Transition Structure Research Articles

A novel design of transitional layer structure between reduced activation ferritic martensitic steels and tungsten for plasma facing materials

Plasma-facing components (PFCs) are among the most critical gaps for fusion energy to establish technical and economic feasibility. Tungsten as a first wall/blanket material in PFCs requires to be integrating with reduced activation ferritic martensitic (RAFM) steels as a structural component. Currently, major drawbacks are the requirement of brazing, the formation of a brittle interface, and a large difference between the coefficients of thermal expansion of tungsten and steel. Here, a novel transitional multilayer structure was designed and investigated to join tungsten and RAFM steels using three interlayers. The composition of each interlayer was selected based on computational thermodynamics and diffusion kinetics to ensure a body-centered cubic (bcc) single-phase structure and prevent the formation of a brittle intermetallic phase region in the temperature range of 600–1150 °C. Although the transitional layer structure was designed for additive manufacturing, spark plasma sintering (SPS) as proof of concept was used to bond the individual layers. Interfaces were investigated using scanning and transmission electron microscopy methods but no layered intermetallic phase was observed. Nanoindentation maps across the interface suggest major hardness differences at the interface between tungsten and the vanadium interlayer, as well as the interface between RAFM steel and the FeCrAl interlayer.

Structural Transformation by Crystal Engineering Endows Aqueous Zinc-Ion Batteries with Ultra-long Cyclability.

Manganese oxide is a promising cathode material for aqueous zinc batteries. However, its weak structural stability, low electrical conductivity, and sluggish reaction kinetics lead to rapid capacity fading. Herein, a crystal engineering strategy is proposed to construct a novel MnO2 cathode material. Both experimental results and theoretical calculations demonstrate that Al-doping plays a crucial role in phase transition and doping-superlattice structure construction, which stabilizes the structure of MnO2 cathode materials, improves conductivity, and accelerates ion diffusion dynamics. As a result, 1.98% Al-doping MnO2 (AlMO) cathode shows an incredible 15 000 cycle stability with a low capacity decay rate of 0.0014% per cycle at 4Ag-1 . Additionally, it provides superior specific capacity of 311.2mAhg-1 at 0.1Ag-1 and excellent rate performance (145.2mAhg-1 at 5.0Ag-1 ). To illustrate the potential of 1.98%AlMO to be applied in actual practice, flexible energy storage devices are fabricated and measured. These discoveries provide a new insight for structural transformation via crystal engineering, as well as a new avenue for the rational design of electrode material in other battery systems.

π‐π Catalysis Made Asymmetric—Enantiomerization Catalysis Mediated by the Chiral π‐System of a Perylene Bisimide Cyclophane

AbstractEnzymes actuate catalysis through a combination of transition state stabilization and ground state destabilization, inducing enantioselectivity through chiral binding sites. Here, we present a supramolecular model system which employs these basic principles to catalyze the enantiomerization of [5]helicene. Catalysis is hereby mediated not through a network of functional groups but through π‐π catalysis exerted from the curved aromatic framework of a chiral perylene bisimide (PBI) cyclophane offering a binding pocket that is intricately complementary with the enantiomerization transition structure. Although transition state stabilization originates simply from dispersion and electrostatic interactions, enantiomerization kinetics are accelerated by a factor of ca. 700 at 295 K. Comparison with the meso‐congener of the catalytically active cyclophane shows that upon configurational inversion in only one PBI moiety the catalytic effect is lost, highlighting the importance of precise transition structure recognition in supramolecular enzyme mimics.

π-π Catalysis Made Asymmetric-Enantiomerization Catalysis Mediated by the Chiral π-System of a Perylene Bisimide Cyclophane.

