M Zamponi

Forschungszentrum Jülich, Jülich, North Rhine-Westphalia, Germany

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Publications (27)102.07 Total impact

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    ABSTRACT: We investigate the possibility of using the prompt γ rays emitted by aluminum windows in order to monitor the neutron flux of the beam. A Nal scintillation detector is used to detect the prompt γ rays. No additional material apart from the unavoidable Al windows along the flight path is placed in the beam. The performance of the monitor is compared to that of a standard BF3-monitor placed in the beam. Influences of a magnetic field on the photomultiplier of the Nal monitor is discussed, as well as the influence of activation gammas. At an instrument using a beam chopper the time behaviour is discussed.
    Journal of Physics Conference Series 07/2014; 528(1):012038. DOI:10.1088/1742-6596/528/1/012038
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    ABSTRACT: The functional efficacy of colocalized, linked protein domains is dependent on linker flexibility and system compaction. However, the detailed characterization of these properties in aqueous solution presents an enduring challenge. Here, we employ a novel, to our knowledge, combination of complementary techniques, including small-angle neutron scattering, neutron spin-echo spectroscopy, and all-atom molecular dynamics and coarse-grained simulation, to identify and characterize in detail the structure and dynamics of a compact form of mercuric ion reductase (MerA), an enzyme central to bacterial mercury resistance. MerA possesses metallochaperone-like N-terminal domains (NmerA) tethered to its catalytic core domain by linkers. The NmerA domains are found to interact principally through electrostatic interactions with the core, leashed by the linkers so as to subdiffuse on the surface over an area close to the core C-terminal Hg(II)-binding cysteines. How this compact, dynamical arrangement may facilitate delivery of Hg(II) from NmerA to the core domain is discussed.
    Biophysical Journal 07/2014; 107(2):393-400. DOI:10.1016/j.bpj.2014.06.013 · 3.83 Impact Factor
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    ABSTRACT: We have investigated the thermal behavior, local structure, and dynamics in a system where 25 wt % PEO [poly(ethylene oxide)] linear chains are mixed with 75 wt % PMMA [poly(methyl methacrylate)] soft nanoparticles. Calorimetric and wide-angle X-ray scattering experiments point to a weak penetration of the PEO chains in the nanoparticles, qualifying the mixture as a nanocomposite. Quasi-elastic neutron scattering (QENS) experiments on partially deuterated samples has selectively revealed the component dynamics in the system. The α-methyl group dynamics of PMMA, which fall within the QENS time scale in the temperature range investigated, are hardly affected by the presence of PEO except for hints of a more heterogeneous environment in the nanocomposite than in bulk PMMA. The effects on the dynamics of PEO are more interesting. The observation of dynamics in the microseconds range for the PEO component of the nanocomposite at temperatures at which the calorimetric experiments indicate the freezing of its segmental relaxation provides evidence for confined dynamics below the main glass transition of the mixture—attributable to the effective glass transition of the slow component. A parallel study on an equivalent blend of PEO and linear PMMA chains shows that these effects are independent of the topology of the PMMA. However, well above the effective glass transition of the slow component, the dynamics of PEO differ in both systems. In the linear blend, PEO segments move with the typical features of supercooled polymers in metastable equilibrium, while in the nanocomposite PEO dynamics exhibit an anomalously strong deviation from Gaussian behavior. This deviation grows with increased mobility of the nanoparticles. PEO segments are seemingly trapped in effective cages imposed by the nanoparticles for a very long time—more than 2 orders of magnitude longer than in bulk or when surrounded by linear PMMA chains—before the subdiffusive process leading to segmental relaxation sets in. We speculate that local loops in the surface of the nanoparticles may play an important role in this trapping mechanism.
