Hans-Peter Helfrich - Academia.edu (original) (raw)
Papers by Hans-Peter Helfrich
Journal of Nutrition, 2012
L-Theanine, an amino acid in green tea, is suggested to improve cognition and mood. Therefore, L-... more L-Theanine, an amino acid in green tea, is suggested to improve cognition and mood. Therefore, L-theanine is available as a supplement and is now used as an ingredient in functional drinks. Because data on the metabolic fate of L-theanine from human studies are lacking, we investigated the kinetics of L-theanine uptake and its metabolites, ethylamine and glutamic acid, in healthy participants. Within a randomized crossover study, 12 participants ingested a bolus of 100 mg L-theanine via capsules or green tea. On further occasions, 3 participants received 50 and 200 mg L-theanine via capsules. Blood and urine were collected before and up to 24 h postconsumption to determine the concentrations of L-theanine, proteinogenic amino acids, and ethylamine in plasma, erythrocytes, and urine by HPLC. L-Theanine increased in plasma, erythrocytes, and urine with comparable results after both treatments. The maximum plasma concentration of L-theanine occurred 0.8 h after intake of 100 mg L-theanine via capsules (24.3 6 5.7 mmol/L) and tea (26.5 6 5.2 mmol/L), respectively. The AUC of L-theanine in plasma increased dose dependently after intake of 50, 100, and 200 mg L-theanine via capsules. Moreover, ethylamine and glutamic acid increased in plasma and were excreted by urine after intake of capsules and tea. In conclusion, L-theanine is rapidly absorbed and seems to be hydrolyzed to ethylamine and glutamic acid. A minor part of L-theanine is retained in erythrocytes. Kinetics and urinary excretion of L-theanine, ethylamine, and glutamic acid are comparable after both treatments. Thus, functional effects of L-theanine intake may result from L-theanine, ethylamine, or glutamic acid.
Zeitschrift f�r Lebensmittel-Untersuchung und -Forschung, 1991
Summary The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin ... more Summary The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout have been assessed by statistical analysis. Confidence intervals were computed using a normal distribution of residual data and an empirical distribution by the Bootstrap method. Both methods produced similar statistics for the two drugs. Simulation of the residue data according to the regression lines of
Nutrients
Flavan-3-ols are claimed to be responsible for the cardioprotective effects of cocoa. Alkalized c... more Flavan-3-ols are claimed to be responsible for the cardioprotective effects of cocoa. Alkalized cocoa powder (ALC), commonly used for many non-confectionary products, including beverages, provides less (+)-catechin, (−)-epicatechin, and procyanidins and more (−)-catechin than nonalkalized cocoa powder (NALC). This may affect the plasma appearance of monomeric flavan-3-ol stereoisomers after consumption of NALC vs. ALC. Within a randomized, crossover trial, 12 healthy nonsmokers ingested a milk-based cocoa beverage providing either NALC or ALC. Blood was collected before and within 6 h postconsumption. (+)-Catechin, (−)-catechin, and epicatechin were analyzed in plasma by HPLC as sum of free and glucuronidated metabolites. Pharmacokinetic parameters were obtained by a one-compartment model with nonlinear regression methods. For epicatechin in plasma, total area under the curve within 6 h postconsumption (AUC0–6h) and incremental AUC0–6h were additionally calculated by using the linea...
Nutrients
Randomized controlled trials indicate that flavanol-rich cocoa intake may improve postprandial gl... more Randomized controlled trials indicate that flavanol-rich cocoa intake may improve postprandial glucose and lipid metabolism in patients with type 2 diabetes (T2D), based on studies with meals that impose a strong metabolic load. Hence, the aim of the present study was to investigate whether flavanol-rich cocoa powder ingested as part of a diabetic-suitable meal may beneficially affect glucose, lipid metabolism, and blood pressure (BP) in patients with T2D. Twelve adults with T2D, overweight/obesity, and hypertension ingested capsules with 2.5 g of flavanol-rich cocoa or microcrystalline cellulose with a diabetic-suitable breakfast in a randomized, placebo-controlled, double-blind crossover study. BP was measured and blood samples were taken before, 2 and 4 h after breakfast and capsule intake. Cocoa treatment did not affect glucose, insulin, homeostasis model assessment for insulin resistance (HOMA-IR), triglycerides, total cholesterol, low density lipoprotein-cholesterol, high dens...
