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Frequency
FREQUENCY is the number of occurrences of a repeating event per unit time . It is also referred to as TEMPORAL FREQUENCY, which emphasizes the contrast to spatial frequency and angular frequency . The PERIOD is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second (that is, 60 seconds divided by 120 beats ). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio (sound ) signals, radio waves , and light . CONTENTS * 1 Definitions * 2 Units * 3 Period versus frequency * 4 Related types of frequency * 5 In wave propagation * 6 Measurement * 6.1 Counting * 6.2 Stroboscope * 6.3 Frequency counter * 6.4 Heterodyne methods * 7 Examples * 7.1 Light * 7.2 Sound * 7.3 Line current * 8 See also * 9 Notes and references * 10 Further reading * 11 External links DEFINITIONS As time elapses—here moving left to right on the horizontal axis—the five sinusoidal waves vary, or cycle, regularly at different rates
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Aperiodic Frequency
APERIODIC FREQUENCY is the rate of incidence or occurrence of non-cyclic phenomena, including random processes such as radioactive decay . It is expressed in units of measurement of reciprocal seconds or, in the case of radioactivity, becquerels . It is defined as a ratio , f = N/T, involving the number of times an event happened (N) during a given time duration (T); it is a physical quantity of type temporal rate . SEE ALSO * Frequency (statistics) This science article is a stub . You can help by expanding it . * v * t * e Retrieved from "https://en.wikipedia.org/w/index.php?title=Aperiodic_frequency additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy .® is a registered trademark of the Wikimedia Foundation, Inc
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Frequency (statistics)
In statistics the FREQUENCY (or ABSOLUTE FREQUENCY) of an event i {displaystyle i} is the number n i {displaystyle n_{i}} of times the event occurred in an experiment or study. :12–19 These frequencies are often graphically represented in histograms . CONTENTS * 1 Types of frequency * 2 Depictions of frequency * 2.1 Histograms * 2.2 Bar graphs * 2.3 Frequency distribution table * 3 Frequentist interpretation of probability * 4 See also * 5 References TYPES OF FREQUENCYThe CUMULATIVE FREQUENCY is the total of the absolute frequencies of all events at or below a certain point in an ordered list of events. :17–19 The RELATIVE FREQUENCY (or empirical probability ) of an event is the absolute frequency normalized by the total number of events: f i = n i N = n i j n j . {displaystyle f_{i}={frac {n_{i}}{N}}={frac {n_{i}}{sum _{j}n_{j}}}.} The values of f i {displaystyle f_{i}} for all events i {displaystyle i} can be plotted to produce a frequency distribution . In the case when n i = 0 {displaystyle n_{i}=0} for certain i, pseudocounts can be added
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Temporal Rate
In mathematics , a RATE is the ratio between two related quantities . If the denominator of the ratio is expressed as a single unit of one of these quantities, and if it is assumed that this quantity can be changed systematically (i.e., is an independent variable ), then the numerator of the ratio expresses the corresponding rate of change in the other (dependent) variable. The most common type of rate is "per unit of time", such as speed , heart rate and flux . Ratios that have a non-time denominator include exchange rates , literacy rates and electric field (in volts/meter). In describing the units of a rate, the word "per" is used to separate the units of the two measurements used to calculate the rate (for example a heart rate is expressed "beats per minute"). A rate defined using two numbers of the same units (such as tax rates ) or counts (such as literacy rate ) will result in a dimensionless quantity , which can be expressed as a percentage (for example, the global literacy rate in 1998 was 80%) or fraction or as a multiple
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Si Unit
The INTERNATIONAL SYSTEM OF UNITS (abbreviated as SI, from the French _Système internationale (d'unités)_) is the modern form of the metric system , and is the most widely used system of measurement . It comprises a coherent system of units of measurement built on seven base units . The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metre-kilogram-second system of units (MKS) rather than any variant of the centimetre–gram–second system (CGS). SI is intended to be an evolving system, so prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves. The 24th and 25th General Conferences on Weights and Measures (CGPM) in 2011 and 2014, for example, discussed a proposal to change the definition of the kilogram , linking it to an invariant of nature rather than to the mass of a material artefact, thereby ensuring long-term stability. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems and the lack of coordination between the various disciplines that used them
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Hertz
The HERTZ (symbol: Hz) is the derived unit of frequency in the International System of Units
International System of Units
(SI) and is defined as one cycle per second . It is named for Heinrich Rudolf Hertz
Hertz
, the first person to provide conclusive proof of the existence of electromagnetic waves . Hertz
Hertz
are commonly expressed in multiples : kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), and terahertz (1012 Hz, THz). Some of the unit's most common uses are in the description of sine waves and musical tones , particularly those used in radio - and audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven. CONTENTS * 1 Definition * 2 History * 3 Applications * 3.1 Vibration * 3.2 Electromagnetic radiation * 3.3 Computers * 4 SI multiples * 5 See also * 6 Notes and references * 7 External links DEFINITIONThe hertz is equivalent to cycles per second , i.e., "1/second" or s 1 {displaystyle {text{s}}^{-1}}
