Unoccupied Region Research Articles

Phosphorus-doped cobalt oxide/cobalt sulfide heterostructure for enhanced oxygen evolution

Regulating the distribution of valence charges near the Fermi level and d-band center of metal atom active sites is crucial for developing highly efficient and stable catalysts for oxygen evolution reaction (OER), yet it remains a significant challenge. In this study, we prepared phosphorus-doped Co3O4/Co9S8 catalysts with a mesoporous nanorod morphology and Mott-Schottky heterojunction. Compared to Co3O4, Co9S8 and Co3O4/Co9S8, this catalyst exhibits enhanced OER properties with an overpotential of 156 mV at 10 mA cm−2, 380 mV at 50 mA cm−2, and 450 mV at 100 mA cm−2. Moreover, when a voltage of 2.0 V vs. RHE is applied, the current density reaches 350 mA cm−2. Density functional theory (DFT) calculations reveal that the coupling of Co3O4 and Co9S8 interfaces and phosphorus doping lead to the rearrangement of d-orbital electrons of Co atoms on the crystal plane, optimizing the d-band center. Crystal orbital Hamilton population (COHP) analysis shows that the partial anti-bonding state transitions into the unoccupied region, reducing the anti-bonding state and enhancing the bonding state, thus significantly improving the adsorption for the target intermediate (*OOH), resulting in higher intrinsic activity. This study demonstrates that the pathway of doping this heterojunction with P synergistically enhances the catalytic activity of this composite for OER in water splitting electrocatalysis.

The γ-ray deposition histories of calcium-rich supernovae

ABSTRACT Calcium-rich supernovae (Ca-rich SNe) are faint, rapidly evolving transients whose progenitor system is yet to be determined. We derive the γ-ray deposition histories of five Ca-rich SNe from the literature in order to place constraints on possible progenitor systems. We find that the γ-ray escape time, t0, of the Ca-rich SNe sample is $\approx 35\!-\!65 \, \rm {d},$ within the unoccupied region between Type Ia SNe and stripped-envelope supernovae (SESNe). The t0−MNi56 distribution of these SNe, where MNi56 is the synthesized 56Ni mass in the explosion, creates a continuum between the Type Ia and SESNe t0−MNi56 distribution, hinting at a possible connection between all the events. By comparing our results to models from the literature, we were able to determine that helium shell detonation models and core-collapse models of ultra-stripped stars are unlikely to explain Ca-rich SNe since the gamma-ray escape time in these models is smaller than the observed values. Models that agree with the observed t0−MNi56 distribution are explosions of low mass, $M\approx 0.75\!-\!0.8\, \mathrm{M}_\odot,$ white dwarfs and core-collapse models of stripped stars with an ejecta mass of $M\approx 1\!-\!3\, {\rm M}_{\odot}.$

Revealing trend of electron momentum densities, electronic and optical response of dichalcogenides MS2-xTex (M=Ti, Zr; x=0,1,2)

Role of replacement of S atom by Te atoms in transition metal layered dichalcogenides (MS2; M = Ti and Zr) in amending the electronic response is reported. Different exchange and correlation potentials within linear combination of atomic orbitals (LCAO) have been used to interpret the experimental momentum densities, electronic and optical properties. It is seen that Compton profiles (CPs) based on hybrid functional combining Hartree-Fock with density functional theory namely WC1LYP reconciles better with the measured momentum densities than other considered schemes of exchange and correlation potentials. More covalent character of TiSTe than that in ZrSTe as predicted by Mulliken's population is in accordance with the measured equal-valence-electron-density profiles. Moreover, electronic and optical response using the modified Becke-Johnson (mBJ) potential as facilitated in the full potential linearized augmented plane wave method are reported. From energy bands and DOS, we conclude that concentration of Te reduces band gap in ZrS2 due to lowering of Te-5p states in the unoccupied region, while the TiS2 based mixed compounds depict metallic character.

