Polarization Dynamics Research Articles

Polarization time of unpolarized light

Light produced by most natural and artificial sources is unpolarized or partially polarized. At any instant of time, however, such random light can be regarded as fully polarized, but the polarization state may vary drastically within short time intervals. This rate of change is another attribute that separates one unpolarized beam from another. Here, we study such polarization dynamics and, for the first time to our knowledge, measure the characteristic time, called the polarization time, in which the instantaneous polarization state stays essentially unaltered. The technique employs a polarization-sensitive Michelson interferometer and two-photon absorption detection valid for electromagnetic light, yielding superior femtosecond time resolution. We analyze two unpolarized light sources: amplified spontaneous emission from a fiber amplifier and a dual-wavelength laser source. The characterization of polarization dynamics can have significant applications in optical sensing, polarimetry, telecommunication, and astronomy, as well as in quantum and atom optics.

Influence of thermal vibrations on polarization switching in the model of local fields

A microscopic model to simulate the polarization dynamics, the model of local fields, is improved by considering thermal vibrations. The model is based on a sequence of single dipole flips which are thermally activated. The time to flip a single dipole depends on its deterministic transition rate which depends on the local electric field and on a probabilistic factor. In each step, the dipole with the shortest flip time is switched. Thermal vibrations of the dipoles cause changes of the distances between the dipoles. The variation of distances effects variations of the local field at the dipoles. In the framework of the extended model, these variations are considered by multiplying the local fields in each step with a Gaussian distributed random number. The model is applied to simulate polarization switching and polarization hysteresis loops of two and of three dimensional systems based on the barium titanate structure. The simulations yield intrinsic dead layers close to the electrodes and around defects which cannot be switched even in very strong fields. These nonswitchable layers are nuclei for domains and thus nuclei for polarization switching. The switching time of the system vastly decreases with the amplitude of the thermal vibrations. Moreover, the thermal vibrations enable the polarization switching in low external fields and decrease the coercive fields.

Agent-Based Modelling Approach for Multidimensional Opinion Polarization in Collective Behaviour

Opinion polarization in a group is an important phenomenon in collective behaviour that has become increasingly frequent during periods of social transition. In general, an opinion includes several dimensions in reality. By combining social judgement theory with the multi-agent model, we propose a multidimensional opinion evolution model for studying the dynamics of opinion polarization. Compared with previous models, a major contribution is that the opinion of the agent is extended to multiple dimensions, and the BA network is used as a model of real social networks. The results demonstrate that polarization is influenced by the average degree of the network, and the polarization process is affected by the parameters of the assimilation effect and contrast effect. Moreover, the evolution processes in different dimensions of opinion show correlation under certain specific conditions, and the discontinuous equilibrium phenomenon is observed in multidimensional opinion evolution in subsequent experiments.

Spatial polarization of agriculture of Czechia during the integration into the European Union

The primary focus of Czech agricultural and rural geographers in the past decade was put on the regional impacts triggered by the transformation of agriculture and the influences of the Common Agricultural Policy on agriculture. Multifunctionality or spatial polarization of agriculture of Czechia remained the object of marginal scientific interest, despite the fact that such topics were largely discussed amongst foreign experts in connection with a theoretical transformation of the rural space. Therefore, relying on indicators of crop and livestock production, the ambition of the paper is to uncover the dynamics of spatial polarization of agriculture in Czechia. Its conclusions reveal an increasing spatial polarization of agriculture during the Czech integration into the European Union between regions with different natural conditions (areas with favourable conditions for agriculture and mountainous areas). It turns out, however, that while the fertile regions have been gradually specializing on crop production, spatial polarization in livestock production increases due to the rising role of mountainous areas.

Live-cell imaging of the dynamics of plant zygote polarization

Live-cell imaging of the dynamics of plant zygote polarization

Probe dependence on polar solvation dynamics from fs broadband fluorescence.

