Ultrahigh breakdown current density of van der Waals One Dimensional PdBr2\mathrm{PdBr_2}

One-dimensional (1D) van der Waals (vdW) materials offer nearly defect-free strands as channel material in the field-effect transistor (FET) devices and probably, a better interconnect than conventional copper with higher current density and resistance to electro-migration with sustainable down-scaling. We report a new halide based "truly" 1D few-chain atomic thread, PdBr$_2$, isolable from its bulk which crystallizes in a monoclinic space group C2/c. Liquid phase exfoliated nanowires with mean length (20$\pm$1)$\mu$m transferred onto SiO$_2$/Si wafer with a maximum aspect ratio of 5000 confirms the lower cleavage energy perpendicular to chain direction. Moreover, an isolated nanowire can also sustain current density of 200 MA/cm$^\mathrm{2}$ which is atleast one-order higher than typical copper interconnects. However, local transport measurement via conducting atomic force microscopy (CAFM) tip along the cross direction of the single chain records a much lower current density due to the anisotropic electronic band structure. While 1D nature of the nanoobject can be linked with non-trivial collective quantum behavior, vdW nature could be beneficial for the new pathways in interconnect fabrication strategy with better control of placement in an integrated circuit (IC)

Spin-crossover assisted metallization of few-layer FePS3_3 at 1.45 GPa

Magnetic insulators in reduced dimension are the ideal model systems to study spin-crossover(SCO) induced cooperative behavior under pressure. Similar to the external perturbations like light illumination or temperature, external pressure may provide new pathway to accelerate giant lattice collapse,and subsequently Mott transition in van der Waals (vdW) materials with diminishing effect of the third dimension. Here, we investigate room-temperature layer-dependent SCO and insulator-metal transition in vdW magnet,FePS3, under high pressure using micro-Raman scattering.Experimentally obtained spectra, in agreement with the computed Raman modes, indicates evidence of IMT of FePS3 started off with a spin-state transition from a high (S=2) to low spin state (S=0) with a thickness dependent critical pressure (P_c) which reduces to 1.45 GPa in 3-layer flakes compared to 10.8 GPa for the bulk counterpart. Additionally, a broad Raman mode (P*) emerges between 310 cm^{-1} and 370 cm^{-1} at elevated pressure for three different thicknesses of FePS3 flakes (3-100 layers), also corroborated with computational results which suggests the pressure dependent decrease of metal-ligand bond distance(Fe-S) with lowering of magnetic moment in FePS3. Phenomenologically, our results in few-layer flakes with strong structural anisotropy which enhances the in-plane strain with applied pressure can be understood by adopting Hubbard model and considering the spectral-range (bandwidth W) as a function of layer numbers and pressure with a power-law scaling. Reduction of the critical pressure for phase transition in few-layer vdW magnets to 1-2 GPa marks the possibility of using nano-enclosure fit for use in device electronics where the pressure is induced due to interfacial adhesion, like in vdW heterostructure or molecules trapped between layers,and thereby,avoiding the conventional use of diamond anvil cell

Proximitized spin-phonon coupling in topological insulator due to two-dimensional antiferromagnet

Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of two-dimensional (2D) van der Waals (vdW) materials. Herein, we report the observation of spin-phonon coupling in the otherwise non-magnetic TI Bi$_\mathrm{2}$Te$_\mathrm{3}$, due to the proximity of FePS$_\mathrm{3}$ (an antiferromagnet (AFM), $T_\mathrm{N}$ $\sim$ 120 K), in a vdW heterostructure framework. Temperature-dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of the characteristic phonon modes of Bi$_{2}$Te$_{3}$ (106 cm$^{-1}$ and 138 cm$^{-1}$) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism, where the respective phonon frequencies of Bi$_{2}$Te$_{3}$ couple to phonons of similar frequencies of FePS$_3$ in the AFM phase, has been adopted to understand the origin of the hybrid magneto-elastic modes. At the same time, the reduction of characteristic $T_\mathrm{N}$ of FePS$_3$ from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe-S-Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, our data suggest a double softening of phonon modes of Bi$_\mathrm{2}$Te$_\mathrm{3}$ (at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible probe for delineating the magnetic ordering in bulk and surface of a hybrid topological insulator

