title: Hilbert transform

text: In mathematics and in signal processing, the Hilbert transform is a specific linear operator that takes a function, of a real variable and produces another function of a real variable . This linear operator is given by convolution with the function formula_1 (see ). The Hilbert transform has a particularly simple representation in the frequency domain: It imparts a phase shift of ±90° ( radians) to every frequency component of a function, the sign of the shift depending on the sign of the frequency (see ). The Hilbert transform is important in signal processing, where it is a component of the analytic representation of a real-valued signal . The Hilbert transform was first introduced by David Hilbert in this setting, to solve a special case of the Riemann–Hilbert problem for analytic functions.


title: Hilbert transform

text: The Hilbert transform of can be thought of as the convolution of with the function , known as the Cauchy kernel. Because is not integrable across , the integral defining the convolution does not always converge. Instead, the Hilbert transform is defined using the Cauchy principal value (denoted here by ). Explicitly, the Hilbert transform of a function (or signal) is given by


title: Hilbert transform

text: provided this integral exists as a principal value. This is precisely the convolution of with the tempered distribution . Alternatively, by changing variables, the principal value integral can be written explicitly as


title: Hilbert transform

text: provided the integrals defining both iterations converge in a suitable sense. In particular, the inverse transform is


title: Hilbert transform

text: formula_5. This fact can most easily be seen by considering the effect of the Hilbert transform on the Fourier transform of (see , below).


title: Hilbert transform

text: For an analytic function in the upper half-plane, the Hilbert transform describes the relationship between the real part and the imaginary part of the boundary values. That is, if is analytic in the upper half complex plane , and , then up to an additive constant, provided this Hilbert transform exists.


title: Hilbert transform

text: In signal processing the Hilbert transform of is commonly denoted by formula_6. However, in mathematics, this notation is already extensively used to denote the Fourier transform of . Occasionally, the Hilbert transform may be denoted by formula_7. Furthermore, many sources define the Hilbert transform as the negative of the one defined here.


title: Hilbert transform

text: The Hilbert transform arose in Hilbert's 1905 work on a problem Riemann posed concerning analytic functions, which has come to be known as the Riemann–Hilbert problem. Hilbert's work was mainly concerned with the Hilbert transform for functions defined on the circle. Some of his earlier work related to the Discrete Hilbert Transform dates back to lectures he gave in Göttingen. The results were later published by Hermann Weyl in his dissertation. Schur improved Hilbert's results about the discrete Hilbert transform and extended them to the integral case. These results were restricted to the spaces and. In 1928, Marcel Riesz proved that the Hilbert transform can be defined for "u" in formula_8 (L space) for , that the Hilbert transform is a bounded operator on formula_8 for , and that similar results hold for the Hilbert transform on the circle as well as the discrete Hilbert transform. The Hilbert transform was a motivating example for Antoni Zygmund and Alberto Calderón during their study of singular integrals. Their investigations have played a fundamental role in modern harmonic analysis. Various generalizations of the Hilbert transform, such as the bilinear and trilinear Hilbert transforms are still active areas of research today.


title: Hilbert transform

text: The Hilbert transform is a multiplier operator. The multiplier of is , where is the signum function. Therefore:


title: Hilbert transform

text: where formula_11 denotes the Fourier transform. Since , it follows that this result applies to the three common definitions of formula_12.


title: Hilbert transform

text: Therefore, has the effect of shifting the phase of the negative frequency components of by +90° ( radians) and the phase of the positive frequency components by −90°, and has the effect of restoring the positive frequency components while shifting the negative frequency ones an additional +90°, resulting in their negation (i.e., a multiplication by −1).


title: Hilbert transform

text: When the Hilbert transform is applied twice, the phase of the negative and positive frequency components of are respectively shifted by +180° and −180°, which are equivalent amounts. The signal is negated; i.e., , because


title: Hilbert transform

text: It is by no means obvious that the Hilbert transform is well-defined at all, as the improper integral defining it must converge in a suitable sense. However, the Hilbert transform is well-defined for a broad class of functions, namely those in formula_8 for .


title: Hilbert transform

text: exists for almost every . The limit function is also in formula_8 and is in fact the limit in the mean of the improper integral as well. That is,


title: Hilbert transform

text: In the case , the Hilbert transform still converges pointwise almost everywhere, but may itself fail to be integrable, even locally. In particular, convergence in the mean does not in general happen in this case. The Hilbert transform of an function does converge, however, in -weak, and the Hilbert transform is a bounded operator from to . (In particular, since the Hilbert transform is also a multiplier operator on , Marcinkiewicz interpolation and a duality argument furnishes an alternative proof that is bounded on .)


title: Hilbert transform

text: If , then the Hilbert transform on formula_8 is a bounded linear operator, meaning that there exists a constant such that


title: Hilbert transform

text: An easy way to find the best formula_23 for formula_26 being a power of 2 is through the so-called Cotlar's identity that formula_27 for all real valued . The same best constants hold for the periodic Hilbert transform.


title: Hilbert transform

text: The boundedness of the Hilbert transform implies the formula_8 convergence of the symmetric partial sum operator


title: Hilbert transform

text: The Hilbert transform is an anti-self adjoint operator relative to the duality pairing between formula_8 and the dual space where and are Hölder conjugates and . Symbolically,


title: Hilbert transform

text: provided each transform is well-defined. Since preserves the space this implies in particular that the Hilbert transform is invertible on and that


title: Hilbert transform

text: Because ("" is the identity operator) on the real Banach space of "real"-valued functions in the Hilbert transform defines a linear complex structure on this Banach space. In particular, when , the Hilbert transform gives the Hilbert space of real-valued functions in formula_35 the structure of a "complex" Hilbert space.


title: Hilbert transform

text: The (complex) eigenstates of the Hilbert transform admit representations as holomorphic functions in the upper and lower half-planes in the Hardy space by the Paley–Wiener theorem.


title: Hilbert transform

text: Formally, the derivative of the Hilbert transform is the Hilbert transform of the derivative, i.e. these two linear operators commute:


title: Hilbert transform

text: This is rigorously true as stated provided and its first derivatives belong to One can check this easily in the frequency domain, where differentiation becomes multiplication by .


title: Hilbert transform

text: However, "a priori" this may only be defined for a distribution of compact support. It is possible to work somewhat rigorously with this since compactly supported functions (which are distributions "a fortiori") are dense in . Alternatively, one may use the fact that "h"("t") is the distributional derivative of the function ; to wit


title: Hilbert transform

text: For most operational purposes the Hilbert transform can be treated as a convolution. For example, in a formal sense, the Hilbert transform of a convolution is the convolution of the Hilbert transform applied on "only one" of either of the factors:


title: Hilbert transform

text: Up to a multiplicative constant, the Hilbert transform is the only bounded operator on with these properties.


title: Hilbert transform

text: In fact there is a wider set of operators that commute with the Hilbert transform. The group formula_46 acts by unitary operators on the space formula_35 by the formula


title: Hilbert transform

text: This unitary representation is an example of a principal series representation of formula_49 In this case it is reducible, splitting as the orthogonal sum of two invariant subspaces, Hardy space formula_50 and its conjugate. These are the spaces of boundary values of holomorphic functions on the upper and lower halfplanes. formula_50 and its conjugate consist of exactly those functions with Fourier transforms vanishing on the negative and positive parts of the real axis respectively. Since the Hilbert transform is equal to , with being the orthogonal projection from formula_35 onto formula_53 and the identity operator, it follows that formula_54 and its orthogonal complement are eigenspaces of for the eigenvalues . In other words, commutes with the operators . The restrictions of the operators to formula_54 and its conjugate give irreducible representations of formula_46 – the so-called limit of discrete series representations.


title: Hilbert transform

text: It is further possible to extend the Hilbert transform to certain spaces of distributions . Since the Hilbert transform commutes with differentiation, and is a bounded operator on , restricts to give a continuous transform on the inverse limit of Sobolev spaces:


title: Hilbert transform

text: The Hilbert transform can then be defined on the dual space of formula_58, denoted formula_59, consisting of distributions. This is accomplished by the duality pairing:


title: Hilbert transform

text: It is possible to define the Hilbert transform on the space of tempered distributions as well by an approach due to Gel'fand and Shilov, but considerably more care is needed because of the singularity in the integral.


title: Hilbert transform

text: The Hilbert transform can be defined for functions in formula_61 as well, but it requires some modifications and caveats. Properly understood, the Hilbert transform maps formula_61 to the Banach space of bounded mean oscillation (BMO) classes.


title: Hilbert transform

text: Interpreted naïvely, the Hilbert transform of a bounded function is clearly ill-defined. For instance, with , the integral defining diverges almost everywhere to . To alleviate such difficulties, the Hilbert transform of an function is therefore defined by the following regularized form of the integral


title: Hilbert transform

text: The modified transform agrees with the original transform on functions of compact support from a general result by Calderón and Zygmund. Furthermore, the resulting integral converges pointwise almost everywhere, and with respect to the BMO norm, to a function of bounded mean oscillation.


title: Hilbert transform

text: A deep result of Fefferman's work is that a function is of bounded mean oscillation if and only if it has the form for some


title: Hilbert transform

text: is the boundary value of a holomorphic function in the upper half-plane. Under these circumstances, if and are sufficiently integrable, then one is the Hilbert transform of the other.


title: Hilbert transform

text: Suppose that formula_66 Then, by the theory of the Poisson integral, admits a unique harmonic extension into the upper half-plane, and this extension is given by


title: Hilbert transform

text: Furthermore, there is a unique harmonic function defined in the upper half-plane such that is holomorphic and


title: Hilbert transform

text: The function obtained from in this way is called the harmonic conjugate of . The (non-tangential) boundary limit of as is the Hilbert transform of . Thus, succinctly,


title: Hilbert transform

text: Titchmarsh's theorem (named for E. C. Titchmarsh who included it in his 1937 work) makes precise the relationship between the boundary values of holomorphic functions in the upper half-plane and the Hilbert transform. It gives necessary and sufficient conditions for a complex-valued square-integrable function on the real line to be the boundary value of a function in the Hardy space of holomorphic functions in the upper half-plane .


