Friday, February 26th, 2016

John A. Doces – Magee, Christopher S. and Doces, John A. “Reconsidering Regime Type and Growth: Lies, Dictatorships, and Statistics.” International Studies Quarterly 59, no. 2 (2015) : 223-237.

John A. Doces, Associate Professor of Political Science

Some recent papers have concluded that authoritarian regimes have faster economic growth than democracies. These supposed growth benefits of autocracies are estimated using data sets in which growth rates rely heavily on data reported by each government. Governments have incentives to exaggerate their economic growth figures, however, and authoritarian regimes may have fewer limitations than democracies on their ability to do so. This paper argues that growth data submitted to international agencies are overstated by authoritarian regimes compared to democracies. If true, it calls into question the estimated relationship between government type and economic growth found in the literature. To measure the degree to which each government’s official growth statistics are overstated, the economic growth rates reported in the World Bank’s World Development Indicators are compared to a new measure of economic growth based on satellite imaging of nighttime lights. This comparison reveals whether or not dictators exaggerate their true growth rates and by how much. Annual GDP growth rates are estimated to be overstated by 0.5-1.5 percentage points in the statistics that dictatorships report to the World Bank.

Magee, Christopher S. and Doces, John A. “Reconsidering Regime Type and Growth: Lies, Dictatorships, and Statistics.” International Studies Quarterly 59, no. 2 (2015) : 223-237.

Continue reading John A. Doces – Magee, Christopher S. and Doces, John A. “Reconsidering Regime Type and Growth: Lies, Dictatorships, and Statistics.” International Studies Quarterly 59, no. 2 (2015) : 223-237. »

Friday, February 26th, 2016

Katharina Vollmayr-Lee – Helfferich, J.; Vollmayr-Lee, Katharina; Ziebert, F.; Meyer, H.; and Baschnagel, J. “Glass Formers Display Universal Non-Equilibrium Dynamics on the Level of Single-Particle Jumps.” EPL 109, no. 3 (2015) : 36004.

Katharina Vollmayr-Lee, Professor of Physics

Glasses are inherently out-of-equilibrium systems evolving slowly toward their equilibrium state in a process called physical aging. During aging, dynamic observables depend on the history of the system, hampering comparative studies of dynamics in different glass formers. Here, we demonstrate how glass formers can be directly compared on the level of single-particle jumps, i. e. the structural relaxation events underlying the a-process. Describing the dynamics in terms of a continuous-time random walk, an analytic prediction for the jump rate is derived. The result is subsequently compared to molecular-dynamics simulations of amorphous silica and a polymer melt as two generic representatives of strong and fragile glass formers, and good agreement is found. Copyright (C) EPLA, 2015

Helfferich, J.; Vollmayr-Lee, Katharina; Ziebert, F.; Meyer, H.; and Baschnagel, J. “Glass Formers Display Universal Non-Equilibrium Dynamics on the Level of Single-Particle Jumps.” EPL 109, no. 3 (2015) : 36004.

Continue reading Katharina Vollmayr-Lee – Helfferich, J.; Vollmayr-Lee, Katharina; Ziebert, F.; Meyer, H.; and Baschnagel, J. “Glass Formers Display Universal Non-Equilibrium Dynamics on the Level of Single-Particle Jumps.” EPL 109, no. 3 (2015) : 36004. »

Friday, February 26th, 2016

Katharina Vollmayr-Lee – Helfferich, Julian; Vollmayr-Lee, Katharina; Ziebert, Falko; Meyer, Hendrik; and Baschnagel, Joerg. “Glass Formers Display Universal Non-Equilibrium Dynamics on the Level of Single-Particle Jumps.” European Physical Letters 109, (2015) : 36004-p1-36004-p9.

Katharina Vollmayr-Lee, Professor of Physics

Glasses are inherently out-of-equilibrium systems evolving slowly toward their equilibrium state in a process called physical aging. During aging, dynamic observables depend on the history of the system, hampering comparative studies of dynamics in different glass formers. Here, we demonstrate how glass formers can be directly compared on the level of single-particle jumps, i.e. the structural relaxation events underlying the alpha-process. Describing the dynamics in terms of a continuous-time random walk, an analytic prediction for the jump rate is derived. The result is subsequently compared to molecular-dynamics simulations of amorphous silica and a polymer melt as two generic representatives of strong and fragile glass formers, and good agreement is found.

Helfferich, Julian; Vollmayr-Lee, Katharina; Ziebert, Falko; Meyer, Hendrik; and Baschnagel, Joerg. “Glass Formers Display Universal Non-Equilibrium Dynamics on the Level of Single-Particle Jumps.” European Physical Letters 109, (2015) : 36004-p1-36004-p9.

