Tunable Channel Research Articles

Covalent organic frameworks embedded membrane via acetic-acid-catalyzed interfacial polymerization for dyes separation: Enhanced permeability and selectivity

With the increasing demand of high water-quality, membrane filtration technologies are playing further important roles in water treatment owing to their small footprints, reduced use of chemicals and stable performances. However, the inherent permeability-selectivity trade-off is still a significant obstacle restricting the broad applications of membrane separation. Hydrophilic modification via doping nanoparticles into membranes is considered an effective solution to improve the permeability while maintaining selectivity. However, agglomeration of nanoparticles often results in inhomogeneity of the modified membranes. In this study, hybrid membranes with separated covalent organic framework (COF) particles that were uniformly embedded in the membrane surface pores were firstly fabricated via acetic-acid-catalyzed in situ synthesis. Owing to the ample hydrophilic chemical groups and tunable molecular transport channels in COFs, the modified membranes yielded almost twice higher water flux (about 200 L m−2·h−1·bar) than the pristine membranes with simultaneously enhanced rejection of water pollutants (i.e., dyes). In addition, the pure organic structure of COF improves the polymer-filler interaction of the mixed film, thereby reducing the risk of leakage. Therefore, the hybrid membranes also exhibited relatively high stability in long-term operations and different pH conditions, which makes them promising candidates in future membrane applications.

Experimental test of exchange fluctuation relations in an open quantum system

Elucidating the energy transfer between a quantum system and a reservoir is a central issue in quantum non-equilibrium thermodynamics, which could provide novel tools to engineer quantum-enhanced heat engines. The lack of information on the reservoir inherently limits the practical insight that can be gained on the exchange process of open quantum systems. Here, we investigate the energy transfer for an open quantum system in the framework of quantum fluctuation relations. As a novel toolbox, we employ a nitrogen-vacancy center spin qubit in diamond, subject to repeated quantum projective measurements and a tunable dissipation channel. In the presence of energy fluctuations originated by dissipation and quantum projective measurements, the experimental results, supplemented by numerical simulations, show the validity of the energy exchange fluctuation relation, where the energy scale factor encodes missing reservoir information in the system out-of-equilibrium steady state properties. This result is complemented by a theoretical argument showing that, also for an open three-level quantum system, the existence of an out-of-equilibrium steady state dictates a unique time-independent value of the energy scale factor for which the fluctuation relation is verified. Our findings pave the way to the investigation of energy exchange mechanisms in arbitrary open quantum systems.

Tunable arc-shaped acoustic metasurface carpet cloak

In this paper, a tunable arc-shaped acoustic metasurface (AAM) carpet cloak has been proposed and systematically investigated. The AAM carpet cloak consists of covers, rotors, bolts and nuts. The rotors can be rotated continuously within the covers to form a reconfigurable hook channel mechanism. By setting various rotational angles, we construct two-dimensional (2D) tunable AAM carpet cloaks to achieve excellent stealth performances under different operating conditions. Numerical simulations and experimental results for the 2D carpet cloaks show good agreements. Furthermore, simulated results for three-dimensional (3D) carpet cloaks have demonstrated that tapered objects are successfully escaping from being detected. The tunable hook channel mechanism can be flexibly applied to arbitrarily curved metasurface carpet cloaks, making them closer to practical invisibility acoustic devices.

Microstrip Tunable Diplexer With Separately-Designable Channels

A microstrip tunable diplexer with two separately- designable channels and multiple transmission zeroes (TZs) using common element-loaded uniform impedance resonator (UIR) is proposed. The common UIR operating in third harmonic ( ${f} _{3}$ ) and fifth harmonic ( ${f} _{5}$ ) is used for designing the two diplexer channels. The stub is loaded at the voltage-null point of ${f} _{3}$ on the common UIR and the varactor is loaded at the open end of the stub. The varactor-loaded stub can separately tune ${f} _{5}$ but has no effect on ${f} _{3}$ so that the two channels can be separately designed. Meanwhile, the input port is tap-connected to the common UIR, which necessarily produces a common TZ between ${f} _{3}$ and ${f} _{5}$ , existing in both channel filtering responses. In the tunable high channel design (at ${f} _{5}$ ), the major design concept relies on choosing the properly values of three varactor diodes, the desired external quality factor and coupling coefficient can be easily obtained for realizing the constant absolute bandwidth (ABW). By properly choosing coupling schemes of the two channels, more TZs are realized at the desired locations. For demonstration, a diplexer with a fixed low channel and a tunable high channel with the constant ABW is designed, fabricated and measured.

