Slow Decay Research Articles

Mechanistic description of spontaneous loss of memory persistent activity based on neuronal synaptic strength

Persistent neural activity associated with working memory (WM) lasts for a limited time duration. Current theories suggest that its termination is actively obtained via inhibitory currents, and there is currently no theory regarding the possibility of a passive memory-loss mechanism that terminates memory persistent activity. Here, we develop an analytical-framework, based on synaptic strength, and show via simulations and fitting to wet-lab experiments, that passive memory-loss might be a result of an ionic-current long-term plateau, i.e., very slow reduction of memory followed by abrupt loss. We describe analytically the plateau, when the memory state is just below criticality. These results, including the plateau, are supported by experiments performed on rats. Moreover, we show that even just above criticality, forgetfulness can occur due to neuronal noise with ionic-current fluctuations, yielding a plateau, representing memory with very slow decay, and eventually a fast memory decay. Our results could have implications for developing new medications, targeted against memory impairments, through modifying neuronal noise.

Anti‐Counterfeiting Application of Persistent Luminescence Materials and Its Research Progress

AbstractPersistent luminescent materials can continue to emit light after stopping excitation, and their stored energy is gradually released during the decay time after persistent emitting, which makes the color and luminance changes in slow decay and plays an important role in protecting information and combating forgery. When combined with other anti‐counterfeiting technologies to form a multi‐modal and multi‐process anti‐counterfeiting design, it perfectly hides the real information and has a broad application prospect in anti‐counterfeiting logo design. A brief overview of the design of three different persistent luminescence‐based anti‐counterfeiting applications in unimodality to achieve information encryption in the time dimension. The energy stored in the trap is studied to be released by different physical stimuli and applied to stimulus‐like responsive persistent luminescent materials, and the design of persistent luminescence anti‐counterfeiting applications based on many different processes in dual‐modality, obtaining the dynamic anti‐counterfeiting effect of multiple processes in multiple modes. This work reviews the research background of persistent luminescent materials in the field of anti‐counterfeiting in recent years, compares the important breakthrough progress of persistent luminescent materials applied to anti‐counterfeiting research, and finally puts forward the current problems, future challenges, and development directions.

Spectroscopy of a mesospheric ghost reveals iron emissions

Mesospheric Green emissions from excited Oxygen in Sprite Tops (ghosts) are infrequent and faint greenish transient luminous events that remain for hundreds of milliseconds on top of certain energetic sprites. The main hypothesis to explain this glow persistence is the long lifetime of excited atomic oxygen at 557.73 nm, a well-known emission line in aurora and airglow. However, due to the lack of spectroscopic campaigns to analyse such events to date, the species involved in the process can not yet be identified. Here we report observational results showing the temporal evolution of a ghost spectrum between 500 nm and 600 nm. Besides weak -but certain- traces of excited atomic oxygen, our results show four main contributors related to the slow decay of the glow: atomic iron and nickel, molecular nitrogen and ionic molecular oxygen. Additionally, we are able to identify traces of atomic sodium, and ionic silicon, these observations being consistent with previous direct measurements of density profiles of meteoric metals in the mesosphere and lower thermosphere. This finding calls for an upgrade of current air plasma kinetic understanding under the influence of transient luminous events.

System design study of a VLEO satellite platform using the IRS RF helicon-based plasma thruster

To achieve a feasible lifetime of several years, most satellites are deployed in orbits higher than 400 km. Drag of residual atmosphere causes a slow orbit decay, resulting in the deorbit of the spacecraft. However, e.g. optical instruments or communication devices would significantly benefit from lower altitudes in the range of 150–250 km. A solution to achieve this could be the application of atmosphere-breathing electric propulsion (ABEP), where the residual atmosphere is used to generate continuous thrust that compensates the drag.Within the EU-funded DISCOVERER project, the Institute of Space Systems (IRS) developed an electrode-less RF Helicon-based Plasma Thruster (IPT) suitable for such applications. Ignition and preliminary discharge characterizations of the IPT have been carried out at IRS facilities, using argon, nitrogen and oxygen. To further characterize the plasma plume, a torsional pendulum has been designed to determine the (local) momentum flux in the plasma jet, as well as a three-axis magnetic B-dot probe to carry out time-varying magnetic field measurements. Various intake designs were investigated, opening the possibility to conduct studies on potential satellite platforms within the frame of the ESA-funded project RAM-CLEP.A design study for an Earth Observation and Telecommunication satellite operating at 150–250 km with an extended mission lifetime is currently being carried out. The first system assessment focused on the comparison of different spacecraft configurations (“slender body” and “flat body”) and intake designs (specular or diffuse) with regard to overall drag and ABEP performance requirements.In this contribution, the design approaches for the current thruster and the diagnostic methods are depicted. Moreover, the current status of the system assessment is presented. Upcoming experimental studies of the ABEP system e.g. within the ESA-project RAM-CLEP and additional activities planned on system assessment are outlined.

