Contactless electromagnetic measuring system using conventional calibration algorithms to determine scattering parameters

In this paper, a contactless measuring system for the determination of the S-parameters of planar circuits is presented. With a contactless measuring system it is possible to characterise a device-under-test (DUT) embedded in a planar circuit environment without cutting the planar transmission lines connecting the DUT. The technique utilizes four identical capacitive probes in conjunction with a vector network analyser (VNA). For the usage of electromagnetic probes compared to other coupling techniques like the electro-optic probing, there is no need for expensive and complex equipment in addition to the typical equipment of a common microwave laboratory. The S-parameters are determined accurately using conventional calibration methods. A simple analytical model for the representation of the basic characteristics is developed. Furthermore, the influences on the S-parameters as a result of a variation in the coupling are presented. With the knowledge of the system characteristics, an accurate contactless measurement system is set up. The comparison between conventional and contactless measurements in a frequency range of 1-20 GHz shows a very good agreement with a phase error smaller than 1°

Coexistence of antiferrodistortive and ferroelectric distortions at the PbTiO3_3 (001) surface

The c(2$\times$2) reconstruction of (001) PbTiO$_3$ surfaces is studied by means of first principles calculations for paraelectric (non-polar) and ferroelectric ([001] polarized) films. Analysis of the atomic displacements in the near-surface region shows how the surface modifies the antiferrodistortive (AFD) instability and its interaction with ferroelectric (FE) distortions. The effect of the surface is found to be termination dependent. The AFD instability is suppressed at the TiO$_2$ termination while it is strongly enhanced, relative to the bulk, at the PbO termination resulting in a c(2x2) surface reconstruction which is in excellent agreement with experiments. We find that, in contrast to bulk PbTiO$_3$, in-plane ferroelectricity at the PbO termination does not suppress the AFD instability. The AFD and the in-plane FE distortions are instead concurrently enhanced at the PbO termination. This leads to a novel surface phase with coexisting FE and AFD distortions which is not found in PbTiO$_3$ bulk

First-principles accurate total-energy surfaces for polar structural distortions of BaTiO3, PbTiO3, and SrTiO3: consequences to structural transition temperatures

Specific forms of the exchange correlation energy functionals in first-principles density functional theory-based calculations, such as the local density approximation (LDA) and generalized-gradient approximations (GGA), give rise to structural lattice parameters with typical errors of -2% and 2%. Due to a strong coupling between structure and polarization, the order parameter of ferroelectric transitions, they result in large errors in estimation of temperature dependent ferroelectric structural transition properties. Here, we employ a recently developed GGA functional of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] and determine total-energy surfaces for zone-center distortions of BaTiO3, PbTiO3, and SrTiO3, and compare them with the ones obtained with calculations based on standard LDA and GGA. Confirming that the Wu and Cohen functional allows better estimation of structural properties at 0 K, we determine a new set of parameters defining the effective Hamiltonian for ferroelectric transition in BaTiO3. Using the new set of parameters, we perform molecular-dynamics (MD) simulations under effective pressures p=0.0 GPa, p=-2.0 GPa, and p=-0.005T GPa. The simulations under p=-0.005T GPa, which is for simulating thermal expansion, show a clear improvement in the cubic to tetragonal transition temperature and c/a parameter of its ferroelectric tetragonal phase, while the description of transitions at lower temperatures to orthorhombic and rhombohedral phases is marginally improved. Our findings augur well for use of Wu-Cohen functional in studies of ferroelectrics at nano-scale, particularly in the form of epitaxial films where the properties depend crucially on the lattice mismatch.Comment: 10 pages, 7 figures, 3 tables, resubmitted to PR

Influence of 1 Alpha, 25-Dihydroxyvitamin D3 on T helper 17 cells and related cytokines in systemic lupus erythematosus