Reticular chemistry in electrochemical carbon dioxide reduction

Electrochemical CO2 reduction (ECR) represents a promising strategy for utilizing CO2, an industrial waste, as an abundant and cheap carbon source for organic synthesis as well as storing intermittent renewable electricity from renewable sources. Efficient electrocatalysts allowing CO2 to be reduced selectively and actively are crucial since the ECR is a complex and sluggish process producing a variety of products. Metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) have emerged as versatile materials applicable in many fields due to their unique properties including high surface areas and tunable pore channels. Besides, the emerging reticular chemistry makes tuning their features on the atomic/molecular levels possible, thereby lending credence to the prospect of their utilizations. Herein, an overview of recent progress in employing framework material-based catalysts, including MOFs, COFs and their derivatives, for ECR is provided. The pertinent challenges, future trends, and opportunities associated with those systems are also discussed.

2-$\mu$ m Free-Space Data Transmission Based on an Actively Mode-Locked Holmium-Doped Fiber Laser

We experimentally demonstrate a 2- $\mu \text{m}$ free-space data transmission system in a simulated atmospheric turbulent device with an actively mode-locked holmium-doped fiber laser. The central wavelength can be adjusted from 2035.6 nm to 2050.2 nm with optional repetition rates of 1.01 GHz and 2.02 GHz, respectively, and the pulse is stabilized by adding a fiber Fabry-Perot filter in the laser cavity. The pulse sequence can be modulated by a digital signal and transmitted in a tunable simulated atmospheric turbulent channel. Compared with back-to-back (BTB), the optical signal-to-noise ratio (OSNR) of 2- $\mu \text{m}$ laser carrier reduces from 15.04 dB to 6.67 dB under the condition of $\text{C}_{\mathrm {n}}^{2}=5.71 \times 10^{-16}\text{m}^{-2/3}$ , and the received power jitter increases from ±0.04 dB to ±0.74 dB. The sensitivity of the 2- $\mu \text{m}$ data transmission system is −19.52 dBm. In addition, we compare the average receiving power standard deviation and power penalty between the 2- $\mu \text{m}$ laser and a 1.55- $\mu \text{m}$ laser under the same propagation conditions. The experimental results demonstrate that the 2- $\mu \text{m}$ laser communication system realizes superior performance in a weak turbulent channel.

Structure and topological transport in Pb-doping topological crystalline insulator SnTe (001) film

Topological crystalline insulator (TCI) as a new type of topological materials has attracted extensive research interests for its tunable topological properties. Due its symmetry topological protection essence, the structure investigation provides a solid basement for tuning its topological transport properties. On SrTiO3 (111) substrate, the SnTe film was found to be epitaxial growth only along [001] while not [111] direction. The detailed structural study was performed and a structural model was proposed to elucidate epitaxial growth of the SnTe (001) film. The transport properties of SnTe (001) film were further investigated and a typical weak anti-localization effect was observed. By Pb-doping into SnTe, the bulk carriers were inhibited and its topological surface states were strengthened to induce the enhanced surface transport contribution. With tunable multiple transport channels from the even Dirac cones, the TCI SnTe film systems will have the potential application in future spintronics devices.

S/S+-band tunable dual-wavelength thulium doped fluoride fiber laser

A simple S/S+-band dual-wavelength thulium doped fluoride fiber laser (DWFL) with tunable channel spacing is demonstrated. The system utilizes a 24 channel arrayed waveguide grating to control the spacing between the two lasing wavelengths. The widest spacing that can obtained between two lasing wavelengths is 17.49 nm, while the narrowest is 0.75 nm. The cavity loss in the DWFL is controlled using two variable optical attenuators to equalize the power of the two lasing wavelengths. The DWFL has a maximum signal to noise ratio (SNR) of approximately 49.60 dB and good stability over long periods of operation, with only minor SNR fluctuations of less than 5.00 dB observed. The DWFL’s output also has side-mode suppression ratio (SMSR) of between 0.12 dB and 1.56 dB, indicating that there is little to no suppression of one wavelength over another, as well as a balanced power output that is highly desirable when used as reference or signal sources.

