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A photonic-based technique for the generation of highly-linear ultra-wideband stepped-frequency microwave signals with large time-bandwidth product is proposed and experimentally demonstrated. The double-gated recirculating frequency-shifting optical fiber loop enables the frequency of the generated microwave signal to hop step-wisely at exact increment. The generation of signals with up to 20 GHz bandwidth and ~ 300 s temporal duration, corresponding to a time-bandwidth product of 6,000,000, is achieved by the proof-of-concept system with electronics of only up to 80 MHz bandwidth. Nonlinearity of less than 10-7 and high intra- and inter-period coherence are also experimentally validated. This work provides applications such as high resolution radar with a promising low-cost solution for generating large time-bandwidth product waveforms with frequency scalability and extreme linearity.

Steam reforming is an effective measure for biomass tar elimination as well as H2-rich syngas (H2 + CO) production. However, the granular or powdery Ni-based catalysts are prone to deactivation, which is caused by inappropriate mass transfer and clogging of catalyst bed. Herein, monolithic wood carbon (WC) with low-tortuosity microchannels is armed with a carbon-coated mesoporous nickel-silica nanocomposite (Ni-SiO2@C) layer via an evaporation-induced self-assembly and calcination procedure for toluene (tar model compound) steam reforming. The quality of the Ni-SiO2@C layer growing on the surface of WC microchannel is affected by the molar ratios of Si/Ni feed. A uniform thin-layer coverage is obtained on the Ni-15SiO2@C/WC (Si/Ni = 15) catalyst, where highly dispersed Ni nanoparticles (average size of 6.6 nm) with appropriate metal-support interaction and remarkable mechanical strength are achieved. The mass transfer, coke resistance, and hydrothermal stability of the Ni-15SiO2@C/WC catalyst were significantly improved by the multilevel structure assembled from the WC microchannels and the secondary ordered SiO2 mesopores. A stable toluene conversion over 97% with an H2 yield of 135 μmol/min was obtained at 600 °C on the Ni-15SiO2@C/WC catalyst. This work opens a new window for facilely constructing high-performance wood carbon-based monolithic tar reforming catalyst.

Distributed sensing plays an important role in many industrial applications. Sensor arrays consisting of identical ultraweak fiber Bragg gratings can be applied to such scenarios by monitoring the optical spectral response of the sensors. Yet, the spatial resolution, the sampling speed, and the supported number of sensors in the array are mostly determined by the interrogation scheme. While dual-optical frequency comb techniques had been successfully demonstrated as a high-resolution spectroscopic technique in metrology, it had been beyond the reach of industrial sensing applications because of its high complexity and costs. It is proposed and demonstrated here that, enabled by a simple fiber-optic, dual-comb spectroscopy setup consisting of a fiber laser without frequency stabilization, interrogation of an ultraweak fiber sensor array can be realized. High spatial and spectral resolution as well as kilohertz interrogation speed is achieved in both static and dynamic measurements. It is expected that our depth-resolved dual-comb scheme can measure hundreds of sensors response in less than 1 ms. It is also flexible to deal with targets closely spaced or farther apart from each other. This shows the potential of applying dual-comb spectroscopy to more and more industrial application areas.

Black phosphorus (BP) attracts huge interest in photonic and optoelectronic applications ranging from passive switch for ultrafast lasers to photodetectors. However, the instability of chemically unfunctionalized BP in ambient environment due to oxygen and moisture remains a critical barrier to its potential applications. Here, the parylene-C layer was used to protect inkjet-printed BP-saturable absorbers (BP-SA), and the efficacy of this passivation layer was demonstrated on the stable and continuous operation of inkjet-printed BP-SA in harsh environmental conditions. BP-SA was integrated in an erbium-doped ring laser cavity and immersed in water at ~60°C during operation for investigation. Mode-locked pulses at ~1567.3 nm with ~538 fs pulse width remained stable for >200 h. The standard deviation of spectral width, central wavelength, and pulse width were 0.0248 nm, 0.0387 nm, and 2.3 fs, respectively, in this period, underscoring the extreme stability of BP-SA against high temperature and humidity. This approach could enable the exploitation of BP-based devices for photonic applications when operating under adverse environmental conditions.

A robust fractional-order linear super-twisting sliding mode observer (LSTSMO) for an induction motor speed sensorless system is proposed in this study to solve the problem of balance between sliding mode chattering and estimation accuracy. First, the stability of the linear super-twisting algorithm is proven with the Lyapunov function, and the convergence and gain coefficient range of the algorithm are analyzed. Next, the fractional integral sliding mode surface based on the stator current error term is established, and the linear super-twisting algorithm is introduced to design the fractional LSTSMO. In addition, a flux correction link is added to enhance the robust performance of the observer. The results of the simulations and experiments verify that the observer has high flux linkage estimation accuracy, which can enhance transient performance rapidity and chattering suppression ability simultaneously, thereby improving robustness against parameter drifts. Moreover, the designed observer improves the dynamic and steady state performance of the motor in the full-speed range.

