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1
Carter, R. E., I. M. Miller, and K. Klinka. "Relationships Between Growth Form and Stand Density in Immature Douglas-fir." Forestry Chronicle 62, no. 5 (October 1, 1986): 440–45. http://dx.doi.org/10.5558/tfc62440-5.
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Stem form of the whole tree and branching characteristics at whorls 6 to 10 were examined in 27-year-old Dougias-tir (Pseudoisuga menziesii [Mirb.] Franco) trees established at each of three spacings (1.8 × 1.8 m, 3.6 × 3.6 m, and 4.6 × 4.6 m) and replicated across two blocks. A total of 30 trees from each spacing were analysed. Spacings were found to affect stem, crown, and branching characteristics. Tree height, diameter at breast height, and stem diameter at the base of the live crown all increased significantly with spacing (p < 0.01), while age and height at the base of the live crown both decreased (p < 0.01). Increased spacing resulted in significantly greater branch diameters at whorls 6 to 10; and, in some whorls, an increase in branch number. Swelling of the stern at branch whorls, the number of lammas whorls, knottiness ratio, and a subjective index of stem form (higher index indicates poorer form) all increased with increased spacing (p < 0.01).The considerations involved with choosing high or low initial stocking levels are discussed and the study concludes that intensive management practices such as thinning and pruning will be necessary in all regimes if clear wood is to be produced over short rotations.
2
Cook, Kevin L., and Leonard M. Pike. "OPTIMUM SPACING AND HARVEST TIME FOR `INTERMEDIATE LEAF' HYBRID PICKLING CUCUMBERS FOR ONCE-OVER MECHANICAL HARVEST." HortScience 26, no. 5 (May 1991): 488e—488. http://dx.doi.org/10.21273/hortsci.26.5.488e.
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An `intermediate leaf' hybrid pickling cucumber (TAMU 884304 X ARK H-19 `little leaf') was direct-seeded at four plant densities (94,570; 48,440; 32,290; 25,375 plants/ha) using four within-row spacings (15, 30, 45, 60cm) at two locations and two seasons. Optimum yield based on marketable fruit number, grade distribution and fruit quality occurred with 94,570 plants/ha. Optimum harvest time depended on location and season. Delayed harvest times were also evaluated. Harvests with fruit >5.1cm in diameter had severely reduced brining quality. Fruit did not enlarge or enlarged slowly to oversize. This resulted in a mixture of fruit ages within the largest marketable fruit grades. It is recommended that `little leaf' lines and their hybrids such as `intermediate leaf' be harvested when fruit 3.8 to 5.1cm in diameter appear and before oversize fruit are produced. Spacing did not significantly effect length/diameter ratio(LDR) but LDR was significantly greater for delayed harvests.
3
Larocque, Guy R., and Peter L. Marshall. "Crown development in red pine stands. I. Absolute and relative growth measures." Canadian Journal of Forest Research 24, no. 4 (April 1, 1994): 762–74. http://dx.doi.org/10.1139/x94-101.
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The crown development of red pine (Pinusresinosa Ait.) plantations originating from different initial spacings was studied between 13 and 33 years of age. First, the effect of spacing on models used to predict crown width and crown ratio from diameter at breast height (DBH) and height was examined. Models for trees of different ages that included all the spacings were found to predict crown growth measures as well as separate models derived for each spacing. Second, the following crown relative growth measures were studied: crown width/crown length (crown shape ratio), crown surface/crown volume, and foliage biomass/crown volume. The way such measures changed over time under different initial spacings was studied; these findings were compared with changes in relative growth rate (RGR), which can be used to evaluate the effect of competitive stress. Crown shape ratio decreased with an increase in DBH in the absence of severe competition, and increased with DBH under severe competitive stress. The other two crown relative growth measures were always negatively correlated with DBH; this shows that large trees use their aerial growing space less efficiently than small trees at all stages of stand development. Only crown shape ratio changed in the same way as RGR.
4
Nourmohammadi, Khosrow, P. K. Hopke, and J. J. Stukel. "Turbulent Air Flow Over Rough Surfaces: II. Turbulent Flow Parameters." Journal of Fluids Engineering 107, no. 1 (March 1, 1985): 55–60. http://dx.doi.org/10.1115/1.3242440.
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The objective of the present study was to examine experimentally the turbulent flow structure in a repeated rib geometry rough wall surface as a function of the ratio of the roughness height to the pipe diameter (K/D), the ratio of the spacing between the elements to the roughness height (P/K), the axial position within a rib cycle, and the Reynolds number. For small P/K values, the turbulent intensities and Reynolds shear stress variations were similar to those found for smooth wall pipe flow. Unique relationships for the u′ and v′ were found that were valid in the outer layer of the flow for all axial positions and all values of P/K and K/D.
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Zhang, Yunyan, Pingmei Ming, Runqing Li, Ge Qin, Xinmin Zhang, Liang Yan, Xinchao Li, and Xingshuai Zheng. "Numerical Analysis and Experimental Study on Fabrication of High Aspect Ratio Tapered Ultrafine Holes by Over-Growth Electroforming Process." Micromachines 10, no. 12 (November 27, 2019): 824. http://dx.doi.org/10.3390/mi10120824.
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High aspect ratio (HAR) ultrafine tapered holes (diameter ≤5 μm; AR ≥5) are the most important elements for some high-tech perforated metallic products, but they are very difficult to manufacture. Therefore, this paper proposes a nontraditional over-growth electroforming process. The formation mechanism of the HAR ultrafine tapered holes is investigated, and the factors controlling the geometric shape evolution are analyzed numerically. It was found that the geometric shape and dimensions of the holes are highly dependent on the diameter and thickness of the photoresist film patterns, but are hardly affected by the spacing between two neighboring patterns; the achievable diameter for a given hole depth becomes small with the increasing pattern diameter, but it becomes big with the increasing pattern thickness. These correlations can be well interpreted by the established two empirical equations that characterize the relationship between the minimum orifice of the tapered hole and the structural parameters of the photoresist film patterns previously formed on the substrate. Application of the fabricated 1500 tapered holes with 3-μm diameter and 17-AR as the nozzles of the medical precision nebulizer is also examined. The studies show that the over-growth electroforming process is highly applicable in fabricating the perforated metallic plate with HAR ultrafine tapered holes.
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Zhao, Guang. "Aerodynamics Study of Flow Past Two Tandem Bluff Bodies at Low Reynolds Number." Applied Mechanics and Materials 668-669 (October 2014): 138–41. http://dx.doi.org/10.4028/www.scientific.net/amm.668-669.138.
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Aerodynamics of flow past two tandem bluff bodies is a critical problem in fluid mechanics. In this work, the flow over two circular cylinders with unequal diameters in tandem arrangement is numerical investigated using lattice Boltzmann method. The diameter of the bigger one is adopted as the characteristic length, the diameter ratio is fixed as 2, and the Reynolds number is 100. Spacing between two cylinders (scaled by the characteristic length) are varied from 0 to 3 characteristic diameter, and the effects of which on the flow patterns of such a system are studied. The results show that flow patterns behind two tandem unequal circular cylinders are significantly different from that behind a single one. Due to the downstream cylinder, two classic vortex interaction modes are observed, known as destruction interaction mode and construction mode.
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Bowers, Morris B., and Issam Mudawar. "Two-Phase Electronic Cooling Using Mini-Channel and Micro-Channel Heat Sinks: Part 1—Design Criteria and Heat Diffusion Constraints." Journal of Electronic Packaging 116, no. 4 (December 1, 1994): 290–97. http://dx.doi.org/10.1115/1.2905700.
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Mini-channel (D = 2.54 mm) and micro-channel (D = 510 μm) heat sinks with a 1-cm2 heated surface were tested for their high heat flux performance with flow boiling of R-113. Experimental results yielded CHF values in excess of 200 W cm−2 for flow rates less than 95 ml min−1 (0.025 gpm) over a range of inlet subcooling from 10 to 32°C. Heat diffusion within the heat sink was analyzed to ascertain the optimum heat sink geometry in terms of channel spacing and overall thickness. A heat sink thickness to channel diameter ratio of 1.2 provided a good compromise between minimizing overall thermal resistance and structural integrity. A ratio of channel pitch to diameter of less than two produced negligible surface temperature gradients even with a surface heat flux of 200 W cm−2. To further aid in determining channel diameter for a specific cooling application, a pressure drop model was developed, which is presented in the second part of the study.
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Zheng, Shaokai, and Ellen K. Longmire. "Perturbing vortex packets in a turbulent boundary layer." Journal of Fluid Mechanics 748 (April 29, 2014): 368–98. http://dx.doi.org/10.1017/jfm.2014.185.
