Linear Polarization Measurements Research Articles

Study of electrochemical hydrogen charge/discharge properties of FePO4 for application as negative electrodes in hydrogen batteries

We report the electrochemical hydrogen charge/discharge properties of electrodes containing crystalline and amorphous FePO 4 as active material in KOH electrolyte. Crystalline and amorphous FePO 4 were synthesized by an alcohol-assisted precipitation method, and the powders obtained were characterized by X-ray diffraction. X-ray photoelectron spectroscopy is used to investigate the mechanism of hydrogen charge/discharge behavior of FePO 4 . The electrochemical hydrogen charge/discharge properties of electrodes containing crystalline and amorphous FePO 4 were investigated for potential application as negative electrodes in rechargeable hydrogen batteries. In galvanostatic discharge/charge mode at 25 °C, the crystalline FePO 4 showed a maximum discharge capacity of 109 mA h g −1 , while the amorphous FePO 4 showed a maximum discharge capacity of 81.4 mA h g −1 . The electrochemical kinetic properties, exchange current density, and proton diffusivity were calculated using linear polarization measurement and the potential-step method.

Polarization of Saturn’s moon Iapetus

Context. The surface properties of atmosphereless solar system objects can be constrained by investigating the nature of the polarized light scattered from their surfaces. Aims. We provide new and precise measurements of the phase angle and the wavelength dependence of linear polarization on the leading side of Iapetus over the maximum phase angle range accessible from Earth (∼0.5−6.0 ◦ ) and over a broad spectral range (400–800 nm), thereby identifying the polarimetric characteristics of its dark material. Moreover, we provide circular spectral polarization measurement of the same side of Iapetus at one phase angle, which was performed aiming at detection of chiral signatures on its surface. We also compare our new polarization measurements with those of the trailing hemisphere of Iapetus which were obtained in our previous work. Methods. Using the FORS2 instrument of the ESO VLT, we performed spectro-polarimetric observations of Iapetus’ leading side. Results. While the linear polarization measurements of Iapetus’ leading side show an opposite trend in phase angle dependence to that of its trailing hemisphere, the polarization values measured for the two hemispheres around similar phase angles (in the range ∼3.0−6.0 ◦ )d iffer by a factor of three. Besides this, the degree of negative linear polarization of Iapetus’ leading hemisphere shows a slight dependence on the wavelengths of observations. Furthermore, like that of its trailing hemisphere, the circular polarization measurement of Iapetus’ leading side indicates no evidence of a significant amount of optically active (chiral) molecules on its surface.

Effect of chromium on the corrosion behavior of low alloy steel in sulfuric acid

The effects of a chromium (Cr) addition on the corrosion resistance of low alloy steel used in flue gas desulfurization systems were examined by electrochemical (potentiodynamic polarization tests, linear polarization measurements and electrochemical impedance spectroscopy) and weight loss measurements in a 10 wt% H2SO4 solution at room temperature. All measurements revealed a decrease in corrosion rate with increasing Cr content. SEM, EPMA and XPS examinations of the corroded surfaces after the immersion test indicated that 0.6% Cr addition decreased corrosion damage to the steels because protective Cr oxides formed in all the rust layers and Fe oxides dominated over Fe sulphate compounds in the inner rust layers.

Direct Determination of the Magnetic Quadrupole Contribution to the Lyman-α1 Transition in U91+

We report on the first measurement of the Lyman-α1 polarization in a high-Z systems, namely in U91+. We show that the combination of linear polarization and angular distribution measurements enables a very precise determination of the ratio of the E1 and the M2 transition amplitudes and the corresponding transition rates.

Polarimetry of trans-Neptunian objects (136472) Makemake and (90482) Orcus

Context. We study the surface properties of transneptunian populations of Solar-system bodies. Aims. We investigate the surface characteristics of the dwarf planet (136472) Makemake and the resonant object (90482) Orcus. Methods. Using the FORS2 instrument of the ESO-VLT we have carried out linear polarisation measurements of Makemake and Orcus. Results. Polarisation of Orcus is similar to that of smaller size objects. The polarimetric properties of Makemake are very close to those of Eris and Pluto. We have not found any significant differences in the polarisation properties of objects from different dynamical classes. However, there are significant differences in polarisation of large and smaller size objects, and between large TNOs with water-ice and methane-ice dominated surfaces. Conclusions. We confirm the different types of polarisation phase behavior for the largest and smaller size TNOs. To explain subtle surface polarisation of Pluto, Makemake and Eris we assume that their surfaces are covered by a thin layer of hoarfrost masking the surface structure.

