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  • Aerodynamics  (4)
  • Theoretical, Physical and Computational Chemistry  (4)
  • Mice
  • 1995-1999  (9)
  • 1
    Electronic Resource
    Electronic Resource
    The location of transition states: A comparison of Cartesian, Z-matrix, and natural internal coordinates (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 888-904 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A comparison is made between geometry optimization in Cartesian coordinates, in Z-matrix coordinates, and in natural internal coordinates for the location of transition states. In contrast to the situation with minima, where all three coordinate systems are of comparable efficiency if a reliable estimate of the Hessian matrix is available at the starting geometry, results for 25 different transition states covering a wide range of structural types demonstrate that in practice Z-matrix coordinates are generally superior. For Cartesian coordinates, the commonly used Hessian update schemes are unable to guarantee preservation of the necessary transition state eigenvalue structure, while current algorithms for generating natural internal coordinates may have difficulty handling the distorted geometries associated with transition states. The widely used Eigenvector Following (EF) algorithm is shown to be extremely efficient for optimizing transition states. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Molecular energies and properties from density functional theory: Exploring basis set dependence of Kohn - Sham equation using several density functionals (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 775-795 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The performance of four commonly used density functionals (VWN, BLYP, BP91, and Becke's original three-parameter approximation to the adiabatic connection formula, referred to herein as the adiabatic connection method or ACM) was studied with a series of six Gaussian-type atomic basis sets [DZP, 6-31G**, DZVP, TZVP, TZ2P, and uncontracted aug-cc-pVTZ (UCC)]. The geometries and dipole moments of over 100 first-row and second-row molecules and reaction energies of over 300 chemical reactions involving such molecules were computed using each of the four density functionals in combination with each of the six basis sets. The results were compared to experimentally determined values. Based on overall mean absolute theory versus experiment errors, it was found that ACM is the best choice for predictions of both energies of reaction [overall mean absolute theory versus experiment error (MATvEE) of 4.7 kcal/mol with our most complete (UCC) basis set] and molecular geometries (overall MATvEE of 0.92 pm for bond distances and 0.88° for bond angles with the UCC basis set). For routine calculations with moderate basis sets (those of double-ζ type: DZP, 6-31G**, and DZVP) the DZVP basis set was, on average, the best choice. There were, however, examples of reactions where significantly larger basis sets were required to achieve reasonable accuracy (errors ≤ 5 kcal/mol). For dipole moments, ACM, BP91, and BLYP performed comparably (overall MATvEE of 0.071, 0.067, and 0.059 debye, respectively, with the UCC basis set). Basis sets that include additional polarization functions and diffuse functions were found to be important for accurate density functional theory predictions of dipole moments. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Predicting the vibrational spectra of some simple fluorocarbons by direct scaling of primitive valence force constants (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1187-1204 
    Details
    ISSN: 0192-8651
    Keywords: vibrational spectra ; SQM force fields ; fluorocarbons ; density functional theory ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Using the scaled quantum-mechanical (SQM) force field approach with direct scaling of individual primitive force constants, we derive optimal scaling factors by a least-squares fit to the experimentally observed fundamentals of some selected “simple” fluorocarbons. We use the derived scaling factors to predict the vibrational spectra of all possible fluoromethanes, fluoroethylenes, fluoroethanes, and monofluoropropenes, proposing a reassignment of some experimental fundamentals. Two separate sets of scaling factors are derived for both traditional Hartree-Fock (HF) calculations and density functional theory (DFT) calculations using the hybrid three-parameter B3-PW91 density functional. With the split-valence 6-31G(d) basis set, our scaling procedure gives an average error of less than 9 cm-1 in the scaled frequencies with the B3-PW91 functional. The average percentage error is around 1%. The HF results are not as good - the average error is 12.6 cm-1 - showing that hybrid density functional SQM schemes are better for predicting vibrational spectra than basic Hartree-Fock.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1187-1204, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Constrained optimization in delocalized internal coordinates (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1079-1095 
    Details
    ISSN: 0192-8651
    Keywords: geometry optimization ; constraints ; delocalized internal coordinates ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Using the recently introduced delocalized internal coordinates, in conjunction with the classical method of Lagrange multipliers, an algorithm for constrained optimization is presented in which the desired constraints do not have to be satisfied in the starting geometry. The method used is related to a previous algorithm by the same author for constrained optimization in Cartesian coordinates [J. Comput. Chem., 13, 240 (1992)], but is simpler and far more efficient. Any internal (distance or angle/torsion) constraint can be imposed between any atoms in the system whether or not the atoms involved are formally bonded. Imposed constraints can be satisfied exactly. © 1997 John Wiley & Sons, Inc. J Comput Chem 18:1079-1095, 1997
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
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    Effects of the obese gene product on body weight regulation in ob/ob mice (1995)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1995-07-28
    Description: C57BL/6J mice with a mutation in the obese (ob) gene are obese, diabetic, and exhibit reduced activity, metabolism, and body temperature. Daily intraperitoneal injection of these mice with recombinant OB protein lowered their body weight, percent body fat, food intake, and serum concentrations of glucose and insulin. In addition, metabolic rate, body temperature, and activity levels were increased by this treatment. None of these parameters was altered beyond the level observed in lean controls, suggesting that the OB protein normalized the metabolic status of the ob/ob mice. Lean animals injected with OB protein maintained a smaller weight loss throughout the 28-day study and showed no changes in any of the metabolic parameters. These data suggest that the OB protein regulates body weight and fat deposition through effects on metabolism and appetite.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pelleymounter, M A -- Cullen, M J -- Baker, M B -- Hecht, R -- Winters, D -- Boone, T -- Collins, F -- New York, N.Y. -- Science. 1995 Jul 28;269(5223):540-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Neurobiology, Amgen, Inc., Thousand Oaks, CA 91320, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7624776" target="_blank"〉PubMed〈/a〉
