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  • American Institute of Physics (AIP)  (31,708)
  • American Physical Society (APS)
  • International Union of Crystallography (IUCr)
  • 2020-2024  (2)
  • 1985-1989  (37,958)
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  • 1
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    Critical Drift in a Neuro-Inspired Adaptive Network (2023)
    American Physical Society (APS)
    In:  EPIC3Physical Review Letters, American Physical Society (APS), 130(18), pp. 188401-188401, ISSN: 0031-9007
    Details
    Publication Date: 2023-12-05
    Description: It has been postulated that the brain operates in a self-organized critical state that brings multiple benefits, such as optimal sensitivity to input. Thus far, self-organized criticality has typically been depicted as a one-dimensional process, where one parameter is tuned to a critical value. However, the number of adjustable parameters in the brain is vast, and hence critical states can be expected to occupy a high-dimensional manifold inside a high-dimensional parameter space. Here, we show that adaptation rules inspired by homeostatic plasticity drive a neuro-inspired network to drift on a critical manifold, where the system is poised between inactivity and persistent activity. During the drift, global network parameters continue to change while the system remains at criticality.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
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    Master stability functions for metacommunities with two types of habitats (2022)
    American Physical Society (APS)
    In:  EPIC3Physical Review E, American Physical Society (APS), 105(4), pp. 044310-044310, ISSN: 2470-0045
    Details
    Publication Date: 2023-12-05
    Description: Current questions in ecology revolve around instabilities in the dynamics on spatial networks and particularly the effect of node heterogeneity. We extend the master stability function formalism to inhomogeneous biregular networks having two types of spatial nodes. Notably, this class of systems also allows the investigation of certain types of dynamics on higher-order networks. Combined with the generalized modeling approach to study the linear stability of steady states, this is a powerful tool to numerically asses the stability of large ensembles of systems. We analyze the stability of ecological metacommunities with two distinct types of habitats analytically and numerically in order to identify several sets of conditions under which the dynamics can become stabilized by dispersal. Our analytical approach allows general insights into stabilizing and destabilizing effects in metapopulations. Specifically, we identify self-regulation and negative feedback loops between source and sink populations as stabilizing mechanisms and we show that maladaptive dispersal may be stable under certain conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
    Electronic Resource
    Electronic Resource
    Anisotropic intermolecular potentials. III. Rare-gas–hydrogen bromide systems (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4455-4461 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Intermolecular potentials for Ar and Kr interacting with HBr are obtained by least-squares fitting of potential parameters to data obtained from the molecular-beam microwave spectra of the Ar–HBr and Kr–HBr van der Waals complexes. The equilibrium geometry is linear Rg–H–Br in each case, but there are substantial secondary minima at the linear Rg–Br–H geometries; for Ar–HBr, the secondary minimum is only about 5 cm−1 shallower than the primary minimum. This potential feature is found to explain the anomalous H/D isotope effects in centrifugal distortion constants that have been observed for the Rg–HBr complexes. It is predicted that Ar–HBr will have a very low-energy bending state, only 11 cm−1 above the ground state, arising from the secondary minimum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456782
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  • 4
    Electronic Resource
    Electronic Resource
    Excited rovibronic level dependence of the magnetic quenching of slow fluorescence of pyrazine vapor (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4477-4484 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excited rotational level dependence of the external magnetic field effects both on intensity and on decay of fluorescence of pyrazine vapor has been carefully examined for the zero-point vibrational level in S1 with a field strength of 0–170 G. The magnetic quenching of the slow fluorescence becomes more effective with increasing rotational quantum number J' of the excited level, and the field strength at which the amount of fluorescence quenching becomes one-half of the total amount of quenching at the saturated fields is roughly proportional to (2J'+1)−1. The magnetic quenching is also found to depend on K' of the excited level. The rotational level dependence of the magnetic quenching of the slow fluorescence is related to a difference in the number of the triplet levels coupled to the optically excited singlet rovibronic level, based on the spin decoupling mechanism of the singlet–triplet mixed level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456785
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of collision-induced-dipole absorption bands in strontium–rare-gas mixtures. II. Bands involving high-lying states (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4499-4503 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have observed many collision-induced-dipole (CID) absorption bands arising from the transitions between quasimolecular ground and high-lying (n≤10) states in the strontium–rare-gas systems. For each absorption band, we have measured the energy shift of the absorption peak from the energy of the correlating atomic forbidden transition and the effective oscillator strength per unit perturber density fCID/Np. The shift is roughly proportional to the electron scattering length L0 for each rare-gas atom, whereas the fCID/Np is roughly proportional to L20. The shift decreases in general as the principal quantum number n increases, and increases as one goes from the s state to the d state, and to the degenerate manifold state with l≥3. These general features of the shift and fCID/Np are consistent with the predictions by a simple Fermi-potential model, suggesting the important role of the interaction between a Rydberg electron and a rare-gas atom in the CID absorption processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456788
