The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform

Jeffrey A. Reimer - One of the best experts on this subject based on the ideXlab platform.

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    The Journal of Physical Chemistry C, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates...

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66­(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66­(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr) C
    The Journal of Physical Chemistry, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign ¹H and ¹³C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials.

Aditya Nandy - One of the best experts on this subject based on the ideXlab platform.

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    The Journal of Physical Chemistry C, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates...

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66­(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66­(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr) C
    The Journal of Physical Chemistry, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign ¹H and ¹³C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials.

Kurt Maute - One of the best experts on this subject based on the ideXlab platform.

  • Hole seeding in level set topology optimization via density fields
    Structural and Multidisciplinary Optimization, 2020
    Co-Authors: Jorge L. Barrera, Markus J. Geiss, Kurt Maute
    Abstract:

    Two approaches that use a density field for seeding holes in level set topology optimization are proposed. In these approaches, the level set field describes the Material-Void interface while the density field describes the Material distribution within the Material phase. Both fields are optimized simultaneously by coupling them through either a single abstract design variable field or a penalty term introduced into the objective function. These approaches eliminate drawbacks of level set topology optimization methods that rely on seeding the initial design domain with a large number of holes. Instead, the proposed approaches insert holes during the optimization process where beneficial. The dependency of the optimization results on the initial hole pattern is reduced, and the computational costs are lowered by keeping the number of elements intersected by the Material interface at a minimum. In comparison with level set methods that use topological derivatives to seed small holes at distinct steps in the optimization process, the proposed approaches introduce holes continuously during the optimization process, with the hole size and shape being optimized for the particular design problem. The proposed approaches are studied using the extended finite element method for spatial discretization, and the solid isotropic Material with penalization for Material interpolation using fictitious densities. Their robustness with respect to algorithmic parameters, dependency on the density penalization, and performance are examined through 2D and 3D benchmark linear elastic numerical examples, and a geometrically complex mass minimization with stress constraint design problem.

  • Stress-based topology optimization using spatial gradient stabilized XFEM
    Structural and Multidisciplinary Optimization, 2018
    Co-Authors: Ashesh Sharma, Kurt Maute
    Abstract:

    This paper presents an immersed boundary approach for level set topology optimization considering stress constraints. A constraint agglomeration technique is used to combine the local stress constraints into one global constraint. The structural response is predicted by the eXtended Finite Element Method. A Heaviside enrichment strategy is used to model strong and weak discontinuities with great ease of implementation. This work focuses on low-order finite elements, which given their simplicity are the most popular choice of interpolation for topology optimization problems. The predicted stresses strongly depend on the intersection configuration of the elements and are prone to significant errors. Robust computation of stresses, regardless of the interface position, is essential for reliable stress constraint prediction and sensitivities. This study adopts a recently proposed fictitious domain approach for penalization of displacement gradients across element faces surrounding the Material interface. In addition, a novel XFEM informed stabilization scheme is proposed for robust computation of stresses. Through numerical studies the penalized spatial gradients combined with the stabilization scheme is shown to improve prediction of stresses along the Material interface. The proposed approach is applied to the benchmark topology optimization problem of an L-shaped beam in two and three dimensions using Material-Void and Material-Material problem setups. Linear and hyperelastic Materials are considered. The stress constraints are shown to be efficient in eliminating regions with high stress concentration in all scenarios considered.

  • Numerical instabilities in level set topology optimization with the extended finite element method
    Structural and Multidisciplinary Optimization, 2014
    Co-Authors: David Makhija, Kurt Maute
    Abstract:

    This paper studies level set topology optimization of structures predicting the structural response by the eXtended Finite Element Method (XFEM). In contrast to Ersatz Material approaches, the XFEM represents the geometry in the mechanical model by crisp boundaries. The traditional XFEM approach augments the approximation of the state variable fields with a fixed set of enrichment functions. For complex Material layouts with small geometric features, this strategy may result in interpolation errors and non-physical coupling between disconnected Material domains. These defects can lead to numerical instabilities in the optimized Material layout, similar to checker-board patterns found in density methods. In this paper, a generalized Heaviside enrichment strategy is presented that adapts the set of enrichment functions to the Material layout and consistently interpolates the state variable fields, bypassing the limitations of the traditional approach. This XFEM formulation is embedded into a level set topology optimization framework and studied with “Material-Void” and “Material-Material” design problems, optimizing the compliance via a mathematical programming method. The numerical results suggest that the generalized formulation of the XFEM resolves numerical instabilities, but regularization techniques are still required to control the optimized geometry. It is observed that constraining the perimeter effectively eliminates the emergence of small geometric features. In contrast, smoothing the level set field does not provide a reliable geometry control but mainly improves the convergence rate of the optimization process.

Alexander C. Forse - One of the best experts on this subject based on the ideXlab platform.

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    The Journal of Physical Chemistry C, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates...

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66­(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66­(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal-Organic Framework UiO-66(Zr)
    eScholarship University of California, 2018
    Co-Authors: Nandy A, Alexander C. Forse, Vj Witherspoon, Ja Reimer
    Abstract:

    © 2018 American Chemical Society. We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr-OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr) C
    The Journal of Physical Chemistry, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign ¹H and ¹³C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials.

Velencia J. Witherspoon - One of the best experts on this subject based on the ideXlab platform.

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    The Journal of Physical Chemistry C, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates...

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr)
    2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign 1H and 13C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66­(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66­(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials

  • NMR Spectroscopy Reveals Adsorbate Binding Sites in the Metal–Organic Framework UiO-66(Zr) C
    The Journal of Physical Chemistry, 2018
    Co-Authors: Aditya Nandy, Alexander C. Forse, Velencia J. Witherspoon, Jeffrey A. Reimer
    Abstract:

    We assign ¹H and ¹³C NMR resonances emanating from acetone, methanol, and cyclohexane adsorbed inside the pores of UiO-66(Zr). These results are informed by density functional theory (DFT) calculations, which probe the role of two competing effects inside of the pore environment: (i) nucleus independent chemical shifts (NICSs) generated by ring currents in conjugated linkers and (ii) small molecule coordination to the metal-oxyhydroxy cluster. These interactions are found to perturb the chemical shift of in-pore adsorbate relative to ex-pore adsorbate (which resides in spaces between the MOF particles). Changes in self-solvation upon adsorption may also perturb the chemical shift. Our results indicate that cyclohexane preferentially adsorbs in the tetrahedral pores of UiO-66(Zr), while acetone and methanol adsorb at the Zr–OH moieties on the metal-oxyhydroxy clusters in a more complex fashion. This method may be used to probe molecular adsorption sites and Material Void saturation with selected adsorbates, and with further development may eventually be used to trace in-pore chemistry of MOF Materials.