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Alan D. Sokal has written:
'Impostures intellectuelle'
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Roman Sokal was born on August 12, 1974, in Hamilton, Ontario, Canada.
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Michael M. Sokal has written:
'A guide to manuscript collections in the history of psychology and related areas' -- subject(s): History, Psychology, Manuscripts, Archival resources, MANU CATA
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Daily Sotter Sokal is an online news portal that aims to provide accurate and objective news and views for the audience across the country. With the slogan of ‘আমরা সত্যের পথযাত্রী’, the online news portal started its journey in 29 November 2020. Due to its bold journalism, rich content and presentation with unique layout and design, Daily Sotter Sokal ( has quickly won the hearts of people, even highly sophisticated and fanatical readers have increased their loyalty to it. Since then, Daily Sotter Sokal has illuminated every corner of Bangladesh, including 200 countries and regions around the world, through its digital offers.
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Dr. Karen Sokal-Gutierrez is a pediatrician and educator who has written articles and research papers on a wide range of topics related to child health and development, particularly focusing on early childhood literacy, parenting, and oral health. She has also co-authored books on parenting and child development.
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Mieczyslaw Swiecicki was born on March 26, 1936, in Sokal, Lwowskie, Poland [now Lviv Oblast, Ukraine].
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The cast of Lost at Home - 2010 includes: Kirsty Meares as Alice Evan Sokal as Alex
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Sokol is a Jewish surname, though today many non-Jews (i.e., David Sokol) bear it, as a result of conversion or intermarriage, etc.
It means Falcon in most eastern European languages and is akin to Vogel in German.
The name takes many forms. As many Sokols left their native lands, the name took on various spellings -- i.e., Socol (as in Howard Socol, former Barney's CEO) or Sokal (as in Robert Reuben Sokal, the Austian academic). Both are/were Jewish.
In Israel, there is a prominent street named Sokolov in Tel Aviv. Sokol, Socol, Sokal and Sokolov (et al) are equivalent in meaning and origin.
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Md Anas Molla is a Bangladeshi journalist, public figure and teenage poet. He is a Executive editor at Sotter Sokal. He is also currently working as the Information Technology Secretary of Mohanpur Press Club.
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The cast of The Invisibles - 1999 includes: Katherine Brooks as Groupie Terry Camilleri as Le Pizza Guy Portia de Rossi as Joy Alan Polk as Band Member Jonathan Segel as John Lennon Roman Sokal as Band Member
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The cast of 3. November 1918 - 1965 includes: Erich Auer as Rittmeister Orvanyi Erik Frey as Oberst von Radosin Wolfgang Gasser as Oberleutnant Zierowitz Hugo Gottschlich as Infanterist Josip Ingrid Kohr as Schwester Christina Walter Kohut as Oberleutnant Ludoltz Peter Matic as Leutnant Vanini Hanns Obonya as Leutnant Sokal Kurt Sowinetz as Pjotr Kaciuk - Maschinenmaat Peter Weihs as Oberleutnant von Kaminski
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David Harscheid has: Played Grandpa Yoder in "For Richer or Poorer" in 1997. Played Harold in "Magic Hour" in 1997. Played Old Man in "Hearts in Atlantis" in 2001. Played Lucif in "Cryptic" in 2005. Played Old Driver in "Darken" in 2006. Played Dr. Abraham Van Helsing in "Alucard" in 2008. Played Doc in "Atone" in 2008. Played Grandpa in "Two-Minute Heist" in 2009. Played Gravedigger in "Plan 9" in 2009. Played Mr. Putnam in "The Good Parts" in 2010. Played Bram Sokal in "Spade" in 2010. Played Gravedigger in "Plan 9" in 2013.
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Hanns Obonya has: Performed in "Der junge Baron Neuhaus" in 1934. Played Piccolo in "Lumpacivagabundus" in 1936. Played Cafe Busboy in "Rendezvous in Wien" in 1936. Performed in "Hannerl und ihre Liebhaber" in 1936. Played Ein Pikkolo in "Konfetti" in 1936. Played Klops - Schiffsjunge in "Florentine" in 1937. Played Klobner in "Der rote Rausch" in 1962. Played Plinke in "Deutschland - deine Sternchen" in 1962. Played Sockel, Baumeister in "Der Verschwender" in 1964. Performed in "Nicht verzagen - Stangl fragen" in 1964. Performed in "Heinrich VI" in 1964. Played Patriarch von Jerusalem in "Nathan der Weise" in 1964. Performed in "Othello, der Mohr in Wien" in 1965. Played Leutnant Sokal in "3. November 1918" in 1965. Played Prokop in "Ein Bruderzwist in Habsburg" in 1966. Played Hofrat in "Tatort" in 1969. Played Hofrat Neloda in "Tatort" in 1969. Played Capitano in "Der Kurier der Kaiserin" in 1970. Played Armer Nachbar in "Jedermann" in 1970. Played Oberst in "Der Hauptmann" in 1971. Performed in "Wenn der Vater mit dem Sohne" in 1971. Played Oberstleutnant Willi in "Briefe von gestern" in 1972. Performed in "Die Insel der Seligen" in 1976. Played Offizier in "Alpensaga" in 1976.
