Mineralogy of the deep lower mantle in the presence of H2O

Understanding the mineralogy of the Earth''s interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H₂O to form a previously unknown (Mg, Fe)O₂H_x (x ≤ 1) phase. The (Mg, Fe)O₂H_x has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg_0.6Fe_0.4)O or beyond 2300 km for (Mg_0.7Fe_0.3)O. The (Mg, Fe)O₂H_x is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg²⁺, Fe³⁺ and H⁺). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.     

Solution pH change in non-uniform alternating current electric fields at frequencies above the electrode charging frequency

AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (f_c), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above f_c. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H⁺] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5f_c). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H⁺] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 V_pp potential, and voltage dependency was explored from 3.5 to 7.5 V_pp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position.     

Ionic liquid-based electrolytes for CO2 electroreduction and CO2 electroorganic transformation

CO₂ is an abundant and renewable C1 feedstock. Electrochemical transformation of CO₂ can integrate CO₂ fixation with renewable electricity storage, providing an avenue to close the anthropogenic carbon cycle. As a new type of green and chemically tailorable solvent, ionic liquids (ILs) have been proposed as highly promising alternatives for conventional electrolytes in electrochemical CO₂ conversion. This review summarizes major advances in the electrochemical transformation of CO₂ into value-added carbonic fuels and chemicals in IL-based media in the past several years. Both the direct CO₂ electroreduction (CO₂ER) and CO₂-involved electroorganic transformation (CO₂EOT) are discussed, focusing on the effect of electrocatalysts, IL components, reactor configurations and operating conditions on catalytic activity, selectivity and reusability. The reasons for the enhanced CO₂ conversion performance by ILs are also discussed, providing guidance for the rational design of novel IL-based electrochemical processes for CO₂ conversion. Finally, the critical challenges remaining in this research area and promising directions for future research are proposed.     

Periodic solutions to systems of reaction-diffusion equations

In this paper, necessary and sufficient conditions are derived for the existence of temporally periodic “dissipative structure” solutions in cases of weak diffusion with the reaction rate terms dominant in a generic system of reaction-diffusion equations ?c_i/?t = D_i?²c_i+Q_i(c), where the enumerator index i runs 1 to n, c_i = c_i(x, t) denotes the concentration or density of the ith participating molecular or biological species, D_i is the diffusivity constant for the ith species and Q_i(c), an algebraic function of the n-tuple c = (c₁,\3., c_n), expresses the local rate of production of the ith species due to chemical reactions or biological interactions.     

Nuclear Resonance Flourescence Studies of Levels in 206Pb, 207Pb, 208Pb and 209Bi below about 5MeV

Capabilities of the resonance flourescence technique are discussed. Specific reference is given to the study of ground state dipole and electric quadrople transitions below about 5 MeV in ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb and ²⁰⁹Bi. It is suggested that many of the states observed in ²⁰⁷Pb and ²⁰⁹Bi arise from the weak-coupling of a p_{$\text{1}\text{2}$} neutron hole or an h_{$\text{9}\text{2}$} proton to collective levels of ²⁰⁸Pb.     

Periodic solutions for a kind of Rayleigh equation with two deviating arguments

In this paper, we use the coincidence degree theory to establish new results on the existence of T-periodic solutions for the Rayleigh equation with two deviating arguments of the form

x^″+f(x^′(t))+g₁(t,x(t-τ₁(t)))+g₂(t,x(t-τ₂(t)))=p(t).     

Graphdiyne-based metal atomic catalysts for synthesizing ammonia

Development of novel catalysts for nitrogen reduction at ambient pressures and temperatures with ultrahigh ammonia (NH₃) yield and selectivity is challenging. In this work, an atomic catalyst with separated Pd atoms on graphdiyne (Pd-GDY) was synthesized, which shows fascinating electrocatalytic properties for nitrogen reduction. The catalyst has the highest average NH₃ yield of 4.45 ± 0.30 mg_NH3 mg_Pd⁻¹ h⁻¹, almost tens of orders larger than for previously reported catalysts, and 100% reaction selectivity in neutral media. Pd-GDY exhibits almost no decreases in NH₃ yield and Faradaic efficiency. Density functional theory calculations show that the reaction pathway prefers to perform at the (Pd, C1, C2) active area because of the strongly coupled (Pd, C1, C2), which elevates the selectivity via enhanced electron transfer. By adjusting the p–d coupling accurately, reduction of self-activated nitrogen is promoted by anchoring atom selection, and side effects are minimized.     

