X-ray Emission from an Asymmetric Blast Wave and a Massive White Dwarf in the Gamma-ray Emitting Nova V407 Cyg

Classical nova events in symbiotic stars, although rare, offer a unique opportunity to probe the interaction between ejecta and a dense environment in stellar explosions. In this work, we use X-ray data obtained with Swift and Suzaku during the recent classical nova outburst in V407 Cyg to explore such an interaction. We find evidence of both equilibrium and non-equilibrium ionization plasmas at the time of peak X-ray brightness, indicating a strong asymmetry in the density of the emitting region. Comparing a simple model to the data, we find that the X-ray evolution is broadly consistent with nova ejecta driving a forward shock into the dense wind of the Mira companion. We detect a highly absorbed soft X-ray component in the spectrum during the first 50 days of the outburst that is consistent with supersoft emission from the nuclear burning white dwarf. The high temperature and short turn off time of this emission component, in addition to the observed breaks in the optical and UV lightcurves, indicate that the white dwarf in the binary is extremely massive. Finally, we explore the connections between the X-ray and GeV gamma-ray evolution, and propose that the gamma ray turn-off is due to the stalling of the forward shock as the ejecta reach the red giant surface.Comment: Accepted for publication in ApJ. 17 pages, 9 figure

Growing a local organic movement: The Mexican Network of Organic Markets

Over the past several years, in response to the rapid growth in global demand for organic goods, the amount of organic production in Mexico has increased dramatically. Indeed, while Mexican agriculture as a whole has suffered severe crises, the organic sector has boomed, and today more than 83 000 producers farm organically on over 300 000 hectares of land. Of these producers, 98 percent are small scale, farming an average of three hectares, and over 50 percent are indigenous people. Unfortunately, as is the case in many developing countries, the vast majority of organic production remains focused on export crops – particularly coffee, but also cocoa, coconut, and other fruit and vegetables – with 85 percent of organic goods being sent to foreign markets. From an environmental point of view, exportoriented production is extremely damaging because of the amounts of fossil fuels required for transportation. In addition, packaging for export consumes precious resources and creates mountains of waste. Moreover, an export-oriented focus constrains the degree to which domestic markets are developed, and it leaves Mexican producers highly vulnerable to international market fluctuations

Classroom 4.0

Artificial intelligence, once the stuff of futuristic books and films, is finding its way onto college campuses. How is American higher education adapting to the digital age

Why Firefighting Is Never Enough: Preserving High-Quality Product

In this paper, we add to insights already developed in single-project models about insufficient resource allocation and the "firefighting" and last-minute rework that often result by asking why dysfunctional resource allocation persists from project to project. We draw on data collected from a field site concerned about its new product development process and its quality of output to construct a simple model that portrays resource allocation in a multi-project development environment. The main insight of the analysis is that under-allocating resources to the early phases of a given project in a multi-project environment can create a vicious cycle of increasing error rates, overworked engineers, and declining performance in all future projects. Policy analysis begins with those that were under consideration by the organization described in our data set. Those policies turn out to offer relatively low leverage in offsetting the problem. We then test a sequence of new policies, each designed to reveal a different feature of the system's structure and conclude with a strategy that we believe can significantly offset the dysfunctional dynamics we discuss. The paper concludes with a discussion of the challenges managers may face in implementing the strategy that can prevent persistent under-allocation of resources to projects.MIT Center for Innovation in Product Development under NSF Cooperative Agreement Number EEC-952914

Elementary simulation of tethered Brownian motion

We describe a simple numerical simulation, suitable for an undergraduate project (or graduate problem set), of the Brownian motion of a particle in a Hooke-law potential well. Understanding this physical situation is a practical necessity in many experimental contexts, for instance in single molecule biophysics; and its simulation helps the student to appreciate the dynamical character of thermal equilibrium. We show that the simulation succeeds in capturing behavior seen in experimental data on tethered particle motion.Comment: Submitted to American Journal of Physic

Alumni Notes

Schedule of upcoming events, brief articles about alumni activities, and a column by the alumni directo

Vaginal Preparation with Povidone Iodine prior to Cesarean Delivery

Objectives: To reduce the rate of postoperative endometritis in patients undergoing cesarean delivery by implementing a new departmental guideline for vaginal preparation prior to cesarean sections, after labor or rupture of membraneshttps://jdc.jefferson.edu/patientsafetyposters/1053/thumbnail.jp

