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  • 1
    ISSN: 1432-0649
    Keywords: 87.50.Hj ; 42.55.Rz ; 87.90.+y
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Plasma-mediated ablations of brain tissue have been performed using picosecond laser pulses obtained from a Nd:YLF oscillator/regenerative amplifier system. The laser pulses had a pulse duration of 35 ps at a wavelength of 1.053 µm. The pulse energy varied from 90 µJ to 550 µJ at a repetition rate of 400 Hz. The energy density at the ablation threshold was measured to be 20 J/cm2. Comparisons have been made to 19 ps laser pulses at 1.68 µm and 2.92 µm from an OPG/OPA system and to microsecond pulse trains at 2.94 µm from a free running Er:YAG laser. Light microscopy and scanning electron microscopy were performed to judge the depth and the quality of the ablated cavities. No thermal damage was induced by either of the picosecond laser systems. The Er:YAG laser, on the other hand, showed 20 µm wide lateral damage zones due to the longer pulse durations and the higher pulse energies.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0942-0940
    Keywords: Tissue ablation ; laser/tissue interaction ; shortpulsed lasers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The basis for most laser applications in neurosurgery is the conversion of laser light into heat when the incident laser beam is absorbed by the tissue. Irradiation of neural tissue with laser light therefore leads to its thermal damage. However, due to the diffusion of heat energy into the surrounding tissue, often there is thermal damage to neural tissue outside the area of the target volume. These are the characteristics of thermal laser/tissue interaction. In this paper we discuss how we used three different short-pulsed lasers to achieve non-thermal ablation of neural tissue. Three different short-pulsed lasers were used to generate ultrashort laser pulses in the picosecond to femtosecond range. The interaction of such laser pulses with tissue was predicted to be nonthermal. The short-pulsed lasers were used for the ablation of neural tissue using an in vitro calf brain model. The histopathological examination of the lesions revealed that the neural tissue had been removed very precisely without any sign of thermal damage to the surrounding tissue.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical pharmacology 39 (1990), S. 603-605 
    ISSN: 1432-1041
    Keywords: Galanthamine ; Alzheimer's disease ; stereoselectivity ; cholinesterase inhibition ; side effects ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of galanthamine (GAL) and its 2 major metabolites on human cholinesterases has been explored. Epigalanthamine, a diastereomer of GAL, was 130-times less potent in vitro in its effect on acetylcholinesterase (AChE) in erythrocytes than the parent compound, and it did not differ significantly from the ketone galanthaminone. In vivo, the maximal 36–55% inhibition of AChE was approached 30 min after oral administration of 10 mg GAL. The duration of the catalytic inhibition corresponded to an elimination half-life of approximately 5–7 h. GAL was well tolerated in 8/8 healthy volunteers, and 3/4 Alzheimer patients tolerated the drug up to a daily dose of 40 mg.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 264 (1986), S. 554-560 
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The radical copolymerization of α-methylstyrene with styrene in the temperature range from 60 to 150°C can be described according to the equations derived by WITTMER with the assumption, that the addition steps of α-methylstyrene may be reversibel.For the temperature range from 60 to 110°C it could be demonstrated that it would be sufficient to consider only the reversibility of the addition steps of α-methylstyrene to a radical end with α-methylstyrene as the terminal unit. At a reaction temperature of 150°C the addition of α-methylstyrene to a styryl chain end is also reversible, the equilibrium constant being only 1/30 of the α-methylstyrene homopolymerization.The retardation of the polymerization rate by admixture of small amounts of α-methylstyrene to styrene was measured. The results allow an estimation of the rate constants and activation energies of the chain propagation and depolymerization steps.
