Raman scattering study of electron-doped Prx_xCa1−x_{1-x}Fe2_2As2_2 superconductors

Temperature-dependent polarized Raman spectra of electron-doped superconducting Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ ($x \approx 0.12$) single crystals are reported. All four allowed by symmetry even-parity phonons are identified. Phonon mode of B$_{1g}$ symmetry at 222 cm$^{-1}$, which is associated with the c-axis motion of Fe ions, is found to exhibit an anomalous frequency hardening at low temperatures, that signals non-vanishing electron-phonon coupling in the superconducting state and implies that the superconducting gap magnitude $2\Delta_c < 27$meV.Comment: 4 pages, 3 figure

Raman scattering study of (Kx_xSr1−x_{1-x})Fe2_2As2_2 (xx = 0.0, 0.4)

Polarized Raman spectra of non-superconducting SrFe$_2$As$_2$ and superconducting K$_{0.4}$Sr$_{0.6}$Fe$_2$As$_2$ ($T_c = 37$ K) are reported. All four phonon modes (A$_{1g}$ + B$_{1g}$ + 2E$_g$) allowed by symmetry, are found and identified. Shell model gives reasonable description of the spectra. No detectable anomalies are observed near the tetragonal-to-orthorhombic transition in SrFe$_2$As$_2$ or the superconducting transition in K$_{0.4}$Sr$_{0.6}$Fe$_2$As$_2$.Comment: 4 pages, 4 figures, 2 table

Superconductivity at 22 K in Co-doped BaFe2As2 Crystals

Here we report bulk superconductivity in BaFe1.8Co0.2As2 single crystals below Tc = 22 K, as demonstrated by resistivity, magnetic susceptibility, and specific heat data. Hall data indicate that the dominant carriers are electrons, as expected from simple chemical reasoning. This is the first example of superconductivity induced by electron doping in this family of materials. In contrast to the cuprates, the BaFe2As2 system appears to tolerate considerable disorder in the FeAs planes. First principles calculations for BaFe1.8Co0.2As2 indicate the inter-band scattering due to Co is weak.Comment: 9 pages, 3 figure

Towards a Practical Behavior Analytic Multitiered Consultation Model for Early Childhood Educators

Early childhood educators are in a critical position to support young children’s social-emotional, behavioral, and learning development, which can be accomplished through consistent use of evidence-based practices delivered in day-to-day interactions. However, early childhood educators may require support for implementing evidence-based practices. The purpose of this paper is to introduce a novel form of behavioral consultation for early childhood educators. Specifically, a behavior analytic multitiered consultation model in which implementation supports become increasingly more intensive is described. Rationale, implementation, evidence-base, and implications for practice and research are described. Finally, this paper concludes with an empirical case study to illustrate this model’s implementation. This paper is also meant to serve as a call-to-action for researchers and practitioners to replicate this consultation model

Fermi surfaces and quasi-particle band dispersions of the iron pnictides superconductor KFe2As2 observed by angle-resolved photoemission spectroscopy

We have performed an angle-resolved photoemission study of the iron pnictide superconductor KFe2As2 with Tc 4 K. Most of the observed Fermi surfaces show almost two-dimensional shapes, while one of the quasi-particle bands near the Fermi level has a strong dispersion along the kz direction, consistent with the result of a band-structure calculation. However, hole Fermi surfaces \alpha and \zeta are smaller than those predicted by the calculation while other Fermi surfaces are larger. These observations are consistent with the result of a de Haas-van Alphen study and a theoretical prediction on inter-band scattering, possibly indicating many body effects on the electronic structure.Comment: 4 pages, 5 figures. Proceeding of the 9th International Conference on Spectroscopies in Novel Superconductors (SNS2010

Measurment of Depositing and Bombarding Species Involved in the Plasma Production of Amorphous Silicon and Silicon/Germanium Solar Cells: Annual Technical Report, 1 June 2002 - 31 May 2005

The objective of this study is to measure the molecular species that lead to the growth of hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (..mu..c-Si) photovoltaic (PV) devices from RF discharges. Neutral radicals produce most of the film growth during this PV-device production, and, by implication, radicals primarily determine the device structure and electrical characteristics. The most important feature of the present experiment is thus the measurement of neutral-radical fluxes to the substrate. Additional depositing species that can influence film properties are positive ions and silicon-based particles produced by the discharge; we also measure these positive-ion species here. Some studies have already measured some of these radical and positive-ion species in silane and silane/argon discharges, but not for discharge conditions similar to those used to produce most photovoltaic devices. Our objective is to measure all of these species for conditions typically used for device production. In particular, we have studied 13.6 MHz-excited discharges in pure silane and silane/hydrogen vapors

