Cosmic microwave background polarization signals from tangled magnetic fields

Tangled, primordial cosmic magnetic fields create small rotational velocity perturbations on the last scattering surface of the cosmic microwave background radiation. For fields which redshift to a present value of B0 = 3 x 10(-9) G, these vector modes are shown to generate polarization anisotropies of order 0.1-4 microK on small angular scales (500相似文献   

Laser Raman spectra of mixed crystals of [(NH4)1−x Kx]2 SO4

The Raman spectra of mixed crystals of [(NH₄)_1?x K _x ]₂ SO₄ in the region 50–3400 cm^?1 at 293 K and below 223 K have been reported. At room temperature 293 K, as the concentration of K⁺ ion increases in the crystal up to 50%, the frequencies of the totally symmetric vibrations of SO ₄ ^2? and NH ₄ ⁺ ions increase and thereafter the frequency of SO ₄ ^2? vibration decreases and attains the value in K₂SO₄. This change in frequency up to 50% of potassium concentration is due to the breaking of hydrogen bonds of the type N-H...O. The behaviour of Raman intensities of A _g (v ₁) mode of SO ₄ ^2? for various concentrations (x=0, 0·03, 0·11, 0·5, 0·85) suggest that the phase transition changes from first order type to one of second order. The phase transition in mixed crystals of [(NH₄)_1?x K _x ]₂ SO₄ can be a cooperative phenomenon arising from a coupling between (NH₄)⁺ ions through hydrogen bonds with the distorted SO ₄ ^2? ions in the low temperature phase.     

Numerical simulation of partially coherent broadband optical imaging using the finite-difference time-domain method

Rigorous numerical modeling of optical systems has attracted interest in diverse research areas ranging from biophotonics to photolithography. We report the full-vector electromagnetic numerical simulation of a broadband optical imaging system with partially coherent and unpolarized illumination. The scattering of light from the sample is calculated using the finite-difference time-domain (FDTD) numerical method. Geometrical optics principles are applied to the scattered light to obtain the intensity distribution at the image plane. Multilayered object spaces are also supported by our algorithm. For the first time, numerical FDTD calculations are directly compared to and shown to agree well with broadband experimental microscopy results.     

Improved electrochemical properties of Sr2+-doped LiNi0.8Co0.2O2 synthesized via a sol-gel route using tartaric acid as a chelating agent

Single-phase undoped LiNi_0.8Co_0.2O₂ and Sr²⁺-doped LiNi_0.8Co_0.2O₂ were synthesized by a low temperature tartaric acid assisted sol-gel method. Small quantities of Sr²⁺ were used as dopants in order to improve the electrochemical characteristics, especially the capacity and cycling performance of LiNi_0.8Co_0.2O₂. The electrochemical performance of the undoped material was promising with a first discharge capacity of 174 mAh/g and 165 mAh/g after 10 cycles with a 100% cycling efficiency in the tenth cycle. Addition of Sr²⁺ for Li in minimum quantities with the Sr²⁺/Li⁺ dopant mole ratio ranging from 10⁻⁴ to 10⁻⁸ resulted in improved electrochemical properties for dopant mole ratio of 10⁻⁶. The first discharge capacity was 182 mAh/g and the tenth was 174 mAh/g at the 10th discharge. The synthesis of Sr²⁺-doped LiNi_0.8Co_0.2O₂ and its improved electrochemical properties have been discussed for the first time. The improved electrochemical properties of Sr²⁺-doped LiNi_0.8Co_0.2O₂ system are explained based on defect models.     

Evidence for internal resistive barriers in a crystal of the giant dielectric constant material: CaCu3Ti4O12

Complex impedance spectra were obtained on a crystal of CaCu₃Ti₄O₁₂ (CCTO) from 289 to 456 K. As in the case of ceramic CCTO, these spectra can be interpreted as arising from a conducting material containing insulating barriers. This is then further evidence for the existence of planar defects within crystals of CCTO that act as insulating barriers and produce the large dielectric constant through a space charge mechanism.     

Studies on evaporated titanium oxide thin films for oxygen gas detection

Present work deals with the preparation of TiO₂ thin films of different thicknesses by PVD technique using an electron beam and to characterize the films for oxygen gas detection. The films were characterized using optical transmission measurements, XRD and atomic force microscopy. From the spectral data, the extinction, absorption coefficient and refractive index of the films are evaluated and reported. The optical band gap energy varies between 3 and 3.68 eV. The XRD pattern confirms the formation of polycrystalline anatase structure of Titanium with preferred orientation of (110) plane. The AFM images indicate the presence of coarse and fine grains with uniform as well as smooth surfaces over the entire range of the analyzed surface. Response characteristics of TiO₂ thin films for oxygen gas detection are studied, which indicate a low response time of 120 seconds and high sensitivity of 16 at the operating temperature 450 °C. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.