Bidirectional Growth Research Articles

The Potential of Aloe Vera in Solution and in Blended Nanofibers Containing Poly (3-Hydroxybutyrate-Co-3-Hydroxyvalerate) as Substrates for Neurite Outgrowth.

This pilot study investigated the potential of aloe vera (AV) to promote neurite outgrowth in organotypic dorsal root ganglia (DRG) explants (n = 230) from neonatal rats (n = 15). Using this invitro model of acute axotomy, we assessed neurite outgrowth exceeding 1.5 times the explant diameter (viable explants) and measured the longest neurite length. These parameters were evaluated under control conditions and in cultures supplemented with commercial AV and four aligned scaffolds: poly-L-lactate (PLLA), polydioxanone (PDS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and blended PHBV/AV. After 6 days of culture, explants were immunostained using neuron-specific marker Tuj1 and Schwann cell marker S100. Measurements were obtained with Image J software and analyzed using Jamovi 2.3. In control and AV dilution media, the study revealed radial tissue growth from the explant body with randomly oriented neurites, whereas in all scaffolds, bidirectional tissue growth occurred parallel to nanofibers. Binomial logistic regression analyses indicated that viable explants were more likely in the control group compared to PDS (p = 0.0042) and PHBV (p < 0.0001), with non-significant differences when compared to AV dilution, PLLA, and PHBV/AV. AV dilution showed a greater association with viable explants than PLLA (p = 0.0459), while non-significant difference was found between AV dilution and PHBV/AV. Additionally, the PHBV/AV scaffold predicted higher odds of viable explants than PLLA (p = 0.0479), PDS (p = 0.0001), and PHBV (p < 0.0001). Groups with similar probabilities of obtaining viable explants (control, AV dilution, and PHBV/AV) exhibited non-significant differences in their longest neurite lengths. In conclusion, control, AV dilution, and PHBV/AV yielded the highest probability of developing viable explants and the longest neurite lengths. This is the first study demonstrating the direct permissiveness of AV for axonal outgrowth. Furthermore, the blended PHBV/AV scaffold showed significant potential as a suitable scaffold for axonal regrowth and Schwann cell migration, ensuring controlled tissue formation for tissue engineering applications.

Surface Orthogonal Patterning and Bidirectional Self-Assembly of Nanoparticles Tethered by V-Shaped Diblock Copolymers.

We investigated the surface orthogonal patterning and bidirectional self-assembly of binary hairy nanoparticles (NPs) constructed by uniformly tethering a single NP with multiple V-shaped AB diblock copolymers using Brownian dynamics simulations in a poor solvent. At low concentration, the chain collapse and microphase separation of binary polymer brushes can lead to the patterning of the NP surface into A- and B-type orthogonal patches with various numbers of domains (valency), n = 1-6, that adopt spherical, linear, triangular, tetrahedral, square pyramidal, and pentagonal pyramidal configurations. There is a linear relationship between the valency and the average ratio of NP diameter to the polymers' unperturbed root-mean-square end-to-end distance for the corresponding valency. The linear slope depends on the grafting density and is independent of the interaction parameters between polymers. At high concentration, the orthogonal patch NPs serve as building blocks and exhibit directional attractions by overlapping the same type of domains, resulting in self-assembly into a series of fascinating architectures depending on the valency and polymer length. Notably, the 2-valent orthogonal patch NPs have the bidirectional bonding ability to form the two-dimensional (2D) square NP arrays by two distinct pathways. Simultaneously patching A and B blocks enables the one-step formation of 2D square arrays via bidirectional growth, whereas step-by-step patching causes the directional formation of 1D chains followed by 2D square arrays. Moreover, the gap between NPs in the 2D square arrays is related to the polymer length but independent of the NP diameter. These 2D square NP arrays are of significant value in practical applications such as integrated circuit manufacturing and nanotechnology.