Continue reading Katharina Vollmayr-Lee – Helfferich, Julian; Vollmayr-Lee, Katharina; Ziebert, Falko; Meyer, Hendrik; and Baschnagel, Joerg. “Glass Formers Display Universal Non-Equilibrium Dynamics on the Level of Single-Particle Jumps.” European Physical Letters 109, (2015) : 36004-p1-36004-p9. »

Friday, February 26th, 2016

Thomas H. Solomon – Megson, P. W.; Najarian, M. L.; Lilienthal, Katie; and Solomon, Thomas H. “Pinning of Reaction Fronts by Burning Invariant Manifolds in Extended Flows.” Physics of Fluids 27, no. 2 (2015) : 023601.

Thomas H. Solomon, Professor of Physics

We present experiments on the behavior of reaction fronts in extended, vortex-dominated flows in the presence of an imposed wind. We use the ferroin-catalyzed, excitable Belousov-Zhabotinsky chemical reaction, which produces pulse-like reaction fronts. Two time-independent flows are studied: an ordered (square) array of vortices and a spatially disordered flow. The flows are generated with a magneto-hydrodynamic forcing technique, with a pattern of magnets underneath the fluid cell. The magnets are mounted on a translation stage which moves with a constant speed V-d under the fluid, resulting in motion of the vortices within the flow. In a reference frame moving with magnets, the flow is equivalent to one with stationary vortices and a uniform wind with speed W = V-d. For a wide range of wind speeds, reaction fronts pin to the vortices (in a co-moving reference frame), propagating neither forward against the wind nor being blown backward. We analyze this pinning phenomenon and the resulting front shapes using a burning invariant manifold (BIM) formalism. The BIMs are one-way barriers to reaction fronts in the advection-reaction-diffusion process. Pinning occurs when several BIMs overlap to form a complete barrier that spans the width of the system. In that case, the shape of the front is determined by the shape of the BIMs. For the ordered array flow, we predict the locations of the BIMs numerically using a simplified model of the velocity field for the ordered vortex array and compare the BIM shapes to the pinned reaction fronts. We also explore transient behavior of the fronts (before reaching their steady state) to highlight the one-way nature of the BIMs. (C) 2015 Author(s).

Megson, P. W.; Najarian, M. L.; Lilienthal, Katie; and Solomon, Thomas H. “Pinning of Reaction Fronts by Burning Invariant Manifolds in Extended Flows.” Physics of Fluids 27, no. 2 (2015) : 023601.

Continue reading Thomas H. Solomon – Megson, P. W.; Najarian, M. L.; Lilienthal, Katie; and Solomon, Thomas H. “Pinning of Reaction Fronts by Burning Invariant Manifolds in Extended Flows.” Physics of Fluids 27, no. 2 (2015) : 023601. »

Friday, February 26th, 2016

Thomas H. Solomon – Mahoney, John R.; Li, John; Boyer, Carleen; and Solomon, Thomas H. “Frozen Reaction Fronts in Steady Flows: A Burning-Invariant-Manifold Perspective.” Physical Review E 92, no. 6 (2015) : 063005.

Thomas H. Solomon, Professor of Physics

The dynamics of fronts, such as chemical reaction fronts, propagating in two-dimensional fluid flows can be remarkably rich and varied. For time-invariant flows, the front dynamics may simplify, settling in to a steady state in which the reacted domain is static, and the front appears “frozen.” Our central result is that these frozen fronts in the two-dimensional fluid are composed of segments of burning invariant manifolds, invariant manifolds of front-element dynamics in xy theta space, where theta is the front orientation. Burning invariant manifolds (BIMs) have been identified previously as important local barriers to front propagation in fluid flows. The relevance of BIMs for frozen fronts rests in their ability, under appropriate conditions, to form global barriers, separating reacted domains from nonreacted domains for all time. The second main result of this paper is an understanding of bifurcations that lead from a nonfrozen state to a frozen state, as well as bifurcations that change the topological structure of the frozen front. Although the primary results of this study apply to general fluid flows, our analysis focuses on a chain of vortices in a channel flow with an imposed wind. For this system, we present both experimental and numerical studies that support the theoretical analysis developed here.

Mahoney, John R.; Li, John; Boyer, Carleen; and Solomon, Thomas H. “Frozen Reaction Fronts in Steady Flows: A Burning-Invariant-Manifold Perspective.” Physical Review E 92, no. 6 (2015) : 063005.

