Time-dependent Polarization Research Articles

Self-consistent screening enhances the stability of the nonequilibrium excitonic insulator phase

The nonequilibrium excitonic insulator (NEQ-EI) is an excited state of matter characterized by a finite density of coherent excitons and a time-dependent macroscopic polarization. The stability of this exciton superfluid as the density grows is jeopardized by the increased screening efficiency of the looser excitons. In this work we put forward a Hartree plus screened exchange scheme to predict the critical density at which the transition toward a free electron-hole plasma occurs. The dielectric function is calculated self-consistently using the NEQ-EI polarization and found to vanish in the long-wavelength limit. This property makes the exciton superfluid stable up to relatively high densities. Numerical results for the ${\mathrm{MoS}}_{2}$ monolayers indicate that the NEQ-EI phase survives up to densities of the order of ${10}^{12}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$.

Resolution of Pulmonary Inflammation Induced by Carbon Nanotubes and Fullerenes in Mice: Role of Macrophage Polarization.

Pulmonary exposure to certain engineered nanomaterials (ENMs) causes chronic lesions like fibrosis and cancer in animal models as a result of unresolved inflammation. Resolution of inflammation involves the time-dependent biosynthesis of lipid mediators (LMs)—in particular, specialized pro-resolving mediators (SPMs). To understand how ENM-induced pulmonary inflammation is resolved, we analyzed the inflammatory and pro-resolving responses to fibrogenic multi-walled carbon nanotubes (MWCNTs, Mitsui-7) and low-toxicity fullerenes (fullerene C60, C60F). Pharyngeal aspiration of MWCNTs at 40 μg/mouse or C60F at a dose above 640 μg/mouse elicited pulmonary effects in B6C3F1 mice. Both ENMs stimulated acute inflammation, predominated by neutrophils, in the lung at day 1, which transitioned to histiocytic inflammation by day 7. By day 28, the lesion in MWCNT-exposed mice progressed to fibrotic granulomas, whereas it remained as alveolar histiocytosis in C60F-exposed mice. Flow cytometric profiling of whole lung lavage (WLL) cells revealed that neutrophil recruitment was the greatest at day 1 and declined to 36.6% of that level in MWCNT- and 16.8% in C60F-treated mice by day 7, and to basal levels by day 28, suggesting a rapid initiation phase and an extended resolution phase. Both ENMs induced high levels of proinflammatory leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) with peaks at day 1, and high levels of SPMs resolvin D1 (RvD1) and E1 (RvE1) with peaks at day 7. MWCNTs and C60F induced time-dependent polarization of M1 macrophages with a peak at day 1 and subsequently of M2 macrophages with a peak at day 7 in the lung, accompanied by elevated levels of type 1 or type 2 cytokines, respectively. M1 macrophages exhibited preferential induction of arachidonate 5-lipoxygenase activating protein (ALOX5AP), whereas M2 macrophages had a high level expression of arachidonate 15-lipoxygenase (ALOX15). Polarization of macrophages in vitro differentially induced ALOX5AP in M1 macrophages or ALOX15 in M2 macrophages resulting in increased preferential biosynthesis of proinflammatory LMs or SPMs. MWCNTs increased the M1- or M2-specific production of LMs accordingly. These findings support a mechanism by which persistent ENM-induced neutrophilic inflammation is actively resolved through time-dependent polarization of macrophages and enhanced biosynthesis of specialized LMs via distinct ALOX pathways.

On the two-potential constitutive modeling of dielectric elastomers

This work lays out the two-potential framework for the constitutive modeling of dielectric elastomers. After its general presentation, where the constraints imposed by even electromechanical coupling, material frame indifference, material symmetry, and entropy imbalance are all spelled out, the framework is utilized to put forth a specific constitutive model for the prominent class of isotropic incompressible dielectric elastomers. The model accounts for the non-Gaussian elasticity and electrostriction typical of such materials, as well as for their deformation-enhanced shear thinning due to viscous dissipation and their time-dependent polarization due to electric dissipation. The key theoretical and practical features of the model are discussed, with special emphasis on its specialization in the limit of small deformations and moderate electric fields. The last part of this paper is devoted to the deployment of the model to fully describe the electromechanical behavior of a commercially significant dielectric elastomer, namely, the acrylate elastomer VHB 4910 from 3M.

