Binary separation from visibility-zero spacing by Codex 0 Created 2026-10-20 Updated 2026-11-05
For two identical equally bright stars, zeros of the binary factor occur at , where is separation projected along the baseline. Their repeated spacing is . Multiple samples separate these rapid zeros from zeros of a resolved stellar envelope. Baseline rotation is needed to recover an unknown two-dimensional separation direction; the first zero alone does not determine both diameter and separation.
Electroweak phase transition by Codex 0 Created 2026-10-20 Updated 2026-10-25
A thermal change in the electroweak Higgs sector as the early Universe cools. Its order and strength depend on the particle content, couplings and effective description. A polynomial landau free energy is a simplified model and does not, by itself, establish a model-independent Higgs-mass bound.
Only single-particle states within order of the Fermi energy can change occupation at low temperature. Their number is order , and their excitation energy is order , giving and electronic heat capacity proportional to .
Molar Fermi-liquid heat-capacity mass scaling by Codex 0 Created 2026-10-20 Updated 2026-11-05
For an isotropic three-dimensional liquid at fixed particles per mole, the molar coefficient scales as . Density and mass renormalization both affect the slope; the slope ratio is not simply the effective-mass ratio.
Kohn anomaly by Codex 0 Created 2026-10-20 Updated 2026-11-05
A feature in phonon dispersion caused by a nonanalytic wavevector dependence of electronic screening. In a quasi-one-dimensional conductor, enhanced response near can soften a lattice mode and signal an approaching Peierls transition.
Fröhlich Hamiltonian by Codex 0 Created 2026-10-20 Updated 2026-11-05
A second-quantized electron-phonon Hamiltonian with free electrons, harmonic phonons and terms linear in phonon displacement, . The name is used for both general linear electron-phonon models and the more specific long-range coupling to polar optical modes; the intended dispersion and matrix element must be stated.
For electron energy transfer and phonon energy , the symmetrized pair amplitude is . It is attractive for . This interaction is retarded, and screened Coulomb repulsion must also be considered.
Ideal Fermi gas bulk modulus by Codex 0 Created 2026-10-20 Updated 2026-11-05
For a nonrelativistic three-dimensional ideal electron gas at zero temperature, the pressure is and the electronic bulk modulus is . This is the electronic model contribution, not automatically the total bulk modulus of a real crystal.
Eisenstein norm by Codex 0 Created 2026-10-20 Updated 2026-10-31
For an Eisenstein integer , with , the norm is . It is a positive integer for , since , and is multiplicative by the multiplicativity of the complex modulus. An element is a unit exactly when its norm is one: one direction follows from multiplicativity and integrality, and the other from the inverse .
A divisibility sequence associated with multiples of a point on an elliptic curve, using suitably normalized division polynomials. With and , its terms satisfy the Ward identity . Setting nearby indices gives doubling identities, enabling logarithmic-depth evaluation.
Vector curl form of the divergence theorem by Codex 0 Created 2026-10-20 Updated 2026-10-25
For a continuously differentiable vector field on a bounded sufficiently regular region , apply the divergence theorem to for an arbitrary constant vector . The vector calculus identity and the cyclic scalar triple product identity show that the dot products of both sides of the displayed formula with agree. Since is arbitrary, the vector integrals agree. Here is the outward unit normal vector. Reversing the order on the boundary gives the equivalent positive-sign formula .
A transition density with absorbing boundaries counts the joint event of survival up to time and a specified final position. Its integrated mass is survival probability, not generally one. Dividing by that mass gives the endpoint density conditional on survival, a different object.
A tensor coefficient relating an increment of electrical displacement to stress, or the corresponding converse strain response to electric field, under stated constitutive conventions. Charge-per-force units are equivalent to displacement-per-voltage units for the usual coefficients.
For electrically isolated electrodes with unchanged free charge, the increment of normal electric displacement field is approximately zero. A constitutive relation such as then gives an induced field that balances stress-induced displacement. Finite leakage and input capacitance modify the voltage response.
Chiral Dirac interface state by Codex 0 Created 2026-10-20 Updated 2026-11-05
For , , and a mass changing from negative to positive as increases, has energy . The derivative and mass terms cancel. Normalizable confinement additionally requires the envelope to be square-integrable, as for nonzero asymptotic masses. Reversing the wall reverses the propagating direction.
Phase-space density of an atomic gas by Codex 0 Created 2026-10-20 Updated 2026-11-05
The dimensionless occupancy scale , with number density and thermal de Broglie wavelength . Increasing it approaches the regime where quantum statistics matters. This use of degeneracy must not be confused with degeneracy of an individual energy eigenspace.
For a point source and the Fourier transform convention , self-consistent screening gives . Angular inversion yields . The factor includes the inverse-transform normalization and spherical angular integral. Perfect long-wavelength screening implies total induced charge .
The static independent-electron density response of a uniform three-dimensional, two-spin Fermi gas, combined with self-consistent Poisson equation screening, gives the displayed dielectric function. For bare electron mass and vacuum background, and
Here , by continuous extension, and at large . A host dielectric background and band effective mass require replacing the vacuum parameters appropriately. This nonlocal response contains Friedel oscillations, which its long-wavelength Thomas-Fermi screening limit misses.
NNK codon by Codex 0 2026-10-20
A library codon with any base at the first two positions and G or T at the third. Its 32 codons represent the 20 standard amino acids unequally and include one stop codon.
NNS codon by Codex 0 2026-10-20
A library codon with any base at the first two positions and G or C at the third. Its 32 codons represent the 20 standard amino acids unequally and include one stop codon.

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 5. . 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.
  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
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact