No basalt accumulation and segregation atop the 660-km discontinuity beneath the Sea of Okhotsk

Recent seismic evidence shows that basalt accumulation is widespread in the mantle transition zone(MTZ),yet its ubiquity or sporadic nature remains uncertain.To investigate this phenomenon further,we characterized the velocity structure across the 660-km discontinuity that separates the upper mantle from the lower mantle beneath the Sea of Okhotsk by modeling the waveform of the S660P phase,a downgoing S wave converting into a P wave at the 660-km interface.These waves were excited by two regional>410-km-deep events and were recorded by stations in central Asia.Our findings showed no need to introduce velocity anomalies at the base of the MTZ to explain the S660P waveforms because the IASP91 model adequately reproduced the waveforms.This finding indicates that the basalt accumulation has not affected the bottom of the MTZ in the study area.Instead,this discontinuity is primarily controlled by temperature or water content variations,or both.Thus,we argue that the basalt accumulation at the base of the MTZ is sporadic,not ubiquitous,reflecting its heterogeneous distribution.

Sharpness of the paired 660-km discontinuity beneath the Izu-Bonin area

The 660-km discontinuity that separates the Earth's upper and lower mantle has primarily been attributed to phase changes in olivine and other minerals.Resolving the sharpness is essential for predicting the composition of the mantle and for understanding its dynamic effects.In this study,we used S-to-P conversions from the 660-km interface,termed S660P,arriving in the P-wave coda from one earthquake in the Izu–Bonin subduction zone recorded by stations in Alaska.The S660P signals were of high quality,providing us an unprecedented opportunity to resolve the sharpness of the discontinuity.Our study demonstrated,based on the impedance contrast given by the IASP91 model,that the discontinuity has a transitional thickness of^5 km.In addition,we observed a prominent arrival right after the S660P,which was best explained by S-to-P conversions from a deeper discontinuity at a depth of^720 km with a transitional thickness of^20 km,termed S720P.The 720-km discontinuity is most likely the result of a phase transition from majoritic garnet to perovskite in the segregated oceanic crust(mainly the mid-oceanic ridge basalt composition)at the uppermost lower mantle beneath this area.The inferred phase changes are also consistent with predictions from mineral physics experiments.

Seismic evidence for the existence of an entrained mantle flow coupling the northward advancing Indian plate under Tibet

The Tibetan Plateau, known as "the roof of the world" and "the third pole of the earth", is a product of the collision between India and Asia during the last ～50 Ma.The regional tectonics–in particular, growth and expansion of the plateau–has been attributed primarily to deformation within the lithosphere.The role and pattern of the underlying asthenospheric flow, however, remain mostly unaddressed.In light of recent seismic tomographic images and published seismic anisotropic descriptions of the upper mantle, here we propose that an entrained mantle flow is likely to exist under Tibet, induced by the northward advancing Indian plate.The direction of mantle flow is characterized by a gradual rotation from northward in the south to eastward in the north as a result of deflection by the deep root of the Tarim block.The presence of an underlying mantle flow is not only able to account for the west-east oriented fast-axis of seismic anisotropy in northern Tibet, but can also adequately explain the sporadic null splitting in southern Tibet.Specifically, the null splitting results, at least in part, from upwellings of asthenospheric flow through tears of the underthrusting Indian plate that have been revealed by various seismic observations.The mantle flow may in turn promote the block extrusion under Tibet that has been observed in GPS measurements; hot asthenospheric upwellings may also lead to widespread post-collisional magmatism in southern Tibet.

