title: Azadi Tower

text: Among the earliest items on display are square flagstones, gold sheeting, and terracotta tablets from Susa covered with cuneiform characters. Before the 1979 Revolution, the main display was occupied by a copy of the Cyrus Cylinder, the original being kept at the British Museum. A translation of the cylinder's cuneiform inscription is inscribed in golden letters on the wall of one of the galleries leading to the museum's audio-visual center. A similar plaque facing the cylinder listed the Twelve Points of the White Revolution. Next, to the Cyrus Cylinder, there was a gold plaque commemorating the original presentation of the museum to Mohammad Reza Pahlavi by the Mayor of Tehran. Potteries, ceramics, varnished porcelains (such as a seventh-century blue and gold dish from Gorgan), an illuminated Quran, and miniatures highlighted milestones in the country's history up to the 19th century, which were represented by two painted panels from Empress and the structure was to represent Farah Pahlavi as in is stated in some ancient texts.


title: Azadi Tower

text: The original show, devised in 1971, was replaced in 1975 by a new one which invited visitors to discover Iran's geographic and natural diversity along with its fundamental historical elements. It exhibited a number of national achievements, technical undertakings, calligraphed poems, and miniature paintings. The project, devised by a Czechoslovak company, required 12,000 metres of film, 20,000 color slides, 20 movie projectors, and 120 slide projectors. The audiovisual programmes were directed by professor Jaroslav Frič (1928–2000). Five computers operated the entire system.


title: Azadi Tower

text: German artist Philipp Geist organized a projection mapping installation named "Gate of Words" at the Azadi Tower, on the occasion of the German Unity Day. The show was held from October 3 to 5, 2015.


title: Azadi Tower

text: In this project, the artist visualized the topics of freedom, peace, space and time in a poetical manner. Geist developed a light installation made of colored words and concepts in different languages, and abstract painterly compositions of images. The glowing words were in English, German and Persian, moving in sync with live music on the walls of the tower.


title: Where on Earth Is Carmen Sandiego?

text: Where on Earth Is Carmen Sandiego? is an American animated television series based on the series of computer games. The show was produced by DIC Productions L.P. and originally aired from 1994 to 1999, on Saturday mornings during FOX's Fox Kids Network block. Reruns aired on the Qubo television network from June 9, 2012 (alongside "Animal Atlas") to May 26, 2018.


title: Where on Earth Is Carmen Sandiego?

text: The series won a Daytime Emmy Award for Outstanding Children's Animated Program in 1995, and in the same year was spun-off into a "Where in the World"-styled video game entitled "Carmen Sandiego Junior Detective". Its theme song uses the melody from the chorus "Singt dem großen Bassa Lieder" ("Sing Songs of the Great Pasha") from Mozart's opera "Die Entführung aus dem Serail" ("The Abduction from the Seraglio").


title: Where on Earth Is Carmen Sandiego?

text: The script for every "Earth" episode had to meet the approval of Broderbund, which created and, at the time, owned the "Carmen" franchise. Their cause for concern was the level of the violence on other FOX children's shows such as "" and "Mighty Morphin Power Rangers". Broderbund did not require this of the creators of the "World" and "Time" game shows that aired on PBS, presumably since PBS, as the distributor of such shows as "Sesame Street", had a long-standing reputation for non-violent educational children's programming. The lead characters of "Earth" were featured in "Carmen Sandiego Junior Detective", released in 1995. The opening theme song for the show is "Singt dem großen Bassa Lieder" from "Wolfgang Amadeus Mozart's Die Entführung aus dem Serail", with new lyrics, pop instrumentation, and a backbeat. The Rainbow Animation Group (later renamed Galaxy World, Inc., not to be confused with the Italian studio Rainbow S.p.A.), and Han Yang Productions contributed some animation for this series.


title: Where on Earth Is Carmen Sandiego?

text: Fox Video originally released the series on VHS through their Fox Kids Video label, which contained two episodes each.


title: Where on Earth Is Carmen Sandiego?

text: In November 2001, Lions Gate Home Entertainment and Trimark Home Video released two VHS tapes, "Carmen's Revenge" and "Time Traveler", consisting of the show's three-part episodes ("Retribution" and "Labyrinth") in a feature-length format. "Time Traveller" was also released on DVD, and alongside the "Labyrinth" episode, also came with a demo of "Where in the World is Carmen Sandiego? Treasures of Knowledge". A video of the episode "Timing is Everything" was included with some versions of the mentioned game.


title: Where on Earth Is Carmen Sandiego?

text: In September 2003, Sterling Entertainment released "Into the Maelstrom" and "No Place like Home" on VHS and DVD. "Into the Maelstrom" contained the three part "Retribution" episode, while "No Place like Home" contained the episode "The Remnants" and the two-part episode "Can You Ever Go Home Again?" The DVD versions contained "When it Rains..." and "Follow My Footprints" as bonus episodes, respectively. NCircle Entertainment reissued both DVDs in 2007.


title: Where on Earth Is Carmen Sandiego?

text: In June 2006, Shout! Factory and Sony BMG Music Entertainment released the first season on DVD. Due to poor sales, no further seasons were released.


title: Where on Earth Is Carmen Sandiego?

text: Mill Creek Entertainment released "Where on Earth Is Carmen Sandiego? – The Complete Series" on DVD in Region 1 on February 21, 2012. This four-disc set contains all forty episodes of the series. They also released a ten-episode best-of collection the same day. These releases have been discontinued and are now out of print. Mill Creek re-released the complete series on DVD in Region 1 in June 2017.


title: Where on Earth Is Carmen Sandiego?

text: PIDAX, a German company, released the complete series on DVD for Region 2 in 3 Volumes in 2019 in English and German.


title: Where on Earth Is Carmen Sandiego?

text: Following the plot of the "Carmen Sandiego" franchise, "Earth" sees international thief Carmen Sandiego (voiced by Rita Moreno) lead the organization V.I.L.E. in stealing treasures from around the world and leaving clues behind for ACME agents Zack (voiced by Scott Menville) and Ivy (voiced by Jennifer Hale), under the guidance of the Chief (voiced by Rodger Bumpass), to find, in order to capture her. In this version, Carmen Sandiego is a former agent of ACME who left to seek a greater challenge, and has a strong code of ethics when stealing items. The Player is an unseen live-action character who bookends acts by communicating with Carmen; it is implied that to them the television series is a video game that they are playing from a computer.


title: Where on Earth Is Carmen Sandiego?

text: While Carmen is originally presented as the show's antagonist, she becomes more like an anti-hero as the series progresses; she even helps Zack and Ivy against mutual enemies.


title: Where on Earth Is Carmen Sandiego?

text: As Carmen Sandiego became less villainous and evolved into more of an antihero, other characters began to fill her original role as the show's antagonist. The following villains are:


title: Where on Earth Is Carmen Sandiego?

text: The show was given a rating of 4 stars out of 5 by "Common Sense Media", noting that the format of the show – which includes trivia sessions between acts, vocabulary definitions, and the use of foreign languages – is "designed to pique kids' interest in these subjects". "DVD Talk" noted that the show exceeded the obligatory action of comedy of a cartoon, by respecting its audience with an intelligent sensibility rarely seen in children's television.


title: Teddy Sears

text: Edward M. Sears (born April 6, 1977) is an American actor, known for his roles as Richard Patrick Woolsley on the TNT legal drama series "Raising the Bar", Patrick on the first season of FX anthology horror drama "American Horror Story" (retroactively titled ""), Dr. Austin Langham on the "Showtime" period drama series "Masters of Sex", and DC Comics supervillain Hunter Zolomon / Zoom on "The Flash".


title: Teddy Sears

text: Sears was born in Washington, D.C., and raised in Chevy Chase, Maryland. He attended high school at the Landon School in Bethesda, MD. Sears played varsity football for the University of Maryland, but transferred and graduated from the University of Virginia with a degree in business management in 1999.


title: Teddy Sears

text: Sears' business career in New York was put on hold as he won a role on his first audition, with a two-year contract role on the daytime series "One Life to Live". Then, after several appearances on the "Law & Order" franchise and "Whoopi", he attended the William Esper Studio. This training led to comedy stints on the "Late Show with David Letterman" and "Late Night with Conan O'Brien".


title: Teddy Sears

text: He co-starred on the TNT original series "Raising the Bar" portraying public defender Richard Patrick Woolsley.


title: Teddy Sears

text: Sears appeared in Joss Whedon's "Dollhouse", the Lifetime original film "The Client List", and as Thomas Cole in "The Defenders".


title: Teddy Sears

text: In 2013, Sears joined the cast of the Showtime drama "Masters of Sex", about the work of Masters and Johnson. From 2015 to 2016, Sears had been cast in the second season in a recurring role of The CW's DC Comics television series "The Flash", initially introduced as Jay Garrick, until it was revealed that his character was actually Hunter Zolomon / Zoom. In 2017, he starred as Keith Mullins in "".


title: Teddy Sears

text: In 2020, Sears appeared as a guest on the "Studio 60 on the Sunset Strip" marathon fundraiser episode of "The George Lucas Talk Show."


title: Teddy Sears

text: Sears married actress Milissa Skoro on October 5, 2013. In his free time he surfs and plays ice hockey. He has two brothers, Christian and Ricky, and a sister Dana.


title: Teddy Sears

text: His great-grandfather won a gold medal in the 1912 Olympics for pistol shooting, and his aunt won a bronze medal in the 1956 Olympics for the 100-yard butterfly.


title: Good to Great

text: Good to Great: Why Some Companies Make the Leap... and Others Don't is a management book by Jim C. Collins that describes how companies transition from being good companies to great companies, and how most companies fail to make the transition. The book was a bestseller, selling four million copies and going far beyond the traditional audience of business books. The book was published on October 16, 2001.


title: Good to Great

text: Collins finds eleven examples of "great companies" and comparators, similar in industry-type and opportunity, but which failed to achieve the good-to-great growth shown in the great companies:


title: Good to Great

text: Collins includes 6 examples of companies that did not sustain their change to greatness. These companies, "... are looked at separately as a clump":


title: Good to Great

text: The book was "cited by several members of "The Wall Street Journal"'s CEO Council as the best management book they've read."


title: Good to Great

text: "Publishers Weekly" called it "worthwhile", although "many of Collins' perspectives on running a business are amazingly simple and commonsense".


