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Topic Review
Antenna Aperture
In electromagnetics and antenna theory, antenna aperture, effective area, or receiving cross section, is a measure of how effective an antenna is at receiving the power of electromagnetic radiation (such as radio waves). The aperture is defined as the area, oriented perpendicular to the direction of an incoming electromagnetic wave, which would intercept the same amount of power from that wave as is produced by the antenna receiving it. Assume a plane wave in a particular direction has an irradiance or power flux density [math]\displaystyle{ S }[/math]; this is the amount of power passing through a unit area of one square meter. Then if an antenna delivers [math]\displaystyle{ P_o }[/math] watts to the load connected to its output terminals (e.g. the receiver) when irradiated by a uniform field of power density [math]\displaystyle{ S }[/math] watts per square meter, the antenna's aperture for the direction of that plane wave is [math]\displaystyle{ A_e }[/math] in square meters, given by: So the power received by an antenna (in watts) is equal to the power density of the electromagnetic energy (in watts per square meter), multiplied by its aperture (in square meters). Radio waves from a direction where the antenna's aperture is larger thus collect a greater amount of that wave's power; this is more often referred to as antenna gain. To actually obtain that available power [math]\displaystyle{ P_o }[/math], the incoming radiation must be in the state of polarization specified for that antenna, and the load (receiver) must be impedance matched to the antenna's feedpoint impedance. The meaning of aperture is thus based on a receiving antenna, however any receiving antenna can also be used for transmission. Due to reciprocity, an antenna's gain in receiving and transmitting are identical, so the power transmitted by an antenna in different directions (the radiation pattern) is always proportional to the effective area [math]\displaystyle{ A_e }[/math] in each direction; that proportionality factor is derived below. When no direction is specified, [math]\displaystyle{ A_e }[/math] (or "antenna gain") is understood to refer to its maximum value, that is, in the intended direction(s) that the antenna is designed to receive from and/or transmit toward.
  • 7.4K
  • 27 Oct 2022
Topic Review
Control Techniques in Photovoltaic Systems
Complex control structures are required for the operation of photovoltaic electrical energy systems. In this paper, a general review of the controllers used for photovoltaic systems is presented. This entry is based on the most recent papers presented in the literature. The control architectures considered are complex hybrid systems that combine classical and modern techniques, such as artificial intelligence and statistical models. The main contribution of this paper is the synthesis of a generalized control structure and the identification of the latest trends. The main findings are summarized in the development of increasingly robust controllers for operation with improved efficiency, power quality, stability, safety, and economics.
  • 7.4K
  • 19 Feb 2021
Topic Review
Ingredients of Moisturizers
Moisturizers are one of the most widely used preparations in cosmetics and have been extensively used to soften the skin for consumers. Moisturizers work effectively in combating dry skin which may cause pain, tightness, itch, stinging, and/or tingling. Knowing the characteristics and interactions of active ingredients with the skin will allow for better utilization of available moisturizers.
  • 7.4K
  • 11 Jul 2022
Topic Review
Penn State Child Sex Abuse Scandal
The Penn State child sex abuse scandal concerned allegations and subsequent convictions of child sexual abuse committed by Jerry Sandusky, an assistant coach for the Penn State Nittany Lions football team, over a period of at least fifteen years. The scandal began to emerge publicly in March 2011 and broke in early November 2011 when Sandusky was indicted on 52 counts of child molestation, stemming from incidents that occurred between 1994 and 2009. Sandusky was ultimately convicted on 45 counts of child sexual abuse on June 22, 2012, and was sentenced to a minimum of 30 years and a maximum of 60 years in prison. Additionally, three Penn State officials – school president Graham Spanier, vice president Gary Schultz and athletic director Tim Curley – were charged with perjury, obstruction of justice, failure to report suspected child abuse, and related charges. The Penn State Board of Trustees commissioned an independent investigation by former FBI Director Louis Freeh, whose report stated that Penn State's longtime head football coach Joe Paterno, along with Spanier, Curley and Schultz, had known about allegations of child abuse by Sandusky as early as 1998, had shown "total and consistent disregard...for the safety and welfare of Sandusky's child victims", and "empowered" Sandusky to continue his acts of abuse by failing to disclose them.:14 Shortly after the scandal broke, Spanier resigned. The Board of Trustees terminated the contracts of Paterno and Curley. As a result of the scandal, the National Collegiate Athletic Association (NCAA) imposed sanctions on the Penn State football program: a $60 million fine, a four-year postseason ban, scholarship reductions, and a vacation of all victories from 1998 to 2011. These sanctions were considered to be among the most severe ever imposed on an NCAA member school. NCAA President Mark Emmert stated that the sanctions were levied "not to be just punitive, but to make sure the university establishes an athletic culture and daily mindset in which football will never again be placed ahead of educating, nurturing and protecting young people." The Big Ten Conference subsequently imposed an additional $13 million fine. The Paterno family retained former Attorney General Richard Thornburgh to conduct a review of the Freeh report, which concluded that the report constituted a "rush to injustice" that could not be relied upon and that Freeh's evidence fell "far short" of showing that Joe Paterno attempted to conceal the scandal, but rather that "the contrary is true". In January 2013, state senator Jake Corman and state treasurer Rob McCord sued the NCAA, seeking to overturn the Penn State sanctions on the basis that Freeh had been actively collaborating with the organization and that due process had not been followed. In November 2014, Corman released emails showing "regular and substantive" contact between Freeh's investigators and the NCAA, suggesting that Freeh's conclusions were orchestrated. As part of a settlement, the NCAA restored the 111 wins to Paterno's record on January 16, 2015. On March 25, 2017, Curley, Schultz, and Spanier pleaded or were found guilty of misdemeanor charges of child endangerment. All conspiracy charges against Curley and Schultz were dropped, and Spanier was acquitted of conspiracy, the charges central to Louis Freeh's allegation of a cover-up. In June 2017, all three were sentenced to jail terms, fines, and probation for the misdemeanors. Spanier was sentenced to four to twelve months in jail, a $7,500 fine, and two years of probation. Spanier's misdemeanor conviction was subsequently overturned on appeal.