Polar solvation dynamics of six 7-aminocoumarins and 4-aminophthalimide (4AP) are investigated using broadband FLuorescence UP-conversion Spectroscopy (FLUPS) combined with a global analysis based on time-dependent band-shape functions. The solvation dynamics of the coumarins in ethanol exhibit only minor differences but are, however, significantly different from that of 4AP. The band-shape parameters, width and asymmetry, exhibit much larger variation even among the coumarins and are correlated with the amount of excess excitation energy. Differences in the solvation dynamics of 4AP and a selected coumarin, C151, are also observed in dimethyl sulfoxide demonstrating the molecularity of solvation i.e. solvation depends on the solute and does not solely reflect the dynamic properties of the solvent. These differences are attributed to specific solute-solvent interactions due to hydrogen bonding. In a weakly interacting solvent, benzonitrile, the solvation dynamics of 4AP and C151 are nearly identical.

Transient Expression of Chimeric Fluorescent Reporter Proteins in Pollen Tubes to Study Protein Polar Secretion and Dynamics.

Transient expression of chimeric fluorescent reporter proteins by biolistic bombardment is a quick and useful procedure for studying subcellular protein localization and dynamics in plants. It is especially beneficial in specific plant cells which are not suitable for protoplast-based and Agrobacterium-mediated protein transient expression. Polar protein secretion and vesicular trafficking play essential functions for cell polarization and tip growth. The growing pollen tube is regarded as an ideal model plant cell system to study the machinery and regulation of polar protein trafficking and targeting. A large amount of newly synthesized proteins are packed and polarly transported to the apical region to support the rapid and highly polarized tip growth. Here, we described a detailed step-by-step protocol for the transient expression of chimeric fluorescent reporter proteins in growing Arabidopsis and tobacco pollen tubes to study polar transportation logistics and mechanisms. In addition, we have optimized the Arabidopsis and tobacco in vitro pollen germination medium and the conditions to maximize the efficiency of protein expression. As a proof of concept, we have used this protocol to express actin microfilament and late endosomal fluorescent markers in Arabidopsis and tobacco pollen tubes.

A sensitive fluorescent probe for the polar solvation dynamics at protein-surfactant interfaces.

Relaxation dynamics at the surface of biologically important macromolecules is important taking into account their functionality in molecular recognition. Over the years it has been shown that the solvation dynamics of a fluorescent probe at biomolecular surfaces and interfaces account for the relaxation dynamics of polar residues and associated water molecules. However, the sensitivity of the dynamics depends largely on the localization and exposure of the probe. For noncovalent fluorescent probes, localization at the region of interest in addition to surface exposure is an added challenge compared to the covalently attached probes at the biological interfaces. Here we have used a synthesized donor-acceptor type dipolar fluorophore, 6-acetyl-(2-((4-hydroxycyclohexyl)(methyl)amino)naphthalene) (ACYMAN), for the investigation of the solvation dynamics of a model protein-surfactant interface. A significant structural rearrangement of a model histone protein (H1) upon interaction with anionic surfactant sodium dodecyl sulphate (SDS) as revealed from the circular dichroism (CD) studies is nicely corroborated in the solvation dynamics of the probe at the interface. The polarization gated fluorescence anisotropy of the probe compared to that at the SDS micellar surface clearly reveals the localization of the probe at the protein-surfactant interface. We have also compared the sensitivity of ACYMAN with other solvation probes including coumarin 500 (C500) and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM). In comparison to ACYMAN, both C500 and DCM fail to probe the interfacial solvation dynamics of a model protein-surfactant interface. While C500 is found to be delocalized from the protein-surfactant interface, DCM becomes destabilized upon the formation of the interface (protein-surfactant complex). The timescales obtained from this novel probe have also been compared with other femtosecond resolved studies and molecular dynamics simulations.

Probing Cdc42 Polarization Dynamics in Budding Yeast Using a Biosensor.

