Joint equalization and decoding with per-survivor processing based on super-trellis in time-varying underwater acoustic channels.

This Letter proposes a low-complexity joint equalization and decoding reception scheme based on super-trellis per-survivor processing, making it possible to apply maximum likelihood sequence estimation in high-order underwater acoustic communications under fast time-varying channels. The technique combines trellis-coded modulation states and intersymbol interference states and uses per-survivor processing to track channel parameters. Furthermore, a general trellis configuration for arbitrary order quadrature amplitude modulation signal is provided when truncate the channel is used to describe the intersymbol interference state to 1. Sea trials results show that the performance of proposed method can be more than 1.4 dB superiority than conventional schemes.

Comments on "Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding".

In a recent communication (Angew. Chem. Int. Ed. 2024, 63, e202317312), Kalita et al. studied In4H+ system within the frame of single-reference approximation (SRA) and found that the global energy minimum (1 a) adopted the singlet state and a planar tetracoordinate hydrogen (ptH), while the second lowest isomer (1 b) located 3.0 kcal/mol above 1 a and adopted the triplet state as well as non-planar structure with a quasi-ptH. They assessed the reliability of SRA by checking the T1-diagnostic values of coupled cluster calculations. However, according to our multi-configurational second-order perturbation theory calculations at the CASPT2(12,13)/aug-cc-pVQZ (aug-cc-pVQZ-PP for In) level, both 1 a and 1 b exhibit obvious multi-referential characters, as reflected by their largest reference coefficients of 0.928 (86.1 %) and 0.938 (88.0 %), respectively. Moreover, 1 b is 5.05 kcal/mol lower than 1 a at this level, that is, what can be observed in In4H+ system is the quasi-ptH.

CBe4H6: a molecular rotor with a built-in on-off switch.

It is highly challenging to control (stop and resume as needed) molecular rotors because their intramolecular rotations are electronically enabled by delocalized σ bonding, and the desired control needs to be able to destroy and restore such σ bonding, which usually means difficult chemical manipulation (substitution or doping atom). In this work, we report CBe4H6, a molecular rotor that can be controlled independently of chemical manipulation. This molecule exhibited the uninterrupted free rotation of Be and H atoms around the central carbon in first-principles molecular dynamics simulations at high temperatures (600 and 1000 K), but the rotation cannot be witnessed in the simulation at room temperature (298 K). Specifically, when a C-H bond in the CBe4H6 molecule adopts the equatorial configuration at 298 K, it destroys the central delocalized σ bonding and blocks the intramolecular rotation (the rotor is turned "OFF"); when it can adopt the axial configuration at 600 and 1000 K, the central delocalized σ bonding can be restored and the intramolecular rotation can be resumed (the rotor is turned "ON"). Neutral CBe4H6 is thermodynamically favorable and electronically stable, as reflected by a wide HOMO-LUMO gap of 7.99 eV, a high vertical detachment energy of 9.79 eV, and a positive electron affinity of 0.24 eV, so it may be stable enough for the synthesis, not only in the gas phase, but also in the condensed phase.

Tetracoordinate or tricoordinate? Planar tetracoordinate nitrogen in the NBe4H4- cluster stabilized by multicenter bonds.

Realization of planar tetracoordinate arrangements of nitrogen atoms is challenging because their preference for localized bonding (caused by its high electronegativity) makes them typically tricoordinate. This is especially true for the more electronegative oxygen atoms. Herein, we computationally designed two clusters NBe4H4- and OBe4H4; they contain a planar tetracoordinate nitrogen (ptN) and planar tetracoordinate oxygen (ptO) atom, respectively. Remarkably, the former is a dynamically stable global minimum, while the latter is not. The bonding analysis proves that planar tetracoordination in NBe4H4- favors over tricoordination because of the presence of multicenter delocalized bonds. In contrast, the planar tricoordination dominates due to its weak delocalized bonding ability of oxygen in the OBe4H4 cluster. Moreover, the 6σ/2π double aromaticity due to multicenter delocalized bonds allows the NBe4H4- cluster to obtain additional stability. This cluster is a promising synthetic due its dynamic and thermodynamic stability.

CB4Se5: a planar tetracoordinate carbon CB4 core stabilized by peripheral Se/Se2 bridges.