One-Pot template free synthesis of bimetallic alloy Pt-M/C (M = Fe, Co & Cu) with improved activity for electrocatalytic oxidation of methanol

We prepared a simple, one-step synthesis of Pt-M (M = Co, Cu & Fe)/C supported on Vulcan-XC-72 carbon using the polyol reduction method. The morphology, structure and elemental composition of the prepared catalysts were confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Electrochemical characterization including electrochemical impedance, cyclic voltammetry and chronoamperometry were studied to compare the electrochemical activity of the as-prepared catalyst with standard 20 wt % Pt/C. From transmission electron microscopy studies, the estimated average particle size for PtFe/C, PtCo/C and PtCu/C were 16, 12 and 10 nm respectively. In cyclic voltammetry studies, the PtFe/C catalyst exhibited the maximum current density for electrooxidation of methanol (14.88 mA cm−2), compared to PtCu/C (9.96 mA cm−2), PtCo/C (4.66 mA cm−2) and Pt/C (2.34 mA cm−2). Also, the negative sweep onset potential and greater If/Ib ratio verified the enhanced activity of the PtFe/C catalyst. The stability of the catalyst was studied using chronoamperometric methods, which reveals the slow decay of the prepared catalyst and higher current density for initial and final time intervals. Impedance studies confirm that the PtFe/C catalyst exhibits the smallest semicircle, suggesting a significantly higher electrooxidation rate in comparison to the other catalysts. The electrocatalytic activity of the prepared catalyst follows the order: PtFe/C > PtCu/C > PtCo/C > Pt/C.

Fractional derivative method for anomalous aquitard flow in a leaky aquifer system with depth-decaying aquitard hydraulic conductivity

Aquitards significantly affect groundwater flow in multi-aquifer systems through adjacent aquifer leakage. Despite this, studies focusing on their heterogeneity and the non-conventional diffusion patterns of their flow are still limited. In this study, a factional derivative approach was first extended to explore the time-dependent behavior of flow transport in the aquitard. Two analytical solutions were derived for specific discharges in independent aquitards under different boundary conditions. The findings revealed that aquitard flow exhibits obvious anomalous diffusion behaviors, characterized by slower decay and heavy-tailed specific discharge data. The fractional derivative model provided a more accurate representation of this behavior than traditional models, as evidenced by its superior agreement with experimental data. Moreover, a transient model for pumping tests in a leaky aquifer system was developed, incorporating the memory effect of anomalous flow and vertical heterogeneity in aquitards. Relevant semi-analytical solutions were derived to explore the impacts of memory factor β and decay exponent of aquitard hydraulic conductivity (K) on the leakage aquifer system. Theoretical results demonstrated that stronger memory effect reduces drawdowns in the aquitard and confined aquifer during mid-to-late times. A larger dimensionless decay exponent (Ad) decreases aquitard drawdown and increases aquifer drawdown at late times. Sensitivity analysis showed aquitard drawdown experiences two peaks in sensitivity to β and Ad at early- or mid-times, affected by memory effect and decay exponent of aquitard K, signifying maximal impact at these specific intervals. This study provides a practical model to effectively manage groundwater resources by accurately reflecting aquitard memory and heterogeneity effects.

Radioluminescence properties of Sm3+-doped Y3Al5O12 single crystals

0.1, 0.3, 0.5, 1.0, 5.0, and 10.0 % Sm3+-doped Y3Al5O12 single crystals were grown by the floating zone method. Photoluminescence (PL) and radioluminescence (RL) properties of the samples were evaluated and the emission peaks due to 4f-4f transitions of Sm3+ ions were observed. The PL quantum yield of the 0.3 % Sm3+-doped sample was highest among all the samples (approximately 48 %). PL and RL decay times of the samples were 0.7–2.7 and 0.6–2.9 ms, respectively. The light yield of the 0.5 % Sm3+-doped sample under γ-ray excitation was highest and its value was estimated to be approximately 8400 photons/MeV using a measurement system for scintillators with slow decay times.

