Self-absorption correction method based on intensity self-calibration of doublet lines.

The self-absorption effect in an optically thick plasma seriously affects the spectral line intensity and the measurement accuracy of laser-induced breakdown spectroscopy (LIBS). In this work, a self-absorption correction method based on intensity self-calibration of doublet lines belonging to the same multiplet is proposed. The K/Δλ0 parameter and self-absorption coefficient (SA) of the doublet lines of the analytical element can be calculated based on the measured actual lines intensity ratio and the K parameters ratio. Compared with the generally applied self-absorption correction methods, this method can effectively reduce the influence of laser energy and plasma plume fluctuations and the non-uniformity distribution of the element in the plasma, and is independent of the availability of Stark broadening coefficients. So it has obvious advantages of high computation efficiency, high analysis accuracy and good applicability. Univariate quantitative analysis results of aluminum (Al) show that the correlation coefficient of calibration curves and the measurement accuracy of elemental content have been significantly improved with the self-absorption correction.

An In-Situ Tester for Extracting Piezoresistive Coefficients.

In this study, an electrostatic force-driven on-chip tester consisting of a mass with four guided cantilever beams was employed to extract the process-related bending stiffness and piezoresistive coefficient in-situ for the first time. The tester was manufactured using the standard bulk silicon piezoresistance process of Peking University, and was tested on-chip without additional handling. In order to reduce the deviation from process effects, the process-related bending stiffness was first extracted as an intermediate value, namely, 3590.74 N/m, which is 1.66% lower than the theoretical value. Then, the value was used to extract the piezoresistive coefficient using a finite element method (FEM) simulation. The extracted piezoresistive coefficient was 9.851 × 10-10 Pa-1, which essentially matched the average piezoresistive coefficient of the computational model based on the doping profile we first proposed. Compared with traditional extraction methods, such as the four-point bending method, this test method is on-chip, achieving automatic loading and precise control of the driving force, so it has high reliability and repeatability. Because the tester is manufactured together with the MEMS device, it has the potential to be used for process quality evaluation and monitoring on MEMS sensor production lines.

High-flux wavelength tunable XUV source in the 12-40.8†eV photon energy range with adjustable energy and time resolution for Tr-ARPES applications.

High-order harmonic generation (HHG) has a broad spectrum covering vacuum ultraviolet to extreme ultraviolet (XUV) bands, which is useful for applications involving material analyses at different information depths. Such an HHG light source is perfect for time- and angle-resolved photoemission spectroscopy. Here, we demonstrate a high-photon flux HHG source driven by a two-color field. Applying a fused silica compression stage to reduce the driving pulse width, we obtained a high XUV photon flux of 2 × 1012 phs/s @21.6 eV on target. We designed a classical diffraction mounted (CDM) grating monochromator that can achieve a wide range of photon energy from 12 to 40.8 eV, while the time resolution is improved by reducing the pulse front tilt after the harmonic selection. We designed a spatial filtering method to adjust the time resolution using the CDM monochromator and significantly reduced the pulse front tilt of the XUV pulses. We also demonstrate a detailed prediction of the energy resolution broadening which is caused by the space charge effect.

Cathode diffusion layer and current collector with slotted foam stainless steel for a micro direct methanol fuel cell.

In order to reduce the contact and mass transfer impedance of the diffusion layer and current collector of a Micro Direct Methanol Fuel Cell (µDMFC), a novel Membrane Electrode Assembly (MEA) structure is designed by using Foam Stainless Steel (FSS) with a slotting rate of 38.47% for both the cathode diffusion layer and the current collector. Electrochemical tests are performed on the Foam Stainless Steel Membrane Electrode Assembly (FSS-MEA) and the Conventional Carbon Paper Membrane Electrode Assembly (CCP-MEA) µDMFCs. The experimental results show that the maximum power density of FSS-MEA µDMFC is 46.55 mW cm-2 at 343 K, which is 42.88% higher than that of CCP-MEA µDMFC, and the optimum working concentration of FSS-MEA µDMFC is 2.5 mol L-1, which is 1 mol L-1 higher than that of CCP-MEA µDMFC. Electrochemical Impedance Spectroscopy (EIS) test results show that the contact impedance of FSS-MEA µDMFC is 0.55 Ω cm-2, which is 15.38% lower than that of CCP-MEA µDMFC. The mass transfer impedance of FSS-MEA µDMFC is 0.99 Ω cm-2, which is 25.56% lower than that of CCP-MEA µDMFC. This implies that the novel slotted FSS-MEA structure alleviates the methanol crossover and reduces the contact and mass transfer impedance, thus improving µDMFC power density.

