Rapid Tuning Research Articles

Neural Underpinnings of Phonotactic Rule Learning

This study used behavioral measures and ERP difference waves to measure the underlying brain processes during the categorization of grammatical vs ungrammatical stimuli according to a lab learned phonotactic rule. The results show that participants learned the simple rule at the behavioral level (as measured with d-prime, a sensitivity measure to rule violations). This rule learning is also reflected in the brain response to violations of the rule, which is indexed by the P3 rare-minus-frequent difference waveform. The neural results indicate that this learning took the form of a neural commitment. Participants learned the rule and used it to make active predictions, categorizing words as ungrammatical at the exact point of violation. This ability must be instantiated at the neural level, meaning rapid neural tuning has occurred in this lab setting.

Enhancement of efficiency in femtosecond optical parametric oscillators using group-velocity-matching in long nonlinear crystals

The authors describe the exploitation of group-velocity-matching in femtosecond optical parametric oscillators (OPOs) for enhanced down-conversion efficiency into the mid-infrared (mid-IR). We demonstrate the concept in a femtosecond OPO based on a long MgO:PPLN crystal, for the first time, by utilizing group-velocity-matching between pump and idler pulses. Taking advantage of the wide phase-matching bandwidth when pumped near 1 µm enables the use of a 42-mm-long crystal, resulting in an oscillation threshold as low as 5 mW, pump depletion of 78%, and an idler quantum conversion efficiency up to 48% into the mid-IR. Using 80–100 fs pump pulses tunable across 997–1070 nm, we have generated idler radiation across 3132–4273 nm (2340–3193 cm−1) with spectral bandwidth of 140–180 nm, providing up to 65 mW of average power at 80 MHz repetition rate. The near-IR signal is tunable across 1392–1568 nm, with up to 76 mW of average power in transform-limited pulses of ∼400–600 fs duration without dispersion compensation. Preferential operation at group-velocity-matched wavelengths leads to intrinsically high passive power stability with <1% rms fluctuation over 1 h for both signal and idler. With the capability for rapid pump tuning in the mid-IR, this OPO represents a viable source for spectroscopic applications, which we demonstrate using CH4 gas. Extension to other quasi-phase-matched nonlinear crystals is also discussed.

Broadband lumped-element Josephson parametric amplifier with single-step lithography

We present a lumped-element Josephson parametric amplifier (JPA) fabricated using a straightforward e-beam lithography process. Our strongly coupled flux-pumped JPA achieves a gain of 20 dB with a bandwidth of 95 MHz around 5 GHz, while the center frequency is tunable by more than 1 GHz, with the additional possibility for rapid tuning by varying the pump frequency alone. Analytical calculations based on the input-output theory reproduce our measurement results closely.

Active control of photo-induced electromagnetically induced transparency in terahertz region

The characteristic of an all-optical electromagnetically induced transparency (EIT) analogue generated on GaAs substrate in terahertz (THz) region has been investigated. By increasing power of pump laser, a phenomena of EIT analogue emerged. It was found that the resonance frequency as well as the time delay can be dynamic tuned by controlling the power of pump laser, which displayed a blue shift by increasing the conductivity. Furthermore, the coupled Lorentz oscillator model has been used to analyze the physical mechanism of photo-generated EIT analogue as well. This approach may provide a reference for the design of the rapid tuning device.

Controlled synthesis of multi-branched gold nanodendrites by dynamic microfluidic flow system

The synthesis of gold nanostructures with unique architectures has attracted a great deal of attention because of their architecture-dependent sensing, optical, and electrical properties. Gold nanodendrites with a tailored morphology have unique properties due to their enhanced surface areas caused by nanoscale branches. Although gold nanodendrites have been synthesized by many different methods, controllable and high-yield synthesis of gold nanodendrites remains a challenge. Here, for the first time, we show that multi-branched gold nanodendrite synthesis can be controlled using a dynamic microfluidic flow system with high yield and fluid dynamics that control the branching structure of the nanodentrites. The study shows that the architecture of the gold nanodendrites mainly depends on synthesis conditions such as flow dynamics, HAuCl4 concentration, and reaction time. Dendrites grew faster when the flow rate reached 3 µL min−1. We further show that by using microfluidic-assisted synthesis, simple and rapid gold nanodendrite length tuning (0.7 cm) is possible with a threefold branching and textured structure. It is shown that the growth of gold nanodendrites is significantly enhanced (1.7 times faster) under flow conditions in the microfluidic channel. This bottom-up method reduces undesirable effects related to the poor control of static growth and increased reproducibility. Such highly controllable and inexpensive microfluidic flow systems could potentially be used to fabricate high-yield gold nanodendrites for bioelectronics and sensing applications.

