Weak Field Research Articles

On Earth’s habitability over the Sun’s main-sequence history: joint influence of space weather and Earth’s magnetic field evolution

ABSTRACT The aim of this study is to analyse the Earth habitability with respect to the direct exposition of the Earth atmosphere to the solar wind (SW) along the Sun’s evolution on the main sequence including the realistic evolution of the space weather conditions and the Earth magnetic field. The MHD code PLUTO in spherical coordinates is applied to perform parametric studies with respect to the SW dynamic pressure and the interplanetary magnetic field intensity for different Earth magnetic field configurations. Quiet space weather conditions may not impact the Earth habitability. On the other hand, the impact of interplanetary coronal mass ejections (ICME) could lead to the erosion of the primary Earth atmosphere during the Hadean eon. A dipolar field of 30 μT is strong enough to shield the Earth from the Eo-Archean age as well as 15 and 5 μT dipolar fields from the Meso-Archean and Meso-Proterozoic, respectively. Multipolar weak field period during the Meso-Proterozoic age may not be a threat for ICME-like space weather conditions if the field intensity is at least 15 μT and the ratio between the quadrupolar (Q) and dipolar (D) coefficients is $\frac{Q}{D} \le 0.5$. By contrast, the Earth habitability in the Phanerozoic eon (including the present time) can be hampered during multipolar low field periods with a strength of 5 μT and $\frac{Q}{D} \ge 0.5$ associated with geomagnetic reversals. Consequently, the effect of the SW should be considered as a possible driver of Earth’s habitability.

Demonstration of Weak Polarization Electric Field III‐N LEDs based on Polar Plane

AbstractA strong polarization electric field (PEF) in III‐nitride semiconductors has adverse effects on the performance of III‐N light‐emitting diodes (LEDs). However, to reduce the PEF of III‐N LEDs based on the polar plane (c‐plane) remains a big challenge. Here, a weak PEF blue LED on c‐plane GaN with an InGaN/AlGaN superlattices (SLs) quantum barrier and InGaN quantum well grown by metal‐organic chemical vapor deposition is proposed. The InGaN/SLs multiple quantum wells (MQWs) show a significant reduction of PEF compared with traditional InGaN/GaN MQWs. A low electric field of 0.5 MV cm−1 is obtained, which is confirmed by power‐dependent photoluminescence (PL) and time‐resolved PL measurements. The proposed LEDs with InGaN/AlGaN SLs barriers present a low efficiency droop, a great wavelength stability, and a high −3 dB E‐O modulation bandwidth up to 1.01 GHz. This work demonstrates the role of InGaN/AlGaN SLs barriers in reducing the PEF of III‐N LEDs and provides a feasible technical route to achieve the weak PEF LEDs on c‐plane, which can be expanded and applied to the preparation of high‐performance, long wavelength, and deep UV III‐N LEDs.

Conformational Fluctuations and Induced Orientation of a Protein, Its Solvation Shell, and Bulk Water in Weak Non-Unfolding External Electric Fields.

Extreme external electric fields have been reported to disrupt the tertiary structure of stably folded proteins; however, the effects of weaker electric fields on many biomolecules, especially net-uncharged proteins, and on the surrounding aqueous environment have been rarely discussed. To explore these effects at the atomic level, here, we have used molecular dynamics simulations to estimate rotational motion and induced structural fluctuations in the model protein ubiquitin and its hydration layer due to applied non-unfolding electrostatic fields. When exposed to weak electric fields of up to 0.2 V nm-1, ubiquitin displayed competition between internal structure-maintaining molecular interactions and the external orienting force, which disrupted the local structure in certain regions of the protein. Moreover, relative to hydration water, bulk water showed a greater tendency to align with the electric field, indicating that the presence of protein caused hydration water to acquire rotational mobility different from that in a pure-water system. The differential influence of the applied electric field on the hydration and bulk water surrounding ubiquitin will be common to almost all (nonmembrane) biomacromolecules. Our findings highlight the importance of local dipoles and their electric polarizability even in net-uncharged biomolecules.