Cytological and ultrastructural investigation of pathogen infection pathway and host responses in asparagus stem infected by Phomopsis asparagi

Asparagus stem blight, a highly destructive disease in global asparagus cultivation, is caused by the fungus Phomopsis asparagi. However, the underlying mechanisms of the infectious process and pathogenesis of P. asparagi remain poorly understood. This study aims to elucidate the infection event of P. asparagi at the cytological and ultrastructural levels in asparagus stem through a microscopic observation. The host responses were also examined by microscopic observation and fluorescent probe. It revealed that P. asparagi germinated at either the tip or the middle of the conidia to produce short germ tubes on the surfaces of the asparagus stem at 20 h post-inoculation (hpi). The germ tubes penetrated the host cell wall with appressorium-like structures or narrow pegs at 1 day post-inoculation (dpi). At 3 − 5 dpi, a large number of P. asparagi hyphae colonized the epidermal cells. The hyphae were found to grow both intracellularly and intercellularly. The movement of hyphae between cells was facilitated by constricted invasive hyphae pegs. The hyphae exhibited bidirectional intracellular growth, extending and branching along the inner side of the cell wall within the stem cortex and towards the central cylinder. The fungal colonization resulted in cellular damage in plants, which is characterized by plasmolysis, rupture of the cell wall, and disruption of the cytoplasm. At 11 dpi, the fungi penetrated the parenchyma cells, and the fungal pycnidia were formed. At 13 dpi, the fungi penetrated the stem center parenchyma cell, where the conidia were released. In addition, the host defense response was investigated, which revealed a notably reduced germination rate of conidium, the formation of callose analogs, and the reactive oxygen burst. These findings provide unexpected perspectives on the infection process and host response in P. asparagi-plant interaction.

3D vertical ultra-sodiophilic leaf-vein-like MXene/Sn@CNF array of structured sodium enabling high-rate and long-life sodium metal batteries

Uncontrolled Na dendrite growth and infinite volume change during cycling have greatly impeded the practical application of Na metal anode for high-energy-density batteries. To address these two issues simultaneously, a 3D vertical ultra-sodiophilic leaf-vein-like MXene/Sn@CNF array (VL-MXene/Sn@CNF) aerogel, integrated by 1D Sn@CNF and 2D MXene, was prepared by an ingenious hydrogen bonding self-assembly and unidirectional ice template method. The low-tortuosity and ultra-sodiophilic vertical array facilitates uniform and rapid Na+ transport along the ordered interspaces, achieving a negligible nucleation overpotential of 1.0 mV. Furthermore, experimental results and theoretical calculations revealed a unique bidirectional growth mode of Na, in which vertical leaf-vein-like lamellae and bridging fibers guided Na to be densely deposited along the vertical and horizontal directions, respectively. Benefitting from the ultra-sodiophilic vertical array of structured Na, the designed material exhibits an endurance of 1000 cycles for asymmetric cell at 3.0 mA cm−2 and 3.0 mAh cm−2, and the symmetrical cell delivers an ultra-long lifespan of 6000 h at 1.0 mA cm−2 and 3.0 mAh cm−2 with a high depth of discharge up to 50 %. Remarkably, at the high current of 15 C, the full cell based on NaTi2(PO4)3 cathode and Na@VL-MXene/Sn@CNF anode can deliver a reversible capacity of 88.94 mAh g−1 after 9200 cycles with an ultralow 0.0016 % capacity decay per cycle, which represents the most impressive full cell performance so far.

Overcoming Division and Bias in Mentorship: Maximizing Bidirectional Growth in Medical Training.

Overcoming Division and Bias in Mentorship: Maximizing Bidirectional Growth in Medical Training.

Experimental study on gas separation from the oil–water-emulsion mixture via hydrate method

The gas separation technology based on hydrate method offers several advantages, including a short process flow, simple equipment, no pollution, less corrosion, and lower energy consumption. It has a broad application prospect in the acid gas purification, biogas purification and CO2 sequestration., etc. However, demanding hydrate formation conditions and lower gas separation effects constrain its application. Oil-water emulsion shows promise in improving mass and heat transfer efficiency, enhancing hydrate slurry fluidity, and reducing hydrate aggregates. Thus, this study investigates the effects of different oil–water ratios, promoter concentrations, and surfactants on hydrate formation and separation efficiency in an oil–water emulsion system. At an oil–water ratio of 1:1, the purification rate increased to 6.06, five times higher than in a pure water system. The addition of 1,3-Dioxolane (DIOX) facilitated bidirectional growth properties of hydrate formation on droplet surfaces, enhancing hydrate nucleation and formation, leading to a CO2 recovery increase to 87% with 1.5 wt% DIOX. Furthermore, lipophilic surfactants were more likely to promote hydrate slurry fluidization. The addition of Span80 reduced hydrate agglomeration and increased the rate of hydrate formation as concentration rose. The results suggest that adding DIOX and increasing the concentration of Span80 could improve the hydrate method’s separation efficiency at an oil–water ratio of 1:1.

