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296 results on '"Gutmann, H"'

2. Bang-Bang refocusing of a qubit exposed to telegraph noise

Author

Gutmann, H., Wilhelm, F. K., Kaminsky, W. M., and Lloyd, S.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity
Abstract

We investigate the decoherence effect of telegraph noise on a single qubit, usually provoked by bistable fluctuators. To diminish the dephasing and relaxation impact an effective refocusing scheme (so-called Bang-Bang pulses) is proposed. Detailed numerical as well as analytical random walk analysis allows in particular to evaluate the applicability of non-perfect Bang-Bang pulses.

Published
2004

3. Compensation of decoherence from telegraph noise by means of bang-bang control

Author

Gutmann, H., Wilhelm, F. K., Kaminsky, W. M., and Lloyd, S.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity, Quantum Physics
Abstract

With the growing efforts in isolating solid-state qubits from external decoherence sources, the origins of noise inherent to the material start to play a relevant role. One representative example are charged impurities in the device material or substrate, which typically produce telegraph noise and can hence be modelled as bistable fluctuators. In order to demonstrate the possibility of the active suppression of the disturbance from a {\em single} fluctuator, we theoretically implement an elementary bang-bang control protocol. We numerically simulate the random walk of the qubit state on the Bloch sphere with and without bang-bang compensation by means of the stochastic Schr\"odinger equation and compare it with an analytical saddle point solution of the corresponding Langevin equation in the long-time limit. We find that the deviation with respect to the noiseless case is significantly reduced when bang-bang pulses are applied, being scaled down approximately by the ratio of the bang-bang period and the typical flipping time of the bistable fluctuation. Our analysis gives not only the effect of bang-bang control on the variance of these deviations, but also their entire distribution. As a result, we expect that bang-bang control works as a high-pass filter on the spectrum of noise sources. This indicates how the influence of $1/f$-noise ubiquitous to the solid state world can be reduced., Comment: 4 pages, 3 figures; update of references, slight changes of figure layout

Published
2003

4. Radial basis function methods for global optimization

Author

Gutmann, H.-M.

Subjects
530.1
Abstract

In many real world optimization problems it is essential or desirable to determine the global minimum of the objective function. The subject of this dissertation is a new class of methods that tackle such problems. In particular, we have in mind problems where function evaluations are expensive and no additional information is available. The methods employ radial basis functions that have been proved to be useful for interpolation problems. Examples include thin plate splines and multiquadrics. Specifically, in each iteration, radial basis function interpolation is used to define a utility function. A maximizer of this function is chosen to be the next point where the objective function is evaluated. Relations to similar optimization methods are established, and a general framework is presented that combines these methods and our methods. A large part of the dissertation is devoted to the convergence theory. We show that convergence can be achieved for most types of basis functions without further assumptions on the objective function. For other types, however, a similar results could not be obtained. This is due to the properties of the so-called native space that is associated with a basis function. In particular, it is of interest whether this space contains sufficiently smooth functions with compact support. In order to address this question, we present two approaches. First, we establish a characterization of the native space in terms of generalized Fourier transforms. For many types, for example thin plate splines, this helps to derive conditions on the smoothness of a function that guarantee that it is in the native space. For other types, for example multiquadrics, however, we show that the native space does not contain a nonzero function with compact support. The second approach we present gives slightly weaker results, but it employs some new theory using interpolation on an infinite regular grid.

Published
2002

7. Adaptive regulation of the ileal apical sodium dependent bile acid transporter (ASBT) in patients with obstructive cholestasis

Author

Hruz, P., Zimmermann, C., Gutmann, H., Degen, L., Beuers, U., Terracciano, L., Drewe, J., and Beglinger, C.

