Impact of aortic repair based on flow field computer simulation within the thoracic aorta

Purpose of this computational study is to examine the hemodynamic parameters of velocity fields and shear stress in the thoracic aorta with and without aneurysm, based on an individual patient case and virtual surgical intervention. These two cases, case I (with aneurysm) and II (without aneurysm), are analyzed by computational fluid dynamics. The 3D Navier-Stokes equations and the continuity equation are solved with an unsteady stabilized finite element method. The vascular geometries are reconstructed based on computed tomography angiography images to generate a patient-specific 3D finite element mesh. The input data for the flow waveforms are derived from MR phase contrast flow measurements of a patient before surgical intervention.The computed results show velocity profiles skewed towards the inner aortic wall for both cases in the ascending aorta and in the aortic arch, while in the descending aorta these velocity profiles are skewed towards the outer aortic wall. Computed streamlines indicate that flow separation occurs at the proximal edge of the aneurysm, i.e. computed flow enters the aneurysm in the distal region, and that there is essentially a single, slowly rotating, vortex within the aneurysm during most of the systole.In summary, after virtual surgical intervention in case II higher shear stress distribution along the descending aorta could be found, which may produce more healthy reactions in the endothelium and benefit of vascular reconstruction of an aortic aneurysm at this particular location.     

Development of a model for part reorientation in vibratory bowl feeders with active air jet tooling

Vibratory bowl feeders (VBFs) are widely used in industry for feeding and reorienting small parts in high volume production. Standard VBF tooling consists of various mechanical barriers inserted in the bowl path which are prone to jamming and limit the feeder to only one type of part. Programmable feeders have been developed to improve the flexibility of these devices, however feed rates are often low. This research describes the development of a model of part behavior required for reorienting a part with an air-jet-based computer controlled orienting system. This system can be used to eliminate jamming and improve feed rates in VBFs. The control algorithm accepts the part's weight, geometry, and its orientation. Sensors then compare the present with the desired orientation and the algorithm determines the appropriate pulse of air to produce the desired orientation.     

Assessing Well Drilling Disturbance Effects on Offshore Foundation Piles in Clay

It is widely recognized that hydrocarbon well drilling from offshore platforms affects the surrounding ground. In clays, the level of disturbance can be severe when sections of open well collapse during drilling, impeding fluid return to the seabed (termed “packing-off”), and drilling fluid pressure is increased in order to obtain a breakthrough return path for the fluid. Significant swelling and hydraulic fracturing can take place in the surrounding soil mass. With time the excess pore pressures will dissipate and could cause increases in pore pressures far from the wells, potentially affecting areas occupied by the platform’s foundation piles. There is no established procedure to quantify the impact of such processes on foundation performance. This paper presents a numerical approach that involves a series of finite-element analyses in which drilling disturbance is treated as an idealized fluid injection process. The entry of pressurized drilling water into progressively enlarging fractured disturbed zones, and hence into the surrounding soil mass, is simulated with two- and three-dimensional nonlinear finite-element (FE) models, without modeling the actual hydraulic fracturing processes. The analyses make use of key observations made in the field at a piled offshore platform. The FE analyses predict marginal foundation capacity reductions, as well as significant global vertical and horizontal movements developing around the piles. It is demonstrated that the ground movement predictions are heavily influenced by the degree of geometric idealization.     

Numerical and experimental analysis of factors leading to suture dehiscence after Billroth II gastric resection

The main goal of this study was to numerically quantify risk of duodenal stump blowout after Billroth II (BII) gastric resection. Our hypothesis was that the geometry of the reconstructed tract after BII resection is one of the key factors that can lead to duodenal dehiscence. We used computational fluid dynamics (CFD) with finite element (FE) simulations of various models of BII reconstructed gastrointestinal (GI) tract, as well as non-perfused, ex vivo, porcine experimental models. As main geometrical parameters for FE postoperative models we have used duodenal stump length and inclination between gastric remnant and duodenal stump. Virtual gastric resection was performed on each of 3D FE models based on multislice Computer Tomography (CT) DICOM. According to our computer simulation the difference between maximal duodenal stump pressures for models with most and least preferable geometry of reconstructed GI tract is about 30%. We compared the resulting postoperative duodenal pressure from computer simulations with duodenal stump dehiscence pressure from the experiment. Pressure at duodenal stump after BII resection obtained by computer simulation is 4–5 times lower than the dehiscence pressure according to our experiment on isolated bowel segment. Our conclusion is that if the surgery is performed technically correct, geometry variations of the reconstructed GI tract by themselves are not sufficient to cause duodenal stump blowout. Pressure that develops in the duodenal stump after BII resection using omega loop, only in the conjunction with other risk factors can cause duodenal dehiscence. Increased duodenal pressure after BII resection is risk factor. Hence we recommend the routine use of Roux en Y anastomosis as a safer solution in terms of resulting intraluminal pressure. However, if the surgeon decides to perform BII reconstruction, results obtained with this methodology can be valuable.     

