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  • Springer  (26)
  • American Institute of Physics (AIP)  (4)
  • 1990-1994  (30)
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3808-3816 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general method is presented to reduce the simulation time required to compute the relative free energy between two states X and Y of a molecular system by computer simulation. Although the free energy difference ΔAx→y is, in principle, independent of the pathway chosen to change X into Y, in practice its choice strongly affects the accuracy of the obtained ΔA value. The optimum path is the one for which the relaxation time of the system τsystem attains a minimum, allowing the system to remain as close as possible near equilibrium during a simulation. Downscaling the relevant parts of the potential energy function before the change from X to Y is made, and upscaling afterwards is a rather general way to shorten τsystem and thus save computing time. For a model system of butane like molecules the proposed procedure is more than 1 order of magnitude more efficient than the conventional technique of direct interconversion from state X to state Y.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1508-1510 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Picosecond reflection high-energy electron diffraction is used as a time-resolved surface-lattice temperature probe. A picosecond laser pulse is split into two beams. The first interacts with the sample. The second activates the cathode of an electron gun creating a collimated and focused electron pulse that is well synchronized with the heating laser pulse. The electron pulse is used to generate a reflection high-energy electron diffraction pattern of the sample. Since heating results in an intensity reduction of the elastically scattered electrons (Debye–Waller effect), the diffraction pattern provides information on the surface temperature as well as structure. Time-resolved measurements of the picosecond laser-heated surface show general agreement with a heat diffusion model.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 1636-1647 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A laser-driven picosecond time-resolved electron diffraction system operating in ultrahigh vacuum is described. A picosecond laser pulse is split into two beams. The first interacts with the sample under study. The second activates the cathode of an electron gun creating a collimated and focused electron pulse that is well synchronized with the heating laser pulse. By spatially delaying the part of the laser pulse that photoactivates the cathode from that which irradiates the sample, the electron pulse can be set to arrive at the sample at a specific time after sample irradiation. When a flat smooth sample is aligned such that the electrons are in grazing incidence on its surface, a reflection high-energy electron diffraction pattern of its first few atomic layers is generated. Analysis of the diffraction pattern provides information on the surface structure and temperature at a set time lapse between the arrival of the laser and the electron pulse to the sample. Design, characterization, and operation of this system along with an example of its application to monitor the transient surface temperature using the surface Debye–Waller effect are discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 716-717 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improvement in the electrical properties of the GaAs surface has been accomplished using a room-temperature hydrogen sulfide plasma. The surface has then been protected by a 300 °C plasma enhanced chemical vapor deposition (PECVD) SiO2 film. This treatment is highly reproducible due to computer control of process parameters and long-lasting due to the SiO2 cap. Improved C-V characteristics were observed, showing interface trap densities in the high 1011 cm−2 eV−1 range. Photoluminescence (PL) measurements on the sulfided samples showed increased intensity over the untreated samples.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0533
    Keywords: Innervation ; Axonal regeneration ; Nerve terminal ; Motor endplate ; Collateral sprouting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the present study we examined the effect of recombinant human ciliary neurotrophic factor (rH-CNTF) on muscle fibre reinnervation. After facial nerve crush, rats were treated systemically with either rH-CNTF (1 mg/kg per 48h) or saline and were killed on days 10–13 after nerve crush when muscle fibre reinnervation becomes apparent. Blind counting of the numbers of reinnervated motor endplates and the length of the synaptophysin-positive staining was used to assess the effect of CNTF treatment on muscle fibre reinnervation in the whisker muscle. On day 10, both treatment groups showed a limited number of reinnervated motor endplates. Both the saline-and CNTF-treated rats showed a significant increase in the percentage of reinnervated motor endplates and in the length of the synaptophysin-positive staining with time. On days 10 and 11, there was no difference in muscle fibre reinnervation between the treated groups. On days 12 and 13, the CNTF-treated rats showed an increased muscle fibre reinnervation which was significant compared to the saline-treated rats. These results suggest that after facial nerve crush in young rats, CNTF enhances muscle fibre reinnervation, most probably by stimulating the intramuscular branching. There is no support for an effect of CNTF on nerve sprouting in the proximal axonal part or on axonal elongation; the CNTF effect on intramuscular branching might be mediated by the muscle fibres.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International archives of occupational and environmental health 64 (1992), S. 281-291 
    ISSN: 1432-1246
    Keywords: Shipyard ; Welding ; Turnover ; Selected employment ; Work disability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A 40-year historical cohort study of medical wastage among about 550 shipyard welders and 1100 controls (shipwrights and engine fitters), all employed at the same shipyard, was carried out. The welders left their job 20% more often than the controls; the excess considerably increased with duration of employment. Wastage was particularly due to respiratory, cardiovascular, locomotor and mental disorders. Both welders and controls contributed considerably (about 20%) to permanent work disability. Medical wastage among welders because of respiratory diseases was more than four times higher than among controls, which could not be explained by differential smoking habits alone. The study raises concern about locomotor health hazards for shipyard workers. Moreover, it underscores the need to reduce the large excess risk of respiratory diseases among shipyard welders. The same may be true for welders in other large metal construction plants, e.g. in boiler production.