    Keywords: Adipose Tissue/drug effects ; Analysis of Variance ; Animals ; Blood Glucose/analysis ; Body Composition/drug effects ; Body Temperature/drug effects ; Dose-Response Relationship, Drug ; Drinking/drug effects ; Eating/*drug effects ; Energy Metabolism/drug effects ; Female ; Insulin/blood ; Leptin ; Mice ; Mice, Inbred C57BL ; Mice, Obese ; Motor Activity/drug effects ; Obesity/genetics/*physiopathology ; Oxygen Consumption/drug effects ; Proteins/genetics/*pharmacology ; Recombinant Proteins/pharmacology ; Weight Loss/*drug effects
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    PAPER CURRENT
  • 6
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    Simulated Inlet Unstart and Nacelle/Diverter Effects for the Boeing Reference H Configuration (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The Boeing Reference H configuration was tested in the NASA Ames 9x7 Supersonic Wind Tunnel. A simulated unstarted inlet was evaluated as well as the aerodynamic performance of the configuration with and without nacelle and diverter components. These experimental results were compared with computational results from the unstructured grid Euler flow solver AIRPLANE. The comparisons between computational and experimental results were good, and demonstrated that the Euler code is capable of efficiently and accurately predicting the changes in the aerodynamic coefficients associated with inlet unstart and the effects of the nacelle and diverter components.
    Keywords: Aerodynamics
    Type: First NASA/Industry High-Speed Research Configuration Aerodynamics Workshop; Part 3; 1285-1325; NASA/CP-1999-209690/PT3
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Airplane Mesh Development with Grid Density Studies (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Automatic Grid Generation Wish List Geometry handling, including CAD clean up and mesh generation, remains a major bottleneck in the application of CFD methods. There is a pressing need for greater automation in several aspects of the geometry preparation in order to reduce set up time and eliminate user intervention as much as possible. Starting from the CAD representation of a configuration, there may be holes or overlapping surfaces which require an intensive effort to establish cleanly abutting surface patches, and collections of many patches may need to be combined for more efficient use of the geometrical representation. Obtaining an accurate and suitable body conforming grid with an adequate distribution of points throughout the flow-field, for the flow conditions of interest, is often the most time consuming task for complex CFD applications. There is a need for a clean unambiguous definition of the CAD geometry. Ideally this would be carried out automatically by smart CAD clean up software. One could also define a standard piece-wise smooth surface representation suitable for use by computational methods and then create software to translate between the various CAD descriptions and the standard representation. Surface meshing remains a time consuming, user intensive procedure. There is a need for automated surface meshing, requiring only minimal user intervention to define the overall density of mesh points. The surface mesher should produce well shaped elements (triangles or quadrilaterals) whose size is determined initially according to the surface curvature with a minimum size for flat pieces, and later refined by the user in other regions if necessary. Present techniques for volume meshing all require some degree of user intervention. There is a need for fully automated and reliable volume mesh generation. In addition, it should be possible to create both surface and volume meshes that meet guaranteed measures of mesh quality (e.g. minimum and maximum angle, stretching ratios, etc.).
    Keywords: Aerodynamics
    Type: 1998 NASA High-Speed Research Program Aerodynamic Performance Workshop; Volume 1; Part 1; 75-145; NASA/CP-1999-209692/VOL1/PT1
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Computational Analysis of Compressibility Effects on a High-Lift Wing (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The objective of this study was to investigate compressibility effects on a high-lift flowfield by simulating the flow about a three-dimensional multi-element wing. The computations were performed by solving both the incompressible and compressible Navier-Stokes equations (using the INS3D and OVERFLOW codes) on structured, overset grids. Turbulence was modeled via the one-equation, fully turbulent Spalart-Allmaras model. The computational results were validated with surface pressure measurements acquired at the NASA Ames 7- by 10-Foot Wind Tunnel. The geometry used for all computations consisted of an unswept wing in a landing configuration with a half-span flap and a three-quarter-span slat mounted inside a rectangular duct approximating the wind tunnel walls. The solutions were carefully examined to account for effects due to differences in algorithms. Compressibility effects were demonstrated by comparing surface particle traces, sectional pressure coefficient and boundary layer profile plots. It was found that small regions of compressibility near the slat and main-element leading edge can largely impact the flow. Even small compressibility regions can have significant global effects on the circulation and separation of each of the high-lift elements.
    Keywords: Aerodynamics
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Aerodynamic Influence of a Slat on a Flapped Wing (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Three high-lift configurations were computationally studied to assess the aerodynamic influence of slats. A flapped wing was simulated with no slat, a full-span slat, and a three quarter-span slat at a chord based Reynolds number of 3.7 million. The flows were computed using a compressible Navier-Stokes solver on structured grids with the Spalart-Allmaras turbulence model. All cases were compared with experimental data to validate the approach. The slats not only increase the lift generated by the wing but alter the topology of the flowfield considerably. The changes in the flow give insight into the working of a slat and contribute to a better understanding of high-lift flows in general.
    Keywords: Aerodynamics
    Type: 16th AIAA Applied Aerodynamics Conference; Jun 15, 1998 - Jun 18, 1998; Albuquerque, NM; United States
    Format: text
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    NASA TECHNICAL REPORTS
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