Characterising protein,salt and water interactions with combined vibrational spectroscopic techniques

In this paper a combination of NIR spectroscopy and FTIR and Raman microspectroscopy was used to elucidate the effects of different salts (NaCl, KCl and MgSO₄) on structural proteins and their hydration in muscle tissue. Multivariate multi-block technique Consensus Principal Component Analysis enabled integration of different vibrational spectroscopic techniques: macroscopic information obtained by NIR spectroscopy is directly related to microscopic information obtained by FTIR and Raman microspectroscopy. Changes in protein secondary structure observed at different concentrations of salts were linked to changes in protein hydration affinity. The evidence for this was given by connecting the underlying FTIR bands of the amide I region (1700–1600 cm⁻¹) and the water region (3500–3000 cm⁻¹) with water vibrations obtained by NIR spectroscopy. In addition, Raman microspectroscopy demonstrated that different cations affected structures of aromatic amino acid residues differently, which indicates that cation–π interactions play an important role in determination of the final structure of protein molecules.     

One method for electric field determination in the vicinity of infinitely thin electrode shells

One numerical method, the so-called equivalent electrodes method (EEM), has been applied to electric field calculation at planar and axially symmetric, extremely thin electrodes. The results obtained for characteristic impedance and effective relative dielectric constant of strip lines are presented, as well as electric field and potential distribution at geometrically modelled cable terminations. The accuracy of results of EEM depends on the number of used equivalent electrodes (EEs) and the error is inversely proportional to the selected number of EES. The method is very simple and exact and in limit process, with the number of the EES, gives exact results. However, in calculations certain problems may appear because of the increase EEs number, especially at very thin electrodes. The electric field being extremely high at the sharp electrode's ends, compared to other parts of the electrode, so it is possible to use smaller and denser EEs. The improvement proposed in this paper enables accurate calculation using a smaller number of EEs. Since the density of equivalent electrodes is higher, equivalent radii are smaller and EEs are not set at the same distances. The number of EEs in other regions is reduced. Some results obtained by the application of EEM have been compared with values obtained using the finite elements method (FEM) and very good matches have been identified.     

Optimizing bag-of-tasks scheduling on cloud data centers using hybrid swarm-intelligence meta-heuristic

The Journal of Supercomputing - Usually, a large number of concurrent bag-of-tasks (BoTs) application execution requests are submitted to cloud data centers (CDCs), which needs to be optimally...     

Influence of imperfect carrier recovery on satellite QPSK communication system performance

The purpose of this paper is to provide the theoretical approach for determining the bit error probability in detecting a coherent quaternary phase-shift-keyed signal transmitted over a soft-limited channel in the presence of the uplink and downlink noise, as well as the noisy carrier reference signal. The uplink noise is considered in the specific way through the envelope variations and the frequency offset of the signal remitted by the satellite station having influence on the variations of the phase-locked loop parameters in the receiving ground station, consequently on the probability density function of the phase error, i.e. the average bit error probability. The downlink noise is also taken into consideration. The determined results are based on the non-linear phase-locked loop model with primary emphasis on the degradations in the system performance produced by the imperfect carrier signal extraction. Copyright © 1999 John Wiley & Sons, Ltd.     

Fast Transformation-Invariant Component Analysis

Dimensionality reduction techniques such as principal component analysis and factor analysis are used to discover a linear mapping between high-dimensional data samples and points in a lower-dimensional subspace. Previously, Frey and Jojic introduced transformation-invariant component analysis (TCA) to learn a linear mapping, invariant to a set of known form of global transformations. However, parameter estimation in that model using the previously-proposed expectation maximization (EM) algorithm required scalar operations in the order of N ² where N is the dimensionality of each training example. This is prohibitive for many applications of interest such as modeling mid-to large-size images, where, for instance, N may be as high as 786432 (512×512 RGB image). In this paper, we present an efficient algorithm that reduces the computational requirements to order of Nlog N. With this speedup, we show the effectiveness of transformation-invariant component analysis in various applications including tracking, learning video textures, clustering, object recognition and object detection in images. Software for TCA can be downloaded from .     

Development and characterization of microfabricated disposable gold working electrodes for high-performance ion chromatography and integrated pulsed amperometric detection

We have developed a new type of microfabricated thin-film electrode on polymeric substrates. The microfabrication process allows for inexpensive and reproducible mass production of disposable working electrodes for high-performance ion chromatography and integrated pulsed amperometric detection (IPAD). These microfabricated electrodes are disposable and have been optimized for use in flow-through low-dead-volume electrochemical cells. The analytical performance of microfabricated gold electrodes was characterized with the help of the IPAD method for amino acid detection under alkaline conditions required for anion-exchange separations. When used with a new optimized six-potential IPAD waveform, the electrodes functioned properly for weeks. Compared to nondisposable working electrodes, the disposable working electrodes generated equal or better results in the limit of detection, linearity of calibration, and reproducibility. Disposable electrodes make it possible to avoid polishing and reconditioning, which are required with nondisposable electrodes.