Thinning Phenomenon Research Articles

Isolated apical perfusion defect in SPECT-CT scans, is there any prognostic value?

Abstract Background Myocardial perfusion imaging (MPI) plays a significant role in diagnostic and therapeutic decision making in coronary artery disease (CAD). An isolated apical defect in the 17th segment in SPECT/CT scans is a common finding, sometimes attributed to the apical thinning phenomenon. However, the clinical significance of apical thinning or other isolated apical defects is unknown. Purpose The purpose of this study is to assess the prognostic impact of an isolated apical perfusion defect (17th segment) in patients (P) with suspicion of significant CAD. Methods A cohort of 612 consecutive P that underwent a MPI test with a SPECT/CT scanner, between January 2017 and December 2017, in a single nuclear medicine centre, was included in this retrospective study. The inclusion criteria for this study were either a normal perfusion exam (group 1 – G1) or only an isolated apical defect in the 17th segment, either reversible suggesting ischemia (group 2 – G2) or fixed suggesting necrosis (group 3 – G3). Images with and without attenuation correction were analysed. Mean follow-up was 29±4 months. The chi square test was used for categorical variables, and analysis of variance for continuous variables. Binary logistic regression was used to control for confounding. Results A total of 612 P were included (57% male sex, mean age of 69±10) and divided in G1 (n=494, 80.7%), G2 (n=62, 10%) and G3 (n=56, 9.2%). P in G3 had higher body mass index (31±7, p=0.028) and higher prevalence of dyslipidemia (84%, p=0.001), while P in G1 had lower ejection fraction at rest (54±15, p=0.001). There was no association between the presence of isolated apical defect and all- cause mortality (G1 = 7.3% vs G2 = 6.5% vs G3 = 5.4%, p=0.851). There was a statistically significant difference between groups in the referral for coronary angiography in the bivariate analysis (G1 = 7.9% vs G2 = 35.5% vs G3 = 10.7%, p=0.001), but this association did not remain when accounted for potential confounders (angina, ejection fraction, previous CAD and diabetes) – OR=3.94, 95% CI: [0.968–16.093], p=0.056. In those P that underwent coronary angiography, there was no statistically significant difference between the 3 groups in revascularization of significant CAD (G1 = 38.5% vs G2 = 36.4% vs G3 = 50%, p=0.830). During the follow-up time, 11 P of group 1 suffered an acute coronary syndrome (ACS), but there were no events in group 2 or 3. Conclusion Isolated apical myocardial defect on a SPECT/CT exam has no association with all-cause mortality in this patients. There is no significant difference in referral for coronary angiography or need for coronary revascularization between P with normal exams and P with isolated apical defects. Funding Acknowledgement Type of funding source: None

Influence of hybrid nano-structures on thermal performance of shear rate dependent viscosity fluid over a heated rotating cone with Hall and ion slip currents

The fluid of shear rate dependent viscosity has totally different rheology and exhibits dynamics which play a key role in heat transfer rate and friction experienced by surface over which this type of fluid is considered in this study as this type of fluids are extensively used in thermal processes. The governing laws and constitutive equations for hyperbolic tangent fluid and thermo-physical relation correlation for hybridity of nano-structures are simultaneously solved via finite element method (FEM). The predictions are recorded, and outcomes are explained. It is found from outcomes that suspension of hybrid nano-structures is the most approximate technique for the enhancement of thermal performance of coolant (hyperbolic tangent fluid). The process of diffusion of wall momentum into fluid speeds down as viscosity decreases as a function of shear rate. It is predicted from simulations that mono nanofluid is less shear thinning than hybrid nanofluid. Hence, if it is desired to reduce shear thinning phenomenon, enhance the thermal performance and suspension of hybrid nano-structures are recommended. The results are validated by comparing them with already published benchmarks. The parameters are varied, and simulations are recorded in term of numerical values and graphical data. The rotation of micro-structures has shown significant reduction in angular velocity of mono and hybrid nanofluids. Angular field has depicted an increasing trend when vortex viscosity parameter is varied through increasing values. Temperature decreases as a result of an increase in thermal relaxation time. Hence, thermal memory effects play a significant role in controlling the thermal boundary layer thickness.