Lasing in Zn-doped GaAs nanowires on an iron film

In this work, we demonstrate optically pumped lasing in highly Zn-doped GaAs nanowires (NWs) lying on an iron film. The conically shaped NWs are first covered with an 8 nm thick Al2O3 film to prevent atmospheric oxidation and mitigate band-bending effects. Multimode and single-mode lasing have been observed for NWs with a length greater or smaller than 2 μm, respectively. Finite difference time domain calculations reveal a weak electric field enhancement in the Al2O3 layer at the NW/iron film interface for the lasing modes. The high Zn acceptor concentration in the NWs provides enhanced radiative efficiency and enables lasing on the iron film despite plasmonic losses. Our results open avenues for integrating NW lasers on ferromagnetic substrates to achieve new functionalities, such as magnetic field-induced modulation.

Computational study on the adsorption of small molecules to surface-supported Ni-porphyrins

With their flexible oxidation and spin states, surface-supported metalloporphyrins are attractive building blocks for tuneable, periodic spin interfaces. A technique to manipulate the spin in such systems is based on the adsorption of external gas ligands to the chelated metal center. In the search for promising interfaces, computational studies allow for a convenient scan through potential ligand candidates. In this contribution, we perform density functional theory calculations to investigate the coordination of six exemplary gases (CH4, H2O, NH3, CO, NO and NO2) to nickel tetraphenylporphyrin interfaces. Analyzing the formed complexes, we distinguish four major interaction mechanisms between metal center and ligand: non-interacting, weak field d-splitting, competing surface trans-effect and redox reaction. We find that a surface-mediated redox reaction between a strong π-acceptor (e.g.: NO2) and an unusually reduced metal (e.g.: Ni d9) has the strongest potential to induce spin changes at ambient conditions. Furthermore, we demonstrate how commonly chosen theoretical approximations may influence the interpretation of DFT calculations for metalloporphyrins and their complexes. By highlighting the limitations and possibilities of theoretical approaches, we hope to contribute to a better understanding and more selective harnessing of the special properties of surface-supported metalloporphyrins.

Achieving Broadband NIR-I to NIR-II Emission in an All-Inorganic Halide Double-Perovskite Cs2NaYCl6:Cr3+ Phosphor for Night Vision Imaging.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) offer numerous advantages, including compact size, tunable emission spectra, energy efficiency, and high integration potential. These features make them highly promising for various applications, such as night vision monitoring, food safety inspection, biomedical imaging, and theragnostics. All-inorganic halide double-perovskite materials, known for their large absorption cross section, excellent defect tolerance, and long carrier diffusion radius, serve as unique matrices for constructing near-infrared fluorescent materials. In this study, we successfully prepared the all-inorganic metal halide double-perovskite Cs2NaYCl6:Cr3+ using a grinding-sintering method. A small fraction of the [YCl6] octahedra within the host material's lattice was substituted with Cr3+ ions, resulting in the creation of the Cs2NaYCl6:Cr3+ phosphor. When excited with λ = 310 nm UV light, the phosphor exhibited a broad emission range spanning from 800 to 1400 nm, covering the NIR-I and NIR-II regions. It had a broad bandwidth emission of 185 nm and achieved a fluorescence quantum yield of 20.2%. The unique broadband emission of the phosphor originates from the weak crystal field environment provided by the Cs2NaYCl6 host matrix, which enhances the luminescence properties of the Cr3+ ions. To create NIR pc-LEDs, the phosphor was encapsulated onto a commercially available UV LED chip operating at 310 nm. The potential application of these NIR pc-LEDs in night vision imaging was successfully validated.

Long-Wavelength Near-Infrared Divalent Nickel-Activated Double-Perovskite Ba2MgWO6 Phosphor as Imaging for Human Fingers.

