Small Expansion Research Articles

LiLnGeS4 (Ln=La-Nd): Designing High Performance Infrared Nonlinear Optical Sulfides through "Band Reformation of AGS".

AgGaS2 (AGS) is the most commonly used commercial infrared nonlinear optical (IR NLO) material. However, AGS has a narrow band gap (Eg=2.58 eV) and a low laser-induced damage threshold (LIDT), primarily attributed to its mobile liquid-like Ag+ constituent and the unstable Ag-S chemical bond. Herein, we propose a "band reformation of AGS" strategy, which leads to the successful syntheses of four lanthanide sulfides, LiLnGeS4 (Ln=La-Nd), crystalizing in an asymmetric Ama2 structure. LiLaGeS4 demonstrates that eliminating the presence of Ag-4d band increases the Eg to 3.32 eV and enhances the LIDT (14-29×AGS, measured by both powder and single crystal); while increasing the nonbonding density of states of the S-3p band enhances the 2nd-nonlinear optical coefficient (1.06×AGS). Besides, the bond length discrepancy between [LiS4], [GeS4] and [LaS8] units leads to a moderate birefringence (Δn=0.052). Such a unique structure further results in extremely small thermal expansion with αL=0.41-1.74×10-5 K-1, along different crystallographic axes. Our theoretical studies indicate that the synergy of the structure building units contribute to the second harmonic generation performance. These results suggest that the "band reformation of AGS" strategy provides effective guidance to discover new NLO crystals with optimized performance.

LiLnGeS4 (Ln=La−Nd): Designing High Performance Infrared Nonlinear Optical Sulfides through “Band Reformation of AGS”

AbstractAgGaS2 (AGS) is the most commonly used commercial infrared nonlinear optical (IR NLO) material. However, AGS has a narrow band gap (Eg=2.58 eV) and a low laser‐induced damage threshold (LIDT), primarily attributed to its mobile liquid‐like Ag+ constituent and the unstable Ag−S chemical bond. Herein, we propose a “band reformation of AGS” strategy, which leads to the successful syntheses of four lanthanide sulfides, LiLnGeS4 (Ln=La−Nd), crystalizing in an asymmetric Ama2 structure. LiLaGeS4 demonstrates that eliminating the presence of Ag‐4d band increases the Eg to 3.32 eV and enhances the LIDT (14–29×AGS, measured by both powder and single crystal); while increasing the nonbonding density of states of the S‐3p band enhances the 2nd‐nonlinear optical coefficient (1.06×AGS). Besides, the bond length discrepancy between [LiS4], [GeS4] and [LaS8] units leads to a moderate birefringence (Δn=0.052). Such a unique structure further results in extremely small thermal expansion with αL=0.41–1.74×10−5 K−1, along different crystallographic axes. Our theoretical studies indicate that the synergy of the structure building units contribute to the second harmonic generation performance. These results suggest that the “band reformation of AGS” strategy provides effective guidance to discover new NLO crystals with optimized performance.

Precision tests of bulk entanglement entropy

We consider linear superpositions of single particle excitations in a scalar field theory on AdS3 and evaluate their contribution to the bulk entanglement entropy across the Ryu-Takayanagi surface. We compare the entanglement entropy of these excitations obtained using the Faulkner-Lewkowycz-Maldacena formula to the entanglement entropy of linear superposition of global descendants of a conformal primary in a large c CFT obtained using the replica trick. We show that the closed form expressions for the entanglement entropy in the small interval expansion both in gravity and the CFT precisely agree. The agreement serves as a non-trivial check of the FLM formula for the quantum corrections to holographic entanglement entropy as well as the methods developed in the CFT to evaluate entanglement entropy of descendants. Our checks includes an example in which the state is time dependent and spatially in-homogenous as well another example involving a coherent state with a Bañados geometry as its holographic dual.

