The eye of the beholder

This article falls into four broad sections.

1. A background to the physical, political, social and cultural attributes of Saudi Arabia.

2. Problems encountered by designers, such as communications, contractors, plant and construction materials, irrigation water.

3. An attempt to establish some design principles, particularly pertinent to working in an arid Islamic environment.

4. Concludes with some recent projects carried out in the Kingdom, which follow some of these principles.

     

Nonsmooth model for dynamic simulation of phase changes

Dynamic modeling of processes involving phase changes can be challenging due to changes in the model equations caused by appearance and disappearance of equilibrium phases. Dynamic simulation of these processes requires the ability to detect the change in the number of phases and adapt the model to the new phase regime on the fly. In this work, an easy‐to‐use nonsmooth model for dynamic simulation of processes with vapor‐liquid equilibrium is presented. The presented model does not introduce any auxiliary variables or equations, nor does it require solution of an optimization problem to determine the new phase regime during the dynamic simulation. It can therefore be used for comprehensive simulation of, e.g., distillation columns, where the number of phases present can change during startup and shutdown. The nonsmooth model is illustrated through examples of an evaporator and a distillation column. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3334–3351, 2016     

Computer simulation of viscoelastic flow at the entry region

Non-Newtonian flow has a nonlinear constitutive relationship with an advective nature. It was found that in highly advective (convective) problems, the Galerkin formulation “under-diffused,” resulting in divergence at low elastic numbers. The use of the Streamline-Upwinding (SU) method improved the solution, especially when used with the Phan-Thien-Tanner (PTT) model. At the boundary discontinuity, however, the stress gradient did not necessarily flow along the streamline direction, and oscillations still remained at the corner. The Discontinuity-Capturing (DC) method resolved this problem by applying control in the direction of the stress gradient rather than the stream line direction, and a smoother solution at the corner region was achieved.     

Effect of constitutive models on the numerical simulation of viscoelastic flow at an entry region

The poor solutions of numerical simulations at a contraction has often been attributed to the numerical scheme used. However, the solution of a numerical simulation is also highly dependent on the constitutive equation. A study of various constitutive equations on the simulation of the 4:1 contraction flow is made in this paper, and their effects on the results analyzed. The constitutive models considered include the Upper Convected Maxwell model, the Oldroyd-B model, the White-Metzner model, the Phan-Thien-Tanner model and the Giesekus-Leonov model. It was found that although the Phan-Thien-Tanner model gave the best results, the solution at higher shear rates were still not satisfactory.     

Role of Tyrosine Kinase Syk in Thrombus Stabilisation at High Shear

Understanding the pathways involved in the formation and stability of the core and shell regions of a platelet-rich arterial thrombus may result in new ways to treat arterial thrombosis. The distinguishing feature between these two regions is the absence of fibrin in the shell which indicates that in vitro flow-based assays over thrombogenic surfaces, in the absence of coagulation, can be used to resemble this region. In this study, we have investigated the contribution of Syk tyrosine kinase in the stability of platelet aggregates (or thrombi) formed on collagen or atherosclerotic plaque homogenate at arterial shear (1000 s⁻¹). We show that post-perfusion of the Syk inhibitor PRT-060318 over preformed thrombi on both surfaces enhances thrombus breakdown and platelet detachment. The resulting loss of thrombus stability led to a reduction in thrombus contractile score which could be detected as early as 3 min after perfusion of the Syk inhibitor. A similar loss of thrombus stability was observed with ticagrelor and indomethacin, inhibitors of platelet adenosine diphosphate (ADP) receptor and thromboxane A₂ (TxA₂), respectively, and in the presence of the Src inhibitor, dasatinib. In contrast, the Btk inhibitor, ibrutinib, causes only a minor decrease in thrombus contractile score. Weak thrombus breakdown is also seen with the blocking GPVI nanobody, Nb21, which indicates, at best, a minor contribution of collagen to the stability of the platelet aggregate. These results show that Syk regulates thrombus stability in the absence of fibrin in human platelets under flow and provide evidence that this involves pathways additional to activation of GPVI by collagen.     

MEMS陀螺仪在恶劣高温环境下提供准确的惯性检测

越来越多的应用需要从处于高温环境中的传感器收集数据.相比同等的分立式传感器,MEMS通常更小巧,功耗和成本都更低.此外,它们还可以在同样大小的半导体封装内集成信号调理电路.除了可以提供高精度倾斜(倾角)测量,还需要更加灵活和自由,以准确测量系统在严苛环境应用下的移动,在这些环境下,最终产品可能遭受冲击、振动和剧烈移动....     