Colloidal Multi-Dot Nanorods.

Colloidal nanorod heterostructures consisting of multiple quantum dots within a nanorod (n-DNRs, where n is the number of quantum dots within a nanorod) are synthesized with alternating segments of CdSe "dot" and CdS "rod" via solution heteroepitaxy. The reaction temperature, time dependent ripening, and asymmetry of the wurtzite lattice and the resulting anisotropy of surface ligand steric hindrance are exploited to vary the morphology of the growing quantum dot segments. The alternating CdSe and CdS growth steps can be easily repeated to increment the dot number in unidirectional or bidirectional growth regimes. As an initial exploration of electron occupation effects on their optical properties, asymmetric 2-DNRs consisting of two dots of different lengths and diameters are synthesized and are shown to exhibit a change in color and an unusual photoluminescence quantum yield increase upon photochemical doping.

Bidirectional zigzag growth from clusters of active colloidal shakers

Driven or self-propelling particles moving in viscoelastic fluids recently emerged as a novel class of active systems showing a complex yet rich set of phenomena due to the non-Newtonian nature of the dispersing medium. Here we investigate the one-dimensional growth of clusters made of active colloidal shakers, which are realized by oscillating magnetic rotors dispersed within a viscoelastic fluid and at different concentrations of the dissolved polymer. These magnetic particles when actuated by an oscillating field display a flow profile similar to that of a shaker force dipole, i.e., without any net propulsion. We design a protocol to assemble clusters of colloidal shakers and induce their controlled expansion into elongated zigzag structures. We observe a power law growth of the mean chain length and use theoretical arguments to explain the measured 1/3 exponent. These arguments agree well with both experiments and particle based numerical simulations. Published by the American Physical Society 2024

Telechelic sequence-defined oligoamides: their step-economical synthesis, depolymerization and use in polymer networks.

The application of sequence-defined macromolecules in material science remains largely unexplored due to their challenging, low yielding and time-consuming synthesis. This work first describes a step-economical method for synthesizing unnatural sequence-defined oligoamides through fluorenylmethyloxycarbonyl chemistry. The use of a monodisperse soluble support enables homogeneous reactions at elevated temperature (up to 65 °C), leading to rapid coupling times (<10 min) and improved synthesis protocols. Moreover, a one-pot procedure for the two involved iterative steps is demonstrated via an intermediate quenching step, eliminating the need for in-between purification. The protocol is optimized using γ-aminobutyric acid (GABA) as initial amino acid, and the unique ability of the resulting oligomers to depolymerize, with the formation of cyclic γ-butyrolactame, is evidenced. Furthermore, in order to demonstrate the versatility of the present protocol, a library of 17 unnatural amino acid monomers is synthesized, starting from the readily available GABA-derivative 4-amino-2-hydroxybutanoic acid, and then used to create multifunctional tetramers. Notably, the obtained tetramers show higher thermal stability than a similar thiolactone-based sequence-defined macromolecule, which enables its exploration within a material context. To that end, a bidirectional growth approach is proposed as a greener alternative that reduces the number of synthetic steps to obtain telechelic sequence-defined oligoamides. The latter are finally used as macromers for the preparation of polymer networks. We expect this strategy to pave the way for the further exploration of sequence-defined macromolecules in material science.

Screening competition and cross-feeding interactions during utilization of human milk oligosaccharides by gut microbes.