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  • 6
    Electronic Resource
    Electronic Resource
    Detection of the silylene ν2 band by infrared diode laser kinetic spectroscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4582-4586 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν2 band of the silylene SiH2 molecule in X˜ 1 A1 was observed for the first time in the gas phase by using infrared diode laser kinetic spectroscopy. Silylene molecules were generated by the photolysis of phenylsilane at 193 nm. The observed spectrum was analyzed to determine the rotational and centrifugal distortion constants in the ground and v2 =1 states and the band origin ν0 =998.6241(3) cm−1 with one standard deviation in parentheses. The significance of the derived parameters is discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456746
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  • 7
    Electronic Resource
    Electronic Resource
    Dissociation dynamics of the d 1Πg and C 3Πg v=0–2 vibrational states in O2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4597-4602 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using translational spectroscopy we have studied the d 1Πg and C 3 Πg Rydberg states of O2 . The dissociation of the vibrational levels v=0–2 to all energetically accessible dissociation limits has been followed. The dissociation pathways directly reflect the predissociation mechanisms involved. For the d 1 Πg Rydberg state competition between predissociation by a 3 Πg valence state, due to singlet–triplet mixing, and by a 1 Πg valence state has been observed. Using the Fermi golden rule the observed vibrationally dependent competition is reproduced, corroborating the positions of the lower 1 Πg and 3 Πg valence state curves and yielding various coupling strengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456749
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  • 8
    Electronic Resource
    Electronic Resource
    Quantum state-resolved study of pure rotational excitation of CO2 by hot atoms (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4636-4642 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotationally inelastic scattering of carbon dioxide by translationally hot H, D, and Cl atoms was studied by time-resolved diode laser absorption. The high J rotational distribution falls off quite rapidly between J=60 and J=80. D atom collisions have roughly twice the excitation cross section versus H atom collisions, with the H*/D* ratio decreasing with increasing J. These results are consistent with a constraint on the total reagent orbital angular momentum available for rotational excitation. Transient Doppler profiles measured immediately after hot atom/CO2 collisions indicate that CO2 molecules excited to high J levels have a larger recoil velocity than molecules excited to lower J levels. This result is consistent with predictions based on a simple model which treats the CO2 potential as a hard shell ellipsoid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456753
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  • 9
    Electronic Resource
    Electronic Resource
    Diffusion-controlled reactions. I. Molecular dynamics simulation of a noncontinuum model (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4643-4650 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecular dynamics simulation method is extended to study a model of diffusion-controlled reactions. This allows a molecular description of solvent at an equal footing of reactants. Nondiffusional dynamic behavior of reactive molecules is found at short times. It enhances the rate of reactive encounter in comparison to the prediction of Smoluchowski theory. The model studied in this work can be regarded as a theoretical prototype of fluorescence quenching. In this context it is shown that the nondiffusional dynamics is mainly responsible for the discrepancy between Stern–Volmer plots measured in a continuous excitation experiment or obtained by integrating the time resolved fluorescence intensity. The other aspects such as the long-time behavior of survival probability, solvent effect as well as competing effect from finite concentration of one reactive species are also studied in some detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456754
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  • 10
    Electronic Resource
    Electronic Resource
    The reactions of iron clusters with water (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4714-4727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reactions of neutral iron clusters Fe7–27 with water are studied in a laser-vaporization cluster source coupled to a continuous-flow reactor. Reaction products are detected via laser ionization and time-of-flight mass spectrometry. The reactions of room-temperature clusters with H2O show adsorbate decomposition and hydrogen desorption, as do the reactions with D2O at elevated temperatures. The room-temperature reaction with D2O appears not to involve any decomposition, and is at equilibrium under the conditions of these experiments. The dependence of reaction extent on D2O pressure yields equilibrium constants for the addition of the first and second D2O molecules. The analysis is complicated by the presence of two-photon ionization processes that are treated quantitatively with a rate-equation model. This treatment also yields estimates for cluster photoabsorption cross sections, which are found to be approximately linear in cluster size, having a magnitude of 2.3×10−17 cm2 per iron atom. From the derived equilibrium constants and estimated adsorption entropies, approximate D2O–cluster binding energies are determined. They range from 0.42 to 0.59 eV, and their dependence on cluster size shows a remarkable similarity to the dependence of the rate constants for reaction of iron clusters with H2. The implications of this similarity are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456760
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