Functional and structural characterization of interactions between opposite subunits in HCN pacemaker channels

Hyperpolarization-activated and cyclic nucleotide (HCN) modulated channels are tetrameric cation channels. In each of the four subunits, the intracellular cyclic nucleotide-binding domain (CNBD) is coupled to the transmembrane domain via a helical structure, the C-linker. High-resolution channel structures suggest that the C-linker enables functionally relevant interactions with the opposite subunit, which might be critical for coupling the conformational changes in the CNBD to the channel pore. We combined mutagenesis, patch-clamp technique, confocal patch-clamp fluorometry, and molecular dynamics (MD) simulations to show that residue K464 of the C-linker is relevant for stabilizing the closed state of the mHCN2 channel by forming interactions with the opposite subunit. MD simulations revealed that in the K464E channel, a rotation of the intracellular domain relative to the channel pore is induced, which is similar to the cAMP-induced rotation, weakening the autoinhibitory effect of the unoccupied CL-CNBD region. We suggest that this CL-CNBD rotation is considerably involved in activation-induced affinity increase but only indirectly involved in gate modulation. The adopted poses shown herein are in excellent agreement with previous structural results.

Intersections of random sets

AbstractWe consider a variant of a classical coverage process, the Boolean model in $\mathbb{R}^d$ . Previous efforts have focused on convergence of the unoccupied region containing the origin to a well-studied limit C. We study the intersection of sets centered at points of a Poisson point process confined to the unit ball. Using a coupling between the intersection model and the original Boolean model, we show that the scaled intersection converges weakly to the same limit C. Along the way, we present some tools for studying statistics of a class of intersection models.

Orbital-enhanced warping effect in px,py-derived Rashba spin splitting of monatomic bismuth surface alloy

Spin-split Rashba bands have been exploited to efficiently control the spin degree of freedom of moving electrons, which possesses a great potential in frontier applications of designing spintronic devices and processing spin-based information. Given an intrinsic breaking of inversion symmetry and sizeable spin–orbit interaction, two-dimensional (2D) surface alloys formed by heavy metal elements exhibit a pronounced Rashba-type spin splitting of the surface states. Here, we have revealed the essential role of atomic orbital symmetry in the hexagonally warped Rashba spin-split surface state of the sqrt 3 times sqrt 3 R30^0 BiCu2 monatomic alloy by scanning tunneling spectroscopy (STS) and density functional theory (DFT). From dI/dU spectra and calculated band structures, three hole-like Rashba-split bands hybridized from distinct orbital symmetries have been identified in the unoccupied energy region. Because of the hexagonally deformed Fermi surface, quasi-particle interference (QPI) mappings have resolved scattering channels opened from interband transitions of px,py (mj = 1/2) band. In contrast to the s,pz-derived band, the hexagonal warping is predominately accompanied by substantial out-of-plane spin polarization Sz up to 24% in the dispersion of px,py (mj = 1/2) band with an in-plane orbital symmetry.

Spin-Dependent Tunneling Barriers in CoPc/VSe2 from Many-Body Interactions.

Mixed-dimensional magnetic heterostructures are intriguing, newly available platforms to explore quantum physics and its applications. Using state-of-the-art many-body perturbation theory, we predict the energy level alignment for a self-assembled monolayer of cobalt phthalocyanine (CoPc) molecules on magnetic VSe2 monolayers. The predicted projected density of states on CoPc agrees with experimental scanning tunneling spectra. Consistent with experiment, we predict a shoulder in the unoccupied region of the spectra that is absent from mean-field calculations. Unlike the nearly spin-degenerate gas-phase frontier molecular orbitals, the tunneling barriers at the interface are spin-dependent, a finding of interest for quantum information and spintronics applications. Both the experimentally observed shoulder and the predicted spin-dependent tunneling barriers originate from many-body interactions in the interface-hybridized states. Our results showcase the intricate many-body physics that governs the properties of these mixed-dimensional magnetic heterostructures and suggests the possibility of manipulating the spin-dependent tunneling barriers through modifications of interface coupling.