Cdc42 is a small guanosine triphosphatase (GTPase) that plays a central role in polarity development in diverse cell types. Since the activity of Cdc42 is dynamically controlled in time and space, it is required to develop a biosensor to monitor its activation in vivo. In this chapter, we describe the construction and usage of a simple and robust biosensor for monitoring active Cdc42 in budding yeast. This affinity-based biosensor uses a red fluorescent protein fused to a Cdc42- and Rac-interactive binding motif from one of the Cdc42 effector proteins. Because it binds specifically to the GTP-bound Cdc42, this biosensor can be used to monitor Cdc42 activation in vivo. This or similar biosensors can be widely used for studying GTPase signaling in other cell types because of the conserved CRIB motif present among GTPase targets.

Trends of centre-periphery polarization in Sverdlovsk region between 2008 and 2015

The significant imbalances in the economic space of a region, particularly between the centre and the periphery, present a serious challenge for economists, politicians and policy makers. Which measures are to be taken to remedy this situation? What should they be aimed at? These are the main questions to be addressed by the researchers and the government. To develop a competent policy it is essential to understand the dynamics of intra-regional variations in a long-time period. This article seeks to describe the trends in the centre-periphery polarization dynamics of a Russian region by analyzing the indicators of socio-economic development of its constituent municipalities. In their calculations the authors used the coefficient of centre-periphery variation and the methods of statistical analysis. The comparative analysis of the contribution made by peripheral and central municipalities to the key socio-economic indicators of the region in the period of 2008-2015 has shown that there is a growing centre-periphery polarization within Sverdlovsk region. The authors calculated the coefficient of centre-periphery variation for specific municipalities and the periphery in general by using the average volume indices of the retail turnover, investments in the main capital, new housing supply, the turnover of organizations and average monthly salary. The dynamics of this coefficient and that of the GRP in the given period demonstrates that while the centre-periphery gap is narrowed during the recession, it widens when the economic situation stabilizes. The scientific novelty of this research is achieved through identifying the main trends in the centre-periphery polarization within Sverdlovsk region at various stages of its socio-economic development. These research results can be applied to develop a regional policy aimed at reducing the centre-periphery differences and polarization of the regional economic space.

Imaging the Effector CD8 Synapse.

Here, we describe 4D imaging of effector CD8+ T cells as they conjugate and kill live targets in vitro and analyze the polarization dynamics of intracellular compartments to this cell-cell interface.

Extracellular Regulation of the Mitotic Spindle and Fate Determinants Driving Asymmetric Cell Division.

Stem cells use mode of cell division, symmetric (SCD) versus asymmetric (ACD), to balance expansion with self-renewal and the generation of daughter cells with different cell fates. Studies in model organisms have identified intrinsic mechanisms that govern this process, which involves partitioning molecular components between daughter cells, frequently through the regulation of the mitotic spindle. Research performed in vertebrate tissues is revealing both conservation of these intrinsic mechanisms and crucial roles for extrinsic cues in regulating the frequency of these divisions. Morphogens and positional cues, including planar cell polarity proteins and guidance molecules, regulate key signaling pathways required to organize cell/ECM contacts and spindle pole dynamics. Noncanonical WNT7A/VANGL2 signaling governs asymmetric cell division and the acquisition of cell fates through spindle pole orientation in satellite stem cells of regenerating muscle fibers. During cortical neurogenesis, the same pathway regulates glial cell fate determination by regulating spindle size, independent of its orientation. Sonic hedgehog (SHH) stimulates the symmetric expansion of cortical stem and cerebellar progenitor cells and contributes to cell fate acquisition in collaboration with Notch and Wnt signaling pathways. SLIT2 also contributes to stem cell homeostasis by restricting ACD frequency through the regulation of spindle orientation. The capacity to influence stem cells makes these secreted factors excellent targets for therapeutic strategies designed to enhance cell populations in degenerative disease or restrict cell proliferation in different types of cancers.