Advanced Synthesis of Wide-Tuning-Range Frequency-Adaptive Bandpass Filter With Constant Absolute Bandwidth

This article proposes an advanced synthesis of the frequency-adaptive bandpass filter (FA-BPF) with constant absolute bandwidth (ABW). The proposed synthesis is based on the element-variable coupling matrix (EVCM), which is directly extracted from the classical filter polynomials. The extraction method is presented, investigated in detail, and confirmed by a set of numerical simulations. All frequency-dependent couplings between the resonators in an FA-BPF are uniquely modeled by the new coupling matrix, and the element variation of the EVCM directly accounts for the frequency tuning behavior of an FA-BPF. This one-to-one correspondence tackles the difficulty of the FA-BPF synthesis and design with a different center frequency tuning range (FTR), a different bandwidth (BW), and a different BW variation rate. This article also proposes the predefined coupling technique in the new synthesis. It allows both nonfrequency-dependent matrix and frequency-dependent matrix in an EVCM to be separately implemented in practice. For experimental demonstration, two four-pole/four-transmission zero (TZ) FA-BPFs with identical passband and constant ABW are implemented and then constitute a frequency-adaptive bandpass diplexer (FA-BPD) with two tunable channels that have identical passband and constant ABW. The measurement results exhibited performance superiority of the design and validated the proposed design method.

Decoupling Ionic and Electronic Pathways in Low-Dimensional Hybrid Conductors.

The construction of two-dimensional (2D) layered compounds for nanofluidic ion transport has recently attracted increasing interest due to the facile fabrication, tunable channel size, and high flux of these materials. Here we design a nacre-mimetic graphite-based nanofluidic structure in which the nanometer-thick graphite flakes are wrapped by negatively charged nanofibrillated cellulose (NFC) fibers to form multiple 2D confined spacings as nanochannels for rapid cation transport. At the same time, the graphite-NFC structure exhibits an ultralow electrical conductivity (σe ≤ 10-9 S/cm), even when the graphite concentration is up to 50 wt %, well above the percolation threshold (∼1 wt %). By tuning the hydration degree of graphite-NFC composites, the surface-charge-governed ion transport in the confined ∼1 nm spacings exhibits nearly 12 times higher ionic conductivity (1 × 10-3 S/cm) than that of a fully swollen structure (∼1.5 nm, 8.5 × 10-5 S/cm) at salt concentrations up to 0.1 M. The resulting charge selective conductor shows intriguing features of both high ionic conductivity and low electrical conductivity. Moreover, the inherent stability of the graphite and NFC components contributes to the strong functionality of the nanofluidic ion conductors in both acidic and basic environments. Our work demonstrates this 1D-2D material hybrid system as a suitable platform to study nanofluidic ion transport and provides a promising strategy to decouple ionic and electronic pathways, which is attractive for applications in new nanofluidic device designs.

Exceptional points in tunable superconducting resonators

Superconducting quantum circuits are potential candidates to realize a large-scale quantum computer. The envisioned large density of integrated components, however, requires a proper thermal management and control of dissipation. To this end, it is advantageous to utilize tunable dissipation channels and to exploit the optimized heat flow at exceptional points (EPs). Here, we experimentally realize an EP in a superconducting microwave circuit consisting of two resonators. The EP is a singularity point of the Hamiltonian, and corresponds to the most efficient heat transfer between the resonators without oscillation of energy. We observe a crossover from underdamped to overdamped coupling via the EP by utilizing photon-assisted tunneling as an \emph{in situ} tunable dissipative element in one of the resonators. The methods studied here can be applied to different circuits to obtain fast dissipation, for example, for initializing qubits to their ground states. In addition, these results pave the way towards thorough investigation of parity--time ($\mathcal{PT}$) symmetric systems and the spontaneous symmetry breaking in superconducting microwave circuits operating at the level of single energy quanta.