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The cast of The Cincinnati Kid - 1965 includes: Andy Albin as Referee Joan Blondell as Lady Fingers Cab Calloway as Yeller William Challee as Old Man Gene Coogan as Poker Game Spectator Jeff Corey as Hoban Robert DoQui as Philly Larry Duran as Gambler - First Game Donald Elson as Bit Part Sweet Emma as Blues Singer Claude Hall as Gambler Virginia Harrison as Employee John Hart as Poker Player Harry Hines as Old Man in Pool Hall John Indrisano as Gambler - First Game Colin Kenny as Spectator at Cockfight Karl Malden as Shooter Theodore Marcuse as Felix Pat McCaffrie as Poker Player Sandy McPeak as Poker Player Steve McQueen as The Cincinnati Kid Burt Mustin as Old Man in Pool Hall Brett Pearson as Gambler - First Game Joyce Perry as Mrs. Hoban Christopher Riordan as Railroad Worker Milton Selzer as Sokal Ron Soble as Danny Olan Soule as Desk Clerk Karl Swenson as Mr. Rudd Hal Taggart as Bettor Dub Taylor as Dealer Irene Tedrow as Mrs. Rudd Rip Torn as Slade Paul Verdier as Second Bettor Charles Wagenheim as Old Man Midge Ware as Mrs. Slade Jesse Wayne Tuesday Weld as Christian Howard Wendell as Charlie Jack Weston as Pig Harry Wilson as Spectator at Cockfight Dick Winslow as Second Player Bill Zuckert as Poker Player
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The cast of Die rote Kapelle - 1972 includes: Werner Abrolat as Russischer General Max Buchsbaum as Oberst Gehrts Georges Claisse as Kent Edeltraut Elsner as Libertas Schulze-Boysen Yves Favien as Legendre Peter Fricke as Harro Schulze-Boysen Jacques Galland as Boris Norbert Gastell as Feldwebel Traxi Norbert Gastell as Feldwebel Traxl Anna Gaylor as Madame Likhonine Ute Gerhard as Erika von Brockdorff Christine Gerlach as Mildred Harnack Raoul Guylad as Raichmann Norbert Hansing as Paulsen Jos Hartmann as Novotny Alexander Hegarth as Piepe Ursula Herwig as Greta Kuckhoff Wilfried Jan Heyn as Oberleutnant Vauck Klaus Jepsen as Alexandrow Werner Kreindl as Leopold Trepper Werner Kreindl as Trepper Leopold Julie Laroche as Rita Arnould Philippe Lemaire as Pierre Albert Michel as Ozols Candice Patou as Georgie de Winter Rada Rassimov as Margarete Barcza Jacques Rispal as Hillel Katz Hans Schulze as Adam Kuckhoff Friedrich Siemers as Boemelburg Henri Sokal as Isidor Springer Henri Soxal as Isidor Springer Manfred Spies as Makarow Peter Thom as Coppi, Hans Peter Thom as Hans Coppi Erich Ude as Oberstleutnant Dischler Theresa van der Hallen as Anna Maurice Reinhard Vom Bauer as Horst Heillmann Reinhard Vom Bauer as Horst Heilmann Dieter Wagner as Arvid Harnack Karl Walter Diess as Oberleutnant Grassmann
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Milton Selzer has: Played Roy in "Kraft Television Theatre" in 1947. Played Gerald in "Studio One" in 1948. Played Drunk in "Studio One" in 1948. Played 2nd Guard in "Studio One" in 1948. Played Harold Rich in "Studio One" in 1948. Played Mr. Weston in "Studio One" in 1948. Played Dave in "The Big Story" in 1949. Played Corporal Miley in "The Big Story" in 1949. Played Melvin in "Danger" in 1950. Performed in "Armstrong Circle Theatre" in 1950. Performed in "Omnibus" in 1952. Played George Goss in "General Electric Theater" in 1953. Played Henderickson in "The United States Steel Hour" in 1953. Played Mahatma Gandhi in "You Are There" in 1953. Played French Prisoner in "You Are There" in 1953. Played General Knox in "You Are There" in 1953. Played Albert Schiller in "Gunsmoke" in 1955. Played Pa Hack in "Gunsmoke" in 1955. Played Jezra in "Gunsmoke" in 1955. Played Pike in "The Alcoa Hour" in 1955. Played Upton in "The Alcoa Hour" in 1955. Played Painter in "Gunsmoke" in 1955. Played Fisherman Father in "The Alcoa Hour" in 1955. Played Second Convict in "Playhouse 90" in 1956. Played Fernando in "Playhouse 90" in 1956. Played Dr. Max Taylor in "Perry Mason" in 1957. Played Rabbi Reb Elya in "Have Gun - Will Travel" in 1957. Played Dr. Alfred Nobel in "Have Gun - Will Travel" in 1957. Played 1st Officer Denning in "Decoy" in 1957. Played Dr. Aaron Stuart in "Perry Mason" in 1957. Played Lou Warren in "Peter Gunn" in 1958. Played Mathmetician in "Play of the Week" in 1959. Played Alan Sitkin in "The Untouchables" in 1959. Played Harry Gordon in "The Untouchables" in 1959. Played Tumarin in "Five Fingers" in 1959. Played Masters in "Deadline" in 1959. Played Ozzie in "The Detectives" in 1959. Played Jason Fiddler in "The Untouchables" in 1959. Played Harry Cooler in "Sunday Showcase" in 1959. Played Peddie in "The Last Mile" in 1959. Played Julian Blumberg in "Sunday Showcase" in 1959. Played Messenger in "Play of the Week" in 1959. Played Alien in "The Twilight Zone" in 1959. Played Maxie Schram in "The Untouchables" in 1959. Played Wilfred Harper in "The Twilight Zone" in 1959. Performed in "Buick-Electra Playhouse" in 1959. Played Slaight in "Adventures in Paradise" in 1959. Played Charles Morgan in "Brenner" in 1959. Played Wladyslaw Szorny in "Checkmate" in 1960. Played Freddy in "Checkmate" in 1960. Played Salvation Army Player in "North to Alaska" in 1960. Played Ernie in "The Robert Herridge Theater" in 1960. Played Ray Parker in "The Aquanauts" in 1960. Played Gunther in "Route 66" in 1960. Played Sam Rolston in "Michael Shayne" in 1960. Played Lieutenant Jamison in "The Aquanauts" in 1960. Performed in "The Fifth Column" in 1960. Played Mr. Raymond in "The DuPont Show of the Week" in 1961. Played Browder in "The Investigators" in 1961. Played Dr. Walsh in "The Young Savages" in 1961. Played Rozinsky in "Alcoa Premiere" in 1961. Played Billy Noonan in "The DuPont Show of the Week" in 1961. Played The Professor - Doc Stehlmeyer in "The Asphalt Jungle" in 1961. Played Sol Raidman in "The Dick Powell Show" in 1961. Played Raymond Kimble in "The Defenders" in 1961. Played Dr. Harmon in "The New Breed" in 1961. Played Paul Look in "The Defenders" in 1961. Played Lou Gordon in "The Asphalt Jungle" in 1961. Played Dr. Paul Silberman in "The Defenders" in 1961. Played Dr. Barnaby Taylor in "Ben Casey" in 1961. Played Dr. Laird in "Stoney Burke" in 1962. Played Dr. Michaels in "Sam Benedict" in 1962. Played Harold Bitz in "The Virginian" in 1962. Played Ben Willoughby in "The Fugitive" in 1963. Played Lou Cartwright in "The Fugitive" in 1963. Played Vecchio in "The Yellow Canary" in 1963. Played Ted Canford in "Mr. Novak" in 1963. Played Captain Chick Wasnik in "Bob Hope Presents the Chrysler Theatre" in 1963. Played Pop Snyder (1979) in "General Hospital" in 1963. Played Dr. Shtallmacher in "The Man from U.N.C.L.E." in 1964. Played Pete Johnson in "Bewitched" in 1964. Played Schilling in "Profiles in Courage" in 1964. Played Man at Track in "Marnie" in 1964. Played Gilbert Foster in "The Rogues" in 1964. Played Dr. Melton in "Voyage to the Bottom of the Sea" in 1964. Played Isaac Delf in "Daniel Boone" in 1964. Played Emmet Stark in "The Wild Wild West" in 1965. Played Captain Crowell in "A Man Called Shenandoah" in 1965. Played Jordan James Alexander in "The F.B.I." in 1965. Played Sokal in "The Cincinnati Kid" in 1965. Played Miller in "The F.B.I." in 1965. Played Danny in "Green Acres" in 1965. Performed in "The Wackiest Ship in the Army" in 1965. Played Mr. Ragatzy in "The F.B.I." in 1965. Played Eric Sturm in "Convoy" in 1965. Played Parker in "Get Smart" in 1965. Performed in "Jericho" in 1966. Played Joe Coyne in "Felony Squad" in 1966. Played Al Morgenthaler in "That Girl" in 1966. Played Tobar in "The Rat Patrol" in 1966. Played Sidney Gold in "That Girl" in 1966. Played Dr. Corey in "That Girl" in 1966. Played Colonel Schweiger in "The Rat Patrol" in 1966. Played Phil Sosgornik in "Hawk" in 1966. Played Stanley in "Mission: Impossible" in 1966. Played Inspector Koder in "Mission: Impossible" in 1966. Played Dr. Erich Rojak in "Mission: Impossible" in 1966. Played Thaddeus Bancroft in "Iron Horse" in 1966. Played January Vornitz in "Mission: Impossible" in 1966. Played Dave Wright in "Mannix" in 1967. Played A.J. Richards in "The Invaders" in 1967. Played Judge Wade in "Judd for the Defense" in 1967. Played Albie in "Mannix" in 1967. Played Mr. Gold in "Ironside" in 1967. Played Lt. Maury Strauss in "Mannix" in 1967. Played Jack Brady in "Ironside" in 1967. Played Sody Marcum in "The High Chaparral" in 1967. Played Lester Willighby in "Hawaii Five-O" in 1968. Played Alfred Weaver in "The Mod Squad" in 1968. Played Sam Green in "Hawaii Five-O" in 1968. Played Bartowski in "In Enemy Country" in 1968. Played Ghoriades in "Hawaii Five-O" in 1968. Played Ron in "Hawaii Five-O" in 1968. Played Bart Langner in "The Legend of Lylah Clare" in 1968. Played Kellman in "Hawaii Five-O" in 1968. Played Tabernash in "Hawaii Five-O" in 1968. Played Everett Calvin in "Room 222" in 1969. Played Kurawitz in "The Bill Cosby Show" in 1969. Played Bender in "The Bold Ones: The Protectors" in 1969. Played Dr. Gray in "My World and Welcome to It" in 1969. Played Wilmer Frye in "The Bold Ones: The Lawyers" in 1969. Played Dr. Mazer in "Marcus Welby, M.D." in 1969. Played Otologist in "The Bold Ones: The New Doctors" in 1969. Performed in "Matt Lincoln" in 1970. Played Flynn in "McCloud" in 1970. Performed in "Dan August" in 1970. Played Dr. Leonard Schuster in "Along Came a Spider" in 1970. Played Dr. Terminer in "Crowhaven Farm" in 1970. Played Dr. Seymour Shapiro in "All in the Family" in 1971. Played Mr. Mullins in "Blood and Lace" in 1971. Performed in "Owen Marshall, Counselor at Law" in 1971. Played Marty Kaufman in "Cannon" in 1971. Played Myron in "Awake and Sing" in 1972. Played Charlie Darwin in "The ABC Afternoon Playbreak" in 1972. Played Bascomb in "ABC Afterschool Specials" in 1972. Played Sam in "Temperatures Rising" in 1972. Played Pink in "Keep the Faith" in 1972. Played Psychologist in "Jigsaw" in 1972. Played The Doctor in "Lady Sings the Blues" in 1972. Played Sam Gittleman in "Sanford and Son" in 1972. Played Mr. Brimskill in "The Bob Newhart Show" in 1972. Played Lucas D. Kaplos in "Search" in 1972. Played Manny Judson in "The Streets of San Francisco" in 1972. Played Margolies in "Temperatures Rising" in 1972. Played Beal in "The Streets of San Francisco" in 1972. Played Dr. Hall in "Police Story" in 1973. Played Dr. Schwartz in "Rx for the Defense" in 1973. Played Sam Benson in "Barnaby Jones" in 1973. Played Dr. Molter in "Police Story" in 1973. Played Stauffer in "Key West" in 1973. Played Nathan Davidoff in "Kojak" in 1973. Played Dr. Anders in "Police Story" in 1973. Played Alex Pochek in "The Magician" in 1973. Played Police Psychiatrist in "Police Story" in 1973. Played Julius Singer in "Needles and Pins" in 1973. Played Lt. in "The Wide World of Mystery" in 1973. Played Lou Gold in "Police Story" in 1973. Performed in "The Lie" in 1973. Played Elija Pattman in "Little House on the Prairie" in 1974. Played Moe Harris in "Police Woman" in 1974. Played Howard Sohrbeck in "Lucas Tanner" in 1974. Played Patrick Elber in "The Rockford Files" in 1974. Played Pa Wellman in "This Is the West That Was" in 1974. Played Murray Grossman in "Barney Miller" in 1974. Played Irving Rockfelt in "The Rockford Files" in 1974. Played Dr. Losey in "The Six Million Dollar Man" in 1974. Played Dr. Simon Roth in "The Abduction of Saint Anne" in 1975. Played Captain Louie in "Wonder Woman" in 1975. Played Mr. Wexler in "The Jeffersons" in 1975. Played Harley Wilton in "NBC Special Treat" in 1975. Performed in "Archer" in 1975. Played Jannos in "Bronk" in 1975. Performed in "Jigsaw John" in 1976. Played Mr. Avery in "Quincy M.E." in 1976. Played Sidney in "One of My Wives Is Missing" in 1976. Performed in "Hunter" in 1976. Played Gardella in "The Feather and Father Gang" in 1976. Played Mr. Jackson in "Quincy M.E." in 1976. Played Claude Cunningham in "Lou Grant" in 1977. Played Jake Winkleman in "The Harvey Korman Show" in 1977. Played Dr. Burroughs in "Capricorn One" in 1977. Played Albert Hastings in "Code R" in 1977. Played Willie in "Fantasy Island" in 1977. Played Miller in "Un autre homme, une autre chance" in 1977. Performed in "Sword of Justice" in 1978. Played Sumabitch in "Blue Collar" in 1978. Played Myron Klopfman in "To Kill a Cop" in 1978. Played Benson in "The Runaways" in 1978. Played The Realtor in "The Evil" in 1978. Played Mr. Trankis in "Trapper John, M.D." in 1979. Played Mr. Levin in "The Triangle Factory Fire Scandal" in 1979. Played Sid Amos in "Scruples" in 1980. Performed in "Dan August: The Jealousy Factor" in 1980. Played Dr. Vogel in "Raise the Titanic" in 1980. Played Barris in "Hagen" in 1980. Played Mr. Melman in "Dynasty" in 1981. Played Dr. Roth in "The People vs. Jean Harris" in 1981. Played Dr. Woodville in "The Adventures of Nellie Bly" in 1981. Performed in "The Million Dollar Face" in 1981. Played Florist in "No Place to Hide" in 1981. Played Murray Kaplan in "Hill Street Blues" in 1981. Played Leo Finklestein in "Fame" in 1982. Played Rabbi Tolkien in "St. Elsewhere" in 1982. Played Landlord in "The Buddy System" in 1984. Played Izzy in "MacGyver" in 1985. Played Otto Romburg in "MacGyver" in 1985. Played Phil Kagan in "Mirrors" in 1985. Played Judge Morris Hood in "L.A. Law" in 1986. Played Granpa in "Sid and Nancy" in 1986. Played Judge in "Walker" in 1987. Played Max in "A Year in the Life" in 1987. Played Mr. Berger in "Shoot to Kill" in 1988. Played Merlin Hinkle in "Tapeheads" in 1988. Played Abe Werkfinder in "The Famous Teddy Z" in 1989. Played The Judge in "Doogie Howser, M.D." in 1989. Played Baldrik Exmachina in "She-Wolf of London" in 1990. Played Rabbi in "Reasonable Doubts" in 1991. Played Uncle Shimon in "Miss Rose White" in 1992. Played Dr. Feldman in "Down the Shore" in 1992. Played Larry in "Walker, Texas Ranger" in 1993. Played Manny Henry in "Valley of the Dolls" in 1994.