Reply to the Comment on “A New Boson Expansion Theory Utilizing a Norm Operator”

Abstract The comment is based on misunderstandings and, as a result, does not evaluate the norm operator method. We refute the comment. The structure of the norm operator composed of all the excitation modes determines whether the form of a practical boson expansion is a small parameter expansion. KT-3 is chimerical. It should be taken seriously that the small parameter expansions do not hold with truncating the contributions of all phonon excitation modes that are not adopted as boson excitations. The formulation using the boson expansion of the projection operator on to the boson vacuum does not allow the limitation of the phonon excitation number beforehand.

Improved mechanical properties of W-Zr-Ti-Nb alloys via adding Ti and Nb

Formation of the W2Zr intermetallic is the key reason for the low relative density and brittleness of W-Zr alloys. In this study, 65 W-Zr-Ti-Nb alloys with different Ti and Nb content were prepared by powder metallurgy. With the increase of Ti and Nb content, the proportion of the W2Zr in the alloy decreases, causing the densification of 65 W-Zr-Ti-Nb alloys. The thermodynamic calculation shows that the addition of both Ti and Nb results in a narrowing stabilized temperature range of W2Zr and an expanding stabilized temperature range of BCC-WTixNby, respectively, ultimately causing the disappearance of the W2Zr and formation of the WTixNby during non-equilibrium cooling. Both high ductility and strength can be achieved in the W-Zr-Ti-Nb alloys by assistance of the disappearance of the brittle W2Zr phase and the formation of the ductility WTixNby. The first principle calculation indicates that the co-doping Ti and Nb results in a larger expansion on the spacing of the {110} close-packed plane and a smaller expansion or even shrinkage on the atomic spacing along the close-packed direction of the WTixNby. Further, integrated crystal orbital Hamilton population (ICOHP) results proved that the bonding strength of W-Ti and W-Nb was weaker than that of W-W in WTixNby. Both increased spacing of {110} plane and decreased interatomic bonding strength aid in reducing Peierls-Nabarro stress, promoting plastic deformation. This study provides a new method for improving mechanical properties by tailoring the phase constitution in W-Zr alloys through co-doping Ti and Nb.

Superconductivity in Monolayer Carbon Allotropes with High Thermal Stability.

Intrinsic superconductivity is rarely discovered in sp2-hybridized monolayer carbon allotropes. Here we design a carbon monolayer configured of pentagon, heptagon, and hexagon rings with p2 plane group symmetry. Full-sp2 hybridization is proposed to favor thermal metastability on a low Gibbs free energy. The extremely small thermal expansion coefficient is predicted to the turn negative value to positive with elevating temperature. Carbon polygon structures remain intact at a high thermal temperature of 3,000 K. The high specific surface area is found to approach 2,700 m2/g, with O2-adsorption being advantageous over pristine graphene. We reveal electronic Fermi surfaces mediated by phonon modes of carbon out-of-plane vibrations. By calculating the Eliashberg equation, we evaluate intrinsic superconductivity with a large electron-phonon coupling coefficient. The superconducting transition temperature is estimated to reach 20 K under a high logarithmic average frequency. These first-principles calculations shall stimulate experimentalists' interest in exploring low-dimensional carbon superconductors with gas sensitivity.

Two-dimensional BC12 as an ultra-high performance anode material for lithium-ion batteries

With the gradual development of renewable energy, search for high-performance energy storage materials as anodes for lithium-ion batteries (LIBs) has become urgent. Two-dimensional (2D) materials are considered as candidates for anode materials due to their unique structure and physicochemical properties. Based on first-principles calculations, we propose a 2D material, BC12 monolayer, as an excellent anode for LIBs. BC12 exhibits outstanding dynamic, mechanical, and thermal stability. In addition, BC12 monolayers show not only remarkably high storage capacity (2767.57 mA h g−1) but also low diffusion barrier energy (0.175 eV) and appropriate open circuit voltage (0.3 V). A small volume expansion (0.38%) is also observed during the lithiation process. Furthermore, we undertake a comprehensive analysis on the impact of carbon vacancy in BC12. The presence of carbon vacancy makes the adsorption and diffusion of Li relatively weak, which should be carefully handled in the experimental synthesis process. The above-mentioned investigation offers valuable insights and guidance for the future development and application of 2D anode materials in metal-ion batteries.

