Dynamics and non-equilibrium structure of colloidal dumbbell-shaped particles in dense suspensions

Neben ihrer Bedeutung in industriellen Anwendungen dienen Kolloide als Modellsysteme in Experimenten und in der Theorie, um die Struktur und Dynamik von kondensierter Materie zu untersuchen. Kürzlich wurde experimentell gezeigt, dass eine kleine Anisotropie ausreicht, um die viskoelastische Antwort im Vergleich zu harten Kugeln drastisch zu ändern. Die mikroskopischen Ursachen hierfür sind bisher nicht verstanden. In dieser Arbeit werden daher Nichtgleichgewichts-Brownsche-Dynamik-Simulationen (NEBD) von harten kolloidalen Dumbbells in oszillatorischen Scherfeldern entwickelt und eingesetzt, um diese Resultate mit Verbindung zu Rheologie- und Neutronenstreuexperimenten zu erklären. Weiterhin wird die Bedeutung der Anisotropie für Struktur und Dynamik von solchen Suspensionen im Gleichgewicht mit Hilfe von "Linear-Response"-Theorie und Brownsche-Dynamik-Simulationen analysiert. Im linearen Limit zeigt die Scherviskosität bei hohen Packungsdichten einen dramatischen Anstieg jenseits eines kritischen Anisotropieparameters. Dies weist darauf hin, dass schon bei den kleinen Anisotropien kollektive Rotations-Translations-Kopplungen für langsame Zeitskalen verantwortlich sind. Weiterhin wird ein Nichtgleichgewichtsübergang mittels NEBD-Simulationen von Suspensionen harter Dumbbells im PC unter oszillatorischer Scherung ersichtlich. Es wird gezeigt, dass der kontinuierliche Übergang nur für sehr kleine Aspektverhältnisse erhalten bleibt. Oberhalb eines bestimmten Aspektverhältnisses wird der Übergang durch einen ungeordneten Zustand vermittelt. Außerdem wird ein Sliding-Layer Zustand mit kollektiver Ordnung der Teilchenausrichtung bei hohen Scheramplituden beobachtet. Somit zeigt diese Arbeit, dass die NEBD-Simulationen Phänomene in Rheologie- und Streuexperimenten erklären. Angesichts dieser Experimente wird gezeigt, dass der Orientierungsfreiheitsgrad einen starken Einfluss auf den strukturellen Übergang bei steigenden Amplituden hat.Besides being important for industrial applications, colloidal suspensions have long served as model systems for investigating the structure and dynamics of condensed matter. Recently, it has been demonstrated experimentally that apparently a small particle anisotropy is sufficient to dramatically change the viscoelastic response under external shearing fields, of which the microscopic mechanisms are not yet sufficiently understood. In the present work, NEBD simulations of colloidal hard dumbbells in oscillatory shear fields are developed and employed to elucidate the novel findings in close connection with comprehensive rheology and SANS experiments. Furthermore, by utilising BD simulations and linear response theory, the impact of anisotropy on structure and dynamics of such suspensions in equilibrium is analysed. In the linear response limit, the shear viscosity exhibits a dramatic increase at high packing fractions beyond a critical anisotropy of the particles. This indicates that newly occurring, collective rotational-translational couplings must be made responsible for slow time scales appearing in the PC. Moreover, a non-equilibrium transition emerging at moderate aspect ratios is revealed by NEBD of plastic crystalline suspensions under oscillatory shear. This transition behaviour is systematically studied. It is demonstrated that the continuous nature of the transition is retained for very low aspect ratios only. Above a certain aspect ratio, the transition is mediated by an intermediate disordered state. Furthermore, a partially oriented sliding layer state featuring a finite collective order in the particles'' orientations is observed at high strains. Hence, this thesis demonstrates that the NEBD simulations explain novel phenomena in rheology and scattering experiments. In the light of these experiments, it is shown that the orientational degree of freedom has a vigorous impact on the structural transition under increasing oscillatory shear