Nutrients
Regular cocoa consumption has been shown to improve blood pressure (BP), insulin sensitivity, and... more Regular cocoa consumption has been shown to improve blood pressure (BP), insulin sensitivity, and lipid levels in patients with type 2 diabetes (T2D), using up to 100 g of chocolate or 54 g of cocoa. These effects, attributed to cocoa flavanols, would be beneficial for patients with T2D if they could be achieved by a usual serving size of flavanol-rich cocoa. Forty-two hypertensive patients with T2D (stable pharmacological treatment, with good adjustment for glucose metabolism, lipids, and BP) ingested capsules with 2.5 g/day of a flavanol-rich cocoa or cocoa-free capsules for 12 weeks in a double-blinded, randomized, placebo-controlled study with parallel group design. Participants had to maintain diet, lifestyle, and medication. Before and after intervention, fasting blood samples were collected; BP and nutritional status were investigated. Cocoa treatment did not affect BP, nor glucose metabolism (glucose, HbA1c, insulin, HOMA-IR) and lipids (triglycerides, total cholesterol, low...
The American journal of clinical nutrition, 2018
Regular cocoa consumption has been shown to reduce blood pressure, improve lipid profiles, and in... more Regular cocoa consumption has been shown to reduce blood pressure, improve lipid profiles, and increase insulin sensitivity and flow-mediated dilatation in healthy adults. It is assumed that these effects can be attributed to polyphenolic cocoa ingredients such as flavanols, especially to (-)-epicatechin. Nutritive intervention studies to prove this hypothesis are scarce. We aimed to evaluate whether regular consumption of 25 mg of pure (-)-epicatechin can affect increased cardiometabolic risk factors [blood pressure, glucose and lipid metabolism, low-density lipoprotein (LDL) oxidation] in overweight-to-obese subjects. Forty-eight overweight or obese nonsmokers [body mass index (kg/m2) ≥25.0, ages 20-65 y] with clear signs of metabolic syndrome (blood pressure ≥130/85 mm Hg, glucose >5.55 mmol/L, or triglycerides >1.69 mmol/L or cholesterol >5.2 mmol/L in fasting blood) and without chronic diseases were included in a randomized, placebo-controlled, double-blind crossover s...
RAIRO. Analyse numérique
Simultaneous approximation in negative norms of arbitrary order RAIRO-Analyse numérique, tome 15,... more Simultaneous approximation in negative norms of arbitrary order RAIRO-Analyse numérique, tome 15, n o 3 (1981), p. 231-235. <http://www.numdam.org/item?id=M2AN_1981__15_3_231_0> © AFCET, 1981, tous droits réservés. L'accès aux archives de la revue « RAIRO-Analyse numérique » implique l'accord avec les conditions générales d'utilisation (http://www.numdam.org/ legal.php). Toute utilisation commerciale ou impression systématique est constitutive d'une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/
Lecture Notes in Earth Sciences, 2000
Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists thi... more Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliographie; detailed bibliographic data is available in the Internetat <http://dnb.ddb.de>.
Obesity surgery, Aug 24, 2015
Osteomalacia and cardiometabolic disorders are favored in morbidly obese patients due to an inade... more Osteomalacia and cardiometabolic disorders are favored in morbidly obese patients due to an inadequate vitamin D (VD) status. Former trials supplementing orally VD (20-50 μg/day) in crystalline form after sleeve gastrectomy (SG) could not stabilize serum 25-hydroxycholecalciferol levels at predefined concentrations (≥50 nmol/l). We hypothesized that VD in an oily suspension would increase its bioavailability resulting in normal serum VD levels minimizing markers of cardiometabolic risk. Morbidly obese patients (n = 94, BMI 51.8 ± 11.5 kg/m(2)) received orally 80 μg/day VD3 dissolved in oil or placebo (pure oil) in a randomized, double-blind, parallel-group study for 12 weeks after SG. 25-hydroxycholecalciferol, parathyroid hormone, albumin, alkaline phosphatase, phosphate, magnesium, calcium, creatinine, C-reactive protein, lipids, glucose, and glycated hemoglobin were determined in serum/plasma before surgery and after 4 and 12 weeks of supplementation. Intake of energy, fat, and V...
