Insight into the Origin of Second Harmonic Generation and Rational Design in the Metal Halide Borates.

Metal halide borates are promising candidates for high-performance nonlinear optical (NLO) applications, yet the origins of their second harmonic generation (SHG) properties remain unclear. Using atom response theory combined with density functional theory calculations, this study investigates why halogen substitution leads to distinctly different SHG responses in halide monoborates (PbBOX) versus halide pentaborates (PbBOX). We find that the SHG origins vary between these two families due to differences in the strength of the Pb-X interactions.

Automatic Pavlov ratio measurement method based on spinal landmarks identification by a deep-learning model.

Background: Cervical canal stenosis is one of the important pathogenic factors of cervical spondylosis. The accuracy of the Pavlov ratio measurement is crucial for the diagnosis and treatment of cervical spinal stenosis. Manual measurement is influenced by observer variability, accompanied by its inefficiency, which affects clinical evaluation.

The Preparation of a Challenging Superconductor NbAl by Exploiting Nano Effect.

The NbAl superconductor with excellent physical and working properties is one of the most promising materials in high-magnetic-field applications. However, it is difficult to prepare high-quality NbAl with a desired superconducting transition temperature () because of its narrow phase formation area at high temperatures (>1940 °C). This work reports a method to prepare stoichiometric NbAl powder samples at a relatively low temperature (1400 °C) by exploiting the nano effect of Nb particles with pretreatment of Nb powder under H/Ar atmosphere.

MTHFD1 is critical for the negative regulation of retinoic acid receptor signalling in anencephaly.

Neural tube defects are the most severe congenital malformations that result from failure of neural tube closure during early embryonic development, and the underlying molecular mechanisms remain elusive. Retinoic acid, an active derivative of vitamin A, is critical for neural system development, and retinoic acid receptor (RAR) signalling malfunctions have been observed in human neural tube defects. However, retinoic acid-retinoic acid receptor signalling regulation and mechanisms in neural tube defects are not fully understood.

Microscopic Mechanism of the Heat-Induced Blueshift in Phosphors and a Logarithmic Energy Dependence on the Nearest Dopant-Vacancy Distance.

Heat-induced blueshift (HIB) observed in many luminescent materials is a puzzling phenomenon that has remained unexplained for decades. By using the high-throughput first-principles calculations and energy-screening techniques, we generated a number of model structures for five phosphors, RbLi[Li SiO ] :Eu , Na[Li SiO ]:Eu , K[Li SiO ]:Eu , Sr[LiAl N ]:Eu , and Ca[LiAl N ]:Eu . Our analyses suggest, to a first approximation, a logarithmic energy dependence on the nearest distance between the dopant and the metal-cation vacancy.

Dehydrated UiO-66(SH) : The Zr-O Cluster and Its Photocatalytic Role Mimicking the Biological Nitrogen Fixation.

This work reports the dehydrated Zr-based MOF UiO-66(SH) as a visible-light-driven photocatalyst to mimic the biological N fixation process. The N and other control experiments demonstrated that the new photocatalyst is highly efficient in converting N to ammonia. In-situ TGA, XPS, and EXAFS as well as first-principles simulations were used to demonstrate the role of the thermal treatment and the changes of the local structures around Zr due to the dehydration.

Structure and Origin of the Second-Harmonic Generation Response of Nonlinear Optical Material SrBeBO.

SrBeBO (SBBO) has long been considered as one of the most promising deep-ultraviolet nonlinear optical materials, but its crystal structure described by space group 6̅2 in previous studies has remained questionable. On the basis of first-principles calculations coupled with the high-throughput crystal structure prediction method, we found three energetically favorable structures for SBBO with space groups , , and 6̅. These structures and a superstructure of space group -S derived from the structure were refined by the Rietveld method using the available powder X-ray diffraction data.

Harnessing Electrostatic Interactions for Enhanced Conductivity in Metal-Organic Frameworks.

The poor electrical conductivity of metal-organic frameworks (MOFs) has been a stumbling block for its applications in many important fields. Therefore, exploring a simple and effective strategy to regulate the conductivity of MOFs is highly desired. Herein, anionic guest molecules are incorporated inside the pores of a cationic MOF (PFC-8), which increases its conductivity by five orders of magnitude while maintaining the original porosity.

