Presets
Playback
Flow, detector and field
Positive droplets read about 0.78 and negative ones about 0.23, each with Gaussian noise. A droplet is steered into the collection lane only if its reading is above the threshold and the voltage is high enough.
Model checks
The science
What is modelled
Water droplets form at a T-junction in oil; their length grows with the aqueous-to-oil flow ratio. Each droplet passes a fluorescence detector whose reading is a fixed level for positives or negatives plus Gaussian noise. A threshold turns the reading into a decision, and a dielectrophoretic force, represented by a steering authority, diverts the chosen droplets into the collection lane if it is strong enough.
Equations
- Droplet length:
L = w (1 + 1.1 Qaq/Qoil)(squeezing-regime rule of thumb). - Mean velocity
U = (Qoil + Qaq)/(w h), Reynolds numberRe = ρ U Dh/μ. - Recall
Φ((μpos - t)/σ)and specificityΦ((t - μneg)/σ)for a threshold t. - Steering authority
∝ V²/(μ U), active above 0.66.
Checks run in the page
- Recall and specificity of a long run against the Gaussian formulas.
- Velocity and Reynolds number recomputed from the inputs.
- Droplet generation rate against flow divided by droplet volume.
- The V squared scaling of the steering and its gate.
Honest simplifications
The detector levels and the steering authority are model parameters, not an electric-field solution or an electrode calibration; droplet breakup, coalescence and cell content are not modelled; the geometry on screen is magnified. Not a calibrated cell sorter.
What to try
- Press Noisy detector and watch the purity and recovery fall; the gold dot on the ROC curve follows the threshold.
- Press Low voltage and see that no droplet is collected even though the detector sees them.
- Slide the threshold to trade purity for recovery along the ROC curve.