Enzymes actuate catalysis through a combination of transition state stabilization and ground state destabilization, inducing enantioselectivity through chiral binding sites. Here, we present a supramolecular model system which employs these basic principles to catalyze the enantiomerization of [5]helicene. Catalysis is hereby mediated not through a network of functional groups but through π-π catalysis exerted from the curved aromatic framework of a chiral perylene bisimide (PBI) cyclophane offering a binding pocket that is intricately complementary with the enantiomerization transition structure. Although transition state stabilization originates simply from dispersion and electrostatic interactions, enantiomerization kinetics are accelerated by a factor of ca. 700 at 295 K. Comparison with the meso-congener of the catalytically active cyclophane shows that upon configurational inversion in only one PBI moiety the catalytic effect is lost, highlighting the importance of precise transition structure recognition in supramolecular enzyme mimics.

Intransitivity as a dynamic assembly engine of competitive communities

Historically, those ecological communities thought to be dominated by competitive interactions among their component species have been assumed to exhibit transitive competition, that is, a hierarchy of competitive strength from most dominant to most submissive. A surge of recent literature takes issue with this assumption and notes that some species in some communities are intransitive, where a rock/scissors/paper arrangement characterizes some components of some communities. We here propose a merging of these two ideas, wherein an intransitive subgroup of species connects with a distinct subcomponent that is organized hierarchically, such that the expected eventual takeover by the dominant competitor in the hierarchy is thwarted, and the entire community can be sustained. This means that the combination of transitive and intransitive structures can maintain many species even when competition is strong. Here, we develop this theoretical framework using a simple variant on the Lotka-Volterra competition equations to illustrate the process. We also present data for the ant community in a coffee agroecosystem in Puerto Rico, that appears to be organized in this way. A detailed study on one typical coffee farm illustrates an intransitive loop of three species that seems to maintain a distinct competitive community of at least 13 additional species.

Synthesis and Structure of P-Halogenated Benzazaphospholes and Their Reactivity toward Pt(0) Sources

Dearomatization of the five-membered ring of N-Dipp (Dipp = 2,6-diisopropylphenyl)-substituted benzazaphosphole 2 with HCl generated 1–Cl, which undergoes substitution with halide sources to provide the remaining members of the P-halogenated series (1–F, 1–Br, and 1–I). These P-heterocycles (1) were characterized by multinuclear [31P{1H}, 1H, 13C{1H}, and 19F (if applicable)] NMR spectroscopy, elemental analysis, and X-ray crystallography. 1H and 13C{1H} NMR spectroscopy revealed that derivatives 1–F, 1–Cl, and 1–Br have C1 symmetry in solution. In contrast, 1–I has effective Cs symmetry in solution due to a rapid, concentration-dependent, inversion at phosphorus, shown by density functional theory (DFT) calculations (B3LYP-D3/6-311G**++) to involve a dimeric iodine-bridged transition structure. In the solid state, 1–F through 1–I all exhibited C1 symmetry with varying degrees of elongation of their P–X bonds. Elongation of the P–X bonds is shown by DFT/natural bond orbital studies to involve NLP → σ*(P–X) negative hyperconjugation, which increases down the halogen series but is less pronounced than that for the closely related NHP–X counterparts (3–F through 3–I). Treatment of 1–Br/I with [Pt(P(t-Bu)3)2] afforded Pt(I)–Pt(I) dimers 4–Br/I, which were characterized by 31P{1H}, 1H, and 13C{1H} NMR spectroscopy, elemental analysis, and X-ray crystallography. Addition of 1–F to Pt(PPh3)4 gave Pt(1–F)(PPh3)2 (6), a coordination compound in which the P-heterocyclic ligand is bound through its lone pair without P–F bond cleavage. Recrystallization attempts resulted in ligand exchange, furnishing Pt(0) complex 7, which features 1–F and PPh3 donors in a 2:1 ratio. Reactions of 1–Cl with all tested starting materials produced unidentifiable product mixtures by 31P{1H} NMR spectroscopy, but the combination of Pt(PPh3)4 or Pt(PPh3)2(C2H4) and 1–Cl in acetone generated an unisolable Pt complex containing tentatively assigned PtP2 metallacyclopropane structural unit 8.

Adjacency Constraint for Efficient Hierarchical Reinforcement Learning.