Nonequilibrium Structure of Colloidal Dumbbells under Oscillatory Shear

We investigate the nonequilibrium behavior of dense, plastic-crystalline suspensions of mildly anisotropic colloidal hard dumbbells under the action of an oscillatory shear field by employing Brownian dynamics computer simulations. In particular, we extend previous investigations, where we uncovered novel nonequilibrium phase transitions, to other aspect ratios and to a larger nonequilibrium parameter space, that is, a wider range of strains and shear frequencies. We compare and discuss selected results in the context of novel scattering and rheological experiments. Both simulations and experiments demonstrate that the previously found transitions from the plastic crystal phase with increasing shear strain also occur at other aspect ratios. We explore the transition behavior in the strain-frequency phase and summarize it in a nonequilibrium phase diagram. Additionally, the experimental rheology results hint at a slowing down of the colloidal dynamics with higher aspect ratio

Investigation of ion-ion-recombination at atmospheric pressure with a pulsed electron gun

For future development of simple miniaturized sensors based on pulsed atmospheric pressure ionization as known from ion mobility spectrometry, we investigated the reaction kinetics of ion-ion-recombination to establish selective ion suppression as an easy to apply separation technique for otherwise non-selective ion detectors. Therefore, the recombination rates of different positive ion species, such as protonated water clusters H +(H 2O) n (positive reactant ions), acetone, ammonia and dimethyl-methylphosphonate ions, all recombining with negative oxygen clusters O 2 -(H 2O) n (negative reactant ions) in a field-free reaction region, are measured and compared. For all experiments, we use a drift tube ion mobility spectrometer equipped with a non-radioactive electron gun for pulsed atmospheric pressure ionization of the analytes. Both, ionization and recombination times are controlled by the duty cycle and repetition rate of the electron emission from the electron gun. Thus, it is possible to investigate the ion loss caused by ion-ion-recombination depending on the recombination time defined as the time delay between the end of the electron emission and the ion injection into the drift tube. Furthermore, the effect of the initial total ion density in the reaction region on the ion-ion-recombination rate is investigated by varying the density of the emitted electrons. © 2012 The Royal Society of Chemistry

Temporary Fecal Diversion in the Management of Colorectal and Perianal Crohn’s Disease

Aim. To evaluate the results of temporary fecal diversion in colorectal and perianal Crohn’s disease. Method. We retrospectively identified 29 consecutive patients (14 females, 15 males; median age: 30.0 years, range: 18–76) undergoing temporary fecal diversion for colorectal (n=14), ileal (n=4), and/or perianal Crohn’s disease (n=22). Follow-up was in median 33.0 (3–103) months. Response to fecal diversion, rate of stoma reversal, and relapse rate after stoma reversal were recorded. Results. The response to temporary fecal diversion was complete remission in 4/29 (13.8%), partial remission in 12/29 (41.4%), no change in 7/29 (24.1%), and progress in 6/29 (20.7%). Stoma reversal was performed in 19 out of 25 patients (76%) available for follow-up. Of these, the majority (15/19, 78.9%) needed further surgical therapies for a relapse of the same pathology previously leading to temporary fecal diversion, including colorectal resections (10/19, 52.6%) and creation of a definitive stoma (7/19, 36.8%). At the end of follow-up, only 4/25 patients (16%) had a stable course without the need for further definitive surgery. Conclusion. Temporary fecal diversion can induce remission in otherwise refractory colorectal or perianal Crohn’s disease, but the chance of enduring remission after stoma reversal is low

Reducing the Mast Vibration of Single-Mast Stacker Cranes by Gain-Scheduled Control

In the frame structure of stacker cranes harmful mast vibrations may appear due to the inertial forces of acceleration or the braking movement phase. This effect may reduce the stability and positioning accuracy of these machines. Unfortunately, their dynamic properties also vary with the lifted load magnitude and position. The purpose of the paper is to present a controller design method which can handle the effect of a varying lifted load magnitude and position in a dynamic model and at the same time reveals good reference signal tracking and mast vibration reducing properties. A controller design case study is presented step by step from dynamic modeling through to the validation of the resulting controller. In the paper the dynamic modeling possibilities of single-mast stacker cranes are summarized. The handling of varying dynamical behavior is realized via the polytopic LPV modeling approach. Based on this modeling technique, a gain-scheduled controller design method is proposed, which is suitable for achieving the goals set. Finally, controller validation is presented by means of time domain simulations