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AbstractA zero pressure gradient turbulent boundary layer of $\textit {Re}_{\tau }=2500$ was perturbed by a single spanwise array of finite cylinders mounted on the bounding surface and extending through the logarithmic region. The cylinder height was $H/\delta =0.2$ ($H^{+}=500$), where $\delta $ is the boundary layer thickness, with an aspect ratio ($AR$) (height/diameter) of four. Streamwise–spanwise ($x\text {--}y$) planes of the flow were examined by particle image velocimetry (PIV) up to $7\delta $ downstream at a wall-normal location of $z^{+}=300$ for cylinder array spacings ranging from $0.2\delta $ to $0.8\delta $. Average streamwise velocity fields showed a splitting, then merging pattern of cylinder wakes which occurred further downstream as the cylinder spacing increased. Based on measurements at the furthest downstream location, both the spanwise variation of average streamwise velocity and the Fourier content in the instantaneous fields suggested that the case with $0.6\delta $ cylinder spacing, which matched the dominant spanwise scale in the unperturbed flow, yielded the most persistent downstream flow organization. A flying PIV method was implemented to track specific packet structures over a range $-2<x/\delta <7$ with respect to the cylinder array, corresponding to a time scale of $12.4\delta /U_{\infty }$. Packets approaching the $0.2\delta $ spacing array first lost their organization but then regained it a distance $2\delta $ downstream, suggesting that a persistent outer layer organization propagated inwards into the log region. For arrays with larger spanwise spacing, approaching packets were generally redirected into the spanwise location midway between cylinders and sometimes enhanced.
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Abdlrahem, Maged A., and M. Hesham El Naggar. "Axial performance of micropile groups in cohesionless soil from full-scale tests." Canadian Geotechnical Journal 57, no. 7 (July 2020): 1006–24. http://dx.doi.org/10.1139/cgj-2018-0695.
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Hollow bar micropile (HBMP) groups are used for supporting large loads as an alternative foundation option to large diameter drilled shafts. In such cases, it may be necessary to increase the micropile’s diameter by increasing the drill bit diameter (Db). This paper investigates experimentally and numerically the effect of increasing Db and micropile spacing on the group performance. A field load testing program was conducted on four groups of HBMPs installed in sand; each group comprised four micropiles arranged in a square configuration. All micropiles were constructed with the same size hollow bar, Dh = 51 mm; two groups comprised micropiles constructed with drill bit, Db = 115 mm, and two groups comprised micropiles constructed with drill bit, Db = 152 mm. One group of each set was installed with spacing to micropile diameter ratio, S/Db = 3 and the other group with S/Db = 5. In addition, full 3D finite element model (FEM) was developed and calibrated to simulate the behaviour of micropile groups and to evaluate the failure load for groups that were not loaded to failure. The results demonstrated that micropile groups constructed with the large diameter drill bits displayed higher stiffness and load carrying capacity than the groups constructed with small diameter bits, which confirms the effectiveness of using a larger drill bit. In addition, the group efficiency ratio values at both working load and ultimate capacity were found to be close to unity for all groups. The ultimate skin friction values of grouted micropiles obtained from this study were higher than the values suggested by the US Federal Highway Administration for medium to very dense sand. It was also found that the settlement of the 4-HBMP group increased by 25% to 33% over that of a single HBMP due to group effect.
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Ligrani, P. M., and S. W. Mitchell. "Effects of Embedded Vortices on Injectant From Film Cooling Holes With Large Spanwise Spacing and Compound Angle Orientations in a Turbulent Boundary Layer." Journal of Turbomachinery 116, no. 4 (October 1, 1994): 709–20. http://dx.doi.org/10.1115/1.2929464.
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Experimental results are presented that describe the effects of embedded, longitudinal vortices on heat transfer and film injectant downstream of a single row of film cooling holes with compound angle orientations. Holes are spaced 7.8 hole diameters apart in the spanwise direction so that information is obtained on the interactions between the vortices and the injectant from a single hole. The compound angle holes are oriented so that their angles with respect to the test surface are 30 deg in a spanwise/normal plane projection, and 35 deg in a streamwise/normal plane projection. A blowing ratio of 0.5 is employed and the ratio of vortex core diameter to hole diameter is 1.6–1.67 just downstream of the injection holes (x/d=10.2). At the same location, vortex circulation magnitudes range from 0.15 m2/s to 0.18 m2/s. The most important conclusion is that local heat transfer and injectant distributions are strongly affected by the longitudinal embedded vortices, including their directions of rotation and their spanwise positions with respect to film injection holes. To obtain information on the latter, clockwise rotating vortices R0–R4 and counterclockwise rotating vortices L0–L4 are placed at different spanwise locations with respect to the central injection hole located on the spanwise centerline. With vortices R0–R4, the greatest disruption to the film is produced by the vortex whose downwash passes over the central hole (R0). With vortices L0–L4, the greatest disruption is produced by the vortices whose cores pass over the central hole (L1 and L2). To minimize such disruptions, vortex centers must pass at least 1.5 vortex core diameters away from an injection hole on the upwash sides of the vortices and 2.9 vortex core diameters away on the downwash sides of the vortices. Differences resulting from vortex rotation are due to secondary flow vectors, especially beneath vortex cores, which are in different directions with respect to the spanwise velocity components of injectant after it exits the holes. When secondary flow vectors near the wall are in the same direction as the spanwise components of the injectant velocity (vortices R0–R4), the film injectant is more readily swept beneath vortex cores and into vortex upwash regions than for the opposite situation in which near-wall secondary flow vectors are opposite to the spanwise components of the injectant velocity (vortices L0–L4). Consequently, higher Stanton numbers are generally present over larger portions of the test surface with vortices R0–R4 than with vortices L0–L4.
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Thuy Anh, Nguyen, and Ly Hai Bang. "Development of ANN-based models to predict the bond strength of GFRP bars and concrete beams." Transport and Communications Science Journal 71, no. 7 (September 30, 2020): 814–27. http://dx.doi.org/10.47869/tcsj.71.7.7.
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The use of glass fiber-reinforced polymer (GFRP) has gained increasing attention over the past decades, aiming at replacing traditional steel rebar in concrete structures, especially in corrosion or magnetic conditions. Understanding the working mechanism between the reinforcements and concrete is crucial in many practical applications, in which the corresponding bond strength is considered as a critical element. In this study, a database including 159 experimental beam results gathered from the available literature was used for the development of an artificial neural network (ANN) model in an effort to predict the bond strength between GFRP bars and concrete. Two ANN models using BFGS quasi-Newton backpropagation and conjugate gradient backpropagation with Polak-Ribiére algorithms were constructed and evaluated in terms of bond strength prediction accuracy. The considered database consisted of five input parameters, including the bar diameter, concrete compressive strength, minimum cover to bar diameter ratio, bar development length to bar diameter ratio, the ratio of the area of transverse reinforcement to the product of transverse reinforcement spacing, the number of developed bars and bar diameter. The evaluation of the models was conducted and compared using well-known statistical measurements, namely the correlation coefficient (R), root mean square error (RMSE), and absolute mean error (MAE). The results demonstrated that both ANN models could accurately predict the bond strength between GFRP bars and concrete, paving the way for engineers to possess a useful alternative design solution for reinforced concrete structures
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Thuy-Anh, Nguyen, and Ly Hai-Bang. "Development of ANN-based models to predict the bond strength of GFRP bars and concrete beams." Transport and Communications Science Journal 71, no. 7 (September 30, 2020): 814–27. http://dx.doi.org/10.25073/tcsj.71.7.7.
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The use of glass fiber-reinforced polymer (GFRP) has gained increasing attention over the past decades, aiming at replacing traditional steel rebar in concrete structures, especially in corrosion or magnetic conditions. Understanding the working mechanism between the reinforcements and concrete is crucial in many practical applications, in which the corresponding bond strength is considered as a critical element. In this study, a database including 159 experimental beam results gathered from the available literature was used for the development of an artificial neural network (ANN) model in an effort to predict the bond strength between GFRP bars and concrete. Two ANN models using BFGS quasi-Newton backpropagation and conjugate gradient backpropagation with Polak-Ribiére algorithms were constructed and evaluated in terms of bond strength prediction accuracy. The considered database consisted of five input parameters, including the bar diameter, concrete compressive strength, minimum cover to bar diameter ratio, bar development length to bar diameter ratio, the ratio of the area of transverse reinforcement to the product of transverse reinforcement spacing, the number of developed bars and bar diameter. The evaluation of the models was conducted and compared using well-known statistical measurements, namely the correlation coefficient (R), root mean square error (RMSE), and absolute mean error (MAE). The results demonstrated that both ANN models could accurately predict the bond strength between GFRP bars and concrete, paving the way for engineers to possess a useful alternative design solution for reinforced concrete structures
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Kabzems, Richard D., George Harper, and Peter Fielder. "Growing Space Management in Boreal Mixedwood Forests: 11-Year Results." Western Journal of Applied Forestry 26, no. 2 (April 1, 2011): 82–90. http://dx.doi.org/10.1093/wjaf/26.2.82.
