computer science

VITESS

VITESS is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand VITESS rather than just read about it. In short: The Virtual Instrumentation Tool for the ESS (VITESS) is an open source software package for the simulation of neutron scattering experiments. The software is maintained and developed by the Forschungszentrum Jülich (FZJ), and available for Windows, Linux and Macintosh on the VITESS homepage.

Key takeaways

VITESS belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect VITESS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of VITESS from memory before moving on to harder problems.

Reference excerpt

The Virtual Instrumentation Tool for the ESS (VITESS) is an open source software package for the simulation of neutron scattering experiments. The software is maintained and developed by the Forschungszentrum Jülich (FZJ), and available for Windows, Linux and Macintosh on the VITESS homepage. It is widely used for simulation of existing neutron scattering instruments as well as for the development of new instruments. VITESS was initiated by F. Mezei in 1998, closely followed by the first release of VITESS in 1999 and version 2 in 2001. The best source of information about the current version and planned releases is the software homepage. Although it was initially developed to aid the design of neutron scattering instruments for the European Spallation Source (ESS) as the name implies, VITESS serves as a generic simulation tool for a large variety of neutron scattering instruments at all major pulsed or continuous neutron sources. It comprises all established instrument hardware such as neutron optics (e.g. guides, apertures, lenses), wavelength selectors (e.g. disc choppers, velocity selectors) and a growing variety of samples, allowing to perform virtual experiments including sophisticated setups like polarized neutrons in magnetic fields. Parameters specifying the instrument components can be given by means of a graphical user interface, which makes VITESS comparably easy to use and quick to learn for new users, while advanced users can contribute their own modules. The validity of VITESS simulations is tested by comparison with other neutron simulation packages and with measurements at neutron scattering facilities. Other simulation packages for neutron scattering instruments include McStas, Restrax, NISP and IDEAS.

Working principle VITESS simulations are carried out by means of a Monte Carlo ray-tracing method. Neutron trajectories are created in a source module or loaded from a file created in a previous simulation. Each neutron is assigned a count rate which is modified on each interaction with the instrument, like the reflection at or transmission through a (super)mirror plate. The trajectory is discarded if the neutron does not hit the subsequent component or gets absorbed. Some components (e.g. sample environment) can multiply neutron trajectories by splitting the neutrons into several possible final states and assigning the appropriate probability to each of them, thus keeping the total neutron intensity either constant or decreasing if neutrons are lost. Instrument parts are represented by modules which run independently in a pipe structure during simulation. Neutrons are passed from one module to the next in packages of typically 10000 neutrons, meaning that for most simulations that require more statistics, all modules run in parallel. This modular structure allows to split the simulation into several parts, and e.g. save the neutrons in any part of the instrument to feed them as input to the subsequent part in a separate simulation.

Version history VITESS 1.0 (1999) VITESS 2.0 (2001) VITESS 2.10 (Oct 2011) parallel threads reduce simulation time on multi-processor computers, visualization of trajectories in neutron guide, output compression, new components: elliptic mirror, lens, beamstop VITESS 2.11 (Dec 2011) first Macintosh version, new generic 2-dimensional monitor, new sample: imaging VITESS 3.0 (Nov 2012) visualization of instrument and neutron trajectories, new components: ideal guide, brilliance and generic 1-dimensional monitors, FRM-2 source, updated ESS cold and HZB cold/bi-spectral source

References

External links Official VITESS homepage

Worked examples

Example 1 — a first encounter with VITESS

Start with the simplest possible case. Write down what VITESS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to VITESS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about VITESS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of VITESS

In research: VITESS appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses VITESS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: VITESS is common in secondary-school and first-year university syllabi. It links to neighbouring topics Free software programmed in C, Neutron scattering, so understanding it makes those chapters shorter.
In everyday life: Look for VITESS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study VITESS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what VITESS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain VITESS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is VITESS in simple terms?

Why does VITESS matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study VITESS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on VITESS.