88 research outputs found
Hot spots and waves in Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks -a study by Low Temperature Scanning Laser Microscopy
Recently, it has been shown that large stacks of intrinsic Josephson
junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization
presumably triggered by a cavity resonance. To investigate this effect we use
Low Temperature Scanning Laser Microscopy to image electric field
distributions. Apart from verifying the appearance of cavity modes at low bias
we find that, in a high input power regime, standing-wave patterns are created
through interactions with a hot spot, possibly pointing to a new mode of
generating synchronized radiation in intrinsic Josephson junction stacks.Comment: 6 pages, 5 figures, supplementary information include
Coherent THz emission of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks in the hot spot regime
We report on THz emission measurements and low temperature scanning laser
imaging of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks. Coherent
emission is observed at large dc input power, where a hot spot and a standing
wave, formed in the "cold" part of the stack, coexist. By varying the hot spot
size the cavity resonance frequency and the emitted radiation can be tuned. The
linewidth of radiation is much smaller than expected from the quality factor of
the cavity mode excited. Thus, an additional mechanism of synchronization seems
to play a role, possibly arising from nonequilibrium processes at the hot spot
edge.Comment: 4.1 pages, 5 figure
Interaction of hot spots and THz waves in Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks of various geometry
At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson
junctions a hot spot (a region heated to above the superconducting transition
temperature) coexists with regions still in the superconducting state. In the
``cold'' regions cavity resonances can occur, synchronizing the ac Josephson
currents and giving rise to strong coherent THz emission. We investigate the
interplay of hot spots and standing electromagnetic waves by low temperature
scanning laser microscopy and THz emission measurements, using stacks of
various geometries. For a rectangular and a arrow-shaped structure we show that
the standing wave can be turned on and off in various regions of the stack
structure, depending on the hot spot position. We also report on standing wave
and hot spot formation in a disk shaped mesa structure
Attenuation by all-trans-retinoic acid of sodium chloride-enhanced gastric carcinogenesis induced by N-methyl-N′-nitro-N-nitrosoguanidine in Wistar rats
The effect of prolonged administration of all-trans-retinoic acid (RA) on sodium chloride-enhanced gastric carcinogenesis induced by N-methyl-N′-nitro-N-nitrosoguanidine, and the labelling and apoptotic indices and immunoreactivity of transforming growth factor (TGF) α in the gastric cancers was investigated in Wistar rats. After 25 weeks of carcinogen treatment, the rats were given chow pellets containing 10% sodium chloride and subcutaneous injections of RA at doses of 0.75 or 1.5 mg kg−1 body weight every other day. In week 52, oral supplementation with sodium chloride significantly increased the incidence of gastric cancers compared with the untreated controls. Long-term administration of RA at both doses significantly reduced the incidence of gastric cancers, which was enhanced by oral administration of sodium chloride. RA at both doses significantly decreased the labelling index and TGF-α immunoreactivity of gastric cancers, which were enhanced by administration of sodium chloride, and significantly increased the apoptotic index of cancers, which was lowered by administration of sodium chloride. These findings suggest that RA attenuates gastric carcinogenesis, enhanced by sodium chloride, by increasing apoptosis, decreasing DNA synthesis, and reducing TGF-α expression in gastric cancers. © 1999 Cancer Research Campaig
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