title: Hilbert transform

text: The theorem states that the following conditions for a complex-valued square-integrable function formula_74 are equivalent:


title: Hilbert transform

text: A weaker result is true for functions of class for . Specifically, if is a holomorphic function such that


title: Hilbert transform

text: for all , then there is a complex-valued function in formula_8 such that in the norm as (as well as holding pointwise almost everywhere). Furthermore,


title: Hilbert transform

text: This is not true in the case . In fact, the Hilbert transform of an function need not converge in the mean to another function. Nevertheless, the Hilbert transform of does converge almost everywhere to a finite function such that


title: Hilbert transform

text: This result is directly analogous to one by Andrey Kolmogorov for Hardy functions in the disc. Although usually called Titchmarsh's theorem, the result aggregates much work of others, including Hardy, Paley and Wiener (see Paley–Wiener theorem), as well as work by Riesz, Hille, and Tamarkin


title: Hilbert transform

text: One form of the Riemann–Hilbert problem seeks to identify pairs of functions and such that is holomorphic on the upper half-plane and is holomorphic on the lower half-plane, such that for along the real axis,


title: Hilbert transform

text: where is some given real-valued function of The left-hand side of this equation may be understood either as the difference of the limits of from the appropriate half-planes, or as a hyperfunction distribution. Two functions of this form are a solution of the Riemann–Hilbert problem.


title: Hilbert transform

text: The circular Hilbert transform is used in giving a characterization of Hardy space and in the study of the conjugate function in Fourier series. The kernel,


title: Hilbert transform

text: is known as the Hilbert kernel since it was in this form the Hilbert transform was originally studied.


title: Hilbert transform

text: The Hilbert kernel (for the circular Hilbert transform) can be obtained by making the Cauchy kernel periodic. More precisely, for


title: Hilbert transform

text: Many results about the circular Hilbert transform may be derived from the corresponding results for the Hilbert transform from this correspondence.


title: Hilbert transform

text: Another more direct connection is provided by the Cayley transform , which carries the real line onto the circle and the upper half plane onto the unit disk. It induces a unitary map


title: Hilbert transform

text: Bedrosian's theorem states that the Hilbert transform of the product of a low-pass and a high-pass signal with non-overlapping spectra is given by the product of the low-pass signal and the Hilbert transform of the high-pass signal, or


title: Hilbert transform

text: where and are the low- and high-pass signals respectively. A category of communication signals to which this applies is called the "narrowband signal model." A member of that category is amplitude modulation of a high-frequency sinusoidal "carrier":


title: Hilbert transform

text: where is the narrow bandwidth "message" waveform, such as voice or music. Then by Bedrosian's theorem:


title: Hilbert transform

text: known as the "analytic representation" of formula_95 The name reflects its mathematical tractability, due largely to Euler's formula. Applying Bedrosian's theorem to the narrowband model, the analytic representation is:


title: Hilbert transform

text: A Fourier transform property indicates that this complex heterodyne operation can shift all the negative frequency components of above 0 Hz. In that case, the imaginary part of the result is a Hilbert transform of the real part. This is an indirect way to produce Hilbert transforms.


title: Hilbert transform

text: is called angle modulation, which includes both phase modulation and frequency modulation. The instantaneous frequency is  formula_97  For sufficiently large , compared to


title: Hilbert transform

text: For a discrete function, with discrete-time Fourier transform (DTFT), and discrete Hilbert transform the DTFT of formula_106 in the region is given by:


title: Hilbert transform

text: which is an infinite impulse response (IIR). When the convolution is performed numerically, an FIR approximation is substituted for , as shown in "Figure 1". An FIR filter with an odd number of anti-symmetric coefficients is called Type III, which inherently exhibits responses of zero magnitude at frequencies 0 and Nyquist, resulting in this case in a bandpass filter shape. A Type IV design (even number of anti-symmetric coefficients) is shown in "Figure 2". Since the magnitude response at the Nyquist frequency does not drop out, it approximates an ideal Hilbert transformer a little better than the odd-tap filter. However


title: Hilbert transform

text: and returns one cycle ( samples) of the periodic result in the imaginary part of a complex-valued output sequence. The convolution is implemented in the frequency domain as the product of the array  formula_113  with samples of the distribution (whose real and imaginary components are all just 0 or ). "Figure 3" compares a half-cycle of with an equivalent length portion of . Given an FIR approximation for formula_114 denoted by formula_115 substituting formula_116 for the samples results in an FIR version of the convolution.


title: Hilbert transform

text: The real part of the output sequence is the original input sequence, so that the complex output is an analytic representation of . When the input is a segment of a pure cosine, the resulting convolution for two different values of is depicted in "Figure 4" (red and blue plots). Edge effects prevent the result from being a pure sine function (green plot). Since is not an FIR sequence, the theoretical extent of the effects is the entire output sequence. But the differences from a sine function diminish with distance from the edges. Parameter is the output sequence length. If it exceeds the length of the input sequence, the input is modified by appending zero-valued elements. In most cases, that reduces the magnitude of the differences. But their duration is dominated by the inherent rise and fall times of the impulse response.


title: Hilbert transform

text: An appreciation for the edge effects is important when a method called overlap-save is used to perform the convolution on a long sequence. Segments of length are convolved with the periodic function:


title: Hilbert transform

text: When the duration of non-zero values of formula_118 is formula_119 the output sequence includes samples of formula_120 outputs are discarded from each block of , and the input blocks are overlapped by that amount to prevent gaps.


title: Hilbert transform

text: "Figure 5" is an example of using both the IIR hilbert(·) function and the FIR approximation. In the example, a sine function is created by computing the Discrete Hilbert transform of a cosine function, which was processed in four overlapping segments, and pieced back together. As the FIR result (blue) shows, the distortions apparent in the IIR result (red) are not caused by the difference between and (green and red in "Figure 3"). The fact that is tapered ("windowed") is actually helpful in this context. The real problem is that it's not windowed enough. Effectively, , whereas the overlap-save method needs .


title: Hilbert transform

text: The number theoretic Hilbert transform is an extension of the discrete Hilbert transform to integers modulo an appropriate prime number. In this it follows the generalization of discrete Fourier transform to number theoretic transforms. The number theoretic Hilbert transform can be used to generate sets of orthogonal discrete sequences.


title: Expo 2023

text: Expo 2023 was the name given to an upcoming specialized exhibition that was initially scheduled to be held in 2023 in Buenos Aires, Argentina. The Bureau International des Expositions (BIE) awarded Buenos Aires as the host on November 15, 2017. This was to have been the first time that a BIE Expo was held in Argentina, and the first in Latin America since BIE's creation. The 1875 exposition was the last one held in Latin America. In October 2020, Argentina announced that due to the COVID-19 pandemic in Argentina and the ensuing financial crisis, the Expo would not be held as planned in 2023.


title: Expo 2023

text: The estimated number of visitors was 9.4 million, with 79% visiting for a day and 4% international visitors.


title: Expo 2023

text: The exhibition will have a theme of “Science, Innovation, Art and Creativity for Human Development. Creative Industries in Digital Convergence”. It will have three sub themes: "How digital convergence reshapes the creative industries and everyday life",


title: Expo 2023

text: "Socio-economic impacts of the creative industries in digital convergence", and "Cultural impacts of the creative industries in digital convergence".


title: Expo 2023

text: The expo called for proposals for six building works as part of a "Architectural ideas Competition". There were 200 submissions from over 2000 participants.


title: Expo 2023

text: The projects were for the Argentine Pavilion; Mini Stadium and International Pavilion; International Pavilions; Antenna and Viewpoint; Thematic Pavilions; and Public Space, Boulevard and Bridge.


title: Expo 2023

text: The second for the “Small Stadium and the International Pavilions Building” which was to update two existing buildings and to creating a connecting foyer. Walter Casola was the winning architect for this.


title: Expo 2023

text: The sixth project for public spaces includes a bridge to cross the Avenida General Paz linking two parts of the exposition ground and act as future legacy. The winning architects are Rodrigo Grassi; María Hojman; Karla Montauti; and Pablo Pschepiurca.


title: Expo 2023

text: The "Recognition Dossier" for the Argentine expo was submitted to the BIE on 14 January 2019. On 14 October 2020 the government told the BIE that they will not be able to host as planned and need more time.


title: Expo 2023

text: There were two other bids to host the specialized exhibition. Łódź, Poland submitted the bid with a “City Re:Invented” theme on 15 June 2016.


title: Expo 2023

text: And Minneapolis, Minnesota, United States submitted a bid with theme “Healthy People, Healthy Planet: Wellness and Well Being for All”.


title: Expo 2023

text: A secret ballot took place to select the winner at BIE's 162nd General Assembly on 15 November 2017. The first ballot awarded 46 votes to both Buenos Aires and Łódź, with Minneapolis gathering only 25 (and 1 abstention). This meant that Minneapolis was eliminated and a second round ballot held which gave 62 votes to Buenos Aires and 56 to Łódź.


title: STOL

text: A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh conditions (such as high altitude or ice). STOL aircraft, including those used in scheduled passenger airline operations, have also been operated from STOLport airfields which feature short runways.


title: STOL

text: Many fixed-wing STOL aircraft are bush planes, though some, like the de Havilland Canada Dash-7, are designed for use on prepared airstrips; likewise, many STOL aircraft are taildraggers, though there are exceptions like the PAC P-750 XSTOL, the Quest Kodiak, the de Havilland Canada DHC-6 Twin Otter and the Peterson 260SE. Autogyros also have STOL capability, needing a short ground roll to get airborne, but capable of a near-zero ground roll when landing.


title: STOL

text: Runway length requirement is a function of the square of the minimum flying speed (stall speed), and most design effort is spent on reducing this number. For takeoff, large power/weight ratios and low drag help the plane to accelerate for flight. The landing run is minimized by strong brakes, low landing speed, thrust reversers or spoilers (less common). Overall STOL performance is set by the length of runway needed to land or take off, whichever is longer.


title: STOL

text: Of equal importance to short ground run is the ability to clear obstacles, such as hills, on both take off and landing. For takeoff, large power/weight ratios and low drag result in a high rate of climb required to clear obstacles. For landing, high drag allows the aeroplane to descend steeply to the runway without building excess speed resulting in a longer ground run. Drag is increased by use of flaps (devices on the wings) and by a forward slip (causing the aeroplane to fly somewhat sideways through the air to increase drag).


title: STOL

text: Normally, a STOL aircraft will have a large wing for its weight. These wings often use aerodynamic devices like flaps, slots, slats, and vortex generators. Typically, designing an aircraft for excellent STOL performance reduces maximum speed, but does not reduce payload lifting ability. The payload is critical, because many small, isolated communities rely on STOL aircraft as their only transportation link to the outside world for passengers or cargo; examples include many communities in the Canadian north and Alaska.