Kunitz-type proteins or peptides have been found in many blood-sucking animals, but the identity of them in leeches remained elusive. In the present study, five Kunitz-type peptides named WPK1-WPK5 were identified from the leech Whitmania pigra. Recombinant WPK1-WPK5 were expressed in Pichia pastoris GS115, and their inhibitory activity against Factor XIa (FXIa) was tested. WPK5 showed inhibitory activity against FXIa with an IC50 value of 978.20 nM. To improve its potency, the loop replacement strategy was used. The loop 1 (TGPCRSNLER) and loop 2 (QYGGC) in WPK5 were replaced by loop 1 (TGPCRAMISR) and loop 2 (FYGGC) in PN2KPI, respectively, and the resulting peptide named WPK5-Mut showed an IC50 value of 8.34 nM to FXIa, which is about 100-fold the potency of FXIa compared to that of WPK5. WPK5-Mut was further evaluated for its extensive bioactivity in vitro and in vivo. It dose-dependently prolonged APTT on both murine plasma and human plasma, and potently inhibited FeCl3-induced carotid artery thrombosis in mice at a dose of 1.5 mg/kg. Additionally, WPK5-Mut did not show significant bleeding risk at a dose of 6 mg/kg. Together, these results showed that WPK5-Mut is a promising candidate for the development of an antithrombotic drug.

Background An appropriate electrolyte solution is important for safe intraoperative anesthesia management in children. This trial assessed the effectiveness of a novel 1% glucose isotonic electrolyte solution in intraoperative fluid therapy in children. Methods This trial analyzed data from 100 patients aged older than 1 month with an ASA score of I to II who received general anesthesia. Patients were randomly assigned to receive either the novel electrolyte solution (containing glucose, sodium, potassium, chloride, and bicarbonate) or lactated Ringer’s solution intraoperatively as a maintenance fluid. Patient demographics and the results of blood gas analysis at 1, 2, and 3 hours were documented, and changes in glucose and electrolyte concentrations and the acid–base status were analyzed. Results During infusion of the novel solution, the glucose and potassium concentrations were stable. Conversely, the solution was linked to increased sodium levels but decreased bicarbonate levels, although both changes were within the physiological ranges. In addition, pH remained stable during the intraoperative period. Hypoglycemia, hyperglycemia, hyponatremia, or hypernatremia was not detected. Conclusions The novel 1% glucose isotonic electrolyte solution helped to maintain glucose and electrolyte concentrations and acid–base stability, and it may therefore improve children’s safety during the intraoperative period.

In this Letter, an actively stabilized photonic system for millimeter-wave (mmW) signal distribution is proposed and experimentally demonstrated. By interlocking two baseband RF signals obtained from a dual-heterodyne detection through a single carrier compensation module, the phase fluctuations induced by the fiber transmission link is suppressed without the need of a local frequency reference. In the proof-of-concept experiment, a 108 GHz mmW is transmitted over a 10 km fiber link with a performance matching that of the back-to-back case. The feedback system reduces the phase noise of the delivered mmW signal by 37 dB and 28 dB at 0.1 Hz and 1 Hz frequency offset, respectively, and the long-term stability is improved by nearly two orders of magnitude.

By introducing an additional comb beyond its dual-comb predecessor, tri-comb consisting of three combs with different mode spacing has shown its unique potential in several metrology areas such as nonlinear spectroscopy, frequency, and distance measurement. However, tri-comb generation based on three frequency-stabilized comb lasers would be overly complicated and costly for many potential applications. Previous studies had realized dual-comb generation from a single-cavity laser by leveraging multiplexing in one of the waveguiding dimensions of the optical pulses. Such sources with built-in passive mutual coherence could greatly reduce system complexity. Yet, squeezing more combs into one multiplexing dimension becomes increasingly difficult without significant sacrifice in performance, which could jeopardize the usefulness of such a scheme. In this paper, it is proposed and demonstrated that multi-comb generation could be realized by tapping into the multidimensional joint parameter space. Up to four wavelength/polarization multiplexed, asynchronous ultrashort pulse sequences can be generated with good stability from an all-fiber, mode-locked ring-cavity laser. This could offer an attractive alternative solution as the low-complexity light sources for field-deployable multi-comb metrology applications.

Purpose In spite of the vehicle, magnetic field interference can be reduced by some measures and techniques in ammunition design and manufacturing stage, the corruption of the vehicle magnetic field can still reach hundreds to thousands of nanoteslas. Besides, the magnetic field that the ferromagnetic materials generate in response to the strong magnetic field in the vicinity of the body. So, a real-time and accurate vehicle magnetic field calibration method is needed to improve the real-time measurement accuracy of the geomagnetic field for spinning projectiles. Design/methodology/approach Unlike the past two-step calibration method, the algorithm uses a linear model to calibrate the magnetic measurement error in real-time. In the method, the elliptical model of magnetometer measurement is established to convert the coefficients of hard and soft iron errors into the parameters of the elliptic equation. Then, the parameters are estimated by recursive least square estimator in real-time. Finally, the initial conditions for the estimator are established using prior knowledge method or static calibration method. Findings Studies show the proposed algorithm has remarkable estimation accuracy and robustness and it realizes calibration the magnetic measurement error in real-time. A turntable experiments indicate that the post-calibration residuals approximate the measurement noise of the magnetometer and the roll accuracy is better than 1°. The algorithm is restricted to biaxial magnetometers’ calibration in real-time as expressed in this paper. It, however, should be possible to broaden this method’s applicability to triaxial magnetometers' calibration in real-time. Originality/value Unlike the past two-step calibration method, the algorithm uses a linear model to calibrate the magnetic measurement error in real-time and the calculation is small. Besides, it does not take up storage space. The proposed algorithm has remarkable estimation accuracy and robustness and it realizes calibration the magnetic measurement error in real time. The algorithm is restricted to biaxial magnetometers’ calibration in real-time as expressed in this paper. It, however, should be possible to broaden this method’s applicability to triaxial magnetometers’ calibration in real-time.