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Abstract Managing boreal mixed stands of trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca [Moench] Voss) is more likely to sustain a diversity of values and has the potential to increase productivity at both the site and landscape levels compared with pure broadleaf or conifer management. In this study, we examine growth of white spruce and aspen after 11 growing seasons over a range of aspen densities created by spot and broadcast treatment of broadleaves using manual and chemical means, aspen spacing, and an untreated control. Results indicate that survival and growth of both spruce and aspen were similar across the range of treatments. Spruce groundline diameter was greater, and height to groundline diameter ratio was lower, for the treatments in which aspen was chemically controlled or uniformly spaced compared with the control. Light measurements at the individual tree level suggested that increased light availability improved white spruce diameter growth. Spruce height growth did not vary by treatment. The status of these experimental mixedwoods was compared with current conifer and mixedwood regeneration evaluations, as well as the preharvest composition of the original stand. After 11 growing seasons, growth of aspen and white spruce indicated that opportunities exist to further modify aspen density to enhance treatment longevity and effectiveness to produce a greater range of boreal mixedwood stand types.
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Gau, C., and C. M. Chung. "Surface Curvature Effect on Slot-Air-Jet Impingement Cooling Flow and Heat Transfer Process." Journal of Heat Transfer 113, no. 4 (November 1, 1991): 858–64. http://dx.doi.org/10.1115/1.2911214.
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Experiments are performed to study surface curvature effects on the impingement cooling flow and the heat transfer processes over a concave and a convex surface. A single air jet issuing from different size slots continuously impinges normally on the concave side or the convexside of a heated semicylindrical surface. An electrical resistance wire is used to generate smoke, which allows us to visualize the impinging flow structure. The local heat transfer Nusselt number along the surfaces is measured. For impingement on a convex surface, three-dimensional counterrotating vortices on the stagnation point are initiated, which result in the enhancement of the heat transfer process. For impingement on a concave surface, the heat transfer Nusselt number increases with increasing surface curvature, which suggests the initiation of Taylor–Go¨rtler vortices along the surface. In the experiment, the Reynolds number ranges from 6000 to 350,000, the slot-to-plate spacing from 2 to 16, and the diameter-to-slot-width ratio D/b from 8 to 45.7. Correlations of both the stagnation point and the average Nusselt number over the curved surface, which account for the surface curvature effect, are presented.
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Ahamed, S., MRH Rakib, and MA Jalil. "Forage growth, biomass yield and nutrient content of two different hybrid Napier cultivars grown in Bangladesh." Bangladesh Journal of Animal Science 50, no. 1 (September 8, 2021): 43–49. http://dx.doi.org/10.3329/bjas.v50i1.55568.
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A 2×3 factorial experiment was conducted to compare two cultivars; Bangladesh Livestock Research Institute developed Napier hybrid-3 (BN-3) (Pennisetum purpureum) and Pakchong-1 (Pennisetum purpureum× P. glaucum) in terms of forage growth, biomass yield, and nutritional quality. Cultivars were cultivated in 03 blocks with 03 replicates and were harvested at 03 cutting periods (40, 50, and 60 days). Plot sizes for each cultivar were 25 m2 (5m × 5m), and in every plot, twenty-five stem cuttings with two healthy nodes per cutting were planted with (1×1) m spacing. The effects of cultivar and cutting period were significant on plant height, leaves per tiller, leaf DM production, and leaf stem ratio (LSR). Highest plant height (P<0.01) and leaves per tiller (P<0.05) were consistently produced by BN-3, while Pakchong-1 produced the highest amount of CP (P<0.05), LSR (P<0.05), tiller diameter (P<0.01) and diameter of the lowest node (P<0.01). Based on the %DM, DM yield, and CP yield, BN-3 performed better cutting at 50 days after the first plantation, but Pakchong-1 performed better cutting at 60 days after the first plantation. From the forage standpoint, Pakchong-1 seems to have little advantages over BN-3 because of its higher DM, LSR, and CP production.
Bang. J. Anim. Sci. 2021. 50 (1):43-49
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Nirmalan, N. V., J. A. Weaver, and L. D. Hylton. "An Experimental Study of Turbine Vane Heat Transfer With Water–Air Cooling." Journal of Turbomachinery 120, no. 1 (January 1, 1998): 50–60. http://dx.doi.org/10.1115/1.2841387.
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This paper presents data showing the improvement in cooling effectiveness of turbine vanes through the application of water–air cooling technology in an industrial/utility engine application. The technique utilizes a finely dispersed water-in-air mixture that impinges on the internal surfaces of turbine airfoils to produce very high cooling rates. An airfoil was designed to contain a standard impingement tube, which distributes the water–air mixture over the inner surface of the airfoil. The water flash vaporizes off the airfoil inner wall. The resulting mixture of air–steam–water droplets is then routed through a pin fin array in the trailing edge region of the airfoil where additional water is vaporized. The mixture then exits the airfoil into the gas path through trailing edge slots. Experimental measurements were made in a three-vane, linear, two-dimensional cascade. The principal independent parameters—Mach number, Reynolds number, wall-to-gas temperature ratio, and coolant-to-gas mass flow ratio—were maintained over ranges consistent with typical engine conditions. Five impingement tubes were utilized to study geometry scaling, impingement tube-to-airfoil wall gap spacing, impingement tube hole diameter, and impingement tube hole patterns. The test matrix was structured to provide an assessment of the independent influence of parameters of interest, namely, exit Mach number, exit Reynolds number, gas-to-coolant temperature ratio, water-and air-coolant-to-gas mass flow ratios, and impingement tube geometry. Heat transfer effectiveness data obtained in this program demonstrated that overall cooling levels typical for air-cooled Vanes could be achieved with the water–air cooling technique with reductions of cooling air flow of significantly more than 50 percent.
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Liu, Wenxiu, and Eric M. Lui. "Mathematical modeling and parametric study of magnetic negative stiffness dampers." Advances in Structural Engineering 23, no. 8 (January 20, 2020): 1702–14. http://dx.doi.org/10.1177/1369433219900289.
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This article presents mathematical modeling and parametric study of a type of magnetic negative stiffness dampers. A magnetic negative stiffness damper uses the interaction forces and movement of magnets inside a conductive pipe to achieve inverse force–deformation response and create frequency dependent damping. One advantage of magnetic negative stiffness dampers over other conventional dampers is that they do not add stiffness to the system and hence will not increase the force in the structural members to which the magnetic negative stiffness damper is attached. Using nonlinear regression analysis, simple formulas to describe the magnetic force and electromagnetic damping of a specific type of magnetic negative stiffness dampers are derived. A parametric study is then performed to show that maximum negative stiffness is obtained when the height-to-diameter (aspect) ratio of the magnets is in the range of 0.3–0.4, and for design applications upper bound values for the clear spacing-to-radius ratio and aspect ratio of the magnets are determined to be 3 and 2, respectively. The highest value of damping coefficient is found to correspond to a magnet aspect ratio of 1.6, and for design purpose the pipe wall thickness should be set equal to the height of the magnet. Based on a pushover analysis of three frames modeled as single-degree-of-freedom systems, it is found that the frame with the magnetic negative stiffness damper experiences lower base shear at the expense of a slightly higher residual drift. The effect of base shear reduction is more pronounced when the target displacement is small.
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Lau, S. C., J. C. Han, and Y. S. Kim. "Turbulent Heat Transfer and Friction in Pin Fin Channels With Lateral Flow Ejection." Journal of Heat Transfer 111, no. 1 (February 1, 1989): 51–58. http://dx.doi.org/10.1115/1.3250657.
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Experiments were conducted to study the effects of lateral flow ejection on the overall heat transfer and pressure drops for turbulent flow through pin fin channels. The two test sections of the investigation were rectangular channels with staggered arrays of six and eight streamwise rows of pins, respectively. The pin length-to-diameter ratio was one and both the streamwise and spanwise pin spacings were 2.5 times the pin diameter. Heat transfer and friction data were obtained for various ejection exit geometries, for ejection ratios between 0 and 1, and for Reynolds numbers between 6000 and 60,000. The results of the study show that, for any given ejection ratio, the overall Nusselt number increases with increasing Reynolds number. However, the overall Nusselt number is reduced by as much as 25 percent as the ejection ratio is increased from 0 to 1 over the range of Reynolds number studied. The Nu–Re–ε relationship, which is insensitive to varying the ejection exit geometry, can be correlated by the equation (Nu/Nu0) = (Nu1/Nu0)ε, where Nu0 = c0Rem and Nu1 = c1Ren are the overall Nusselt numbers in the 0 and 100 percent lateral flow ejection cases, respectively. The results also show that the overall friction factor is independent of the flow Reynolds number over the range of Reynolds number studied. However, the friction factor is strongly dependent on the ejection ratio as well as the geometries of the straight flow exit and lateral ejection flow exit.