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50% of the input signal is used (Θ = 180° or π; i.e., the active element works in its linear range half of the time and is more or less turned off for the other half). In most Class B, there are two output devices (or sets of output devices), each of which conducts alternately (push-pull) for exactly 180° (or half cycle) of the input signal; selective RF amplifiers can also be implemented using a single active element.
These amplifiers are subject to crossover distortion if the transition from one active element to the other is not perfect, as when two complementary transistors (i.e., one PNP, one NPN) are connected as two emitter followers with their base and emitter terminals in common, requiring the base voltage to slew across the region where both devices are turned off.Class ABHere the two active elements conduct more than half of the time as a means to reduce the cross-over distortions of Class B amplifiers. In the example of the complementary emitter followers a bias network allows for more or less quiescent current thus providing an operating point somewhere between Class A and Class B. Sometimes a figure is added (e.g., AB1 or AB2) for vacuum tube stages where the grid voltage is always negative with respect to the cathode (Class AB1) or may be slightly positive (hence drawing grid current, adding more distortion, but giving slightly higher output power) on signal peaks (Class AB2); another interpretation being higher figures implying a higher quiescent current and therefore more of the properties of Class A.Class CLess than 50% of the input signal is used (conduction angle Θ < 180°). The advantage is potentially high efficiency, but a disadvantage is high distortion.Class D
Main article: Switching amplifier These use switching to achieve a very high power efficiency (more than 90% in modern designs). By allowing each output device to be either fully on or off, losses are minimized. The analog output is created by pulse-width modulation; i.e., the active element is switched on for shorter or longer intervals instead of modifying its resistance. There are more complicated switching schemes like sigma-delta modulation, to improve some performance aspects like lower distortions or better efficiency.Additional classesThere are several other amplifier classes, although they are mainly variations of the previous classes. For example, Class G and Class H amplifiers are marked by variation of the supply rails (in discrete steps or in a continuous fashion, respectively) following the input signal. Wasted heat on the output devices can be reduced as excess voltage is kept to a minimum. The amplifier that is fed with these rails itself can be of any class. These kinds of amplifiers are more complex, and are mainly used for specialized applications, such as very high-power units. Also, Class E and Class F amplifiers are commonly described in literature for radio frequencies applications where efficiency of the traditional classes in are important, yet several aspects not covered elsewhere (e.g.: amplifiers often simply said to have a gain of x dB - so what power gain?) deviate substantially from their ideal values. These classes use harmonic tuning of their output networks to achieve higher efficiency and can be considered a subset of Class C due to their conduction angle characteristics.
The classes can be most easily understood using the diagrams in each section below. For the sake of illustration, a bipolar junction transistor is shown as the amplifying device, but in practice this could be a MOSFET or vacuum tube device. In an analog amplifier (the most common kind), the signal is applied to the input terminal of the device (base, gate or grid), and this causes a proportional output drive current to flow out of the output terminal. The output drive current comes from the power supply.
Class AClass A amplifier
Amplifying devices operating in Class A conduct over the whole of the input cycle such that the output signal is an exact scaled-up replica of the input with no clipping. A Class A amplifier (or operational amplifier) is distinguished by the output stage (and perhaps the driver) device(s) being biased into Class A; even Class AB and B amplifiers normally have early stages operating in Class A. Class A is the usual means of implementing small-signal amplifiers, so the term Class A design applied to equipment such as preamplifiers (for example, in recording studios) implies not so much their use of Class A, but that their sound is top quality - good enough to be matched with top quality Class A power amplifiers.
Advantages of Class A Amplifiers- Class A designs are simpler than other classes; for example Class AB and B designs require two devices (push-pull output) to handle both halves of the waveform, and circuitry to keep the quiescent bias optimal during temperature changes; Class A can use either single-ended or push-pull and bias is usually less critical.
- The amplifying element is biased so the device is always conducting to some extent, normally implying the quiescent (small-signal) collector current (for transistors; drain current for FETs or anode/plate current for vacuum tubes) is close to the most linear portion (sometimes called the "sweet spot") of its characteristic curve (known as its transfer characteristic or transconductance curve), giving the least audio distortion.
- Because the device is never shut off completely there is no "turn on" time, little problem with charge storage, and generally better high frequency performance and feedback loop stability (and usually fewer high-order harmonics).
- The point at which the device comes closest to being cut off (and so significant change in gain, hence non-linearity) is not close to zero signal, so the problem of crossover distortion associated with Class AB and B designs is avoided, even in Class A double-ended stages.
- They are very inefficient; a theoretical maximum of 50% is obtainable with inductive output coupling and only 25% with capacitive coupling, unless Square law output stages are used. In a power amplifier this not only wastes power and limits battery operation, it may place restrictions on the output devices that can be used (for example: ruling out some audio triodes if modern low-efficiency loudspeakers are to be used), and will increase costs. Inefficiency comes not just from the fact that the device is always conducting to some extent (that happens even with Class AB, yet its efficiency can be close to that of Class B); it is that the standing current is roughly half the maximum output current (although this can be less with Square law output stage), together with the problem that a large part of the power supply voltage is developed across the output device at low signal levels (as with Classes AB and B, but unlike output stages such as Class D). If high output powers are needed from a Class A circuit, the power waste (and the accompanying heat) will become significant. For every watt delivered to the load, the amplifier itself will, at best, dissipate another watt. For large powers this means very large and expensive power supplies and heat sinking.
Class A designs have largely been superseded by the more efficient designs for power amplifiers, though they remain popular with some hobbyists, mostly for their simplicity. Also, many audiophiles believe that Class A gives the best sound quality (for their absence of crossover distortion and reduced odd-harmonic and high-order harmonic distortion) which provides a small market for expensive high fidelity Class A amps.
Single-Ended and Triode Class A AmplifiersSome aficionados who prefer Class A amplifiers also prefer the use of thermionic valve (or "tube") designs instead of transistors, especially in Single-ended triode output configurations for several claimed reasons:
- Single-ended output stages (be they tube or transistor) have an asymmetrical transfer function, meaning that even harmonics in the created distortion tend not to be canceled (as they are in push-pull output stages); by using tubes OR FETs most of the distortion is from the square law transfer characteristic and so second-order, which some consider to be "warmer" and more pleasant.
