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The two main types of tests detect either the presence of the virus or antibodies produced in response to infection. [ 1 ][ 2 ] Molecular tests for viral presence through its molecular components are used to diagnose individual cases and to allow public health authorities to trace and contain outbreaks.
This is a list of countries and other inhabited territories of the world by total population, based on estimates published by the United Nations in the 2024 revision of World Population Prospects. It presents population estimates from 1950 to the present. [2] List. Data are mid-year estimates from the United Nations and are for 2022 and 2023. [2]
Croatia (/ k r oʊ ˈ eɪ ʃ ə / , kroh-AY-shə; Croatian: Hrvatska, pronounced [xř ʋaːtskaː]), officially the Republic of Croatia (Croatian: Republika Hrvatska listen ), [d] is a country in Central and Southeast Europe, on the coast of the Adriatic Sea.It borders Slovenia to the northwest, Hungary to the northeast, Serbia to the east, Bosnia and Herzegovina and Montenegro to the ...
- Earth
- History
- Basic Concepts
- Equations
- Dependence on The Properties of The Medium
- Altitude Variation and Implications For Atmospheric Acoustics
- Details
- Effect of Frequency and Gas Composition
- Mach Number
- Experimental Methods
In Earth's atmosphere, the speed of sound varies greatly from about 295 m/s (1,060 km/h; 660 mph) at high altitudes to about 355 m/s (1,280 km/h; 790 mph) at high temperatures.
Sir Isaac Newton's 1687 Principia includes a computation of the speed of sound in air as 979 feet per second (298 m/s). This is too low by about 15%. The discrepancy is due primarily to neglecting the (then unknown) effect of rapidly fluctuating temperature in a sound wave (in modern terms, sound wave compression and expansion of air is an adiabati...
The transmission of sound can be illustrated by using a model consisting of an array of spherical objects interconnected by springs. In real material terms, the spheres represent the material's molecules and the springs represent the bondsbetween them. Sound passes through the system by compressing and expanding the springs, transmitting the acoust...
The speed of sound in mathematical notation is conventionally represented by c, from the Latin celeritasmeaning "swiftness". For fluids in general, the speed of sound cis given by the Newton–Laplace equation: 1. K s {\displaystyle K_{s}} is a coefficient of stiffness, the isentropic bulk modulus(or the modulus of bulk elasticity for gases); 2. ρ {\...
The speed of sound is variable and depends on the properties of the substance through which the wave is travelling. In solids, the speed of transverse (or shear) waves depends on the shear deformation under shear stress (called the shear modulus), and the density of the medium. Longitudinal (or compression) waves in solids depend on the same two fa...
In the Earth's atmosphere, the chief factor affecting the speed of sound is the temperature. For a given ideal gas with constant heat capacity and composition, the speed of sound is dependent solely upon temperature; see § Detailsbelow. In such an ideal case, the effects of decreased density and decreased pressure of altitude cancel each other out,...
Speed of sound in ideal gases and air
For an ideal gas, K (the bulk modulus in equations above, equivalent to C, the coefficient of stiffness in solids) is given by 1. γ is the adiabatic index also known as the isentropic expansion factor. It is the ratio of the specific heat of a gas at constant pressure to that of a gas at constant volume (C p / C v {\displaystyle C_{p}/C_{v}} ) and arises because a classical sound wave induces an adiabatic compression, in which the heat of the compression does not have enough time to escape th...
Effects due to wind shear
The speed of sound varies with temperature. Since temperature and sound velocity normally decrease with increasing altitude, sound is refracted upward, away from listeners on the ground, creating an acoustic shadow at some distance from the source. Wind shear of 4 m/(s · km) can produce refraction equal to a typical temperature lapse rate of 7.5 °C/km. Higher values of wind gradient will refract sound downward toward the surface in the downwind direction,eliminating the acoustic shadow on the...
Tables
In the standard atmosphere: 1. T0 is 273.15 K (= 0 °C = 32 °F), giving a theoretical value of 331.3 m/s (= 1086.9 ft/s = 1193 km/h = 741.1 mph = 644.0 kn). Values ranging from 331.3 to 331.6 m/smay be found in reference literature, however; 2. T20 is 293.15 K (= 20 °C = 68 °F), giving a value of 343.2 m/s (= 1126.0 ft/s = 1236 km/h = 767.8 mph = 667.2 kn); 3. T25 is 298.15 K (= 25 °C = 77 °F), giving a value of 346.1 m/s (= 1135.6 ft/s = 1246 km/h = 774.3 mph = 672.8 kn). In fact, assuming an...
General physical considerations
The medium in which a sound wave is travelling does not always respond adiabatically, and as a result, the speed of sound can vary with frequency. The limitations of the concept of speed of sound due to extreme attenuation are also of concern. The attenuation which exists at sea level for high frequencies applies to successively lower frequencies as atmospheric pressure decreases, or as the mean free path increases. For this reason, the concept of speed of sound (except for frequencies approa...
Practical application to air
By far, the most important factor influencing the speed of sound in air is temperature. The speed is proportional to the square root of the absolute temperature, giving an increase of about 0.6 m/sper degree Celsius. For this reason, the pitch of a musical wind instrument increases as its temperature increases. The speed of sound is raised by humidity. The difference between 0% and 100% humidity is about 1.5 m/sat standard pressure and temperature, but the size of the humidity effect increase...
Mach number, a useful quantity in aerodynamics, is the ratio of air speed to the local speed of sound. At altitude, for reasons explained, Mach number is a function of temperature.Aircraft flight instruments, however, operate using pressure differential to compute Mach number, not temperature. The assumption is that a particular pressure represents...
A range of different methods exist for the measurement of sound in air. The earliest reasonably accurate estimate of the speed of sound in air was made by William Derham and acknowledged by Isaac Newton. Derham had a telescope at the top of the tower of the Church of St Laurence in Upminster, England. On a calm day, a synchronized pocket watch woul...
TSMC Global R＆D Center at night. Taiwan Semiconductor Manufacturing Company Limited (TSMC or Taiwan Semiconductor) [4][5] is a Taiwanese multinational semiconductor contract manufacturing and design company. It is the world's second-most valuable semiconductor company, [6] the world's largest dedicated independent ("pure-play") semiconductor ...
The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).
Salma Valgarma Hayek Pinault (/ ˈhaɪɛk / HY-ek, [2] Spanish: [ˈsalma ˈxaʝek]; née Hayek Jiménez; born September 2, 1966) [3][4][5] is an actress and film producer. She began her career in Mexico with starring roles in the telenovela Teresa (1989–1991) as well as the romantic drama Midaq Alley (1995).
