Dominant Polarization Research Articles

Cytoarchitectonic and dynamic origins of giant positive local field potentials in the dentate gyrus.

To determine why some pathways but not others produce sizable local field potentials (LFPs) and how far from the source can these be recorded, complementary experimental analyses and realistic modeling of specific brain structures are required. In the present study, we combined multiple in vivo linear recordings in rats and a tridimensional finite element model of the dentate gyrus, a curved structure displaying abnormally large positive LFPs. We demonstrate that the polarized dendritic arbour of granule cells (GCs), combined with the curved layered configuration of the population promote the spatial clustering of GC currents in the interposed hilus and project them through the open side at a distance from cell domains. LFPs grow up to 20 times larger than observed in synaptic sites. The dominant positive polarity of hilar LFPs was only produced by the synchronous activation of GCs in both blades by either somatic inhibition or dendritic excitation. Moreover, the corresponding anatomical pathways must project to both blades of the dentate gyrus as even a mild decrease in the spatial synchronization resulted in a dramatic reduction in LFP power in distant sites, yet not in the GC domains. It is concluded that the activation of layered structures may establish sharply delimited spatial domains where synaptic currents from one or another input appear to be segregated according to the topology of afferent pathways and the cytoarchitectonic features of the target population. These also determine preferred directions for volume conduction in the brain, of relevance for interpretation of surface EEG recordings.

Space charge polarization induced augmented in vitro bioactivity of piezoelectric (Na,K) NbO3

The present study reports the influence of chemical and electrical treatments (CET) of Li-modified sodium potassium niobate [Li0.06(Na0.5K0.5)0.94NbO3, LNKN] piezo-biomaterial on in vitro bioactivity. The chemical treatment of LNKN substrate was performed by Ti sputtering, followed by immersion in NaOH aqueous solution for various time durations and subsequently, the heat treatment. The chemically treated LNKN substrates were then corona poled. The in vitro biomineralization study suggested that the integrated effect of chemical as well as electrical treatments of LNKN piezoceramics stimulates the early stage apatite crystallization as compared to that of the mere chemical treatment. To reveal the mechanism of polarization on crystal formation, the thermally stimulated depolarization currents (TSDC) were measured before and after the chemically as well as electrically treated substrates being soaked in simulated body fluid for various time durations. It has been observed that the release of surface charge in the low temperature region (∼60 °C) has significant effect on apatite formation and growth. The surface charge density decreases with increase in the soaking period and hence, the influence of surface charge on apatite crystallization can be realized. The dielectric relaxation in the low frequency region as well as TSDC analysis suggests that the space charge polarization is dominant polarization mechanism in the CET piezo-biomaterial.

Monitoring increases in fracture connectivity during hydraulic stimulations from temporal variations in shear wave splitting polarization

SUMMARY Hydraulic overpressure can induce fractures and increase permeability in a range of geological settings, including volcanological, glacial and petroleum reservoirs. Here we consider an example of induced hydraulic fracture stimulation in a tight-gas sandstone. Successful exploitation of tight-gas reservoirs requires fracture networks, either naturally occurring, or generated through hydraulic stimulation. The study of seismic anisotropy provides a means to infer properties of fracture networks, such as the dominant orientation of fracture sets and fracture compliances. Shear wave splitting from microseismic data acquired during hydraulic fracture stimulation allows us to not only estimate anisotropy and fracture properties, but also to monitor their evolution through time. Here, we analyse shear wave splitting using microseismic events recorded during a multistage hydraulic fracture stimulation in a tight-gas sandstone reservoir. A substantial rotation in the dominant fast polarization direction (ψ )i s observed between the events of stage 1 and those from later stages. Although large changes in ψ have often been linked to stress-induced changes in crack orientation, here we argue that it can better be explained by a smaller fracture rotation coupled with an increase in the ratio of normal to tangential compliance (ZN/ZT) from 0.3 to 0.6. ZN/ZT is sensitive to elements of the internal architecture of the fracture, as well as fracture connectivity and permeability. Thus, monitoring ZN/ZT with shear wave splitting can potentially allow us to remotely detect changes in permeability caused by hydraulic stimulation in a range of geological settings.