Transmission near-infrared (NIR) imaging technology has great potential for biomedical imaging because of its lower water absorption coefficient and highly reduced photon scattering effect in biological tissues compared to visible light. The extent of biological tissue photon scattering is inversely proportional to wavelength; therefore, in principle, imaging with long-wavelength NIR helps improve the resolution of the optical image, but deep tissue high-resolution luminescence imaging is still very challenging technically. Here, we report the discovery of a Ba2MgWO6:Ni2+ double perovskite phosphor that emits broadband long-wavelength NIR (1200-2000 nm) under 365 nm near-ultraviolet (UV) excitation, with a full width at half-maximum of 255 nm. The luminescence quantum efficiency of the phosphor with optimized composition reached 16.67%. The analysis of the crystal structure of Ba2MgWO6:Ni2+ suggests that Ni2+ ions preferentially occupy the W6+ site in octahedrons with a weak crystal field, which leads to a large Stokes shift. An as-prepared long-wavelength NIR pc-LED device was built by packaging an optimized phosphor with a low-power near-UV-LED chip, which was tested to generate clear imaging of venous vessels in human fingers. These unique properties of the Ba2MgWO6:Ni2+ double perovskite phosphor makes it a promising application in the field of imaging sources for body tissue..

Anisotropy of out-of-phase magnetic susceptibility in titanomagnetite-bearing rocks due to weak field hysteresis

Anisotropy of out-of-phase magnetic susceptibility in titanomagnetite-bearing rocks due to weak field hysteresis

Weak field and slow motion limits in energy–momentum powered gravity

We explore the weak field and slow motion limits, Newtonian and Post-Newtonian limits, of the energy–momentum powered gravity (EMPG), viz., the energy–momentum squared gravity (EMSG) of the form f(TμνTμν)=α(TμνTμν)η with α and η being constants. We have shown that EMPG with η≥0 and general relativity (GR) are not distinguishable by local tests, say, the Solar System tests; as they lead to the same gravitational potential form, PPN parameters, and geodesics for the test particles. However, within the EMPG framework, Mast, the mass of an astrophysical object inferred from astronomical observations such as planetary orbits and deflection of light, corresponds to the effective mass Meff(α,η,M)=M+Mempg(α,η,M), M being the actual physical mass and Mempg being the modification due to EMPG. Accordingly, while in GR we simply have the relation Mast=M, in EMPG we have Mast=M+Mempg. Within the framework of EMPG, if there is information about the values of {α,η} pair or M from other independent phenomena (from cosmological observations, structure of the astrophysical object, etc.), then in principle it is possible to infer not only Mast alone from astronomical observations, but M and Mempg separately. For a proper analysis within EMPG framework, it is necessary to describe the slow motion condition (also related to the Newtonian limit approximation) by |peff/ρeff|≪1 (where peff=p+pempg and ρeff=ρ+ρempg), whereas this condition leads to |p/ρ|≪1 in GR.

Generation of Second-Order Sideband through Nonlinear Magnetostrictive Interaction

Nonlinear interaction between the magnon mode and the mechanical mode in a magnomechanical system is treated analytically where the magnon mode is coherently driven by a bichromatic microwave drive field consisting of a strong pumping field and a weak probe field and that works within a perturbative regime. Using experimentally achievable parameters, we show that the magnonic second-order sideband is generated and can be considerably enhanced by increasing the power of the pumping field. The suppression of the magnonic second-order sideband generation at the resonance point is discussed. Furthermore, the efficiency of magnonic second-order sideband generation can be well controlled by adjusting the applied bias magnetic field strength, which is a particular feature compared to the optical second-order sideband. In addition to offering insights into the magnomechanical nonlinearity, the present results have the potential to pave the way for exploring practical applications for achieving high-precision measurement in magnonics.

General formalism of the quantum equivalence principle

A consistent theory of quantum gravity will require a fully quantum formulation of the classical equivalence principle. Such a formulation has been recently proposed in terms of the equality of the rest, inertial and gravitational mass operators, and for non-relativistic particles in a weak gravitational field. In this work, we propose a generalization to a fully relativistic formalism of the quantum equivalence principle, valid for all background space-times, as well as for massive bosons and fermions. The principle is trivially satisfied for massless particles. We show that if the equivalence principle is broken at the quantum level, it implies the modification of the standard Lorentz transformations in flat space-time and a corresponding modification of the metric in curved space-time by the different mass ratios. In other words, the observed geometry would effectively depend on the properties of the test particle. Testable predictions of potential violations of the quantum equivalence principle are proposed.

