Bar induction is a mathematical technique used to prove statements about all natural numbers, particularly statements concerning well-ordering and induction principles that extend beyond standard mathematical induction. It applies to structures that have the properties of natural numbers (like well-ordering) but may involve more complex or abstract systems, such as ordinals or certain algebraic structures. The concept is particularly important in set theory and is often used in the context of proving results about various classes of sets or functions.
Constructive set theory is an approach to set theory that emphasizes constructions as a way of understanding mathematical objects, rather than relying on classical logic principles such as the law of excluded middle. It is grounded in the principles of constructivism, particularly within the context of logic and mathematics, where the existence of an object is only accepted if it can be explicitly constructed or exhibited.
Constructivism in the philosophy of mathematics is a viewpoint that emphasizes the importance of constructive proofs and methods in mathematical practice. Constructivists assert that mathematical objects do not exist unless they can be explicitly constructed or demonstrated through a finite procedure. This philosophical stance diverges from classical mathematics, which often accepts the existence of mathematical objects based on non-constructive proofs, such as those that rely on the law of excluded middle or other principles that do not provide an explicit construction.
Flow plasticity theory is a framework used in materials science and engineering to describe the behavior of materials that undergo plastic deformation when subjected to stress. It is often applied to metals, polymers, and soils, among other materials. ### Key Concepts of Flow Plasticity Theory: 1. **Plastic Deformation**: This refers to the permanent deformation that occurs when a material is subjected to stress beyond its yield point. Unlike elastic deformation, which is reversible, plastic deformation leads to a permanent change in shape.
The Representative Elementary Volume (REV) is a concept used primarily in the fields of materials science, geophysics, and hydrology. It refers to the smallest volume over which measurements can be taken so that the average properties of the material or medium are representative of the whole sample. The concept is crucial for understanding the macroscopic behavior of heterogeneous materials, such as soils, rocks, and composite materials.
Classical control theory is a framework for analyzing and designing control systems that operate in continuous time. It primarily deals with linear time-invariant (LTI) systems, where the behavior of the system can be described using ordinary differential equations. The main components of classical control theory include: 1. **System Modeling**: Classical control relies on mathematical models to represent dynamic systems. These models can be expressed in terms of transfer functions, which relate the input to the output of a system in the frequency domain.
Optimal control refers to a mathematical and engineering discipline that deals with finding a control policy for a dynamic system to optimize a certain performance criterion. The goal is to determine the control inputs that will minimize (or maximize) a particular objective, which often involves the system's state over time. ### Key Concepts of Optimal Control: 1. **Dynamic Systems**: These are systems that evolve over time according to specific rules, often governed by differential or difference equations.
In control theory, a compensator is a device or algorithm that modifies the behavior of a control system to improve its performance or stability. The purpose of a compensator is to enhance the system’s response to input changes, improve stability margins, reduce steady-state error, or shape the frequency response of the system.
The internal environment refers to the elements, factors, and conditions within an organization that can influence its operations, performance, and strategic direction. These elements are typically controllable and directly managed by the organization. Key components of the internal environment include: 1. **Organizational Structure**: This involves how the organization is arranged, including its hierarchy, roles, and communication channels.
Boltzmann constant by Ciro Santilli 40 Updated 2025-07-16
This is not a truly "fundamental" constant of nature like say the speed of light or the Planck constant.
Rather, it is just a definition of our Kelvin temperature scale, linking average microscopic energy to our macroscopic temperature scale.
The way to think about that link is, at 1 Kelvin, each particle has average energy:
per degree of freedom.
This is why the units of the Boltzmann constant are Joules per Kelvin.
For an ideal monatomic gas, say helium, there are 3 degrees of freedom. so each helium atom has average energy:
If we have 2 atoms at 1 K, they will have average energy , and so on.
Another conclusion is that this defines temperature as being proportional to the total energy. E.g. if we had 1 helium atom at 2 K then we would have about energy, 3 K and so on.
This energy is of course just an average: some particles have more, and others less, following the Maxwell-Boltzmann distribution.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
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