1,123 research outputs found
Flow and acoustic characteristics of subsonic and supersonic jets from convergent nozzle
Acoustic and flow characteristics of subsonic and supersonic jets from convergent nozzle
Temperature- and magnetic-field-dependent resistivity of MgB2 sintered at high temperature and high pressure condition
We report the temperature- and magnetic-field-dependent resistivity of MgB2
sintered at high temperature and high pressure condition. The superconducting
transition width for the resistivity measurement was about 0.4 K, and the
low-field magnetization showed a sharp superconducting transition with a
transition width of about 1 K. The resistivity in the normal state roughly
followed T^2 behavior with smaller residual resistivity ratio (RRR) of 3 over
broad temperature region above 100 K rather than reported T^3 behavior with
larger RRR value of ~ 20 in the samples made at lower pressures. Also, the
resistivity did not change appreciably with the applied magnetic field, which
was different from previous report. These differences were discussed with the
microscopic and structural change due to the high-pressure sintering.Comment: 2 pages, 3 figures. Accepted by Physica
Orientation Characteristics of Non-regiocontrolled Poly (3-hexyl-thiophene) Film by FTM on Various Liquid Substrates
Orientation characteristics of non-regiocontrolled poly (3-hexylthiophene) (NR-P3HT) films prepared by dynamic casting of floating film and transferring method (FTM) has been investigated. The film was first cast on liquid-substrate to obtain as a floating-film followed by its transfer on solid-substrate such as white-glass or Si-wafer in order to evaluate their optoelectronic characteristics. As a possible key-factor to generate the orientation of conjugated polymer in this method we focused on the components of liquid-substrate in this study. The orientation dependence upon various liquid-substrates reveals that dichroic ratio strongly changes with liquid-substrates. Pictures of floating-film show the change in size of floating-parts depending upon the liquid-substrate, representing the expansion length of casting solution upon the viscosity. These findings have indicated that spreading speed of polymer solution and solvent evaporation speed controls the size of floating-film leading to change in the orientation intensity. The multilayer coatings of oriented NR-P3HT films were used for polarized FTIR analysis exhibiting clear dichroism. The obtained dichroic characteristics were well corresponded with in-plane, out-of-plane and non-oriented vibronic modes of P3HT.India-Japan Expert Group Meeting on Biomolecular Electronics & Organic Nanotechnology for Environment Preservation (IJEGMBE 2015), December 23-26, 2015, Fukuoka, Japa
Very fast formation of superconducting MgB2/Fe wires with high Jc
In this paper we have investigated the effects of sintering time and
temperature on the formation and critical current densities of Fe-clad MgB2
wires. MgB2 wires were fabricated using the powder-in-tube process and sintered
for different periods of time at predetermined temperatures. All the samples
were examined using XRD, SEM and magnetisation measurements. In contrast to the
common practice of sintering for several hours, the present results show that
there is no need for prolonged heat treatment in the fabrication of Fe-clad
MgB2 wires. A total time in the furnace of several minutes is more than enough
to form nearly pure MgB2 with high performance characteristics. The results
from Tc, Jc and Hirr show convincingly that the samples which were sintered for
3 minutes above 800 oC are as good as those sintered for longer times. In fact,
the Jc field performance for the most rapidly sintered sample is slightly
better than for all other samples. Jc of 4.5 times 10 ^5 A/cm2 in zero field
and above 10 ^5 A/cm2 in 2T at 15 K has been achieved for the best Fe-clad MgB2
wires. As a result of such a short sintering there is no need for using high
purity argon protection and it is possible to carry out the heat treatment in a
much less protective atmosphere or in air. These findings substantially
simplify the fabrication process, making it possible to have a continuous
process for fabrication and reducing the costs for large-scale production of
MgB2 wires.Comment: 15 pages, one table, 9 figures, submitted to Physica C on June 8,
200
A comparative study of spin coated and floating film transfer method coated poly (3-hexylthiophene)/poly (3-hexylthiophene)-nanofibers based field effect transistors