We consider the fitting of geometric elements, such as lines, planes, circles, cones, and cylinde... more We consider the fitting of geometric elements, such as lines, planes, circles, cones, and cylinders, in such a way that the sum of distances or the maximal distance from the element to the data points is minimized. We refer to this kind of distance based fitting as orthogonal distance regression or ODR. We present a separation of variables algorithm for l1 and l∞ ODR fitting of geometric elements. The algorithm is iterative and allows the element to be given in either implicit form f(x, β) = 0 or in parametric form x = g(t, β), where β is the vector of shape parameters, x is a 2- or 3-vector, and s is a vector of location parameters. The algorithm may even be applied in cases, such as with ellipses, in which a closed form expression for the distance is either not available or is difficult to compute. For l1 and l∞ fitting, the norm of the gradient is not available as a stopping criterion, as it is not continuous. We present a stopping criterion that handles both the l1 and the l∞ ca...
Wavelets have shown to be an indispensable tool for a scale{ sensitive representation and analysi... more Wavelets have shown to be an indispensable tool for a scale{ sensitive representation and analysis of spatial or temporal data. In this chapter we illustrate the basic mathematical background for wavelets as well as fast algorithms for concrete multivariate wavelet constructions on bounded domains. Finally, we will show an application of wavelets to analysis and compression of precipitation data.
Lecture Notes in Earth Sciences, 2003
Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists thi... more Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliographie; detailed bibliographic data is available in the Internetat <http://dnb.ddb.de>.
Zeitschrift für Lebensmittel-Untersuchung und -Forschung, 1991
The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout... more The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout have been assessed by statistical analysis. Confidence intervals were computed using a normal distribution of residual data and an empirical distribution by the Bootstrap method. Both methods produced similar statistics for the two drugs. Simulation of the residue data according to the regression lines of the decay curves has shown that the Bootstrap method is better for use when the residue patterns are not distributed normally. Using confidence intervals, a statistical mean of withdrawal times can be assessed. Taking into account the decays of the individual antibiotics in all treated trout, tolerance intervals for the regression lines are obtained: the calculated 10-20% longer withdrawal time includes values for which the antibiotic concentration in 95% of the treated trout is decreased below the tolerance level of Toltrazuril or Enrofloxacin.
Funktionalanalytische Methoden der numerischen Mathematik, 1969
Phytopathology, 2009
Plant diseases are dynamic systems that progress or regress in spatial and temporal dimensions. S... more Plant diseases are dynamic systems that progress or regress in spatial and temporal dimensions. Site-specific or temporally optimized disease control requires profound knowledge about the development of each stressor. The spatiotemporal dynamics of leaf rust (Puccinia recondite f. sp. tritici) and powdery mildew (Blumeria graminis f. sp. tritici) in wheat was analyzed in order to evaluate typical species-dependent characteristics of disease spread. During two growing seasons, severity data and other relevant plant growth parameters were collected in wheat fields. Spatial characteristics of both diseases were assessed by cluster analyses using spatial analysis by distance indices, whereas the temporal epidemic trends were assessed using statistical parameters. Multivariate statistics were used to identify parameters suitable for characterizing disease trends into four classes of temporal dynamics. The results of the spatial analysis showed that both diseases generally occurred in pat...
Numerische Mathematik, 1987
semilinear evolution equations with non-smooth initial data are given. In concrete cases almost o... more semilinear evolution equations with non-smooth initial data are given. In concrete cases almost optimal order of convergence for linear finite elements results.
Numerical Algorithms, 1995
The nonlinear least distance problem is a special case of equality constrained optimization. Let ... more The nonlinear least distance problem is a special case of equality constrained optimization. Let a curve or surface be given in implicit form via the equation f(x) = 0, x E R d, and let z E ~d be a fixed data point. We discuss two algorithms for solving the following problem: Find a point x* such that f(x*) = 0 and IIz-x*ll 2 is minimal among all such x. The algorithms presented use the trust region approach in which, at each iteration, an approximation to the objective function or merit function is minimized in a given neighborhood (the trust region) of the current iterate. Among other things, this allows one to prove global convergence of the algorithm.
Numerical Algorithms, 1993
Let a family of curves or surfaces be given in implicit form via the model equation f(x,/3) = 0, ... more Let a family of curves or surfaces be given in implicit form via the model equation f(x,/3) = 0, where x e R d and/3 e IR m is a parameter vector. We present a trust region algorithm for solving the problem: find a parameter vector/3* such that the contour f(x, ~*) = 0 is a best fit to given data {zi}i~l c IR d in a least squares sense. Specifically, we seek/3* and {x~}7= 1 such that f(x*,/3*) = O, i = 1,... ,n, and ~-:~i~l Llzi-x711~ is minimal. The term orthogonal distance regression is used to describe such constrained nonlinear least squares problems.