Replacing one of the peripheral Se with a Se2 bridge is an effective strategy to flatten the C4v CB4Se4 cluster. The global minimum of CB4Se5 contains one fan-shaped planar tetracoordinate carbon (ptC) CB4 core, possessing double 2π + 6σ aromaticity. The peripheral Se2 bridge is dexterous and crucial for the stability of CB4Se5.

Rapid Adaptation for Active Pantograph Control in High-Speed Railway via Deep Meta Reinforcement Learning.

Active pantograph control is the most promising technique for reducing contact force (CF) fluctuation and improving the train's current collection quality. Existing solutions, however, suffer from two significant limitations: 1) they are incapable of dealing with the various pantograph types, catenary line operating conditions, changing operating speeds, and contingencies well and 2) it is challenging to implement in practical systems due to the lack of rapid adaptability to a new pantograph-catenary system (PCS) operating conditions and environmental disturbances. In this work, we alleviate these problems by developing a revolutionary context-based deep meta-reinforcement learning (CB-DMRL) algorithm. The proposed CB-DMRL algorithm combines Bayesian optimization (BO) with deep reinforcement learning (DRL), allowing the general agent to adapt to new tasks quickly and efficiently. We evaluated the CB-DMRL algorithm's performance on a proven PCS model. The experimental results demonstrate that meta-training DRL policies with latent space swiftly adapt to new operating conditions and unknown perturbations. The meta-agent adapts quickly after two iterations with a high reward, which require only ten spans, approximately equal to 0.5 km of PCS interaction data. Compared with state-of-the-art DRL algorithms and traditional solutions, the proposed method can promptly traverse scenario changes and reduce CF fluctuations, resulting in an excellent performance.

Dynamic evolution and impact mechanism of human capital mismatch in strategic emerging industries: Evidence from the Yangtze River Delta region of China.

China's "demographic dividend" has gradually disappeared since 2013, but the problem of human capital mismatch prevails in various industries and sectors, and improving human capital mismatch and optimizing the allocation of human capital has become an important measure for high-quality economic development. This study uses panel data at the provincial level in the Yangtze River Delta region from 2012 to 2021 and employs spatial econometric models to quantitatively analyze the index of human capital mismatch, the impact mechanism, and spatial interaction effects in strategic emerging industries. The results show that the spatial agglomeration and dependence of human capital mismatch decreased in the Yangtze River Delta region, and the index of human capital mismatch in strategic emerging industries is generally insufficient. The shortage of talent supply within industries is particularly severe in high-end equipment manufacturing and biotechnology industries. Second, fiscal subsidies have exacerbated human capital mismatches in both local and neighboring areas, with significant spatial spillover effects. Urbanization has exacerbated local human capital mismatches but has improved the degree of human capital mismatch in neighboring areas. The index of industrial structural adjustment is generally conducive to alleviating human capital mismatches. Distorted markets and financial levels have accelerated human capital mismatches by distorting the efficiency of human capital allocation. Third, regional heterogeneity significantly influences the spatial interaction effects of human capital mismatches. This study contributes to improving the situation of human capital mismatch in strategic emerging industries in the Yangtze River Delta and provides theoretical and policy recommendations for local governments.

[(OB)2-M©B7O7-BO]- (M = Mn, Tc, Re): Chemically Stable and Triply Aromatic Ballet Rotors.

Single-molecule nanorotors are generally constructed based on boron atoms to obtain structural fluxionality via possessing the delocalized multicenter bonds. However, the electron-deficient boron atoms are commonly exposed in these nanorotors, which leads to extremely high chemical reactivity, which blocks the synthesis in the condensed phase. In this work, we computationally designed a series of transition-metal-doped boron oxide clusters MB10O10- (in structural configuration of [(OB)2-M©B7O7-BO]-, M = Mn, Tc, Re, © means "centered" in a planar or quasi-planar hypercoordinate environment), which can be vividly named as "ballet rotors" to label their anthropomorphic dynamic rotational behaviors. The rotational fluxionality in ballet rotors originates from the completely delocalized nature of the bonding within their MB10 core moieties. Remarkably, compared with single-molecule nanorotors having bare boron atoms and the narrow HOMO-LUMO gaps (≤4.00 eV) as well as low vertical detachment energies (VDEs, ≤4.46 eV for anions), the ballet rotors possess significantly improved chemical stability, as evidenced sterically by the absence of exposed boron atoms and electronically by much wider HOMO-LUMO gaps (5.66-5.98 eV) as well as obviously higher VDEs between 5.36 and 5.47 eV. Specifically, the ballet rotors are mainly stabilized by the delicately placed peripheral oxygen atoms, which can compensate for all electron-deficient boron atoms via O → B π back bonds and sterically protect them. Simultaneously, they are additionally stabilized by aromatic stabilization effect from possessing the novel S + P + D triple aromaticity. We expect that the proposal of chemically stable ballet rotors in this work can arouse the rational design of nanorotors for experimental realization in the condensed phase.

