Initial Polarization Research Articles

Study of Multi-Pixel Scintillator Detector Configurations for Measuring Polarized Gamma Radiation

When a positron annihilates, two gamma photons are created with orthogonal polarizations. It is possible to use coincidence measurements where both photons undergo Compton scattering to estimate their initial relative polarization orientation. This information is of great interest in gamma imaging systems, such as Positron Emission Tomography, where it may be used as an additional tool to distinguish true coincidence events from scatter and random background. The successful utilization of this principle critically depends on the detector’s angular and energy resolution, which determine its polarimetric performance. In this study, we use Monte Carlo simulations based on the Geant4 toolkit to model two multi-pixel detector configurations identified as prospective for the measurement of gamma-ray polarization in PET. One is based on 2 mm × 2 mm × 20 mm LYSO scintillators and the other is based on 3 mm × 3 mm × 20 mm GAGG scintillators. Each configuration has a pair of modules, each consisting of 64 crystals set up in a single 8 × 8 matrix, where both the recoil electron and the Compton-scattered photon are absorbed. We simulate positron annihilation by generating two back-to-back gamma photons of 511 keV with orthogonal polarizations. The Compton scattering is successfully identified and the modulation of the azimuthal angle difference is clearly observed. The configuration based on GAGG crystals demonstrates slightly better polarimetric performance than the one based on LYSO crystals, reflected in the more pronounced azimuthal modulation.

Na Diffusion in Hard Carbon Studied with Positive Muon Spin Rotation and Relaxation.

The diffusive nature of Na+ in Na-inserted hard carbon (C x Na), which is the most common anode material for a Na-ion battery, was studied with a positive muon spin rotation and relaxation (μ+SR) technique in transverse, zero, and longitudinal magnetic fields (TF, ZF, and LF) at temperatures between 50 and 375 K, where TF (LF) denotes the applied magnetic field perpendicular (parallel) to the initial muon spin polarization. At temperatures above 150 K, TF-μ+SR measurements showed a distinct motional narrowing behavior, implying that Na+ begins to diffuse above 150 K. The presence of two different muon sites in C x Na was confirmed with ZF- and LF-μ+SR measurements; one is in the Na-inserted graphene layer, and the other is in the Na-vacant graphene layer adjacent to the Na-inserted graphene layer. A systematic increase in the field fluctuation rate (ν) with increasing temperature also evidenced a thermally activated Na diffusion, particularly above 150 K. Assuming the two-dimensional diffusion of Na+ in the graphene layers, the self-diffusion coefficient of Na+ (D Na J) at 300 K was estimated to be 2.5 × 10-11 cm2/s with a thermal activation energy of 39(7) meV.

Almost complete revivals in quantum many-body systems

Revivals of initial non-equilibrium states is an ever-present concern for the theory of dynamic thermalization in many-body quantum systems. Here we consider a nonintegrable lattice of interacting spins 1/2 and show how to construct a quantum state such that a given spin 1/2 is maximally polarized initially and then exhibits an almost complete recovery of the initial polarization at a predetermined moment of time. An experimental observation of such revivals may be utilized to benchmark quantum simulators with a measurement of only one local observable. We further propose to utilize these revivals for a delayed disclosure of a secret.

Laser induced tunable Ge2Sb2Te5 phase-change gratings

Periodic photonic nano- and microstructures are routinely used for light manipulation at the nanoscale. However, their fabrication process is demanding in terms of time, cost and facilities. Here we demonstrate a rapid laser-assisted method for fabrication of gratings in Ge2Sb2Te5 (GST) thin films, based on the formation of laser induced periodic surface structures (LIPSS). LIPSS formation mechanisms dependent on the wavelength of the operating laser, lead to high flexibility of the process, producing gratings with tunable period and orientation with respect to the initial laser polarization. The phase-change properties of GST, on the other hand, allows to fabricate phase gratings with strong modulation of refractive index, which are rewritable in nature.