Probing micro-environment of lipid droplets in a live breast cell: MCF7 and MCF10A

Local environment of the lipid droplets inside the breast cancer cells, MCF7 and in non-malignant breast cells, MCF10A is monitored using time-resolved confocal microscopy. For this study, a coumarin-based dye C153 has been used. The local polarity and the solvation dynamics indicate that a cytoplasmic lipid droplet is less polar and displays slower solvation dynamics compared to the cytosol. Significant differences in terms of number of lipid droplets, polarity and solvation dynamics are observed between the cancer cell (MCF7) and its non-malignant cell (MCF10A).

Annual boom–bust cycles of polar phytoplankton biomass revealed by space-based lidar

Polar plankton communities are among the most productive, seasonally dynamic and rapidly changing ecosystems in the global ocean. However, persistent cloud cover, periods of constant night and prevailing low solar elevations in polar regions severely limit traditional passive satellite ocean colour measurements and leave vast areas unobserved for many consecutive months each year. Consequently, our understanding of the annual cycles of polar plankton and their interannual variations is incomplete. Here we use space-borne lidar observations to overcome the limitations of historical passive sensors and report a decade of uninterrupted polar phytoplankton biomass cycles. We find that polar phytoplankton dynamics are categorized by ‘boom–bust’ cycles resulting from slight imbalances in plankton predator–prey equilibria. The observed seasonal-to-interannual variations in biomass are predicted by mathematically modelled rates of change in phytoplankton division. Furthermore, we find that changes in ice cover dominated variability in Antarctic phytoplankton stocks over the past decade, whereas ecological processes were the predominant drivers of change in the Arctic. We conclude that subtle and environmentally driven imbalances in polar food webs underlie annual phytoplankton boom–bust cycles, which vary interannually at each pole. Phytoplankton productivity is high in the polar oceans. Lidar observations from 2006–2015 reveal that phytoplankton biomass was characterized by annual cycles influenced by sea-ice extent in the Antarctic and ecological processes in the Arctic.

Long-Lived Valley Polarization of Intravalley Trions in Monolayer WSe_{2}.

We investigate valley dynamics associated with trions in monolayer tungsten diselenide (WSe_{2}) using polarization resolved two-color pump-probe spectroscopy. When tuning the pump and probe energy across the trion resonance, distinct trion valley polarization dynamics are observed as a function of energy and attributed to the intravalley and intervalley trions in monolayer WSe_{2}. We observe no decay of a near-unity valley polarization associated with the intravalley trions during ∼ 25 ps, while the valley polarization of the intervalley trions exhibits a fast decay of ∼4 ps. Furthermore, we show that resonant excitation is a prerequisite for observing the long-lived valley polarization associated with the intravalley trion. The exceptionally robust valley polarization associated with resonantly created intravalley trions discovered here may be explored for future valleytronic applications such as valley Hall effects.

Rapid mapping of polarization switching through complete information acquisition.

Polarization switching in ferroelectric and multiferroic materials underpins a broad range of current and emergent applications, ranging from random access memories to field-effect transistors, and tunnelling devices. Switching in these materials is exquisitely sensitive to local defects and microstructure on the nanometre scale, necessitating spatially resolved high-resolution studies of these phenomena. Classical piezoresponse force microscopy and spectroscopy, although providing necessary spatial resolution, are fundamentally limited in data acquisition rates and energy resolution. This limitation stems from their two-tiered measurement protocol that combines slow (∼1 s) switching and fast (∼10 kHz–1 MHz) detection waveforms. Here we develop an approach for rapid probing of ferroelectric switching using direct strain detection of material response to probe bias. This approach, facilitated by high-sensitivity electronics and adaptive filtering, enables spectroscopic imaging at a rate 3,504 times faster the current state of the art, achieving high-veracity imaging of polarization dynamics in complex microstructures.

