World Library  
Flag as Inappropriate
Email this Article

Ablation

Article Id: WHEBN0000529953
Reproduction Date:

Title: Ablation  
Author: World Heritage Encyclopedia
Language: English
Subject: Glacier, Laser scalpel, High-intensity focused ultrasound, Névé, List of glaciers
Collection: Materials Degradation, Plasma Physics
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Ablation

Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. 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 near the electrode in a flashtube. The high-energy electrical arc slowly erodes the glass, leaving a frosted appearance.

Contents

  • Biology 1
  • Glaciology 2
  • Laser ablation 3
  • Marine surface coatings 4
  • Medicine 5
  • Passive fire protection 6
  • Spaceflight 7
  • See also 8
  • References 9
  • External links 10

Biology

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

Genetic ablation is another term for gene silencing, in which gene expression is abolished through the alteration or deletion of genetic sequence information. In cell ablation, individual cells in a population or culture are destroyed or removed. Both can be used as experimental tools, as in loss-of-function experiments.[1]

Glaciology

In glaciology and meteorology, ablation—the opposite of accumulation—refers to all processes that remove snow, ice, or water from a glacier or snowfield.[2] Ablation refers to the melting of snow or ice that runs off the glacier, evaporation, sublimation, calving, or erosive removal of snow by wind. Air temperature is typically the dominant control of ablation, with precipitation exercising secondary control. In a temperate climate during ablation season, ablation rates typically average around 2 mm/h.[3] 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.[4]

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

Laser ablation

An Nd:YAG laser drills a hole through a block of nitrile. The intense burst of infrared radiation ablates the highly absorbing rubber, releasing an eruption of plasma.
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. While these lasers can average a low power, they can offer peak intensity and fluence given by:

\text{Intensity } (\mathrm{W}/\mathrm{cm}^2) = \frac{\text{average power } (\mathrm{W})}{\text{focal spot area } (\mathrm{cm}^2)}
\text{Peak intensity } (\mathrm{W}/\mathrm{cm}^2) = \frac{\text{peak power } (\mathrm{W})}{\text{focal spot area } (\mathrm{cm}^2)}
\text{Fluence } (\mathrm{J}/\mathrm{cm}^2) = \frac{\text{laser pulse energy } (\mathrm{J})}{\text{focal spot area } (\mathrm{cm}^2)}

while the peak power is

\text{Peak power } (\mathrm{W}) = \frac{\text{pulse energy } (\mathrm{J})}{\text{pulse duration } (\mathrm{s})}

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

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.[5]

Marine surface coatings

barnacles for the bottom hull surfaces of recreational, commercial and military sea vessels. Ablative paints are often utilized for this purpose to prevent the dilution or deactivation of the antifouling agent. Over time, the paint will slowly decompose in the water, exposing fresh antifouling compounds on the surface. Engineering the antifouling agents and the ablation rate can produce long-lived protection from the deleterious effects of biofouling.

Medicine

In medicine, ablation is the same as removal of a part of biological tissue, usually by surgery. Surface ablation of the skin (dermabrasion, also called resurfacing because it induces regeneration) can be carried out by chemicals (which cause peeling) or by lasers. Its purpose is to remove skin spots, aged skin, wrinkles, thus rejuvenating it. Surface ablation is also employed in otolaryngology for several kinds of surgery, such as for snoring. 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. The term is often used in the context of laser ablation, a process in which a laser dissolves a material's molecular bonds. 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.

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

Radiofrequency ablation (RFA) is a method of removing aberrant tissue from within the body via minimally invasive procedures. I.e., RFA in an electrophysiology study to remove cells that are issuing abnormal electrical activity leading to arrhythmia.

Bone marrow ablation is a process whereby the human bone marrow cells are eliminated in preparation for a bone marrow transplant. This is performed using high-intensity chemotherapy and total body irradiation. As such, it has nothing to do with the vaporization techniques described in the rest of this article.

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

Recently, some researchers reported successful results with genetic ablation. 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. Genetically ablated lines can be maintained for a prolonged period of time and shared within the research community. Researchers at Columbia University report of reconstituted caspases combined from C. elegans and humans, which maintain a high degree of target specificity. The genetic ablation techniques described could prove useful in battling cancer.[6]

Passive fire protection

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

Spaceflight

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

In a basic sense, ablative material is designed to slowly burn away in a controlled manner, so that heat can be carried away from the spacecraft by the gases generated by the ablative process while the remaining solid material insulates the craft from superheated gases. 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.[7] 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.

See also

References

  1. ^ Cell Ablation definition at Change Bioscience.
  2. ^ Paterson, W. S. B. 1999. The Physics of Glaciers. Tarrytown, N.Y., Pergamon. 496 p.
  3. ^ Glossary of Meteorology
  4. ^ Betterton, M. D. "Theory of structure formation in snowfields motivated by penitentes, suncups, and dirt cones." Physical Review E 63.5 (2001): 056129.
  5. ^ Amir Yousef Sajjadi, Kunal Mitra, Michael Grace, Ablation of subsurface tumors using an ultra-short pulse laser, Optics and Lasers in Engineering, Volume 49, Issue 3, March 2011, Pages 451-456, ISSN 0143-8166
  6. ^ Chelur, Dattananda S.; Chalfie, Martin (February 2007). "Targeted cell killing by reconstituted caspases". Proceedings of the National Academy of Sciences 104 (7): 2283–8.  
  7. ^ Parker, John and C. Michael Hogan, "Techniques for Wind Tunnel assessment of Ablative Materials," NASA Ames Research Center, Technical Publication, August, 1965.

External links

  • Chemical Peeling. American Society for Dermatological Surgery.
  • Heart Arrhythmias Respond to Ablation UCLA Healthcare
  • Lasik Laser Eye Surgery. USA Food an Drugs Administration info.
  • Physical Modalities, Including Laser. eMedicine index of articles on the subject.
  • Physics of laser ablation
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.