High-performance silk-based hybrid membranes employed for osmotic energy conversion

The salinity gradient between seawater and river water is a clean energy source and an alternative solution for the increasing energy demands. A membrane-based reverse electrodialysis technique is a promising strategy to convert osmotic energy to electricity. To overcome the limits of traditional membranes with low efficiency and high resistance, nanofluidic is an emerging technique to promote osmotic energy harvesting. Here, we engineer a high-performance nanofluidic device with a hybrid membrane composed of a silk nanofibril membrane and an anodic aluminum oxide membrane. The silk nanofibril membrane, as a screening layer with condensed negative surface and nanochannels, dominates the ion transport; the anodic aluminum oxide membrane, as a supporting substrate, offers tunable channels and amphoteric groups. Thus, a nanofluidic membrane with asymmetric geometry and charge polarity is established, showing low resistance, high-performance energy conversion, and long-term stability. The system paves avenues for sustainable power generation, water purification, and desalination.

Fish scale-extracted hydroxyapatite/chitosan composite scaffolds fabricated by freeze casting—An innovative strategy for water treatment

In this study, low-cost and eco-friendly hydroxyapatite (HA) minerals were extracted from scales of Tilapia fish (Oreochromis mossambicus). After calcination, fish-scale extracted powder was further confirmed to be HA by X-ray diffraction with mean particle size of 5.96 μm determined by particle size analyzer. The calcined powder was utilized as the raw material and combined with chitosan (CS) to synthesize composite scaffolds by freeze casting and cross-linking. Mercury porosimetry results showed that the scaffolds possessed hierarchical porous structure. Microstructural features characterized by SEM revealed unidirectional channel structures with channel sizes ranged from 10 to 100 μm and 1 to 50 μm for scaffolds freeze-casted at 2 ℃/min and 5 ℃/min cooling rates, respectively. The adsorption kinetics of HA/CS composite scaffolds with varying channel sizes were investigated by both batch and fixed-bed processes with different Pb(П) initial concentrations (100 and 1000 mg/L). The adsorption capability was optimized by tuning the cooling rates and the maximum adsorption amount could reach 75–570 mg/g in batch process and 94 mg/g in fixed bed process. In summary, the HA/CS composite scaffolds showed great capability to remove heavy metal ions from waste water and their tunable channel sizes could be applied in suitable fields under both statistic and flowing conditions.

Microchannel Stiffness and Confinement Jointly Induce the Mesenchymal-Amoeboid Transition of Cancer Cell Migration.

The physical confinement of cell microenvironment could enhance the invasive capability and drug resistance of cancer cells. However, due to the lack of in vitro experimental platform to mimic both stiffness and confinement of the tumor microenvironment, the underlying mechanism remains elusive. Here, we developed a hydrogel-based microchannel platform with independently tunable channel stiffness and width in a physiological range. We found that the migration speed of the cancer cell is influenced by the synergistic effect of channel stiffness and width. In addition, the mesenchymal-amoeboid transition has a strong correlation with the channel stiffness. Besides, with a developed computational model, the role of nuclear stiffness on cancer migration speed and thus the mesenchymal-amoeboid transition in microchannels was also revealed. This platform is capable of mimicking the native physical microenvironment during metastasis, providing a powerful tool for high-throughput screening applications and investigating the interaction between cancer migration and biophysical microenvironment.

Free-space transmission system in a tunable simulated atmospheric turbulence channel using a high-repetition-rate broadband fiber laser

We demonstrate free-space transmission based on a broadband fiber laser at 16 Gbit/s over a simulated atmospheric turbulence channel. The broadband laser pulse is part of a supercontinuum generated by a homemade picosecond laser based on Raman gain soliton compression pumping a segment of highly nonlinear fiber. The scintillation indices, eye patterns, and bit error rates of transmission based on the broadband laser and a narrow-linewidth laser are compared. The results show a 29.5% reduction in the scintillation index and sensitivity of -28.6 dBm at the forward error correction limit, which has a 2.9 dB improvement compared with the narrow-linewidth system. It is feasible to use broadband lasers as carriers combining optical time division multiplexing as a multiplexing method to improve the communication performance under weak atmospheric turbulent conditions.

