The recombination of short homologous ends in Escherichia coli has been known for 30 years, and it is often used for both site‐directed mutagenesis and in vivo cloning. For cloning, a plasmid and ...target DNA fragments were converted into linear DNA fragments with short homologous ends, which are joined via recombination inside E. coli after transformation. Here this mechanism of joining homologous ends in E. coli was determined by a linearized plasmid with short homologous ends. Two 3ʹ‐5ʹ exonucleases ExoIII and ExoX with nonprocessive activity digested linear dsDNA to generate 5ʹ single‐strand overhangs, which annealed with each other. The polymerase activity of DNA polymerase I (Pol I) was exclusively employed to fill in the gaps. The strand displacement activity and the 5ʹ‐3ʹ exonuclease activity of Pol I were also required, likely to generate 5ʹ phosphate termini for subsequent ligation. Ligase A (LigA) joined the nicks to finish the process. The model involving 5ʹ single‐stranded overhangs is different from established recombination pathways that all generate 3ʹ single‐stranded overhangs. This recombination is likely common in bacteria since the involved enzymes are ubiquitous.
We report the pathway that Escherichia coli uses to stich linear DNA fragments with short homologous ends. ExoIII and ExoX are needed to generate 5' single‐strand overhangs for annealing, Pol I is required to fill in the gaps and produce 5'‐phosphate termini, and ligation occurs by LigA. This mechanism is likely common among bacteria and may be useful for developing tools in synthetic biology.
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•A novel sliding/rotating overhangs is presented and evaluated for US residential buildings.•Both energy efficiency and environmental impacts of the dynamic overhangs are evaluated.•PV-integrated ...control strategies are considered to operate the dynamic overhangs.•The PV-integrated dynamic overhangs can result in net-zero building designs.
The paper evaluates the benefits of integrating PV arrays with sliding and rotating overhangs to both generate electricity and reduce heating and cooling thermal loads for housing units in US apartment buildings. Optimal controls to operate the sliding-rotating overhangs are considered to minimize annual net energy demands with and without the integrated PV arrays. A series of sensitivity analyses is performed to assess the impact of design and operating conditions on the energy performance as well as the environmental impacts of the sliding-rotating overhangs. The analysis results clearly indicate that when integrated with PV modules, sliding overhangs can significantly reduce the energy demand for US housing units especially when they are set at the optimal angles specific to the building location to maximize their electricity generation and solar shading effects. Specifically, it is found that sliding overhangs can not only reduce energy demand but also can achieve net-zero energy conditions for US apartment units with large windows and located in mild climates even when monthly adjustments are applied to operate the shading systems. For instance, 9.2% of the total energy use of an apartment housing unit located in Boulder, CO, can be reduced using the sliding-rotating overhang with no-PV. In San Francisco, CA, more than 100% of the apartment housing unit energy demand can be avoided using PV-integrated sliding-rotating overhangs. To minimize design and operation complexities, it is recommended to consider sliding-only overhangs set at the latitude of the location to reduce both heating and cooling demand as well as increase PV array output. For instance, it is found that sliding overhang set at the latitude angle can be sufficient to achieve net-zero status and even a carbon-neutral operation for an apartment housing unit located in San Francisco, CA, even when adjusted on a monthly basis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The energy and cost benefits of dynamic PV-integrated shading devices are assessed.•Both energy efficiency and on-site energy generation benefits are considered.•Optimal design and operation of ...PV-integrated shading systems are determined.•PV-integrated overhangs can allow office spaces to achieve net zero energy operation.•For Australian office buildings, PV-integrated shading systems are highly cost-effective.