Rapid task-dependent tuning of the mouse olfactory bulb.

Adapting neural representation to rapidly changing behavioural demands is a key challenge for the nervous system. Here, we demonstrate that the output of the primary olfactory area of the mouse, the olfactory bulb, is already a target of dynamic and reproducible modulation. The modulation depends on the stimulus tuning of a given neuron, making olfactory responses more discriminable through selective amplification in a demand-specific way.

Rapidly tunable and highly reversible bio-inspired dry adhesion for transfer printing in air and a vacuum.

Tunable and reversible dry adhesion has attracted much attention in academia and industry due to its wide applications ranging from releasable joints to stamps for transfer printing. Here, a simple yet robust magnetically actuated, aphid-inspired design of an elastomeric surface that provides rapidly tunable and highly reversible adhesion strength is reported. The magnetically actuated adhesive features open reservoirs filled with magnetic particles and encapsulated by a thin surface membrane, which can be deformed in a controlled manner via the magnetic field, thus, to tune the adhesion. The combination of the rate dependent effect and magnetic actuation of the thin surface membrane offers continuously tunable adhesion with a great switchability and a quick response. Experimental and theoretical studies reveal the underlying physics and provide design guidelines to optimize geometries for the broad control of adhesion. Demonstrations of this concept in stamps for transfer printing of silicon wafers in air and in a vacuum with a selective and programmable mode illustrate the capabilities for deterministic assembly and the potential in the semiconductor industry.

Reversible dynamic full-color phototuning with a new chiral molecular switch containing linking group between chiral center and photosensitive group

In this study, a new photoresponsive chiral molecular switch, where azobenzene was not directly connected to the axially chiral binaphthyl group, was successfully synthesized and used to induce helical superstructures in the achiral nematic liquid crystal (LC) host E7. Photoisomerization of the chiral molecular switch was carried out in both organic solvent and LC host upon light irradiation, contributing to the HTP difference at different photostationary states. The phototunable property of chiral molecular switch in E7 allowed dynamic, rapid and reversible tuning of the reflection color in cholesteric LC phase over the entire visible spectrum. The strategy breaks the restriction in common structures of photoresponsive chiral molecular switches, providing exciting insight into design for novel binaphthyl azobenzene derivatives with axial chirality.

Operating in a Reverberating Regime Enables Rapid Tuning of Network States to Task Requirements.

Neural circuits are able to perform computations under very diverse conditions and requirements. The required computations impose clear constraints on their fine-tuning: a rapid and maximally informative response to stimuli in general requires decorrelated baseline neural activity. Such network dynamics is known as asynchronous-irregular. In contrast, spatio-temporal integration of information requires maintenance and transfer of stimulus information over extended time periods. This can be realized at criticality, a phase transition where correlations, sensitivity and integration time diverge. Being able to flexibly switch, or even combine the above properties in a task-dependent manner would present a clear functional advantage. We propose that cortex operates in a “reverberating regime” because it is particularly favorable for ready adaptation of computational properties to context and task. This reverberating regime enables cortical networks to interpolate between the asynchronous-irregular and the critical state by small changes in effective synaptic strength or excitation-inhibition ratio. These changes directly adapt computational properties, including sensitivity, amplification, integration time and correlation length within the local network. We review recent converging evidence that cortex in vivo operates in the reverberating regime, and that various cortical areas have adapted their integration times to processing requirements. In addition, we propose that neuromodulation enables a fine-tuning of the network, so that local circuits can either decorrelate or integrate, and quench or maintain their input depending on task. We argue that this task-dependent tuning, which we call “dynamic adaptive computation,” presents a central organization principle of cortical networks and discuss first experimental evidence.

