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Related Concept Videos

AC Sources01:20

AC Sources

Direct current is a flow of electric charge in only one direction and has a steady state of constant voltage in the circuit. Rectifiers, batteries, commutator-equipped generators, and fuel cells are some examples of devices that generate direct current. Nowadays, most applications use a time-varying voltage source. Alternating current is a flow of electric charge that periodically reverses direction. An alternating current is produced by an alternating emf that is generated in a power plant. If...
Source Transformation for AC Circuits01:11

Source Transformation for AC Circuits

The process of source transformation in the frequency domain entails the conversion of a voltage source, positioned in series with an impedance, into a current source that is parallel to an impedance, or the other way around. It is essential to maintain the following relationships while transitioning from one source type to another.
Conservation of AC Power01:15

Conservation of AC Power

The principle of power preservation is applicable to both ac and dc circuits. This principle, when applied to AC power, asserts that the complex, real, and reactive powers produced by the source are equal to the total complex, real, and reactive powers absorbed by the loads. When two load impedances are connected in parallel to an ac source V, the complex power provided by the source can be calculated using the relation
Newton’s Method01:30

Newton’s Method

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A Single-Component System01:24

A Single-Component System

In the field of chemistry, the terms "component" and "phase" hold significant importance. A component refers to a chemically distinct substance in a system that has specific properties. It is chemically homogeneous, meaning it has the same properties throughout. For example, in a mixture of salt and water, both salt and water are considered separate components because they have different chemical properties.On the other hand, a phase is a form of matter that has a consistent chemical...
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Updated: Jun 20, 2026

Analysis of Multidimensional Microscopy Data Using Cell-ACDC
06:17

Analysis of Multidimensional Microscopy Data Using Cell-ACDC

Published on: November 7, 2025

ACORN2: new developments of the ACORN concept.

E J Dodson1, M M Woolfson

  • 1York Structural Biology Department, Department of Chemistry, University of York, Heslington, York, UK. e.dodson@ysbl.york.ac.uk

Acta Crystallographica. Section D, Biological Crystallography
|August 20, 2009
PubMed
Summary

ACORN2 significantly improves crystal structure solution by enabling refinement from minimal starting data, even a single atom. This advancement aids in solving complex structures with poor initial phase information.

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Area of Science:

  • Crystallography
  • Structural Biology
  • Computational Chemistry

Background:

  • Density modification is crucial for solving crystal structures from limited initial data.
  • ACORN, a CCP4 program, has been successful with starting fragments of 1-8% scattering power.

Purpose of the Study:

  • To report improvements in ACORN, leading to the ACORN2 program.
  • To demonstrate ACORN2's ability to solve structures from extremely poor starting sets, including single atoms.

Main Methods:

  • Utilizing density modification procedures within the ACORN2 program.
  • Applying ACORN2 to crystal structures with space group P1, including those starting with single atoms.
  • Testing ACORN2 with existing trial structures and structures with phases from MAD or molecular replacement.

Main Results:

  • ACORN2 successfully solves and refines structures using starting fragments as small as 0.25% scattering power.
  • ACORN2 breaks centricity in initial phases, converging to correct enantiomorphs even from a single atom at the origin.
  • Demonstrated applications to known structures and refinement with existing phase information.

Conclusions:

  • ACORN2 represents a significant advancement in solving and refining crystal structures.
  • The program is highly effective even with minimal or no prior structural information.
  • ACORN2 expands the applicability of density modification techniques in structural biology.