Electrolyte Analysis in Blood Serum by Laser-Induced Breakdown Spectroscopy Using a Portable Laser.

The fast and reliable analysis of electrolytes such as K, Na, Ca in human blood serum has become an indispensable tool for diagnosing and preventing diseases. Laser-induced breakdown spectroscopy (LIBS) has been demonstrated as a powerful analytical technique on elements. To apply LIBS to the quantitative analysis of electrolyte elements in real time, a self-developed portable laser was used to measure blood serum samples supported by glass slides and filter paper in this work. The partial least squares regression (PLSR) method was employed for predicting the concentrations of K, Na, Ca from serum LIBS spectra. Great prediction accuracies with excellent linearity were obtained for the serum samples, both on glass slides and filter paper. For blood serum on glass slides, the prediction accuracies for K, Na, Ca were 1.45%, 0.61% and 3.80%. Moreover, for blood serum on filter paper, the corresponding prediction accuracies were 7.47%, 1.56% and 0.52%. The results show that LIBS using a portable laser with the assistance of PLSR can be used for accurate quantitative analysis of elements in blood serum in real time. This work reveals that the handheld LIBS instruments will be an excellent tool for real-time clinical practice.

Reduced Graphene Oxide/Carbon Paper for the Anode Diffusion Layer of a Micro Direct Methanol Fuel Cell.

The diffusion layer (DL) in the structure of the membrane electrode assembly (MEA) of a micro direct methanol fuel cell (µDMFC) plays an essential role in reactant/product mass transfer and catalyst loading. The material selection and structure design of the µDMFC affects its performance. In this work, a reduced graphene oxide/carbon paper (rGO/CP) was proposed and prepared for the anode DL of a µDMFC. It was prepared using electrophoretic sedimentation combined with an in situ reduction method. The rGO/CP reduced the cell's ohmic and charge transfer resistances. Meanwhile, it provided more significant mass transfer resistance to reduce the methanol crossover, allowing the cell to operate stably at higher concentrations for a longer duration than conventional µDMFCs. The experimental results showed that the maximum power density increased by 53% compared with the traditional anode DL of carbon paper.

Internal Characterization-Based Prognostics for Micro-Direct-Methanol Fuel Cells under Dynamic Operating Conditions.

Micro-direct-methanol fuel cells (µDMFCs) use micro-electro mechanical system (MEMS) technology, which offers high energy density, portable use, quick replenishment, and free fuel reforming and purification. However, the µDMFC is limited by a short effective service life due to the membrane electrode's deterioration in electrochemical reactions. This paper presents a health status assessment and remaining useful life (RUL) prediction approach for µDMFC under dynamic operating conditions. Rather than making external observations, an internal characterization is used to describe the degradation indicator and to overcome intrusive influences in operation. Then, a Markov-process-based usage behavior prediction mechanism is proposed to account for the randomness of real-world operation. The experimental results show that the proposed degradation indicator alleviates the reduction in µDMFC output power degradation behavior caused by the user loading profile. Compared with the predictions of RUL using traditional external observation, the proposed approach achieved superior prognostic performance in both accuracy and precision.

A Thermal Actuated Bistable Structure for Generating On-Chip Shock Loads.

In this paper, we propose a bistable shock structure based on the thermal actuation principle, which overcomes the response time limitation of heating and cooling in typical thermal actuators and enables a rapid release of energy. Thus, force with a steep rising edge can be applied on a target. Using a bistable shock structure to generate on-chip shock loads, we propose an automated and resettable method for shock testing of microstructures. We characterize the microscale shock process by high-speed camera and finite element simulation (FEM). The method can simulate the dynamic response of key structures in MEMS devices under mechanical shock conditions, and therefore, can be used to evaluate shock fracture strength of microstructures.

Performance study of µDMFC with foamed metal cathode current collector.