title: STOL

text: Most STOL aircraft can land either on- or off-airport. Typical off-airport landing areas include snow or ice (using skis), fields or gravel riverbanks (often using special fat, low-pressure tundra tires), and water (using floats): these areas are often extremely short and obstructed by tall trees or hills. Wheel skis and amphibious floats combine wheels with skis or floats, allowing the choice of landing on snow/water or a prepared runway.


title: STOL

text: A STOLport is an airport designed with STOL operations in mind, normally having a short single runway.


title: STOL

text: STOLports are not common but can be found, for example, at London City Airport in London, United Kingdom. There were also several STOLports in the United States that were used for scheduled passenger airline operations but are now no longer in existence.


title: STOL

text: Cruise-efficient short takeoff and landing (CESTOL), is an aircraft with both very short runway requirements and high cruise speeds (greater than Mach 0.8).


title: STOL

text: Many different definitions of STOL have been used by different authorities and nations at various times and for a myriad of regulatory and military purposes. Some accepted definitions of STOL include:


title: STOL

text: Additionally, some aircraft manufacturers market their products as STOL without providing evidence that the aircraft meets any accepted definition.


title: Qom

text: Qom (also spelled as "Ghom", "Ghum", or "Qum") ( ) is the seventh largest metropolis and also the seventh largest city in Iran. Qom is the capital of Qom Province. It is located to the south of Tehran. At the 2016 census, its population was 1,201,158. It is situated on the banks of the Qom River.


title: Qom

text: Qom is considered holy in Shi'a Islam, as it is the site of the shrine of Fatimah bint Musa, sister of Imam Ali ibn Musa Rida (Persian: "Imam Reza"; 789–816). The city is the largest center for Shi'a scholarship in the world, and is a significant destination of pilgrimage, with around twenty million pilgrims visiting the city every year, the majority being Iranians but also other Shi'a Muslims from all around the world. Qom is also famous for a Persian brittle toffee known as "sohan" (Persian: ), considered a souvenir of the city and sold by 2,000 to 2,500 "sohan" shops.


title: Qom

text: Qom has developed into a lively industrial center owing in part to its proximity to Tehran. It is a regional center for the distribution of petroleum and petroleum products, and a natural gas pipeline from Bandar Anzali and Tehran and a crude oil pipeline from Tehran run through Qom to the Abadan refinery on the Persian Gulf. Qom gained additional prosperity when oil was discovered at Sarajeh near the city in 1956 and a large refinery was built between Qom and Tehran.


title: Qom

text: Qom, the capital of Qom province, is located 125 kilometers south of Tehran, on a low plain. The shrine of Fatimeh Masumeh, the sister of Imam Reza, is located in this city, which is considered by Shiʿa Muslims holy. The city is located in the boundary of the central desert of Iran ("Kavir-e Markazi"). At the 2011 census its population was 1,074,036, comprising 545,704 males and 528,332 females.


title: Qom

text: Qom is a focal center of the Shiʿah. Since the revolution, the clerical population has risen from around 25,000 to more than 45,000 and the non-clerical population has more than tripled to about 700,000. Substantial sums of money in the form of alms and Islamic taxes flow into Qom to the ten "Marja'-e taqlid" or "Source to be Followed" that reside there. The number of seminary schools in Qom is now over fifty, and the number of research institutes and libraries somewhere near two hundred and fifty.


title: Qom

text: Its theological center and the Fatima Masumeh Shrine are prominent features of Qom. Another very popular religious site of pilgrimage formerly outside the city of Qom but now more of a suburb is called Jamkaran. Qom's proximity to Tehran has allowed the clerical establishment easy access to monitor the affairs and decisions of state. Many Grand Ayatollahs possess offices in both Tehran and Qom; many people simply commute between the two cities as they are only apart. Southeast of Qom is the ancient city of Kashan. Directly south of Qom lie the towns of Delijan, Mahallat, Naraq, Pardisan City, Kahak, and Jasb. The surrounding area to the east of Qom is populated by Tafresh, Saveh, and Ashtian and Jafarieh.


title: Qom

text: Qom has a hot desert climate bordering a cold desert climate (Köppen "BWh" border on "BWk") with low annual rainfall due to remoteness from the sea and being situated in the vicinity of the subtropical anticyclone aloft. Summer weather is very hot and essentially rainless, whilst in winter weather can vary from warm to – when Siberian air masses are driven south across the Elburz Mountains by blocking over Europe – frigid. An example of the latter situation was in January 2008 when minima fell to on the 15th, whilst earlier similar situations occurred in January 1964 and to a lesser extent January 1950, January 1972 and December 1972.


title: Qom

text: The highest recorded temperature was on 11 July 2010 and the lowest recorded temperature was on 15 January 2008.


title: Qom

text: The present town of Qom in Central Iran dates back to ancient times. Its pre-Islamic history can be partially documented, although the earlier epochs remain unclear. Excavations at Tepe Sialk indicate that the region had been settled since ancient times (Ghirshman and Vanden Berghe), and more recent surveys have revealed traces of large inhabited places south of Qom, dating from the 4th and 1st millennium BC. While nothing is known about the area from Elamite, Medes, and Achaemenid times, there are significant archeological remains from the Seleucid and Parthian epochs, of which the ruins of Khurha (about southwest of Qom) are the most famous and important remnants. Their dating and function have instigated long and controversial debates and interpretations, for they have been interpreted and explained variously as the remains of a Sasanian temple, or of a Seleucid Dionysian temple, or of a Parthian complex. Its true function is still a matter of dispute, but the contributions by Wolfram Kleiss point to a Parthian palace that served as a station on the nearby highway and was used until Sasanian times.


title: Qom

text: The recently published results of the excavations carried out in 1955 by Iranian archeologists have, however, revived the old thesis of a Seleucid religious building. Besides Khurha, which is already mentioned as Khor Abad at Qomi in the 9th century, the region has turned up a few other remnants from this epoch, including the four Parthian heads found near Qom, now kept in the National Museum of Iran in Tehran. Qomi names Parthian personalities as founders of villages in the Qom area. The possible mention of Qom in the form of Greek names in two ancient geographical works (the Tabula Peutingera and Ptolemy's geographical tables) remains doubtful.


title: Qom

text: The Sasanian epoch offers many archeological findings and remnants, besides the fact that various sources mention Qom. The most interesting building from an archeological point of view is the Qalʿa-ye Doḵtar in Qom itself, which was long thought to have served religious purposes, while more recent research points to an administrative use. The wider surroundings of Qom also contain numerous traces from palaces, religious, military and administrative buildings. Some of these are mentioned by Qomi, who also names many more fire temples in the urban area of present Qom and its region, of which no archeological traces are left although the location of one fire temple can probably be equated with today's Masjed-e Emām in the city. According to Qomi, the most important fire temple of the area stood in the nearby village of Dizijan.


title: Qom

text: Tāriḵ-e Qom and some other sources also speak of genuine historical figures of the Sasanian epoch in connection with Qom and its region. They shed new light on the time of the seizure of power by the first Sasanian king Ardashir I, who fought his decisive battles near Qom, and the collapse of the Sasanian empire, which is extensively reported by Ebn Aʿṯam Kufi and the Nehāyat al-Erab and names a certain Šērzād as the satrap of the region. The existence of an urban settlement in the Sasanian epoch is furthermore verified by Middle Persian sources (literary sources, inscriptions, and seals) that mention in the time of Shapur I and Kawād I the names Godmān/Gomān and Ērān Win(n)ārd Kawād, both of which could be identified as Qom. Altogether one can assume that Qom functioned as a small administrative unit throughout the whole Sasanian era. Probably the urban structure of the Sasanian settlement of Qom can be compared with the type of city of Ctesiphon (Or. Madāʾen) and consisted of several villages and little towns with Abaraštejān, Mamajjān and Jamkarān as the bigger settlements that were loosely connected by defense installations.


title: Qom

text: It is difficult to decipher the actual process of the Arab conquest of Qom from the extant Arabic sources. According to Balāḏori, the first tentative conquest of Qom took place in 23/644 by Abu Musa Ashaari after a few days of fighting (although Abu Musa's route through Western Persia, as narrated by Balāḏori, appears somewhat confusing). It remains unclear who the defenders of Qom were; probably fleeing Sasanian nobles and local soldiers returning from the great battles against the Arabs formed the core of the resistance. The area remained largely untouched for 60 years after the initial conquest and was probably administered from Isfahan.


title: Qom

text: The first permanent settlement of Arab settlers in Qom took place during the revolts of Mukhtar al-Thaqafi and Moṭarref b. Moḡira b. Šaʿba in 66–77/685–96, when small groups of refugees moved there and Qom itself was affected by the fighting between the Umayyad state power and the rebels


title: Qom

text: The decisive step for the later urban development of Qom occurred when a group of Ashaari Arabs came to the area. These Ashaaries originated in Yemen and the first important figure among them was the first conqueror of the area of Qom, the above-mentioned Abu Musa Ashaari. ʿAbd-Allāh b. Saʿd and Aḥwaṣ b. Saʿd were grandsons of Abi Musa's nephew and led the group of Ashaaries that emigrated from Kufa to the region of Qom. It is not exactly clear why they migrated, but it might have also been a general opposition to the Umayyad dynasty. A central element was the early contact with the leading local Zoroastrian Persian noble Yazdanfadar.


title: Qom

text: As the Arabs required a great deal of pasture for their large herds of cattle and were much wealthier than the local Persians, they slowly started to buy land and take over more villages. The decisive step for controlling the area was the elimination of the local Persian noble class that took place after the death of Yazdanfadar in 733. The emigration and the subsequent settlement and building activities led to the fusion of the original six villages on the area of Qom to an urban conglomerate which probably happened within two generations after the first coming of Arabs.


title: Qom

text: Although a few names of governors and their tax assessments are known from the time after the administrative independence, the death of Fātimah bint Mūsā, the sister of the eighth Imam of Shias Ali al-Ridha in the city in 201/816–17 proved to be of great importance for the later history of Qom. Fātimah bint Mūsā died while following her brother to Khorasan, a region in northern Iran. The place of her entombment developed from 869–70 into a building that was transformed over time into today's magnificent and economically important sanctuary.


title: Qom

text: In 825–26 a major rebellion against the tax regulations of the caliphate broke out in Qom. It was caused by the refusal of the caliph Al-Ma'mun to lower the yearly tax assessment as he had done in Ray. The revolt was led by an Ashaari named Yahya ibn Emran, maintaining that taxes should not be paid to an unlawful ruler. Yahya was killed by troops sent by the caliph and the citizens were severely punished; the taxes were raised from 2 million to 7 million dirhams. Two years later the taxes were again raised by 700,000 dirham by the Ashaari governor Ali ibn Isa, who was subsequently deposed because he was strongly rejected by the inhabitants of Qom. But in 833 Ali returned to the post of governor (wali) and forcefully collected tax debts that were laid upon him by the caliph. He destroyed parts of Qom and handed over a wanted rebel to caliphal authorities under Al-Moʿtasem. Between 839–42 two contradicting tax assessments were carried out under turbulent circumstances which amounted to a sum of 5 million dirhams. The names of those involved have survived.


