An approximate Riemann solver for shallow water equations and heat advection in horizontal centrifugal casting

AbstractAn approximate Riemann solver was developed for solving modified shallow water equations (SWE) and energy transport describing the average flow dynamics of a single layer spreading inside a horizontally rotating cylinder. The numerical model was particularly developed for simulating the horizontal centrifugal casting (HSC) of the outer shell of a work roll. The SWE were derived in the rotating frame of reference; therefore, fictitious forces (the centrifugal force and the Coriolis force) were considered. In addition, other forces such as the bed shear force, the force of gravity, the wind shear force and forces arising from the variable liquid/solid interface were taken into account. The Jacobian matrix of the nonlinear hyperbolic system of PDEs was decomposed into a set of eigenvalues and corresponding eigenvectors using standard and corrected Roe averages. A Harten–Hyman entropy fix was used to prevent expansion shocks (entropy violating solutions) typically occurring during transonic rarefactions. Source terms were applied as a stationary discontinuity and were physically bounded and well-balanced for steady states (producing non-oscillatory solutions). Each wave was upwinded using the explicit Godunov’s method. The high resolution corrections with flux limiters were used to achieve second order of accuracy and dispersion free solutions at discontinuities. In addition to the Riemann solver, a central scheme FV model was used to solve the heat diffusion inside the cylinder (mold) and partially solidified liquid layer, coupled with the solidification model. Several simulations were performed, results were analyzed and discussed

Dynamics of bound states of dihydrogen at Cu(I) and Cu(II) species coordinated near one and two zeolite framework aluminium atoms: A combined sorption, INS, IR and DFT study

Abstract Ambient conditions sorption isotherms of dihydrogen in a series of various levels of Cu-exchanged ZSM-5 zeolites, with two different Si/Al ratios, namely 11.5 and 25, show the presence of different amount of Cu centres able to strongly bind H2. Although the isosteric heats of adsorption derived from these isotherms are rather similar, of the order of 30 kJ/mol H2, Inelastic Neutron Scattering (INS) of adsorbed dihydrogen and Fourier-Transformed Infra-Red (FTIR) spectroscopy measurements of adsorbed CO and NO reveal that copper is encountered in two oxidation states. At least two types of Cu(I) ions are clearly detected as well as some heterogeneity of the Cu(II) species. The number of these Cu species is different in the two investigated ZSM-5 materials and depends on the Cu exchange level. With the aid of DFT model cluster calculations we find that under different coordination environments, determined by the Al distribution, both mono- and divalent Cu ions could bind H2 with a different strength. Unprecedentedly, we found that Cu-ions compensating two Al atoms, i.e. formally Cu(II) species, relatively far apart from each other, may behave very similarly to the monovalent Cu-species or alternatively viewed – as Cu(I) species that compensate for two framework Al-atoms. Such Cu-species also form stable η2 dihydrogen complexes

Antegrade anterior column acetabulum fracture fixation with cannulated compression headless screws-A biomechanical study on standardized osteoporotic artificial bone

PURPOSE Due to the increase in life expectancy and high-energy traumas, anterior column acetabular fractures (ACFs) are also increasing. While open reduction and internal fixation (ORIF) is still the standard surgical procedure, minimally invasive, percutaneous fixation of osteoporotic acetabulum fractures (AF) are growing in popularity. The aim of this biomechanical study was to evaluate the biomechanical competence following antegrade fixation with a standard screw versus a cannulated compression headless screw. METHODS Eight anatomical osteoporotic composite pelvises were given an anterior column fracture. Two groups of eight specimens each (n = 8) for fixation with either a 6.5 mm cannulated compression headless screw in group Anterior Acetabulum Canulated Compression Headless Screw (AACCH), or with a 6.5 mm partially threaded cannulated screw in group Anterior Acetabulum Standard Screw (AASS) where compared. Each specimen was biomechanically loaded cyclically at a rate of 2 Hz with monotonically increasing compressive load until failure. Motions were assessed by means of optical motion tracking. RESULTS Initial construct stiffness trended higher in group AACCH at 152.4 ± 23.1 N/mm compared to group AASS at 118.5 ± 34.3 N/mm, p = 0.051. Numbers of cycles and corresponding peak load at failure, were significantly higher in group AACCH at 6734 ± 1669 cycles and 873.4 ± 166.9 N versus group AASS at 4440 ± 2063 cycles and 644.0 ± 206.3 N, p = 0.041. Failure modes were breakout of the screws around the proximal entry point. CONCLUSION From a biomechanical perspective, group AACCH was associated with superior biomechanical competence compared to standard partially threaded cannulated screws and could therefore be considered as valid alternative for fixation of anterior acetabulum fractures