X‐Ray Absorption Fingerprints from Cs Atoms in Cs3Sb

X‐ray absorption spectroscopy represents a valuable characterization tool for complex materials like multialkali antimonides. The interpretation of such experimental results greatly benefits from state‐of‐the‐art theoretical references. In a first‐principles work based on density‐functional theory and many‐body perturbation theory, the fingerprints of X‐ray absorption near‐edge structure (XANES) of Cs3Sb from the Cs K‐ and L3‐edge are unraveled. From the electronic structure and the orbital character of the conduction bands, the contributions to the XANES spectra from the two inequivalent Cs atoms in the adopted stoichiometric unit cell are analyzed. The predominant weight of Cs s‐ and d‐electrons in the unoccupied region anticipates the relatively high signal yielded by the L3‐edge. Clear atomic signatures, in the form of a pronounced excitonic peak, are visible in the Cs K‐edge spectra. In the XANES from the L3‐edge, both Cs atoms yield similar contributions, which are yet distinguishable in the presented calculations. Quantitative analysis enabled by the adopted methodology reveals that electron–hole correlation effects manifest themselves mainly through a redistribution of the oscillator strength to lower energies, whereas exciton binding energies are on the order of a few hundred meV.

Effect of sonication on results of ChIP-seq experiments involving PRC2 related proteins

Sonication is one of the essential strategies of chromatin fragmentation in Chromatin immunoprecipitation (ChIP) assay. The impact of proteins with different molecular weights generated under different duration of sonication on the results of Chromatin immunoprecipitation sequencing (ChIP-seq) experiments involving the Polycomb Repressive Complex 2 (PRC2) related protein EZH2, which is a histone methyltransferase, and its product H3K27me3 was investigated. The results indicate that in the promoter region or nonpromoter region, there were hardly any differences among the H3K27me3 peaks annotated genes from different duration of sonication, which suggesting that the duration of sonication had little effect on histone ChIP-seq results. In contrast, in the promoter region newly gained EZH2 peaks annonated genes at 20 min sonication time were significantly clustered in the gene ontology (GO) pathways related to actin filament bundle compared with 10 min. In the nonpromoter region, compared with 10 min, the GO pathways of newly gained EZH2 peaks annonated genes at 20 min sonication time is much more than that of lost EZH2 peaks annonated genes. And in the nonpromoter region, compared with 20 min, the GO pathways of lost EZH2 peaks annonated genes at 30 min sonication time is much more than that of newly gained EZH2 peaks annonated genes. Most of these pathways are associated with RNA polymerase II (RNAPII), organ development and cell morphogenesis. These suggest that the genomic information of EZH2 will be lost if the duration of sonication is not enough or too long. Different duration of sonication mainly affect the EZH2 peaks in PRC2 unoccupied region and the bivalent promoter in the promoter region, as well as the PRC2 occupied region, PRC2 unoccupied region and the activated enhancer in the nonpromoter region. Therefore, the sonication for the chromatin related proteins with high molecular weights need to be optimized to make chromatin fragments size vary from 100 bp to 500 bp, which will yield relatively comprehensive genomic information of the target protein. For histones, which are of small molecular weights, duration of sonication has little effect on them.

Effects of mass extinction and recovery dynamics on long-term evolutionary trends: a morphological study of Strophomenida (Brachiopoda) across the Late Ordovician mass extinction

AbstractMass extinctions affect the history of life by decimating existing diversity and ecological structure and creating new evolutionary and ecological pathways. Both the loss of diversity during these events and the rebound in diversity following extinction had a profound effect on Phanerozoic evolutionary trends. Phylogenetic trees can be used to robustly assess the evolutionary implications of extinction and origination.We examine both extinction and origination during the Late Ordovician mass extinction. This mass extinction was the second largest in terms of taxonomic loss but did not appear to radically alter Paleozoic marine assemblages. We focus on the brachiopod order Strophomenida, whose evolutionary relationships have been recently revised, to explore the disconnect between the processes that drive taxonomic loss and those that restructure ecological communities.A possible explanation for this disconnect is if extinction and origination were random with respect to morphology. We define morphospace using principal coordinates analysis (PCO) of character data from 61 Ordovician–Devonian taxa and their 45 ancestral nodes, defined by a most parsimonious reconstruction in Mesquite. A bootstrap of the centroid of PCO values indicates that genera were randomly removed from morphospace by the Late Ordovician mass extinction, and new Silurian genera were clustered within a smaller previously unoccupied region of morphospace. Diversification remained morphologically constrained throughout the Silurian and into the Devonian. This suggests that the recovery from the Late Ordovician mass extinction resulted in a long-term shift in strophomenide evolution. More broadly, recovery intervals may hold clues to understanding the evolutionary impact of mass extinctions.