Ag₃PO₄/sulfur-doped g-C₃N₄ heterojunctions were fabricated by the means of a facile calcination and co-precipitation method. Structural characterization suggested that Ag₃PO₄ was successfully loaded onto sulfur-doped g-C₃N₄. The absorption band edges of sulfur-doped g-C₃N₄ were shifted to the longer wavelength in comparison with bulk g-C₃N₄. The Ag₃PO₄/sulfur-doped g-C₃N₄ heterojunctions manifested substantially higher visible-light photocatalytic performance as compared with Ag₃PO₄/bulk g-C₃N₄. Photoluminescence spectra suggested that the stable Ag₃PO₄/SGCN heterojunctions could effectively address the electron-hole recombination rate, together with remarkably enhancing the photocatalytic activity. The enhancement of light absorption and better dispersion in Ag₃PO₄/sulfur-doped g-C₃N₄ provide more migration channels, together with posing crucial responsibility for the enhanced photocatalytic performance.

Hyperactivation of the type 2 immune response is the major mechanism of allergic asthma, in which both group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells participate. Myeloid‐derived suppressor cells (MDSCs) alleviate asthma by suppressing Th2 cells. However, the potential effects of MDSCs on the biological functions of ILC2s remain largely unknown. Here, we examined the roles of MDSCs (MDSCs) in the modulation of ILC2 function. Our results showed that polymorphonuclear (PMN)‐MDSCs, but not monocytic (M‐) MDSCs, effectively suppressed the cytokine production of ILC2s both in vitro and in vivo, thereby alleviating airway inflammation. Further analyses showed that cyclo‐oxygenase‐1 may mediate the suppressive effects of PMN‐MDSCs on ILC2 responses. Our findings demonstrated that PMN‐MDSCs may serve as a potent therapeutic target for the treatment of ILC2‐driven allergic asthma.

Given the high ammonia nitrogen (NH3-N) concentration and low biological oxygen demand/chemical oxygen demand (BOD/COD) ratio (

MoS2/S-doped porous g-C3N4 (MoS2/SPGCN) hybrids were fabricated via a facile calcination and ultrasound assembly method. Structural characterization indicated MoS2 nanosheets were successfully loaded on SPGCN isotype heterojunction hybrids. The MoS2/SPGCN photocatalysts showed more visible light absorption, larger specific surface area, and faster electron-hole separation. MoS2/SPGCN significantly accelerated Rhodamine B photodegradation under visible light irradiation, which was mainly because the enriched active sites, broadened visible light absorption, and newly-formed heterojunction between MoS2 nanosheets and SPGCN together suppressed the recombination of photoinduced electron-hole pairs. MoS2/SPGCN also showed excellent recyclability and chemical stability. Thus, this work presents a good strategy of designing efficient photocatalysts by substituting the single catalyst base with metal-free isotype heterojunction hybrids.

Summary Background Patients with locoregionally advanced nasopharyngeal carcinoma have a high risk of disease relapse, despite a high proportion of patients attaining complete clinical remission after receiving standard-of-care treatment (ie, definitive concurrent chemoradiotherapy with or without induction chemotherapy). Additional adjuvant therapies are needed to further reduce the risk of recurrence and death. However, the benefit of adjuvant chemotherapy for nasopharyngeal carcinoma remains controversial, highlighting the need for more effective adjuvant treatment options. Methods This multicentre, open-label, parallel-group, randomised, controlled, phase 3 trial was done at 14 hospitals in China. Patients (aged 18–65 years) with histologically confirmed, high-risk locoregionally advanced nasopharyngeal carcinoma (stage III–IVA, excluding T3–4N0 and T3N1 disease), no locoregional disease or distant metastasis after definitive chemoradiotherapy, an Eastern Cooperative Oncology Group performance status of 0 or 1, sufficient haematological, renal, and hepatic function, and who had received their final radiotherapy dose 12–16 weeks before randomisation, were randomly assigned (1:1) to receive either oral metronomic capecitabine (650 mg/m2 body surface area twice daily for 1 year; metronomic capecitabine group) or observation (standard therapy group). Randomisation was done with a computer-generated sequence (block size of four), stratified by trial centre and receipt of induction chemotherapy (yes or no). The primary endpoint was failure-free survival, defined as the time from randomisation to disease recurrence (distant metastasis or locoregional recurrence) or death due to any cause, in the intention-to-treat population. Safety was assessed in all patients who received at least one dose of capecitabine or who had commenced observation. This trial is registered with ClinicalTrials.gov, NCT02958111. Findings Between Jan 25, 2017, and Oct 25, 2018, 675 patients were screened, of whom 406 were enrolled and randomly assigned to the metronomic capecitabine group (n=204) or to the standard therapy group (n=202). After a median follow-up of 38 months (IQR 33–42), there were 29 (14%) events of recurrence or death in the metronomic capecitabine group and 53 (26%) events of recurrence or death in the standard therapy group. Failure-free survival at 3 years was significantly higher in the metronomic capecitabine group (85·3% [95% CI 80·4–90·6]) than in the standard therapy group (75·7% [69·9–81·9]), with a stratified hazard ratio of 0·50 (95% CI 0·32–0·79; p=0·0023). Grade 3 adverse events were reported in 35 (17%) of 201 patients in the metronomic capecitabine group and in 11 (6%) of 200 patients in the standard therapy group; hand-foot syndrome was the most common adverse event related to capecitabine (18 [9%] patients had grade 3 hand-foot syndrome). One ( Interpretation The addition of metronomic adjuvant capecitabine to chemoradiotherapy significantly improved failure-free survival in patients with high-risk locoregionally advanced nasopharyngeal carcinoma, with a manageable safety profile. These results support a potential role for metronomic chemotherapy as an adjuvant therapy in the treatment of nasopharyngeal carcinoma. Funding The National Natural Science Foundation of China, the Key-Area Research and Development Program of Guangdong Province, the Natural Science Foundation of Guangdong Province, the Innovation Team Development Plan of the Ministry of Education, and the Overseas Expertise Introduction Project for Discipline Innovation. Translation For the Chinese translation of the abstract see Supplementary Materials section.