title: Qom

text: The move of a Hadith transmitter from Kufa to Qom, which took place probably in the middle of the 9th century, indicates the increased importance of Qom as a center of Shia learning. At about the same time another military attack on the city occurred in 254/868, when Mofleḥ, the Turkish officer of the caliph Al-Mostaʿin, executed some of its inhabitants because of the city's refusal to pay taxes. Mofleḥ became governor of Qom and lasted in that position for at least five years. During his governorship important Alids moved to Qom and there are references to close contacts between the representative of the 11th Shia's Imam, Hassan al-Askari, in Qom and other Qomis. The representative Aḥmad b. Esḥāq was at the same time administrator of the Fāṭema sanctuary and the agent (wakil) responsible for the pensions of the Alids.


title: Qom

text: The first Friday mosque in Qom was built in 878–79 on the site of a fire temple, although there are also confusing reports concerning a possible earlier Friday mosque. In 881–82 Qom was occupied by the Turkish military leader Edgu Tegin (Arabic: Yadkutakin b. Asātakin or Aḏkutakin), who tried to collect the tax arrears for seven years which partially ruined the guarantors (some of whom are known) of these taxes. At about the same time the early orthodox Shias achieved their victory in the town. In 893–94, at the latest, all extremists (ḡolāt) were driven out of town by the leading Shia shaikh of Qom, Aḥmad b. Moḥammed b. Isa Ashaari. Probably one year later the famous Islamic mystic Ḥosayn b. Manṣur Ḥallaj stayed in Qom, where he was arrested.


title: Qom

text: From 895–96 onwards the history of Qom was connected with a family of Turkish military leaders from the army of the caliph Al-Mu'tadid, including the governor Berun (Birun). In the same year, Berun destroyed a big and probably still active fire temple located on the territory of the evolving city and probably opposite today's sanctuary of Fātimah bint Mūsā. In these unstable political times, Qom was visited by the vizier of Al-Moʿtazed, Obayd-Allah ibn Solayman, and two tax assessments were organized. An administrative peculiarity of Qom was put to an end at about the same time, to wit the independent appointment of judges through the Arab inhabitants of Qom until the time of al-Moktafi, which, together with the dispatch of a joint Arab-Persian delegation to the vizier Ḥamid ibn Abbas indicate the end of the elevated position of the Arabs in Qom. The period of the governor Abbas ibn Amr Ganawi (292–96/904–09) is remarkable for the presence of non-Twelver Shias in Qom and the establishment of the office of the jahbaḏ (financial officer) as the tax broker for the city, which fostered local self-determination.


title: Qom

text: In 909 Hosayn ibn Hamdan ibn Hamdun was appointed governor of Qom and Kāšān by the caliph Al-Moqtader and had to assist the caliph's army against the Saffarids in Fars. Altogether he stayed in power only for two years before he had to return to Baghdad. In the years 301/913–14 to 315/927 the people of Qom had, besides another tax assessment (meanwhile the eighth), a caliphal intervention that resulted in the appointment of a governor to stabilize the administrative grip over the region. This move caused more unrest and affected the balance of power in an area that was disputed between the powers of the time (Daylamites, Samanids). Beginning in 316/928 Qom fell into the sphere of interest of Daylami warlords and was relieved from the direct authority of the caliph, although it changed hands several times between 928 and 943. The Daylamites brutally exploited the city through harsh taxes. With the firm establishment of Buyids control from 340/951–52 on, the political circumstances were less troubled than before, although the economic situation deteriorated.


title: Qom

text: No outstanding events are reported for the relatively stable political period until 988–89, but Qom seems to have been isolated inside Persia because of its Shia creed. At the same time, the Fatima sanctuary was enlarged and the number of sayyeds residing in Qom reached a considerable number. In 373/984 Qom and its environs were affected by the revolt of the Kurdish Moḥammad Barzikāni against the Buyid Fakr-Al-Dawla.


title: Qom

text: The population amounted to 50,000 inhabitants at the most and consisted of Persians and Arabs who had adopted the Persian of the time as their language and many social customs from the Persians, whose proportion was probably smaller than the Arabs. The Kurds lived in the countryside to the west. The Twelver Shia constituted the great majority of the population and many important Shia scholars of the time came from Qom or lived there. As many as 331 male Alids lived in Qom in 988–89, and they produced a good number of community leaders and there is also mention of one prominent female ʿAlid besides Fātimah bint Mūsā. These Alids descended from the Imams and were supported by pensions.


title: Qom

text: Apart from the Shia mainstream, other Shia sects existed in the city and one can also assume the presence of Sunnies. Ḏemmis, or followers of other revealed religions (Jews, Christians, and Zoroastrians) must have lived in the city, too, as the payment of poll tax (jezya) indicates, although their number can only be very roughly estimated at a few thousand at the end of the 9th century and must have shrunk drastically in the 10th century. The majority of these non-Muslims were Zoroastrians, who made their living mostly as farmers. Jews must have lived in Qom as well, but information on them is scant. It is striking that the formerly dominant Ashaaries had lost their leading positions by the end of the 10th century. This points at a new social situation that allowed assimilated Persians to join the local establishment.


title: Qom

text: The city's topography in the 10th century still reflected the evolutionary merging of the original six villages; these were still separated by fields. The town center was located in the village of Mamajjān, which was connected to other parts of the city on the other side of the river by four bridges. There were about eight squares whose function is not clear and three mosques within the city. There is almost no information about madrasas. The sanctuary must have still been quite small as only two cupolas are mentioned. A bazaar and bathhouses must have existed, too, as well as certain administrative buildings (prison, mint). Five bigger and eight smaller roads indicate good traffic connections, which were supported by at least three or maybe even nine city gates.


title: Qom

text: Qom was then in a difficult economical and social position. Many houses inside the city as well as bridges and mills were ruined and the roads and agriculture were suffering from an insecure situation. This has to be attributed to difficult social circumstances and excessive taxation. The water supply seems to have been satisfactory and the Ashaaries seem to have undertaken continuous renovation works on the irrigation channels between 733 and 900. The Ašʿaris were also the proprietors of the water rights, which were safeguarded in the water authority (divān-e āb) that regulated the water shares. The system made the Ašʿaris the wealthiest inhabitants of Qom and stayed in place until 347/958–59 when they were expropriated by the Buyids, which consequently brought about a decline in the whole system of irrigation. Although there were attempts at restoration in 371/981–82, only three of originally twenty-one channels had flowing water which meant enough drinking water was supplied for the population, but the available amount could not have been adequate for agricultural purposes.


title: Qom

text: Altogether the state of cultivation in Qom seems to have resembled that of the other regions of Persia, although the thirty different crops and plants are only indirectly mentioned in connection with the tax assessments. The soil is reported to have good quality and produced big quantities of food. Little is known about animal husbandry in the region, but the considerable number of fifty-one mills existed, of which a fifth was in decay. Legends speak of mineral deposits and mines of silver, iron, gold and lead, while Kurds seem to have produced salt from a lake nearby (see Qom Lake). The production of chairs, textiles, and saddle equipment indicates craftsmanship.


title: Qom

text: The city's taxation has to be distinguished between the more proper rule of the Abbasid tax bureaucracy and the time of the Deylamid warlords where rules were bent arbitrarily. A stunning diversity of taxes is known (often meant to serve the ever greedy Abbasid bureaucracy and the Deylamid and Buyid war machinery) but the Karaj (land tax), which was composed of many different separate sums, was the most important single tax existing in Qom at least since post-Sasanian times. Within the known 18 tax figures ranging over 160 years there are great differences and the tax figures vary from 8 million to 2 million dirhams with a mean value at around 3 million. In taxation Qom always followed the solar calendar with its own local variation, starting from the death of the Sasanian Yazdegerd III. A highly differentiated tax administration existed and is known in great detail; 24 tax collectors (ʿommāl) are listed from 189/804–05 to 371/981–82 plus two jahabaḏa who acted as mediators after the attempt to enforce collective responsibility by the taxpayers had failed. The information in the Tāriḵ-e Qom on taxation also mention by name 21 tax districts (rasātiq) in the region with 900 villages.


title: Qom

text: Little is known about the time until the period of Seljuki dominance. In 387/997, Qom became involved in internal Buyid quarrels and was subsequently unsuccessfully besieged. In 418/1027–28, Qom fell under the rule of Šahryuš from the Kakuyid dynasty and a few years later (1030–40) it became part of the Ghaznavid domain. The Seljuki did not occupy Qom at once but left the town and Jebāl in Kakuyid hands for ten years. From 442/1050–51 on, the city was under Seljuk rule and nothing is known about its fate until 487/1094. Afterwards the growing instability of the Seljuk empire involved Qom in the power struggles between the competing Seljuk factions in Jebāl and the city changed hands many times. The most stable period seem to have been the 14 years (513–27/1119–33) when Qom lay in Sanjar's sphere of power and witnessed the construction of a second Friday mosque.


title: Qom

text: Surprisingly, Qom enjoyed relative prosperity in its economy in the Seljuk period. The rigidly Sunni Seljuks seem to have practiced a pragmatic policy and one of the main sources of this time (ʿAbd-al-Jalil Qazvini) speaks of good relations between the famous vizier Nizam al-Mulk and Seljuk sultans on the one hand, and members of the local nobility on the other. Sultans reportedly visited the sanctuary (although no specific sultan is mentioned by name) and in general no religiously motivated punitive action against Qom is known to have taken place. Under Seljuk rule a considerable number of religious buildings were erected. At least ten madrasas are known by name. Two Friday mosques seem to have existed in Seljuk times: the old one was renovated and a new one, located outside of the town area, was built in 528/1133–34 by the order of Sultan Togrel II ("Persian:" ). Qom must have expanded during this period, but precise reasons for its prosperity are not known. A family of Ḥosaynid Alids was influential and provided a number of community leaders. Another important Shia family was that of the Daʿwidār ("Persian:" ), whose members were judges ("Arabic:" ) in town, which indicates the transformation of Qom from a town governed by the Sunnis to a completely Shai domain.


