Search

The warmer-than-present (5–10 °C) climate during the Miocene Climate Optimum (MMCO, approximately 16.9–14.7 Ma) is likely to serve as a reference for future pessimistic warming scenarios. Forced with MMCO boundary conditions, the warming and ocean circulation changes are simulated by the fully coupled climate model FGOALS-g3 with a nominal 1° horizontal resolution ocean component model. Under a 400 ppmv CO 2 concentration, the model generally simulates the MMCO temperature well with small biases at mid and low latitudes compared to the proxy data. Large biases at high latitudes show that FGOALS-g3 fails to reproduce the weak meridional gradient indicated by the proxy record. MMCO surface albedo decreases significantly owing to changes in worldwide forest cover in the boundary condition and the amount of sea ice melt due to the warming climate compared with the PI run. Based on the Energy Balance Model decomposition, warming by the lower surface albedo reaches 1.4–2.7 °C, which is comparable to greenhouse effect warming (∼2.7 °C). Accompanied by MMCO global ocean warming and land–sea distribution changes, both oceanic wind-driven and thermohaline circulations strengthen. The Antarctic Circumpolar Current in the MMCO is stronger due to the enhanced westerly wind stress and the reduced sea ice extent. The intensified MMCO Atlantic Meridional Overturning Cell (AMOC) relative to PI is likely linked to the altered ocean-gateway configuration, particularly at low and middle latitudes. When the MMCO Panama Seaway and Tethys Seaway open, waters from the Pacific and the Indian Ocean converge and mix in the western North Atlantic. Combined with the supplemental water (∼30 Sv), the Gulf Stream is enhanced and flows more poleward, causing the sea ice to retreat, leading to a deeper mixed layer. Consequently, the Subpolar North Atlantic salinification causes stronger convective motion and the appearance of the Atlantic Meridional Overturning Cell. • The model simulates the reconstructed MMCO temperature well in low and mid latitudes. • Intensified greenhouse effect and low surface albedo mainly cause MMCO warmth. • Strengthened AMOC results from the convergence of Pacific and Indian Ocean water. [ABSTRACT FROM AUTHOR]

Six low-lying states ( X 2 Σ g + , A 2 Π u , B 2 Σ u + , 4 Σ g + , 4 Π u and 4 Σ u + ) of C 2 − anion are studied by highly correlated ab initio calculations. The potential energy curves (PECs) are computed in the internuclear separation from 0.8 to 5.0 Å using the complete active space self-consistent field method, and then performing the internally contracted multireference configuration interaction with Davidson correction. Core–valence correlation and scalar relativistic effect are considered through employing the aug-cc-pcV5Z-dk basis set. The spin–orbit coupling of the A 2 Π u state is also calculated using Breit–Pauli Hamiltonian. Based on the PECs derived from the high-level ab initio calculations, the spectroscopic parameters are obtained by fitting the ro-vibrational levels that are acquired by solving the ro-vibrational Schrödinger equation. These spectroscopic parameters, especially for low-lying doublet states, are in good agreement with the previously calculated and experimental results. Finally, the electronic transition dipole moment matrix elements, Franck–Condon factors, radiative lifetimes and oscillator strengths of A 2 Π u – X 2 Σ g + and B 2 Σ u + - X 2 Σ g + are calculated and discussed as well. [ABSTRACT FROM AUTHOR]

The defect classification is investigated by using features-based giant-magnetoresistive pulsed eddy current (GMR-PEC) sensor. The power spectrum density of the intrinsic mode functions (IMFs) is extracted as the classification feature, considering the disadvantage of selecting a wavelet base determined in previous work on spectral analysis combined with wavelet-decomposition. The IMFs are derived through empirical mode decomposition (EMD) and ensemble EMD. Principal component analysis, linear discriminant analysis, and Bayesian classifier are employed for defect classification algorithm. The proposed approach is validated by experiments, and results indicate that the cracks and cavities in the surface and subsurface can be classified satisfactorily. [ABSTRACT FROM AUTHOR]