Continue reading Thomas H. Solomon – Mahoney, John R.; Li, John; Boyer, Carleen; and Solomon, Thomas H. “Frozen Reaction Fronts in Steady Flows: A Burning-Invariant-Manifold Perspective.” Physical Review E 92, no. 6 (2015) : 063005. »

Friday, February 26th, 2016

Thomas H. Solomon – Gowen, Savannah and Solomon, Thomas H. “Experimental Studies of Coherent Structures in an Advection-Reaction-Diffusion System.” Chaos (Woodbury, N.Y.) 25, no. 8 (2015) : 087403.

Thomas H. Solomon, Professor of Physics

We present experimental studies of reaction front propagation in a single vortex flow with an imposed external wind. The fronts are produced by the excitable, ferroin-catalyzed Belousov-Zhabotinsky chemical reaction. The flow is generated using an electromagnetic forcing technique: an almost-radial electrical current interacts with a magnetic field from a magnet below the fluid layer to produce the vortex. The magnet is mounted on crossed translation stages allowing for movement of the vortex through the flow. Reaction fronts triggered in or in front of the moving vortex form persistent structures that are seen experimentally for time-independent (constant motion), time-periodic, and time-aperiodic flows. These results are examined with the use of burning invariant manifolds that act as one-way barriers to front motion in the flows. We also explore the usefulness of finite-time Lyapunov exponent fields as an instrument for analyzing front propagation behavior in a fluid flow.

Gowen, Savannah and Solomon, Thomas H. “Experimental Studies of Coherent Structures in an Advection-Reaction-Diffusion System.” Chaos (Woodbury, N.Y.) 25, no. 8 (2015) : 087403.

Continue reading Thomas H. Solomon – Gowen, Savannah and Solomon, Thomas H. “Experimental Studies of Coherent Structures in an Advection-Reaction-Diffusion System.” Chaos (Woodbury, N.Y.) 25, no. 8 (2015) : 087403. »

Friday, February 26th, 2016

Jack F. Gallimore – Sales, Dinalva; Robinson, Andy; Axon, David J.; Gallimore, Jack F.; Kharb, Preeti; Curran, Rachel L.; O’Dea, Christopher P.; Baum, Stefi A.; Elitzur, Moshe; and Mittal, Rupal. “An Embedded Active Nucleus in the OH Megamaser Galaxy IRAS16399-0937.” The Astrophysical Journal 799, (2015) : 25.

Jack F. Gallimore, Associate Professor of Physics

We present a multiwavelength study of the OH megamaser galaxy IRAS16399-0937, based on new Hubble Space Telescope (HST)/Advanced Camera for Surveys F814W and Hα+[N II] images and archive data from HST, Two Micron All Sky Survey, Spitzer, Herschel and the Very Large Array. This system has a double nucleus, whose northern (IRAS16399N) and southern (IRAS16399S) components have a projected separation of ~6” (3.4 kpc) and have previously been identified based on optical spectra as a low ionization nuclear emission line region (LINER) and starburst nucleus, respectively. The nuclei are embedded in a tidally distorted common envelope, in which star formation is mostly heavily obscured. The infrared spectrum is dominated by strong polycyclic aromatic hydrocarbon, but deep silicate and molecular absorption features are also present, and are strongest in the IRAS16399N nucleus. The 0.435-500 μm spectral energy distribution was fitted with a model including stellar, interstellar medium and active galactic nucleus (AGN) torus components using our new Markov Chain Monte Carlo code, CLUMPYDREAM. The results indicate that the IRAS16399N contains an AGN (L bol ~ 1044 erg s-1) deeply embedded in a quasi-spherical distribution of optically thick clumps with a covering fraction ≈1. We suggest that these clumps are the source of the OHM emission in IRAS16399-0937. The high torus covering fraction precludes AGN photoionization as the origin of the LINER spectrum, however, the spectrum is consistent with shocks (v ~ 100-200 km s-1). We infer that the ~108 M black hole in IRAS16399N is accreting at a small fraction (~1%) of its Eddington rate. The low accretion rate and modest nuclear star formation rates suggest that while the gas-rich major merger forming the IRAS16399-0937 system has triggered widespread star formation, the massive gas inflows expected from merger simulations have not yet fully developed.

Sales, Dinalva; Robinson, Andy; Axon, David J.; Gallimore, Jack F.; Kharb, Preeti; Curran, Rachel L.; O’Dea, Christopher P.; Baum, Stefi A.; Elitzur, Moshe; and Mittal, Rupal. “An Embedded Active Nucleus in the OH Megamaser Galaxy IRAS16399-0937.” The Astrophysical Journal 799, (2015) : 25.