Microlensing effects of wormholes associated to blackhole spacetimes

In this paper, we investigate the microlensing effects of wormholes associated to black hole spacetimes. Specifically, we work on three typical wormholes (WH): Schwarzschild WH, Kerr WH, and RN WH, as well as their blackhole correspondences. We evaluate the deflection angle upon the second order under weak field approximation using Gauss-Bonnet theorem. Then, we study their magnification with numerics.We find that a Kerr WH could lead to multi peaks in the magnification with certain parameters in the prograde case, while a Kerr BH predicts one peak. Therefore, the multi-peak feature of can be used to distinguish the Kerr WH from other compact objects. We also find that the magnification of RN BH will be one peak compared to RN WH, in which the magnification of RN WH is negative in some situations. For other cases, the behavior of magnification from wormholes and their corresponding blackholes is similar. Our result may shed new light on exploring compact objects through the microlensing effect.

Constraining study of circular orbits and accretion disk around nonlinear electrodynamics black hole

The very latest observation of M87 supermassive black hole (BH) by the Event Horizon Telescope (EHT) provides the accretion onto BHs is an interesting study in the theory of gravity. We study the geodesics structure and accretion near a nonlinear electrodynamics BH in strong and weak field approximations. These approximations provide the disc-like structure under the geodesic motion and accretion around the BH. Near the equatorial plane, we provide some new reasons to make circular orbits and accretion of test particles around the BH. Then we investigate perturbations, the critical speed of the fluid and the mass accretion rate of particles around the central object. The physical validity of this study shows that the parameter β and Q play an important role in the circular orbits and the mass accretion rate in strong and weak field approximations.

White dwarf mass-radius relation in theories beyond general relativity

We explore the internal structures of the white dwarfs in two different modified theories of gravity: (i) scalar-tensor-vector gravity and (ii) beyond Horndeski theories of G 3 type. The modification of the gravitational force inside the white dwarf results in the modification of the mass and radius of the white dwarf. We use observational data from various astrophysical probes including Gaia to test the validity of these two classes of modified theories of gravity. We update the constraints on the parameters controlling the deviation from general relativity (and Newtonian gravity in the weak field limit) as: 0.001 ≤ α for the scalar-tensor-vector gravity and -0.079 ≤ γ ≤ 0.004 for the beyond Horndeski theories of G 3 type. Finally, we demonstrate the selection effect of the astrophysical data on the tests of the nature of gravity using white dwarf mass-radius relations specially in cases where the number of data-points are not many.

Classical interpretation for the influence of XUV pulse width on the streaking time delay and the oscillation amplitude of the momentum shift

We numerically investigate both the streaking time delay and the oscillation amplitude of the momentum shift of the photoelectron and justify them physically by developing a classical model based on the weak field approximation. The streaking time delay is insensitive to the extreme ultraviolet (XUV) pulse duration, while the oscillation amplitude obviously reduces as the XUV duration increases. This XUV duration dependence is attributed to the ionization probability of electron at initial times other than the peak of the XUV pulse. We propagate the classical electron trajectories originating at different initial times in the coupled Coulomb-laser (IR) potential and average the momentum shift for each trajectory over the width of the XUV pulse. By extracting the streaking time delay and the oscillation amplitude from this averaged momentum shift, the classical model results and the time-dependent Schrödinger equation results are found to be in good agreement. Both the insensitivity of the streaking time delay and the sensitivity of the oscillation amplitude on the XUV pulse width are well explained by our classical model considering initial ionization time average. Analytical estimation for the oscillation amplitude is obtained from the model of initial ionization time average.

Control of high-harmonic generation from periodic asymmetric lattices

Periodic asymmetric lattices, viewed from one side to the other, have different spatial potential energies. This difference affects the electronic structure of valence electrons. Our work shows that pronounced even harmonic signals are observed from periodic asymmetric lattices driven by a multi-cycle pulse field. The phases of the odd and even harmonics driven by parallel and anti-parallel laser polarization directions are compared and show different dependences on laser polarization direction. Moreover, it is found that each burst in the synthesized attosecond pulse trains in a periodic asymmetric lattice shows the same carrier-envelope phase. We also show that the even-order harmonic efficiency in periodic asymmetric lattices can be enhanced (reduced) by using a multi-cycle driving laser in the presence of a weak terahertz pulse field.

