Evaluating the stability and volumetric flowback rate of proppant packs in hydraulic fractures using the lattice Boltzmann-discrete element coupling method

The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method(LB-DEM).This study starts with a preliminary proppant settling test,from which a solid volume fraction of 0.575 is calibrated for the proppant pack in the fracture.In the established workflow to investigate proppant flowback,a displacement is applied to the fracture surfaces to compact the generated proppant pack as well as further mimicking proppant embedment under closure stress.When a pressure gradient is applied to drive the fluid-particle flow,a critical aperture-to-diameter ratio of 4 is observed,above which the proppant pack would collapse.The results also show that the volumetric proppant flowback rate increases quadratically with the fracture aperture,while a linear variation between the particle flux and the pressure gradient is exhibited for a fixed fracture aperture.The research outcome contributes towards an improved understanding of proppant flowback in hydraulic fractures,which also supports an optimised proppant size selection for hydraulic fracturing operations.

Therapeutic potential of dental pulp stem cell transplantation in a rat model of Alzheimer’s disease

Dental pulp stem cells are dental pulp-derived mesenchymal stem cells that originate from the neural crest.They exhibit greater potential for the treatment of nervous system diseases than other types of stem cells because of their neurogenic differentiation capability and their ability to secrete multiple neurotrophic factors.Few studies have reported Alzheimer’s disease treatment using dental pulp stem cells.Rat models of Alzheimer’s disease were established by injecting amyloid-β1–42 into the hippocampus.Fourteen days later,5×106 dental pulp stem cells were injected into the hippocampus.Immunohistochemistry and western blot assays showed that dental pulp stem cell transplantation increased the expression of neuron-related doublecortin,NeuN,and neurofilament 200 in the hippocampus,while the expression of amyloid-βwas decreased.Moreover,cognitive and behavioral abilities were improved.These findings indicate that dental pulp stem cell transplantation in rats can improve cognitive function by regulating the secretion of neuron-related proteins,which indicates a potential therapeutic effect for Alzheimer’s disease.This study was approved by the Animal Ethics Committee of Harbin Medical University,China(approval No.KY2017-132)on February 21,2017.

Therapeutic effects of dental pulp stem cells on vascular dementia in rat models

Dental pulp stem cells are a type of adult stem cells with strong proliferative ability and multi-differentiation potential. There are no studies on treatment of vascular dementia with dental pulp stem cells. In the present study, rat models of vascular dementia were established by two-vessel occlusion, and 30 days later, rats were injected with 2 × 10^(7) dental pulp stem cells via the tail vein. At 70 days after vascular dementia induction, dental pulp stem cells had migrated to the brain tissue of rat vascular dementia models and differentiated into neuronlike cells. At the same time, doublecortin, neurofilament 200, and Neu N m RNA and protein expression levels in the brain tissue were increased, and glial fibrillary acidic protein m RNA and protein expression levels were decreased. Behavioral testing also revealed that dental pulp stem cell transplantation improved the cognitive function of rat vascular dementia models. These findings suggest that dental pulp stem cell transplantation is effective in treating vascular dementia possibly through a paracrine mechanism. The study was approved by the Animal Ethics Committee of Harbin Medical University(approval No. KY2017-132) in 2017.

Observations of contrasted glacial-interglacial dissolution of foraminifera above the lysocline in the Bay of Bengal,northeastern Indian Ocean

Site U1446(19°50’N,85°44’E,at water depth 1430 m)was drilled during Expedition 353(Indian monsoon rainfall)of the International Ocean Discovery Program(IODP).It is located in the Mahanadi offshore basin,on the northern Bay of Bengal.Sedimentation rates and contents of biocarbonates are high at this relatively shallow site.Using a micropaleontological approach,we examined planktonic and benthic foraminifera in the upper around 40 m of this site,spanning the last around 190 ka.A striking feature of the foraminiferal record is the occurrence of strong but varying dissolution although the site is located well above the modern lysocline.Such strong dissolution has never been reported in this area.We estimated the flux of foraminifera and quantified the ratio of benthic foraminifera over total foraminifera(benthic/total foraminifera)along with the foraminifer fragmentation index in order to characterize past changes in this above-lysocline dissolution.This study reveals a clear glacialinterglacial contrast,with a stronger dissolution during marine isotope stages(MISs)1 and 5 than during MISs 2–4 and 6.Such a difference in preservation is likely to have a strong impact on geochemical proxies measured on foraminifera.Our new observations call for an in-depth study of the causes of such above-lysocline dissolution in the region,and an evaluation of its impact on the foraminifera-based proxies used for paleoenvironmental reconstruction.