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Fahmi, Mohammed, Bukhari Manshoor, Amir Khalid, and Mohammed Al-Hafiz. "Numerical Study of Circle Fractal Grid Perforated Plate as a Turbulent Generator in Combustion Chamber." Applied Mechanics and Materials 663 (October 2014): 387–91. http://dx.doi.org/10.4028/www.scientific.net/amm.663.387.
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Fractal grids can be used to design turbulent flows with low power losses and high turbulence intensities for intense yet economic mixing over a region of designed length and location. The introducing circle grid perforated plate is the main aim of this present paper. In this numerical work, we want to ascertain a new approach in turbulence generators on the structure of premixes flames using perforated plate fractal-grids pattern. In this paper, we compared circle grid perforated plate by varies using its diameters, spacing and number of holes on the plate. The result showed good perceptivity of the fractal generated turbulence and the fractal flow physics. The turbulent intensity can be increased by a grid with higher blockage ratio.
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Seymour, Robert S. "Low-Density Management of White Pine Crop Trees: A Primer and Early Research Results." Northern Journal of Applied Forestry 24, no. 4 (December 1, 2007): 301–6. http://dx.doi.org/10.1093/njaf/24.4.301.
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Abstract Growing white pines at low density after pruning appears to offer many advantages over more conventional silvicultural systems. This article describes how to design and implement a low-density thinning schedule using published relationships between crown architecture and stemwood growth; empirically, appropriate crown development can be maintained by keeping Wilson's spacing/height ratio between 0.4 (before thinning) and 0.5 (residual stand). Short-term results from a replicated thinning study in east central Maine show that diameter growth of heavily released crop trees was 2.8 times that of similar trees in the unthinned controls and 1.6 times that of similar trees in plots thinned to the B line on the pine stocking guide. Despite the important differences in tree development between thinning methods, total stemwood volume growth per acre of the low-density treatment was only 5% less (and not statistically different) than the B-line treatment. Gross stemwood growth was strongly and linearly related to four parameters of stand density; no evidence of an optimum density zone (the Langsaeter hypothesis) was found. The traditional B line on the white pine stocking guide is shown to have little relevance to either low-density or high-production thinning schedules and should be replaced by a more flexible, less prescriptive approach.
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Wadia, A. R., and D. A. Nealy. "Experimental Simulation of Turbine Airfoil Leading Edge Film Cooling." Journal of Turbomachinery 110, no. 2 (April 1, 1988): 226–32. http://dx.doi.org/10.1115/1.3262185.
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Leading edge showerhead cooling designs represent an important feature of certain classes of high-temperature turbine airfoils. This paper outlines a methodology for predicting the surface temperatures of showerhead designs with spanwise injection through an array of discrete holes. The paper describes a series of experiments and analyses on scaled cylinder models with injection through holes inclined at 20, 30, 45, and 90 deg for typical radial and circumferential spacing-to-diameter ratios of 10 and 4, respectively. The experiments were conducted in a wind tunnel on several stainless steel test specimens in which flow and heat transfer parameters were measured over the simulated airfoil leading edge surfaces. Based on the experiments, an engineering design model is proposed that treats the gas-to-surface heat transfer coefficient with film cooling in a manner suggested by a recent Purdue–NASA investigation and includes the important contribution of upstream (coolant inlet face) heat transfer. The experiments suggest that the averaged film cooling effectiveness in the showerhead region is primarily influenced by the inclination of the injection holes. The effectiveness parameter is not strongly affected by variations in coolant-to-gas stream pressure ratio, free-stream Mach number, gas-to-coolant temperature ratio, and gas stream Reynolds number. The model is employed to determine (inferentially) the average Stanton number reduction parameter for a series of pressure ratios varying from 1.004 to 1.3, Mach numbers ranging from 0.1 to 0.2, temperature ratios between 1.6 and 2.0, and Reynolds numbers ranging from 3.5×104 to 9.0×104.
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Ahmad, Shafee, and Shams Ul-Islam. "Numerical Investigation of Fluid Flow past Four Cylinders at Low Reynolds Numbers." Mathematical Problems in Engineering 2021 (July 26, 2021): 1–24. http://dx.doi.org/10.1155/2021/1127324.
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A numerical investigation on the effects of separation ratios and Reynolds numbers on the flow around four square cylinders in diamond arrangement has been carried out using the lattice Boltzmann method. The separation ratios between the cylinders vary from g ∗ = 1 to 15. The Reynolds numbers based on the diameter of the square cylinder and the inlet uniform inflow velocity are selected from Re = 80 to 160. The computations show that a total of five different flow regimes are observed over the selected ranges: single bluff-body, quasi-unsteady, chaotic flow, in-phase synchronized vortex shedding, and antiphase synchronized vortex shedding flow regimes. It is found that the flow features significantly depend on both the separation ratio and Reynolds number, with the former’s influence being more than the latter’s. We found that the critical spacing for four square cylinders in diamond arrangement for selected Reynolds numbers (80 ≤ Re ≤ 160) is in the range of 2 ≤ g ∗ ≤ 5. The results reveal that the presence of secondary cylinder interaction frequencies indicates that, for chaotic flow regime, the wake pattern is not stable and there is a strong interaction of gap flows and continuous change in the direction of shed vortices behind the cylinders. The effects of the g ∗ and Re on fluid forces, vortex shedding frequency, and flow separation have been examined in detail.
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Yokoyama, Kazushige, Kieran Brown, Peter Shevlin, Jack Jenkins, Elizabeth D’Ambrosio, Nicole Ralbovsky, Jessica Battaglia, Ishan Deshmukh, and Akane Ichiki. "Examination of Adsorption Orientation of Amyloidogenic Peptides Over Nano-Gold Colloidal Particle Surfaces." International Journal of Molecular Sciences 20, no. 21 (October 28, 2019): 5354. http://dx.doi.org/10.3390/ijms20215354.
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The adsorption of amyloidogenic peptides, amyloid beta 1–40 (Aβ1–40), alpha-synuclein (α-syn), and beta 2 microglobulin (β2m), was attempted over the surface of nano-gold colloidal particles, ranging from d = 10 to 100 nm in diameter (d). The spectroscopic inspection between pH 2 and pH 12 successfully extracted the critical pH point (pHo) at which the color change of the amyloidogenic peptide-coated nano-gold colloids occurred due to aggregation of the nano-gold colloids. The change in surface property caused by the degree of peptide coverage was hypothesized to reflect the ΔpHo, which is the difference in pHo between bare gold colloids and peptide coated gold colloids. The coverage ratio (Θ) for all amyloidogenic peptides over gold colloid of different sizes was extracted by assuming Θ = 0 at ΔpHo = 0. Remarkably, Θ was found to have a nano-gold colloidal size dependence, however, this nano-size dependence was not simply correlated with d. The geometric analysis and simulation of reproducing Θ was conducted by assuming a prolate shape of all amyloidogenic peptides. The simulation concluded that a spiking-out orientation of a prolate was required in order to reproduce the extracted Θ. The involvement of a secondary layer was suggested; this secondary layer was considered to be due to the networking of the peptides. An extracted average distance of networking between adjacent gold colloids supports the binding of peptides as if they are “entangled” and enclosed in an interfacial distance that was found to be approximately 2 nm. The complex nano-size dependence of Θ was explained by available spacing between adjacent prolates. When the secondary layer was formed, Aβ1–40 and α-syn possessed a higher affinity to a partially negative nano-gold colloidal surface. However, β2m peptides tend to interact with each other. This difference was explained by the difference in partial charge distribution over a monomer. Both Aβ1–40 and α-syn are considered to have a partial charge (especially δ+) distribution centering around the prolate axis. The β2m, however, possesses a distorted charge distribution. For a lower Θ (i.e., Θ <0.5), a prolate was assumed to conduct a gyration motion, maintaining the spiking-out orientation to fill in the unoccupied space with a tilting angle ranging between 5° and 58° depending on the nano-scale and peptide coated to the gold colloid.
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Kure, Nicodemus, Isaac Hyuk Daniel, B. U. Machu, I. A. Bello, and M. Ansnawi. "COMPARATIVE STUDY ON THE SYNTHESES OF CARBON NANOMATERIALS USING POLYETHYLENE AND RISK HUSK AS CARBON PRECURSOR." FUDMA JOURNAL OF SCIENCES 4, no. 3 (September 30, 2020): 731–34. http://dx.doi.org/10.33003/fjs-2020-0403-315.
