Tunable System Research Articles

Molecular Copper(I)-Sensitized Photoanodes for Alcohol Oxidation under Ambient Conditions.

Dye-sensitized photoelectrochemical cells can enable the production of molecules currently accessible through energetically demanding syntheses. Copper(I)-based dyes represent electronically tunable charge transfer and separation systems. Herein, we report a Cu(I)-bisdiimine donor-chromophore-acceptor dye with an absorbance in the visible part of the solar spectrum composed of a phenothiazine electron donor, and dipyrido[3,2-a:2',3'-c]phenazine electron acceptor. This complex is incorporated onto a zinc oxide nanowire semiconductor surface effectively forming a photoanode that is characterized spectroscopically and electrochemically. We investigate the photo-oxidation of hydroquinone, and the photosensitization of 2,2,6,6-tetramethylpiperidine-1-oxyl and N-hydroxyphthalimide for the oxidation of furfuryl alcohol to furfuraldehyde, resulting in near quantitative conversions, with poor selectivity to the alcohol.

Tunable translation-level CRISPR interference by dCas13 and engineered gRNA in bacteria

Although CRISPR-dCas13, the RNA-guided RNA-binding protein, was recently exploited as a translation-level gene expression modulator, it has still been difficult to precisely control the level due to the lack of detailed characterization. Here, we develop a synthetic tunable translation-level CRISPR interference (Tl-CRISPRi) system based on the engineered guide RNAs that enable precise and predictable down-regulation of mRNA translation. First, we optimize the Tl-CRISPRi system for specific and multiplexed repression of genes at the translation level. We also show that the Tl-CRISPRi system is more suitable for independently regulating each gene in a polycistronic operon than the transcription-level CRISPRi (Tx-CRISPRi) system. We further engineer the handle structure of guide RNA for tunable and predictable repression of various genes in Escherichia coli and Vibrio natriegens. This tunable Tl-CRISPRi system is applied to increase the production of 3-hydroxypropionic acid (3-HP) by 14.2-fold via redirecting the metabolic flux, indicating the usefulness of this system for the flux optimization in the microbial cell factories based on the RNA-targeting machinery.

Dynamic analysis and circuit design of tunable multi-vortex chaotic systems based on memristors

Dynamic analysis and circuit design of tunable multi-vortex chaotic systems based on memristors

High-Repetition-Rate 2.3–2.7 µm Acousto-Optically Tuned Narrow-Line Laser System Comprising Two Master Oscillators and Power Amplifiers Based on Polycrystalline Cr2+:ZnSe with the 2.1 µm Ho3+:YAG Pulsed Pumping

High-average-power narrow-linewidth tunable solid-state lasers in the wavelength region between 2 and 3 μm are attractive light sources for many applications. This paper reports a narrow-linewidth widely tunable laser system based on the polycrystalline Cr2+:ZnSe elements pumped by repetitively pulsed 2.1 µm Ho3+:YAG laser operating at a pulse rate of tens of kilohertz. An advanced procedure of ZnSe element doping and surface improvement was applied to increase the laser-induced damage threshold, which resulted in an increase in the output power of the Cr2+:ZnSe laser system. The high-average-power laser system comprised double master oscillators and power amplifiers: Ho3+:YAG and Cr2+:ZnSe laser oscillators, and Ho3+:YAG and Cr2+:ZnSe power amplifiers. The output wavelength was widely tuned within 2.3–2.7 µm by means of an acousto-optical tunable filter inside a Cr2+:ZnSe master oscillator cavity. The narrow-linewidth operation at the pulse repetition rate of 20–40 kHz in a high-quality beam with an average output power of up to 9.7 W was demonstrated.