title: Good to Great

text: It was described as "a deeply-researched analysis..." in the "Time (magazine)" list of "The 25 Most Influential Business Management Books".


title: Good to Great

text: Holt and Cameron state the book provides a "generic business recipe" that ignores "particular strategic opportunities and challenges."


title: Good to Great

text: Steven D. Levitt noted that some of the companies selected as "great" have since gotten into serious trouble, such as Circuit City and Fannie Mae, while only Nucor had "dramatically outperformed the stock market" and "Abbott Labs and Wells Fargo have done okay". He further states that investing in the portfolio of the 11 companies covered by the book, in the year of 2001, would actually result in "underperforming" the S&P 500. Levitt concludes that books like this are "mostly backward-looking" and can't offer a guide for the future."


title: Good to Great

text: John Greathouse alleges in a critical review that Collins once made a comment stating, "The books never promised that these companies would always be great, just that they were once great." Greathouse claims the statement was an attempt by Collins to defend the book, and other previous works. Greathouse also represents the view that Collins' book "How the Mighty Fall: And Why Some Companies Never Give In" blames some of the failed companies themselves for having drastically changed after Collins' books were printed.


title: Savitzky–Golay filter

text: A Savitzky–Golay filter is a digital filter that can be applied to a set of digital data points for the purpose of smoothing the data, that is, to increase the precision of the data without distorting the signal tendency. This is achieved, in a process known as convolution, by fitting successive sub-sets of adjacent data points with a low-degree polynomial by the method of linear least squares. When the data points are equally spaced, an analytical solution to the least-squares equations can be found, in the form of a single set of "convolution coefficients" that can be applied to all data sub-sets, to give estimates of the smoothed signal, (or derivatives of the smoothed signal) at the central point of each sub-set. The method, based on established mathematical procedures, was popularized by Abraham Savitzky and Marcel J. E. Golay, who published tables of convolution coefficients for various polynomials and sub-set sizes in 1964. Some errors in the tables have been corrected. The method has been extended for the treatment of 2- and 3-dimensional data.


title: Savitzky–Golay filter

text: Savitzky and Golay's paper is one of the most widely cited papers in the journal "Analytical Chemistry" and is classed by that journal as one of its "10 seminal papers" saying "it can be argued that the dawn of the computer-controlled analytical instrument can be traced to this article".


title: Savitzky–Golay filter

text: The data consists of a set of points {"x", "y"}, "j" = 1, ..., "n", where "x" is an independent variable and "y" is an observed value. They are treated with a set of "m" convolution coefficients, "C", according to the expression


title: Savitzky–Golay filter

text: Selected convolution coefficients are shown in the tables, below. For example, for smoothing by a 5-point quadratic polynomial, "m" = 5, "i" = −2, −1, 0, 1, 2 and the "j"th smoothed data point, "Y", is given by


title: Savitzky–Golay filter

text: where, "C" = −3/35, "C" = 12 / 35, etc. There are numerous applications of smoothing, which is performed primarily to make the data appear to be less noisy than it really is. The following are applications of numerical differentiation of data. Note When calculating the "n"th derivative, an additional scaling factor of formula_3 may be applied to all calculated data points to obtain absolute values (see expressions for formula_4, below, for details).


title: Savitzky–Golay filter

text: A moving average filter is commonly used with time series data to smooth out short-term fluctuations and highlight longer-term trends or cycles. It is often used in technical analysis of financial data, like stock prices, returns or trading volumes. It is also used in economics to examine gross domestic product, employment or other macroeconomic time series.


title: Savitzky–Golay filter

text: An unweighted moving average filter is the simplest convolution filter. Each subset of the data set is fitted by a straight horizontal line. It was not included in the Savitzsky-Golay tables of convolution coefficients as all the coefficient values are simply equal to .


title: Savitzky–Golay filter

text: When the data points are equally spaced, an analytical solution to the least-squares equations can be found. This solution forms the basis of the convolution method of numerical smoothing and differentiation. Suppose that the data consists of a set of "n" points ("x", "y") ("j" = 1, ..., "n"), where "x" is an independent variable and "y" is a datum value. A polynomial will be fitted by linear least squares to a set of "m" (an odd number) adjacent data points, each separated by an interval "h". Firstly, a change of variable is made


title: Savitzky–Golay filter

text: For example, for a cubic polynomial fitted to 5 points, "z"= −2, −1, 0, 1, 2 the normal equations are solved as follows.


title: Savitzky–Golay filter

text: Now, the normal equations can be factored into two separate sets of equations, by rearranging rows and columns, with


title: Savitzky–Golay filter

text: The coefficients of "y" in these expressions are known as convolution coefficients. They are elements of the matrix


title: Savitzky–Golay filter

text: Tables of convolution coefficients, calculated in the same way for "m" up to 25, were published for the Savitzky–Golay smoothing filter in 1964, The value of the central point, "z" = 0, is obtained from a single set of coefficients, "a" for smoothing, "a" for 1st derivative etc. The numerical derivatives are obtained by differentiating Y. This means that the "derivatives are calculated for the smoothed data curve". For a cubic polynomial


title: Savitzky–Golay filter

text: In general, polynomials of degree (0 and 1), (2 and 3), (4 and 5) etc. give the same coefficients for smoothing and even derivatives. Polynomials of degree (1 and 2), (3 and 4) etc. give the same coefficients for odd derivatives.


title: Savitzky–Golay filter

text: It is not necessary always to use the Savitzky–Golay tables. The summations in the matrix JJ can be evaluated in closed form,


title: Savitzky–Golay filter

text: so that algebraic formulae can be derived for the convolution coefficients. Functions that are suitable for use with a curve that has an inflection point are:


title: Savitzky–Golay filter

text: Higher derivatives can be obtained. For example, a fourth derivative can be obtained by performing two passes of a second derivative function.


title: Savitzky–Golay filter

text: An alternative to fitting "m" data points by a simple polynomial in the subsidiary variable, "z", is to use orthogonal polynomials.


title: Savitzky–Golay filter

text: where "P", ..., "P" is a set of mutually orthogonal polynomials of degree 0, ..., "k". Full details on how to obtain expressions for the orthogonal polynomials and the relationship between the coefficients b and a are given by Guest. Expressions for the convolution coefficients are easily obtained because the normal equations matrix, JJ, is a diagonal matrix as the product of any two orthogonal polynomials is zero by virtue of their mutual orthogonality. Therefore, each non-zero element of its inverse is simply the reciprocal the corresponding element in the normal equation matrix. The calculation is further simplified by using recursion to build orthogonal Gram polynomials. The whole calculation can be coded in a few lines of PASCAL, a computer language well-adapted for calculations involving recursion.


title: Savitzky–Golay filter

text: Savitzky–Golay filters are most commonly used to obtain the smoothed or derivative value at the central point, "z" = 0, using a single set of convolution coefficients. ("m" − 1)/2 points at the start and end of the series cannot be calculated using this process. Various strategies can be employed to avoid this inconvenience.


title: Savitzky–Golay filter

text: It is implicit in the above treatment that the data points are all given equal weight. Technically, the objective function


title: Savitzky–Golay filter

text: being minimized in the least-squares process has unit weights, "w" = 1. When weights are not all the same the normal equations become


title: Savitzky–Golay filter

text: If the same set of diagonal weights is used for all data subsets, formula_32, an analytical solution to the normal equations can be written down. For example, with a quadratic polynomial,


title: Savitzky–Golay filter

text: An explicit expression for the inverse of this matrix can be obtained using Cramer's rule. A set of convolution coefficients may then be derived as


title: Savitzky–Golay filter

text: Alternatively the coefficients, C, could be calculated in a spreadsheet, employing a built-in matrix inversion routine to obtain the inverse of the normal equations matrix. This set of coefficients, once calculated and stored, can be used with all calculations in which the same weighting scheme applies. A different set of coefficients is needed for each different weighting scheme.


title: Savitzky–Golay filter

text: It was shown that Savitzky–Golay filter can be improved by introducing weights that decrease at the ends of the fitting interval.


title: Savitzky–Golay filter

text: Two-dimensional smoothing and differentiation can also be applied to tables of data values, such as intensity values in a photographic image which is composed of a rectangular grid of pixels.


title: Savitzky–Golay filter

text: The Jacobian has 10 columns, one for each of the parameters "a" − "a", and 35 rows, one for each pair of "v" and "w" values. Each row has the form


title: Savitzky–Golay filter

text: The first row of C contains 35 convolution coefficients, which can be multiplied with the 35 data values, respectively, to obtain the polynomial coefficient formula_39, which is the smoothed value at the central node of the kernel (i.e. at the 18th node of the above table). Similarly, other rows of C can be multiplied with the 35 values to obtain other polynomial coefficients, which, in turn, can be used to obtain smoothed values and different smoothed partial derivatives at different nodes.


title: Savitzky–Golay filter

text: Nikitas and Pappa-Louisi showed that depending on the format of the used polynomial, the quality of smoothing may vary significantly. They recommend using the polynomial of the form


title: Savitzky–Golay filter

text: because such polynomials can achieve good smoothing both in the central and in the near-boundary regions of a kernel, and therefore they can be confidently used in smoothing both at the internal and at the near-boundary data points of a sampled domain. In order to avoid ill-conditioning when solving the least-squares problem, "p" < "m" and "q" < "n". For software that calculates the two-dimensional coefficients and for a database of such C's, see the section on multi-dimensional convolution coefficients, below.


title: Savitzky–Golay filter

text: The idea of two-dimensional convolution coefficients can be extended to the higher spatial dimensions as well, in a straightforward manner, by arranging multidimensional distribution of the kernel nodes in a single row. Following the aforementioned finding by Nikitas and Pappa-Louisi in two-dimensional cases, usage of the following form of the polynomial is recommended in multidimensional cases:


title: Savitzky–Golay filter

text: where D is the dimension of the space, formula_42's are the polynomial coefficients, and u's are the coordinates in the different spatial directions. Algebraic expressions for partial derivatives of any order, be it mixed or otherwise, can be easily derived from the above expression. Note that C depends on the manner in which the kernel nodes are arranged in a row and on the manner in which the different terms of the expanded form of the above polynomial is arranged, when preparing the Jacobian.