- For those who prefer low distortion figures, the use of tubes with Class A (generating little odd-harmonic distortion, as mentioned above) together with symmetrical circuits (such as push-pull output stages, or balanced low-level stages) results in the cancellation of most of the even distortion harmonics, hence the removal of most of the distortion.
- Though good amplifier design can reduce harmonic distortion patterns to almost nothing, distortion is essential to the sound of electric guitar amplifiers, for example, and is held by recording engineers to offer more flattering microphones and to enhance "clinical-sounding" digital technology.
- Historically, valve amplifiers often used a Class A power amplifier simply because valves are large and expensive; many Class A designs use only a single device.
Transistors are much cheaper, and so more elaborate designs that give greater efficiency but use more parts are still cost-effective. A classic application for a pair of class A devices is the long-tailed pair, which is exceptionally linear, and forms the basis of many more complex circuits, including many audio amplifiers and almost all op-amps. Class A amplifiers are often used in output stages of high quality op-amps (although the accuracy of the bias in low cost op-amps such as the 741 may result in Class A or Class AB or Class B, varying from device to device or with temperature). They are sometimes used as medium-power, low-efficiency, and high-cost audio amplifiers. The power consumption is unrelated to the output power. At idle (no input), the power consumption is essentially the same as at high output volume. The result is low efficiency and high heat dissipation.
Class B and ABClass B amplifiers only amplify half of the input wave cycle, thus creating a large amount of distortion, but their efficiency is greatly improved and is much better than Class A. Class B has a maximum theoretical efficiency of 78.5% (i.e., π/4). This is because the amplifying element is switched off altogether half of the time, and so cannot dissipate power. A single Class B element is rarely found in practice, though it has been used for driving the loudspeaker in the early IBM Personal Computers with beeps, and it can be used in RF power amplifier where the distortion levels are less important. However Class C is more commonly used for this.Class B Amplifier
A practical circuit using Class B elements is the push-pull stage, such as the very simplified complementary pair arrangement shown below. Here, complementary or quasi-complementary devices are each used for amplifying the opposite halves of the input signal, which is then recombined at the output. This arrangement gives excellent efficiency, but can suffer from the drawback that there is a small mismatch in the cross-over region - at the "joins" between the two halves of the signal, as one output device has to take over supplying power exactly as the other finishes. This is called crossover distortion. An improvement is to bias the devices so they are not completely off when they're not in use. This approach is called Class AB operation.
In Class AB operation, each device operates the same way as in Class B over half the waveform, but also conducts a small amount on the other half. As a result, the region where both devices simultaneously are nearly off (the "dead zone") is reduced. The result is that when the waveforms from the two devices are combined, the crossover is greatly minimised or eliminated altogether. The exact choice of quiescent current, the standing current through both devices when there is no signal, makes a large difference to the level of distortion (and to the risk of thermal runaway, that may damage the devices); often the bias voltage applied to set this quiescent current has to be adjusted with the temperature of the output transistors (for example in the circuit at the beginning of the article the diodes would be mounted physically close to the output transistors, and chosen to have a matched temperature coefficient). Another approach (often used as well as thermally-tracking bias voltages) is to include small value resistors in series with the emitters.
Class AB sacrifices some efficiency over class B in favor of linearity, thus is less efficient (below 78.5% for full-amplitude sinewaves in transistor amplifiers, typically; much less is common in Class AB vacuum tube amplifiers). It is typically much more efficient than class A.
Class B push-pull amplifier
Class B or AB push-pull circuits are the most common design type found in audio power amplifiers. Class AB is widely considered a good compromise for audio amplifiers, since much of the time the music is quiet enough that the signal stays in the "class A" region, where it is amplified with good fidelity, and by definition if passing out of this region, is large enough that the distortion products typical of class B are relatively small. The crossover distortion can be reduced further by using negative feedback. Class B and AB amplifiers are sometimes used for RF linear amplifiers as well. Class B amplifiers are also favored in battery-operated devices, such as transistor radios.
Digital Class BA limited power output Class-B amplifier with a single-ended supply rail of 5±0.5 V.
Class CClass C amplifier
Class C amplifiers conduct less than 50% of the input signal and the distortion at the output is high, but high efficiencies (up to 90%) are possible. Some applications (for example, megaphones) can tolerate the distortion. A much more common application for Class C amplifiers is in RF transmitters, where the distortion can be vastly reduced by using tuned loads on the amplifier stage. The input signal is used to roughly switch the amplifying device on and off, which causes pulses of current to flow through a tuned circuit.
The Class C amplifier has two modes of operation: tuned and untuned.[10] The diagram shows a waveform from a simple class C circuit without the tuned load. This is called untuned operation, and the analysis of the waveforms shows the massive distortion that appears in the signal. When the proper load (e.g., a pure inductive-capacitive filter) is used, two things happen. The first is that the output's bias level is clamped, so that the output variation is centered at one-half of the supply voltage. This is why tuned operation is sometimes called a clamper. This action of elevating bias level allows the waveform to be restored to its proper shape, allowing a complete waveform to be re-established despite having only a one-polarity supply. This is directly related to the second phenomenon: the waveform on the center frequency becomes much less distorted. The distortion that is present is dependent upon the bandwidth of the tuned load, with the center frequency seeing very little distortion, but greater attenuation the farther from the tuned frequency that the signal gets.
The tuned circuit will only resonate at particular frequencies, and so the unwanted frequencies are dramatically suppressed, and the wanted full signal (sine wave) will be extracted by the tuned load (e.g., a high-quality bell will ring at a particular frequency when it is hit periodically with a hammer). Provided the transmitter is not required to operate over a very wide band of frequencies, this arrangement works extremely well. Other residual harmonics can be removed using a filter.
Class DMain article: Class D Amplifier
Block diagram of a basic switching or PWM (Class-D) amplifier.
Boss Audio Class D mono car audio amplifier with a low pass filter for powering subwoofers
In the Class D amplifier the input signal is converted to a sequence of higher voltage output pulses. The averaged-over-time power values of these pulses are directly proportional to the instantaneous amplitude of the input signal. The frequency of the output pulses is typically ten or more times the highest frequency in the input signal to be amplified. The output pulses contain inaccurate spectral components (that is, the pulse frequency and its harmonics) which must be removed by a low-pass passive filter. The resulting filtered signal is then an amplified replica of the input.
These amplifiers use pulse width modulation, pulse density modulation (sometimes referred to as pulse frequency modulation) or more advanced form of modulation such as Delta-sigma modulation (for example, in the Analog Devices AD1990 Class-D audio power amplifier). Output stages such as those used in pulse generators are examples of Class D amplifiers. The term Class D is usually applied to devices intended to reproduce signals with a bandwidth well below the switching frequency.
Class D amplifiers can be controlled by either analog or digital circuits. The digital control introduces additional distortion called quantization error caused by its conversion of the input signal to a digital value.