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The study compares the syntheses of carbon nanostructures (CNS) using polyethylene (PE) and Rice husk (RH) as carbon precursor via commercial microwave oven at 2.45 GHz. The Microwave energy offers the requisite temperature for catalytic disintegration of the carbon precursors at 750 °C under atmospheric pressure. The CNS were grown on coated silicon dioxide. The as-synthesized CNS was analysed with Raman spectroscopy which shows carbon quality was found to be 0.92 and 1.01 in PE and RH respectively, indicating good graphitic nature with average diameter at (16.0 to 20.0) ± 0.5 nm. The high intensity ratio is attributed to the defect mode in the CNS. The Field Emission Scanning Microscope (FESEM) analysis shows a warped and randomly oriented structures with an interlayer spacing of about 0.35 nm in the internal structure of most CNS. Furthermore, the level of purity in the graphitic nature of the CNS were obtained with Thermogravimetric Analysis (TGA) technique with 90 % in PE and 50 % in RH. Hence, a fast and cheaper method of synthesizing CNS utilizing microwave energy was demonstrated at 750 °C under atmospheric pressure. Lastly, the presence of catalyst, carbon precursors and plasma are necessary for the microwave heating and synthesis process.
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Stage, Albert R., and Thomas Ledermann. "Effects of competitor spacing in a new class of individual-tree indices of competition: semi-distance-independent indices computed for Bitterlich versus fixed-area plots." Canadian Journal of Forest Research 38, no. 4 (April 2008): 890–98. http://dx.doi.org/10.1139/x07-192.
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We illustrate effects of competitor spacing for a new class of individual-tree indices of competition that we call semi-distance-independent. This new class is similar to the class of distance-independent indices except that the index is computed independently at each subsampling plot surrounding a subject tree for which growth is to be modelled. We derive the effects of distance for this class as the expected value over independent samples containing a particular subject tree. In a previous paper, we illustrated distance effects implicit in eight indices of the distance-dependent class. Here, we present distance effects of four semi-distance-independent indices: density, sum of diameters, basal area, and tree-area ratio; each determined for small fixed-area plots of 0.04 ha and for Bitterlich samples of 6 m2·ha–1. We show that several members of this new class have distance effects very similar to the distance-dependent class and should, therefore, be equally effective in accounting for competitive effects in individual-tree increment models. The comparisons should inform selection of competition indices and sampling designs for growth modelling.
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Zhou, Jian, Claudia Cenedese, Tim Williams, Megan Ball, Subhas K. Venayagamoorthy, and Roger I. Nokes. "On the propagation of gravity currents over and through a submerged array of circular cylinders." Journal of Fluid Mechanics 831 (October 13, 2017): 394–417. http://dx.doi.org/10.1017/jfm.2017.604.
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The propagation of full-depth lock-exchange bottom gravity currents past a submerged array of circular cylinders is investigated using laboratory experiments and large eddy simulations. Firstly, to investigate the front velocity of gravity currents across the whole range of array density $\unicode[STIX]{x1D719}$ (i.e. the volume fraction of solids), the array is densified from a flat bed ($\unicode[STIX]{x1D719}=0$) towards a solid slab ($\unicode[STIX]{x1D719}=1$) under a particular submergence ratio $H/h$, where $H$ is the flow depth and $h$ is the array height. The time-averaged front velocity in the slumping phase of the gravity current is found to first decrease and then increase with increasing $\unicode[STIX]{x1D719}$. Next, a new geometrical framework consisting of a streamwise array density $\unicode[STIX]{x1D707}_{x}=d/s_{x}$ and a spanwise array density $\unicode[STIX]{x1D707}_{y}=d/s_{y}$ is proposed to account for organized but non-equidistant arrays ($\unicode[STIX]{x1D707}_{x}\neq \unicode[STIX]{x1D707}_{y}$), where $s_{x}$ and $s_{y}$ are the streamwise and spanwise cylinder spacings, respectively, and $d$ is the cylinder diameter. It is argued that this two-dimensional parameter space can provide a more quantitative and unambiguous description of the current–array interaction compared with the array density given by $\unicode[STIX]{x1D719}=(\unicode[STIX]{x03C0}/4)\unicode[STIX]{x1D707}_{x}\unicode[STIX]{x1D707}_{y}$. Both in-line and staggered arrays are investigated. Four dynamically different flow regimes are identified: (i) through-flow propagating in the array interior subject to individual cylinder wakes ($\unicode[STIX]{x1D707}_{x}$: small for in-line array and arbitrary for staggered array; $\unicode[STIX]{x1D707}_{y}$: small); (ii) over-flow propagating on the top of the array subject to vertical convective instability ($\unicode[STIX]{x1D707}_{x}$: large; $\unicode[STIX]{x1D707}_{y}$: large); (iii) plunging-flow climbing sparse close-to-impermeable rows of cylinders with minor streamwise intrusion ($\unicode[STIX]{x1D707}_{x}$: small; $\unicode[STIX]{x1D707}_{y}$: large); and (iv) skimming-flow channelized by an in-line array into several subcurrents with strong wake sheltering ($\unicode[STIX]{x1D707}_{x}$: large; $\unicode[STIX]{x1D707}_{y}$: small). The most remarkable difference between in-line and staggered arrays is the non-existence of skimming-flow in the latter due to the flow interruption by the offset rows. Our analysis reveals that as $\unicode[STIX]{x1D719}$ increases, the change of flow regime from through-flow towards over- or skimming-flow is responsible for increasing the gravity current front velocity.
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Atofarati, E. O., A. O. Muritala, B. O. Malomo, and S. A. Adio. "Control of vortex shedding around a circular cylinder using bubble tabs in the laminar flow regime." Nigerian Journal of Technology 39, no. 4 (March 24, 2021): 1108–16. http://dx.doi.org/10.4314/njt.v39i4.18.
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Vortex induced vibration (VIV) is the major cause of several catastrophic disasters due to fatigue failures induced by drag and lift forces in aerodynamic systems. This study investigates the control of VIV phenomenon through passive bubble tab(s) having a small diameter (d) relative to the main circular cylinder (D) in a two-dimensional (2-D) flow domain. Using ANSYS Fluent computational software, flow analysis was conducted at a Reynolds number (Re) of 80 for various bubble tab configurations at different spacing ratios (x/D) and diameter ratios (d/D). The drag coefficient, the velocity and pressure contours, along with the flow streamlines in eachcase were studied. The results indicated the optimized tab(s) positions for different spacing ratios, diameter ratios, and configurations. The study effectively established that passive bubble tabs can potentially control VIV associated with flows around a circular cylinder.
Keywords: Vortex Shedding; Drag Coefficient; Circular Cylinder; Bubble Tab(S); Spacing Ratio; Diameter Ratio.
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Li, Xiao Bing, and Ying Liu. "Contact Angle Model and Wettability of Regular Microsurfaces." Advanced Materials Research 199-200 (February 2011): 678–82. http://dx.doi.org/10.4028/www.scientific.net/amr.199-200.678.
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Wettability of solid surfaces is one of very important properties, which is governed by both the interface energy and the microstructures. In the paper, four microstructure surfaces were designed such as square concave, column concave, square convex and column convex. The contact angle and wettability of solid surfaces with regular microstructures were discussed for five contact angle models such as Young, Wenzel, Cassie, Cassie-Baxter and Wenzel-Cassie models. Then, the impacts of interfacial energy and microstructures to wettability were analyzed. The study shows that the character of hydrophobic or hydrophilic is decided by the interfacial energy between solid and liquid, and the wettability can be changed by adjusting the parameters of microstructures, such as the ratio of transverse spacing and diameter α, the ratio of longitudinal spacing and diameter β, the ratio of the deep and diameter γ or the ratio of soaking deep and diameter λ. And, the convex microstructure is more propitious to hydrohobic surface than concave microstructure.
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Lugo, Ariel E., and Julio Figueroa. "Performance of Anthocephaluschinensis in Puerto Rico." Canadian Journal of Forest Research 15, no. 3 (June 1, 1985): 577–85. http://dx.doi.org/10.1139/x85-094.
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The growth of kadam (Anthocephaluschinensis (Lam.) A. Rich. ex Walp.), a fast-growing Asiatic species, was studied under different soil and climatic conditions in Puerto Rico. Plantings included a 10-year-old line planting, a 12.5-year-old plantation, 12 localities with 20-year-old single tree plots, and 1 locality with four 52-year-old trees. Over 600 trees were measured in all. Growth rates were comparable to those of fast-growing species elsewhere in the tropics; e.g., the 12.5-year-old plantation had a volume growth of 27.8 m3•ha−1•year−1 (77% was merchantable wood), a basal area growth of 1.82 m2•ha−1•year−1, and a total aboveground biomass production of 11.5 t•ha−1•year−1. Trees grew well both in plantations and in lines under natural forest. The 20-year-old single tree plots averaged up to 1 m•year−1 in height growth and 53 cm2•year−1 in basal area growth. Highest rates were observed in localities with high annual rainfall (>2500 mm) and with phosphorus- and silt-rich soils of high bulk density and low pH. After 10 years, basal area growth of trees was fastest in volcanic deep clay locations, followed, in order, by trees on volcanic shallow loams, calcareous soils, and plutonic sandy loams. However, basal area growth during the first 5 years was fastest in the plutonic sandy loams and slowest in the calcareous soils. After 20 years, volcanic deep clay soils still supported the fastest basal area growth rate (about 100 cm2•year−1), while the other locations converged at about 30 cm2•year−1. Trees reached maximum height after 20 years (average, 19 m; maximum, 26.5 m). Kadam growth was limited by close spacings (below 2.5 × 2.5 m). Trees exhibited excellent form (ratio of diameter at 1.3 m to diameter at 4.9 m > 0.8). We found no evidence of pest or disease attacks on trees, but noted severe tapering and stem twist in localities having poor growth rates. Results underline the need for caution when making species adaptability assessments in the tropics with short-term (<10 years) data.