Hybrid architecture design enhances the areal capacity and cycling life of low-overpotential nanoarray oxygen electrode for lithium–oxygen batteries

Transition metal oxide(TMO)nanoarrays are promising architecture designs for self-supporting oxygen electrodes to achieve high catalytic activities in lithium-oxygen(Li-O2)batteries.However,the poor conductive nature of TMOs and the confined growth of nanostructures on the limited surfaces of electrode substrates result in the low areal capacities of TMO nanoarray electrodes,which seriously deteriorates the intrinsically high energy densities of Li-O2 batteries.Herein,we propose a hybrid nanoarray architecture design that integrates the high electronic conductivity of carbon nanoflakes(CNFs)and the high catalytic activity of Co3 O4 nanosheets on carbon cloth(CC).Due to the synergistic effect of two differently featured components,the hybrid nanoarrays(Co3 O4-CNF@CC)achieve a high reversible capacity of3.14 mA h cm-2 that cannot be achieved by only single components.Further,CNFs grown on CC induce the three-dimensionally distributed growth of ultrafine Co3 O4 nanosheets to enable the efficient utilization of catalysts.Thus,with the high catalytic efficiency,hybrid Co3 O4-CNF@CC also achieves a more prolonged cycling life than pristine TMO nanoarrays.The present work provides a new strategy for improving the performance of nanoarray oxygen electrodes via the hybrid architecture design that integrates the intrinsic properties of each component and induces the three-dimensional distribution of catalysts.

A CO_(2)/N_(2)-Responsive Pickering Emulsion Stabilized by Novel Switchable Surface-Active Alumina Nanoparticles

This article reports the development of a novel switchable Pickering emulsion with rapid CO_(2)/N_(2) respon-siveness,which is stabilized using alumina nanoparticles hydrophobized in situ with a trace amount of a switchable superamphiphile via electrostatic interactions.With the introduction of CO_(2) for 30 s,the Pickering emulsion can be spontaneously demulsified with complete phase separation;the emulsion can then be reconstructed in response to N_(2) purging for 10 min followed by homogenization.Moreover,the stable Pickering emulsion can be stored for more than 60 days at room temperature with-out any visible change.The CO_(2)/N_(2)-responsive behavior of the switchable Pickering emulsion is attribu-ted to the reversible desorption/adsorption of the switchable surfactants on the surfaces of the alumina nanoparticles upon the alternative bubbling of CO_(2)or N_(2).Thanks to the simple fabrication of the surfac-tant and the hydrophobization of the alumina nanoparticles,this research has developed an extremely facile and cost-efficient method for preparing a rapidly CO_(2)/N_(2)-responsive switchable Pickering emul-sion.The dosage of the switchable surfactants has been significantly reduced by nearly 1500 times(from 150 to 0.1 mmol·L^(-1))as compared with the dosage used in previous studies.Moreover,the as-prepared CO_(2)/N_(2)-responsive switchable Pickering emulsion is environmentally friendly,mild,and nontoxic;thus,it holds great potential for practical applications with considerable economic and environmental benefits,such as oil transport,fossil fuel production,environmental gases detection,and the encapsulation and release of active ingredients.

Advances in the Application of Intestinal Flora in Anti-Tumor Therapy

The intestinal flora is the normal microecosystem of the gastrointestinal tract. The intestinal flora has great complexity, and plays crucial roles in nutrient intake, host metabolism, endocrine signaling, homeostasis and immune regulation. Disorders of the intestinal flora can lead to an out-of-balance in immune system, and even results in an increased risk of diseases, including the occurrence and development of malignant tumors. Accumulating evidence shows that intestinal microorganisms may assist in systemic therapy by increasing the “heterogeneity” of the tumor, thereby promoting anti-tumor therapy. Targeting intestinal flora during the treatment of cancer has shown good efficacy. This review focuses on recent advances in research about intestinal flora, the relationship with tumor development, and the potential anti-tumor effects.