title: Savitzky–Golay filter

text: Accurate computation of C in multidimensional cases becomes challenging, as precision of standard floating point numbers available in computer programming languages no longer remain sufficient. The insufficient precision causes the floating point truncation errors to become comparable to the magnitudes of some C elements, which, in turn, severely degrades its accuracy and renders it useless. Chandra Shekhar has brought forth two open source softwares, and , which handle these accuracy issues adequately. ACCC performs the computation by using floating point numbers, in an iterative manner. The precision of the floating-point numbers is gradually increased in each iteration, by using GNU MPFR. Once the obtained C's in two consecutive iterations start having same significant digits until a pre-specified distance, the convergence is assumed to have reached. If the distance is sufficiently large, the computation yields a highly accurate C. PCCC employs rational number calculations, by using GNU Multiple Precision Arithmetic Library, and yields a fully accurate C, in the rational number format. In the end, these rational numbers are converted into floating point numbers, until a pre-specified number of significant digits.


title: Savitzky–Golay filter

text: A database of C's that are calculated by using ACCC, for symmetric kernels and both symmetric and asymmetric polynomials, on unity-spaced kernel nodes, in the 1, 2, 3, and 4 dimensional spaces, is made available. Chandra Shekhar has also laid out a mathematical framework that describes usage of C calculated on unity-spaced kernel nodes to perform filtering and partial differentiations (of various orders) on non-uniformly spaced kernel nodes, allowing usage of C provided in the aforementioned database. Although this method yields approximate results only, they are acceptable in most engineering applications, provided that non-uniformity of the kernel nodes is weak.


title: Savitzky–Golay filter

text: It is inevitable that the signal will be distorted in the convolution process. From property 3 above, when data which has a peak is smoothed the peak height will be reduced and the half-width will be increased. Both the extent of the distortion and S/N (signal-to-noise ratio) improvement:


title: Savitzky–Golay filter

text: For example, If the noise in all data points is uncorrelated and has a constant standard deviation, "σ", the standard deviation on the noise will be decreased by convolution with an "m"-point smoothing function to


title: Savitzky–Golay filter

text: These functions are shown in the plot at the right. For example, with a 9-point linear function (moving average) two thirds of the noise is removed and with a 9-point quadratic/cubic smoothing function only about half the noise is removed. Most of the noise remaining is low-frequency noise(see "Frequency characteristics of convolution filters", below).


title: Savitzky–Golay filter

text: Although the moving average function gives the best noise reduction it is unsuitable for smoothing data which has curvature over "m" points. A quadratic filter function is unsuitable for getting a derivative of a data curve with an inflection point because a quadratic polynomial does not have one. The optimal choice of polynomial order and number of convolution coefficients will be a compromise between noise reduction and distortion.


title: Savitzky–Golay filter

text: One way to mitigate distortion and improve noise removal is to use a filter of smaller width and perform more than one convolution with it. For two passes of the same filter this is equivalent to one pass of a filter obtained by convolution of the original filter with itself. For example, 2 passes of the filter with coefficients (1/3, 1/3, 1/3) is equivalent to 1 pass of the filter with coefficients


title: Savitzky–Golay filter

text: The disadvantage of multipassing is that the equivalent filter width for formula_45 passes of an formula_46–point function is formula_47 so multipassing is subject to greater end-effects. Nevertheless, multipassing has been used to great advantage. For instance, some 40–80 passes on data with a signal-to-noise ratio of only 5 gave useful results. The noise reduction formulae given above do not apply because correlation between calculated data points increases with each pass.


title: Savitzky–Golay filter

text: Convolution maps to multiplication in the Fourier co-domain. The discrete Fourier transform of a convolution filter is a real-valued function which can be represented as


title: Savitzky–Golay filter

text: θ runs from 0 to 180 degrees, after which the function merely repeats itself. The plot for a 9-point quadratic/cubic smoothing function is typical. At very low angle, the plot is almost flat, meaning that low-frequency components of the data will be virtually unchanged by the smoothing operation. As the angle increases the value decreases so that higher frequency components are more and more attenuated. This shows that the convolution filter can be described as a low-pass filter: the noise that is removed is primarily high-frequency noise and low-frequency noise passes through the filter. Some high-frequency noise components are attenuated more than others, as shown by undulations in the Fourier transform at large angles. This can give rise to small oscillations in the smoothed data and phase reversal, i.e., high-frequency oscillations in the data get inverted by Savitzky–Golay filtering.


title: Savitzky–Golay filter

text: Convolution affects the correlation between errors in the data. The effect of convolution can be expressed as a linear transformation.


title: Savitzky–Golay filter

text: By the law of error propagation, the variance-covariance matrix of the data, A will be transformed into B according to


title: Savitzky–Golay filter

text: To see how this applies in practice, consider the effect of a 3-point moving average on the first three calculated points, , assuming that the data points have equal variance and that there is no correlation between them. A will be an identity matrix multiplied by a constant, "σ", the variance at each point.


title: Savitzky–Golay filter

text: In general, the calculated values are correlated even when the observed values are not correlated. The correlation extends over calculated points at a time.


title: Savitzky–Golay filter

text: To illustrate the effect of multipassing on the noise and correlation of a set of data, consider the effects of a second pass of a 3-point moving average filter. For the second pass


title: Savitzky–Golay filter

text: After two passes, the standard deviation of the central point has decreased to formula_55, compared to 0.58"σ" for one pass. The noise reduction is a little less than would be obtained with one pass of a 5-point moving average which, under the same conditions, would result in the smoothed points having the smaller standard deviation of 0.45"σ".


title: Savitzky–Golay filter

text: The advantage obtained by performing two passes with the narrower smoothing function is that it introduces less distortion into the calculated data.


title: Savitzky–Golay filter

text: Compared with other smoothing filters, e.g. convolution with a Gaussian or multi-pass moving-average filtering, Savitzky–Golay filters have an initially flatter response and sharper cutoff in the frequency domain, especially for high orders of the fit polynomial (see frequency characteristics). For data with limited signal bandwidth, this means that Savitzky–Golay filtering can provide better signal-to-noise ratio than many other filters; e.g., peak heights of spectra are better preserved than for other filters with similar noise suppression. Disadvantages of the Savitzky–Golay filters are comparably poor suppression of some high frequencies (poor stopband suppression) and artifacts when using polynomial fits for the first and last points.


title: Savitzky–Golay filter

text: Alternative smoothing methods that share the advantages of Savitzky–Golay filters and mitigate at least some of their disadvantages are Savitzky–Golay filters with properly chosen fitting weights, Whittaker–Henderson smoothing (a method closely related to smoothing splines), and convolution with a windowed sinc function.


title: Savitzky–Golay filter

text: Consider a set of data points . The Savitzky–Golay tables refer to the case that the step is constant, "h". Examples of the use of the so-called convolution coefficients, with a cubic polynomial and a window size, "m", of 5 points are as follows.


title: Savitzky–Golay filter

text: Selected values of the convolution coefficients for polynomials of degree 1, 2, 3, 4 and 5 are given in the following tables The values were calculated using the PASCAL code provided in Gorry.


title: Drow

text: The drow ( or ) or dark elves are a dark-skinned and white-haired subrace of elves connected to the subterranean Underdark in the "Dungeons & Dragons" fantasy roleplaying game. The drow have traditionally been portrayed as generally evil and connected to the evil goddess Lolth. However, later editions of "Dungeons & Dragons" have moved away from this portrayal and preassigned alignment. More recent publications have explored drow societies unconnected to Lolth.


title: Drow

text: The word "drow" is from the Orcadian and Shetland dialects of Scots, an alternative form of "trow", which is a cognate with "troll". The "Oxford English Dictionary" gives no entry for "drow", but two of the citations under "trow" name it as an alternative form of the word. Trow/drow was used to refer to a wide variety of evil sprites. Everything about the "Dungeons & Dragons" drow was invented by "Dungeons & Dragons" co-creator Gary Gygax except for the basic concept of "dark elves". However, in the Prose Edda, Snorri Sturluson wrote about the black elves: "... the dark elves however live down below the ground. ... [and] are blacker than pitch."


title: Drow

text: Gygax stated, "Drow are mentioned in Keightley's "The Fairy Mythology", as I recall (it might have been "The Secret Commonwealth"—neither book is before me, and it is not all that important anyway), and as Dark Elves of evil nature, they served as an ideal basis for the creation of a unique new mythos designed especially for the AD&D game." The form "drow" can be found in neither work. Gygax later stated that he took the term from a listing in the "Funk & Wagnall's Unexpurgated Dictionary", and no other source at all. "I wanted a most unusual race as the main power in the Underdark, so used the reference to 'dark elves' from the dictionary to create the Drow." There seems to be no work with this title. However, the following entry can be found in abridged editions of Funk & Wagnall's "Standard Dictionary of the English Language", such as "The Desk Standard Dictionary of the English Language": "[Scot.] In folk-lore, one of a race of underground elves represented as skillful workers in metal. Compare TROLL. [Variant of TROLL.] trow "


title: Drow

text: The drow were first mentioned in the "Dungeons & Dragons" game in the 1st Edition 1977 "Advanced Dungeons & Dragons" "Monster Manual" under the "Elf" entry, where it is stated that "The 'Black Elves,' or drow, are only legend." No statistics are given for the drow in this book, apart from the statistics for normal elves. The drow are described as purportedly dwelling deep beneath the surface world, in strange subterranean realms. They are said to be evil, "as dark as faeries are bright", and pictured in tales as poor fighters but strong magic-users. From 1978 to 1980, the "Greyhawk" adventure module series explored the drow in depth, including statblocks for drow and an introduction to their Underdark society.


title: Drow

text: The first hardcover "D&D" rulebook featuring statistical information on the drow was the original "Fiend Folio" (1981). Gygax wrote this entry, listed under "Elf, Drow", according to the book's credits section. The text is a slightly abridged version of the text originally found in modules G3 and D3. Likewise, Lolth's description from module D3 is reprinted in the "Fiend Folio" under the "Demon" heading.


title: Drow

text: The drow were first presented as a player character race in "Unearthed Arcana" (1985), also written by Gygax. Several elven sub-races are described in the book, including gray elves, wood elves, wild elves, and valley elves; the dark elves are described as the most divergent sub-race, and dark elf player characters are considered outcasts from their homeland, either by choice, differing from the standard chaotic evil alignment of the race, or having lost in some family-wide power struggle.


