Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing many neutrons without themselves decaying. These elements have different neutron capture cross sections for neutrons of various energies. Boiling water reactors (BWR), pressurized water reactors (PWR), and heavy-water reactors (HWR) operate with thermal neutrons, while breeder reactors operate with fast neutrons. Each reactor design can use different control rod materials based on the energy spectrum of its neutrons. Control rods have been used in nuclear aircraft engines like Project Pluto as a method of control. Operating principle Control rods are inserted into the core of a nuclear reactor and adjusted in order to control the rate of the nuclear chain reaction and, thereby, the thermal power output of the reactor, the rate of steam production, and the electrical power output of the power station. The number of control rods inserted, and the distance to which they...

En días pasados fuimos invitados por la NHRA (National Hot Rod Association) a la ciudad de Las Vegas para tener una experiencia de primera mano en las carreras de Hot Rods que se celebraron ahí.

NEW DELHI (AP) - India's increasing coronavirus caseload made the Asian giant the world's second-worst-hit country behind the United States on Monday, as its efforts to head off economic disaster from the pandemic gain urgency. The 90,802 cases added in the past 24 hours pushed India's total past Brazil with more than 4.2 million cases. India is now behind only the United States, where more than 6.2 million people have been infected, according to Johns Hopkins University. India's Health Ministry on Monday also reported 1,016 new deaths for a total of 71,642, the third-highest national toll. The world's second-most populous country with 1.4 billion people, India has been recording the world's largest daily increases in coronavirus cases for almost a month. Despite over 2 million new cases in the past month and the virus spreading through the country's smaller towns and villages, the Indian government has continued relaxing restrictions to try and resuscitate the economy. On Monday, the Delhi Metro, which serves India's sprawling capital, New Delhi, and adjoining areas, resumed operations after remaining shuttered for more than five months. The commuters were scarce and stations deserted. Only asymptomatic people were allowed to board the trains, with masks, social distancing and temperature checks mandatory. Security personnel used metal detectors attached to rods to ensure social distancing during frisking at the stations, and commuters were allowed to enter only after sanitizing their hands. New Delhi's streets have already returned to their normal bustle, and people are again flocking to markets. The city's bars will reopen on Wednesday. The reopenings come after India's economy shrank faster than any other major nation's, nearly 24% in the last...

Passive autocatalytic recombiner (PAR) is a device that removes hydrogen from the containment of a nuclear power plant during an accident. Its purpose is to prevent hydrogen explosions. Recombiners come into action spontaneously as soon as the hydrogen concentration increases. They are passive devices because their operation does not require external energy.Hydrogen may be generated in a nuclear accident if the reactor fuel overheats and zirconium cladding of the fuel rods reacts chemically with steam. If the hydrogen is released from the reactor to the containment, it may get mixed with air and form a flammable or even explosive mixture. A hydrogen explosion could break the containment and cause radioactive materials to be released to the environment. Recombiners aim at removing hydrogen and thereby preventing explosions.Inside a recombiner there are plates or pellets that are coated with platinum or palladium catalyst. On the surface of the catalyst, hydrogen and oxygen molecules react chemically at low temperature and low hydrogen concentration. The reaction generates steam. The reaction starts spontaneously when the hydrogen concentration reaches 1...

A warhead is the forward section of a device that contains the explosive agent or toxic (biological, chemical, or nuclear) material that is delivered by a missile, rocket, torpedo, or bomb. Classification Types of warheads include: Explosive: An explosive charge is used to disintegrate the target, and damage surrounding areas with a blast wave. Conventional: Chemicals such as gunpowder and high explosives store significant energy within their molecular bonds. This energy can be released quickly by a trigger, such as an electric spark. Thermobaric weapons enhance the blast effect by utilizing the surrounding atmosphere in their explosive reactions. Blast: A strong shock wave is provided by the detonation of the explosive. Fragmentation: Metal fragments are projected at high velocity to cause damage or injury. Continuous rod: Metal bars welded on their ends form a compact cylinder of interconnected rods, which is violently expanded into a contiguous zig-zag-shaped ring by an explosive detonation. The rapidly expanding ring produces a planar cutting effect that is devastating...

A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities decrease according to the inverse square law as they expand into three-dimensional space. There are different types of waveguides for different types of waves. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves. Dielectric waveguides are used at higher radio frequencies, and transparent dielectric waveguides and optical fibers serve as waveguides for light. In acoustics, air ducts and horns are used as waveguides for sound in musical instruments and loudspeakers, and specially-shaped metal rods conduct ultrasonic waves in ultrasonic machining. The geometry of a waveguide reflects its function; in addition to more common types that channel the wave in one dimension, there are two-dimensional slab waveguides which confine waves to two dimensions. The frequency of the transmitted wave also dictates the size...

An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. Afterimages occur because photochemical activity in the retina continues even when the eyes are no longer experiencing the original stimulus.The remainder of this article refers to physiological afterimages. A common physiological afterimage is the dim area that seems to float before one's eyes after briefly looking into a light source, such as a camera flash. Palinopsia is a common symptom of visual snow. Negative afterimages Negative afterimages are primarily caused by neural adaptation of the cells that carry signals from the retina of the eye to the rest of the brain, the retinal ganglion cells. There is also a small contribution when the eye's photoreceptors, the rods and cones, adapt to overstimulation and lose sensitivity. There is brain contribution as well.Normally, any image is moved over...

A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting rods.The crankpins are also called rod bearing journals, and they rotate within the "big end" of the connecting rods. Most modern crankshafts are located in the engine block. They are made from steel or cast iron, using either a forging, casting or machining process. Design The crankshaft located within the engine block, held in place via main bearings which allow the crankshaft to rotate within the block. The up-down motion of each piston is transferred to the crankshaft via connecting rods. A flywheel is often attached to one end of the crankshaft, in order to smoothen the power delivery and reduce vibration.A crankshaft is subjected to enormous stresses, in some cases more than 8.6 tonnes (19,000 pounds) per cylinder. Crankshafts for single-cylinder engines are usually a simpler design than for engines with multiple cylinders. Bearings...