KINETIC PLASMA TURBULENCE IN THE FAST SOLAR WIND MEASURED BYCLUSTER

The k-filtering technique and wave polarization analysis are applied to Cluster magnetic field data to study plasma turbulence at the scale of the ion gyroradius in the fast solar wind. Waves are found propagating in directions nearly perpendicular to the background magnetic field at such scales. The frequencies of these waves in the solar wind frame are much smaller than the proton gyro-frequency. After the wave vector ${\bf k}$ is determined at each spacecraft frequency $f_{sc}$, wave polarization property is analyzed in the plane perpendicular to ${\bf k}$. Magnetic fluctuations have $\delta B_\perp>\delta B_\parallel$ (here the $\parallel$ and $\perp$ refer to the background magnetic field ${\bf B}_0$). The wave magnetic field has right-handed polarization at propagation angles $\theta_{\bf kB}<90^\circ$ and $>90^\circ$. The magnetic field in the plane perpendicular to ${\bf B}_0$ however has no clear sense of a dominant polarization but local rotations. We discuss the merits and limitations of linear kinetic Aflv\'en waves (KAWs) and coherent Alfv\'en vortices in the interpretation of the data. We suggest that the fast solar wind turbulence may be populated with KAWs, small scale current sheets and Alfv\'en vortices at ion kinetic scales.

The vapor-liquid interface potential of (multi)polar fluids and its influence on ion solvation

The interface between the vapor and liquid phase of quadrupolar-dipolar fluids is the seat of an electric interfacial potential whose influence on ion solvation and distribution is not yet fully understood. To obtain further microscopic insight into water specificity we first present extensive classical molecular dynamics simulations of a series of model liquids with variable molecular quadrupole moments that interpolates between SPC/E water and a purely dipolar liquid. We then pinpoint the essential role played by the competing multipolar contributions to the vapor-liquid and the solute-liquid interface potentials in determining an important ion-specific direct electrostatic contribution to the ionic solvation free energy for SPC/E water-dominated by the quadrupolar and dipolar parts-beyond the dominant polarization one. Our results show that the influence of the vapor-liquid interfacial potential on ion solvation is strongly reduced due to the strong partial cancellation brought about by the competing solute-liquid interface potential.

Effects of hybrid fillers on the electrical conductivity and EMI shielding efficiency of polypropylene/conductive filler composites

In this study, the effects of hybrid fillers on the electrical conductivity and electromagnetic interference shielding efficiency (EMI SE) of the polypropylene (PP)/Ni-coated carbon fiber (NCCF) composites with the second fillers, such as multi-walled carbon nanotube (MWCNT), carbon black and TiO2, were investigated. The morphological behavior showed that the NCCF and the second fillers, such as MWCNT, carbon black and TiO2, seemed to disperse evenly in the PP phase. Among the PP/NCCF composites with MWCNT, carbon black and TiO2, the PP/NCCF/TiO2 composites showed the higher electrical conductivity and EMI SE compared with those of the PP/NCCF/MWCNT and PP/NCCF/carbon black composites. This was the case because TiO2 has high dielectric constant with dominant dipolar polarization. The estimated EMI SE values of the PP/NCCF composites with MWCNT, carbon black and TiO2 are in good agreement with the experimentally obtained values of the composites. Based on the electrical properties of the composites, it was suggested that TiO2 was the most effective second filler when it was hybridized with the NCCF of the PP/NCCF/TiO2 composite. Based on the analysis of the flexural modulus, the PP/NCCF/MWCNT composite had a higher flexural modulus than the PP/NCCF/TiO2 and PP/NCCF/carbon black composites because of the higher aspect ratio of the MWCNT. Open image in new window

Deorientation Effect Investigation for Model-Based Decomposition Over Oriented Built-Up Areas

Deorientation processing has been incorporated into model-based decomposition to cure the overestimation of volume scattering contribution, by rotating the coherency matrix to minimize the cross-polarization term. First, the derivation of the rotation angle is clarified for avoiding the ambiguity. Moreover, even with the implementation of deorientation processing, oriented built-up areas with large orientation angles are still misjudged as volume scattering dominant. Further to the investigation of the deorientation effect, we focus on oriented built-up patches. A parameter, named dominant polarization orientation angle ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">POA</sub> ), is introduced to label each patch. The behavior of the deorientation on coherency matrix and model-based decomposition over purely oriented built-up areas with respect to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">POA</sub> is disclosed. Experimental studies from the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR) polarimetric SAR data set demonstrate that model-based decompositions with deorientation work well for oriented built-up areas when | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">POA</sub> | ≤ 22.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> . However, for large | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">POA</sub> | (e.g., | <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">POA</sub> | >; 22.5°), even with the deorientation processing, for the conventional decompositions which assume that only the volume scattering contributes to the cross-polarization term, the decomposed volume scattering power may also be dominant even for purely oriented built-up areas. Thereby, misinterpretation still occurs, motivating further advancements.