    Macromolecules 05/2014; 47(9):3005–3016. DOI:10.1021/ma500215f · 5.93 Impact Factor
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    ABSTRACT: We have selectively studied the component dynamics in a nanocomposite where 25 wt % of PMMA [poly(methyl methacrylate)] soft nanoparticles (SNPs) are dispersed in PEO [poly(ethylene oxide)] by means of quasi-elastic neutron scattering (QENS) experiments on partially deuterated samples. We have covered a time range from subpico to nanosecond regime and a momentum transfer range 0.5 ≤ Q ≤ 1.8 Å–1 by combining three different spectrometers. Complementary diffraction measurements with polarization analysis have facilitated the data analysis, by providing the coherent and incoherent contributions to the scattered intensities. Regarding the SNPs, the α-methyl group dynamics of PMMA—to which the QENS experiments are most sensitive in the temperature range investigated—turn to be faster than in bulk PMMA. This could be due to the plasticization effect induced by the fast PEO chains. In fact, calorimetric measurements show the coexistence of two glass-transition temperatures in the system, associated with each of the components, but modified with respect to those in the neat materials. The QENS results on the PEO component for large length scales reveal Rouse-like dynamics slowed down by the presence of the SNPs with respect to that in the bulk. With decreasing temperature indications for distributed chain mobilities are found, probably due to the enhancement of the concentration fluctuations. At local scales, deviations from Rouse-like dynamics occur, that could be attributed to an extra-friction related to the local potentials, and also to non-Gaussian effects arising from the discrete character of the elementary processes underlying the subdiffusive dynamics in the polymer. The deviations take place in a very similar way as in bulk PEO.
    Macromolecules 12/2013; 47(1):304–315. DOI:10.1021/ma402023n · 5.93 Impact Factor
  • Joachim Wuttke, Michaela Zamponi
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    ABSTRACT: The resolution of neutron backscattering spectrometers deteriorates at small scattering angles where analyzers deviate from exact backscattering. By reducing the azimuth angle range of the analyzers, the resolution can be improved with little loss of peak intensity. Measurements at the spectrometer SPHERES are in excellent agreement with simulations, which proves the dominance of geometric effects.
    The Review of scientific instruments 11/2013; 84(11):115108. DOI:10.1063/1.4831815 · 1.58 Impact Factor
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    ABSTRACT: By means of quasielastic neutron scattering we have investigated the hydrogen dynamics in poly(alkylene oxide)s (PAOs) with different side-chain lengths at temperatures below as well as above the glass-transition. The combination of results from three different spectrometers (a time-of-flight and two backscattering instruments) has allowed covering almost 4 orders of magnitude in time—from the ps to ns range—with spatial resolution. The results evidence the simultaneous occurrence of vibrations and localized side-group motions at low temperatures and additional diffusive-like (segmental) dynamics at high temperatures. The localized processes of the side groups show (i) stretching of the scattering function, (ii) associated activation energies similar to those found for single and cooperative bond rotations of polyethylene, and (iii) spatial extents that increase with increasing temperature. Compared with poly(ethylene oxide) (PEO), the diffusive segmental process in PAOs presents (i) the same spectral shape, (ii) slower characteristic times—antiplasticization—(iii) similar deviations from Gaussian behavior. For comparison, we also report on backscattering results on the side-group dynamics of poly(n-hexyl methacrylate) in the same temperature range, that show evidence for confinement effects. We suggest that the dynamic asymmetry in systems with intrinsic dynamic heterogeneities between constituent parts is the key ingredient leading to both plasticization and confinement effects.