中国北方干旱半干旱区植被-气候响应关系特征

气候变化背景下干旱区植被的时空分布及变化特征,是区域植被恢复和国家自然保护区建设等亟需研究的关键生态环境问题。在建立中国北方干旱半干旱区潜在植被分类及对Holdridge生命地带模型进行修正和拓展的基础上,结合中国气象模拟数据(1981—2020年),引入植被面积转移矩阵、Kappa系数和平均中心模型等方法,对中国北方干旱半干旱区气候要素进行分析并实现了潜在植被定量识别和空间分布格局模拟。结果显示:40年间年降水量、年平均生物温度和可能蒸散率总体均呈上升趋势,研究区存在暖干化现象;研究区共出现6种潜在植被类型,在不同年代际均呈地带性分布;温带荒漠植被、温带草本植被和温带森林植被是主要植被类型,共占总覆盖面积约71%;温带森林植被的面积总体增长最快,平均每10年增加1.1%,温带荒漠植被减少最快,平均每10年减少1.3%;相邻年代际间,各类潜在植被的面积转换关系较为稳定,差别在于转换程度;山地森林植被、温带荒漠植被和温带森林植被的平均中心总体偏移距离大于50 km,除温带荒漠植被,其他植被的平均中心总体均往西移。

GNSS techniques for real-time monitoring of landslides:a review

Currently,Global Navigation Satellite System(GNSS)Real-Time Kinematic positioning(RTK)and Precise Point Positioning(PPP)techniques are widely employed for real-time monitoring of landslides.However,both RTK and PPP monitoring techniques have their limitations,such as limited service coverage or long convergence times.PPP-RTK technique which integrates RTK and PPP is a novel approach for monitoring landslides with the advantages of rapid convergence,high-precision,and a wide service area.This study summarizes the limitations of RTK,PPP,and PPP-RTK monitoring techniques and suggests some improved strategies.Their performances are compared and analyzed using real monitoring data.The experiment results demonstrate that RTK is the best option for small-scale(the baseline distance<15 km)and real-time landslide monitoring without considering the cost.PPP technique converges to centimeter-level accuracy in tens of minutes,only suitable for the stability analysis of reference stations.Over a large area(the baseline distance<100 km),PPP-RTK can provide excellent horizontal accuracy and adapt the service range in response to the demand for monitoring accuracy,as the vertical accuracy is signifcantly impacted by the service range and elevation diference.Finally,the characteristics of three techniques are integrated to form a comprehensive landslide monitoring technique that considers intelligence,robustness,and real-time.

Speculation of fluid dynamics equations based on Liutex theory and constitutive relation of symmetric shearing deformation

The fluid kinematics of Liutex decomposes a velocity gradient tensor(VGT)of∇v into four components,including rotation(R),stretching/compressing(SC),anti-symmetric shear(Santi-sym)and symmetric shear(Ssym),as oppose to the traditional Cauchy-Stokes decomposition where a VGT was decomposed into the strain rate and vorticity tensors.The current study limpidly clarified the physical meanings of these deformations in the newly-proposed decomposition from the perspectives of both fluid kinematics and dynamics.With in-depth understanding the physical connotations of these deformations,the present study further suggests that the Ssym be the only deformation appropriately correlated to the stress tensor,leading to the establishment of a new constitutive relation for Newtonian fluids with the modified model assumptions originated from Stokes in 1845.Moreover,the present research finds that the“principal decomposition”proposed by Liu is not mathematically unique when a VGT has three real eigenvalues(TR).Within the context,a new decomposition method is introduced to avoid the non-uniqueness issue arising from using the principal decomposition to establish fluid dynamics equations.Based on the modified Stokes assumptions and the novel VGT decomposition method,a set of new fluid dynamics momentum equations are obtained for Newtonian fluid.The added stress tensor of Fadd is identified as the key difference between the newly-derived governing equations and the conventional Navier-Stokes(N-S)equations,which is caused by excluding the SC correlation to the stress tensor in the new constitutive equation.Finally,a preliminary analysis of Fadd is conducted using the existing channel turbulence direct numerical simulations(DNS)data based on the traditional N-S equations.The Fadd is found widely existing in turbulence and is of the same order of magnitude with the other force terms.Therefore,the Fadd is expected to have some nonnegligible effects on altering the current DNS data based on the traditional N-S equations,which will be further verified by performing the“DNS”simulation using the newly-derived fluid dynamics equations in near future.