The Estimation of Corrosion Behavior of NiTi and NiTiNb Alloys Using Dynamic Electrochemical Impedance Spectroscopy

Linear anodic potentiodynamic polarization and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out for NiTi and NiTiNb alloys in physiological 0.9 wt% NaCl solution in order to assess their corrosion resistance. DEIS measurements were performed from open circuit potential to dissolution potential. It was shown that the impedance measurements in potentiodynamic conditions allow simultaneous investigation of changes in passive layer structure. The impedance spectra of various potential regions were fitted and also discussed. The surface morphology of the alloys after linear anodic polarization test was studied using scanning electron microscopy (SEM) technique.

Estimation of flow rate and direction of medium with low scattering coefficient via linear polarization measurement

Many biological systems involve flow of various types of liquids. Estimation of the rate and direction of the flow is highly important for a large number of bio-medical related applications. The working point discussed in this paper involves a medium with a relatively low scattering coefficient such that the polarized light going through it is not depolarized, but rather modifies its polarization state instead. An experimental validation is presented, which shows that illuminating flow in a medium with linear polarized light, and measuring the change in polarization state at the output of the medium, can correlate highly with the direction and flow rate through that medium. By inspecting the spatial shape change in the spot of light, and the change of polarization state in relation to different integration times as well, the direction and flow rate can be fully extracted.

Conversion of 3×3 Mueller matrix to 4×4 Mueller matrix for non-depolarizing samples

A minimum of 16 measurements involving both linear and circularly polarized light are required to determine the Mueller matrix of a sample which completely describes the polarization properties of the sample. In contrast a 3×3 partial Mueller matrix, devoid of last row and column of conventional Mueller matrix, can be obtained by using nine linear polarization measurements. Further, with only linear polarization measurements the limitation on spectral coverage imposed by quarter wave plates required for circular polarization measurements is avoided. However, a drawback of this approach is that the data analysis tools developed for 4×4 Mueller matrix cannot be applied in this case. To address this issue we show that for non-depolarizing media the various symmetry constraints on Muller matrix elements can be used to obtain the 4×4 Mueller matrix from the measured 3×3 Mueller matrix. This method should prove particularly useful for measurement of Mueller matrix in the spectral region for which retarders are either not readily available or inconvenient to use.

Electrochemical properties of LaMO3 (M=Co or Fe) as the negative electrode in a hydrogen battery

Undoped orthorthombic LaFeO3 and monoclinic LaCoO3 oxides were selected as an anode material for Ni–H battery due to their high electron conductivity by multivalent transition status of B-site cation. Both groups of oxides were prepared by a conventional solid-state reaction method, and their electrochemical charge/discharge properties were investigated. The electrochemical kinetic properties, exchange current density, and proton diffusivity were also extracted using linear polarization measurement and the potential-step method. X-ray photoelectron spectroscopy (XPS) analysis was used to measure the oxidation state of the transition metal in the specimens. A non-linear least-square fitting deconvoluted the peaks, suggesting that the valence state of Fe and Co in the sample was mainly +3. The hydrogen diffusion rate was also estimated using the potential-step method, giving 5.42×10−16 and 5.72×10−16cm2s−1 for LaCoO3 and LaFeO3, respectively which are an order of magnitude larger than that of Sr doped LaFeO3 oxide electrodes.

Analytic detection thresholds for measurements of linearly polarized intensity using rotation measure synthesis

A fully analytic statistical formalism does not yet exist to describe radio-wavelength measurements of linearly polarized intensity that are produced using rotation measure synthesis. In this work we extend the analytic formalism for standard linear polarization, namely that describing measurements of the quadrature sum of Stokes Q and U intensities, to the rotation measure synthesis environment. We derive the probability density function and expectation value for Faraday-space polarization measurements for both the case where true underlying polarized emission is present within unresolved Faraday components, and for the limiting case where no such emission is present. We then derive relationships to quantify the statistical significance of linear polarization measurements in terms of standard Gaussian statistics. The formalism developed in this work will be useful for setting signal-to-noise ratio detection thresholds for measurements of linear polarization, for the analysis of polarized sources potentially exhibiting multiple Faraday components, and for the development of polarization debiasing schemes.

