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Topic Review
Damping Ratio
Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples include viscous drag in mechanical systems, resistance in electronic oscillators, and absorption and scattering of light in optical oscillators. Damping not based on energy loss can be important in other oscillating systems such as those that occur in biological systems and bikes. The damping ratio is a dimensionless measure describing how oscillations in a system decay after a disturbance. Many systems exhibit oscillatory behavior when they are disturbed from their position of static equilibrium. A mass suspended from a spring, for example, might, if pulled and released, bounce up and down. On each bounce, the system tends to return to its equilibrium position, but overshoots it. Sometimes losses (e.g. frictional) damp the system and can cause the oscillations to gradually decay in amplitude towards zero or attenuate. The damping ratio is a measure describing how rapidly the oscillations decay from one bounce to the next. The damping ratio is a system parameter, denoted by ζ (zeta), that can vary from undamped (ζ = 0), underdamped (ζ < 1) through critically damped (ζ = 1) to overdamped (ζ > 1). The behaviour of oscillating systems is often of interest in a diverse range of disciplines that include control engineering, chemical engineering, mechanical engineering, structural engineering, and electrical engineering. The physical quantity that is oscillating varies greatly, and could be the swaying of a tall building in the wind, or the speed of an electric motor, but a normalised, or non-dimensionalised approach can be convenient in describing common aspects of behavior.
  • 31.0K
  • 12 Oct 2022
Topic Review
Free-Space Path Loss
In telecommunication, the free-space path loss (FSPL) is the attenuation of radio energy between the feedpoints of two antennas that results from the combination of the receiving antenna's capture area plus the obstacle free, line-of-sight path through free space (usually air). The "Standard Definitions of Terms for Antennas", IEEE Std 145-1993, defines "free-space loss" as "The loss between two isotropic radiators in free space, expressed as a power ratio." It does not include any power loss in the antennas themselves due to imperfections such as resistance. Free space loss increases with the square of distance between the antennas because the radio waves spread out due the inverse square law and decreases with the square of the wavelength of the radio waves. The FSPL is rarely used standalone, but rather as a part of the Friis transmission formula, which includes the gain of antennas. It is a factor that must be included in the power link budget of a radio communication system, to ensure that sufficient radio power reaches the receiver that the transmitted signal is received intelligibly.
  • 18.5K
  • 02 Jun 2023
Topic Review
List of Qualcomm Snapdragon Systems-on-chip
This is a list of Qualcomm Snapdragon chips. Snapdragon is a family of mobile system on a chip (SoC) made by Qualcomm for use in smartphones, tablets, laptops, 2-in-1 PCs, smartwatches , and smartbooks devices.
  • 17.9K
  • 19 Oct 2022
Topic Review
Hydrogen Storage and Transportation
In the current hydrocarbon economy, transportation is fueled primarily by petroleum. Burning of hydrocarbon fuels emits carbon dioxide and other pollutants. The supply of economically usable hydrocarbon resources in the world is limited, and the demand of hydrocarbon fuels is increasing, particularly in China, India and other countries. Proponents of a world-scale hydrogen economy argue that hydrogen can be environmentally cleaner source of energy to end-users, particularly in transportation applications, without release of pollutants (such as particulate matter) or carbon dioxide at the point of end use. A recent analysis asserted that “most of the hydrogen supply chain pathways would release significantly less carbon dioxide into the atmosphere than would gasoline used in hybrid electric vehicles” and that significant reductions in carbon dioxide emissions would be possible if carbon capture or carbon sequestration methods were utilized at the site od energy or hydrogen production. Hydrogen storage can be distributed continuously in pipelines or batch wise by ships, trucks, railway or airplanes. All batch transportation requires a storage system also pipelines can be used as pressure storage system. Hydrogen exhibits the highest heating value per weight of all chemical fuels. Furthermore, hydrogen is regenerative and environment friendly. But two difficulties with hydrogen are that hydrogen is just an energy carrier and has a low critical temperature of 35 K, i.e., hydrogen is a gas at room temperature. For mobile and in many cases also for stationary applications the volumetric and gravimetric density of hydrogen in a storage system is crucial. Hydrogen can be stored by six different methods and phenomena: high pressure gas cylinders (up to 800 bar), liquid hydrogen in cryogenic tanks (at 21 K), adsorbed hydrogen on materials with a large specific surface area (at T< 100K), absorbed on interstitial sites in a host metal (at ambient pressure and temperature), chemically bond in covalent and ionic compounds (at ambient pressure), oxidation of reactive metals e.g., Li, Na, Mg, Al, Zn with water. These metals easily react with water to the corresponding hydroxide and liberate the hydrogen from the water. Finally, the metal hydroxides can be thermally reduced to the metals in a solar furnace. In conclusion, routes for the transmission and storage of hydrogen for chemical processes, and hydrogen-based energy systems are increasing their establishment. Here, these routes are described, considering their attractions and difficulties.