Tracking the state transitions in changing-look active galactic nuclei through their polarized-light echoes

Context.Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are now labeled “changing-look” AGNs and are key objects for understanding the physics of accretion onto supermassive black holes.Aims.We aim to complement the analysis and interpretation of changing-look AGNs by modeling the polarization variations that can be observed, in particular, polarized-light echoes.Methods.We built a complex and representative model of an AGN and its host galaxy and ran radiative transfer simulations to obtain realistic time-dependent polarization signatures of changing-look objects. Based on actual data, we allowed the system to become several times fainter or brighter within a few years, assuming a rapid change in accretion rate.Results.We obtain time-dependent polarization signatures of distant high-luminosity (quasars) and nearby low-luminosity (Seyferts) changing-look AGNs for a representative set of inclinations. We predict the evolution of the continuum polarization for future polarimetric campaigns with the goal to better understand the physics at work in these objects. We also investigate highly inclined AGNs that experience strong accretion rate variations without appearing to change state. We apply our modeling to Mrk 1018, the best-documented case of a changing-look AGN, and predict a variation in its polarization after the recent dimming of its continuum.Conclusions.We demonstrate that polarization monitoring campaigns that cover the transitions that are observed in changing-look AGNs might bring crucial information on the geometry and composition of all the reprocessing regions within the nucleus. In particular, specific features in the time variation of the polarization position angle can provide a new and efficient method for determining AGN inclinations.

Sub-cycle coherent control of ionic dynamics via transient ionization injection

Ultrafast ionization of atoms or molecules by intense laser pulses creates extremely non-stationary ionic states. This process triggers attosecond correlated electron-hole dynamics and subsequent ultrafast non-equilibrium evolution of matters. Here we investigate the interwoven dynamic evolutions of neutral nitrogen molecules together with nitrogen ions created through transient tunnel ionization in an intense laser field. Based on the proposed theoretical frame, it is found that nitrogen molecular ions are primarily populated in the electronically excited states, rather than staying in the ground state as predicted by the well-known tunneling theory. The unexpected result is attributed to sub-cycle switch-on of time-dependent polarization by transient ionization and dynamic Stark shift mediated near-resonant multiphoton transitions. These findings corroborate the mechanism of nitrogen molecular ion lasing and are likely to be universal. The present work opens a route to explore the important role of transient ionization injection in strong-field induced non-equilibrium dynamics.

Signals of axion like dark matter in time dependent polarization of light

We consider the search for axion-like particles (ALPs) by using time series data of the polarization angle of the light. If the condensation of an ALP plays the role of dark matter, the polarization plane of the light oscillates as a function of time and we may be able to detect the signal of the ALP by continuously observing the polarization. In particular, we discuss that the analysis of the Fourier-transformed data of the time-dependent polarization angle is powerful to find the signal of the ALP dark matter. We pay particular attention to the light coming from astrophysical sources such as protoplanetary disks, supernova remnants, the foreground emission of the cosmic microwave background, and so on. We show that, for the ALP mass of ∼10−22–10−19eV, ALP searches in the Fourier space may reach the parameter region which is unexplored by other searches yet.

Time-varying Extinction, Polarization, and Colors of Type Ia Supernovae due to Rotational Disruption of Dust Grains

Abstract Observations toward type Ia supernovae (SNe Ia) frequently report an unusually low total-to-selective extinction ratio (R V < 2) and a small peak wavelength of polarization (λ max < 0.4 μm). Hoang et al. proposed that the dominance of small grains near SNe Ia due to RAdiative Torque Disruption (RATD) can explain the puzzle. To test this scenario, we model the dust extinction and polarization of SNe Ia, accounting for grain disruption and alignment by radiative torques and different grain tensile strengths from . We find that R V decreases from ∼3.1 to ∼1.5 after disruption time t disr < 40 days for clouds at a distance d < 4 pc from SNe Ia. We then calculate the observed lightcurves of SNe Ia and find that their colors change with time, due to varying dust extinction. The peak wavelength λ max also decreases from ∼0.55 to ∼0.15 μm over an alignment time of t align < 10 days, due to the enhanced alignment of small grains. By fitting the theoretical polarization with the Serkowski law characterized by the K and λ max parameters, we find that K increases when large grains are disrupted by RATD, which is consistent with the unusual K versus λ max relationship of SNe Ia. Nevertheless, an accurate measurement of K and λ max is challenging, due to atmospheric effects and potential contamination of polarization by Rayleigh scattering by circumstellar matter. Our results demonstrate the importance of RATD for time-dependent extinction, polarization, and colors of SNe Ia.

