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Topic Review
Mass Transfer in Packed-Bed Columns
This review provides a thorough analysis of the most famous mass transfer models for random and structured packed-bed columns used in absorption/stripping and distillation processes, providing an overview of the equations to calculate the mass transfer parameters, i.e.: gas-side coefficient per unit surface ky [kmol·m-2·s-1], liquid-side coefficient per unit surface kx [kmol·m-2·s-1], interfacial packing area ae [m2·m-3], which constitute the ingredients to assess the mass transfer rate of packed-bed columns. This work also provides the ranges of model validity and applicability together with their main pros and cons and the criticalities behind these models, which mostly rely on the assessment of fluid-dynamics parameters such as liquid film thickness, liquid hold-up and interfacial area, or the real liquid paths or any mal-distributions flow. 
  • 4.5K
  • 01 Sep 2021
Topic Review
Two-Dimensional Space
Two-dimensional space (also known as 2D space, 2-space, or bi-dimensional space) is a geometric setting in which two values (called parameters) are required to determine the position of an element (i.e., point). The set [math]\displaystyle{ \mathbb{R}^2 }[/math] of pairs of real numbers with appropriate structure often serves as the canonical example of a two-dimensional Euclidean space. For a generalization of the concept, see dimension. Two-dimensional space can be seen as a projection of the physical universe onto a plane. Usually, it is thought of as a Euclidean space and the two dimensions are called length and width.
  • 4.5K
  • 28 Nov 2022
Topic Review
Around the World Sailing Record
The first around the world sailing record for circumnavigation of the world was Juan Sebastián Elcano and the remaining members of Ferdinand Magellan's crew who completed their journey in 1522. The first solo record was set by Joshua Slocum in the Spray (1898). The current record holders are IDEC 3, skippered by Francis Joyon in 40 days, 23 hours, 30 minutes and 30 seconds for a crewed journey, and François Gabart with Macif in 42 days, 16 hours, 40 minutes and 35 seconds for a solo journey. Most races or solo attempts start from Europe. Due to the configuration of the continents, sailing around the world consists of sailing on the Southern Ocean around the Antarctica continent, passing south of Cape Horn, Cape of Good Hope and Cape Leeuwin. Since 1918 the Panama Canal is an option but the locks must be entered and exited using engine power. Large stretches of the canal can be crossed under sail power. Sailing around the world can be done by two directions: eastward or westward. The dominant winds and currents (outside tropical areas) make the voyage eastwards on the Southern hemisphere faster, most skippers and yachts who race prefer this route. Today, the multihulls perform much better than monohulls and hold the best times. Leisure yacht skippers who prefer tropical seas more often go westward, using the trade winds (and the Panama canal). The Jules Verne Trophy is awarded to the skipper who breaks the previous Jules Verne record, starting from an imaginary line between the Créac'h lighthouse on Ouessant (Ushant) Island, France , and the Lizard Lighthouse, United Kingdom . This has not always been the OUTRIGHT record. The records are homologated by the World Sailing Speed Record Council (WSSRC). According to the WSSRC, for around the world sailing records, there is a rule saying that the length must be at least 21,600 nmi calculated along the shortest possible track from the starting port and back that does not cross land and does not go below 63°S. The great-circle distance formulas are to be used, assuming that the great circle length is 21,600 nmi. It is allowed to have one single waypoint to lengthen the calculated track. The equator must be crossed. In reality, this means that the boat should pass a waypoint at or not far from the antipode of the starting port of the journey (the exact position depends on how short the shortest possible track is). For example, the Vendée Globe starts at 46°N 2°W, has a waypoint at 57°S 180°E, and barely makes the distance requirement. The participants don't have to go to the antipode at 46°S 178°E since the rounding of Africa gives extra distance.
