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Now showing items 1 - 16 of 75

  • Prof. Dr. Michel Perrut (March 29, 1947 July 7, 2018) In memoriam

    Badens, Elisabeth   Sarrade, Stephane   Fages, Jacques   Brunner, Gerd   Kiran, Erdogan  

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  • In memoriam Prof. Dr. Michel Perrut (March 29, 1947–July 7, 2018)

    Badens, Elisabeth   Sarrade, Stéphane   Fages, Jacques   Brunner, Gerd   Kiran, Erdogan  

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  • Postprandial effects on arterial stiffness parameters in healthy young adults.

    Murray, Tyler   Yang, Eric Y   Brunner, Gerd   Kumar, Anirudh   Lakkis, Nasser   Misra, Arunima   Virani, Salim S   Hartley, Craig J   Morrisett, Joel D   Ballantyne, Christie M   Nambi, Vijay  

    Postprandial lipemia has been associated with acute endothelial dysfunction. Endothelial dysfunction, in turn, is associated with increased arterial stiffness. However, the relationship between postprandial lipemia and acute changes in arterial stiffness has not been extensively investigated. Therefore, we conducted a pilot study on the effects of postprandial lipemia on arterial stiffness in 19 healthy young adults before and after consumption of a high-fat mixed meal. Arterial stiffness was assessed locally with echo-tracking carotid arterial strain (CAS) and globally with carotid-femoral pulse wave velocity (PWV). As assessed by these two benchmark parameters, arterial stiffness did not differ significantly postprandially. However, the arterial distension period (ADP) was significantly lower 2 hours after mixed meal ingestion. In addition, slopes of carotid artery area (CAA) curves were significantly steeper postprandially. Therefore, we concluded that ADP may be a more sensitive marker of arterial stiffness in healthy young adults when compared to PWV and CAS. =C2=A9 The Author(s) 2015.
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  • Ultrasound in Cardiovascular Risk Prediction: Don't Forget the Plaque!

    Nambi, Vijay   Brunner, Gerd   Ballantyne, Christie M.  

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  • Separation of CO2/N2 by Means of a Carbon Membrane

    Wall, Yuliya   Braun, Gerd   Kaltenborn, Nadine   Voigt, Ingolf   Brunner, Gerd  

    The permeation and separation performance of an ultramicroporous carbon membrane for separation of CO2/N2 mixtures were investigated. The experiments were conducted using the steady-state measurement method with pure gases (dead-end mode) and a CO2/N2 gas mixture (20/80?mol.-%) (cross-flow mode) in the temperature range from 293?K to 363?K and at feed pressures of up to 1.4?MPa and atmospheric pressure on the permeate side. The membrane exhibited a selectivity of about 25 and permeability of about 500?Barrer for CO2 in the mixture with N2. The single-gas measurements do not reflect the membrane performance correctly. An adsorption-selective effect is assumed to be the main separation mechanism. Moreover, membrane-aging effects causing blocking due to pore constrictions through adsorption were observed. These pore constrictions lower the permeability, but they raise the selectivity. Operation at high temperatures leads to a reduction of aging effects.
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  • Segmental Analysis of Carotid Arterial Strain Using Speckle-Tracking

    Yang, Eric Y.   Dokainish, Hisham   Virani, Salim S.   Misra, Arunima   Pritchett, Allison M.   Lakkis, Nasser   Brunner, Gerd   Bobek, Jaromir   McCulloch, Marti L.   Hartley, Craig J.   Ballantyne, Christie M.   Nagueh, Sherif F.   Nambi, Vijay  