Journal of Nutrition, 2012
L-Theanine, an amino acid in green tea, is suggested to improve cognition and mood. Therefore, L-... more L-Theanine, an amino acid in green tea, is suggested to improve cognition and mood. Therefore, L-theanine is available as a supplement and is now used as an ingredient in functional drinks. Because data on the metabolic fate of L-theanine from human studies are lacking, we investigated the kinetics of L-theanine uptake and its metabolites, ethylamine and glutamic acid, in healthy participants. Within a randomized crossover study, 12 participants ingested a bolus of 100 mg L-theanine via capsules or green tea. On further occasions, 3 participants received 50 and 200 mg L-theanine via capsules. Blood and urine were collected before and up to 24 h postconsumption to determine the concentrations of L-theanine, proteinogenic amino acids, and ethylamine in plasma, erythrocytes, and urine by HPLC. L-Theanine increased in plasma, erythrocytes, and urine with comparable results after both treatments. The maximum plasma concentration of L-theanine occurred 0.8 h after intake of 100 mg L-theanine via capsules (24.3 6 5.7 mmol/L) and tea (26.5 6 5.2 mmol/L), respectively. The AUC of L-theanine in plasma increased dose dependently after intake of 50, 100, and 200 mg L-theanine via capsules. Moreover, ethylamine and glutamic acid increased in plasma and were excreted by urine after intake of capsules and tea. In conclusion, L-theanine is rapidly absorbed and seems to be hydrolyzed to ethylamine and glutamic acid. A minor part of L-theanine is retained in erythrocytes. Kinetics and urinary excretion of L-theanine, ethylamine, and glutamic acid are comparable after both treatments. Thus, functional effects of L-theanine intake may result from L-theanine, ethylamine, or glutamic acid.
Zeitschrift f�r Lebensmittel-Untersuchung und -Forschung, 1991
Summary The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin ... more Summary The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout have been assessed by statistical analysis. Confidence intervals were computed using a normal distribution of residual data and an empirical distribution by the Bootstrap method. Both methods produced similar statistics for the two drugs. Simulation of the residue data according to the regression lines of
Nutrients
Flavan-3-ols are claimed to be responsible for the cardioprotective effects of cocoa. Alkalized c... more Flavan-3-ols are claimed to be responsible for the cardioprotective effects of cocoa. Alkalized cocoa powder (ALC), commonly used for many non-confectionary products, including beverages, provides less (+)-catechin, (−)-epicatechin, and procyanidins and more (−)-catechin than nonalkalized cocoa powder (NALC). This may affect the plasma appearance of monomeric flavan-3-ol stereoisomers after consumption of NALC vs. ALC. Within a randomized, crossover trial, 12 healthy nonsmokers ingested a milk-based cocoa beverage providing either NALC or ALC. Blood was collected before and within 6 h postconsumption. (+)-Catechin, (−)-catechin, and epicatechin were analyzed in plasma by HPLC as sum of free and glucuronidated metabolites. Pharmacokinetic parameters were obtained by a one-compartment model with nonlinear regression methods. For epicatechin in plasma, total area under the curve within 6 h postconsumption (AUC0–6h) and incremental AUC0–6h were additionally calculated by using the linea...
Nutrients
Randomized controlled trials indicate that flavanol-rich cocoa intake may improve postprandial gl... more Randomized controlled trials indicate that flavanol-rich cocoa intake may improve postprandial glucose and lipid metabolism in patients with type 2 diabetes (T2D), based on studies with meals that impose a strong metabolic load. Hence, the aim of the present study was to investigate whether flavanol-rich cocoa powder ingested as part of a diabetic-suitable meal may beneficially affect glucose, lipid metabolism, and blood pressure (BP) in patients with T2D. Twelve adults with T2D, overweight/obesity, and hypertension ingested capsules with 2.5 g of flavanol-rich cocoa or microcrystalline cellulose with a diabetic-suitable breakfast in a randomized, placebo-controlled, double-blind crossover study. BP was measured and blood samples were taken before, 2 and 4 h after breakfast and capsule intake. Cocoa treatment did not affect glucose, insulin, homeostasis model assessment for insulin resistance (HOMA-IR), triglycerides, total cholesterol, low density lipoprotein-cholesterol, high dens...