Effects of multi-element composition regulation on the structure and electrochemistry of P2-type layered cathode materials

P2-type Mn-based oxides are promising cathode materials for sodium-ion batteries due to their low cost and high capacity virtue. However, the irreversible phase transition and unstable anion redox at high operating voltages (∼4.2 V) will cause structural distortions, leading to slow sodium-ion diffusion kinetics and severe capacity degradation. Herein, a multi-elemental composition regulation strategy is proposed to enhance the structural stability of P2-type cathode by optimizing the structure and modulating the irreversible oxygen redox during high-voltage cycling. A series of multi-element cathodes Na0.67(Fe1/4Co1/4Ni1/4Ti1/4)1-xMnxO2 (x = 0.4,0.5,0.6,0.7,0.8,0.9) are designed and the effects of component modulation on their structure and electrochemical behavior are systematically investigated. Especially, the optimized Na0.67Fe0.05Co0.05Ni0.05Ti0.05Mn0.8O2 cathode maintains P2 phase during the initial charging/discharging between 1.5 V and 4.5 V, inhibits irreversible oxygen redox, and exhibits small lattice expansion. Impressively, the above optimized cathode exhibits superior cycling stability with capacity retention of nearly 90 % and reversible capacity of 130.1 mAhg−1 after 100 cycles at 1C rate. Furthermore, the optimized cathode also displays an excellent rate capability (capacity of 108.2 mAh g−1 at 5 C rate) due to the enhanced Na+ diffusion kinetics. This work provides new insight into developing high-stable Mn-based oxide cathodes operating at high voltage for sodium-ion batteries.

Characteristics of spatial and temporal changes in ecosystem service value and threshold effect in Henan along the Yellow River, China

Ecosystem services (ES), which serve as the link between human activities and natural ecosystems, are crucial for maintaining ecological balance and supporting economic development. The Ecosystem Services Value (ESV) is an indicator used to quantifying ecosystem services. Accurately estimating the dynamics of ESV and the threshold effects of influencing factors is of great importance for the sustainable development of the region. This study constructs an ESV valuation model based on the equivalent factor method, incorporating construction land, and corrects the initial valuation results in three dimensions. By constructing a random forest model and integrating partial dependence analysis, Elevation, Evapotranspiration, Normalized Difference Vegetation Index, and the proportion of built-up land area were identified as significant factors in determining ecologically vulnerable areas within the study region. The results show that: (1) The total ESV in Henan along the Yellow River in 2000, 2005, 2010, 2015, and 2020 was 204.612 billion yuan, 249.775 billion yuan, 239.100 billion yuan, 234.868 billion yuan and 202.767 billion yuan, respectively. The overall trend of change is first growth and then decline, with spatial features remaining relatively stable, and ESV polarization becoming more pronounced. (2) The spatial clustering characteristics of ESV in Henan along the Yellow River are remarkable, and the cold and hot spot areas show a bidirectional expansion trend. The cold spot areas expand substantially around the construction land, whilethe hot spot areas show a small expansion around the western mountain areas and the vegetation areas along the Yellow River, but the overall growth is slower. (3) The main factors affecting ESV include three natural factors and one anthropogenic factor, namely evapotranspiration (ET), the proportion of built-up land area (POB), normalized vegetation index (NDVI) and elevation (ELEV). ESV is at a high level when ELEV>718 m, ET<90 mm, NDVI>0.7, and POB<25.67 % approximately. The study results can provide an important theoretical basis for the development of comprehensive ecological protection measures. Furthermore, they can contribute to the sustainable development of the Yellow River Basin.

Modeling heat conduction with dual-dissipative variables: A mechanism-data fusion method.