    Background: Increased arterial stiffness has been shown to be associated with aging and cardiovascular risk factors. Speckle-tracking algorithms are being used to measure myocardial strain. The aims of this study were to evaluate whether speckle-tracking could be used to measure carotid arterial strain (CAS) reproducibly in healthy volunteers and to determine if CAS was lesser in individuals with diabetes. Methods: Bilateral electrocardiographically gated ultrasound scans of the distal common carotid arteries (three cardiac cycles; 14-MHz linear probe; mean frame rate, 78.7 +/- 8.9 frames/sec) were performed twice (2-4 days apart) on 10 healthy volunteers to test repeatability. Differences in CAS between healthy subjects (n = 20) and patients with diabetes (n = 21) were examined. Peak CAS was measured in each of six equal segments, and averages of all segments (i.e., the global average), of the three segments nearest the probe, and of the three segments farthest from the probe (i.e., the far wall average) were obtained. Results: Global CAS (intraclass correlation coefficient = 0.40) and far wall average (intraclass correlation coefficient = 0.63) had the greatest test-retest reliability. Global and far wall averaged CAS values were lower in patients with diabetes (4.29% [SE, 0.27%] and 4.30% [SE, 0.44%], respectively) than in controls (5.48% [SE, 0.29%], P=.001, and 5.58% [SE, 0.44%], P=.003, respectively). This difference persisted after adjustment for age, gender, race, and hemodynamic parameters. Conclusions: Speckle-tracking to measure CAS is feasible and modestly reliable. Patients with diabetes had lower CAS obtained with speckle-tracking compared with healthy controls. (J AmSoc Echocardiogr 2011; 24: 1276-84.)
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  • Supercritical fluid chromatographic separation on preparative scale and in continuous mode

    Johannsen, Monika   Brunner, Gerd  

    Chromatography with supercritical fluids (SFC) is a powerful tool for carrying out separations of substances with very similar structure and volatility, such as isomers of various kinds. In this contribution, we discuss the separation process aiming at the recovery of products on a much larger scale than analytical. Nevertheless, for developing such a process, the separation is carried out first on analytical scale to determine optimum operating conditions and select stationary phase, mobile phase, and co-solvent (modifier), if necessary. Determination of isotherms is helpful for simulating the separation process. Verification of the separation process includes the recycling of the mobile phase. The chromatographic process can be a batch process in the elution mode, or a continuous process, approximated as simulated moving bed (SMB). The batch SFC process, although using a higher quantity of mobile phase is less cost intensive than the SFC-SMB process.
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  • Applications of Supercritical Fluids

    Brunner, Gerd  

    This review discusses supercritical fluids in industrial and near-to-industry applications. Supercritical fluids are flexible tools for processing materials. Supercritical fluids have been applied to mass-transfer processes, phase-transition processes, reactive systems, materials-related processes, and nanostructured materials. Some applications are already at industrial capacity, whereas others remain under development. In addition to extraction, application areas include impregnation and cleaning, multistage countercurrent separation, particle formation, coating, and reactive systems such as hydrogenation, biomass gasification, and supercritical water oxidation. Polymers are modified with supercritical fluids, and colloids and emulsions as well as nanostructured materials exhibit interesting phenomena when in contact with supercritical fluids that can be industrially exploited. For these applications to succeed, the properties of supercritical fluids in combination with the materials processed must be clearly determined and fundamental knowledge of the complex behavior must be made readily available.
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  • Gas transport through ceramic membranes under super-critical conditions

    Wall, Yuliya   Ompe-Aime-Mudimu   Braun, Gerd   Brunner, Gerd  

    In order to select and to apply a porous membrane under supercritical conditions, it is necessary to understand the transport mechanism affecting the permeation behaviour. This paper describes the investigation of gas transport through micro porous ceramic membranes consisting of several layers. The separation layer is made from TiO(2) with a nominal pore size diameter of 0.9 nm Single. gas permeation of helium, nitrogen, argon, methane, and carbon dioxide was measured in the temperature range of 293-443 K and in the pressure range of 1-10 MPa. Observation of the permeability of these membranes revealed that the transport of non adsorbing gases under these conditions is governed by Knudsen diffusion and viscous flow. (C) 2009 Elsevier B.V. All rights reserved.
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  • Semi-continuous liquid hot water pretreatment of rye straw

    Ingram, Thomas   Rogalinski, Tim   Bockemuehl, Vera   Antranikian, Garabed   Brunner, Gerd  

