Ablation

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Not to be confused with oblation or ablution. Ablation_sentence_0

Ablation is removal or destruction of material from an object by vaporization, chipping, or other erosive processes. Ablation_sentence_1

Examples of ablative materials are described below, and include spacecraft material for ascent and atmospheric reentry, ice and snow in glaciology, biological tissues in medicine and passive fire protection materials. Ablation_sentence_2

Artificial intelligence Ablation_section_0

Further information: Ablation (artificial intelligence) Ablation_sentence_3

In artificial intelligence (AI), especially machine learning, ablation is the removal of a component of an AI system. Ablation_sentence_4

The term is by analogy with biology: removal of components of an organism. Ablation_sentence_5

Biology Ablation_section_1

Biological ablation is the removal of a biological structure or functionality. Ablation_sentence_6

Genetic ablation is another term for gene silencing, in which gene expression is abolished through the alteration or deletion of genetic sequence information. Ablation_sentence_7

In cell ablation, individual cells in a population or culture are destroyed or removed. Ablation_sentence_8

Both can be used as experimental tools, as in loss-of-function experiments. Ablation_sentence_9

Electro-ablation Ablation_section_2

Electro-ablation, is an electrochemical process similar to electro-polishing, that removes material from a metallic workpiece to reduce surface roughness. Ablation_sentence_10

It is similar to electro-polishing in that it uses a current flowing through an electrolyte from the workpiece (anode) to remove metal from the surface of the workpiece, producing a smoother surface. Ablation_sentence_11

It differs from electro-polishing in its current flow, frequency and high rate of metal removal (ablation). Ablation_sentence_12

Electro-polishing uses low currents, usually much less than 1 Amp/cm, that are usually constant or changing at very low frequency. Ablation_sentence_13

This limits the speed of electro-polishing. Ablation_sentence_14

Components often requiring several hours of immersed electro-polishing for significant reduction in surface roughness. Ablation_sentence_15

This reduces the attractiveness of electro-polishing for post-processing of metallic components, such as those produced by metal additive manufacturing (3D printing of metals). Ablation_sentence_16

Electro-ablation uses a combination of very high current flow (usually in excess of 10 Amps/cm) combined with very high frequency (up to 200kHz) changes in current flow. Ablation_sentence_17

This allows electro-ablation to break through highly resistive oxide surfaces, such as those found on Titanium and other exotic metals and alloys. Ablation_sentence_18

Through software control, electro-ablation processes are able to quickly remove (via ablation) tough protective oxide layers and then immediately reduce the current flow to avoid melting the underlying non-oxidised metal or alloy. Ablation_sentence_19

This allows very quick surface finishing. Ablation_sentence_20

The process is capable of providing surface finishing for a wide range of exotic and widely used metals and alloys, including: titanium, stainless steel, niobium, chromium–cobalt, Inconel, aluminium, and a range of widely available steels and alloys. Ablation_sentence_21

Due to its use of very high frequencies, electro-ablation is very effective at achieving high levels of surface finishing in holes, valleys and hidden or internal surfaces on metallic workpieces (parts). Ablation_sentence_22

The process is particularly applicable to components produced by additive manufacturing process, such as 3D-printed metals. Ablation_sentence_23

These components tend to be produced with roughness levels well above 5–20 micron. Ablation_sentence_24

Electro-ablation can be used to quickly reduce the surface roughness to less than 0.8 micron, allowing the post-process to be used for volume production surface finishing. Ablation_sentence_25

The electro-ablation process can be applied in two ways, "brush" or "immersion" in a bath. Ablation_sentence_26

The brush method occurs in air, above a drain tank, with the electrolyte and cathode contained in a brush, that is either handheld or positioned by robotic control. Ablation_sentence_27

This method is preferred for objects that only require surface finishing on limited areas or on objects that are too large to be used in an immersion tank. Ablation_sentence_28

The immersion method requires the object to be immersed in a tank containing an electrolyte, usually phosphoric acid, and cathodic probes. Ablation_sentence_29