The inverse lure problem of optimal control

Given the linear system $\text{x}\text{}$ = Ax - bu, y = c^Tx, it is shown that, for a certain non-quadratic cost functional, the optimal control is given by u_opt(x) = h(c^Tx), where the function h(y) must satisfy the conditions ky²?h(y)y>0 for y≠0, h(0) = 0 and existence of h^-1 everywhere. The linear system considered must satisfy the Popov condition 1/k + (1 +?ωβ) G(?ω)>0 for all ω, G(s) being the y(s)/u(s) transfer function.     

Evidence for oxygenation of Fe-Mg oxides at mid-mantle conditions and the rise of deep oxygen

As the reaction product of subducted water and the iron core, FeO₂ with more oxygen than hematite (Fe₂O₃) has been recently recognized as an important component in the D” layer just above the Earth''s core-mantle boundary. Here, we report a new oxygen-excess phase (Mg, Fe)₂O_3+δ (0 < δ < 1, denoted as ‘OE-phase’). It forms at pressures greater than 40 gigapascal when (Mg, Fe)-bearing hydrous materials are heated over 1500 kelvin. The OE-phase is fully recoverable to ambient conditions for ex situ investigation using transmission electron microscopy, which indicates that the OE-phase contains ferric iron (Fe³⁺) as in Fe₂O₃ but holds excess oxygen through interactions between oxygen atoms. The new OE-phase provides strong evidence that H₂O has extraordinary oxidation power at high pressure. Unlike the formation of pyrite-type FeO₂Hx which usually requires saturated water, the OE-phase can be formed with under-saturated water at mid-mantle conditions, and is expected to be more ubiquitous at depths greater than 1000 km in the Earth''s mantle. The emergence of oxygen-excess reservoirs out of primordial or subducted (Mg, Fe)-bearing hydrous materials may revise our view on the deep-mantle redox chemistry.     

Altering the rate-determining step over cobalt single clusters leading to highly efficient ammonia synthesis

Activation of high-energy triple-bonds of N₂ is the most significant bottleneck of ammonia synthesis under ambient conditions. Here, by importing cobalt single clusters as strong electron-donating promoter into the catalyst, the rate-determining step of ammonia synthesis is altered to the subsequent proton addition so that the barrier of N₂ dissociation can be successfully overcome. As revealed by density functional theory calculations, the N₂ dissociation becomes exothermic over the cobalt single cluster upon the strong electron backdonation from metal to the N₂ antibonding orbitals. The energy barrier of the positively shifted rate-determining step is also greatly reduced. At the same time, advanced sampling molecular dynamics simulations indicate a barrier-less process of the N₂ approaching the active sites that greatly facilitates the mass transfer. With suitable thermodynamic and dynamic property, a high ammonia yield rate of 76.2 μg h^–1 mg and superior Faradaic efficiency of 52.9% were simultaneously achieved.     

Extraterrestrial artificial photosynthetic materials for in-situ resource utilization