We propose a photonic approach for the frequency-stabilized distribution of millimeter waves based on a self-referenced feedback control technique. The implementation is demonstrated over an optical fiber link of 10 km.

The rapid growth of global energy demand necessitates high-performance water-based drilling fluids (WDFs) with excellent-plugging performance in the deep excavation of shale gas formation. Herein, we report an organic-inorganic nanocomposite (NS-D) as a plugging agent in WDFs to plug the nanoporous of shale and abate the hydration expansion of shale by integrating the advantages of inorganic and polymer nano plugging agents. The results of Fourier Transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (H-NMR) revealed that NS-D had been successfully obtained. Additionally, thermogravimetric analysis (TGA) showed that the thermal degradation temperature of NS-D occurred after 354 °C. The results of plugging theory analysis showed that the presence of rich amide groups and rigid material silica not only made NS-D adhere to shale efficiently by hydrogen bonding, but also firmly blocked the nanoporous of shale. The plugging ability was evaluated by pressure transfer test and nitrogen adsorption test. The results showed that WDFs with NS-D can significantly improve plugging efficiency and reduce fluid invasion. On the other hand, NS-D sharply abated the fluid loss of WDFs due to its positive plugging performance. The filtrate volume of WDFs decreased by 90.5% and 88.3%, respectively, before and after hot rolling at 150°C for 16 h. Moreover, the plugging performance of NS-D for WDFs was significantly better than polymer plugging agent crosslinked polyacrylamide microspheres and inorganic plugging agent silica nanoparticles. This work provides a novel strategy to plug the nanoporous of shale in the process of shale gas exploration.

We demonstrate a self-starting, all-fiber erbium-doped laser mode-locked by graphdiyne-based saturable absorber, delivering 364 fs pulses with 9.18 nm spectral bandwidth. Our work highlights the potential of graphdiyne-based devices for future photonic technologies.

Cracking of wind turbine blades is one of the main faults affecting the safety and efficiency of wind turbines. Because the unit has multiple operating conditions, under different working conditions, the influence weight of each dimensional feature on the final result is different. To solve this problem, a network model based on self-attention mechanism and long and short-term memory network is proposed, which can not only dynamically adjust each feature in space according to different input data, but also capture temporal correlation of data. The model is divided into three stages. First, the self-attention mechanism is used to obtain the correlation between time and space, and the weight of each feature is dynamically adjusted according to the different input data. Then the processed features are segmented and the self-attention mechanism is used for local sequential processing. Finally, the global temporal correlation of the segmented data is obtained through LSTM network. Based on the actual problems of unit and time, this model presents an end-to-end fault warning scheme. The model integrates the self-attention mechanism and LSTM network together, which is more conducive to deeply mining the characteristics of data in time and space, so as to realize accurate warning of blade cracking fault. Finally, the experimental results show that the proposed model is superior to the traditional classification model in detection performance.

We demonstrate an all-fiber, thulium-doped, mode-locked laser using a black phosphorus (BP) saturable absorber (SA). The BP-SA, exhibiting strong nonlinear response, is fabricated by inkjet printing. The oscillator generates self-starting 139 fs dispersion-managed soliton pulses centered at 1859nm with 55.6 nm spectral bandwidth. This is the shortest pulse duration and widest spectral bandwidth achieved directly from an all-fiber thulium-doped fiber laser mode-locked with a nanomaterial saturable absorber to date. Our findings demonstrate the applicability of BP for femtosecond pulse generation at 2 µm spectral region.

Multifunctional silica-based aerogels are an emerging material due to their unique properties and wide applications. However, their large-scale production and application are limited due to the high cost and cumbersome preparation process. Herein, we prepare graphene oxide (GO)/silica-based composite aerogels via a simple in situ sol-gel reaction. GO nanosheets (GOs) are functionalized with polyethylenimine (PEI) and 3-glycidyloxypropyltrimethoxysilane (GPTMS) successively. After a cohydrolysis and condensation of trimethoxymethylsilane (MTMS) and dimethoxydimethylsilane (DMDMS) in the presence of GOs and a convenient ambient-pressure drying process, the composite aerogels are obtained. In addition to the normal cross-linking of MTMS and DMDMS, the GOs also behave as cross-linking points to significantly enhance the mechanical properties and thermal stability of the network of the composite aerogels. The pore structure of the aerogels is tailored by varying the GO loads as well as its surface modification. The Young's modulus of a composite aerogel with a GO load of 0.5 wt % is about 5 times that for a neat polysiloxane aerogel, and the maximum degradation rate temperature is increased to over 90 °C. Compared with pure polysiloxane aerogel, the thermal insulation and flame resistance are also improved by a small addition of GOs. Moreover, GO/silica-based composite aerogels show stable piezo-resistive behavior. With the excellent mechanical properties, thermal stability, and multifunctionality, GO/silica-based composite aerogels show promising applications under some harsh and extreme conditions.