Expectation-maximization vector approximate message passing-based frequency-domain turbo equalization for underwater acoustic communications.

Channel equalization plays a crucial role in single-carrier underwater acoustic (UWA) communications. Recently, a frequency-domain turbo equalization (FDTE) scheme enabled by the vector approximate message passing (VAMP) algorithm, was proposed, and it outperformed classic linear minimum mean square error FDTE at acceptable complexity cost. The operation of the VAMP-FDTE requires knowledge of noise power, which is predetermined before the equalization starts. In practice, however, it is difficult to obtain prior knowledge of noise power due to factors of unknown channel estimation errors and dynamic underwater environments. Motivated by this fact, we propose an enhanced VAMP-FDTE scheme, which learns the noise power knowledge during the equalization process via the expectation-maximization (EM) algorithm. The EM-based noise power estimation makes use of intermediate results of the VAMP-FDTE and, thus, only incurs a small extra computational overhead. The improved VAMP-FDTE, named EM-VAMP-FDTE, was tested by experimental data collected in shallow-sea horizontal UWA communication trials with MIMO configuration. It showed better performance than the existing VAMP-FDTE scheme, attributed to the online noise power learning.

Planar Hexacoordinate Beryllium: Covalent Bonding Between s-block Metals.

Achieving a planar hypercoordinate arrangement of s-block metals through covalent bonding with ligands is challenging due to the strong ionicity involved. Herein, we report the first case of a neutral binary global minimum containing a planar hexacoordinate beryllium atom. The central Be atom is coordinated by six active Be atoms, the latter in turn are enclosed by an equal number of more electronegative chlorine atoms in the periphery, forming a star-like phBe cluster (Be©Be6 Cl6 ). Importantly, the cluster exhibits dynamically stabilized stemming geometrically from the appropriate matching of metal-ligand size and electronically from adherence to the octet rule as well as possessing a 6σ/2π double aromaticity. Remarkably, energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) analysis reveals a significant covalent interaction between the ligand and the central metal beryllium atoms, a fact further supported by a large Wiberg bond index. This cluster is a promising synthetic as its excellent electronic, dynamic and thermodynamic stability.

Rumen bacterial cluster identification and its influence on rumen metabolites and growth performance of young goats.

Enterotypes, which are defined as bacterial clusters in the gut microbiome, have been found to have a close relationship to host metabolism and health. However, this concept has never been used in the rumen, and little is known about the complex biological relationships between ruminants and their rumen bacterial clusters. In this study, we used young goats (n = 99) as a model, fed them the same diet, and analyzed their rumen microbiome and corresponding bacterial clusters. The relationships between the bacterial clusters and rumen fermentation and growth performance in the goats were further investigated. Two bacterial clusters were identified in all goats: the P-cluster (dominated by genus Prevotella, n = 38) and R-cluster (dominated by Ruminococcus, n = 61). Compared with P-cluster goats, R-cluster goats had greater growth rates, concentrations of propionate, butyrate, and 18 free amino acids¸ and proportion of unsaturated fatty acids, but lower acetate molar percentage, acetate to propionate ratio, and several odd and branched chain and saturated fatty acids in rumen fluid (P < 0.05). Several members of Firmicutes, including Ruminococcus, Oscillospiraceae NK4A214 group, and Christensenellaceae R-7 group were significantly higher in the R-cluster, whereas Prevotellaceae members, such as Prevotella and Prevotellaceae UCG-003, were significantly higher in P-cluster (P < 0.01). Co-occurrence networks showed that R-cluster enriched bacteria had significant negative correlations with P-cluster enriched bacteria (P < 0.05). Moreover, we found the concentrations of propionate, butyrate and free amino acids, and the proportions of unsaturated fatty acids were positively correlated with R-cluster enriched bacteria (P < 0.05). The concentrations of acetate, acetate to propionate ratio, and the proportion of odd and branched chain and saturated fatty acids were positively correlated with P-cluster enriched bacteria (P < 0.05). Overall, our results indicated that rumen bacterial clusters can influence rumen fermentation and growth performance of young goats, which may shed light on modulating the rumen microbiome in early life to improve the growth performance of ruminant animals.