THE EFFECT OF LIMITED SPATIAL RESOLUTION OF STELLAR SURFACE MAGNETIC FIELD MAPS ON MAGNETOHYDRODYNAMIC WIND AND CORONAL X-RAY EMISSION MODELS

We study the influence of the spatial resolution on scales of $5\deg$ and smaller of solar surface magnetic field maps on global magnetohydrodynamic solar wind models, and on a model of coronal heating and X-ray emission. We compare the solutions driven by a low-resolution Wilcox Solar Observatory magnetic map, the same map with spatial resolution artificially increased by a refinement algorithm, and a high-resolution Solar and Heliospheric Observatory Michelson Doppler Imager map. We find that both the wind structure and the X-ray morphology are affected by the fine-scale surface magnetic structure. Moreover, the X-ray morphology is dominated by the closed loop structure between mixed polarities on smaller scales and shows significant changes between high and low resolution maps. We conclude that three-dimensional modeling of coronal X-ray emission has greater surface magnetic field spatial resolution requirements than wind modeling, and can be unreliable unless the dominant mixed polarity magnetic flux is properly resolved.

Alfvén waves in coronal holes: formation of discontinuities in inhomogeneous magnetic fields

Context. Solar wind fluctuations are characterized by discontinuities. The nature and properties of these structures have been largely studied in the literature, and different mechanisms have been proposed to explain their formation.Aims. We investigate the evolution of Alfvenic perturbations propagating in the inhomogeneous magnetic field of a coronal open-field region, in order to study both the way that small-scale structures are generated and the possible formation of discontinuities.Methods. We constructed a model for the equilibrium magnetic field in a coronal hole. The model represents a potential field with a complex structure: regions of opposite polarity or of only the dominant polarity are present at low or high altitudes, respectively. The evolution of small-amplitude Alfven waves in the inhomogeneous structure is studied by employing a WKB approach that describes how the perturbation wavevector and the wave phase vary along magnetic lines.Results. We find that small-scale structures form in the perturbation at relatively low altitudes (~3 × 104 km) above the coronal base. An initially monochromatic perturbation develops a steep power-law spectrum with slope α ≃ 2.3, which is strongly anisotropic with a predominance of quasi-perpendicular wavevectors. Small-scale structures are localized around separatrices of the magnetic structures. In many cases they contain quasi-perpendicular rotational discontinuities that can propagate to the upper corona, eventually reaching the solar wind. Conclusions. The considered mechanism could be responsible for forming a fraction of the population of discontinuities detected in the solar wind.

Ultrafast polarization modulation in vertical cavity surface emitting lasers with frequency dependent current injection

We report on a polarization modulation in vertical cavity surface emitting lasers (VCSEL), based on RF electrical injection. Complex polarization dynamics in the single mode regime is studied as a function of RF frequency and power at different bias currents. It has been observed that the polarization state of the VCSEL can be altered by changing the frequency of RF current modulation. Time resolved measurements show that by injecting periodic bursts of RF modulation in the VCSEL, it is possible to change the dominant polarization between the two orthogonal modes at gigahertz rates.

Coronal hole boundaries at small scales

We study the magnetic properties of small-scale transients in coronal hole. We found all brightening events are associated with bipolar regions and caused by magnetic flux emergence followed by cancellation with the pre-existing and newly emerging magnetic flux. In the coronal hole, 19 of 22 events have a single stable polarity which does not change its position in time. In eleven cases this is the dominant polarity. The dominant flux of the coronal hole form the largest concentration of magnetic flux in terms of size while the opposite polarity is distributed in small concentrations. In the coronal hole the number of magnetic elements of the dominant polarity is four times higher than the non-dominant one. The supergranulation configuration appears to preserve its general shape during approximately nine hours of observations although the large concentrations in the network did evolve and were slightly displaced, and their strength either increased or decreased. The emission fluctuations seen in the X-ray bright points are associated with reoccurring magnetic cancellation in the footpoints. Unique observations of an X-ray jet reveal similar magnetic behaviour in the footpoints, i.e. cancellation of the opposite polarity magnetic flux. We found that the magnetic flux cancellation rate during the jet is much higher than in bright points. Not all magnetic cancellations result in an X-ray enhancement, suggesting that there is a threshold of the amount of magnetic flux involved in a cancellation above which brightening would occur at X-ray temperatures. Our study demonstrates that the magnetic flux in coronal holes is continuously recycled through magnetic reconnection which is responsible for the formation of numerous small-scale transient events. The open magnetic flux forming the coronal-hole phenomenon is largely involved in these transient features.