The paper summarizes a comprehensive analysis to determine the energy and cost benefits of static and dynamic photovoltaic (PV)-integrated shading devices when applied to windows of office spaces located in different climate zones across Australia. The evaluated dynamic shading systems consist of rotating overhangs placed above the windows and operated to minimize the annual energy demands of office spaces. For the first time, the study determines through optimization-based controls the best angle settings for the rotating overhangs on hourly, daily, or monthly basis to minimize the energy consumption of office spaces in Australia. The analysis results indicate that both optimally designed static and optimally operated dynamic PV-integrated overhangs have substantial potential to reduce the annual energy needs of office spaces for all Australian climates with annual energy savings ranging from 45% to over 100% depending on the building orientation, window size, glazing type, and overhang depth. This high energy benefits are attributed to the multi-function capability of the PV-integrated shading systems to minimize cooling and space thermal loads while maximizing on-site electricity generation. Unlike the case of static shading devices, it is found that dynamic PV-integrated overhangs allow office spaces to reach net-zero energy operation for certain climate zones in Australia.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The development of additive manufacturing has allowed for increased flexibility and complexity of designs over formative and subtractive manufacturing. However, a limiting factor of additive ...manufacturing is the as-built surface quality as well as the difficulty in maintaining an acceptable surface roughness in overhanging structures. In order to optimize surface roughness in these structures, samples covering a range of overhang angles and process parameters were built in a laser powder bed fusion system. Analysis of the surface roughness was then performed to determine a relationship between process parameters, angle of the overhanging surface, and surface roughness. It was found that the analysis of surface roughness metrics, such as Rpc, Rsm, and Rc, can indicate a shift between surfaces dominated by partially melted powder particles and surfaces dominated by material from the re-solidified melt track.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Fine α plates can be obtained with decline of heat input, leading to the improvement of mechanical strength.•Low heat input deposition has no significant effect on the refinement of β grain ...size.•The formation process of coarse columnar β grain was analyzed.•Horizontal structures without supports were fabricated successfully using low-frequency pulse current.•The formation mechanism of horizontal structures was proposed.
Arc additive manufacturing can be used to fabricate large scale titanium alloy parts with high deposition rate and low costs. However, coarse columnar β grains in deposited Ti-6Al-4V components and unsupported overhangs fabrication are two challenges in arc additive manufacturing. In order to handle these issues, low heat input deposition using pulse current is investigated in this study. The results indicate that the reduction of heat input can increase the cooling rate, but has no significant effect on the refinement of β grain size due to the increasing temperature gradient and the preferred growth of β grain. Nonetheless, fine α plates can be obtained as the cooling rate increases. Tensile testing parallel to the deposition plane reveals that the ultimate tensile strength is between 963 and 1008MPa and ductility is between 11.4% and 17.8%. With the decline of heat input, the ultimate strength and yield strength are improved. Besides, horizontal structures without supports are fabricated successfully using low frequency pulse current. According to the force conditions of the molten pool, a contact angle hysteresis model is applied to reveal the fabrication mechanism.
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The applicability of pressure-impulse theory is evaluated for predicting wave impact loading magnitudes for non-breaking standing wave impacts on vertical hydraulic structures with relatively short ...overhangs. To this end, tests were carried out on a schematized but realistic configuration with low steepness regular wave impacts on a straight overhang perpendicular to a vertical wall. This paper aims to fill the existing knowledge gap on this type of wave impact with reliable and simple expressions. Pressure-impulses and force-impulses are the wave impact loading magnitudes considered in this study, which are defined as the integral of the impulsive pressures/forces over time during a wave impact. These impulses can be used to determine the resulting stresses in a structure for sudden, impulsive loads. The proposed theoretical model is based on the pressure-impulse theory and validated with laboratory experiments. The laboratory tests are done with regular waves for relatively short overhangs, with ratios of wave length to overhang length between 12.1 and 43.6, and ratios of overhang height to overhang length of 3 and 6. Thus, the theory is verified for conditions where the wave impact takes place along the full length of the overhang. From the experimental results, a mean effective bounce-back factor β=1.17 is obtained, accounting for the bounce-back effect of entrapped air and other secondary sources of discrepancies between theoretical and experimental results. The standard deviation of β for all the different tests is σβ=0.11. This method seems suitable for carrying out preliminary loading estimations, including the pressure-impulse profile at the wall and the total force-impulse at the wall. This study also shows that the force-impulse is a more stable magnitude compared with the force peaks, with about half the relative standard deviation. The impulses predicted by this model are recommended to be coupled with fluid-structure interaction models for analysing the response of the loaded structure.
•This paper addresses wave impacts on vertical hydraulic structures with overhangs caused by standing waves.•Pressure-impulse theory is thoroughly validated for standing wave impacts on vertical structures with short overhangs.•The effective bounce-back factor for standing wave impacts on short overhangs is determined at β = 1.17 (σβ = 0.11).•Pressure-impulse theory is a promising method to determine wave impact loadings on hydraulic structures with overhangs.•The peak forces are confirmed to have a larger variability than the force-impulses.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The energy benefits of integrating PV panels with dynamic overhangs are evaluated for US residential buildings. Various control strategies are investigated to operate the dynamic overhangs to ...minimize annual net energy demands to account for both building energy needs and PV electricity generation yields. The analysis results indicate that dynamic overhangs can reduce significantly the annual energy demand for US residences compared to no-overhang and static overhang options even when controlled on a monthly basis and without any PV panels. Specifically, it is found that dynamic overhangs applied to southern facing windows for houses located in Golden, CO, can save up to 6% when no-PV array is installed and more than 35% when integrated with PV panels using monthly adjustments. Even higher savings up to 90% can be achieved for houses located in warm climates and those with larger windows. Moreover, PV-integrated dynamic overhangs can provide energy savings for windows oriented in any direction especially when adjusted on daily basis.
