Browse Articles

Correction for Armstrong et al., Genetic differentiation and precolonial Indigenous cultivation of hazelnut ( <i>Corylus cornuta</i> , Betulaceae) in western North America

Correction for Yun et al., GPCR targeting of E3 ubiquitin ligase MDM2 by inactive β-arrestin

Correction for Zhou et al., A genome-wide microRNA screen identifies the microRNA-183/96/182 cluster as a modulator of circadian rhythms

Correction for Huo et al., Hierarchical behavior control by a single class of interneurons

Nocturnal camouflage through background matching against moonlight

Camouflage is often considered a daytime phenomenon based on light and shade. Nocturnal camouflage can also occur, but its mechanistic basis remains unclear. Here, we analyze the conditions for background matching (BM) of avian predators against the night sky. Such concealment is achieved when the contrast between the predator and the sky is smaller than the contrast detection threshold of prey. This condition cannot be fulfilled under isotropic skies, as in fully overcast or moonless nights. However, on clear moonlit nights, the isotropy of the sky radiance is broken due to the presence of the Moon, and the conditions for BM can be met for a wide range of sky directions. This effect is mainly dependent on the altitude of the Moon above the horizon, rather than on Moon phase. We have modeled the feasibility of concealment through BM of a typically white barn owl ( Tyto alba ) when hunting rodents, based on its contrast against the moonlit sky. We considered the radiometric quantities of the sky, the ground, and the bird’s undersides. Our results show that a barn owl with highly reflecting underparts may approach a rodent from broad regions of the moonlit sky while keeping itself below the contrast detection threshold of the mouse M-cones and rods. S-cones, in turn, remain below their excitation threshold for most of the lunar cycle. Our results demonstrate that the white color of barn owls serves as camouflage tailored to the moonlit sky background, providing a mechanistic basis for understanding nocturnal camouflage.

<i>Ab initio</i> study of randomly disordered hexagonal close-packed (rhcp) phase in platinum

Platinum is one of the most important technological materials, and one of the most studied transition metals. Yet, its phase diagram remains virtually unknown. The solid phase of Pt at ambient conditions is face-centered cubic (fcc). However, in a previous paper [L. Burakovsky et al., J. Phys. Conf. Ser. 500, 162001 (2014)], we predicted Pt to undergo a phase transformation from fcc to another solid phase, namely, randomly disordered hexagonal close-packed (hcp) or simply random hcp (rhcp), which spans a pressure interval of ∼35–300 GPa and exists at temperatures ∼&amp;gt;3000 K. Since then, rhcp-Pt has been widely discussed in the literature but has been neither confirmed experimentally nor completely ruled out theoretically. In this work, using the technique of three-phase ab initio quantum molecular dynamics (QMD) simulations, we demonstrate the appearance of rhcp-Pt and determine the phase boundary that separates rhcp from fcc on the Pt phase diagram. These three-phase simulations consist in evolving a system containing two different hexagonal polytypes separated by liquid until the system reaches its final equilibrium state. It then appears that the results of the most recent experimental study on Pt melting, by Geballe et al. [Phys. Rev. Mater. 5, 033803 (2021)], map out a curve identified by Geballe et al. as the Pt melting curve, which virtually coincides with the fcc-rhcp solid–solid phase boundary presented in our work. We discuss the reasons for misinterpreting the fcc-rhcp solid–solid phase transition as melting. We calculate the equation of state (EOS) of fcc-Pt and refine its melting curve via more accurate QMD simulations using the Z method implemented with Vienna Ab initio Simulation Package. We also calculate the EOS and melting curve of rhcp-Pt. The two melting curves, along with the fcc-rhcp phase boundary, define the ab initio phase diagram of Pt that we present here. Our results extend the pressure range of rhcp-Pt by more than twice compared to the original result of 2014, namely, to ∼50–650 GPa. Finally, we argue that, despite being polymorphic, Pt should be considered as reliable EOS and shock-wave standards.

