[en] We compare three datasets of high-resolution O₃ cross sections and evaluate the effects of using these cross sections on O₃ profile retrievals from OMI UV (270–330 nm) measurements. These O₃ cross sections include Brion–Daumont–Malicet (BDM), Bass–Paur (BP) and a new dataset measured by Serdyuchenko et al. (SGWCB), which is made from measurements at more temperatures and in a wider temperature range than BDM and BP, 193–293 K. Relative to the BDM dataset, the SGWCB data have systematic biases of −2 to +4% for 260–340 nm, and the BP data have smaller biases of 1–2% below 315 nm but larger spiky biases of up to ±6% at longer wavelengths. These datasets show distinctly different temperature dependences. Using different cross sections can significantly affect atmospheric retrievals. Using SGWCB data leads to retrieval failure for almost half of the OMI spatial pixels, producing large negative ozone values that cannot be handled by radiative transfer models and using BP data leads to large fitting residuals over 310–330 nm. Relative to the BDM retrievals, total ozone retrieved using original SGWCB data (with linear temperature interpolation/extrapolation) typically shows negative biases of 5–10 DU; retrieved tropospheric ozone column generally shows negative biases of 5–10 DU and 5–20 DU for parameterized and original SGWCB data, respectively. Compared to BDM retrievals, ozone profiles retrieved with BP/SGWCB data on average show large altitude-dependent oscillating differences of up to ±20–40% biases below ∼20 km with almost opposite bias patterns. Validation with ozonesonde observations demonstrates that the BDM retrievals agree well with ozonesondes, to typically within 10%, while both BP and SGWCB retrievals consistently show large altitude-dependent biases of up to ±20–70% below 20 km. Therefore, we recommend using the BDM dataset for ozone profile retrievals from UV measurements. Its improved performance is likely due to its better characterization of temperature dependence in the Hartley and Huggins bands. -- Highlights: • Compare 3 UV O₃ cross sections: BDM, BP, and new Serdyuchenko et al. data. • The new data show biases (−2 to 4%) vs. BDM and different temperature dependences. • Different data affect OMI O₃ profile retrieval by up to 40% on average below 20 km. • BDM retrievals agree with ozonesonde to ∼10%, others show up to ±20–70% biases. • Recommend using the BDM dataset for UV ozone profile retrieval

[en] Highlights: • Utilization of commercial nanomaterials to freestanding sodium electrode is demonstrated. • Free-standing electrodes composed of TiO_2 and MWCNTs are hierarchically porous. • Hierarchical porous architecture benefits charge transport and interfacial Na"+ adsorption. • Free-standing hierarchical porous electrodes exhibit superior Na storage performance. - Abstract: Freestanding hierarchical porous assemblies of commercial TiO_2 nanocrystals and multi-wall carbon nanotubes (MWCNTs) as electrode materials for sodium ion batteries (SIBs) are prepared via modified vacuum filtration, free-drying and annealing. Microstructure characterizations reveal that TiO_2 nanocrystals are confined in hierarchically porous, highly electrically conductive and mechanically robust MWCNTs networks with cross-linking of thermally-treated bovine serum albumin. The hierarchical porous architecture not only enables rapid charge transportation and sufficient interaction between electrode and electrolyte, but also guarantees abundant interfacial sites for Na"+ adsorption, which benefits substantial contribution from pseudocapacitive Na storage. When it is used directly as an anode for sodium-ion batteries, the prepared electrode delivers high specific capacity of 100 mA h g"−"1 at a current density of 3000 mA g"−"1, and 150 mA h g"−"1 after 500 cycles at a current density of 500 mA g"−"1. The low-cost TiO_2-based freestanding anode has large potential application in high-performance SIBs for portable, flexible and wearable electronics.