title: Qom

text: The following epochs of the Eldiguzids and Khawrazmshahs lasted for almost 30 years and brought different systems of rule in quick succession. The two noteworthy events of this period are the execution of ʿEzz-al-Din Yaḥyā, the naqib of the Shias, by the Tekesh in 592/1196 and the work on the tiles of the sanctuary (probably in 605–13/1208–17), which indicate a certain economic prosperity at a time of unstable political conditions. From 614/1217–18 until the Mongol attack, Qom remained under Muhammad II of Khwarezm.


title: Qom

text: The Mongol invasion led to the total destruction of Qom by the armies of the Mongol generals, Jebe and Sübedei, in 621/1224 and left the city in ruins for at least twenty years, when the sources (Jovayni) tell of the levying of taxes. Twenty years later, reconstruction and repair works, probably sponsored by some wealthy inhabitants, were being done on the mausoleums of Shia saints in the city, which contradict those sources, such as Ḥamd-Allāh Mostawfi, that describe Qom as a ruined and depopulated city throughout the Ilkhanid period. Besides, the fact that the Ilkhanid vizier Šams-al-Din Jovayni took refuge in the Fātimah bint Mūsā sanctuary in 683/1284, indicates that the city must have experienced at least a modest comeback. The city walls were probably rebuilt and, moreover, four graves of saints are known to have been constructed between 720/1301 and 1365. Additionally some fine tiles are known from this period. Nothing is known about the irrigation systems of the town, but nearby a dam was built in the Ilkhanid period and the local administration must have functioned again, as the name of a judge shows. The agricultural situation is described as flourishing with a variety of cultivated plants and a good supply of water, and legends indicate the use of deposits of mineral resources. Information exists concerning taxes for the post-Mongolian period. Qom paid 40,000 dinars, but more remarkable is the fact that some of the surrounding rural districts paid as much as Qom or even more, which suggests that the whole administrative structure of districts had also changed.


title: Qom

text: In the late 14th century, the city was plundered by Tamerlane and the inhabitants were massacred. Qom gained special attention and gradually developed due to its religious shrine during the Saffavid dynasty. By 1503, Qom became one of the important centers of theology in relation to Shia Islam, and became a significant religious pilgrimage site and pivot.


title: Qom

text: The city suffered heavy damage again during the Afghan invasions, resulting in consequent severe economic hardships. Qom further sustained damage during the reign of Nader Shah and the conflicts between the two households of Zandieh and Qajariyeh in order to gain power over Iran. Finally in 1793 Qom came under the control of Agha Muhammad Khan Qajar. On being victorious over his enemies, the Qajar Sultan Fath Ali Shah was responsible for the repairs done on the sepulchre and Holy Shrine of Hæzræt Mæ'sume, as he had made such a vow.


title: Qom

text: The city of Qom began another era of prosperity in the Qajar era. After Russian forces entered Karaj in 1915, many of the inhabitants of Tehran moved to Qom due to reasons of proximity, and the transfer of the capital from Tehran to Qom was even discussed. But the British and Russians defeated prospects of the plan by putting Ahmad Shah Qajar under political pressure. Coinciding with this period, a "National Defense Committee" was set up in Tehran, and Qom turned into a political and military apex opposed to the Russian and British colonial powers.


title: Qom

text: As a center of religious learning Qom fell into decline for about a century from 1820 to 1920, but had a resurgence when Shaykh Abdul Karim Haeri Yazdi accepted an invitation to move from Sultanabad (now called Arak, Iran), where he had been teaching, to Qom.


title: Qom

text: In 1964–65, before his exile from Iran, the Ayatollah Khomeini led his opposition to the Pahlavi dynasty from Qom. After the Islamic revolution in 1979, Khomeini spent time in the city before and after moving to Tehran.


title: Qom

text: On 19 February 2020, the Iranian Students News Agency reported that the first two cases of the COVID-19 pandemic in Iran were detected in Qom.


title: Qom

text: Authority for the city lies with the mayor, who is elected by a municipal board. The municipal board is periodically elected by the city's residents. The municipal central office is located on Saheli Street. The current mayor of Qom is Mohammad Delbari.


title: Qom

text: Iran's Cultural Heritage Organization lists 195 sites of historical and cultural significance in Qom. But the more visited sites of Qom are:


title: Qom

text: Qom is well known for its many religious seminaries and institutes that offer advanced religious studies, which made this city the largest center for Shia scholarship in the world. There are an estimated 50,000 seminarians in the city coming from 80 countries, including 6,000 from Pakistan alone. Qom has seminaries for women and some non-Shia students. Most of the seminaries teach their students modern social sciences and Western thought as well as traditional religious studies.


title: Qom

text: The Hawzah (a short form of al-Hawzah al-Ilmiyya), which presently consists of over 200 education and research centres and organisations, catering for over 40,000 scholars and students from over 80 List of sovereign states. The modern Qom hawza was revitalized by Abdul Karim Haeri Yazdi and Grand Ayatollah Borujerdi and is barely a century old. There are nearly three hundred thousand clerics in Iran's seminaries. At present Hossein Vahid Khorasani heads Hawza 'Ilmiyya Qom.


title: Qom

text: The Fordow uranium enrichment facility is located 20 miles north east of Qom. In January 2012 the International Atomic Energy Agency (IAEA) announced that Iran had started producing uranium enriched up to 20% for medical purposes and that material "remains under the agency's containment and surveillance.” Iranian authorities state the facility is built deep in a mountain because of repeated threats by Israel to attack such facilities, which Israel believes can be used to produce nuclear weapons. However, attacking a nuclear facility so close to a city considered so holy in Shia Islam brings concern of a potential risk of a Shiite religious response.


title: Qom

text: Qom space center is one of the two places where the Iranian Space Agency is launching its suborbital Shahab-3 ballistic missiles, the other being the Emamshahr space center.


title: Musical keyboard

text: A musical keyboard is the set of adjacent depressible levers or keys on a musical instrument. Keyboards typically contain keys for playing the twelve notes of the Western musical scale, with a combination of larger, longer keys and smaller, shorter keys that repeats at the interval of an octave. Pressing a key on the keyboard makes the instrument produce sounds—either by mechanically striking a string or tine (acoustic and electric piano, clavichord), plucking a string (harpsichord), causing air to flow through a pipe organ, striking a bell (carillon), or, on electric and electronic keyboards, completing a circuit (Hammond organ, digital piano, synthesizer). Since the most commonly encountered keyboard instrument is the piano, the keyboard layout is often referred to as the "piano keyboard".


title: Musical keyboard

text: The twelve notes of the Western musical scale are laid out with the lowest note on the left. The longer keys (for the seven "natural" notes of the C major scale: C, D, E, F, G, A, B) jut forward. Because these keys were traditionally covered in ivory they are often called the "white notes" or "white keys". The keys for the remaining five notes—which are not part of the C major scale—(i.e., C/D, D/E, F/G, G/A, A/B) (see Sharp and Flat) are raised and shorter. Black keys form a pentatonic scale. Because these keys receive less wear, they are often made of black colored wood and called the "black notes" or "black keys". The pattern repeats at the interval of an octave.


title: Musical keyboard

text: The arrangement of longer keys for C major with intervening, shorter keys for the intermediate semitones dates to the 15th century. Many keyboard instruments dating from before the nineteenth century, such as harpsichords and pipe organs, have a keyboard with the colours of the keys reversed: the "white notes" are made of ebony and the "black notes" are covered with softer white bone. A few electric and electronic instruments from the 1960s and subsequent decades have also done this; Vox's electronic organs of the 1960s, Farfisa's FAST portable organs, Hohner's Clavinet L, one version of Korg's Poly-800 synthesizer and Roland's digital harpsichords.


title: Musical keyboard

text: Some 1960s electronic organs used reverse colors or gray sharps or naturals to indicate the lower part (or parts) of a single keyboard divided into two parts, each controlling a different registration or sound. Such keyboards accommodate melody and contrasting accompaniment without the expense of a second manual, and were a regular feature in Spanish and some English organs of the renaissance and baroque eras. The break was between middle C and C-sharp, or outside of Iberia between B and C. Broken keyboards reappeared in 1842 with the harmonium, the split occurring at E4/F4.


title: Musical keyboard

text: The reverse-colored keys on Hammond organs such as the B3, C3 and A100 are latch-style radio buttons for selecting pre-set sounds.


title: Musical keyboard

text: The chromatic range (also called "compass") of keyboard instruments has tended to increase. Harpsichords often extended over five octaves (>60 keys) in the 18th century, while most pianos manufactured since about 1870 have 88 keys. The lowest pitch (frequency: 27.5 Hz) of an 88-key piano is equivalent to a sub contrabass in the range name. Some modern pianos have even more notes (a Bösendorfer 290 "Imperial" has 97 keys, and a Stuart & Sons model has 108 keys). While modern synthesizer keyboards commonly have either 61, 76 or 88 keys, small MIDI controllers are available with 25 keys. (Digital systems allow shifting octaves, pitch, and "splitting" ranges dynamically, which, in some cases, reduce the need for dedicated keys. However, smaller keyboards will typically limit which musical scores can be played.) Organs normally have 61 keys per manual, though some spinet models have 44 or 49. An organ pedalboard is a keyboard with long pedals played by the organist's feet. Pedalboards vary in size from 12 to 32 notes or 42 in the case of the international touring Organ from "Cameron Carpenter".


title: Musical keyboard

text: In a typical keyboard layout, "black note" keys have uniform width, and "white note" keys have uniform width and uniform spacing at the front of the keyboard. In the larger gaps between the "black" keys, the width of the natural notes C, D and E differ slightly from the width of keys F, G, A and B. This allows close to uniform spacing of 12 keys per octave while maintaining uniformity of seven "natural" keys per octave.


title: Musical keyboard

text: Over the last three hundred years, the octave span distance found on historical keyboard instruments (organs, virginals, clavichords, harpsichords, and pianos) has ranged from as little as to as much as . Modern piano keyboards ordinarily have an octave span of , resulting in the width of black keys averaging and white keys about at the base, disregarding space between keys.


