Achieving High Rate and Long Cycle Performance of Na2FePO4F Cathode Through Co-Modification of Ti Doping and Carbon Coating.

Layered Na2FePO4F (NFPF) cathode material has received widespread attention due to its green nontoxicity, abundant raw materials, and low cost. However, its poor inherent electronic conductivity and sluggish sodium ion transportation seriously impede its capacity delivery and cycling stability. In this work, NFPF by Ti doping and conformal carbon layer coating via solid-state reaction is modified. The results of experimental study and density functional theory calculations reveal that Ti doping enhances intrinsic conductivity, accelerates Na-ion transport, and generates more Na-ion storage sites, and pyrolytic carbon from polyvinylpyrrolidone (PVP) uniformly coated on the NFPF surface improves the surface/interface conductivity and suppresses the side reactions. Under the combined effect of Ti doping and carbon coating, the optimized NFPF (marked as 5T-NF@C) exhibits excellent electrochemical performance, with a high capacity of 108.4 mAh g-1 at 0.2C, a considerable capacity of 80.0 mAh g-1 even at high current density of 10C, and a high capacity retention rate of 81.8% after 2000 cycles at 10C. When assembled into a full cell with a hard carbon anode, 5T-NF@C also show good applicability. This work indicates that co-modification of Ti doping and carbon coating makes NFPF achieve high rate and long cycle performance for sodium-ion batteries.

Group-III nitride heteroepitaxial films approaching bulk-class quality.

III-nitride wide bandgap semiconductors are promising materials for modern optoelectronics and electronics. Their application has progressed greatly thanks to the continuous quality improvements of heteroepitaxial films grown on large-lattice-mismatched foreign substrates. But compared with bulk single crystals, there is still tremendous room for the further improvement of the material quality. Here we show a paradigm to achieve high-quality III-nitride heteroepitaxial films by the controllable discretization and coalescence of columns. By adopting nano-patterned AlN/sapphire templates with regular hexagonal holes, discrete AlN columns coalesce with uniform out-of-plane and in-plane orientations guaranteed by sapphire nitridation pretreatment and the ordered lateral growth of cleavage facets, which efficiently suppresses the regeneration of threading dislocations during coalescence. The density of dislocation etch pits in the AlN heteroepitaxial film reaches 3.3 × 104 cm-2, close to the present available AlN bulk single crystals. This study facilitates the growth of bulk-class quality III-nitride films featuring low cost and scalability.

A 300†km fiber channel mapping using neural networks for Gb/s physical-layer key distribution.

Physical-layer secure key distribution (PLSKD) generally acquires highly correlated entropy sources via bidirectional transmission to share the channel reciprocity. For long-haul fiber links, the non-negligible backscattering noise (BSN) and the challenge of bidirectional optical amplification degrade the key generation performances. Since the channel reciprocity can be precisely mapped using neural networks (NNs), unidirectional PLSKD provides a feasible PLSKD for longer fiber links. Here, a final error-free key generation rate (KGR) in unidirectional PLSKD of 3.07 Gb/s is demonstrated over a 300 km fiber link using NNs. Moreover, the channel mapping is analyzed in terms of fiber distance, chromatic dispersion, the nonlinearity of random source, and BSN.

Variational autoencoder-assisted unsupervised hardware fingerprint authentication in a fiber network.

Physical-layer authentication (PLA) based on hardware fingerprints can safeguard optical networks against large-scale masquerade or active injection attacks. However, traditional schemes rely on massive labeled close-set data. Here, we propose an unsupervised hardware fingerprint authentication based on a variational autoencoder (VAE). Specifically, the triplets are generated through variational inference on unlabeled optical spectra and then applied to train the feature extractor, which has an excellent generalization ability and enables fingerprint feature extraction from previously unknown optical transmitters. The feasibility of the proposed scheme is experimentally verified by the successful classification of eight optical transmitters after a 20 km standard single-mode fiber (SSMF) transmission, to distinguish efficiently the rogue from legal devices. A recognition accuracy of 99% and a miss alarm rate of 0% are achieved even under the interference of multiple rogue devices. Moreover, the proposed scheme is verified to have a comparable performance with the results obtained from supervised learning.

Sodium octanoate alleviates cardiac and cerebral injury after traumatic cardiac arrest in a porcine model.

