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Related Concept Videos

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,...
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...
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.
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...
Phase Transitions02:31

Phase Transitions

Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to occupy...

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Related Experiment Video

Updated: Jun 14, 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

Introduction to phasing.

Garry L Taylor1

  • 1Centre for Biomolecular Sciences, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland. glt2@st-andrews.ac.uk

Acta Crystallographica. Section D, Biological Crystallography
|April 13, 2010
PubMed
Summary
This summary is machine-generated.

The X-ray crystallography phase problem hinders molecular imaging. Modern methods, including anomalous scattering and single-wavelength anomalous diffraction (SAD), increasingly resolve this challenge for protein structure determination.

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Related Experiment Videos

Last Updated: Jun 14, 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

Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station
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Characterization of SiN Integrated Optical Phased Arrays on a Wafer-Scale Test Station

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Phase Contrast and Differential Interference Contrast (DIC) Microscopy
06:49

Phase Contrast and Differential Interference Contrast (DIC) Microscopy

Published on: August 6, 2008

Area of Science:

  • Crystallography
  • Structural Biology
  • Biophysics

Background:

  • X-ray diffraction measures scattered wave intensities from crystal planes.
  • The experimental process loses crucial phase information, creating the 'phase problem' essential for molecular imaging.
  • Reconstructing molecular images requires both wave amplitudes and phases.

Purpose of the Study:

  • To explore methods for solving the phase problem in X-ray crystallography.
  • To highlight advancements in protein structure determination using diffraction data.
  • To discuss the evolution of phase determination techniques from historical approaches to modern applications.

Main Methods:

  • Small-molecule crystallography methods leverage atomicity assumptions for phase extraction.
  • Protein crystallography commonly employs molecular replacement or heavy-atom methods (MIR, SIR, MAD, SAD).
  • Anomalous scattering, particularly with selenium or sulfur, and single-wavelength anomalous diffraction (SAD) are increasingly utilized.

Main Results:

  • Traditional methods like isomorphous replacement pioneered by Perutz and Kendrew involved adding heavy atoms.
  • Modern techniques integrate small-molecule crystallography approaches to find heavy-atom substructures.
  • Advances in X-ray sources, detectors, and software enable routine use of anomalous scattering for phase determination.

Conclusions:

  • The phase problem remains a central challenge in X-ray crystallography, especially for proteins.
  • Anomalous scattering and SAD, often requiring only a single dataset, offer powerful solutions.
  • These advanced methods, combined with density modification, facilitate the complete structure determination of proteins.