Investigation of self-heating and dissipative effects in ferroelectric ceramics subjected to compressive mechanical cyclic loading

In this study the behavior of a soft PZT ceramic subjected to compressive cyclic loadings is investigated with the aim of providing an insight into different dissipative processes which affect the ferroelastic cyclic behavior of the material. Two quantitative imaging techniques, infrared (IR) thermography and digital image correlation (DIC), are employed to measure superficial temperature and in-plane displacement of the sample under mechanical cyclic loadings. Thermal and strain responses are further deduced from these measurements. This allows to quantify the energy dissipated by the material during applied mechanical loadings. Self-heating (SH) and DIC measurements reveal that, even in the piezoelectric regime, the level of dissipation is significant. This suggests that PZT ceramic response under cyclic compression is significantly influenced by domain switching mechanisms. The two imaging techniques are shown to be efficient tools to identify domain wall activity in ferroelectric ceramics and can be advantageously substituted for polarization measurements when polarization variations are too small to be detected. It is also shown that, due to the initial compressive stress experienced by all specimens, the domain wall activity under cyclic uniaxial compressive stress is almost independent of the initial polarization state of the material.

Polarization singularities in the self-focusing of an elliptically polarized laser beam in the isotropic phase of a cholesteric liquid crystal close to the temperature of mesophase transition

Self-action of an initially elliptically polarized Gaussian beam in the isotropic phase of a cholesteric liquid crystal near the temperature of phase transition is studied. It is shown that nonlocality of the optical properties of the crystal leads to significantly different self-action behavior of light beams with right-hand and left-hand elliptical polarization. Numerous lines of circular polarization singularity (C-lines) can appear in beam cross sections during its self-focusing. These lines are circumferences of various radii with centers located on the beam axis and lying in planes perpendicular to the direction of its propagation. The position and contrast of the lines is subject to the total beam power and initial polarization state, and in certain cases some of the singleC-lines split into multiple lines, and vice versa.

Generation of polarized positron beams via collisions of ultrarelativistic electron beams

A novel scheme is proposed for generating a polarized positron beam via multiphoton Breit-Wheeler process during the collision of a 10 GeV, pC seeding electron beam with the other 1 GeV, nC driving electron beam. The driving beam provides the strong self-generated field, and a suitable transverse deviation distance between two beams enables the field experienced by the seeding beam to be unipolar, which is crucial for realizing the positron polarization. We employ the particle simulation with a Monte-Carlo method to calculate the spin- and polarization-resolved photon emission and electron-positron pair production in the local constant field approximation. Our simulation results show that a highly polarized positron beam with polarization above $40\%$ can be generated in several femtoseconds, which is robust with respect to parameters of two electron beams. Based on an analysis of the influence of $\gamma$-photon polarization on the polarized pair production, we find that a polarized seeding beam of the proper initial polarization can further improve the positron polarization to $60\%$.

Generation of a vector light field based on polarization holography.

We propose a simple and effective method for generating a vector light field based on the faithful reconstruction (FR) effect of polarization holography, where the arbitrary linear polarization waves can be faithfully reconstructed by the polarization-sensitive recording media. The scheme incorporates the tunable and switchable dynamics exposure system to manufacture vector beams. By regulating the velocity and the initial polarization through the angle-aperture and the half-wave plate in the dynamics exposure system, the generated optical element can convert a linear polarization wave into a vector beam. We have analyzed the feasibility in theory and demonstrated the generation of the vector beams experimentally which shows good agreement with the theoretical simulations.

The 3'UTR of the Drosophila CPEB translation factor gene orb2 plays a crucial role in spermatogenesis.

CPEB proteins are conserved translation regulators involved in multiple biological processes. One of these proteins in Drosophila, Orb2, is a principal player in spermatogenesis. It is required for meiosis and spermatid differentiation. During the later process, orb2 mRNA and protein are localized within the developing spermatid. To evaluate the role of the orb2 mRNA 3'UTR in spermatogenesis, we used the CRISPR/Cas9 system to generate a deletion of the orb2 3'UTR, orb2R. This deletion disrupts the process of spermatid differentiation but has no apparent effect on meiosis. Differentiation abnormalities include defects in the initial polarization of the 64-cell spermatid cysts, mislocalization of mRNAs and proteins in the elongating spermatid tails, altered morphology of the elongating spermatid tails, and defects in the assembly of the individualization complex. These disruptions in differentiation appear to arise because orb2 mRNA and protein are not properly localized within the 64-cell spermatid cyst.