[en] We investigate the superconducting phases and boundary modes for a quasi-1D system formed by up to three Fe chains on an s-wave superconductor, motivated by a recent experiment. While the Rashba type spin–orbit coupling together with a magnetic ordering is necessary to drive the system to be of nontrivial topology, we show that the onsite $\stackrel{\to <!--\; ???\; -->}{l}\cdot <!--\; ???\; -->\stackrel{\to <!--\; ???\; -->}{s}$ spin–orbit term, inter-chain diagonal hopping couplings, and magnetic disorders in the Fe chains are crucial in determining the symmetry classes of superconducting phases, which can be topologically trivial or nontrivial in different parameter regimes. In general multiple low-energy Andreev bound states, as well as a single Majorana zero mode if the phase is topological, are obtained in the ends of Fe chains. The nontrivial symmetry reduction mechanism is uncovered to provide an understanding of the present results, and may explain the zero-bias peak observed in the experiment. The present study can be applied to generic multiple-chain system. (paper)

[en] Highlights: • A full-scale CO₂ pipeline burst test to generate model validation data. • Validated CFD models for CO₂ dispersion simulations. • Comprehensive studies of CO₂ dispersion due to pipeline fracture. • Determination of consequence distances due to full-scale pipeline fracture. -- Abstract: Transportation of Carbon Dioxide (CO₂) via high-pressure pipelines from source to storage site forms an important link in the Carbon Capture and Storage (CCS) chain. To ensure the safety of the operation, it is necessary to develop a comprehensive understanding of the consequences of possible pipeline failure. CO₂ is a hazardous substance and an accidental release may lead to catastrophic damage. This paper describes an experimental investigation of the dispersion of CO₂ in the atmosphere in a full-scale burst test of a pipeline containing high-pressure dense phase CO₂. The experiment was carried out to simulate a CO₂ pipeline failure in the real world. The test rig consisted of a buried 85 m long, 610 mm diameter pipeline test section connected at either end to 116 m long reservoirs. An explosive charge detonated at test section half-length initiated a rupture in the pipe wall top surface, releasing the high-pressure contents. The atmospheric dispersion of the CO₂ following the explosive release was measured. The paper also describes Computational Fluid Dynamics (CFD) simulations of the dispersion of CO₂ following the release. The CFD models were validated against the experimental data. The models were then extended to estimate the consequence distances related to CO₂ dispersion following failure of longer pipelines of various diameters under different wind speeds and directions. Comparison of the results with prior studies was carried out.

[en] Highlights: • Multi-phase CFD model for decompression simulation of CO₂ mixtures. • Incorporation of GERG-2008 EOS into CFD code for decompression modelling. • Predicted decompression wave speed validated by measurements in shock tube experiments. • Investigation of effects of delayed bubble formation on the decompression wave speed. Carbon Capture and Storage (CCS) is widely seen as an effective technique to reduce what is perceived as excessive CO₂ concentration in the atmosphere. This technique includes transporting CO₂ from source point to the storage site, usually through high-pressure pipelines. In order to ensure safe transport (i.e. to prevent the contents from being released into the atmosphere), it is important to estimate the required pipe toughness in the design stage. This requires an accurate prediction of the speed of the ‘decompression wave’ in the fluid, which is created when the high-pressure fluid escapes into the ambient. In this paper, a multi-phase Computational Fluid Dynamics (CFD) model is presented to simulate the decompression of high-pressure pipelines carrying CO₂ mixtures. A ‘real gas’ Equation of State (EOS), the GERG-2008 EOS, is incorporated into the CFD code to model the thermodynamic properties of the fluid in both liquid and vapour states. The non-equilibrium liquid/vapour transition is modelled by introducing ‘source terms’ for mass transfer and latent heat. The model is validated through simulation of a ‘shock tube’ test. A ‘time relaxation factor’ is used to control the inter-phase mass transfer rate. The measured decompression wave speed is compared with that predicted using different values of the time relaxation factor. It is found that the non-equilibrium phase transition has a significant influence on the decompression wave speed. Also, the effects of delayed bubble formation and of various impurities on the decompression wave speed are investigated.

