01
Acoustofluidics
Sorting Is a Force Ratio
Acoustic cell sorting resolves populations when the ratio of acoustic radiation force to viscous drag exceeds a threshold, so resolution is set by the ratio rather than by drive amplitude.
Thirty-one subfields · two claims each · not peer reviewed
Thirty-one subfields, two claims each, running from acoustofluidics through biophysics and bioprocessing to quantum sensing. Every entry carries a mechanism, two predictions and the result that would kill it.
Acoustic cell sorting resolves populations when the ratio of acoustic radiation force to viscous drag exceeds a threshold, so resolution is set by the ratio rather than by drive amplitude.
Cavitation damage in acoustofluidic devices is set by the ratio of driving frequency to bubble resonance frequency rather than by power, so damage peaks at a frequency where the two coincide.
Optomechanical cooling is limited by the ratio of mechanical frequency to cavity linewidth, so a system in the resolved-sideband regime cools far better at the same input power.
The bandwidth over which a mechanical oscillator can be squeezed is set by the ratio of optomechanical coupling to cavity decay rate rather than by coupling alone.
Spin-torque switching current is set by the ratio of magnetic anisotropy energy to spin-torque efficiency, so two devices with the same anisotropy need different currents.
The spin Seebeck voltage is set by the ratio of magnon diffusion length to film thickness, so a thin film can show a larger signal per unit length than a thick one.
The upper critical field of a disordered superconductor is set by the ratio of coherence length to mean free path rather than by coherence length alone.
The maximum pinning force is set by the ratio of vortex spacing to defect spacing, peaking when the two match rather than at maximum defect density.
Channel mobility degrades when the channel thickness falls below a critical ratio of inversion-layer width, because interface roughness scattering overtakes phonon scattering.
Trap-assisted tunnelling current is set by the ratio of trap depth to barrier width rather than by trap density, so deep traps in thin barriers leak more than shallow traps in thick ones.
Dielectric breakdown strength is set by the ratio of free volume to trap density rather than by trap density alone, so a looser polymer with more traps can be stronger.
Relaxor behaviour appears when the ratio of polar nanoregion size to correlation length falls below a threshold, so the same composition can be a normal ferroelectric at larger regions.
Coercivity is maximised when the grain size approaches the single-domain size, falling for both smaller and larger grains.
Exchange bias in a ferromagnet-antiferromagnet bilayer is set by the ratio of antiferromagnet thickness to domain wall width, vanishing when the layer is thin enough to rotate as a whole.
The bandwidth over which a metamaterial shows a negative index is set by the ratio of resonance strength to loss rather than by the resonance quality factor.
The bandwidth of a cloaking shell is set by the ratio of shell thickness to wavelength, so a thin shell cloaks over a wider band at the cost of imperfect suppression.
Dissipation in nanomechanical resonators is set by the ratio of surface loss to volume loss, so shrinking a device increases loss even in the same material.
The onset of nonlinear behaviour in a nanoresonator is set by the ratio of vibration amplitude to beam thickness rather than by absolute amplitude.
Colloidal stability is set by the ratio of electrostatic screening length to van der Waals attraction range rather than by surface charge alone.
The structure formed by settling colloids is set by the ratio of Péclet number to volume fraction rather than by either alone.
Contact angle hysteresis on a real surface is set by the ratio of defect density to droplet size rather than by the equilibrium contact angle.
The adhesion between a soft particle and a surface is set by the ratio of capillary length to elastic deformation length, so humidity changes adhesion only past a threshold.
Crystal habit is set by the ratio of supersaturation to surface diffusion rate rather than by supersaturation alone, so the same solution can give needles or blocks.
The density of growth defects is set by the ratio of growth rate to interface roughness, so faster growth is cleaner on a rough interface and dirtier on a smooth one.
The pressure at which a solid-solid transition occurs is set by the ratio of bulk modulus to volume change rather than by the enthalpy difference alone.
Pressure-induced metallisation occurs when the band gap falls below the thermal energy scale rather than at a fixed pressure, so warmer samples metallise sooner.
Cryo-EM resolution is set by the ratio of electron dose to beam-induced motion rather than by dose alone, so more dose can reduce resolution on a moving specimen.
Phase contrast in cryo-EM is set by the ratio of defocus to specimen thickness, so thick specimens lose contrast even at strong defocus.
Protein folding rates are set by the ratio of barrier height to attempt frequency, so two proteins with the same stability can fold at very different rates.
The force resolution of a single-molecule trap is set by the ratio of trap stiffness to thermal noise rather than by the sensor's displacement resolution.
Membrane pore formation occurs when the applied tension exceeds the ratio of line tension to pore radius, so the same tension is safe on one membrane and lytic on another.