Modelling of Neutral Line Parameter for Sheet Metal Stamping and Roll Forming Processes

The blank development of sheet metal for the stamping and the roll forming processes is crucial for the dimensional accuracy of the products. The neutral line parameter is the indicator to present the thinning phenomenon at the bending corners of the products. The basic assumption of the neutral line position is the surface that the sheet metal remains un-deformed after the stamping or the roll forming process. The conventional determination method of the neutral line position is based on the zero strain position through the thickness direction of the blank. In this paper, a different neutral line factor calculation method based on the mean profile length was proposed to find the neutral line factor, which is directly related to the profile length and more precise for the bland development calculation. A cross sectional profile was obtained after the forming process and the mean profile length of the upper and the lower surface was obtained. The ratios of the bending radius to the sheet thickness were calculated using the FEM simulation. A neutral line equation was proposed considering the material mechanical properties and the bending tool parameters. The initial blank width was compared to the forming result of the CAE simulation to validate the neutral line model. This model is able to take into consideration of the thinning effect at the entire bending zone of the metal forming without the assumption of the uniform thinning and is more accuracy for the blank width calculation.

Experimental study on the performance of goaf filling materials with high content of fly ash

In this paper, fly ash is studied as the main cementing material for coal mine goaf filling. The performance of the filling materials with 90% fly ash such as compressive strength, impermeability, viscosity, additive effect and diffusion rule are studied experimentally and theoretically. The results show that compressive strength and impermeability are positively correlated with cement content when water-solid ratio is 0.7:1.0 with 90% fly ash. The compressive strength increases slowly in the early stage while it increases with a faster speed in the later stage. The compressive strength of the material after 60 days of curing is 1.90 times that of 28 days. Additive could promote the activity of fly ash and improve hydration reaction. The interparticle porosity is reduced, but strength at early stage and impermeability are increased. The viscosity of the filling material has an obvious shear thinning phenomenon as shear rate increases. An inflection point appears when shear rate is 30s−1. The filling material with high content of fly ash presents the rule of horizontal diffusion and longitudinal accumulation in goaf filling treatment. The diffusion distance and accumulation height are positively correlated with grouting pressure.

Heat Flow Data in an Area of the Eastern Southern Basin and Range in Arizona Contribute to an Analysis of Neogene Lithosphere Thinning Greater than 100 Km

Abstract Heat flow data and thermochronologic derived paleotemperature gradient data are examined to calculate heat flow ~25 Ma and, at present, for a southern Basin and Range location north of Tucson, Arizona. An increase in the surface heat flow is estimated from ~25 Ma to the present; changing from ~47 to ~83 mW m-2. Steady-state conduction temperature vs. depth profiles provide estimates of lithosphere thicknesses both for the present and for ~25 Ma. Different heat transfer models for present heat flow predict present LAB depth that agrees with seismic studies. From these temperature profiles, lithosphere thinning from ~184 km to ~70 km is suggested during the Neogene. Mantle lithosphere thinning caused by thermal phenomena is likely a fundamental driving force for southern Basin and Range extension. Because the mantle lithosphere has likely thinned much more than the crust, it is shown that additional vertical advection, such as an asthenosphere plume, delaminating part of the mantle lithosphere, convection cells, and rising magmas along conduits, add to the vertical advection component of upper mantle lithosphere extension. Interestingly, values of heat flow 25 Ma, lithosphere thicknesses 25 Ma, and Neogene lithosphere thinning are somewhat similar for the Four Corners area of the Colorado Plateau and the southern Basin and Range, even though Neogene tectonic development was quite different, i.e., no Neogene extension in the Colorado Plateau vs. ~57% in the southern Basin and Range. Neogene lithosphere thinning phenomena are likely different in the two regions.

On the thickness distribution and the maximum thinning ratio in hydrostatic forming for sheet metal

In manufacturing, thickness distribution and maximum thinning greatly affect product quality in sheet metal forming. They depend on many input parameters, such as technological parameters, geometric shape of die, workpiece’s materials and forming methods. Hydrostatic forming technology is particularly suitable for forming thin-shell products with complex shapes. However, due to the forming characteristics, the thinning phenomenon in this technology is much more intense than in other forming methods. Therefore, this study aims to determine the thickness distribution and the relationship between the maximum thinning ratio and input parameters including blank holder pressure, relative depth of the die and relative thickness of the workpiece in this technology. The chosen product shape is cylinder and the chosen method is the orthogonal second-order design. The results are expressed in graphs and functions and they can be applied in product design, calculation and control of input parameters in industrial manufacturing.

