Search

The formation of many hydrothermal gold deposits is closely related to iron-rich rocks. The host rocks of the Madiyi Formation of the Mid- to Late Neoproterozoic Banxi Group for the Woxi Au (-Sb-W) deposit, which is located in western Hunan Province of the western Jiangnan Orogen, South China, is rich in hematite, which provides a good example for studying the relationship between the formation of gold deposit and iron-rich rocks. Field investigation and petrographic observation on the unaltered, weakly altered and strongly altered rocks demonstrate that the bleaching is caused by a combination of carbonatization, sulfidation and sericitization. Mass balance calculation suggests that, during decolourization there is no change in TFe2O3, while FeO is gained and Fe2O3 is lost. Geochemical modeling found that Au was mainly present as AuHS(aq) and Au(HS)2−, and that the water-rock interactions decreased the sulfur fugacity which destroyed the stability of such aqueous complexes. Combined with the locally occurred native gold in quartz veins, it is concluded that the major gold precipitation mechanisms are sulfidation and fluid boiling. Based on previous geochronological and geochemical research further gold mineralization is proposed to be generated by deep sourced magmatic or metamorphic fluid migrated upward along the Woxi fault, and the iron-rich Madiyi Formation is the idea chemical trap for gold deposition. The decrease of sulfur contents caused by fluid-rock interactions and fluid boiling are the major mechanisms for gold mineralization. [ABSTRACT FROM AUTHOR]

The remobilization, migration, precipitation, and enrichment of ore-forming elements are closely related to structures. Therefore, detailed regional and ore-field structural analyses are critical for determining the genesis of a mineral deposit. The Jiangnan Orogenic Belt (JOB) is an important gold polymetallic metallogenic belt in South China, which is characterized by multiple periods of gold mineralization in the Paleozoic and Mesozoic. However, the genesis of these gold polymetallic deposits is still not well understood due to a lack of systematic research on the regional geology, ore-controlling structures and metallogenic mechanism. In this study, a detailed structural survey at the surface and in the subsurface tunnels was conducted on the Woxi Au-Sb-W deposit, the genesis of which is relatively controversial among the gold polymetallic deposits in the JOB due to poor structural constraints. In addition, a wolframite U-Pb dating was carried out to further constrain the relationship between structures and mineralization. Based on the results of these studies, together with those from previous studies, it is proposed that the Woxi deposit and surrounding areas likely underwent six periods of regional deformation, which are constrained in time and geodynamic setting. Furthermore, we present a systematic discussion on the roles of ore-controlling structures in the transportation, distribution, and deposition of ore-forming elements and localization of orebodies. According to the wolframite dating results, structural analyses, and previous data, we propose that the Woxi Au-Sb-W deposit was formed in two stages during the Yanshanian: a W (wolframite)-Au mineralization stage at ca. 140 Ma and an Au-Sb-W (scheelite) mineralization stage at <130 Ma. These mineralizing events are interpreted to have a tight relationship with tectonic reactivation, and the ore-forming fluids were derived from deep sources, including those of magmatic or metamorphic origins. The Woxi deposit can therefore be classified as an "intracontinental reactivation-type", and the mineralization is related to lithospheric extension caused by plate retreat, retention, and delamination following the cessation of westward subduction of the Paleo-Pacific Plate beneath the East Asian continent. [ABSTRACT FROM AUTHOR]

