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  • 1
    Language: English
    In: International Journal of Computer Assisted Radiology and Surgery, 2010, Vol.5(1), pp.69-76
    Description: Byline: Joerg Meyer (1) Abstract: Purpose We present a new, hybrid visualization method that can assist in assessing the degree of osseointegration of dental implants. Method The method is based on radiographic imaging, three-dimensional (3-D) volume reconstruction, and color coding of bone density. It provides both a 3-D image of the titanium implant and the implant site, and a two-dimensional (2-D) profile of the lingual and buccal sides of the implant, exposing possible weaknesses in the supporting bone structure. The visualization procedure described here consists of 2-D cross-sectional CT imaging, 3-D gradient-based hardware-accelerated volume rendering using 3-D texture mapping, implant site extraction using 3-D selection of a 2-D cross-sectional, tri-linearly interpolated 2-D image, computation of a bone density profile and line integral along the implant, and 3-D hybrid rendering of the implant site and the derived bone density information in its anatomical context. This method has been demonstrated to be successful in enabling the mapping of information derived from virtual bone density measurements onto a geometric object, thus providing the necessary information to relate other information from mechanical testing or simulations to the respective site. Results A high-resolution scan of a cadaver was used as a reference data set. The hybrid view, a combination of 2-D density profile and 3-D color-coded density rendering, turned out to be very intuitive and easy to interpret. The 2-D view was also useful for relating standard 2-D X-ray imaging with enhanced 3-D imaging of bone density. On top of this, our image-based method was used for cross-validation of a mechanical testing method. It turned out that the results from mechanical testing of osseointegration were very well correlated with the results from our image-based 2-D and 3-D methods. Conclusions Since these two methods work in completely different ways (mechanical vs. radiographic) and the results came out are the same, the results provide evidence that both methods for assessing the degree and location of osseointegration are valid. Further studies using additional scans on living subjects will be conducted to provide additional evidence. Cost-efficient X-ray imaging can be used to replace the simulated implant-aligned 2-D X-ray views that were obtained from a 3-D scan. Author Affiliation: (1) University of California, Irvine, USA Article History: Registration Date: 09/06/2009 Received Date: 12/01/2009 Accepted Date: 08/06/2009 Online Date: 30/06/2009
    Keywords: Dental Implants ; Bone Density ; Cat Scans;
    ISSN: 1861-6410
    E-ISSN: 1861-6429
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  • 2
    Language: English
    In: Angewandte Chemie International Edition, 25 April 2014, Vol.53(18), pp.4721-4724
    Description: We present an embedding technique for metallic systems that makes it possible to model energy dissipation into substrate phonons during surface chemical reactions from first principles. The separation of chemical and elastic contributions to the interaction potential provides a quantitative description of both electronic and phononic band structure. Application to the dissociation of O at Pd(100) predicts translationally “hot” oxygen adsorbates as a consequence of the released adsorption energy (ca. 2.6 eV). This finding questions the instant thermalization of reaction enthalpies generally assumed in models of heterogeneous catalysis. : An embedding technique for metallic systems makes it possible to model energy dissipation into substrate phonons during surface chemical reactions from first principles. Application to O dissociation at Pd(100) predicts translationally “hot” oxygen adsorbates as a consequence of the released adsorption energy (ca. 2.6 eV). This calls into question the instant thermalization of reaction enthalpies generally assumed in heterogeneous catalysis modeling.
    Keywords: Ab Initio Molecular Dynamics ; Embedding ; Energy Dissipation ; Hot Adatoms ; Oxygen Adsorption
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 3
    Language: English
    In: Physical Review B, 10/2014, Vol.90(16)
    Description: We outline a possibility to determine the adatom density of individual nano-objects via measurement of their electronic structure. For this aim, the nonlinear shift of image potential states measured on individual Cu nanoclusters on Ag(100) by low-temperature scanning tunneling spectroscopy is carefully analyzed. The quantitative analysis is confirmed by density-functional theory calculations. A peak width analysis furthermore reveals whether the clusters are purely metallic or alloyed.
