Precision characteristics of simple spectrophotometers

A step-by-step procedure for the analysis of the precision characteristics of spectrophotometers is described. A high-resolution digital voltmeter is connected to the output of two common simple spectrophotometers, so that noise is obvious and the ultimate factors which limit measurement precision can be determined. The precision of measurement is limited by cell positioning irreproducibility and noise independent of the photon signal (0 % T noise) but not limited by fundamental signal shot noise or source flicker noise.     

Polarization switching properties of spray deposited CsNO3: PVA composite films

The ferroelectric and switching properties of spray deposited cesium nitrate: poly (vinyl alcohol) composite films at different substrate temperatures (T _s ) have been studied. The optimum value of remanent polarization was obtained in the film deposited at T _s =200°C, which may be due to larger structural distortion (c/a ratio) and less porosity as revealed by x-ray diffraction and field emission scanning electron microscope (FESEM) analysis. The switching current transients have been analyzed by nucleation limited switching model (NLS) with the Lorentzian distribution function. This model gives excellent agreement with the experimental polarization current throughout the whole time range. The switching parameters were determined in the composite films deposited at different T _s and found to be optimum at T _s =200°C. The effect of pulse amplitude on the domain switching properties has also been studied and analyzed. The peak value of polarization current exhibits an exponential dependence on the external applied field.     

XANES of the AuLIII edge in gold metal and in two compounds AuCN and AuCl3

The X-ray Absorption Near Edge Structure (XANES) of the AuL_III edge in gold metal and in its two compounds AuCN and AuCl₃ have been recorded. The observed chemical shifts of the edge and the fine structure peaks in the compounds are discussed. It is observed that the energy shifts ΔE of the AuL_III due to chemical effects in aurous cyanide (AuCN) and auric chloride (AuCl₃) with respect to the pure Au edge is 2.9 eV in AuCN and 0.7eV in AuCl₃. The edge widths in AuCN and AuCl₃ are found to be almost the same for both the compounds, presumably because electronegativities of CN and Cl are not very different. The observed fine structure peaks of the discontinuities of AuCN and AuCl₃ are displaced progressively away from the main edge.     

Efficient Krylov subspace methods for uncertainty quantification in large Bayesian linear inverse problems

Uncertainty quantification for linear inverse problems remains a challenging task, especially for problems with a very large number of unknown parameters (e.g., dynamic inverse problems) and for problems where computation of the square root and inverse of the prior covariance matrix are not feasible. This work exploits Krylov subspace methods to develop and analyze new techniques for large‐scale uncertainty quantification in inverse problems. In this work, we assume that generalized Golub‐Kahan‐based methods have been used to compute an estimate of the solution, and we describe efficient methods to explore the posterior distribution. In particular, we use the generalized Golub‐Kahan bidiagonalization to derive an approximation of the posterior covariance matrix, and we provide theoretical results that quantify the accuracy of the approximate posterior covariance matrix and of the resulting posterior distribution. Then, we describe efficient methods that use the approximation to compute measures of uncertainty, including the Kullback‐Liebler divergence. We present two methods that use the preconditioned Lanczos algorithm to efficiently generate samples from the posterior distribution. Numerical examples from dynamic photoacoustic tomography demonstrate the effectiveness of the described approaches.     

Fermi surface and quasiparticle excitations of Sr2RhO4

The electronic structure of the layered 4d transition metal oxide Sr2RhO4 is investigated by angle resolved photoemission. We find well-defined quasiparticle excitations with a highly anisotropic dispersion, suggesting a quasi-two-dimensional Fermi-liquid-like ground state. Markedly different from the isostructural Sr2RuO4, only two bands with dominant Rh 4dxz,zy character contribute to the Fermi surface. A quantitative analysis of the photoemission quasiparticle band structure is in excellent agreement with bulk data. In contrast, it is found that state-of-the-art density functional calculations in the local density approximation differ significantly from the experimental findings.