Whether a protein senses membrane curvature is set by the ratio of its footprint to the curvature radius, so the same protein is a sensor on small vesicles and blind on large ones.
The stiffness of an actin network is set by the ratio of crosslink density to filament length, so dense short filaments form stiff gels while sparse long ones form compliant ones.
Cell contractility is set by the ratio of myosin activity to crosslinker unbinding rate rather than by myosin activity alone, so a network that remodels quickly cannot sustain force.
ATP yield from a metabolic substrate is set by the ratio of proton leak to coupling efficiency rather than by substrate identity, so the same fuel yields differently across tissues.
Resting metabolic rate is set by the ratio of membrane area to cell volume rather than by mass, so a cell's cost per unit mass rises as it shrinks.
Enzyme promiscuity is set by the ratio of transition-state complementarity to substrate fit, so a rigid active site is less promiscuous than a flexible one of the same affinity.
The magnitude of allosteric activation is set by the ratio of ligand affinities between the two states rather than by the effector's own affinity.
Aggregation propensity is set by the ratio of hydrophobic patch area to net charge rather than by hydrophobicity alone, so a strongly hydrophobic protein can stay soluble if it is charged enough.
Whether a protein requires chaperones is set by the ratio of its folding rate to translation rate, so a slow-folding domain on a fast ribosome needs help.
Nucleic acid hybridisation rate is set by the ratio of salt concentration to duplex length rather than by salt alone, so long duplexes need more salt to reach the same rate.
G-quadruplex stability is set by the ratio of loop length to cation radius, so the same sequence folds differently with different ions.
The mode of cell migration is set by the ratio of adhesion strength to contractility, with adhesion-dominated cells moving by protrusion and contractility-dominated cells moving by blebbing.
The deformation a nucleus can survive is set by the ratio of lamin stiffness to chromatin stiffness, so softening chromatin increases deformability only when lamin is high.
The maximum thickness of an engineered tissue is set by the ratio of oxygen diffusion length to cell density rather than by scaffold design.
Matrix stiffness for tissue growth peaks at an optimum set by the ratio of cell traction to matrix modulus, rather than increasing monotonically.
T-cell activation is set by the ratio of ligand spacing to receptor size, so the same ligand density can be activating or silent depending on arrangement.
The depot effect of a vaccine formulation is set by the ratio of particle persistence to antigen release rate rather than by total antigen dose.
The leak of a genetic circuit is set by the ratio of promoter strength to repressor affinity rather than by promoter strength, so a strong promoter can be tight with a strong repressor.
The fitness burden of an engineered circuit is set by the ratio of heterologous to native protein expression, not by heterologous expression alone.
Pathway flux is set by the ratio of enzyme capacity to pathway demand, so overexpressing one enzyme helps only until it stops being the limiting capacity.
Intermediate toxicity in an engineered pathway is set by the ratio of production rate to efflux capacity rather than by the intermediate's intrinsic toxicity.
Enzyme stability in organic solvent is set by the ratio of surface charge to hydrophobic patch area, so a more charged enzyme tolerates more solvent.
The benefit of immobilising an enzyme is set by the ratio of mass transfer rate to intrinsic catalytic rate, so a fast enzyme gains nothing from a poorly permeable support.
Bioprocess scale-up failure is set by the ratio of mixing time to reaction time, so a process that works at small scale can fail at large scale at identical conditions.
Aerobic yield is set by the ratio of oxygen transfer capacity to oxygen demand rather than by dissolved oxygen setpoint.
The environmental persistence of a chemical is set by the ratio of its degradation rate to its partitioning into protected phases, so a compound can persist long after it becomes undetectable in water.
Bioaccumulation is set by the ratio of uptake rate to elimination rate rather than by lipophilicity alone, so highly lipophilic compounds can fail to accumulate if they are metabolised.
Whether an aerosol activates into a cloud droplet is set by the ratio of particle size to the critical size at the ambient supersaturation, not by size alone.
Aerosol lifetime is set by the ratio of wet deposition rate to production rate rather than by deposition velocity alone.
Quantum sensor sensitivity is set by the ratio of coherence time to averaging time rather than by coherence time alone, so a short-coherence sensor can win if it can be averaged faster.
The dynamic range of a quantum sensor is set by the ratio of decoherence rate to drive strength, so stronger driving widens range at the cost of coherence.
Twenty-nine subfields that the series had either skipped or treated as background. The entries are short by design: a claim, the mechanism that would make it true, two predictions, and the result that kills it. No bibliography; the evidence is the standard picture of each subfield rather than a specific paper.
Entry page: crypt.html. There is deliberately no index.html.
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