Background: The infant gut microbiome is a complex community that influences short- and long-term health. Its assembly and composition are governed by variables such as the feeding type. Breast milk provides infants an important supply of human milk oligosaccharides (HMO), a broad family of carbohydrates comprising neutral, fucosylated, and sialylated molecules. There is a positive association between HMOs and the overrepresentation of Bifidobacterium species in the infant gut, which is sustained by multiple molecular determinants present in the genomes of these species. Infant-gut-associated Bifidobacterium species usually share a similar niche and display similar HMO inclinations, suggesting they compete for these resources. There is also strong evidence of cross-feeding interactions between HMO-derived molecules and bifidobacteria. Methods: In this study, we screened for unidirectional and bidirectional interactions between Bifidobacterium and other species using individual HMO. Bifidobacterium bifidum and Bacteroides thetaiotaomicron increased the growth of several other species when their supernatants were used, probably mediated by the partial degradation of HMO. In contrast, Bifidobacterium longum subsp. infantis. supernatants did not exhibit positive growth. Results: Bifidobacterium species compete for lacto-N-tetraose, which is associated with reduced bidirectional growth. The outcome of these interactions was HMO-dependent, in which the two species could compete for one substrate but cross-feed on another. 2'-fucosyllactose and lacto-N-neotetraose are associated with several positive interactions that generally originate from the partial degradation of these HMOs. Conclusion: This study presents evidence for complex interactions during HMO utilization, which can be cooperative or competitive, depending on the nature of the HMO. This information could be useful for understanding how breast milk supports the growth of some Bifidobacterium species, shaping the ecology of this important microbial community.

Dual effect to improve the electrical properties of SZO films grown by nitrogen pneumatic spray pyrolysis.

The principal aim of this study is to reduce considerably, via Sn doping, the resistivity of ZnO thin films prepared by simple, flexible, and cost-effective nitrogen pneumatic spray pyrolysis (NPSP) method on glass substrates at a temperature of 400°C. Different Sn content was tested (Sn/Zn = 0, 1, 3, 5 wt%) in an attempt to reduce the concentration of excessive oxygen atoms and create more free electrons. The microstructural, optical, morphological, and electrical properties of the films have been studied. The x-ray diffraction analysis demonstrated that tin-doped SZO films exhibited polycrystalline nature with a preferential orientation along (002) plane with the appearance of a new orientation (101) with the increase of Sn concentration leading then to bidirectional growth. The deposited SZO films showed an average optical transmittance of about 80% in the UV-visible region (200-800 nm) with optical band gap values at around 3.27 eV. Photoluminescence emissions of SZO samples presented three main peaks: near band edge emission, violet emission, and the blue-green emission. The surface morphology of the films obtained by scanning electron microscope (SEM) exhibited the change in morphology with increasing the Sn content. A minimum electrical resistivity value of about 17·10-3 Ω·cm was obtained for 3% SZO films. SZO films prepared by the NPSP method can be used as transparent window layer and electrodes in solar cells. RESEARCH HIGHLIGHTS: Highly oriented, conducting, and transparent Sn-doped ZnO films are successfully synthesized. The film growth orientation changed from mono-directional (002) axis to bi-directional (002) and (101) axis according to Sn doping. Ultraviolet and green emissions are noted by photoluminescence investigation. A minimum resistivity is observed for 3 wt% SZO film. The dual positive effect of the carrier gas used (N2) and Sn doping is confirmed.

Decellularized Scaffolds with Double-Layer Aligned Microchannels Induce the Oriented Growth of Bladder Smooth Muscle Cells: toward Urethral and Ureteral Reconstruction.

There is a great clinical need for regenerating the urinary tissue. Native urethra and ureter have bidirectional aligned smooth muscle cells (SMCs) layers, which plays a pivotal role for micturition and transport the urine and inhibit reflux. Up to now, urinary scaffolds have not been designed to induce the native-mimicking aligned arrangement of SMCs. In this study, we engineered a tubular decellularized extracellular matrix (dECM) with an intact internal layer and bidirectional aligned microchannels in the tubular wall, which was realized by the subcutaneous implantation of a template, followed by the removal of the template, and decellularization. The dense and intact internal layer effectively increased the leakage pressure of the tubular dECM scaffolds. The rat-derived dECM scaffolds with three different sizes of microchannels were fabricated by tailoring the fiber diameter of the templates. The rat-derived dECM scaffolds exhibiting microchannels of ∼ 65μm showed suitable mechanical properties, good ability to induce the bidirectional alignment and growth of human bladder SMCs (HBdSMC) and elevated higher functional protein expression in vitro. These data indicated that rat-derived tubular dECM scaffolds manifesting double-layer aligned microchannel may be promising candidates to induce the native-mimicking regeneration of SMCs in urethra and ureter reconstruction. This article is protected by copyright. All rights reserved.