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Jiao, Jun Ting, and Rong Hua Yang. "Sensitivity Parameter Analysis of Bearing Capacity and Ductility of Reinforced Concrete Columns with Z-Shaped Cross-Section." Advanced Materials Research 831 (December 2013): 158–63. http://dx.doi.org/10.4028/www.scientific.net/amr.831.158.
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In order to select sensitivity parameter of bearing capacity and ductility, the orthogonal design method was used to research reinforced concrete (RC) columns with Z-shaped cross-section under compression and bending, by the nonlinear analysis computer program of RC columns with irregularly-shaped cross-section. The seven parameters and four levels of orthogonal design were researched, for example ratio of limb length to limb thickness, ratio of axial compression, loading angle, concrete strength, long reinforce ratio, stirrup diameter and stirrup spacing. The results indicated that the best sensitivity factor of bearing capacity was ratio of limb length to limb thickness, next were loading angle and long reinforce ratio; the best sensitivity factor of ductility was ratio of axial compression, next were stirrup diameter and stirrup spacing. These would afford references for the design of RC columns with Z-shaped cross-section.
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Gao, Chao, Haiwang Li, Huimin Zhou, Yiwen Ma, and Ruquan You. "Numerical investigation about backflow of film cooling in static turbine blade leading edge." Advances in Mechanical Engineering 11, no. 11 (November 2019): 168781401988581. http://dx.doi.org/10.1177/1687814019885817.
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In this article, film cooling characteristics, especially the phenomenon of backflow for the straight turbine blade leading edge, are investigated. Shear stress transport k-ω turbulence model and structured grids are employed to assure the accuracy of the simulation, and the computational method is verified by the available experimental data. The influences of blow ratio, hole diameter, and the spacing between holes in each row are analyzed. The formation mechanism of backflow is discussed to prevent it from happening or relieve the degree of backflow, thereby to improve the cooling efficiency. The results showed that backflow can be avoided by adjusting the structure and the layout of film cooling holes. With increase in blow ratio, the cooling film becomes more obvious at first and then fades gradually for departing from the blade surface. The jet flow is influenced by the total pressure ratio between coolant cavity and surface of blade leading edge. Smaller film hole diameter and larger hole spacing makes it easier to eject coolant and form continuous film by slowing down the pressure in the cavity. Increasing ratio of hole spacing to hole diameter ( p/ d) can effectively prevent backflow, whereas larger p/ d also makes the film coverage area smaller.
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Hoang, Huy T., and Hamid R. Rahai. "The Distortion of a Jet by Coil Inserts." Journal of Fluids Engineering 124, no. 2 (May 28, 2002): 500–504. http://dx.doi.org/10.1115/1.1470476.
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Results of experimental investigations of the effects of distortion caused by coil inserts on a turbulent jet are presented. The coils have different wire diameters with constant pitch spacing. The ratios of the coil wire diameter to the tube inside diameter, d/D, are 0.06, 0.08, 0.11, 0.13, and 0.16 and the ratio of the pitch spacing to the tube inside diameter, p/D, is 1.2. Results show that the coil inserts enhance the mixing process. At the jet-outlet, mixing enhancement is increased when d/D<0.1. However, further downstream, the highest mixing is achieved for the coil with the largest d/D ratio. Results suggest that the streamwise vortices generated by the coil inserts are the mechanism behind the high entrainments and the mixing process.
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Li, Zhe, Shao Ji Chen, Cui Ping Zhang, and Shuai Zhang. "Study on the Bearing Capacity and Ductility of Steel Reinforced Concrete T-Shaped Columns." Advanced Materials Research 368-373 (October 2011): 28–32. http://dx.doi.org/10.4028/www.scientific.net/amr.368-373.28.
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Compared with reinforced concrete shaped columns, bearing capacity and ductility of steel reinforced concrete shaped columns are significantly improved, so it is with theoretical significance and practical application of value to research. Based on the plain cross section presume, with material T-section boundary calculation unit, 15 steel reinforced concrete T-shaped columns(SRCTSC) have made nonlinear full-rang numerical analysis. It demonstrates that the most adverse curvature ductility load angle of SRCCRSC is 180°.Loading angle ( ), axial compression ratio ( ), and the ratio of spacing and diameter of longitudinal reinforcements (s/d) are the principal factors in curvature ductility of SRCTSC subjected to biaxial eccentric compression. It include 36 sets for load angle, 6 sets for axial load ratio, 3 sets for concrete strength, 3 sets for the content of steel, 2 sets for steel style, 3 sets for stirrup ratio, 3 sets for steel location, 3 sets for section size, 3 sets for stirrup diameter about SRCTSC. The ductile behavior of T-shaped, with calculating 1068 loading conditions, are investigated. It concluded that axial load ratio, load angle, and ratio of the spacing of stirrups and longitudinal reinforcement’s diameter (s/d) are most important factors.
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Lian, Y., Z. Xu, H. Pei, C. Liang, Y. Zhang, Z. Wen, and Z. Yue. "Influence of Film-Cooling Hole Arrangement on Mechanical Properties of Cooled Turbine Blade Based on the Crystal Plastic Theory." Journal of Mechanics 35, no. 6 (August 8, 2019): 809–28. http://dx.doi.org/10.1017/jmech.2019.4.
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ABSTRACTThe crystal plastic theory was used to examine the effect of film-cooling hole arrangements on mechanical properties of cooled turbine blade. The finite element method was used to analyze the maximum von Mises stress and resolved shear stress of an octahedral slip system considering the number of rows, diameter, spacing, and tangential-to-longitudinal hole spacing (h/l) ratio. The different arrangements were found to have a significant influence on the maximum von Mises stress and resolved shear stress. For the triangular arrangement, the von Mises stress and resolved shear stress were highest with double rows, followed by a single row and then triple rows. For the quadrilateral arrangement, the stresses were highest with double rows, followed by triple rows and then a single row. Increasing the spacing or decreasing the diameter reduced the maximum von Mises stress and weakened the multi-hole interference effect. Both the maximum von Mises stress and resolved shear stress decreased with the h/l ratio.
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Choi, JinSeok, TianFeng Yuan, SeHee Hong, and YoungSoo Yoon. "Evaluating of Electromagnetic Shielding Characteristics of Reinforced Concrete Using Reinforcing Details." Journal of the Korean Society of Hazard Mitigation 20, no. 5 (October 31, 2020): 245–54. http://dx.doi.org/10.9798/kosham.2020.20.5.245.
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In this study, experimental tests were performed to determine the electromagnetic shielding characteristics of reinforced concrete based on the thickness of concrete and rebar. In addition, the electromagnetic shielding characteristics based on the steel-fiber volume ratio and rebar spacing of fiber-reinforced concrete were evaluated. Concrete showed significant Shielding Effectiveness (SE) in a high-frequency band with increasing thickness, but the rebar exhibited significant SE in the low-frequency band with increasing diameter, decreasing rebar spacing, and increasing layer. The SE increased with the steel fiber volume ratio, and it also increased owing to the decrease in the rebar spacing for 1.5 vol.% steel fibers.
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Moriya, M., and H. Sakamoto. "Effect of a Vibrating Upstream Cylinder on a Stationary Downstream Cylinder." Journal of Fluids Engineering 108, no. 2 (June 1, 1986): 180–84. http://dx.doi.org/10.1115/1.3242560.
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The flow around two circular cylinders in tandem arrangement in uniform flow where the upstream cylinder is forcibly vibrated in direction normal to the approach flow was experimentally studied at Reynolds number of 6.54 × 104. The spacing ratio 1/d (1: distance between centers of cylinders, d: diameter of circular cylinders) and the ratio of amplitude to cylinder diameter a/d (a: amplitude of transverse vibration of cylinder) were varied from 2 to 6 and 0 to 0.029 respectively. The effects of the vibration of the upstream cylinder on the downstream cylinder were discussed. In particular, two distinct “lock-in” regions were observed when the upstream cylinder was vibrated with a spacing ratio of 1/d = 3.0. The cylinder vibration was so effective even for a/d as small as 0.017 to cause two different flow patterns.