The main advantage of a Class D amplifier is power efficiency. Because the output pulses have a fixed amplitude, the switching elements (usually MOSFETs, but valves and bipolar transistors were once used) are switched either completely on or completely off, rather than operated in linear mode. A MOSFET operates with the lowest resistance when fully-on and thus has the lowest power dissipation when in that condition, except when fully off. When operated in a linear mode the MOSFET has variable amounts of resistance that vary linearly with the input voltage and the resistance is something other than the minimum possible, therefore more electrical energy is dissipated as heat. Compared to Class A/B operation, Class D's lower losses permit the use of a smaller heat sink for the MOSFETS while also reducing the amount of AC power supply power required. Thus, Class D amplifiers do not need as large or as heavy power supply transformers or heatsinks, so they are smaller and more compact in size than an equivalent Class AB amplifier.
Class D amplifiers have been widely used to control motors, and almost exclusively for small DC motors, but they are now also used as audio amplifiers, with some extra circuitry to allow analogue to be converted to a much higher frequency pulse width modulated signal. The relative difficulty of achieving good audio quality means that nearly all are used in applications where quality is not a factor, such as modestly-priced bookshelf audio systems and "DVD-receivers" in mid-price home theater systems.
High quality Class D audio amplifiers are now, however, starting to appear in the market:
- Tripath have called their revised Class D designs Class T.
- Bang and Olufsen's ICEPower Class D system has been used in the Alpine PDX range and some of Pioneer's PRS range and for other manufacturers' equipment.
These revised designs have been said to rival good traditional AB amplifiers in terms of quality.
Before these higher quality designs existed an earlier use of Class D amplifiers and prolific area of application was high-powered, subwoofer amplifiers in cars. Because subwoofers are generally limited to a bandwidth of no higher than 150 Hz, the switching speed for the amplifier does not have to be as high as for a full range amplifier. The drawback with Class D designs being used to power subwoofers is that their output filters (typically inductors that convert the pulse width signal back into an analogue waveform) lower the damping factor of the amplifier.
This means that the amplifier cannot prevent the subwoofer's reactive nature from lessening the impact of low bass sounds (as explained in the feedback part of the Class AB section). Class D amplifiers for driving subwoofers are relatively inexpensive, in comparison to Class AB amplifiers. A 1000 W Class D subwoofer amplifier that can operate at about 80% to 95% efficiency costs about US$250, much less than a Class AB amplifier of this power, which would cost several thousand dollars.
The letter D used to designate this amplifier class is simply the next letter after C, and does not stand for digital. Class D and Class E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of digital symbols, but a Class D amplifier merely converts an input waveform into a continuously pulse-width modulated (square wave) analog signal. (A digital waveform would be pulse-code modulated.)
Additional classesClass EThe Class E/F amplifier is a highly efficient switching power amplifier, typically used at such high frequencies that the switching time becomes comparable to the duty time. As said in the Class D amplifier, the transistor is connected via a serial LC circuit to the load, and connected via a large L (inductor) to the supply voltage. The supply voltage is connected to ground via a large capacitor to prevent any RF signals leaking into the supply. The Class E amplifier adds a C (capacitor) between the transistor and ground and uses a defined L1 to connect to the supply voltage.
Class E Amplifier
The following description ignores DC, which can be added easily afterwards. The above mentioned C and L are in effect a parallel LC circuit to ground. When the transistor is on, it pushes through the serial LC circuit into the load and some current begins to flow to the parallel LC circuit to ground. Then the serial LC circuit swings back and compensates the current into the parallel LC circuit. At this point the current through the transistor is zero and it is switched off. Both LC circuits are now filled with energy in C and L0. The whole circuit performs a damped oscillation. The damping by the load has been adjusted so that some time later the energy from the Ls is gone into the load, but the energy in both C0 peaks at the original value to in turn restore the original voltage so that the voltage across the transistor is zero again and it can be switched on.
With load, frequency, and duty cycle (0.5) as given parameters and the constraint that the voltage is not only restored, but peaks at the original voltage, the four parameters (L, L0, C and C0) are determined. The Class E amplifier takes the finite on resistance into account and tries to make the current touch the bottom at zero. This means that the voltage and the current at the transistor are symmetric with respect to time. The Fourier transform allows an elegant formulation to generate the complicated LC networks and says that the first harmonic is passed into the load, all even harmonics are shorted and all higher odd harmonics are open.
Class E uses a significant amount of second-harmonic voltage. The second harmonic can be used to reduce the overlap with edges with finite sharpness. For this to work, energy on the second harmonic has to flow from the load into the transistor, and no source for this is visible in the circuit diagram. In reality, the impedance is mostly reactive and the only reason for it is that Class E is a Class F (see below) amplifier with a much simplified load network and thus has to deal with imperfections.
In many amateur simulations of Class E amplifiers, sharp current edges are assumed nullifying the very motivation for Class E and measurements near the transit frequency of the transistors show very symmetric curves, which look much similar to Class F simulations.
The Class E amplifier was invented in 1972 by Nathan O. Sokal and Alan D. Sokal, and details were first published in 1975.[11] Some earlier reports on this operating class have been published in Russian.
Class FIn push-pull amplifiers and in CMOS, the even harmonics of both transistors just cancel. Experiment shows that a square wave can be generated by those amplifiers and theory shows that square waves do consist of odd harmonics only. In a Class D amplifier, the output filter blocks all harmonics; i.e., the harmonics see an open load. So even small currents in the harmonics suffice to generate a voltage square wave. The current is in phase with the voltage applied to the filter, but the voltage across the transistors is out of phase. Therefore, there is a minimal overlap between current through the transistors and voltage across the transistors. The sharper the edges, the lower the overlap.
While Class D sees the transistors and the load as two separate modules, Class F admits imperfections like the parasitics of the transistor and tries to optimise the global system to have a high impedance at the harmonics. Of course there has to be a finite voltage across the transistor to push the current across the on-state resistance. Because the combined current through both transistors is mostly in the first harmonic, it looks like a sine. That means that in the middle of the square the maximum of current has to flow, so it may make sense to have a dip in the square or in other words to allow some overswing of the voltage square wave. A Class F load network by definition has to transmit below a cutoff frequency and reflect above.
Any frequency lying below the cutoff and having its second harmonic above the cutoff can be amplified, that is an octave bandwidth. On the other hand, an inductive-capacitive series circuit with a large inductance and a tunable capacitance may be simpler to implement. By reducing the duty cycle below 0.5, the output amplitude can be modulated. The voltage square waveform will degrade, but any overheating is compensated by the lower overall power flowing. Any load mismatch behind the filter can only act on the first harmonic current waveform, clearly only a purely resistive load makes sense, then the lower the resistance, the higher the current.
Class F can be driven by sine or by a square wave, for a sine the input can be tuned by an inductor to increase gain. If Class F is implemented with a single transistor, the filter is complicated to short the even harmonics. All previous designs use sharp edges to minimise the overlap.
Classes G and HThere are a variety of amplifier designs that enhance Class AB output stages with more efficient techniques to achieve greater efficiencies with low distortion. These designs are common in large audio amplifiers since the heatsinks and power transformers would be prohibitively large (and costly) without the efficiency increases. The terms "Class G" and "Class H" are used interchangeably to refer to different designs, varying in definition from one manufacturer or paper to another.
