321 research outputs found
Properties of KCoAs and Alloys with Fe and Ru: Density Functional Calculations
Electronic structure calculations are presented for KCoAs and alloys
with KFeAs and KRuAs. These materials show electronic
structures characteristic of coherent alloys, with a similar Fermi surface
structure to that of the Fe-based superconductors, when the electron count
is near six per transition metal. However, they are less magnetic than the
corresponding Fe compounds. These results are discussed in relation to
superconductivity.Comment: 5 page
Raman scattering study of electron-doped PrCaFeAs superconductors
Temperature-dependent polarized Raman spectra of electron-doped
superconducting PrCaFeAs () single crystals
are reported. All four allowed by symmetry even-parity phonons are identified.
Phonon mode of B symmetry at 222 cm, 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
meV.Comment: 4 pages, 3 figure
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
Corelaţie între substanţa uscată solubilă şi conţinutul de β-1,3 d-glucan la ciupercile Agaricus Blazei Murrill
Experiments carried out by the researchers,aboutthe extraction of the anti-tumour substances, likeprotein complex polysaccharides, whichhave demonstrated favorable effects of the immunostimulatory preparations and biologically active biomass obtained from certain species of fungi from the Basidiomicetaegroup.Thus, the antitumor activity of the β-1.3-D-glucan polysaccharide fractions extracted from mycelial biomass and fructification bodies of Agaricus blazei Murrill are well known.Mushrooms grown on synthetic substratewith wheat bran addition have a higher content of soluble dry substance (8.80%) and proteins (30.63% of the dm).The content of β-1.3-D-glucan, a specific substance in Agaricus blazei Murrill mushrooms, with a high biological value, is relatively high in the product obtained on the classic compost with the addition of cornflour and wheat bran (3.22-3.41mg100g-1dm).Regression obtained from the correlation of these,shows strong link between the two components beingvery significant in both case
Raman scattering study of (KSr)FeAs ( = 0.0, 0.4)
Polarized Raman spectra of non-superconducting SrFeAs and
superconducting KSrFeAs ( K) are reported.
All four phonon modes (A + B + 2E) 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 SrFeAs or the superconducting transition in
KSrFeAs.Comment: 4 pages, 4 figures, 2 table
Response Mixture Modeling of Intraindividual Differences in Responses and Response Times to the Hungarian WISC-IV Block Design Test
Response times may constitute an important additional source of information about cognitive ability as it enables to distinguishing between different intraindividual response processes. In this paper, we present a method to disentangle interindividual variation from intraindividual variation in the responses and response times of 978 subjects to the 14 items of the Hungarian WISC-IV Block Design test. It is found that faster and slower responses differ in their measurement properties suggesting that there are intraindivual differences in the response processes adopted by the subjects
Interacţiunea dintre conţinutul de azot al substratului de cultură şi conţinutul de proteină al ciupercilor Agaricus Blazei Murrill
Mushrooms provide important sources of protein extracted from materials of very low economic value, such as manure, agricultural waste, forestry, wood industry.Cultivated mushrooms having a saprophyte diet are forced to feed their enzymes from decomposing organic substances.During the composting and pasteurization of the substrate, the proteinnitrogen is transformed into peptides and amino acids that are absorbed by mycelialhippocampal cells.Research has shown that there is a direct correlation between the total nitrogen content of the nutrient substrate (up to 2.7%), the production of mushrooms and the protein content of the mushrooms.In this study, four types of compost and three types of additional protein additions were investigated.The highest values of correlation coefficient (r = 0.88187) were obtained with the addition of3% wheat bran,additional protein supplement in the substrate
Breaking through the Mermin-Wagner limit in 2D van der Waals magnets
The Mermin-Wagner theorem states that long-range magnetic order does not
exist in one- or two-dimensional (2D) isotropic magnets with short-ranged
interactions. The theorem has been a milestone in magnetism and has been
driving the research of recently discovered 2D van der Waals (vdW) magnetic
materials from fundamentals up to potential applications. In such systems, the
existence of magnetic ordering is typically attributed to the presence of a
significant magnetic anisotropy, which is known to introduce a spin-wave gap
and circumvent the core assumption of the theorem. Here we show that in
finite-size 2D vdW magnets typically found in lab setups (e.g., within
millimetres), short-range interactions can be large enough to allow the
stabilisation of magnetic order at finite temperatures without any magnetic
anisotropy for practical implementations. We demonstrate that magnetic ordering
can be created in flakes of 2D materials independent of the lattice symmetry
due to the intrinsic nature of the spin exchange interactions and finite-size
effects in two-dimensions. Surprisingly we find that the crossover temperature,
where the intrinsic magnetisation changes from superparamagnetic to a
completely disordered paramagnetic regime, is weakly dependent on the system
length, requiring giant sizes (e.g., of the order of the observable universe
~10 m) in order to observe the vanishing of the magnetic order at
cryogenic temperatures as expected from the Mermin-Wagner theorem. Our findings
indicate exchange interactions as the main driving force behind the
stabilisation of short-range order in 2D magnetism and broaden the horizons of
possibilities for exploration of compounds with low anisotropy at an atomically
thin level
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
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