Accurate determination of terahertz optical constants by vector network analyzer of Fabry-Perot response

This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.38.005438. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.We present a method based on a Fabry-Perot model to efficiently and accurately estimate optical constants of wafer samples in transmission-only measurements performed by a vector network analyzer (VNA). The method is demonstrated on two separate wafer samples: one of silicon and the other of polymethylmethacrylate. Results show that the method can not only acquire optical constants accurately and simply over a broad frequency domain but also overcome the limitations of calculation for dispersive and lossy materials to which existing methods are susceptible, such as those based on VNA-driven quasi-optical transmissometers and terahertz time-domain spectrometry

Geochemistry of reduced inorganic sulfur, reactive iron, and organic carbon in fluvial and marine surface sediment in the Laizhou Bay region, China

Understanding the geochemical cycling of sulfur in sediments is important because it can have implications for both modern environments (e.g., deterioration of water quality) and interpretation of the ancient past (e.g., sediment C/S ratios can be used as indicators of palaeodepositional environment). This study investigates the geochemical characteristics of sulfur, iron, and organic carbon in fluvial and coastal surface sediments of the Laizhou Bay region, China. A total of 63 sediment samples were taken across the whole Laizhou Bay marine region and the 14 major tidal rivers draining into it. Acid volatile sulfur, chromium (II)-reducible sulfur and elemental sulfur, total organic carbon, and total nitrogen were present in higher concentrations in the fluvial sediment than in the marine sediment of Laizhou Bay. The composition of reduced inorganic sulfur in surface sediments was dominated by acid volatile sulfur and chromium (II)-reducible sulfur. In fluvial sediments, sulfate reduction and formation of reduced inorganic sulfur were controlled by TOC and reactive iron synchronously. High C/S ratios in the marine sediments indicate that the diagenetic processes in Laizhou Bay have been affected by rapid deposition of sediment from the Yellow River in recent decades

A modified atmospheric non-hydrostatic model on low aspect ratio grids

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tellus A 64 (2012): 17516, doi:10.3402/tellusa.v64i0.17516.It is popular to use a horizontal explicit and a vertical implicit (HE-VI) scheme in the compressible nonhydrostatic (NH) model. However, when the aspect ratio becomes small, a small time-interval is required in HE-VI, because the Courant-Fredrich-Lewy (CFL) criterion is determined by the horizontal grid spacing. Furthermore, simulations from HE-VI can depart from the forward–backward (FB) scheme in NH even when the time interval is less than the CFL criterion allowed. Hence, a modified non-hydrostatic (MNH) model is proposed, in which the left-hand side of the continuity equation is multiplied by a parameter d (45d516, in this study). When the linearized MNH is solved by FB (can be other schemes), the eigenvalue shows that MNH can suppress the frequency of acoustic waves very effectively but does not have a significant impact on the gravity waves. Hence, MNH enables to use a longer time step than that allowed in the original NH. When the aspect ratio is small, MNH solved by FB can be more accurate and efficient than the NH solved by HE-VI. Therefore, MNH can be very useful to study cloud, Large Eddy Simulation (LES), turbulence, flow over complex terrains, etc., which require fine resolution in both horizontal and vertical directions

Pressure-Temperature Phase Diagram of Multiferroic Ni3V2O8Ni_3V_2O_8

The pressure-temperature phase diagram of multiferroic $Ni_3V_2O_8$ is investigated for hydrostatic pressures up to 2 GPa. The stability range of the ferroelectric phase associated with the incommensurate helical spin order is reduced by pressure and ferroelectricity is completely suppressed at the critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at ambient pressure show strong step-like anomalies of the lattice parameters associated with the lock-in transition into the commensurate paraelectric phase. The expansion anomalies are highly anisotropic, the related volume change is consistent with the high-pressure phase diagram

The Suppression and Recovery of the Ferroelectric Phase in Multiferroic MnWO4MnWO_4

We report the discovery of a complete suppression of ferroelectricity in $MnWO_4$ by 10 % iron substitution and its restoration in external magnetic fields. The spontaneous polarization in $Mn_{0.9}Fe_{0.1}WO_4$ arises below 12 K in external fields above 4 T. The magnetic/ferroelectric phase diagram is constructed from the anomalies of the dielectric constant, polarization, magnetization, and heat capacity. The observations are qualitatively described by a mean field model with competing interactions and strong anisotropy. We propose that the magnetic field induces a non-collinear inversion symmetry breaking magnetic structure in $Mn_{0.9}Fe_{0.1}WO_4$

Low temperature dielectric anomalies in HoMnO_3: The complex phase diagram

The dielectric constant of multiferroic hexagonal HoMnO_3 exhibits an unprecedented diversity of anomalies at low temperatures (1.8 K< T <10 K) and under external magnetic fields related to magnetic phase transitions in the coupled system of Ho moments, Mn spins, and ferroelectric polarization. The derived phase diagram is far more complex than previously assumed including reentrant phases, phase transitions with distinct thermal and field hysteresis, as well as several multicritical points. Magnetoelastic interactions introduce lattice anomalies at the magnetic phase transitions. The re-evaluation of the T-H phase diagram of HoMnO_3 is demanded.Comment: 12 pages, 3 figure