title: Drow

text: It is hinted in G1 "Steading of the Hill Giant Chief" (1978) that there is a "secret force, some motivational power behind this unusual banding of different races of giants." G2 "The Glacial Rift of the Frost Giant Jarl" (1978) mentions this guiding force again in its introduction. The third module in the series, G3 "Hall of the Fire Giant King" (1978) again mentions the party's need to find out whatever is behind the giants' alliance, and this time mentions the drow specifically by name. In the adventure, the player characters can discover the first hint of drow involvement in the fire giant king's council room, on a scroll which promises "powerful help from the Drow", signed by Eclavdra. Actual drow can be encountered starting on level #2 of the king's hall, beginning with a group of drow priests, and then other drow later.


title: Drow

text: Having discovered that the drow instigated the alliance between the races of giants and its warfare against mankind, in "D1 Descent into the Depths of the Earth" (1978) the party follows the fleeing drow into the tunnels leading northwest and deep into the earth, to eliminate the threat they pose. Examining a golden spider pin found on one of the drow priestesses, the party can discover runes in the drow language reading "Lolth, Death Queen Mother". The party continues to pursue the drow in D2 "Shrine of the Kuo-Toa" (1978). In "D3 Vault of the Drow" (1978), the adventurers eventually make it to Erelhei-Cinlu, the vast subterranean city of the drow, which is thoroughly described in the module. An extensive overview of the drow power structure is given for the purpose of creating any number of mini-campaigns or adventures taking place inside the drow capital. The characters travel on to the Egg of Lolth, where they must enter the dungeon level and fight the demoness herself. The statistics and information for drow are reprinted from "Hall of the Fire Giant King" in the back of this module, along with statistics for Lolth herself.


title: Drow

text: The story concludes in module "Q1 Queen of the Demonweb Pits" (1980). The astral gate from "D3" leads to the Abyssal realm of Lolth, goddess of the drow elves and Demon Queen of Spiders; Lolth is the architect of the sinister plot described in the two previous series of modules. At the very end of the module, the players face a final confrontation with Lolth, an exceptionally difficult challenge. The G1-G3 modules were later published together in 1981 as a single combined module as "G1-2-3 Against the Giants", and the entire series of modules in which the drow originally appeared were later published together in "Queen of the Spiders" (1986).


title: Drow

text: Gary Gygax's 1986 novel for TSR's "Greyhawk Adventures" series, "Artifact of Evil", was the first novel to feature the drow prominently. Gygax's subsequent "Gord the Rogue" novels, published by New Infinities, Inc., continued the story and the drow's involvement, in the novels "Sea of Death" (1987), "Come Endless Darkness" (1988), and "Dance of Demons" (1988).


title: Drow

text: R. A. Salvatore's 1988–1990 "The Icewind Dale Trilogy" featured the unlikely hero Drizzt Do'Urden as one of the protagonists, and the 1990–1991 followup "The Dark Elf Trilogy" focused on Drizzt and the drow of the Forgotten Realms setting. Salvatore continued the story of Drizzt and the drow in his subsequent series "Legacy of the Drow" (1992–1996), "Paths of Darkness" (1998–2001), and "The Hunter's Blades Trilogy" (2002–2004). Other works continuing the story of the drow in the Forgotten Realms include Elaine Cunningham's "Starlight and Shadows" series (1995–1996, 2003), the "War of the Spider Queen" series (2002–2005, various authors), and Lisa Smedman's "The Lady Penitent" series (2007–2008).


title: Drow

text: Keith Baker's "The Dreaming Dark" trilogy (2005–2006) featured the story of the drow in Baker's world of Eberron.


title: Drow

text: The drow appear first for this edition in the "Monstrous Compendium Volume Two" (1989), which expands the information on drow society. Also included in the entry for drow is a description and statistics for the drider. This entry is reprinted with some minor modifications in the "Monstrous Manual" (1993).


title: Drow

text: Drow society, religion, history, magic, craftwork, and language for the Forgotten Realms campaign setting is detailed significantly in "The Drow of the Underdark" (1991), by Ed Greenwood. Greenwood appears in the book's introduction as a narrator, explaining how he came across the information in the book: a discussion with Elminster, and chance encounter with a former apprentice of Elminster—the drow lady, Susprina Arkhenneld—as the two explain the drow of the world to the narrator.


title: Drow

text: The drow are presented as a player character race for 2nd edition in "The Complete Book of Elves" (1992). Drow deities Lolth, Kiaransalee, Vhaeraun, and Zinzerena are described in "Monster Mythology" (1992). The drow are later presented as a playable character race again in "" (1995).


title: Drow

text: The drow appears in the "Monster Manual" for this edition (2000). The drow of the Forgotten Realms setting appear in the hardcover "Forgotten Realms Campaign Setting" (2001), and in "Races of Faerûn" (2003). The drow also appears in the revised "Monster Manual" for the 3.5 edition (2003).


title: Drow

text: The "Underdark" hardcover for the Forgotten Realms setting (2003) features the drow yet again as a player character race, as does the "Player's Guide to Faerûn" (2004). "Lost Empires of Faerûn" describes the drow werebat (2005). The drow paragon 3-level prestige class appears in "Unearthed Arcana" (2004).


title: Drow

text: In 2004, the new Eberron campaign setting introduced drow in a world where Lolth doesn't exist; various drow societies were then explored in more detail in "Secrets of Xen'drik" (2006). Additionally, the umbragen for the setting appeared as a player character race in "Dragon" #330 (April 2005).


title: Drow

text: The arcane guard drow, the dark sniper drow, the drow priestess, the Lolth's sting, and the Lolth-touched drow ranger appear in "Monster Manual IV" (2006). The deepwyrm drow is presented as a player character race in "Dragon Magic" (2006).


title: Drow

text: The drow are presented as a player character race for the 3.5 edition in "Expedition to the Demonweb Pits" (2007) and "Drow of the Underdark" (2007). "Drow of the Underdark" also features the arcane guard, the drow assassin, the house captain, the house wizard, the drow inquisitor, the favored consort, the drow priestess, the drow slaver, the spider sentinel, the albino drow (szarkai), the szarkai fighters, the szarkai druids, and the drow warrior, along with numerous prestige classes and other monsters related to drow.


title: Drow

text: The release of the Open Game License and the System Reference Document's inclusion of the drow race also led to a number of books related to drow being published by companies not affiliated with Wizards of the Coast, such as "The Quintessential Drow", "The Complete Guide to Drow", and "Encyclopaedia Arcane: Drow Magic".


title: Drow

text: The drow appear in the "Monster Manual" for this edition (2008), including the drow warrior, the drow arachnomancer, the drow blademaster, and the drow priest. The drow appear as a playable race in the "Forgotten Realms Player's Guide" (2008) and the "Essentials" rulebook "Heroes of the Forgotten Kingdoms" (2010).


title: Drow

text: The drow feature in a pre-written playable module called "Demon Queen's Enclave" (2008) which takes adventurers from levels 14 through 17 into the Underdark to battle the forces of Orcus and possibly ally with members of the treacherous dark elves and/or their minions. The drow of Xen'drik are also outlined in the 4E "Eberron Campaign Guide" (2009).


title: Drow

text: The drow appear as a playable elf subrace in the "Player's Handbook" (2014) for this edition. They also appear in the "Monster Manual" (2014) for this edition. In the adventure module "Out of the Abyss" (2015), the players are captured by the drow at the beginning of the adventure. The drow are also discussed in the "Sword Coast Adventurer's Guide" (2015) and in the "Mordenkainen's Tome of Foes" (2018) supplements, including write-ups for their pantheon updated to the 5E "Forgotten Realms" status-quo.


title: Drow

text: The drow of Xen'drik are again outlined in "" (2019). The new Exandria campaign setting added a non-Lolth based society of drow which was introduced in the "Explorer's Guide to Wildemount" (2020). Per Wizards of the Coast, the drow of these settings are presented as more "morally and culturally complex".


title: Drow

text: Christian Hoffer, for "ComicBook.com", highlighted a 2021 update on Drizzt Do'Urden by Wizards of the Coast and wrote, "it also notes one major change to D&D canon that relates to the drow culture that Drizzt ultimately abandoned. The website points out that while Drizzt grew up in a 'cult of Lolth' [...], there are two other entire cultures of drow who have no ties to Lolth whatsoever. [...] The reveal of the Lorendrow and Aevendrow seem to suggest that "Dungeons & Dragons" is officially moving past some long-held canon about the drow". Tika Viteri, for "Book Riot", highlighted that Salvatore's "Starlight Enclave" (2021) "contains a singular shift in the narrative of the story of the drow; Salvatore reveals that drow are not, in fact, the only dark-skinned elves in the Forgotten Realms".


title: Drow

text: Made famous by R. A. Salvatore's Drizzt novels, these dark elves from the game influenced subsequent works of fantasy. Drow have a gender-based caste system that says "a great deal about attitudes towards gender roles in the real world".


title: Drow

text: The drow originally created by Gary Gygax are now "essentially the drow of fantasy fiction today", according to Ed Greenwood, who believes them to be "arguably Gary Gygax's greatest, most influential fantasy creation" after the D&D game itself. Designer James Jacobs considers the drow to be a rare example of a D&D-invented monster becoming mainstream, with even non-gamers recognizing them. Rob Bricken, for io9, named the drow as the eighth most memorable "D&D" monster. Drow have been proven to draw additional sales of products which feature them. While Paizo Publishing was printing "Dragon" and "Dungeon", covers featuring drow often sold better than other issues in the same year.


title: Drow

text: The drow, especially when used as player characters, are surrounded by much controversy, especially after the release of R. A. Salvatore's novel, "The Crystal Shard". Game designer James Jacobs has said that the drow player characters often spark arguments, with some players refusing to play in a campaign that allows drow PCs. Jacobs says that "even the name" is controversial, having at least two pronunciations. Matthew Beilman, for "CBR", highlighted multiple reasons to play as a drow character and wrote "you will love playing a drow if you enjoy making others uncomfortable. In most "D&D" settings, the drow civilization is evil. [...] This makes them excellent campaign villains but also gives them great potential as antiheroes who lack traditional heroic attributes [...]. Playing a drow can also present an opportunity to play against traditional gender norms. [...] The drow are outsiders, even in settings that do not include Lolth and her corruptive influence. These campaigns might not have evil societies of dark elves, but they still tend to make them into foreigners with strange customs [...]. Playing a misunderstood, feared yet potentially heroic character can be great fun". Alex Lucard, in his review of "" for "DieHard GameFan", wrote, "I'll be honest: I've never understood the appeal of the Drow at all. They just seemed overly angsty and dark for the sake of being dark. I've been bored by the novels where they are the featured race and I've generally avoided them unless someone is making fun of them". Rob Bricken, for "Kotaku", wrote that there "has been one good Drow in the history of D&D, and that's Drizzt Do'Urden, who is one of the Mary Sue-iest characters in all of fiction—and he's been the star of countless novels and is the only reason any D&D player has even been interested in the Drow, of which now there is a terrifying amount of material".