Continue reading Jack F. Gallimore – Sales, Dinalva; Robinson, Andy; Axon, David J.; Gallimore, Jack F.; Kharb, Preeti; Curran, Rachel L.; O’Dea, Christopher P.; Baum, Stefi A.; Elitzur, Moshe; and Mittal, Rupal. “An Embedded Active Nucleus in the OH Megamaser Galaxy IRAS16399-0937.” The Astrophysical Journal 799, (2015) : 25. »

Friday, February 26th, 2016

Jiajia Dong – Dong, JiaJia. “Spatial Structures in a Simple Model of Population Dynamics for Parasite-Host Interactions.” Europhysics Letters 111, no. 4 (2015) : 48001.

Jiajia Dong, Associate Professor of Physics & Astronomy

Spatial patterning can be crucially important for understanding the behavior of interacting populations. Here we investigate a simple model of parasite and host populations in which parasites are random walkers that must come into contact with a host in order to reproduce. We focus on the spatial arrangement of parasites around a single host, and we derive using analytics and numerical simulations the necessary conditions placed on the parasite fecundity and lifetime for the population’s long-term survival. We also show that the parasite population can be pushed to extinction by a large drift velocity, but, counterintuitively, a small drift velocity generally increases the parasite population.

Dong, JiaJia. “Spatial Structures in a Simple Model of Population Dynamics for Parasite-Host Interactions.” Europhysics Letters 111, no. 4 (2015) : 48001.

Continue reading Jiajia Dong – Dong, JiaJia. “Spatial Structures in a Simple Model of Population Dynamics for Parasite-Host Interactions.” Europhysics Letters 111, no. 4 (2015) : 48001. »

Friday, February 26th, 2016

Jiajia Dong – Sahoo, Mamata; Dong, Jiajia; and Klumpp, Stefan. “Dynamic Blockage in an Exclusion Process.”Journal of Physics A–Mathematical and Theoretical 48, no. 1 (2015) : 015007.

Jiajia Dong, Associate Professor of Physics & Astronomy

We study an asymmetric exclusion model with one dynamic roadblock particle. The roadblock particle is allowed to move diffusively as well as by longrange jumps mimicking an unbinding/rebinding process. Using Monte Carlo simulations and analytical arguments, the two types of roadblock moves are considered both separately and in combination. Several interesting dynamic phenomena are observed. The long-range jumps of the roadblock lead to a current that depends on the number of particles in the system rather than on the particle density, and thus scales linearly with the system size (up to a critical size). This behavior can be explained by a collective motion of all particles following the roadblock. The diffusive roadblock movements on the other hand lead to a ratcheting motion with the active (driven) particles pushing the roadblock forward.

Sahoo, Mamata; Dong, Jiajia; and Klumpp, Stefan. “Dynamic Blockage in an Exclusion Process.”Journal of Physics A–Mathematical and Theoretical 48, no. 1 (2015) : 015007.

Continue reading Jiajia Dong – Sahoo, Mamata; Dong, Jiajia; and Klumpp, Stefan. “Dynamic Blockage in an Exclusion Process.”Journal of Physics A–Mathematical and Theoretical 48, no. 1 (2015) : 015007. »

Friday, February 26th, 2016

Katelyn Allers – Petigura, Erik A.; Schlieder, Joshua E.; Crossfield, Ian J.M.; Howard, Andrew W.; Deck, Katherine M.; Ciardi, David R.; Sinukoff, Evan; Allers, Katelyn N.; Best, William M.J.; Liu, Michael C.; Beichman, Charles A.; Isaacson, Howard; Hansen, Brad M.S.; and Lepine, Sebastien. “Two Transiting Earth-Size Planets Near Resonance Orbiting a Nearby Cool Star.” Astrophysical Journal 811, no. 2 (2015) : 102.

Katelyn Allers, Associate Professor of Physics & Astronomy

Discoveries from the prime Kepler mission demonstrated that small planets (<3R(circle plus)) are common outcomes of planet formation. While Kepler detected many such planets, all but a handful orbit faint, distant stars and are not amenable to precise follow up measurements. Here, we report the discovery of two small planets transiting K2-21, a bright (K = 9.4) M0 dwarf located 65 +/- 6 pc from Earth. We detected the transiting planets in photometry collected during Campaign 3 of NASA's K2 mission. Analysis of transit light curves reveals that the planets have small radii compared to their host star, R-P/R-star = 2.60 +/- 0.14% and 3.15 +/- 0.20%, respectively. We obtained follow up NIR spectroscopy of K2-21 to constrain host star properties, which imply planet sizes of 1.59 +/- 0.43 R-circle plus and 1.92 +/- 0.53 R-circle plus, respectively, straddling the boundary between high-density, rocky planets and low-density planets with thick gaseous envelopes. The planets have orbital periods of 9.32414 days and 15.50120 days, respectively, and a period ratio P-c/P-b = 1.6624, very near to the 5: 3 mean motion resonance, which may be a record of the system's formation history. Transit timing variations due to gravitational interactions between the planets may be detectable using ground-based telescopes. Finally, this system offers a convenient laboratory for studying the bulk composition and atmospheric properties of small planets with low equilibrium temperatures.