[Cs©C18]+ and [Na©C14]+: perfect planar alkaline-metal-centered polyynic cyclo[n]carbon complexes with record coordination numbers.

Searching for the maximum coordination number (CN) in planar species with novel bonding patterns has fascinated chemists for many years. Using the experimentally observed polyynic cyclo[18]carbon D9h C18 and theoretically predicted polyynic cyclo[14]carbon D7h C14 as effective ligands and based on extensive first-principles theory calculations, we predict herein their perfect planar alkaline-metal-centered complexes D9h Cs©C18+ (1) and D7h Na©C14+ (4) which as the global minima of the systems possess the record coordination numbers of CN = 18 and 14 in planar polyynic species, respectively. More interestingly, detailed energy decomposition and adaptive natural density partitioning bonding analyses indicate that the hypercoordinate alkaline-metal centers in these complexes exhibit obvious transition metal behaviors, with effective in-plane (π-6s)σ, (π-7p)σ, and (π-5d)σ coordination bonds formed in Cs©C18+ (1) and (π-3s)σ, (π-3p)σ, and (π-3d)σ coordination interactions fabricated in Na©C14+ (4) to dominate the overall attractive interactions between the metal center and its cyclo[n]carbon ligand. Similarly, alkaline-metal-centered planar Cs Cs©C17B (2), C2v Cs©C17- (3), C2v Na©C13B (5), and C2v Na©C13- (6) have also been obtained with CN = 18, 17, 14, and 13, respectively.

[Sc©[3]CPP]+: A Viable Metal-Centered [3]Cycloparaphenylene.

[n]Cycloparaphenylenes ([n]CPPs, n denotes the number of phenyl groups) are difficult to synthesize because of the strain related to their bent phenyl rings. In particular, the strain in [3]CPP is high enough to destroy the π electron delocalization, leading to the spontaneous structural transition to an energetically more stable "bond-shift" (BS) isomer ([3]BS). In this contribution, we propose to achieve [3]CPP by enhancing the π electron delocalization through hosting a guest metal atom. Our computations revealed that Sc could stabilize [3]CPP by forming the [Sc©[3]CPP]+ complex through the favorable π-Sc donation-backdonation interactions. Thermodynamically, the binding energy between the Sc atom and [3]CPP was -205.7 kcal/mol, which could well compensate not only the energy difference of 44.2 kcal/mol between [3]CPP and [3]BS but also the extremely high strain energy of 170.3 kcal/mol in [3]CPP. Simultaneously, the [Sc©[3]CPP]+ complex is stable up to 1500 K in dynamic simulations, suggesting its high viability in the synthesis.

Probabilistic constellation shaping-aided underwater acoustic communication with vector approximate message passing iterative equalization.

A probabilistic constellation shaping (PCS)-aided single-carrier transceiver is proposed to improve spectral efficiency for underwater acoustic (UWA) communications. At the transmitter, the information bits are input into a distribution matcher followed by a systematic binary encoder, which yields a sequence of sign bits with a uniform distribution and a sequence of amplitude bits with a non-uniform distribution. Based on these two sequences, the PCS is then realized by mapping coded bits onto a quadrature amplitude modulation constellation. At the receiver, an improved frequency-domain turbo equalizer based on the vector approximate message passing (VAMP) is proposed for the PCS-UWA communication system to eliminate the multipath interference. It exploits the a priori symbol probability information benefiting from the PCS at the beginning of the turbo iteration and over the self-iteration of the VAMP soft equalizer, improving the symbol detection performance. Finally, the first experimental demonstration of a deep-sea PCS-UWA communication system and numerical simulation of shallower water are presented. The experimental results reveal the PCS-UWA communication system significantly outperforms traditional systems with no PCS. Also, the proposed receiver is superior to the classical adaptive turbo equalizer based on the improved proportionate normalized least mean square algorithm even with data reuse.

How hexafluoroisopropanol solvent promotes Diels-Alder cycloadditions: ab initio metadynamics simulations.

The solvent effects in Diels-Alder cycloadditions were studied by using ab initio molecular dynamics simulations with explicit molecular treatments for both substrates and solvents. Energy decomposition analysis was used to investigate the role of H-bonding networks of hexafluoroisopropanol solvent in promoting both reactivity and regioselectivity.

