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Related Concept Videos

Linear Approximation in Frequency Domain01:26

Linear Approximation in Frequency Domain

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Linear systems are characterized by two main properties: superposition and homogeneity. Superposition allows the response to multiple inputs to be the sum of the responses to each individual input. Homogeneity ensures that scaling an input by a scalar results in the response being scaled by the same scalar.
In contrast, nonlinear systems do not inherently possess these properties. However, for small deviations around an operating point, a nonlinear system can often be approximated as linear....
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Frequency-Domain Interpretation of PD Control01:24

Frequency-Domain Interpretation of PD Control

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Proportional-Derivative (PD) controllers are widely used in fan control systems to improve stability and performance. A fan control system can be effectively represented using a Bode plot to illustrate the impact of a PD controller through its transfer function. The Bode plot visually conveys how PD control modifies the fan's response across various frequencies, providing a frequency domain interpretation of the controller's behavior.
The proportional control gain, combined with the...
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Time and frequency -Domain Interpretation of PI Control01:27

Time and frequency -Domain Interpretation of PI Control

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Proportional-Integral (PI) controllers are essential in many control systems to improve stability and performance. They are commonly used in everyday devices like thermostats to enhance system damping and reduce steady-state error. When the zero in the controller's transfer function is optimally placed, the system benefits significantly in terms of stability and accuracy.
Acting as a low-pass filter, the PI controller slows the system's response and extends settling times. This requires...
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Time and frequency -Domain Interpretation of Phase-lead Control01:24

Time and frequency -Domain Interpretation of Phase-lead Control

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Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
The design of phase-lead control involves the strategic placement of poles and zeros to balance steady-state error and system...
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Time and frequency -Domain Interpretation of Phase-lag Control01:21

Time and frequency -Domain Interpretation of Phase-lag Control

423
Phase-lag controllers are widely used in control systems to improve stability and reduce steady-state errors. A dimmer switch controlling the brightness of a light bulb serves as a practical example of phase-lag control, gradually adjusting the bulb's brightness. Mathematically, phase-lag control or low-pass filtering is represented when the factor 'a' is less than 1.
Phase-lag controllers do not place a pole at zero, but instead influence the steady-state error by amplifying any...
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The Wave Nature of Light02:12

The Wave Nature of Light

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The nature of light has been a subject of inquiry since antiquity. In the seventeenth century, Isaac Newton performed experiments with lenses and prisms and was able to demonstrate that white light consists of the individual colors of the rainbow combined together. Newton explained his optics findings in terms of a "corpuscular" view of light, in which light was composed of streams of extremely tiny particles traveling at high speeds according to Newton's laws of motion.
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Frequency domain fluorometry with pulsed light-emitting diodes.

Petr Herman1, Jaroslav Vecer

  • 1Faculty of Mathematics and Physics, Charles University, Institute of Physics, Ke Karlovu 5, 121 16 Prague 2, Czech Republic. herman@karlov.mff.cuni.cz

Annals of the New York Academy of Sciences
|July 4, 2008
PubMed
Summary

This study introduces pulsed light-emitting diodes (LEDs) to enhance the time resolution of frequency domain (FD) fluorometers. This cost-effective method improves FD fluorescence spectroscopy by enabling higher modulation frequencies.

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Area of Science:

  • Spectroscopy
  • Analytical Chemistry
  • Physical Chemistry

Background:

  • Frequency domain (FD) fluorometry is a powerful technique for analyzing fluorescence lifetimes.
  • High temporal resolution in FD fluorometry requires excitation light modulated at high frequencies.
  • Standard FD fluorometers often use continuous wave light sources with electro-optical modulators.

Purpose of the Study:

  • To present a simple method for extending the time resolution of standard FD fluorometers.
  • To investigate the use of pulsed light-emitting diodes (LEDs) as an alternative excitation source.
  • To demonstrate an inexpensive approach for FD fluorescence spectroscopy.

Main Methods:

  • Utilized subnanosecond-pulsed LEDs as the excitation source for FD fluorometry.
  • Leveraged the harmonic content of pulsed LEDs to generate modulated excitation light.
  • Replaced the conventional light source and modulator system with pulsed LEDs.

Main Results:

  • Achieved an increased upper frequency limit of 500-600 MHz, nearly tripling the standard limit.
  • Enabled higher temporal resolution in fluorescence decay measurements.
  • Eliminated the need for a separate light modulator, synthesizer, and radio frequency power amplifier.

Conclusions:

  • Pulsed LEDs offer a simple and effective way to enhance the time resolution of FD fluorometers.
  • This method provides an inexpensive alternative to pulsed laser sources for FD fluorescence spectroscopy.
  • The improved instrument performance is demonstrated for ultraviolet-excited fluorescence decays.