Study of charging-up effect for a single mask triple GEM detector

With the advancement of the accelerator systems and the requirements of high luminosity particle beams to reach different physics goals, detectors with good position resolution and high rate handling capability have become essential for designing any High Energy Physics (HEP) experiments. The Gas Electron Multiplier (GEM) detectors are widely used in many HEP experiments as a tracking device because of their good spatial resolution and rate handling capability.The presence of the dielectric medium inside the active volume of the GEM detector changes its behaviour when exposed to external radiation. This mechanism is commonly referred as the charging-up effect. In this article, the effect of the charging-up phenomenon and the initial polarisation effect of the dielectric on the gain of the chamber are reported for a single mask triple GEM chamber with Ar/CO2 gas mixture.

Temperature and initial polarization dependences of the electrooptic coefficient of BaTiO3 crystal film

In this work, the temperature dependence of polarization degree of ferroelectric phase barium titanate (BaTiO3) film is first modelled based on a conservation of the energy-focusing cost of a microstructural domain cell, and then the dual dependences on both temperature and initial polarization degree of an off-axis tensor electrooptic coefficient (r51) is modelled. Further, the correlation between the initial polarization degree and the r51 is investigated based on the correlative electrooptic and elasto-optic effects of a perovskite crystal. With the output of theoretical models for the attributes of r51, numerical simulations are carried out. It was found that both the polarization degradation of out-of-plane polarization (Pz) and the electrooptic coefficient r51 of c-axis oriented crystal films exhibit significant nonlinear dependences on the initial fraction of in-plane polarization (Px) and the working temperature. Consequently, the temperature dependences of the measured results of r51 with respect to the selected working temperatures in the range of 20°C∼100°C are consistent with the above numerical results, showing that the out-of-plane polarization degree presents the biggest degradation in the temperature range from 50°C to 70°C. This work provides a valuable reference to the research and development of high-speed electro-optic devices and applications.

Inherited apicobasal polarity defines the key features of axon-dendrite polarity in a sensory neuron

Neurons are highly polarized cells with morphologically and functionally distinct dendritic and axonal processes. The molecular mechanisms that establish axon-dendrite polarity invivo are poorly understood. Here, we describe the initial polarization of posterior deirid (PDE), a ciliated mechanosensory neuron, during development invivo through 4D live imaging with endogenously tagged proteins. PDE inherits and maintains apicobasal polarity from its epithelial precursor. Its apical domain is directly transformed into the ciliated dendritic tip through apical constriction, which is followed by axonal outgrowth from the opposite basal side of the cell. The apical Par complex and junctional proteins persistently localize at the developing dendritic domain throughout this transition. Consistent with their instructive role in axon-dendrite polarization, conditional depletion of the Par complex and junctional proteins results in robust defects in dendrite and axon formation. During apical constriction, a microtubule-organizing center (MTOC) containing the microtubule nucleator γ-tubulin ring complex (γ-TuRC) forms along the apical junction between PDE and its sister cell in a manner dependent on the Par complex and junctional proteins. This junctional MTOC patterns neuronal microtubule polarity and facilitate the dynein-dependent recruitment of the basal body for ciliogenesis. When non-ciliated neurons are genetically manipulated to obtain ciliated neuronal fate, inherited apicobasal polarity is required for generating ciliated dendritic tips. We propose that inherited apicobasal polarity, together with apical cell-cell interactions drive the morphological and cytoskeletal polarity in early neuronal differentiation.

