Rapid Tuning Research Articles

Rapid Tuning of Auditory “What” and “Where” Pathways by Training

Behavioral improvement within the first hour of training is commonly explained as procedural learning (i.e., strategy changes resulting from task familiarization). However, it may additionally reflect a rapid adjustment of the perceptual and/or attentional system in a goal-directed task. In support of this latter hypothesis, we show feature-specific gains in performance for groups of participants briefly trained to use either a spectral or spatial difference between 2 vowels presented simultaneously during a vowel identification task. In both groups, the neuromagnetic activity measured during the vowel identification task following training revealed source activity in auditory cortices, prefrontal, inferior parietal, and motor areas. More importantly, the contrast between the 2 groups revealed a striking double dissociation in which listeners trained on spectral or spatial cues showed higher source activity in ventral ("what") and dorsal ("where") brain areas, respectively. These feature-specific effects indicate that brief training can implicitly bias top-down processing to a trained acoustic cue and induce a rapid recalibration of the ventral and dorsal auditory streams during speech segregation and identification.

Supercritical xenon-filled hollow-core photonic bandgap fiber

We demonstrate that filling a hollow-core photonic-bandgap fiber with supercritical xenon creates a medium with a controllable density up to several hundred times that at STP, while working at room temperature. The high compressibility of the supercritical fluid allows rapid tuning of the spectral guidance window by making small changes of gas pressure near the critical point. We discuss potential applications of this system in linear and nonlinear optics.

High-speed multi-THz-range mode-hop-free tunable mid-IR laser spectrometer

We report on a widely (2.25 THz or 75 cm(-1)) and rapidly (4.5 THz/s) mode-hop-free (MHF) tunable mid-IR laser source at ~3.3 μm, consisting of a 5%-MgO:LiNbO(3) singly resonant optical parametric oscillator (SRO) pumped by an automated broadly MHF tunable extended-cavity diode laser (ECDL). The broad and rapid MHF tuning capability of the ECDL is readily transferred to the SRO idler wave owing to the quasi-noncritical pump spectral acceptance bandwidth of the quasi-phase-matching. Fast and broadband high-resolution Doppler spectroscopy measurements of the ν(3) band of CH(4) are presented to illustrate the performance of the mid-IR optical parametric oscillator spectrometer.

Active Control of SPR by Thermoresponsive Hydrogels for Biosensor Applications.

The use of thermoresponsive poly(N-isopropylacrylamide)-based hydrogel (pNIPAAm) for rapid tuning of surface plasmon resonance (SPR) is reported. This approach is implemented by using an SPR layer architecture with an embedded indium tin oxide microheater and pNIPAAm film on its top. It takes advantage of rapid thermally induced swelling and collapse of pNIPAAm that is accompanied by large refractive index changes and leads to high thermo-optical coefficient of dn/dT = 2 × 10–2 RIU/K. We show that this material is excellently suited for efficient control of refractive index-sensitive SPR and that it can serve simultaneously as a 3D binding matrix in biosensor applications (if modified with biomolecular recognition elements for a specific capture of target analyte). We demonstrate that this approach enables modulating of the output signal in surface plasmon-enhanced fluorescence spectroscopy biosensors and holds potential for simple time-multiplexing of sensing channels for parallelized readout of fluorescence assays.

Method for fabrication and verification of conjugated nanoparticle-antibody tuning elements for multiplexed electrochemical biosensors

There is a critical need for more accurate, highly sensitive and specific assay for disease diagnosis and management. A novel, multiplexed, single sensor using rapid and label free electrochemical impedance spectroscopy tuning method has been developed. The key challenges while monitoring multiple targets is frequency overlap. Here we describe the methods to circumvent the overlap, tune by use of nanoparticle (NP) and discuss the various fabrication and characterization methods to develop this technique. First sensors were fabricated using printed circuit board (PCB) technology and nickel and gold layers were electrodeposited onto the PCB sensors. An off-chip conjugation of gold NP’s to molecular recognition elements (with verification technique) is described as well. A standard covalent immobilization of the molecular recognition elements is also discussed with quality control techniques. Finally use and verification of sensitivity and specificity is also presented. By use of gold NP’s of various sizes, we have demonstrated the possibility and shown little loss of sensitivity and specificity in the molecular recognition of inflammatory markers as “model” targets for our tuning system. By selection of other sized NP’s or NP’s of various materials, the tuning effect can be further exploited. The novel platform technology developed could be utilized in critical care, clinical management and at home health and disease management.