  • 7.4K
  • 25 Oct 2022
Topic Review
Anaphase Bridges
Anaphase bridges are DNA threads stretching between the two DNA masses as cells attempt to segregate them during anaphase. Anaphase bridges arise from unresolved DNA intertwines between sister chromatids. Sister chromatid intertwines (SCIs) naturally arise during DNA replication and represent a non-proteinaceous source of cohesion between sister chromatids. SCIs and are mainly resolved in S phase, although some do persist and must be fully removed during mitosis to allow faithful chromosome segregation and avoid the arising of DNA lesions and genome instability, a hallmark of cancer development. As complete resolution of SCIs only occurs during chromosome segregation, it is not clear whether intertwines that persist in mitosis are simply an unwanted leftover or whether they have a functional role.
  • 7.3K
  • 04 Sep 2020
Topic Review
Straight-Six Engine
The straight-six engine (also referred to as an inline-six engine; abbreviated I6 or L6) is an internal combustion engine, with six cylinders mounted in a straight line along the crankcase with all the pistons driving a common crankshaft (straight engine). The bank of cylinders may be oriented at any angle, and where the bank is inclined away from the vertical, the engine is sometimes called a slant-six (although this is also a Chrysler-specific design). The straight-six layout is the simplest engine layout that possesses both primary and secondary mechanical engine balance, resulting in much less vibration than engines with fewer cylinders.
  • 7.3K
  • 15 Nov 2022
Topic Review
Ginger and Iron Deficiency Anaemia
Ginger (Zingiber officinale) is rich in natural polyphenols and may potentially complement oral iron therapy in treating and preventing iron deficiency anaemia (IDA). Ginger possesses several health-promoting properties and has been traditionally used in East Asia to ease fatigue and weaknesses. Contemporarily, ginger is considered a functional food that can confer health benefits beyond its nutritional values for preventing, managing, or treating disease. As a rich source of natural polyphenols, ginger may potentially complement oral iron therapy in treating IDA and be a supportive dietary strategy for preventing IDA. 
  • 7.3K
  • 31 Oct 2022
Topic Review
Parallelism Measurement Methods
At present, the parallelism error was evaluated by contact probe, laser interferometer, and  autocollimator, etc. Moreover, it can also be divided into contact method and non-contact method based on the measurement principle.
  • 7.3K
  • 29 Oct 2020
Topic Review
Inelastic Neutron Scattering
Inelastic neutron scattering (INS) is a spectroscopy based on the energy analysis of neutrons after they have been scattered by a sample. A detected energy transfer can be related to a physical interaction of the corresponding atoms with their environment. An energy transfer of several meVs typically arises from vibrations of atoms. Thus, INS provides an amplitude-of-motion and neutron incoherent cross section weighted phonon density of states.  Given the much higher incoherent scattering cross section of hydrogen relative to that of all other elements, INS is particular sensitive to hydrogen based vibrations. The method is widely used in condensed matter physics and solid state chemistry, because the vibrational properties of matter define various physical properties such as the heat capacity. If used as a fingerprint method, INS can be used to characterize chemical bonds both in the bulk as well as on the surface.
  • 7.3K
  • 30 Oct 2020
Topic Review Peer Reviewed
Prefabricated Building Systems—Design and Construction
Modern Methods of Construction with Offsite Manufacturing is an advancement from prefabricated technologies that existed for decades in the construction industry, and is a platform to integrate various disciplines into providing a more holistic solution. Due to the rapid speed of construction, reduced requirement of labour and minimised work on site, offsite manufacturing and prefabricated building systems are becoming more popular, and perhaps a necessity for the future of the global construction industry. The approach to the design and construction of prefab building systems demands a thorough understanding of their unique characteristics.
  • 7.2K
  • 13 Apr 2022
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