Convective inhibition: Difference between revisions

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[[File:Cassegrain.en.png|thumb|300px|Light path in a Cassegrain reflecting telescope.]]
It is very common to have a dental emergency -- a fractured tooth, an abscess, or severe pain when chewing. Over-the-counter pain medication is just masking the problem. Seeing an emergency dentist is critical to getting the source of the problem diagnosed and corrected as soon as possible.<br><br>Here are some common dental emergencies:<br>Toothache: The most common dental emergency. This generally means a badly decayed tooth. As the pain affects the tooth's nerve, treatment involves gently removing any debris lodged in the cavity being careful not to poke deep as this will cause severe pain if the nerve is touched. Next rinse vigorously with warm water. Then soak a small piece of cotton in oil of cloves and insert it in the cavity. This will give temporary relief until a dentist can be reached.<br><br>At times the pain may have a more obscure location such as decay under an old filling. As this can be only corrected by a dentist there are two things you can do to help the pain. Administer a pain pill (aspirin or some other analgesic) internally or dissolve a tablet in a half glass (4 oz) of warm water holding it in the mouth for several minutes before spitting it out. DO NOT PLACE A WHOLE TABLET OR ANY PART OF IT IN THE TOOTH OR AGAINST THE SOFT GUM TISSUE AS IT WILL RESULT IN A NASTY BURN.<br><br>Swollen Jaw: This may be caused by several conditions the most probable being an abscessed tooth. In any case the treatment should be to reduce pain and swelling. An ice pack held on the outside of the jaw, (ten minutes on and ten minutes off) will take care of both. If this does not control the pain, an analgesic tablet can be given every four hours.<br><br>Other Oral Injuries: Broken teeth, cut lips, bitten tongue or lips if severe means a trip to a dentist as soon as possible. In the mean time rinse the mouth with warm water and place cold compression the face opposite the injury. If there is a lot of bleeding, apply direct pressure to the bleeding area. If bleeding does not stop get patient to the emergency room of a hospital as stitches may be necessary.<br><br>Prolonged Bleeding Following Extraction: Place a gauze pad or better still a moistened tea bag over the socket and have the patient bite down gently on it for 30 to 45 minutes. The tannic acid in the tea seeps into the tissues and often helps stop the bleeding. If bleeding continues after two hours, call the dentist or take patient to the emergency room of the nearest hospital.<br><br>Broken Jaw: If you suspect the patient's jaw is broken, bring the upper and lower teeth together. Put a necktie, handkerchief or towel under the chin, tying it over the head to immobilize the jaw until you can get the patient to a dentist or the emergency room of a hospital.<br><br>Painful Erupting Tooth: In young children teething pain can come from a loose baby tooth or from an erupting permanent tooth. Some relief can be given by crushing a little ice and wrapping it in gauze or a clean piece of cloth and putting it directly on the tooth or gum tissue where it hurts. The numbing effect of the cold, along with an appropriate dose of aspirin, usually provides temporary relief.<br><br>In young adults, an erupting 3rd molar (Wisdom tooth), especially if it is impacted, can cause the jaw to swell and be quite painful. Often the gum around the tooth will show signs of infection. Temporary relief can be had by giving aspirin or some other painkiller and by dissolving an aspirin in half a glass of warm water and holding this solution in the mouth over the sore gum. AGAIN DO NOT PLACE A TABLET DIRECTLY OVER THE GUM OR CHEEK OR USE THE ASPIRIN SOLUTION ANY STRONGER THAN RECOMMENDED TO PREVENT BURNING THE TISSUE. The swelling of the jaw can be reduced by using an ice pack on the outside of the face at intervals of ten minutes on and ten minutes off.<br><br>If you have any concerns about where and how to use [http://www.youtube.com/watch?v=90z1mmiwNS8 dentist DC], you can speak to us at the webpage.
The '''Cassegrain reflector''' is a combination of a primary [[concave mirror]] and a secondary [[convex mirror]], often used in [[optical telescope]]s and [[Antenna (radio)|radio antenna]]s.
 