Adaptive Certainty-Equivalence Control With Regulation-Triggered Finite-Time Least-Squares Identification

For general nonlinear control systems, we present a novel approach to adaptive control, which employs a certainty-equivalence (indirect) control law and an identifier with event-triggered updates of the plant parameter estimates, where the triggers are based on the size of the plant's state, and the updates are conducted using a nonrecursive least-squares estimation over certain finite time intervals, with updates employing delayed measurements of the state. With a suitable nonrestrictive parameter-observability assumption, our adaptive controller guarantees global stability, regulation of the plant state, and our identifier achieves parameter convergence, in finite time, even in the absence of persistent excitation, for all initial conditions other than those where the initial plant state is zero. The robustness of our event-triggered adaptive control scheme to vanishing and nonvanishing disturbances is verified in simulations with the assistance of a dead-zone-like modification of the update law. The major distinctions of our approach from supervisory adaptive schemes are that our approach is indirect and our triggering is related to the control objective (the regulation error). The major distinction from the classical indirect Lyapunov adaptive schemes based on tuning related to the regulation error is that our approach does not involve a complex redesign of the controller to compensate for the detrimental effects of rapid tuning on the transients by incorporating the update law into the control law. Instead, our approach allows for the first time to use a simple certainty-equivalence adaptive controller for general nonlinear systems.

Pore-Forming Monopeptides as Exceptionally Active Anion Channels.

We describe here a unique family of pore-forming anion-transporting peptides possessing a single-amino-acid-derived peptidic backbone that is the shortest among natural and synthetic pore-forming peptides. These monopeptides with built-in H-bonding capacity self-assemble into an H-bonded 1D columnar structure, presenting three types of exteriorly arranged hydrophobic side chains that closely mimic the overall topology of an α-helix. Dynamic interactions among these side chains and membrane lipids proceed in a way likely similar to how α-helix bundle is formed. This subsequently enables oligomerization of these rod-like structures to form ring-shaped ensembles of varying sizes with a pore size of smaller than 1.0 nm in diameter but sufficiently large for transporting anions across the membrane. The intrinsic high modularity in the backbone further allows rapid tuning in side chains for combinatorial optimization of channel's ion-transport activity, culminating in the discovery of an exceptionally active anion-transporting monopeptide 6L10 with an EC50 of 0.10 μM for nitrate anions.

Direct Laser Writing of Nanophotonic Structures on Contact Lenses.

Contact lenses are ubiquitous biomedical devices used for vision correction and cosmetic purposes. Their application as quantitative analytical devices is highly promising for point-of-care diagnostics. However, it is a challenge to integrate nanoscale features into commercial contact lenses for application in low-cost biosensors. A neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm, 3 ns pulse, 240 mJ) in holographic interference patterning mode was utilized to produce optical nanostructures over the surface of a hydrogel contact lens. One-dimensional (925 nm) and two-dimensional (925 nm × 925 nm) nanostructures were produced on contact lenses and analyzed by spectroscopy and angle-resolve measurements. The holographic properties of these nanostructures were tested in ambient moisture, fully hydrated, and artificial tear conditions. The measurements showed a rapid tuning of optical diffraction from these nanostructures from 41 to 48°. The nanostructures were patterned near the edges of the contact lens to avoid any interference and obstruction to the human vision. The formation of 2D nanostructures on lenses increased the diffraction efficiency by more than 10%. The versatility of the holographic laser ablation method was demonstrated by producing four different 2D nanopattern geometries on contact lenses. Hydrophobicity of the contact lens was characterized by contact angle measurements, which increased from 59.0° at pristine condition to 62.5° at post-nanofabrication. The holographic nanostructures on the contact lens were used to sense the concentration of Na+ ions. Artificial tear solution was used to simulate the conditions in dry eye syndrome, and nanostructures on the contact lenses were used to detect the electrolyte concentration changes (±47 mmol L–1). Nanopatterns on a contact lens may be used to sense other ocular diseases in early stages at point-of-care settings.