    Macromolecules 05/2012; 45(10):4394-4405. DOI:10.1021/ma3003399 · 5.93 Impact Factor
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    ABSTRACT: The diffusive motions of covalently tethered 1, 3 diphenylpropane (DPP) via a silyl-aryl-ether linkage in the mesopores of MCM-41 were studied by quasielastic neutron scattering. The geometric effect of pore radius was investigated with samples having pores that ranged from 1.6 to 3.0 nm in diameter and highest achievable DPP grafting density. The effect of molecular crowding was investigated in 3.0 nm diameter pores for surface coverage ranging from 0.60 to 1.61 DPP/nm2. Temperature dependence was determined for large pore diameter samples from 240 K to 370 K. As the DPP molecules remain attached over this entire temperature range, data were analyzed in terms of a model of localized diffusion inside a sphere. Only the motions of the DPP hydrogen atoms were considered because of the high sensitivity of neutron scattering to the presence of hydrogen. As atoms far from the attachment point have a greater range of motion than those nearer the tether, the radius of the sphere limiting the motion of individual hydrogen atoms was allowed to increase based on the atom s distance from the tether point. Both smaller pore diameters and higher DPP surface coverage resulted in larger amplitude motion while the diffusion coefficient was greatest in the largest pores at highest surface coverage. These observations support a model where the DPP molecules prefer an orientation allowing close proximity to the MCM-41 pore surface and are forced into the pore interior by either the steric effect of small pore diameter or by increased competition for surface area at high molecule surface coverage.
    The Journal of Physical Chemistry C 01/2012; 116(1):923-932. DOI:10.1021/jp209458a · 4.84 Impact Factor
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    ABSTRACT: Transitions within the tunneling multiplet of CH(4) in phase II have been measured in an experiment at the backscattering instrument BASIS of the Neutron Source SNS. They all involve transitions from or to T-states. A statistical model is put forward which accounts for local departures from tetrahedral symmetry at the sites of ordered molecules. Different from previous work, in which discrete sets of overlap matrix elements have been studied, now large numbers of elements as well as the ensemble of T-states are considered. The observed neutron spectra can be explained rather well, all based on the pocket state formalism of A. Hüller [Phys. Rev. B 16, 1844 (1977)]. A completely new result is the observation and simulation of transitions between T-states, which give rise to a double peaked feature close to the elastic position and which reflect the disorder in the system. CH(2)D(2) molecules in the CH(4) matrix are largely responsible for the disorder and an interesting topic for their own sake. The simple model presented may lend itself to a broader application.
    The Journal of Chemical Physics 12/2011; 135(22):224509. DOI:10.1063/1.3664726 · 3.12 Impact Factor
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    ABSTRACT: The transition metal based oxide YBaCo3FeO7 is structurally related to the mineral Swedenborgite SbNaBe4O7, a polar non-centrosymmetric crystal system. The magnetic Co3Fe sublattice consists of a tetrahedral network containing kagome-like layers with trigonal interlayer sites. This geometry causes frustration effects for magnetic ordering, which were investigated by magnetization measurements, M\"ossbauer spectroscopy, polarized neutron diffraction, and neutron spectroscopy. Magnetization measurement and neutron diffraction do not show long range ordering even at low temperature (1 K) although a strong antiferromagnetic coupling (~2000 K) is deduced from the magnetic susceptibility. Below 590 K, we observe two features, a spontaneous weak anisotropic magnetization hysteresis along the polar crystallographic axis and a hyperfine field on the Fe kagome sites, whereas the Fe spins on the interlayer sites remain idle. Below ~50 K, the onset of a hyperfine field shows the development of moments static on the M\"ossbauer time scale also for the Fe interlayer sites. Simultaneously, an increase of spin correlations is found by polarized neutron diffraction. The relaxation part of the dynamic response has been further investigated by high-resolution neutron spectroscopy, which reveals that the spin correlations start to freeze in below ~50 K. Monte Carlo simulations show that the neutron scattering results at lower temperatures are compatible with a recent proposal that the particular geometric frustration in the Swedenborgite structure promotes quasi one dimensional partial order.