This method is preferred for objects produced in a high-volume production environment, where low-skilled labour is available for loading and unloading components, or where longer surface finishing times are required. Ablation_sentence_30

Glaciology Ablation_section_3

Further information: Ablation zone Ablation_sentence_31

In glaciology and meteorology, ablation—the opposite of accumulation—refers to all processes that remove snow, ice, or water from a glacier or snowfield. Ablation_sentence_32

Ablation refers to the melting of snow or ice that runs off the glacier, evaporation, sublimation, calving, or erosive removal of snow by wind. Ablation_sentence_33

Air temperature is typically the dominant control of ablation, with precipitation exercising secondary control. Ablation_sentence_34

In a temperate climate during ablation season, ablation rates typically average around 2 mm/h. Ablation_sentence_35

Where solar radiation is the dominant cause of snow ablation (e.g., if air temperatures are low under clear skies), characteristic ablation textures such as suncups and penitentes may develop on the snow surface. Ablation_sentence_36

Ablation can refer either to the processes removing ice and snow or to the quantity of ice and snow removed. Ablation_sentence_37

Debris-covered glaciers have also been shown to greatly impact the ablation process. Ablation_sentence_38

There is a thin debris layer that can be located on the top of glaciers that intensifies the ablation process below the ice. Ablation_sentence_39

The debris-covered parts of a glacier that is experiencing ablation are sectioned into three categories which include ice cliffs, ponds, and debris. Ablation_sentence_40

These three sections allow scientists to measure the heat digested by the debris-covered area and is calculated. Ablation_sentence_41

The calculations are dependent on the area and net absorbed heat amounts in regards to the entire debris-covered zones. Ablation_sentence_42

These types of calculations are done to various glaciers to understand and analyze future patterns of melting. Ablation_sentence_43

Moraine (glacial debris) is moved by natural processes that allow for down-slope movement of materials on the glacier body. Ablation_sentence_44

It is noted that if the slope of a glacier is too high then the debris will continue to move along the glacier to a further location. Ablation_sentence_45

The sizes and locations of glaciers vary around the world, so depending on the climate and physical geography the varieties of debris can differ. Ablation_sentence_46

The size and magnitude of the debris is dependent on the area of glacier and can vary from dust-size fragments to blocks as large as a house. Ablation_sentence_47

There has been many experiments done to demonstrate the effect of debris on the surface of glaciers. Ablation_sentence_48

Yoshiyuki Fujii, a professor at the National Institute of Polar Research designed an experiment that showed ablation rate was accelerated under a thin debris layer and was retarded under a thick one as compared with that of a natural snow surface. Ablation_sentence_49

This science is significant due to the importance of long-term availability of water resources and assess glacier response to climate change. Ablation_sentence_50

Natural resource availability is a major drive behind research conducted in regards to the ablation process and overall study of glaciers. Ablation_sentence_51

Laser ablation Ablation_section_4

Main article: laser ablation Ablation_sentence_52

Laser ablation is greatly affected by the nature of the material and its ability to absorb energy, therefore the wavelength of the ablation laser should have a minimum absorption depth. Ablation_sentence_53

While these lasers can average a low power, they can offer peak intensity and fluence given by: Ablation_sentence_54

while the peak power is Ablation_sentence_55

Surface ablation of the cornea for several types of eye refractive surgery is now common, using an excimer laser system (LASIK and LASEK). Ablation_sentence_56

Since the cornea does not grow back, laser is used to remodel the cornea refractive properties to correct refraction errors, such as astigmatism, myopia, and hyperopia. Ablation_sentence_57

Laser ablation is also used to remove part of the uterine wall in women with menstruation and adenomyosis problems in a process called endometrial ablation. Ablation_sentence_58

Recently, researchers have demonstrated a successful technique for ablating subsurface tumors with minimal thermal damage to surrounding healthy tissue, by using a focused laser beam from an ultra-short pulse diode laser source. Ablation_sentence_59

Marine surface coatings Ablation_section_5

Antifouling paints and other related coatings are routinely used to prevent the buildup of microorganisms and other animals, such as barnacles for the bottom hull surfaces of recreational, commercial and military sea vessels. Ablation_sentence_60