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Bach Vu Hoang, Lan. "Static loading tests on small-scale pile groups." Transport and Communications Science Journal 72, no. 1 (January 25, 2021): 84–94. http://dx.doi.org/10.47869/tcsj.72.1.10.
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36 small-scale model tests in soft clay were conducted to research the performances of pile groups under rigid caps. The parameters studied were the effect of pile length, pile spacing, and the number of piles in a group. The group piles consisted of 4, 6, and 9 circular model piles of 16mm in outer diameter (D), while four kinds of the pile spacing between pile centers 3; 4; 5; and 6 times of the diameter and three types of the embedded pile lengths: 20D; 25D; and 30D were used. For comparison, three single piles with the same diameter and length were also tested under the same condition. The experimental results were discussed based on the following 3 points of view: the pile group efficiency, the settlement ratio, load distribution per pile location in the group pile. All discussion suggested that the pile number and pile spacing in a pile group caused a remarkable interactional effect between piles, whereas the settlement ratios are significantly affected by the pile length. Besides, each pile in the group of 6D pile spacing behaved more individually.
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Gao, Yang-yang, Chang-shan Yin, Hao-qiang Zhang, Kang Yang, Xi-zeng Zhao, and Zhilin Sun. "Numerical Study on Flow around Four Square-Arranged Cylinders at Low Reynolds Numbers." Mathematical Problems in Engineering 2017 (2017): 1–18. http://dx.doi.org/10.1155/2017/6381256.
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In this paper, numerical simulations of flow past four square-arranged cylinders are carried out at different spacing ratios (1.5≤L/D≤5.0; L is the center to center distance; D is the cylinder diameter) and Reynolds numbers (100≤Re≤1000). The effects of spacing ratio and Reynolds number on the wake flow characteristics are investigated, such as the instantaneous vorticity contours, force coefficients, and vortex shedding frequencies. The results show that the flow characteristics behind the four-cylinder cases are significantly affected by the spacing ratios and Reynolds numbers. At the same spacing ratio, the transformation of flow pattern is advanced quickly with increasing of Reynolds numbers, the values of force coefficients are correspondingly fluctuated with large amplitude, and the vortex shedding frequency is increased significantly with Re.
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Omari, Kwadwo, John Marty Kranabetter, and Louise de Montigny. "Productivity of coastal Douglas-fir and western redcedar in response to species mixture, planting density, and soil carbon:nitrogen ratio." Canadian Journal of Forest Research 51, no. 5 (May 2021): 668–74. http://dx.doi.org/10.1139/cjfr-2020-0223.
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Mixed-species plantations have been suggested as ecologically and economically viable alternatives to monocultures. We examined the growth response of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) and western redcedar (Thuja plicata Donn ex D. Don in Lamb.) to different species mixtures (Douglas-fir : western redcedar mixtures of 1:0, 1:1, 1:3, and 0:1) and planting densities (500, 1000, and 1500 stems·ha−1) in a dry maritime forest on eastern Vancouver Island, Canada. Twenty-two years postplanting, species mixture significantly affected diameter and height growth (p < 0.001), with stand diameter and height generally decreasing with increasing redcedar composition. Inherent variation in soil productivity across the plantation (carbon:nitrogen ratio) equally constrained stand growth. The widest spacing had larger diameter than the closest spacing (p = 0.025) but the least stand basal area compared with the other spacing treatments (p = 0.003–0.031). Stand volume was significantly affected by mixture × density interaction (p = 0.024) and generally declined with increasing proportion of redcedar and decreasing stand density. In the first decades after plantation establishment, inherent species growth traits and soil fertility were most important in dictating stand productivity. Because of the differences in resource utilization of both species, stand dynamics may change as competition for light and soil resources increases. Evaluation of silvicultural recommendations regarding mixtures of both species will continue with plantation development.
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Sharma, Mahadev, Harold E. Burkhart, and Ralph L. Amateis. "Spacing rectangularity effect on the growth of loblolly pine plantations." Canadian Journal of Forest Research 32, no. 8 (August 1, 2002): 1451–59. http://dx.doi.org/10.1139/x02-079.
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The effect of spacing rectangularity on tree growth and stand development was evaluated using tree data obtained annually from a loblolly pine (Pinus taeda L.) spacing trial monitored through age 16 years. In this trial, plots with an initial planting density of 2240 trees/ha occur at slightly and highly rectangular spacings. Spacings with rectangularities 3:4 and 1:3 were used to evaluate the rectangularity effect. Survival and the development of height, diameter, volume per hectare, and basal area per hectare of loblolly pine trees were not affected by rectangularity. Diameter and height distributions were found to be a function of age but not a function of the rectangularity of initial spacing. Crown width, however, was affected by rectangularity. The crown width was larger at larger row or column distance than at smaller row or column distance, but the ratio of crown widths between and within rows was not equal to the rectangularity of the original planting spacing.
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Tandel, Yogendra K., Chandresh H. Solanki, and Atul K. Desai. "3D FE Analysis of an Embankment Construction on GRSC and Proposal of a Design Method." ISRN Civil Engineering 2013 (March 7, 2013): 1–11. http://dx.doi.org/10.1155/2013/348973.
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Stone column is often employed for strengthening of an embankment seated on deep soft clay. But in very soft clay having undrained shear strength less than or equal to 15 kPa, stone column may not derive adequate load carrying capacity and undergo large lateral deformation due to inadequate lateral confinement. In such circumstances, reinforcement to individual stone column by geosynthetics enhances load carrying capacity and reduces lateral deformation. This paper addresses parametric study on behaviour of embankment resting on Geosynthetic Reinforced Stone Column (GRSC) considering parameters such as stone column spacing to diameter ratio, deformation modulus of stone column material, geosynthetic stiffness, thickness of soft clay, and height of embankment by 3D numerical analysis. Finally, equation for Settlement Improvement Factor (SIF), defined as ratio between settlement of embankment without treatment and with geosynthetic reinforced stone column, is proposed that correlates with the major influence parameters such as stone column spacing to diameter ratio, deformation modulus of soft clay, and geosynthetic stiffness.
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Liu, Bing-Rui, Jian-Zhong Lin, and Xiao-Ke Ku. "Migration and Alignment of Three Interacting Particles in Poiseuille Flow of Giesekus Fluids." Fluids 6, no. 6 (June 11, 2021): 218. http://dx.doi.org/10.3390/fluids6060218.
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Effect of rheological property on the migration and alignment of three interacting particles in Poiseuille flow of Giesekus fluids is studied with the direct-forcing fictitious domain method for the Weissenberg number (Wi) ranging from 0.1 to 1.5, the mobility parameter ranging from 0.1 to 0.7, the ratio of particle diameter to channel height ranging from 0.2 to 0.4, the ratio of the solvent viscosity to the total viscosity being 0.3 and the initial distance (y0) of particles from the centerline ranging from 0 to 0.2. The results showed that the effect of y0 on the migration and alignment of particles is significant. The variation of off-centerline (y0 ≠ 0) particle spacing is completely different from that of on-centerline (y0 = 0) particle spacing. As the initial vertical distance y0 increased, the various types of particle spacing are more diversified. For the off-centerline particle, the change of particle spacing is mainly concentrated in the process of cross-flow migration. Additionally, the polymer extension is proportional to both the Weissenberg number and confinement ratio. The bigger the Wi and confinement ratio is, the bigger the increment of spacing is. The memory of shear-thinning is responsible for the reduction of d1. Furthermore, the particles migrate abnormally due to the interparticle interaction.
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Amiri, Amin, Alimohammad Karami, Tooraj Yousefi, and Mohammad Zanjani. "Artificial neural network to predict the natural convection from vertical and inclined arrays of horizontal cylinders." Polish Journal of Chemical Technology 14, no. 4 (December 1, 2012): 46–52. http://dx.doi.org/10.2478/v10026-012-0101-6.
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Abstract The main focus of the present study is to utilize the artificial neural network (ANN) in predicting the natural convection from horizontal isothermal cylinders arranged in vertical and inclined arrays. The effects of the vertical separation spacing to the cylinder diameter ratio (Py/d), horizontal separation spacing to the cylinder diameter ratio (Px/d) and Rayleigh number (Ra) variation on the average heat transfer from the arrays are considered via this prediction. The training data for optimizing the ANN structure is based on available experimental data. The Levenberg-Marquardt back propagation algorithm is used for ANN training. The proposed ANN is developed using MATLAB functions. For the best ANN structure obtained in this investigation, the mean relative errors of 0.027% and 0.482% were reached for the training and test data, respectively. The results show that the predicted values are very close to the experimental ones.
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Liegel, L. H., W. E. Balmer, and G. W. Ryan. "Honduras Pine Spacing Trial Results in Puerto Rico." Southern Journal of Applied Forestry 9, no. 2 (May 1, 1985): 69–75. http://dx.doi.org/10.1093/sjaf/9.2.69.