    Keywords: Clusters ; Density ; Quantitative Analysis ; Electronic Structure ; Scanning Tunneling Microscopy ; Nonlinearity ; Condensed Matter ; Nanostructure ; Mathematical Analysis ; Condensed Matter Physics (General) (So) ; Solid-State Physics (Ah);
    ISSN: 1098-0121
    E-ISSN: 1550-235X
    Source: American Physical Society (APS) (via CrossRef)
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  • 4
    Language: English
    In: International Journal of Computer Assisted Radiology and Surgery, 2015, Vol.10(7), pp.1175-1175
    Description: Byline: Joerg Meyer (1), Cherilyn G. Sheets (2), James C. Earthman (3) Author Affiliation: (1) University of California, Irvine, Irvine, CA, USA (2) Newport Coast Oral Facial Institute, Newport Beach, CA, USA (3) Chemical Engineering and Materials Science Department, University of California, Irvine, Irvine, CA, USA Article History: Registration Date: 02/03/2015 Online Date: 07/04/2015 Article note: The online version of the original article can be found under doi: 10.1007/s11548-009-0382-2. The online version of the original article can be found at http://dx.doi.org/10.1007/s11548-009-0382-2.
    Keywords: Dental Implants;
    ISSN: 1861-6410
    E-ISSN: 1861-6429
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  • 5
    Language: English
    In: Physical review letters, 24 July 2015, Vol.115(4), pp.046102
    Description: We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intramolecular contributions and overcomes the systematic underestimation of the nonadiabatic losses obtained within the prevalent independent-atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM scheme as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions.
    Keywords: Condensed Matter - Materials Science;
    ISSN: 00319007
    E-ISSN: 1079-7114
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  • 6
    Language: English
    In: The Journal of Chemical Physics, 21 July 2015, Vol.143(3)
    Description: We present first-principles calculations of the sticking coefficient of O 2 at Pd(100) to assess the effect of phononic energy dissipation on this kinetic parameter. For this, we augment dynamical simulations on six-dimensional potential energy surfaces (PESs) representing the molecular degrees of freedom with various effective accounts of surface mobility. In comparison to the prevalent frozen-surface approach, energy dissipation is found to qualitatively affect the calculated sticking curves. At the level of a generalized Langevin oscillator model, we achieve good agreement with experimental data. The agreement is similarly reached for PESs based on two different semi-local density-functional theory functionals. This robustness of the simulated sticking curve does not extend to the underlying adsorption mechanism, which is predominantly directly dissociative for one functional or molecularly trapped for the other. Completely different adsorption mechanisms therewith lead to rather similar sticking curves that agree equally well with the experimental data. This highlights the danger of the prevalent practice to extract corresponding mechanistic details from simple fingerprints of measured sticking data for such exothermic surface reactions.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 7
    Language: English
    In: The Journal of Chemical Physics, 14 October 2016, Vol.145(14)
    Description: We have performed calculations on the dissociative chemisorption of H 2 on un-reconstructed and reconstructed Au(111) with density functional theory, and dynamics calculations on this process on un-reconstructed Au(111). Due to a very late barrier for dissociation, H 2 + Au(111) is a candidate H 2 -metal system for which the dissociative chemisorption could be considerably affected by the energy transfer to electron-hole pairs. Minimum barrier geometries and potential energy surfaces were computed for six density functionals. The functionals tested yield minimum barrier heights in the range of 1.15-1.6 eV, and barriers that are even later than found for the similar H 2 + Cu(111) system. The potential energy surfaces have been used in quasi-classical trajectory calculations of the initial (v, J ) state resolved reaction probability for several vibrational states v and rotational states J of H 2 and D 2 . Our calculations may serve as predictions for state-resolved associative desorption experiments, from which initial state-resolved dissociative chemisorption probabilities can be extracted by invoking detailed balance. The vibrational efficacy η v =0→1 reported for D 2 dissociating on un-reconstructed Au(111) (about 0.9) is similar to that found in earlier quantum dynamics calculations on H 2 + Ag(111), but larger than found for D 2 + Cu(111). With the two functionals tested most extensively, the reactivity of H 2 and D 2 exhibits an almost monotonic increase with increasing rotational quantum number J . Test calculations suggest that, for chemical accuracy (1 kcal/mol), the herringbone reconstruction of Au(111) should be modeled.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 8