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-203X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cell suspension cultures, derived from roots of Podophyllum hexandrum Royle (Berberidaceae), accumulate podophyllotoxin. In this study the use of β-cyclodextrin in feeding the poorly water-soluble precursor coniferyl alcohol to these cultures is described. By complexation with β-cyclodextrin, a solution of 3 mM coniferyl alcohol could be fed, resulting in enhanced podophyllotoxin accumulation. The same concentration of non-complexed suspended coniferyl alcohol had only little effect on the podophyllotoxin accumulation. β-Cyclodextrin itself was proven to be non-toxic for the cells. It did not influence the podophyllotoxin content and it was not metabolized or used as a carbon source by the cells. For comparison, coniferin, the water-soluble β-D-glucoside of coniferyl alcohol, was also fed in the same concentration. The effect of coniferin on the podophyllotoxin accumulation was stronger than that of coniferyl alcohol complexed with β-cyclodextrin, but coniferin is not commercially available.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 22 (1994), S. 423-436 
    ISSN: 1432-1017
    Keywords: Computer simulation ; DPPC ; Bilayer ; Liquid crystalline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We present the results of molecular dynamics (MD) simulations of a phospholipid membrane in water, including full atomic detail. The goal of the simulations was twofold: first we wanted to set up a simulation system which is able to reproduce experimental results and can serve as a model membrane in future simulations. This goal being reached it is then further possible to gain insight in to those properties that are experimentally more difficult to access. The system studied is dipalmitoylphosphatidylcholine/water, consisting of 5408 atoms. Using original force field parameters the membrane turned out to approach a gel-like state. With slight changes of the parameters, the system adopted a liquid-crystalline state. Separate 80 ps runs were performed on both the gel and liquid-crystalline systems. Comparison of MD results with reliable experimental data (bilayer repeat distance, surface area per lipid, tail order parameters, atom distributions) showed that our simulations, especially the one in the liquid-crystalline phase, can serve as a realistic model for a phospholipid membrane. Further analysis of the trajectories revealed valuable information on various properties. In the liquid-crystalline phase, the interface turns out to be quite diffuse, with water molecules penetrating into the bilayer to the position of the carbonyl groups. The 10–90% width of the interface turns out to be 1.3 nm and the width of the hydrocarbon interior 3.0 nm. The headgroup dipoles are oriented at a small angle with respect to the bilayer plane. The resulting charge distribution is almost completely cancelled by the water molecules. The electron density distribution shows a large dip in the middle of the membrane. In this part the tails are more flexible. The mean life time between dihedral transitions is 20 ps. The average number of gauche angles per tail is 3.5. The occurrence of kinks is not a significant feature.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1009
    Keywords: Environmental impact ; Assessment process ; Watershed modification ; Impoundment ; River diversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This article reviews the application of environmental impact assessment (EIA) procedures and practices to three watershed modification projects situaled in western Canada. These ventures were justified for accelerating regional economic development, and cover the period during which public concerns for protecting the environment rapidly made their way into the national political agenda. An historical account and analysis of the situation, therefore, seems desirable in order to understand the development of EIA processes, practices, and methodologies since the start of construction of the first project in 1961. This study concludes that there has been good progress in predicting and evaluating environmental and related social impacts of watershed modification proposals. However, a number of obstacles need to be overcome before EIA can firmly establish itself as an effective planning tool. These difficulties include jurisdictional confusions and conflicts, division of authority and responsibility in designing and implementing appropriate mitigative and monitoring measures, lack of tested EIA methodologies, and limited availability of qualified human resources. A number of conclusions and suggestions are offered so that future watershed modification proposals may be planned and implemented in a more environmentally sustainable fashion. These include: (1) EIA processes must be completed before irrevocable decisions are made. (2) Any major intrusion into a watershed is likely to impact on some major components of the ecosystem(s). (3) Mitigation costs must form part of the benefit-cost analysis of any project proposal. (4) Interjurisdictional cooperation is imperative where watersheds cross political boundaries. (5) The EIA process is a public process, hence public concerns must be dealt with fairly. (6) The role of science in the EIA process must be at arms length from project proponents and regulators, and allowed to function in the interest of the protection of the environment and public health and safety.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 35 (1990), S. 1146-1152 
    ISSN: 1573-2568
    Keywords: myenteric plexus ablation ; smooth muscle ; enteric innervation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Alterations in smooth muscle responsiveness and neural pathways in adjacent tissue may occur after local myenteric denervation. The in vitro contractile responses of both longitudinal and circular muscle to the mixed muscarinic and nicotinic cholinergic agonist carbachol were determined 15, 30, and 45 days after localized myenteric plexus ablation. Denervated longitudinal muscle exhibited decreased responsiveness to carbachol at all times examined. Denervated circulated muscle was initially supersensitive, but with time became subsensitive. These changes probably reflect the loss of the nicotinic (neuronal) component of the action of carbachol. Muscle orad to the site of denervation appeared subsensitive, while muscle caudad to the lesion was supersensitive (circular) or unaffected (longitudinal). These results suggest that there are changes in ascending and descending neural pathways. Alterations in the cholinergic responsiveness of intestinal smooth muscle, both at and beyond the site of myenteric plexus ablation, may result in altered intestinal motility that could lead to functional obstruction.
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