Class G amplifiers (which use "rail switching" to decrease power consumption and increase efficiency) are more efficient than Class AB amplifiers. These amplifiers provide several power rails at different voltages and switch between them as the signal output approaches each level. Thus, the amplifier increases efficiency by reducing the wasted power at the output transistors. Class G amplifiers are more efficient than Class AB but less efficient when compared to Class D, without the negative EMI effects of Class D.
Class H amplifiers take the idea of Class G one step further creating an infinitely variable supply rail. This is done by modulating the supply rails so that the rails are only a few volts larger than the output signal at any given time. The output stage operates at its maximum efficiency all the time. Switched-mode power supplies can be used to create the tracking rails. Significant efficiency gains can be achieved but with the drawback of more complicated supply design and reduced THD performance.
The voltage signal shown is thus a larger version of the input, but has been changed in sign (inverted) by the amplification. Other arrangements of amplifying device are possible, but that given (that is, common emitter, common source or common cathode) is the easiest to understand and employ in practice. If the amplifying element is linear, then the output will be faithful copy of the input, only larger and inverted. In practice, transistors are not linear, and the output will only approximate the input. Non-linearity from any of several sources is the origin of distortion within an amplifier. Which class of amplifier (A, B, AB or C) depends on how the amplifying device is biased - in the diagrams the bias circuits are omitted for clarity.
Any real amplifier is an imperfect realization of an ideal amplifier. One important limitation of a real amplifier is that the output it can generate is ultimately limited by the power available from the power supply. An amplifier will saturate and clip the output if the input signal becomes too large for the amplifier to reproduce or if operational limits for a device are exceeded.
For additional information on Class H: Efficiency Class H
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Bruce Davison has: Played Andy Fry in "Insight" in 1960. Played Greg - Psych Intern in "Insight" in 1960. Played William in "Insight" in 1960. Played Randy King in "Insight" in 1960. Played Wilhelm Van Schlagel in "General Hospital" in 1963. Played Wilhelm in "General Hospital" in 1963. Played Wilhelm VonSchlagel in "General Hospital" in 1963. Performed in "NBC Experiment in Television" in 1967. Played Dan in "Last Summer" in 1969. Performed in "Marcus Welby, M.D." in 1969. Played Mickey Peters in "Medical Center" in 1969. Played (segment "Love and the Secret Spouse") in "Love, American Style" in 1969. Played Simon in "The Strawberry Statement" in 1970. Played Fitzgore in "Been Down So Long It Looks Like Up to Me" in 1971. Played Willard Stiles in "Willard" in 1971. Played Bob Hill in "The Waltons" in 1971. Played Josh Hollister in "Hec Ramsey" in 1972. Played David Armonstrong in "The Jerusalem File" in 1972. Played Victor Joe Vero in "Police Story" in 1973. Played Greg in "Peege" in 1973. Played Jamie Patterson in "The Affair" in 1973. Played Detective Dennis Till in "Cops" in 1973. Played Jeffrey in "Love Story" in 1973. Played Clyde Griffiths in "Police Story" in 1973. Played Binns in "Police Woman" in 1974. Played The Older Patrick in "Mame" in 1974. Performed in "Ma and Pa" in 1974. Performed in "The Lives of Benjamin Franklin" in 1974. Played Michael Larsen in "The Last Survivors" in 1975. Played Bobby Allen in "Grand Jury" in 1976. Played Bruce - as a Young Man in "ABC Weekend Specials" in 1977. Played Andrew Raines in "Lou Grant" in 1977. Played Clark Davis in "Short Eyes" in 1977. Played George in "The Gathering" in 1977. Played Orin Mannon in "Mourning Becomes Electra" in 1978. Played Anton Reiker in "Summer of My German Soldier" in 1978. Played Col. Robert Dawson in "Brass Target" in 1978. Performed in "The Horror Show" in 1979. Played George in "The Gathering, Part II" in 1979. Played Jason in "Mind Over Murder" in 1979. Played George Orr in "The Lathe of Heaven" in 1980. Played Dan in "High Risk" in 1981. Played Ben Ross in "The Wave" in 1981. Played Clint Larsen in "Incident at Crestridge" in 1981. Played Dolin T. Pike in "Kiss My Grits" in 1982. Played Technical Officer David Ackroyd in "The Astronauts" in 1982. Played Calvin Oberst in "Ghost Dancing" in 1983. Played Richard Hagstrom in "Tales from the Darkside" in 1983. Played Tranio in "The Taming of the Shrew" in 1983. Played Anthony Mortlake in "Hotel" in 1983. Played Captain Wyler in "Hunter" in 1984. Played David Carroll in "Murder, She Wrote" in 1984. Played John Langley in "V" in 1984. Played Capt. Wyler in "Hunter" in 1984. Played Deputy Chief Wyler in "Hunter" in 1984. Played Stuart Russell in "Lies" in 1985. Played Ruby in "Spies Like Us" in 1985. Played Richard in "Amazing Stories" in 1985. Played Richard Harrison in "The Ladies Club" in 1986. Played Cpl. Joseph Porta in "The Misfit Brigade" in 1987. Played Congressman Mainway in "thirtysomething" in 1987. Played Luden Sandelton in "Tales from the Crypt" in 1989. Played Wyck in "Seinfeld" in 1989. Played Bill Guthrie in "Lady in the Corner" in 1989. Played himself in "The More You Know" in 1989. Played David in "Longtime Companion" in 1989. Played Councilman Gene Whalen in "City" in 1990. Played Doctor Peter Foley in "Stolen: One Husband" in 1990. Played Himself - Nominee: Best Actor in a Supporting Role in "The 63rd Annual Academy Awards" in 1991. Played Albert Morton in "Steel and Lace" in 1991. Played Himself - Winner: Best Actor in a Supporting Role in a Motion Picture in "The 48th Annual Golden Globe Awards" in 1991. Played George Henderson in "Harry and the Hendersons" in 1991. Played Richard Robbins in "Desperate Choices: To Save My Child" in 1992. Played himself in "The Tonight Show with Jay Leno" in 1992. Played Senator Robert Kelly in "HBO First Look" in 1992. Played Himself - Co-Host in "In a New Light: A Call to Action in the War Against AIDS" in 1992. Played Larkin in "Six Degrees of Separation" in 1993. Played Howard Finnigan in "Short Cuts" in 1993. Played Bill Betts in "An Ambush of Ghosts" in 1993. Played Dr. Burt Peters in "Chicago Hope" in 1994. Played himself in "The 5th Annual GLAAD Media