Micro Direct Methanol Fuel Cells (µDMFCs) often have application in moveable power due to their green and portable nature. In a µDMFC's structure, a current collector of the µDMFC needs to have high corrosion resistance such that the µDMFC can work for a long time in a redox reaction and respond to variable environmental conditions. To this end, four cathode current collectors were prepared. The materials selected were foam stainless steel (FSS) and foam titanium (FT), with fields of hole type and grid type. The performance of µDMFC with different cathode collector types was investigated by I-V-P polarization curves, Electrochemical Impedance Spectroscopy (EIS), and discharge test. The experimental results show that the maximum power density of the hole-type FSS cathode current collector µDMFC (HFSS-µDMFC) is 49.53 mW cm-2 at 70 °C in the methanol solution of 1 mol L-1, which is 70.15% higher than that of the hole-type FT cathode current collector µDMFC (HFT-µDMFC). The maximum power density of the grid-type FSS cathode current collector µDMFC (GFSS-µDMFC) is 22.60 mW cm-2, which is 11.99% higher than that of the grid-type FT cathode current collector µDMFC (GFT-µDMFC). The performance of the HFSS-µDMFC is optimal in the methanol solution of 1 mol L-1.

Optical Coupling Efficiency of a Coupler with Double-Combined Collimating Lenses and Thermally Expanded Core Fibers.

Improving the coupling efficiency of two optical signals is a hot issue, where the efficiency of optical coupling has a significant effect on the signal transmission over the fiber link. To this end, the Large-Beam Fiber Coupler (LBFC) with a Double-combined Collimating Lens (DCL) and a single-mode TEC fiber structure are proposed in this study. Based on the propagation principle of Gaussian beams and the coupling requirements, the coupling mechanism of the fiber coupler and the coupling mismatch between the coupler is analytically modeled. The model and the optical path are optimized, then the ray tracing is used to calculate the coupling efficiency of inter-coupler signals for different SMF. The coupling efficiency is evaluated through experiments in terms of coupling efficiency and the radial, axial, and angular mismatches between the couplers. The results showed that with a large Mode Field Diameter (MFD), better coupling efficiency can be obtained, i.e., a large MFD of 28 µm is tested with its maximal efficiency of 95.16%. Moreover, the angular mismatch has the most significant impact on the coupling efficiency, while the axial mismatch has the least. The use of large MFD can alleviate the angular mismatch and thus improve the optical coupling efficiency.

Thermal Transfer Characteristics of Flat Plate Micro Heat Pipe with Copper Spiral Woven Mesh and a Copper Foam Composite Wick.

The thermal efficiency limitation of the Flat-plate Micro Heat Pipe (FMHP) is a major challenge in the development of the FMHP, where the effect of wick structure and wettability on its thermal performance is studied to improve the thermal efficiency of the FMHP. In this work, a copper spiral woven mesh and copper foam Composite Wick FMHP (CW-FMHP) is designed based on the conventional Copper Foam Wick FMHP (CFW-FMHP), and its thermal performance is analyzed regarding the wick structure and internal gas-liquid two-phase flow characteristics. An oxidized copper spiral woven mesh and copper foam Composite Wick FMHP (OCW-FMHP) has been further developed through the modification of composite wick wettability. The performance tests are carried out with the thermal transfer characteristics of CW-FMHP, OCW-FMHP, and CFW-FMHP under different filling rates and different thermal powers. The experimental results show that the thermal transfer performance of CW-FMHP reaches the optimal under a liquid filling rate of 150%, where the maximum thermal power is 15.7 W, 35.3% higher than that of the CFW-FMHP under the same filling rate. Moreover, the dynamic response characteristics of the CW-FMHP are significantly improved. The thermal resistance of the CW-FMHP is 0.48 °C/W under the filling rate of 150% at the thermal power of 10 W with a reduction of 9.4% compared to the CFW-FMHP under the same condition. Furthermore, the optimal filling rate for OCW-FMHP is lower compared with the CW-FMHP. The maximum thermal power of OCW-FMHP increases to 17.8 W while the thermal resistance reduces to 0.34 °C/W under the liquid filling rate of 140%. This implies that the composite wick structure designed in this work can improve the thermal transfer performance of the FMHP, and the composite wick with wettability modification is more effective regarding both thermal resistance and maximum thermal power.

Measurements of Excavation Damaged Zone by Using Fiber Bragg Grating Stress Sensors.