Ablative paints are often utilized for this purpose to prevent the dilution or deactivation of the antifouling agent. Ablation_sentence_61

Over time, the paint will slowly decompose in the water, exposing fresh antifouling compounds on the surface. Ablation_sentence_62

Engineering the antifouling agents and the ablation rate can produce long-lived protection from the deleterious effects of biofouling. Ablation_sentence_63

Medicine Ablation_section_6

In medicine, ablation is the same as removal of a part of biological tissue, usually by surgery. Ablation_sentence_64

Surface ablation of the skin (dermabrasion, also called resurfacing because it induces regeneration) can be carried out by chemicals (chemoablation), by lasers (laser ablation), by freezing (cryoablation), or by electricity (fulguration). Ablation_sentence_65

Its purpose is to remove skin spots, aged skin, wrinkles, thus rejuvenating it. Ablation_sentence_66

Surface ablation is also employed in otolaryngology for several kinds of surgery, such as for snoring. Ablation_sentence_67

Ablation therapy using radio frequency waves on the heart is used to cure a variety of cardiac arrhythmiae such as supraventricular tachycardia, Wolff–Parkinson–White syndrome (WPW), ventricular tachycardia, and more recently as management of atrial fibrillation. Ablation_sentence_68

The term is often used in the context of laser ablation, a process in which a laser dissolves a material's molecular bonds. Ablation_sentence_69

For a laser to ablate tissues, the power density or fluence must be high, otherwise thermocoagulation occurs, which is simply thermal vaporization of the tissues. Ablation_sentence_70

Rotoablation is a type of arterial cleansing that consists of inserting a tiny, diamond-tipped, drill-like device into the affected artery to remove fatty deposits or plaque. Ablation_sentence_71

The procedure is used in the treatment of coronary heart disease to restore blood flow. Ablation_sentence_72

Radiofrequency ablation (RFA) is a method of removing aberrant tissue from within the body via minimally invasive procedures. Ablation_sentence_73

Microwave ablation (MWA) is similar to RFA but at higher frequencies of electromagnetic radiation. Ablation_sentence_74

High-intensity focused ultrasound (HIFU) ablation removes tissue from within the body noninvasively. Ablation_sentence_75

Bone marrow ablation is a process whereby the human bone marrow cells are eliminated in preparation for a bone marrow transplant. Ablation_sentence_76

This is performed using high-intensity chemotherapy and total body irradiation. Ablation_sentence_77

As such, it has nothing to do with the vaporization techniques described in the rest of this article. Ablation_sentence_78

Ablation of brain tissue is used for treating certain neurological disorders, particularly Parkinson's disease, and sometimes for psychiatric disorders as well. Ablation_sentence_79

Recently, some researchers reported successful results with genetic ablation. Ablation_sentence_80

In particular, genetic ablation is potentially a much more efficient method of removing unwanted cells, such as tumor cells, because large numbers of animals lacking specific cells could be generated. Ablation_sentence_81

Genetically ablated lines can be maintained for a prolonged period of time and shared within the research community. Ablation_sentence_82

Researchers at Columbia University report of reconstituted caspases combined from C. Ablation_sentence_83 elegans and humans, which maintain a high degree of target specificity. Ablation_sentence_84

The genetic ablation techniques described could prove useful in battling cancer. Ablation_sentence_85

Passive fire protection Ablation_section_7

Firestopping and fireproofing products can be ablative in nature. Ablation_sentence_86

This can mean endothermic materials, or merely materials that are sacrificial and become "spent" over time while exposed to fire, such as silicone firestop products. Ablation_sentence_87

Given sufficient time under fire or heat conditions, these products char away, crumble, and disappear. Ablation_sentence_88

The idea is to put enough of this material in the way of the fire that a level of fire-resistance rating can be maintained, as demonstrated in a fire test. Ablation_sentence_89

Ablative materials usually have a large concentration of organic matter that is reduced by fire to ashes. Ablation_sentence_90

In the case of silicone, organic rubber surrounds very finely divided silica dust (up to 380 m² of combined surface area of all the dust particles per gram of this dust). Ablation_sentence_91