[en] Silicon as a high capacity alloying anode material in lithium-ion batteries (LIBs) has recently been reported to have a promising specific capacity suitable for sodium-ion batteries (SIBs). However, the low gravimetric capacity and large volume expansion in traditional electrodes arising from the slurry-coating process has restrained the development. Here, we report the fabrication of a self-supported composite composed of silicon nanocrystals in a 3D hierarchical carbon network as an anode for reversible sodium storage by a three-step process involving electrostatically assisted hetero-assembly, vacuum filtration, and thermal treatment. The silicon nanocrystals decorated with a carbon coating are dispersed in interconnected carbon nanotubes with close contact. The structure provides abundant interfacial active sites for capacitive Na storage. Furthermore, the conductive 3D network of carbon nanotubes and carbon coating provide the high-speed pathways for charge transport and buffer to accommodate the volume change during Na⁺ insertion/extraction in silicon nanocrystals. As a binder-free anode in SIBs, the self-supported electrode delivers outstanding electrochemical performance such as stable cyclability with a capacity of 80% at a current density of 0.2 A g⁻¹ after 1000 cycles and high-rate capability with a capacity of 105 mAh g⁻¹ at a current density of 2 A g⁻¹. The self-supported Si-based electrode has great potential in high-performance SIBs.

[en] Though pulsars spin regularly, the differences between the observed and predicted ToA (time of arrival), known as “timing noise^, can still reach a few milliseconds or more. We try to understand the noise in this study. As proposed by Xu and Qiao in 2001, both dipole radiation and particle emission would result in pulsar braking. Accordingly, possible fluctuation of particle current flow is suggested here to contribute significant ToA variation of pulsars. We find that the particle emission fluctuation could lead to timing noise which cannot be eliminated in timing process and that a longer period fluctuation would arouse a stronger noise. The simulated timing noise profile and amplitude are in agreement with the observed timing behaviors on the timescale of years. (geophysics, astronomy, and astrophysics)

[en] The inhomogenous ocean waveguide, which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate, is one of the causes that make the array gain deviate from its ideal value. The relationship between the array gain and the fluctuant acoustic channel is studied theoretically. The analytical expression of the array gain is derived via an acoustic channel transfer function on the assumption that the ambient noise field is isotropic. The expression is expanded via the Euler formula to give an insight into the effect of the fluctuant acoustic channel on the array gain. The result demonstrates that the amplitude fluctuation of the acoustic channel transfer functions has a slight effect on the array gain; however, the uniformity of the phase difference between the weighting coefficient and the channel transfer function on all the hydrophones in the array is a major factor that leads the array gain to further deviate from its ideal value. The numerical verification is conducted in the downslope waveguide, in which the gain of a horizontal uniform linear array (HLA) with a wide-aperture operating in the continental slope area is considered. Numerical result is consistent with the theoretical analysis. (special topic)

[en] With the constraint from gravitational wave emission of a binary merger system (GW170817) and two-solar-mass pulsar observations, we investigate the r-mode instability windows of strange stars with unpaired and color-flavor-locked phase strange quark matter. Shear viscosities due to surface rubbing and electron-electron scattering are taken into account in this work. The results show that the effects of the equation of state of unpaired strange quark matter are only dominant at low temperature, but do not have significant effects on strange stars in the color-flavor-locked phase. A color-flavor-locked phase strange star, which is surrounded by an insulating nuclear crust, seems to be consistent with observational data of young pulsars. We find that an additional enhanced dissipation mechanisms might exist in SAX J1808.4–3658. Fast spinning young pulsar PSR J0537–6910 is a primary source for detecting gravitational waves from a rotating strange star, and young pulsars might be strange stars with color-flavor-locked phase strange quark matter. (paper)

[en] At present, the feature extraction of frequency signal based on empirical mode decomposition (EMD) has been widely studied and applied in fault diagnosis of rolling bearings. However, there are still some shortcomings in fault diagnosis based on EMD. Therefore, a fault diagnosis method based on the combination of EMD and target feature selection (TFS) is proposed in this paper. The method firstly analyzes the fault signal through EMD and extracts the fault features. Then, it removes the redundant features and optimizes the feature subsets by using TFS. TFS selects the most effective feature for each target sample space through filtering evaluation criteria and heuristic search strategy, thereby effectively improving the accuracy and efficiency of fault diagnosis. (paper)