In a symmetrical Cassegrain both mirrors are aligned about the [[optical axis]], and the primary mirror usually contains a hole in the centre thus permitting the light to reach an [[eyepiece]], a [[camera]], or a [[light detector]]. Alternatively, as in many radio telescopes, the final focus may be in front of the primary. In an asymmetrical Cassegrain, the mirror(s) may be tilted to avoid obscuration of the primary or the need for a hole in the primary mirror (or both).
 
The classic Cassegrain configuration uses a [[parabolic reflector]] as the primary while the secondary mirror is [[hyperboloid|hyperbolic]].<ref>{{cite web | url = http://www.astromia.com/glosario/cassegrain.htm | title = Diccionario de astronomía y geología. Las ciencias de la Tierra y del Espacio al alcance de todos. Cassegrain | publisher = AstroMía}}</ref> Modern variants often have a hyperbolic primary for increased performance, or the primary and/or secondary are spherical or elliptical for ease of manufacturing.
 
The Cassegrain reflector is named after a published [[reflecting telescope]] design that appeared in the April 25, 1672 ''[[Journal des sçavans]]'' which has been attributed to [[Laurent Cassegrain]].<ref>[http://www.ingenta.com/isis/searching/Expand/ingenta?pub=infobike://iop/jopt/1997/00000028/00000004/art00004 André Baranne and Françoise Launay, ''Cassegrain: a famous unknown of instrumental astronomy''], Journal of Optics, 1997, vol.&nbsp;28, no.&nbsp;4, pp.&nbsp;158-172(15)</ref> Similar designs using convex secondaries have been found in the [[Bonaventura Cavalieri]]'s 1632 writings describing burning mirrors<ref>[http://books.google.com/books?hl=en&lr=&id=ZX64AAAAIAAJ&oi=fnd&pg=PA1&dq=%22lo+specchio+ustorio%22&ots=CzX83kjdXO&sig=bZmh3XzXN2mWZdIa32OGlyypwEk Lo specchio ustorio, overo, Trattato delle settioni coniche]</ref><ref>''Stargazer, the Life and Times of the Telescope'', by Fred Watson, [http://books.google.com/books?id=2LZZginzib4C&pg=PA134&dq=gregory+cassegrain+mersenne p.&nbsp;134]</ref> and [[Marin Mersenne]]'s 1636 writings describing telescope designs.<ref>''Stargazer'', [http://books.google.com/books?id=2LZZginzib4C&pg=PA115&dq=mersenne+zucchi+parallel#PPA115,M1 p.&nbsp;115].</ref> [[James Gregory (mathematician)|James Gregory]]'s 1662 attempts to create a reflecting telescope included a Cassegrain configuration, judging by a convex secondary mirror found among his experiments.<ref>''Stargazer'', [http://books.google.com/books?id=2LZZginzib4C&pg=PA132&dq=Gregory++telescope+French+convex pp.&nbsp;123 and&nbsp;132]</ref>
 
The Cassegrain design is also used in [[catadioptric system]]s.
 
==Cassegrain designs==
[[File:Cassegrain-Telescope.svg|center|thumb|500px|Light path in a Cassegrain reflector telescope]]
 
=== The "Classic" Cassegrain ===
 
The "Classic" Cassegrain has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. Folding the optics makes this a compact design. On smaller telescopes, and camera lenses, the secondary is often mounted on an optically flat, optically clear glass plate that closes the telescope tube. This support eliminates the "star-shaped" diffraction effects caused by a straight-vaned support spider. The closed tube stays clean, and the primary is protected, at the cost of some loss of light-gathering power.
 