Nutrients
Regular cocoa consumption has been shown to improve blood pressure (BP), insulin sensitivity, and... more Regular cocoa consumption has been shown to improve blood pressure (BP), insulin sensitivity, and lipid levels in patients with type 2 diabetes (T2D), using up to 100 g of chocolate or 54 g of cocoa. These effects, attributed to cocoa flavanols, would be beneficial for patients with T2D if they could be achieved by a usual serving size of flavanol-rich cocoa. Forty-two hypertensive patients with T2D (stable pharmacological treatment, with good adjustment for glucose metabolism, lipids, and BP) ingested capsules with 2.5 g/day of a flavanol-rich cocoa or cocoa-free capsules for 12 weeks in a double-blinded, randomized, placebo-controlled study with parallel group design. Participants had to maintain diet, lifestyle, and medication. Before and after intervention, fasting blood samples were collected; BP and nutritional status were investigated. Cocoa treatment did not affect BP, nor glucose metabolism (glucose, HbA1c, insulin, HOMA-IR) and lipids (triglycerides, total cholesterol, low...
The American journal of clinical nutrition, 2018
Regular cocoa consumption has been shown to reduce blood pressure, improve lipid profiles, and in... more Regular cocoa consumption has been shown to reduce blood pressure, improve lipid profiles, and increase insulin sensitivity and flow-mediated dilatation in healthy adults. It is assumed that these effects can be attributed to polyphenolic cocoa ingredients such as flavanols, especially to (-)-epicatechin. Nutritive intervention studies to prove this hypothesis are scarce. We aimed to evaluate whether regular consumption of 25 mg of pure (-)-epicatechin can affect increased cardiometabolic risk factors [blood pressure, glucose and lipid metabolism, low-density lipoprotein (LDL) oxidation] in overweight-to-obese subjects. Forty-eight overweight or obese nonsmokers [body mass index (kg/m2) ≥25.0, ages 20-65 y] with clear signs of metabolic syndrome (blood pressure ≥130/85 mm Hg, glucose >5.55 mmol/L, or triglycerides >1.69 mmol/L or cholesterol >5.2 mmol/L in fasting blood) and without chronic diseases were included in a randomized, placebo-controlled, double-blind crossover s...
RAIRO. Analyse numérique
Simultaneous approximation in negative norms of arbitrary order RAIRO-Analyse numérique, tome 15,... more Simultaneous approximation in negative norms of arbitrary order RAIRO-Analyse numérique, tome 15, n o 3 (1981), p. 231-235. <http://www.numdam.org/item?id=M2AN_1981__15_3_231_0> © AFCET, 1981, tous droits réservés. L'accès aux archives de la revue « RAIRO-Analyse numérique » implique l'accord avec les conditions générales d'utilisation (http://www.numdam.org/ legal.php). Toute utilisation commerciale ou impression systématique est constitutive d'une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/
Lecture Notes in Earth Sciences, 2000
Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists thi... more Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliographie; detailed bibliographic data is available in the Internetat <http://dnb.ddb.de>.
Obesity surgery, Aug 24, 2015
Osteomalacia and cardiometabolic disorders are favored in morbidly obese patients due to an inade... more Osteomalacia and cardiometabolic disorders are favored in morbidly obese patients due to an inadequate vitamin D (VD) status. Former trials supplementing orally VD (20-50 μg/day) in crystalline form after sleeve gastrectomy (SG) could not stabilize serum 25-hydroxycholecalciferol levels at predefined concentrations (≥50 nmol/l). We hypothesized that VD in an oily suspension would increase its bioavailability resulting in normal serum VD levels minimizing markers of cardiometabolic risk. Morbidly obese patients (n = 94, BMI 51.8 ± 11.5 kg/m(2)) received orally 80 μg/day VD3 dissolved in oil or placebo (pure oil) in a randomized, double-blind, parallel-group study for 12 weeks after SG. 25-hydroxycholecalciferol, parathyroid hormone, albumin, alkaline phosphatase, phosphate, magnesium, calcium, creatinine, C-reactive protein, lipids, glucose, and glycated hemoglobin were determined in serum/plasma before surgery and after 4 and 12 weeks of supplementation. Intake of energy, fat, and V...