Phonon softening and direct to indirect band gap crossover in strained single-layer MoSe2

Motivated by recent experimental observations of Tongay et al. [Tongay et al., Nano Letters, 12(11), 5576 (2012)] we show how the electronic properties and Raman characteristics of single layer MoSe2 are affected by elastic biaxial strain. We found that with increasing strain: (1) the E' and E" Raman peaks (E1g and E2g in bulk) exhibit significant red shifts (up to 30 cm-1), (2) the position of the A1' peak remains at 180 cm-1 (A1g in bulk) and does not change considerably with further strain, (3) the dispersion of low energy flexural phonons crosses over from quadratic to linear and (4) the electronic band structure undergoes a direct to indirect bandgap crossover under 3% biaxial tensile strain. Thus the application of strain appears to be a promising approach for a rapid and reversible tuning of the electronic, vibrational and optical properties of single layer MoSe2 and similar MX2 dichalcogenides.

Optically tunable long wavelength infrared quantum cascade laser operated at room temperature

We demonstrate rapid tuning of the emission frequency of a room-temperature mid-infrared quantum cascade laser by external optical pumping. Emission frequency tuning over 0.3 cm−1 (10 GHz) has been achieved for a λ = 9 μm device by optical generation of electron-hole pairs along the entire length of the laser stripe. Measurements indicate that this approach allows for rapid broadband frequency-modulation of mid-infrared quantum cascade lasers at above 300 MHz modulation frequencies.

Hydrogen-bond-driven ‘homogeneous intercalation’ for rapid, reversible, and ultra-precise actuation of layered clay nanosheets

The use of hydrogen bonds permits a fluidic motion of differently sized alcohol molecules across the interlayer gap in LDH, which enables rapid and reversible tuning of interlayer spacing of the LDH at sub-Ångström precision by changing the mole ratio of the different alcohols.

Iterative plug-and-play methodology for constructing and modifying synthetic gene networks

We present a methodology for the design, construction, and modification of synthetic gene networks. This method emphasizes post-assembly modification of constructs based on network behavior, thus facilitating iterative design strategies and rapid tuning and repurposing of gene networks. The ease of post-construction modifications afforded by this approach and the ever-increasing repository of components within the framework will help to fast-track the development of functional genetic circuits for synthetic biology.

COP1 mediates the coordination of root and shoot growth by light through modulation of PIN1- and PIN2-dependent auxin transport in Arabidopsis

When a plant germinates in the soil, elongation of stem-like organs is enhanced whereas leaf and root growth is inhibited. How these differential growth responses are orchestrated by light and integrated at the organismal level to shape the plant remains to be elucidated. Here, we show that light signals through the master photomorphogenesis repressor COP1 to coordinate root and shoot growth in Arabidopsis. In the shoot, COP1 regulates shoot-to-root auxin transport by controlling the transcription of the auxin efflux carrier gene PIN-FORMED1 (PIN1), thus appropriately tuning shoot-derived auxin levels in the root. This in turn directly influences root elongation and adapts auxin transport and cell proliferation in the root apical meristem by modulating PIN1 and PIN2 intracellular distribution in the root in a COP1-dependent fashion, thus permitting a rapid and precise tuning of root growth to the light environment. Our data identify auxin as a long-distance signal in developmental adaptation to light and illustrate how spatially separated control mechanisms can converge on the same signaling system to coordinate development at the whole plant level.

Electrically-controlled rapid femtosecond pulse duration switching and continuous picosecond pulse duration tuning in an ultrafast Cr^4+:forsterite laser

We demonstrate rapid switching between picosecond and femtosecond operational regimes in a Cr(4+):forsterite laser, using an electrically-contacted GaInNAs SESAM with saturable absorption characteristics controlled via the quantum-confined Stark effect. Additionally, continuous picosecond pulse duration tuning by over a factor 3 is reported.