Highlights • A portable laser sensor for trace NH3 is developed based on FPGA. • WMS-2 f /1 f is employed to reduce the random fluctuations. • The adsorption of NH3 is studied and minimized in measurements. • The sensor is deployed for in-situ measurement of NH3 slip in SCR. Abstract A portable laser sensor for trace ammonia (NH 3) is developed based on near-infrared laser absorption spectroscopy. Tunable diode laser absorption spectroscopy in conjunction with wavelength modulation spectroscopy is implemented by a system-on-chip based on field-programmable gate array. A variable temperature multipass cell with a 15 m optical path length is adopted to enhance the absorption path length and avoid the NH 3 adsorption. The physical dimension of the sensor is minimized into 43 × 18 × 16 cm3 on the benefit of home-made electronic system and compact optical design. A unique absorption line of NH 3 around 1.51 µm covered by a distributed feedback diode laser is selected to reduce the influence from carbon dioxide, vapor and other trace gases. Calibration-free modulation spectroscopy is employed to avoid the random fluctuations due to laser noise and non-absorption transmission losses. The performance of sensor including adsorption of NH 3 , stability and flow of gas are examined and discussed in detail. For removing the adsorption of NH 3 , the temperature-dependent curve is obtained by the direct absorption spectroscopy, and it shows that the adsorption is significantly suppressed at (or higher than) 415 K. According to Allan deviation analysis, the minimum detection limit is 0.16 ppm at 184 s, and the rise time and the fall time of system are about 4.5 s and 3.7 s, respectively. The feasibility of the sensor is validated and deployed to monitor the NH 3 slip in selective catalytic reduction (SCR) of coke oven flue gas. The work provides a potentially valuable control sensor for SCR. [ABSTRACT FROM AUTHOR]

Highlights • The sensor utilized a DFB laser around 2.33 μm as source. • The sensor was developed by using a high performance microcontroller and simple DLIA algorithm. • The LoD of 0.45 ppm is achieved while a precision of 0.0875 ppm is observed with an optimal time of ∼24 s. • The response times were significantly shorted with the detectable threshold being set at 5 ppm instead of 100 ppm. Abstract A distributed feedback laser-based carbon monoxide (CO) sensor has been developed for early warning detection of fire. The sensor, based on a system-on-chip with high-performance 32-bit microcontroller (MCU), features a digital lock-in amplifier (DLIA) for wavelength modulation spectroscopy (WMS) to improve detection sensitivity. The ramp scanning signal and a sinusoidally modulated signal were generated and superimposed by the MCU, and converted by a digital-to-analog converter to scan the absorption line of CO around 2.327 μm. The n -harmonic components obtained through multiplication of the n- th cosine wave data of the spectral signal, were then processed by integration and filter algorithms. The Allan-Werle deviation was used to evaluate the long-term performance of the sensor. The limit of detection (LoD) for CO was calculated to be 0.0875 ppm based on an optimal integration time of ∼24 s. In field tests, five small-scale standard fires were investigated in accord with EN54 and the results for the test substances – cotton rope (smoldering fire), polyurethane foam (smoldering fire), beech wood, a sheet of A4 paper and polyvinylchloride – verified the reliability and robustness of the developed sensor. Relatively fast response times (110 s for foam and A4 paper; 250 s for PVC, beech wood and cotton rope) were realized based on a threshold of 5 ppm CO. The CO sensor is considered suitable for integration into portable devices for industrial application, particularly for in-situ early warning fire detection. [ABSTRACT FROM AUTHOR]

Based on the non-Kolmogorov spectrum, using the extended Huygens–Fresnel principle, the analytical expressions for the spectrum of the coherent and incoherent superpositions of rectangular array Gaussian Schell-model (RAGSM) beams propagating through non-Kolmogorov atmospheric turbulence are derived, and are used to study the influence of non-Kolmogorov atmospheric turbulence on spectral changes of coherent and incoherent superpositions RAGSM beams. It is shown that, with the increment of the general exponent α and the inner scale of turbulence l 0 , as well as the decrement of the general structure constant C ˜ n 2 , the magnitude of the spectral shift will increase, the magnitude of spectral transition will decrease and the critical position of spectral transition will decrease. The outer scale of turbulence L 0 has little effect on the spectral shift and spectral transition. [ABSTRACT FROM AUTHOR]

