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Mechanics and Mathematics in Ancient Greece
This entry presents an overview on how mechanics in Greece was linked to geometry. In ancient Greece, mechanics was about lifting heavy bodies, and mathematics almost coincided with geometry. Mathematics interconnected with mechanics at least from the 5th century BCE and became dominant in the Hellenistic period. The contributions by thinkers such as Aristotle, Euclid, and Archytas on fundamental problems such as that of the lever are sketched. This entry can be the starting point for a deeper investigation on the connections of the two disciplines through the ages until our present day.
  • 1.9K
  • 13 Apr 2022
Topic Review
Multilevel Inverters for PV Systems
Over the last decade, energy demand from the power grid has increased significantly due to the increasing number of users and the emergence of high-power industries. This has led to a signifi-cant increase in global emissions with conventional energy generation. Therefore, the penetration of renewable energy resources into the power grid has increased significantly. Photovoltaic sys-tems have become the most popular resources as their protentional is enormous, thus, the world-wide installed PV capacity has increased to more than 635 gigawatts (GW), covering approxi-mately 2% of the global electricity demand. Power electronics are an essential part of photovoltaic generation; the drive for efficient power electronic converters is gaining more and more momen-tum. Presently, multilevel inverters (MLI) have become more attractive to researchers compared to two-level inverters due to their abilities to provide lower electromagnetic interference, higher efficiency, and larger DC link voltages. 
  • 1.9K
  • 23 Mar 2021
Topic Review
Self-Driving Cars
Self-driving cars are a hot research topic in science and technology, which has a great influence on social and economic development. Deep learning is one of the current key areas in the field of artificial intelligence research. It has been widely applied in image processing, natural language understanding, and so on. In recent years, more and more deep learning-based solutions have been presented in the field of self-driving cars and have achieved outstanding results. This paper presents a review of recent research on theories and applications of deep learning for self-driving cars. This survey provides a detailed explanation of the developments of self-driving cars and summarizes the applications of deep learning methods in the field of self-driving cars. Then the main problems in self-driving cars and their solutions based on deep learning methods are analyzed, such as obstacle detection, scene recognition, lane detection, navigation and path planning. In addition, the details of some representative approaches for self-driving cars using deep learning methods are summarized. Finally, the future challenges in the applications of deep learning for self-driving cars are given out.
  • 1.9K
  • 29 Jan 2021
Topic Review
Hybrid Ship Propulsion Systems
Following the trends in the automobile industry, hybrid electric propulsion systems have been proposed and used in ships to achieve higher efficiency, mitigate carbon emissions and reduce overall operational costs by combining traditional mechanical propulsion with electrical propulsion. Studies have been conducted on the diverse types of hybrid marine power systems to understand the behaviour of the ships at different operating and loading conditions to optimise the cost function of the hybrid system model. 
  • 1.9K
  • 06 Jan 2023
Topic Review
Kepler (Spacecraft)
Kepler is a space observatory launched by NASA to discover Earth-size planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched on March 7, 2009, into an Earth-trailing heliocentric orbit. The principal investigator was William J. Borucki. Designed to survey a portion of our region of the Milky Way to discover Earth-size exoplanets in or near habitable zones and estimate how many of the billions of stars in the Milky Way have such planets, Kepler's sole scientific instrument is a photometer that continually monitors the brightness of approx 150,000 main sequence stars in a fixed field of view. These data are transmitted to Earth, then analyzed to detect periodic dimming caused by exoplanets that cross in front of their host star. Kepler is part of NASA's Discovery Program of relatively low-cost, focused primary science missions. The telescope's construction and initial operation were managed by NASA's Jet Propulsion Laboratory, with Ball Aerospace responsible for developing the Kepler flight system. The Ames Research Center is responsible for the ground system development, mission operations since December 2009, and scientific data analysis. The initial planned lifetime was 3.5 years, but greater-than-expected noise in the data, from both the stars and the spacecraft, meant additional time was needed to fulfill all mission goals. Initially, in 2012, the mission was expected to be extended until 2016, but on July 14, 2012, one of the spacecraft's four reaction wheels used for pointing the spacecraft stopped turning, and completing the mission would only be possible if all other reaction wheels remained reliable. Then, on May 11, 2013, a second reaction wheel failed, disabling the collection of science data and threatening the continuation of the mission. On August 15, 2013, NASA announced that they had given up trying to fix the two failed reaction wheels. This meant the current mission needed to be modified, but it did not necessarily mean the end of planet hunting. NASA had asked the space science community to propose alternative mission plans "potentially including an exoplanet search, using the remaining two good reaction wheels and thrusters". On November 18, 2013, the K2 "Second Light" proposal was reported. This would include utilizing the disabled Kepler in a way that could detect habitable planets around smaller, dimmer red dwarfs. On May 16, 2014, NASA announced the approval of the K2 extension. (As of January 2015), Kepler and its follow-up observations had found 1,013 confirmed exoplanets in about 440 star systems, along with a further 3,199 unconfirmed planet candidates.[upper-alpha 2] Four planets have been confirmed through Kepler's K2 mission. In November 2013, astronomers estimated, based on Kepler space mission data, that there could be as many as 40 billion rocky, Earth-size exoplanets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. It is estimated that 11 billion of these planets may be orbiting Sun-like stars. The nearest such planet may be 3.7 parsecs (12 ly) away, according to the scientists. On January 6, 2015, NASA announced the 1,000th confirmed exoplanet discovered by the Kepler Space Telescope. Four of the newly confirmed exoplanets were found to orbit within habitable zones of their related stars: three of the four, Kepler-438b, Kepler-442b and Kepler-452b, are almost Earth-size and likely rocky; the fourth, Kepler-440b, is a super-Earth. On May 10, 2016, NASA verified 1,284 new exoplanets found by Kepler, the single largest finding of planets to date. Kepler data has also helped scientists observe and understand supernovae; measurements were collected every half-hour so the light curves were especially useful for studying these types of astronomical events.