Void Dynamics

Cosmic voids are becoming key players in testing the physics of our Universe. Here we concentrate on the abundances and the dynamics of voids as these are among the best candidates to provide information on cosmological parameters. Cai, Padilla \& Li (2014) use the abundance of voids to tell apart Hu \& Sawicki $f(R)$ models from General Relativity. An interesting result is that even though, as expected, voids in the dark matter field are emptier in $f(R)$ gravity due to the fifth force expelling away from the void centres, this result is reversed when haloes are used to find voids. The abundance of voids in this case becomes even lower in $f(R)$ compared to GR for large voids. Still, the differences are significant and this provides a way to tell apart these models. The velocity field differences between $f(R)$ and GR, on the other hand, are the same for halo voids and for dark matter voids. Paz et al. (2013), concentrate on the velocity profiles around voids. First they show the necessity of four parameters to describe the density profiles around voids given two distinct void populations, voids-in-voids and voids-in-clouds. This profile is used to predict peculiar velocities around voids, and the combination of the latter with void density profiles allows the construction of model void-galaxy cross-correlation functions with redshift space distortions. When these models are tuned to fit the measured correlation functions for voids and galaxies in the Sloan Digital Sky Survey, small voids are found to be of the void-in-cloud type, whereas larger ones are consistent with being void-in-void. This is a novel result that is obtained directly from redshift space data around voids. These profiles can be used to remove systematics on void-galaxy Alcock-Pacinsky tests coming from redshift-space distortions.Comment: 8 pages, 4 figures, to appear in the proceedings of IAU308 Symposium "The Zeldovich Universe

Why Firefighting Is Never Enough: Preserving High-Quality Product Development

Understanding the wide range of outcomes achieved by firms trying to implement TQM and similar process improvement initiatives presents a challenge to management science and organization theory: a few firms reap sustained benefits from their programs, but most efforts fail and are abandoned. A defining feature of such techniques is the reliance on the front-line workforce to do the work of improvement, thus creating the possibility of agency problems; different incentives facing managers and workers. Specifically, successfully improving productivity can lead to lay-offs. The literature provides two opposing theories of how agency interacts with the ability of quality-oriented improvement techniques to dramaticlly increase productivity. The 'Drive Out Fear' school argues that firms must commit to job security, while the 'Drive In Fear' school emphasizes the positive role that insecurity plays in motivating change. In this study a contract theoretic model is developed to analyze the role of agency in process improvement. The main insight of the study is that there are two types of job security, internal and external, that have opposite impacts on the firm's abilty to implement improvement initiatives. The distinction is useful in explaining the results of different case studies and can reconcile the two change theories.National Science Foundation, grant SBR-9422228, the Ford Motor Company and the Harley-Davidson Motor Company. MIT Sloan School of Management, Center for Innovation in Product Developmen

Clues on void evolution II: Measuring density and velocity profiles on SDSS galaxy redshift space distortions

Using the redshift-space distortions of void-galaxy cross-correlation function we analyse the dynamics of voids embedded in different environments. We compute the void-galaxy crosscorrelation function in the Sloan Digital Sky Survey (SDSS) in terms of distances taken along the line of sight and projected into the sky. We analyse the distortions on the cross-correlation isodensity levels and we find anisotropic isocontours consistent with expansion for large voids with smoothly rising density profiles and collapse for small voids with overdense shells surrounding them. Based on the linear approach of gravitational collapse theory we developed a parametric model of the void-galaxy redshift space cross-correlation function. We show that this model can be used to successfully recover the underlying velocity and density profiles of voids from redshift space samples. By applying this technique to real data, we confirm the twofold nature of void dynamics: large voids typically are in an expansion phase whereas small voids tend to be surrounded by overdense and collapsing regions. These results are obtained from the SDSS spectroscopic galaxy catalogue and also from semi-analytic mock galaxy catalogues, thus supporting the viability of the standard ΛCDM model to reproduce large scale structure and dynamics.Fil: Paz, Dante Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; ArgentinaFil: Lares Harbin Latorre, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; ArgentinaFil: Ceccarelli, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; ArgentinaFil: Padilla, Nelson David. Pontificia Universidad Católica de Chile; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garcia Lambas, Diego Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; Argentin