25,464 research outputs found
High Input Impedance Voltage-Mode Universal Biquadratic Filters With Three Inputs Using Three CCs and Grounding Capacitors
Two current conveyors (CCs) based high input impedance voltage-mode universal biquadratic filters each with three input terminals and one output terminal are presented. The first circuit is composed of three differential voltage current conveyors (DVCCs), two grounded capacitors and four resistors. The second circuit is composed of two DVCCs, one differential difference current conveyor (DDCC), two grounded capacitors and four grounded resistors. The proposed circuits can realize all the standard filter functions, namely, lowpass, bandpass, highpass, notch and allpass filters by the selections of different input voltage terminals. The proposed circuits offer the features of high input impedance, using only grounded capacitors and low active and passive sensitivities. Moreover, the x ports of the DVCCs (or DDCC) in the proposed circuits are connected directly to resistors. This design offers the feature of a direct incorporation of the parasitic resistance at the x terminal of the DVCC (DDCC), Rx, as a part of the main resistance
Bounce-free spherical hydrodynamic implosion
In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot
core plasma does not expand against the imploding flow. Such an implosion
scheme has the advantage of improving the dwell time of the burning fuel,
resulting in a higher fusion burn-up fraction. The existence of bounce-free
spherical implosions is demonstrated by explicitly constructing a family of
self-similar solutions to the spherically symmetric ideal hydrodynamic
equations. When applied to a specific example of plasma liner driven
magneto-inertial fusion, the bounce-free solution is found to produce at least
a factor of four improvement in dwell time and fusion energy gain.Comment: accepted by Phys. Plasmas (Nov. 7, 2011); for Ref. 11, please see
ftp://ftp.lanl.gov/public/kagan/liner_evolution.gi
Intrapore-Texturized Vanadia-Hydrate Supercapacitor with Ultrahigh Area-Normalized Capacitance
A pressing need for ultrahigh area‐normalized capacitance emerges from the migration to miniaturized composite supercapacitors. Herein, an advanced electric field‐assisted sol–gel synthesis protocol that allows to obtain ribbon‐like vanadium oxides that preferentially creep along the porous tunnels in a commercially available carbon host of low density is demonstrated. In particular, this design offers 1) to convert the original submicrometer‐sized pore network into hierarchically macroporous yet 3D‐interconnected bicontinuous composite frameworks and 2) to considerably add pseudo‐capacitive functionalities onto a highly conductive carbon cloth backbone. Both are demonstrated by an unprecedented area‐normalized capacitance exceeding 5 F cm−2. Moreover, the as‐designed symmetric supercapacitor is characterized by a maximum area‐normalized cell capacitance in the order of 1 F cm−2, a geometric energy density of 0.34 mW h cm−2, and a geometric power density of 28.3 mW cm−2. These features outperform commercial double‐layer supercapacitors as well as many state‐of‐the‐art composite pseudo‐capacitors and lithium‐ion microbatteries
Nonmagnetic impurity perturbation to the quasi-two-dimensional quantum helimagnet LiCu2O2
A complete phase diagram of Zn substituted quantum quasi-two-dimensional
helimagnet LiCu2O2 has been presented. Helical ordering transition temperature
(T_h) of the original LiCu2O2 follows finite size scaling for less than ~ 5.5%
Zn substitution, which implies the existence of finite helimagnetic domains
with domain boundaries formed with nearly isolated spins. Higher Zn
substitution > 5.5% quenches the long-range helical ordering and introduces an
intriguing Zn level dependent magnetic phase transition with slight thermal
hysteresis and a universal quadratic field dependence for T_c (Zn > 0.055,H).
The magnetic coupling constants of nearest-neighbor (nn) J1 and
next-nearest-neighbor (nnn) J2 (alpha=J2/J1) are extracted from high
temperature series expansion (HTSE) fitting and N=16 finite chain exact
diagonalization simulation. We have also provided evidence of direct
correlation between long-range helical spin ordering and the magnitude of
electric polarization in this spin driven multiferroic material
Fabrication and Low Temperature Thermoelectric Properties of Na_xCoO_2 (x = 0.68 and 0.75) Epitaxial Films by the Reactive Solid-Phase Epitaxy
We have fabricated Na_xCoO_2 thin films via lateral diffusion of sodium into
Co_3O_4 (111) epitaxial films (reactive solid-phase epitaxy: Ref. 4). The
environment of thermal diffusion is key to the control of the sodium content in
thin films. From the results of x-ray diffraction and in-plane resistivity, the
epitaxial growth and the sodium contents of these films were identified. The
thermoelectric measurements show a large thermoelectric power similar to that
observed in single crystals. The quasiparticle scattering rate is found to
approach zero at low temperatures, consistent with the small residual
resistivity, indicating high quality of the Na_xCoO_2 thin films.Comment: 16 pages. 4 figures. To appear in Applied Physics Letter
Precise Pressure Dependence of the Superconducting Transition Temperature of FeSe: Resistivity and ^77Se--NMR Study
We report the precise pressure dependence of FeSe from a resistivity
measurement up to 4.15 GPa. Superconducting transition temperature (T_c)
increases sensitively under pressure, but shows a plateau between 0.5-1.5 GPa.
The maximum T_c, which is determined by zero resistance, is 21 K at
approximately 3.5 GPa. The onset value reaches ~37 K at 4.15 GPa. We also
measure the nuclear spin-lattice relaxation rate 1/T_1 under pressure using
77Se--NMR measurement. 1/T_1 shows that bulk superconductivity is realized in
the zero-resistance state. The pressure dependence of 1/T_1T just above T_c
shows a plateau as well as the pressure dependence of T_c, which gives clear
evidence of the close relationship between 1/T_1T and T_c. Spin fluctuations
are suggested to contribute to the mechanism of superconductivity.Comment: 4pages, 6figures: to be published in J. Phys. Soc. Jpn. Vol.78 No.6
(2009
Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry
Three dimensional hydrodynamic simulations have been performed using smoothed
particle hydrodynamics (SPH) in order to study the effects of discrete jets on
the processes of plasma liner formation, implosion on vacuum, and expansion.
The pressure history of the inner portion of the liner was qualitatively and
quantitatively similar from peak compression through the complete stagnation of
the liner among simulation results from two one dimensional
radiationhydrodynamic codes, 3D SPH with a uniform liner, and 3D SPH with 30
discrete plasma jets. Two dimensional slices of the pressure show that the
discrete jet SPH case evolves towards a profile that is almost
indistinguishable from the SPH case with a uniform liner, showing that
non-uniformities due to discrete jets are smeared out by late stages of the
implosion. Liner formation and implosion on vacuum was also shown to be robust
to Rayleigh-Taylor instability growth. Interparticle mixing for a liner
imploding on vacuum was investigated. The mixing rate was very small until
after peak compression for the 30 jet simulation.Comment: 28 pages, 16 figures, submitted to Physics of Plasmas (2012
Brushing Element Fields
Aggregate elements following certain directions have a variety
of applications in graphics, design, and visualization. However,
authoring oriented elements in various output domains, especially
in 3D, remains challenging. We propose a novel brushing system to
facilitate interactive authoring of aggregate elements with diverse
properties over given output domains via an element synthesis
approach. To increase output quality and reduce input workload,
we further propose element fields that can automatically orient
the entire elements in better alignments over the output domains
according to partially user-specified strokes. The proposed system
can effectively synthesize distinct types of elements within various
output domains in higher quality and efficiency and offer more user
friendliness than existing practices. Our method can be applied to
practical applications such as graphic design, artistic collage, and
aggregate modelin
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