Design, Control and in Situ Visualization of Gas Nitriding Processes

The article presents a complex system of design, in situ visualization and control of the commonly used surface treatment process: the gas nitriding process. In the computer design conception, analytical mathematical models and artificial intelligence methods were used. As a result, possibilities were obtained of the poly-optimization and poly-parametric simulations of the course of the process combined with a visualization of the value changes of the process parameters in the function of time, as well as possibilities to predict the properties of nitrided layers. For in situ visualization of the growth of the nitrided layer, computer procedures were developed which make use of the results of the correlations of direct and differential voltage and time runs of the process result sensor (magnetic sensor), with the proper layer growth stage. Computer procedures make it possible to combine, in the duration of the process, the registered voltage and time runs with the models of the process

Cytokeratin 18 in plasma of patients with gastrointestinal adenocarcinoma as a biomarker of tumour response

BACKGROUND: Plasma biomarkers may be particularly useful as a predictor or early marker of clinical response to treatment in addition to radiological imaging. Cytokeratin 18 (CK18) is an epithelial-specific cytokeratin that undergoes cleavage by caspases during apoptosis. Measurement of caspase-cleaved (CK18-Asp396) or total cytokeratin 18 (CK18) from epithelial-derived tumours could be a simple, non-invasive way to monitor or predict responses to treatment. METHODS: Soluble plasma CK18-Asp396 and CK18 were measured by ELISA from 73 patients with advanced gastrointestinal adenocarcinomas before treatment and during chemotherapy, as well as 100 healthy volunteers. RESULTS: Both CK18-Asp396 and total CK18 plasma levels were significantly higher in patients compared with the healthy volunteers (P = 0.015, P < 0.001). The total CK18 baseline plasma levels before treatment were significantly higher (P = 0.009) in patients who develop progressive disease than those who achieve partial response or stable disease and this correlation was confirmed in an independent validation set. The peak plasma levels of CK18 occurring in any cycle following treatment were also found to be associated with tumour response, but peak levels of CK18-Asp396 did not reach significance (P = 0.01, and P = 0.07, respectively). CONCLUSION: Plasma levels CK18 are a potential marker of tumour response in patients with advanced gastrointestinal malignancy

The anatomy, physiology, functional significance and evolution of specialized hearing organs of gerbilline rodents

Middle and inner ear anatomy correlates with neurophysiological responses to a wide range of sound frequencies for species of the Gerbillinae representing generalized, intermediate, and specialized anatomical conditions. Neurophysiological data were recorded from 81 specimens of 13 species representing six genera. Anatomical parameters involved in the process of hearing were correlated with the neurophysiological data to assess the effects of different degrees of anatomical specialization on hearing. The 13 species tested in this manner have graphic curves of auditory sensitivity of remarkably similar disposition over the frequencies tested and to those published for Kangaroo Rats. Ears with anatomical specializations show greater auditory sensitivity. The natural history of the Gerbillinae, particularly the kinds of predators, degree of predation, and habitat is reviewed and utilized to interpret the significance of the degree of auditory specialization in the forms studied and to evaluate the prevailing hypothesis that these specializations enhance the ability of these rodents to survive in open desert situations by detecting and evading predators. The middle ear anatomy of five additional genera and species was also studied. Thus, data on the entire spectrum of gerbilline middle ear morphology provide an evolutionary sequence. Certain anatomical parameters of the organ of Corti show a degree of specialization parallel to that of features of the middle ear. The morphological changes and possible functional roles of these features are considered. A very high correlation exists for degree of specialization and aridity of habitat, thus specialization increases with increasing aridity. This increased specialization may result from more effective predation in open xeric environments. Auditory acuity for a wide range of low frequency sounds augmented by auditory specialization is hence more advantageous here. There does not appear to be selection for hearing at particular frequencies in this range. The peaks of greatest auditory sensitivity appear to correspond to the resonant frequencies of the different components of the middle ear transformer and cavity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50256/1/1051380103_ftp.pd