Polarization properties of solid-state organic lasers

The polarization states of lasers are crucial issues both for practical applications and fundamental research. In general, they depend in a combined manner on the properties of the gain material and on the structure of the electromagnetic modes. In this paper, we address this issue in the case of solid-state organic lasers, a technology which enables one to vary independently gain and mode properties. Different kinds of resonators are investigated: in-plane microresonators with Fabry-Perot, square, pentagon, stadium, disk, and kite shapes, and external vertical resonators. The degree of polarization $P$ is measured in each case. It is shown that although transverse electric modes prevail generally ($P$ &gt; 0), the kite-shaped microlaser generates negative values for $P$ (i.e., a flip of the dominant polarization which becomes mostly transverse magnetic polarized). In general, we demonstrate that both the pump polarization and the resonator geometry can be used to tailor the polarization of organic lasers. With this aim in view, we, at last, investigate two other degrees of freedom, namely upon using resonant energy transfer and upon pumping the laser dye to a higher excited state. We then demonstrate that significantly lower $P$ factors can be obtained.

Organic Transistors: Inversion of Dominant Polarity in Ambipolar Polydiketopyrrolopyrrole with Thermally Removable Groups (Adv. Funct. Mater. 19/2012)

Organic Transistors: Inversion of Dominant Polarity in Ambipolar Polydiketopyrrolopyrrole with Thermally Removable Groups (Adv. Funct. Mater. 19/2012)

Assessing the resilience of small socio‐ecological systems based on the dominant polarity of their feedback structure

AbstractDespite being an important concept to assess vulnerability of ecological systems, the literature is still unclear on how to measure resilience in different systems and therefore on how well the concept of resilience translates into the practice of analyzing the vulnerability of social systems. This paper presents a practical procedure to assess the degree of resilience of socio‐ecological systems which builds on system dynamics analysis, in particular on loop polarity analysis. It shows that socio‐ecological systems lose resilience when they exceed certain thresholds in which dominant polarity of their feedback structures shifts sign. Copyright © 2012 System Dynamics Society.

Dielectrophoresis force spectroscopy for colloidal clusters

Optical trapping-based force spectroscopy was used to measure the frequency-dependent DEP forces and DEP crossover frequencies of colloidal polymethyl methacrylate spheres and clusters. A single sphere or cluster, held by an optical tweezer, was positioned near the center of a pair of gold-film electrodes where alternating current elecroosmosis flow was negligible. Use of amplitude modulation and phase-sensitive lock-in detection for accurate measurement of the DEP force yielded new insight into dielectric relaxation mechanisms near the crossover frequencies. On one hand, the size dependence of the DEP force near the crossover frequencies indicates that the dominant polarization mechanism is a volume effect. On the other hand, the power-law dependence of the crossover frequency on the particle radius with an exponent of -2 indicates the dielectric relaxation is more likely because of ionic diffusion across the particle surface, suggesting the dominant polarization mechanism may be a surface polarization effect. Better theories are needed to explain the experiment. Nevertheless, the strong size dependence of the crossover frequencies suggests the use of DEP for size sorting of micron-sized particles.

Hadronic contributions to the muon anomaly in the constituent chiral quark model

Abstract The hadronic contributions to the anomalous magnetic moment of the muon which are relevant for the confrontation between theory and experiment at the present level of accuracy, are evaluated within the same framework: the constituent chiral quark model. This includes the contributions from the dominant hadronic vacuum polarization as well as from the next-to-leading order hadronic vacuum polarization, the contributions from the hadronic light-by-light scattering, and the contributions from the electroweak hadronic Zγγ vertex. They are all evaluated as a function of only one free parameter: the constituent quark mass. We also comment on the comparison between our results and other phenomenological evaluations.

Inversion of Dominant Polarity in Ambipolar Polydiketopyrrolopyrrole with Thermally Removable Groups