A New Viscosity Constitutive Model for Generalized Newtonian Fluids Using Theory of Micropolar Continuum

In this paper, a new viscosity constitutive relation for the analysis of generalized Newtonian fluids is presented and analyzed. The theory of micropolar continuum is considered for the derivation of constitutive relations where the kinematics at the macroscopic level leads to incorporate the micro-rotational effects in existing rheology of Carreau Yasuda model. It provides a more realistic approach to analyze the flow behavior of generalized Newtonian fluids. To the best of author’s knowledge such generalization of the existing rheology of Carreau-Yasuda is not present in literature. In order to show the effects of micro-rotations on the viscosity of generalized fluids, different computational experiments are performed using finite volume method (FVM). The method is implemented and validated for accuracy by comparison with existing literature in the limiting case through graphs and tables and a good agreement is achieved. It is observed that with the increase of micro-rotations the shear thinning phenomena slower down whereas the shear thickening is enhanced. Moreover, the effects of various model parameters on horizontal and vertical velocities as well as on boundary layer thickness are shown through graphs and contour plots It is worth mentioning that the proposed constitutive model can be utilized to analyze the generalized Newtonian fluids and has wider applications in blood rheology.

Analysis of Thickness Distribution in Cup Produced by Rubber Pad Forming

In many manufacturing fields such as the aeroplanes and automobiles industries, the control of the thinning variations in produced parts is a major point to investigate since good thickness distribution mean the reliability of these products. In this framework, several experimental and numerical modeling tests have been developed for the purpose of studying phenomenon of thinning during rubber pad forming process. The low carbon steel (AISI 1080) has been used as the blank material. Three forming block shapes had been used (flat, hemispherical and complex), rubber pad with three different hardness (50, 60 and 70 Shore A) also the rubber pad thickness have (40, 60 and 80 mm). The results have showed that improvement in thickness distribution occurred with decrease in rubber hardness and thickness distribution is various from one deformation style to other.

Analysis of Thickness Distribution in Cup Produced by Rubber Pad Forming

In many manufacturing fields such as the aeroplanes and automobiles industries, the control of the thinning variations in produced parts is a major point to investigate since good thickness distribution mean the reliability of these products. In this framework, several experimental and numerical modeling tests have been developed for the purpose of studying phenomenon of thinning during rubber pad forming process. The low carbon steel (AISI 1080) has been used as the blank material. Three forming block shapes had been used (flat, hemispherical and complex), rubber pad with three different hardness (50, 60 and 70 Shore A) also the rubber pad thickness have (40, 60 and 80 mm). The results have showed that improvement in thickness distribution occurred with decrease in rubber hardness and thickness distribution is various from one deformation style to other.

Superior-tensile property of CoCrFeMnNi alloys achieved using friction-stir welding for cryogenic applications

The friction-stir weld (FSW) was investigated based on the relationship between microstructural and mechanical properties at room and cryogenic temperatures for rolled and cast Co0.2Cr0.2Fe0.2Mn0.2Ni0.2 high entropy alloys (HEAs). The rolled and cast HEA welds exhibited good weldability without welding defects. The grain size (GS) of the stir zone (SZ) for rolled and cast HEAs was smaller than that of the base metal (BM). The W, Cr, and C particles caused by the wear of the WC-Co tool formed fine M23C6 carbides, due to the heat generated during the FSW, and accelerated the recrystallization via the particle stimulated nucleation (PSN) effect. Therefore, the area with M23C6 carbide exhibited a finer grain size compared with the area without M23C6 carbide. The rolled HEA was fractured in the SZ owing to the thinning phenomenon, and the cast HEA was fractured in the BM owing to the GS of the SZ, which was much finer than the GS of the BM. However, both HEA welds had larger room temperature strength than BM, and the cryogenic strength was also improved owing to the primary twin, secondary twin, and tangled dislocation. The PSN effect due to the carbides contributed to the increase in strength. Therefore, the FSW of the rolled and cast HEAs produced in this study is suitable for cryogenic applications.

