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Related Concept Videos

Frequency-dependent Selection01:21

Frequency-dependent Selection

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When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.
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What is a Frequency Distribution00:51

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A frequency is the number of times a value of the data occurs. The sum of all the frequency values represents the total number of students included in the sample. It is commonly used to group data of quantitative types. Frequency distributions can be displayed in a table, histogram, line graph, dot plot, or pie chart, just to name a few. A histogram is a graphical representation of tabulated frequencies, shown as adjacent rectangles, erected over discrete intervals (bins), with an area equal to...
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Sometimes, data gathered from an experiment on a large sample or population are organized into concise tables. In such cases, the frequency of the quantitative data set is plotted in the form of a table. Or else, the data values are grouped into the quantity’s intervals, which form classes, and their respective frequencies are known. That is, the data values are distributed over different categories or classes. This is known as frequency distribution.
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The frequency response of a Bipolar Junction Transistor (BJT) in a common-emitter configuration is critical to its functionality, especially in applications involving amplification of alternating current (AC) signals. This response can be analyzed through low-frequency and high-frequency equivalent circuits, considering various internal parameters and external conditions.
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Load-frequency control

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Load-frequency control (LFC) is vital for maintaining power system stability, ensuring that frequency and power flows remain within acceptable limits during load changes. Turbine-governor control eliminates rotor accelerations and decelerations following load changes. However, a steady-state frequency error persists when the change in the turbine-governor reference setting is zero. In an interconnected power system, each area agrees to export or import a scheduled amount of power through...
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Muscle Stimulation Frequency01:22

Muscle Stimulation Frequency

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The contraction strength of muscles is regulated by motor neurons, which modulate the frequency of action potentials dispatched to the motor units based on the body's requirements. This process of varying the muscle stimulation frequency allows muscles to contract with a force that is precisely tailored to the needs of the moment, whether lifting a feather or a heavy box.
Wave summation
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Related Experiment Video

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Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies
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Frequency-tunable continuous-wave random lasers at terahertz frequencies.

Simone Biasco1, Harvey E Beere2, David A Ritchie2

  • 11NEST, CNR - Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy.

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This study demonstrates continuous-wave (CW) random lasers using electrically pumped quantum-cascade gain media. These high-radiance sources offer tunable, artifact-free imaging and sensing applications.

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Area of Science:

  • Optics and Photonics
  • Semiconductor Lasers
  • Disordered Systems

Background:

  • Random lasers offer low spatial coherence ideal for artifact-free imaging.
  • High-radiance, continuous-wave (CW) sources are crucial for sensing, spectroscopy, and speckle-free imaging.

Purpose of the Study:

  • To demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser.
  • To achieve a highly collimated vertical emission at ~3 THz.

Main Methods:

  • Utilized an electrically pumped quantum-cascade laser gain medium.
  • Patterned a bi-dimensional (2D) random distribution of air holes into the top metal waveguide.
  • Employed an external cavity with a movable mirror for tuning.

Main Results:

  • Achieved CW random laser operation at ~3 THz with a 430 GHz bandwidth.
  • Demonstrated device operation up to 110 K, with peak pulsed power of 21 mW and CW emission of 1.7 mW.
  • Obtained continuous frequency tuning over 11 GHz using an external cavity.

Conclusions:

  • The developed random laser provides a high-radiance, tunable CW source.
  • This technology is promising for applications in artifact-free imaging, sensing, and spectroscopy.