Goal-conditioned Hierarchical Reinforcement Learning (HRL) is a promising approach for scaling up reinforcement learning (RL) techniques. However, it often suffers from training inefficiency as the action space of the high-level, i.e., the goal space, is large. Searching in a large goal space poses difficulty for both high-level subgoal generation and low-level policy learning. In this article, we show that this problem can be effectively alleviated by restricting the high-level action space from the whole goal space to a k-step adjacent region of the current state using an adjacency constraint. We theoretically prove that in a deterministic Markov Decision Process (MDP), the proposed adjacency constraint preserves the optimal hierarchical policy, while in a stochastic MDP the adjacency constraint induces a bounded state-value suboptimality determined by the MDP's transition structure. We further show that this constraint can be practically implemented by training an adjacency network that can discriminate between adjacent and non-adjacent subgoals. Experimental results on discrete and continuous control tasks including challenging simulated robot locomotion and manipulation tasks show that incorporating the adjacency constraint significantly boosts the performance of state-of-the-art goal-conditioned HRL approaches.

Basin Crustal Structure at the Multiring Basin Transition

AbstractTwo impact basins on the Moon—Freundlich‐Sharonov and Hertzsprung—are nearly the same size but exhibit different surface morphologies and subsurface structures. Gravity data reveal a bench‐like transitional structure in the crust‐mantle interface between the outer ring and the inner basin cavity in Hertzsprung, unlike that beneath both Freundlich‐Sharonov and larger multi‐ring basins. We use iSALE‐2D to model the formation of impact basins into a 40‐km thick pre‐impact crust with a range of thermal conditions to understand the divergent development of these basins and gain insight into the factors affecting whether a basin forms with a peak‐ring or multiring basin structure. We find that thermal gradients of at least 30 K/km result in Freundlich‐Sharonov‐type basins, in agreement with previous work. Cooler thermal gradients of approximately 15–20 K/km are needed to develop Hertzsprung‐like multiring basins with observed bench‐like structures in the crust‐mantle topography. We find that for cooler models, the bench structure develops early in the cratering process as a rotated inner normal fault cutting the crust‐mantle interface, whereas models with higher thermal gradients instead develop diffuse deformation zones instead of a discrete inner fault. The peak rings of both basins develop later in the cratering process as the collapsed central uplift. These results highlight the complex interplay between a strong lithosphere needed to develop ring faults and accessible ductile rocks that facilitate multiring basin formation. The varying thermal conditions giving rise to Hertzsprung and Freundlich‐Sharonov impact basins may be a possible constraint on the lunar cooling rate and chronology.

A Miniature Wideband Active Magnetic Probe Design With High Spatial Resolution and High Sensitivity for Near-Field Measurement

In this letter, a miniature wideband active magnetic probe with high spatial resolution and high sensitivity is designed for near-field signal measurement. The wideband amplifier and the horizontal transition structure, which is stripline (SL) to spoof surface plasmon polariton (SSPP) transition, are applied for the wide bandwidth. The loop area is designed as 0.04 mm2 to improve spatial resolution. The amplifier chip and the corresponding power circuit are integrated into the probe to enhance the sensitivity. The proposed probe is fabricated under a multilayer printed circuit board (PCB) process. The measurement results show that the bandwidth of the proposed probe is from 16 to 43.5 GHz, the spatial resolution is 0.48 mm at 43.5 GHz, and the sensitivity is much higher than that of the reference probe without an amplifier.

Hippocampal spatio-predictive cognitive maps adaptively guide reward generalization

The brain forms cognitive maps of relational knowledge—an organizing principle thought to underlie our ability to generalize and make inferences. However, how can a relevant map be selected in situations where a stimulus is embedded in multiple relational structures? Here, we find that both spatial and predictive cognitive maps influence generalization in a choice task, where spatial location determines reward magnitude. Mirroring behavior, the hippocampus not only builds a map of spatial relationships but also encodes the experienced transition structure. As the task progresses, participants’ choices become more influenced by spatial relationships, reflected in a strengthening of the spatial map and a weakening of the predictive map. This change is driven by orbitofrontal cortex, which represents the degree to which an outcome is consistent with the spatial rather than the predictive map and updates hippocampal representations accordingly. Taken together, this demonstrates how hippocampal cognitive maps are used and updated flexibly for inference.

