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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 47 (1987), S. 17-55 
    ISSN: 1572-9613
    Keywords: Path integral ; influence functional ; fermion bath ; real-time density matrix ; Grassmann algebra ; quantum Langevin equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Quantum dynamics of a particle coupled to a fermionic environment is considered, with particular emphasis on the formulation of macroscopic quantum phenomena. The framework is based on a path integral formalism for the real-time density matrix. After integrating out of the fermion variables of the environment, we embed the whole environmental effects on the particle into the so-called influence functional in analogy to Feynman and Vernon's initial work. We then show that to the second order of the coupling constant, the exponent of the influence functional is in exact agreement with that due to a linear dissipative environment (boson bath). Having obtained this, we turn to a specific model in which the influence functional can be exactly evaluated in a long-time limit (long compared to the inverse of the cutoff frequency of the environmental spectrum). In this circumstance, we mainly address our attention to the quantum mechanical representation of the system-plus-environment from the known classical properties of the particle. It is shown that, in particular, the equivalence between the fermion bath and the boson bath is generally correct for a singlechannel coupling provided we make a simple mapping between the nonlinear interaction functions of the baths. Finally, generalizations of the model to more complicated situations are discussed and significant applications and connections to certain practically interesting problems are mentioned.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 49 (1987), S. 811-826 
    ISSN: 1572-9613
    Keywords: Adiabatic transformation ; fermion bath ; Grassmann algebra ; influence functional ; path integral ; real-time density matrix
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The general path-integral formalism for real-time dynamics for a quantum system in a fermionic environment proposed previously is investigated by using a new method called local adiabatic transformation. This method is based on the observation that in the long-time limit (the time scale of the system is much larger than that of the environment, typically characterized by the inverse of the cutoff frequency of the environment), most degrees of freedom of the environment will follow the dynamics adiabatically. This feature is utilized by transforming the original problem of coordinate coupling into a problem of velocity coupling. This is achieved by making some simple unitary transformation on the fermion field (before path-integrating out of that field). By doing perturbations on the new problem, all the previous important results are recovered. Further-more, generalizations to more realistic situations [for example, a particle traveling over a large distance and coupled to a Fermi gas through the phase factor exp(ik·R) (the coupling may involve many channels of angular momentum)] are considered and significant results obtained.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of biomedical science 5 (1998), S. 401-414 
    ISSN: 1423-0127
    Keywords: Oxidative stress ; Reactive oxygen species ; Excitotoxicity ; Hydroxyl radical ; Peroxynitrite ; Antioxidants ; Polyphenols ; Neurodegenerative disorders ; Apoptosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Oxidative insults, whether over-excitation, excessive release of glutamate or ATP caused by stroke, ischemia or inflammation, exposure to ionizing radiation, heavy-metal ions or oxidized lipoproteins may initiate various signaling cascades leading to apoptotic cell death and neurodegenerative disorders. Among the various reactive oxygen species (ROS) generated in the living organism, hydroxyl and peroxynitrite are the most potent and can damage proteins, lipids and nucleic acids. It appears that some natural antioxidants (tocopherol, ascorbic acid and glutathione) and defense enzyme systems (superoxide dismutase, catalase and glutathione peroxidase) may provide some protection against oxidative damage. Recent findings indicate several polyphenols and antioxidant drugs (probucol, seligilline) are effective in protecting the cells from ROS attack. Further development of these antioxidant molecules may be of value in preventing the development of neurodegenerative diseases.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1106
    Keywords: Key words Perinatal asphyxia ; Apoptosis ; Necrosis ; Hematoxylin-eosin ; DNA fragmentation ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The consequences of perinatal asphyxia on the rat brain were studied 80 min to 8 days after birth with hematoxylin-eosin and in situ DNA double-strand-breaks labeling histochemistry. Asphyxia was induced by immersing fetus-containing uterus horns, removed from ready-to-deliver Sprague-Dawley rats, in a water bath at 37°C for various time periods (0–22 min). Spontaneous- and cesarean-delivered pups were used as controls. Perinatal asphyxia led to a decrease in the rate of survival, depending upon the length of the insult. No gross morphological changes could be seen in the brain of either control or asphyctic pups at any of the studied time points after delivery. However, in all groups, nuclear chromatin fragmentation, corresponding to in situ detection of DNA fragmentation, was observed at different stages. Nuclear fragmentation in control pups showed a specific distribution that appeared to be related to brain maturation, thus indicating programmed cell death. A progressive and delayed increase in nuclear fragmentation was found in asphyctic pups, which was dependent upon the length of the perinatal insult. The most evident effect was seen in frontal cortex, striatum, and cerebellum at postnatal day 8, although changes were also found in ventral-posterior thalamus, at days 1 and 2. Thus, nuclear chromatin fragmentation in asphyctic pups indicates a delayed post-asphyctic neuronal death. The absence of signs of inflammation or necrosis suggests that delayed neuronal cell death following perinatal asphyxia is an active, apoptosis-like phenomenon.