Subducting passive continental margins with crustal (ultra)mafic intrusions: An underappreciated mechanism for recycling water back into the mantle

It is well known that outer rise bending-assisted oceanic plate hydration is an important mechanism for transporting substantial amounts of water into the mantle.A key question is:Are there other equally or more important water transport mechanisms?Here we propose,for the first time,that subducting passive continental margins,particularly those with crustal(ultra)mafic intrusions,play a critical role in recycling water back into the mantle.Evidence for this mechanism is the exceptionally high outer rise seismicity observed in a subducting passive continental margin(i.e.,the northeastern South China Sea continental margin)near the northern Manila trench,characterized by a high-velocity lower crust that has been attributed to(ultra)mafic intrusions.Our interpretation of this correlation between high outer rise seismicity and lower crust(ultra)mafic intrusions is that(ultra)mafic intrusions alter the crustal rheology and increase brittle deformation in the lower crust in this region,thereby promoting lithospheric fracturing and plate hydration,which is evidenced by increased outer rise seismicity.

Dissolved organic carbon fractionation in wet deposition and its potential impact on radiative forcing in the central Tibetan Plateau

As an important component of carbonaceous matters,dissolved organic carbon(DOC)can absorb and scatter the solar radiation at ultraviolet and blue wavelengths.The wet deposition process has great impact on the con-centration and light absorption ability of precipitation DOC,affecting the climatic effect caused by DOC in the atmosphere.In this study,light absorption and fluorescence characteristics of precipitation DOC was investigated in the central Tibetan Plateau(TP).The results showed that the mean DOC concentration and mass absorption cross-section measured at 365 nm(MAC_(365)) in Tanggula(TGL)station were 0.59±0.42 mg/L and 0.37±0.19 m^(2)/g,respectively,while both values showed much higher volatilities than those of aerosols.DOC concentrations had significant negative correlation with the precipitation amount,while MAC_(365) values increase with the precipitation amount in TGL station.Therefore,DOC with high light-absorbing ability was preferred to be retained in the atmosphere during wet deposition.In this study,precipitation DOC contained three fluorescent components(one humic-like component and two tyrosine-like components)mainly from local biomass burning sources.DOC concentration showed a negative relationship with MAC_(365) value in TGL station.The wet deposition of DOC with low light-absorbing ability can reduce the strong negative radiative forcing caused by secondary organic aerosol due to high proportion of DOC in secondary organic carbon.Similar phenomenon was also found in Nam Co,Lulang and Everest stations of previous study,which may have a potential impact on radiative forcing in the atmosphere of TP.

High Asia cryospheric observation:a proposed network under Global Cryosphere Watch(GCW)

In coordination with Global Cryosphere Watch （GCW） initiated by World Meteorology Administration （WMO）, a regional ob- servation network is proposed based on existing stations/sites over High Asia and cryospberic elements required by GCW. Thus, High Asian Cryosphere （HAC） network is preliminary designed, composing of seven ＂supersites＂, each containing several refer- ence sites. The network covers major mountain ranges in High Asia, such as East Tianshan, Qilian, Tanggula, Nyainqentanglha, Himalayas as well as the central and eastern Qinghai-Xizang （Tibet） Plateau. Although multiple cryospberic elements were ob- served at the existing HAC network, many others, which are required by Integrated Global Observation System-Cryosphere Theme （IGOS-Cryosphere）, are not yet included. More comprehensive observations are necessary to be included into ＂supersites＂ of HAC, so that the basic requirements for validation of satellite data, assimilation and coupled regional models can be met.

Metal-organic frameworks for highly efficient oxygen electrocatalysis

Metal‐organic frameworks(MOFs)are a series of highly porous crystalline materials,which are built from inorganic metal nodes and organic linkers through coordination bonds.Their unique porous structural features(such as high porosity,high surface areas,and highly ordered nanoporous structures)and designable structures and compositions have facilitated their use in gas capture,separation,catalysis,and energy storage and conversion.Recently,the design and synthesis of pure MOFs and their derivatives have opened new routes to develop highly efficient electrocatalysts toward oxygen reduction reactions(ORR)and oxygen evolution reactions(OER),which are the core electrode reactions in many energy storage and conversion techniques,such as metal‐air batteries and fuel cells.This review first discusses recent progress in the synthesis and the electrocatalytic applications of pure MOF‐based electrocatalysts toward ORR or OER,including pure MOFs,MOFs decorated with active species,and MOFs incorporated with conductive materials.The following section focuses on the advancements of the design and preparation of various MOF‐derived materials-such as inorganic nano‐(or micro‐)structures/porous carbon composites,pure porous carbons,pure inorganic nano‐(or micro‐)structured materials,and single‐atom electrocatalysts-and their applications in oxygen electrocatalysis.Finally,we present a conclusion and an outlook for some general design strategies and future research directions of MOF‐based oxygen electrocatalysts.