    Physical review. B, Condensed matter 06/2011; 84:224426. DOI:10.1103/PhysRevB.84.224426 · 3.66 Impact Factor
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    ABSTRACT: We use quasi-elastic neutron scattering (QENS) to study the dynamics of water confined inside reverse micelles. As a model system we use a water-in-oil droplet microemulsion based on the anionic surfactant AOT (sodium bis[2-ethylhexyl] sulfosuccinate), that forms spherical water droplets coated by a monolayer of AOT dispersed in the continuous oil matrix. Combining neutron time-of-flight (TOF) and backscattering (BS) spectroscopy, we access the dynamical behaviour of water over three decades in time from pico- to nanoseconds. We investigate the influence of reverse micelle size on the water dynamics by comparing two sample systems with bigger and smaller water core radii of about R(c) approximate to 12 angstrom and 7 angstrom. The temperature is varied over a range where both microemulsion systems are stable, from room temperature down to the region where the confined water is supercooled: 260 K <= T <= 300 K. Taking explicitly into account the previously measured diffusion of entire reverse micelles in the oil matrix we find the average mobility of the confined water to be considerably slowed with respect to bulk water. The translational diffusion decreases with decreasing reverse micelle size. Dependent on the reverse micelle size we can interpret our data by assuming two dynamically separated water fractions. We identify the faster one with bulk-like water in the middle of the core while the slower one seems to be surfactant bound water. We find that 4 molecules of water per AOT molecule are immobilized on the timescale of QENS, i.e. shorter than nanoseconds.
    Soft Matter 06/2011; 7(12):5745-5755. DOI:10.1039/c1sm05204g · 4.15 Impact Factor
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    ABSTRACT: A combined quasi-elastic neutron scattering (QENS) and high-resolution solution NMR spectroscopy study was conducted to investigate the internal dynamics of aqueous (D 2 O) G5 PAMAM dendrimer solutions as a function of molecular protonation at room temperature. Localized motion of the dendrimer segments was clearly exhibited in the QENS data analysis while the global, center-of-mass translational diffusion was measured by NMR. Our results unambiguously demonstrate an increased rapidity in local scale ($ 3 A) motion upon increasing the molecular protonation. This is contrary to an intuitive picture that increased charge stiffens the dendrimer segments thereby inhibiting local motion. These charge-induced changes may be a result of interactions with the surrounding counterions and water molecules as the segments explore additional intra-dendrimer volume made available by slight electrostatic swelling and redistribution of mass in the dendrimer interior. This observation is relevant to development of a microscopic picture of dendrimer-based packages as guest-molecule delivery vehicles because reorganization of the confining dendrimer segments must be a precursor to guest-molecule release.
    Soft Matter 01/2011; 7(2). DOI:10.1039/C0SM00671H · 4.15 Impact Factor
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    ABSTRACT: It seems to be increasingly accepted that the diversity and composition of lipids play an important role in the function of biological membranes. A prime example of this is the case of lipid rafts; regions enriched with certain types of lipids which are speculated to be relevant to the proper functioning of membrane embedded proteins. Although the dynamics of membrane systems have been studied for decades, the microscopic dynamics of lipid molecules, even in simple model systems, is still an active topic of debate. Neutron scattering has proven to be an important tool for accessing the relevant nanometre length scale and nano to picosecond time scales, thus providing complimentary information to macroscopic techniques. Despite their potential relevance for the development of functionalized surfaces and biosensors, the study of single supported membranes using neutron scattering poses the challenge of obtaining relevant dynamic information from a sample with minimal material. Using state of the art neutron instrumentation we were, for the first time, able to model lipid diffusion in single supported lipid bilayers. We find that the diffusion coefficient for the single bilayer system is comparable to the multi-lamellar lipid system. More importantly, the molecular mechanism for lipid motion in the single bilayer was found to be a continuous diffusion, rather than the flow-like ballistic motion reported in the stacked membrane system. We observed an enhanced diffusion at the nearest neighbour distance of the lipid molecules. The enhancement and change of character of the diffusion can most likely be attributed to the effect the supporting substrate has on the lipid organization.