Stability analysis of reference station and compensation for monitoring stations in GNSS landslide monitoring

The Real-Time Kinematic(RTK)positioning method of the Global Navigation Satellite System(GNSS)has been widely used for landslide monitoring.The stability of its reference station is crucial to obtain accurate and reliable monitoring results.Unstable reference stations due to the geological environment and human activities are difficult to detect and in practical applications often ignored.As a result,it affects the positioning solutions and subsequently the interpretation and detection of landslide motions,which must be addressed in GNSS landslide monitoring.To solve this problem,we propose using the Precise Point Positioning(PPP)technique to analyze the stability of the reference station by verifying its position.The deformations of the monitoring stations are then compensated.First,the reference station coordinates are obtained by the PPP technique and tectonic motion is considered in data processing.The change or breakout of the reference station position is then determined using a cumulative sum control chart method.Finally,each monitoring station’s displacements are compensated according to the displacements of the reference station.According to the results of the Tengqing landslide experiment,the PPP technique can be used in GNSS landslide monitoring to analyze the stability of reference stations.With PPP,millimeter-level accuracy for the coordinates of reference stations is achieved.Compared to the traditional deformation series,the compensated displacement series more reliably reflects the landslide motions.This study will increase the reliability of monitoring results and contribute to implementing GNSS in monitoring landslides.

Synthesis of MOF-derived nitrogen-doped carbon microtubules via template self-consumption

Herein,by optimizing nano-ZnO template,N-doped hollow carbon microtubules with controllable thickness are synthesized deriving from ZnO@zeolitic lmidazolate framework(ZIF-8)nanorod by template self-consumption method,and a superior structure with graphene-like layers of an average length of 5μm and diameter of 200 nm are proposed to be used as the cathode carries for Li-S batteries.Through electrochemical testing,we found that the prepared hollow carbon microtubules have higher discharge capacity and better rate performance than the ZIF-8 derived carbon,showing potential application value.Our work provides a feasible way for the preparation of monodisperse graphene-like hollow materials.

Law-of-the-wall analytical formulations for Type-A turbulent boundary layers

In-depth analyses of existing direct numerical simulations(DNS)data led to a logical and important classification of generic turbulent boundary layers(TBLs),namely Type-A,-B and-C TBL,based on the distribution patterns of the time-averaged wall-shear stress.Among these types,Type-A TBL and its related law formulations were investigated in terms of the analytical velocity profiles independent on Reynolds number(Re).These formulations were benchmarked by the DNS data of turbulence on a zero-pressure-gradient flat-plate(ZPGFP).With reference to the analysis from von Karman in developing the traditional law-of-the-wall,the current study first physically distinguished the time-averaged local scale used by von Karman from the time-space-averaged scale defined in the current paper,and then derived the governing equations with the Re—independency under the time-space-averaged scales.Based on the indicator function(IDF)and TBL thickness,the sublayer partitions were quantitatively defined.The analytical formulations for entire ZPGFP TBL were derived,including the formula in the inner,buffer,semi-logarithmic(semi-log)and wake layers.The research profoundly understood the damping phenomenon and its controlling mechanism in the TBL with its associated mathematical expressions,namely the damping function under both linear and logarithmic coordinates.Based on these understandings and the quantified TBL partitions,the analytical formulations for the entire ZPGFP TBL were established and were further proved being uniform and consistent under both the time-averaged local and the time-space-averaged scales.Comparing to the traditional law,these formulations were validated by the existing DNS data with more accuracy and wider applicability.The findings advance the current understandings of the conventional TBL theory and its well-known foundation of law-of-the-wall.

