Volumetric lattice Boltzmann method for pore-scale mass diffusionadvection process in geopolymer porous structures

Porous materials present significant advantages for absorbing radioactive isotopes in nuclear waste streams.To improve absorption efficiency in nuclear waste treatment,a thorough understanding of the diffusion-advection process within porous structures is essential for material design.In this study,we present advancements in the volumetric lattice Boltzmann method(VLBM)for modeling and simulating pore-scale diffusion-advection of radioactive isotopes within geopolymer porous structures.These structures are created using the phase field method(PFM)to precisely control pore architectures.In our VLBM approach,we introduce a concentration field of an isotope seamlessly coupled with the velocity field and solve it by the time evolution of its particle population function.To address the computational intensity inherent in the coupled lattice Boltzmann equations for velocity and concentration fields,we implement graphics processing unit(GPU)parallelization.Validation of the developed model involves examining the flow and diffusion fields in porous structures.Remarkably,good agreement is observed for both the velocity field from VLBM and multiphysics object-oriented simulation environment(MOOSE),and the concentration field from VLBM and the finite difference method(FDM).Furthermore,we investigate the effects of background flow,species diffusivity,and porosity on the diffusion-advection behavior by varying the background flow velocity,diffusion coefficient,and pore volume fraction,respectively.Notably,all three parameters exert an influence on the diffusion-advection process.Increased background flow and diffusivity markedly accelerate the process due to increased advection intensity and enhanced diffusion capability,respectively.Conversely,increasing the porosity has a less significant effect,causing a slight slowdown of the diffusion-advection process due to the expanded pore volume.This comprehensive parametric study provides valuable insights into the kinetics of isotope uptake in porous structures,facilitating the development of porous materials for nuclear waste treatment applications.

3D near-surface P-wave velocity structure imaging with Distributed Acoustic Sensing and electric hammer source

Distributed Acoustic Sensing(DAS) is an emerging technique for ultra-dense seismic observation, which provides a new method for high-resolution sub-surface seismic imaging. Recently a large number of linear DAS arrays have been used for two-dimensional S-wave near-surface imaging in urban areas. In order to explore the feasibility of three-dimensional(3D) structure imaging using a DAS array, we carried out an active source experiment at the Beijing National Earth Observatory. We deployed a 1 km optical cable in a rectangular shape, and the optical cable was recast into 250 sensors with a channel spacing of 4 m. The DAS array clearly recorded the P, S and surface waves generated by a hammer source. The first-arrival P wave travel times were first picked with a ShortTerm Average/Long-Term Average(STA/LTA) method and further manually checked. The P-wave signals recorded by the DAS are consistent with those recorded by the horizontal components of short-period seismometers. At shorter source-receiver distances, the picked P-wave arrivals from the DAS recording are consistent with vertical component recordings of seismometers, but they clearly lag behind the latter at greater distances.This is likely due to a combination of the signal-to-noise ratio and the polarization of the incoming wave. Then,we used the Tomo DD software to invert the 3D P-wave velocity structure for the uppermost 50 m with a resolution of 10 m. The inverted P-wave velocity structures agree well with the S-wave velocity structure previously obtained through ambient noise tomography. Our study indicates the feasibility of 3D near-surface imaging with the active source and DAS array. However, the inverted absolute velocity values at large depths may be biased due to potential time shifts between the DAS recording and seismometer at large source-receiver distances.

Norepinephrine-Astrocyte Signaling Regulates Cortical State Homeostasis

Cortical states such as high and low arousal during wakefulness or rapid eye movement(REM)and non-REM(NREM)phases of sleep are fundamental biological processes that are highly conserved across species.An intricate balance or homeostasis of cortical states during wakefulness or sleep is necessary for an organism's survival and well-being.