Emerging functionalities in two-dimensional materials, such as ferromagnetism, superconductivity and ferroelectricity, open new avenues for promising nanoelectronic applications. Here, we report the discovery of intrinsic in-plane room-temperature ferroelectricity in two-dimensional Bi2TeO5 grown by chemical vapor deposition, where spontaneous polarization originates from Bi column displacements. We found an intercalated buffer layer consist of mixed Bi/Te column as 180° domain wall which enables facile polarized domain engineering, including continuously tunable domain width by pinning different concentration of buffer layers, and even ferroelectric-antiferroelectric phase transition when the polarization unit is pinned down to single atomic column. More interestingly, the intercalated Bi/Te buffer layer can interconvert to polarized Bi columns which end up with series terraced domain walls and unusual fan-shaped ferroelectric domain. The buffer layer induced size and shape tunable ferroelectric domain in two-dimensional Bi2TeO5 offer insights into the manipulation of functionalities in van der Waals materials for future nanoelectronics. Tunability of ferroelectric domain structure is significant in ferroelectric materials. Here, the authors present in-plane ferroelectricity in 2D Bi2TeO5 in which the ferroelectric domain size and shape can be continuously tuned by the Bi/Te ratio. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have gained huge research interest within few decades due to their optoelectronic applications. Recently, inorganic metal halide perovskites CsPbX3 (X = Cl, Br, I) has shown the improved stability with promising optical and electrical properties. We report the enhancement of PL intensity and the extension of carrier lifetime from strained CsPbBr3 microwires in air environment. PL intensity is enhanced more than fivefold for all the studied microwires under strain than the original. Maximum enhancement in PL intensity of more than 25-fold has been observed from a wire with lateral width of 630 nm. Based on the experiment and simulation results, we conclude that tensile strain can improve the oxygen adsorption by the defects on the surface of CsPbBr3 microwires, which will suppress the non-radiative transitions and enhance the light emission efficiency. These findings demonstrate that the strain engineering is an effective way to improve the performance of CsPbBr3 microstructures for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Beyond the absence of long-range magnetic orders, the most prominent feature of the elusive quantum spin liquid (QSL) state is the existence of fractionalized spin excitations, i.e., spinons. When the system orders, the spin-wave excitation appears as the bound state of the spinon-antispinon pair. Although scarcely reported, a direct comparison between similar compounds illustrates the evolution from spinon to magnon. Here, we perform the Raman scattering on single crystals of two quantum kagome antiferromagnets, of which one is the kagome QSL candidate Cu3Zn(OH)6FBr, and another is an antiferromagnetically ordered compound EuCu3(OH)6Cl3. In Cu3Zn(OH)6FBr, we identify a unique one spinon-antispinon pair component in the E2g magnetic Raman continuum, providing strong evidence for deconfined spinon excitations. In contrast, a sharp magnon peak emerges from the one-pair spinon continuum in the Eg magnetic Raman response once EuCu3(OH)6Cl3 undergoes the antiferromagnetic order transition. From the comparative Raman studies, we can regard the magnon mode as the spinon-antispinon bound state, and the spinon confinement drives the magnetic ordering. Spinon excitations of a Kagome quantum spin liquid are expected to give rise to a magnetic continuum in Raman spectroscopy. Here, the authors report a magnetic Raman continuum in the Kagome spin liquid candidate Cu3Zn(OH)6FBr, in contrast to a sharp magnon Raman peak in the Kagome antiferromagnet EuCu3(OH)6Cl3. [ABSTRACT FROM AUTHOR]

Cloud computing has proven to be applicable in smart grid systems with the help of the cloud-based Internet of things (IoT) technology. In this concept, IoT is deployed as a front-end enabling the acquisition of smart grid-related data and its outsourcing to the cloud for data storage purposes. It is obvious that data storage is a pertinent service in cloud computing. However, its wide adoption is hindered by the concern of having a secure access to data without a breach on confidentiality and authentication. To address this problem, we propose a novel data access control scheme that simultaneously accomplishes confidentiality and authentication for cloud-based smart grid systems. Our scheme can enable the storing of encrypted smart grid-related data in the cloud. When a user prefers to access the data, the data owner issues a delegation command to the cloud for data re-encryption. The cloud is unable to acquire any plaintext information on the data. Only authorized users are capable of decrypting the data. Moreover, the integrity and authentication of data can only be verified by the authorized user. We obtain the data access control scheme by proposing a pairing free certificateless signcryption with proxy re-encryption (CLS-PRE) scheme. We prove that our CLS-PRE scheme has indistinguishability against adaptive chosen ciphertext attack under the gap Diffie–Hellman problem and existential unforgeability against adaptive chosen message attack under elliptic curve discrete logarithm problem in the random oracle model. [ABSTRACT FROM AUTHOR]

Most electronic devices exploit the electric charge of electrons, but it is also possible to build devices that rely on other properties of electrons. Spintronic devices, for example, make use of the spin of electrons. Valleytronics is a more recent development that relies on the fact that the conduction bands of some materials have two or more minima at equal energies but at different positions in momentum space. To make a valleytronic device it is necessary to control the number of electrons in these valleys, thereby producing a valley polarization. Single-layer MoS2 is a promising material for valleytronics because both the conduction and valence band edges have two energy-degenerate valleys at the corners of the first Brillouin zone. Here, we demonstrate that optical pumping with circularly polarized light can achieve a valley polarization of 30% in pristine monolayer MoS2. Our results, and similar results by Mak et al., demonstrate the viability of optical valley control and valley-based electronic and optoelectronic applications in MoS2 monolayers. [ABSTRACT FROM AUTHOR]