缺氧激活前药evofosfamide(TH-302)在体内和体外对鼻咽癌的疗效

背景与目的肿瘤缺氧被认为是肿瘤转移和疾病复发的重要因素。Evofosfamide是一种缺氧激活前药,可选择性地靶向实体瘤的缺氧区域。由于缺氧诱导因子?1α(hypoxia?inducible factor?1α,HIF?1α)在鼻咽癌(nasopharyngeal carcinoma,NPC)组织中高表达,本研究探讨了evofosfamide在鼻咽癌中的疗效。方法我们评估了evofosfamide作为单药或联合顺铂(DDP)在NPC细胞系CNE?2、HONE?1和HNE?1以及裸鼠异种移植瘤模型中的疗效。结果 Evofosfamide在NPC细胞系中表现出缺氧选择性细胞毒性。在缺氧条件下,对CNE?2、HNE?1和HNE?1细胞的50%抑制浓度(50%inhibition concentration,IC50)分别为8.33±0.75、7.62±0.67和0.31±0.07μmol/L。与常氧对照组相比,在缺氧条件下其增敏率为9–300倍。通过联合指数值评估,evofosfamide联合DDP对NPC细胞的细胞毒性具有协同效应。在缺氧条件下用0.05μmol/L的evofosfamide处理后,细胞周期G2期被阻滞。在缺氧条件下用evofosfamide处理后,组蛋白H2AX磷酸化(Histone H2AXphosphorylation,γH2AX)(DNA损伤的标志之一)表达增强,而HIF?1α表达受到抑制。在HNE?1 NPC异种移植瘤模型中,evofosfamide作为单药或联合DDP显示出抗肿瘤活性。异种移植物组织缺氧区在evofosfamide单药治疗和联合DDP治疗后均明显减少。结论我们的结果为evofosfamide作为单药或联合DDP可选择性靶向鼻咽癌缺氧部分提供了临床前证据,为evofosfamide治疗鼻咽癌的潜在临床应用提供了理论依据。

High halogenated nitrobenzene hydrogenation selectivity over nano Ir particles

The selective hydrogenation of halogenated nitrobenzene over noble metal catalysts(Pd, Pt, and Ir) has attracted much attention owing to its high efficiency and environmental friendliness. However, the effect of size on the catalytic performance varies among different metal catalysts. In this study, sub-nano(<3 nm) Ir and Pd particles were prepared, and their catalytic properties for hydrogenation of halogenated nitrobenzene were evaluated.Results show that high selectivity(N 99%) was achieved over small Ir nanoparticles, in which the selectivity over the Pd with same size was much lower than that on Ir nanoparticles. Meanwhile, Ir and Pd have different hydrogen consumption rates and reaction rates. Density functional theory calculations showed that p-chloronitrobenzene(CNB) has different adsorption properties on Ir and Pd. The distance between oxygen(cholorine) and Ir is much shorter(longer) than that between oxygen and Pd. The reaction barriers of dechlorination of p-CNB and p-chloroaniline over different Ir models are much larger than those on Pd. Especially,lower coordination of Ir leads to larger barriers of dechlorination reaction. These theoretical results explain the difference between Ir and Pd on hydrogenation of halogenated nitrobenzene.