Experimental Demonstration of a Tunable Energy-Selective Gamma-Ray Imaging System Based on Recoil Electrons

The domain of gamma-ray imaging necessitates technological advancements to surmount the challenge of energy-selective imaging. Conventional systems are constrained in their dynamic focus on specific energy ranges, a capability imperative for differentiating gamma-ray emissions from diverse sources. This investigation introduces an innovative imaging system predicated on the detection of recoil electrons, addressing the demand for adjustable energy selectivity. Our methodology encompasses the design of a gamma-ray imaging system that leverages recoil electron detection to execute energy-selective imaging. The system’s efficacy was investigated experimentally, with emphasis on the adaptability of the energy selection window. The experimental outcomes underscore the system’s adeptness at modulating the energy selection window, adeptly discriminating gamma rays across a stipulated energy spectrum. The results corroborate the system’s adaptability, with an adjustable energy resolution that coincides with theoretical projections and satisfies the established criteria. This study affirms the viability and merits of utilizing recoil electrons for tunable energy-selective gamma-ray imaging. The system’s conceptualization and empirical validation represent a notable progress in gamma-ray imaging technology, with prospective applications extending from medical imaging to astrophysics. This research sets a solid foundation for subsequent inquiries and advancements in this domain.

Exploring plant-derived phytochrome chaperone proteins for light-switchable transcriptional regulation in mammals

Synthetic biology applications require finely tuned gene expression, often mediated by synthetic transcription factors (sTFs) compatible with the human genome and transcriptional regulation mechanisms. While various DNA-binding and activation domains have been developed for different applications, advanced artificially controllable sTFs with improved regulatory capabilities are required for increasingly sophisticated applications. Here, in mammalian cells and mice, we validate the transactivator function and homo-/heterodimerization activity of the plant-derived phytochrome chaperone proteins, FHY1 and FHL. Our results demonstrate that FHY1/FHL form a photosensing transcriptional regulation complex (PTRC) through interaction with the phytochrome, ΔPhyA, that can toggle between active and inactive states through exposure to red or far-red light, respectively. Exploiting this capability, we develop a light-switchable platform that allows for orthogonal, modular, and tunable control of gene transcription, and incorporate it into a PTRC-controlled CRISPRa system (PTRCdcas) to modulate endogenous gene expression. We then integrate the PTRC with small molecule- or blue light-inducible regulatory modules to construct a variety of highly tunable systems that allow rapid and reversible control of transcriptional regulation in vitro and in vivo. Validation and deployment of these plant-derived phytochrome chaperone proteins in a PTRC platform have produced a versatile, powerful tool for advanced research and biomedical engineering applications.

Topological rainbow trapping of shear horizontal waves in a phononic crystal plate with tapered surface

Topological interface states have localized field enhancement characteristics. Integrating them with the concept of rainbow trapping undoubtedly be a more effective method for elastic energy localization and collection. In this paper, the tunable interface state of shear horizontal (SH) waves is realized in a one-dimensional (1D) phononic crystal (PC) plate by modifying the structural parameters of unit cells with tapered surfaces, where the interface state emerges in the overlapping band gaps of two types of unit cells with different Zak phases. Furthermore, we assembled seven types of unit cells with gradient variations, achieving topological rainbow trapping. Meanwhile, the robustness of the rainbow state has been demonstrated, and more separated frequencies are obtained by changing the order of these unit cells. The results of the study demonstrate that the highly localized, compact, and broadband tunable topological rainbow system we designed holds promise for applications in areas such as elastic energy harvesting, filtering, and multi-frequency signal processing.

Surface Charged Polymeric Micelles─A Tunable Model System Studied by SANS

Surface Charged Polymeric Micelles─A Tunable Model System Studied by SANS

Surface-Functionalized Microgels as Artificial Antigen-Presenting Cells to Regulate Expansion of T Cells.

Artificial antigen-presenting cells (aAPCs) are currently used to manufacture T cells for adoptive therapy in cancer treatment, but a readily tunable and modular system can enable both rapid T cell expansion and control over T cell phenotype. Here, it is shown that microgels with tailored surface biochemical properties can serve as aAPCs to mediate T cell activation and expansion. Surface functionalization of microgels is achieved via layer-by-layer coating using oppositely charged polymers, forming a thin but dense polymer layer on the surface. This facile and versatile approach is compatible with a variety of coating polymers and allows efficient and flexible surface-specific conjugation of defined peptides or proteins. The authors demonstrate that tethering appropriate stimulatory ligands on the microgel surface efficiently activates T cells for polyclonal and antigen-specific expansion. The expansion, phenotype, and functional outcome of primary mouse and human T cells can be regulated by modulating the concentration, ratio, and distribution of stimulatory ligands presented on microgel surfaces as well as the stiffness and viscoelasticity of the microgels.

