13,801 research outputs found
Drastic annealing effects in transport properties of single crystals of the YbNi2B2C heavy fermion system
We report temperature dependent resistivity, specific heat, magnetic
susceptibility and thermoelectric power measurements made on the heavy fermion
system YbNi2B2C, for both as grown and annealed single crystals. Our results
demonstrate a significant variation in the temperature dependent electrical
resistivity and thermoelectric power between as grown crystals and crystals
that have undergone optimal (150 hour, 950 C) annealing, whereas the
thermodynamic properties: (c_p(T) and chi(T)) remain almost unchanged. We
interpret these results in terms of redistributions of local Kondo temperatures
associated with ligandal disorder for a small (~ 1%) fraction of the Yb sites.Comment: 5 pages, 4 figures, submitted to PR
Meson Structure Functions in Valon Model
Parton distributions in a {\it{valon}} in the next-to-leading order is used
to determine the patron distributions in pion and kaon. The validity of the
valon model is tested and shown that the partonic content of the valon is
universal and independent of the valon type. We have evaluated the valon
distribution in pion and kaon, and in particular it is shown that the results
are in good agreement with the experimental data on pion structure in a wide
range of Comment: 13 pages with 7 figures included, The manuscript is revised, figures
are added and some errors are corrected. Accepted for publication in Physical
Review
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Numerical investigation of high-speed droplet impact using a multiscale two-fluid approach
A single droplet impact onto solid surfaces remains a fundamental and challenging topic in both experimental and numerical studies with significant importance in a plethora of industrial applications, ranging from printing technologies to fuel injection in internal combustion engines. Under high-speed impact conditions, additional complexities arise as a result of the prompt droplet splashing and the subsequent violent fragmentation; thus, different flow regimes and a vast spectrum of sizes for the produced secondary flow structures coexist in the flow field. The present work introduces a numerical methodology to capture the multiscale processes involved with respect to local topological characteristics. The proposed methodology concerns a compressible Σ-Υ two-fluid model with dynamic interface sharpening based on an advanced flow topology detection algorithm. The model has been developed in OpenFOAM® and provides the flexibility of dealing with the multiscale character of droplet splashing, by switching between a sharp and a diffuse interface within the Eulerian-Eulerian framework in segregated and dispersed flow regions, respectively. An additional transport equation for the interface surface area density (Σ) introduces important information for the sub-grid scale phenomena, which is exploited in the dispersed flow regions to provide an insight into the extended cloud of secondary droplets after impact on the target. A high-speed water droplet impact case has been examined and evaluated against new experimental data; these refer to a millimetre size droplet impacting a solid dry smooth surface at velocity as high as 150m/s, which corresponds to a Weber number of ~7.6×10^5. At the investigated impact conditions compressibility effects dominate the early stages of droplet splashing. A strong shock wave forms and propagates inside the droplet, where transonic Mach numbers occur; local Mach numbers up to 2.5 are observed for the expelled surrounding gas outside the droplet. The proposed numerical approach is found to capture relatively accurately the phenomena and provide significant information regarding the produced flow structure dimensions, which is not available from the experiment
Direct observation of Fe spin reorientation in single crystalline YbFe6Ge6
We have grown single crystals of YbFe6Ge6 and LuFe6Ge6 and characterized
their anisotropic behaviour through low field magnetic susceptibility,
field-dependent magnetization, resistivity and heat capacity measurements. The
Yb+3 valency is confirmed by LIII XANES measurements. YbFe6Ge6 crystals exhibit
a field-dependent, sudden reorientation of the Fe spins at about 63 K, a unique
effect in the RFe6Ge6 family (R = rare earths) where the Fe ions order
anti-ferromagnetically with Neel temperatures above 450 K and the R ions'
magnetism appears to behave independently. The possible origins of this unusual
behaviour of the ordered Fe moments in this compound are discussed.Comment: 12 pages, 8 figures, accepted in J. Phys.: Cond. Matte
Anomalous infrared spectra of hybridized phonons in type-I clathrate BaGaGe
The optical conductivity spectra of the rattling phonons in the clathrate
BaGaGe are investigated in detail by use of the terahertz
time-domain spectroscopy. The experiment has revealed that the lowest-lying
vibrational mode of a Ba(2) ion consists of a sharp Lorentzian peak at
1.2 THz superimposed on a broad tail weighted in the lower frequency regime
around 1.0 THz. With decreasing temperature, an unexpected linewidth broadening
of the phonon peak is observed, together with monotonic softening of the phonon
peak and the enhancement of the tail structure. These observed anomalies are
discussed in terms of impurity scattering effects on the hybridized phonon
system of rattling and acoustic phonons.Comment: Submitted to JPS
Anisotropic superconducting properties of aligned MgB2 crystallites
Samples of aligned MgB2 crystallites have been prepared, allowing for the
first time the direct identification of an upper critical field anisotropy
Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40
A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background
signal was identified, possibly related to the raw materials purity.Comment: 4 pages, 4 figures; Revised version to appear in Phys. Rev. Let
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