Knowledge and intake of folic acid to prevent neural tube defects among pregnant women in urban China: a cross-sectional study.

Background: The prevalence of neural tube defects (NTDs) in China declined during 2000-2017 with periconceptional folic acid (FA) supplementation, which is effective in reducing the risk of birth defects. We aimed to assess the knowledge and actual use of FA among Chinese pregnant women and to explore factors associated with FA use before pregnancy.

Methods: All data were collected in face-to-face interviews during health visits among pregnant women.

Engineering the Bandgap and Surface Structure of CsPbCl Nanocrystals to Achieve Efficient Ultraviolet Luminescence.

Herein, we report the design of novel ultraviolet luminescent CsPbCl nanocrystals (NCs) with the emission peak at 381 nm through doping of cadmium ions. Subsequently, a surface passivation strategy with CdCl is adopted to improve their photoluminescence quantum yield (PLQY) with the maximum value of 60.5 %, which is 67 times higher than that of the pristine counterparts.

The partition principles for atomic-scale structures and their physical properties: application to the nonlinear optical crystal material KBeBOF.

In implementing the materials genome approach to search for new materials with interesting properties or functions, it is necessary to find the correct functional motif. To this end, it is common to partition an extended structure into various building units and then partition its properties to find the appropriate functional motif. We have developed the general principles for partitioning a structure and its properties in terms of a set of atoms and bonds by analyzing the differential cross-sections of neutron and X-ray scattering phenomena and proposed the procedures with which to partition an extended structure and its properties.

Second harmonic generation responses of KHPO: importance of K and breaking down of Kleinman symmetry.

The second harmonic generation (SHG) responses of the paraelectric and ferroelectric phases of KHPO (KDP) were calculated by first-principles density functional theory (DFT) calculations, and the individual atom contributions to the SHG responses were analyzed by the atom response theory (ART). We show that the occurrence of static polarization does not enhance the SHG responses of the ferroelectric KDP, and that the Kleinman symmetry is reasonably well obeyed for the paraelectric phase, but not for the ferroelectric phase despite that the latter has a larger bandgap. This is caused most likely by the fact that the ferroelectric phase has lower-symmetry local structures than does the paraelectric phase.

Physical Properties of Molecules and Condensed Materials Governed by Onsite Repulsion, Spin-Orbit Coupling and Polarizability of Their Constituent Atoms.

The onsite repulsion, spin-orbit coupling and polarizability of elements and their ions play important roles in controlling the physical properties of molecules and condensed materials. In celebration of the 150th birthday of the periodic table this year, we briefly review how these parameters affect the physical properties and are interrelated.

Key Factors Controlling the Large Second Harmonic Generation in Nonlinear Optical Materials.

The second harmonic generation (SHG) responses of nonisostructural nonlinear optical (NLO) compounds, β-BaBO, LiBO, CsBO, CsLiBO, KBeBOF, and LiCsPO, were examined by density functional theory (DFT) calculations, and the contributions of their individual cations and anions were determined by performing atomic response theory analyses. In all of these compounds, the contribution of all metal cations lies in the range of ∼9.3 to ∼29.

Folate deficiency induced H2A ubiquitination to lead to downregulated expression of genes involved in neural tube defects.

Background: Neural tube defects (NTDs) are common congenital malformations resulting in failure of the neural tube closure during early embryonic development. Although it is known that maternal folate deficiency increases the risk of NTDs, the mechanism remains elusive.

Results: Herein, we report that histone H2A monoubiquitination (H2AK119ub1) plays a role in neural tube closure.

Electronic Structure and Lithium Diffusion in LiAl(OH)Cl Studied by First Principle Calculations.

First-principles calculations based on the density functional theory (DFT) were carried out to study the atomic structure and electronic structure of LiAl(OH)Cl, the only material in the layered double hydroxide family in which delithiation was found to occur. Ab initio molecular dynamics (AIMD) simulations were used to explore the evolution of the structure of LiAl(OH)Cl during a thermally induced delithiation process. The simulations show that this process occurs due to the drastic dynamics of Li at temperatures higher than ~450 K, in which the [Al(OH)] host layers remain stable up to 1100 K.

