ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Stress relaxation in a diatomic liquid (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4984-4991 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By the use of nonequilibrium molecular dynamics we have studied the stress relaxation following imposition of a constant-volume elongation in the x1 direction on a model diatomic liquid. Three consecutive modes of relaxation of the stress difference τ=t11−〈fraction SHAPE="CASE"〉12(t22+t33) are found, each governed by exponentials e−αit with α1〉α2〉α3. Each mode is shown to correspond to the return to isotropy of a different characteristic of the liquid structure that has been rendered anisotropic by the deformation, namely (1) r¯(θ), the mean distance from a generic atom of interacting atoms in the θ direction, with the angle θ measured from the stretch axis x1; (2) N¯(θ), the mean number density of interacting atoms in the θ direction; and (3) 〈〈P2(θb)〉〉, a measure of the orientation θb of molecular axes with respect to x1. The first two modes are identical in form to those studied previously [R. C. Picu and J. H. Weiner, J. Chem. Phys. 107, 7214 (1997)] for stress relaxation in a monatomic liquid, but their rates of decay differ because of differences in packing and in atomic mobility. During the third mode of relaxation it is found that τ=C〈〈P2(θb)〉〉, where C may be understood in terms of the intrinsic stress tensor, a tensor referred to a coordinate system fixed to the molecule [J. Gao and J. H. Weiner, J. Chem. Phys. 90, 6749 (1989)]. The relevance of these results to stress relaxation in polymer melts is discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475907
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Optical collimation and compression of a thermal atomic beam (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 8-14 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two-dimensional version of a magneto-optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362774
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Structural changes during stress relaxation in simple liquids (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7214-7222 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the structural changes that accompany the stress relaxation in simple liquids by means of nonequilibrium molecular dynamics (NEMD) simulations. It is shown that during elongational deformation of the system, the statistical distribution of interacting neighbors about a given atom in the system, as measured by the mean interatomic distance in an arbitrary direction, becomes ellipsoidal with the largest semiaxis oriented in the stretch direction. Also, the mean number of particles in the distribution is smaller in that direction than normal to the stretch axis. Therefore, the return to isotropy consists on the one hand of a return of the spatial distribution of neighbors to the spherical shape and, on the other hand, of an isotropization of the number density distribution. These two processes, which take place with widely different rates, are shown to be closely related to the two modes of stress relaxation characteristic for the simple liquids. The first of these, which is the fastest and corresponds to the most significant stress decay, is shown to be related to the fast return of the distribution of neighbors to the spherical shape. The second mode is intimately related to the isotropization of the density distribution on the sphere through a quasidiffusional process. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474962
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Simulated polymer melt stress relaxation. I. Plateau behavior (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1614-1620 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The computer simulation of stress relaxation in a model polymer melt is performed with a nonequilibrium molecular dynamics algorithm. The chains are freely jointed with N=30, 100, and 200 bonds and with both intra- and interchain excluded volume interactions. For N=200, the model exhibits incipient plateau behavior as evidenced by an inflection point in the stress relaxation history. Comparison is made between the stress history as computed on the atomic level by the virial stress formula and on the molecular level using the entropic spring formulation. The two histories are in agreement only for the case of N=200, with entanglement length Ne=40, and only for the time period following the inflection point. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469784
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Simulated polymer melt stress relaxation. II. Search for entanglements (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1621-1626 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Simulations, described in the previous paper, by nonequilibrium molecular dynamics of stress relaxation in a model polymer melt of freely jointed chains with N=200 bonds exhibited an incipient plateau, followed by a period in which the relaxing stress corresponded to the entropic stress with an entanglement length of Ne=40 bonds. This paper describes two types of diagnostic subroutines used to search for the entanglements or obstacles responsible for these phenomena. The first examined the rate of separation of initially neighboring interchain atom pairs but did not serve to uncover many topological entanglements. The second introduced a measure of time-averaged atomic mobility and found that intrachain atoms of relatively low mobility tended to cluster in groups along the chain. The average spacing between clusters appears to introduce a new length scale in polymer melts that is independent of the conventional picture of interchain entanglements. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469733