It makes use of the special properties of parabolic and hyperbolic reflectors. A concave [[parabolic reflector]] will reflect all incoming light rays parallel to its axis of symmetry to a single point, the focus. A convex hyperbolic reflector has two foci and will reflect all light rays directed at one of its two foci towards its other focus. The mirrors in this type of telescope are designed and positioned so that they share one focus and so that the second focus of the hyperbolic mirror will be at the same point at which the image is to be observed, usually just outside the eyepiece. The parabolic mirror reflects parallel light rays entering the telescope to its focus, which is also the focus of the hyperbolic mirror. The hyperbolic mirror then reflects those light rays to its other focus, where the image is observed.
 
The [[radius of curvature (optics)|radii of curvature]] of the primary and secondary mirrors, respectively, in the classic configuration are
 
:<math>R_1 = -\frac{2DF}{F - B}</math>
and
:<math>R_2 = -\frac{2DB}{F - B - D}</math>
 
where
* <math>F</math> is the effective [[focal length]] of the system,
* <math>B</math> is the back focal length (the distance from the secondary to the focus), and
* <math>D</math> is the distance between the two mirrors.
 
If, instead of <math>B</math> and <math>D</math>, the known quantities are the focal length of the primary mirror, <math>f_1</math>, and the distance to the focus behind the primary mirror, <math>b</math>, then <math>D = f_1(F - b)/(F + f_1)</math> and <math>B = D + b</math>.
 
The [[conic constant]] of the primary mirror is that of a parabola, <math>K_1 = -1</math>, and that of the secondary mirror, <math>K_2</math>, is chosen to shift the focus to the desired location:
 
:<math>K_2 = -1 - \alpha - \sqrt{\alpha(\alpha+2)}</math>,
 
where
:<math>\alpha = \frac{1}{2}\left[ \frac{4DBM}{(F + BM - DM)(F - B - D)}\right] ^2</math>,
 
and <math>M=(F-B)/D</math> is the secondary magnification.
 
===Ritchey-Chrétien===
{{main|Ritchey-Chrétien telescope}}
The Ritchey-Chrétien is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary). It is free of [[coma (optics)|coma]] and spherical aberration at a flat focal plane, making it well suited for wide field and photographic observations. It was invented by [[George Willis Ritchey]] and [[Henri Chrétien]] in the early 1910s.
 
===Dall-Kirkham===
The Dall-Kirkham Cassegrain telescope's design was created by Horace Dall in 1928 and took on the name in an article published in [[Scientific American]] in 1930 following discussion between amateur astronomer Allan Kirkham and Albert G. Ingalls, the magazine editor at the time. It uses a concave [[ellipse|elliptical]] primary mirror and a convex [[Sphere|spherical]] secondary. While this system is easier to grind than a classic Cassegrain or Ritchey-Chretien system, it does not correct for off-axis coma and field curvature so the image degrades quickly off-axis. Because this is less noticeable at longer [[F-number|focal ratio]]s, Dall-Kirkhams are seldom faster than f/15.
 
===Off-axis configurations===
An unusual variant of the Cassegrain is the ''Schiefspiegler'' telescope ("skewed" or "oblique reflector", also known as "kutter telescope" after its inventor [[Anton Kutter]]<ref>[http://www.telescopemaking.org/schief.html .telescopemaking.org - The Kutter Schiefspiegler]</ref>) which uses tilted mirrors to avoid the secondary mirror casting a shadow on the primary. However, while eliminating diffraction patterns this leads to several other aberrations that must be corrected.
 
Several different off-axis configurations are used for radio antennas.<ref>{{cite book |title=Modern antenna design |author=Milligan, T.A. |year=2005 |publisher=Wiley-IEEE Press |isbn=0-471-45776-0}} pp.&nbsp;424-429</ref>
 
Another off-axis, unobstructed design and variant of the cassegrain is the 'YOLO' reflector invented by Arthur Leonard. This design uses a spherical or parabolic primary and a mechanically warped spherical secondary to correct for off-axis induced astigmatism. When set up correctly the yolo can give uncompromising unobstructed views of planetary objects and non-wide field targets, with no lack of contrast or image quality caused by spherical aberration. The lack of obstruction also eliminates the diffraction associated with cassegrain and newtonian reflector astrophotography.
 