Uniaxial stress effect on quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8)

Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue.We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8) by electric transport and AC heat capacity measurements.CeCo_(2)Ga_(8) is speculated to sit in close vicinity but on the quantum-disordered side of a quantum critical point.Upon compressing the c axis,parallel to the Ce-Ce chain,the onset of coherent Kondo effect is enhanced.In contrast,the electronic specific heat diverges more rapidly at low temperature when the intra-chain distance is elongated by compressions along a or b axis.These results suggest that a tensile intra-chain strain(ε_(c)>0)pushes CeCo_(2)Ga_(8) closer to the quantum critical point,while a compressive intra-chain strain(ε_(c)<0)likely causes departure.Our work provides a rare paradigm of manipulation near a quantum critical point in a quasi-1D Kondo lattice by uniaxial stress,and paves the way for further investigations on the unique feature of quantum criticality in the quasi-1D limit.

No seamount subduction,no magmatic arc?

Water is essential for the formation of a magmatic arc by lowering the melting temperature of materials in the mantle wedge.As such,it is logical to attribute the absence of a magmatic arc to insufficient water released from the subducting plate,although a number of other factors may cause volcanic arc quiescence as well,such as a slab window or flat slab subduction.In this contribution,we present a possible but testable correlation between the occurrence of a magmatic arc and seamount subduction in light of bathymetric data obtained near trenches.This correlation,if it holds true,in turn means that a magmatic arc is unlikely to occur when the subducting slabs have not been severely fractured and that one of the main reasons for excluding effects such as the slab window or flat slab subduction may be that the plate is not accompanied by seamounts.Therefore,the role that seamount subduction plays in recycling water back into the mantle deserves more attention from the earth sciences community.

Carbonaceous matter in glacier at the headwaters of the Yangtze River:Concentration,sources and fractionation during the melting process

Carbonaceous matter has an important impact on glacial retreat in the Tibetan Plateau,further affecting the water resource supply.However,the related studies on carbonaceous matter are still scarce in Geladaindong(GLDD)region,the source of the Yangtze River.Therefore,the concentration,source and variations of carbonaceous matter at Ganglongjiama(GLJM)glacier in GLDD region were investigated during the melting period in 2017,which could deepen our understanding on carbonaceous matter contribution to glacier melting.The results showed that dissolved organic carbon(DOC)concentration of snowpit samples(283±200μg/L)was much lower than that of precipitation samples(624±361μg/L),indicating that large parts of DOC could be rapidly leached from the snowpit during the melting process.In contrast,refractory black carbon(rBC)concentration measured by Single Particle Soot Photometer of snowpit samples(4.27±3.15μg/L)was much higher than that of precipitation samples(0.97±0.49μg/L).Similarly,DOC with high mass absorption cross-section measured at 365 nm value was also likely to enrich in snowpit during the melting process.In addition,it was found that both r BC and DOC with high light-absorbing ability began to leach from the snowpit when melting process became stronger.Therefore,rBC and DOC with high light-absorbing ability exhibited similar behavior during the melting process.Based on relationship among DOC,rBC and K^+ in precipitation,the main source of carbonaceous matter in GLJM glacier was biomass burning during the study period.

Unintended Consequences of Lockdowns:Evidence from Domestic Helpers in Urban China

This paper addresses the reactions of domestic helpers to the Wuhan(Hubei Province)lockdown that began on January 23,2020.We use a novel dataset containing the information of over 40,000 Chinese domestic helpers registered on a leading professional website from November 2019 to June 2020.The results indicate a declining pattern of short-term labor supply of domestic helpers across 11 major Chinese cities,which shows an increase in the expected monthly wage of domestic helpers in these cities.More importantly,using a difference-in-difference(DID)model,this paper provides some evidence on the existence of labor market discrimination against domestic helpers bom in Hubei Province due to employers’fear of infection.

Small-Scale Heterogeneity and Seismic Anisotropy in the Mid-Mantle:Oceanic Crust versus Meta-Stable Olivine

The mid-mantle(i.e.,the top lower mantle) roughly represents the mantle portion ranging from ~700 to 1 600 km depths.It has received increasing attention mainly due to two facts including(i) subducted slabs largely trapped there(Fukao and Obayashi,2013) and(ii) plume necking and lateral ponding at ~1 000 km depth(French and Romanowicz,2015).