INTRODUCTION: Traumatic cardiac arrest (TCA) is a severe condition with a high mortality rate, and patients who survive from TCA face a poor prognosis due to post-resuscitation injury, including cardiac and cerebral injury, which remains a serious challenge. Sodium octanoate has shown protective effects against various diseases. The present study aims to investigate sodium octanoate's protective effects against cardiac and cerebral injury after TCA in a porcine model. METHODS: The study included a total of 22 male domestic pigs divided into three groups: Sham group (n = 7), TCA group (n = 7), and sodium octanoate (SO) group (n = 8). Hemorrhage was initiated via the right femoral artery by a blood pump at a rate of 2 ml·kg-1·min-1 to establish TCA model. The Sham group underwent only endotracheal intubation and arteriovenous catheterization, without experiencing the blood loss/cardiac arrest/resuscitation model. At 5 min after resuscitation, the SO group received a continuous sodium octanoate infusion while the TCA group received the same volume of saline. General indicators were monitored, and blood samples were collected at baseline and at different time points after resuscitation. At 24 h after resuscitation, pigs were sacrificed, and heart and brain were obtained for cell apoptosis detection, iron deposition staining, oxidative stress detection, and the expression of ferroptosis-related proteins (ACSL4 and GPX4). RESULTS: Sodium octanoate significantly improved mean arterial pressure, cardiac output and ejection fraction induced by TCA. Serum biomarkers of cardiac and cerebral injury were found to increase at all time points after resuscitation, while sodium octanoate significantly reduced their levels. The apoptosis rates of cardiomyocytes and cerebral cortex cells in the SO group were significantly lower than in the TCA group, along with a reduced area of iron deposition staining. The sodium octanoate also reduced oxidative stress and down-regulated ferroptosis which was indicated by protein level alteration of ACSL4 and GPX4. CONCLUSION: Our study's findings suggest that early infusion of sodium octanoate significantly alleviates post-resuscitation cardiac and cerebral injury in a porcine model of TCA, possibly through inhibition of cell apoptosis and GPX4-mediated ferroptosis. Therefore, sodium octanoate could be a potential therapeutic strategy for patients with TCA.

In-Situ Ultrafast Construction of Zinc Tungstate Interface Layer for Highly Reversible Zinc Anodes.

Constructing artificial solid electrolyte interface on the Zn anode surface is recognized as an appealing method to inhibit zinc dendrites and side reactions, whereas the current techniques are complex and time-consuming. Here, a robust and zincophilic zinc tungstate (ZnWO4) layer has been in situ constructed on the Zn anode surface (denoted as ZWO@Zn) by an ultrafast chemical solution reaction. Comprehensive characterizations and theoretical calculations demonstrate that the ZWO layer can effectively modulate the interfacial electric field distribution and promote the Zn2+ uniform diffusion, thus facilitating the uniform Zn2+ nucleation and suppressing zinc dendrites. Besides, ZWO layer can prevent direct contact between the Zn/water and increase the hydrogen evolution reaction overpotential to eliminate side reactions. Consequently, the in situ constructed ZWO layer facilitates remarkable reversibility in the ZWO@Zn||Ti battery, achieving an impressive Coulombic efficiency of 99.36 % under 1.0 mA cm-2, unprecedented cycling lifespan exceeding 1800 h under 1.0 mA cm-2 in ZWO@Zn||ZWO@Zn battery, and a steady and reliable operation of the overall ZWO@Zn||VS2 battery. The work provides a simple, low cost, and ultrafast pathway to crafting protective layers for driving advancements in aqueous zinc-metal batteries.

10 Gb/s physical-layer key distribution in fiber using amplified spontaneous emission.

High-speed physical-layer secure key generation and distribution (SKGD) schemes via channel reciprocity are achieved using external electro-optical modulation or random source distribution via additional fiber links. Here, we propose and demonstrate an SKGD scheme using the fluctuation of polarization states from an amplified spontaneous emission (ASE) source, without any external electro-optical modulation or additional fiber link. Experimentally, an error-free key generation rate (KGR) of 10.1 Gb/s is achieved over a 10-km standard single-mode fiber (SSMF), with true randomness originating from ASE. Moreover, the single fiber channel can be shared for SKGD as well as data transmission, allowing the integration of the proposed SKGD with the deployed fiber infrastructure.