Petigura, Erik A.; Schlieder, Joshua E.; Crossfield, Ian J.M.; Howard, Andrew W.; Deck, Katherine M.; Ciardi, David R.; Sinukoff, Evan; Allers, Katelyn N.; Best, William M.J.; Liu, Michael C.; Beichman, Charles A.; Isaacson, Howard; Hansen, Brad M.S.; and Lepine, Sebastien. “Two Transiting Earth-Size Planets Near Resonance Orbiting a Nearby Cool Star.” Astrophysical Journal 811, no. 2 (2015) : 102.

Continue reading Katelyn Allers – Petigura, Erik A.; Schlieder, Joshua E.; Crossfield, Ian J.M.; Howard, Andrew W.; Deck, Katherine M.; Ciardi, David R.; Sinukoff, Evan; Allers, Katelyn N.; Best, William M.J.; Liu, Michael C.; Beichman, Charles A.; Isaacson, Howard; Hansen, Brad M.S.; and Lepine, Sebastien. “Two Transiting Earth-Size Planets Near Resonance Orbiting a Nearby Cool Star.” Astrophysical Journal 811, no. 2 (2015) : 102. »

Friday, February 26th, 2016

Katelyn Allers – Garcia, E. V.; Dupuy, Trent J.; Allers, Katelyn N.; Liu, Michael C.; and Deacon, Niall R. “On the Binary Frequency of the Lowest Mass Members of the Pleiades with Hubble Space Telescope Wide Field Camera 3.” Astrophysical Journal 804, no. 1 (2015) : 65.

Katelyn Allers, Associate Professor of Physics & Astronomy

We present the results of a Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging survey of 11 of the lowest mass brown dwarfs in the Pleiades known (25-40M(Jup)). These objects represent the predecessors to T dwarfs in the field. Using a semi-empirical binary point-spread function (PSF)-fitting technique, we are able to probe to 0 ”.03 (0.75 pixel), better than 2x the WFC3/UVIS diffraction limit. We did not find any companions to our targets. From extensive testing of our PSF-fitting method on simulated binaries, we compute detection limits which rule out companions to our targets with mass ratios of greater than or similar to 0.7 and separations greater than or similar to 4 AU. Thus, our survey is the first to attain the high angular resolution needed to resolve brown dwarf binaries in the Pleiades at separations that are most common in the field population. We constrain the binary frequency over this range of separation and mass ratio of 25-40M(Jup) Pleiades brown dwarfs to be < 11% for 1 sigma (< 26% at 2s). This binary frequency is consistent with both younger and older brown dwarfs in this mass range.

Garcia, E. V.; Dupuy, Trent J.; Allers, Katelyn N.; Liu, Michael C.; and Deacon, Niall R. “On the Binary Frequency of the Lowest Mass Members of the Pleiades with Hubble Space Telescope Wide Field Camera 3.” Astrophysical Journal 804, no. 1 (2015) : 65.

Continue reading Katelyn Allers – Garcia, E. V.; Dupuy, Trent J.; Allers, Katelyn N.; Liu, Michael C.; and Deacon, Niall R. “On the Binary Frequency of the Lowest Mass Members of the Pleiades with Hubble Space Telescope Wide Field Camera 3.” Astrophysical Journal 804, no. 1 (2015) : 65. »

Friday, February 26th, 2016

Matthew H. Slater – Slater, Matthew H. “Natural Kindness.” British Journal for the Philosophy of Science 66, no. 2 (2015) : 375-411.

Matthew H. Slater, Associate Professor of Philosophy

Philosophers have long been interested in a series of interrelated questions about natural kinds. What are they? What role do they play in science and metaphysics? How do they contribute to our epistemic projects? What categories count as natural kinds? And so on. Owing, perhaps, to different starting points and emphases, we now have at hand a variety of conceptions of natural kinds-some apparently better suited than others to accommodate a particular sort of inquiry. Even if coherent, this situation isn’t ideal. My goal in this article is to begin to articulate a more general account of ‘natural kind phenomena’. While I do not claim that this account should satisfy everyone-it is built around a certain conception of the epistemic role of kinds and has an obvious pragmatic flavour-I believe that it has the resources to go further than extant alternatives, in particular the homeostatic property cluster view of kinds.