Efficacy of the hypoxia-activated prodrug evofosfamide (TH-302) in nasopharyngeal carcinoma in vitro and in vivo

Background:Tumor hypoxia is considered an important factor in metastasis and disease relapse.Evofosfamide is a hypoxia-activated prodrug that selectively targets the hypoxic regions of solid tumors.As hypoxia-inducible factor-1α(HIF-1α)is overexpressed in nasopharyngeal carcinoma(NPC)tissues,we performed the present study to evaluate the efficacy profile of evofosfamide in NPC.Methods:We evaluated the efficacy of evofosfamide as a single agent or combined with cisplatin(DDP)in the NPC cell lines CNE-2,HONE-1 and HNE-1,and in nude mouse xenograft tumor models.Results:Evofosfamide exhibited hypoxia-selective cytotoxicity in NPC cell lines,with 50%inhibition concentration(IC50)values of 8.33±0.75,7.62±0.67,and 0.31±0.07μmol/L under hypoxia in CNE-2,HONE-1 and HNE-1 cells,respectively.The sensitization ranged from ninefold to greater than 300-fold under hypoxia compared with normoxia controls.The combination of evofosfamide with DDP had a synergistic effect on cytotoxicity in the NPC cell lines by combination index values assessment.Cell cycle G2 phase was arrested after treated with 0.05μmol/L evofosfamide under hypoxia.Histone H2AX phosphorylation(γH2AX)(a marker of DNA damage)expression increased while HIF-1αexpression suppressed after evofosfamide treatment under hypoxic conditions.In the HNE-1 NPC xenograft models,evofosfamide exhibited antitumor activity both as a single agent and combined with DDP.Hypoxic regions in xeno-graft tissue were reduced after both evofosfamide monotherapy and combined therapy with DDP.Conclusions:Our results present preclinical evidence for targeting the selective hypoxic portion of NPC by evofosfa-mide as a single agent and combined with DDP and provide rationale for the potential clinical application of evofosfa-mide for the treatment of nasopharyngeal carcinoma.

Steering of second-harmonic emission by the mode-selective excitation in a hybrid waveguide

Realization of the efficient steering for photons streams from nano sources is essential for further progress in integrated photonic circuits,especially when involving nonlinear sources.In general,steering for nonlinear sources needs additional optical control elements,limiting their application occasions as photonic devices.Here,we propose a simple and efficient beam steering scheme for the second-harmonic(SH)emission in the hybrid waveguide(consisting of CdSe nanobelts on the Au film)by mode-selective excitation.Adjusting the position of the incident beam illuminating on the tapered waveguide,the excitation types of guided modes can be selected,realizing the directionality control of SH emission.Stable steering of 6.1°for the SH emission is observed when the interference modes change from TE_(00)&TE_(01)to TE_(00)&TE_(02),which is confirmed by SH Fourier imaging and simulations.Our approach gets rid of the complex structural design and provides a new idea for beam steering of nonlinear optical devices with various nonlinear wavefronts.

Pressure-tuning domain-wall chirality in noncentrosymmetric magnetic Weyl semimetal CeAlGe

Topological magnetic Weyl semimetals have been proposed to host controllable chiral domain walls which bear a great prospect in device applications. To exploit them in applications, it is important to have a proper way to tune and manipulate these domain walls. One possible means is through magnetoelastic coupling. The involvement of rare earth in the lately proposed RAl X(R =rare earth, X = Si and Ge) family magnetic Weyl semimetals may provide such a platform. Here we present the transport and thermodynamic properties of Ce Al Ge under hydrostatic pressure. We find that pressure enhances the antiferromagnetic exchange in Ce Al Ge but essentially retains its magnetic structure. A large topological Hall effect with a pronounced loop shape is observed within the magnetically ordered state, and it splits into two regions under pressure. Such an unusual electromagnetic response is inferred to be a consequence of chiral magnetic domain walls. The unprecedented concomitance of its evolution under pressure and the reentrance of antiferromagnetic order strongly suggest the capability of switching on/off this electromagnetic response in noncentrosymmetric magnetic Weyl semimetals via magnetoelastic coupling.