Rapid acousto-optic focus tuning for improvement of imaging performance in confocal microscopy [Invited

We demonstrate the application of focus-tunable acousto-optic lens technology in confocal microscopy for a high-speed axial scanning of the object. The advantages of the proposed approach include high axial scan rate, no mechanical sample movement, no additional non-symmetric aberrations, and the control of the effective depth of focus. The acousto-optic lens operating at the focus tuning rate of 300 kHz is developed and implemented in scanning laser confocal microscopy. The performance of the instrumentation is presented using test targets. Rapid focus tuning may enhance in vivo three-dimensional imaging in confocal microscopy.

Measurement of Non-Stationary Gas Flow Parameters Using Diode Laser Absorption Spectroscopy at High Temperatures and Pressures

The layout of an absorption spectrometer with diode lasers for contactless measurement of the temperature and water-vapor concentration in gas flows with mixture pressures of up to 3 atm and temperatures of 300–2000 K has been designed. The technique is based on the rapid tuning of the radiation wavelength of two lasers, the registration of the absorption lines of water molecules that are located in the tuning range, and the fitting of the experimental absorption spectra by theoretical ones that have been simulated using spectroscopic databases. The original components of the spectrometer and different algorithms of the processing of experimental spectra are described. The performance of the spectrometer and processing methods were tested in the laboratory with a cuvette at a pressure of 1 atm and temperatures of 300–1500 K. The different processing algorithms give a reasonable coincidence of data on hot zone parameters that were obtained by the method of diode laser absorption spectrometry, and the temperature that was measured using standard sensors. The designed layout of the spectrometer passed the first tests on the T-131 experimental stand at the TsAGI (Central Aerohydrodynamics Institute).

Tunable 30 fs light pulses at 1 W power level from a Yb-pumped optical parametric oscillator.

We report on a Yb-pumped optical parametric oscillator (OPO) that delivers 30fs pulses with spectral coverage from 680 to 910nm and an average output power of up to 1.1W. The resulting peak power is ∼0.5 MW, which is, to the best of our knowledge, the highest ever demonstrated in a femtosecond OPO. The intensity noise remains at a level of 0.2% rms, and rapid wavelength tuning is obtained by simply scanning the resonator length. The performances of the OPO are promising for a variety of applications in nonlinear microscopy and ultrafast spectroscopy.

Proximal tubule apical endocytosis is modulated by fluid shear stress via an mTOR-dependent pathway.

Cells lining the proximal tubule (PT) have unique membrane specializations that are required to maintain the high-capacity ion transport and endocytic functions of this nephron segment. PT cells in vivo acutely regulate ion transport in response to changes in glomerular filtration rate (GFR) to maintain glomerulotubular balance. PT cells in culture up-regulate endocytic capacity in response to acute changes in fluid shear stress (FSS); however, it is not known whether GFR modulates PT endocytosis to enable maximally efficient uptake of filtered proteins in vivo. Here, we show that cells cultured under continuous FSS develop an expanded apical endocytic pathway and increased endocytic capacity and lysosomal biogenesis. Furthermore, endocytic capacity in fully differentiated cells is rapidly modulated by changes in FSS. PT cells exposed to continuous FSS also acquired an extensive brush border and basolateral membrane invaginations resembling those observed in vivo. Culture under suboptimal levels of FSS led to intermediate phenotypes, suggesting a threshold effect. Cells exposed to FSS expressed higher levels of key proteins necessary for PT function, including ion transporters, receptors, and membrane-trafficking machinery, and increased adenine nucleotide levels. Inhibition of the mechanistic target of rapamycin (mTOR) using rapamycin prevented the increase in cellular energy levels, lysosomal biogenesis, and endocytic uptake, suggesting that these represent a coordinated differentiation program. In contrast, rapamycin did not prevent the FSS-induced increase in Na+/K+-ATPase levels. Our data suggest that rapid tuning of the endocytic response by changes in FSS may contribute to glomerulotubular balance in vivo. Moreover, FSS provides an essential stimulus in the differentiation of PT cells via separate pathways that up-regulate endocytosis and ion transport capacity. Variations in FSS may also contribute to the maturation of PT cells during kidney development and during repair after kidney injury.