As a universal phenomenon in nonlinear optical systems, pulsating behaviors of solitons have attracted increasingly more investigations. While pulsating solitons and their likely generation conditions had been widely theoretical studied, their detailed spectro-temporal dynamics had been hardly reported in experiments. Here, three types of pulsating solitons are experimentally generated and observed in a dispersion-managed, hybrid mode-locked fiber laser. By controllably generating such states through intracavity tuning and leveraging the dispersive Fourier transform technique that maps spectral information into the time domain, real-time ultrafast spectro-temporal evolutions of the pulsating behaviors are revealed. The numerical results further show the generation of the pulsating soliton could be caused by the intracavity spectral filtering effect, consistent with the experimental configurations. Our findings could provide further insights into the complex nonlinear dynamics in lasers and potential ways to the design such systems to deliver targeted soliton outputs for potential applications.

Skull optical clearing window permits us to perform in vivo cortical imaging without craniotomy, but mainly limits to visible (vis)-near infrared (NIR)-I light imaging. If the skull optical clearing window is available for NIR-II, the imaging depth will be further enhanced. Herein, we developed a vis-NIR-II skull optical clearing agents with deuterium oxide instead of water, which could make the skull transparent in the range of visible to NIR-II. Using a NIR-II excited third harmonic generation microscope, the cortical vasculature of mice could be clearly distinguished even at the depth of 650 μm through the vis-NIR-II skull clearing window. The imaging depth after clearing is close to that without skull, and increases by three times through turbid skull. Furthermore, the new skull optical clearing window promises to realize NIR-II laser-induced targeted injury of cortical single vessel. This work enhances the ability of NIR-II excited nonlinear imaging techniques for accessing to cortical neurovasculature in deep tissue.

Reconfigurable beam steering components are indispensable to support optical and photonic network systems operating with high adaptability and with various functions. Currently, almost all such components are made of solid parts whose structures are rigid, and hence their functions are difficult to be reconfigured. Also, optical concentration beam steering is still a very challenging problem compared to radio frequency/microwave steering. Here we show a watermill-like beam steering system that can adaptively guide concentrating optical beam to targeted receivers. The system comprises a liquid droplet actuation mechanism based on electrowetting-on-dielectric, a superlattice-structured rotation hub, and an enhanced optical reflecting membrane. The specular reflector can be adaptively tuned within the lateral orientation of 360°, and the steering speed can reach ~353.5° s−1. This work demonstrates the feasibility of driving a macro-size solid structure with liquid microdroplets, opening a new avenue for developing reconfigurable components such as optical switches in next-generation sensor networks. Adaptive elements for optical beam steering are increasingly important to support nascent optical and photonic networks. This work presents a beam steering device based on a liquid droplet actuation method, capable of providing 360 degrees lateral steering with low energy consumption and a fast response time.

We report an ultra-wideband channel sounding enabled by an optical dual-comb and photonic asynchronous sampling. A 2-18 GHz rich-multipath wireless channel is measured by a 1 kHz highest refresh rate.

Three types of pulsating soliton dynamics are experimentally observed in a hybrid, dispersion-managed mode-locked fiber laser. It provides new insights into the complex nonlinear soliton behavior in ultrafast lasers and potential ways to control them.

We study on the timing jitter characteristics of a passively mode-locked dual-wavelength dual-comb Er-fiber laser that generates two femtosecond optical frequency combs with an offset repetition rate in a shared cavity. The relative timing jitter is characterized directly in the time domain with tens of attoseconds precision by utilizing the intrinsic asynchronous optical sampling process between the two laser beams. This sensitive measurement reveals an amplified spontaneous emission (ASE) noise dominated random walk of the relative pulse timing, which has not been observed before in a dual-comb laser. The quantum-limited relative timing jitter behavior shows that the common-mode noise suppression based on a shared cavity does not apply to quantum noise. We further conduct a time-of-flight ranging experiment and a Fourier-transform spectroscopy simulation based on this dual-comb laser, showing that the quantum-limited relative timing jitter sets an ultimate limit on the reachable performance in time- and frequency-domain dual-comb applications particularly when the high acquisition rate is desired.

Corrosion in internal cavity is one of the most common problems occurs in many hollow metallic components, such as pipes containing corrosive fluids and high temperature turbines in aircraft. It is highly demanded to non-destructively detect the corrosion inside hollow components and determine the corrosion extent from the external side. In this work, we present two high-frequency ultrasonic non-destructive testing (NDT) technologies, including piezoelectric pulse-echo and laser-ultrasonic methods, for detecting corrosion of Ni superalloy from the opposite side. The determination of corrosion layer thickness below ∼100 µm has been demonstrated by both methods, in comparison with X-CT and SEM. With electron microscopic examination, it is found that with multilayer corrosion structure formed over a prolonged corrosion time, the ultrasonic NDT methods can only reliably reveal outer corrosion layer thickness because of the resulting acoustic contrast among the multiple layers due to their respective different mechanical parameters. A time-frequency signal analysis algorithm is employed to effectively enhance the high frequency ultrasonic signal contrast for the piezoelectric pulse-echo method. Finally, a blind test on a Ni superalloy turbine blade with internal corrosion is conducted with the high frequency piezoelectric pulser-receiver method.