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 4077-4086 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some properties of photocrosslinked high density polyethylene (2 mm thick sheets) have been studied. The homogeneity of the network is greatly improved by the application of triallylcyanurate (TAC) as crosslinking agent. The role of TAC in promoting the crosslinking is discussed. The crosslinked PE is found to be durable towards immersion in boiling water. Oxygen permeability increases while density and melting point decrease with increasing degree of crosslinking. The network chain density is obtained using conventional swelling method in boiling xylene, which together with data from melting point depression show that contribution of chain entanglement is insignificant to the gel formation of PE in this work.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 4051-4075 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High density polyethylene has been photocrosslinked in the melt by using 4-chlorobenzophenone (4-CBP) as photoinitiator and triallylcyanurate (TAC) as crosslinking agent. Various factors affecting the crosslinking process (photoinitiator used and its concentration, irradiation temperature and time, atmosphere, UV light source, light intensity) were examined. By optimizing the irradiation conditions, it was found that samples up to 2 mm thick could readily be crosslinked to high gel content (≈ 90%) with satisfactory homogeneity within very short irradiation times (≈ 15 s). The kinetic analysis of the crosslinking process showed a linear relation between log S and log t (S is the sol fraction t is the irradiation time). An induction period was observed, the length of which decreased with increasing concentration of 4-CBP and increasing light intensity. An upper limit of gel content was also found for long irradiation times at a level depending on the concentration of 4-CBP. The crosslinking rate was proportional to the second order of light intensity at lower intensity and changed to first order at higher light intensity. A mechanism based on the recombination of chain radicals through both allyl and alkyl type radicals of TAC was proposed.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 1847-1859 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal oxidative stability of photocrosslinked high density polyethylene was studied. The relative effectiveness of various antioxidants (hindered phenols and amines, aromatic amine, organic sulfides, and phosphites) was examined by comparing the oxidation induction time (OIT) which was measured using differential scanning calorimetry. Hindered phenol antioxidants were found to be most effective. At an antioxidant concentration of 0.20 wt % which gave an OIT value of 20 min at 200°C, the photocrosslinking rate was decreased only to a limited extent as evidenced by a small drop in gel content. However, the efficiency of the antioxidants as stabilizers decreased to a considerable extent after the photocrosslinking process. Serious surface deterioration was found which was ascribed to depletion of antioxidant at the surface mainly due to high rate of oxidation and evaporation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 661-666 
    ISSN: 0899-0042
    Keywords: chiral dendrimers ; dendrimers ; axial chirality ; (R)-(+)-1,1′-bi-2,2′-naphthol ; optical rotation ; circular dichroism ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and optical activity of novel chiral dendrimers with axial chirality are reported. The dendrimers were constructed by coupling of the polyether dendritic bromides with (R)-(+)-1,1′-bi-2-naphthol (1). The uniform (2, 3, 4) and non-uniform double-O-alkylated (8, 9, 10) as well as mono-O-alkylated (5, 6, 7) products were thus obtained. These chiral molecules were characterized by 1H- and 13C-NMR, elemental analysis, optical rotation, adsorption spectra, and circular dichroism. It was found that the specific rotation decreases with the increase of the number of generation for each group of dendrimers (2-4, 5-7, and 8-10, respectively). In terms of the molar rotation, it was quite different; the molar rotation increased sharply for dendrimers, 2-4, but only slightly for dendrimers 5-7. The dihedral angle change of bi-naphthyl in the synthesized dendrimers was discussed based on the CD spectra. Chirality 10:661-666, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 401-407 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkyl methacrylate monomers with three kinds of dendritic fragments as alkyl groups, two kinds of Fréchet-type and a new type with 3,5-diphenoxybenzyl as first generation, were prepared by reaction of the corresponding dendritic bromides with methacrylic acid in good yield and were homopolymerized with a radical initiator. Polymers with side groups in first generation had a degree of polymerization (P̄n) of 17-24, markedly higher than those with side groups in second generation, P̄n ≈ 6-7.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 6 (1994), S. 515-524 
    ISSN: 1040-7685
    Keywords: electrospray ionization ; ion mobility detection ; ion mobility spectrometry ; liquid chromatography detector ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrospray ionization ion mobility spectrometry (ESI-IMS), a technique which has only recently become analytically useful, has been evaluated for use as a detector for microbore liquid chromatography and capillary electrophoresis. Figures of merit for ESI-IMS were determined. Detection limits as low as 1 × 10-15 mol s-1 were measured, with a linear response range of 3 to 4 orders of magnitude and with reproducibility within 3% (relative standard deviation of peak area). Gradient elution with water/methanol mobile phase did not perturb chromatographic baseline, compound response, or product ion mobility. Both positive and negative ion mobility spectra for more than 30 compounds demonstrated the sensitivity of ESI-IMS response to a wide range of analytes. Finally, the concept of using ESI-IMS as an ionization source for gasphase samples was presented, potentially unifying detector application for both gas and liquid chromatography.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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