Toward Bioactive Hydrogels: A Tunable Approach via Nucleic Acid-Collagen Complexation

Abstract Purpose Nucleic acid-collagen complexes (NACCs) are unique biomaterials formed by binding short, monodisperse single-stranded DNA (ssDNA) with type I collagen. These complexes spontaneously generate microfibers and nanoparticles of varying sizes, offering a versatile platform with potential applications in tissue engineering and regenerative medicine. However, the detailed mechanisms behind the nucleic acid-driven assembly of collagen fibers still need to be established. We aim to understand the relationship between microscopic structure and bulk material properties and demonstrate that NACCs can be engineered as mechanically tunable systems. Methods We present a study to test NACCs with varying molar ratios of collagen to random ssDNA oligonucleotides. Our methods encompass the assessment of molecular interactions through infrared spectroscopy and the characterization of gelation and rheological behavior. We also include phase contrast, confocal reflectance, and transmission electron microscopy to provide complementary information on the 3D structural organization of the hydrogels. Results We report that adding DNA oligonucleotides within collagen robustly reinforces and rearranges the hydrogel network and accelerates gelation by triggering rapid fiber formation and spontaneous self-assembly. The elasticity of NACC hydrogels can be tailored according to the collagen-to-DNA molar ratio, ssDNA length, and collagen species. Conclusion Our findings hold significant implications for the design of mechanically tunable DNA-based hydrogel systems. The ability to manipulate hydrogel stiffness by tailoring DNA content and collagen concentration offers new avenues for fine tuning material properties, enhancing the versatility of bioactive hydrogels in diverse biomedical applications. Lay Summary This work is an example of forming fibers and gels with tunable elasticity that stems from the complexation of short-length nucleic acids (on the order of size of aptamers) and collagen, which can be potentially extended to a variety of functionalized hydrogel designs and tailored biomedical applications. Incorporating DNA induces mechanical changes in NACCs. Graphical Abstract

A Chlorinated Indolium‐Based Nonlinear Optical Crystal Achieving Effective Terahertz‐Wave Generation and Highly Sensitive Detection

AbstractNonlinear optical (NLO) crystals have shown great potential in generating and detecting coherent terahertz waves, which have a wide range of applications. However, designing the microscopic structure of NLO crystals to obtain excellent macroscopic properties has been a challenge. In this work, by the introduction of chloro substitution into the cation part of indolium‐based salt structure, a new acentric OH5CI‐BS crystal, namely, [(C19H19NOCl)+∙(C6H5SO3)−, P1] is synthesized and grown using a feasible evaporation method. The cut‐off edge of the grown OH5CI‐BS crystal reaches 524 nm, corresponding to a bandgap of 2.37 eV. The largest single crystals of OH5CI‐BS with the size of ≈ 9 × 8 × 0.3 mm3 are grown. Remarkably, by use of OH5CI‐BS crystals as both the THz‐wave emitter and detector, a widely tunable (from 2.23 to 33.54 THz) and monochromatic THz system is demonstrated for the first time, and the detection depth of the OH5CI‐BS based up‐conversion at room temperature is >4 orders better than a commercial Golay Cell and even 2 orders better than a 4‐K‐Bolometer. This work indicates that OH5CI‐BS is a promising future NLO material for terahertz technology, and also provides a feasible design strategy for other organic optoelectronic functional materials.

In Vitro Investigation of Vocal Fold Cellular Response to Variations in Hydrogel Porosity and Elasticity.