Comparison of the Bacterial Inactivation Efficiency of Water Activated by a Plasma Jet Source and a Pin-to-Pin Electrode Configuration Source

In this comparative study, the bacterial inactivation efficiency of plasma-activated water (PAW) generated by two distinct plasma reactors, one utilizing a nitrogen plasma jet electrode and the other a hybrid argon plasma reactor, was explored. The present study involved the assessment of antimicrobial activity against suspensions of three Gram-positive and three Gram-negative bacterial strains in their planktonic cell state. Bacterial suspensions were introduced into PAW five days after generation. Subsequently, the viability of the bacteria was assessed at various time intervals, specifically at 0.5, 1, 3, 5, 10, and 24 h, in order to evaluate the effect of inactivation. Structural changes in bacteria after PAW treatment were assessed using a scanning electron microscope (SEM). The physicochemical properties of PAW, including pH, conductivity, and concentrations of H2O2, NO2−, and NO3− during aging were measured. The present study demonstrated the effective inactivation of the tested bacterial strains by PAW. Gram-positive bacteria displayed greater resistance compared to Gram-negative species, with the lowest reductions in bacterial counts observed for B. cereus, and the highest for Escherichia coli O157:H7. Morphological damage was evident across all bacterial species examined. Physicochemical measurements showed slow decay of the reactive species in the aging process. This study illustrated the potential utility of PAW as an alternative disinfectant.

An alkaline S/Fe redox flow battery endowed with high volumetric-capacity and long cycle-life

The S/Fe redox flow battery (RFB) with abundant sulfide and iron as redox-active species shows promising applications for energy storage. It exhibits advantages including low cost, high safety, and flexible operation. However, limited by the low solubility limit of [Fe(CN)6]4-, the volumetric capacity of reported S/Fe RFBs is too low to meet commercial requirements. Herein, an alkaline S/Fe RFB with high volumetric energy density and improved cycling stability enabled by the diverse-ion effect in the catholyte is successfully demonstrated. In a 0.50 M KOH solution, the concentration of [Fe(CN)6]4- achieves 1.52 M under ambient temperature which is increased by two times than the solubility limit of K4[Fe(CN)6] (0.76 M) in deionized water. The corresponding theoretical volumetric capacity can reach as high as 40.74 Ah L−1. With 1.30 M [Fe(CN)6]4-in the catholyte, the alkaline S/Fe RFB displays high performance, including a long cycle-life of 3153 h (over 4 months), high Coulombic efficiency (CE) above 99 %, and slow capacity decay of only 0.0166 % per cycle (0.1134 % per day). In addition, at higher temperatures and larger scales, the concentrated catholyte maintains excellent cycling performance, verifying the present strategy is highly reliable in improving the performance of a cost-effective S/Fe RFB system for practical applications.

Spectro-polarimetric Properties of Sunquake Sources in X1.5 Flare and Evidence for Electron and Proton Beam Impacts

The first significant sunquake event of Solar Cycle 25 was observed during the X1.5 flare of 2022 May 10, by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. We perform a detailed spectro-polarimetric analysis of the sunquake photospheric sources, using the Stokes profiles of the Fe i 6173 Å line, reconstructed from the HMI linear and circular polarized filtergrams. The results show fast variations of the continuum emission with rapid growth and slower decay lasting 3–4 minutes, coinciding in time with the hard X-ray impulses observed by the Konus instrument on board the Wind spacecraft. The variations in the line core appeared slightly ahead of the variations in the line wings, showing that the heating started in the higher atmospheric layers and propagated downward. The most significant feature of the line profile variations is the transient emission in the line core in three of the four sources, indicating intense, impulsive heating in the lower chromosphere and photosphere. In addition, the observed variations of the Stokes profiles reflect transient and permanent changes in the magnetic field strength and geometry in the sunquake sources. Comparison with the radiative hydrodynamics models shows that the physical processes in the impulsive flare phase are substantially more complex than those predicted by proton and electron beam flare models currently presented in the literature.