title: Drow

text: On June 26, 2020, Netflix and Hulu removed the Advanced Dungeons & Dragons episode of the TV series "Community" from their platforms due to scenes with Chang playing a dark elf by wearing elf ears and makeup resembling blackface. A statement from Sony Pictures Television said that the studio supported the decision to remove the episode.


title: Drow

text: Some critics have highlighted that the drow are "dark skinned and inherently evil" and are connected to the "racist idea that non-white people are inherently bad". In 2010, scholar Cory Lowell Grewell found that in the "Baldur's Gate" video game series, "issues of contemporary race relations are brought to the fore in the player-Character's interactions with the dark-skinned Drow Elves." In the book "Dungeons and Dragons and Philosophy" (2012), author James Rocha states that the difference between drow and dark elves in the Forgotten Realms setting is rooted in racist stereotypes: "an acceptable lighter skinned dark race side by side with only the most rare exceptions in the darker race, which is thought to be inherently evil, mirrors American history in a very uncomfortable fashion". In response to this criticism in 2020, Wizards of the Coast stated: "we present orcs and drow in a new light in two of our most recent books, "" and "Explorer's Guide to Wildemount". In those books, orcs and drow are just as morally and culturally complex as other peoples. We will continue that approach in future books, portraying all the peoples of D&D in relatable ways and making it clear that they are as free as humans to decide who they are and what they do". Christian Hoffer, for "ComicBook.com", highlighted a 2021 "Forgotten Realms" lore update on the Wizards of the Coast website and wrote that "while Drizzt himself is proof that all drow aren't inherently evil, many fans still think that "Dungeons & Dragons" lore needs major updates when it comes to the drow. The main issue is that the drow (like other 'evil' races) are presented as a large monolithic society dedicated to evil instead of a group with multiple competing interests and beliefs. It's not that some drow, or even a city or country of drow, are seen as evil—it's that "Dungeons & Dragons" lore has traditionally considered evil drow to be the default. [...] By bringing in two entirely new cultures of drow that have rejected Lolth, it seems that the lore will show that drow are just as complex and multi-faceted as the many other elven subraces in the game".


title: Drow

text: In the "Io9" series revisiting older "Dungeons & Dragons" novels, in his review of "Homeland", Rob Bricken says that "its greatest strength is how it explores drow society, which up to that point was best summarized as “very evil.” Prior to Drizzt, in the vein of orcs, trolls, and primary-colored dragons, the Drow were essentially categorized as more monsters for players to battle and defeat. Their skin was obsidian black, earning them the alternate name of dark elves, and marking them as the evil counterpart to the good and heroic lighter-skinned elves of the surface."


title: Drow

text: The drow made their first statistical appearance in the Greyhawk adventure module "Hall of the Fire Giant King" (1978) at the end of the module, and received a lengthy writeup. The history of the drow within the game is revealed; in ages past, the elves were torn by discord and warfare, driving out from their surface lands their selfish and cruel members, who sought safety in the underworld. These creatures, later known as the "dark elvenfolk" or drow, grew strong in the arcane arts over the centuries and content with their gloomy fairyland beneath the earth, though they still bear enmity towards and seek revenge against their distant kin, the elves and faeries who drove them down. They are described as chaotic evil in alignment, and highly intelligent. They are described as black-skinned and pale haired in appearance, around 5-feet tall and slight of build with somewhat sharp features, with large eyes and large pointed ears. Drow are difficult to surprise as they are able to see very well in the dark, have an intuitive sense about their underground world similar to that of dwarves, and can detect hidden or secret doors as easily as other elves do. Drow are highly resistant to magic, while all drow have the ability to use some inherent magical abilities even if they are not strictly spellcasters. The module also reveals that there are rumors of vast caverns housing whole cities of drow which exist somewhere deep beneath the earth, and now that the drow have dwelled in these dark labyrinthe places they dislike daylight and other forms of bright light as it hampers their abilities. They are able to communicate using a silent language composed of hand movements, and when coupled with facial and body expression, movement, and posture, this form of communication is the equal of any spoken language.


title: Drow

text: The "Advanced Dungeons & Dragons" game's second edition product "Monstrous Compendium Volume Two" (1989) describes the world of the drow, where violent conflict is part of everyday life, so much so that most drow encountered are ready for a fight. Their inherent magic use comes from training in magic, which all drow receive. Not long after the creation of the elves, they were torn into rival factions, one evil and one good; after a great civil war, those who followed the path of evil and chaos were driven far from the world's forests and into the bleak, lightless caverns and tunnels of the underworld. Drow society is fragmented into opposing noble houses and merchant families, and they base their rigid class system on the belief that the strongest should rule. Female drow tend to fill many positions of great importance, with priests of the dark goddess Lolth holding a very high place in society. Drow fighters are required to go through rigorous training in their youth, and those who fail are put to death. Drow constantly war with other underground neighbors such as dwarves and dark gnomes (svirfneblin), and keep slaves of all types - including allies who fail to live up to drow expectations.


title: Drow

text: "The Complete Book of Elves" (1993) by Colin McComb focuses some of its attention on the drow. The "Elfwar" is presented, an elven myth in which the elves were one people until the Spider Queen Lolth used the dissent among the elves to gain a foothold; the elves of Lolth took the name Drow to signify their new allegiance, but as they massed to conquer the other elves, Corellon Larethian and his followers drove Lolth and her people deep into the earth, where they chose to remain. The dark elves who became the drow were originally simply elves who held more with the tenets of might than those of justice, and as they quested for power they became corrupted and turned against their fairer brethren. Any elf character of good or neutral alignment, even drow, is allowed into the realm of Arvanaith where elves go upon reaching old age. The book notes that drow player characters have a large number of benefits while suffering few disadvantages, but that "the major disadvantage to being a drow "is" being a drow." Drow characters are extraordinarily dexterous and intelligent, but have the typically low elf constitution; also, their personalities are described as grating at best, and all other elves "hate" the drow which affects their reactions to a drow character.


title: Drow

text: In the 5th Edition Basic Rules, drow are described as a subrace of elves with a connection to Underdark magic. Additionally, it states, "the cult of the god Lolth, Queen of Spiders, has corrupted some of the oldest drow cities, especially in the worlds of Oerth and Toril. Eberron, Krynn, and other realms have escaped the cult's influence—for now. Wherever the cult lurks, drow heroes stand on the front lines in the war against it, seeking to sunder Lolth's web". "Mordenkainen's Tome of Foes" (2018) retells the story of Corellon and Lolth; the elves who supported Lolth were cast "into darkness. They became a people wholly dedicated to Lolth and her scheming and for many, many centuries were viewed in the multi-verse as a people of evil". However, since all elves are descended from Corellon, the drow have the ability to "break free of Lolth's influence" and turn to "the light within themselves".


title: Drow

text: With the ability to resist magic and powerful darkvision, drow are more powerful than many of "Dungeons & Dragons" races. Drow possess natural magical abilities which enables them to summon globes of darkness, outline targets in faerie fire which causes no harm but makes the target brightly visible to everyone who sees them, and create magical balls of light. They can also levitate for short periods of time. They live to extraordinarily long ages if not killed by violence first, over a thousand years in some cases. Their hearing and vision are better than that of a human being and they are difficult to sneak up on because of this. They naturally excel at moving silently. Drow also employ the unusual hand crossbow, firing small, though very lethal, darts.


title: Drow

text: In Lolth based societies, drow males are commonly wizards or fighters. Females are almost always clerics and almost never wizards.


title: Drow

text: As a race, drow were traditionally portrayed evil. There were unusual exceptions, the most notable being Drizzt Do'Urden, Jarlaxle Baenre, and Liriel Baenre. Originally, drow were chaotic evil in alignment. Beginning with 3rd edition "D&D", drow were usually neutral evil. There have been encounters with non-evil drow, but these are distrusted as much as their brethren, due to their reputation. In the "Forgotten Realms" setting, the Drow followers of Eilistraee were originally the largest group of good Drow, as Eilistraee is the patron goddess of all Drow that have a good alignment.


title: Drow

text: The 4th Edition "Heroes of the Forgotten Kingdoms" (2010) does not suggest any typical alignment for drow player characters, however, it highlights the drow that break away from the evil Lolth based societies. The 5th Edition "Player's Handbook" (2014) described drow as "more often evil than not". In 2021, official errata removed the suggested alignments for playable races, including drow, in all 5th Edition sourcebooks. As of "" (2022), creature stat blocks that also have playable races "now state that they can be any alignment".


title: Drow

text: Within the context of many "Dungeons & Dragons" campaign settings, the drow were forced underground in what is now known as the Underdark after the great war amongst the elves, a vast system of caverns and tunnels spanning much of the continent. The drow live in city-states in the Underdark, becoming one of the most powerful races therein.


title: Drow

text: The drow are well adapted to seeing in the dark, and they loathe, are terrified of, and are easily blinded by the light of the surface. Some magic weapons, armor, and various other items of the drow disintegrate or lose their magical properties if exposed to the sun.


title: Drow

text: Drow characters are extremely intelligent, charismatic and dexterous, but share surface elves' comparative frailty and slight frames. Females tend to be bigger and stronger than males. Drow are characterized by white or silver hair and obsidian black skin. Their eyes are red (or rarely gray, violet, or yellow) in darkness and can be many different colors in normal light. In 5th Edition, drow typically have "white hair and grayish skin of many hues" along with better darkvision and a sensitivity to sunlight.


title: Drow

text: Drow have several kinds of innate spell powers and spell resistance. This is balanced by their weakness in daylight. Half-drow are the result of crossbreeding between another race and a drow, and share characteristics of both.