Chemical instability of Cu(3)(BTC)(2) by reaction with thiols

In contrast to Fe(BTC) (BTC: 1,3,5-benzenetricarboxylate), the crystal structure of Cu3(BTC)2, a commercial metal organic framework widely used as solid catalyst, collapses when contacted with thiols under mild reaction conditions forming copper nanoparticles.Financial support by the Spanish DGI (CTQ2009-11587 and CTQ2010-18671) is gratefully acknowledged. Maykel de Miguel is thanked for helping to record TEM images.Dhakshinamoorthy, A.; Alvaro Rodríguez, MM.; Concepción Heydorn, P.; García Gómez, H. (2011). Chemical instability of Cu(3)(BTC)(2) by reaction with thiols. Catalysis Communications. 12(11):1018-1021. https://doi.org/10.1016/j.catcom.2011.03.018S10181021121

Successful Craniotomy for Advanced Basal Cell Carcinomas with Cranial Bone Invasion and Dura Mater Infiltration - Unique Presentation in a Bulgarian Patient

BACKGROUND: Basal cell carcinomas (BCC) located in the sun-exposed regions are a serious therapeutic challenge. Therefore early diagnosis and adequate therapy should be of a high priority for every dermatologic surgeon.CASE PRESENTATION: We are presenting a patient with multiple BCCs, located on the area of the scalp, who had been treated several years ago with electrocautery and curettage after histopathological verification. However, the last few years the tumours have advanced, infiltrating firstly the tabula external and a year later the tabula interna of the cranium. A computed -tomography (CT) imaging and radiography of the skull were performed to reveal the definite tumour localisation, needed for planning an one - step surgical intervention. Both of the instrumental examinations confirmed the existence of osteolytic tumour lesions. Craniotomy with precise removal of the BCCs infiltrating the cranial bone in all of its thickness was performed. Partial resection of dura mater was also performed also because intraoperative findings established the involvement of the dura. Histopathological verification revealed bone and dural invasion with clean resection margins. The bone defect was recovered with hydroxyapatite cement. Reconstruction as the shape of the skull was carefully modified and adapted to its initial size and form. Layered closure of the skin and soft tissues were performed after the complete removal of the BCCs. The postoperative period had no serious complications.CONCLUSION: Precisely managed therapy of BCC is curative in most of the cases as it ensures good prognosis for the patient

Mechanical assessment of two hybrid plate designs for pancarpal canine arthrodesis under cyclic loading