•PV-integrated rotating overhangs are evaluated for US residential buildings.•Optimal control strategies are determined for the dynamic PV-integrated overhangs.•The dynamic overhangs can reduce the annual energy demand up to 90% for US homes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Large-scale wind tunnel testing is carried out to investigate the wind-induced loads on hip roof overhangs.•Investigation of wind loads effect on different overhang widths.•Correlation of pressure ...coefficients on roof soffits and adjacent walls under wind loads.•Code-ready guidelines are produced based on the research findings.
Recent funding opportunities for Wind Engineering research have generated a significant amount of knowledge that has the potential to both develop new or enhance existing wind standards and building codes of practice. Building codes tend to get more rigorous over time to better mitigate damage on buildings and structures. Roof overhangs which are an integral part of the roofing system in low-rise buildings, is particularly vulnerable to damage in wind events due to its exposure to wind-induced loads on both upper and lower surfaces. Large scale wind tunnel testing was carried out at the Wall of Wind (WOW) Research Experimental Facility to investigate the wind-induced loads on roof overhangs of low-rise residential buildings. The physical testing protocol included six 1:10 scaled models with varying geometrical parameters such as roof slope and roof overhang width. Peak wind pressures on both the upper and lower surfaces were measured to calculate the simultaneous net pressure coefficients along the overhangs. Area-averaged pressure analysis was carried out to investigate the pressure gradients on single or groups of taps on the overhangs, soffits, and walls. The experimentally derived area averaged GCp values were compared to previous and current versions of wind standards to evaluate their adequacy. The findings revealed that the provisions’ design guidelines are less conservative for some roofing and wall zones, which justified the need for a codification study that can provide enhanced design guidelines for overhangs and adjacent walls. A detailed discussion of the codified design guidelines, which are formed based on statistical determination rather than the enveloped procedures as commonly used, is presented in this paper.
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A novel dynamic overhang system is evaluated in this paper when applied to control solar heat gains through windows of US residential buildings. In particular, the energy performance ...of the dynamic overhangs is compared to static systems using various operation scenarios. The main objective for the control strategies evaluated in the analysis is to minimize annual heating and cooling energy consumption when dynamic instead of static overhangs are applied to US residential buildings. The operation of the dynamic overhangs is adjusted to account for the range of positions allowed as well as the setting frequencies. In particular, the dynamic overhangs can be set on hourly, daily, and monthly basis depending on the window orientation and the time of the year. The analysis has indicated that the performance of the dynamic overhangs depend on their design specifications as well as on the window glazing type. However, the energy saving potential for the dynamic overhangs compared to static devices depend largely on the window size and the climate with significant reduction in cooling energy use achieved in hot and mild US climatic zones. Indeed, the dynamic overhangs can save over 45% of the air conditioning needs for US homes with window-to-wall ratio of 30% located in Phoenix, AZ, and San Francisco, CA, when automatically operated on hourly basis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Passive design strategies are the most feasible and economic ways of energy and thermal management in buildings, if appropriately incorporated at the conceptual design stage. Though many works have ...been reported on the application of external shading options, a shading strategy that incorporates the features of both external shading devices and self-shading envelope, is yet to be explored. The present study was focused on the energy saving potential and economics of incorporating external shading devices with self-shading envelope for a multi-story hotel building in hot-humid climate of Saudi Arabia. The modeling and the energy simulations were performed by DesignBuilder (Version 4.5.0.148). According to the base-design geometry of the building, appropriate shading options were proposed for the north, south, north-east, north-west, south-east and south-west facades. External walls and roof were insulated with fiber glass and windows were double-glazed (DG), in compliance with the Saudi Building Code - 601. The shading strategy was chosen in such a way that it forms part of a self-shading envelope while improving energy performance and contributing additional space at very affordable cost. The results show that the proposed shading could save the annual energy consumption of the building by 20.5% compared to the base case. The payback period for the additional investment required for incorporating the passive shading strategy is estimated to be 2 years. Study of another option by improving the baseline insulation and glazing (with polyurethane in walls and roof and triple low-e glazed shows, without shading) shows that it saves only 5% of annual energy consumption, and the payback period is unacceptably long (84 years).
•Effect of shading strategy on energy performance of multi-story hotel building.•The shading strategy combines shading devices and self-shading envelope.•The proposed shading configuration could save 20.5% of annual energy consumption.•The additional cost for the shading can be recovered in 2 years.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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