  • 14.4K
  • 18 Jun 2021
Topic Review
BMW 5 Series (E39)
The BMW E39 is the fourth generation of BMW 5 Series, which was sold from 1995 to 2004. It was launched in the sedan body style, with the wagon/estate body style (marketed as "Touring") introduced in 1996. The E39 was replaced by the E60 5 Series in 2003, however E39 Touring models remained in production until May 2004. The proportion of chassis components using aluminium significantly increased for the E39, and it was the first 5 Series to use aluminium for all major components in the front suspension or any in the rear. It was also the first 5 Series where a four-cylinder diesel engine was available. Rack and pinion steering was used for the first time in a 5 Series (with the exception of the E34 525iX), being fitted to the four-cylinder and six-cylinder models. Unlike its E34 predecessor and E60 successor, the E39 was not available with all-wheel drive. The high performance M5 sedan was introduced in 1998, powered by the 4.9-litre S62 V8 engine. It was the first M5 model to be powered by a V8 engine.
  • 13.5K
  • 05 Dec 2022
Topic Review
CCR Model (DEA)
The first Data Envelopment Analysis (DEA) model developed by Charnes, Cooper and Rhodes (1978) under the assumption of a Constant Returns to Scale production technology, i.e.,  when an increase in the production resources results in a proportional increase in the output.
  • 13.4K
  • 30 May 2021
Topic Review
BMW 5 Series (E34)
The BMW E34 is the third generation of the BMW 5 Series, which was produced from 1987 until 1996. Initially launched as a sedan in January 1988, the E34 also saw a "Touring" wagon (estate) bodystyle in September 1992, a first for the 5 Series. BMW replaced the E34 with the E39 5 Series in December 1995, although E34 Touring models remained in production until June 1996. The E34 generation marked the first time all-wheel drive was incorporated into the 5 Series with the 525iX, and the first V8 engine to be used in a 5 Series. The E34 also saw the introduction of stability control (ASC), traction control (ASC+T) a 6-speed manual transmission and adjustable damping (EDC) to the 5 Series range. There was an unusually large range of engines fitted over its lifetime as nine different engine families were used. These consisted of straight-four, straight-six and V8 engines. The E34 M5 is powered by the S38 straight-six engine and was produced in sedan and wagon body styles.
  • 11.4K
  • 31 Oct 2022
Topic Review
Power Electronic Switches
As the need for green and effective utilization of energy continues to grow, the advancements in the energy and power electronics industry are constantly driven by this need, as both industries are intertwined for obvious reasons. The developments in the power electronics industry has over the years hinged on the progress of the semiconductor device industry. The semiconductor device industry could be said to be on the edge of a turn into a new era, a paradigm shift from the conventional silicon devices to the wide band gap semiconductor technologies. While a lot of work is being done in research and manufacturing sectors, it is important to look back at the past, evaluate the current progress and look at the prospects of the future of this industry. This paper is unique at this time because it seeks to give a good summary of the past, the state-of-the-art, and highlight the opportunities for future improvements. A more or less ‘forgotten’ power electronic switch, the four-quadrant switch, is highlighted as an opportunity waiting to be exploited as this switch presents a potential for achieving an ideal switch.
  • 11.3K
  • 29 Dec 2020
Topic Review
Chinese Swords
Historically, all Chinese swords are classified into two types, jian and dao. Jians are double-edged straight swords while daos are single-edged, and mostly curved from the Song dynasty forward. The jian has been translated at times as a long sword, and the dao a saber or a knife. Bronze jians appeared during the Western Zhou period and switched to wrought iron and steel during the late Warring States period. In modern times, the ceremonial commissioned officer's sword of the Chinese navy has been patterned after the traditional jian since 2008. Other than specialized weapons like the Divided Dao, Chinese swords are usually 70–110 cm (28–43 in) in length, although longer swords have been found on occasion. Outside of China, Chinese swords were also used in Japan from the third to the sixth century AD, but were replaced with Korean and native Japanese swords by the middle Heian era.
  • 11.1K
  • 30 Sep 2022
Topic Review
Data Envelopment Analysis (DEA)
Data Envelopment Analysis (DEA) is a non-parametric methodology for measuring the efficiency of Decision Making Units (DMUs) using multiple inputs to outputs configurations. This is the most commonly used tool for frontier estimations in assessments of productivity and efficiency applied to all fields of economic activities.
  • 10.0K
  • 28 Jan 2022
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