Confining ZnS/SnS2 Ultrathin Heterostructured Nanosheets in Hollow N-Doped Carbon Nanocubes as Novel Sulfur Host for Advanced Li-S Batteries.

Hollow nanostructured hosts are important scaffolds to achieve high sulfur loading, fast charge transfer, and conspicuous restraint of lithium polysulfides (LiPSs) shuttling in lithium-sulfur (Li-S) batteries. However, developing high-efficiency hollow hosts for improving utilization and conversion of aggregated sulfur in the hollow chamber remains a longstanding challenge. Herein, hollow N-doped carbon nanocubes confined petal-like ZnS/SnS2 heterostructures (ZnS/SnS2 @NC) as a conceptually novel host for Li-S batteries are reported. Specifically, compared to consubstantial hollow double-shelled hosts, the ZnS/SnS2 @NC with higher effective active surface area brings dense contact with sulfur and enhances efficient adsorption sites for binding LiPSs and accelerating their conversion. Benefiting from the unique structure and sophisticated composition, the resulting S@ZnS/SnS2 @NC cathodes exhibit 1294 mAh g-1 at 0.2 C, an ultralow capacity decay of 0.016% per cycle over 500 cycles at 1.0 C, and a high area capacity of 4.77 mAh cm-2 at 0.5 C (5.9 mg cm-2 ). Meanwhile, the performance evolution of S@ZnS/SnS2 @NC cathodes under various sulfur loadings is further investigated by using EIS, which provides the beneficial guidance to explore viable strategies further optimizing their performance. This work sheds new insights into the design of hollow nanostructured hosts with a distinguished ability to regulate LiPSs in Li-S batteries.

Manipulating Oxidation of Silicon with Fresh Surface Enabling Stable Battery Anode.

Silicon (Si)-based material is a promising anode material for next-generation lithium-ion batteries (LIBs). Herein, we report the fabrication of a silicon oxide-carbon (SiOx/C) nanocomposite through the reaction between silicon particles with fresh surface and H2O in a mild hydrothermal condition, as well as conducting carbon coating synchronously. We found that controllable oxidation could be realized for Si particles to produce uniform SiOx after the removal of the native passivation layer. The uniform oxidation and conductive coating offered the as-fabricated SiOx/C composite good stability at both particle and electrode level over electrochemical cycling. The as-fabricated SiOx/C composite delivered a high reversible capacity of 1133 mAh g-1 at 0.5 A g-1 with 89.1% capacity retention after 200 cycles. With 15 wt % SiOx/C composite, graphite-SiOx/C hybrid electrode displayed a high reversible specific capacity of 496 mAh g-1 and stable electrochemical cycling with a capacity retention of 90.1% for 100 cycles.

Point to multi-point physical-layer key generation and distribution in passive optical networks.

A point to multi-point physical-layer secure key generation and distribution (SKGD) scheme is proposed and demonstrated in passive optical networks (PONs), where the optical line terminal (OLT) broadcasts optical lights with fast fluctuating states of polarization (SOPs) to the optical network units (ONUs). The highly correlated key waveforms are shared between OLT and ONUs, and the high-level security of the SKGD scheme is guaranteed by the high sensitivity of SOP dynamics associated with the specific fiber links. As a proof of concept, a 3.9 Gb/s SKGD is achieved over 11 km single-mode fiber, where a Sagnac interferometer-based polarization scrambler is constructed as the high-speed random source. Moreover, the generated key sequences are verified to be error free and truly random. The proposed SKGD scheme offers a flexible solution for security enhancement in PONs, and is also compatible with the current PON infrastructure.

Strain-enhanced high Q-factor GaN micro-electromechanical resonator.

We report on a highly sensitive gallium nitride (GaN) micro-electromechanical (MEMS) resonator with a record quality factor (Q) exceeding 105 at the high resonant frequency (f) of 911 kHz by the strain engineering for the GaN-on-Si structure. The f of the double-clamped GaN beam bridge is increased from 139 to 911 kHz when the tensile stress is increased to 640 MPa. Although it is usually regarded that the energy dissipation increases with increasing resonant frequency, an ultra-high Q-factor which is more than two orders of magnitude higher than those of the other reported GaN-based MEMS is obtained. The high Q-factor results from the large tensile stress which can be intentionally introduced and engineered in the GaN epitaxial layer by utilizing the lattice mismatch between GaN and Si, leading to the stored elastic energy and drastically decreasing the energy dissipation. The developed GaN MEMS is further demonstrated as a highly sensitive mass sensor with a resolution of 10-12 g/s through detecting the microdroplet evaporation process. This work provides an avenue to improve the f × Q product of the MEMS through an internally strained structure.