== Catadioptric Cassegrains ==
 
===Schmidt-Cassegrain===
{{Main|Schmidt-Cassegrain telescope}}
[[File:Schmidt-Cassegrain-Telescope.svg|thumb|Light path in a [[Schmidt-Cassegrain telescope|Schmidt-Cassegrain]]]]
The Schmidt-Cassegrain was developed from the wide-field [[Schmidt camera]], although the Cassegrain configuration gives it a much narrower field of view. The first optical element is a [[Schmidt corrector plate]]. The plate is [[Figuring|figured]] by placing a vacuum on one side, and grinding the exact correction required to correct the [[spherical aberration]] caused by the primary mirror. Schmidt-Cassegrains are popular with amateur astronomers. An early Schmidt-Cassegrain camera was patented in 1946 by artist/architect/physicist [[Roger Hayward]],<ref>[http://www.freepatentsonline.com/2403660.pdf US Patent 2,403,660, Schmidt-Cassegrain camera]</ref> with the film holder placed outside the telescope.
 
===Maksutov-Cassegrain===
{{main|Maksutov telescope}}
[[File:Maksutov-Cassegrain-Telescope.svg|thumb|Light path in a [[Maksutov telescope|Maksutov-Cassegrain]]]]
The Maksutov-Cassegrain is a variation of the [[Maksutov telescope]] named after the [[Soviet Union|Soviet]]/[[Russia]]n [[Scientific equipment optician|optician]] and [[astronomer]] [[Dmitri Dmitrievich Maksutov]]. It starts with an optically transparent corrector lens that is a section of a hollow sphere. It has a spherical primary mirror, and a spherical secondary that in this application is usually a mirrored section of the corrector lens.
 
===Argunov-Cassegrain===
{{main|Argunov-Cassegrain telescope}}
In the Argunov-Cassegrain telescope all optics are spherical, and the classical Cassegrain secondary mirror is replaced by a [[Catadioptric_system#Sub-aperture_correctors|sub-aperture corrector]] consisting of three air spaced lens elements. The element farthest from the primary mirror is a [[Mangin mirror]], in which the element acts as a second surface mirror, having a reflective coating applied to the surface facing the sky.
 
===Klevtsov-Cassegrain===
[[File:Diagram Reflector KlevtsovCassegrain.svg|right|thumb|Light path in a [[Klevtsov-Cassegrain telescope]]]]
{{main|Klevtsov-Cassegrain telescope}}
The Klevtsov-Cassegrain, like the Argunov-Cassegrain, uses a sub-aperture corrector. It consisting of a small meniscus lens and Mangin mirror as its "secondary mirror".<ref>[http://www.opticsinfobase.org/abstract.cfm?URI=JOT-67-2-176 New optical systems for small-size telescopes]</ref>
 
==Cassegrain radio antennas==
[[File:DSN Antenna details.jpg|thumb|A Cassegrain radio antenna - the 70 meter dish at [[Jet Propulsion Laboratory|JPL]]'s [[Goldstone Deep Space Communications Complex|Goldstone antenna complex]]. In this case the final focus is in front of the primary, at the top of the pedestal protruding from the mirror.]]
Cassegrain designs are also utilized in satellite telecommunications [[earth station]] antennas and [[radio telescope]]s, ranging in size from 2.4&nbsp;metres to 70&nbsp;metres. The centrally located sub-reflector serves to focus radio frequency signals in a similar fashion to optical telescopes.
 
