14,594 research outputs found
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2
The in-plane resistivity and thermal conductivity of
FeAs-based superconductor KFeAs single crystal were measured down to 50
mK. We observe non-Fermi-liquid behavior at =
5 T, and the development of a Fermi liquid state with when
further increasing field. This suggests a field-induced quantum critical point,
occurring at the superconducting upper critical field . In zero field
there is a large residual linear term , and the field dependence of
mimics that in d-wave cuprate superconductors. This indicates that
the superconducting gaps in KFeAs have nodes, likely d-wave symmetry.
Such a nodal superconductivity is attributed to the antiferromagnetic spin
fluctuations near the quantum critical point.Comment: 4 pages, 4 figures - replaces arXiv:0909.485
High-temperature electrical and thermal transport properties of fully filled skutterudites RFe_(4)Sb_(12) (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb)
Fully filled skutterudites RFe_(4)Sb_(12) (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb) have been prepared and the high-temperature electrical and thermal transport properties are investigated systematically. Lattice constants of RFe_(4)Sb_(12) increase almost linearly with increasing the ionic radii of the fillers, while the lattice expansion in filled structure is weakly influenced by the filler valence charge states. Using simple charge counting, the hole concentration in RFe_(4)Sb_(12) with divalent fillers (R = Ca, Sr, Ba, Eu, and Yb) is much higher than that in RFe4Sb12 with trivalent fillers (R = La, Ce, Pr, and Nd), resulting in relatively high electrical conductivity and low Seebeck coefficient. It is also found that RFe_(4)Sb_(12) filled skutterudites having similar filler valence charge states exhibit comparable electrical conductivity and Seebeck coefficient, and the behavior of the temperature dependence, thereby leading to comparable power factor values in the temperature range from 300 to 800 K. All RFe_(4)Sb_(12) samples possess low lattice thermal conductivity. The correlation between the lattice thermal resistivity WL and ionic radii of the fillers is discussed and a good relationship of W_L ~ (r_(cage)−r_(ion))^3 is observed in lanthanide metal filled skutterudites. CeFe_(4)Sb_(12), PrFe_(4)Sb_(12), and NdFe_(4)Sb_(12) show the highest thermoelectric figure of merit around 0.87 at 750 K among all the filled skutterudites studied in this work
Nodeless superconductivity in IrPtTe with strong spin-orbital coupling
The thermal conductivity of superconductor IrPtTe
( = 0.05) single crystal with strong spin-orbital coupling was measured down
to 50 mK. The residual linear term is negligible in zero magnetic
field. In low magnetic field, shows a slow field dependence. These
results demonstrate that the superconducting gap of IrPtTe is
nodeless, and the pairing symmetry is likely conventional s-wave, despite the
existence of strong spin-orbital coupling and a quantum critical point.Comment: 5 pages, 4 figure
Effects of a finite size reflecting disk in sound power measurements
© 2018 Elsevier Ltd In practical sound power measurements in an anechoic room, a baffle sometimes has to be used to support the sound source under test so that the anechoic room can be used as a hemi-anechoic room by laying a reflecting plane. To understand the effects of a finite size reflecting plane on measurements quantitatively, this paper investigates the effects of a disk on sound power measurements by formulating an exact solution to the problem based on the spheroidal wave functions. Three practical measurement cases are considered and the correction terms for the cases are presented based on numerical simulations. Experiments are conducted to validate the analytical solutions and numerical results
Phytochemical and Anticancer Studies on Ten Medicinal Plants Used in Nigeria
Ten medicinal plants used in Nigerian ethno medicine were subjected to phytochemical and anticancer studies using established standard procedures. The result of the study revealed the presence of phytochemical constituents such as alkaloids, saponins, tannins and flavonoids. Anona muricata, Andrographis paniculata and Garcinia kola were active against the lung cancer cell lines at different concentrations. The study justifies the use of the plant in traditional medicine as remedy against cancer.
Keywords: cytotoxic, anticancer, plant extract
Resummation of nuclear enhanced higher twist in the Drell Yan process
We investigate higher twist contributions to the transverse momentum
broadening of Drell Yan pairs in proton nucleus collisions. We revisit the
contribution of matrix elements of twist-4 and generalize this to matrix
elements of arbitrary twist. An estimate of the maximal nuclear broadening
effect is derived. A model for nuclear enhanced matrix elements of arbitrary
twist allows us to give the result of a resummation of all twists in closed
form. Subleading corrections to the maximal broadening are discussed
qualitatively.Comment: 10 pages, 5 figures; v2: minor changes in text, acknowledgement
added; v3: mistake in fig. 1 correcte
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