The Effects of Bituminous Binder on the Performance of Gussasphalt Concrete for Bridge Deck Pavement.

As bituminous binders greatly influence the engineering performance of gussasphalt concrete for bridge deck pavement, selecting appropriate bitumen is a critical procedure for mixture design. In this study, five different combinations of bituminous binder for potential use in the “Hong Kong–Zhuhai–Macao Bridge” project were prepared and tested. To meet the strict requirements of quality control, a new Guss-Mastic Asphalt (GMA) system was developed. Three key indices, Lueer fluidity, impact toughness, and dynamic stability, were used for GMA design and construction quality control. The test results show that the fluidity of the GMA mixtures was affected by the shear thinning phenomenon. After mixing for three hours, the Lueer value of all GMA mixtures met the requirements of pouring construction. Moreover, it was found that the influence of mixing time on GMA with styrene butadiene styrene (SBS) modified bitumen was different to other prepared mixtures. This difference is ascribed to the degradation of SBS during the blending process at an elevated temperature. Finally, the blended bitumen (30% Pen60/70 + 70% Trinidad lake asphalt (TLA)) was applied to the project of the Hong Kong–Zhuhai–Macao Bridge.

Experimental study on the viscosity-temperature characteristics and rheological properties of offshore heavy oil

The viscosity-temperature characteristics and rheological properties of heavy oil were investigated experimentally. Experimental results indicate that viscosity is sensitive to temperature, and it is a binary function of temperature and shear rate meeting preferably Arrhenius equation. In addition, the semi-log curve of viscosity-temperature can be divided into three regions and there is no obvious turning point, which exhibits that the internal microstructure of heavy oil during the heating process changes gradually. Besides, activation energy of low temperature range is higher than that of high temperature range. Moreover, the heavy oil always behaves as Newtonian fluid when temperature is higher than crystallisation temperature. Furthermore, on condition that temperature is less than crystallisation temperature, the heavy oil behaves as pseudo-plastic fluid characterising shear thinning phenomenon when shear rate is less than critical shear rate, and it presents as Bingham fluid with yield stress when shear rate falls between 10 and 50 s−1. [Received: March 16, 2018; Accepted: October 24, 2018]

Study on the yielding behaviors of ferrofluids: a very shear thinning phenomenon.

The yielding behaviors of the ferrofluids are vital for many applications. However, previous studies have mainly focused on the magnetoviscous effect under relatively high shear rates and rarely involved the yielding process of ferrofluids under very low shear rates. In this study, ferrofluid samples of different particle volume concentrations were prepared and their shear thinning behaviors within a wide shear stress range were systematically studied under various magnetic field strengths and temperatures. The very shear thinning phenomenon of ferrofluids was first observed and its microscopic mechanism was analyzed. A precipitous fall-off stage as the mark of yielding appeared between the low shear and high shear plateaus in the viscosity curves of ferrofluids. The precipitous fall-off stage in the viscosity curves became steeper with the increase of the magnetic field strength or decrease in the temperature. For ferrofluids with relatively low particle volume concentrations, the high viscosity limit under the low shear region disappeared when temperature exceeded a certain value and was interpreted as the disappearance of the equilibrium columnar structures under high Brownian thermal interaction level. A composite Ellis model was proved to be suitable for the fitting of different types of yield stresses and a structural number, Sn was proposed for the dimensionless analysis of the shear thinning behaviors of ferrofluids. The findings in this study contribute to a better understanding of the microscopic mechanism of yielding behaviors of ferrofluids and also provide guidance for many practical applications.