Accelerated key generation and distribution using polarization scrambling in optical fiber.

The physical-layer properties of the classical optical fiber channel provide an inherent, unique, random and reciprocal source for secure key generation and distribution (SKGD). However, the key generation rate (KGR) is generally less than kbit/s in the reported SKGD schemes. In this paper, an accelerated SKGD scheme based on active polarization scrambling is proposed in the classical optical fiber channel. A combination of unique birefringence distribution of optical fiber channel and active scrambling of instant state of polarization (SOP) enables a fast and random SOP fluctuation to be securely shared between the legitimate users for accelerated SKGD. The proposed SKGD scheme is experimentally demonstrated over 24-km standard single-mode fiber (SSMF), where a KGR of 200-kbit/s with an error-free operation is achieved after the post-processing procedure. Moreover, the possible fiber-tapping attacks are theoretically and experimentally analyzed for the security robustness of the proposed scheme. The results imply that a faster SKGD scheme could be achieved by incorporating an active polarization scrambling mechanism into the random properties of the fiber channel.

Error-free secure key generation and distribution using dynamic Stokes parameters.

This paper proposes and experimentally demonstrates an error-free secure key generation and distribution (SKGD) scheme in classical optical fiber link by exploiting Stokes parameters (SPs) of the state of polarization (SOP). Due to the unique birefringence distribution of the optical fiber channel, random but high-correlated SPs are shared between Alice and Bob. The dynamic SPs are also affected by the time-varying environmental factors, providing the source of randomness for the secret key extraction. As a proof of concept, key generation rate (KGR) of 213-bits/s is successfully demonstrated over 25-km standard single-mode fiber (SSMF). The error-free SKGD is realized in fiber channel using the information reconciliation (IR) technology, where Bose-Chaudhuri-Hocquenghem (BCH) codes are applied. Due to the channel uniqueness and the high-sensitivity to the initial SOP of optical signals, high-level security is provided by the proposed scheme, which is analyzed and verified against the possible fiber-tapping attacks. Moreover, the proposed SKGD scheme offers additional benefits such as simple structure, low cost, and suitablity for long-haul transmission.

Role of hole trapping in the unintentionally doped GaN layer in suppressing the two-dimensional electron gas degradation in AlGaN/GaN heterostructures on Si.

We identify the spatially resolved trapping mechanism and clarify the role of the unintentionally doped (UID) GaN layer in suppressing the two-dimensional electron gas (2DEG) degradation in AlGaN/GaN heterostructures on Si. The trapping mechanism is characterized by measuring C-V dispersion after three different configurations of bias stress: high drain-substrate voltage stress, high drain-gate voltage stress and combined stress (with both high drain-gate voltage and drain-substrate voltage stress). Under the combined stress, the 2DEG degradation is the overall effect of electron trapping and hole trapping. By comparing samples with and without the UID GaN layer, we confirm the role of the UID layer in suppressing the 2DEG degradation by hole trapping in that layer. The electron and hole trap states are further identified by reversed vertical stress and current transient measurements. The electron trap with an activation energy of 0.53 eV and the hole trap with an activation energy of 0.81 eV are distinguished.

Unambiguous Identification of Carbon Location on the N Site in Semi-insulating GaN.

Carbon (C) doping is essential for producing semi-insulating GaN for power electronics. However, to date the nature of C doped GaN, especially the lattice site occupation, is not yet well understood. In this work, we clarify the lattice site of C in GaN using polarized Fourier-transform infrared and Raman spectroscopies, in combination with first-principles calculations. Two local vibrational modes (LVMs) at 766 and 774 cm^{-1} in C doped GaN are observed. The 766 cm^{-1} mode is assigned to the nondegenerate A_{1} mode vibrating along the c axis, whereas the 774 cm^{-1} mode is ascribed to the doubly degenerate E mode confined in the plane perpendicular to the c axis. The two LVMs are identified to originate from isolated C_{N}^{-} with local C_{3v} symmetry. Experimental data and calculations are in outstanding agreement both for the positions and the intensity ratios of the LVMs. We thus provide unambiguous evidence of the substitutional C atoms occupying the N site with a -1 charge state in GaN and therefore bring essential information to a long-standing controversy.