Effect of electroplating polyaniline on electrochemical kinetics of La–Mg–Ni-based hydrogen storage alloy

A new polyaniline (PANI)-coated technique is adopted for the La–Mg–Ni-based alloy La0.80Mg0.20Ni2.70Mn0.10Co0.55Al0.10 in order to advance its electrochemical kinetic characteristics. In this treatment, the aniline monomers are electroplated on the alloy particles to form polyaniline films. FE-SEM observation and UV–vis analysis results revealed that the coral-like atrovirens PANI particles are deposited on the surface of the alloy. Through the PANI-coating the capacity retention rate at the 200th cycle of the La–Mg–Ni-based alloy electrodes amounts up from original 82.3% to 86.4% and the high rate discharge ability increased from 24.7% to 35.6% at a discharge current density of 1500mAg−1. Linear polarization, anodic polarization and cyclic voltammetry measurements suggest that charge-transfer resistance decreases and the hydrogen absorption rate of the alloys increases after PANI-coating.

Shape evolution in odd-A 137 Pm

The odd mass nucleus 137Pm has been studied to high spins through the 109Ag(32S, 2p2n)137Pm reaction at an incident beam energy of 150 MeV. The de-exciting γ-rays were detected using an array of 18 Compton suppressed clover detectors. The level scheme of 137Pm has been extended up to \(J^\pi = \tfrac{{43}} {2}^ -\) and excitation energy of E x ≅ 6 MeV with the observation of 42 new gamma transitions. The linear polarization (IPDCO) measurements for the γ-ray transitions have been done for the first time. The spin and parity assignments for most of the reported levels have been made using these results and the coincidence angular anisotropy (RDCO) measurements. The nuclear shape evolution is discussed in the light of Total Routhian Surface (TRS) and Cranked Shell Model (CSM) calculations.

The impact of signal–noise ratio on degree of linear polarization measurement

The radiometric measurement is the basics of polarimetric measurement. This paper presents a simple approach for estimating the degree of linear polarization errors caused by the radiometric measurement uncertainty. According to the measurement principle of polarization CCD camera, we deduce the relation of the degree of linear polarization error to the signal–noise ratio and the polarization state (polarization angle or degree of linear polarization) of the incident light. It clearly shows that polarimetric accuracy of polarization CCD camera could deteriorate due to the low signal–noise ratio; The degree of linear polarization error has also been influenced by the polarization state of the incident light except the signal–noise ratio, and the large degree of linear polarization of the incident beams often contribute to the bigger measured degree of linear polarization errors for a fixed signal–noise ratio.

Linear polarization measurements with clouds of tholins produced by radio-frequency plasma

The linear polarization of the light scattered by fluffy agglomerates of tholins produced by a RF plasma is correlated to the physical properties of the samples. The results are compared to space observations of Titan's aerosols.

OPTICAL POLARIMETRY OF THE BLAZAR CGRaBS J0211+1051 FROM MOUNT ABU INFRARED OBSERVATORY

We report the detection of high polarization in the first detailed optical linear polarization measurements on the BL Lac object CGRaBS J0211+1051, which flared in $\gamma$-rays on 2011 January 23 as reported by Fermi. The observations were made during 2011 January 30 - February 3 using photo-polarimeter mounted at the 1.2m telescope of Mt Abu InfraRed Observatory(MIRO). The CGRaBS J0211+1051 was detected to have $\sim21.05\pm 0.41%$ degree of polarization (DP) with steady position angle (PA) at 43$^\circ$ on 2011 January 30. During Jan 31 and Feb 1, while polarization shows some variation, position angle remains steady for the night. Several olarization flashes occurred during February 2 and 3 resulting in changes in the DP by more than 4% at short time scales ($\sim$ 17 to 45 mins). A mild increase in the linear polarization with frequency is noticed during the nights of February 2 & 3. The source exhibited significant inter-night variations in the degree of polarization (changed by about 2 to 9%) and position angle (changed by 2 to 22$^\circ$) during the five nights of observations. The intra-night activity shown by the source appears to be related to turbulence in the relativistic jet. Sudden change in the PA accompanied by a rise in the DP could be indicative of the fresh injection of electrons in the jet. The detection of high and variable degree of polarization categorizes the source as low energy peaked blazar.