Methotrexate-Loaded Gelatin and Polyvinyl Alcohol (Gel/PVA) Hydrogel as a pH-Sensitive Matrix

The aim was to formulate and evaluate Gel/PVA hydrogels as a pH-sensitive matrix to deliver methotrexate (MTX) to colon. The primed Gel/PVA hydrogels were subjected to evaluation for swelling behavior, diffusion coefficient, sol-gel characteristic and porosity using an acidic (pH 1.2) and phosphate buffer (PBS) (pH 6.8 & pH 7.4) media. Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA) were performed to evaluate the chemical compatibility of the Gel/PVA hydrogel. The shape alteration and release of Gel/PVA hydrogel was conducted at pH 1.2, pH 6.8 and pH 7.4. The drug release kinetic mechanism was determined using various kinetic equations. The physicochemical evaluation tests and drug release profile results were found to be significant (p < 0.01). However, it was dependent on the polymers' concentration, the pH of the release media and the amount of the cross-linking agent. Hydrogels containing the maximum amount of gel showed a dynamic equilibrium of 10.09 ± 0.18 and drug release of 93.75 ± 0.13% at pH 1.2. The kinetic models showed the release of MTX from the Gel/PVA hydrogel was non-Fickian. The results confirmed that the newly formed Gel/PVA hydrogels are potential drug delivery systems for a controlled delivery of MTX to the colo

Maternal Bacterial Engraftment in Multiple Body Sites of Cesarean Section Born Neonates after Vaginal Seeding—a Randomized Controlled Trial

ABSTRACT Children delivered by elective, prelabor Cesarean section (C-section) are not exposed to the birth canal microbiota and, in relation to vaginally delivered children, show altered microbiota development. Perturbed microbial colonization during critical early-life windows of development alters metabolic and immune programming and is associated with an increased risk of immune and metabolic diseases. In nonrandomized studies, vaginal seeding of C-section-born neonates partially restores their microbiota colonization to that of their vaginally delivered counterparts, but without randomization, confounding factors cannot be excluded. In a double-blind, randomized, placebo-controlled trial, we determined the effect of vaginal seeding versus placebo seeding (control arm) on the skin and stool microbiota of elective, prelabor C-section-born neonates (n = 20) at 1 day and 1 month after birth. We also examined whether there were between-arm differences in engraftment of maternal microbes in the neonatal microbiota. In relation to the control arm, vaginal seeding increased mother-to-neonate microbiota transmission and caused compositional changes and a reduction in alpha diversity (Shannon Index) of the skin and stool microbiota. The neonatal skin and stool microbiota alpha diversity when maternal vaginal microbiota is provided is intriguing and highlights the need of larger randomized studies to determine the ecological mechanisms and effects of vaginal seeding on clinical outcomes. IMPORTANCE Children delivered by elective C-section are not exposed to the birth canal and show altered microbiota development. Impairing microbial colonization during early life alters metabolic and immune programming and is associated with an increased risk of immune and metabolic diseases. In a double-blind, randomized, placebo-controlled trial, we determined the effect of vaginal seeding on the skin and stool microbiota of elective C-section born neonates and found that vaginal seeding increased mother-to-neonate microbiota transmission and caused compositional changes and a reduction in the skin and stool microbiota diversity. The reduction of neonatal skin and stool microbiota diversity when maternal vaginal microbiota is provided is intriguing and highlights the need of larger randomized studies to determine the ecological mechanisms and effects of vaginal seeding on clinical outcomes