== See also ==
{{commons category|Cassegrain telescopes}}
* [[Refracting telescope]]
* [[Catadioptric system]]
* [[Celestron]] (Schmidt-Cassegrains, Maksutov Cassegrains)
* [[List of telescope types]]
* [[Meade Instruments]] (Schmidt-Cassegrains, Maksutov Cassegrains)
* [[Questar Telescope|Questar]] (Maksutov Cassegrains)
* [[Vixen (telescopes)|Vixen]] (Cassegrains, Klevtsov-Cassegrain)
 
== References ==
<references />
 
[[Category:Radio frequency antenna types]]
[[Category:Radio frequency propagation]]
[[Category:Telescope types]]

Latest revision as of 02:12, 31 August 2014

It is very common to have a dental emergency -- a fractured tooth, an abscess, or severe pain when chewing. Over-the-counter pain medication is just masking the problem. Seeing an emergency dentist is critical to getting the source of the problem diagnosed and corrected as soon as possible.

Here are some common dental emergencies:
Toothache: The most common dental emergency. This generally means a badly decayed tooth. As the pain affects the tooth's nerve, treatment involves gently removing any debris lodged in the cavity being careful not to poke deep as this will cause severe pain if the nerve is touched. Next rinse vigorously with warm water. Then soak a small piece of cotton in oil of cloves and insert it in the cavity. This will give temporary relief until a dentist can be reached.

At times the pain may have a more obscure location such as decay under an old filling. As this can be only corrected by a dentist there are two things you can do to help the pain. Administer a pain pill (aspirin or some other analgesic) internally or dissolve a tablet in a half glass (4 oz) of warm water holding it in the mouth for several minutes before spitting it out. DO NOT PLACE A WHOLE TABLET OR ANY PART OF IT IN THE TOOTH OR AGAINST THE SOFT GUM TISSUE AS IT WILL RESULT IN A NASTY BURN.

Swollen Jaw: This may be caused by several conditions the most probable being an abscessed tooth. In any case the treatment should be to reduce pain and swelling. An ice pack held on the outside of the jaw, (ten minutes on and ten minutes off) will take care of both. If this does not control the pain, an analgesic tablet can be given every four hours.

Other Oral Injuries: Broken teeth, cut lips, bitten tongue or lips if severe means a trip to a dentist as soon as possible. In the mean time rinse the mouth with warm water and place cold compression the face opposite the injury. If there is a lot of bleeding, apply direct pressure to the bleeding area. If bleeding does not stop get patient to the emergency room of a hospital as stitches may be necessary.

Prolonged Bleeding Following Extraction: Place a gauze pad or better still a moistened tea bag over the socket and have the patient bite down gently on it for 30 to 45 minutes. The tannic acid in the tea seeps into the tissues and often helps stop the bleeding. If bleeding continues after two hours, call the dentist or take patient to the emergency room of the nearest hospital.

Broken Jaw: If you suspect the patient's jaw is broken, bring the upper and lower teeth together. Put a necktie, handkerchief or towel under the chin, tying it over the head to immobilize the jaw until you can get the patient to a dentist or the emergency room of a hospital.

Painful Erupting Tooth: In young children teething pain can come from a loose baby tooth or from an erupting permanent tooth. Some relief can be given by crushing a little ice and wrapping it in gauze or a clean piece of cloth and putting it directly on the tooth or gum tissue where it hurts. The numbing effect of the cold, along with an appropriate dose of aspirin, usually provides temporary relief.

In young adults, an erupting 3rd molar (Wisdom tooth), especially if it is impacted, can cause the jaw to swell and be quite painful. Often the gum around the tooth will show signs of infection. Temporary relief can be had by giving aspirin or some other painkiller and by dissolving an aspirin in half a glass of warm water and holding this solution in the mouth over the sore gum. AGAIN DO NOT PLACE A TABLET DIRECTLY OVER THE GUM OR CHEEK OR USE THE ASPIRIN SOLUTION ANY STRONGER THAN RECOMMENDED TO PREVENT BURNING THE TISSUE. The swelling of the jaw can be reduced by using an ice pack on the outside of the face at intervals of ten minutes on and ten minutes off.

If you have any concerns about where and how to use dentist DC, you can speak to us at the webpage.