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Topic Review
Prestressed Concrete Girders
Prestressing methods were used to realize long-span bridges in the last few decades. For their maintenance, dynamic nondestructive procedures for identifying prestress losses were mainly developed since serviceability and safety of Prestressed Concrete (PC) girders depend on the effective state of prestressing. In fact, substantial long term prestress losses can induce excessive deflections and cracking in PC bridge girders. However, old unsolved problematics exist since a variation in prestress force does not significantly affect the vibration responses of such PC girders. As a result, this makes uncertain the use of natural frequencies as appropriate parameters for prestress loss determinations. Thus, amongst emerging techniques, static identification based on vertical deflections has preliminary proved to be a reliable method. In fact, measured vertical deflections take accurately and instantaneously into account the changes of structural geometry of PC girders due to prestressing losses. Given the current state of methodologies, the manuscript represents a state-of-the-art review of some important works on determining prestress losses. The attention is principally focused on a static nondestructive method, and a comparison with dynamic ones is elaborated.
  • 2.6K
  • 05 Nov 2020
Topic Review Peer Reviewed
Low-Pressure Turbine Cooling Systems
Modern low-pressure turbine engines are equipped with casings impingement cooling systems. Those systems (called Active Clearance Control) are composed of an array of air nozzles, which are directed to strike turbine casing to absorb generated heat. As a result, the casing starts to shrink, reducing the radial gap between the sealing and rotating tip of the blade. Cooling air is delivered to the nozzles through distribution channels and collector boxes, which are connected to the main air supply duct. The application of low-pressure turbine cooling systems increases its efficiency and reduces engine fuel consumption.
  • 2.5K
  • 13 Apr 2022
Topic Review
Bitumen Aging and Rejuvenation Chemistry
Bitumen aging and rejuvenation include a series of chemical transformations that the material undergoes and that results in the variation of its physical characteristics.
  • 2.6K
  • 30 Jun 2021
Topic Review
Waveguide (Electromagnetism)
In electromagnetics and communications engineering, the term waveguide may refer to any linear structure that conveys electromagnetic waves between its endpoints. However, the original and most common meaning is a hollow metal pipe used to carry radio waves. This type of waveguide is used as a transmission line mostly at microwave frequencies, for such purposes as connecting microwave transmitters and receivers to their antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave radio links. A dielectric waveguide employs a solid dielectric rod rather than a hollow pipe. An optical fibre is a dielectric guide designed to work at optical frequencies. Transmission lines such as microstrip, coplanar waveguide, stripline or coaxial cable may also be considered to be waveguides. The electromagnetic waves in a (metal-pipe) waveguide may be imagined as travelling down the guide in a zig-zag path, being repeatedly reflected between opposite walls of the guide. For the particular case of rectangular waveguide, it is possible to base an exact analysis on this view. Propagation in a dielectric waveguide may be viewed in the same way, with the waves confined to the dielectric by total internal reflection at its surface. Some structures, such as non-radiative dielectric waveguides and the Goubau line, use both metal walls and dielectric surfaces to confine the wave.
  • 2.6K
  • 07 Oct 2022
Topic Review
Reverse Water Gas Shift Reaction
The catalytic conversion of CO2 to CO by the reverse water gas shift (RWGS) reaction followed by well-established synthesis gas conversion technologies could be a practical technique to convert CO2 to valuable chemicals and fuels in industrial settings. For catalyst developers, prevention of side reactions like methanation, low-temperature activity, and selectivity enhancements for the RWGS reaction are crucial concerns. Cerium oxide (ceria, CeO2) has received considerable attention due to its exceptional physical and chemical properties. 
  • 2.6K
  • 09 Oct 2022
Topic Review
Energy-Saving and Sustainable Building Systems
Generally, energy used in a building can be accrued in various ways and a statistical process can be used for studying the building’s overall performance and minimizing the energy requirement of the building. Different statistical models are used to interpret the real-world data in terms of individual theory to develop energy-efficient buildings. Underfloor air distribution, double-glazed windows, use of highly efficient electric motors and variable speed drives may play a great role in reducing building energy consumption. In the UK, the application of double-glazed windows in commercial buildings can save 39–53% energy. The proper maintenance of a building’s central heating system can save up to 11% energy. The automatic HVAC control system can reduce up to 20% of the building’s total heating load. Proper utilization of a VSD system in motor and building performance optimization by an ANOVA tool also proved instrumental in saving energy.
  • 2.6K
  • 10 Feb 2022
Topic Review
Woodward Effect
The Woodward effect, also referred to as a Mach effect, is part of a hypothesis proposed by James F. Woodward in 1990. The hypothesis states that transient mass fluctuations arise in any object that absorbs internal energy while undergoing a proper acceleration. Harnessing this effect could generate a reactionless thrust, which Woodward and others claim to measure in various experiments. Hypothetically, the Woodward effect would allow for field propulsion spacecraft engines that would not have to expel matter. Such a proposed engine is sometimes called a Mach effect thruster (MET) or a Mach Effect Gravitational Assist (MEGA) drive. So far, experimental results have not strongly supported this hypothesis, but experimental research on this effect, and its potential applications, continues. The Space Studies Institute was selected as part of NASA's Innovative Advanced Concepts program as a Phase I proposal in April 2017 for Mach Effect research. The year after, NASA awarded a NIAC Phase II grant to the SSI to further develop these propellantless thrusters. The effect is controversial within mainstream physics because the underlying model proposed for it appears to be faulty, resulting in violations of energy conservation as well as momentum conservation.
  • 2.6K
  • 16 Nov 2022
Topic Review
D-10 Tank Gun
The D-10 is a Soviet 100 mm tank gun developed in late World War II. It originally equipped the SU-100 tank destroyers and was later selected for the T-55 tank, equipping these as late as 1979. On the T-55 the D-10 continues to be in active service in many countries.
  • 2.6K
  • 19 Oct 2022
Topic Review
Hydro Generation Scheduling
The optimal generation scheduling (OGS) of hydropower units holds an important position in electric power systems, which is significantly investigated as a research issue. Hydropower has a slight social and ecological effect when compared with other types of sustainable power source. The target of long-, mid-, and short-term hydro scheduling (LMSTHS) is to optimize the power generation schedule of the accessible hydropower units, which generate maximum energy by utilizing the available potential during a specific period. Numerous traditional optimization procedures are first presented for making a solution to the LMSTHS problem. Lately, various optimization approaches, which have been assigned as a procedure based on experiences, have been executed to get the optimal solution of the generation scheduling of hydro systems. This article offers a complete survey of the implementation of various methods to get the OGS of hydro systems by examining the executed methods from various perspectives. Optimal solutions obtained by a collection of meta-heuristic optimization methods for various experience cases are established, and the presented methods are compared according to the case study, limitation of parameters, optimization techniques, and consideration of the main goal. Previous studies are mostly focused on hydro scheduling that is based on a reservoir of hydropower plants. Future study aspects are also considered, which are presented as the key issue surrounding the LMSTHS problem.
  • 2.6K
  • 25 Jan 2022
Topic Review
Early-Age Cracking in Concrete
Cracking is a common problem in concrete structures in real-life service conditions. In fact, crack-free concrete structures are very rare to find in real world. Concrete can undergo early-age cracking depending on the mix composition, exposure environment, hydration rate, and curing conditions.
  • 2.6K
  • 27 Jun 2021
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