Data-driven snapshot calibration via monotonic feature matching

Snapshot matrices of hyperbolic equations have a slow singular value decay, resulting in inefficient reduced-order models. We develop on the idea of inducing a faster singular value decay by computing snapshots on a transformed spatial domain, or the so-called snapshot calibration/transformation. We are particularly interested in problems involving shock collision, shock rarefaction-fan collision, shock formation, etc. For such problems, we propose a realizable algorithm to compute the spatial transform using monotonic feature matching. We consider discontinuities and kinks as features, and by carefully partitioning the parameter domain, we ensure that the spatial transform has properties that are desirable both from a theoretical and an implementation standpoint. We use these properties to prove that our method results in a fast Kolmogorov m-width decay of a calibrated manifold. A crucial observation we make is that due to calibration, the m-width does not only depend on m but also on the accuracy of the full-order model, which is in contrast to elliptic and parabolic problems that do not need calibration. The method we propose only requires the solution snapshots and not the underlying partial differential equation (PDE) and is therefore, data-driven. We perform several numerical experiments to demonstrate the effectiveness of our method.

CaMKIIdelta-mediated SR Ca leak contributes to long-term Doxorubicin-induced cardiotoxicity

Abstract Background Cardiotoxicity represents a major complication of cancer therapy with anthracyclines, whose main known compound is doxorubicine (DOX). Although mechanisms of DOX-induced toxic cardiomyopathy (DICM) are not entirely understood, CaMKIIδ-activity is known to be increased upon acute DOX exposure, contributing to impaired Calcium (Ca) handling. However, currently no studies have addressed the question, whether CaMKIIδ is involved in DOX-induced long-term cardiotoxicity. Purpose We aimed to investigate cardiac function and intracellular Ca handling using an in-vivo DOX treated mouse model, examining whether CaMKIIδ is involved in DOX-induced long-term cardiotoxicity. Methods Cardiac function and excitation-contraction coupling of CaMKIIdWT and CaMKIId-/- (global CaMKIId knockout) mice were tested in an in-vivo DOX treated mouse model (cumulative dose 12 mg/kg, intraperitoneal injection). Cardiac function was determined by echocardiography after 12 weeks. Ca handling of freshly isolated cardiomyocytes was assessed by epifluorescence microscopy (Fura2-AM) and confocal microscopy (Fluo4-AM). Histological analyses regarding cardiac fibrosis and cell dimensions were examined. Results Long-term DOX exposure reduced left ventricular ejection fraction (EF) by ∼13% and markedly increased cardiac fibrosis in CaMKIIδWT mice. Moreover, CaMKIIdWT hearts displayed decreased cell volume indicating atrophy following DOX treatment. Coinciding with the reduction in EF, CaMKIIdWT mice showed depressed Ca transient amplitudes as well as slowed Ca transient decay indicating depressed Ca uptake into the sarcoplasmic reticulum (SR). In addition, spontaneous diastolic Ca leakage from the SR was dramatically increased. In contrast, CaMKIId-/- mice showed preserved EF following 12 weeks of DOX treatment as compared to CaMKIIdWT in line with maintained Ca transient amplitudes. As an underlying cause, SR Ca leakage was not increased in CaMKIId-/- myocytes despite DOX-treatment. Pharmacological CaMKII inhibition using AIP (1µM) prevented SR Ca leak and restored Ca transient amplitudes in DOX-treated CaMKIIdWT myocytes. Conclusion Our study shows that CaMKIId contributes to long-term DOX-induced cardiotoxicity. We found that chronic DOX treatment induced depressed cardiac function and myocardial fibrosis, associated with impaired calcium handling as a consequence of CaMKIId-mediated SR Ca leak, which was absent in our CaMKIId-/- mouse model. In line, pharmacological inhibition of CaMKII rescued impaired Ca handling in DOX-treated CaMKIIdWT myocytes.

Alignment of Heptagonal Diimide and Triazine Enables Narrowband Pure-Blue Organic Light-Emitting Diodes with Low Efficiency Roll-Off.

The endeavor to develop high-performance narrowband blue organic light-emitting diodes (OLEDs) with low efficiency roll-off represents an attractive challenge. Herein, we introduce a hetero-acceptor design strategy centered around the heptagonal diimide (BPI) building block to create an efficient thermally activated delayed fluorescence (TADF) sensitizer. The alignment of a twisted BPI unit and a planar diphenyltriazine (TRZ) fragment imparts remarkable exciton dynamic properties to 26tCz-TRZBPI, including a fast radiative decay rate (kR ) of 1.0×107 s-1 and a swift reverse intersystem crossing rate (kRISC ) of 1.8×106 s-1 , complemented by a slow non-radiative decay rate (kNR ) of 6.0×103 s-1 . Consequently, 26tCz-TRZBPI facilitates the fabrication of high-performance narrowband pure-blue TADF-sensitized fluorescence OLEDs (TSF-OLEDs) with a maximum external quantum efficiency (EQEmax ) of 24.3 % and low efficiency roll-off even at a high brightness level of 10000 cd m-2 (EQE10000 : 16.8 %). This showcases a record-breaking external quantum efficiency at a high luminance level of 10000 cd m-2 for narrowband blue TSF-OLEDs.