Linear scanning tunneling spectroscopy over a large energy range in black phosphorus

We reveal the unique electronic characteristics of the conduction band (CB) of black phosphorus (BP) by combining low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), density functional theory calculations, analytic fitting, and model simulations. We discover that the differential conductance spectrum, which represents the local density of states (LDOS) of BP, exhibits a linear character over a large energy range in the unoccupied electronic state region. Combining theoretical calculations, we demonstrate that the linear character right above the conduction band minimum originates from a specific combination of the anisotropic band dispersions of BP's CB. In particular, the wave function of BP's CB possesses a pronounced density between BP layers and extends into the vacuum significantly, which is in sharp contrast to those of adjacent bands. This makes the CB dominate STS signals even when the energy is sufficiently high to involve other bands, and maintains the linearity of the STS spectrum over a wide energy range. The fact that the CB provides linear DOS and possesses pronounced wave function density in BP interlayers provides new insights for engineering the electronic structures and properties of BP and BP based materials.

Electrical Properties of Single-Walled Carbon Nanotubes due to Compressive Load

In this paper we report the study of the change in electrical properties of semiconducting carbon nanotubes (CNTs) under uniaxial compressive deformations using the “Vienna ab initio simulation package” (VASP). We present an extension of density functional theory calculations to the electronic properties of the tubes, namely the density of states obtained for the optimized geometries of the tubes. There is an energy gap of 0.772 eV between occupied and unoccupied region in the optimized structure calculation. The band gap for the semi-conducting zigzag (10,0) CNTs decreases as the strain increases. It suggests that the semiconducting CNTs may become semimetal or metal upon deformation.

Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap

We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above EF provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.

Dynamically generated flat-band phases in optical kagome lattices

Motivated by recent advances in the realization of complex two-dimensional optical lattices, we investigate theoretically the quantum transport of ultracold fermions in an optical kagome lattice. In particular, we focus on its extensively degenerate localized states (flat band). By loading fermions in a partial region of the lattice and depleting the mobile atoms at the far boundary of the initially unoccupied region, we find a dynamically generated flat-band insulator, which is also a population-inverted state. We further show that inclusion of weak repulsion leads to a dynamical stripe phase for two-component fermions in a similar setup. Finally, by preparing a topological insulating state in a partially occupied kagome lattice, we find that the topological chiral current decays but exhibits an interesting oscillating dynamics during the nonequilibrium transport. Given the broad variety of lattice geometries supporting localized or topological states, our work suggests new possibilities to use geometrical effects and their dynamics in atomtronic devices.

Efficient environment representation for mobile robot path planning using CVT-PRM with Halton sampling

A centroidal Voronoi tessellation-based probabilistic roadmap (CVT-PRM) and its construction method for mobile robot path planning are introduced. The CVT-PRM efficiently encoded the entire unoccupied region of the environment by autonomously rearranging the positions of nodes via CVT and Halton sampling. Simulation results verified that the CVT-PRM can encode the entire unoccupied region efficiently, using evenly distributed nodes.

Dynamical crossover between the infinite-volume and empty-lattice limits of ultra-cold fermions in 1D optical lattices

Unlike typical condensed-matter systems, ultra-cold atoms loaded into optical lattices allow separate control of both the particle number and system size. As a consequence, there are two distinct “thermodynamic” limits that can be defined for these systems: i) “infinite-volume limit” at constant finite density, and ii) “empty-lattice limit” at constant particle number. To probe the difference between these two limits and their crossover, we consider a partially occupied lattice and study the transport of non-interacting fermions and fermions interacting at the mean-field level into the unoccupied region. In the infinite-volume limit, a finite steady-state current emerges. On the other hand, in the empty-lattice limit there is no finite steady-state current. By changing the initial filling, we find a smooth crossover between the two limits. Our predictions may be verified using available experimental tools and demonstrate a fundamental difference between isolated small systems such as ultra-cold atoms and conventional condensed-matter systems.