Clocked Domain Wall Logic Using Magnetoelectric Effects

A new digital device scheme based on the magnetoelectric coupling and automotion of the magnetic domain wall is proposed. A single device is composed of a ferromagnetic wire and two ferroelectric capacitors served as the input and the output. It is shown that with the initialization in the magnetic states, a single device and the corresponding majority gate can realize the NOT, NAND, and NOR functions. Furthermore, the device has the cascadability, input–output isolation, gain, and nonreciprocity. The device concepts are justified by the numerical calculation, including the Landau–Lifshitz–Gilbert equation for the magnetization dynamics, the Landau–Khalatnikov equation for the electric polarization dynamics, and the electrostatic equations for the open-circuit output voltage and the charge sharing process between devices. The energy dissipation is also quantified and shown to be two to three orders of magnitude less than that in spin-torque-driven devices.

Marine birds and mammals foraging in the rapidly deglaciating Arctic fjord - numbers, distribution and habitat preferences

Climate-induced glacier retreat is considered in the context of its reducing the sea-ice contact zone used by marine birds and mammals as important foraging grounds and may cause declines in their numbers. To test this hypothesis, a survey was conducted in diversified habitats of a rapidly deglaciating Arctic fjord in Svalbard. Of the fifteen seabird and four mammal species found, coastal surface-feeders prevailed over benthic-feeders and pelagic pursuit-divers. Deep tidewater glacier bays were used by the most numerous but least heterogeneous foraging community, in contrast to the shallow lagoons of coastline-terminating glaciers and deglaciated shorelines. After the 15 years of glaciers retreat documented in Hornsund, the sea-ice contact zone used by birds and mammals has not declined. On the contrary, the increasing freshwater supply from underwater glacial rivers raising zooplankton up to the surface, thus making it available to seabirds, enhances the attractiveness of tidewater glacier bays. Along with the stage of retreat, the importance of glacier bays as feeding grounds changes. Foraging conditions deteriorate when the glacier terminus reaches the coastline and the glacier bay becomes shallower. However, glacier retreat enlarges the area of littoral habitats accessible to benthophages. Glacier-related habitats situated close to colony are used as alternative/emergency feeding grounds by seabirds that normally forage outside the fjord. This is especially important during the chick-rearing period and also during bad weather conditions in the open sea. Our study demonstrates that, so far, the abundance and species diversity of seabirds foraging in the rapidly deglaciating Hornsund are both high, suggesting that they benefit from the current intensive glacier melt. However, with further climate change an apparent biodiversity paradox may occur. Here, overall biodiversity will increase but local diversity of pagophilic species will decline. Such nonlinear responses complicate the prediction of future polar ecosystem dynamics.

Quantum hydrodynamics in the rotating reference frame

In this paper, we apply quantum hydrodynamics (QHD) to study the quantum evolution of a system of spinning particles and particles that have the electric dipole moments (EDM) in the rotating reference frame. The method presented is based on the many-particle microscopic Schrodinger equation in the rotating reference frame. Fundamental QHD equations for charged or neutral spinning and EDM-bearing particles were shaped due to this method and contain the spin-dependent inertial force field. The polarization dynamics in systems of neutral particles in the rotating frame is shown to cause formation of a new type of waves, the dipole-inertial waves. We have analyzed elementary excitations in a system of neutral polarized fluids placed into an external electric field in 2D and 3D cases. We predict the novel type of 2D dipole-inertial wave and 3D-polarization wave modified by rotation in systems of particles with dipole-dipole interactions.

Laser wakefield acceleration of polarized electron beams

The acceleration of highly polarized electron beams are widely used in state-of-the-art high-energy physics experiments. In this work, a model for investigation of polarization dynamics of electron beams in the laser-plasma accelerator depending on the initial energy of electrons was developed and tested. To obtain the evolution of the trajectory and momentum of the electron for modeling its acceleration the wakefield structure was determined. The spin precession of the beam electron was described by Thomas-Bargman-Michel-Telegdi equations. The evolution of the electron beam polarization was investigated for zero-emittance beams with zero-energy spread.