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SI Base Unit
The International System of Units
International System of Units
(SI) defines seven units of measure as a basic set from which all other SI units can be derived . The SI BASE UNITS and their physical quantities are the metre for measurement of length , the kilogram for mass , the second for time , the ampere for electric current , the kelvin for temperature , the candela for luminous intensity , and the mole for amount of substance . The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology. The names and symbols of SI base units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter. For example, the metre (US English: meter) has the symbol m, but the kelvin has symbol K, because it is named after Lord Kelvin
Kelvin
and the ampere with symbol A is named after André-Marie Ampère
André-Marie Ampère
. Other units, such as the litre (US English: liter), are formally not part of the SI, but are accepted for use with SI
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Second
The SECOND (symbol: S) (abbreviated S or SEC) is the base unit of time in the International System of Units
International System of Units
/ Système International d'Unités (SI). It is qualitatively defined as the second division of the hour by sixty, the first division by sixty being the minute . The SI definition of second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". Seconds may be measured using a mechanical, electrical or an atomic clock . SI prefixes are combined with the word second to denote subdivisions of the second, e.g., the millisecond (one thousandth of a second), the microsecond (one millionth of a second), and the nanosecond (one billionth of a second). Though SI prefixes may also be used to form multiples of the second such as kilosecond (one thousand seconds), such units are rarely used in practice. The more common larger non-SI units of time are not formed by powers of ten; instead, the second is multiplied by 60 to form a minute, which is multiplied by 60 to form an hour , which is multiplied by 24 to form a day . The second is also the base unit of time in other systems of measurement : the centimetre–gram–second , metre–kilogram–second , metre–tonne–second , and foot–pound–second systems of units
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Dimensional Analysis
In engineering and science , DIMENSIONAL ANALYSIS is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length , mass , time , and electric charge ) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms vs. grams) and tracking these dimensions as calculations or comparisons are performed. Converting from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the FACTOR-LABEL METHOD, also known as the UNIT-FACTOR METHOD, is a widely used technique for such conversions using the rules of algebra . The concept of PHYSICAL DIMENSION was introduced by Joseph Fourier
Joseph Fourier
in 1822. Physical quantities that are of the same kind (also called commensurable) have the same dimension (length, time, mass) and can be directly compared to each other, even if they are originally expressed in differing units of measure (such as inches and meters, or pounds and newtons). If physical quantities have different dimensions (such as length vs. mass), they cannot be expressed in terms of similar units and cannot be compared in quantity (also called incommensurable). For example, asking whether a kilogram is greater than, equal to, or less than an hour is meaningless
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Multiplicative Inverse
In mathematics , a MULTIPLICATIVE INVERSE or RECIPROCAL for a number x, denoted by 1/x or x−1, is a number which when multiplied by x yields the multiplicative identity , 1. The multiplicative inverse of a fraction a/b is b/a. For the multiplicative inverse of a real number, divide 1 by the number. For example, the reciprocal of 5 is one fifth (1/5 or 0.2), and the reciprocal of 0.25 is 1 divided by 0.25, or 4. The RECIPROCAL FUNCTION, the function f(x) that maps x to 1/x, is one of the simplest examples of a function which is its own inverse (an involution ). The term reciprocal was in common use at least as far back as the third edition of Encyclopædia Britannica (1797) to describe two numbers whose product is 1; geometrical quantities in inverse proportion are described as reciprocall in a 1570 translation of Euclid
Euclid
's Elements . In the phrase multiplicative inverse, the qualifier multiplicative is often omitted and then tacitly understood (in contrast to the additive inverse ). Multiplicative inverses can be defined over many mathematical domains as well as numbers. In these cases it can happen that ab ≠ ba; then "inverse" typically implies that an element is both a left and right inverse . The notation f −1 is sometimes also used for the inverse function of the function f, which is not in general equal to the multiplicative inverse
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Time
_TIME_ is an American weekly news magazine published in New York City . It was founded in 1923 and for decades was dominated by Henry Luce
Henry Luce
, who built a highly profitable stable of magazines. A European edition (_ Time
Time
Europe_, formerly known as _ Time
Time
Atlantic_) is published in London and also covers the Middle East, Africa and, since 2003, Latin America. An Asian edition (_ Time
Time
Asia_) is based in Hong Kong
Hong Kong