Dual-comb spectroscopy schemes have been demonstrated as an attractive solution for advanced optical spectroscopic analysis. The widely used fiber Bragg grating (FBG) sensing could benefit from the high spectral resolution and broad spectral coverage they could offer. However, the complexity, cost, and size of traditional dual-comb systems are prohibitively high for FBG applications. Dual-wavelength mode-locked fiber laser can generate two asynchronous ultrashort pulse trains and could enable the development of compact and low-complexity dual-comb application systems. In this paper, we propose and demonstrate a high-resolution, dynamic FBG interrogation scheme based on dual-comb spectroscopy with one free-running fiber laser. Accurate spectroscopic measurement of the FBG’s reflective spectrum is realized with each acquired dual-comb interferogram without further averaging. In our experiments, the resolution of such single-shot FBG wavelength measurement results can reach 1.7 pm, while the spectral non-aliasing measurement range is over 10 nm. Enabled by this capability of making fast dual-comb spectroscopy measurement of the FBG sensor response, the sampling speed of the interrogation system can reach the repetition rate difference of the dual combs, e.g., 1 kHz in this demonstration. Dynamic measurements of FBG responses driven by frequency up to 400 Hz are experimentally demonstrated. Our results further illustrate the potential and advantages of such single-cavity dual-comb laser sources in realizing low-complexity dual-comb systems that could appeal to a wider variety of applications.

Microwave photonic solutions of frequency measurement have advantages in broad frequency coverage, but achieving high-resolution measurement remains a challenge. Those schemes based on optical frequency combs could achieve high-resolution measurement over a broad frequency range. Here, a dead-band-free, high-resolution microwave frequency measurement scheme based on undersampling the microwave signal by three pulse sequences generated from a triple-wavelength mode-locked fiber laser is proposed and demonstrated. The triple-wavelength ultrashort pulses generated in one laser cavity have slightly different repetition rates due to chromatic dispersion. This eliminates the needs of multiple mode-locked lasers and frequency control between them and drastically reduces the system complexity. The absolute frequency of the microwave signal can be determined based on three down-converted low-frequency beat notes of the microwave signal with the nearest comb lines without ambiguity. A 10–10 relative measurement precision at a sampling speed of 100 Hz is demonstrated from 1 to 20 GHz, and the measurement accuracy remains within 0.3 Hz. Microwave signal with an RF power as low as −75 dBm can be measured with a 10 Hz precision at 10 GHz by using RF frontend amplifiers. The simple and compact triple-comb fiber laser would enable the development of low-complexity, high-performance microwave characterization instrument.

Farfarae Flos (FF) is widely used for the treatment of cough, bronchitis, and asthmatic disorders in the Traditional Chinese Medicine (TCM). According to the experience of TCM, only the flower bud can be used as herbal drug, and its medicinal quality becomes lower after blooming. However, the underlying scientific basis for this phenomenon is not fully understood. In this study, the chemical components and the bioactivities of the FF collected at three different development stages were compared systematically. NMR based fingerprint coupled with multivariate analysis showed that the flower buds differed greatly from the fully opened flower both on the secondary and primary metabolites, and the animal experiments showed that the fully opened flower exhibited no antitussive or expectorant effect. In addition, the endogenous metabolites correlated with the antitussive and expectorant effect of FF were also identified. These findings are useful for understanding the rationality of the traditional use of FF, and also suggested the components responsible for the antitussive and expectorant effect of FF.

For large-scale pressurized water reactor (PWR) deep-penetration shielding calculation, Monte Carlo (MC) method requires simulating a great number of particles to obtain reliable results, thus huge amount of computation time is the main problem of the MC method. Discrete Ordinates-Monte Carlo (SN-MC) coupling method combines the advantage of the SN method with high efficiency and the MC method with fine geometrical modeling. This paper studies the 3D SN-MC coupling method, generates surface source using the angular fluence rates of a SN code JSNT, and develops a source sampling subroutine for a MC code JMCT. The coupling method is verified on measurements and applied to CAP1400 cavity streaming calculation. Numerical results show that the coupling method increases calculation efficiency by 2–10 times for deep-penetration shielding calculation with high precision compared with reference results. The coupling method is effective for large-scale PWR deep-penetration shielding calculation.

Graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst was prepared by a simple incipient wetness impregnation and calcination method. The catalytic performance of the prepared catalyst was tested by catalytic steam reforming of toluene (a biomass tar model compound). Compared with mesoporous SBA-15 supported catalyst, the GMC supported catalyst has a higher toluene conversion efficiency of 98% at 700 °C and remained stable during 24 h of continuous reaction. The excellent catalytic performance is mainly attributed to the better dispersion of Ni nanoparticles on GMC support and the reduced carbon deposition because of the Ce-doping.

Stretchable hydrogels have undergone a rapid development in recent years particularly for wearable strain sensors. However, most of hydrogel-based sensors exhibit poor mechanical properties. Here, we report a highly stretchable porous composite hydrogel that has a tensile strain of 400% and a compressive strain of 80%. The porous hydrogel is composed of polyvinyl alcohol (PVA) and copolymer of N-(3-sulfopropyl)-N-methacroyloxyethyl-N,N-dimethylammonium betaine (SBMA) and acrylamide (AM) prepared via graphene oxide (GO)-stabilized Pickering aqueous foam templates. The pore morphology of the composite hydrogels was observed by field emission scanning electron microscope (FE-SEM). The tensile and compressive curves of porous hydrogels with different GO concentrations were characterized. GO can act as Pickering stabilizer to produce aqueous foams and also construct the physical cross-linking network in porous hydrogels to improve their mechanical strength. In addition, when GO is reduced by L-ascorbic acid, it provides effective electric pathways in porous hydrogels with the conductive percolation of less than 0.40 wt%. The composite hydrogels thus exhibit excellent strain sensitivity and can be used to detect various human motions. The facile preparation process of the porous composite hydrogels with outstanding performance properties facilitates the development of flexible wearable strain sensing materials.

