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  • Industrial Chemistry  (9)
  • cerebral blood flow  (5)
  • 15A48  (3)
  • 90C20  (3)
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  • 1
    Digitale Medien
    Digitale Medien
    Convexity preserving interpolation with exponential splines (1986)
    Springer
    Computing 36 (1986), S. 335-342 
    Details
    ISSN: 1436-5057
    Schlagwort(e): 65D07 ; 41A15 ; 90C20 ; Convexity conditions ; weakly coupled system of inequalities ; numerical algorithms ; quadratic programming ; unconstrained dual program with tridiagonal Hessian
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Während die Aufgabe der konvexen Interpolation im Falle kubischer Splines im allgemeineen nicht lösbar ist, kann jetzt gezeigt werden, daß sie bei Verwendung von Exponentialsplines Lösungen besitzt sofern die vorkommenden Parameter hinreichend roß sind, und es werden konkrete hinreichende und notwendige Lösbarkeitsbedingungen hergeleitet. Da eindeutige Lösbarkeit in der Regel nicht vorliegt, wird eine Auswahlfunktion eingeführt und das entstehende quadratische Optimierungsproblem nach Dualisierung numerisch behandelt.
    Notizen: Abstract Sufficient and necessary conditions are derived under which interpolating splines are convex if the data set is in convex position. In order to select one of the interpolants, by means of a well-known objective function a quadratic optimization problem is stated which can be solved effectively by passing to a dual program.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02240208
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  • 2
    Digitale Medien
    Digitale Medien
    Convex spline interpolants with minimal curvature (1985)
    Springer
    Computing 35 (1985), S. 219-229 
    Details
    ISSN: 1436-5057
    Schlagwort(e): 65K05 ; 65D07 ; 90C20 ; 41A15 ; Existence conditions ; quadratic programming ; dual optimization problem ; tridiagonal Hessian ; Newton's method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Das Problem, konvexe Interpolationssplines mit minimaler mittlerer Krümmung zu ermitteln, führt auf eine speziell strukturierte quadratische Optimierungsaufgabe. In der vorliegenden Note wird eine zugehörige duale Aufgabe aufgestellt, die ohne Nebenbedingungen auskommt, deren Zielfunktion stückweise quadratisch ist und die daher eine effektive numerische Behandlung erlaubt.
    Notizen: Abstract The problem of finding convex spline interpolants with minimal mean curvature leads to a quadratic optimization problem of special structure. In the present note a corresponding dual problem without constraints is derived. Its objective function is piecewise quadratic and therefore admits an effective numerical treatment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02260507
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  • 3
    Digitale Medien
    Digitale Medien
    On theR-order of coupled sequences arising in single-step type methods (1988)
    Springer
    Numerische Mathematik 53 (1988), S. 653-661 
    Details
    ISSN: 0945-3245
    Schlagwort(e): AMS(MOS): 65H10 ; 15A48 ; CR: G1.5
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Summary As shown in preceding papers of the authors, the verification of anR-convergence order τ for sequences coupled by a system (1.1) of basic inequalities can be reduced to the positive solvability of system (3.3) of linear inequalities. Further, the bestR-order $$\bar \tau$$ implied by (1.1) is equal to the minimal spectral radius of certain matrices composed from the exponents occuring in (1.1). Now, these results are proven in a unified and essentially simpler way. Moreover, they are somewhat extended in order to facilitate applications to concrete methods.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01397134
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  • 4
    Digitale Medien
    Digitale Medien
    An unconstrained dual program for computing convexC 1-spline approximants (1987)
    Springer
    Computing 39 (1987), S. 133-140 
    Details
    ISSN: 1436-5057
    Schlagwort(e): 65D10 ; 41A15 ; 90C20 ; Specially structured optimization problem ; Fenchel dualization ; return-formula
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Es wird die Aufgabe betrachtet, eine vorgegebene Datenmenge durch konvexe kubischeC 1-Splines zu approximieren. Zu diesem Problem wird eine zugehörige duale Optimierungsaufgabe konstruiert, welche den Vorteil hat, daß keine Nebenbedingungen auftreten, und welche sich daher effektiver als das Ausgangsproblem numerisch behandeln läßt.