Experimental study on the viscosity-temperature characteristics and rheological properties of offshore heavy oil

The viscosity-temperature characteristics and rheological properties of heavy oil were investigated experimentally. Experimental results indicate that viscosity is sensitive to temperature, and it is a binary function of temperature and shear rate meeting preferably Arrhenius equation. In addition, the semi-log curve of viscosity-temperature can be divided into three regions and there is no obvious turning point, which exhibits that the internal microstructure of heavy oil during the heating process changes gradually. Besides, activation energy of low temperature range is higher than that of high temperature range. Moreover, the heavy oil always behaves as Newtonian fluid when temperature is higher than crystallisation temperature. Furthermore, on condition that temperature is less than crystallisation temperature, the heavy oil behaves as pseudo-plastic fluid characterising shear thinning phenomenon when shear rate is less than critical shear rate, and it presents as Bingham fluid with yield stress when shear rate falls between 10 and 50 s−1. [Received: March 16, 2018; Accepted: October 24, 2018]

A Study of the Synergistic Interaction of Konjac Glucomannan/Curdlan Blend Systems under Alkaline Conditions.

To improve the gelation performance of konjac glucomannan (KGM) thermo-irreversible gel in the condition of alkaline, this study investigated the interactions between KGM and curdlan (CUD) in terms of the sol state and gelation process. The apparent viscosity, rheological properties during heating and cooling, thermodynamic properties, gelation properties and water holding capacity of KGM/CUD blend systems in an alkaline environment were studied using physical property testing instruments and methods. The results showed that the viscosity of the KGM/CUD blended solution was greater than the value calculated from the ideal mixing rules in the condition of alkaline (pH = 10.58). As the proportion of CUD in the system increased, the intersection of storage modulus (G’) and loss modulus (G”) shifted to low frequencies, the relaxation time gradually increased, and the degree of entanglement of molecular chains between these two components gradually increased. The addition of CUD helped decrease the gelation temperature of KGM, increased the gelation rate and inhibited the thinning phenomenon of KGM gels at low temperatures (2–20 °C). The addition of CUD increased the hardness and gel strength of KGM but did not significantly improve the water holding capacity of the KGM/CUD blend gel. The process of mixing KGM and CUD improved the thermal stability of the gel. In summary, KGM/CUD exhibited excellent compatibility under alkaline conditions, and the blend systems produced a “viscosifying effect”. KC8 and KC5 show better thermal stability, low temperature resistance and gel strength compared to KGM. This blended gel can be used as a structural support material to provide reference for the development of konjac bionic vegetarian products.

Processing rheological behavior of functionalized silica/natural rubber composites

The filler networks of natural rubber (NR) silica-filled coupling agents KH560, Si69, and NXT were studied using a rubber processing analyzer (RPA). The effects of different coupling agents on the rheological behavior of silica-filled NR were investigated. The results showed that the three types of coupling agents could control the surface properties of silica, diminish the silica network, reduce the storage modulus and loss modulus, weaken the Payne effect, and improve processability. A comprehensive modification effect was observed for the coupling agent NXT. For different modified silica loading scenarios, the rheological properties of natural rubber composites filled with silica modified by the silane coupling agent NXT were assessed. The Payne effects were more obvious with the increased loading of fillers, while G′ and G″ nonlinearly rose with the increase of frequency. Finally, the platform effect appeared, demonstrating the shear thinning phenomenon. The best compatibility and minimum extent of agglomeration of silica was obtained from the composite filled with 50 phr silica.

Insight on the influence of nano zinc oxide on the thermal, dynamic mechanical, and flow characteristics of Poly(lactic acid)– zinc oxide composites

Composites of Poly(lactic acid) (PLA) and spherical zinc oxide (ZnO) nanoparticles were prepared using melt processing followed by injection molding. The effect of nanosized ZnO on the molecular structure, thermal properties, dynamic mechanical properties, and flow characteristics of PLA composites were analyzed. Scanning electron microscopy images illustrated the formation of ZnO aggregates through PLA matrix. The molecular weight of PLA‐ZnO experienced a substantial decline by 55%, suggesting the presence of ZnO provoked degradation of PLA during composite preparation. Glass transition temperature of PLA‐ZnO decreased by 18% as compared with pure PLA, confirming the deleterious role of ZnO in PLA. The ZnO nanoparticles acted as a reactant and increased the thermal degradation rate. However, the incorporation of ZnO into PLA increased the crystallinity up to 20% and the storage modulus of composites in glassy state by 10%. The higher peak value of tan δ in composites suggested the more viscous behavior, which was further supported by lower number average molecular weight. The complex viscosity of composites exhibited a large Newtonian region over low shear rate, followed by shear thinning phenomenon. A significant decrease (96%) in complex viscosity was observed with the addition of ZnO into PLA. POLYM. ENG. SCI., 59:1242–1249 2019. © 2019 Society of Plastics Engineers