Corrosion resistance of Ca-P coating induced by layer-by-layer assembled polyvinylpyrrolidone/DNA multilayer on magnesium AZ31 alloy

A hydrothermal deposition method was utilized to fabricate Ca-P composite coating induced by the layer-by-layer(LbL)assembled polyvinylpyrrolidone/deoxyribonucleic acid(PVP/DNA)_(20) multilayer on AZ31 alloy.The surface morphology and compositions were characterized by SEM,EDS,FTIR and XRD.Besides,the corrosion resistance and degradation behavior of the coating were tested via electrochemical polarization,impedance spectroscopy and immersion measurements.Results show that the main components of Ca-P coatings are hydroxyapatite,Ca_(3)(PO_(4))_(2) and Mg_(3)(PO_(4))_(2)·nH_(2)O.The LbL-assembled DNA and PVP promote the adsorption of Ca-P deposits on the sample surface,and structures and functional groups of the polyelectrolyte in the outermost layer are the primary influencing factor for the induction of the Ca-P coating.Carboxyl groups have the best biomineralization effect among all related functional groups.The enhanced corrosion resistance and adhesion highlight a promising use of(PVP/DNA)_(20)-induced Ca-P coatings in the field of biomedical magnesium alloys.

Effective syngas cleanup and reforming using Ni/γ-Al_(2)O_(3) catalyst

This work reports the performance of a selective Ni-based catalyst in tar removal and syngas reforming.Benzene was used as the model tar to optimize catalytic reaction conditions.Parameters investigated were reaction temperature(700℃ to 900℃),gas residence time(0.1 s to 1.1 s),and catalyst loadings(3%to 21%of the weight of γ-Al_(2)O_(3) support).On the basis of the benzene test,a reaction temperature of 800℃,catalyst loading of 15wt%,and residence time of 0.3 s were chosen as optimum reaction conditions.Testing of these conditions showed that the Ni/γ-Al_(2)O_(3) catalyst removed more than 99%of tars in syngas in the downdraft gasifier and 98%in the updraft gasifier.Concentrations of combustible compounds of syngas also increased significantly.H_(2) concentration increased from 19.96%to 51.78%in the downdraft gasifier and from 23.97%to 37.39%in the updraft gasifier;CO concentration increased from 16.26%to 21.10%in the downdraft gasifier and from 22.95%to 25.64%in the updraft gasifier.The results indicate that the Ni/γ-Al_(2)O_(3) catalyst and associated catalytic conditions could not only effectively eliminate tars but also improve the quality of syngas in biomass gasification.

Driving and tilt-hovering-An agile and manoeuvrable aerial vehicle with tiltable rotors

Driving and tilt-hovering help unmanned aerial vehicles extend their time of operation and the visible range of the equipped sensors.Standard quadrotors are underactuated,whose translational and rotational motions are strongly coupled.As a result,it is impossible to maintain the attitude invariably while changing position.Meanwhile,larger flying speed results in greater air resistance,which is also not desirable.A novel aerial platform with tiltable rotors is proposed.Compared with standard quadrotors,the aerial vehicle has three special capabilities:vector-flying,tilt-hovering,and driving.The platform consists of two tilting-axes to change the direction of thrusts with respect to the aircraft body.To guarantee flexible manoeuvres,a geometric tracking control scheme that adapts on the fly to the thrust vectoring is exploited.Manoeuvrability of the proposed vehicle in different manoeuvres is demonstrated,such as flight with vectoring thrust that can reduce the flight resistance,tilt-hovering expanding the reachable set of the equipped sensors.The prototype equipped with an electromechanical controller is constructed,and several associated preliminary experiments are performed.The feasibility of the mechanical design and the geometric control strategy are demonstrated.

Corrosion Resistance and Semiconducting Properties of Passive Films Formed on 00Cr13Ni5Mo2 Supermartensitic Stainless Steel in Cl^- Environment

The semiconducting properties of passive films grown on 00Crl3Ni5Mo2 supermartensitic stainless steel were investigated in comparison with conventional 2Cr13 martensitic stainless steel. Cyclic vohammetry and electro- chemical impedance spectroscopy （EIS） were used for the studies. 00Crl3NiSMo2 steel exhibited a good corrosion resistance performance, attributing to its passive capability. The results of Mott-Schottky analysis demonstrated n- type semiconductors for the passive films with doping densities of about 1020- 1021 cm -3, and the thickness of space- charge layers was also calculated. The experimental results confirmed that Mo plays an important role in improving the corrosion resistance of 00Crl3Ni5Mo2 steel due to its impact on the doping density.