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Anisotropy of optical suppression in photoassociative ionization collisions within a slow, collimated sodium atom beam (1998)
    Springer
    The European physical journal 4 (1998), S. 139-144 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping - 34.50.Rk Laser-modified scattering and reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We report the observation of polarization anisotropy in the optical suppression of photoassociative ionization (PAI) collisions. Binary collisions occur within a tightly collimated and optically cooled velocity group of a single sodium beam. A laser beam, blue-detuned with respect to the atomic resonance transition, crosses the atomic beam and suppresses the PAI rate. We measure this suppression as a function of intensity and electric field vector aligned parallel or perpendicular to the atomic beam axis. Quantum close-coupling and multichannel curve-crossing calculations of model systems yield insight into the nature of the anisotropy and are in reasonable agreement with the measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050193
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Direct measurement of fine structure changing collisional losses in cold trapped 85Rb (1999)
    Springer
    The European physical journal 7 (1999), S. 317-321 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping - 33.80.Ps Optical cooling of molecules; trapping - 34.50.Rk Laser-modified scattering and reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Using a technique that consists in ionizing atoms out of the 5P 1/2 fragments originated in the cold collision process, we have measured the contribution of the fine structure changing collision (FS) to the total trap loss rate of cold 85Rb. Our results show that FS contribution is responsible for about 4% of the total trap loss. This result should stimulate new theoretical discussions involving exoergic cold collisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050574
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Real-time observation of ultrafast ionization and fragmentation of mercury clusters (1999)
    Springer
    The European physical journal 9 (1999), S. 399-403 
    Details
    ISSN: 1434-6079
    Keywords: PACS: 33.80.Rv Multiphoton ionization and excitation to highly excited states – 36.40.Qv Stability and fragmentation of clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We report on time-resolved multiphoton ionization and fragmentation dynamics of free Hg n -clusters (n≤110) with femtosecond laser pulses. Already at laser intensities of 1011 W/cm2 we observe prompt formation of singly, doubly, and triply charged Hg n clusters. In pump-probe experiments short-time (0–5 ps) oscillatory modulations of the transient Hg n + and Hg n 2+ signals are observed which indicate an intermediate state dynamics common to all observed cluster sizes and charge states. Long-time (0–200 ps) transient ionization signals show caged dissociation and recombination chromophore dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050465
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Atomic level picture of stress relaxation in polymer melts (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 143-154 
    Details
    ISSN: 0887-6266
    Keywords: polymer simulation ; stress relaxation ; molecular dynamics ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have been developing a physical picture on the atomic level of stress relaxation in polymer melts by means of computer simulation of the process in model systems. In this article we treat a melt of freely jointed chains, each with N = 200 bonds and with excluded-volume interactions between all nonbonded atoms, that has been subjected to an initial constant-volume uniaxial extension. We consider both the stress relaxation history σ(t) based on atomic interactions, and the stress history σe(t; NR) based on subdividing the chain into segments with NR bonds each, with each segment regarded as an entropic spring. It is found that at early times σ(t) 〉 σe(t; NR) for all NR, and that, for the remainder of the simulation, there is no value of NR for which σ(t) = σe(t; NR) for an extended period; by the end of the simulation σ(t) has fallen just below the value σe(t; 50). The decay of segment orientation, 〈P2(t; NR)〉, and of bond orientation 〈P2(t; 1)〉, is computed during the simulation. It is found that the decay of the atom-based stress σ(t) is closely related to that of 〈P2(t; 1)〉. This result may be understood through the concept of steric shielding. The change in local structure of the polymer melt during relaxation is also studied. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 143-154, 1998
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 10
    facet.materialart.
    Unknown
    D-AKAP2, a novel protein kinase A anchoring protein with a putative RGS domain (1997)
    National Academy of Sciences
    Details
    Publication Date: 1997-10-14
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...