Enhanced germination and electrotactic behaviour of Phytophthora palmivora zoospores in weak electric fields

Soil-dwelling microorganisms use a variety of chemical and physical signals to navigate their environment. Plant roots produce endogenous electric fields which result in characteristic current profiles. Such electrical signatures are hypothesised to be used by pathogens and symbionts to track and colonise plant roots. The oomycete pathogen Phytophthora palmivora generates motile zoospores which swim towards the positive pole when exposed to an external electric field in vitro. Here, we provide a quantitative characterization of their electrotactic behaviour in 3D. We found that a weak electric field (0.7–1.0 V cm−1) is sufficient to induce an accumulation of zoospore at the positive pole, without affecting their encystment rate. We also show that the same external electric field increases the zoospore germination rate and orients the germ tube’s growth. We conclude that several early stages of the P. palmivora infection cycle are affected by external electric fields. Taken together, our results are compatible with the hypothesis that pathogens use plant endogenous electric fields for host targeting.

Study of the Deflection Angle and Shadow of Black Hole Solutions in Non‐Plasma and Plasma Mediums Under the Effect of Einstein–Gauss–Bonnet Gravity

AbstractIn this paper, the Gibbons and Werner technique is used to calculate the weak deflection angle for the black hole solution under the effects of Einstein–Gauss–Bonnet gravity. The Gauss–Bonnet theorem in the limits of weak field is used to evaluate the Gaussian optical curvature in order to obtain the results. The visual effects of the deflection angle on the impact parameter is also looked at and the smallest radius in the non‐plasma/plasma medium. Moreover, in order to check the consistency of the results concerning the weak deflection angle, the Keeton and Petters approach is applied to study the deflection angle, which is the expansion of series with a single mass variable, which can be directly addressed by using the post–post Newtonian framework. Furthermore, the deflection angle and shadow under the influence of the plasma is examined by using the motion of particle in a non‐magnetized plasma and pressure‐free plasma medium as described by the new ray‐tracing algorithm. It is shown that plasma as well as Einstein–Gauss‐Bonnet gravity corrections are affected by shadows.

Nonlinear optical switch based on coherent perfect absorption.

Coherent perfect absorption (CPA) or reflection (CPR) are methods to realize the extreme manipulation on an optical field. We propose a scheme to operate a bistable switch with convertible CPA and/or CPR. Generally, CPA and CPR occur with different input-field phases. For example, CPA is realized when two input probe beams are in phase; instead, CPR is achieved when they are out of phase. In this scheme, a CPA state can be converted to a CPR state by an incoherent field although two input fields are in phase. When we use the incoherent field as a switching field, the CPA (CPR) state is treated as the closed (open) state. As a result, the switching efficiency can theoretically reach a maximum value, i.e., η = 1. In addition, the switch can be operated in the linear regime with a weak input field, and in the nonlinear or bistable regime with a strong input field. Moreover, the efficiency of the bistable switch is sensitively dependent on the input-field intensity. It provides a potential application of this work on sensitive optical detecting.

Propagation-based phase-contrast imaging method for full-field X-ray microscopy using advanced Kirkpatrick-Baez mirrors.

We demonstrate a propagation-based phase-contrast imaging method for full-field X-ray microscopy based on advanced Kirkpatrick-Baez (AKB) mirrors to achieve high-contrast observations of weak phase objects and correct field curvature aberrations. Through a demonstration performed at SPring-8, the phase contrast of weak phase objects such as polystyrene spheres and chemically fixed cells was successfully observed with high sensitivity (∼0.03 rad). Furthermore, the field of view of the AKB mirrors was expanded to the full area of the obtained images (25 × 30 µm) by correcting the field curvature aberration using reconstructed complex wavefields.