In this paper, a Fiber Bragg Grating (FBG) stress sensor is developed to measure the stress variation between the lower Excavation Damaged Zone (EDZ) and the upper undistributed rock. The disturbance brought by the environmental temperature can be differentially compensated with two FBGs mounted symmetrically on the spokes. Through finite element analysis, it can be known that the direct stress and shear stress are pointed at the angles of 45° and 60° on both sides of the coal mine roadway, respectively. The anchor ends of the sensors are installed into the upper undistributed rock and the bolt tails of the mine roadway with a depth of 700 m and fastened by nuts to secure the load sensing device on the surface of the rock. When the shallow foundation of surrounding rock is pressed and deformed toward the coal mining road, the structural modifications can be converted into the stress of rock bolt and the strain of spoke. Thus, the FBG mounted on the surface of the spoke receives the shift information of the Bragg wavelength. The monitoring results indicate that the FBG stress sensors are sensitive to the variation of the EDZ. During the blasting, the stress amplitude varies from 40.256 to 175.058 kPa, and the creep time changes from 21 to 74 min. The proposed method can be applied in the field of underground coal mines for safety condition monitoring of the EDZ and forecasting the coal mine roadway stability.

Development trajectory for the temporal and spatial evolution of the resilience of regional tourism environmental systems in 14 cities of Gansu Province, China.

The rapid development of the urban economy in China and the accompanying income growth experienced by urban residents have increased demand for tourism and leisure, which has brought pressure on the urban tourism environment system (UTES), making the contradiction between tourism economic development and the ecological environment increasingly acute. While seeking to rationalize the economic, social, and ecological benefits of tourism, reducing the fragility of the UTES and improving its anti-interference and recovery capabilities have become attracted significant attention from scholars in China and elsewhere. This paper establishes a definition of resilience for an UTES and constructs an evaluation index system for it in terms of the social, economic, and ecological environments. It also establishes an entropy weight-TOPSIS resilience evaluation model to measure resilience in regional systems, using ArcGIS to analyze the standard deviation ellipse and center of the gravity track of the resilience. System dynamics was used to construct diagrams of causal relationships and stock flow for the constituent elements of UTES to show the mechanisms that promote its resilience. This paper investigates 14 cities of Gansu Province in particular to simulate the resilience model of a regional system.

2-GHz watt-level Kerr-lens mode-locked Yb:KGW laser.

We report on a 2-GHz high-power Kerr-lens mode-locked Yb:KGW laser pumped by a single-mode fiber laser. The output performance for two different output coupling rates was investigated. Stable bidirectional mode-locking operation at the repetition rate of 2.157 GHz was obtained with a 0.6% output coupler. The average output powers of bidirectional operation are 741 mW and 746 mW, with 123-fs and 126-fs pulse durations, respectively. By using a 1.6% output coupler, unidirectional mode-locking is achieved with 145-fs pulse duration and 1.7-W average output power, which, to the best of our knowledge, is the highest average power from Kerr-lens mode-locked GHz femtosecond oscillators.

10-W-scale Kerr-lens mode-locked Yb:CALYO laser with sub-100-fs pulses.

We reported a high-power pure Kerr-lens mode-locked Yb:CALYO laser based on the dual-confocal cavity delivering sub-100-fs pulses. The output pulses at 81 MHz have an average power of 10.4 W and the pulse duration of 98 fs, corresponding to the peak power of 1.14 MW. This is, to the best of our knowledge, the highest average power ever reported for a Kerr-lens mode-locked Yb-bulk oscillator. Analysis of the dual-confocal cavity was also conducted, which indicates a way to achieve higher average power. We believe the result described in this Letter may pave a way to develop Kerr-lens mode-locked bulk lasers with much higher average power.

Analytical Evaluation and Experiment of the Dynamic Characteristics of Double-Thimble-Type Fiber Bragg Grating Temperature Sensors.