. The South Pacific edition, which covers Australia, New Zealand and the Pacific Islands , is based in Sydney
Sydney
, Australia. In December 2008, _Time_ discontinued publishing a Canadian advertiser edition. _Time_ has the world's largest circulation for a weekly news magazine, and has a readership of 26 million, 20 million of which are based in the United States. In mid-2016, its circulation was 3,032,581, having fallen from 3.3 million in 2012. Richard Stengel was the managing editor from May 2006 to October 2013, when he joined the U.S. State Department . Nancy Gibbs has been the managing editor since October 2013
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Spatial Frequency
In mathematics , physics , and engineering , SPATIAL FREQUENCY is a characteristic of any structure that is periodic across position in space . The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier transform ) of the structure repeat per unit of distance. The SI unit of spatial frequency is cycles per meter . In image-processing applications, spatial frequency is often expressed in units of cycles per millimeter or equivalently line pairs per millimeter. In wave mechanics, the spatial frequency is commonly denoted by {displaystyle xi } or sometimes {displaystyle nu } , although the latter is also used to represent temporal frequency . It is related to the wavelength {displaystyle lambda } by the formula = 1 . {displaystyle xi ={frac {1}{lambda }}.} Likewise, the angular wave number k {displaystyle k} , measured in radians per meter, is related to spatial frequency and wavelength by k = 2 = 2 . {displaystyle k=2pi xi ={frac {2pi }{lambda }}.} CONTENTS* 1 Visual perception * 1.1 Spatial-frequency theory * 1.2 Sinusoidal gratings and Michelson equation * 2 See also * 3 References * 4 External links VISUAL PERCEPTIONIn the study of visual perception , sinusoidal gratings are frequently used to probe the capabilities of the visual system
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Angular Frequency
In physics , ANGULAR FREQUENCY ω (also referred to by the terms ANGULAR SPEED, RADIAL FREQUENCY, CIRCULAR FREQUENCY, ORBITAL FREQUENCY, RADIAN FREQUENCY, and PULSATANCE) is a scalar measure of rotation rate. It refers to the angular displacement per unit time (e.g., in rotation) or the rate of change of the phase of a sinusoidal waveform (e.g., in oscillations and waves), or as the rate of change of the argument of the sine function. Angular frequency (or angular speed) is the magnitude of the vector quantity angular velocity . The term ANGULAR FREQUENCY VECTOR {displaystyle {vec {omega }}} is sometimes used as a synonym for the vector quantity angular velocity. One revolution is equal to 2π radians , hence = 2 T = 2 f , {displaystyle omega ={{2pi } over T}={2pi f},} where: ω is the angular frequency or angular speed (measured in radians per second ), T is the period (measured in seconds ), f is the ordinary frequency (measured in hertz ) (sometimes symbolised with ν ). CONTENTS * 1 Units * 2 Circular motion * 2.1 Oscillations of a spring * 2.2 LC circuits * 3 See also * 4 References and notes * 5 External links UNITSIn SI units , angular frequency is normally presented in radians per second , even when it does not express a rotational value
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Turn (geometry)
A TURN is a unit of plane angle measurement equal to 2π radians , 360 degrees or 400 gradians . A turn is also referred to as a REVOLUTION or COMPLETE ROTATION or FULL CIRCLE or CYCLE or REV or ROT. A turn can be subdivided in many different ways: into half turns, quarter turns, centiturns, milliturns, binary angles, points etc. CONTENTS * 1 Subdivision of turns * 2 History * 3 Unit conversion * 4 Tau
Tau
proposal * 5 Examples of use * 6 Kinematics
Kinematics
of turns * 7 See also * 8 Notes and references * 9 External links SUBDIVISION OF TURNSA turn can be divided in 100 centiturns or 1000 milliturns, with each milliturn corresponding to an angle of 0.36°, which can also be written as 21′ 36″. A protractor divided in centiturns is normally called a percentage protractor. Binary fractions of a turn are also used. Sailors have traditionally divided a turn into 32 compass points . The binary degree, also known as the binary radian (or brad), is  1⁄256 turn. The binary degree is used in computing so that an angle can be represented to the maximum possible precision in a single byte . Other measures of angle used in computing may be based on dividing one whole turn into 2n equal parts for other values of n. The notion of turn is commonly used for planar rotations
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Heart Sound
HEART SOUNDS are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation , an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart. In healthy adults, there are two normal heart sounds often described as a lub and a dub (or dup), that occur in sequence with each heartbeat. These are the FIRST HEART SOUND (S1) and SECOND HEART SOUND (S2), produced by the closing of the atrioventricular valves and semilunar valves , respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs , adventitious sounds , and gallop rhythms S3 and S4 . Heart
Heart
murmurs are generated by turbulent flow of blood, which may occur inside or outside the heart. Murmurs may be physiological (benign) or pathological (abnormal). Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, resulting in turbulence as blood flows through it. Abnormal murmurs may also occur with valvular insufficiency (regurgitation ), which allows backflow of blood when the incompetent valve closes with only partial effectiveness. Different murmurs are audible in different parts of the cardiac cycle , depending on the cause of the murmur
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