A comparative study on electrical performance, optical properties, and surface morphology of poly(3-hexylthiophene) (P3HT) and P3HT-nanofibers based “normally on” type p-channel field effect transistors (FETs), fabricated by two different coating techniques has been reported here. Nanofibers are prepared in the laboratory with the approach of self-assembly of P3HT molecules into nanofibers in an appropriate solvent. P3HT (0.3 wt. %) and P3HT-nanofibers (∼0.25 wt. %) are used as semiconductor transport materials for deposition over FETs channel through spin coating as well as through our recently developed floating film transfer method (FTM). FETs fabricated using FTM show superior performance compared to spin coated devices; however, the mobility of FTM films based FETs is comparable to the mobility of spin coated one. The devices based on P3HT-nanofibers (using both the techniques) show much better performance in comparison to P3HT FETs. The best performance among all the fabricated organic field effect transistors are observed for FTM coated P3HT-nanofibers FETs. This improved performance of nanofiber-FETs is due to ordering of fibers and also due to the fact that fibers offer excellent charge transport facility because of point to point transmission. The optical properties and structural morphologies (P3HT and P3HT-nanofibers) are studied using UV-visible absorption spectrophotometer and atomic force microscopy , respectively. Coating techniques and effect of fiber formation for organic conductors give information for fabrication of organic devices with improved performance
Two-Dimensional Sigma-Hole Systems in Boron Layers: A First-Principles Study on Mg_{1-x}Na_xB_2 and Mg_{1-x}Al_xB_2
We study two-dimensional sigma-hole systems in boron layers by calculating
the electronic structures of Mg_{1-x}Na_xB_2 and Mg_{1-x}Al_xB_2. In
Mg_{1-x}Na_xB_2, it is found that the concentration of sigma holes is
approximately described by (0.8 + 0.8 x) * 10^{22} cm^{-3} and the largest
attainable concentration is about 1.6 * 10^{22} cm^{-3} in NaB_2. In
Mg_{1-x}Al_xB_2, on the other hand, it is found that the concentration of sigma
holes is approximately described by (0.8 - 1.4 x) * 10^{22} cm^{-3} and sigma
holes are disappeared at x of about 0.6. These relations can be used for
experimental studies on the sigma-hole systems in these materials.Comment: 5 pages, 5 figure
Casting Control of Floating-films into Ribbon-shape Structure by modified Dynamic FTM
We have developed a new method to obtain Ribbon-shaped floating films via dynamic casting of floating-film and transfer method (dynamic-FTM). Dynamic-FTM is a unique method to prepare oriented thin-film of conjugated polymers (CPs) which is quick and easy. This method has several advantages as compared to the other conventional casting procedure to prepare oriented CP films. In the conventional dynamic FTM appearance of large scale circular orientation poses difficulty not only for practical applications but also hinders the detailed analysis of the orientation mechanism. In this present work, pros and cons of this newly proposed ribbon-shaped floating-film have been discussed in detail from those of the conventional floating-film prepared by dynamic-FTM.12th International Conference on Nanomolecular Electronics (ICNME-2016), December 14-16, 2016, Kobe International Conference Center, Kobe, Japa
Substitution induced pinning in MgB_2 superconductor doped with SiC nano-particles
By doping MgB_2 superconductor with SiC nano-particles, we have successfully
introduced pinning sites directly into the crystal lattice of MgB_2 grains
(intra-grain pinning). It became possible due to the combination of
counter-balanced Si and C co-substitution for B, leading to a large number of
intra-granular dislocations and the dispersed nano-size impurities induced by
the substitution. The magnetic field dependence of the critical current density
was significantly improved in a wide temperature range, whereas the transition
temperature in the sample MgB_2(SiC)_x having x = 0.34, the highest doping
level prepared, dropped only by 2.6 K.Comment: 4 pages, 6 figure
Dependence of the Superconducting Transition Temperature of MgB2 on Pressure to 20 GPa
The dependence of Tc on nearly hydrostatic pressure has been measured for an
isotopically pure (11B) MgB2 sample in a helium-loaded diamond-anvil-cell to
nearly 20 GPa. Tc decreases monotonically with pressure from 39.1 K at ambient
pressure to 20.9 K at 19.2 GPa. The initial dependence is the same as that
obtained earlier (dTc/dP = -1.11(2) K/GPa) on the same sample in a He-gas
apparatus to 0.7 GPa. The observed pressure dependence Tc(P) to 20 GPa can be
readily described in terms of simple lattice stiffening within standard
phonon-mediated BCS superconductivity.Comment: 9 pages, 3 figure
Electronic Structures of CaAlSi with Different Stacking AlSi Layers by First-Principles Calculations
The full-potential linear augmented plane-wave calculations have been applied
to investigate the systematic change of electronic structures in CaAlSi due to
different stacking sequences of AlSi layers. The present ab-initio calculations
have revealed that the multistacking, buckling and 60 degrees rotation of AlSi
layer affect the electronic band structure in this system. In particular, such
a structural perturbation gives rise to the disconnected and cylindrical Fermi
surface along the M-L lines of the hexagonal Brillouin zone. This means that
multistacked CaAlSi with the buckling AlSi layers increases degree of
two-dimensional electronic characters, and it gives us qualitative
understanding for the quite different upper critical field anisotropy between
specimens with and without superstructure as reported previously.Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jp
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