    Soft Matter 11/2010; 6(23):5864-5867. DOI:10.1039/C0SM00637H · 4.15 Impact Factor
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    ABSTRACT: The diffusion of methane confined in nano-porous carbon aerogel with the average pore size 48 Å and porosity ∼60% was investigated as a function of pressure at T = 298 K using quasi-elastic neutron scattering (QENS). The diffusivity of methane shows a clear effect of confinement: it is about two orders of magnitude lower than in bulk at the same thermodynamic conditions and is close to the diffusivity of liquid methane at 100 K (i.e. ∼90 K below the liquid–gas critical temperature TC ≈ 191 K). The diffusion coefficient (D) of methane initially increases with pressure by a factor of ∼2.5 from 3.47 ± 0.41 × 10−10 m2 s−1 at 0.482 MPa to D = 8.55 ± 0.33 × 10−10 m2 s−1 at 2.75 MPa and starts to decrease at higher pressures. An explanation of the observed non-monotonic behavior of the diffusivity in the confined fluid is based on the results of small-angle neutron scattering experiments of the phase behavior of methane in a similar carbon aerogel sample. The initial increase of the diffusion coefficient with pressure is explained as due to progressive filling of bigger pores in which molecular mobility in the internal pore volume is less affected by the sluggish liquid-like molecular mobility in the adsorbed phase. Subsequent decrease of D, is associated with the effect of intermolecular collisions, which result in a lower total molecular mobility with pressure, as in the bulk state. The results are compared with the available QENS data on the methane diffusivity in zeolites, metal organic frameworks, and porous silica as well as with the molecular dynamics simulations of methane in nano-porous carbons and silica zeolites.
    Microporous and Mesoporous Materials 07/2010; 132(1-2-132):148-153. DOI:10.1016/j.micromeso.2010.02.012 · 3.21 Impact Factor
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    ABSTRACT: The high flux and low background of the new backscattering spectrometer at the SNS combine to produce an excellent signal to noise ratio, allowing us to investigate a low lying weak excitation never seen before in the spin ice, Ho2Ti2O7. This non-dispersive excitation has been observed at E = 26.3 µeV below 100 K but is resolution limited only below ∼ 65 K. It is indifferent to magnetic fields below µ0H = 4.5 T, at 1.6 K. These characteristics help us to identify the excitation as due to the nuclear spin system.
    Journal of Physics Conference Series 01/2010; 25121949. DOI:10.1088/1742-6596/251/1/012003
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    ABSTRACT: Using neutron spin echo (NSE) spectroscopy and a labeling scheme unique to neutron scattering the motion of a labeled branch point of a three-arm polyethylene star has been observed on a molecular level. The measured dynamic structure factor shows a clear transition to a plateau, signifying the stronger confinement of the star center in comparison to a corresponding center labeled linear chain. A shortening of one star arm to about only one entanglement length leads to the same topological confinement as for the symmetric star within the accessible time range of NSE. This reflects a stronger effect of such a small branch than expected and is consistent with rheological measurements on the same system.
    Macromolecules 11/2009; 43(1). DOI:10.1021/ma9017185 · 5.93 Impact Factor
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    ABSTRACT: A single nondispersive excitation is observed by means of neutron backscattering, at E_{0}=26.3 microeV in the spin ice Ho2Ti2O7 but not in the isotopically enriched 162Dy2Ti2O7 analogue. The intensity of this excitation is rather small, less, similar0.2% of the elastic intensity. It is clearly observed below 80 K but resolution limited only below approximately 65 K. The application of a magnetic field up to micro_{0}H=4.5 T, at 1.6 K, has no measurable effect on the energy or intensity. This nuclear excitation is believed to perturb the electronic, Ising spin system resulting in the persistent spin dynamics observed in spin ice compounds.
