The aim of this initial study was to incorporate an acoustic metric into the flight control system of an unmanned aerial vehicle. This could be used to mitigate the noise impact of unmanned aerial systems operating near residential communities. To incorporate an acoustic metric into a flight control system, two things were required: a source noise model, and an acoustic controller. An acoustic model was developed based on Gutin's work to estimate propeller noise. The flight control system was augmented with a controller to reduce propeller noise using feedback control of the commanded flight speed until an acoustic target was met. This control approach focused on modifying flight speed only, with no perturbation to the trajectory. Multiple flight simulations were performed and the results show that integrating an acoustic metric into the flight control system of an unmanned aerial system is possible. Nomenclature c = Speed of sound in air (m/s) ì c(t) = Roll and pitch rates from the path following controller, flight dynamics controller input E = Total energy used (J) e a (t) = Acoustic error (dB re. 10 −12 W) J qn (x) = qn th order Bessel function of the first kind, of the argument x Kv = Motor constant (r pm/V) K p = Proportional gain, tuning parameter (m/s · dB −1 ) K i = Integral gain, tuning parameter (m/s 2 · dB −1 ) K b = Saturation error gain, tuning parameter (s −1 ) k = qω 1 /c, acoustic wave number L W = Total radiated sound power level (dB re. 10 −12 W) M max = Maximum value allowed for u sat (t) (m/s) M min = Minimum value allowed for u sat (t) (m/s) n = Number of propeller blades p r ms = Sound pressure (RMS) at a specified distance, r, and angle, ϑ, from the center of propeller rotation (Pa) P m = Electrical motor power (W) Q = Motor torque (N · m) q = Harmonic index R = Radius of propeller blade (m) r = Distance from center of propeller rotation (m) r(t) = Acoustic target, reference sound power level (dB re. 10 −12 W) ì s d (t) = [x (t) , y (t) , z (t)], time-varying desired point, path following controller input (m) r a (t) = Filtered reference (dB re. 10 −12 W) T = Thrust produced by propeller (N) u(t) = Unsaturated velocity command in the acoustic controller (m/s) u sat (t) = Saturated velocity command in the acoustic controller (m/s) ì u(t) = Flight dynamics controller output vector, plant model input v n (t) = Nominal velocity command, defined by mission requirements (m/s) ∆v a (t) = Change in velocity command based on acoustic error (m/s) v c (t) = Velocity command modified by acoustic controller, path following controller input (m/s) W = Sound power of propellers (W) W 0 = 10 −12 W, reference sound power x = k R sin ϑ, Bessel function argument y a (t) = Source noise estimate, output from acoustic model (dB re. 10 −12 W) ì y(t) = Flight properties vector, system output ϑ = Angle from propeller rotation axis (rad) ρ = Density of air (kg/m 3 ) θ = Motor angular velocity (r pm) Ω = Angular velocity of propeller (rad/s) ω 1 = nΩ, Blade passage frequency (rad/s)

Here we demonstrate a switchable DNA electron‐transfer catalyst, enabled by selective destabilization of secondary structure by the denaturant, perchlorate. The system is comprised of two strands, one of which can be selectively switched between a G‐quadruplex and duplex or single‐stranded conformations. In the G‐quadruplex state, it binds hemin, enabling peroxidase activity. This switching ability arises from our finding that perchlorate, a chaotropic Hofmeister ion, selectively destabilizes duplex over G‐quadruplex DNA. By varying perchlorate concentration, we show that the DNA structure can be switched between states that do and do not catalyze electron‐transfer catalysis. State switching can be achieved in three ways: thermally, by dilution, or by concentration.

† These authors contributed equally to this work. AbstractWe are nearing the end of a remarkable period that began in the 1960s in which semiconductor manufacturers succeeded in shrinking die and feature sizes logarithmically, thus growing transistor counts exponentially with time. As we reach the theoretical physical limits of classical MOSFET semiconductors, DNA is a highly attractive candidate for future miniaturization of microprocessors. Here we show a foundational electronic device -a transistor -can be constructed from DNA. The nanodevice is comprised of two strands, one of which can be selectively switched between a G-quadruplex and duplex or single-stranded conformations. This switching ability arises from our discovery that perchlorate, a chaotropic Hofmeister ion, selectively destabilizes duplex over G-quadruplex DNA. By varying perchlorate concentration, we show that the device can be operated as a switch or signal amplifier. State switching can be achieved in three ways: thermally, by dilution, or by concentration. In each case, when operated in the presence of the cofactor hemin, the device catalyzes electron transfer in only the Gquadruplex state.

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