Emergence of a Non-van der Waals Magnetic Phase in a van der Waals Ferromagnet

International audienceManipulation of long-range order in two-dimensional (2D) van der Waals (vdW) magnetic materials (e.g., CrI$_3$, CrSiTe$_3$ etc.), exfoliated in few-atomic layer, can be achieved via application of electric field, mechanical-constraint, interface engineering, or even by chemical substitution/doping. Usually, active surface oxidation due to the exposure in the ambient condition and hydrolysis in the presence of water/moisture causes degradation in magnetic nanosheets which, in turn, affects the nanoelectronic/spintronic device performance. Counterintuitively, our current study reveals that exposure to the air at ambient atmosphere results in advent of a stable nonlayered secondary ferromagnetic phase in the form of Cr$_2$Te$_3$ (T$_{C2}$~ 160 K) in the parent vdW magnetic semiconductor Cr$_2$Ge$_2$Te$_6$ (T$_{C1}$~ 69 K). In addition, the magnetic anisotropy energy (MAE) enhances in the hybrid by an order from the weakly anisotropic pristine Cr$_2$Ge$_2$Te$_6$ crystal, increasing the stability of the FM ground state with time. Comparing with the freshly prepared Cr$_2$Ge$_2$Te$_6$, the coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is confirmed through systematic investigation of crystal structure along with detailed dc/ac magnetic susceptibility, specific heat, and magnetotransport measurement. To capture the concurrence of the two ferromagnetic phases in a single material, Ginzburg-Landau theory with two independent order parameters (as magnetization) with a coupling term can be introduced. In contrast to rather common poor environmental stability of the vdW magnets, our results open possibilities of finding air-stable novel materials having multiple magnetic phases

Cross-ancestry atlas of gene, isoform, and splicing regulation in the developing human brain

INTRODUCTION Genome-wide association studies (GWASs) have identified thousands of loci associated with neurodevelopmental and psychiatric disorders, yet our lack of understanding of the target genes and biological mechanisms underlying these associations remains a major challenge. GWAS signals for many neuropsychiatric disorders, including autism spectrum disorder, schizophrenia, and bipolar disorder, are particularly enriched for gene-regulatory elements active during human brain development. However, the lack of a unified population-scale, ancestrally diverse gene-regulatory atlas of human brain development has been a major obstacle for the functional assessment of top loci and post-GWAS integrative analyses. RATIONALE To address this critical gap in knowledge, we have uniformly processed and systematically characterized gene, isoform, and splicing quantitative trait loci (cumulatively referred to as xQTLs) in the developing human brain across 672 unique samples from 4 to 39 postconception weeks spanning European, African-American, and Latino/admixed American ancestries). With this expanded atlas, we sought to specifically localize the timing and molecular features mediating the greatest proportion of neuropsychiatric GWAS heritability, to prioritize candidate risk genes and mechanisms for top loci, and to compare with analogous results using larger adult brain functional genomic reference panels. RESULTS In total, we identified 15,752 genes harboring a gene, isoform and/or splicing cis-xQTL, including 49 genes associated with four large, recurrent inversions. Highly concordant effect sizes were observed across populations, and our diverse reference panel improved resolution to fine-map underlying candidate causal regulatory variants. Substantially more genes were found to harbor QTLs in the first versus second trimester of brain development, with a notable drop in gene expression and splicing heritability observed from 10 to 18 weeks coinciding with a period of rapidly increasing cellular heterogeneity in the developing brain. Isoform-level regulation, particularly in the second trimester, mediated a greater proportion of heritability across multiple psychiatric GWASs compared with gene expression regulation. Through colocalization and transcriptome-wide association studies, we prioritized biological mechanisms for ~60% of GWAS loci across five neuropsychiatric disorders, with >2-fold more colocalizations observed compared with larger adult brain functional genomic reference panels. We observed convergence between common and rare-variant associations, including a cryptic splicing event in the high-confidence schizophrenia risk gene SP4. Finally, we constructed a comprehensive set of developmentally regulated gene and isoform coexpression networks harboring unique cell-type specificity and genetic enrichments. Leveraging this cell-type specificity, we identified >8000 module interaction QTLs, many of which exhibited additional GWAS colocalizations. Overall, neuropsychiatric GWASs and rare variant signals localized more strongly within maturing excitatory- and interneuron-associated modules compared with those enriched for neural progenitor cell types. Results can be visualized at devbrainhub.gandallab.org. CONCLUSION We have generated a large-scale, cross-population resource of gene, isoform, and splicing regulation in the developing human brain, providing comprehensive developmental and cell-type-informed mechanistic insights into the genetic underpinnings of complex neurodevelopmental and psychiatric disorders