    Physical Review Letters 02/2009; 102(1):016405. DOI:10.1103/PhysRevLett.102.016405 · 7.73 Impact Factor
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    ABSTRACT: We present a comparison between theoretical predictions of the generalized Langevin equation for cooperative dynamics (CDGLE) and neutron spin echo data of dynamic structure factors for polyethylene melts. Experiments cover an extended range of length and time scales, providing a compelling test for the theoretical approach. Samples investigated include chains with increasing molecular weights undergoing dynamics across the unentangled to entangled transition. Measured center-of-mass (com) mean-square displacements display a crossover from subdiffusive to diffusive dynamics. The generalized Langevin equation for cooperative dynamics relates this anomalous diffusion to the presence of the interpolymer potential, which correlates the dynamics of a group of slowly diffusing molecules in a dynamically heterogeneous liquid. Theoretical predictions of the subdiffusive behavior, of its crossover to free diffusion, and of the number of macromolecules undergoing cooperative motion are in quantitative agreement with experiments.
    The Journal of Physical Chemistry B 01/2009; 112(50):16220-9. DOI:10.1021/jp807035z · 3.38 Impact Factor
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    ABSTRACT: A new spectrometer named BASIS has recently entered the general user program at the Spallation Neutron Source. BASIS is an acronym for Backscattering Silicon Spectrometer. While there are several operational reactor-based spectrometers that utilize backscattering reflection from silicon single crystals, such as IN10 and IN16 [1] at the ILL, France; HFBS [2] at the NCNR, USA; and SPHERES [3] at the FRM-II, JCNS, Germany, BASIS is the first silicon backscattering spectrometer built on a spallation neutron source. Conceptually, it is similar to previously built time-of-flight backscattering spectrometers that utilize reflections from pyrolytic graphite or mica, such as IRIS [4] and OSIRIS [5] at the ISIS, UK; LAM-80 [6] at the KENS, Japan; or MARS [7] at the SINQ, Switzerland.
    Neutron News 07/2008; 19(3):22-24. DOI:10.1080/10448630802210578
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    ABSTRACT: We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho(2)Ti(2)O(7), where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho(2-x)La(x)Ti(2)O(7) was characterized by x-ray and neutron diffraction and by Ho L(III)-edge and Ti K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that the pyrochlore structure remains intact until about x = 0.3, but a systematic increase in local disorder with increasing La concentration is observed in the EXAFS data, especially from the Ti K edge. Quasi-elastic neutron scattering and ac susceptibility measurements show that, in x≤0.4 samples at temperatures above macroscopic freezing, the spin-spin correlations are short ranged and dynamic in nature. The main difference with pure spin ice in the dynamics is the appearance of a second, faster, relaxation process.
    Journal of Physics Condensed Matter 06/2008; 20(23):235206. DOI:10.1088/0953-8984/20/23/235206 · 2.22 Impact Factor
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    ABSTRACT: Understanding the catalytic role of titanium-based additives on the reversible hydrogenation of complex metal hydrides is an essential step towards developing hydrogen storage materials for the transport sector. Improved bulk diffusion of hydrogen is one of the proposed catalytic effects, and here we study hydrogen dynamics in undoped and TiCl 3 -doped samples of NaAlH 4 and Na 3 AlH 6 using a combination of density functional theory calculations and quasielastic neutron scattering. Hydrogen dynamics is found to be limited and mediated by hydrogen vacancies in both alanate phases, requiring an activation in excess of 0.3 eV. Even at 390 K, less than 1% of the hydrogen in NaAlH 4 performs long range diffusion, and only localized hydrogen dynamics is observed in Na 3 AlH 6 . The effect of the TiCl 3 dopant on hydrogen bulk diffusion is found to be negligible.
    Journal of Alloys and Compounds 10/2007; 446447:469-473. DOI:10.1016/j.jallcom.2007.04.041 · 2.73 Impact Factor

Publication Stats

250 Citations
102.07 Total Impact Points

Institutions

  • 2004–2014
    • Forschungszentrum Jülich
      • Jülich Centre for Neutron Science (JCNS)
      Jülich, North Rhine-Westphalia, Germany
  • 2008–2011
    • Oak Ridge National Laboratory
      • • Neutron Scattering Science Division
      • • Spallation Neutron Source
      Oak Ridge, Florida, United States
  • 2010
    • Indiana University Bloomington
      Bloomington, Indiana, United States