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Topic Review
Guidelines for Measuring Particulate Matter at Construction Sites
PM is a set of air pollutants consisting of solid or liquid particles. These particles are suspended in the atmosphere, but they can also be sedimented on surfaces. Despite a number of differences, PM is mainly classified by its aerodynamic diameter into three groups: (1) fine or breathable particles (PM2.5) with aerodynamic diameter up to 2.5 µm, (2) coarse or inhalable particles (PM10) with an aerodynamic diameter up to 10 µm, and (3) total suspended particles (TSP) that have a wide particle size range, typically with an equivalent aerodynamic cutting diameter of 100 µm.
  • 709
  • 19 Apr 2022
Topic Review
Guitar Technician
A guitar technician (or 'guitar tech') is a member of a music ensemble's road crew who maintains and sets up the musical equipment for one or more guitarists. Depending on the type and size of band, the guitar tech may be responsible for stringing, tuning, and adjusting electric guitars and acoustic guitars, and maintaining and setting up guitar amplifiers and other related electronic equipment such as effect pedals. Once the guitar equipment has been set up onstage, the guitar tech does a soundcheck to ensure that the equipment is working well. If there are any problems, the guitar tech replaces or repairs the faulty components or equipment. Since guitar techs need to soundcheck the instruments and amplifiers, they must have basic guitar-playing skills, a musical "ear" for tuning, and a familiarity with the way guitars, amplifiers, and effect pedals are supposed to sound in the style of music of their band. Guitar techs learn their craft either "on the job", by working in a range of music, sound engineering, and instrument repair jobs; by completing a guitar repair program at a college or lutherie school; or from a combination of these two routes. The salaries and conditions of work for guitar techs vary widely, depending on whether a guitar tech is working for a minor or regional touring bar band or a major international touring act.
  • 424
  • 06 Dec 2022
Topic Review
Guitarrón Chileno
The Guitarrón Chileno (literally: "large Chilean guitar") is a guitar-shaped plucked string instrument from Chile , with 25 or 24 (rarely) strings. Its primary contemporary use is as the instrumental accompaniment for the traditional Chilean genre of singing poetry known as Canto a lo Poeta, though a few virtuosi have also begun to develop the instrument's solo possibilities.
  • 716
  • 02 Dec 2022
Topic Review
Gun Carrier Mark I
The Gun Carrier Mark I was the first piece of self-propelled artillery ever to be produced, a British development from the First World War. Gun carriers were first used in the Battle of Pilckem Ridge (31 July – 2 August 1917) during the Third Battle of Ypres (31 July – 10 November 1917).
  • 582
  • 21 Nov 2022
Biography
Gustav Otto
Gustav Otto (12 January 1883 – 28 February 1926) was a German aircraft and aircraft engine designer and manufacturer. Gustav was born in Cologne to Nikolaus August Otto, the founder of N. A. Otto & Cie. and inventor of the four-stroke internal combustion engine. It is therefore regarded that his interest in engines, specifically aircraft and the manufacture thereof, was something he inherited
  • 1.3K
  • 22 Nov 2022
Topic Review
GVL Production with Levulinic Acid
Levulinic acid (LA) is considered as one of the “Top 10” building blocks for future bio-refineries as proposed by the US Department of Energy. It is  one of the most important platform molecules for the production of fine chemicals and fuels based on its compatibility with existing processes, market economics, and industrial ability to serve as a platform for the synthesis of important derivatives. Hydrogenation of LA to produce γ-valerolactone (GVL) is an active area of research due to the potential of GVL to be used as a biofuel in its own right and for its subsequent transformation into hydrocarbon fuels. This paper contains a new design for a simple, cost effective, and safe hydrogenation reactor for the transformation of levulinic acid to γ-valerolactone (GVL) by utilizing high boiling point organic fluid. The hydrogenation reactor is composed of a heating source—organic fluid (called “DOWTHERM A” or “thermex”) and the catalytic reactor. The advantages of high boiling temperature fluids, along with advances in hydrocracking and reforming technologies driven by the oil and gas industries, make the organic concept more suitable and safer (water coming in contact with liquid metal is well understood in the metallurgical industry to be a steam explosion hazard) for heating the hydrogenation reactor. COMSOL multi-physics software version 4.3b was applied in this work and simultaneously solves the continuity, Navier-Stokes (fluid flow), energy (heat transfer), and diffusion with chemical reaction kinetics equations. It was shown that the heat flux supplied by the DOWTHERM A organic fluid could provide the necessary heat flux required for maintaining the hydrogenation process. It was found that the mass fractions of hydrogen and levulinic acid decreased along the reactor axis. The GVL mass fraction increased along the reactor axis.