Flow-pattern-altered syntheses of core–shell and hole–shell microparticles in an axisymmetric microfluidic device

Droplet-based microfluidics offers unique advantages to create platforms that fabricate functionalized particles with increased accessibility,robustness,and simplicity.Herein we present a three-phase microfluidic device that can control the flow pattern to directly generate either core–shell or hole–shell microparticles.The major benefits of this device are the ease of controlling the morphology of the compound droplets by the flow rates and thus the microstructure of the synthesized microparticles.The transition between flow patterns enables the generation of either core–shell particles or Janus particles in a single device.We further show the versatility of the proposed device in fabrication of functionalized particles:the hole size of the hole–shell microparticle can be fine-tuned while its outer diameter is kept constant,and by adding Fe_(3)O_(4) nanoparticles into the photocurable phase,the obtained magnetoresponsive microparticle can move rotationally or translationally under an external magnetic field.We anticipate that the present method could facilitate the fabrication of the functional microparticles for diverse applications.

A multifunctional nanotheranostic agent potentiates erlotinib to EGFR wild-type non-small cell lung cancer

Epidermal growth factor receptor(EGFR)tyrosine kinase inhibitors(TKI),such as Erlotinib,have demonstrated remarkable efficacy in the treatment of non-small cell lung cancer(NSCLC)patients with mutated EGFR.However,the efficacy of EGFR-TKIs in wild-type(wt)EGFR tumours has been shown to be marginal.Methods that can sensitize Erlotinib to EGFR wild-type NSCLC remain rare.Herein,we developed a multifunctional superparamagnetic nanotheranostic agent as a novel strategy to potentiate Erlotinib to EGFR-wt NSCLCs.Our results demonstrate that the nanoparticles can co-escort Erlotinib and a vascular epithermal growth factor(VEGF)inhibitor,Bevacizumab(Bev),to EGFR-wt tumours.The nanotheranostic agent exhibits remarkable effects as an inhibitor of EGFR-wt tumour growth.Moreover,Bev normalizes the tumour embedded vessels,further promoting the therapeutic efficacy of Erlotinib.In addition,the tumour engagement of the nanoparticles and the vascular normalization could be tracked by magnetic resonance imaging(MRI).Collectively,our study,for the first time,demonstrated that elaborated nanoparticles could be employed as a robust tool to potentiate Erlotinib to EGFR-wt NSCLC,paving the way for imaging-guided nanotheranostics for refractory NSCLCs expressing EGFR wild-type genes.

Surface carboxyl groups enhance the capacities of carbonaceous oxygen electrodes for aprotic lithiumoxygen batteries: A direct observation on binder-free electrodes

In order to achieve the high capacities of carbonaceous oxygen diffusion electrodes for aprotic lithiumoxygen batteries(Li-O2 batteries),most efforts currently focus on the design of rational porous architectures.Only few works study the surface chemistry effect that might be a critical factor influencing the capacities of carbonaceous electrodes.In addition,the surface chemistry effect is very difficult to be studied in composite electrodes due to the influences of binders and additives.Herein,we propose chemically activated carbon cloth(CACC) as an ideal model to investigate the effect of surface functional groups on the discharge capacities of carbonaceous oxygen electrodes for Li-O2 batteries.The intrinsic surface chemistry effect on the performance of carbonaceous cathode is directly observed for the first time without the influences of binders and additives.Results indicate that the surface carboxyl groups introduced by the chemical treatment not only function as the appropriate nucleation sites for Li2 O2 but also induce the formation of toroid-like Li2 O2.Thus,the surface carboxyl modification enhances the discharge capacities from 0.48 mAh/cm^2 of pristine carbon cloth to 1.23 mAh/cm^2 of CACC.This work presents an effective way to further optimize the carbonaceous oxygen electrodes via surface functional group engineering.