Slater, Matthew H. “Natural Kindness.” British Journal for the Philosophy of Science 66, no. 2 (2015) : 375-411.

Continue reading Matthew H. Slater – Slater, Matthew H. “Natural Kindness.” British Journal for the Philosophy of Science 66, no. 2 (2015) : 375-411. »

Friday, February 26th, 2016

Sheila Lintott – Lintott, Sheila. “Friendship and Bias: Ethical and Epistemic Considerations.” Journal of Social Philosophy 46, no. 3 (2015) : 318-339.

Sheila Lintott, Associate Professor of Philosophy

Lintott, Sheila. “Friendship and Bias: Ethical and Epistemic Considerations.” Journal of Social Philosophy 46, no. 3 (2015) : 318-339.

Continue reading Sheila Lintott – Lintott, Sheila. “Friendship and Bias: Ethical and Epistemic Considerations.” Journal of Social Philosophy 46, no. 3 (2015) : 318-339. »

Friday, February 26th, 2016

Karen M. Morin – Morin, Karen M. “The Late-Modern American Jail: Epistemologies of Space and Violence.” The Geographical Journal forthcoming (2015).

Karen M. Morin, Associate Provost

One of the most troubling aspects of current trends in American mass incarceration is the extent to which ‘criminality’ is produced within prison walls, primarily in the form of inmate–inmate or inmate–staff assaults. Most methods of prison or jail control have the adverse, and perverse, effect of increasing inmates’ levels of fear, terror, and ultimately violence – with stabbings, beatings, and other types of assaults common occurrences. The design of podular ‘direct supervision’ jails and their accompanying philosophies of punishment aspire to change these conditions. Direct supervision features correctional officers inside each housing unit with no physical barriers impeding supervision, and is intended to create a safe, more humane, stress-free environment for both inmates and staff. This study draws on ethnographic evidence of inmate experiences with direct supervision at Douglas County Department of Corrections in Omaha, Nebraska (USA). The respondents generally do feel safe in this jail environment, for a combination of reasons, some of which are related to spatial design. Inmates identified a number of implications – gains and losses – of this more ‘humane’ form of incarceration in terms of power and empowerment. The study also documents the potential for inmate activism on their own behalf through this design.

Morin, Karen M. “The Late-Modern American Jail: Epistemologies of Space and Violence.” The Geographical Journal forthcoming (2015).

Continue reading Karen M. Morin – Morin, Karen M. “The Late-Modern American Jail: Epistemologies of Space and Violence.” The Geographical Journal forthcoming (2015). »

Friday, February 26th, 2016

Karen M. Morin – Morin, Karen M. “Carceral Space: Prisoners and Animals.” Antipode: A Radical Journal of Geography (2016).

Karen M. Morin, Associate Provost

This paper develops a framework for exploring resonances across human and nonhuman carceral geographies. I illustrate the close linkages across prisoner and animal carcerality and captivity focusing on three types of sites and institutions: the prison execution chamber and the animal slaughterhouse; sites of medical (and other) laboratory testing of pharmaceutical and other products on incarcerated humans and captive animals; and sites and institutions of exploited prisoner and animal labor. The main themes that call for a ‘carceral comparison’ among these sites include the emotional and psychological strain and violence enacted on bodies that is interwoven into their day-to-day operations; their geographies (locations, design and layout) and the carefully choreographed and regulated movements within them that speak to regimes of surveillance, power, and control; and the ethical questions that arise when we consider the potential for these sites to become locations of genocide and extinction of particular populations.

Morin, Karen M. “Carceral Space: Prisoners and Animals.” Antipode: A Radical Journal of Geography (2016).

Continue reading Karen M. Morin – Morin, Karen M. “Carceral Space: Prisoners and Animals.” Antipode: A Radical Journal of Geography (2016). »

Friday, February 26th, 2016

Constance W. Ziemian – Ziemian, Sophia; Okwara, Maryvivian; and Ziemian, Constance W. “Tensile and Fatigue Behavior of Layered Acrylonitrile Butadiene Styrene.” Rapid Prototyping Journal 21, no. 3 (2015) : 270-278.

Constance W. Ziemian, Professor of Mechanical Engineering

Purpose – This paper aims to define the effect of specimen mesostructure on the monotonic tensile behavior and tensile-fatigue life of layered acrylonitrile butadiene styrene (ABS) components fabricated by fused deposition modeling (FDM).