Tissue regeneration is intricately influenced by the dynamic interplay between the physical attributes of tissue engineering scaffolds and the resulting biological responses. A tunable microporous hydrogel system was engineered using gelatin methacryloyl (GelMA) and polyethylene glycol diacrylate (PEGDA), with polyethylene glycol (PEG) serving as a porogen. Through systematic variation of PEGDA molecular weights, hydrogels with varying mechanical and architectural properties were obtained. The objective of the present study was to elucidate the impact of substrate mechanics and architecture on the immunological and reparative activities of vocal fold tissues. Mechanical characterization of the hydrogels was performed using tensile strength measurements and rheometry. Their morphological properties were investigated using scanning electron microscopy (SEM) and confocal microscopy. A series of biological assays were conducted. Cellular morphology, differentiation, and collagen synthesis of human vocal fold fibroblasts (hVFFs) were evaluated using immunostaining. Fibroblast proliferation was studied using the WST-1 assay, and cell migration was investigated via the Boyden chamber assay. Macrophage polarization and secretions were also examined using immunostaining and ELISA. The results revealed that increasing the molecular weight of PEGDA from 700 Da to 10,000 Da resulted in decreased hydrogel stiffness, from 62.6 to 8.8 kPa, and increased pore dimensions from approximately 64.9 to 137.4 μm. Biological evaluations revealed that hydrogels with a higher stiffness promoted fibroblast proliferation and spreading, albeit with an increased propensity for fibrosis, as indicated by a surge in myofibroblast differentiation and collagen synthesis. In contrast, hydrogels with greater molecular weights had a softer matrix with expanded pores, enhancing cellular migration and promoting an M2 macrophage phenotype conducive to tissue healing. The findings show that the hydrogels formulated with a PEGDA molecular weight of 6000 Da are best among the hydrogels considered for vocal fold repair. The microporous hydrogels could be tuned to serve in other tissue engineering applications.

Microfluidic Assembly of Degradable, Stereocomplexed Hydrogel Microparticles.

Hydrogel microparticles (HMPs) have been investigated widely for their use in tissue engineering and drug delivery applications. However, translation of these highly tunable systems has been hindered by covalent cross-linking methods within microparticles. Stereocomplexation, a stereospecific form of physical cross-linking, provides a robust yet degradable alternative for creating translationally relevant HMPs. Herein, 4-arm polyethylene glycol (PEG) stars were used as macromolecular initiators from which oligomeric poly(l-lactic acid) (PLLA) was polymerized with a degree of polymerization (DPn) of 20 on each arm. Similarly, complementary propargyl-containing ABA cross-linkers with enantiomeric poly(d-lactic acid) (PDLA) segments (DPn = 20) on each arm. Droplets of these gel precursors were formed via a microfluidic organic-in-oil-in-water system where microparticles self-assembled via stereocomplexation and were stabilized after precipitation in deionized water. By varying the flow rate of the dispersed phase, well-defined microparticles with diameters of 33.7 ± 0.5, 62.4 ± 0.6, and 105.7 ± 0.8 μm were fabricated. Gelation due to stereocomplexation was confirmed via wide-angle X-ray scattering in which HMPs exhibited the signature diffraction pattern of stereocomplexed PLA at 2θ = 12.2, 21.2, 24.2°. Differential scanning calorimetry also confirmed stereocomplexation by the appearance of a crystallization exotherm (Tc = 37 °C) and a high-temperature endotherm (Tm = 159 °C) that does not appear in the homocrystallization of PLLA or the hydrogel precursors. Additionally, the propargyl handle present on the cross-linker allows for pre- or post-assembly thiol-yne "click" functionalization as demonstrated by the addition of thiol-containing fluorophores to the HMPs.

