On the stability of 2 \sqrt{2} x 2 \sqrt{2} oxygen ordered superstructures in YBa2Cu3O6+x

We have compared the ground-state energy of several observed or proposed " 2 \sqrt{2} x 2 \sqrt{2} oxygen (O) ordered superstructures " (from now on HS), with those of "chain superstructures" (CS) (in which the O atoms of the basal plane are ordered in chains), for different compositions x in YBa2Cu3O6+x. The model Hamiltonian contains i) the Madelung energy, ii) a term linear in the difference between Cu and O hole occupancies which controls charge transfer, and iii) covalency effects based on known results for $t-J$ models in one and two dimensions. The optimum distribution of charge is determined minimizing the total energy, and depends on two parameters which are determined from known results for x=1 and x=0.5. We obtain that on the O lean side, only CS are stable, while for x=7/8, a HS with regularly spaced O vacancies added to the x=1 structure is more stable than the corresponding CS for the same x. We find that the detailed positions of the atoms in the structure, and long-range Coulomb interactions, are crucial for the electronic structure, the mechanism of charge transfer, the stability of the different phases, and the possibility of phase separation.Comment: 24 text pages, Latex, one fig. included as ps file, to be publisheb in Phys. Rev.

Ratiometric G-quadruplex assay for robust lead detection in food samples

Lead (Pb2+) pollution is a serious food safety issue, rapid detection of Pb2+ residual in food is vital to guarantee food quality and safety. Here we proposed ratiometric aptamer probes, allowing robust Pb2+ supervision in food samples. Pb2+ specific aptamer can bolster a transition of G-quadruplex structural response to Pb2+; this process can be monitored by N-methyl mesoporphyrin IX (NMM), which is highly specific to G-quadruplex. Particularly, the utilization of G-quadruplex specific dye and terminal-labeled fluorophore allowed to endue ratiometric signal outputs towards Pb2+, dramatically increase the robustness for lead detection. The ratiometric G-quadruplex assay allowed a facile and one-pot Pb2+ detection at room temperature using a single-stranded DNA aptamer. We demonstrated its feasibility for detecting lead pollution in fresh eggs and tap water samples. The ratiometric G-quadruplex design is expected to be used for on-site Pb2+ testing associated with food safet

Life after herbarium digitisation: physical and digital collections, curation and use

Societal Impact StatementCollections of dried plant specimens (herbaria) provide an invaluable resource for the study of many areas of scientific interest and conservation globally. Digitisation increases access to specimens and metadata, enabling efficient use across a broad spectrum of research. The value of physical specimens is enhanced by digitisation, but these specimens remain fundamental for the study of traits not yet captured digitally. We investigate the requirements for physical access and the curation and facilities needed to maximise specimen use and value. We present recommendations to ensure that specimens and data are both fully accessible to support research into global challenges.SummaryHerbarium management has traditionally focused on providing direct access to the physical specimens, but this scope must now expand to also embrace digital collections. Advances in technologies such as artificial intelligence and high‐throughput genomics are increasing the amount of information that can be extracted from specimens, and it is becoming commonplace to provide digital access to specimen images and collection metadata. These developments are facilitating the use of herbarium collections to inform conservation planning and in studies plant and fungal taxonomy, distribution and evolution. This paper examines how herbaria are transitioning from physical specimen‐centric collection management practices to increasingly digitised curation, and the effects that digital availability of data are having on demands for physical access. We provide a set of recommendations to institutions holding herbarium collections. We emphasise the critical importance of further digitising herbaria of all sizes; the need to ensure that historical inequalities in deposition of specimens are not perpetuated; and that the capacity to utilise new technologies must be further developed, especially in biodiverse regions from which most herbarium collections are derived.To improve access to collection data, herbarium managers need to more rigorously adopt community‐agreed data standards, and more strongly support open access platforms such as the Global Biodiversity Information Facility either directly or through regional coalitions. As digitisation and open data access increase, herbaria will need to offer users with seamless hybrid access to physical and digital records while continuing to develop their collections to advance research and conservation