Joint Path and Multi-Hop Communication Node Location Planning in Cluttered Environment

In the communication-constrained operating environment, a unmanned aerial vehicle (UAV) needs to plan a feasible path from the starting point to the endpoint while planning the node deployment location for multi-hop communication to establish an information pathway. In this study, a new algorithm was designed for joint path and multi-hop communication node location planning in cluttered environments based on rapidly-exploring random trees star (RRT*) algorithm. The maximum communication distance constraint between nodes was obtained based on the signal-free propagation model, whereas the communication node loss and path loss were established as joint optimization objectives. In bidirectional random tree growth, the structure of the trees was optimized according to the value of the loss function, and optimal path and node location planning were finally achieved through continuous growth and iteration. When tested in different complexity-barrier environments and compared to RRT*, Informed-RRT*, and IB-RRT* algorithms, the paths in the planning results of the new algorithm are close to those of the comparison algorithms; however, the number of nodes decreases significantly, which proves the effectiveness of the newly proposed algorithm.

UAV trajectory planning based on bi-directional APF-RRT* algorithm with goal-biased

In recent decades, RRT* algorithm has attracted much attention because of its asymptotic optimization. However, the RRT* algorithm still suffers from slow convergence rate and large randomness of search range. To overcome the shortcomings of this algorithm, this paper proposes UAV trajectory planning based on bi-directional APF-RRT* algorithm with goal-biased. Firstly, goal-biased strategy is used to guide the generation of random sampling points, and two mutually alternating random search trees are established by the bi-directional RRT* algorithm to perform the search, thus increasing the convergence rate of the algorithm. Secondly, the number of iterations is greatly reduced by incorporating an modified artificial potential field method into the bi-directional growth tree. In the process of smoothing the paths, a cubic spline interpolation algorithm is applied to optimize the paths to obtain the best trajectory. The combination of the two algorithms improves the direction of new node generation and reduces the path cost. Finally, the algorithm of this paper is compared with Informed-RRT*, Bi-RRT* and improved P-RRT* algorithms, and it enhances the search performance of the growing tree.

Path planning of a 5-dof robotic arm based on BiRRT-APF algorithm considering obstacle avoidance

In robotic applications, an efficient path planning in a prescribed environment is the central issue, which is a challenging task for multiple degree-of-freedom articulated robotic arms. In this light, the path planning for robotic manipulators based on the combined artificial potential field method and bidirectional rapidly exploring random tree (BiRRT-APF) algorithm is proposed in this paper, aiming to handle the problems of highly possible randomness and low search efficiency. In order to improve the attraction function to speed up the efficiency of searching path, the characteristics of the Bi-RRT algorithm (i.e., bi-directional growth of random trees), is integrated to reduce the search time. Subsequently, a path construction strategy is proposed to remove the redundant nodes of the path, for the increased smoothness of the path and reduced memory storages of the algorithm. The effectiveness of the proposed path planning algorithm is illustrated with a 5-dof robotic arm, and is verified with MATLABTM and CoppeliaSimTM co-simulation, through a comparative study among different algorithms. The results show that the proposed BiRRT-APF algorithm can decrease the randomness of node growth and reduce the number of algorithm iterations, resulting in faster convergence of a smooth path for reduced computational burden.

Time Course of Activity-Dependent Changes in Auditory Nerve Synapses Reveals Multiple Underlying Cellular Mechanisms.