Wavelength-Tunable Chirped Pulse Amplification System (1720 nm–1800 nm) Based on Thulium-Doped Fiber

Chirped pulse amplification (CPA) has been a commonly used methodology to obtain powerful ultrashort laser pulses ever since its first demonstration. However, wavelength-tunable CPA systems are much less common. Wavelength-tunable ultrashort and intense laser pulses are desirable in various fields such as nonlinear spectroscopy and optical parametric amplification. In this work, we report a 1720 nm–1800 nm tunable CPA system based on Tm-doped fiber. The tunable CPA system contains a seed laser, a pulse stretcher, two cascaded amplifiers and a pulse compressor. The dispersion-managed seed laser cavity emits wavelength-tunable laser pulses with pulse durations of several ps and spectral widths from 25 nm to 34 nm. After being stretched temporally to tens of ps, the laser pulses are then amplified in two-stage amplifiers and compressed in a Treacy-type compressor. At 1720 nm, the maximum average power of 126 mW is obtained with a pulse duration of 507 fs; at 1800 nm, the maximum average power of 264 mW is obtained with a pulse duration of 294 fs. The pulse repetition rates are around 22.7 MHz. We perform an analysis of the system design based on numerical simulations and go on to suggest further steps for improvement. To the best of our knowledge, this is the first demonstration of a tunable CPA system beyond 1.1 μm. Considering the specific wavelength range, this wavelength-tunable CPA system is highly desirable for biomedical imaging, sensing, and parametric amplifiers.

Confined-Coordination Induced Intergrowth of Metal-Organic Frameworks into Precise Molecular Sieving Membranes.

Metal-organic framework (MOF) membranes with rich functionality and tunable pore system are promising for precise molecular separation; however, it remains a challenge to develop defect-free high-connectivity MOF membrane with high water stability owing to uncontrollable nucleation and growth rate during fabrication process. Herein, we report on a confined-coordination induced intergrowth strategy to fabricate lattice-defect-free Zr-MOF membrane towards precise molecular separation. The confined-coordination space properties (size and shape) and environment (water or DMF) were regulated to slow down the coordination reaction rate via controlling the counter-diffusion of MOF precursors (metal cluster and ligand), thereby inter-growing MOF crystals into integrated membrane. The resulting Zr-MOF membrane with angstrom-sized lattice apertures exhibits excellent separation performance both for gas separation and water desalination process. It was achieved H2 permeance of ~1200 GPU and H2/CO2 selectivity of ~67; water permeance of ~8 L ⋅ m-2 ⋅ h-1 ⋅ bar-1 and MgCl2 rejection of ~95 %, which are one to two orders of magnitude higher than those of state-of-the-art membranes. The molecular transport mechanism related to size-sieving effect and transition energy barrier differential of molecules and ions was revealed by density functional theory calculations. Our work provides a facile approach and fundamental insights towards developing precise molecular sieving membranes.

Confined‐Coordination Induced Intergrowth of Metal–Organic Frameworks into Precise Molecular Sieving Membranes

AbstractMetal–organic framework (MOF) membranes with rich functionality and tunable pore system are promising for precise molecular separation; however, it remains a challenge to develop defect‐free high‐connectivity MOF membrane with high water stability owing to uncontrollable nucleation and growth rate during fabrication process. Herein, we report on a confined‐coordination induced intergrowth strategy to fabricate lattice‐defect‐free Zr‐MOF membrane towards precise molecular separation. The confined‐coordination space properties (size and shape) and environment (water or DMF) were regulated to slow down the coordination reaction rate via controlling the counter‐diffusion of MOF precursors (metal cluster and ligand), thereby inter‐growing MOF crystals into integrated membrane. The resulting Zr‐MOF membrane with angstrom‐sized lattice apertures exhibits excellent separation performance both for gas separation and water desalination process. It was achieved H2 permeance of ~1200 GPU and H2/CO2 selectivity of ~67; water permeance of ~8 L ⋅ m−2 ⋅ h−1 ⋅ bar−1 and MgCl2 rejection of ~95 %, which are one to two orders of magnitude higher than those of state‐of‐the‐art membranes. The molecular transport mechanism related to size‐sieving effect and transition energy barrier differential of molecules and ions was revealed by density functional theory calculations. Our work provides a facile approach and fundamental insights towards developing precise molecular sieving membranes.