Customized optimization of metabolic pathways by combinatorial transcriptional engineering

A major challenge in metabolic engineering and synthetic biology is to balance the flux of an engineered heterologous metabolic pathway to achieve high yield and productivity in a target organism. Here, we report a simple, efficient and programmable approach named ‘customized optimization of metabolic pathways by combinatorial transcriptional engineering (COMPACTER)’ for rapid tuning of gene expression in a heterologous pathway under distinct metabolic backgrounds. Specifically, a library of mutant pathways is created by de novo assembly of promoter mutants of varying strengths for each pathway gene in a target organism followed by high-throughput screening/selection. To demonstrate this approach, a single round of COMPACTER was used to generate both a xylose utilizing pathway with near-highest efficiency and a cellobiose utilizing pathway with highest efficiency that were ever reported in literature for both laboratory and industrial yeast strains. Interestingly, these engineered xylose and cellobiose utilizing pathways were all host-specific. Therefore, COMPACTER represents a powerful approach to tailor-make metabolic pathways for different strain backgrounds, which is difficult if not impossible to achieve by existing pathway engineering methods.

Biaxial Stage Contouring Control with a Novel Anti-Windup PID Controller Strategy

For stage systems performing precision contouring actions under the conventional proportional–integral–derivative (PID) control structures, the phenomenon of actuator saturation is a common problem which can easily lead to the windup effect and cause unexpected results to the overall performance. To conquer this problem, this paper presents a new strategy for suppressing the windup effect in the conventional PID contouring control structures. In the proposed approach, the windup effect is modeled as a disturbance input to the PID controller such that an observer-based auxiliary control is designed to minimize the difference between the computed control force and the actual axial input based on an H-infinite optimization criterion. From theoretical analyses, it can show that the proposed anti-windup (AW) scheme can provide a more robust performance under the effects of windup than the conventional PID AW schemes. Moreover, it can also bring about better noise rejection capability to the controlled systems. Furthermore, the design of the proposed PID AW scheme is system independent and can be formulated based on the original PID controller parameters such that it can utilize a rapid on-line tuning of the controller parameters in order to prevent the windup effect. To validate the approach, a biaxial x-y stage system performing contouring action is applied which originally has obvious windup effect in both axial inputs under the conventional PID scheme. After the implementation, the experimental results show that the proposed PID AW scheme indeed improves the windup effect and also provides a better system robustness performance compared to the original one. It can be obtained that the experimental results are in accordance with the theoretical analyses, and show the effectiveness of the proposed method.

Wavelength-swept optical parametric oscillator for broadband mid-infrared spectroscopy

In this work we describe a wavelength-swept continuous-wave optical parametric oscillator (OPO) for the rapid acquisition of mid-infrared spectra spanning over hundreds of wavenumbers. Rapid tuning of a ytterbium-doped fibre pump laser resulted in the OPO idler tuning over 900 cm−1 in 3.36 ms at a resolution of 4.5 cm−1, within a total accessible range of 2.67 to 4.34 μm (2304–3752 cm−1). Predictable tuning characteristics allowed simple online calibration of recorded spectra for absolute mid-infrared frequency. The system thus offers a viable approach to broadband spectral acquisition in applications requiring high-radiance illumination.

Comb-based radiofrequency photonic filters with rapid tunability and high selectivity

Photonic technologies have received considerable attention for enhancement of radio-frequency (RF) electrical systems, including high-frequency analog signal transmission, control of phased arrays, analog-to-digital conversion, and signal processing. Although the potential of radio-frequency photonics for implementation of tunable electrical filters over broad RF bandwidths has been much discussed, realization of programmable filters with highly selective filter lineshapes and rapid reconfigurability has faced significant challenges. A new approach for RF photonic filters based on frequency combs offers a potential route to simultaneous high stopband attenuation, fast tunability, and bandwidth reconfiguration. In one configuration tuning of the RF passband frequency is demonstrated with unprecedented (~40 ns) speed by controlling the optical delay between combs. In a second, fixed filter configuration, cascaded four-wave mixing simultaneously broadens and smoothes comb spectra, resulting in Gaussian RF filter lineshapes exhibiting extremely high (>60 dB) main lobe to sidelobe suppression ratio and (>70 dB) stopband attenuation.