Superconductivity at 38 K in the iron arsenide (Ba1-xKx)Fe2As2

The ternary iron arsenide BaFe2As2 becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. We have discovered bulk superconductivity up to Tc = 38 K in (Ba1-xKx)Fe2As2 with x = 0.4. The parent compound BaFe2As2 as well as KFe2As2 both crystallize in the tetragonal ThCr2Si2-type structure, which consists of (FeAs)- iron arsenide layers separated by barium or potassium ions. BaFe2As2 is a poor metal and exhibits a SDW anomaly at 140 K. By substituting Ba2+ for K+ ions we have introduced holes in the (FeAs)- layers, which suppress the SDW anomaly and induce superconductivity. This scenario is very similar to the recently discovered arsenide-oxide superconductors. The Tc of 38 K in (Ba1-xKx)Fe2As2 is the highest observed critical temperature in hole doped iron arsenide superconductors so far. Therefore, we were able to expand this class of superconductors by oxygen-free compounds with the ThCr2Si2-type structure. Our results suggest, that superconductivity in these systems essentially evolves from the (FeAs)- layers and may occur in other related compounds.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

BaT2As2 Single Crystals (T = Fe, Co, Ni) and Superconductivity upon Co-doping

The crystal structure and physical properties of BaFe2As2, BaCo2As2, and BaNi2As2 single crystals are surveyed. BaFe2As2 gives a magnetic and structural transition at TN = 132(1) K, BaCo2As2 is a paramagnetic metal, while BaNi2As2 has a structural phase transition at T0 = 131 K, followed by superconductivity below Tc = 0.69 K. The bulk superconductivity in Co-doped BaFe2As2 below Tc = 22 K is demonstrated by resistivity, magnetic susceptibility, and specific heat data. In contrast to the cuprates, the Fe-based system appears to tolerate considerable disorder in the transition metal layers. First principles calculations for BaFe1.84Co0.16As2 indicate the inter-band scattering due to Co is weak.Comment: Accepted to Physica

Aprecierea influenţei factorilor asupra indexului vigorii-i, tratament x genotip x durata păstrării la sămânţa de porumb (Zea Mays L.)

The size of the values of the parameters that characterize the quality of the seed from the aspect of thephysiological and physical manifestation, has a very important role in the measures to improve the cultivation technologies for obtaining safe and superior harvests qualitatively and quantitatively, therefore it is necessary to promote a seed with high biological value, high production capacity, resistance to diseases, pests and stress conditions. The particularity of the seeds destined for sowing is that they can be kept in different forms for a longer period of time, offering the safety of production. Analysing the data by the size of the range and the size of the coefficient of variation (Cv) it can be seen that there are obvious differences between the variants, regarding the value of these indicators. There were large decreases in the values of the index the force registered in this stage "after 12 months", in the variant treated with fungicide + insecticide, except for Turda 200 and Turda Star hybrids

Acousto-optical Scanning-Based High-Speed 3D Two-Photon Imaging In Vivo.

Recording of the concerted activity of neuronal assemblies and the dendritic and axonal signal integration of downstream neurons pose different challenges, preferably a single recording system should perform both operations. We present a three-dimensional (3D), high-resolution, fast, acousto-optic two-photon microscope with random-access and continuous trajectory scanning modes reaching a cubic millimeter scan range (now over 950 × 950 × 3000 μm3) which can be adapted to imaging different spatial scales. The resolution of the system allows simultaneous functional measurements in many fine neuronal processes, even in dendritic spines within a central core (>290 × 290 × 200 μm3) of the total scanned volume. Furthermore, the PSF size remained sufficiently low (PSFx < 1.9 μm, PSFz < 7.9 μm) to target individual neuronal somata in the whole scanning volume for simultaneous measurement of activity from hundreds of cells. The system contains new design concepts: it allows the acoustic frequency chirps in the deflectors to be adjusted dynamically to compensate for astigmatism and optical errors; it physically separates the z-dimension focusing and lateral scanning functions to optimize the lateral AO scanning range; it involves a custom angular compensation unit to diminish off-axis angular dispersion introduced by the AO deflectors, and it uses a high-NA, wide-field objective and high-bandwidth custom AO deflectors with large apertures. We demonstrate the use of the microscope at different spatial scales by first showing 3D optical recordings of action potential back propagation and dendritic Ca2+ spike forward propagation in long dendritic segments in vitro, at near-microsecond temporal resolution. Second, using the same microscope we show volumetric random-access Ca2+ imaging of spontaneous and visual stimulation-evoked activity from hundreds of cortical neurons in the visual cortex in vivo. The selection of active neurons in a volume that respond to a given stimulus was aided by the real-time data analysis and the 3D interactive visualization accelerated selection of regions of interest