Many macroscopic non-Fourier heat conduction models have been developed in the past decades based on Chapman-Enskog, Hermite, or other small perturbation expansion methods. These macroscopic models have achieved great success in capturing non-Fourier thermal behaviors in solid materials, but most of them are limited by small Knudsen numbers and incapable of capturing highly nonequilibrium or ballistic thermal transport. In this paper, we provide a different strategy for constructing macroscopic non-Fourier heat conduction modeling, that is, using data-driven deep-learning methods combined with nonequilibrium thermodynamics instead of small perturbation expansion. We present the mechanism-data fusion method, an approach that seamlessly integrates the rigorous framework of conservation-dissipation formalism (CDF) with the flexibility of machine learning to model non-Fourier heat conduction. Leveraging the conservation-dissipation principle with dual-dissipative variables, we derive an interpretable series of partial differential equations, fine tuned through a training strategy informed by data from the phonon Boltzmann transport equation. Moreover, we also present the inner-step operation to narrow the gap from the discrete form to the continuous system. Through numerical tests, our model demonstrates excellent predictive capabilities across various heat conduction regimes, including diffusive, hydrodynamic, and ballistic regimes, and displays its robustness and precision even with discontinuous initial conditions.

Effects of nano MgO and light-burnt MgO on mechanical properties and long-term expansion of paste mixed with Portland cement and slag

Nano MgO and light-burnt MgO were added into pastes mixed with Portland cement and slag to compensate for the shrinkage of mass concrete. The results indicated that an increased nano MgO content improved strength within a certain range. The strength of group with 8 % nano MgO increased by 12 % and 8 % under autoclaving and water curing, respectively, while increased light-burned MgO content deteriorated strength. The nano MgO-based group exhibited enhanced compressive strength and smaller expansion than the light-burnt MgO-based group, due to its higher efficiency of filling pores by uniformly distributed brucite. Moreover, MgO hydration mainly occurred within 365 d of water curing, and nano MgO and light-burnt MgO were fully hydrated at 730 d. Overall, this study provided the theoretical basis for adding nano-MgO and light-burnt MgO to compensate for the shrinkages of mass concrete on a large scale.

Yttria substitution effect of tantalate aluminosilicate glasses with ultra‐high Young's modulus

AbstractWe report novel oxide glasses that are compatible with ultra‐high Young's modulus (∼150 GPa) and a small coefficient of thermal expansion (∼5.0 ppm/K). These glasses were prepared using a conventional melt‐quenching technique. The viscosity–temperature relation provides the reshaping temperature for the stiff and less dilated oxide glasses. The origin of the ultra‐high Young's modulus is the inclusion of Y2O3 as well as five‐ and six‐coordinated alumina oxide and Ta2O5, which has a large ionic packing ratio due to higher oxygen coordination numbers. On the other hand, the small thermal expansion coefficient originates from including Ta2O5 and SiO2 with large dissociation energy due to strong bonds.

The AdS Veneziano amplitude at small curvature

We compute the AdS Veneziano amplitude for type IIB gluon scattering in AdS5 × S3 to all orders in α′ in a small curvature expansion. This is achieved by combining a dispersion relation in the dual 4dN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 2 SCFT with an ansatz for the amplitude as a worldsheet integral in terms of multiple polylogarithms. The first curvature correction is fully fixed in this way and satisfies consistency checks in the high energy limit, the low energy expansion as previously fixed using supersymmetric localisation, and for the energy of massive string operators, which we independently compute using a semiclassical expansion. We also combine localisation with this first curvature correction to fix the unprotected D4F4 correction to the amplitude at finite curvature.

X marks the spot: Accurate energies from intersecting extrapolations of continuum quantum Monte Carlo data.

We explore the application of an extrapolative method that yields very accurate total and relative energies from variational and diffusion quantum Monte Carlo (VMC and DMC) results. For a trial wave function consisting of a small configuration interaction (CI) wave function obtained from full CI quantum Monte Carlo and reoptimized in the presence of a Jastrow factor and an optional backflow transformation, we find that the VMC and DMC energies are smooth functions of the sum of the squared coefficients of the initial CI wave function and that quadratic extrapolations of the non-backflow VMC and backflow DMC energies intersect within uncertainty of the exact total energy. With adequate statistical treatment of quasi-random fluctuations, the extrapolate and intersect with polynomials of order two method is shown to yield results in agreement with benchmark-quality total and relative energies for the C2, N2, CO2, and H2O molecules, as well as for the C2 molecule in its first electronic singlet excited state, using only small CI expansion sizes.