High transmission efficiency collection system for laser-accelerated proton beams based on permanent magnet quadrupoles prefocusing

A new high transmission efficiency, easily tunable, and cost-effective beam collection system is proposed for laser-accelerated proton beams with large divergence angles and wide energy spectra. In previous experiments conducted at the compact laser plasma accelerator platform of Peking University, a beamline was initially constructed with a collection system based on an electromagnetic quadrupoles (EMQs) triplet. However, due to the limited acceptance angle, the EMQs exhibited a monoenergetic transmission efficiency of only 10% to 20% for laser accelerated proton beams. Permanent magnet quadrupoles (PMQs), known for their high magnetic field gradients, compact size, and lower expenses, are well suited for integration with other readily adjustable transmission elements like EMQs and solenoids, effectively enhancing the beam collection capabilities of the system. In this paper, we show that by introducing a pair of centimeter-sized PMQs in front of the EMQs for beam prefocusing, the beam’s transverse size is quickly compressed, enabling transmission of highly divergent protons. Experimental results demonstrate that the prefocusing by PMQs increased the system’s transmission efficiency by a factor of 2.44 to 6.01 compared to the original setup, while also enhancing the energy selection based on stronger chromatic effect. This method can be extended to 100 MeV high-energy proton beamlines and is crucial for applications of laser plasma accelerators. Published by the American Physical Society 2024

Development and calibration of a multi-delay coherence imaging diagnostic on the MAST-U tokamak.

The MAST-U Super-X divertor provides the opportunity to study fusion plasma exhaust under novel conditions. However, in order to study these conditions, advanced diagnostics are required. Following the development of the MAST-U Multi-Wavelength Imaging (MWI) diagnostic, we present the installation of a multi-delay coherence imaging spectroscopy (CIS) system within the MAST-U MWI, along with modifications made to the MWI for effective operation. This diagnostic will measure either carbon ion flow velocities and temperatures or electron densities through Dγ emission. We have extended previously developed techniques for wavelength calibration to account for errors due to the misalignment of interferometer components. In addition, we have developed a comprehensive calibration procedure to account for the temperature dependence of the instrument's delays by fitting to a linearly modified version of the delay equation presented by Veiras etal. [Appl. Opt. 49(15), 2769 (2010)]. Together, these procedures reduce the cost and hardware complexity of implementing CIS instruments when compared to those that use in situ or tunable laser calibration systems, as calibrations can be generated to good accuracy using previously measured data.

Programming tunable active dynamics in a self-propelled robot.

We present a scheme for producing tunable active dynamics in a self-propelled robotic device. The robot moves using the differential drive mechanism where two wheels can vary their instantaneous velocities independently. These velocities are calculated by equating robot's equations of motion in two dimensions with well-established active particle models and encoded into the robot's microcontroller. We demonstrate that the robot can depict active Brownian, run and tumble, and Brownian dynamics with a wide range of parameters. The resulting motion analyzed using particle tracking shows excellent agreement with the theoretically predicted trajectories. Later, we show that its motion can be switched between different dynamics using light intensity as an external parameter. Intriguingly, we demonstrate that the robot can efficiently navigate through many obstacles by performing stochastic reorientations driven by the gradient in light intensity towards a desired location, namely the target. This work opens an avenue for designing tunable active systems with the potential of revealing the physics of active matter and its application for bio- and nature-inspired robotics.

Laser Excitation of the Th-229 Nucleus.

The 8.4eV nuclear isomer state in Th-229 is resonantly excited in Th-doped CaF_{2} crystals using a tabletop tunable laser system. A resonance fluorescence signal is observed in two crystals with different Th-229 dopant concentrations, while it is absent in a control experiment using Th-232. The nuclear resonance for the Th^{4+} ions in Th:CaF_{2} is measured at the wavelength 148.3821(5)nm, frequency 2020.409(7)THz, and the fluorescence lifetime in the crystal is 630(15)s, corresponding to an isomer half-life of 1740(50)s for a nucleus isolated in vacuum. These results pave the way toward Th-229 nuclear laser spectroscopy and realizing optical nuclear clocks.