Time-Dependent Electric Field Distribution in Layered Paper-Oil Insulation

Layered paper–oil insulation is used in several types of HVDC equipment. In order to better understand breakdown mechanisms and optimize the design, it is important to understand the electric field distribution in the insulation. In the present work, a test object with such insulation has been modeled as a series connection of oil and impregnated paper. The permittivity, conductivity, and the dielectric response function has been measured for impregnated paper and oil separately and used as parameters in a dielectric response model for the layered insulation system. A system of differential equations has been established describing the voltages across each material, i.e. across each layer of the test object. These equations have been solved considering a DC step voltage across the whole test object. Based on this, the time-dependent electric field in each material as well as the time-dependent polarization current density in the test object have been calculated. The calculated polarization current density was found to agree well with the measured polarization current density of the test object. This indicates that application of dielectric response theory gives a good estimate of the time-dependent electric field distribution in layered insulation systems. The results show that 90 % of the change from initial values to steady-state values for the electric fields has occurred within the first 35 minutes after the voltage step. This applies to the electric fields in both of the materials of the examined test object at a temperature of 323 K.

Probing the Emission Mechanism and Magnetic Field of Neutrino Blazars with Multiwavelength Polarization Signatures

Abstract The characteristic two-component blazar spectral energy distribution (SED) can be of either leptonic and/or hadronic origins. The potential association of the high-energy neutrino event IceCube-170922A with the flaring blazar TXS 0506+056 indicates that hadronic processes may operate in a blazar jet. Despite multiwavelength follow-ups of the event and extensive theoretical modelings, the radiation mechanisms and the underlying magnetic field strength and configuration remain poorly understood. In this paper, we consider generic leptonic and hadronic blazar spectral models with distinct magnetic field strengths and radiation mechanisms. We analytically reproduce the SEDs and neutrino flux of hadronic models, and predict their X-ray to γ-ray polarization degrees. Furthermore, by performing relativistic magnetohydrodynamic simulations taking into account the polarization-dependent radiation transfer, we study the time-dependent multiwavelength polarization variability of the proton synchrotron (PS) model under a shock scenario. Our results suggest that the high-energy polarization degree and the neutrino flux can be jointly used to pinpoint the leptonic and/or hadronic blazar radiation mechanisms in the X-ray and γ-ray bands, and to infer the magnetic field strength in the emission region. In addition, the temporal multiwavelength polarization signatures in the PS shed light on the jet energy composition and the dynamical importance of magnetic fields in the blazar emission region. Future multiwavelength polarimetry facilities such as the Imaging X-ray Polarimetry Explorer and All-sky Medium Energy Gamma-ray Observatory together with neutrino telescopes such as IceCube can provide unprecedented observational constraints to probe the blazar radiation mechanisms and jet dynamics.

Influence of crystallographic structure on polarization reversal in polycrystalline ferroelectric/ferroelastic materials

Polarization reversal is the most fundamental physical process in ferroelectrics and directly or indirectly influences all functional properties of these materials. While this process is influenced by various intrinsic material’s properties and external boundary conditions, arguably one of the most dominant parameters is the material’s crystallographic structure. In this work, the influence of the crystallographic structure on the polarization reversal was investigated on the model ferroelectric system Pb(Zr,Ti)O3 using simultaneous time-dependent polarization and strain measurements. This method enabled one to extend the understanding beyond the widely investigated relationship between the structure and coercive fields. Polarization reversal was described by three regimes, which represent a sequence of well-defined non-180° and 180° switching events. The crystallographic structure was found to largely influence the mobility of the non-180° domain walls during the first switching regime, the amplitude of negative strain, and the broadness of the transition between the first and the second switching regimes, as well as the speed of the second (main) switching regime. The observed changes could be related to the amount of possible polarization directions, distribution of the local electric fields, and strain mismatch at domain wall junctions influenced by the lattice distortion. Moreover, activation fields for the first and the second regimes were experimentally determined for the investigated series of Pb(Zr,Ti)O3 samples. Besides providing insight into fundamental mechanisms of polarization reversal, these results can also be used as input parameters for micromechanical or stochastic models.