Multicaloric effect in FeRh, exploiting the thermal hysteresis in a multi-stimuli cycle combining pulsed magnetic field and uniaxial load

Large magnetocaloric effects can be observed in materials with first-order magneto-structural phase transition. However, materials with large thermal hysteresis show a reduced effect in moderate fields (∼2 T) because the external field is insufficient to induce a fully reversible transformation. The hysteresis can be overcome or even exploited by applying a second external stimulus. A multi-stimuli test bench has been built to demonstrate the multicaloric effect in FeRh alloy using a pulsed magnetic field up to 9 T and a uniaxial stress of up to 700 MPa. A cyclic multicaloric effect of ±2.5 K could be observed for a sequential application of a pulsed field of 3 T and a uniaxial stress of 700 MPa. The interplay among external field strength, thermal hysteresis, and the transition width enables the use of pulsed magnetic fields and allows a decoupling of the applied magnetic field and the heat transfer process in the multi-stimuli cycle.

Magnetic properties and enhanced magnetocaloric effect in EuAl3Si single crystals

This study presents systematic investigations into the growth and physical properties of EuAl3Si single crystals, encompassing magnetic, transport, and thermodynamic analyses. EuAl3Si undergoes a ferromagnetic transition at TC = 15 K. A significant reversible magnetocaloric effect was observed around TC. Strikingly, with a small change of magnetic field 2 T, the maximum values of magnetic entropy change (13.4 J/kg K), refrigerant capacity (166 J/kg), and adiabatic temperature change (7.2 K) are found. These parameters, respectively, are 60%, 148%, and 64% larger than those of the parent compound EuAl4 and suggest EuAl3Si as an excellent candidate for magnetic-refrigeration applications near the temperature of liquid hydrogen. The possible mechanism for this enhancement is also discussed.

Study on chemical mechanism of processing silicon by PMMA in water

In a previous study, an eco-friendly planarization method for glass and silicon was proposed, utilizing the chemical properties of polymethyl methacrylate (PMMA) in water. Atomically flat, defect-free glass and silicon surfaces were observed using atomic force microscopy, indicating that the underlying processing phenomenon is based on chemical reactions. To date, PMMA remains the only material capable of achieving such surface flattening in water. Understanding the chemical processing mechanism is crucial for improving processing conditions and identifying other suitable polymer materials. In this study, ATR-FTIR spectroscopy and XPS were employed to analyze both the PMMA and the processed silicon surfaces. Based on various observations, we concluded that the O = C–O–C groups on the PMMA surface undergo hydrolysis during processing in water, leading to their rupture. This rupture creates active sites on the PMMA surface, which promote the formation of C–O–Si bonds between the PMMA and the silicon surface, facilitating the removal of silicon atoms.

Spectroscopic ellipsometry of epitaxially stressed ferroelectric films

Explicit knowledge of the optical properties of epitaxial perovskite oxide ferroelectric thin films is crucial for photonic applications and fundamental understanding of such films. Accurate assessment of these properties is difficult because of the presence of substrate and substrate-imposed stress, as well as small thicknesses of the films. Here, we explore capabilities of spectroscopic ellipsometry to establish the optical NIR–VIS–VUV dielectric function in epitaxial Ba0.5Sr0.5TiO3 films (thicknesses from 15 to 100 nm) subjected to substrate-imposed in-plane compression. The experimentally acquired data were processed assuming films which are either optically homogeneous or gradually varying out-of-plane, or containing two distinct phases. The obtained results were evaluated considering mathematical accuracy of the models and physical relevance of the extracted dielectric functions. It is shown that homogeneous approximation is valid for films with thicknesses of 15 and 100 nm. The homogeneous approximation is unsuitable, whereas the others are marginally acceptable, for films with thicknesses of 30 and 50 nm. The results are discussed in terms of substrate-induced inhomogeneous stress. The demonstrated approach can be useful for ellipsometric investigations of many other epitaxial films of ferroelectrics and related materials.