Broadband multimodal THz waveguides for efficient transfer of high-power radiation in space-confined conditions

Terahertz (THz) range, which lies between the microwave and infrared regions of the electromagnetic spectrum, presents a new frontier containing an abundance of technical applications and fundamental research problems. There are several challenges limiting the progress in the THz science and technology. One of them is the limited range ofthe guided-wave propagation of THz radiation, owing to the high loss from the finite conductivity of metals and the high absorption coefficient of dielectric materials in the THz range. In this work, we discuss the design and fabrication of multimodal hollow THz waveguides used at the X-band Electron Paramagnetic Resonance (EPR) endstation located at the Novosibirsk Free Electron Laser facility (NovoFEL). Experiments carried out at the EPR endstation are aimed to investigate the impact of THz and far infrared radiation on the spin system of different inorganic complexes and organic radicals. The EPR probehead and cryostat impose strict constraints on the possible ways of transferring the THz radiation to the sample, requiring the development, manufacturing, and characterization of specific waveguides. The proposed waveguides for X-band EPR measurements under THz radiation resemble hollow metal/dielectric waveguides. They have the shape of ahollow cylinder, tapering towards the end, with a silver-coated inner surface, and allow THz radiation to be transmitted over a distance of about 60 cm in a wide frequency range from THz to middle infrared. The waveguides performance was characterized at different frequencies of NovoFEL radiation and compared with numerical simulations. Following the requirements ofpolarization-sensitive EPR experiments, the waveguides were further modified by a miniature attachment, consisting of a polarizer, a semiconductor mirror, and a quarter-wave plate. The attachment allows preserving the initial polarization properties of THz radiation, turns its propagation vector, and creates the circular-polarized light irradiating the sample – all inside the limited volume of the EPR probehead.

The impact of the nonlinear effects on thermally stimulated depolarization currents in ion dielectrics

In this paper, the methods described the calculation of thermally stimulated depolarization currents in materials of the HBC class. In the identification of nonlinear processes of thermally stimulated depolarization, at this stage of the research, as defining criteria the authors consider the calculation of the dielectric initial polarization in the infinite approximation of perturbation theory (at the fundamental frequency fields) and calculation of kinetic coefficients in functions of the polarizing field intensity. Generalized nonlinear expressions for the complex dielectric constant and polarization are formulated, which are performed at the fundamental frequency of the alternating polarizing field. The generalized equations that are nonlinear by the field for kinetic coefficients of the kinetic equation are formulated. The obtained theoretical results are of current interest from the perspective of further development of analytical and computer methods of research and prediction of HBC properties as perspective nonlinear materials for a number of branches of modern industry.

The impact of the nonlinear effects on thermally stimulated depolarization currents in ion dielectrics

In this paper, the methods described the calculation of thermally stimulated depolarization currents in materials of the HBC class. In the identification of nonlinear processes of thermally stimulated depolarization, at this stage of the research, as defining criteria the authors consider the calculation of the dielectric initial polarization in the infinite approximation of perturbation theory (at the fundamental frequency fields) and calculation of kinetic coefficients in functions of the polarizing field intensity. Generalized nonlinear expressions for the complex dielectric constant and polarization are formulated, which are performed at the fundamental frequency of the alternating polarizing field. The generalized equations that are nonlinear by the field for kinetic coefficients of the kinetic equation are formulated. The obtained theoretical results are of current interest from the perspective of further development of analytical and computer methods of research and prediction of HBC properties as perspective nonlinear materials for a number of branches of modern industry.

Vector analysis of inverse objective function for electrochemical impedance spectroscopy of big capacity lead-acid battery

The important emergency power supply needs a large capacity battery. The batteries are long-term float charging. Electrochemical impedance spectroscopy (EIS) is important for remaining useful capacity warnings. This paper establishes the EIS inverse calculation technique that is centered in the vector objective function and linear interpolation search algorithm. This technique simplifies the initial value preparation and the gradient descent direction search for the inverse calculation of EIS. The root-mean-square errors of online embedded programming are smaller than the offline results of numerical software for EIS. The vector objective function targets the rotation angle of the initial polarization impedance vector to be zero during the EIS inverse calculation. This equivalently replaces the regular minimization of root-mean-square error. The linear interpolation algorithm simplifies the gradient descent direction search to a one-dimensional search for the double-layer capacitance of the initial polarization impedance. This algorithm replaces the conventional graphic method and evolutionary algorithm. The proposed algorithm is verified by the microcontroller at Valve-regulated lead-acid (VRLA) batteries (4200 Ah). The result of the algorithm is close to special numerical software for EIS. This algorithm improves the performance of an embedded management board.