title: Musical keyboard

text: In recent years, there has been evidence of a correlation between pianists with smaller hand spans and hand or arm injuries. Several reduced-size standards have been proposed for these pianists. A 7/8 size ( octave span) keyboard was developed by Canadian Christopher Donison in the 1970s. This size, along with the 15/16 size ( octave span) and a smaller size (130 mm (5.1 in) octave span) have since been developed and marketed by Steinbuhler & Company in Pennsylvania. These three sizes are registered as DS6.0, DS5.5 and DS5.1. The company was converted to the non-profit DS Standard Foundation in 2018. Hailun USA manufactures pianos in the two alternative DS6.0 and DS5.5 sizes through an agreement with the DS Standard Foundation. Since 2013, a global network of pianists, teachers and performing arts health professionals has been increasingly advocating for change to the 'one size fits all' approach to piano keyboard manufacturing by major companies. This network is known as PASK (Pianists for Alternatively Sized Keyboards). U.S. pianist Hannah Reimann has promoted piano keyboards with narrower octave spans and has a U.S. patent on the apparatus and methods for modifying existing pianos to provide interchangeable keyboards of different sizes. Narrower keyboards are available from Steinway & Sons USA in new grand pianos or as a retrofit to existing pianos.


title: Musical keyboard

text: There have been variations in the design of the keyboard to address technical and musical issues. The earliest designs of keyboards were based heavily on the notes used in Gregorian chant (the seven diatonic notes plus B-flat) and as such would often include B and B both as diatonic "white notes", with the B at the leftmost side of the keyboard and the B at the rightmost. Thus, an octave would have "eight" "white keys" and only four "black keys". The emphasis on these eight notes would continue for a few centuries after the "seven and five" system was adopted, in the form of the short octave: the eight aforementioned notes were arranged at the leftmost side of the keyboard, compressed in the keys between E and C (at the time, accidentals that low were very uncommon and thus not needed). During the sixteenth century, when instruments were often tuned in meantone temperament, some harpsichords were constructed with the G and E keys split into two. One portion of the G key operated a string tuned to G and the other operated a string tuned to A, similarly one portion of the E key operated a string tuned to E, the other portion operating a string tuned to D. This type of keyboard layout, known as the enharmonic keyboard, extended the flexibility of the harpsichord, enabling composers to write keyboard music calling for harmonies containing the so-called "wolf" fifth (G-sharp to E-flat), but without producing aural discomfort in the listeners (see Split sharp). The "broken octave", a variation of the aforementioned short octave, similarly used split keys to add accidentals left out of the short octave. Other examples of variations in keyboard design include the Jankó keyboard and the chromatic keyboard systems on the chromatic button accordion and bandoneón.


title: Musical keyboard

text: Simpler electronic keyboards have switches under each key. Depressing a key connects a circuit, which triggers tone generation. Most keyboards use a keyboard matrix circuit, in which 8 rows and 8 columns of wires cross — thus, 16 wires can provide 8 × 8 = 64 crossings, which the keyboard controller scans to determine which key was pressed. The problem with this system is that it provides only a crude binary on/off signal for each key. Better electronic keyboards employ two sets of slightly offset switches for each key. By determining the timing between the activation of the first and second switches, the velocity of a key press can be determined, greatly improving the performance dynamic of a keyboard. The best electronic keyboards have dedicated circuits for each key, providing polyphonic aftertouch.


title: Musical keyboard

text: Advanced electronic keyboards may provide hundreds of key touch levels and have 88 keys, as most pianos do.


title: Musical keyboard

text: Despite their visual similarity, different keyboard instrument types require different techniques. The piano hammer mechanism produces a louder note the faster the key is pressed, while the harpsichord's plectrum mechanism does not perceptibly vary the volume of the note with different touch on the keyboard. The pipe organ's volume and timbre are controlled by the flow of air from the bellows and the stops preselected by the player. Players of these instruments therefore use different techniques to color the sound. An arranger keyboard may be preset to produce any of a range of voices as well as percussion and other accompaniments that respond to chords played by the left hand.


title: Musical keyboard

text: Even though the keyboard layout is simple and all notes are easily accessible, playing requires skill. A proficient player has undertaken much training to play accurately and in tempo. Beginners seldom produce a passable rendition of even a simple piece due to lack of technique. The sequences of movements of the player's hands can be very complicated. Problems include wide-spanned chords, which can be difficult for people with small hands, chords requiring unusual hand positions that can initially be uncomfortable, and fast scales, trills and arpeggios.


title: Musical keyboard

text: Playing instruments with "velocity sensitive" (or "dynamic") keyboards (i.e., that respond to varying playing velocity) may require finger independence, so that some fingers play "harder" while others play more softly. Pianists call this control of touch velocity "voicing" (not to be confused with a piano technician's "voicing" of a piano by modifying the hardness of the hammers). Keyboardists speak of playing harder and softer, or with more or less force. This may accurately describe the player's experience—but in the mechanics of the keyboard, velocity controls musical dynamics. The faster the player depresses the key, the louder the note. Players must learn to coordinate two hands and use them independently. Most music is written for two hands; typically the right hand plays the melody in the treble range, while the left plays an accompaniment of bass notes and chords in the bass range. Examples of music written for the left hand alone include several of Leopold Godowsky's 53 Studies on Chopin's Etudes, Maurice Ravel's Piano Concerto for the Left Hand and Sergei Prokofiev's Piano Concerto No. 4 for the left hand. In music that uses counterpoint technique, both hands play different melodies at the same time.


title: Musical keyboard

text: A number of percussion instruments—such as the xylophone, marimba, vibraphone, or glockenspiel— have pitched elements arranged in the keyboard layout. Rather than depress a key, the performer typically strikes each element (bell, metal or wood bar, etc.) with a mallet.


title: Musical keyboard

text: There are some examples of a musical keyboard layout used for non-musical devices. For example, some of the earliest printing telegraph machines used a layout similar to a piano keyboard.


title: Musical keyboard

text: There are some rare variations of keyboards with more or fewer than 12 keys per octave, mostly used in microtonal music, after the discoveries and theoretical developments of musician and inventor Julián Carrillo (1875–1965).


title: Musical keyboard

text: Some free-reed instrument keyboards such as accordions and Indian harmoniums include microtones. Electronic music pioneer Pauline Oliveros played one of these. Egyptian belly-dance musicians like Hassam Ramzy use custom-tuned accordions so they can play traditional scales. The small Garmon accordion played in the Music of Azerbaijan sometimes has keys that can play microtones when a "shift" key is pressed.


title: Muenster cheese

text: Muenster ( ) or munster is a semi-soft cheese from the United States. It is thought to be an imitation of the Alsatian washed-rind Munster cheese, introduced by German immigrants. It is distinct from the processed dairy food "Sweet Muenster Cheese". Its name is not related to the German cities of Münster in Westphalia or in Lower Saxony or the Irish province of Munster, but rather to the city of Munster in Alsace, which was part of Germany at the time the cheese was introduced in the US by German immigrants, but is now in France.


title: Muenster cheese

text: Muenster is pale in color and smooth in texture with an orange rind. The cheese is made from pasteurized cow's milk. The rind's orange color is from annatto, a sweet and nutty seasoning used to add flavor and color to cheeses such as Cheddar, Colby, Red Leicester, and Mimolette. Muenster usually has a very mild flavor and smooth, soft texture. In some cases, when properly aged, it can develop a strong flavor with a pungent aroma. This cheese is commonly served as an appetizer. Because it melts well, it is also often used in dishes such as grilled cheese sandwiches, tuna melts, quesadillas, cheeseburgers, macaroni and cheese, and pizza.


title: Muenster cheese

text: The spelling "Muenster" distinguishes the American cheese from Munster cheese, which is made from unpasteurized cow's milk in the Vosges mountains in Alsace. The orange tinge of Munster's rind occurs naturally as a byproduct of the cheese-making process. A regional variation is also produced in the Franche-Comté region in France. The name Munster-Géromé, used today in France, is a protected A.O.C. and is strictly regulated in its production technique and source geography.


title: FC Akhmat Grozny

text: Republican Football Club Akhmat (; ), commonly known as Akhmat Grozny, is a Russian professional football club based in Grozny that plays in the Russian Premier League. The team was named "Terek" between 1958 and 2017.


title: FC Akhmat Grozny

text: It was founded in 1946, as "Dynamo"; it changed its name in 1948 to "Neftyanik" and in 1958 to "Terek", it changed the name again in 2017 to "Akhmat". The club is named after Akhmat Kadyrov.


title: FC Akhmat Grozny

text: In the 1990s the club was disbanded for some time due to the war in Chechnya. From the 1990s to 2007 the club played its home games in the neighbouring resort city of Pyatigorsk, Stavropol Krai. Before the start of the 2008 Premier League season, the Russian Football Union granted Terek the right to host Premier League matches in Grozny.


title: FC Akhmat Grozny

text: They won the Russian Cup by beating Krylya Sovetov Samara in the final and the Russian First Division in 2004. In 2004 they advanced through the UEFA Cup qualification by beating the Polish team Lech Poznań 1–0 in both legs but lost to Swiss outfit FC Basel in the first round. They played in the Russian Premier League in 2005 but were relegated after finishing last. Terek finished second in the First Division in 2007 and were promoted back into the Premier League.


title: FC Akhmat Grozny

text: On 3 July 2008, Terek signed three Romanian players at once: Andrei Margaritescu (Dinamo București), Florentin Petre (CSKA Sofia) and Daniel Pancu (Rapid București). Terek finished 12th in the 2010 Russian Premier League season.


title: FC Akhmat Grozny

text: Cameroonian FC Lotus-Terek Yaoundé, founded by Terek player Guy Stephane Essame and coached by Thomas Libiih, is a farm team of the Russian club.


title: FC Akhmat Grozny

text: In January 2011 the club signed former Dutch international Ruud Gullit to an 18-month contract to manage the club. On 14 June 2011 Gullit was sacked for poor results.


title: FC Akhmat Grozny

text: On 7 June 2017, the team was renamed from FC Terek to FC Akhmat, after Akhmad Kadyrov, former President of the Chechen Republic.


title: FC Akhmat Grozny

text: On 30 October 2017, manager Oleg Kononov resigned, with Mikhail Galaktionov taking over in a caretaker capacity, before being announced as Akhmat's permanent manager on 14 December 2017.


title: FC Akhmat Grozny

text: On 30 September 2019, after a 2–0 away defeat to Sochi, Rashid Rakhimov resigned as manager, with Igor Shalimov being appointed as Rakhimov's replacement the same day. On 26 July 2020, Igor Shalimov's contract as manager expired and he left Akhmat Grozny, to be replaced by Andrei Talalayev.


title: FC Akhmat Grozny

text: On 11 September 2022, Andrei Talalayev was relieved of his duties as Head Coach, with Yury Nagaytsev taking over in a caretaker capacity. On 22 September 2022, Sergei Tashuyev was announced as Akhmat Grozny's new permanent Head Coach.