Numerical simulation of debris-flow behavior based on the SPH method incorporating the Herschel-Bulkley-Papanastasiou rheology model

A rational rheology model is critical for the numerical simulation of debris-flow behavior. The Bingham model commonly used in many current studies has failed to simulate the shear thickening and thinning phenomenon in experiments. We report an alternative solution by incorporating the Herschel-Bulkley-Papanastasiou (HBP) model with the smoothed particle hydrodynamic (SPH) method. The SPH simulation is based on the open-source DualSPHysics scheme, upon which we built a development by the Bingham-based rheology model in our previous study. In this paper, a straightforward improvement is made such that the HBP model is incorporated to describe the constitutive law between particles, extending the compatibility of the simulation to dilatant and pseudoplastic fluids. To illustrate the performance of the HBP-based SPH method, first, a sensitivity analysis was performed to investigate the influence of important rheological coefficients. The proposed method was then verified by a dam-break experiment of water-clay mixtures and the case study of the 2010 Yohutagawa debris-flow event in Japan. The results indicate a good accordance between simulation and observation. A discussion regarding the potential and limitations of the current method concludes the paper.

Electromechanical Instability of Dielectric Elastomer Actuators With Active and Inactive Electric Regions

Electrically driven dielectric elastomers (DEs) suffer from an electromechanical instability (EMI) when the applied potential difference reaches a critical value. A majority of the past investigations address the mechanics of this operational instability by restricting the kinematics to homogeneous deformations. However, a DE membrane comprising both active and inactive electric regions undergoes inhomogeneous deformation, thus necessitating the solution of a complex boundary value problem. This paper reports the numerical and experimental investigation of such DE actuators with a particular emphasis on the EMI in quasistatic mode of actuation. The numerical simulations are performed using an in-house finite element framework developed based on the field theory of deformable dielectrics. Experiments are performed on the commercially available acrylic elastomer (VHB 4910) at varying levels of prestretch and proportions of the active to inactive areas. In particular, two salient features associated with the electromechanical response are addressed: the effect of the flexible boundary constraint and the locus of the dielectric breakdown point. To highlight the influence of the flexible boundary constraint, the estimates of the threshold value of potential difference on the onset of electromechanical instability are compared with the experimental observations and with those obtained using the lumped parameter models reported previously. Additionally, a locus of localized thinning, near the boundary of the active electric region, is identified using the numerical simulations and ascertained through the experimental observations. Finally, an approach based on the Airy stress function is suggested to justify the phenomenon of localized thinning leading to the dielectric breakdown.

Influence of MoS₂ Nanosheet Size on Performance of Drilling Mud.

Water-based drilling mud (WBM) is a non-Newtonian fluid that has a variety of applications such as in transporting cuttings during drilling, protecting the borehole, and cooling the drill bit. With the development of nano-technology, various nanoparticles have been synthesized and have been added to WBM to improve its performance. Shear thinning is the most important factor in drilling mud and this attribute can be improved when two-dimensional particles are added. MoS2 nanoparticles, which represent a typical two-dimensional material, are easy to synthesize in large quantities and have a high thermal conductivity and low coefficient of friction. Since the two-dimensional structure, thermal conductivity, and low coefficient of friction of MoS2 would improve the performance of WBM, we experimented with MoS2 nanosheets as an additive, under optimal conditions, using various samples each with uniform sizes and thicknesses of nanosheets. A large amount of MoS2 nanosheets was synthesized, sorted by thickness and diameter, and added to drilling mud. The diameter of MoS2 was divided into a small diameter group (about 100–400 nm) and a big diameter group (about 300–650 nm), and the thickness was divided into 1–2 nm and 5–10 nm groups. Experimental results showed that when MoS2 is added to WBM, shear thinning occurs more strongly. In addition, the addition of MoS2 with a thickness of 1–2 nm and a diameter of 300–650 nm resulted in the highest increase in viscosity and thermal conductivity of WBM. As a result, we experimentally confirmed that MoS2 can be used as an additive to increase the thermal conductivity and viscosity of WBM and to make shear thinning phenomenon more.