Wafer bow in diamond heteroepitaxy: Causes, their analytical description, and viable solutions

Wafer bow is of considerable technological relevance for virtually all semiconductor materials grown by heteroepitaxy. In the case of diamond, the reported curvature values are exceptionally large for synthesis by plasma chemical vapor deposition on oxide substrates. In contrast to the usual explanation by differences in coefficients of thermal expansion (CTEs), the present analysis reveals that the CTE α of the substrate combined with its thermal conductivity λ controls the radius of the surface on which the diamond layer will grow. The ratio λ/α represents a figure of merit for the choice of favorable substrates facilitating maximum flatness. Calculated radii under typical process conditions fit with literature reports. Bow values exceeding these predictions significantly are attributed to the formation of intrinsic stress in diamond according to the effective climb of dislocations mechanism. Stress profiles inside of thick diamond layers after the removal of the substrate are calculated based on this mechanism taking into consideration the experimentally observed decrease in the dislocation density. They predict compressive stress in the center and tensile stress at the nucleation as well as at the growth surface in accordance with literature reports and Raman measurements. High intrinsic stress in the growing film can heavily deform the growth substrate provided that the deposition temperature is above its brittle/ductile transition. In all cases, deformation caused by extrinsic stress occurring during cooldown is =apparently of minor relevance. Two alternative strategies for the achievement of flat wafers are presented.

Identification of paramagnetic species in silver-doped barium–germanium–gallium glass exposed to electron irradiation

Ionizing irradiation was performed on barium–germanium–gallium (BGG) glasses using a 2.5 MeV electron beam. Through electron spin resonance spectroscopy, paramagnetic point defects, such as germanium- and gallium-related electron and hole trap centers, have been identified. The presence of silver in the BGG glass appears to hinder the stability of these defects at lower energy doses (104 Gy), with silver becoming the main trapping center. At higher energy doses (106 Gy), the glass undergoes structural modifications, hindering the trapping process of silver ions. Additionally, we evidence the importance of alkaline elements such as potassium and sodium on silver ions trapped centers’ formation.

Computational study of a novel microwave electrothermal thruster using dielectric resonators (DRs)

This paper presents the study of a novel microwave electrothermal thruster with a dielectric resonator based approach for the plasma localization and propellant gas heating. The study is purely computational in a two-dimensional planar geometry and establishes the concept and demonstrates feasibility as an electric propulsion device. The resonant structure consists of a two cylindrical high dielectric constant (ɛr = 172.5) resonator enclosed within a plasma chamber that terminates at a convergent-divergent nozzle. The plasma chamber is irradiated by an incoming microwave that experiences a large wave electric field amplification of about 25 000 at a resonant frequency of 18.5 GHz. The field amplification results in breakdown and establishment of a steady plasma in a helium propellant in close vicinity to the nozzle. With a microwave power input of 40 W mm−1 (depth) at 1 atm. discharge pressure, the peak gas temperature is about 1300 K, with an electron number density of approximately 1020 m−3, resulting in a peak specific impulse of 245 s. The corresponding cold gas specific impulse is 150. The high specific impulse is attributed to the plasma hot zone being located in close vicinity of the nozzle, which effectively increases thrust. However, the thrust increase is accompanied by significant heat conduction losses, particularly as the dielectric gap size increases, underscoring the importance of thermal management in the system.

Interlayer and intralayer magnetic interactions for room-temperature strong ferrimagnetism of layered organic–inorganic hybrid nanoplates