    Notizen: Abstract In the present paper the problem of approximating given data sets by convex cubicC 1-splines is considered. To this programming problem a dual program is constructed which is unconstrained. Therefore an efficient computational treatment is possible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02310102
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  • 5
    Digitale Medien
    Digitale Medien
    On the R-order of coupled sequences III (1983)
    Springer
    Computing 30 (1983), S. 157-169 
    Details
    ISSN: 1436-5057
    Schlagwort(e): 65H10 ; 15A48 ; Iterative parallel processes ; best individualR-orders ; ordered positive decomposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Für konvergente Folgen {x n,1 },...,{x n,s }, welche über ein System (2) von Ungleichungen miteinander verkoppelt sind, werden die besten individuellenR-Ordnungen τ1,...,τ s bestimmt. Dazu wird gezeigt, daß diese gleich den Spektralradien von bestimmten Matrizen sind, welche aus Exponenten in (2) gebildet werden.
    Notizen: Abstract For convergent sequences {x n,1 },...{x n,s } coupled by a system (2) of inequalities the optimal individualR-orders τ1,...,τ s are determined as the spectral radii of certain matrices composed of exponents appearing in (2).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02280786
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  • 6
    Digitale Medien
    Digitale Medien
    Determination of the cone radius for positive concave operators (1984)
    Springer
    Computing 33 (1984), S. 37-49 
    Details
    ISSN: 1436-5057
    Schlagwort(e): 65H10 ; 90C30 ; 15A48 ; Iterative processes ; bestR-orders ; cone radius of concave operators ; spectral radii ; partial ordering
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Berechnung der bestenR-Ordnung von Folgen aus iterativen Näherungsverfahren führt auf die Ermittlung des hier eingeführten Kegelradius bestimmter konkaver Operatoren. Das Hauptergebnis der Arbeit ist die Darstellung des Kegelradius als Infimum der Spektralradien aller den konkaven Operator majorisierenden linearen Operatoren. Diese Charakterisierung ist von numerischem Intersse.
    Notizen: Abstract The computation of bestR-orders of sequences produced by iterative methods leads to the determination of the cone radius of certain concave operators. The main result of the paper is the representation of the cone radius as the infimum of spectral radii of all linear operators majorizing the concave operator. This characterization is of numerical interest.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02243074
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  • 7
    Digitale Medien
    Digitale Medien
    The effect of ketanserin on cerebral blood flow and cerebrovascular CO2 reactivity in healthy volunteers (1992)
    Springer
    Acta neurochirurgica 119 (1992), S. 7-11 
    Details
    ISSN: 0942-0940
    Schlagwort(e): Carbon dioxide ; cerebral blood flow ; cerebral oxygen metabolism ; cerebral vascular reactivity ; ketanserin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The effect of the anti-hypertensive agent ketanserin on the cerebral blood flow (CBF) and the cerebrovascular CO2 reactivity was examined in 10 healthy volunteers. Ketanserin was administered as an intravenous bolus of 10 mg followed by an infusion of 6mg/h. Before administration CBF was measured by single photon emission computerized tomography (SPECT) of inhaled133 Xenon. Then arterial CO2 tension was subsequently decreased by voluntary hyperventilation and increased by breathing an air/CO2 mixture. The relative changes in CBF induced by the changes in arterial CO2 tension were estimated by the cerebral arterio-venous oxygen content difference method. One hour following the start of ketanserin infusion the SPECT measurement and CO2 manipulations were repeated. The CO2 reactivity (expressed as the slope of the regression line of the linear relation between CBF and PaCO2), was unchanged, i.e. 3.2%/0.1 kPa before ketanserin and 4. 1%/0.1 kPa during ketanserin, respectively. Using regression lines from a semi-logarithmic plot the CO2 reactivity was also unchanged 3.4%/0.1 kPa and 3.5%/0.1 kPa, respectively. Ketanserin did not change CBF. The cerebral oxygen metabolism (CMRO2) was decreased 19% one hour after the start of infusion of ketanserin. In conclusion administration of ketanserin in a clinically relevant dose to healthy volunteers does not change the regional CBF not the cerebrovascular CO2 reactivity, but a decrease in CMRO2 was observed. However further studies are needed to clarify whether ketanserin in fact has a depressing effect on CMRO2 or whether the different results are caused by methodological errors or stocastic variation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01541774
