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Related Concept Videos

Phase Changes01:19

Phase Changes

Phase transitions play an important theoretical and practical role in the study of heat flow. In melting or fusion, a solid turns into a liquid; the opposite process is freezing. In evaporation, a liquid turns into a gas; the opposite process is condensation.
A substance melts or freezes at a temperature called its melting point and boils or condenses at its boiling point. These temperatures depend on pressure. High pressure favors the denser form of the substance, so typically, high pressure...
Phasors01:12

Phasors

Phasors are a powerful mathematical tool used to analyze alternating current (AC) circuits. They provide a complex number representation of sinusoids, with the magnitude of the phasor equating to the amplitude of the sinusoid and the angle of the phasor representing the phase measured from the positive x-axis.
One of the significant benefits of using phasors is that they simplify the analysis of AC circuits by eliminating the time dependence of the current and voltage. This transformation...
Phasor Arithmetics01:13

Phasor Arithmetics

Phasors and their corresponding sinusoids are interrelated, offering unique insights into the behavior of alternating current (AC) circuits. One way to understand this relationship is through the operations of differentiation and integration in both the time and phasor domains.
When the derivative of a sinusoid is taken in the time domain, it transforms into its corresponding phasor multiplied by j-omega (jω) in the phasor domain, where j is the imaginary unit, and ω is the angular frequency.
The Phase Rule01:20

The Phase Rule

The phase rule describes the relationship between the variance (degrees of freedom), the number of components, and the number of phases in a system at equilibrium.Variance is a concept that denotes the number of independent intensive properties (properties are those that do not depend on the amount of material in the system), such as temperature, pressure, and composition, that can be altered without impacting the number of phases in equilibrium.In a single-component system, such as pure water,...
Phase-lead and Phase-lag Controllers01:22

Phase-lead and Phase-lag Controllers

Understanding the working function of different types of controllers can be illustrated with practical analogies, such as adjusting a stereo's volume equalizer. Cranking up the bass involves a phase-lead controller, which functions as a high-pass filter, while increasing the treble uses a phase-lag controller, which acts as a low-pass filter. PD controllers, similar to high-pass filters, enhance the system's response to high-frequency components. PI controllers, akin to low-pass filters, manage...
Time and frequency -Domain Interpretation of Phase-lead Control01:24

Time and frequency -Domain Interpretation of Phase-lead Control

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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Related Experiment Video

Updated: Jun 8, 2026

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator
08:39

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator

Published on: January 28, 2019

Phasing from an envelope.

Q Hao1

  • 1Cornell High-Energy Synchrotron Source and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA. qh22@cornell.edu

Acta Crystallographica. Section D, Biological Crystallography
|September 22, 2001
PubMed
Summary
This summary is machine-generated.

This study presents a novel method for solving the crystallographic phase problem using low-resolution molecular shapes from X-ray scattering. This approach aids ab initio protein structure determination when homologous structures are unknown.

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Area of Science:

  • Structural Biology
  • Crystallography
  • Biophysics

Background:

  • Solving the phase problem is crucial for crystallographic structure determination.
  • Conventional molecular replacement fails without homologous protein structures.

Purpose of the Study:

  • To develop and generalize a method for ab initio protein structure determination.
  • To facilitate structure determination when homologous structures are unavailable.

Main Methods:

  • Utilizing low-resolution molecular shape from solution X-ray scattering data.
  • Performing direct real-space searches for orientation and translation.
  • Reducing the search space from six to four dimensions using self-rotation analysis.
  • Generalizing the FSEARCH program for all space groups and various envelope sources.

Main Results:

  • Successfully located molecular shapes within the crystallographic unit cell for trimeric nitrite reductase (105 kDa) and dimeric superoxide dismutase (32 kDa).
  • Demonstrated the program's versatility for different space groups and envelope data (e.g., electron microscopy, solution scattering).

Conclusions:

  • The developed method effectively aids in solving the crystallographic phase problem.
  • This approach significantly facilitates ab initio protein structure determination and provides a foundation for refinement.