  • 1.8K
  • 30 Oct 2020
Topic Review
Gyro-Stabilized Camera Systems
Gyro-stabilized camera systems use modern electronic position data to correct for movements of the platforms they are mounted on to enable a high degree of stabilization. The systems often use a multi-axis gyro stabilization to enable the use of zoom lenses and high definition capture, despite the high amounts of vibrations and movements in aircraft, helicopters or other vehicles. The applications range from security and military operations, law enforcement, ENG, sports broadcasting documentary, natural history, and feature film productions..
  • 3.3K
  • 14 Oct 2022
Topic Review
Gyrotrons
Gyrotrons are among the most powerful sources of coherent radiation that operate in CW and long pulse regimes in the sub-THz and the THz frequency ranges of the electromagnetic spectrum, i.e. between 0.3 THz and 3.0 THz (corresponding to wavelengths from 1.0 to 0.1 mm). This region, which spans between the frequency bands occupied by various electronic and photonic devices, respectively, is habitually called a THz power gap. The underlying mechanism of the operation of the gyrotron involves a formation of bunches of electrons gyrating in a helical electron beam and their synchronous interaction with a fast (i.e. having a superluminal phase velocity) electromagnetic wave, producing a bremsstrahlung radiation. In contrast to the slow-wave tubes, which utilize tiny structures with dimensions comparable to the wavelength of the radiation, the gyrotrons have a simpler resonant system (cavity resonator) with dimensions that are much greater than the wavelength. This allows much more powerful electron beams to be used and thus higher output powers to be achieved. Although in comparison with the classical microwave tubes the gyrotrons are characterized by greater volume and weight due to the presence of bulky parts (such as superconducting magnets and massive collectors where the energy of the spent electron beam is dissipated) they are much more compact and can easily be embedded in a sophisticated laboratory equipment (e.g. spectrometers, technological systems, etc.) than other devices such as free-electron lasers (FEL) and radiation sources based on electron accelerators. Nowadays, the gyrotrons are used as powerful sources of coherent radiation in the wide fields of high-power sub-THz and THz science and technologies [1][2][3].
  • 2.0K
  • 29 Oct 2020
Topic Review
H Bridge
An H bridge is an electronic circuit that switches the polarity of a voltage applied to a load. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards. Most DC-to-AC converters (power inverters), most AC/AC converters, the DC-to-DC push–pull converter, most motor controllers, and many other kinds of power electronics use H bridges. In particular, a bipolar stepper motor is almost invariably driven by a motor controller containing two H bridges.
  • 2.5K
  • 24 Oct 2022
Topic Review
H-500 Holon
The H-500 project is an outline planning scheme in accordance with the Planning and Building Law for South Holon, Israel. The area of the project is approximately 4,080 dunams and it is the largest, undeveloped land reserve remaining in Holon. The scheme is bounded in the north by Sderot Yerushalayim and the Kiryat Sharet and Kiryat Pinhas Ayalon neighbourhoods, in the east by Highway no. 4, in the south by the border with the city of Rishon LeZion and in the west by Highway 20 (Israel) (the Ayalon Highway).
  • 271
  • 02 Nov 2022
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