Tailoring the interactions of heterostructured Ni_(4)N/Ni_(3)ZnC_(0.7)for efficient CO_(2)electroreduction

Electrocatalytic CO_(2)reduction into CO has been regarded as one of the most promising strategies for sustainable carbon cycles at ambient conditions,but still faces challenges to achieve both high product selectivity and large current density.Here,we report a Ni_(4)N/Ni_(3)ZnC_(0.7)heterostructured electrocatalyst embedded in accordion-like N-doped carbon through a simple molten salt annealing strategy.The optimal Ni_(4)N/Ni_(3)ZnC_(0.7)electrocatalyst achieves a high CO Faraday efficiency of 92.3%and a large total current density of-15.8 m A cm^(-2)at-0.8 V versus reversible hydrogen electrode,together with a long-term stability about 30 h.Density functional theory results reveal that the energy barrier for*COOH intermediate formation largely decreased on Ni_(4)N/Ni_(3)ZnC_(0.7)heterostructure compared with Ni_(4)N and Ni_(3)ZnC_(0.7),thus giving rise to enhanced activity and selectivity.A rechargeable Zn-CO_(2)battery is further assembled with Ni_(4)N/Ni_(3)ZnC_(0.7)catalyst as the cathode,which shows a maximum power density of 0.85 mW cm^(-2)and excellent stability.

Fine relocation, mechanism, and tectonic indications of middle-small earthquakes in the Central Tibetan Plateau

The medium-small earthquakes that occurred in the middle part of Tibetan Plateau(32°N–36°N, 90°E–93°E) from August 2016 to June 2017 were relocated using the absolute earthquake location method Hypo2000. Compared to the reports of Chinese Seismological Networks, our relocation results are more clustered on the whole, the horizontal location differences exceed 10 km, and the focal depths are concentrated in 0–8 km, which indicates that the upper crust inside the Tibetan Plateau is tectonically active. In June2017 altogether eight earthquakes above magnitude 3.0 took place; their relocated epicenters are concentrated around Gêladaindong.The relocation results of M<3.0 small earthquakes also showed obvious differences. Therefore, we used the CAP method to invert for the focal mechanisms of the M ≥3.0 earthquakes; results generally tally with the surface geological structures, indicating that the Tibetan Plateau is still under the strong compressional force from the India Plate. Among them the eight earthquakes that occurred near Gêladaindong in June 2017 are all of normal fault type or with some strike-slip at the same time; based on previous research results we conjecture that these events are intense shallow crust responses to deep crust-mantle activities.

Extraction of lanthanide ions with N,N,N′,N′-tetrabutyl-3-oxadiglycolamide from nitric acid media

Extractability and extraction mechanism of lanthanide ions were investigated by using a new extractant,N,Nn,N′,N′-tetrabutyl-3-oxa-diglycolamide(TBDGA),in toluene from nitric acid media.The effects of HNO_3 and TBDGA concentrations,and temperature,on extraction of lanthanide ions were studied.Stoichiometrics of the main extracted species were HNO_3·TBDGA and M(NO_3)_3-3TBDGA(M = Er,Dy,Tb,Gd,La,Ce,Nd,Sm and Eu).The extracted species for metal ions were established to be ionic complex.In this complex,nitrate anion was not coordinated to the central ion.The extraction pattern increased gradually across the lanthanide ions series,showing enhanced affinity of TBDGA toward heavy lanthanide ions.Thermodynamic parameters were investigated for the exothermic extraction reaction.

Probing dark matter particles from evaporating primordial black holes via electron scattering in the CDEX-10 experiment

Dark matter(DM)is a major constituent of the Universe.However,no definite evidence of DM particles(denoted as“χ”)has been found in DM direct detection(DD)experiments to date.There is a novel concept of detectingχfrom evaporating primordial black holes(PBHs).We search forχemitted from PBHs by investigating their interaction with target electrons.The examined PBH masses range from 1×10^(15)to 7×10^(16)g under the current limits of PBH abundance fPBH.Using 205.4 kg·day data obtained from the CDEX-10 experiment conducted in the China Jinping Underground Laboratory,we exclude theχ-electron(χ-e)elastic-scattering cross sectionσ_(χe)~5×10^(-29)cm^(2)forχwith a mass■keV from our results.With the higher radiation background but lower energy threshold(160 eV),CDEX-10 fills a part of the gap in the previous work.If(m_(χ),σ_(χe))can be determined in the future,DD experiments are expected to impose strong constraints on fPBHfor large MPBHs.