title: Drow

text: Lolth based drow society is primarily matriarchal, with priestesses of their evil spider goddess Lolth in the highest seats of power. This society is based upon violence, murder, cunning, and the philosophy that only the strong survive. Hence, most drow plot endlessly to murder or otherwise incapacitate their rivals and enemy drow using deceit and betrayal. Drow, particularly in higher positions, are constantly wary of assassins and the like. One of the quirks of this constant infighting is the relatively short lifespan of the average drow. While being just as long lived as their surface cousins, living as long as a thousand years, elderly drow are rarely encountered. Consequently, they are the only race of elves that matches the fertility of 'lesser' races, such as humans. Their society, as a whole, is seemingly nonviable. The only reason they do not murder themselves to extinction is by the will of Lolth, working primarily through her clergy. Lolth does not tolerate any drow that threaten to bring down her society, and the clergy make certain that perpetrators cease their destructive actions by either threatening or killing them. Matron mothers lead the various noble houses and act as "high priestesses of Lolth". Matthew Beilman, for "CBR", highlighted that Lolth based "drow society is a lethal cloak-and-dagger affair – like a constant "Game of Thrones" but if every character were playing by Lannister/Bolton rules. That is to say, playing dirty and playing to "win"".


title: Drow

text: There are exceptions to the rule, of course. Some communities of drow worship other gods (like Vhaeraun or Eilistraee), and thus, their hierarchy changes, reverses the roles of males and females, or (such as in the case of Eilastree) even approaching something like a workable, progressive society. Drow societies can also vary vastly depending on the "Dungeons & Dragons" campaign setting.


title: Drow

text: Inhabiting the jungles and Underdark in the continental isle of Xen'drik, the drow in Eberron have a much more tribalistic culture than their other "Dungeons & Dragons" counterparts. They are not an offshoot of the elven race like in many other worlds but rather a separate, if similar, race. Instead of the spider goddess Lolth, most tribes worship a male scorpion deity known as Vulkoor, though exceptions are common. It is believed that Vulkoor is actually one of the forms of the Mockery (a member of the Dark Six). The tribes are often xenophobic, and the social structure varies from tribe to tribe. It is known that the drow mastered elemental binding before gnomes did- including a cultural group of fire-elemental binders called the Sulatar. There is also a subgroup called the "umbragen", or shadow elves, who worship the Mockery in the form of a scorpion god and Khyber or the Umbra, the Consuming Shadow, for whom the umbragen are named; the umbragen dwell underground beneath Xen'drik and are noted for producing many warlocks and soulknives.


title: Drow

text: Drow in Eberron run the gamut from almost feral in nature to being fully civilized and on par with the cultural level of Khorvaire, varying from tribe to tribe.


title: Drow

text: The region of Xhorhas, the eastern side of the Wildemount continent in the Exandria setting, is governed by the Kryn Dynasty and ruled by the Bright Queen Leylas Kryn. The Dynasty was founded by drow who escaped to surface after rejecting Lolth for a god of light known as the Luxon. The nation is now home to many creatures others in Wildemount would see as monstrous or evil. Due to the Luxon, the Kryn Dynasty also established a new source of magic called Dunamancy which "involves the manipulation of entropy, gravity, and time" where "dunamancers draw power from alternate timelines and unseen realities, subtly affect the flow of time, and even tighten or loosen the grip of gravity". Compared to their neighboring country, the human-run monarchy of the Dwendalian Empire, "the Dynasty is freer, both politically and culturally. They accept anyone and everyone while the Empire is restrictive and nearly inaccessible to outsiders". The Kryn Dynasty was first explored in depth in the second campaign of the web series "Critical Role" before being added to the "Dungeons & Dragons" canon in the "Explorer's Guide to Wildemount" (2020).


title: Drow

text: Critics have highlighted that this setting breaks from traditional fantasy tropes especially around evil races. James Grebey, for "Syfy Wire", highlighted "it's a country of cast-offs and scrappy upstarts who are simply trying to thrive in a world that's prejudiced toward them. Due in no small part to a religion that allows for souls to be reborn in another body, the Kryn society is race-neutral in a way that's rarely seen in fantasy lore. It's borderline progressive, even. Crucially, while there are bad actors among the Kryn, they're not evil solely because of their race".


title: Drow

text: 1991's "The Drow of the Underdark", a 128-page sourcebook all about the drow, expanded the drow significantly for the Advanced Dungeons & Dragons second edition version of the "Forgotten Realms" setting. In the "Forgotten Realms", the dark elves were once ancient tribes of Ilythiir and Miyeritar. They were transformed into drow by the Seldarine and were cast down and driven underground by the light-skinned elves because of the Ilythiirian's savagery during the Crown Wars. The drow had fallen under the influence of Araushnee, who was transformed into Lolth and was cast down into the Demonweb Pits along with her son Vhaeraun by the elven god Corellon Larethian because of Lolth's and Vhaeraun's attempt to take control of the elven pantheon (which included Araushnee's seduction of Corellon Larethian). Drow society, being strongly matriarchal, allows the females to hold all positions of power in the government, and to choose and discard mates freely. Social station is the most important thing in drow society, making ascension to greater power a drow's ultimate goal. Drow have a strong affinity for arachnids, as most worship the spider goddess Lolth, and spiders dwell freely among drow communities. The largest drow civilization is the subterranean city of Llurth Dreier. However, Menzoberranzan is featured most prominently in the novels.


title: Drow

text: Prior to the Spellplague descendants of the Miyeritar dark elves later succeed in reversing their transformation and are recreated as a distinct dark elf race. According to "The Complete Book of Elves", drow are not welcome in Evermeet and are turned away. Drow could also worship Ghaunadaur, Kiaransalee, Selvetarm or Vhaeraun. A special case is Eilistraee, the only drow goddess who is chaotic good instead of chaotic evil; she wants the drow to return to the light. However, all of these alternative deities (except perhaps Ghaunadaur) were killed or forgotten in the last years before the Spellplague, but they managed to return to life and regain their followers, about a century later, during the Sundering.


title: Drow

text: Amongst the most infamous of drow are the members of House Baenre, whilst Abeir-Toril is also home to some famous benevolent drow including Drizzt Do'Urden and his deceased father Zaknafein (both of House Do' Urden), Liriel Baenre (formerly of Menzoberranzan's aforementioned House Baenre), and Qilué of the Seven Sisters. The drow Jarlaxle is also well-known, as he is one of the few males in Menzoberranzan to obtain a position of great power. He is the founder and leader of the mercenary band Bregan D'aerthe. These characters are from "The Dark Elf Trilogy" (1990–1991), a series of books by R. A. Salvatore (except for Liriel Baenre and Qilue). The six drow in the "War of the Spider Queen" series have also gained some renown since the novels have been published.


title: Drow

text: In 2021, two new Underdark based drow societies, the Lorendrow and the Aevendrow, were introduced; both of these societies have rejected Lolth and are not evil. The Lolth based society of Menzoberranzan is now referred to as Unadrow. This retcon "suggests that the beliefs and evil practices once seen as common to all drow are specifically related to the 'Unadrow,' the culture of drow who have become corrupted by the evil spider goddess".


title: Drow

text: In the "Dragonlance" setting, Drow do not exist; rather, "dark elves" are elves who have been cast out by the other elves for various crimes, such as worship of the evil deities. Dalamar, a student of Raistlin Majere, is the most notable of Krynn's dark elves. However, over the years Drow have accidentally appeared in a few "Dragonlance" modules and novels. Similar mistakes have occurred with other standard AD&D races, such as orcs and lycanthropes, which are not part of the "Dragonlance" setting. Some theories say that these rare Drow may have accidentally been sent there during a plane shifting spell or related magic, a misfire as like as not that is corrected before the respective timelines are tampered with too drastically.


title: Drow

text: In the world of "Greyhawk", the drow were driven underground by their surface-dwelling relatives because of ideological differences. There they eventually adapted to their surroundings, especially by attracting the attention of the goddess Lolth, "Queen of Spiders". The center of drow civilization is the subterranean city Erelhei-Cinlu, and its surrounding Vault, commonly called the Vault of the Drow. Drow rank structure was based much more on personal experience level and proven personal abilities rather than on gender. Males were just as likely to have positions of authority over both males and females, and the tradition of matriarchy, where the highest-ranking member was always a female, was not a special directive of the Demon Queen Lolth. The vast majority of Drow Elves both male and female in the original campaign setting of Greyhawk have no authority or ranking at all and live an idle and degenerate life in the great city of the Drow.


title: Drow

text: Known drow of Greyhawk include Clannair Blackshadow, Derken Gale, Jawal Severnain, and Landis Bree of Greyhawk City; Eclavdra of House Eilserv; and Edralve of the Slave Lords. In the drow city Erelhei-Cinlu, player characters may freely enter the city and spend time there, unless they attempt to organize any escaped slave groups for open warfare against the drow; the threat of a slave uprising will bring the chaotic drow into full cooperation.


title: Drow

text: Some drow worship a nameless Elder Elemental God (said to have ties to Tharizdun) instead of Lolth. The module "Vault of the Drow" showcases that the House of Eilservs, led by Eclavdra in Erelhei-Cinlu, turned from worship of Lolth to the Elder Elemental God when the city's other noble houses allied against them after proclaiming that their mistress should be the Queen of All Drow. Eilservs attempted to establish a power base through a puppet kingdom in the surface world dedicated to the worship of their new deity, so that their demands of supreme power in the Vault can no longer be denied, but this scheme was ruined.


title: Drow

text: Lolth is a fictional goddess in the "Dungeons & Dragons" fantasy role-playing game. Lolth ("Lloth" in the drow language), the Demon Queen of Spiders, is the chief goddess of the Drow. She is also known as the "Spider Queen" and the "Queen of the Demonweb Pits"; her realm, the 66th layer of the Abyss, is referred to as the Demonweb Pits. Lolth usually appears in two forms: drow and arachnid. In drow form, the Spider Queen appears as an "exquisitely beautiful" female dark elf, sometimes covered in clinging spiders. In her arachnid form, Lolth takes the appearance of a giant black widow spider with the head of a female drow or human peering from between the eight spider-eyes. Sometimes, the two foremost pair of her spider-legs are actually humanoid arms. In third edition, her arachnid form has taken more of a drider-like appearance, due to the events of the "War of the Spider Queen" novel series.