3D bioprinting of complex channels within cell-laden hydrogels

3D bioprinting is an emerging manufacturing approach to fabricate (cell-laden) hydrogel constructs with embedded microchannels, which are potentially useful for fundamental studies to understand vascularization and angiogenesis, and for developing organ-on-a-chip devices for disease modeling. Although numerous printing approaches have been developed, novel approaches are still needed that enable printing of channels with user-defined and tunable size, morphology, and complexity. Here, we report a novel bioprinting approach enabling printing of a sacrificial ink within commonly used photocurable hydrogels using a sequential printing approach. To achieve this, photocurable hydrogel is printed layer-by-layer as usual, but each layer is exposed to light briefly (seconds) to create partially crosslinked, self-supporting layers. At a desired thickness, immediately after the layer is printed (prior to partial crosslinking step), sacrificial hydrogel is directly printed within this viscous uncrosslinked layer. The layer was then exposed to light to confine and support the sacrificial hydrogel. After fully crosslinking the system, the sacrificial hydrogel is washed away, forming a channel. This approach allows bioprinting of cells with the matrix material and seeding of cells into channels after the sacrificial ink is removed. This approach can potentially provide a robust platform for fabricating vascularized tissues and studying cell behaviors on diverse channel surfaces. Statement of significance3D bioprinting is an emerging platform for the fabrication of hydrogel-based constructs for in vitro tissue/disease modelling or tissue and organ printing. Although several approaches have been developed to print channels within these constructs, it is still challenging to incorporate microchannels (for vascularization) within 3D bioprinted constructs. This study presents a novel bioprinting approach to create user-defined and tunable channels embedded within cell-laden hydrogel constructs. We report an important advance as our approach does not require complex device modifications for bioprinters or complex synthesis and processing hurdles for the inks. Since our approach does not require special chemistries, there are potentially a greater number of commercially available options for ink materials.

Embedded Near-Infrared Sensor With Tunable Sensitivity for Nanoscale CMOS Technologies

Near-infrared (NIR) sensors has become one of the key components in applications, such as temperature, proximity, and even fingerprint sensing. A novel full-CMOS (Complementary Metal-Oxide-Semiconductor) compatible near-infrared sensor is proposed and demonstrated in this article. This sensing device consists of a gateless transistor, enabling near-infrared photon absorption in the channel region. With a tunable channel barrier, this near-IR sensor also features a dynamic photo-response with an extending sensing range up to 60 dB.

Carbon gel monoliths with introduced straight microchannels for phenol adsorption

Adsorption of phenol using carbon adsorbents in the form of a packed bed of particles inherently suffers from the incompatibility between low hydraulic resistance and short diffusion path length. In this work, carbon gel monoliths made from resorcinol–formaldehyde gels with introduced straight microchannels in the range of 60–160 µm were successfully synthesized using polyesters fibers as templates. The advantage of this synthesis method is that both channel size and channel density can be tuned independently. Introduced microchannels were effective in minimizing the pressure drop of a fluid flowing through the sample to less than a hundredth of beds packed with particles having the same diffusion path length. Synthesized monoliths also possess sufficient mechanical strength (more than 12 kg per monolith) to be activated to increase their adsorption capacity. Adsorption experiments of phenol in a continuous flow system show that synthesized monoliths can be used as effective adsorbents for phenol removal. The tunable channel size and channel density of the proposed synthesis method has the potential for the synthesis of monoliths which could be used to fulfill various process demands.

Scalable graphene oxide membranes with tunable water channels and stability for ion rejection

Graphene oxide membranes with tunable water channels and stability for ion rejections were fabricated by the blade casting technique and cation intercalation.

Plasmons in Ballistic Nanostructures With Stubs: Transmission Line Approach

The plasma wave instabilities in ballistic Field Effect Transistors (FETs) have a promise of developing sensitive THz detectors and efficient THz sources. One of the difficulties in achieving efficient resonant plasmonic detection and generation is assuring proper boundary conditions at the contacts and at the heterointerfaces and tuning the plasma velocity. We propose using the tunable narrow channel regions of an increased width, which we call "stubs" for optimizing the boundary conditions and for controlling the plasma velocity. We developed a compact model for THz plasmonic devices using the transmission line (TL) analogy. The mathematics of the problem is similar to the mathematics of a TL with a stub. We applied this model to demonstrate that the stubs could effectively control the boundary conditions and/or the conditions at interfaces. We derived and solved the dispersion equation for the device with the stubs and showed that periodic or aperiodic systems of stubs allow for slowing down the plasma waves in a controllable manner in a wide range. Our results show that the stub designs provide a way to achieve the optimum boundary conditions and could also be used for multi finger structures - stub plasmonic crystals - yielding better performance of THz electronic detectors, modulators, mixers, frequency multipliers and sources.