81 research outputs found

    High photo-excited carrier multiplication by charged InAs dots in AlAs/GaAs/AlAs resonant tunneling diode

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    We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs/GaAs/AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10nA photocurrent in this structure, corresponding to the photo-excited carrier multiplication factor of 10^7. This high multiplication factor is achieved by the quantum dot induced memory effect and the resonant tunneling tuning effect of QD-RTD structure.Comment: 10 pages,5 figures. Submitted to Applied Physics Letter

    Control of spectral extreme events in ultrafast fibre lasers by a genetic algorithm

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    Extreme wave events or rogue waves (RWs) are both statistically rare and of exceptionally large amplitude. They are observed in many complex systems ranging from oceanic and optical environments to financial models and Bose-Einstein condensates. As they appear from nowhere and disappear without a trace, their emergence is unpredictable and non-repetitive, which make them particularly challenging to control. Here, we extend the use of genetic algorithms (GAs), which have been exclusively designed for searching and optimising stationary or repetitive processes in nonlinear optical systems, to the active control of extreme events in a fibre laser cavity. Feeding real-time spectral measurements into a GA controlling the electronics to optimise the cavity parameters, we are able to trigger wave events in the cavity that have the typical statistics of RWs in the frequency domain. This accurate control enables the generation of the optical RWs with a spectral peak intensity 32.8 times higher than the significant intensity threshold. A rationale is proposed and confirmed by numerical simulations of the laser model for the related frequency up- and down-shifting of the optical spectrum that are experimentally observed

    On effects of regular S=1 dilution of S=1/2 antiferromagnetic Heisenberg chains by a quantum Monte Carlo simulation

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    The effects of regular S=1 dilution of S=1/2 isotropic antiferromagnetic chain are investigated by the quantum Monte Carlo loop/cluster algorithm. Our numerical results show that there are two kinds of ground-state phases which alternate with the variation of S1=1S^1=1 concentration. When the effective spin of a unit cell is half-integer, the ground state is ferrimagnetic with gapless energy spectrum and the magnetism becomes weaker with decreasing of the S1S^1 concentration ρ=1/M\rho = 1/M. While it is integer, a non-magnetic ground state with gaped spectrum emerges and the gap gradually becomes narrowed as fitted by a relation of Δ1.25ρ\Delta \approx 1.25\sqrt{\rho}.Comment: 6 pages, 9 figure

    Machine learning control of complex nonlinear dynamics in fibre lasers

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    We review our recent work on the use of genetic algorithms to control non-stationary nonlinear wave dynamics in ultrafast fibre lasers, including the generation of breathing-soliton dynamics with controlled characteristics, the disclosure of the fractal dynamics of breathers, and the generation of rogue waves with controlled intensity

    Self-optimising breather ultrafast fibre laser

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    We demonstrate the self-optimisation of the breather regime in an ultrafast fibre laser through an evolutionary algorithm. Depending on the specified merit function, single breathers with controllable breathing ratio and period, and breather molecular complexes with a controllable number of constituents can be obtained

    Role of AP-1 in the Coordinate Induction of Rat Glutamate-cysteine Ligase and Glutathione Synthetase by tert -Butylhydroquinone

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    GSH synthesis occurs via two enzymatic steps catalyzed by glutamate-cysteine ligase (GCL, made up of two subunits) and GSH synthetase (GS). Recently, we described coordinate induction of GCL subunits and GS. To study GS transcriptional regulation, we have cloned and characterized a 2.2-kb 5'-flanking region of the rat GS (GenBank accession number AF333982). One transcriptional start site is located at 51 nucleotides upstream of the translational start site. The rat GS promoter drove efficiently luciferase expression in H4IIE cells. Sequential deletion analysis revealed DNA regions that are involved in positive and negative regulation. One repressor identified was NF1. tert-Butylhydroquinone (TBH) exerted a dose- and time-dependent increase in the mRNA level and promoter activity of both GCL subunits and GS. TBH increased protein binding to several regions of the GS promoter, c-jun expression, and activator protein 1 (AP-1) binding activity to several of the putative AP-1-binding sites of the GS promoter. Blocking AP-1 binding with dominant-negative c-jun led to decreased basal expression and significantly blocked the TBH-induced increase in promoter activity and mRNA level of all three genes. In conclusion, AP-1 is required for basal expression of GCL and GS; while NF1 serves as a repressor of GS, increased AP-1 transactivation is the predominant mechanism for coordinate induction of GCL and GS expression by TBH
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