Polarization Oscillations in Birefringent Emitter-Cavity Systems.

We present the effects of resonator birefringence on the cavity-enhanced interfacing of quantum states of light and matter, including the first observation of single photons with a time-dependent polarization state that evolves within their coherence time. A theoretical model is introduced and experimentally verified by the modified polarization of temporally long single photons emitted from a ^{87}Rb atom coupled to a high-finesse optical cavity by a vacuum-stimulated Raman adiabatic passage process. Further theoretical investigation shows how a change in cavity birefringence can both impact the atom-cavity coupling and engender starkly different polarization behavior in the emitted photons. With polarization a key resource for encoding quantum states of light and modern micron-scale cavities particularly prone to birefringence, the consideration of these effects is vital to the faithful realization of efficient and coherent emitter-photon interfaces for distributed quantum networking and communications.

Crystal orientation-dependent polarization state of high-order harmonics.

We analyze the crystal orientation-dependent polarization state of extreme ultraviolet high-order harmonics from bulk magnesium oxide crystals subjected to intense linearly polarized laser fields. We find that only along high-symmetry directions do high-order harmonics follow the polarization direction of the laser field. In general, there are strong deviations that depend on harmonic order, strength of the laser field, and crystal orientation. We use a real-space electron trajectory picture to understand the origin of polarization deviations. These results have implications in all-optical probing of electronic band structure in momentum space and valence charge distributions in real space, and in producing attosecond pulses with time-dependent polarization in compact setups.

Conception of Magnetic Memory Switched by Time Dependent Current Density and Current Electron Spin Polarization

In this article the magnetic memory model with nano-meter size made from iron cells was proposed. For a purpose of determining the model specifications, the magnetic probes group with different geometrical parameters were examined using numeric simulations for the two different time duration of transitions among quasi-stable magnetic distributions found in the system, derived from the energy minimums. The geometrical parameters range was found, for which the 16 quasi–stable energetic states exist for the each probe. Having considered these results the 4 bits magnetic cells systems can be designed whose state is changed by spin-polarized current. Time dependent current densities and the current electron spin polarization directions were determined for all cases of transitions among quasi–stable states, for discovered set of 4 bits cells with different geometrical parameters. The 16-states cells, with the least geometrical area, achieved the 300 times bigger writing density in comparison to actual semiconductor solutions with the largest writing densities. The transitions among quasi-stable states of cells were examined for the time durations 10 5 times shorter than that for up to date solutions.

From γ to Radio: The Electromagnetic Counterpart of GW170817

Abstract The gravitational waves from the first binary neutron star merger, GW170817, were accompanied by a multiwavelength electromagnetic counterpart, from γ-rays to radio. The accompanying γ-rays seem at first to confirm the association of mergers with short gamma-ray bursts (sGRBs). The common interpretation was that we see an emission from an sGRB jet seen off-axis. However, a closer examination of the subluminous γ-rays and the peculiar radio afterglow was inconsistent with this simple interpretation. Here we present results of 3D and 2D numerical simulations that follow the hydrodynamics and emission of the outflow from a neutron star merger, form its ejection and up to its deceleration by the circum-merger medium. Our results show that the current set of γ-rays, X-rays, and radio observations can be explained by the emission from a mildly relativistic cocoon material (Lorentz factor ∼2–5) that was formed while a jet propagated through the material ejected during the merger. The γ-rays are generated when the cocoon breaks out from the engulfing ejecta, while the afterglow is produced by interaction of the cocoon matter with the interstellar medium. The strong early UV/optical signal may be a Lorentz-boosted macronova/kilonova. The fate of the jet itself is currently unknown, but our full-electromagnetic (EM) models define a path to resolving between successful and choked jet scenarios, outputting coupled predictions for the image size, morphology, observed time-dependent polarization, and light-curve behavior from radio to X-ray. The predictive power of these models will prove key in interpreting the ongoing multifaceted observations of this unprecedented event.

Attosecond electronic recollision as field detector

We demonstrate the complete reconstruction of the electric field of visible–infrared pulses with energy as low as a few tens of nanojoules. The technique allows for the reconstruction of the instantaneous electric field vector direction and magnitude, thus giving access to the characterization of pulses with an arbitrary time-dependent polarization state. The technique combines extreme ultraviolet interferometry with the generation of isolated attosecond pulses.