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  • 8
    Digitale Medien
    Digitale Medien
    Angiotensin converting enzyme inhibition, CBF autoregulation, and ICP in patients with normal-pressure hydrocephalus (1990)
    Springer
    Acta neurochirurgica 106 (1990), S. 9-12 
    Details
    ISSN: 0942-0940
    Schlagwort(e): Intracranial pressure ; cerebral blood flow ; autoregulation ; angiotensin converting enzyme inhibition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Fourteen patients with normal pressure hydrocephalus had the autoregulation of cerebral blood flow (CBF) and intracranial pressure (ICP) investigated. In 8 of the patients the effect of Captopril on ICP and CBF was also investigated. The mean arterial blood pressure (MABP) was 109 mmHg (intra-arterially), and ICP was 11 mmHg (intraventricularly). Changes in global CBF were estimated by the arterio-venous oxygen difference method. The autoregulation of CBF was present in 13 of the patients (p 〈 0.01). The lower limit of CBF autoregulation was 86% of the baseline perfusion pressure. One hour after 50 mg of captopril perorally, MABP was reduced 16 mmHg, and ICP and CBF were unchanged. The autoregulation was maintained and the lower limit was decreased 19 mmHg. Thus patients would be expected to benefit from captopril treatment in hypotensive anaesthesia.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01809326
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  • 9
    Digitale Medien
    Digitale Medien
    The acute effect of nimodipine on cerebral blood flow, its CO2 reactivity, and cerebral oxygen metabolism in human volunteers (1991)
    Springer
    Acta neurochirurgica 111 (1991), S. 49-53 
    Details
    ISSN: 0942-0940
    Schlagwort(e): Arterial blood pressure ; calcium antagonist ; cerebral blood flow ; cerebral metabolic rate of oxygen ; carbon dioxide reactivity ; nimodipine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The present study was undertaken in 8 healthy volunteers to examine the effect of a clinically relevant dose of nimodipine (NIM) (15 and 30 microgram/kg/h) on CBF, its CO2 reactivity, and CMRO2. Mean arterial blood pressure (MABP) was measured intra-arterially. Regional CBF was measured by SPECT of inhaled Xenon-133. During the CO2 reactivity tests changes in CBF were estimated by the arterio-venous-oxygen-difference method. Median CBF was 52 ml/ 100 g/min (48–53) with a normal regional distribution, and median baseline MABP was 96 mmHg (92–99). MABP was slightly reduced, by 8 mmHg (7–9), and 9 mmHg (4–11) after infusion of NIM for 2 and 4 hours, respectively. CBF, however, remained constant, although correction for changes in PaCO2, revealed a slight increase after 4 hours (p=0.08). CMRO2 was 3.5 ml/100 g/min (3.2–3.5) and was not changed by the infusion of NIM. At arterial CO2 tensions ranging from 4.0 to 6.5 Kpa the CO2 reactivity was 3.0% CBF/ 0.1 kPa (2.6–3.7) and decreased significantly to 2.6% CBF/0.1 kPa (1.8–3.2) after the infusion of NIM for 3 hours (p=0.02). The median slope of the LnCBFsat/PaCO2 relationship was 1.5 at baseline compared to 1.3 after NIM (p〈0.01). No side effects were observed. The present study shows a decreased CO2 of the cerebral vessels and a maintained coupling of CBF and CMRO2 during the infusion of nimodipine.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01402513
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  • 10
    Digitale Medien
    Digitale Medien
    The effect of nimodipine on ICP and CBF in patients with normal-pressure hydrocephalus (1990)
    Springer
    Acta neurochirurgica 102 (1990), S. 11-13 
    Details
    ISSN: 0942-0940
    Schlagwort(e): Intracranial pressure ; cerebral blood flow ; perfusion pressure ; nimodipine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Eight patients with normal-pressure hydrocephalus (NPH) were studied. The resting mean arterial blood pressure (MABP) was 100 (90–125)mmHg and the mean intracranial pressure (ICP) was 11 (5–17)mmHg. ICP and MABP were continuously measured intraventricularly and intra-arterially, respectively. Changes in global cerebral blood flow (CBF) were estimated by the arteriovenous oxygen difference method. Intravenous nimodipine (15 microgram/kg/hour) was given in the first 2 hours and 30 microgram/kg/hour in the next 2 hours. MABP was reduced 23 (4–47)mmHg (p〈0.05). ICP was increased 3 (0–10)mmHg (p 〈 0.05). CBF was unchanged in the group on the whole, but in 4 of patients a major drop in perfusion pressure was seen, and CBF decreased 6, 11, 23 and 34%, respectively. Thus these findings underline the importance of maintaining the perfusion pressure under treatment with nimodipine.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01402178
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