    This article is based upon the findings of our recent publication dealing with the liquid hot water (LHW) hydrolysis of lignocellulosic materials (LCM) in different reactor types [T. Rogalinski, T. Ingram, G. Brunner, Hydrolysis of Iignocellulosic biomass in water under elevated temperatures and pressures, J. Supercrit. Fluids (2008), doi:10.1016/j.supflu.2008.05.003.]. As an advancement of these results, semi-continuous fixed-bed reactors were constructed aiming at the efficient hydrolysis of rye straw at elevated temperatures as a pretreatment process for bioethanol production. The temperature range between 170 degrees C and 230,C was found to be most suitable for the thermal pretreatment of rye straw. The resulting liquid hydrolyzates as well as the solid residues were enzymatically converted to monomeric sugars (xylose/glucose) using cellulases and xylanases from Penicillium janthinellum. Ninety-five percentage of the initial xylan and 92% of the glucan was converted using a pretreatment temperature of 200-215 degrees C. The solubilization of the biomass in the fixed-bed reactor could be described by a reaction model following first-order kinetics. For that reason, the lambda(max)-factor was introduced, which describes the maximum ratio of biomass that can be hydrolyzed at a certain temperature, related to the initial mass. The usage of a fixed-bed reactor combines several advantages compared to other reactor types, namely high solid-to-water-ratios, the prevention of degradation product formation, and considerable energy savings since no biomass comminution is necessary. (C) 2008 Elsevier B.V. All rights reserved.
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  • Hydrolysis kinetics of biopolymers in subcritical water

    Rogalinski, Tim   Liu, Kaiyue   Albrecht, Tobias   Brunner, Gerd  

    The unique properties of water at elevated temperatures and pressures, namely the alterability of ionic product, dielectric constant, and density, make it an interesting and promising reaction medium. Several investigations have been made in order to obtain valuable products from biopolymers or, more general, biomass. Biopolymers can react with high-temperature water in very short residence times and with high rates of conversion. The achievable products are manifold and can be varied to a large extent by changing the operating conditions. The possibilities of sub- and supercritical water can even be significantly expanded by adding carbon dioxide since it reacts to carbonic acid, which serves as a catalyst. This work deals with the hydrolysis kinetics of different kinds of biopolymers, namely starch, cellulose (polysaccharides), and proteins (polypeptides). Kinetics was conducted over a broad range of experimental conditions using a continuous-flow reactor. In all three cases, the obtained experimental results could be described by a reaction model according to the approach of a single consecutive reaction following first order kinetics. The rate constants of the hydrolytic conversion were determined for the resulting monomers (glucose and amino acids), and the values were found to strongly depend on the type of bond. The peptide bonds in proteins exhibited a much higher stability compared to the beta-1,4- and beta-1,6-glycosidic linkages in cellulose and starch, respectively. The stability of the resulting monomers and their conversion to further degradation products were determined. The addition of carbon dioxide to water under hydrothermal conditions resulted in a significant increase in acid catalyzed reaction rates, which could be confirmed by the obtained rate constants. (C) 2007 Elsevier B.V. All rights reserved.
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  • From plant materials to ethanol by means of supercritical fluid technology

    Schacht, Christian   Zetzl, Carsten   Brunner, Gerd  

    Plant and waste material from agriculture or food industry represents on of the the worlds largest resources of ligno-cellulose and therefore fermentable sugars. Conversion of these sugars to ethanol is one way to take optimized profit of the solar energy incorporated in the plant growth. For the target product of ethanol of > 99.8 wt.%, there are several plant material sources available. The carbohydrate compounds of these materials can be pretreated and partly hydrolyzed by nearcritical water. CO2 dissolved in water may be used as catalyst. Hydrolysis is favorably accomplished by enzymatic catalysis. The product streams from the hydrolytic treatment are fermented. The resulting diluted ethanol solution is processed by multistage counter-current supercritical carbon dioxide extraction to ethanol of 99.8 wt.% concentration. Non-fermentable residues may be subjected to a second hydrolysis or transferred to a biogas production. Solid residues of the biogas reactor, in particular lignin containing fractions, can be oxidized with near and supercritical water to mainly gas and a smaller fraction of mainly short chain fatty acids, which can be reintroduced to the biogas reactor. (C) 2008 Elsevier B.V. All rights reserved.
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  • Extraction of Oil and Minor Compounds from Oil Palm Fruit with Supercritical Carbon Dioxide

