COSESAI

The Half-Life Equation, Five Ways - cover image

The Half-Life Equation, Five Ways: A Field Guide to Exponential Decay

By xiezixing 2026年7月16日

Same e^(-λt), three different worlds. How one equation drives isotope calibration in nuclear medicine, drug accumulation in pharmacokinetics, and radiocarbon dating in archaeology.

API Contract Mutation Tester poster showing defended vs accepted vs documented mutations

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API Contract Mutation Tester: 5 mutation families, 3 report labels, 0 happy-path blind spots

By xiezixing 2026年7月15日

Paste an OpenAPI 3.x document. The tool mutates every documented operation into semantically risky variants, then reports which mutations your backend actually rejects — and which ones it cheerfully accepts.

CSV Malformed Row Surgeon — 6 repair passes for damaged CSV files

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CSV Malformed Row Surgeon: six deterministic fixes for damaged CSV files

By xiezixing 2026年7月15日

Six repair passes — BOM strip, stray-quote escape, field quoting, line-ending normalization, empty-line drop, mixed-delimiter rewrite — with a per-row red/green diff as the audit trail.

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Cron Expression Visualizer: 5 fields, 2 dialects, 1 timeline that tells the truth

By xiezixing 2026年7月15日

Before you ship that cron job to prod, paste the expression into a visualizer and check the next 10 runs land where you expect. Standard vs Quartz, timezone drift, and field-by-field parsing.

Backdrop-filter hero poster showing the six-layer glass card mental model

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Glass, But the Browser Doesn’t Speak It: The Six-Layer Backdrop-Filter Stack That Survives Safari

By xiezixing 2026年7月15日

Backdrop-filter is not one property; it is a six-knob convolution pipeline. Here is the mental model, the alpha pair, and the @supports fallback that keeps the card working on Safari and Firefox 102.

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The A/B Test Verdict: When “Significant” Isn’t the Whole Story

By xiezixing 2026年7月15日

A single p-value is not a decision. Here are the three numbers — p-value, lift, confidence interval — that turn a dashboard spike into a verdict you can defend, plus how Bonferroni and sequential-testing corrections keep multiple A/B tests honest.

Audio Frequency Analyzer: five-band spectrum display

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Five Bands, Twenty Hertz to Twenty Kilohertz: How to Read an Audio Frequency Analyzer

By xiezixing 2026年7月14日

A spectrum analyzer turns your ears into a screen you can defend in a mix review. Here is what the five-band display actually tells you — and the three traps that make it lie.

Entropy Calculator poster — Shannon, Min-Entropy, Strong/Medium/Weak rating and CPU-vs-GPU cracking times for sample inputs

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Measuring Cryptographic Strength with an Entropy Calculator

By xiezixing 2026年7月14日

Length is not a security metric. Use Min-Entropy to measure how unpredictable a password, key, or token really is — and how long it would take an adversary with 10⁶ to 10¹² guesses/sec to crack it.

Dice Probability Calculator cover with title and stats row

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Why Dice Probability Doesn’t Behave the Way Your Gut Says

By xiezixing 2026年7月14日

Two six-sided dice have 36 ordered outcomes. Sum 7 hits 1/6 of the time. The triangular histogram is your mental model for craps, Yahtzee, Catan robber rolls, and every D&D attack roll.