Design/methodology/approach – Tensile tests were performed on FDM dogbone specimens with four different raster orientations according to ASTM standard D638-03. Resulting ultimate tensile stresses (UTS) for each raster orientation were used to compute the maximum stress for fatigue testing, i.e. 90, 75, 60 and 50 or 45 per cent nominal values of the UTS. Multiple specimens were subjected to tension – tension fatigue cycling with stress ratio of R = 0.10 in accordance with ASTM standard D7791-12.

Findings – Both tensile strength and fatigue performance exhibited anisotropic behavior. The longitudinal (0 degrees) and default (+45/-45 degrees) raster orientations performed significantly better than the diagonal (45 degrees) or transverse (90 degrees) orientations in regards to fatigue life, as displayed in the resulting Wohler curves.

Practical implications – Raster orientation has a significant effect on the fatigue performance of FDM ABS components. Aligning FDM fibers along the axis of the applied stress provides improved fatigue life. If the direction of applied stresses is not expected to be constant in given application, the default raster orientation is recommended.

Originality/value – This project provides knowledge to the limited work published on the fatigue performance of FDM ABS components. It provides S-N fatigue life results that can serve as a foundation for future work, combining experimental investigations with theoretical principles and the statistical analysis of data.

Ziemian, Sophia; Okwara, Maryvivian; and Ziemian, Constance W. “Tensile and Fatigue Behavior of Layered Acrylonitrile Butadiene Styrene.” Rapid Prototyping Journal 21, no. 3 (2015) : 270-278.

Continue reading Constance W. Ziemian – Ziemian, Sophia; Okwara, Maryvivian; and Ziemian, Constance W. “Tensile and Fatigue Behavior of Layered Acrylonitrile Butadiene Styrene.” Rapid Prototyping Journal 21, no. 3 (2015) : 270-278. »

Friday, February 26th, 2016

Nathan P. Siegel – Siegel, Nathan P.; Gross, Michael D.; and Coury, Robert. “The Development of Direct Absorption and Storage Media for Falling Particle Solar Central Receivers.” ASME Journal of Solar Energy Engineering 137, no. 4 (2015).

Nathan P. Siegel, Assistant Professor of Mechanical Engineering

Spherical sintered bauxite particles between 200 μm and 700 μm in diameter have been shown to be effective in the direct absorption and storage of concentrated solar energy. These particles are commercially available in large quantities and exhibit as-received solar weighted absorptance (αs) greater than 0.90, which gradually degrades with extended heating in air at 700 °C and above. The degradation mechanism is an oxidation reaction that can be reversed via thermal or chemical reduction, resulting in αs > 0.95 along with enhanced resistance to further degradation for some formulations. Certain metal oxide pigments, added to Al2O3:SiO2, have proven to achieve solar weighted absorptance levels similar to those of the commercially available particles and may be promising alternatives to currently available materials.

Siegel, Nathan P.; Gross, Michael D.; and Coury, Robert. “The Development of Direct Absorption and Storage Media for Falling Particle Solar Central Receivers.” ASME Journal of Solar Energy Engineering 137, no. 4 (2015).

Continue reading Nathan P. Siegel – Siegel, Nathan P.; Gross, Michael D.; and Coury, Robert. “The Development of Direct Absorption and Storage Media for Falling Particle Solar Central Receivers.” ASME Journal of Solar Energy Engineering 137, no. 4 (2015). »

Friday, February 26th, 2016

Mala M. Sharma – Sharma, Mala M.; Eden, Timothy; and Golesich, Brock T. “Effect of Surface Preparation on the Microstructure, Adhesion, and Tensile Properties of Cold-Sprayed Aluminum Coatings on AA2024 Substrates.” Journal of Thermal Spray Technology 23, no. 3 (2015): 410-422.

Mala M. Sharma, Associate Professor of Mechanical Engineering

Commercially pure aluminum coatings (CP-Al) were applied to AA 2024-T351 substrates utilizing the cold spray process using different surface preparation methods and carrier gases; the resulting microstructures and mechanical properties were investigated. Substrate preparation methods were examined to understand the effect of substrate roughness on coating properties, to minimize embedded grit, and to identify the surface preparation method that yielded the best combination of coating properties. Three substrate roughing preparations, glass bead, SiC grit, and alumina grit blast, were examined while utilizing both helium and nitrogen as carrier gases in the cold spray process. Coatings that were oxide free, possessing densities greater than 99% were achieved, with the mean coating porosity ranging 0.1-0.5%. The highest mean adhesion strength was 42 MPa for the nitrogen gas and 20 MPa for the helium gas, both using glass bead surface preparation. For the nitrogen process gas samples, the surface preparation methods that produced high pull strengths correlated to bend test specimens that showed no signs of cracking on surfaces or edges. The overall best combination of mechanical property results was achieved with coatings prepared by glass bead surface roughening using nitrogen as a carrier gas.

Sharma, Mala M.; Eden, Timothy; and Golesich, Brock T. “Effect of Surface Preparation on the Microstructure, Adhesion, and Tensile Properties of Cold-Sprayed Aluminum Coatings on AA2024 Substrates.” Journal of Thermal Spray Technology 23, no. 3 (2015): 410-422.

Continue reading Mala M. Sharma – Sharma, Mala M.; Eden, Timothy; and Golesich, Brock T. “Effect of Surface Preparation on the Microstructure, Adhesion, and Tensile Properties of Cold-Sprayed Aluminum Coatings on AA2024 Substrates.” Journal of Thermal Spray Technology 23, no. 3 (2015): 410-422. »

Friday, February 26th, 2016

Mala M. Sharma – Sharma, Mala M.; Tomedi, Josh D.; and Parks, Jeffrey M. “A Microscopic Study on the Corrosion Fatigue of Ultra-Fine Grained and Conventional Al-Mg Alloy.” Corrosion Science 93 (2015): 180-190.

Mala M. Sharma, Associate Professor of Mechanical Engineering

The corrosion behavior of a nanocrystalline (NC)/ultrafine grained (UFG) Al–Mg based alloy was investigated and compared to its conventional counterpart 5083(H111). The corrosion fatigue (CF) was studied with respect to pit initiation, pit location and crack propagation as a function of environment. Scanning electron microscopy (SEM) with EDS was used to analyze the fracture surface of the failed specimen with respect to pitting characteristics, crack propagation and corrosion product. Load vs. cycles to failure was measured and S/N curves were generated for the UFG Al–Mg based alloy and the conventional counterpart 5083 in air and seawater.

Sharma, Mala M.; Tomedi, Josh D.; and Parks, Jeffrey M. “A Microscopic Study on the Corrosion Fatigue of Ultra-Fine Grained and Conventional Al-Mg Alloy.” Corrosion Science 93 (2015): 180-190.

Continue reading Mala M. Sharma – Sharma, Mala M.; Tomedi, Josh D.; and Parks, Jeffrey M. “A Microscopic Study on the Corrosion Fatigue of Ultra-Fine Grained and Conventional Al-Mg Alloy.” Corrosion Science 93 (2015): 180-190. »

Friday, February 26th, 2016

Charles Kim – Krishnan, Girish; Bishop-Moser, Joshua; Kim, Charles; and Kota, Sridhar. “Kinematics of a Generalized Class of Pneumatic Artificial Muscles.” Journal of Mechanisms and Robotics–Transactions of the ASME 7, no. 4 (2015) : 041014.

Charles Kim, Associate Professor of Mechanical Engineering

Fluid filled fiber reinforced elastomeric enclosures (FREEs) have been a popular choice for actuators in prosthetics and soft robots owing to their high power density and cost effective manufacturing. While a narrow class of FREEs known as McKibben’s actuators have been extensively studied, there is a wide unexplored class that could be potentially used as actuators and soft structural members. This paper analyzes the mobility of generalized FREEs based on simple geometric relationships that result from the inextensibility of fibers and fluidic actuation. The analysis conducted can be classified into instantaneous kinematics and global or large deformation kinematics. Instantaneous kinematics reveals that the most general deformation pattern of the FREE is a screw motion about the axis of its cylinder, whose pitch is a function of fiber orientations. Furthermore, a set of fiber angles, which do not deform under volumetric actuation were identified as the locked manifold (LM). Global kinematic analysis revealed that every FREE continued to deform until its fiber configuration approached the LM. These insights were corroborated with finite element analysis (FEA) and testing for a small sample of FREE actuators.

Krishnan, Girish; Bishop-Moser, Joshua; Kim, Charles; and Kota, Sridhar. “Kinematics of a Generalized Class of Pneumatic Artificial Muscles.” Journal of Mechanisms and Robotics–Transactions of the ASME 7, no. 4 (2015) : 041014.

Continue reading Charles Kim – Krishnan, Girish; Bishop-Moser, Joshua; Kim, Charles; and Kota, Sridhar. “Kinematics of a Generalized Class of Pneumatic Artificial Muscles.” Journal of Mechanisms and Robotics–Transactions of the ASME 7, no. 4 (2015) : 041014. »