Subjects
Bile acids -- Research, Carrier proteins -- Research, Messenger RNA -- Research, Cholestasis -- Development and progression, Cholestasis -- Genetic aspects, Jaundice, Obstructive -- Development and progression, Jaundice, Obstructive -- Genetic aspects, Gene expression, Health
Published
2006

13. Changes in mRNA expression levels of solute carrier transporters in inflammatory bowel disease patients

Author

Wojtal, K A, Eloranta, J J, Hruz, P, Gutmann, H, Drewe, J, Beglinger, C, Fried, M, Kullak-Ublick, G A, Vavricka, S R, and University of Zurich

Subjects
10219 Clinic for Gastroenterology and Hepatology, 3004 Pharmacology, 10199 Clinic for Clinical Pharmacology and Toxicology, 10076 Center for Integrative Human Physiology, 3003 Pharmaceutical Science, 570 Life sciences, biology, 610 Medicine & health
Published
2009
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15. Effects of budesonide on P-glycoprotein expression in intestinal cell lines

Author

Maier, A, Zimmermann, C, Beglinger, C, Drewe, J, and Gutmann, H

Subjects
Receptors, Steroid, Pregnane X Receptor, Down-Regulation, Gene Expression, Research Papers, Cell Line, Receptors, Glucocorticoid, Cytochrome P-450 Enzyme System, Cytochrome P-450 CYP3A, Humans, ATP Binding Cassette Transporter, Subfamily B, Member 1, Caco-2 Cells, Budesonide, Glucocorticoids
Abstract

P-glycoprotein (P-gp) is an important efflux transporter that supports the barrier function of the gut against invading antigens and against administered drugs. Since glucocorticoids, such as budesonide, are frequently used during inflammatory bowel disease we investigated how budesonide influences P-gp expression in different intestinal cell lines.LS180 and Caco-2 cells were incubated with budesonide and changes in P-gp expression were determined on mRNA, protein and functional level. The mRNA expression levels of glucocorticoid receptor (GR) and pregnane X receptor (PXR) were determined in these cell lines. PXR receptor was transiently transfected into Caco-2 cells.Budesonide showed an induction of P-gp in LS180 cells and a down-regulation in Caco-2 cells. Expression levels of nuclear receptors revealed high expression of PXR only in LS180 cells and exclusive expression of GR in Caco-2 cells. Mifepristone, an anti-glucocorticoid, could not reverse the down-regulation of P-gp by budesonide in Caco-2 cells. In PXR-transfected Caco-2 cells the budesonide-mediated down-regulation of P-gp was abolished. Furthermore the expression of cytochrome P450 3A4 (CYP3A4), another PXR target gene, was induced in PXR-transfected Caco-2 cells after budesonide treatment.Budesonide has the potential to influence MDR1 expression in vitro. In LS180 cells, the induction of MDR1 by budesonide probably is mediated via PXR. The mechanism of the down-regulation in Caco-2 cells still remains unclear, but GR does not seem to be involved. Further studies are required to evaluate how budesonide alters P-gp expression in vivo.

Published
2006

16. Determination of the Single Nucleotide Polymorphisms C3435 and G2677T in MDR1 and C421A in BCRP in blood samples of patients with inflammatory bowel disease and healthy controls in the swiss population

Author

Hammann, F, Hruz, P, Kullak-Ublick, G A, Vavricka, S R, Beglinger, C, Drewe, J, Gutmann, H, Hammann, F, Hruz, P, Kullak-Ublick, G A, Vavricka, S R, Beglinger, C, Drewe, J, and Gutmann, H

Abstract

Aims: P-glycoprotein (P-gp, ABCB1, MDR1) and breast cancer resistance protein (BCRP, ABCG2) protect the luminal cells of the gastro-intestinal tract from potentially toxic substances. Genetic polymorphisms have previously been associated with disease susceptibility, severity, and treatment prognosis of inflammatory bowel disease. We investigated the prevalence of frequent single nucleotide polymorphisms of P-gp and BCRP in the Swiss population in healthy volunteers (n = 17) and patients newly diagnosed with Crohn’s Disease (CD, n = 34) or Ulcerative Colitis (UC, n = 38). Methods: DNA from peripheral blood cells was used to assess genotype and allele frequencies of MDR1 C3435T, MDR1 G2677T, and BCRP C421A. Results: Weak associations for BCRP C421A (p < 0.18) and MDR1 G2677T (p < 0.27) were seen in UC and a trend towards the wild type allele for MDR1 C3435T (p < 0.46). MDR1 3435CC / BCRP 421CC (Χ2: 1.0142, p < 0.30) in UC and MDR1 2677G / BCRP 421A (Χ2: 1.5615, p < 0.22) also weakly correlated with UC. Results for BCRP C421A in particular justify further study. Conclusions: Trends towards certain alleles and haplotypes were seen. These merit further studies in larger subgroups (e.g. by disease stage, therapy refractory patients, etc.).