NAl4X4 + (X = S, Se, Te): Clusters with a planar tetracoordinate nitrogen and significantly improved stability.

The design of clusters featuring non-classical planar hypercoordinate atoms (phAs) often depends on the delocalized multicenter bonds involving reactive electron-deficient elements, which both destabilize the clusters and lead to difficulty in achieving the phA arrangement for electronegative elements such as nitrogen due to their preference for localized bonds. In this work, we computationally designed a series of aluminum chalcogenide clusters NAl4X4 + (X = S, Se, Te) with a desired planar tetracoordinate nitrogen and meaningfully improved chemical stability, as evidenced by the wide gaps (6.51-7.23 eV) between their highest occupied molecular orbitals and lowest unoccupied molecular orbitals, high molecular rigidity (dynamically stable up to 1500 K), and exclusively low global energy minima nature (their isomers locate at least 51.2 kcal/mol higher). Remarkably, these clusters are stabilized by peripheral chalcogen atoms, which not only sterically protect the NAl4 core moiety but also electronically compensate for the electron-deficient aluminum atoms via X → Al π back bonds, meeting the description of our recently proposed "electron-compensation" strategy.

3-D molecular stars with covalent axial bonding.

In designing three-dimensional (3-D) molecular stars, it is very difficult to enhance the molecular rigidity through forming the covalent bonds between the axial and equatorial groups because corresponding axial groups will generally break the delocalized π bond over equatorial frameworks and thus break their star-like arrangement. In this work, exemplified by designing the 3-D stars Be2 ©Be5 E5 + (E = Au, Cl, Br, I) with three delocalized σ bonds and delocalized π bond over the central Be2 ©Be5 moiety, we propose that the desired covalent bonding can be achieved by forming the delocalized σ bond(s) and delocalized π bond(s) simultaneously between the axial groups and equatorial framework. The covalency and rigidity of axial bonding can be demonstrated by the total Wiberg bond indices of 1.46-1.65 for axial Be atoms and ultrashort Be-Be distances of 1.834-1.841 Å, respectively. Beneficial also from the σ and π double aromaticity, these mono-cationic 3-D molecular stars are dynamically viable global energy minima with well-defined electronic structures, as reflected by wide HOMO-LUMO gaps (4.68-5.06 eV) and low electron affinities (4.70-4.82 eV), so they are the promising targets in the gas phase generation, mass-separation, and spectroscopic characterization.

Origins of Regioselectivity in CuH-Catalyzed Hydrofunctionalization of Alkenes.

Factors controlling the regioselectivity in alkene hydrocupration were computationally investigated using energy decomposition analysis. The results demonstrate that the Markovnikov-selective hydrocupration with electronically activated mono-substituted olefins is mostly affected by the destabilizing Pauli repulsion, which is due to the electron delocalization effect. The anti-Markovnikov-selective hydrocupration with 1,1-dialkyl-substituted terminal olefins is dominated by the repulsive electrostatic interactions, which is because of the unequal π electron distribution caused by the induction effect of alkyl substituents.

Ab Initio Metadynamics Simulations of Hexafluoroisopropanol Solvent Effects: Synergistic Role of Solvent H-Bonding Networks and Solvent-Solute C-H/π Interactions.

The solvent effects in Friedel-Crafts cycloalkylation of epoxides and Cope rearrangement of aldimines were investigated by using ab initio molecular dynamics simulations. Explicit molecular treatments were applied for both reactants and solvents. The reaction mechanisms were elucidated via free energy calculations based on metadynamics simulations. The results reveal that both reactions proceed in a concerted fashion. Key solvent-substrate interactions are identified from the structures of transition states with explicit solvent molecules. The remarkable promotion effect of hexafluoroisopropanol solvent is ascribed to the synergistic effect of H-bonding networks and C-H/π interactions with substrates.

Weak Electrostatic Interactions with Bisphosphine Ligands Facilitate Reductive Elimination of PhCF3 from Pd(II) Complexes.

The origins of ligand effects on PhCF3 reductive elimination from PdII complexes were computationally investigated by using energy decomposition analysis. The results indicate weak electrostatic interactions between ligands and Ph-Pd-CF3 lead to small barriers of PhCF3 reductive elimination. Two major factors affecting the electrostatic interactions are identified.