title: FC Akhmat Grozny

text: Between the 1990s and the 2007 Season, Akhmat Grozny played their home games at the Central Stadium in the neighbouring resort city of Pyatigorsk in Stavropol Krai. At the start of the 2008 season they moved to the Sultan Bilimkhanov Stadium, playing their home games there until the opening of Akhmat-Arena on 20 May 2011, when they beat Anzhi Makhachkala 1–0 in the Russian Premier League.


title: FC Akhmat Grozny

text: In 2013, a professional farm club called FC Terek-2 Grozny was created. It played in the third-tier Russian Professional Football League until they were dissolved after the 2015–16 season.


title: FC Akhmat Grozny

text: Had international caps for their respective countries. Players whose names are listed in bold represented their countries while playing for Akhmat or Terek.


title: Ishant Sharma

text: Ishant Sharma (; born 2 September 1988) is an Indian cricketer who has represented India in Tests, ODIs and T20Is. He is a 6 ft 4 in tall right-arm fast-medium bowler. At the age of 18, Sharma was called to join the Indian squad for the tour of South Africa in 2006–07. However, after receiving the call and organising travel arrangements, he was deselected. In reference to his height and lean physique in his Under-19 days, the bowler was nicknamed "Lambu". In 2011, he became the fifth youngest player to take 100 Test wickets. Against South Africa in 2013, Ishant Sharma became the fifth quickest Indian to grab 100 ODI wickets. While being a "rhythm" bowler, he still is considered one of the fastest Indian bowlers having bowled in excess of 150 km/h on several occasions in international cricket as well as the IPL, his fastest being 152.2 km/h bowled to Ricky Ponting on Boxing Day Test in 2011. In 2020, Indian government has awarded him the Arjuna Award to recognize his outstanding achievement in cricket.


title: Ishant Sharma

text: Ishant plays for Delhi in domestic cricket and has taken 68 wickets in 14 first-class games, including a five-wicket haul against Baroda on the opening day of a match Delhi drew after failing to bowl Baroda out on the fourth day.


title: Ishant Sharma

text: Ishant toured England with the India Under-19s in 2006 and Pakistan in 2006–07. He played three youth tests and six youth One Day Internationals for India. On the basis of his strong performance in Australia in 2008, Ishant Sharma was bought for a winning bid of $950,000 by Kolkata Knight Riders in the player auction for the Indian Premier League. This was the highest amount paid for any bowler in the tournament.


title: Ishant Sharma

text: On 15 February 2018, it was officially announced that Ishant will join Sussex CCC for the first two months of the 2018 county season, available from 4 April to 4 June 2018, thus making him the 9th Indian to play for Sussex.


title: Ishant Sharma

text: In May 2007, Sharma was selected in the test team for the Bangladesh tour and played as a replacement for the fast bowler Munaf Patel. Over there he played for his national side in the second test where he bowled three overs including one maiden and conceded only five runs without taking a wicket. Later on, he was called for the tour of England in July–August 2007.


title: Ishant Sharma

text: Sharma got a call back in the team in the 3rd Test during Pakistan's tour of India in December 2007 due to injury of India's frontline pacers Zaheer Khan, RP Singh, and Sreesanth. Sharma picked up 5 wickets during the third test in Bangalore. This performance earned him a place in India's squad for the tour of Australia.


title: Ishant Sharma

text: Sharma was left out in the Boxing Day Test at Melbourne during the Border–Gavaskar Trophy as India retained their main fast bowlers, Zaheer Khan and RP Singh. However, in January 2008 Sharma was called to represent India once again to replace the injured Zaheer Khan in the second test at the SCG. Sharma started the first day of the match strongly and was involved in a controversial decision from Steve Bucknor when Andrew Symonds nicked the ball to keeper MS Dhoni off his bowling but was given not out. He bowled reasonably in the match, however without much luck.


title: Ishant Sharma

text: Although he had little success, the management retained him for the third Test match at Perth. On the fourth day of the match, he bowled an exceptional spell to Australian captain Ricky Ponting that resulted in his wicket and helped India claim victory. He used the pace and bounce of the WACA wicket to trouble the batsmen. In the following test played in Adelaide he picked up two wickets and impressed everyone with his bowling. He finished the tour of Australia with figures of 6/358, an average of 59.66 and a strike rate of 101.0.


title: Ishant Sharma

text: On 10 February 2008, Sharma bagged four important wickets in the 4th ODI of CB Series against Australia. He ended the match with figures of 4/38 and named Man of the Match. He scalped two important wickets on 18 February 2008 versus Australia in the 7th ODI of CB series.


title: Ishant Sharma

text: During the 2008 Test series against Australia in India, Ishant was the leading wicket-taker, with 16, and was named man-of-the-series as India won 2–0. He thereby became the first Indian paceman to win such an award in a Test series on Indian soil after Kapil Dev who won the award in 1983. He was noted for achieving reverse swing on balls sometimes as young as eight overs, and along with senior opening bowler Zaheer Khan, troubled the touring Australians. He took Australian captain Ricky Ponting's wicket three times during the series, and six times in as many Tests, making the Indian press label Ponting as Ishant's bunny.


title: Ishant Sharma

text: However, in 2009, Ishant's form slumped, and he was dropped for the second Test against Sri Lanka, replaced by Sreesanth.


title: Ishant Sharma

text: On 5 October 2010, Ishant helped VVS Laxman pull off a highly unlikely win over Australia by one wicket in the first Test in Mohali after India had fallen to 8/124 in pursuit of 205. Ishant provided Laxman with support during an 81-run partnership in which he contributed 31 valuable runs.


title: Ishant Sharma

text: In the 2011 IPL auction, Sharma was bought by the Deccan Chargers; he hoped that his performance in the competition would give him a chance to impress selectors and push for selection in India's ODI team. From 12 matches, Sharma took 11 wickets at an average of 28.54. A month after the IPL, which was held in April and May, India toured the West Indies for five ODIs and three Tests. Several senior players were rested from the ODI side and others absent through injury; this mostly affected the batsmen but Zaheer Khan missed the ODI series. India won the first three ODIs, and Sharma was called into the team for the fourth, his first ODI since August 2010. He managed one wicket from two matches in the series while conceding 109 runs. The first Test resulted in a win for India and Sharma took three wickets in each innings. He claimed his 100th Test wicket in the second Test, becoming the fifth youngest to reach the landmark; the fixture was also the first time he took ten wickets in a match for India. The second and third Tests ended in draws and India won the series 1–0; Sharma was the leading wicket-taker on either side with 22 dismissals at an average of 16.86.


title: Ishant Sharma

text: After the tour of West Indies, India suffer a run of eight consecutive defeats in away Tests. In July and August the team played four Tests in England. England inflicted a 4–0 whitewash on India, and in the process replaced India as No. 1 ranked Test team. Playing in all four matches, Sharma managed 11 wickets at an average pushing 60. During the series Sharma suffered an ankle injury and missed the ODI leg, but was sufficiently recovered to face the West Indies in November when India hosted them for three Tests. While India won 2–0, Sharma managed five wickets from three matches at a cost of in excess of 65 runs each. Sharma played in all four Tests of India's tour of Australia in 2011–12. India lost the series 4–0, while Sharma took five wickets at the cost of 451 runs.


title: Ishant Sharma

text: In March 2012, Sharma underwent surgery on his ankle which had been troubling him for over a year. The operation meant that he missed the 2012 IPL.


title: Ishant Sharma

text: In 2013 Ind vs. Aus ODI series, he gave away 30 runs in an over, equalling the most expensive over by an Indian bowler and joining Yuvraj Singh, who himself had previously conceded 30 runs in an ODI match against England in 2007.


title: Ishant Sharma

text: After some bad performances against Australia in 2013 ODI series, he came back strongly against South Africa taking 4/40 in the third ODI on 11 December 2013 at SuperSport Park, which was his 2nd best performance in ODIs.


title: Ishant Sharma

text: In the 2014 tour of England, Sharma secured his career-best figures of 7/74 at the Lord's, with an aggressive spell in England's second innings, bowling India to a 95-run win. During the first test of the series, Sharma suffered the slight ignominy of becoming Alastair Cook's sole Test wicket when caught down the leg side. India finished the series losing 3–1. He finished the 2015 three-match Test series in Sri Lanka with 13 wickets, including a 5-wicket haul in the third Test at SSC. At the end of the match, he was handed a one-match ban by the International Cricket Council (ICC), following an altercation with Dhammika Prasad in the course of the match. The series also saw him pick his 200th wicket in Tests. India won the series 2–1.


title: Ishant Sharma

text: Ishant Sharma has sustained an injury on his right hand during the World Test Championship (WTC) final against New Zealand at the Ageas Bowl in Southampton..


title: Ishant Sharma

text: According to PTI, Ishant Sharma had multiple stitches on his middle and fourth finger in his right hand


title: Ishant Sharma

text: In August 2018, during the fourth Test against England, Sharma took his 250th Test wicket. In the fifth test, he took 3 wickets in England's first innings and thereby equaled Kapil Dev's record of taking the most wickets by an Indian bowler in England. He finished the series as the second-highest wicket taker, with 18 wickets. In following India's tour of Australia, he took 11 wickets in the first 3 tests, before being ruled out of the final test due to an injury.


title: Ishant Sharma

text: In August 2019, Ishant took his 9th Test 5-wicket haul against West Indies in the 1st Test match of India tour of West Indies 2019, at the Sir Vivian Richards Stadium, with figures of 5/43 in the 1st innings. In the 2nd Test match of the same series, batting at No.9, Ishant hit his first half-century in Test Cricket. In February 2021, Ishant completed his 100th Test match against England in the third Test match (2nd day/night Test in India) of England Tour of India, at the Motera Stadium Ishant Sharma became only the 4th Indian bowler to play 100 test matches, the legendary Kapil Dev being the only other fast bowler to achieve the feat.


title: Ishant Sharma

text: A right arm fast-medium bowler, the speed of Sharma's bowling has diminished since he emerged on the international scene, although in 2008 he bowled a delivery at over . Such occurrences were not the norm as his pace dropped to around , but under Eric Simons (who was India's bowling coach from 2010 to 2012) Sharma was regularly bowling in excess of when India toured Australia in 2011/12. According to India's former bowling coach Venkatesh Prasad he is amongst the most dedicated bowler in India's set up.