Published
2012

17. Improvement of toughness and electrical properties of epoxy composites with carbon nanotubes prepared by industrially relevant processes

Author

Hollertz, Rebecca, Chatterjee, S, Gutmann, H, Geiger, T, Nüesch, F A, Chu, B T T, Hollertz, Rebecca, Chatterjee, S, Gutmann, H, Geiger, T, Nüesch, F A, and Chu, B T T

Abstract

The addition of carbon nanotubes (CNTs) to polymeric matrices or master batches has the potential to provide composites with novel properties. However, composites with a uniform dispersion of CNTs have proved to be difficult to manufacture, especially at an industrial scale. This paper reports on processing methods that overcome problems related to the control and reproducibility of dispersions. By using a high pressure homogenizer and a three-roll calendaring mill in combination, CNT reinforced epoxies were fabricated by mould casting with a well dispersed nanofiller content from 0.1 to 2 wt%. The influence of the nano-carbon reinforcements on toughness and electrical properties of the CNT/epoxies was studied. A substantial increase of all mechanical properties already appeared at the lowest CNT content of 0.1 wt%, but further raising the nanofiller concentration only led to moderate further changes. The most significant enhancement was obtained for fracture toughness, reaching up to 82%. The low percolation thresholds were confirmed by electrical conductivity measurements on the same composites yielding a threshold value of only about 0.01 wt%. As corroborated by a thorough microscopic analysis of the composites, mechanical and electrical enhancement points to the formation of an interconnected network of agglomerated CNTs., QC 20150415

Published
2011
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18. Modulation of multidrug resistance protein expression in porcine brain capillary endothelial cells in vitro

Author

Gutmann H, Török M, Fricker G, Huwyler J, Beglinger C, and Jürgen Drewe

Subjects
Brain Chemistry, Lung Neoplasms, Swine, Blotting, Western, In Vitro Techniques, Immunohistochemistry, Bronchodilator Agents, Capillaries, Up-Regulation, Quinolines, Tumor Cells, Cultured, Animals, Humans, ATP-Binding Cassette Transporters, Endothelium, Vascular, Carcinoma, Small Cell, Multidrug Resistance-Associated Proteins, Propionates, Subcellular Fractions
Abstract

Multidrug resistance-associated protein (MRP) is a transport system that is involved in the elimination of xenobiotics and biologically active endogenous substrates. Recently, the presence of MRP has been demonstrated in cultured brain capillary endothelial cells (BCECs). The time-dependent, functional expression of MRP in porcine BCECs was investigated to assess the value of this cell culture model for drug transport at the blood-brain barrier. Western blot analysis was used to investigate MRP expression in freshly isolated porcine BCECs and compared to MRP expression at days 8 and 10 in culture. Subcellular localization of MRP was investigated by immunocytochemistry with an MRP-specific monoclonal antibody, MRPr1. Functional activity of MRP was assessed by efflux studies with the fluorescent MRP substrate glutathione-methylfluorescein (GS-MF). No significant MRP expression was detected in freshly isolated endothelial cells. However, MRP expression is up-regulated in cell culture in a time-dependent manner. Immunostaining revealed predominantly perinuclear and, to a lesser degree, plasma membrane localization of MRP. At 10 degrees C GS-MF efflux was significantly decreased, indicating the involvement of an energy-dependent transport system. Efflux of GS-MF was apparently inhibited by MK571, a specific inhibitor for MRP. Porcine BCECs demonstrate up-regulation of functional MRP expression during culture, as observed in human tissue, and therefore might serve as a useful in vitro system for studying MRP-mediated blood-brain barrier transport.

Published
1999

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