Civil Rights
Movements, leaders, victories and the continuing fight for equality.
q2K BHP
Black History Portal
THE BHP WIRE —
HIDDEN TRUTHS
What's New!
Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Olex[1][2] and Olex2[3][4] are versatile software for crystallographic research. Olex used to be a research project developed during PhD to implement topological (as connectivity) analysis of polymeric chemical structures and still is widely used around the world. Olex2 is an open source project with the C++ code portable to Windows, Mac and Linux. Although the projects share the common name they are not related at the source code level.
The Olex program is designed for the analysis of extended structural networks. It only runs on Windows systems and source code is available only on request. It allows packing the structure, constructing the topological network and the evaluation of the networks Schläfli[5] and vertex[6] symbols[7] and to produce raster pictures of the model visible on screen. This kind of the topological network analysis is normally done to find relevance of considered structures and possibly to predict physical properties of the investigated material.
Olex2 is a relatively mature open source software[8][9] with a BSD licence which provides tools for crystallographic structure solution, refinement, and final report preparation. It is still in the stage of active development. Olex2 provides numerous tools for structure analysis and publication, including Fourier maps, void calculation and visualisation, space group determination, calculation of esd's for almost any possible geometrical parameters, CIF translation to HTML and other document formats, hydrogen atom placement, and many others. Olex2 can also provide the final graphic output as raster images or PostScript, Ortep[10]-like or POV-Ray output.
The independent GUI for the Olex2 platform is provided by wxWidgets.[11] Olex2 has an extended HTML based interface, enhanced by Pillow[12] and OpenGL graphics. The software is provided as pre-built binaries for Windows, Mac and Linux as well as in the source code form. Several build scripts (SCons, CMake and make) are provided to help with Olex2 development, but only SCons is supported throughout and used for each release update. Any problems and bugs have to be reported to the supporters, now under OlexSys Ltd.[13]
As a GUI Olex2 is built from two components - the Olex2 core, written in C++ and exposing the underlying model to the GUI, which is mostly based on Python code. This segregation allows extending Olex2 with custom scripts and exploiting its functionality by the user at various levels, such as Miller index operations, file manipulations, and many others.
Olex2 provides a set of commercial extensions:
{{cite book}}: CS1 maint: publisher location (link)
| Key concepts |
|  | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Characterisation | ||||||||||||||
| Algorithms | ||||||||||||||
| Software | ||||||||||||||
| Databases | ||||||||||||||
| Journals | ||||||||||||||
| Awards | ||||||||||||||
| History | ||||||||||||||
| Organisation |
| |||||||||||||
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Olex and Olex2 are versatile software for crystallographic research. Olex used to be a research project developed during PhD to implement topological (as connectivity) analysis of polymeric chemical structures and still is widely used around the world. Olex2 is an open source project with the C++ code portable to Windows, Mac and Linux. Although the projects share the common name they are not related at the source code level.
Olex may refer to: Olex, Oregon, an unincorporated community in Gilliam County, Oregon, United States Olex2, software for crystallographic research OLEX (company) (Aktiengesellschaft für österreichische und ungarische Mineralölprodukte), a former Austrian-Hungarian oil company
Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes. This article provides an overview of electron diffraction and electron diffraction patterns, collectively referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It also involves the extensive history behind modern electron diffraction, how the combination of developments in the 19th century in understanding and controlling electrons in vacuum and the early 20th century developments with electron waves were combined with early instruments, giving birth to electron microscopy and diffraction in 1920–1935. While this was the birth, there have been a large number of further developments since then. There are many types and techniques of electron diffraction. The most common approach is where the electrons transmit through a thin sample, from 1 nm to 100 nm (10 to 1000 atoms thick), where the results depend upon how the atoms are arranged in the material, for instance a single crystal, many crystals or different types of solids. Other cases such as larger repeats, no periodicity or disorder have their own characteristic patterns. There are many different ways of collecting diffraction information, from parallel illumination to a converging beam of electrons or where the beam is rotated or scanned across the sample which produce information that is often easier to interpret. There are also many other types of instruments. For instance, in a scanning electron microscope (SEM), electron backscatter diffraction can be used to determine crystal orientation across the sample. Electron diffraction patterns can also be used to characterize molecules using gas electron diffraction, liquids, surfaces using lower energy electrons, a technique called LEED, and by reflecting electrons off surfaces, a technique called RHEED. There are also many levels of analysis of electron diffraction, including: The simplest approximation using the de Broglie wavelength for electrons, where only the geometry is considered and often Bragg's law is invoked. This approach only considers the electrons far from the sample, a far-field or Fraunhofer approach. The first level of more accuracy where it is approximated that the electrons are only scattered once, which is called kinematical diffraction and is also a far-field or Fraunhofer approach. More complete and accurate explanations where multiple scattering is included, what is called dynamical diffraction (e.g. refs). These involve more general analyses using relativistically corrected Schrödinger equation methods, and track the electrons through the sample, being accurate both near and far from the sample (both Fresnel and Fraunhofer diffraction). Although similar to x-ray and neutron diffraction, where the simplest approximations are quite accurate, simple models for electron diffraction only provide the geometry of the intensities in a diffraction pattern. Dynamical diffraction approaches are needed to calculate more accurate intensities and the positions of diffraction spots.
The program ShelXle is a graphical user interface for the structure refinement program SHELXL. ShelXle combines an editor with syntax highlighting for the SHELXL-associated .ins (input) and .res (output) files with an interactive graphical display for visualization of a three-dimensional structure including the electron density (Fo) and difference density (Fo-Fc) maps.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Joe Louis.