title: Drow

text: Lolth was created by Gary Gygax for the "World of Greyhawk" campaign setting, later appeared in the "Forgotten Realms" setting, and in the 3rd edition became a member of the default pantheon of "D&D" gods. In those various settings, the drow pantheon of gods consists of the leader Lolth, as well as Kiaransalee, Vhaeraun, and Zinzerena and also the one good goddess Eilistraee. Other drow gods may be present in different campaign settings.


title: Drow

text: According to the Forgotten Realms storyline, Lolth began as an intermediary goddess abiding in the sixty-sixth layer of the Abyss, the Demonweb Pits. Through the events that transpired in War of the Spider Queen series, she transformed herself into a greater goddess as depicted in 4th edition, the Demonweb Pits becoming its own plane.


title: Drow

text: Lolth was first mentioned in the modules "Descent into the Depths of the Earth" (1978) and more fully described in "Vault of the Drow" (1978), and was the main antagonist of the module "Queen of the Demonweb Pits" (1980). These modules were later reprinted as part of the "Queen of the Spiders" collection in 1986. Lolth's role as a deity was first explored in "Deities & Demigods" (1980). Her game statistics were reprinted in the "Fiend Folio" (1981).


title: Drow

text: Lolth's role in the Forgotten Realms campaign setting was first detailed in Ed Greenwood's second edition "AD&D" sourcebook, "Drow of the Underdark" (1991). Lolth was detailed as a deity in the book "Monster Mythology" (1992), including details about her priesthood. Her role in the cosmology of the Planescape campaign setting was described in "On Hallowed Ground" (1996). Lolth received a very detailed description of her role in the Forgotten Realms in "Demihuman Deities" (1998).


title: Drow

text: Lolth is detailed in "Defenders of the Faith" (2000), and "Deities & Demigods" (2002), and her role in the Forgotten Realms is revisited in "Faiths and Pantheons" (2002). Lolth's priesthood is detailed for this edition in "Complete Divine" (2004), and her role in the Abyss is detailed in the "" (2006). Lolth and the drow are further detailed in both "Drow of the Underdark" (2007), and the adventure "Expedition to the Demonweb Pits" (2007). "Dragon" #359 (September 2007), the final print issue of the magazine, described Lolth as one of the 20 most memorable villains of the Dungeons & Dragons game.


title: Drow

text: Lolth appears as one of the evil deities described in the "Dungeon Master's Guide" for the 4th edition of "Dungeons & Dragons" (2008). The story of her dissent from and war against Corellon and Sehanine is fleshed out in the supplements "Underdark" and "". A slightly different (and arguably more powerful) version of Lolth is presented in the "Forgotten Realms Campaign Guide." The Forgotten Realms Lolth has different appearance, dogma and personality than the core Lolth. Wizards of the Coast's D&D Compendium and D&D Character Builder record the core Lolth and the "Realms" Lolth as separate entities. Lolth (Demon Queen of Spiders) appears in the 4th edition's "Monster Manual 3" (2010). She is the mascot for this volume, which includes statistics for Lolth in both drow and spider form.


title: Drow

text: In 2021, Lolth was featured on two cards as a "legendary planeswalker" in the "Adventures in the Forgotten Realms" line from the "" collectible card game.


title: Drow

text: Lolth was #10 on "Screen Rant"s 2018 "Dungeons & Dragons: The 15 Most Powerful Villains, Ranked" list—the article states "The "War of the Spider Queen" series would show Lolth's transformation into a greater goddess, making her one of the most powerful beings in the "Dungeons & Dragons" multiverse. [...] Lolth can appear in the form of a monstrous spider, which many fans have mocked, due to the fact that it only has sixty-six hit points. You likely won't get a chance to get close enough to harm Lolth, due to the fact that you are battling her in her home dimension, which is filled with an army of demonic spiders. Lolth can also transform into the form of a high-level magic-user/cleric, which gives her access to a wide-range of powerful spells. This is to say nothing of her psionic abilities, though these are given to her at the discretion of the dungeon master".


title: Drow

text: Lolth was #8 on "CBR"s 2020 "Dungeons & Dragons: 10 Endgame Bosses You Need To Use In Your Next Campaign" list—the article states "the DMs can even get rather creative with the stage; since Lolth is a creature of the Underdark, the fight leading up to her and the boss herself can take place in a dark and nightmarish cave that requires some spelunking and vertical maneuvers. Bonus points if the fight happens in a web network suspended midair with an abyssal drop".


title: Drow

text: Like elves, drow have other creatures associated with them either by environment or by blood. The drider, a drow transformed into a half-drow half-spider creature as a punishment, is one of the most often cited examples.


title: Drow

text: Only high-level priestesses in good standing with Lolth are able to initiate the transformation of a dark elf into a drider. This transformation is very painful, and lasts at least 12 hours. Driders develop a poisonous bite. Their digestion changes and they must drink blood of living creatures for sustenance. Driders still maintain the spells and special abilities they had developed as a drow. There can exist any character class of drider. They retain intelligence and memories. This usually makes them bitter, spiteful creatures. Some hunt for magic powerful enough to undo the transformation.


title: Drow

text: In previous editions, driders appear sexless due to bloating, but able to magically reproduce. In "Dungeons & Dragons" edition 3.5, driders seem to retain their gender and characteristics after the transformation, but fertility is debatable.


title: Drow

text: Driders play many roles in drow society. The dark elves both fear and are revolted by driders. After transformation, they are usually pushed to the wild area around a drow city. Driders are usually found in company with tiny, huge and giant spiders. Driders speak Common, Elvish, and Undercommon. In the first and second editions of the game, Driders spoke Drow. Driders are almost always Chaotic Evil.


title: Drow

text: In the Fourth Edition of "Dungeons & Dragons", becoming a drider is actually considered holy and a blessing from Lolth.


title: Drow

text: Draegloths are half-demon, half drow monstrosities. Found in any campaign setting, they are particularly numerous in the "Forgotten Realms". They are created by the unholy union between an ascending high priestess of the drow goddess Lolth and a glabrezu.


title: Drow

text: Draegloths are about ten feet tall and have four arms, the upper pair being much larger than the lower. They have large claws on the upper arms and they use them for hand-to-hand combat, for they usually prefer the feeling of tearing flesh and sinew under their claws and fangs. Their face is stretched so it resembles that of a dog. Their flesh is as dark as a drow's, and they are covered in a fine coat of fur; they also have a white mane. They are sacred creatures to the Lolthites and are usually treated with respect.


title: Drow

text: "The chitine and the choldrith are part-elf, part-spider abominations created by magic as servitors of the spider goddess Lolth" appearing in the Forgotten Realms setting. Chitine resembles a sickly, white, four-foot tall humanoid with vaguely spider-like features. They are depicted with wavy hair and sly faces with a set of spider's fangs protruding from their mouths. Chitines also have four arms which feature an additional joint (compared to a human), giving them great flexibility and dexterity. They were created inadvertently by the drow as a result of failed experiments on normal humanoids.


title: Drow

text: Chitines typically hate their former masters, the drow, but keep worshipping Lolth. The role of priests in their society is taken up by a closely related but completely separate race, the choldriths. Chitines strongly live up to their spider heritage; in their underground cities and villages, they build with webs in the same way that humans build with wood and stone. They build everything out of it, homes, traps, clothing, weapons, and more.


title: Yourself or Someone Like You

text: Yourself or Someone Like You is the debut album by American rock band Matchbox 20. It was released on October 1, 1996, by Lava Records and Atlantic Records.


title: Yourself or Someone Like You

text: The album features a sound similar to traditional rock and post-grunge. The album features themes of adolescence, adultery, loneliness, domestic violence, psychological abuse, humiliation, depression, anger, and alcoholism.


title: Yourself or Someone Like You

text: According to Rob Thomas, the album's title was originally to be "Woodshed Diaries". However, that changed when Thomas and Paul Doucette were at a woman's musical performance at Café Largo when the singer said "this song is for you, or someone like you". They loved the phrase so much that they insisted on changing the album's title, despite the fact that 3,500 copies of the album with the original title had already been made. Their labels agreed, however the name change resulted in the album's release being delayed.


title: Yourself or Someone Like You

text: The album sold a mere 610 copies in its first week, but eventually went on to sell several million copies in the United States. "Yourself or Someone Like You" became one of the few albums to achieve the prestigious Diamond certification, and it was also certified multi-platinum in Australia, Canada and New Zealand. To date, the album has sold more than 15 million copies worldwide.


title: Yourself or Someone Like You

text: In 2005, almost a decade after the album's release, the band was sued by Frank Torres, the man on the album's cover. Torres claimed the band never asked for his permission to use his image on the sleeve. In the litigation, Torres claimed the photo was taken as he was walking down the street after being asked to pose. He also claimed the photo had caused him emotional distress. Torres justified the delay in suing Matchbox 20 by claiming he had first seen the album photo within two years of the litigation. Torres died in 2016 at age 73.


title: Jenna Wolfe

text: Jenna Wolfe (born Jennifer Wolfeld; February 26, 1974) is a Jamaican-American journalist and personal trainer. From 2007 to 2014, she was a correspondent for NBC's "Today", and Sunday co-anchor from 2007 to 2012 and news anchor for "Weekend Today" from 2012 to 2014. On September 12, 2014, Wolfe left the weekend "Today" show for a new role as lifestyle and fitness correspondent on the weekday "Today" show and NBC News.


title: Jenna Wolfe

text: From September 2017 through August 2022, Wolfe worked with Fox Sports on FS1 as a host of the show "First Things First" with Kevin Wildes, and Nick Wright. She was also a field correspondent for Yellowstone Live on National Geographic.


title: Jenna Wolfe

text: Wolfe was born in Kingston, Jamaica, and grew up in Pétion-Ville, Haiti. Her father, Bennet Wolfeld, was Jewish and was born and raised in Puerto Rico. He owned a chain of leather factories in Puerto Rico and moved to Jamaica with his wife when he expanded his operations. Her mother, Sheila Greenfeld, was also Jewish and from New Jersey. Wolfe had a religious upbringing and had her bat mitzvah while living in the islands.


title: Jenna Wolfe

text: She moved from Jamaica to Haiti when she was five. In 1989, her family moved to the United States. Wolfe attended SUNY Geneseo from 1992 to 1994. She graduated from Binghamton University with Bachelor of Arts degrees in French and English in 1996.