Aerospace milestones in human history, including returning to the moon and manned Martian missions, have been implemented in recent years. Space exploration has become one of the global common goals, and to ensure the survival and development of human beings in the extraterrestrial extreme environment has been becoming the basic ability and technology of manned space exploration. For the purpose of fulfilling the goal of extraterrestrial survival, researchers in Nanjing University and the China Academy of Space Technology proposed extraterrestrial artificial photosynthesis (EAP) technology. By simulating the natural photosynthesis of green plants on the Earth, EAP converts CO₂/H₂O into fuel and O₂ in an in-situ, accelerated and controllable manner by using waste CO₂ in the confined space of spacecraft, or abundant CO₂ resources in extraterrestrial celestial environments, e.g. Mars. Thus, the material loading of manned spacecraft can be greatly reduced to support affordable and sustainable deep space exploration. In this paper, EAP technology is compared with existing methods of converting CO₂/H₂O into fuel and O₂ in the aerospace field, especially the Sabatier method and Bosch reduction method. The research progress of possible EAP materials for in-situ utilization of extraterrestrial resources are also discussed in depth. Finally, this review lists the challenges that the EAP process may encounter, which need to be focused on for future implementation and application. We expect to deepen the understanding of artificial photosynthetic materials and technologies, and aim to strongly support the development of manned spaceflight.     

Fractional multiple birth-death processes with birth probabilities λi(Δt)+o((Δt))

The usual model for (Poissonian) linear birth-death processes is extended to multiple birth-death processes with fractional birth probabilities in the form λ_i(Δt)^α+o((Δt)^α, 0<α<1. The probability generating function for the time dependent population size is provided by a fractional partial differential equation. The solution of the latter is obtained and comparison with the usual model is made. The probability of ultimate extinction is obtained. One considers the special case of fractional Poissonian processes with individual arrivals only, and then one outlines basic results for continuous processes defined by fractional Poissonian noises. The key is the Taylor’s series of fractional order f(x+h)=E_α(h^αD_x^α)f(x), where E_α(·) is the Mittag-Leffler function, and D_x^α is the modified Riemann-Liouville fractional derivative, as previously introduced by the author.     

中国CO2排放强度下降的结构分解——基于1997年-2007年的投入产出分析

本文以中国1997年和2007年的投入产出表为基础,核算了CO₂排放强度的变化。结果表明,中国1997年CO_排放总量为381788.56万t,强度为5.04t/万元。2007年CO₂排放总量为775346.15万t,强度为4.23t/万元。10年间,CO₂排放强度降低近20%。在此基础上进一步构建结构分解分析模型,将促使CO₂排放强度降低的因素分解为4种效应,即能源效率因素、能源结构因素、产业结构效应和经济增长方式效应。计量结果表明,部门单位产出能源消费强度变化和部门能源消费结构变化是造成CO₂排放强度下降的因素,其中以前者的影响最为显著。而产业结构变化和经济增长方式变化是促使CO₂排放强度上升的因素,并且前者的影响更为显著。因此,未来要实现2020年CO₂排放强度比2005年下降40%～45%的目标,必须调整产业结构,改变经济增长方式,以充分挖掘经济增长结构和方式转变的节能减排潜力。     

Selective catalytic reduction of NOx with NH3: opportunities and challenges of Cu-based small-pore zeolites

Zeolites, as efficient and stable catalysts, are widely used in the environmental catalysis field. Typically, Cu-SSZ-13 with small-pore structure shows excellent catalytic activity for selective catalytic reduction of NO_x with ammonia (NH₃-SCR) as well as high hydrothermal stability. This review summarizes major advances in Cu-SSZ-13 applied to the NH₃-SCR reaction, including the state of copper species, standard and fast SCR reaction mechanism, hydrothermal deactivation mechanism, poisoning resistance and synthetic methodology. The review gives a valuable summary of new insights into the matching between SCR catalyst design principles and the characteristics of Cu²⁺-exchanged zeolitic catalysts, highlighting the significant opportunity presented by zeolite-based catalysts. Principles for designing zeolites with excellent NH₃-SCR performance and hydrothermal stability are proposed. On the basis of these principles, more hydrothermally stable Cu-AEI and Cu-LTA zeolites are elaborated as well as other alternative zeolites applied to NH₃-SCR. Finally, we call attention to the challenges facing Cu-based small-pore zeolites that still need to be addressed.     