  • 1.9K
  • 20 Oct 2022
Topic Review
Natural Fiber Composites
Recent advancements in natural fiber composites have minimized the usage of man-made fibers, especially in the field of structural applications such as aircraft stiffeners and rotor blades. However, large variations in the strength and modulus of natural fiber degrade the properties of the composites and lower the safety level of the structures under dynamic load. Without compromising the safety of the composite structure, it is significant to enrich the strength and modulus of natural fiber reinforcement for real-time applications.
  • 1.9K
  • 17 May 2022
Topic Review
Gel Blasters
Gel blasters, also known as gel guns, gel shooters, gel markers, hydro markers, hydro blasters, water bead blasters or gelsoft, are toy guns similar in design to airsoft guns, but the projectiles they shoot are 6–8 mm (0.24–0.31 in) superabsorbent polymer water beads (most commonly sodium polyacrylate, colloquially called water beads, hydrogel balls, gel balls, water bullets or simply gels), which are often sold commercially as moisture retainers for gardening and pot/vase floriculture. Gel blasters are often played in CQB-style shooting skirmishes similar to paintball by squads or local clubs of enthusiasts often referred to as "gelballers", but follow an airsoft-like honor-based gameplay umpiring system. MilSim games involving players wearing camouflage and dump pouches are very popular, while "SpeedGel" players are more casual with team jerseys and often wear paintball masks. In addition to safety gear such as eye protections, the sport is heavily regulated on the field and players must adhere to safety rules.
  • 1.9K
  • 20 Nov 2022
Topic Review
Time-gated Raman spectroscopy
Raman spectroscopy is a non-destructive technique which provides information on the physical and chemical structure of a material, based on the interaction of molecule vibrational modes with light. Time-gated Raman spectroscopy is an effective technique to reject the strong fluorescence background that overwhelms Raman signal. It profits from the time scale difference in the two responses: Raman photons are scattered almost instantaneously while fluorescence shows a nanoseconds time constant decay. The combination of short laser pulses with time-gated detectors enables the collection of only those photons synchronous with the pulse, thus rejecting fluorescent ones.
  • 1.9K
  • 01 Jul 2021
Topic Review
Seawater Electrolysis
Hydrogen energy, as a clean and renewable energy, has attracted much attention in recent years. Water electrolysis via the hydrogen evolution reaction at the cathode coupled with the oxygen evolution reaction at the anode is a promising method to produce hydrogen. Given the shortage of freshwater resources on the planet, the direct use of seawater as an electrolyte for hydrogen production has become a hot research topic. Direct use of seawater as the electrolyte for water electrolysis can reduce the cost of hydrogen production due to the great abundance and wide availability. Various high-efficiency electrocatalysts have made great progress in seawater splitting and have shown great potential.
  • 1.9K
  • 07 Feb 2022
Topic Review
CO2 and H2S Separation Technologies
The emerging economic activities, modernization of technology and progressive transition from coal utilization to low-carbon fuel drive the rising energy demand. Natural gas is well-known as clean energy resources for electricity generation and fuel for transportation. Currently, CO2 and H2S content in gas fields accounts for up to 90% and 15%, respectively. Apart from fulfilling the market demand, the removal of these contaminants from natural gas is critical due to their corrosive natures, low heating value of natural gas and  greenhouse gas effect. To date, numerous gas fields remain unexplored due to high presence of contaminants. Several technologies such as absorption, adsorption, membrane separation and cryogenic distillation have been developed for natural gas sweetening. This entry comprehensively discussed the mechanisms and state-of-the-art of these conventional technologies.
  • 1.9K
  • 03 Mar 2022
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