title: Jenna Wolfe

text: From 2004 to 2007, she was the weekend morning sports anchor for WABC's "Eyewitness News" in New York City where she had a special segment called "Jenna's Beef," in which she editorialized an event from the world of sports that week. Prior to that, she worked for the Madison Square Garden Network, WPHL-TV in Philadelphia as the first female sportscaster, WICZ-TV in Binghamton, New York, WUHF-TV in Rochester, New York, and the "Today Show" as an intern. Aside from her journalistic duties, Wolfe has appeared as a judge on Food Network's "Iron Chef America".


title: Jenna Wolfe

text: Wolfe speaks English, French and Haitian Creole. On March 27, 2013, Wolfe publicly came out as a lesbian and announced that she was expecting her first child with her partner, NBC News correspondent Stephanie Gosk. Wolfe and Gosk welcomed a girl in August 2013. Their second daughter was born on February 4, 2015.


title: Utility frequency

text: The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains electricity by country.


title: Utility frequency

text: During the development of commercial electric power systems in the late-19th and early-20th centuries, many different frequencies (and voltages) had been used. Large investment in equipment at one frequency made standardization a slow process. However, as of the turn of the 21st century, places that now use the 50 Hz frequency tend to use 220–240 V, and those that now use 60 Hz tend to use 100–127 V. Both frequencies coexist today (Japan uses both) with no great technical reason to prefer one over the other and no apparent desire for complete worldwide standardization.


title: Utility frequency

text: In practice, the exact frequency of the grid varies around the nominal frequency, reducing when the grid is heavily loaded, and speeding up when lightly loaded. However, most utilities will adjust generation onto the grid over the course of the day to ensure a constant number of cycles occur. This is used by some clocks to accurately maintain their time.


title: Utility frequency

text: Several factors influence the choice of frequency in an AC system. Lighting, motors, transformers, generators, and transmission lines all have characteristics which depend on the power frequency. All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise among contradictory requirements.


title: Utility frequency

text: In the late 19th century, designers would pick a relatively high frequency for systems featuring transformers and arc lights, so as to economize on transformer materials and to reduce visible flickering of the lamps, but would pick a lower frequency for systems with long transmission lines or feeding primarily motor loads or rotary converters for producing direct current. When large central generating stations became practical, the choice of frequency was made based on the nature of the intended load. Eventually improvements in machine design allowed a single frequency to be used both for lighting and motor loads. A unified system improved the economics of electricity production, since system load was more uniform during the course of a day.


title: Utility frequency

text: The first applications of commercial electric power were incandescent lighting and commutator-type electric motors. Both devices operate well on DC, but DC could not be easily changed in voltage, and was generally only produced at the required utilization voltage.


title: Utility frequency

text: If an incandescent lamp is operated on a low-frequency current, the filament cools on each half-cycle of the alternating current, leading to perceptible change in brightness and "flicker" of the lamps; the effect is more pronounced with arc lamps, and the later mercury-vapor lamps and fluorescent lamps. Open arc lamps made an audible buzz on alternating current, leading to experiments with high-frequency alternators to raise the sound above the range of human hearing.


title: Utility frequency

text: Commutator-type motors do not operate well on high-frequency AC, because the rapid changes of current are opposed by the inductance of the motor field. Though commutator-type "universal" motors are common in AC household appliances and power tools, they are small motors, less than 1 kW. The induction motor was found to work well on frequencies around 50 to 60 Hz, but with the materials available in the 1890s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse). Once AC electric motors became common, it was important to standardize frequency for compatibility with the customer's equipment.


title: Utility frequency

text: Generators operated by slow-speed reciprocating engines will produce lower frequencies, for a given number of poles, than those operated by, for example, a high-speed steam turbine. For very slow prime mover speeds, it would be costly to build a generator with enough poles to provide a high AC frequency. As well, synchronizing two generators to the same speed was found to be easier at lower speeds. While belt drives were common as a way to increase speed of slow engines, in very large ratings (thousands of kilowatts) these were expensive, inefficient, and unreliable. After about 1906, generators driven directly by steam turbines favored higher frequencies. The steadier rotation speed of high-speed machines allowed for satisfactory operation of commutators in rotary converters.


title: Utility frequency

text: Direct-current power was not entirely displaced by alternating current and was useful in railway and electrochemical processes. Prior to the development of mercury arc valve rectifiers, rotary converters were used to produce DC power from AC. Like other commutator-type machines, these worked better with lower frequencies.


title: Utility frequency

text: With AC, transformers can be used to step down high transmission voltages to lower customer utilization voltage. The transformer is effectively a voltage conversion device with no moving parts and requiring little maintenance. The use of AC eliminated the need for spinning DC voltage conversion motor-generators that require regular maintenance and monitoring.


title: Utility frequency

text: Since, for a given power level, the dimensions of a transformer are roughly inversely proportional to frequency, a system with many transformers would be more economical at a higher frequency.


title: Utility frequency

text: Electric power transmission over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency.


title: Utility frequency

text: Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected in a grid, providing reliability and cost savings.


title: Utility frequency

text: Very early isolated AC generating schemes used arbitrary frequencies based on convenience for steam engine, water turbine, and electrical generator design. Frequencies between  Hz and  Hz were used on different systems. For example, the city of Coventry, England, in 1895 had a unique 87 Hz single-phase distribution system that was in use until 1906. The proliferation of frequencies grew out of the rapid development of electrical machines in the period 1880 through 1900.


title: Utility frequency

text: In the early incandescent lighting period, single-phase AC was common and typical generators were 8-pole machines operated at 2,000 RPM, giving a frequency of 133 hertz.


title: Utility frequency

text: Though many theories exist, and quite a few entertaining urban legends, there is little certitude in the details of the history of 60 Hz vs. 50 Hz.


title: Utility frequency

text: The German company AEG (descended from a company founded by Edison in Germany) built the first German generating facility to run at 50 Hz. At the time, AEG had a virtual monopoly and their standard spread to the rest of Europe. After observing flicker of lamps operated by the 40 Hz power transmitted by the Lauffen-Frankfurt link in 1891, AEG raised their standard frequency to 50 Hz in 1891.


title: Utility frequency

text: Westinghouse Electric decided to standardize on a higher frequency to permit operation of both electric lighting and induction motors on the same generating system. Although 50 Hz was suitable for both, in 1890 Westinghouse considered that existing arc-lighting equipment operated slightly better on 60 Hz, and so that frequency was chosen. The operation of Tesla's induction motor, licensed by Westinghouse in 1888, required a lower frequency than the 133 Hz common for lighting systems at that time. In 1893 General Electric Corporation, which was affiliated with AEG in Germany, built a generating project at Mill Creek to bring electricity to Redlands, California using 50 Hz, but changed to 60 Hz a year later to maintain market share with the Westinghouse standard.


title: Utility frequency

text: The first generators at the Niagara Falls project, built by Westinghouse in 1895, were 25 Hz, because the turbine speed had already been set before alternating current power transmission had been definitively selected. Westinghouse would have selected a low frequency of 30 Hz to drive motor loads, but the turbines for the project had already been specified at 250 RPM. The machines could have been made to deliver  Hz power suitable for heavy commutator-type motors, but the Westinghouse company objected that this would be undesirable for lighting and suggested  Hz. Eventually a compromise of 25 Hz, with 12-pole 250 RPM generators, was chosen. Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC.


title: Utility frequency

text: A General Electric study concluded that 40 Hz would have been a good compromise between lighting, motor, and transmission needs, given the materials and equipment available in the first quarter of the 20th century. Several 40 Hz systems were built. The Lauffen-Frankfurt demonstration used 40 Hz to transmit power 175 km in 1891. A large interconnected 40 Hz network existed in north-east England (the Newcastle-upon-Tyne Electric Supply Company, NESCO) until the advent of the National Grid (UK) in the late 1920s, and projects in Italy used 42 Hz. The oldest continuously operating commercial hydroelectric power station in the United States, Mechanicville Hydroelectric Plant, still produces electric power at 40 Hz and supplies power to the local 60 Hz transmission system through frequency changers. Industrial plants and mines in North America and Australia sometimes were built with 40 Hz electrical systems which were maintained until too uneconomic to continue. Although frequencies near 40 Hz found much commercial use, these were bypassed by standardized frequencies of 25, 50 and 60 Hz preferred by higher volume equipment manufacturers.


title: Utility frequency

text: The Ganz Company of Hungary had standardized on 5000 alternations per minute (41 Hz) for their products, so Ganz clients had 41 Hz systems that in some cases ran for many years.


title: Utility frequency

text: In the early days of electrification, so many frequencies were used that no single value prevailed (London in 1918 had ten different frequencies). As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). Standardization allowed international trade in electrical equipment. Much later, the use of standard frequencies allowed interconnection of power grids. It was not until after World War II – with the advent of affordable electrical consumer goods – that more uniform standards were enacted.


title: Utility frequency

text: In the United Kingdom, a standard frequency of 50 Hz was declared as early as 1904, but significant development continued at other frequencies. The implementation of the National Grid starting in 1926 compelled the standardization of frequencies among the many interconnected electrical service providers. The 50 Hz standard was completely established only after World War II.


title: Utility frequency

text: By about 1900, European manufacturers had mostly standardized on 50 Hz for new installations. The German Verband der Elektrotechnik (VDE), in the first standard for electrical machines and transformers in 1902, recommended 25 Hz and 50 Hz as standard frequencies. VDE did not see much application of 25 Hz, and dropped it from the 1914 edition of the standard. Remnant installations at other frequencies persisted until well after the Second World War.


title: Utility frequency

text: Because of the cost of conversion, some parts of the distribution system may continue to operate on original frequencies even after a new frequency is chosen. 25 Hz power was used in Ontario, Quebec, the northern United States, and for railway electrification. In the 1950s, many 25 Hz systems, from the generators right through to household appliances, were converted and standardized. Until 2009, some 25 Hz generators were still in existence at the Sir Adam Beck 1 (these were retrofitted to 60 Hz) and the Rankine generating stations (until its 2009 closure) near Niagara Falls to provide power for large industrial customers who did not want to replace existing equipment; and some 25 Hz motors and a 25 Hz power station exist in New Orleans for floodwater pumps. The 15 kV AC rail networks, used in Germany, Austria, Switzerland, Sweden, and Norway, still operate at  Hz or 16.7 Hz.