Periodic solutions for a fourth-order p-Laplacian neutral functional differential equation

By means of Mawhin's continuation theorem, we study a kind of fourth-order p-Laplacian neutral functional differential equation with a deviating argument in the form:

(φ_p(x(t)−cx(t−δ))^″)^″=f(x(t))x^′(t)+g(t,x(t−τ(t,|x|_∞)))+e(t).     

Linking deep CO2 outgassing to cratonic destructionOA

Outgassing of carbon dioxide from the Earth’s interior regulates the surface climate through deep time.Here we examine the role of cratonic destruction in mantle CO₂ outgassing via collating and presenting new data for Paleozoic kimberlites, Mesozoic basaltic rocks and their mantle xenoliths from the eastern North China Craton(NCC), which underwent extensive destruction in the early Cretaceous. High Ca/Al and low Ti/Eu and δ²⁶ Mg are widely observed in lamprophyres and mant...     

Efficient interlayer charge release for high-performance layered thermoelectrics

Many layered superlattice materials intrinsically possess large Seebeck coefficient and low lattice thermal conductivity, but poor electrical conductivity because of the interlayer transport barrier for charges, which has become a stumbling block for achieving high thermoelectric performance. Herein, taking BiCuSeO superlattice as an example, it is demonstrated that efficient interlayer charge release can increase carrier concentration, thereby activating multiple Fermi pockets through Bi/Cu dual vacancies and Pb codoping. Experimental results reveal that the extrinsic charges, which are introduced by Pb and initially trapped in the charge-reservoir [Bi₂O₂]²⁺ sublayers, are effectively released into [Cu₂Se₂]²⁻ sublayers via the channels bridged by Bi/Cu dual vacancies. This efficient interlayer charge release endows dual-vacancy- and Pb-codoped BiCuSeO with increased carrier concentration and electrical conductivity. Moreover, with increasing carrier concentration, the Fermi level is pushed down, activating multiple converged valence bands, which helps to maintain a relatively high Seebeck coefficient and yield an enhanced power factor. As a result, a high ZT value of ∼1.4 is achieved at 823 K in codoped Bi_0.90Pb_0.06Cu_0.96SeO, which is superior to that of pristine BiCuSeO and solely doped samples. The present findings provide prospective insights into the exploration of high-performance thermoelectric materials and the underlying transport physics.     

Regulating off-centering distortion maximizes photoluminescence in halide perovskites

Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH₃NH₃GeI₃, HC(NH₂)₂GeI₃, and CsGeI₃]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH₃NH₃⁺ with Cs⁺ to control the distortion in (CH₃NH₃)_1-xCs_xGeI₃, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI₃ further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods.     

Accurate approximate solutions to oscillatory problems with perturbing singular damping

In this paper we attempt to obtain approximate solutions of improved accuracy for a class of differential equations of the form

$\text{d}{}^2\text{y}\text{d}\text{x}{}^2\text{+εμ(x)}\text{d}\text{y}\text{d}\text{x}\text{+ω}{}^2{}_{\mathrm{c}}\text{y = 0}$

, where ε is a real parameter less than unity, ω_c is a positive real constant of order unity and μ(x) is a singular function of x in the region of interest. It does not appear to be possible to find a general analytic expression for the error estimate of the approximate solution. For the case μ(x) = x^?2, however, it is shown that the approximate solution is accurate to 0(ε²), as x → 0^? from negative values, by comparing it with the numerically integrated solution. For the same case, the approximate solution is orders of magnitude more accurate than Poincaré's first-order perturbation solution, which is accurate to $\text{0(}\text{ε}{}^2\text{ln}\text{|x|}\text{|x|}\text{)}$ as x → 0^?. This work arose in search of analytic solutions to a linearized form of the restricted three-body problem.     

Periodic solutions for p-Laplacian neutral Liénard equation with a sign-variable coefficient

Using Lu's continuation theorem, the extension one of Manásevich-Mawhin, we study the existence of periodic solutions for p-Laplacian neutral Liénard equation of the form

(?_p(x(t)-cx(t-σ))^′)^′+f(x(t))x^′(t)+β(t)g(x(t-τ(t))=e(t).