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.     

Vectorially Imprinted Hybrid Nanofilm for Acetylcholinesterase Recognition

Effective recognition of enzymatically active tetrameric acetylcholinesterase (AChE) is accomplished by a hybrid nanofilm composed of a propidium‐terminated self‐assembled monolayer (Prop‐SAM) which binds AChE via its peripheral anionic site (PAS) and an ultrathin electrosynthesized molecularly imprinted polymer (MIP) cover layer of a novel carboxylate‐modified derivative of 3,4‐propylenedioxythiophene. The rebinding of the AChE to the MIP/Prop‐SAM nanofilm covered electrode is detected by measuring in situ the enzymatic activity. The oxidative current of the released thiocholine is dependent on the AChE concentration from ≈0.04 × 10^?6 to 0.4 × 10^?6m . An imprinting factor of 9.9 is obtained for the hybrid MIP, which is among the best values reported for protein imprinting. The dissociation constant characterizing the strength of the MIP‐AChE binding is 4.2 × 10^?7m indicating the dominant role of the PAS‐Prop‐SAM interaction, while the benefit of the MIP nanofilm covering the Prop‐SAM layer is the effective suppression of the cross‐reactivity toward competing proteins as compared with the Prop‐SAM. The threefold selectivity gain provided by i) the “shape‐specific” MIP filter, ii) the propidium‐SAM, iii) signal generation only by the AChE bound to the nanofilm shows promise for assessing AChE activity levels in cerebrospinal fluid.     

Thermometric sensing of nitrofurantoin by noncovalently imprinted polymers containing two complementary functional monomers

Molecularly imprinted polymers (MIPs) for nitrofurantoin (NFT) recognition addressing in parallel of two complementary functional groups were created using a noncovalent imprinting approach. Specific tailor-made functional monomers were synthesized: a diaminopyridine derivative as the receptor for the imide residue and three (thio)urea derivatives for the interaction with the nitro group of NFT. A significantly improved binding of NFT to the new MIPs was revealed from the imprinting factor, efficiency of binding, affinity constants and maximum binding number as compared to previously reported MIPs, which addressed either the imide or the nitro residue. Substances possessing only one functionality (either the imide group or nitro group) showed significantly weaker binding to the new imprinted polymers than NFT. However, the compounds lacking both functionalities binds extremely weak to all imprinted polymers. The new imprinted polymers were applied in a flow-through thermistor in organic solvent for the first time. The MIP-thermistor allows the detection of NFT down to a concentration of 5 μM in acetonitrile + 0.2% dimethyl sulfoxide (DMSO). The imprinting factor of 3.91 at 0.1 mM of NFT as obtained by thermistor measurements is well comparable to the value obtained by batch binding experiments.     

CTOD-R curve construction from surface displacement measurements

The construction of a fracture resistance δ–R (or J–R) curve requires the appropriate measurement of crack-tip opening displacement (CTOD) as a function of crack extension. This can be made by different procedures following ASTM E1820, BS7448 or other standards and procedures (e.g., GTP-02, ESIS-P2, etc.) for the measurement of fracture toughness. However, all of these procedures require standard specimens, displacement gauges, and calibration curves to get intrinsic material properties. This paper deals with some analysis and aspects related to the measurement of fracture toughness by observing the surface of the specimen. Tests were performed using three-dimensional surface displacement measurements to determine the fracture parameters and the crack extension values. These tests can be conducted without using a crack mouth opening displacement-CMOD or load-line displacement gauge, because CMOD can be calculated by using the displacement of the surface points. The presented method offers a significant advantage for fracture toughness testing in cases where a clip gauge is not easy to use, for example, on structural components. Simple analysis of stereo-metrical surface displacements gives a load vs. crack opening displacement curve. Results show that the initiation of stable crack propagation can be easy estimated as the point of the curve’s deviation. It is possible to determine the deviation point if the crack opening displacement measurements are close to crack tip in the plastic zone area. The resistance curve, CTOD-R, is developed by the local measurement of crack opening displacement (COD) in rigid body area of specimen. COD values are used for the recalculation with the CMOD parameter as a remote crack opening displacement, according to the ASTM standard.     

Effect of test variables on apparent activation energy for hot working and critical recrystallization temperatures of V-microalloyed steel

The effect of test variables on the apparent activation energy for hot working of a medium carbon V-microalloyed steel, Q_HW, and the critical recrystallization temperature, T_nr, have been studied by means of isothermal continuous and anisothermal multipass torsion test. The Q_HW is found to be temperature dependent. Above the T_nr, the Q_HW^U is close to that of austenite self diffusion, Q_SD, irrespective of the type of test or test variables. Below the T_nr, the Q_HW^L is not only considerably higher, but that based on multipass flow curve exibits a strong interpass time dependence. With increasing interpass time from 1.8 to 10 s the Q_HW^L and the T_nr increase and decrease respectively. The former is assumed to be controlled by solute drag, while the latter both by solute drag and precipitation pinning. Beyond 10 s, the two parameters exhibit the same trend, and the precipitation pinning is assumed to be the only recrystallization inhibiting mechanism.     