Awards" in 1994. Performed in "Present Tense, Past Perfect" in 1995. Played Dr. Morris Sperling in "JAG" in 1995. Played Mark Davis in "Cybill" in 1995. Played Himself - Presenter: Best Screenplay in "The 52nd Annual Golden Globe Awards" in 1995. Played Burt Squires in "The Skateboard Kid II" in 1995. Played Jareth in "Star Trek: Voyager" in 1995. Played John McCormick in "Far from Home: The Adventures of Yellow Dog" in 1995. Played Watson Brewer in "The Baby-Sitters Club" in 1995. Played Dr. Stevens in "The Cure" in 1995. Played Joseph Smith in "Homage" in 1995. Played himself in "The Daily Show" in 1996. Played Reverend Parris in "The Crucible" in 1996. Played Sam Stapp in "After Jimmy" in 1996. Played John Murray in "Grace of My Heart" in 1996. Played Dr. Michael Millerton in "Hidden in America" in 1996. Played Scott Wallace in "The Practice" in 1997. Played New Lighthouse Keeper in "The Hunger" in 1997. Played Yehiel Katzetnik Dinur in "The Trial of Adolf Eichmann" in 1997. Played Frank Gainer in "Color of Justice" in 1997. Played Bruce in "Lovelife" in 1997. Played Richard Bowden in "Apt Pupil" in 1998. Played Dr. Reingold in "Paulie" in 1998. Played Chase Stewart in "A Memory in My Heart" in 1999. Played Thomas Semmes in "Vendetta" in 1999. Played Dr. Charles Aaron in "At First Sight" in 1999. Played Jim in "Locked in Silence" in 1999. Played Avery Tinsdale in "CSI: Crime Scene Investigation" in 2000. Played Senator Robert Kelly in "The Mutant Watch" in 2000. Played Ray in "The King Is Alive" in 2000. Played Senator Kelly in "X-Men" in 2000. Played Rand Parrish in "Summer Catch" in 2001. Played Narrator in "Le timide" in 2001. Played (segment "The Other Side") in "On the Edge" in 2001. Played Menos in "Enterprise" in 2001. Played Dr. Zimmer in "Off Season" in 2001. Played Brig. Gen. Bill Marks in "High Crimes" in 2002. Played Lawrence Diebenkorn in "L.A. Law: The Movie" in 2002. Played Paul Cartwright in "Without a Trace" in 2002. Played Dane Daniels in "CSI: Miami" in 2002. Played Dan Freeman in "Too Young to Be a Dad" in 2002. Played Lionel Dahmer in "Dahmer" in 2002. Played Senator Kelly in "X2" in 2003. Played Peter Schuman in "Out of the Ashes" in 2003. Played Detective Sgt. Baker in "Rules of the Game" in 2003. Played Rupert Iris in "Manfast" in 2003. Played Narrated by in "Rat People: Friends and Foes" in 2003. Played Durwood Cable in "Runaway Jury" in 2003. Played himself in "The Uncanny Suspects" in 2003. Played himself in "X-Men Production Scrapbook" in 2003. Played Dr. Stegman in "Kingdom Hospital" in 2004. Played Leonard Kroll in "The L Word" in 2004. Played Dr. Michael Robert in "Battlestar Galactica" in 2004. Played Frank in "Evergreen" in 2004. Played Dr. Douglas Brooks in "Lost" in 2004. Played Martin Landrum in "The Clinic" in 2004. Played Daddy in "On the Couch" in 2004. Played Adam in "Going Shopping" in 2005. Played Russell Clark in "The Closer" in 2005. Played Father Davison in "Criminal Minds" in 2005. Played Josh Bedford in "Ghost Whisperer" in 2005. Played Hellman in "Close to Home" in 2005. Played Ambassador Harrington in "8MM 2" in 2005. Played Robert Oliver in "Numb3rs" in 2005. Played Stan Lathem in "The Triangle" in 2005. Played Pastor Boyd in "Hate Crime" in 2005. Played Doug Hellman in "Close to Home" in 2005. Performed in "Untitled Brad Copeland Project" in 2006. Played Senator Kelly in "X-Men: Evolution of a Trilogy" in 2006. Played Walter Snowden in "Psych" in 2006. Played General Preston Rossdale in "Special Ops: Delta Force" in 2006. Played Charles Graiman in "Knight Rider" in 2008. Played Dr. Peter Silberman in "Terminator: The Sarah Connor Chronicles" in 2008. Played Narrator in "Childrens Hospital" in 2008. Played himself in "Celebrity Ghost Stories" in 2008. Played Dan Blackwell in "Leverage" in 2008. Played Dr. Mark Rhodes in "MegaFault" in 2009. Played Rod Wright in "A Golden Christmas" in 2009. Played Lou Karnacki in "Castle" in 2009. Played Roger in "Passengers" in 2009. Played Anthony in "La linea" in 2009. Played himself in "Knight Rider: The Icon Reborn" in 2009. Played Judge Cyrus Maxwell in "Drop Dead Diva" in 2009. Played Nick Anderson in "Christmas Angel" in 2009. Played Walter Winslaw in "Arctic Blast" in 2010. Played President Wilson in "Justice League: Crisis on Two Earths" in 2010. Played Wallace Dosher in "The Glades" in 2010. Played Fr. Phineas McAllister in "Camp Hell" in 2010. Played Max Langford in "Covert Affairs" in 2010. Played Captain Jansen in "Modus Operandi" in 2010. Played Steven Carver in "Hawaii Five-0" in 2010. Played James Maine in "Titanic II" in 2010. Played Chief Kirkhoven in "Munger Road" in 2011. Played Congressman Barber in "Elwood" in 2011. Played Amos Christner in "The Congregation" in 2011. Played Hartstone in "Luck" in 2011. Played Garrison in "Coffin" in 2011. Played Rod Wright in "3 Holiday Tails" in 2011. Played Mr. Lowell in "Stealing Roses" in 2012. Played Sheriff Walt Henderson in "Bigfoot" in 2012. Played Howard in "Brother White" in 2012. Played Admiral Arthur Shepard in "Last Resort" in 2012. Played himself in "That Guy... Who Was in That Thing" in 2012. Played Francis Matthias in "The Lords of Salem" in 2012. Played Jerry Farrell in "Return of the Killer Shrews" in 2012. Played The Roman in "The Millionaire Tour" in 2012. Played Walt in "Words and Pictures" in 2013. Played William H. Seward in "Saving Lincoln" in 2013. Played Old Oliver in "Beyond the Heavens" in 2013. Played Psychic in "37" in 2013. Played himself in "Classic Hollywood Cinemas" in 2014. Played Howard Burgess in "Those Who Kill" in 2014. Performed in "Sister" in 2014. Played D.A. Bonomi in "The Bronx Bull" in 2014. Played Mr. Pearson in "Tao of Surfing" in 2014. Played Coach Scott Deshields in "108 Stitches" in 2014. Played Dr. Bob in "A Schizophrenic Love Story" in 2014. Played Lawrence Wilheimer in "Get a Job" in 2014. Played Dr. Yardley in "Killing Frank" in 2015.
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Psychology emerged in the late 19th century as a scientific field influenced by philosophy and physiology. Early schools of thought, like structuralism and functionalism, focused on understanding the mind's structure and functions. The 20th century saw the rise of behaviorism, psychoanalysis, and the cognitive revolution, which shaped modern psychology as a multi-faceted science studying behavior, cognition, emotions, and neurology.
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