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The forced oscillations of hair bundle of inner hair cells of auditory nervous system evoked by external force from steady state are related to the fast adaption of hair cells, which are very important for auditory amplification. In the present paper, comprehensive and deep understandings to nonlinear dynamics of forced oscillations are acquired in four aspects. Firstly, the complex dynamics underlying the twitch (fast recoil of displacement X which is fast variable) induced from Case-1 and Case-2 steady states by external pulse force are obtained. With help of vector fields and nullclines, the phase trajectory of forced oscillations is identified to be an evolution process between two equilibrium points corresponding to zero force and pulse force, respectively, and then the twitch is obtained as the behavior running along the nonlinear part of X-nullcline. Especially, twitch observed in experiment are classified into 6 types, which are induced by negative change of force, negative and positive changes of force, and positive change of force, respectively, and further build relationships to three subcases of Case-2 steady state with N-shaped X-nullcline (equilibrium point locates on the left, middle, and right branches of X-nullcline, respectively). Secondly, the experimental observation of fatigue of twitch induced by continual two pulse forces, i.e. the reduced amplitude of the latter twitch when interval between two forces is short, is also explained as a nonlinear behavior beginning from an initial value different from that of the former one. Thirdly, the experimental observation of transition between sustained oscillations and steady state induced by pulse force can be simulated for Case-1 steady state with Z-shaped X-nullcline instead of Case-2, due to that there exists bifurcations with respect to external force for Case-1 while no bifurcations for Case-2. Last, the threshold phenomenon induced by simple pulse stimulation exists for Case-1 steady state rather than Case-2, due to that the upper and lower branches of Z-shaped X-nullcline close to the middle branch exhibit coexisting behaviors of variable X while N-shaped X-nullcline does not. The nonlinear dynamics of forced oscillations are helpful for explanations to the complex experimental observations, which presents potential measures to modulate the functions of twitch such as the fast adaption.

Based on the cooling characteristics of dry ice on high heat flux chip, a variety of radiator models with different dry ice inlet and outlet positions are proposed in the present study. The influence of these radiator models on temperature field, velocity field, dry ice distribution and chip cooling time are analyzed. The results demonstrate that when the diameter of inlet and outlet is 12 mm and the chip power P0 = 95W, the average temperature of all models' chip bottom has reached below 50 °C when t = 70 s. The inlet of Model g is located in the center of the upper surface of the radiator and the outlet is located in the center of the side surface, the chip overall temperature of Model g is the most uniform distribution with 90% of the area temperature at 25 °C. Model g combines the advantages of the phase change heat transfer and the jet impingement heat transfer, which can realize the optimal coupling of the flow rate and the heat transfer, ensuring the safety and reliability of the chip more effectively. Moreover, the results of simulation and optimization are in good agreement with the relevant experiments, laying a foundation for further optimization of the structural scale of the radiator and better coupling of the heat flow field of the dry ice cooling system.

It is established that ultrathin layered double hydroxide nanosheets (LDHNS) and zeolitic imidazole frameworks (ZIF) are desirable electrochemical sensing modifiers owing to their large surface area and abundant catalytic sites. Integration of them is thus an effective solution to maximize their electrocatalytic activity. Herein, a novel reaction–diffusion framework (RDF) technique is applied for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (CoAl-LDHNS@ZIF-67). In a confined space of the agar gel matrix of RDF, the coordination reaction between organic ligands and CoAl-LDHNS without an additional Co2+ source achieves the controllable growth of ZIF-67 crystals through a long vertical diffusion. The prepared composite comprises both CoAl-LDHNS and ZIF-67 components with a certain ratio and provides a large surface area and amply catalytic sites, thus realizing a rapid transfer of electron and mass. The CoAl-LDHNS@ZIF-67 modified electrode is employed for the simultaneous detection of naphthol isomers by differential pulse voltammetry. Naphthol isomers display anodic reactions with a wide peak potential difference, allowing their simultaneous detection feasible. Voltammetric responses of α-naphthol and β-naphthol follow good linearity against the concentration in a wide range from 0.3 to 150 μM with limits of detection of 54 and 82 nM, respectively. The proposed sensor also demonstrates excellent selectivity, stability, reproducibility, and practicability for the simultaneous detection of naphthol isomers.

Although the bursting patterns with spike undershoot are involved with the achievement of physiological or cognitive functions of brain with synaptic noise, noise induced-coherence resonance (CR) from resting state or subthreshold oscillations instead of bursting has been widely identified to play positive roles in information process. Instead, in the present paper, CR characterized by the increase firstly and then decease of peak value of power spectrum of spike trains is evoked from a bursting pattern with spike undershoot, which means that the minimal membrane potential within burst is lower than that of the subthreshold oscillations between bursts, while CR cannot be evoked from the bursting pattern without spike undershoot. With bifurcations and fast-slow variable dissection method, the bursting patterns with and without spike undershoot are classified into "Sub-Hopf/Fold" bursting and "Fold/Homoclinic" bursting, respectively. For the bursting with spike undershoot, the trajectory of the subthreshold oscillations is very close to that of the spikes within burst. Therefore, noise can induce more spikes from the subthreshold oscillations and modulate the bursting regularity, which leads to the appearance of CR. For the bursting pattern without spike undershoot, the trajectory of the quiescent state is not close to that of the spikes within burst, and noise cannot induce spikes from the quiescent state between bursts, which is cause for non-CR. The result provides a novel case of CR phenomenon and extends the scopes of CR concept, presents that noise can enhance rather than suppress information of the bursting patterns with spike undershoot, which are helpful for understanding the dynamics and the potential physiological or cognitive functions of the nerve fiber or brain neurons with such bursting patterns.