Magnetoelectric coupling dependent on ferroelectric switching paths in two-dimensional perovskite multiferroics

Two-dimensional (2D) multiferroics have attracted considerable interest since the recent discovery of 2D ferroelectricity and ferromagnetism in van der Waals materials. Here we show the universality of 2D multiferroics in the Ca-based double-perovskite bilayer system and the transition of magnetization that is dependent on the ferroelectric switching paths by combining symmetry analysis and first-principles calculation. We demonstrate that although both the switching of rotation and tilt distortion can lead to polarization reversal, only the latter can cause a change in the direction of magnetization. The breaking of the inversion symmetry correlation between the initial and final polarization states is the key to achieve the transition of magnetization caused by polarization reversal. The ferroelectric switching that reverses tilt distortion via multistep switching generally has the lowest energy barrier, providing the feasibility of controlling magnetization by an electric field.

One-loop electroweak radiative corrections to charged lepton pair production in photon-photon collisions

We provide high-precision predictions for muon-pair and tau-pair productions in a photon-photon collision by considering a complete set of one-loop-level scattering amplitudes, i.e., electroweak (EW) corrections together with soft and hard QED radiation. Accordingly, we present a detailed numerical discussion with particular emphasis on the pure QED corrections as well as genuinely weak corrections. The effects of angular and initial beam polarization distributions on production rates are also discussed. An improvement is observed by a factor of two with oppositely polarized photons. Our results indicate that the one-loop EW radiative corrections enhance the Born cross section and the total relative correction is typically about 10% for both production channels. It appears that the full EW corrections to $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{\ensuremath{-}}{\ensuremath{\ell}}^{+}$ are required to match a percent level accuracy.

Co-development of central and peripheral neurons with trunk mesendoderm in human elongating multi-lineage organized gastruloids

Stem cell technologies including self-assembling 3D tissue models provide access to early human neurodevelopment and fundamental insights into neuropathologies. Gastruloid models have not been used to investigate co-developing central and peripheral neuronal systems with trunk mesendoderm which we achieve here in elongating multi-lineage organized (EMLO) gastruloids. We evaluate EMLOs over a forty-day period, applying immunofluorescence of multi-lineage and functional biomarkers, including day 16 single-cell RNA-Seq, and evaluation of ectodermal and non-ectodermal neural crest cells (NCCs). We identify NCCs that differentiate to form peripheral neurons integrated with an upstream spinal cord region after day 8. This follows initial EMLO polarization events that coordinate with endoderm differentiation and primitive gut tube formation during multicellular spatial reorganization. This combined human central-peripheral nervous system model of early organogenesis highlights developmental events of mesendoderm and neuromuscular trunk regions and enables systemic studies of tissue interactions and innervation of neuromuscular, enteric and cardiac relevance.

Convergence of stochastic-extended Lagrangian molecular dynamics method for polarizable force field simulation

Extended Lagrangian molecular dynamics (XLMD) is a general method for performing molecular dynamics simulations using quantum and classical many-body potentials. Recently several new XLMD schemes have been proposed and tested on several classes of many-body polarization models such as induced dipoles or Drude charges, by creating an auxiliary set of these same degrees of freedom that are reversibly integrated through time. This gives rise to a singularly perturbed Hamiltonian system that provides a good approximation to the time evolution of the real mutual polarization field. To further improve upon the accuracy of the XLMD dynamics in the context of classical polarizable force field simulation, and to potentially extend it to other many-body potentials, we introduce a stochastic modification which leads to a set of singularly perturbed Langevin equations with degenerate noise. We prove that the resulting Stochastic-XLMD converges to the accurate dynamics, and the convergence rate is both sharp and is independent of the accuracy of the initial polarization field. We carefully study the scaling of the damping factor and numerical noise for efficient numerical simulation for Stochastic-XLMD, and we demonstrate the effectiveness of the method for water molecules described by a polarizable force field.