Functional Changes in Astrocytes Lead to Cognitive Deficits After Social Deprivation

Social experience has a far-reaching impact on the brain and behavior.In humans,lacking social experience during childhood is associated with a faster decline in later-life cognitive function[l],while social isolation in the elderly is an independent risk factor for dementia[2].The lack of social experience at different stages of life has significant adverse effects on cognitive development and mental health.Studies have largely been focused on the neuronal activity and synaptic plasticity changes after social deprivation.Two recent studies separately reported increased expression of an astrocyte marker,glial fibrillary acidic protein,in socially isolated perinatal or adult mice demonstrating structural changes in astrocytes after social deprivation[3,4].However,it is still unknown whether and how astrocyte function is impacted by social deprivation.

Diamond Raman laser:a promising high-beam-quality and low-thermal-effect laser

Stimulated Raman-scattering-based lasers provide an effective way to achieve wavelength conversion.However,thermally induced beam degradation is a notorious obstacle to power scaling and it also limits the applicable range where high output beam quality is needed.Considerable research efforts have been devoted to developing Raman materials,with diamond being a promising candidate to acquire wavelength-versatile,high-power,and high-quality output beam owing to its excellent thermal properties,high Raman gain coefficient,and wide transmission range.The diamond Raman resonator is usually designed as an external-cavity pumped structure,which can easily eliminate the negative thermal effects of intracavity laser crystals.Diamond Raman converters also provide an approach to improve the beam quality owing to the Raman cleanup effect.This review outlines the research status of diamond Raman lasers,including beam quality optimization,Raman conversion,thermal effects,and prospects for future development directions.

First experimental constraints on WIMP couplings in the effective field theory framework from CDEX

We present weakly interacting massive particles(WIMPs) search results performed using two approaches of effective field theory from the China Dark Matter Experiment(CDEX), based on the data from both CDEX-1B and CDEX-10 stages. In the nonrelativistic effective field theory approach, both time-integrated and annual modulation analyses were used to set new limits for the coupling of WIMP-nucleon effective operators at 90% confidence level(C.L.) and improve over the current bounds in the low mχregion. In the chiral effective field theory approach, data from CDEX-10 were used to set an upper limit on WIMP-pion coupling at 90% C.L. We for the first time extended the limit to the m_(χ)<6 GeV/c^(2) region.

A review:applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials

Complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature.This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical,thermal,and magnetic properties.The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials.Then,the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiated nuclear materials are reviewed.The review shows that(1)Phase field models can correctly describe important phenomena such as spatial-dependent generation,migration,and recombination of defects,radiation-induced dissolution,the Soret effect,strong interfacial energy anisotropy,and elastic interaction;(2)The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution,including radiation-induced segregation,second phase nucleation,void migration,void and gas bubble superlattice formation,interstitial loop evolution,hydrate formation,and grain growth,and(3)The Phase field method correctly predicts the relationships between microstructures and properties.The final section is dedicated to a discussion of the strengths and limitations of the phase field method,as applied to irradiation effects in nuclear materials.

Phase-field model of pitting corrosion kinetics in metallic materials

Pitting corrosion is one of the most destructive forms of corrosion that can lead to catastrophic failure of structures.This study presents a thermodynamically consistent phase field model for the quantitative prediction of the pitting corrosion kinetics in metallic materials.An order parameter is introduced to represent the local physical state of the metal within a metal-electrolyte system.The free energy of the system is described in terms of its metal ion concentration and the order parameter.Both the ion transport in the electrolyte and the electrochemical reactions at the electrolyte/metal interface are explicitly taken into consideration.The temporal evolution of ion concentration profile and the order parameter field is driven by the reduction in the total free energy of the system and is obtained by numerically solving the governing equations.A calibration study is performed to couple the kinetic interface parameter with the corrosion current density to obtain a direct relationship between overpotential and the kinetic interface parameter.The phase field model is validated against the experimental results,and several examples are presented for applications of the phase-field model to understand the corrosion behavior of closely located pits,stressed material,ceramic particles-reinforced steel,and their crystallographic orientation dependence.