Isospin-Symmetry Breaking within the Nuclear Shell Model: Present Status and Developments

The paper reviews the recent progress in the description of isospin-symmetry breaking within the nuclear shell model and applications to actual problems related to the structure and decay of exotic neutron-deficient nuclei and nuclei along the N=Z line, where N is the neutron number and Z the atomic number. The review recalls the fundamentals of the isospin formalism for two-nucleon and many-nucleon systems, including quantum numbers, the spectrum’s structure and selection rules for weak and electromagnetic transitions; and at the end, summarizes experimental signatures of isospin-symmetry breaking effects, which motivated efforts towards the creation of a relevant theoretical framework to describe those phenomena. The main approaches to construct accurate isospin-nonconserving Hamiltonians within the shell model are briefly described and recent advances in the description of the structure and (isospin-forbidden) decay modes of neutron-deficient nuclei are highlighted. The paper reviews major implications of the developed theoretical tools to (i) the fundamental interaction studies on nuclear decays and (ii) the estimation of the rates of nuclear reactions that are important for nuclear astrophysics. The shell model is shown to be one of the most suitable approaches to describing isospin-symmetry breaking in nuclear states at low energies. Further efforts in extending and refining the description to larger model spaces, and in developing first-principle theories to deal with isospin-symmetry breaking in many-nucleon systems, seem to be indispensable steps towards our better understanding of nuclear properties in the precision era.

Structure, dielectric and energy storage properties of Bi(Mg2/3Nb1/3)O3 modified Na0.5Bi0.5TiO3-NaNbO3 ceramics

Na0.5Bi0.5TiO3-based ceramics are considered to be a prospective material for energy storage applications due to their unique phase transition and crystal structure. However, the large remanent polarization (Pr) and coercive field (Ec) limit their application in energy storage devices. In this work, the composition-dependent structure, dielectric properties and energy storage properties of Bi(Mg2/3Nb1/3)O3 (BMN) modified Na0.5Bi0.5TiO3-NaNbO3 (NBTNN) ceramics were systematically investigated. The introduction of BMN promotes the formation of local random field, which effectively suppresses the hysteresis loss along with Pr, and form “slender” P-E hysteresis loops. The maximum recoverable energy density of 5.26 J/cm3 is obtained in the optimum composition 0.8NBTNN-0.2BMN, which is about three times more than that of the undoped one, while yielding a high energy efficiency of 78%. In addition, the introduction of BMN into NBTNN ceramic results in excellent temperature stability and significant enhancement in band gap of the material. The improved energy storage performance of BMN modified NBTNN ceramic indicates their potential applicability in dielectric capacitors.

Engineering the Structure and Rheological Properties of P407 Hydrogels via Reverse Poloxamer Addition.

Aqueous solutions of poloxamer 407 (P407), a commercially available and nontoxic ABA triblock polymer (PEO-PPO-PEO), undergo a solution-to-gel transition with increasing temperature and are promising candidates for injectable therapeutics. The gel transition temperature, modulus, and structure are all dictated by polymer concentration, preventing independent tuning of these properties. Here, we show that addition of BAB reverse poloxamers (RPs) to P407-based solutions dramatically alters the gelation temperature, modulus, and morphology. Gelation temperature and RP localization within the hydrogel are dictated by RP solubility. Highly soluble RPs increase gelation temperature and incorporate primarily into the micelle corona regions. Alternatively, RPs with low aqueous solubility decrease gelation temperature and associate within the micelle core and core-corona interface. These differences in RP localization have significant implications for the hydrogel modulus and microstructure. The ability to tune gelation temperature, modulus, and structure through RP addition allows for the design of thermoresponsive materials with specific properties that are unobtainable with neat P407-based hydrogels.