Primary Shielding Calculation (PSC) plays an important role in reactor shielding design and analysis. In order to facilitate PSC, a source generation code is developed to generate cumulative distribution functions (CDF) for the source particle sample code of the MCNP code, and a source particle sample code is developed to sample source particle directions, types, coordinates, energy and weights from the CDFs. A source generation code is developed to transform three dimensional (3D) power distributions in xyz geometry to source distributions in rθz geometry for the TORT code. Validation on PSC model of Qinshan No.1 nuclear power plant (NPP), CAP1400 and CAP1700 reactors are performed. Numerical results show that the theoretical model and the codes are both correct.

A new absolute distance measurement system is demonstrated in this paper, which is based on a dual-wavelength passive mode-locked fiber laser. By controlling the intracavity loss and spectral filtering, the cavity mode-locked by a single-wall carbon nanotube saturable absorber is able to generate two pulse trains at slightly different repetition rates simultaneously with high mutual coherence. Comparisons with the commercial interferometers located on the 80-m large-scale dimensional standard show a combined measurement uncertainty of 6 μ m + 1 × 10-7L (k = 2), in an averaging time of 1 s. Our compact dual-comb system provides a low-cost way for ranging, with continuous range, rapid measurement, and high resolution.

We propose that extrasolar asteroid belts can be detected through their gravitational microlensing signatures. Asteroid belt + star lens systems create so-called "pseudo-caustics", regions in the source plane where the magnification exhibits a finite but discontinuous jump. These features allow such systems to generate distinctive signatures in the microlensing light curves for a wide range of belt configurations, with source trajectories as far as tenths of the Einstein ring radius from the centre of the lens. Sample light curves for a range of asteroid belt parameters are presented. In the near future, space-based microlensing surveys like WFIRST, which will have the power to detect percent-level changes in microlensing light curves even with sub-minute exposure times, may be able to discover extrasolar asteroid belts with masses of the order of an earth mass., Comment: 8 pages, 10 figures, accepted for publication in MNRAS

As a substitute for SF 6 , C 4 F 7 N has received much attention in recent years due to its excellent insulation properties and low global warming potential (GWP). However, the compatibility between C 4 F 7 N and the sealing material commonly used in gas-insulated transmission lines, such as EPDM (Ethylene Propylene Diene Monomer), was not thoroughly studied. This paper presents the thermal accelerated ageing results of EPDM in C 4 F 7 N gas environment at different temperatures and over a certain time. The tensile and compression properties of EPDM samples were tested, and the composition of the gas, the surface topography and functional groups of EPDM were investigated by GC, SEM-EDS and FTIR. The change in physical properties of EPDM is mainly affected by temperature rather than the gas environment. Hexafluoropropylene (C 3 F 6 ) and a yellow oil-like product are found as the main products. The results show that the C 4 F 7 N might be incompatible with the additives or plasticizers in EPDM the authors selected and tested. The composition and content of additives and plasticizers from different EPDM suppliers are different. Therefore, the compatibility test needs to be targeted and conducted on a case-by-case. The test method proposed in this paper provides a reference for the selection of the sealing material for GIL.

Nitric oxide (NO) levels in exhaled breath are a non-invasive marker that can be used to diagnose various respiratory diseases and monitor a patient’s response to given therapies. A portable and inexpensive device that can enable selective NO concentration measurements in exhaled breath samples is needed. Herein, the performance of an amperometric Pt-Nafion-based gas phase sensor for detection of NO in exhaled human nasal breath is examined. Enhanced selectivity over carbon monoxide and ammonia is achieved via an in-line zinc oxide-based filter. Exhaled nasal NO levels measured in 21 human samples with the sensor are shown to correlate well with those obtained using a chemiluminescence reference method (R(2) = 0.9836).

A liquid microdroplet could be a naturally simple, miniaturized and effective optical cavity by itself due to the intriguing optofluidic properties associated with its surface tension-induced spherical shape. It had been shown that optical whispering gallery modes (WGMs) can be present along the circular rim in the equatorial plane of a sessile microdroplet, and this phenomenon had been leveraged for biosensing demonstrations. However, optical coupling to such equatorial modes for their excitation and monitoring is mostly based on either tapered fiber coupling or free-space beam coupling, each of which demandingly requires precise alignment of the tapered fiber or the free-space beam adjacent to the equatorial surface of the resonator. In this paper, we show that WGMs could also be stimulated along the meridian plane of a liquid microdroplet resting on a properly designed nanostructured chip surface. The geometrical morphology and optical characteristics of a microdroplet cavity are critical to achieve a high-quality Q factor and therefore to realize high-resolution in situ and in vivo monitoring of trace analytes. The unavoidable deformation along the meridian rim of the sessile microdroplet can be controlled and regulated by tailoring the nanopillar structures and their associated hydrophobicity. The nanostructured superhydrophobic chip surface and its impact on the microdroplet morphology are modeled by Surface Evolver, which is subsequently validated by the Cassie–Wenzel theory of wetting. The influence of the microdroplet morphology on the optical characteristics of WGMs is further numerically studied using the finite-difference time-domain method and it is found that meridian WGMs with intrinsic quality factor Q exceeding 104 can exist. Importantly, such meridian WGMs can be efficiently excited by a waveguiding structure embedded in the planar chip, which could significantly reduce the overall system complexity by eliminating conventional mechanical coupling parts. Our simulation results also demonstrate that this optofluidic resonator can achieve a sensitivity as high as 530 nm/RIU. This on-chip coupling scheme could pave the way for developing lab-on-a-chip resonators for high-resolution sensing of trace analytes in various applications ranging from chemical detections, biological reaction processes to environmental protection.