Abnormal levels of acoustic activity can result in hearing problems such as tinnitus and language processing disorders, but the underlying cellular and synaptic changes triggered by abnormal activity are not well understood. To address this issue, we studied the time course of activity-dependent changes that occur at auditory nerve synapses in mice of both sexes after noise exposure and conductive hearing loss. We found that EPSC amplitude and synaptic depression decreased within 2 d of noise exposure through a decrease in the probability of vesicle release (Pr). This was followed by a gradual increase in EPSC amplitude through a larger pool of releasable vesicles (N). Occlusion of the ear canal led to a rapid decrease in EPSC amplitude through a decrease in N, which was followed by an increase in EPSC amplitude and synaptic depression through an increase in Pr After returning to normal sound levels, synaptic depression recovered to control levels within 1-2 d. However, repeated exposure to noise for as little as 8 h/d caused synaptic changes after 7 d, suggesting recovery did not fully offset changes. Thus, there appear to be three activity-dependent mechanisms in auditory nerve synapses-bidirectional changes in Pr in 1-2 d, slower bidirectional changes in N through synaptic growth or retraction, and rapid downregulation of N with low activity. The dynamic changes indicate that multiple mechanisms are present to fine-tune synaptic fidelity across different acoustic conditions in a simple relay.SIGNIFICANCE STATEMENT Hearing impairments can arise from exposure to noise or conductive hearing loss. This appears to result from changes in the brain, but the mechanisms are not well understood. We study this issue by studying the synapses made by auditory nerve fibers called endbulbs of Held. These synapses undergo bidirectional changes in size and release probability of neurotransmitter in response to increased or decreased activity. Here, we made a close examination of how quickly these synaptic characteristics change, which indicates there are at least three cellular mechanisms underlying changes. Furthermore, repeated exposure to brief periods of noise can produce cumulative effects. These changes could significantly affect hearing, especially because they occur at the start of the central auditory pathway.

Characteristics of continental rifting in rotational systems: New findings from spatiotemporal high resolution quantified crustal scale analogue models

Continental rifts are the expression of regional horizontal stretching and are in modelling studies often assumed to be the result of orthogonal or oblique extension. However, naturally occurring V-shaped rift geometries infer an underlying rotational component, resulting in a divergence velocity gradient. Here we use such analogue models of rifting in rotational settings to investigate and quantify the effect of such a divergence velocity gradient on normal fault growth and rift propagation towards a rotation pole. Particularly, we apply different divergence velocities and use different brittle-ductile ratios to simulate different crustal configurations and analyse its effect on rift propagation and surface deformation. Surface deformation is captured using stereoscopic 3D Digital Image Correlation, which allows for quantifying topographic evolution and surface displacement including vertical displacement. In combination with X-Ray computed tomography, we gain insights into the three-dimensional structures in our two-layer models. Based on our models, we present a novel characterisation of normal fault growth under rotational extension which is described by 1) an early stage of bidirectional stepwise growth in length by fault linkage with pulses of high growth rates followed by a longer and continuous stage of unidirectional linear fault growth; 2) segmented rifting activity which promotes strain partitioning among competing conjugate faults and 3) along-strike segmented migration of active faulting from boundary faults inwards to intra-rift faults allowing different fault generations to be simultaneously active over the entire rift length. For models with higher divergence velocities, inward migration is delayed but other first-order observations are similar to models with lower divergence velocities. Our quantitative analysis provides insights on spatiotemporal fault growth and rift propagation in analogue models of rotational rifting. Although natural rifts present complex systems, our models may contribute to a better understanding of natural rift evolution with a rotational component.

Research on Path Planning Algorithm of Bidirectional Rapidly Exploring Random Tree Improved by Artificial Potential Field

Aiming at the defects of path planning in rapidly exploring random tree(RRT) algorithm, such as low efficiency, strong randomness and slow convergence rate, a new algorithm based on artificial potential field was proposed in this paper. The algorithm used the scheme of bidirectional growth of exploration tree to make two growth trees explore and expand outwards from the starting point and the end point at the same time to accelerate the convergence speed of the algorithm. In the early stage, growth pretreatment was added to make the two growing trees take their respective endpoints as the target points and pass through the obstacle free area rapidly at one time. Artificial potential field method was used to modify the growth tree touching the obstacle and guide the path to grow towards the end. The adaptive change probability was used to select different target points as the growth directions in different periods with different probabilities to accelerate the meeting of two growing trees. After a lot of simulation experiments and data analysis, the improved bidirectional RRT algorithm has higher search efficiency, better growth path and fewer sampling points.