Rapid and Reversible Tuning of Structural Color of a Hydrogel over the Entire Visible Spectrum by Mechanical Stimulation

In this work, we report a rubberlike elastic hydrogel containing microdomains of bilayers periodically stacked into the polymer network that satisfy the Bragg’s law of diffraction. The rubberlike elastic hydrogel has been synthesized by applying double network principle into a viscoelastic hydrogel containing single-domain macroscopic lamellar bilayer. The hydrogel is able to tune the magnificent structural color reversibly over the entire wavelength range of visible spectrum as fast as the uniaxial tensile stretching and compressive deformation are applied and released. Owing to the strength, softness, and rubberlike elastic deformability, the tunable hydrogel can be used extensively to design a new class of soft tactile sensor as an advanced stress sensor that is able to detect a local deformation of a complicated force field.

Rapid Tuning Method of PID Parameters for AC Servo Control System Based on PMAC

This paper introduces the structure and working principle of AC servo control system based on programmable multi-axis controller (PMAC). The configurations and parameter tuning method for PMAC PID filters are discussed. It has been shown that, by combining feed-forward control and feed-back control together, the robustness and stability of the servo control system can be improved and the servo tracking error can be minimized if the controller parameters are tuned properly.

Spontaneous vortex production in driven condensates with narrow Feshbach resonances

We explore the possibility that, at zero temperature, vortices can be created spontaneously in a condensate of cold Fermi atoms, whose scattering is controlled by a narrow Feshbach resonance by rapid magnetic tuning from the BEC to BCS regime. This could be achievable with current experimental techniques.

Broadband, rapidly tunable Ti:sapphire-pumped BiB_3O_6 femtosecond optical parametric oscillator

We report a femtosecond optical parametric oscillator (OPO) based on the nonlinear material BiB₃O₆ (BIBO) pumped directly by a Kerr lens mode-locked Ti:sapphire laser. Using a 1.5 mm long BIBO crystal cut at θ=11.4° for collinear type I (e→o+o) phase matching in the xz optical plane, femtosecond signal pulses across 1.4-1.6 μm, and idler pulses across 1.6-1.87 μm spectral range are generated, limited by the reflectivity bandwidth of the OPO mirrors. The high nonlinear gain and large spectral acceptance for type I interaction in the xz plane of BIBO permit rapid and continuous tuning across the entire range by simple fine adjustment of OPO cavity delay or through small changes in the pump wavelength, without varying any other parameters. Additionally, owing to the near-zero group velocity mismatch and dispersion, the OPO supports broad spectrum as wide as 33 nm, which results in self-compressed signal pulses. For 150 fs pump pulses, signal pulses with durations down to 106 fs with a time-bandwidth product of 0.48 are obtained without the need for intracavity dispersion compensation.

Tunable laser thin film interrogation

Film thickness is not only a crucial parameter in producing processes, such as semiconductor and optics production, but also a monitored variable in chemistry and biology, for example for tissue microscopy. Many working principles have been demonstrated and are in use in different fields due to their different limitations (observation film thickness, accuracy, measurement speed, etc.). One of these working principles is thin film reflectometry (TFR). One method is based on a laser source and monitors the reflected intensity over growing film time. Another one employs a spectrally broad light source and measures the reflected intensity using a spectrometer. We introduce and demonstrate a measurement system based on a tunable laser stage. There are several different setups for laser wavelength tuning. One of the most promising solutions is based on monolithic laser diodes. Rapid tuning of the lasers wavelength is crucial for achieving high measurement rates. Monolithic laser diodes offer highest tuning rates and hence high performance. On the other hand, mechanically tunable lasers show broadband spectra that result in higher thickness accuracy in this particular application. Hence, we show a comparison of thin film measurements with a monolithic and a mechanically tunable laser source. This comparison shows that the measurement accuracy of the monolithic laser diode can compete with mechanical tuning. Furthermore, it is a promising approach when measurement tuning speed is an issue.