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Among the iron-sulfur cluster assembly proteins encoded by gene cluster iscSUA-hscBA-fdx in Escherichia coli, IscA has a unique and strong iron binding activity and can provide iron for iron-sulfur cluster assembly in proteins in vitro. Deletion of IscA and its paralogue SufA results in an E. coli mutant that fails to assemble [4Fe-4S] clusters in proteins under aerobic conditions, suggesting that IscA has a crucial role for iron-sulfur cluster biogenesis. Here we report that among the iron-sulfur cluster assembly proteins, IscA also has a strong and specific binding activity for Cu(I) in vivo and in vitro. The Cu(I) center in IscA is stable and resistant to oxidation under aerobic conditions. Mutation of the conserved cysteine residues that are essential for the iron binding in IscA abolishes the copper binding activity, indicating that copper and iron may share the same binding site in the protein. Additional studies reveal that copper can compete with iron for the metal binding site in IscA and effectively inhibits the IscA-mediated [4Fe-4S] cluster assembly in E. coli cells. The results suggest that copper may not only attack the [4Fe-4S] clusters in dehydratases, but also block the [4Fe-4S] cluster assembly in proteins by targeting IscA in cells.

This paper presents an efficient double-layer ant colony algorithm, called DL-ACO, for autonomous robot navigation. This DL-ACO consists of two ant colony algorithms which run independently and successively. First, a parallel elite ant colony optimization (PEACO) method is proposed to generate an initial collision-free path in a complex map, and then we apply a path improvement algorithm called turning point optimization algorithm (TPOA), in which the initial path is optimized in terms of length, smoothness and safety. Besides, a piecewise B-spline path smoother is presented for easier tracking control of the mobile robot. Our method is tested by simulations and compared with other path planning algorithms. The results show that our method can generate better collision-free path efficiently and consistently, which demonstrates the effectiveness of the proposed algorithm. Furthermore, its performance is validated by experiments in indoor and outdoor environments.

While copper is an essential trace element in biology, pollution of groundwater from copper has become a threat to all living organisms. Cellular mechanisms underlying copper toxicity, however, are still not fully understood. Previous studies have shown that iron-sulfur proteins are among the primary targets of copper toxicity in Escherichia coli under aerobic conditions. Here, we report that, under anaerobic conditions, iron-sulfur proteins in E. coli cells are even more susceptible to copper in medium. Whereas addition of 0.2 mM copper(II) chloride to LB (Luria-Bertani) medium has very little or no effect on iron-sulfur proteins in wild-type E. coli cells under aerobic conditions, the same copper treatment largely inactivates iron-sulfur proteins by blocking iron-sulfur cluster biogenesis in the cells under anaerobic conditions. Importantly, proteins that do not have iron-sulfur clusters (e.g., fumarase C and cysteine desulfurase) in E. coli cells are not significantly affected by copper treatment under aerobic or anaerobic conditions, indicating that copper may specifically target iron-sulfur proteins in cells. Additional studies revealed that E. coli cells accumulate more intracellular copper under anaerobic conditions than under aerobic conditions and that the elevated copper content binds to the iron-sulfur cluster assembly proteins IscU and IscA, which effectively inhibits iron-sulfur cluster biogenesis. The results suggest that the copper-mediated inhibition of iron-sulfur proteins does not require oxygen and that iron-sulfur cluster biogenesis is the primary target of anaerobic copper toxicity in cells.IMPORTANCE Copper contamination in groundwater has become a threat to all living organisms. However, cellular mechanisms underlying copper toxicity have not been fully understood up to now. The work described here reveals that iron-sulfur proteins in Escherichia coli cells are much more susceptible to copper in medium under anaerobic conditions than they are under aerobic conditions. Under anaerobic conditions, E. coli cells accumulate excess intracellular copper, which specifically targets iron-sulfur proteins by blocking iron-sulfur cluster biogenesis. Since iron-sulfur proteins are involved in diverse and vital physiological processes, inhibition of ironsulfur cluster biogenesis by copper disrupts multiple cellular functions and ultimately inhibits cell growth. The results from this study illustrate a new interplay between intracellular copper toxicity and iron-sulfur cluster biogenesis in bacterial cells under anaerobic conditions.

In underwater acoustic (UWA) communications, Doppler estimation is one of the major stages in a receiver. Two Doppler estimation methods are often used: cross-ambiguity function (CAF) method and single-branch autocorrelation (SBA) method. The former results in accurate estimation but with a high complexity, whereas the latter is less complicated but also less accurate. In this paper, we propose and investigate a multi-branch autocorrelation (MBA) Doppler estimation method. The proposed method can be used in communication systems with periodically transmitted pilot signals or repetitive data transmission. For comparison of the Doppler estimation methods, we investigate an OFDM communication system in multiple dynamic scenarios using the Waymark simulator, allowing virtual underwater acoustic signal transmission between moving transmitter and receiver. For the comparison, we also use the OFDM signals recorded in a sea trial. The comparison shows that the receiver with the proposed MBA Doppler estimation method outperforms the receiver with the SBA method and its detection performance is close to that of the receiver with the CAF method, but with a significantly lower complexity.