Engraved bones from the archaic hominin site of Lingjing,Henan Province

The production of abstract engravings is considered an indicator of modern human cognition and a means for the long-term recording and transmission of information. This article reports the discovery of two engraved bones from the Lingjing site in Henan Province, China, dated to 105–125 kya. The carefully engraved nature of the incisions, made on weathered rib fragments, precludes the possibility of unintentional or utilitarian origins. Residue analysis demonstrates the presence of ochre within the incised lines on one specimen. This research provides the first evidence for the deliberate use of ochred engravings for symbolic purposes by East Asian Late Pleistocene hominins

Investigation method of borehole collapse with the multi-field coupled model during drilling in clayey silt hydrate reservoirs

The global reserves of natural gas hydrates are extremely abundant, which is attracting more and more scientists attention. However, hydrate reservoirs are usually clayey silt hydrate reservoirs with low strength, borehole collapse is a key issue during the drilling operation in these clayey silt hydrate reservoirs in the South China Sea. Therefore, investigation method exploration of borehole collapse simulation for wellbores drilled in hydrate-bearing sediments is of great importance for safely and efficiently developing hydrate in deep water. The finite element model coupled seepage, deformation and heat transfer is developed, and borehole collapse investigation during the overbalanced drilling operation in hydrate-bearing sediment is carried out. The results show that changes in temperature and/or pore pressure do not necessarily lead to the hydrate dissociation. For the investigation case, the temperature front reaches to the position of 35.72 cm from borehole within the near-wellbore area when the drilling operation lasted for 3 hours, but hydrate only dissociates for 17.94cm from the borehole, which is smaller than the temperature disturbance distance. Moreover, the applicability of the investigation method developed herein is verified by comparing the equivalent plastic strains obtained by the coupled model developed in this paper and the simplified model (which neglects the seepage and the heat transfer) respectively. All these results demonstrate that both the investigation method and the finite element model can be used for borehole stability simulation in hydrate-bearing sediment

Flame-retardant coating by alternate assembly of poly(vinylphosphonic acid) and polyethylenimine for ramie fabrics

A novel intumescent flame retardant coating, consisting of poly(vinylphosphonic acid) (PVPA) as the acid source and branched polyethylenimine (BPEI) as the blowing agent, was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie. The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie. Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 °C, while the control (uncoated) fabric left less than 1.4 wt% residue. Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time, and the residues well preserved the original weave structure and fiber morphology, whereas, the uncoated fabric left only ashes. Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%, relative to those of the uncoated fabric. © Chinese Chemical Society

Rational design of an air-breathing gas-diffusion electrode with oxygen vacancy-rich ZnO for robust and durable H₂O₂ electrosynthesis

Developing cost-effective and durable cathodes with outstanding oxygen mass transport and selective two-electron oxygen reduction reaction (ORR) is crucial for large-scale H2O2 electrosynthesis. Herein, an oxygen vacancy-rich ZnO-modified air-breathing gas-diffusion electrode (ZnO-V/GDE) was fabricated, thus eliminating the cost of aeration while achieving remarkable O2 utilization efficiency and H2O2 selectivity. This novel cathode led to ultrahigh H2O2 yield of 1005.2 mg L−1 with selectivity of 74.6 %, outperforming both the raw and ZnO-modified air-breathing GDEs. Moreover, the practical applicability of ZnO-V/GDE was demonstrated by its high stability and effectiveness when treating micropollutants in wastewater by ZnO-V/GDE-based electro-Fenton process. Mechanistic insights unveiled the key roles of oxygen vacancies, which not only facilitate the O2 transport by creating a superhydrophobic interface and provide binding centers to O2, but also reduce the energy barrier of the rate-determining step (OOH*-to-H2O2), eventually enhancing the ORR performance