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  • Polymer and Materials Science  (7)
  • Aerospace Medicine  (3)
  • 2010-2014  (3)
  • 1995-1999  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    The origins of avoided crossings in polymer dispersion curvesThis work was supported by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 709-723 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A purely mathematical heuristic model is examined in order to explain the existence of an avoided crossing between two dispersion curves calculated for a certain potential energy surface designed to simulate the dynamics of a linear polyethylene chain. The model shows that a third mode coupled to a two-mode Fermi-resonant system is able to create a marked instability in a vibrational spectrum. It is noted that such an explanation would require a fourth-order coupling term, which is the reason given for the failure of normal mode analysis to properly identify this dynamical effect.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1995.040040408
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  • 2
    Electronic Resource
    Electronic Resource
    On the correspondence between classical and quantum mechanics in macromolecular systems: Too much classical chaosResearch sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corp. (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 7 (1998), S. 203-209 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In a recent study we found the classical dynamics of a polyethylene (PE) chain to exhibit low dimensional chaos at temperatures as low as a few Kelvin. These results strongly suggest that classical molecular dynamic simulations in polymer systems can grossly overestimate vibrational motion, which consequently results in disordered structures. In contrast, quantum mechanical calculations using Internal Coordinate Quantum Monte Carlo (an improved method with an initial conjecture for the correct wave function) indicate that the quantum ground state for a three-dimensional model PE chain is far more rigid than determined from molecular dynamics (MD) simulations, even at energies as low as a small fraction of the ground state energy. This result casts uncertainty on the reliability of MD estimates of dynamical or structural quantities relevant to the study of some macromolecular systems.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    On the determination and ramifications of chaos in many-body systems: A model study of polyethylene (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 577-590 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Computational methods for elucidating information related to the dynamical behavior of multidimensional systems are presented and applied in the area of macromolecular dynamics. Results indicate that the dimensionality of chaotic dynamics for a model of polyethylene can only be characterized for a very narrow range of extremely low temperature (0-2 K). These results provide evidence that suggests the dynamics of this system are completely chaotic at temperatures as low as 10 K. The preponderance of increasing density of low frequency floppy vibrational modes in large molecular systems provides a facile mechanism for the onset of global chaos. Ramifications of such global chaos to the accurate modeling and simulation of macromolecular dynamics is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1997.040060217
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular dynamics treatment of torsional interactions accompanied by dissociationResearch sponsored by the Division of Chemical Sciences, Office of Basic Energy Science, U.S. Department of Energy under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems Inc. (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 909-920 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: When three atoms in a bend sequence move into a linear configuration, any torsional angle involving those three atoms becomes undefined and its Cartesian derivatives singular. In molecular dynamics simulations, this is most likely to occur during and after a bond-breaking process, leading to spuriously large torsional forces and energies which invalidate the simulation. By including appropriate bend angle switching functions in torsional interaction terms, one may approach the linear bend limit in a well-defined manner and make torsional forces vanish around this limit, as expected on physical grounds. Although this expense can be greatly reduced by observing that any internal force must not move the center of mass of the particles involved. Several approximations explored in this paper can reduce this effort even further.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1995.040040504
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  • 5
    Electronic Resource
    Electronic Resource
    Efficient computation of potential energy first and second derivatives for molecular dynamics, normal coordinate analysis, and molecular mechanics calculationsResearch sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-84OR21400 with Lockheed-Martin Energy Systems Inc. (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 5 (1996), S. 771-788 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: By using two- and three-body internal coordinates and their derivatives as intermediates, it is possible to enormously simplify formulas for three- and four-body internal coordinates and their derivatives. Using this approach, simple formulas are presented for stretch (two-body), two types of bend (three-body), and wag and two types of torsion (four-body) internal coordinates and their first and second derivatives. The formulas are eminently suitable for economizing molecular dynamics and molecular mechanics calculations and normal coordinate analysis of complicated potential energy surfaces. Efficient methods for computing derivatives of entire potential energy terms, and in particular cross terms with switching functions, are presented.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1996.040050410
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  • 6
    Electronic Resource
    Electronic Resource
    Quantum-Monte-Carlo simulations on linear chains (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 5 (1996), S. 365-380 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The diffusion Quantum-Monte-Carlo method is applied to a set of coupled oscillators as a first approach to a polyethylene chain. The obtained energy eigenvalues are in good agreement with normal mode analysis. For chains shorter than 50 atoms a distinction between center oscillators and end oscillators is possible. For longer chains non-negligible deviations are discussed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1996.040050301
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  • 7
    Electronic Resource
    Electronic Resource