F-box protein FBXO30 mediates retinoic acid receptor γ ubiquitination and regulates BMP signaling in neural tube defects.

Retinoic acid (RA), an active derivative of vitamin A, is critical for the neural system development. During the neural development, the RA/RA receptor (RAR) pathway suppresses BMP signaling-mediated proliferation and differentiation of neural progenitor cells. However, how the stability of RAR is regulated during neural system development and how BMP pathway genes expression in neural tissue from human fetuses affected with neural tube defects (NTDs) remain elusive.

Dependence of the Second-Harmonic Generation Response on the Cell Volume to Band-Gap Ratio.

The second-harmonic generation (SHG) coefficients of 12 nonlinear optical chalcopyrites, ( = Zn, Cd; = Si, Ge, Sn; = P, As) were calculated by first-principles methods to find that given the primitive cell volume and the band gap of , the SHG coefficients of increase almost linearly with increasing value of /. This suggests that a noncentrosymmetric crystal has a large SHG response when it consists of large atoms, leading to a small band gap.

Large Second Harmonic Generation (SHG) Effect and High Laser-Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide.

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga Se phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.

Nonequivalent Spin Exchanges of the Hexagonal Spin Lattice Affecting the Low-Temperature Magnetic Properties of RInO (R = Gd, Tb, Dy): Importance of Spin-Orbit Coupling for Spin Exchanges between Rare-Earth Cations with Nonzero Orbital Moments.

Rare-earth indium oxides RInO (R = Gd, Tb, Dy) consist of spin-frustrated hexagonal spin lattices made up of rare-earth ions R, where R = Gd (f, L = 0), Tb (f, L = 3), and Dy (f, L = 5). We carried out DFT calculations for RInO, including on-site repulsion U with/without spin-orbit coupling (SOC), to explore if their low-temperature magnetic properties are related to the two nonequivalent nearest-neighbor (NN) spin exchanges of their hexagonal spin lattices. Our DFT + U + SOC calculations predict that the orbital moments of the Tb and Dy ions are smaller than their free-ion values by ∼2μ while the Tb spins have an in-plane magnetic anisotropy, in agreement with the experiments.

The Large Second-Harmonic Generation of LiCs PO is caused by the Metal-Cation-Centered Groups.

We evaluated the individual atom contributions to the second harmonic generation (SHG) coefficients of LiCs PO (LCPO) by introducing the partial response functionals on the basis of first principles calculations. The SHG response of LCPO is dominated by the metal-cation-centered groups CsO and LiO , not by the nonmetal-cation-centered groups PO expected from the existing models and theories. The SHG coefficients of LCPO are determined mainly by the occupied orbitals O 2p and Cs 5p as well as by the unoccupied orbitals Cs 5d and Li 2p.

Superconductivity Induced by Oxygen Doping in Y O Bi.

When doped with oxygen, the layered Y O Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines for discovering new superconductors. We probed these questions in terms of first-principles calculations for undoped and O-doped Y O Bi.

Stable compositions and structures in the Na-Bi system.

At P = 1 atm, the only stable compounds in the Na-Bi binary system are Na3Bi and NaBi, which have recently been discovered to exhibit intriguing electronic behaviour as a 3D topological Dirac semimetal and a topological metal, respectively. By means of first-principles calculations coupled with evolutionary structural searches, we have systematically investigated the phase stabilities, the crystal structures and the corresponding electronic properties of the binary Na-Bi system. At ambient pressure, our calculations have reproduced well the experimentally observed compositions and structures of Na3Bi and NaBi.

Topological metal of NaBi with ultralow lattice thermal conductivity and electron-phonon superconductivity.

By means of first-principles and ab initio tight-binding calculations, we found that the compound of NaBi is a three-dimensional non-trivial topological metal. Its topological feature can be confirmed by the presence of band inversion, the derived effective Z2 invariant and the non-trivial surface states with the presence of Dirac cones. Interestingly, our calculations further demonstrated that NaBi exhibits the uniquely combined properties between the electron-phonon coupling superconductivity in nice agreement with recent experimental measurements and the obviously anisotropic but extremely low thermal conductivity.