Circulating hormones and estrous stage predict cellular and stromal remodeling in murine uterus

The understanding of how estrogen and progesterone (P(4)) drive uterine remodeling in rodents has largely been based on studies involving administration of exogenous hormones, using steroid receptor-deficient mice, or relying on vaginal smears. In all these cases, the actual serum levels of 17beta-estradiol (E(2)) and P(4) are not directly measured, and the relationship between physiological levels of female sex hormones and uterine remodeling in cycling mice has not been fully explored. Here, we measured the circulating levels of E(2) and P(4) in cycling mice and performed correlation analysis between hormone levels and epithelial and stromal uterine parameters, irrespective of the estrous stage. In parallel, these parameters were analyzed in relation to the more conventional method of vaginal smear classification of estrous stage. We found that circulating P(4) inversely correlated with uterine width, luminal epithelial proliferation, stromal apoptosis, and degradation of luminal epithelial basement membrane collagen type-IV. Circulating E(2) positively correlated with uterine width, stromal cell proliferation, and collagen type-I content, while it negatively correlated with glandular epithelial proliferation, loss of collagen type-IV surrounding glandular epithelium, and apoptosis in luminal, glandular, and stromal compartments. Our findings indicate that measuring P(4) or E(2) levels can predict many concurrent cellular and stromal events in the mouse uterus, suggesting that in naturally cycling mice cellular responses to hormone changes are not delayed, but occur very rapidly.     

Fast reactions with nano- and micrometer aluminum: A study on oxidation versus fluorination

The use of fluorine as an oxidizing agent in aluminum (Al)-based thermite reactions yields higher peak pressures and an increase in gas production compared with oxygen-containing oxidizers, such as molybdenum trioxide (MoO₃). Thus fluorination reactions have the potential to excel in situations that require high pressures and flame speeds. This study compares the combustion behaviors of Al/Teflon, Al/MoO₃/Teflon, and Al/MoO₃ in an effort to determine the effects that the replacement of oxygen with fluorine has on the reaction dynamics in both open and confined burning configurations. Data were collected from pressure sensors and high-speed imaging. The mass percent of Al was varied from 10 to 90% to study the effects of composition. The composites were then further tested at the optimum stoichiometry using either 50 nm or 1-3 μm Al to examine the effect of Al particle size. The addition of Teflon in an open configuration hinders the reaction due to a loss of liberated gas. Confining the reaction enables the trapped gases to enhance convection, yielding increased flame speeds. For confined conditions, the reactions containing Teflon exhibit higher peak pressures but lower flame speeds than the reactions with MoO₃. These results imply that a direct relationship between generated gas pressures and flame speeds does not generally exist when comparing different oxidizers. The theoretically predicted relationship for the relative flame speed versus relative particle size based on the melt-dispersion mechanism agrees with experimental data for all Al particle sizes and for the fluorination reaction. Particle synthesis parameters are suggested that could be controlled to enable micrometer-scale Al particles to achieve the performance of nanoscale Al particles. This is of significant practical importance, because nanoparticles are 30 to 50 times more expensive than the micrometer particles.     

Effects of Milling Liquid on the Reaction-Bonded Aluminum Oxide Process

The reaction-bonded aluminum oxide process begins with aluminum, Al₂O₃, and usually ZrO₂ powders that have been attrition-milled in an organic liquid. The attrition-milled powder is then compacted and heat-treated in air to produce polycrystalline, Al₂O₃-based ceramics. Safety considerations have made it desirable for the milling liquid to be changed from acetone to a less-flammable solvent. In this paper, mineral spirits, ethanol, and mineral spirits that contains 2 wt% stearic acid are presented as viable alternatives to acetone. The effects of changing the milling liquid on the reaction process and the properties of the final fired ceramic are investigated.     

Wind speed variability across the UK between 1957 and 2011

By using surface data from 57 UK meteorological stations, a national [British Atmospheric Data Centre (BADC)‐57] and regional wind index for the UK has been calculated for the period 1983–2011. For a subset of seven stations, an additional national index (BADC‐7) has been calculated for the period 1957–2011. The indices show an annual variability of 4% over their respective periods, corresponding to a variation in typical wind turbine capacity factor of 7%. These indices are compared with indices calculated from other sources, namely an index generated using a gridded dataset of observed values interpolated across the UK, an index calculated from an area bounding the UK using the ERA‐40 re‐analysis dataset, indices calculated from bilinear interpolation of the ERA‐40 re‐analysis dataset to the 57 and 7 stations and another independent UK wind index. The indices show variation in trends, with all showing some level of decline with the exception of that generated using the ERA‐40 re‐analysis dataset averaged over the UK, which shows a significant increase. The various indices show varying degrees of agreement with correlation coefficients, after trends are removed, ranging between 0.611 and 0.979. The effect of changes in site exposure, instrument bias and measuring height was considered for the BADC‐7 and BADC‐57 indices. The change in instrument measurement height appears to have a significant biasing effect, and it is likely that this along with changes in exposure at urban sites has caused the decline in annual wind speeds observed for some of the indices. There does not appear to be evidence for significant changes in large‐area (mesoscale) surface roughness. The correlation between annual mean wind speeds at the seven surface station sites used to calculate the BADC‐7 index is seen to be quite weak, indicating very localized variations in inter‐annual variability. When regional differences in the index are investigated, it is seen that wind speeds show a very slight decline across the UK in all regions except the south‐east, which shows a slight increase. The greatest decrease is seen in the north‐west. These changes are in the same direction as the tentative predictions given by climate models for future changes in wind speed across the UK, although the uncertainty is large given the large degree of inter‐annual variation. Copyright © 2013 John Wiley & Sons, Ltd.