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high spatial resolution imaging and three-dimensional reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third-harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, we succesfully demonstrate a simple method for preparing organic nanocrystals based on an aggregation-induced emission (AIE) luminogen (DCCN) with bright near-infrared emission. Under femtosecond laser excitation, the high-order nonlinear optical effects of DCCN were studied in three distinct systems, including monomolecules in solution, amorphous nanopaticles, and crystaline nanopaticles. Results revealed aggregation-induced nonlinear optical (AINLO) effects, including two-photon fluorescence (2PF), three-photon fluorescence (3PF) and THG, of DCCN in nanopaticles, especially for the crystaline nanopaticles. Taking advantage of the strong 2PF and THG properties, the nanocrystals of DCCN have been successfully applied for 2PF microscopy at 1040 nm NIR-II excitation and THG microscopy at 1560 nm NIR-II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy could provide much higher spatial resolution and brightness than the 2PF microscopy and could visualize small vessels with diameters of ~2.7 μm at deepest depth of 800 μm in mouse brain, which is among the largest penetration depth and best spatial resolution of in vivo THG vasculature imaging. Thus, this is expected to inspire new insights into development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.

We report simple and compact all-fiber erbium-doped soliton and dispersion-managed soliton femtosecond lasers mode-locked by the MXene Ti3C2Tx. A saturable absorber device fabricated by optical deposition of Ti3C2Tx onto a microfiber exhibits strong saturable absorption properties, with a modulation depth of 11.3%. The oscillator operating in the soliton regime produces 597.8 fs-pulses with 5.21 nm of bandwidth, while the cavity with weak normal dispersion (~0.008 ps2) delivers 104 fs pulses with 42.5 nm of bandwidth. Our results contribute to the growing body of work studying the nonlinear optical properties of MXene that underpin new opportunities for ultrafast photonic technology.

Vehicle charging power supply is widely used because of its small size and portability. Aiming at the problems of slow dynamic response, subharmonic, oscillation and limited soft-switching range of phase-shifted full-bridge DC/DC converter, the paper proposed a modified PSFB converter by introducing clamp diodes at the primary side of the transformer to suppress voltage oscillation of the transformer’s secondary side. Also, digital peak current phase-shifting control and slope compensation are introduced to avoid subharmonic oscillation. Dynamic dead-time control technology introduced adjust the dead-time in different load ranges through the dead-time adjustment subroutine. Finally, an experimental platform of on-board charging phase-shifted full-bridge DC/DC converter is established. The experimental results show that the power supply eliminates subharmonic oscillation, achieves a wide range of soft-switching, improves the dynamic performance and antiinterference ability of the system, and optimizes the power efficiency.

We experimentally demonstrate a carbide-free femtosecond laser bone drilling with real-time parameter optimization based on on-line spectral monitoring after second-harmonic-generation green positioning, indicating a simple bone processing scheme.

Nowadays, marine electromagnetic method is a geophysical method which can effectively explore natural gas hydrate (NGH) resources. This method acquires seafloor structure and distribution laws of mineral resources by transmitting high-power electromagnetic waves to the seafloor, and its detection depth relies on the intensity of transmitted electromagnetic waves. At present, marine electromagnetic transmitter is not proper for transmission of high-power electromagnetic waves, and therefore, a novel controlled-source circuit of soft switching three-level marine electromagnetic transmitter is proposed in this paper, one step-down winding is added at the secondary side of high-frequency transformer in series connection with a linear inductor, asymmetric phase-shift PWM control is used, and soft switching of controlled-source circuit within the overall power range is realized. A detailed analysis of the operation process and circuit characteristics is given, and finally, a prototype is designed. Experimental results indicate that this circuit is of wide ZVS range and high efficiency, and it meets requirements for deep-sea detection of high-voltage power supply transmitter.

Dual-comb methane spectroscopy at 1650nm is realized based on a dual-comb mode-locked fiber laser at 1560nm, which demonstrates the capability of such single-cavity, dual-comb sources to cover spectral ranges far beyond the laser emission wavelength. © 2019 The Author(s)

Employing a self-assembly method and dual-fiber structure, a compact, low-cost, highly sensitive, fast surface-enhanced Raman scattering (SERS) optical fiber sensor was realized. Through detecting a SERS signal of 10 ppm rhodamine B analyte, sensor parameters such as coupling angle, fiber types, and corresponding glass substrate structure were optimized. The ratio of the SERS signal intensity to excitation light residual peak intensity was used as a significant parameter during the optimization process. Sensor characteristics such as the SERS signal dependence on excitation power, stability related to excitation time, and reusability were studied. Its compatibility in size with microfluidic structure would make it a prospective candidate for integrating into a microfluidic chip.

Terahertz dual-comb spectroscopy (THz-DCS) has the potential to be used as universal THz spectroscopy with high spectral resolution, high spectral accuracy, and broad spectral coverage; however, the requirement for dual stabilized femtosecond lasers hampers its versatility due to the bulky size, high complexity, and high cost. We here report the first demonstration of dual THz comb spectroscopy using a single free-running fiber laser. While greatly reducing the size, complexity, and cost of the laser source, THz-DCS maintains the spectroscopic performance comparable to a system equipped with dual stabilized fiber lasers, and can be effectively applied to gas spectroscopy.