The structures of the network definition language NEDLAN. Its use in defining networks in CAD using interactive computer graphics

NEDLAN is a problem oriented language used to define structure (syntax) of classes of networks, properties of parts of networks and relationships between these parts within the networks. The obtained definitions are used by a CAD software system in exploration (analysis and design) of networks, belonging to the defined classes, in an interactive graphics environment.This paper presents the structures of the language and illustrates its use in defining classes of networks.     

Probabilistic Approach to the Solution of Inverse Problems in Civil Engineering

A wide range of important problems in civil engineering can be classified as inverse problems. In such problems, the observational data regarding the performance of a system is known, and the characteristics of the system and/or the input are sought. There are two general approaches to the solution of inverse problems: deterministic and probabilistic. Traditionally, inverse problems in civil engineering have been solved using a deterministic approach. In this approach, the objective is to find a specific model of a system that its theoretical response best fits the observed data. Obtaining the best fit solution, however, does not provide any information regarding the effect of data and/or theoretical uncertainties on the obtained solution. In this paper, a general probabilistic approach to the solution of the inverse problems is introduced, which provides uncertainty measures for the obtained solution. Techniques for direct analytical evaluation and numerical approximation of the probabilistic solution using Monte Carlo Markov Chains, with and without neighborhood algorithm approximation, are introduced and explained. The presented concepts and techniques and their application are then illustrated in practical terms using a simple example of a modulus determination experiment.     

Correlation Between the Microstructure and the Electrical Properties of ZrTiO4 Ceramics

A series of ZrTiO₄ (ZT) ceramics were prepared by sintering ball-milled precursor powders. Ceramics with homogenously dispersed micropores containing both low-temperature (ordered) and high-temperature (disordered) ZrTiO₄ phases were achieved by sintering at 1400°C. The porosity and the morphology were modified by changing the sintering time. The impedance spectra followed the observed changes in the ceramics' microstructure. The grain boundaries' shape, rather than the grain size, has the major influence on the conductivity. The lowest value for electrical conductivity, 8.1 × 10⁻¹⁰ (Ω·m)⁻¹, was obtained in the ceramics sintered at 1400°C for 4 h. This confirms the blocking effect of the imperfect grain boundaries; i.e., the defects of the grain boundaries, which were formed during the grain growth, were followed by an almost complete loss of pores.     

The Investigation of the Influence of Impeller Blade Inclination on Borax Nucleation and Crystal Growth Kinetics

An influence of impeller blade angle on the crystallization kinetics of borax has been investigated in detail. Its importance was studied in a batch crystallizer equipped with a four-blade turbine, whose angle was varied from 30° to 90°. Heterogeneous nucleation mechanism was dominant at all examined conditions, but the rate of nucleation significantly differed. Kinetic parameters of crystal growth were determined as well. Numerical values of order of crystal growth remain almost unchanged regardless of the blade angle. Different values of crystal growth rate constants are the result of the fluid dynamics in the crystallizer, caused by the different impeller blade inclinations. In all examined systems, crystal growth is integration limited. The transition from axial to radial flow, due to different blade angles, reflects on the crystal size distribution, agglomeration ratio, and crystallization yield.     

Sensor elements made of conductive silicone rubber for passively compliant gripper

Grinding is regarded as a special multiple edge cutting process, in which the abrasive grains remove the workpiece material at the microlevel. The grain–workpiece interaction, which resembles the microcutting process, directly modifies the workpiece surface and dominates all the output measures of grinding process. Recently, a virtual single-layer cubic boron nitride (CBN) grinding wheel model is developed by simulating each wheel fabrication step, which makes the estimation of the single grain material removal mode possible in grinding. Therefore, the study of the grain–workpiece interaction through microcutting behavior on the abrasive grains becomes necessary for the quantitative investigation of grinding processes. In this paper, the influence of the grain orientation on the microcutting performance of CBN grains is studied through finite element method (FEM) simulation based on response surface methodology (RSM). The FEM simulation helps in both qualitative and quantitative understanding of microcutting process. And the RSM analysis is proved to be an effective tool for factorial analysis in this paper. The results indicate that the single grain microcutting force is sensitive to the grain wear condition and orientation status, and there exists preferable orientation condition for microcutting with abrasive grains to achieve minimum cutting force.