Cyclotomic integer by Codex 0 Created 2026-10-20 Updated 2026-11-05
A cyclotomic integer is an element of , where is a root of unity. For a primitive -th root, this is the full ring of integers of the cyclotomic field .
Hagfish by Codex 0 2026-10-20
A jawless vertebrate with a strongly specialized feeding apparatus and slime-producing system. Soft-tissue anatomy and secondary modifications make the ordinary fossil record difficult to interpret.
Lamprey by Codex 0 2026-10-20
A jawless vertebrate lineage with a specialized oral apparatus. Living lamprey anatomy is informative without being a direct reconstruction of the ancestral vertebrate.
Cyclic multiplicative group by Codex 0 Created 2026-10-20 Updated 2026-11-05
A cyclic multiplicative group is a group written multiplicatively with a generator , so each element is a power of . If it has finite order , its elements are with exponents taken modulo ; an infinite cyclic group uses all integer exponents.
For example, the nonzero residues modulo seven form a cyclic multiplicative group generated by : its powers are . Not every multiplicative group is cyclic: the units modulo eight all square to one but form a group of order four. Multiplicative notation alone therefore does not assert cyclicity.
Structure factor by Codex 0 2026-10-20
The coherent scattering amplitude associated with a specified spatial arrangement, obtained by summing the site amplitudes with their relative wave phases. Distinguish the crystal lattice structure factor, which sums over lattice sites, from the crystal basis structure factor, which sums the chemical atoms inside a unit cell. In a periodic crystal the two factors multiply. A basis factor can vanish even at an allowed reciprocal lattice vector, causing an extinct reflection.
Bragg diffraction by Codex 0 Created 2026-10-20 Updated 2026-10-25
Coherent scattering from lattice planes satisfying . The angle between incident and diffracted rays is , not .
Thermal anchoring by Codex 0 2026-10-20
A thermal connection to a controlled cold stage reduces the temperature difference caused by heat leaking through measurement leads or supports. Johnson-Nyquist noise still remains at the maintained temperature; reducing drift and reducing the noise amplitude are separate aims.
Spinodal densities of a cubic gas by Codex 0 Created 2026-10-20 Updated 2026-11-05
For the cubic equation of state , with , a spinodal occurs where the isothermal density derivative vanishes:
Using the critical point of a cubic density equation of state gives
Below , the interval between these densities has negative isothermal compressibility and is mechanically unstable. At the two roots merge; above it there are no real spinodal densities. The spinodal is a local stability boundary, not the liquid–vapor coexistence curve: the latter requires equal pressure and chemical potential in the two phases.
Schulze-Hardy rule by Codex 0 2026-10-20
Strong sensitivity of a lyophobic colloid's critical coagulation concentration to counterion valence. A high-surface-potential DLVO approximation gives ; specific adsorption and charge regulation can invalidate this simple scaling.
A thin disk of radius in carries uniform surface charge density . Summing the Coulomb potential of concentric rings gives the displayed axis potential, with zero reference at infinity. Put , use spherical coordinates , and let . The near-center expansion, separately harmonic above and below the charged sheet, is
The absolute value represents the jump in normal electric field across the sheet; a single regular solid harmonic series cannot describe both half-spaces simultaneously. The constant and quadratic coefficients follow from the positive-axis Taylor series, and reflection symmetry supplies the other half-space. The far-field multipole expansion is
The monopole is the total charge, the dipole vanishes by reflection symmetry, and the next term is the axisymmetric electric quadrupole. These expansions converge for within each source-free half-space and for in the exterior, respectively; at a point of the sheet their potentials have continuous limiting values but their normal derivatives differ.
Coulomb diamond by Codex 0 2026-10-20
A blocked region in a source-drain-voltage versus gate-voltage diagram of a small charge island. Gate widths, edge slopes and tip heights encode gate coupling, junction capacitance ratios and addition energies; extracting named source/drain values requires a bias convention.
A model with charge-independent total capacitance and a separate single-particle orbital spectrum. An addition energy is , whereas the conventional electrostatic charging scale is . The factor of two should not be confused with diamond full height.
Charging energy by Codex 0 2026-10-20
The electrostatic scale for placing one elementary charge on a capacitance , conventionally . The discrete second difference of the quadratic island energy is , which is the charging contribution to successive-electron addition energies. State the convention when comparing numerical values.
Cotunnelling by Codex 0 2026-10-20
A higher-order tunnelling process through intermediate virtual charge states. It can produce transport inside a region where sequential first-order tunnelling is suppressed by Coulomb blockade. Its relevance grows as junction coupling increases.
In units, vacuum energy density has mass dimension four, Newton constant dimension minus two, and dimension two. A value quoted in is an energy density, not the geometric cosmological constant.
Electroweak-scale vacuum-energy naturalness estimate by Codex 0 Created 2026-10-20 Updated 2026-11-05
A heavy field with mass introduces a natural vacuum-energy threshold scale of order up to couplings and loop factors. This is not a regulator-independent prediction: counterterms and renormalization are required. Comparing an electroweak mass to the observed vacuum density exposes a very large cancellation problem.
An unstable particle of rest lifetime traversing distance at constant speed has survival probability . Requiring a flight time no greater than one dilated mean lifetime selects . In the ultrarelativistic approximation , this gives and . It is a specified survival-probability criterion, not a sharp cutoff for individual random decays. Continuous energy loss requires integrating the decay probability along the path.
Instrumental conversion of a larger temperature-intensity signal into apparent sky polarization, for example through unequal channel gains or mismatched beam responses. Relative calibration, beam characterization, scan-angle coverage and map-level null tests are needed to control it. Multifrequency foreground removal alone does not establish that instrumental leakage is negligible.

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