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Aqueous organic redox flow batteries (AORFBs) are regarded as a promising solution for grid-scale and sustainable energy storage, but some long-standing problems such as low energy density and cycling stability should be resolved. Herein, a highly soluble bipyridine modified with a bridging phenylene group and two quaternary ammonium terminals, namely, [(NPr)2PV]·4Cl, was synthesized and used as an ultralow-potential and two-electron storage anolyte for AORFBs. The phenylene group, which is linked but not coplanar with the two pyridinium redox centers, can thus prevent their communication and result in an exceptionally low redox potential (−0.77 V vs standard hydrogen electrode, 2e–). Moreover, the introduction of a phenylene group can warrant a certain degree of large π-conjugation effects and mitigate the intramolecular Coulombic repulsion between the two positively charged pyridinium centers, thus helping to enhance the electrochemical stability. When paired with 4-trimethylammonium-TEMPO as the catholyte, [(NPr)2PV]·4Cl enabled an exceptionally high cell voltage up to 1.71 V. The AORFB delivers outstanding battery performances, specifically, ∼89% energy efficiency, ∼100% Coulombic efficiency, and ∼99.94% capacity retention per cycle during a long-term cycling process. The two overlapped single-electron reductions of [(NPr)2PV]·4Cl from the initial cationic form to the monoradical form and then to the quinoid form during the charging process were clearly verified by a series of spectroscopic techniques, including no-deuterium nuclear magnetic resonance and electron paramagnetic resonance. This work presents a significant improvement for the construction of high-voltage AORFBs by virtue of the designability, diversity, and tunability of multiredox organic molecules.

Fresnel volume tomography (FVT) offers higher resolution and better accuracy than conventional seismic raypath tomography. A key problem in FVT is the sensitivity kernel. We propose amplitude and traveltime sensitivity kernels expressed directly with Green’s functions for transmitted waves for 2D/3D homogeneous/heterogeneous media. The Green’s functions are calculated with a finite-difference operator of the full wave equation in the frequency-space domain. In the special case of homogeneous media, we analyze the properties of the sensitivity kernels extensively and gain new insight into these properties. According to the constructive interference of waves, the spatial distribution ranges of the monochromatic sensitivity kernels in FVT differ from each other greatly and are [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] periods of seismic waves, respectively, for 2D amplitude, 3D amplitude, 2D traveltime, and 3D traveltime conditions. We also have a new understanding of the relationship between raypath tomography and FVT. Within the first Fresnel volume of the dominant frequency, the band-limited sensitivity kernels of FVT in homogeneous media or smoothly heterogeneous media are very close to those of the dominant frequency. Thus, it is practical to replace the band-limited sensitivity kernel with a few selected frequencies or even the single dominant frequency to save computation when performing band-limited FVT. The numerical experiment proves that FVT using our sensitivity kernels can achieve more accurate results than traditional raypath tomography.

Because modeling for full-waveform inversion (FWI) cannot produce reflections unless the velocity model has the scattering potential (high wavenumbers), using a migration/demigration process to generate modeling data, which is a key step in what is now known as reflection FWI (RFWI), is a credible alternative to tackle the reflection nonlinearity associated with FWI. However, because RFWI depends on a conventional data residual or zero-lag correlation objective function, high nonlinearity can still exist when the true amplitude migration is not used, as well as at far offsets due to cycle skipping. To avoid the cycle skipping and the need for a true amplitude migration, we have developed a correlation-based reflection full-waveform inversion method to update the low-wavenumber components of the velocity model. The success of this method relies on a sensitivity kernel decomposition and a correlation-based objective function. The sensitivity kernel decomposition makes it possible to separate out the contributions of different subkernels and to smear the reflected wave residuals along the “rabbit-ear” wavepath to obtain middle and deep background model estimates. The correlation-based objective function measures differences in kinematic information and behaves in a more linear way than the traditional waveform residual misfit. Moreover, our approach is less sensitive to the frequency content and amplitude information of the seismic data, enabling reliable background velocity estimates to be obtained without the need for low frequencies and full-physics modeling. Because the kinematic features of reflected waves are described correctly, the inversion result of the proposed method can be used as a migration model or an initial model for conventional FWI to achieve a correct high-wavenumber model update.

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Campylobacter species are zoonotic pathogens and the leading cause of bacterial enteritis worldwide. With the increase of antimicrobial resistance to fluoroquinolones and macrolides, they have been identified by the World Health Organization (WHO) as high-priority antimicrobial-resistant pathogens. There is currently little known about the prevalence and antimicrobial resistance characteristics of Campylobacter species in Beijing. In this study, we performed a 2-year surveillance of Campylobacter in Beijing, China. We used multilocus sequence typing (MLST) and antimicrobial susceptibility testing to analyze 236 Campylobacter isolates recovered from 230 clinical infectious cases in Beijing between 2017 and 2018. The Campylobacter isolation rate in diarrhea patients was 7.81%, with higher isolation rates in male patients than female patients and in autumn compared with other seasons. We identified 125 sequence types (STs) of 23 cloning complexes (CCs) among the 236 isolates, including four new alleles and 19 new STs. The most commonly isolated STs of Campylobacter jejuni were ST-22 and ST-760 (4.50%), and the most commonly isolated ST of Campylobacter coli was ST-9227 (16.67%). We also compared our isolates with clinical Campylobacter isolates from other countries in Asia, CC-353 of Campylobacter coli was found in eight countries, CC-1034 and CC-1287 of Campylobacter coli were found only in China. All C. jejuni isolates were resistant to at least one antimicrobial. C. jejuni showed the highest rate of resistance toward ciprofloxacin (94.50%), followed by tetracycline (93.50%), and nalidixic acid (92.00%), while C. coli showed highest resistance toward ciprofloxacin (94.44%) and tetracycline (94.44%) followed by nalidixic acid (88.89%). The most commonly observed MDR combination of C. jejuni were quinolone, phenicol and tetracycline (11.50%), while the most commonly observed MDR combination of C. coli were macrolide, quinolone, phenicol, tetracycline and lincosamide (30.56%). Surveillance of molecular characterization will provide important information for prevention of Campylobacter infection. This study enhances insight into Campylobacter infections in diarrheal patients, with relevance for treatment regimens in Beijing.

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