With the help of quantum key distribution (QKD), two distant peers are able to share information-theoretical secure key bits. Increasing the key rate is ultimately significant for the applications of ...QKD in the lossy channel. However, it has been proven that there is a fundamental rate-distance limit, called the linear bound, which restricts the performance of all existing repeaterless protocols and realizations. Surprisingly, a recently proposed protocol, called twin-field (TF) QKD, can beat the linear bound with no need for quantum repeaters. Here, we present one of the first implementations of the TF-QKD protocol and demonstrate its advantage of beating the linear bound at a channel distance of 300 km. In our experiment, a modified TF-QKD protocol that does not assume phase postselection is considered, and thus a higher key rate than the original one is expected. After controlling the phase evolution of the twin fields traveling through hundreds of kilometers of optical fibers, the implemented system achieves high-visibility single-photon interference and allows stable and high-rate measurement-device-independent QKD. Our experimental demonstration and results confirm the feasibility of the TF-QKD protocol and its prominent superiority in long-distance key distribution services.
PFASs are widely distributed in natural and living environment and can enter human bodies via different routes. Many studies have reported that PFASs may be associated with human diseases, such as ...urine acid and thyroid diseases. In this study, we reviewed PFAS levels in human bodies reported in past seven years, including blood, urine, milk, and tissues (hair and nails). Most studies focused on human blood. Blood type, spatiality, human age, and gender were found to have a strong relationship with PFAS levels in blood samples. The PFAS distribution in urine samples was reported to be associated with the chain length of PFASs and human gender. Urinary excretion was found to be an important pathway of PFAS elimination. PFAS levels in human milk might be affected by various factors, such as mothers' age, dietary habit, parity of mothers and the interval of interpregnancy. Data in hair and nails remain very limited, but these matrices offer a non-invasive approach to evaluate human exposure to PFASs.
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•PFOS and PFOA were predominant in human blood and milk.•Urine showed higher elimination of short-chain PFASs than other matrices.•PFASs in blood and urine were found to be related to age and gender.•PFASs in human milk were associated with mothers' age and parity.
Divergent enantioselective total syntheses of five naturally occurring post‐iboga indole alkaloids, dippinine B and C, 10,11‐demethoxychippiine, 3‐O‐methyl‐10,11‐demethoxychippiine, and ...3‐hydroxy‐3,4‐secocoronaridine, as well as the two analogues 11‐demethoxydippinine A and D, are presented for the first time. The enantioenriched aza3.3.1‐bridged cycle, a common core intermediate to the target molecules, was constructed through an asymmetric phase‐transfer‐catalyzed Michael/aldol cascade reaction. The challenging azepane ring fused around the indole ring and the 3.3.1‐bridged cycle were installed through an intramolecular SN2′‐type reaction. These cyclization strategies enabled rapid construction of the 6.5.6.6.7‐pentacyclic core at an early stage. Highlights of the late‐stage synthetic steps include a Pd‐catalyzed Stille coupling and a highly stereoselective catalyst‐controlled hydrogenation to incorporate the side chain at C20 with both R and S configurations in the natural products.
Enantioselective total syntheses of post‐iboga indole alkaloids were achieved in a divergent manner. The construction of the 6.5.6.6.7‐pentacyclic core included an asymmetric Michael/aldol cascade reaction for installing the aza3.3.1‐bridged cycle and an intramolecular SN2′‐type reaction for assembling the azepane ring. The stereoselective incorporation of the side chain involved a Pd‐catalyzed Stille coupling and a catalyst‐controlled hydrogenation.
Quantum key distribution (QKD) provides a promising solution for sharing information-theoretic secure keys between remote peers with physics-based protocols. According to the law of quantum physics, ...the photons carrying signals cannot be amplified or relayed via classical optical techniques to maintain quantum security. As a result, the transmission loss of the channel limits its achievable distance, and this has been a huge barrier towards building large-scale quantum-secure networks. Here we present an experimental QKD system that could tolerate a channel loss beyond 140 dB and obtain a secure distance of 833.8 km, setting a new record for fibre-based QKD. Furthermore, the optimized four-phase twin-field protocol and high-quality set-up make its secure key rate more than two orders of magnitude greater than previous records over similar distances. Our results mark a breakthrough towards building reliable and efficient terrestrial quantum-secure networks over a scale of 1,000 km.Twin-field (TF) quantum key distribution (QKD) over a secure distance of 833.8 km is demonstrated even in the finite-size regime. To this end, an optimized four-phase TF-QKD protocol and a high-speed low-noise TF-QKD system are developed.
The paper studies a distributed constrained optimization problem, where multiple agents connected in a network collectively minimize the sum of individual objective functions subject to a global ...constraint being an intersection of the local constraints assigned to the agents. Based on the augmented Lagrange method, a distributed primal–dual algorithm with a projection operation included is proposed to solve the problem. It is shown that with appropriately chosen constant step size, the local estimates derived at all agents asymptotically reach a consensus at an optimal solution. In addition, the value of the cost function at the time-averaged estimate converges with rate O(1k) to the optimal value for the unconstrained problem. By these properties, the proposed primal–dual algorithm is distinguished from the existing algorithms for distributed constrained optimization. The theoretical analysis is justified by numerical simulations.