Zeolitic imidazole frameworks (ZIF) and ultrathin layered double hydroxide nanosheets (LDHNS) have drawn growing attention in the electrocatalysis field. Combining the merits and maximizing the electrocatalytic activity of each building block in the corresponding composite is imperative but challenging. This work thus proposes a simple strategy for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (LDHNS@ZIF-67) without an additional Co2+ source. Thanks to the ultrathin nature, CoAl-LDHNS provide more Co reactive sites for the ordered growth of ZIF-67 nanocrystals on this 2D matrix via coordination interactions between Co2+ and 2-methylimidazole. The obtained LDHNS@ZIF-67 provides more convenient pathways to rapid electron transportation between the basal electrode and analytes. Hence, the modified electrode can be applied for the truly simultaneous detection of naphthol isomers by differential pulse voltammetry. α-naphthol and β-naphthol exhibit irreversible oxidation peaks at 0.327 and 0.487 V vs. saturated calomel electrode, respectively, making their simultaneous detection feasible. The voltammetric responses of both isomers are linear in concentrations ranging from 0.3 to 150 μM with limits of detection of 62 and 94 nM, respectively. The sensor exhibits advantages including good reproducibility, stability, selectivity, and practicability for the simultaneous detection of naphthol isomers in real water samples.

To meet the diverse energy requirements of clients, a trigenerative system based on advanced adiabatic compressed air energy storage is established. To investigate the thermodynamic performance of systems adopting different working media and heating storage media, four combination modes are proposed and studied. The results indicate that the exergy efficiency and energy density of mode 1 (air as the working medium, and water as the heating storage medium) exceed those of other modes. Among all modes, the maximum exergy destruction emerges in the second heat exchanger. For the system adopting therminol 66 as the heating storage medium, the gas storage chamber has great potential in improving system performance. Moreover, parameter analysis and multi-objective optimization are conducted. As a result, ambient temperature, cold tank temperature and convective heat transfer coefficient are of massive influence on system performance. Under certain optimal conditions, the optimal energy densities of the four modes are 5.28, 4.33, 4.81 and 3.84 MJ m−3, respectively, and the optimal exergy efficiencies are 53.51%, 46.43%, 50.19% and 42.59%, respectively.

In this study, the authors first discuss the existence of Bogdanov–Takens and triple zero singularity of a five neurons neutral bidirectional associative memory neural networks model with two delays. Then, by utilising the centre manifold reduction and choosing suitable bifurcation parameters, the second‐order and the third‐order normal forms of the Bogdanov–Takens bifurcation for the system are obtained. Finally, the obtained normal form and numerical simulations show some interesting phenomena such as the existence of a stable fixed point, a pair of stable non‐trivial equilibria, a stable limit cycles, heteroclinic orbits, homoclinic orbits, coexistence of two stable non‐trivial equilibria and a stable limit cycles in the neighbourhood of the Bogdanov–Takens bifurcation critical point.

The nitrogen doped carbon dots (C-dots) with highly photoluminescence (PL) are synthesized using m-aminobenzoic acid (MAC) as the only precursor by a simple, one-step hydrothermal method. The NH2 groups of MAC have been used as nitrogen source to dope C-dots. The synthesized nitrogen doped (N-doped) C-dots present an unexpectedly large quantum yield of 30.7% and possess an essentially crystalline nature and desirable functional groups. More important, the C-dots can serve as multifunctional fluorescence nanosensors to detect pH and Fe3+. The fluorescent intensity of the C-dots increases dramatically as pH increases from 2 to 10. The fluorescent paper with C-dots coated for visual detection of pH by naked eyes has been successfully prepared. Moreover, the C-dots are employed for assaying Fe3+ based on direct interactions between Fe3+ and COOH and NH2 groups of C-dots. Under the optimal condition, a linear relationship between the decreased fluorescence intensity of C-dots and the concentration of Fe3+ is established in the range from 0 to 1.6 μM. The detection limit is as low as 0.05 μM, suggesting a promising assay for Fe3+. The results reported here provide a new approach for the design of N-doped multifunctional florescent sensor.

In this paper, we study a coupled FitzHugh-Nagumo (FHN) neurons model with time delay. The existence conditions on Hopf-pitchfork singularity are given. By selecting the coupling strength and time delay as the bifurcation parameters, and by means of the center manifold reduction and normal form theory, the normal form for this singularity is found to analyze the behaviors of the system. We perform the bifurcation analysis and numerical simulations, and present the bifurcation diagrams. Some interesting phenomena are observed, such as the existence of a stable fixed point, a stable periodic solution, a pair of stable fixed points, and the coexistence of a pair of stable fixed points and a stable periodic solution near the Hopf-pitchfork critical point.