Lévy movements and a slowly decaying memory allow efficient collective learning in groups of interacting foragers.

Many animal species benefit from spatial learning to adapt their foraging movements to the distribution of resources. Learning involves the collection, storage and retrieval of information, and depends on both the random search strategies employed and the memory capacities of the individual. For animals living in social groups, spatial learning can be further enhanced by information transfer among group members. However, how individual behavior affects the emergence of collective states of learning is still poorly understood. Here, with the help of a spatially explicit agent-based model where individuals transfer information to their peers, we analyze the effects on the use of resources of varying memory capacities in combination with different exploration strategies, such as ordinary random walks and Lévy flights. We find that individual Lévy displacements associated with a slow memory decay lead to a very rapid collective response, a high group cohesion and to an optimal exploitation of the best resource patches in static but complex environments, even when the interaction rate among individuals is low.

A hybrid strategy-based GJO algorithm for robot path planning

Addressing the challenges of low convergence accuracy and stagnation at local optima in the application of the golden jackal optimizer (GJO) to mobile robot path planning, this paper proposes a hybrid strategy-based golden jackal optimizer (HGJO) algorithm. The improved algorithm employs a pre-decreasing slow nonlinear energy decay strategy to balance the global and local search capabilities. The roulette wheel selection algorithm and Lévy flight strategy are introduced into the position update of the GJO algorithm, so the proposed algorithm avoids stagnation at the local optimum. The HGJO algorithm is evaluated against some state-of-the-art optimizers on 23 benchmark functions and the CEC2021 benchmark function. It is also applied to ablation experiments for mobile robot path planning. The experimental results show that the HGJO algorithm improves the average path length in path planning by 0.21%, 82.4%, and 7.9% over the original algorithm in three different environments under 30 independent experiments.

Biphasic decay of intact SHIV genomes following initiation of antiretroviral therapy complicates analysis of interventions targeting the reservoir

The latent reservoir for HIV-1 in resting CD4+ T cells persists despite antiretroviral therapy (ART) and precludes cure. Reservoir-targeting interventions are evaluated in ART-treated macaques infected with simian immunodeficiency virus (SIV) or simian-human immunodeficiency virus (SHIV). Efficacy is determined by reservoir measurements before and after the intervention. However, most proviruses persisting in the setting of ART are defective. In addition, intact HIV-1 and SIV genomes undergo complex, multiphasic decay observable when new infection events are blocked by ART. Intervention-induced elimination of latently infected cells must be distinguished from natural decay. Here, we address these issues for SHIV. We describe an intact proviral DNA assay that allows digital counting of SHIV genomes lacking common fatal defects. We show that intact SHIV genomes in circulating CD4+ T cells undergo biphasic decay during the first year of ART, with a rapid first phase (t1/2 = 30.1 d) and a slower second phase (t1/2 = 8.1 mo) that is still more rapid that the slow decay observed in people with HIV-1 on long-term ART (t1/2 = 3.7 y). In SHIV models, most interventions are tested during 2nd phase decay. Natural 2nd phase decay must be considered in evaluating interventions as most infected cells present at this time do not become part of the stable reservoir. In addition, for interventions tested during 2nd phase decay, a caveat is that the intervention may not be equally effective in people with HIV on long-term ART whose reservoirs are dominated by latently infected cells with a slower decay rate.

Ce3+-based phosphor converter enabling laser lighting to attain both high CRI and high luminous efficacy

Eu2+ doped-CaAlSiN3 possesses broad red emission, enabling a phosphor-converted lighting device to achieve a high color rendering index (CRI) and proper color temperature. However, CaAlSiN3:Eu2+ exhibits relatively slow decay (∼1 μs) and intense re-absorption of luminescence from green/yellow emitters, thereby causing optical saturation and reducing the luminous efficacy. Here, we fabricated a novel phosphor converter comprising Lu3Al5O12:Ce3+ and Y1.3Gd1.6Al5O12:Ce3+ powders. The typical sample, when excited by a blue laser, exhibited a high luminous efficacy of 231 lm/W and a high saturation threshold of 22.2 W/mm2, resulting in a high luminous exitance of 695 lm/mm2. Importantly, the phosphor converter produced a broad emission band that included sufficient cyan and red components, resulting in a full width at half maximum (FWHM) of 134 nm and a high CRI of 81. With this excellent balance between CRI and luminous efficacy, the reported phosphor converter can significantly expand the range of laser lighting applications.