Isofield plasma expansion in kJ petawatt laser-driven ion acceleration with a tailored fast electron temperature

Kilojoule-class relativistic intensity lasers, having multi-picosecond (ps) pulse durations, enable efficient ion acceleration in the interaction with thin foil targets. The foil plasma expands under the laser energy input over picoseconds where fast electrons keep increasing their effective temperature, while they convert a part of the energy into fast ions through generation of a sheath electric field. The temporal evolution of the sheath electric field is the key to understanding the efficient ion acceleration seen in kJ-class laser experiments. Here, we extend the non-isothermal plasma expansion model by introducing a temporal function of the effective temperature of fast electrons to obtain the sheath electric field in the expanding plasma. We theoretically derived that when the effective temperature of fast electrons increases in proportional to the square of the time, the strength of the sheath electric field is kept constant without depletion during the expansion. This ‘isofield’ expansion is confirmed by a quasi-one-dimensional particle-in-cell simulation. The isofield expansion results in a high energy ion acceleration with a small expansion length, which is favorable for realizing an efficient ion acceleration with less lateral energy loss in multi-dimensional situations.

DNA Steganography: Embedding the Secret Messages Using Glass Stack Method and Detecting Errors Made by Different Attacks

Cyber threats pose a significant challenge to protecting cloud-based health data, including DNA sequences and patient information. Steganography is a well-known solution to this problem. Recent studies have limitations, such as not reconstructing the cover or enlarging the original sequence, increasing personal data security risks. In this study, we provide a novel data-hiding technique that uses a secret key, bit padding, and exclusive OR (XOR) operation to insert secrets into a pre-processed DNA sequence. The message encryption and pre-processing of the cover are performed using a new glass stack pattern technique. The message encryption and pre-processing processes using the new glass stack pattern method increase the security and robustness of the system. The method embeds 3 bits per nucleotide which is greater than the existing schemes. It has a relatively small DNA expansion which is 50% and has a low risk of breaking security. The method also preserves the biological properties of DNA sequences. Additionally, a parity check approach further improves security by thwarting attacks like man-in-the-middle, chosen stego, and modification attacks that alter the stego DNA. These advances improve the system's overall security capabilities. The experimental findings demonstrate that the suggested method reconstructs the cover, healthcare data, and DNA sequence properly and error-free, and outperforms competing algorithms on all performance metric dimensions. Highlights The scheme implants a maximum of 3 bits per nucleotide with a small expansion. Its cover pre-processing and message encryption using a glass stack pattern makes strong security. The scheme can detect and fix changed bits caused by attacks. A very low cracking probability shows strong security and robustness. The biological properties of the stego DNA sequence are preserved by this scheme.

A Small Power Margin and Bandwidth Expansion Allow Data Transmission during Rainfall despite Large Attenuation: Application to GeoSurf Satellite Constellations at mm–Waves

The traditional approach of considering the probability distribution of rain attenuation leads to provide very large power margin (overdesign) in data channels. We have extended a method which, with a small power margin, bandwidth expansion and variable symbol rate, avoids overdesign and can transfer the same data volume as if the link were in clear–sky conditions. It is characterized only by the link mean efficiency, suitably defined. It is useful only if: (a) data must be up– and downloaded when it is raining; (b) real–time communication is not required. We have applied it to the links of GeoSurf satellite constellations (in which, at any latitude of ground stations, propagation paths are at the local zenith) by simulating rain attenuation time series at 80 GHz (mm–wave)–the new frontier of satellite frequencies–with the Synthetic Storm Technique, from rain–rate time series recorded on–site, at sites located in different climatic regions. The power margin to be implemented at 80 GHz ranges from 2.0 dB to 7.4 dB–well within the current technology–regardless the instantaneous rain attenuation. The clear–sky bandwidth is expanded 1.75 to 2.80 times, a factor not large per se, but it may challenge current technology if the clear–sky bandwidth is already large.