We consider the fitting of geometric elements, such as lines, planes, circles, cones, and cylinde... more We consider the fitting of geometric elements, such as lines, planes, circles, cones, and cylinders, in such a way that the sum of distances or the maximal distance from the element to the data points is minimized. We refer to this kind of distance based fitting as orthogonal distance regression or ODR. We present a separation of variables algorithm for l1 and l∞ ODR fitting of geometric elements. The algorithm is iterative and allows the element to be given in either implicit form f(x, β) = 0 or in parametric form x = g(t, β), where β is the vector of shape parameters, x is a 2- or 3-vector, and s is a vector of location parameters. The algorithm may even be applied in cases, such as with ellipses, in which a closed form expression for the distance is either not available or is difficult to compute. For l1 and l∞ fitting, the norm of the gradient is not available as a stopping criterion, as it is not continuous. We present a stopping criterion that handles both the l1 and the l∞ ca...
Wavelets have shown to be an indispensable tool for a scale{ sensitive representation and analysi... more Wavelets have shown to be an indispensable tool for a scale{ sensitive representation and analysis of spatial or temporal data. In this chapter we illustrate the basic mathematical background for wavelets as well as fast algorithms for concrete multivariate wavelet constructions on bounded domains. Finally, we will show an application of wavelets to analysis and compression of precipitation data.
Lecture Notes in Earth Sciences, 2003
Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists thi... more Bibliographic information published by Die Deutsche Bibliothek. Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliographie; detailed bibliographic data is available in the Internetat <http://dnb.ddb.de>.
Zeitschrift für Lebensmittel-Untersuchung und -Forschung, 1991
The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout... more The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout have been assessed by statistical analysis. Confidence intervals were computed using a normal distribution of residual data and an empirical distribution by the Bootstrap method. Both methods produced similar statistics for the two drugs. Simulation of the residue data according to the regression lines of the decay curves has shown that the Bootstrap method is better for use when the residue patterns are not distributed normally. Using confidence intervals, a statistical mean of withdrawal times can be assessed. Taking into account the decays of the individual antibiotics in all treated trout, tolerance intervals for the regression lines are obtained: the calculated 10-20% longer withdrawal time includes values for which the antibiotic concentration in 95% of the treated trout is decreased below the tolerance level of Toltrazuril or Enrofloxacin.
Funktionalanalytische Methoden der numerischen Mathematik, 1969
Phytopathology, 2009
Plant diseases are dynamic systems that progress or regress in spatial and temporal dimensions. S... more Plant diseases are dynamic systems that progress or regress in spatial and temporal dimensions. Site-specific or temporally optimized disease control requires profound knowledge about the development of each stressor. The spatiotemporal dynamics of leaf rust (Puccinia recondite f. sp. tritici) and powdery mildew (Blumeria graminis f. sp. tritici) in wheat was analyzed in order to evaluate typical species-dependent characteristics of disease spread. During two growing seasons, severity data and other relevant plant growth parameters were collected in wheat fields. Spatial characteristics of both diseases were assessed by cluster analyses using spatial analysis by distance indices, whereas the temporal epidemic trends were assessed using statistical parameters. Multivariate statistics were used to identify parameters suitable for characterizing disease trends into four classes of temporal dynamics. The results of the spatial analysis showed that both diseases generally occurred in pat...
Numerische Mathematik, 1987
semilinear evolution equations with non-smooth initial data are given. In concrete cases almost o... more semilinear evolution equations with non-smooth initial data are given. In concrete cases almost optimal order of convergence for linear finite elements results.
Numerical Algorithms, 1995
The nonlinear least distance problem is a special case of equality constrained optimization. Let ... more The nonlinear least distance problem is a special case of equality constrained optimization. Let a curve or surface be given in implicit form via the equation f(x) = 0, x E R d, and let z E ~d be a fixed data point. We discuss two algorithms for solving the following problem: Find a point x* such that f(x*) = 0 and IIz-x*ll 2 is minimal among all such x. The algorithms presented use the trust region approach in which, at each iteration, an approximation to the objective function or merit function is minimized in a given neighborhood (the trust region) of the current iterate. Among other things, this allows one to prove global convergence of the algorithm.
Numerical Algorithms, 1993
Let a family of curves or surfaces be given in implicit form via the model equation f(x,/3) = 0, ... more Let a family of curves or surfaces be given in implicit form via the model equation f(x,/3) = 0, where x e R d and/3 e IR m is a parameter vector. We present a trust region algorithm for solving the problem: find a parameter vector/3* such that the contour f(x, ~*) = 0 is a best fit to given data {zi}i~l c IR d in a least squares sense. Specifically, we seek/3* and {x~}7= 1 such that f(x*,/3*) = O, i = 1,... ,n, and ~-:~i~l Llzi-x711~ is minimal. The term orthogonal distance regression is used to describe such constrained nonlinear least squares problems.