Direct numerical simulations and spectral proper orthogonal decomposition analysis of shocklet-containing turbulent channel counter-flows

Counter-flow configurations in a confined channel flow provide an efficient framework to study high intensity turbulent mixing processes. In a previous study (Physical Review Fluids, 6(9), p.094603), a wall-bounded counter-flow turbulent channel configuration was presented as an effective framework for addressing certain challenges related to the study of compressibility effects on turbulence as an alternative to free shear layer and Poiseuille/Couette type flows. Here, the previous direct numerical simulations are extended to a higher Mach number (M=0.7) to quantify direct and indirect effects of compressibility. It is found that the configuration is able to produce large numbers of embedded shocklets, leading to significant asymmetry in probability density functions of dilatation. Reducing the Prandtl number from 0.7 to 0.2 increases the compressibility effect further by reducing the bulk heating in the channel. A peak turbulent Mach number close to unity is obtained, for which the contribution of the dilatational dissipation to the total dissipation is nevertheless found to be limited to ∼6%. Indirect effects of compressibility are much larger, with changes of up to 40% in Favre normal stresses, despite the mean flow and shear stress being almost unaffected by compressibility in this configuration. Given the inflectional nature of the turbulent mean flow it is also interesting to identify large structures. Spectral Proper Orthogonal Decomposition (SPOD) reveals a full spectrum with a slow decay of energy with mode number. Mode shapes are three-dimensional with the low frequencies displaying elongated streaks in the velocity field at the channel centre plane.

Simulating carbon accumulation and loss in the central Congo peatlands.

Peatlands of the central Congo Basin have accumulated carbon over millennia. They currently store some 29 billion tonnes of carbon in peat. However, our understanding of the controls on peat carbon accumulation and loss and the vulnerability of this stored carbon to climate change is in its infancy. Here we present a new model of tropical peatland development, DigiBog_Congo, that we use to simulate peat carbon accumulation and loss in a rain-fed interfluvial peatland that began forming ~20,000 calendar years Before Present (cal. yr BP, where 'present' is 1950 CE). Overall, the simulated age-depth curve is in good agreement with palaeoenvironmental reconstructions derived from a peat core at the same location as our model simulation. We find two key controls on long-term peat accumulation: water at the peat surface (surface wetness) and the very slow anoxic decay of recalcitrant material. Our main simulation shows that between the Late Glacial and early Holocene there were several multidecadal periods where net peat and carbon gain alternated with net loss. Later, a climatic dry phase beginning ~5200 cal. yr BP caused the peatland to become a long-term carbon source from ~3975 to 900 cal. yr BP. Peat as old as ~7000 cal. yr BP was decomposed before the peatland's surface became wetter again, suggesting that changes in rainfall alone were sufficient to cause a catastrophic loss of peat carbon lasting thousands of years. During this time, 6.4 m of the column of peat was lost, resulting in 57% of the simulated carbon stock being released. Our study provides an approach to understanding the future impact of climate change and potential land-use change on this vulnerable store of carbon.

A polarization study of jets interacting with turbulent magnetic fields

ABSTRACT We investigate the effect of the jet’s immediate surroundings on the non-thermal synchrotron emission and its polarization properties. The ambient medium is equipped with a turbulent magnetic field, which is compressed and amplified by the jets as they progress. This leads to high polarization at the forward shock surface. The randomness in the magnetic polarities of the external fields in the shocked ambient medium (SAM) results in vector cancellation of the polarized components from the jet, thereby causing depolarization of the radiation from the cocoon. We find that due to the slow decay of the fields in the SAM, such depolarization by the fields with large correlation lengths is more prominent when compared to the small-scale fields. Also, the low-power jets, which have magnetic fields comparable in strength to those in the SAM, are more severely affected by the SAM’s depolarizing effect, than the high-power ones. The turbulent backflows in the cocoon, as well as the shearing of fields near the contact discontinuity, strengthen the poloidal component in the jet. This causes internal depolarization due to the cancellation of the orthogonally polarized components along the line of sight as the field transitions from ordered toroidal to poloidal. The synchrotron maps display high-emission filaments in the cocoon with magnetic fields aligned along them. The kink instability leads to the wiggling motion of the jet’s spine, resulting in hotspot complexes in low-power sources.