A gradual change is more likely to have caused the Mid-Pleistocene Transition than an abrupt event

The Mid-Pleistocene Transition (~1.2–0.8 million years) corresponds to a time interval when high-amplitude ~100,000 years glacial–interglacial cycles replaced the more subdued ~40,000 years glacial–interglacial cycles. Whether it was triggered by physical processes affecting the climate system at a specific time interval or more gradually over the course of the Pleistocene, is still an open question. Here we use an original approach based on conceptual modelling to identify the temporal structure of the Mid-Pleistocene Transition controlling factors. By comparing our new simulations of global ice volume changes with existing paleo-reconstructions over the past 2 million years, we find that it is more relevant to simulate the Mid-Pleistocene Transition with a gradual-rather-than-abrupt change in the climate system. Our results support the hypothesis that a progressive decrease in atmospheric carbon dioxide concentrations throughout the Pleistocene played a key role in triggering this major climatic transition.

Impact of Erbium Doping in the Structural and Magnetic Properties of the Anisotropic and Frustrated SrYb2O4 Antiferromagnet

We present a systematic study of the structural and magnetic properties of a series of powder samples of SrYb2−xErxO4 with different Yb/Er concentrations. Magnetometry and neutron diffraction have been used to study the magnetic ground states of the compound series, while inelastic neutron scattering was used to investigate the crystal field excitations for a chosen concentration. These results show that the crystal structure remains the same for all compositions, while the lattice parameters increase linearly with the Er content. All compounds showed some type of magnetic transition below 1 K, however, both the magnetic structure and nature of the phase transition vary throughout the series. The samples present a non-collinear magnetic structure with the moments lying on the ab plane for low Er content. For high Er content, the magnetic structure is collinear with the moments aligned along the c-axis. A critical concentration is found where there is a bifurcation between zero-field and field-cooled magnetic susceptibility. This irreversible process could be due to the random mixture of single-ion magnetic anisotropies.

Thermo-physical properties of light-weight aggregate concrete integrated with micro-encapsulation phase change materials: Experimental investigation and theoretical model

The experimental and theoretical determination method of thermo-physical properties of light-weight aggregate concrete integrated with micro-encapsulation phase change materials (MPCM-LWAC) has always been a crucial issue, but severely lacking the study on its theoretical determination method in previous researches. This work aims to construct the theoretical models for thermo-physical properties of MPCM-LWAC. For this purpose, we firstly established the theoretical models of enthalpy, specific heat capacity, and thermal conductivity according to the characteristics of phase transition and pore structure of MPCM-LWAC, and then validated these models by comparing with the experimental data. Results exhibit that (1) In case of the effective thermal conductivity of MPCM-LWAC, the improved two-step Reconstruction Maxwell Model considering the porosity is shown to fit excellently to experimental data. The difference is not more than 3%. (2) The newly constructed theoretical model of enthalpy with liquid phase ratio as a fitting parameter effectivity reflects the effect of temperature on enthalpy. (3) The theoretical model of specific heat capacity is constructed by the assumption that MPCM-LWAC satisfies the proportional mixing law. The theoretical results of specific heat capacity fit to the experimental results with excellent agreement in the range of phase-transition temperature, and the change is less than 5.160%.

How the Exchange Energy Can Affect the Power Laws Used to Extrapolate the Coupled Cluster Correlation Energy to the Thermodynamic Limit.