The round-robin-differential-phase-shift (RRDPS) quantum key distribution (QKD) protocol has attracted intensive study due to its distinct security characteristics; e.g., information leakage is ...bounded without learning the error rate of key bits. Nevertheless, its practicality and performance are still not satisfactory. Here, by observing the phase randomization of the encoding states and its connection with eavesdropper's attack, we develop an improved bound on information leakage. Interestingly, our theory is especially useful for implementations with short trains of pulses, and running without monitoring signal disturbance is still available. As a result, the practicality and performance of RRDPS are improved. Furthermore, we realize a proof-of-principle experiment with up to 140 km of fiber, which has been the longest achievable distance of RRDPS until now, whereas the original theory predicted that no secret key could be generated in our experiment. Our results will help in bringing practical RRDPS closer to practical implementations.
A motor imagery EEG (MI-EEG) signal is often selected as the driving signal in an active brain computer interface (BCI) system, and it has been a popular field to recognize MI-EEG images via ...convolutional neural network (CNN), which poses a potential problem for maintaining the integrity of the time-frequency-space information in MI-EEG images and exploring the feature fusion mechanism in the CNN. However, information is excessively compressed in the present MI-EEG image, and the sequential CNN is unfavorable for the comprehensive utilization of local features. In this paper, a multidimensional MI-EEG imaging method is proposed, which is based on time-frequency analysis and the Clough-Tocher (CT) interpolation algorithm. The time-frequency matrix of each electrode is generated via continuous wavelet transform (WT), and the relevant section of frequency is extracted and divided into nine submatrices, the longitudinal sums and lengths of which are calculated along the directions of frequency and time successively to produce a 3 × 3 feature matrix for each electrode. Then, feature matrix of each electrode is interpolated to coincide with their corresponding coordinates, thereby yielding a WT-based multidimensional image, called WTMI. Meanwhile, a multilevel and multiscale feature fusion convolutional neural network (MLMSFFCNN) is designed for WTMI, which has dense information, low signal-to-noise ratio, and strong spatial distribution. Extensive experiments are conducted on the BCI Competition IV 2a and 2b datasets, and accuracies of 92.95% and 97.03% are yielded based on 10-fold cross-validation, respectively, which exceed those of the state-of-the-art imaging methods. The kappa values and p values demonstrate that our method has lower class skew and error costs. The experimental results demonstrate that WTMI can fully represent the time-frequency-space features of MI-EEG and that MLMSFFCNN is beneficial for improving the collection of multiscale features and the fusion recognition of general and abstract features for WTMI.
Graphical abstract
An efficient method for the synthesis of 1-hydroxy-2,5-dihydrophosphole 1-oxides, a type of five-membered P-containing heterocyclic compound, is presented. The reaction was carried out through a ...4C+1P cyclization of 1,3-dienes with a combination of PBr3 and P(OMe)3 as the P(III) source. To compare with the reported methods, the protocol reported herein not only is much milder and more rapid but also displays a broad substrate scope and affords the products in high yields (50–94%). In addition, the reaction could be reliably scaled up at the gram-scale level and was demonstrated to be a versatile platform for flexible derivatization. Consequently, this method provides a general and reliable way for the synthesis of five-membered phosphole derivatives.
Two-dimensional transition metal dichalcogenide nanoribbons are touted as the future extreme device downscaling for advanced logic and memory devices but remain a formidable synthetic challenge. ...Here, we demonstrate a ledge-directed epitaxy (LDE) of dense arrays of continuous, self-aligned, monolayer and single-crystalline MoS
nanoribbons on β-gallium (III) oxide (β-Ga
O
) (100) substrates. LDE MoS
nanoribbons have spatial uniformity over a long range and transport characteristics on par with those seen in exfoliated benchmarks. Prototype MoS
-nanoribbon-based field-effect transistors exhibit high on/off ratios of 10
and an averaged room temperature electron mobility of 65 cm
V
s
. The MoS
nanoribbons can be readily transferred to arbitrary substrates while the underlying β-Ga
O
can be reused after mechanical exfoliation. We further demonstrate LDE as a versatile epitaxy platform for the growth of p-type WSe
nanoribbons and lateral heterostructures made of p-WSe
and n-MoS
nanoribbons for futuristic electronics applications.
We present the first asymmetric total synthesis and absolute configuration determination of (+)‐tronocarpine. The 6.5.7.6.6 pentacyclic core was constructed at an early stage by using a sequential ...cyclization strategy through a newly developed catalytic asymmetric Michael/aldol cascade to build the aza3.3.1‐bridged cycle and a tandem reduction/hemiamidation procedure to assemble the seven‐membered lactam. The side‐chain functionalities were incorporated at a late stage by several appropriately orchestrated manipulations under mild conditions. The synthesis of enantiomerically pure (+)‐tronocarpine was achieved through a 20‐step longest linear sequence from tryptamine.
Bright and early: The 6.5.7.6.6 pentacyclic core was constructed at an early stage of the synthesis of tronocarpine (see scheme; NPhth=phthalimido) by using a newly devised catalytic asymmetric Michael/aldol cascade to build the aza3.3.1‐bridged ring system and a tandem reduction/hemiamidation procedure to assemble the seven‐membered lactam. Other functionalities were incorporated at a later stage under mild conditions.
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