• A dual-species sensor was constructed based on two-channel ALIA. • A Herriott cell and normalized technique were adopted to improve sensitivity. • A sensitivity for CO and CH 4 was about 0.20 ppm with a 2.5 s sampling time. • The CO emission satisfied the exponential growth tendency during CSC. • Two CTs were recognized and were able to precisely forecast CSC. As a common hazard, coal spontaneous combustion (CSC) causes the loss of coal in piles and mines. To rapidly and reliably forecast CSC, a portable and powerful detection system based on a laser spectroscopic technique is proposed, to precisely measure gaseous inhibitors; the technique uses a single, distributed-feedback diode laser emitting at 2.33 μm as a sensing light source for dual species. The detection system carries out wavelength-modulation spectroscopy to suppress detection noise by using a two-channel analogue lock-in amplifier (ALIA) and a complex programmable logic device (CPLD) controller. To improve detection sensitivity, a Herriott cell is adopted to increase the interaction length between the laser and the target species. The embedded system on a chip (SoC) of STM32F103 is the charge of the current driver and temperature control of the laser. Deployment of the SoC of STM32H743 acquires and digitally filters the original demodulated absorption signal, after which communication with a personal computer takes place. The second demodulation component, normalized by the first demodulation component, is used to improve the signal-to-noise ratio. The sensor-calibration experiment reveals the square of the correlation coefficients R2 to be 0.99718 and 0.99905 for carbon monoxide (CO) and methane (CH 4), respectively, over the concentration range of 5–200 ppm. Using Allan-Werle deviation analysis, the detection sensitivity for CO and CH 4 are 0.27 ppm and 0.20 ppm with a 2.5 s sampling time, and 0.05 ppm and 0.03 ppm with ~125 and 95 s integration times, respectively. Finally, the detection system is used for the online measurement and analysis of the growth pattern of gaseous products which are released during the CSC process, the temperature varying from 30 to 200 °C. Two critical temperatures were correctly determined to further forecast CSC status. On beginning a vigorous oxidation process, the exponential-evolution trends of the CH 4 and CO gases agree with each other. Compared with CH 4 , CO may be more suitable for online, early detection of CSC. [ABSTRACT FROM AUTHOR]

A laser-based spectrometer with a physical size of 60× 30 ×25 cm3 has been developed to continuously monitor CO and CH 4 in atmosphere based on tunable diode laser absorption spectroscopy (TDLAS). Two neighboring lines of CO and CH 4 around 2.3 μ m were selected as candidates for simultaneous measurement by a single diode distributed feedback (DFB) laser. A special Herriott-type multipass absorption cell, with a 72 m optical path length, was designed and used to enhance the absorption signals of sample gases. Normalized wavelength modulation spectroscopy was applied to improve the sensitivity and robustness of the spectrometer and it was implemented on a home-made electronic system based on field programmable gate array (FPGA). Meanwhile, the electronic system controlled the temperature and current of DFB laser with the precision of 0.01 °C and 40 ppm. The 2nd-harmonic signals normalized by the corresponding 1st-harmonic signals for both CO and CH 4 are of high linear response to their concentrations in the range of 0.046–4.6 ppm and 0.487–48.7 ppm, respectively. According to the Allan variance, respective minimum detection limits for CO and CH 4 are 0.73 ppb and 36 ppb at 122 s and 137 s. As an application example, the spectrometer has been validated through real-time and in-situ measurement of atmospheric CO and CH 4 for 48 h. Unlabelled Image • A compact laser-based spectrometer has been developed to monitor atmospheric CO and CH 4 using a single DFB laser emitting at 2.33 μm. • A special Herriott-type multipass cell combined with FPGA system was designed and used to improve the sensitivity and compactness of the system. • The normalized WMS-(2 f /1 f) technique was employed to achieve high robustness of spectrometer. • The spectrometer has been validated for real-time and in-situ measurement of atmospheric CO and CH 4 for 48 h. [ABSTRACT FROM AUTHOR]