title: Ishant Sharma

text: Simons noted height was a factor in the length Sharma bowled, saying "For Ishant to hit the stumps, he has to pitch it fuller, and that means the batsman has more chance of keeping it out". Former West Indies fast bowler Courtney Walsh identified two problems with Sharma's bowling action: his head drops when the ball is delivered and the position of his wrist varies. The first takes some of the speed out of the delivery, while the second reduces the chance of the ball seaming and swinging. The former India batsman Sanjay Manjrekar suggested that the lack of movement in Sharma's bowling discouraged him from pitching the ball up so instead, he tends to bowl short. The slower pace of his bowling when he pitches the ball up may explain why the yorker is not an effective delivery for him. Manjrekar went further, saying that "for all his talent and commitment he just does not take enough wickets"; when the remark was made in January 2012, Sharma had a bowling average of nearly 37 from 43 Tests.


title: Ishant Sharma

text: Former Australian great, Glenn McGrath, feels Ishant is more of a workhorse than a strike bowler and needs to figure out his role in the Indian team, but he is happy that Ishant is slowly adapting to conditions, commenting "When Ishant started off, he took the world by storm bowling good pace. He is probably not bowling at the same pace. But he is much more experienced now with good control. The Edgbaston Test showed that Ishant has started adopting a bit more". McGrath also acknowledged the fact that playing on sub-continent tracks might have contributed to a not so impressive record of Ishant and believes that Ishant has to hit the seam more often, saying "You have got to hit the seam and maybe a bit of movement off the pitch will help. My weapon was bounce and occasionally a bit of seam movement"


title: Ishant Sharma

text: Ishant Sharma played for Kings XI Punjab in the Indian Premier League. In December 2018, he was bought by the Delhi Capitals in the player auction for the 2019 Indian Premier League.


title: Ishant Sharma

text: Sharma comes from a Brahmin family. On 10 December 2016, he married Indian basketball player Pratima Singh.


title: Guillermo Vilas

text: Guillermo Vilas (; born 17 August 1952) is an Argentine former professional tennis player. Vilas was the No. 1 of the Grand Prix seasons in 1974, 1975 and 1977, and won four Grand Slam tournaments, one year-end Masters, nine Grand Prix Super Series titles and a total of 62 ATP titles. "World Tennis", "Agence France-Presse" and "Livre d'or du tennis 1977" (Christian Collin-Bernard Ficot), among other rankings and publications, rated him as world No. 1 in 1977 (while others ranked Björn Borg or Jimmy Connors No. 1). In the ATP computer rankings, he peaked at No. 2 in April 1975, a position he held for a total of 83 weeks. He was inducted into the International Tennis Hall of Fame in 1991, two years after his first retirement.


title: Guillermo Vilas

text: Known for his prolific match play, especially on clay, he became the second man to win more than 900 matches in the Open Era, and his number of match-wins on clay (659) is by far the most of the era. His peak was the 1977 season during which he won two major titles (both on clay), had two long match win streaks of 46 all-surface and 53 on clay, and finished with an Open Era record of match wins. In 2016, "The Daily Telegraph" ranked him as the 3rd best male clay-court player of all time, behind Rafael Nadal and Björn Borg. In 2018, Steve Tignor for "Tennis Magazine" ranked him as the 16th greatest tennis player of the Open Era.


title: Guillermo Vilas

text: Historical and statistical studies presented in 2015 by Argentinian journalist Eduardo Puppo and Romanian mathematician Marian Ciulpan concluded that Vilas should have been No. 1 in the old ATP ranking system for seven weeks between 1975 and 1976. The ATP Tour and its chief executive at that time, Chris Kermode, although not refuting the data, decided not to officially recognize Vilas. The controversy is still in the legal stage. In October 2020, Netflix released a documentary film about the Vilas case titled "Guillermo Vilas: Settling the Score".


title: Guillermo Vilas

text: Raised in the seaside resort of Mar del Plata, Vilas was a left-hander and played his first tour event in 1968. He was in the year-ending top ten from 1974 through 1982. He was a clay-court specialist but also played well on hard-court, grass, and carpet surfaces.


title: Guillermo Vilas

text: He won four Grand Slam titles: the 1977 French Open and the 1977 US Open (both played on clay) and the 1978 and 1979 Australian Open (both played on grass). He was also the runner-up at the French Open three times (1975, 1978, and 1982) and at the Australian Open once (January 1977).


title: Guillermo Vilas

text: In 1974, he won the year-end Masters Grand Prix title. In addition, he won seven Grand Prix Super Series titles (1975–80), the precursors to the current Masters 1000.


title: Guillermo Vilas

text: A left-handed baseliner, Vilas's best year on tour was 1977 when he won two of the four Grand Slam singles tournaments and 16 of the 31 Association of Tennis Professionals tournaments he entered. His playing record for 1977 was 130 wins against 15 losses. Not including the Masters year-end championship, he won 72 of his last 73 ATP matches in 1977. The highest point during this run was winning the last US Open played at Forest Hills against Jimmy Connors 2–6, 6–3, 7–6, 6–0 in a match where Vilas surprised his American rival by attacking the net.


title: Guillermo Vilas

text: In 1977 he won seven consecutive titles after Wimbledon—Kitzbühel (clay), Washington (clay), Louisville (clay), South Orange (clay), Columbus (clay), US Open (clay) and Paris (clay)—and set up a 46-match all-surface winning streak. He also had a record 53-match winning streak on clay courts, which stood until surpassed by Rafael Nadal in 2006. Both his winning streaks were terminated in October 1977 by Ilie Năstase in the final of the Raquette d'Or tournament. In that best of five-set final, Vilas dropped the first two sets by 6–1, 7–5 and then retired in protest of Năstase's use of a spaghetti strung racquet (which was banned shortly after by the ITF). After that he won a further 28 matches in a row with titles at Tehran, Bogotá, Santiago, Buenos Aires (all on clay), and Johannesburg (hard). That run was ended in the Masters semi-finals by Björn Borg.


title: Guillermo Vilas

text: Even though he won 16 ATP singles titles, including the French Open and the US Open and was the runner-up at the January edition of the Australian Open in 1977, Vilas was never ranked by the ATP as world No. 1 during 1977 which was due to the fact that the rankings at the time were based on the average of a player's results. He was instead year-end world No. 2, behind Jimmy Connors (who won the Masters and seven other titles and was the runner-up at Wimbledon and the US Open in 1977). Nevertheless, Vilas was rated number one by "World Tennis", "France Presse", "Tennis de France", "Le Livre d'or du Tennis", Gene Scott, Peter Bodo, Christian Quidet, and Michael Sutter. The International Tennis Hall of Fame inscription for Vilas stated "it was generally considered Vilas was the real No. 1 for 1977". Vilas was also rated number one by Bud Collins and John Barrett by the 2010s.


title: Guillermo Vilas

text: Argentine journalist Eduardo Puppo and Romanian mathematician Marian Ciulpan investigated the 1973–78 period records, and delivered a detailed report with more than 1,200 pages in which they came to the conclusion that Vilas should have been ranked No. 1 for five weeks in 1975 as well as during the first two weeks of 1976 and handed over their research to the ATP at the end of 2014. Although the study was not refuted, in May 2015 the ATP announced it had decided not to make official the No. 1 position for Vilas because it happened in the interval between the publications of the official rankings.


title: Guillermo Vilas

text: In October 2020, Netflix released a documentary about the controversy titled "Guillermo Vilas: Settling the Score". It also covered (briefly) Evonne Goolagong Cawley's recognition as world no. 1 (for two weeks in 1976) retrospectively by the WTA in 2007.


title: Guillermo Vilas

text: Vilas retired from the ATP Tour in 1989 but still played on the ATP Challenger Series until 1992. He was inducted into the International Tennis Hall of Fame in 1991. Vilas was in the stands at Flushing Meadows to cheer on his countryman, Juan Martín del Potro, who beat Roger Federer in an upset in the 2009 US Open final.


title: Guillermo Vilas

text: Vilas married Phiangphathu Khumueang in 2005. They have three daughters and one son. They reside in Monaco. He is reportedly suffering from a form of dementia.


title: Future Games

text: Future Games is the fifth studio album by British-American rock band Fleetwood Mac, released on 3 September 1971. It was recorded in the summer of 1971 at Advision Studios in London and was the first album to feature Christine McVie as a full member. This album was also the first of five albums to feature American guitarist Bob Welch. “He was totally different background – R&B, sort of jazzy. He brought his personality,” Mick Fleetwood said of Welch in a 1995 BBC interview. “He was a member of Fleetwood Mac before we'd even played a note.”


title: Future Games

text: The album peaked at number 91 on the US "Billboard 200" chart dated 18 December 1971. The album was certified gold by the Recording Industry Association of America (RIAA) in 2000.


title: Future Games

text: After founder and original bandleader Peter Green departed Fleetwood Mac in May 1970, the remaining members recorded the album "Kiln House", with bassist John McVie's wife Christine Perfect being a major collaborator during the sessions. She was soon promoted to full-time membership as the band's keyboardist, and began writing and singing her own material with them. After guitarist and vocalist Jeremy Spencer abruptly quit the band in February 1971, Fleetwood Mac held auditions for a replacement during the summer and eventually selected Bob Welch after hearing his demo tape.


title: Future Games

text: Without Spencer's Chicago blues and 1950s rock and roll leanings, the band moved further away from blues and closer to the melodic pop sound that would finally break them into America four years later. After the band completed the album and turned it in, the record label said that it would not release an album with only seven songs, and demanded that they record an eighth. "What a Shame" was recorded hastily as a jam to fulfill this request.


title: Future Games

text: Welch's primary guitar at the time was a Gibson ES-345, which he played on the record along with a Fender Stratocaster.


title: Future Games

text: There is an early version of "Morning Rain" with the title "Start Again", as recorded in a BBC session on 5 January 1971.


title: Future Games

text: "What a Shame" featured saxophone from Christine McVie's brother John Perfect whose son Dan later co-produced and featured as guitarist/co-writer on McVie's 2004 album "In the Meantime".


title: Future Games

text: The title track, written by then-newcomer Bob Welch, was later re-recorded for his 1979 solo album "The Other One" and again for "His Fleetwood Mac Years & Beyond" in 2003. The original version is featured in the 2000 movie "Almost Famous".


title: Future Games

text: A heavily edited version of "Sands of Time" (b/w "Lay It All Down") was an unsuccessful single in the United States and some other territories. An alternate version of "Lay It All Down" appeared on the 1992 compilation "25 Years – The Chain". The single edit of "Sands of Time" was released on the deluxe edition of the "50 Years – Don't Stop" compilation in 2018 and later as a bonus track on the 2020 remastered reissue of "Future Games." Also included on the remastered "Future Games" release were alternate mixes of "Sometimes" and "Show Me a Smile", an extended version of "Lay It All Down", the full jam of "What a Shame", plus an acoustic demo of another Welch song, "Stone".