    Notes: Die radikalische Copolymerisation von α-Methylstyrol mit Styrol läßt sich im Temperaturbereich von 60-150°C nach Gleichungen beschreiben, die WITTMER unter der Annahme abgeleitet hat, daß die Additionsreaktionen von α-Methylstyrol reversibel sein können.Hierbei genügt es, im Temperaturbereich von 60-110°C lediglich die Reversibilität von α-Methylstyrol-Additionsschritten an ein Kettenende mit α-Methylstyrol als letzter Monomereinheit zu berücksichtigen. Für 150°C als Reaktionstemperatur ergibt sich, daß auch die Addition von α-Methylstyrol an ein Styryl-Kettenende meßbar reversibel ist, jedoch mit einer Gleichgewichtskonstante, die um einen Faktor 30 unter der für die α-Methylstyrol-Homopolymerisation liegt.Aus der Retardierung der Styrolpolymerisation durch geringe Zusätze von α-Methylstyrol werden die einzelnen Geschwindigkeitskonstanten und Aktivierungsenergien des Kettenwachstums und der Depolymerisation abgeschätzt.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: An einer Serie von zehn teilweise erstmalig synthetisierten α-substituierten Styrolen wird durch kinetische Messungen bei 110°C gezeigt, daß solche Verbindungen zusammen mit Styrol nach dem Mechanismus einer Copolymerisation reagieren, jedoch je nach dem Charakter des α-Substituenten verschieden stark retardieren oder zur Kettenübertragung führen.Hierbei zeigen α-Alkylstyrole kaum Kettenübertragung, jedoch eine um so größere Retardierung, je sperriger der α-Substituent ist. α-Arylalkylstyrole vom Typ 4-substituierter 2.4-Diphenylbuten(1)-derivate führen hingegen zu einer merklichen Kettenübertragung, wie die übertragungskonstanten von 0,29 und 0,26 der Verbindungen 4-Methyl-2.4-diphenylpenten(1)bzw. 2.4.4-Triphenylpenten(1) beweisen.Die einzelnen Geschwindigkeitskonstanten für Kettenwachstum und Kettenübertragung werden berechnet oder größenordnungsmäßig abgeschätzt.
    Notes: The copolymerization of styrene with a series of ten α-substituted styrenes, partially synthesized for the first time, was investigated by kinetic measurements. All compounds react with styrene according to the mechanism of copolymerization. The extent of the observed retardation or chain transfer reaction depends on the chemical nature of the α-substituent.Some α-alkylstyrenes scarcely show chain transfer, yet the more bulky the α-substituent is, the more retardation could be observed. On the other hand α-arylalkylstyrenes of the type of 4-substituted 2.4-diphenyl-1-butene-derivates cause an evident chain transfer as can be seen from the chain transfer constants of 0,29 and 0,26 from 4-methyl-2.4-diphenyl-1-pentene and 2.4.4-triphenyl-1-pentene, respectively.The single rate constants of chain propagation and chain transfer are calculated or estimated.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 155 (1972), S. 227-238 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: It is shown that the copolymerization of styrene (M1) with 1.1-diphenylethylene (M2) at 110°C can be described by the conventional copolymerization equation with the parameters r1 = 0.34 ± 0.04 and r2 = 0. From these two parameters only r1 follows the Q-e-scheme with Q2 = 2.3 and e2 = -0.35 in the same way as the r1-parameters of other sterically unhindered comonomers of 1.1-diphenylethylene.1.1-Diphenylethylene causes a strong retardation but no inhibition of the styrene polymerization. The quantitative determination of the mentioned retardation leads to the conclusion that the rate constants k12 and k21 of the alternating steps differ at least for two orders of magnitude, k21 as the lower rate constant being responsible for the strong retardation and mainly for the low molecular weights of the copolymers.
    Notes: Für die Copolymerisation von Styrol (M1) mit 1.1-Diphenyläthylen (M2) bei 110°C zeigte sich, daß die konventionelle Copolymerisationsgleichung mit den Parametern r1 = 0,34 ± 0,04 und r2 = 0 zutrifft, wobei der r1-Wert wie für andere sterisch ungehinderte Comonomere des 1.1-Diphenyläthylens das Q-e-Schema mit Q2 = 2,3 und e2 = -0,35 erfüllt.1.1-Diphenyläthylen verursacht eine starke Retardierung, jedoch keine Inhibierung der Styrolpolymerisation. Aus der Retardierung der Styrolpolymerisation bei geringem 1.1-Diphenyläthylengehalt ergibt sich, daß die Geschwindigkeitskonstanten k12 und k21 für die Alternierungsschritte sich um wenigstens zwei Größenordnungen unterscheiden, derart, daß der niedrige k21-Wert sowohl für die starke Retardierung als auch hauptsächlich für die geringen Molekulargewichte der Copolymeren verantwortlich ist.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 85 (1973), S. 456-457 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 107 (1967), S. 253-258 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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