A double-thimble-type fiber Bragg grating (FBG) temperature sensor that isolates the stress strain is developed, and the three materials of air, grease, and copper thimble are employed for encapsulating. To investigate the effect of different encapsulation materials on the time constant of the sensors under dynamic conditions, the transient heat conduction mathematical model is built according to the lumped heat capacity (LHC) system and thermal equilibrium theory, and the time constant is solved by an analytical solution. Then, a proportional three-dimensional sensor simulation model is established and the transient heat transfer process is numerically solved by the finite element analysis method. To verify the models, an experimental system is established to test the response speed of the three-type sensor and the experimental data are compared with the analytical and numerical solution results. The results show that the dynamic response performance depends on the encapsulation material parameters; the response speed is faster than recovery speed; and the response speed of the air packaging sensor is more than 20% faster than that of the grease packaging sensor, and more than 30% faster than that of the copper packaging sensor. The smaller the heat storage capacity and the larger the heat transfer coefficient, the faster the sensor's response speed.

Research on the anti-interference capability of the tourism environment system for the core stakeholders of semi-arid valley-type cities: analysis based on the multi-scenario and time series diversity perspectives.

Given the relatively harsh natural environment in semi-arid valley areas, the attraction and radiation functions of semi-arid valley cities have become the foci of further development in Western China. This study takes Lanzhou City (a semi-arid river valley city) as an example and uses the theoretical framework of pressure-state-response to optimize the response strategies of the tourism environmental needs of the City's core stakeholders from the multi-scenario and time series diversity perspectives. Based on the index system of the tourism environment system (TES) in semi-arid valley cities, the system dynamics model is used to forecast the index system of the tourism environment from multi-scenario perspectives. Based on the evolutionary optimization algorithm NSGA-II, the core stakeholders are optimized to meet the tourism environment needs, and the optimal solution set is selected based on the decision makers' preferences. Finally, several measures to improve the anti-interference ability of semi-arid valley cities' TES are proposed, namely standardizing the preferences of decision makers, improving the resilience of the destination TES, carrying out the safety management of valley cities' TES, and adjusting the seasonality of such cities to improve their tourism environment and promote the welfare of various stakeholders.

Diode-pumped high-power sub-100 fs Kerr-lens mode-locked Yb:CaYAlO4 laser with 1.85 MW peak power.

We demonstrated a diode-pumped high-power Kerr-lens mode-locked Yb:CaYAlO4 (Yb:CALYO) laser with a dual-confocal cavity, directly generating 59-fs pulses with 6.2 W average power, which is the highest average power from any sub-60 fs Yb-doped solid-state lasers. With the repetition rate of 50 MHz, the corresponding single pulse energy was 124 nJ and the peak power was 1.85 MW, which to the best of our knowledge is the highest peak power delivered directly from a sub-100 fs Yb-based bulk lasers ever.

Highly enantioselective one-pot synthesis of chiral ß-hydroxy sulfones via asymmetric transfer hydrogenation in an aqueous medium.

A mild transformation in an aqueous medium for the one-pot synthesis of optically active ß-hydroxy sulfones is described. The intermediates of ß-keto sulfones obtained via a nucleophilic substitution reaction of α-bromoketones and sodium sulfinates in H2O/MeOH (1:3, v/v) at 50 °C were reduced through Ru-catalyzed asymmetric transfer hydrogenation in one-pot using HCOONa as a hydrogen source providing a variety of chiral ß-hydroxy sulfones with high yields and excellent enantioselectivities.

Enantio-relay catalysis constructs chiral biaryl alcohols over cascade Suzuki cross-coupling-asymmetric transfer hydrogenation.

The construction of chiral biaryl alcohols using enantio-relay catalysis is a particularly attractive synthetic method in organic synthesis. However, overcoming the intrinsic incompatibility of distinct organometallic complexes and the reaction conditions used are significant challenges in asymmetric catalysis. To overcome these barriers, we have taken advantage of an enantio-relay catalysis strategy and a combined dual-immobilization approach. We report the use of an imidazolium-based organopalladium-functionalized organic-inorganic hybrid silica and ethylene-coated chiral organoruthenium-functionalized magnetic nanoparticles to catalyze a cascade Suzuki cross-coupling-asymmetric transfer hydrogenation reaction to prepare chiral biaryl alcohols in a two-step, one-pot process. As expected, the site-isolated active species, salient imidazolium phase-transfer character and high ethylene-coated hydrophobicity can synergistically boost the catalytic performance. Furthermore, enantio-relay catalysis has the potential to efficiently prepare a variety of chiral biaryl alcohols. Our synthetic strategy is a general method that shows the potential of developing enantio-relay catalysis towards environmentally benign and sustainable organic synthesis.