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  • Kinetics  (2)
  • 72.40.+w  (1)
  • Preoperative planning  (1)
  • 1
    Electronic Resource
    Electronic Resource
    A comparative study of the accuracy of Ranawat’s and Pierchon’s methods to determine the centre of rotation in bilateral coxopathy (2000)
    Springer
    Skeletal radiology 29 (2000), S. 652-655 
    Details
    ISSN: 1432-2161
    Keywords: Keywords Centre of hip rotation ; Bilateral hip disease ; Total hip prosthesis ; Preoperative planning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Objective. The objective of the study was to compare two methods (Ranawat’s and Pierchon’s) used to determine the centre of rotation of the hip and establish which method calculates a position nearer to the real centre of rotation. Patients and design. We selected 24 patients with unilateral osteoarthritis of the hip. The centre of rotation of the healthy hip was determined in two consecutive radiographic studies by superimposing a template of circles and using two axes as the reference lines (X-axis=teardrop line; Y-axis=a line perpendicular to the X-axis, drawn from the intersection of the ilio-ischiatic line and the teardrop line). After ensuring the stability of these references, both methods were applied to the same radiograph to determine which one established a centre of rotation nearer to the anatomical centre identified by the template of circles. Results. When the values for the healthy hip are compared with those obtained using Ranawat’s method, highly significant differences are observed for both X (P〈0.0001) and Y (P〈0.0001). When the results for the healthy hip are compared with the values obtained using Pierchon’s method, neither the X (P=0.722 ) nor the Y values (P=0.112) show any significant differences. It would be advisable to use Pierchon’s method to determine the centre of rotation during the preoperative planning for a total hip arthroplasty when the anatomical alteration is bilateral.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002560000279
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Sonoluminescence: A new electrical breakdown hypothesis (1996)
    Springer
    JETP letters 64 (1996), S. 907-910 
    Details
    ISSN: 1090-6487
    Keywords: 72.40.+w
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss an hypothesis wherein single-bubble sonoluminescence is attributed to electrical breakdown due to large pressure gradients existing for small bubble radii. These large gradients produce large electric fields (the flexoelectric effect) that lead to electrical breakdown, releasing energies up to 10−10 J, which is much larger than the light energy released in each cycle. This hypothesis appears to be consistent with several observations made in studies of the sonoluminescence process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567246
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of the nuclear and extranuclear substitution on the singlet molecular oxygen [O 2(1Δg)]-mediated photooxidation of tyrosine derivatives: A kinetic study (1995)
    Springer
    Amino acids 8 (1995), S. 367-377 
    Details
    ISSN: 1438-2199
    Keywords: Amino acids ; Tyrosine ; Tyrosine derivatives ; Singlet oxygen ; Photooxidation ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of the substitution pattern on the kinetics of the Type II (O2(1Δg)-mediated) dye-sensitized photooxidation of a series of nine tyrosine derivatives was investigated. Overall (kt) and reactive (kr) rate constants for the interaction of the excited oxygen species with the amino acid derivatives were determined. A parallel study on solvent and pH effects was carried out. The presence of different substituents in nuclear positions or in the amino acid side chain greatly affect the photooxidation rates. An upper limit for photooxidation quantum yield, calculated from the kinetic data, varies from 0.03 to 0.25, being the higher for halogenated tyrosines and the lower for esterified tyrosines and for the nitro-derivative. The variation of solvent polarity and pH of the reaction medium confirm that the presence of the ionized phenolate group in tyrosine, clearly dominates the quenching process. As already postulated for generic phenolic derivatives, it proceeds through a polar intermediate complex which posses some component of charge-transfer character. Esterification of the carboxilic acid of tyrosine selectively decreases the contribution of the reactive step to the overall process of O2(1Δg) quenching. An amide group in the same position does not produce noticiable changes in this sense. The presence of a highly deactivating nitro group in nuclear positions greatly diminishes the magnitude of both overall and reactive interactions. For all three, o-, m- and p-tyrosine the values of photooxidation quantum yields show an excellent parallelism with the rates of consumption of the — NH2 group of the amino acid chain, upon sensitized irradiation. It could react, in the cases of 0- and m-tyrosine in a secondary, non photochemical, step.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806554
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    On the O2(1Δ g )-mediated photooxidative behaviour of tripeptide glycyl-tyrosyl-alanine in alkaline medium A kinetic study (1993)
    Springer
    Amino acids 4 (1993), S. 101-110 
    Details
    ISSN: 1438-2199
    Keywords: Amino acids ; Singlet-oxygen ; Peptides ; Photooxidation ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The type II singlet molecular oxygen [O2(1Δ g )]-mediated photo-oxidation of the tripeptide gly-tyr-ala was studied. It has two non-oxidizable amino-acids (gly and ala) bonded to the oxidizable one, tyr. Overall (k t) and reactive (k r) rate constants for the interaction were determined by time-resolved methods (IR emission of O2(1Δ g )) and stationary photolysis, in water at pH 11.5 as well as in alkaline non-aqueous etOH-MeCN (80:20, v/v, 10 mM in KOH) solutions. An important solvent polarity effect onk t was detected; the rate constant increasing one order of magnitude in going from the organic mixture to water (k t H2O = 2 × 109 M−1 s−1). Nevertheless,k r does not parallel this trend; gly-tyr-ala being less photooxidizable in a more polar environment. The effective quantum yield (∅ r ) forTPE photooxidation is much higher in etOH-MeCN (∅ r = 0.056) than in water (∅ r = 0.023). Results are discussed on the basis of the formation of an exciplex with polar character between the TPE and O2(1Δ g ). Two remarkable points should be taken into account: a) the rate costants for the interaction of O2(1Δ g ) with gly-tyr-ala are practically the same as for free tyr. b) New -NH2 groups are generated upon sensitized irradiation. Both findings indicate that the peptide bonds in the TPE break as a result of the photooxidation. A thorough analysis with data for tyrosine and related dipeptides is undertaken.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00805805
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    Paper (German National Licenses)
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