico γ2.15.9 million dollars of copper waste, 14.4 millions of aluminum scrap and 29.5 million dollars of steel and iron waste were exported from Costa Rica during 2008. The fabrication of heat treatable aluminum bronze alloys, from those materials, is proposed to take a better advantage of them. These aluminum bronze alloys are highly resistant to corrosion and cavitation among some other properties. The alloys that were casted and studied had the following composition: 84.6% Cu, 11.2% Al and 2.9% Fe. As well as: 83.1% Cu, 10.3% Al, and 5.67% Fe. They were quenched from 950°C (1742°F) to 20°C (68°F) and from 950°C (1742°F) to -196°C (-320°F). The quenched samples were tempered 2 hours at different temperatures: 550, 600, 650 and 700°C (1022, 1112, 1202 and 1292°F). In general, after the quenching, the hardness of the alloys went up, compared with the as-cast hardness. The cryogenic quenching did not have any effect upon the microstructure nor the hardness of the alloys. The quenching treatments caused the β’, acicular martensitic microstructure, to appear. The increase in the tempering temperature (550, 600 and 650°C) for the Cu-11%Al-3%Fe alloy, caused a softening of the samples, while the microstructure of the alloys changed to larger grains made of the α solid solution and the variable composition phase α+γ2. For the 700°C the hardness increased again, most likely because of the presence in a larger quantity of the intermetallic compound γ2