503 research outputs found
Compensation for automatic white balance correction with histogram equalization
Histogram equalization rather than hard scaling can be used as an effective technique to counter automatic white balance correction in video processing to facilitate motion detection in video sequences. Benefits of this method are less user interaction needed by not needing to preview the image to select a scaling area and reduction of the non-focused changes in the video caused by using a scaling area. Reduced interaction lends itself to data mining of video
c-axis Josephson Tunneling in Twinned YBCO Crystals
Josephson tunneling between YBCO and Pb with the current flowing along the
c-axis of the YBCO is persumed to come from an s-wave component of the
superconductivity of the YBCO. Experiments on multi-twin samples are not
entirely consistent with this hypothesis. The sign change of the s-wave order
parameter across the N_T twin boundaries should give cancelations, resulting in
a small tunneling current. The actual current is larger than this.
We present a theory of this unexpectedly large current based upon a surface
effect: disorder-induced supression of the d-wave component at the (001)
surface leads to s-wave coherence across the twin boundaries and a non-random
tunneling current. We solve the case of an ordered array of d+s and d-s twins,
and estimate that the twin size at which s-wave surface coherence occurs is
consistent with typical sizes observed in experiments. In this picture, there
is a phase difference of between different surfaces of the material. We
propose a corner junction experiment to test this picture.Comment: 5 pages, 4 eps figure
Observation of high-Tc superconductivity in inhomogeneous combinatorial ceramics
A single-sample synthesis concept based on multi-element ceramic samples can
produce a variety of local products. When applied to cuprate superconductors
(SC), statistical modelling predicts the occurrence of possible compounds in a
concentration range of about 50 ppm. In samples with such low concentrations,
determining which compositions are superconducting is a challenging task and
requires local probes or separation techniques. Here, we report results from
samples with seven components: BaO2, CaCO3, SrCO3, La2O3, PbCO3, ZrO2 and CuO
oxides and carbonates, starting from different grain sizes. The reacted
ceramics show different phases, particular grain growth, as well as variations
in homogeneity and superconducting properties. High-Tc superconductivity up to
118 K was found. Powder x-ray diffraction (XRD) in combination with
energy-dispersive spectroscopy (EDS), scanning transmission electron microscopy
(STEM) can assign Pb1223 and (Sr,Ca,Ba)0.7-1.0CuO2 phases in inhomogeneous
samples milled with 10 mm ball sizes. Rather uniform samples featuring strong
grain growth were obtained with 3 mm ball sizes, resulting in Tc =70 K
superconductivity of the La(Ba,Ca)2Cu3Ox based phase. Scanning SQUID microscopy
(SSM) establishes locally formed superconducting areas at a level of a few
microns in inhomogeneous superconducting particles captured by a magnetic
separation technique. The present results demonstrate a new synthetic approach
for attaining high-Tc superconductivity in compounds without Bi, Tl, Hg, or the
need for high-pressure synthesis
Homeostatic control : the utilitycustomer marketplace for electric power
A load management system is proposed in which the electric utility customer controls his on-site power demand to coincide with the lowest possible cost of power generation. Called Homeostatic Control, this method is founded on feedback between the customer and the utility and on customer independence. The utility has no control beyond the customer's meter. Computers located at the customer's site are continuously fed data on weather conditions, utility generating costs, and demand requirements for space conditioning, lighting, and appliances. The customer then directs the computer to schedule and control the power allotted for these functions. On-site generation by the customer can be incorporated in the system. It is argued that homeostatic control is technically feasible, that the level of control equipment sophistication can be adapted to the benefits received by the customer, that such a system would encourage the use of customer-site energy storage and energy conservation equipment, and that it represents a realistic method for allowing the customer to decide how he will use electric power during an era of increasing costs for power generation. (LCL
Phase-sensitive Evidence for d-wave Pairing Symmetry in Electron-doped Cuprate Superconductors
We present phase-sensitive evidence that the electron-doped cuprates
Nd1.85Ce0.15CuO4-y (NCCO) and Pr1.85Ce0.15CuO4-y (PCCO) have d-wave pairing
symmetry. This evidence was obtained by observing the half-flux quantum effect,
using a scanning SQUID microscope, in c-axis oriented films of NCCO or PCCO
epitaxially grown on tricrystal [100] SrTiO3 substrates designed to be
frustrated for a d(x2-y2) order parameter. Samples with two other
configurations, designed to b unfrustrated for a d-wave superconductor, do not
show the half-flux quantum effect.Comment: 4 pages, Latex, 4 figure
Intrinsic frustration effects in anisotropic superconductors
Lattice distortions in which the axes are locally rotated provide an
intrinsic source of frustration in anisotropic superconductors. A general
framework to study this effect is presented. The influence of lattice defects
and phonons in and layered superconductors is studied.Comment: enlarged versio
Spontaneous Flux and Magnetic Interference Patterns in 0-pi Josephson Junctions
The spontaneous flux generation and magnetic field modulation of the critical
current in a 0-pi Josephson junction are calculated for different ratios of the
junction length to the Josephson penetration depth, and different ratios of the
0-junction length to the pi-junction length. These calculations apply to a
Pb-YBCO c-axis oriented junction with one YBCO twin boundary, as well as other
experimental systems. Measurements of such a junction can provide information
on the nature of the c-axis Josephson coupling and the symmetry of the order
parameter in YBCO. We find spontaneous flux even for very short symmetric 0-pi
junctions, but asymmetric junctions have qualitatively different behavior.Comment: 13 pages, TEX,+ 7 figures, postscrip
Ground state and bias current induced rearrangement of semifluxons in 0-pi long Josephson junctions
We investigate numerically a long Josephson junction with several phase
pi-discontinuity points. Such junctions are usually fabricated as a ramp
between an anisotropic cuprate superconductor like YBCO and an isotropic metal
superconductor like Nb. From the top, they look like zigzags with pi-jumps of
the Josephson phase at the corners. These pi-jumps, at certain conditions, lead
to the formation of half-integer flux quanta, which we call semifluxons (SF),
pinned at the corners. We show (a) that the spontaneous formation of SFs
depends on the junction length, (b) that the ground state without SFs can be
converted to a state with SFs by applying a bias current, (c) that the SF
configuration can be rearranged by the bias current. All these effects can be
observed using a SQUID microscope.Comment: ~8 pages, 6 figures, submitted to PR
Silicon Superconducting Quantum Interference Device
We have studied a Superconducting Quantum Interference SQUID device made from
a single layer thin film of superconducting silicon. The superconducting layer
is obtained by heavily doping a silicon wafer with boron atoms using the Gas
Immersion Laser Doping (GILD) technique. The SQUID device is composed of two
nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at
low temperature and low magnetic field. The overall behavior shows very good
agreement with numerical simulations based on the Ginzburg-Landau equations.Comment: Published in Applied Physics Letters (August 2015
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