In the past few decades, a development of organic magnets with room-temperature strong ferromagnetism is challenged by the difficulty of creating three-dimensional (3D) long-range magnetic orderings in organic materials at a temperature higher than room temperature. Here, we report room-temperature ferrimagnetism of a tetragonal organic–inorganic hybrid Fe14Se16(tepa)III (tepa = tetraethylenepentamine), where III represents a coordination of a tepa molecule with a Fe3+ ion for an organic complex. The layered hybrid in a nanoplate-like shape is formed by periodic incorporation of tetragonal β-Fe3Se4 inorganic layers and organic spacing layers consisting of tepa and Fe3+. Fe14Se16(tepa)III shows a saturation magnetization MS of 7.2 emu g−1 at 300 K and a record-high Néel temperature TN (&amp;gt;560 K) in the organic magnets reported experimentally. A Mössbauer spectrum confirms a 3D long-range magnetic ordering of Fe2+ [S = 2 (71.4%)] and Fe3+ ions [S = 5/2 (21.7%) and 1/2 (4.0%)] in β-Fe3Se4 layers and organic spacing layers of Fe14Se16(tepa)III,9. First-principles calculations explain that the 3D long-range antiferromagnetic interactions between interlayer and intralayer irons result in the strong ferrimagnetism of Fe14Se16(tepa)III. This study unveils the possibility of tuning magnetic couplings of interlayer and intralayer high-spin Fe3+ and Fe2+ for enhancing the ferrimagnetism of layered hybrids and, thus, for future room-temperature magnetic/spintronic applications.

Influence of perpendicular uniaxial anisotropy on the switching of a magnetic vortex

Magnetic vortices are being considered for information storage in magnetic devices. In this study, we used micromagnetic simulations to explore the effect of a perpendicular uniaxial anisotropy (PUA) on switching the vortex core in Permalloy nanodisks. We studied how the presence of the perpendicular uniaxial anisotropy (PUA) changes the spatial profile of the magnetic vortex. We determined the diameters of the vortex core as the perpendicular uniaxial anisotropy constant Kz varied. Additionally, we determined the frequencies and spatial profiles of the radial modes of the spin waves. Our results show that the PUA affects the frequencies of the spin modes of a magnetic vortex in a nanodisk. We have also created phase diagrams demonstrating the areas where reversing the magnetic vortex core is possible by applying a sinusoidal field perpendicular to the nanodisk plane.

Wave transformation in transmission lines with rapid connection and disconnection of reactive elements

Rapid switching of transmission line parameters has emerged as a way to manipulate signals and as a testbed for various electromagnetic processes in time-varying media, including metamaterials. In general, the switching results in wave reflection and transmission similar to that for a spatial interface but at new frequencies. Here, various realizations of parameter switching are studied: connection and disconnection of reactive elements (capacitors and inductors) in series and in parallel. The temporal boundary conditions for the current and voltage distributions are derived rigorously based on the telegrapher’s equations that explicitly model additional elements, instead of taking the equivalent values. It is shown that the temporal boundary conditions depend not only on the parameter values before and after switching but on its specific realization. Connecting or disconnecting reactive elements always involves energy losses. When new elements are added, two types of losses are identified. The first type is related to the creation of static magnetic and electric fields in the elements after switching. The second type is related to a very rapid energy dissipation during switching even for a vanishingly small resistivity in the line. When elements are removed, their energy is also removed from the waves. The effects of finite switching times are discussed. This study defines some serious constraints in using switchable transmission lines for the realization of photonic time crystals and efficient wave manipulation without externally added energy. The results are also applicable to wave propagation phenomena in other media with time-varying parameters.

Oxygenates production in a microfluidic dielectric barrier discharge device sustained in Ar/CH4/O2

Reforming of methane (CH4) is a process to produce syngas (CO/H2) and other value-added chemicals including oxygenates such as methanol (CH3OH). Atmospheric pressure plasmas have the potential to be more energy efficient than traditional reforming methods as value-added chemicals can be synthesized directly in the plasma without requiring an additional step. In this paper, we discuss the results from a computational investigation of the formation of oxygenates by CH4 oxidation in the presence of Ar, including CH3OH and CH2O, in a nanosecond pulsed dielectric barrier discharge. The plasma is formed in a microfluidic channel whose small dimensions are ideal for plasma formation at atmospheric pressure. The production and consumption mechanisms of dominant radicals and long-lived species are discussed in detail for the base case conditions of Ar/CH4/O2 = 50/25/25. CH3OH is produced primarily by CH3O reacting with CH3O and CH3O2 reacting with OH, while CH2O formation relies on reactions involving CH3O and CH3. The most abundant oxygenate formed is CO (produced by H abstraction from CHO). However, the greenhouse gas CO2 is also formed as a by-product. The effects of gas mixture are examined to maximize the CH3OH and CH2O densities while decreasing the CO2 density. Increasing the Ar percentage from 0% to 95% decreased the CH3OH and CH2O densities. At low Ar percentages, this is due to an increase in consumption of CH3OH and CH2O, while at high Ar percentages (&amp;gt;40% Ar), the production of CH3OH and CH2O is decreased. However, both CO and CO2 reached peak densities at 70%–90% Ar. Changing the CH4/O2 ratio while keeping 50% Ar in the discharge led to increased CH3OH and CH2O production, reaching peak densities at 35%–40% CH4. The CO and CO2 densities decreased beyond 20% CH4, indicating that a CH4 rich discharge is ideal for forming the desired oxygenates.

