2 Comments on Gettysburg’s Stone Walls: Restoration or Rehabilitation? “Wirz’s Jewelry”: Memories of Captivity

This post is part of a series featuring behind-the-scenes dispatches from our Pohanka Interns on the front lines of history this summer as interpreters, archivists, and preservationists. See here for the introduction to the series. Captain Henry Wirz remains one of the most controversial figures in Andersonville’s history. One of just a handful of soldiers convicted of and executed for war crimes after the Civil War ended (not the only one, though perhaps the most notorious), he has taken on a dual identity in American memory as a remorseless criminal and an honorable martyr . Few physical reminders of Camp Sumter survive—only the earthworks and underground remains of the stockade wall logs indicate that a grassy Georgia field once held forty-five thousand Union prisoners of war. Written accounts and sketches, however, provide a fairly reliable basis for fabricating reproduction objects. One of the most memorable is “Wirz’s Jewelry”—the ball and chain with which Captain Wirz punished prisoners who attempted escape, stole supplies, or offended the Swiss officer. This instrument of confinement, carries its own complex symbolism, which has influenced historical memory of Civil War prisons. [excerpt

I Am Not A Prisoner of War : Agency, Adaptability, and Fulfillment of Expectations Among American Prisoners of War Held in Nazi Germany

In war memory, the typical prisoner of war narrative is one of either passive survival or heroic resistance. However, captured service members did not necessarily lose their agency when they lost their freedom. This study of Americans held in Germany during the Second World War shows that prisoners generally grounded themselves in their personal and national identities, while compromising ideas of heroism, sometimes passing up opportunities for resistance in order to survive

Project accelerate: increasing STEM opportunities for underserved high school students

Project Accelerate is a NSF-funded project aimed at helping prepare underserved high school students for the AP Physics 1 exam. The students attend schools that do not offer AP Physics 1. All Project Accelerate students are enrolled in a scaffolded small private online course (SPOC) that takes them through the physics material in an interactive way. A significant fraction of the students, including all those in the Boston area, also attend weekly 2.5-hour sessions on campus to do hands-on lab activities and recitation exercises. These sessions are led by undergraduate students who have pedagogical training. Our data indicate that Project Accelerate participants do at least as well on the AP Physics exam as similar students who take an AP Physics 1 through a traditional classroom-based course. One of the main goals of Project Accelerate is to give underserved students access to a rigorous science course, helping these students to build a solid foundation for a possible undergraduate degree in STEM. We also present evidence that successfully completing Project Accelerate makes students more likely to pursue further opportunities in STEM.Published versio

The validity of the semiclassical method for the coupled channel atomic scattering problem

Stationary phase approximation for two-channel atomic scattering system amplitud

Large-scale atomistic density functional theory calculations of phosphorus-doped silicon quantum bits

We present density functional theory calculations of phosphorus dopants in bulk silicon and of several properties relating to their use as spin qubits for quantum computation. Rather than a mixed pseudopotential or a Heitler-London approach, we have used an explicit treatment for the phosphorus donor and examined the detailed electronic structure of the system as a function of the isotropic doping fraction, including lattice relaxation due to the presence of the impurity. Doping electron densities and spin densities are examined in order to study the properties of the dopant electron as a function of the isotropic doping fraction. Doping potentials are also calculated for use in calculations of the scattering cross-sections of the phosphorus dopants, which are important in the understanding of electrically detected magnetic resonance experiments. We find that the electron density around the dopant leads to non-spherical features in the doping potentials, such as trigonal lobes in the (001) plane at energy scales of +12 eV near the nucleus and of -700 meV extending away from the dopants. These features are generally neglected in effective mass theory and will affect the coupling between the donor electron and the phosphorus nucleus. Our density functional calculations reveal detail in the densities and potentials of the dopants which are not evident in calculations that do not include explicit treatment of the phosphorus donor atom and relaxation of the crystal lattice. These details can also be used to parameterize tight-binding models for simulation of large-scale devices.Comment: 22 pages, 8 figure

The evolution of oscillatory behavior in age-structured species

A major challenge in ecology is to explain why so many species show oscillatory population dynamics and why the oscillations commonly occur with particular periods. The background environment, through noise or seasonality, is one possible driver of these oscillations, as are the components of the trophic web with which the species interacts. However, the oscillation may also be intrinsic, generated by density-dependent effects on the life history. Models of structured single-species systems indicate that a much broader range of oscillatory behavior than that seen in nature is theoretically possible. We test the hypothesis that it is selection that acts to constrain the range of periods. We analyze a nonlinear single-species matrix model with density dependence affecting reproduction and with trade-offs between reproduction and survival. We show that the evolutionarily stable state is oscillatory and has a period roughly twice the time to maturation, in line with observed patterns of periodicity. The robustness of this result to variations in trade-off function and density dependence is tested

Variational treatment of electron-polyatomic molecule scattering calculations using adaptive overset grids

The Complex Kohn variational method for electron-polyatomic molecule scattering is formulated using an overset grid representation of the scattering wave function. The overset grid consists of a central grid and multiple dense, atom-centered subgrids that allow the simultaneous spherical expansions of the wave function about multiple centers. Scattering boundary conditions are enforced by using a basis formed by the repeated application of the free particle Green's function and potential, $\hat{G}^+_0\hat{V}$ on the overset grid in a "Born-Arnoldi" solution of the working equations. The theory is shown to be equivalent to a specific Pad\'e approximant to the $T$-matrix, and has rapid convergence properties, both in the number of numerical basis functions employed and the number of partial waves employed in the spherical expansions. The method is demonstrated in calculations on methane and CF$_4$ in the static-exchange approximation, and compared in detail with calculations performed with the numerical Schwinger variational approach based on single center expansions. An efficient procedure for operating with the free-particle Green's function and exchange operators (to which no approximation is made) is also described