Measurement of differential modal group delay of a few-mode fiber using a Fourier domain mode-locked laser

We propose and experimentally demonstrate a method for measuring the differential modal group delay (DMGD) of a few-mode fiber using a Fourier domain mode-locked laser (FDML). We use the fast frequency-swept, wavelength-tunable output of the FDML in order to perform time domain measurements of interference of the modes, which is further postprocessed to extract the DMGD. We demonstrate the measurement of DMGD for a commercial two-mode fiber over the C-band. This method is not limited by the magnitude of DMGD or the number of modes and is minimally affected by time-dependent polarization and mode fluctuations, environmental noise, and spectral resolution of instruments.

Activated Tissue-Resident Mesenchymal Stromal Cells Regulate Natural Killer Cell Immune and Tissue-Regenerative Function.

SummaryThe interaction of mesenchymal stromal cells (MSCs) with natural killer (NK) cells is traditionally thought of as a static inhibitory model, whereby resting MSCs inhibit NK cell effector function. Here, we use a dynamic in vitro system of poly(I:C) stimulation to model the interaction of NK cells and tissue-resident MSCs in the context of infection or tissue injury. The experiments suggest a time-dependent system of regulation and feedback, where, at early time points, activated MSCs secrete type I interferon to enhance NK cell effector function, while at later time points TGF-β and IL-6 limit NK cell effector function and terminate inflammatory responses by induction of a regulatory senescent-like NK cell phenotype. Importantly, feedback of these regulatory NK cells to MSCs promotes survival, proliferation, and pro-angiogenic properties. Our data provide additional insight into the interaction of stromal cells and innate immune cells and suggest a model of time-dependent MSC polarization and licensing.

High-Energy Polarization: Scientific Potential and Model Predictions

Understanding magnetic field strength and morphology is very important for studying astrophysical jets. Polarization signatures have been a standard way to probe the jet magnetic field. Radio and optical polarization monitoring programs have been very successful in studying the space- and time-dependent jet polarization behaviors. A new era is now arriving with high-energy polarimetry. X-ray and γ -ray polarimetry can probe the most active jet regions with the most efficient particle acceleration. This new opportunity will make a strong impact on our current understanding of jet systems. This paper summarizes the scientific potential and current model predictions for X-ray and γ -ray polarization of astrophysical jets. In particular, we discuss the advantages of using high-energy polarimetry to constrain several important problems in the jet physics, including the jet radiation mechanisms, particle acceleration mechanisms, and jet kinetic and magnetic energy composition. Here we take blazars as a study case, but the general approach can be similarly applied to other astrophysical jets. We conclude that by comparing combined magnetohydrodynamics (MHD), particle transport, and polarization-dependent radiation transfer simulations with multi-wavelength time-dependent radiation and polarization observations, we will obtain the strongest constraints and the best knowledge of jet physics.

Dynamical multiferroicity

An appealing mechanism for inducing multiferroicity in materials is the generation of electric polarization by a spatially varying magnetization that is coupled to the lattice through the spin-orbit interaction. Here we describe the reciprocal effect, in which a time-dependent electric polarization induces magnetization even in materials with no existing spin structure. We develop a formalism for this dynamical multiferroic effect in the case for which the polarization derives from optical phonons, and compute the strength of the phonon Zeeman effect, which is the solid-state equivalent of the well-established vibrational Zeeman effect in molecules, using density functional theory. We further show that a recently observed behavior -- the resonant excitation of a magnon by optically driven phonons -- is described by the formalism. Finally, we discuss examples of scenarios that are not driven by lattice dynamics and interpret the excitation of Dzyaloshinskii-Moriya-type electromagnons and the inverse Faraday effect from the viewpoint of dynamical multiferroicity.

Dynamics of trapped atoms around an optical nanofiber probed through polarimetry.

The evanescent field outside an optical nanofiber (ONF) can create optical traps for neutral atoms. We present a non-destructive method to characterize such trapping potentials. An off-resonance linearly polarized probe beam that propagates through the ONF experiences a slow axis of polarization produced by trapped atoms on opposite sides along the ONF. The transverse atomic motion is imprinted onto the probe polarization through the changing atomic index of refraction. By applying a transient impulse, we measure a time-dependent polarization rotation of the probe beam that provides both a rapid and non-destructive measurement of the optical trapping frequencies.