Finite size error is commonly removed from coupled cluster theory calculations by N-1 extrapolations over correlation energy calculations of different system sizes (N), where the N-1 scaling comes from the total energy rather than the correlation energy. However, previous studies in the quantum Monte Carlo community suggest an exchange-energy-like power law of N-2/3 should also be present in the correlation energy when using the conventional Coulomb interaction. The rationale for this is that the total energy goes as N-1 and the exchange energy goes as N-2/3; thus, the correlation energy should be a combination of these two power laws. Further, in coupled cluster theory, these power laws are related to the low G scaling of the transition structure factor, S(G), which is a property of the coupled cluster wave function calculated from the amplitudes. We show here that data from coupled cluster doubles calculations on the uniform electron gas fit a function with a low G behavior of S(G) ∼ G. The prefactor for this linear term is derived from the exchange energy to be consistent with an N-2/3 power law at large N. Incorporating the exchange structure factor into the transition structure factor results in a combined structure factor of S(G) ∼ G2, consistent with an N-1 scaling of the exchange-correlation energy. We then look for the presence of an N-2/3 power law in the energy. To do so, we first develop a plane-wave cutoff scheme with less noise than the traditional basis set used for the uniform electron gas. Then, we collect data from a wide range of electron numbers and densities to systematically test five methods using N-1 scaling, N-2/3 scaling, or combinations of both scaling behaviors. We find that power laws that incorporate both N-1 and N-2/3 scaling perform better than either alone, especially when the prefactor for N-2/3 scaling can be found from exchange energy calculations.

Finding your voice: Voice-specific effects in Tagalog reveal the limits of word order priming

The current research investigated structural priming in Tagalog, a symmetrical voice language containing rich verbal morphology that results in changes in mapping between syntactic positions and thematic roles. This grammatically rare feature, which results in multiple transitive structures that are balanced in terms of the grammatical status of their arguments, provides the opportunity to test whether word order priming is sensitive to the voice morphology of the verb. In three sentence priming experiments (Ns = 64), we manipulated whether the target-verb prompt carried the same voice as the verb in the prime sentence. In all experiments, priming occurred only when the prime and target had the same voice morphology. Additionally, we found that the strength of word order priming depends on voice: stronger priming effects were found for the voice morpheme associated with a more flexible word order. The findings are consistent with learning-based accounts where language-specific representations for syntax emerge across developmental time. We discuss the implications of these results in the context of Tagalog's grammar. The results reveal the value of crosslinguistic data for theory-testing, and the value of structural priming in determining the representational nature of linguistic structure.

Early warnings for multi-stage transitions in dynamics on networks.

Successfully anticipating sudden major changes in complex systems is a practical concern. Such complex systems often form a heterogeneous network, which may show multi-stage transitions in which some nodes experience a regime shift earlier than others as an environment gradually changes. Here we investigate early warning signals for networked systems undergoing a multi-stage transition. We found that knowledge of both the ongoing multi-stage transition and network structure enables us to calculate effective early warning signals for multi-stage transitions. Furthermore, we found that small subsets of nodes could anticipate transitions as well as or even better than using all the nodes. Even if we fix the network and dynamical system, no single best subset of nodes provides good early warning signals, and a good choice of sentinel nodes depends on the tipping direction and the current stage of the dynamics within a multi-stage transition, which we systematically characterize.

Wideband and low‐loss transition from low‐temperature co‐fired ceramic laminated waveguide to subminiature coaxial connector for millimetre‐wave applications

This letter presents a novel transition scheme from laminated waveguide (LWG) to subminiature coaxial connector with wideband and low-loss performance. The laminated waveguide is achieved using multilayer low-temperature co-fired ceramic (LTCC) technology. In the conventional transition scheme, a length of grounded coplanar waveguide (GCPW) is used to connect the LWG and coaxial connector to obtain a wide bandwidth, which increase the transition size and radiation loss, especially in millimetre-wave (MMW) band. To realize a compact and low-loss LWG-to-coaxial connector transition, the GCPW line is removed and the whole LTCC transition structure is designed underneath the coaxial connector. Moreover, two stages of waveguide step are introduced to constrain the electromagnetic field in the transition for lower radiation loss, which also contributes to the wideband impedance matching. The back-to-back transition is designed and fabricated with LTCC technology to validate the proposed transition scheme. A measured bandwidth of 44% from 27.3 to 42.9 GHz is achieved under |S11| < −15 dB and the insertion loss of single transition is about 0.4 dB.