6,798 research outputs found
Anomalous microwave response of high-temperature superconducting thin-film microstrip resonator in weak dc magnetic fields
We have studied an anomalous microwave (mw) response of superconducting
YBa_{2}Cu_{3}O_{7-delta} (YBCO) microstrip resonators in the presence of a weak
dc magnetic field, H_{dc}. The surface resistance (R_{s}) and reactance (X_{s})
show a correlated non-monotonic behaviour as a function of H_{dc}. R_{s} and
X_{s} were found to initially decrease with elevated H_{dc} and then increase
after H_{dc} reaches a crossover field, H_{c}, which is independent of the
amplitude and frequency of the input mw signal within the measurements. The
frequency dependence of R_{s} is almost linear at fixed H_{dc} with different
magnitudes (H_{c}). The impedance plane analysis
demonstrates that r_{H}, which is defined as the ratio of the change in
R_{s}(H_{dc}) and that in X_{s}(H_{dc}), is about 0.6 at H_{dc}<H_{c} and 0.1
at H_{dc}>H_{c}. The H_{dc} dependence of the surface impedance is
qualitatively independent of the orientation of H_{dc}.Comment: REVTex 3.1, 5 pages, 6 EPS figures, submitted to Physica
The Concentration of Manganese, Copper, Zinc, Lead and Thorium in Sediments of Paka Estuary,Terengganu, Malaysia
14 cm cores sediments from the Paka River were analyzed for Mn, Cu, Zn, Pb
and Th using the inductively coupled plasma mass spectrometer (ICP-MS).
Generally, the concentrations of all elements decreased with depth and have
significantly higher concentration at the surface depth of the core. The
concentration of Mn and Cu have average value of 151.1 ± 59.1 mg/g dry
weights and 29.2 ± 6.9 mg/g dry weights, while Zn and Pb averaged at 72.5 ±
15.5 mg/g dry weights and 54.9 ± 2.5 mg/g dry weights, respectively. Th were
slightly varied widely and ranged from 0.6 mg/g dry weights to 1.4 mg/g dry
weights. In this study, only Mn and Th have enrichment factor (EF) values close
to unity and may therefore be considered to be predominantly terrigenous in
origin. On the contrary, the higher EF values found for Cu, Zn and Pb indicate
that these metals might have some influenced from the anthropogenic inpu
Phase coherence and the Nernst effect at magic angles in organic conductors
A giant Nernst signal was recently observed for fields near crystallographic
directions in (TMTSF)PF. Such large Nernst signals are most naturally
associated with the motion of pancake vortices. We propose a model in which
phase coherence is destroyed throughout the sample except in planes closely
aligned with the applied field . A small tilt above or below the plane
changes the direction and density of the penetrating vortices and leads to a
Nernst signal that varies with the tilt angle of as observed. The
resistance notches at magic angles are understood in terms of flux-flow
dissipation from field-induced vortices.Comment: 4 pages, 4 figure
The Nernst effect in high- superconductors
The observation of a large Nernst signal in an extended region above
the critical temperature in hole-doped cuprates provides evidence that
vortex excitations survive above . The results support the scenario that
superfluidity vanishes because long-range phase coherence is destroyed by
thermally-created vortices (in zero field), and that the pair condensate
extends high into the pseudogap state in the underdoped (UD) regime. We present
a series of measurements to high fields which provide strong evidence for
this phase-disordering scenario.Comment: 21 pages, 28 figure
Improvement of dielectric loss of doped Ba0.5Sr0.5TiO3 thin films for tunable microwave devices
Al2O3-Ba0.5Sr0.5TiO3 (Al2O3-BST) thin films, with different Al2O3 contents,
were deposited on (100) LaAlO3 substrate by pulsed laser deposition (PLD)
technique. The Al2O3-BST films was demosnstrated to be a suitable systems to
fabricate ferroelectric thin films with low dielectric loss and higher figure
of merit for tunable microwave devices. Pure BST thin films were also
fabricated for comparison purpose. The films' structure and morphology were
analyzed by X-ray diffractiopn and scanning electron microscopy, respectively;
nad showed that the surface roughness for the Al2O3-BST films increased with
the Al2O3 content. Apart from that, the broadening in the intensity peak in XRD
result indicating the grain size of the Al2O3-BST films reduced with the
increasing of Al2O3 dopant. We measured the dielctric properties of Al2O3-BST
films with a home-made non-destructive dual resonator method at frequency ~ 7.7
GHZ. The effect of doped Al2O3 into BST thin films significantly reduced the
dielectric constant, dielectric loss and tunability compare to pure BST thin
film. Our result shows the figure of merit (K), used to compare the films with
varied dielectric properties, increased with the Al2O3 content. Therefore
Al2O3-BST films show the potential to be exploited in tunable microwave
devices.Comment: 8 pages, 4 figures, 1 table. Accepted & tentatively for Feb 15 2004
issue, Journal of Applied Physic
Anti-fouling double-skinned forward osmosis membrane with zwitterionic brush for oily wastewater treatment
Despite its attractive features for energy saving separation, the performance of forward osmosis (FO) has been restricted by internal concentration polarization and fast fouling propensity that occur in the membrane sublayer. These problems have significantly affected the membrane performance when treating highly contaminated oily wastewater. In this study, a novel double-skinned FO membrane with excellent anti-fouling properties has been developed for emulsified oil-water treatment. The double-skinned FO membrane comprises a fully porous sublayer sandwiched between a highly dense polyamide (PA) layer for salt rejection and a fairly loose dense bottom zwitterionic layer for emulsified oil particle removal. The top dense PA layer was synthesized via interfacial polymerization meanwhile the bottom layer was made up of a zwitterionic polyelectrolyte brush-(poly(3-(N-2-methacryloxyethyl-N,N-dimethyl) ammonatopropanesultone), abbreviated as PMAPS layer. The resultant double-skinned membrane exhibited a high water flux of 13.7 ± 0.3 L/m2.h and reverse salt transport of 1.6 ± 0.2 g/m2.h under FO mode using 2 M NaCl as the draw solution and emulsified oily solution as the feed. The double-skinned membrane outperforms the single-skinned membrane with much lower fouling propensity for emulsified oil-water separation
Magnetic anisotropy and magnetoresistance of sputtered [(FeTaN)/(TaN)](n) multilayers
We studied the in-plane magnetic anisotropy of rf (radio frequency) sputtered
[(FeTaN)/(TaN)](n) multilayers synthesized on Si substrates. In the multilayers
where n=5, the FeTaN thickness is fixed at 30 nm and the thickness of TaN,
t(TaN), is varied from 0 to 6.0 nm, we observed a clear trend that, with
increasing t(TaN), the values of coercivity, grain size, and amplitude of
maximum magnetoresistance (MR) of the samples all decrease first and then
increase after reaching a minimum when t(TaN) is around 2.0-4.0 nm. This trend
is also associated with an evolution of in-plane magnetic anisotropy, where the
multilayers change from uniaxial anisotropy to biaxial at t(TaN) around 4.0 nm
and above. We attribute the phenomena to the interlayer coupling effect of
FeTaN films as a function of the coupling layer (TaN) thickness, rather than to
the thickness dependence observed in single-layered FeTaN films, where the
direction of easy axis switches 90degrees when the film is thicker than 300 nm.
The in-plane anisotropy of the [(FeTaN)/(TaN)](n) multilayers also shows signs
of oscillation when the number of coupling layers varies. The MR effects
observed are mainly due to anisotropy MR (AMR), while the grain size and
exchange coupling may also contribute to the change of maximum MR ratios in the
multilayers with changing t(TaN)
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