    Huan Phan Tai   Brunner, Gerd  

    A significant quantity of tocochromanols and carotenoids remains in the residual from palm oil production by traditional screw pressing. Supercritical carbon dioxide extraction was used as alternative method with the purpose to recover better these valuable minor compounds. Total oil yield and co-extracted water were investigated in the course of extraction. Tocochromanols and carotenoids were evaluated, not only in the extraction oil, but also in the oil of residual fibre. Modelling of extraction process was also performed for a further up-scaling. The results showed that oil yield up to 90% could be observed within 120 min. Supercritical carbon dioxide (SCCO2) could extract tocochromanols and carotenoids with concentration in the same range of normal commercial processing palm oil, while co-extracted water remained rather low at a level of 2-4%. Moreover, recovery efficiencies of these minor compounds were much higher in case of extraction processed with supercritical carbon dioxide than those with screw pressing method.
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  • Extraction of Oil and Minor Compounds from Oil Palm Fruit with Supercritical Carbon Dioxide

    Phan Tai, Huan   Brunner, Gerd  

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  • A supervised classification-based method for coronary calcium detection in non-contrast CT

    Kurkure, Uday   Chittajallu, Deepak R.   Brunner, Gerd   Le, Yen H.   Kakadiaris, Ioannis A.  

    Accurate quantification of coronary artery calcium provides an opportunity to assess the extent of atherosclerosis disease. Coronary calcification burden has been reported to be associated with cardiovascular risk. Currently, an observer has to identify the coronary calcifications among a set of candidate regions, obtained by thresholding and connected component labeling, by clicking on them. To relieve the observer of such a labor-intensive task, an automated tool is needed that can detect and quantify the coronary calcifications. However, the diverse and heterogeneous nature of the candidate regions poses a significant challenge. In this paper, we investigate a supervised classification-based approach to distinguish the coronary calcifications from all the candidate regions and propose a two-stage, hierarchical classifier for automated coronary calcium detection. At each stage, we learn an ensemble of classifiers where each classifier is a cost-sensitive learner trained on a distinct asymmetrically sampled data subset. We compute the relative location of the calcifications with respect to a heart-centered coordinate system, and also use the neighboring regions of the calcifications to better characterize their properties for discrimination. Our method detected coronary calcifications with an accuracy, sensitivity and specificity of 98.27, 92.07 and 98.62%, respectively, for a testing dataset of non-contrast computed tomography scans from 105 subjects.
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  • Hydrolysis of lignocellulosic biomass in water under elevated temperatures and pressures

    Rogalinski, Tim   Ingram, Thomas   Brunner, Gerd  

    The hydrolysis of rye straw and rye silage in liquid hot water (LHW) as a pretreatment process for the utilization of lignocellulosic material (LCM) was investigated. Two different types of reactors, a batch autoclave (BA) and a continuous-flow (CF) apparatus, were used in this work. For both setups a certain time was needed to heat the reactor up to the desired temperature. The temperature profiles for both reactors were calculated and accurately predicted in order to assure comparable and defined operating conditions. For this purpose, a modified severity factor was used that accounted for the different temperatures during the heat-up phase in the reactors. The experimental results show that high degrees of biomass solubilization are possible using LHW, however, the yield of undesired degradation products increases with treatment severity as well. The particle size of the biomass and the substrate concentration seem to have no influence on the solubilization. The solubilization of rye silage seems to be easier compared to rye straw as parts of the protecting hemicellulose-lignin matrix have already been degraded by lactobacilli. The glucose formation and decomposition from rye straw were investigated using a simplified model according to the pattern of a single consecutive reaction following first-order kinetics and the results were compared to literature data dealing with the LHW treatment of starch as well as pure cellulose. Taking into consideration the advantages and disadvantages of the reactor types used, an optimal reactor concept is proposed for future investigations. (c) 2008 Elsevier B.V. All rights reserved.
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