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Abstract Puerto Rico has one of the oldest, continuously measured spacing trials of Honduras pine (Pinus caribaea mor. hondurensis) in existence. At 18 to 20 years, mean survival for all the trial sites except one that suffered hurricane damage in 1979 was 82%. Survival was not related to the triangular spacing treatments of 5, 7, 10, and 14 feet. But spacing did influence diameter growth at all four sites and affected height growth at all but one site Each site had trees ≥100 feet tall at 18 to 20 years; on the two best sites, individual trees reached 90 feet by 12 years. At close spacings, mean annual height increments peaked at 4.0 to 4.5 years on two sites and at 7.2 years on the other two sites. Mean annual diameter increments peaked even earlier, at 3.0 to 3.5 years on the two good sites and at 6.0 years on the two poorer sites. Early effects of competition in reducing both mean annual height and diameter growth, particularly at close spacings, have several managerial implications. The most striking are: (1) underestimating site quality or site index if growth assessments are made only in dense stands, and (2) significant loss of wood volume over long rotations when managers fail to time thinnings before mean annual height and diameter increments decrease.
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Liu, Xiaolan, Xianmin Zhang, and Yadong Wang. "A Rapid Detection Method for Bridges Based on Impact Coefficient of Standard Bumping." Mathematical Problems in Engineering 2018 (September 30, 2018): 1–14. http://dx.doi.org/10.1155/2018/9195289.
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The evaluation method of load transfer efficiency using falling weight deflectometer is unworkable in remote mountain areas and transportation difficult region. Therefore, a novation method of load transfer efficiency evaluation is proposed using the index of amplitude ratio. Finite element method is applied to study the influence of dowel bar parameters (diameter, length, spacing, and elastic modulus) and pavement structures parameters (thickness and modulus) on load transfer efficiency, frequency, and the ratio of amplitude. Results of finite element model show that the effects of dowel bar and pavement structure parameters on load transfer efficiency and the ratio of amplitude are similar. The load transfer efficiency, frequency, and the ratio of amplitude enhance with the increase of dowel bar diameter, length, and elastic modulus and the decrease of dowel bar spacing. The subgrade modulus has more significant influence on the load transfer efficiency, frequency, and the ratio of amplitude than other pavement parameters. Polynomial function method is utilized to established load transfer mode between deflection-based load transfer efficiency and the ratio of amplitude. The feasibility and reliability of new method is verified by static and dynamic load test. All results are helpful for the development of highway engineering and airport engineering.
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Saud, Pradip, Thomas B. Lynch, Anup K. C., and James M. Guldin. "Using quadratic mean diameter and relative spacing index to enhance height–diameter and crown ratio models fitted to longitudinal data." Forestry 89, no. 2 (February 10, 2016): 215–29. http://dx.doi.org/10.1093/forestry/cpw004.
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MAMNOIE, Ebrahim, and Ali DOLATKHAHI. "Plant Spacing and Cultivar Affects Yield Components, Qualitative Traits and Early Ripening of Tomato (Lycopersicon esculentum)." Notulae Scientia Biologicae 5, no. 4 (December 15, 2013): 494–98. http://dx.doi.org/10.15835/nsb549210.
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Two-year field trial was set up on sandy clay soil in the Jiroft and Kahnouj Agricultural Research Center with the objective to determine the effect of plant spacing and different cultivars on the yield and qualitative characteristics of tomato (Lycopersicon esculentum). This experiment was performed as split plot based on complete randomized block design with 3 replications. The main plots were in – row
spacing in 4 levels include 0.3, 0.4, 0.5 and 0.6 m and the subplots were cultivars naming ‘Shef ’, ‘Peto Early CH’ and ‘FDT 202’. The results showed that, fruit length to diameter ratio, total acidity, fruit number per plant, mean fruit weight, yield per plant, total yield and first harvest to total harvests ratio were significantly affected by plant spacing. In addition, cultivars showed significant effect on all traits evaluated (p
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Gautam, Siddharth, and David Cole. "CO2 Adsorption in Metal-Organic Framework Mg-MOF-74: Effects of Inter-Crystalline Space." Nanomaterials 10, no. 11 (November 17, 2020): 2274. http://dx.doi.org/10.3390/nano10112274.
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Metal-Organic Frameworks (MOF) have been identified as highly efficient nanoporous adsorbents for CO2 storage. In particular, Mg-MOF-74 has been shown to promise exceptionally high CO2 sorption. Although several studies have reported adsorption isotherms of CO2 in Mg-MOF-74, the effect of inter-crystalline spacing in Mg-MOF-74 on the sorption of CO2 has not been addressed. These effects have been shown to be profound for a quadrupolar molecule like CO2 in the case of silicalite (Phys. Chem. Chem. Phys. 22 (2020) 13951). Here, we report the effects of inter-crystalline spacing on the adsorption of CO2 in Mg-MOF-74, studied using grand canonical Monte Carlo (GCMC) simulations. The inter-crystalline spacing is found to enhance adsorption at the crystallite surfaces. Larger inter-crystalline spacing up to twice the kinetic diameter of CO2 results in higher adsorption and larger crystallite sizes suppress adsorption. Magnitudes of the inter-crystalline space relative to the kinetic diameter of the adsorbed fluid and the surface to volume ratio of the adsorbent crystallites are found to be important factors determining the adsorption amounts. The results of this study suggest that the ideal Mg-MOF-74 sample for CO2 storage applications should have smaller crystallites separated from each other with an inter-crystalline space of approximately twice the kinetic diameter of CO2.
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Santos, Lúcia F., A. Sofia Silva, Clara R. Correia, and João F. Mano. "Physical immobilization of particles inspired by pollination." Proceedings of the National Academy of Sciences 116, no. 12 (March 4, 2019): 5405–10. http://dx.doi.org/10.1073/pnas.1813336116.
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Biomimetic systems often exhibit striking designs well adapted to specific functions that have been inspiring the development of new technologies. Herein, we explored the remarkable ability of honey bees to catch and release large quantities of pollen grains. Hair spacing and height on bees are crucial for their ability to mechanically fix pollen grains. Inspired by this, we proposed the concept of a micropatterned surface for microparticle entrapment, featuring high-aspect-ratio elastic micropillars spaced to mimic the hairy surface of bees. The hypothesis was validated by investigating the ability of polydimethylsiloxane microfabricated patches to fix microparticles. The geometrical arrangement, spacing, height, and flexibility of the fabricated micropillars, and the diameter of the microparticles, were investigated. Higher entrapment capability was found through the match between particle size and pillar spacing, being consistent with the observations that the diameter of pollen grains is similar to the spacing between hairs on bees’ legs. Taller pillars permitted immobilization of higher quantities of particles, consistent with the high aspect ratio of bees’ hairs. Our biomimetic surfaces were explored for their ability to fix solid microparticles for drug-release applications, using tetracycline hydrochloride as a model antibiotic. These surfaces allowed fixation of more than 20 mg/cm2of antibiotic, about five times higher dose than commercialized patches (5.1 mg/cm2). Such bioinspired hairy surfaces could find applications in a variety of fields where dry fixation of high quantities of micrometer-sized objects are needed, including biomedicine, agriculture, biotechnology/chemical industry, and cleaning utensils.
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Rihan, Abdullah A., Thamer A. Mohamed, and Dr Wissam H. Alawee. "Physical Simulation for the Flow in Straight and Rectangular Loop Manifolds." Journal of Engineering 27, no. 3 (February 27, 2021): 15–32. http://dx.doi.org/10.31026/j.eng.2021.03.02.
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The flow in a manifolds considered as an advanced problem in hydraulic engineering applications. The objectives of this study are to determine; the uniformity qn/q1 (ratio of the discharge at last outlet, qn to the discharge at first outlet, q1) and total head losses of the flow along straight and rectangular loop manifolds with different flow conditions. The straight pipes were with 18 m and 19 m long and with of 25.4 mm (1.0 in) in diameter each. While, the rectangular close loop configuration was with length of 19 m and with diameter of 25.4 mm (1.0 in) also. Constant head in the supply tank was used and the head is 2.10 m. It is found that outlets spacing and manifold configuration are the main factors affecting the uniformity of flow distribution and friction head losses along manifolds. For large value of outlets spacing, the uniformity coefficient (qn/q1) was found with greatest value of 0.96. Thus, the flow distribution improves with bigger spacing between outlets along manifold. For same manifold length, diameter, inlet head and spacing between outlets (S/L=0.079), the uniformity coefficient was found 0.881 or 88.1% for straight manifold and 0.926 for rectangular loop manifold. From the experimental data, a better uniformity is obtained from the rectangular loop manifold, this is because the friction head loss in rectangular loop manifold was lower than that in straight manifold. The lowest of total head losses was found with greatest outlet spacing along manifold, while the highest of total head losses was found with smallest outlets spacing along manifold. And, the lowest of total head loss was found with the rectangular manifold, while the highest of total head loss was found with the straight manifold.