When the organic rubber is exposed to fire, it burns to ash and leaves behind the silica dust with which the product started. Ablation_sentence_92

Protoplanetary disk ablation Ablation_section_8

Protoplanetary disks are rotating circumstellar disks of dense gas and dust surrounding young, newly formed stars. Ablation_sentence_93

Shortly after star formation, stars often have leftover surrounding material that is still gravitationally bound to them, forming primitive disks that orbit around the star's equator – not too dissimilarly from the rings of Saturn. Ablation_sentence_94

This occurs because the decrease in the protostellar material’s radius during formation increases angular momentum, which means that this remaining material gets whipped into a flattened circumstellar disk around the star. Ablation_sentence_95

This circumstellar disk may eventually mature into what is referred to as a protoplanetary disk: a disk of gas, dust, ice and other materials from which planetary systems may form. Ablation_sentence_96

In these disks, orbiting matter starts to accrete in the colder mid-plane of the disk from dust grains and ices sticking together. Ablation_sentence_97

These small accretions grow from pebbles to rocks to early baby planets, called planetesimals, then protoplanets, and eventually, full planets. Ablation_sentence_98

As it is believed that massive stars may play a role in actively triggering star formation (by introducing gravitational instabilities amongst other factors), it is plausible that young, smaller stars with disks may be living relatively nearby to older, more massive stars. Ablation_sentence_99

This has already been confirmed through observations to be the case in certain clusters, e.g. in the Trapezium cluster. Ablation_sentence_100

Since massive stars tend to collapse through supernovae at the end of their lives, research is now investigating what role the shockwave of such an explosion, and the resulting supernova remnant (SNR), would play if it occurred in the line of fire of a protoplanetary disk. Ablation_sentence_101

According to computationally modelled simulations, a SNR striking a protoplanetary disk would result in significant ablation of the disk, and this ablation would strip a significant amount of protoplanetary material from the disk – but not necessarily destroy the disk entirely. Ablation_sentence_102

This is an important point because a disk that survives such an interaction with sufficient material leftover to form a planetary system may inherit an altered disk chemistry from the SNR, which could have effects on the planetary systems that later form. Ablation_sentence_103

Spaceflight Ablation_section_9

Main article: atmospheric reentry § Ablative Ablation_sentence_104

In spacecraft design, ablation is used to both cool and protect mechanical parts and/or payloads that would otherwise be damaged by extremely high temperatures. Ablation_sentence_105

Two principal applications are heat shields for spacecraft entering a planetary atmosphere from space and cooling of rocket engine nozzles. Ablation_sentence_106

Examples include the Apollo Command Module that protected astronauts from the heat of atmospheric reentry and the Kestrel second stage rocket engine designed for exclusive use in an environment of space vacuum since no heat convection is possible. Ablation_sentence_107

In a basic sense, ablative material is designed so that instead of heat being transmitted into the structure of the spacecraft, only the outer surface of the material bears the majority of the heating effect. Ablation_sentence_108

The outer surface chars and burns away – but quite slowly, only gradually exposing new fresh protective material beneath. Ablation_sentence_109

The heat is carried away from the spacecraft by the gases generated by the ablative process, and never penetrates the surface material, so the metallic and other sensitive structures they protect, remain at a safe temperature. Ablation_sentence_110

As the surface burns and disperses into space, while the remaining solid material continues to insulate the craft from ongoing heat and superheated gases. Ablation_sentence_111

The thickness of the ablative layer is calculated to be sufficient to survive the heat it will encounter on its mission. Ablation_sentence_112

There is an entire branch of spaceflight research involving the search for new fireproofing materials to achieve the best ablative performance; this function is critical to protect the spacecraft occupants and payload from otherwise excessive heat loading. Ablation_sentence_113

The same technology is used in some passive fire protection applications, in some cases by the same vendors, who offer different versions of these fireproofing products, some for aerospace and some for structural fire protection. Ablation_sentence_114

See also Ablation_section_10

Ablation_unordered_list_0


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Ablation.