Underwater acoustic (UWA) communication channels are characterized by the spreading of received signals in space (direction of arrival) and in time (delay). The spread is often limited to a small number of space-time clusters. In this paper, the spacetime clustering is exploited in a proposed receiver designed for guard-free orthogonal frequency-division multiplexing (OFDM) with superimposed data and pilot signals. For separation of space clusters, the receiver utilizes a vertical linear array (VLA) of hydrophones, whereas for combining delay-spread signals within a space cluster, a time-domain equalizer is used. We compare a number of space-time processing techniques, including a proposed reduced-complexity spatial filter, and show that techniques exploiting the space-time clustering demonstrate an improved detection performance. The comparison is done using signals transmitted by a moving transducer, and recorded on a 14-element non-uniform VLA in sea trials at distances of 46 km and 105 km. Index Terms OFDM, spatial filter, underwater acoustic communications, vertical linear array I. INTRODUCTION In underwater acoustic (UWA) communication channels, received signals are spread in angle and delay of arrival [1]. In many communication scenarios, e.g., in deep-water channels, the spreading is concentrated around a few specific directions of arrival (DoA) and delays [2]-[6]. We refer to this phenomenon as space-time clustering, and exploit it to improve the detection performance and reduce the complexity of a receiver. The receiver that we consider here utilizes a vertical linear array (VLA) of hydrophones. To improve the detection performance, an efficient way is to combine signals from multiple diversity branches [7], e.g., from the antenna array elements. The joint spatial diversity and equalization when applied directly to signals at the antenna elements can provide significant improvement in the performance compared to the single-branch detection [5], [8]-[11]. However, such combining requires a large number of parameters to be estimated, thus often resulting in numerical instability [12]. Moreover, with combining applied directly to antenna elements, a large number of elements is required to achieve a good bit error rate (BER) performance in scenarios with a low signal-to-noise ratio (SNR). In such receivers, the complexity can be high as it is proportional to the number of antenna elements [13]. A more numerically stable and computationally efficient approach

STUDY QUESTION To evaluate the impact of storage time after vitrification on embryo viability, pregnancy outcomes and neonatal outcomes. SUMMARY ANSWER The prolonged storage time of vitrified embryos negatively affected pregnancy outcomes, including biochemical pregnancy rate, clinical pregnancy and live birth rate; but did not influence neonatal outcomes. WHAT IS KNOWN ALREADY Although vitrification has been the fundamental tool of ART treatments in recent years, few studies have explored the influence of storage period after vitrification on embryonic and clinical outcomes. STUDY DESIGN, SIZE, DURATION A retrospective study was performed among 24 698 patients with the first vitrified embryo transfer following a freeze-all strategy during the period from January 2011 to December 2017. PARTICIPANTS/MATERIAL, SETTING, METHODS A total of 24 698 patients met the inclusion criteria and were grouped according to the storage time (11 330 patients in Group 1 with storage time <3 months, 9614 patients in Group 2 with storage time between 3 and 6 months, 3188 patients in Group 3 with storage time between 6 and 12 months and 566 in Group 4 with storage time between 12 and 24 months). The pregnancy outcomes and neonatal outcomes were compared between different storage time groups. Multivariate logistic regression and linear regression were performed to evaluate the independent effect of storage time on clinical outcomes, adjusting for important confounders. MAIN RESULTS AND THE ROLE OF CHANCE After adjustment for potential confounding factors, the chance of biochemical pregnancy (Group 1 as reference; Group 2: adjusted odds ratio (aOR) = 0.92, 95% CI 0.87–0.97; Group 3: aOR = 0.83, 95% CI 0.76–0.90; Group 4: aOR = 0.68, 95% CI 0.56–0.81), clinical pregnancy (Group 2: aOR = 0.91, 95% CI 0.86–0.96; Group 3: aOR = 0.80, 95% CI 0.73–0.87; Group 4: aOR = 0.65, 95% CI 0.54–0.79) and live birth (Group 2: aOR = 0.89, 95% CI 0.85–0.95; Group 3: aOR = 0.83, 95% CI 0.76–0.91; Group 4: aOR = 0.59, 95% CI 0.48–0.72) significantly decreased with the increasing storage time, whereas the relationship between miscarriage, ectopic pregnancy and storage time did not reach statistical significance. In addition, there was no evidence of differences in adverse neonatal outcomes (preterm birth, low birthweight, high birthweight, macrosomia or birth defects) between groups. LIMITATION, REASONS FOR CAUTION Our study was limited by the retrospective design from a single center, the conclusion from our study needs to be verified in further studies. WIDER IMPLICATIONS OF THE FINDINGS This study provides new findings about the relationship between prolonged storage time of vitrified embryos and clinical outcomes and offers evidence for the safety of using long-stored embryos after vitrification. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Natural Science Foundation of China (grant nos. 81903324, 81771533, 81571397, 81701523), National Key Research and Development Program of China (grant no. SQ2018YFC100163). None of the authors have any conflicts of interest to declare.

This paper studies the mean and mean-square behaviors of the M-estimate based normalized subband adaptive filter algorithm (M-NSAF) with robustness against impulsive noise. Based on the contaminated-Gaussian noise model, the stability condition, transient and steady-state results for the algorithm are formulated analytically. The analysis results help us to better understand the M-NSAF performance in impulsive noise. To further obtain fast convergence and low steady-state estimation error, we derive a variable step size (VSS) M-NSAF algorithm. This VSS scheme is also generalized to proportionate M-NSAF variant for sparse systems. Computer simulations on system identification in impulsive noise and acoustic echo cancellation with double-talk are performed to demonstrate our theoretical analysis and the effectiveness of the proposed algorithms.