We describe the preparation of carbon quantum dots (C-dots) by a one-step hydrothermal method starting from o-aminophenol as the precursor. The C-dots exhibit bright both blue fluorescence (with excitation/emission peaks at 300/410 nm and with quantum yield of 0.40) and green fluorescence (420/500 nm; QY 0.28) without any other element doping. The unique emission properties are attributed to a synergistic effect of amino and hydroxy groups on the surface of the C-dots. The C-dots are shown to be viable fluorescent probes for heparin. The positively charged surface amino groups are assumed to interact with sulfate and carboxy groups in heparin via electrostatic interactions and hydrogen bonding. This causes the blue fluorescence of C-dots to be turned off (quenched). Fluorescence is strongest at a pH value of 6. The fluorometric calibration plot is linear in the 10 to 100 nM concentration range, with an 8.2 nM detection limit (at a signal-to-noise ratio of 3).

Fore the first time, a novel BiOCl/CuS nanocomposite with a heterojunction structure was prepared by a one-step hydrothermal method. The BiOCl/CuS heterojunctions were used as photocatalyst for degradation of organic pollutants, such as rhodamine B (RhB), under visible light irradiation (λ > 420 nm). The results reveal that the heterojunction structure composite exhibits markedly improved efficiency and high photostability for the RhB photodegradation in comparison with pure BiOCl and pure CuS. This is ascribed to the heterojunction structure with an efficient charge separation and transfer across the BiOCl/CuS junction. Moreover, the catalytic activity is related to the ratio of CuS to BiOCl in the nanocomposite, and the BiOCl/CuS heterojunction in a 0.5:1 mol ratio exhibits the highest photocatalytic activity. According to experimental results, the photocatalytic mechanism of BiOCl/CuS photocatalyst is proposed to explain the improvement of the photocatalytic activity.

In this work, for the first time, novel polyaniline/carbon dot (PANI/Cdot) nanocomposites have been synthesized using a simple method. Meanwhile, the bright fluorescence of Cdots is effectively quenched by PANI through fluorescence resonance energy transfer. With the addition of Hg2+, the strong binding affinity between Hg2+ and the amino groups of PANI makes the Cdots break away and release from the PANI, resulting in the restoration of Cdot fluorescence, which can be used as a fluorescent probe for Hg2+ detection. This fluorescence “off–on” signal is sensitive to the concentration of Hg2+, and there is a good linear relationship between the fluorescence intensity of Cdots and Hg2+ concentrations in the range of 0.05 to 1.0 μM. The detection limit for Hg2+ at a given concentration is 0.8 nM. Moreover, it turns out that the nanoprobes represent a rather high selectivity for Hg2+ detection. We believe that PANI/Cdot composites will emerge as a new class of fluorescence materials that could be very likely to be suitable for practical applications.

In this paper, we study the dynamics of an autonomous system for a hair bundle subject to mechanical load. We demonstrated the spontaneous oscillations that arise owing to interactions between the linear stiffness and the adapting stiffness. It is found that by varying the linear stiffness, the system can induce a weakly chaotic attractor in a certain region where the stable periodic orbit is infinitely close to a parabolic curve composed of unstable equilibrium points. By altering the adapting stiffness associated with the calcium concentration, the system is able to trigger the transition from the bistable resting state, through a pair of symmetric Hopf bifurcation, into the bistable limit cycle, even to the chaotic attractor. At a negative adapting stiffness, the system exhibits a double-scroll chaotic attractor. According to the method of qualitative theory of fast-slow decomposition, the trajectory of a double-scroll chaotic attractor in the whole system depends upon the symmetric fold/fold bifurcation in a fast system. Furthermore, the control of the adapting stiffness in the improved system with two slow variables can trigger a new transition from the bistable resting state into the chaotic attractor, even to the hyperchaotic attractor by observing the Lyapunov exponent.

Yttrium(III) trifluoroacetate is used as efficient catalyst for reaction of benzil, aldehydes, and ammonium acetate under mild and solvent-free conditions to afford the corresponding 2,4,5-triarylimidazoles in high yields and short reaction time. Furthermore, the catalyst can be recovered conveniently and reused several times in the reaction without a significant loss of catalytic activity.

A simple and solvent-free procedure to synthesize α,α′-bis(substituted benzylidene) cycloalkanones, catalyzed by copper(II) trifluoroacetate through crossed-aldol condensation of various aromatic aldehydes with cyclic ketones is reported. The reaction proceeded smoothly in good to excellent yields.

A simple and effective synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives from aldehydes, 1,3-dicarbonyl compounds and urea using copper(II) trifluoroacetate as catalyst under solvent-free conditions is described. Compared with the classical Biginelli reaction condition, this new method has the advantage of good to excellent yields and short reaction time.

Aromatic aldehydes undergo crossed aldol condensation with cyclic ketones in the presence of Y(TFA)3 under solvent-free conditions to afford the corresponding α,α’-bis(substituted benzylidene)cyclo...