Background: Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease. Emerging data suggests that T helper 17 (Th17) cells play a pathogenic role in SLE and the increased number of these cells correlates with disease activity. In recent years, 1α, 25-dihydroxyvitamin D3 (1,25VitD3) has been considered as an immunomodulatory factor. Objective: To investigate the effect of 1,25VitD3 on Th17 cells and on the expression of related cytokines in SLE patients. Method: Thirty SLE patients (newly diagnosed or in remission) were sampled for 10 ml whole blood to isolate peripheral blood mononuclear cells (PBMCs) using Ficoll-Hypaque density gradient centrifugation. Isolated cells were cultured in the presence and absence of 50 nM 1,25VitD3. After incubation, cells were harvested and stimulated for 4-5 hours with phorbol myristate acetate (PMA) and ionomycin in the presence of brefeldin A. IL-17 secreting cells were analyzed by flowcytometry. RNA was extracted from cultured cells, cDNA was synthesized, and the expression levels of IL-6, IL-17, IL-23 and TGF-β genes were assessed by real-time PCR. Results: The percentage of Th17 cells (CD3+CD8- IL-17+ T cells) decreased significantly in 1,25VitD3-treated cells (3.67 ± 2.43%) compared to untreated cells (4.65 ± 2.75%) (p=0.003). The expression of TGF-β up regulated (1.38-fold) and the expression of IL-6 (50%), IL-17 (27%) and IL-23 (64%) down regulated after 1,25VitD3 treatment. Conclusion: This study showed that 1,25VitD3 modulates Th17 related pathways in SLE patients and revealed the immunomodulatory effect of 1,25VitD3 on the Th17 mediated autoimmunity. © 2015, Shiraz University of Medical Sciences. All rights reserved

High sensitivity of 17O NMR to p-d hybridization in transition metal perovskites: first principles calculations of large anisotropic chemical shielding

A first principles embedded cluster approach is used to calculate O chemical shielding tensors, sigma, in prototypical transition metal oxide ABO_3 perovskite crystals. Our principal findings are 1) a large anisotropy of sigma between deshielded sigma_x ~ sigma_y and shielded sigma_z components (z along the Ti-O bond); 2) a nearly linear variation, across all the systems studied, of the isotropic sigma_iso and uniaxial sigma_ax components, as a function of the B-O-B bond asymmetry. We show that the anisotropy and linear variation arise from large paramagnetic contributions to sigma_x and sigma_y due to virtual transitions between O(2p) and unoccupied B(nd) states. The calculated isotropic delta_iso and uniaxial delta_ax chemical shifts are in good agreement with recent BaTiO_3 and SrTiO_3 single crystal 17O NMR measurements. In PbTiO_3 and PbZrO_3, calculated delta_iso are also in good agreement with NMR powder spectrum measurements. In PbZrO_3, delta_iso calculations of the five chemically distinct sites indicate a correction of the experimental assignments. The strong dependence of sigma on covalent O(2p)-B(nd) interactions seen in our calculations indicates that 17O NMR spectroscopy, coupled with first principles calculations, can be an especially useful tool to study the local structure in complex perovskite alloys.Comment: 12 pages, 3 figures, and 3 Table

Considerations on radar localization in multi-target environments

In a multitude of applications like e.g. in automotive radar systems a localization of multiple passive targets in the observed area is necessary. This contribution presents a robust approach based on trilateration to detect point scatterers in a two-dimensional plane using the reflection and transmission information of only two antennas. The proposed algorithm can identify and remove ambiguities in target detection which unavoidably occur in certain target constellations in such a two-antenna configuration

Effect of placental transfusion on neonatal resuscitation attempts

Objective: Overall, neonatal mortality has been shown to be reduced by: placental transfusion (the transfer of blood from the placenta to the neonatal circulation after birth); delayed cord clamping (DCM) (waiting for the umbilical cord to stop pulsating before clamping and cutting the cord); and umbilical cord milking (UCM) (clamping and cutting the cord immediately before milking the cord towards the neonate to expel remaining volume). This systematic review aimed to determine whether placental transfusion negatively impacts resuscitation by delaying it or has any effect on infant mortality, and to identify any barriers to performing it. Methods: CINAHL, MEDLINE, AMED and the British Nursing Index were searched using key terms to identify relevant English language publications between 2017 and 2019. Results: Five papers were selected for critical analysis—three randomised control trials and two cohort studies. Conclusion: Placental transfusion was not found to have a negative impact on neonatal resuscitation but, equally, had no significant effect on Apgar at 5 minutes; however, Apgar is a crude measure of infant mortality. The question remains around the proven multifaceted benefit of placental transfusion in the prehospital environment, which requires further research. There is evidence to suggest prehospital clinicians should be looking to change practice. Further research, considerations and consultations are required to ascertain the best way to implement the procedure with a balanced and proportionate approach considering neonatal thermoregulation and maternal management. The main reported barrier to placental transfusion was a lack of appropriate equipment