Endothelial-secreted Endocan activates PDGFRA and regulates vascularity and spatial phenotype in glioblastoma

AbstractExtensive neovascularization is a hallmark of glioblastoma (GBM). In addition to supplying oxygen and nutrients, vascular endothelial cells provide trophic support to GBM cells via paracrine signaling. Here we report that Endocan (ESM1), an endothelial-secreted proteoglycan, confers enhanced proliferative, migratory, and angiogenic properties to GBM cells and regulates their spatial identity. Mechanistically, Endocan exerts at least part of its functions via direct binding and activation of the PDGFRA receptor. Subsequent downstream signaling enhances chromatin accessibility of the Myc promoter and upregulates Myc expression inducing stable phenotypic changes in GBM cells. Furthermore, Endocan confers radioprotection on GBM cells in vitro and in vivo. Inhibition of Endocan-PDGFRA signaling with ponatinib increases survival in the Esm1 wild-type but not in the Esm1 knock-out mouse GBM model. Our findings identify Endocan and its downstream signaling axis as a potential target to subdue GBM recurrence and highlight the importance of vascular-tumor interactions for GBM development.

Electronegative effect in layered double-perovskite La1.9Ba0.1CuSnO6 adjusted by non-magnetic Zn doping

The La1.9Ba0.1Cu1−yZnySnO6 (0 ≤ y ≤ 0.25) (LBCZSO) ceramics were synthesized by the solid-state reaction, and the effect of non-magnetic Zn2+ ion doping on the crystal structure and electrical and magnetic properties is systematically investigated. It is found that all the samples are layered double perovskite with a space group P21/m. The resistivity ρ(T) shows a semiconductor behavior, which follows Mott's 3D variable-range hopping mode. The magnetizations M(T) and the isothermal M-H loops reveal the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions in the 2D CuO2 layer. With increasing Zn doping at Cu sites, the resistivity ρ(T) increases, the FM transition temperature TC decreases, the FM/AFM interactions weaken/enhance, and the ground state of the system changes from FM to AFM one. It is suggested that cationic electronegativity plays an important role in understanding the transport and magnetic properties of the non-magnetic Zn-doped La1.9Ba0.1CuSnO6, besides the cationic radius. Since the smaller electronegativity of Cu2+ ions compared to that of Sn4+ ions, the CuO6 octahedral distortion with the in-plane compressive strain and out-plane tensile strain is induced by the lattice mismatch between CuO2 and SnO2 layers, forming C-type AF structure with the spin-canted weak FM in 2D CuO2 plane. Since the different cationic electronegativities of Zn2+ and Cu2+ ions, non-magnetic Zn doping leads to the charge transfer between Zn and Cu ions, resulting in the electronic redistribution (transformation) along the ordered Cu–O–Zn chains and non-magnetic Cu+ ions in LBCZSO, which further speeds up the decrease of TC, lead to the abnormal change in the hopping energy W and Curie temperature Θ. Besides, it is confirmed that there is a spin-glass state transition at around 26 K in the non-magnetic Zn doping La1.9Ba0.1CuSnO6 compound.

In situ training of an in-sensor artificial neural network based on ferroelectric photosensors