    Recent advances in polymer molecular dynamics simulation and data analysisResearch sponsored by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-96OR22464 with Lockheed-Martin Energy Research Corp. (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 6 (1997), S. 855-880 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Significant advances in molecular simulation methodology over the past decade have greatly reduced the traditional size-timescale bottleneck in molecular dynamics calculations. The development of the geometric statement function method allows for systems up to several hundred thousand atoms to be simulated for up to several nanoseconds in reasonable times on standard workstations. For constant energy simulations, the use of symplectic integrators ensures accurate dynamics, even at long simulation times, without velocity or other artificial rescaling schemes. Finally, new methods of frequency estimation allow for accurate vibrational mode frequency calculations even in the presence of chaotic motion on time scales twenty times shorter than the standard fast Fourier transform, with an additional improvement in the sensitivity of the results when initial dynamics conditions are carefully chosen.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1997.040060501
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  • 8
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    mBAND Analysis of Early and Late Damages in the Chromosome of Human Lymphocytes after Exposures to Gamma Rays and Fe Ions (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Stable type chromosome aberrations that survive multiple generations of cell division include translocation and inversions. An efficient method to detect an inversion is multi-color banding fluorescent in situ hybridization (mBAND) which allows identification of both inter- and intrachromosome aberrations simultaneously. Post irradiation, chromosome aberrations may also arise after multiple cell divisions as a result of genomic instability. To investigate the stable or late-arising chromosome aberrations induced after radiation exposure, we exposed human lymphocytes to gamma rays and Fe ions ex vivo, and cultured the cells for multiple generations. Chromosome aberrations were analyzed in cells collected at first mitosis and at several time intervals during the culture period post irradiation. With gamma irradiation, about half of the damages observed at first mitosis remained after 7 day- and 14 day- culture, suggesting the transmissibility of damages to the surviving progeny. At the doses that produced similar frequencies of gamma-induced chromosome aberrations as observed at first mitosis, a significantly lower yield of aberrations remained at the same population doublings after Fe ion exposure. At these equitoxic doses, more complex type aberrations were observed for Fe ions, indicating that Fe ion-induced initial chromosome damages are more severe and may lead to cell death. Detailed analysis of breaks participating in total chromosome exchanges within the first cell cycle post irradiation revealed a common hotspot located in the 3p21 region, which is a known fragile site corresponding to the band 6 in the mBand analysis. The breakpoint distribution in chromosomes collected at 7 days, but not at 14 days, post irradiation appeared similar to the distribution in cells collected within the first cell cycle post irradiation. The breakpoint distribution for human lymphocytes after radiation exposure was different from the previously published distribution for human mammary epithelial cells, indicating that interphase chromatin folding structures play a role in the distribution of radiation-induced breaks.
    Keywords: Aerospace Medicine
    Type: JSC-CN-28822 , HITSRS2013. Hyeavy Ion in Therapy and Space Radiation Symposium 2013; May 15, 2013 - May 18, 2013; Chiba; Japan
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    NASA TECHNICAL REPORTS
  • 9
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    Karyotyping of Chromosomes in Human Bronchial Epithelial Cells Transformed by High Energy Fe Ions (2014)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Lung cancer induced from exposure to space radiation is believed to be one of the most significant health risks for long-term space travels. In a previous study, normal human bronchial epithelial cells (HBECs), immortalized through the expression of Cdk4 and hTERT, were exposed to gamma rays and high energy Fe ions for the selection of transformed clones induced by low- and high-LET radiation. In this research, we analyzed chromosome aberrations in these selected clones for genomic instability using the multi-color fluorescent in situ hybridization (mFISH), as well as the multi-banding in situ hybridization (mBAND) techniques. In most of the clones, we found chromosomal aberrations involving translocations between different chromosomes, with several of the breaks occurred in the q-arm of chromosome 3. We also identified copy number variations between the transformed clones and the parental HBEC cells regardless of the exposure condition. Our results indicated that the chromosomal aberrations in low- and high radiation-induced transformed clones are inadequately different from spontaneous soft agar growth. Further analysis is underway to reveal the genomic instability in more transformed clones
    Keywords: Aerospace Medicine
    Type: JSC-CN-32211 , NASA''s Human Research Program Investgator''s Workshop; Jan 13, 2015 - Jan 15, 2015; Galveston, TX; United States
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    NASA TECHNICAL REPORTS
  • 10
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    RBE of Energetic Iron Ions for the Induction of Early and Late Chromosome Aberrations in Different Cell Types (2014)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Numerous published studies have reported the RBE values for chromosome chromosomes induced by charged particles of different LET. The RBE for chromosome aberrations in human lymphocytes exposed ex vivo showed a similar relationship as the quality factor for cancer induction. Consequently, increased chromosome aberrations in the astronauts' white blood cells post long-duration missions are used to determine the biological doses from exposures to space radiation. The RBE value is known to be very different for different types of cancer. Previously, we reported that the RBE for initial chromosome damages was high in human lymphocytes exposed to Fe ions. After multiple cell divisions post irradiation, the RBE was significantly smaller. To test the hypothesis that the RBE values for chromosome aberrations are different between early and late damages and also different between different cell types, we exposed human lymphocytes ex vivo, and human fibroblast cells and human mammary epithelial cells in vitro to 600 MeV/u Fe ions. Post irradiation, the cells were collected at first mitosis, or cultured for multiple generations for collections of remaining or late arising chromosome aberrations. The chromosome aberrations were quantified using fluorescent in situ hybridization (FISH) with whole chromosome specific probes. This study attempts to offer an explanation for the varying RBE values for different cancer types.
    Keywords: Aerospace Medicine
    Type: JSC-CN-32212 , NASA''s Human Research Program Investigator''s Workshop; Jan 13, 2015 - Jan 15, 2015; Galveston, TX; United States
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    NASA TECHNICAL REPORTS
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