    Language: English
    In: Physical Review B, 6/2010, Vol.81(24)
    Description: In this work we present a method for simulating the electron-vibration coupling in adsorbate molecules using a tight-binding formalism for the electronic degrees of freedom and a real-space description of the molecular vibrations. First, we derive a formalism which is very transparent in recognizing the effect of a local vibrational perturbation on the local electronic structure at any location. Second, we apply the method to nonresonant inelastic electron-tunneling spectroscopy IETS of two sample molecules on generic model substrates as typically accessible within a scanning tunneling microscopy STM experiment. The foremost observation is that the intensity of the STM-IETS signal is not necessarily strongest in the spatial vicinity of the vibrational perturbation. Instead, it is dependent on the delocalization of the molecular orbitals, which may lead to a strong intensity quite far from the vibration. Since this is an effect of the electronic structure and not related to the transfer of the vibrational motion itself, the molecular orbitals can be treated as "carrier waves" of the signal from a vibrational perturbation. This effect may be important in determining the orientation of an adsorbed molecule on a substrate surface or in manipulating adsorbed molecules with an STM tip.
    Keywords: Physics;
    ISSN: 1098-0121
    E-ISSN: 1550-235X
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  • 9
    In: Chemical Communications, 2015, Vol.51(63), pp.12621-12624
    Description: Novel surface coordination nanostructures based on cyanosexiphenyl molecules are assembled on a gold surface and investigated by scanning tunneling microscopy and density functional theory. Their formation can be tuned by varying the surface temperature during deposition. Diffusing gold adatoms act as coordination centers for the cyano groups present on one end of the nonsymmetrical molecules.
    Keywords: Formations ; Tuning ; Density Functional Theory ; Gold ; Deposition ; Scanning Tunneling Microscopy ; Diffusion ; Nanostructure ; Miscellaneous Sciences (So) ; Chemical and Electrochemical Properties (MD) ; Chemical and Electrochemical Properties (Ep) ; Chemical and Electrochemical Properties (Ed) ; Chemical and Electrochemical Properties (EC);
    ISSN: 1359-7345
    E-ISSN: 1364-548X
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  • 10
    Language: English
    In: Physical Review B, 5/2014, Vol.89(20)
    Description: The quantum dynamics of electrons in bulk states is investigated by scanning tunneling microscopy and spectroscopy on a Ag(100) surface. By measuring conductance maps above a threshold voltage, we observe standing waves at step edges and defects. We interpret these to originate from electrons in a bulk band edge at the [Gamma] point. From the spatially decaying waves, the wave vector and the quantum coherence parameters-coherence length, lifetime, and linewidth-are determined as a function of energy. We measure a coherence length of about 5-7 A, which is order of magnitudes lower than typically observed for surface or image-potential states. The energy of the band edge is extracted from the dispersion relation and agrees with the peak measured in scanning tunneling spectra at 1.9 eV above the Fermi energy. Theoretical calculations confirm the nature of the state elucidating the experimental findings.
    Keywords: Dispersions ; Coherence ; Threshold Voltage ; Scanning Tunneling Microscopy ; Fermi Surfaces ; Decay ; Condensed Matter ; Spectra ; Mathematical Analysis ; Condensed Matter Physics (General) (So) ; Solid-State Physics (Ah);
    ISSN: 1098-0121
    E-ISSN: 1550-235X
    Source: American Physical Society (APS) (via CrossRef)
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