Molecular dynamics simulation of oxygen diffusion in dry and water-containing brown coal

Moisture content of brown coal has a pronounced impact on O2 diffusion during coal oxidation. The transport behaviour of O2 in dry and hydrated brown coal matrix with 10, 20, and 30 wt% moisture contents have been studied by molecular dynamics (MD) simulations at 298.15 K and 0.1 MPa. By analysing the diffusion characteristics of O2, it is found that the diffusion process results from jumps of O2 molecules between adjacent cavities in the coal matrix. With the increase of moisture content, the swelling extent of coal matrix increases in the range of 10–30 wt%, resulting in increased cavity volume, cavity interconnectivity, and mobility of coal macromolecule. These factors are all beneficial to the transport process of O2 molecule. In addition, O2 molecule prefers to reside in the available water-poor coal cavity and unoccupied region of water-rich cavity according to the estimated binding energies.

Paleoindians and the Younger Dryas in the New England-Maritimes Region

This paper examines environmental and archaeological data for the Younger Dryas (YD) (12,900–11,600 calibrated years before present) (cal BP) and early Holocene (11,600–10,000 cal BP) in the New England-Maritimes (NEM) to model environmental changes and possible human responses. For some other regions of North America, researchers argue for negligible environmental changes and human responses, while others suggest that ecological changes associated with cold conditions at the YD onset disrupted regional biota, causing subsistence stress for Paleoindian populations and the end of the Clovis cultural adaptation (circa 13,200–12,900 cal BP). The NEM shows abrupt cooling at the YD onset, which fostered more open habitats favorable to both long-distance migrating and local herds of caribou, and may have encouraged early Paleoindian colonization and settlement of this unoccupied deglacial region. Comparison of the Paleoindian point sequence with calibrated radiocarbon dates indicates fluted point groups probably occupied the NEM during, but not after, the YD. Abrupt warming at the YD terminus (circa 11,600 cal BP) caused a rapid reorganization of the region’s vegetation and prey species populations, coinciding in the archaeological record with a decline in Paleoindian biface fluting technology and altered regional site distributions. In the closed forests of the succeeding early Holocene NEM, late Paleoindian groups (11,600–10,000 cal BP) used unfluted, lanceolate points that may signal post-YD immigration to the NEM.

Discovery of a nearby young brown dwarf binary candidate

In near-infrared NaCo observations of the young brown dwarf 2MASS J0041353-562112, we discovered a companion a little less than a magnitude fainter than the primary. The binary candidate has a separation of 143 mas, the spectral types are M6.5 and M9.0 for the two components. Colors and flux ratios are consistent with the components being located at the same distance minimizing the probability of the secondary being a background object. The brown dwarf is known to show Li absorption constraining the age to less than ~200 Myr, and it was suspected to show ongoing accretion, indicating an age as low as ~10 Myr. We estimate distance and orbital parameters of the binary as a function of age. For an age of 10 Myr, the distance to the system is 50 pc, the orbital period is 126 yr, and the masses of the components are ~30 and ~15 MJup. The binary brown dwarf fills a so far unoccupied region in the parameters mass and age; it is a valuable new benchmark object for brown dwarf atmospheric and evolutionary models.

Overwrite Induced Divergent Transition by Trapezoid Pole Head

Perpendicular magnetic recording has to use a trapezoid writing pole in order not to enlarge the width of the erasing band at large skew angles. During the overwriting process, the footprint of a trapezoidal field bubble occupies a portion of the rectangular or parallelogram shaped bit(s) to be overwritten. When the magnetization of an unoccupied portion is in the opposite direction of the head field, the demagnetizing field from the unoccupied region shifts the trailing edge transition. When the skew angle is large, this effect can make the center transition line not parallel to the reader sensor. In this condition, one can observe a clear variation when the head reads at the two sides of the track. We call it a divergent transition, meaning the transition line diverges away from the plane of reader sensor. In this study, experimental observations prove the existence of this phenomenon. A simulation study illustrates the observation and clearly gives a complete understanding of this phenomenon.