Multi-frequency spin manipulation using rapidly tunable superconducting coplanar waveguide microresonators

In this work, we demonstrate the use of frequency-tunable superconducting NbTiN coplanar waveguide microresonators for multi-frequency pulsed electron spin resonance (ESR) experiments. By applying a bias current to the center pin, the resonance frequency (∼7.6 GHz) can be continuously tuned by as much as 95 MHz in 270 ns without a change in the quality factor of 3000 at 2 K. We demonstrate the ESR performance of our resonators by measuring donor spin ensembles in silicon and show that adiabatic pulses can be used to overcome magnetic field inhomogeneities and microwave power limitations due to the applied bias current. We take advantage of the rapid tunability of these resonators to manipulate both phosphorus and arsenic spins in a single pulse sequence, demonstrating pulsed double electron-electron resonance. Our NbTiN resonator design is useful for multi-frequency pulsed ESR and should also have applications in experiments where spin ensembles are used as quantum memories.

High-Speed Wideband Voltage-Controlled Oscillator via an Injection-Locked Laser

We demonstrate a microwave voltage-controlled oscillator able to synthesize a wide range of frequencies in the GHz regime based on an optically injected semiconductor laser. The ability to understand and experimentally characterize the entire injection-locking domain is crucial for the realization and optimization of such a device. This characterization facilitates the identification of steady-state bias conditions, which lead to microwave oscillations. More importantly, it also identifies a regime in which the oscillation frequency can be tuned solely by adjusting the optically injected power, a parameter, which can easily be changed on a nanosecond time scale. In this letter tuning from 6–16 GHz is demonstrated, while tuning rates of ~ $1\times 10^{18}$ Hz/sec are achieved using a < 1 V drive signal, resulting in a voltage-controlled oscillator with rapid tuning speed when compared with conventional, e.g., YIG-based, oscillators.

Room-temperature, rapidly tunable, green-pumped continuous-wave optical parametric oscillator.

We report a high-power, single-frequency, green-pumped continuous-wave optical parametric oscillator (OPO) capable of providing rapid and continuous tuning across a wide spectral range in the near-infrared at room temperature. By exploiting the nonlinear crystal of MgO:sPPLT in a fan-out grating design pumped at 532nm in the green, the OPO can be tuned continuously across 1097-2100nm in the idler, with corresponding signal tuning over 712-1033nm using simple mechanical translation of the crystal at fixed temperature. The device can deliver hundreds of milliwatts of idler power across the complete tuning range, with as much as 2.2W at 1097nm for 9W of input pump power at 77% pump depletion. The passive power stability of the generated idler at 1110nm, measured at 6.8W of pump power, is better than 1%rms over 30min. The signal frequency stability, measured at 837nm, is 518MHz over 2min, with an instantaneous linewidth of 6.9MHz, in high beam quality.

Orthogonal enzymatic reactions for rapid crosslinking and dynamic tuning of PEG-peptide hydrogels.

Stiffening of the extracellular matrix is a hallmark in cancer progression, embryonic development, and wound healing. To mimic this dynamic process, our work explored orthogonal enzymatic reactions capable of modulating the properties of poly(ethylene glycol) (PEG)-peptide hydrogels. A hepta-mutant bacterial transpeptidase sortase A (SrtA7M) was used to ligate two PEG-peptide macromers (i.e., PEG-YLPRTG and NH2-GGGG-PEG) into a primary hydrogel network. The hydrogels were dynamically stiffened using mushroom tyrosinase (MT), which oxidized tyrosine residues into di-tyrosine and led to increased matrix stiffness. After confirming the expression and enhanced catalytic activity of SrtA7M, we investigated the cytocompatibility of the enzymatic reaction with a mouse insulinoma cell line, MIN6. In addition, we altered peptide substrate concentrations and evaluated their influence on primary hydrogel network properties and MT-triggered stiffening. Using a pancreatic cancer cell line, COLO-357, the effect of MT-triggered stiffening on spheroid formation was investigated. We found that cell spheroids formed in hydrogels that were exposed to MT were significantly smaller than spheroids formed without MT incubation, suggesting that matrix stiffening played a crucial role in the sizes of cancer cell spheroids. Through utilizing highly specific and orthogonal enzymatic reactions, this hydrogel platform permits rapid and mild in situ cell encapsulation, as well as dynamic control of matrix stiffness for investigating the role of matrix stiffening on cell fate processes.