AbstractA narrow bandgap polymeric semiconductor, BOC‐PTDPP, comprising alkyl substituted diketopyrrolopyrrole (DPP) and tert‐butoxycarbonyl (t‐BOC)‐protected DPP, is synthesized and used in organic field‐effect transistors (OFETs). The polymer films are prepared by solution deposition and thermal annealing of precursors featuring thermally labile t‐BOC groups. The effects of the thermal cleavage on the molecular packing structure in the polymer thin films are investigated using thermogravimetric analysis (TGA), UV‐vis spectroscopy, atomic force microscopy (AFM), Fourier transform infrared (FT‐IR) spectroscopy, and X‐ray diffraction (XRD) analysis. Upon utilization of solution‐shearing process, integrating the ambipolar BOC‐PTDPP into transistors shows p‐channel dominant characteristics, resulting in hole and electron mobilities as high as 1.32 × 10−2 cm2 V−1 s−1 and 2.63 × 10−3 cm2 V−1 s−1, which are about one order of magnitude higher than those of the drop‐cast films. Very intriguingly, the dominant polarity of charge carriers changes from positive to negative after the thermal cleavage of t‐BOC groups at 200 °C. The solution‐sheared films upon subsequent thermal treatment show superior electron mobility (μe = 4.60 × 10−2 cm2 V−1 s−1), while the hole mobility decreases by one order of magnitude (μh = 4.30 × 10−3 cm2 V−1 s−1). The inverter constructed with the combination of two identical ambipolar OFETs exhibits a gain of ∼10. Reported here for the first time is a viable approach to selectively tune dominant polarity of charge carriers in solution‐processed ambipolar OFETs, which highlights the electronically tunable ambipolarity of thermocleavable polymer by simple thermal treatment.

Polarization Switching in Vertical-Cavity Surface-Emitting Lasers With Anisotropic Cavity Geometry and Injection

Vertical-cavity surface-emitting lasers with anisotropic cavity geometry and current injection capable of bias-dependent polarization switching are demonstrated. A cruciform-shaped photonic crystal defect and ion-implanted aperture defines the transverse cavity which is combined with perpendicularly positioned metal contacts for orthogonal electron injection paths. The dominant polarization is determined by the direction of current injection rather than the crystallographic axes as found in isotropic cavities. In addition to polarization control and switching, this type of laser has potential for a novel digital modulation scheme with low-operating-power and high-extinction ratio. The authors achieve 9-dB switching contrast with switching amplitude, with the modulation speed thermally limited.

Horizontal polarization of ground motion in the Hayward fault zone at Fremont, California: dominant fault-high-angle polarization and fault-induced cracks

SUMMARY We investigate shear wave polarization in the Hayward fault zone near Niles Canyon, Fremont, CA. Waveforms of 12 earthquakes recorded by a seven-accelerometer seismic array around the fault are analysed to clarify directional site effects in the fault damage zone. The analysis is performed in the frequency domain through H/V spectral ratios with horizontal components rotated from 0° to 180°, and in the time domain using the eigenvectors and eigenvalues of the covariance matrix method employing three component records. The near-fault ground motion tends to be polarized in the horizontal plane. At two on-fault stations where the local strike is N160°, ground motion polarization is oriented N88 ± 19° and N83 ± 32°, respectively. At a third on-fault station, the motion is more complex with horizontal polarization varying in different frequency bands. However, a polarization of N86 ± 7°, similar to the results at the other two on-fault stations, is found in the frequency band 6–8 Hz. The predominantly high-angle polarization from the fault strike at the Hayward Fault is consistent with similar results at the Parkfield section of the San Andreas Fault and the Val d’Agri area (a Quaternary extensional basin) in Italy. In all these cases, comparisons of the observed polarization directions with models of fracture orientation based on the fault movement indicate that the dominant horizontal polarization is near-orthogonal to the orientation of the expected predominant cracking direction. The results help to develop improved connections between fault mechanics and near-fault ground motion.

P-164 - Polarity of the onset episode of bipolar disorder: clinical and prognostic considerations

Several characteristics can be found in bipolar disorder according to the polarity of the first episode. This may affect the clinical course of the illness. The current study explored the relationship between the polarity of the first episode and the sociodemographic characteristics of patients and clinical implications. This was a retrospective and descriptive study. It involved 49 patients with the diagnosis of bipolar disorder I (DSM-IV) who were hospitalized in the department of Psychiatry “C” in Sfax University Hospital (Tunisia), between January 2010 and March 2011. These patients were divided into two groups according to the polarity of the first episode: those with depressive polarity (D) and those with manic polarity (M). All the patients were male. Group (M) consisted of 33 patients and group (D) of 16 patients. The onset age of bipolar disorder, the origin of patients, their marital status and their socio economic level did not vary significantly depending on the polarity of the first episode. However, the level of education was greater and the irregular works was more frequent, significantly, in group (D) (p respectively: 0, 03 and 0,01). The depressive first episode was correlated with a depressive dominant polarity (p = 0,007) in the course of bipolar illness, bad quality of free intervals (p = 0,005) and more suicide attempts (p = 0,003). This study indicates that first episode depressive polarity seems to have a relatively poor prognosis with a negative psychosocial impact.