Native gold enrichment process during growth of chalcopyrite-lined conduits within a modern hydrothermal chimney (Manus Basin, PNG)

Abstract Seafloor hydrothermal chimneys from back-arc basins are important hosts for metals such as Cu, Zn, Pb, Ag, and Au. Although the general growth history of chimneys has been well documented, recent studies have revealed that the fine-scale mineralogy can be highly complex and reflects variable physicochemical conditions of formation. This study utilized a novel combination of scanning electron microscopy (SEM)-based electron backscattered diffraction (EBSD) and synchrotron X-ray fluorescence microscopy (SXFM) to uncover the detailed growth processes of multiple chalcopyrite-lined conduits within a modern chalcopyrite-sphalerite chimney from Manus Basin and to assess the controls on native gold precipitation. On the basis of previous studies, the chimney conduit was thought to develop from an initial sulfate-dominated wall, which was subsequently dissolved and replaced by sphalerite and chalcopyrite during gradual mixing of hydrothermal fluids and seawater. During this process, sphalerite was epitaxially overgrown by chalcopyrite. Accretionary growth of chalcopyrite onto this early formed substrate thickened the chimney walls by bi-directional growth inward and outward from the original tube wall, also enclosing the outgrown pyrite cluster. A group of similar conduits with slightly different mineral assemblages continued to form in the vicinity of the main conduit during the further fluid mixing process. Four types of distinct native gold-sulfide/sulfosalt associations were developed during the varying mixing of hydrothermal fluids and seawater. Previously unobserved chains of gold nanoparticles occur at the boundary of early sphalerite and chalcopyrite, distinct from gold observed in massive sphalerite as identified in other studies. These observations provide baseline data in a well-preserved modern system for studies of enrichment mechanisms of native gold in hydrothermal chimneys. Furthermore, native gold is relatively rarely observed in chalcopyrite-lined conduit walls. Our observations imply that: (1) native gold is closely associated with various sulfides/sulfosalts in chalcopyrite-lined conduit walls rather than limited to the association with tennantite, Bi-rich minerals, and bornite as reported previously; and (2) the broad spectrum of gold occurrence in chalcopyrite-line conduits is likely to be determined by the various mixing process between hot hydrothermal fluids with surrounding fluids or seawater. Quantitative modeling of fluid mixing processes is recommended in the future to probe the precise gold deposition stages to efficiently locate gold in modern hydrothermal chimneys.

Bidirectional growth of the Altyn Tagh Fault since the Early Oligocene

The Cenozoic evolution of the Altyn Tagh Fault (ATF) is still under debate. Here, we present new paleomagnetic rotation evidence on curvatures south of the ATF in the northeastern Tibetan Plateau to shed new light on this issue. A total of 498 core samples representing 53 sites and 6 time intervals (a-f) were collected from the post-Oligocene sequence at the Heishiqiu locality that in the junction of the northwestern and middle of the reverse S-type northern Qaidam marginal thrust belt. Rock magnetic analysis indicated that the main magnetic carriers were hematite and magnetite. After detailed thermal demagnetization analyses, the characteristic remanent magnetizations of 48 sites (387 samples), which exhibited dual polarities and passed a regional fold test, are most likely the primary magnetizations. Two periods of remarkable rotations are identified at Heishiqiu: a clockwise rotation of ~16.0 ± 10.3° during ~27–17 Ma and a subsequent counterclockwise rotation of ~24.3 ± 14.5° during ~17–10 Ma. The rotations were attributed to two periods of strike-slip faulting along the ATF during the Early Oligocene to Late Miocene, yielding at least ~290–380 km of offset at Heishiqiu. The integrated lines of paleomagnetic and geological evidence suggest that the deformation along the ATF has propagated both southwestward and northeastward from Heishiqiu in the middle ATF since the Early Oligocene. We propose a bidirectional growth model for the ATF that might be applicable to the evolution of the Tibetan Plateau.