Electrochemical performance of polyaniline electroless deposited La–Mg–Ni-based hydrogen storage alloys

Polyaniline (PANI) electroless-deposition is applied onto La–Mg–Ni-based La0.80Mg0.20Ni2.70Mn0.10Co0.55Al0.10 hydrogen storage alloy powders in order to improve electrochemical and kinetic properties. FE-SEM and FT-IR results reveal that coral-like PANI particles are deposited on the surface of the alloy. Owing to the PANI coating the initial discharge capacity of the alloy electrodes increases from original 174mAhg−1 to 226mAhg−1, the capacity retention rate at 200 cycles (S200) increases from 85% to 88%, and the high rate discharge ability (HRD) is scaled up by 18% at discharge current density of 1500mAg−1. Linear polarization, EIS, anodic polarization and potential static step discharge measurements indicate that charge transfer resistance decreases and the hydrogen diffusion rate increases after PANI-coating.

Ricean Bias Correction in Linear Polarization Observation

I developed an enhanced correction method for Ricean bias which occurs in linear polarization measurement. Two known methods for Ricean bias correction are reviewed. In low signal-to-noise area, the method based on the mode of the equation gives better representation of the fractional polarization. But a caution should be given that the accurate estimation of noise level, i.e. <TEX>${\sigma}$</TEX> of the polarized flux, is important. The maximum likelihood method is better choice for high signal-to-noise area. I suggest a hybrid method which uses the mode of the equation at the low signal-to-noise area and takes the maximum likelihood method at the high signal-to-noise area. A modified correction coefficient for the mode solution is proposed. The impact on the depolarization measure analysis is discussed.

Optimization of the synthesis conditions for LaNiO 3 catalyst by microwave assisted citrate method for hydrogen production

LaNiO 3 was prepared by microwave assisted citrate method. The effect of the synthesis condition such as, the operating microwave power and the microwave irradiation time, on structural, surface and catalytic properties was investigated by XRD, SEM, Tafel linear polarization and impedance measurements. The XRD results suggested successful incorporation of Ni 3+ at the La 3+ cations sites confirming the formation of the hexagonal distorted rhombohedral perovskite phase of LaNiO 3 at all the investigated microwave operating powers and irradiation times. The average particle size ranges between 18 and 32 nm. The largest surface area ( ca. 25 m 2 g −1) and the highest catalytic activity for LaNiO 3 prepared by the microwave assistant-citrate method toward the hydrogen evolution reaction (HER) were obtained at an operating microwave power of 720 W and increased by increasing the microwave irradiation time. In addition, the reaction order, the activation energy and the reaction mechanism were identified.

Is the Jovian auroral H\hbox{$_{3}^{+}$} emission polarised?

Context. Measurement of linear polarisation in Earth’s thermospheric oxygen red line can be a useful observable quantity for characterising conditions in the upper atmosphere; therefore, polarimetry measurements are extended to other planets. Since FUV emissions are not observable from the ground, the best candidates for Jupiter auroral emissions are infrared lines near 4 μm. This ion is created after a chemical process in the Jovian upper atmosphere. Thus the anisotropy responsible of the polarisation cannot be the particle impact as in the Earth case.

Effect of Nb addition on corrosion behavior of Fe-based metallic glasses in Ringer's solution for biomedical applications

The corrosion behavior of Fe 55 − x Cr 18Mo 7B 16C 4Nb x (x = 0, 3, and 4 at.%) amorphous ribbons in Ringer's solution with pH value 6.5, open to air at 37 °C, was investigated by linear polarization and electrochemical impedance spectroscopy (EIS) methods, aiming to estimate the feasibility of Fe-based metallic glasses as potential biomaterials. It was shown that the corrosion resistance in Ringer's solution significantly increases with an increase in Nb content. The linear polarization and EIS measurements indicated that the Fe 51Cr 18Mo 7B 16C 4Nb 4 possesses larger polarization resistance value than that of 316L stainless steel and Ti–6Al–4V which are used in the human body in biomedical applications. In addition, the ICP test was carried out to measure the concentrations of ions which had dissolved into the electrolyte. It was seen that amorphous alloys do not release any significant ions into the Ringer's solution, implying good biocompatibility of these alloys.