  • 4.5K
  • 11 Nov 2022
Topic Review
Turing Reduction
In computability theory, a Turing reduction from a problem A to a problem B, is a reduction which solves A, assuming the solution to B is already known (Rogers 1967, Soare 1987). It can be understood as an algorithm that could be used to solve A if it had available to it a subroutine for solving B. More formally, a Turing reduction is a function computable by an oracle machine with an oracle for B. Turing reductions can be applied to both decision problems and function problems. If a Turing reduction of A to B exists then every algorithm for B can be used to produce an algorithm for A, by inserting the algorithm for B at each place where the oracle machine computing A queries the oracle for B. However, because the oracle machine may query the oracle a large number of times, the resulting algorithm may require more time asymptotically than either the algorithm for B or the oracle machine computing A, and may require as much space as both together. The first formal definition of relative computability, then called relative reducibility, was given by Alan Turing in 1939 in terms of oracle machines. Later in 1943 and 1952 Stephen Kleene defined an equivalent concept in terms of recursive functions. In 1944 Emil Post used the term "Turing reducibility" to refer to the concept. A polynomial-time Turing reduction is known as a Cook reduction, after Stephen Cook.
  • 4.5K
  • 14 Oct 2022
Topic Review
Cataracts
A cataract is an ophthalmic disorder characterized by the opacification of the lens and occurs commonly in older people. Age-related cataract is a significant cause of blindness affecting the quality of life worldwide. An imbalance between oxidative stress and antioxidant potential of ocular tissue is considered responsible for structural modifications of crystallins, the protein constituents of the lens, which eventually leads to cataracts. Lutein and zeaxanthin are two major carotenoids which are concentrated in the human lens. Many preclinical and clinical studies provide compelling evidence for a protective role of dietary carotenoids in age-related cataracts.
  • 4.5K
  • 28 Sep 2021
Topic Review
Theories of International Trade
Economists have developed theories explaining World Trade, which are called” theories of international trade”. Theories of international trade explain what exactly happens in international trade, such as mercantilist theory. This theory was popular in the sixteenth and eighteenth centuries. During that time, a nation’s wealth consisted only of gold or other types of precious metals, so theorists suggested that nations begin to accumulate more and more gold and other types of metals. 
  • 4.5K
  • 08 Jul 2022
Topic Review
Nanolubricants
Nanolubricants are the name given to the dispersion of nanoparticles in a base oil, and has attracted researchers due to its potential application. In addition to being used in the tribology field, nanoparticles are also used for medical, space, and composites purposes. The addition of nanoparticles in base oils is promising because it enhances specific tribological characteristics including wear-resistance and friction, and the most important reason is that the majority of them are environmentally friendly. 
  • 4.5K
  • 17 Nov 2020
Topic Review
Country Code Top-Level Domain
A country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country, sovereign state, or dependent territory identified with a country code. All ASCII ccTLD identifiers are two letters long, and all two-letter top-level domains are ccTLDs. In 2018, the Internet Assigned Numbers Authority (IANA) began implementing internationalized country code top-level domains, consisting of language-native characters when displayed in an end-user application. Creation and delegation of ccTLDs is described in RFC 1591, corresponding to ISO 3166-1 alpha-2 country codes. While gTLD have to obey international regulations, ccTLD are subjected to requirements that are determined by each country’s domain name regulation corporation. With over 150 million domain name registrations today, ccTLDs make up 40% of the total domain name industry. Country code extension applications began in 1985. The registered first extensions that year were .us (United States), .uk (United Kingdom), and .il (Israel). There are 312 ccTLDs in active use totally. .cn, .tk, .de and .uk contain the highest number of domains.
  • 4.5K
  • 08 Nov 2022
Topic Review
Examination of Apollo Moon Photographs
The examination of Apollo Moon photographs is an endeavour undertaken by certain people engaged in the debate as to the merits of Moon landing conspiracy theories, despite the abundance of third-party evidence for Apollo Moon landings. A number of allegations and refutations with a variable degree of notability are put forward due to this examination.
  • 4.5K
  • 02 Dec 2022
Topic Review
Lotus-Leaf-Inspired Biomimetic Coatings
A universal infrastructural issue is wetting of surfaces; millions of dollars are invested annually for rehabilitation and maintenance of infrastructures including roadways and buildings to fix the damages caused by moisture and frost. The biomimicry of the lotus leaf can provide superhydrophobic surfaces that can repel water droplets, thus reducing the penetration of moisture, which is linked with many deterioration mechanisms in infrastructures, such as steel corrosion, sulfate attack, alkali-aggregate reactions, and freezing and thawing. In cold-region countries, the extent of frost damage due to freezing of moisture in many components of infrastructures will be decreased significantly if water penetration can be minimized. Consequently, it will greatly reduce the maintenance and rehabilitation costs of infrastructures.
  • 4.5K
  • 11 Jun 2022
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