Pancarpal canine arthrodesis (PCA) sets immobilization of all three carpal joints via dorsal plating to result in bony fusion. Whereas the first version of the plate uses a round hole (RH) for the radiocarpal (RC) screw region, its modification into an oval hole (OH) in a later version improves versatility in surgical application. The aim of this study was to mechanically investigate the fatigue life of the PCA plate types implementing these two features–PCA-RH and PCA-OH. Ten PCA-RH and 20 PCA-OH stainless steel (316LVM) plates were assigned to three study groups (n = 10). All plates were pre-bent at 20° and fixed to a canine forelimb model with simulated radius, RC bone and third metacarpal bone. The OH plates were fixed with an RC screw inserted either most proximal (OH-P) or most distal (OH-D). All specimens were cyclically tested at 8 Hz under 320 N loading until failure. Fatigue life outcome measures were cycles to failure and failure mode. Cycles to failure were higher for RH plate fixation (695,264 ± 344,023) versus both OH-P (447,900 ± 176,208) and OH-D (391,822 ± 165,116) plate configurations, being significantly different between RH and OH-D, p = 0.03. No significant difference was detected between OH-P and OH-D configurations, p = 0.09. Despite potential surgical advantages, the shorter fatigue life of the PCA-OH plate design may mitigate its benefits compared to the plate design with a round radiocarpal screw hole. Moreover, the failure risk of plates with an oval hole is increased regardless from the screw position in this hole. Based on these findings, the PCA plate with the current oval radiocarpal screw hole configuration cannot be recommended for clinical use

Effect of Magnesium Addition on the Cell Structure of Foams Produced From Re-melted Aluminum Alloy Scrap

Closed-cell foams were produced from re-melted aluminum alloy scrap that contained 0.13 wt pct Mg magnesium in the as-received state and higher levels after adding 1, 2, or 5 wt pct Mg. The excess Mg gave rise to the fragmentation of long oxide filaments present in the scrap alloy into smaller filaments and improved its distribution and wetting by the Al matrix. Foaming the re-melted scrap alloy containing 1, 2, and 5 wt pct Mg excess showed stability and good expansion in comparison to the scrap alloy containing 0.13 wt pct Mg only, but the cells became non-equiaxed when the Mg concentration was high (≥2 wt pct excess) due to cell wall rupture during solidification. Compressibility and energy absorption behavior were studied for scrap alloy foams containing 1 wt pct Mg excess, which is the optimum level to obtain good expansion, stability, and uniform cell size. Foams with densities in the range of 0.2 to 0.4 g cm−1 produced by holding at the foaming temperature for different times were used for the investigation. A uniform cell structure led to flatter stress plateaus, higher energy absorption efficiencies, and reduced “knockdown” in strength compared with commercial foams made by gas bubbling. The mechanical performance found is comparable to that of commercial foams made by a similar method but the expected costs are lower

Fracture mechanism simulation of inhomogeneous anisotropic rocks by extended finite element method

The vast majority of rock masses is anisotropic due to factors such as layering, unequal in-situ stresses, joint sets, and discontinuities. Meanwhile, given the frequently asymmetric distribution of pores, grain sizes or different mineralogical compounds in different locations, they are often classified as inhomogeneous materials. In such materials, stress intensity factors (SIFs) at the crack tip, which control the initiation of failure, strongly depend on mechanical properties of the material near that area. On the other hand, crack propagation trajectories highly depend on the orthotropic properties of the rock mass. In this study, the SIFs are calculated by means of anisotropic crack tip enrichments and an interaction integral are developed for inhomogeneous materials with the help of the extended finite element method (XFEM). We also use the T-stress within the crack tip fields to develop a new criterion to estimate the crack initiation angles and propagation in rock masses. To verify and validate the proposed approach, the results are compared with experimental test results and those reported in the literature. It is found that the ratio of elastic moduli, shear stiffnesses, and material orientation angles have a significant impact on the SIFs. However, the rate of change in material properties is found to have a moderate effect on these factors and a more pronounced effect on the failure force. The results highlight the potential of the proposed formulation in the estimation of SIFs and crack propagation paths in inhomogeneous anisotropic materials

Tribological characterization of high porosity aluminum based composite materials

The present work aims to study the effect of the reinforcing phase on dynamic coefficient of friction and mass wear of specimen with different compositions under various friction conditions. Porous materials with different compositions and reinforcing phase are obtained by replication method applying salt (NaCl) space holder. The reinforcing phase is Fly Ash (FA) particles. The microstructure of the obtained materials is observed and the tribological properties such as mass losses and the dynamic coefficient of friction are determined. A comparison of the tribological properties between nominally nonporous matrix, porous matrix and porous composite are presented in this study