Performances of a prototype point-contact germanium detector immersed in liquid nitrogen for light dark matter search

The CDEX-10 experiment searches for light weakly interacting massive particles, a form of dark matter, at the China Jinping Underground Laboratory, where approximately 10 kg of germanium detectors are arranged in an array and immersed in liquid nitrogen. Herein, we report on the experimental apparatus, detector characterization, and spectrum analysis of one prototype detector. Owing to the higher rise-time resolution of the CDEX-10 prototype detector as compared with CDEX-1 B, we identified the origin of an observed category of extremely fast events. For data analysis of the CDEX-10 prototype detector, we introduced and applied an improved bulk/surface event discrimination method. The results of the new method were compared to those of the CDEX-1 B spectrum. Both sets of results showed good consistency in the 0-12 ke Vee energy range, except for the 8.0 keV K-shell X-ray peak from the external copper.

A prototype segmented planar high purity germanium detector using wraparound lithium diffusion electrode and amorphous germanium blocking contact

Purpose Segmented high purity germanium(HPGe)detectors have been used in many experiments to measure the position and energy deposition of gamma ray interactions.Significant efforts have been made to optimize the design and simplify the fabrication process.Amorphous germanium(aGe)coating is a desirable method to realize blocking contact and facilitate the segmentation.Method In this study,a prototype segmented planar HPGe detector is fabricated using a wraparound lithium diffusion electrode for bias voltage applying and reliable mechanical mounting.A low leakage current design is realized based on conventional chemical polishing and aGe blocking.A guard ring(GR)is used to protect the metal strip electrodes within it from the surface leakage current.The GR and strip electrodes are coated onto the aGe layer.A multichannel charge sensitive preamplifier is connected to the strip electrodes,and the signal waveforms are digitized using a multichannel 100 MS/s analog-to-digital converter.Results and conclusion The charge collection time and amplitude are analyzed.An average energy resolution of 2 keV(full width at half maximum,FWHM)is realized at 662 keV.Charge collection is simulated via a Monte Carlo program.The spatial resolution is also estimated using the program.The front-end response and measured noise level are considered.According to the simulation results,sub-millimeter(FWHM at 122 keV)resolution can be achieved at the current noise level.

First results on ^(76)Ge neutrinoless double beta decay from CDEX-1 experiment

We report the first results on 76Ge neutrinoless double beta decay from stage one of the China dark-matter experiment （CDEX）. A p-type point-contact high-purity germanium detector with a mass of 994g has been installed to detect neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304kgd has been analyzed over a wide spectral band from 500keV to 3MeV. The average event rate obtained was about 0.012 counts per keV per kg per day over the 2.039MeV energy range. The half-life of76Ge neutrinoless double beta decay derived based on this result is 70v2〉6.4× 1022 yr （90%C.L.）. An upper limit on the effective Majorana-neutrino mass of 5.0eV has been achieved.

Improving NiNX and pyridinic N active sites with space-confined pyrolysis for effective CO_(2)electroreduction

Even though various nickel-nitrogen-carbon(Ni-N-C)combinations are prospective low-cost catalysts for the CO_(2)electroreduction reaction(CO_(2)RR),which is one avenue for attaining carbon neutrality,the detailed role of different N species has hardly been investigated.Here,we report a hollow porous N-doped carbon nanofiber with NiNX-pyridinic N active species(denoted as h-Ni-N-C)developed using a facile electrospinning and SiO_(2)space-confined pyrolysis strategy.The NiNX-pyridinic N species are facilely generated during the pyrolysis process,giving rise to enhanced activity and selectivity for the CO_(2)RR.The optimized h-Ni-N-C exhibits a high CO Faradaic efficiency of 91.3%and a large current density of−15.1 mA cm^(−2)at−0.75 V versus reversible hydrogen electrode in an H-cell.Density functional theory(DFT)results show that NiN4-pyridinic N species demonstrate a lower free energy for the catalyst's rate-determining step than isolated NiN4 and pyridinic N species,without affecting the desorption of CO∗intermediate.