Enhanced Hydrogen Detection Based on Mg-Doped InN Epilayer.

It is a fact that surface electron accumulation layer with sheet electron density in the magnitude of ~1013 cm−2 on InN, either as-grown or Mg-doped, makes InN an excellent candidate for sensing application. In this paper, the response of hydrogen sensors based on Mg-doped InN films (InN:Mg) grown by molecular beam epitaxy has been investigated. The sensor exhibits a resistance variation ratio of 16.8% with response/recovery times of less than 2 min under exposure to 2000 ppm H2/air at 125 °C, which is 60% higher in the magnitude of response than the one based on the as-grown InN film. Hall-effect measurement shows that the InN:Mg with suitable Mg doping level exhibits larger sheet resistance, which accords with buried p-type conduction in the InN bulk. This work shows the advantage of InN:Mg and signifies its potential for sensing application.

Direct evidence of recombination between electrons in InGaN quantum discs and holes in p-type GaN.

Intense emission from an InGaN quantum disc (QDisc) embedded in a GaN nanowire p-n junction is directly resolved by performing cathodoluminescence spectroscopy. The luminescence observed from the p-type GaN region is exclusively dominated by the emission at 380 nm, which has been usually reported as the emission from Mg induced impurity bands. Here, we confirm that the robust emission from 380 nm is actually not due to the Mg induced impurity bands, but rather due to being the recombination between electrons in the QDisc and holes in the p-type GaN. This identification helps to get a better understanding of the confused luminescence from nanowires with thin QDiscs embedded for fabricating electrically driven single photon emitters.

Investigations on Zr incorporation into Li3V2(PO4)3/C cathode materials for lithium ion batteries.

Li3V2(PO4)3/C (LVP/C) composites have been modified by different ways of Zr-incorporation via ultrasonic-assisted solid-state reaction. The difference in the effect on the physicochemical properties and the electrochemical performance of LVP between Zr-doping and ZrO2-coating has also been investigated. Compared with pristine LVP/C, Zr-incorporated LVP/C composites exhibit better rate capability and cycling stability. In particular, the LVP/C-Zr electrode delivers the highest initial capacity of 150.4 mA h g-1 at 10C with a capacity retention ratio of 88.4% after 100 cycles. The enhanced electrochemical performance of Zr-incorporated LVP/C samples (LVZrP/C and LVP/C-Zr) is attributed to the increased ionic conductivity and electronic conductivity, the improved stability of the LVP structure, and the decreased charge-transfer resistance.

Lattice-Polarity-Driven Epitaxy of Hexagonal Semiconductor Nanowires.

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires (NWs) is demonstrated on InN NWs. In-polarity InN NWs form typical hexagonal structure with pyramidal growth front, whereas N-polarity InN NWs slowly turn to the shape of hexagonal pyramid and then convert to an inverted pyramid growth, forming diagonal pyramids with flat surfaces and finally coalescence with each other. This contrary growth behavior driven by lattice-polarity is most likely due to the relatively lower growth rate of the (0001̅) plane, which results from the fact that the diffusion barriers of In and N adatoms on the (0001) plane (0.18 and 1.0 eV, respectively) are about 2-fold larger in magnitude than those on the (0001̅) plane (0.07 and 0.52 eV), as calculated by first-principles density functional theory (DFT). The formation of diagonal pyramids for the N-polarity hexagonal NWs affords a novel way to locate quantum dot in the kink position, suggesting a new recipe for the fabrication of dot-based devices.

Discovery of novel dihydrobenzofuran cyclopropane carboxylic acid based calcium sensing receptor antagonists for the treatment of osteoporosis.

In a search for novel small molecule calcium-sensing receptor (CaSR) antagonists as oral bone anabolic agents, we discovered dihydrobenzofuran cyclopropane carboxylic acid derivatives, such as 12f (IC50=27.6nM), are highly potent calcium-sensing receptor antagonists. Studies in rats established that compound 12f stimulates parathyroid hormone (PTH) release in a fast-acting, pulsatile manner.