Cosmology in Lorentzian Regge calculus: causality violations, massless scalar field and discrete dynamics

We develop a model of spatially flat, homogeneous and isotropic cosmology in Lorentzian Regge calculus, employing four-dimensional Lorentzian frusta as building blocks. By examining the causal structure of the discrete spacetimes obtained by gluing such four-frusta in spatial and temporal direction, we find causality violations if the sub-cells connecting spatial slices are spacelike. A Wick rotation to the Euclidean theory can be defined globally by a complexification of the variables and an analytic continuation of the action. Introducing a discrete free massless scalar field, we study its equations of motion and show that it evolves monotonically. Furthermore, in a continuum limit, we obtain the equations of a homogeneous scalar field on a spatially flat Friedmann background. Vacuum solutions to the causally regular Regge equations are static and flat and show a restoration of time reparametrisation invariance. In the presence of a scalar field, the height of a frustum is a dynamical variable that has a solution if causality violations are absent and if an inequality relating geometric and matter boundary data is satisfied. Edge lengths of cubes evolve monotonically, yielding a contracting or an expanding branch of the Universe. In a small deficit angle expansion, the system can be deparametrised via the scalar field and a continuum limit of the discrete theory can be defined which we show to yield the relational Friedmann equation. These properties are obstructed if higher orders of the deficit angle are taken into account. Our results suggest that the inclusion of timelike sub-cells is necessary for a causally regular classical evolution in this symmetry restricted setting. Ultimately, this works serves as a basis for forthcoming investigations on the cosmological path integral within the framework of effective spin foams.

TD-graphene: Theoretical prediction of a high-performance anode material for sodium-ion batteries with intrinsic metallicity, high capacity, and fast ion mobility

The utilization of pristine graphene as an anode material in sodium-ion batteries (SIBs) is limited by its inherent chemical inertness toward Na-ions. To address this issue, we propose a two-dimensional carbon allotrope (named as TD-graphene) by assembling tricyclo[4.4.1.11,6]dodecane (C12H20) skeleton. The topological non-hexagonal feature of C12H20 increases the degree of local carbon-ring disorder and introduces additional electron-deficient regions on the surface, thus enhancing the adsorption capability of Na. TD-graphene demonstrates exceptional stability across the energetic, thermodynamic, dynamic, and mechanical aspects. As a promising anode for SIBs, it exhibits an intrinsic metallicity, an ultra-high storage capacity (1487.58 mA h g−1), a low diffusion barrier (0.20 eV), a low average open-circuit voltage (0.33 V), and a small lattice expansion (0.6%). The presence of solvents with high dielectric constants improves the adsorption and migration capability of Na. Furthermore, taking into account the limitation of single-layer materials in practical applications, we employ h-BN as a promising substrate for TD-graphene, which can boost the Na adsorption and diffusion performance. These results render TD-graphene as a promising high-performance anode material for SIBs.

Homogeneously dispersed silicon/graphite composite toward enhanced lithium-ion batteries

At present, silicon/graphite composite is the most promising anode material for high energy density lithium-ion batteries. However, during the preparation, nanoscale silicon will inevitably undergo agglomeration, which will cause serious volume changes and breakage during the charging/discharging process. How to achieve uniform dispersion of nanoscale silicon onto the surface of graphite becomes a great challenge. Here, by grafting functional groups on the surface of silicon, both the repulsive force between silicon particles and the binding force between silicon/graphite have been improved, thereby highly uniform dispersed silicon is achieved. After being coated with asphalt and etching off the functional groups, the conductivity and ion migration ability of the composite are further improved. Resultantly, the modified composite provides a high discharging capacity of 598.4 mAh·g−1 at 0.2C and can still maintain a high-capacity retention of 90.7 % and a small volume expansion rate of 30.8 % after 500 cycles.