38,078 research outputs found
Pumping Current in a Quantum Dot by an Oscillating Magnetic Field
We investigate spin and charge current through a quantum dot pumped by a
time-varying magnetic field. Using the density matrix method, quantum rate
equations for the electronic occupation numbers in the quantum dot are obtained
and solved in the stationary state limit for a wide set of setup parameters.
Both charge and spin current are expressed explicitly in terms of several
relevant parameters and analyzed in detail. The results suggest a way of
optimizing experimental setup parameters to obtain an maximal spin current
without the charge current flow.Comment: to appear in the proceedings of the international conference on
frontiers in nonlinear and complex systems as a special issue in the
International Journal of Modern Physics B, vol. 21
Topological Protection from Random Rashba Spin-Orbit Backscattering: Ballistic Transport in a Helical Luttinger Liquid
The combination of Rashba spin-orbit coupling and potential disorder induces
a random current operator for the edge states of a 2D topological insulator. We
prove that charge transport through such an edge is ballistic at any
temperature, with or without Luttinger liquid interactions. The solution
exploits a mapping to a spin 1/2 in a time-dependent field that preserves the
projection along one randomly undulating component (integrable dynamics). Our
result is exact and rules out random Rashba backscattering as a source of
temperature-dependent transport, absent integrability-breaking terms.Comment: 6+3 pages, 2+1 figure
Augmenting the Calvin-Benson-Bassham cycle by a synthetic malyl-CoA-glycerate carbon fixation pathway.
The Calvin-Benson-Bassham (CBB) cycle is presumably evolved for optimal synthesis of C3 sugars, but not for the production of C2 metabolite acetyl-CoA. The carbon loss in producing acetyl-CoA from decarboxylation of C3 sugar limits the maximum carbon yield of photosynthesis. Here we design a synthetic malyl-CoA-glycerate (MCG) pathway to augment the CBB cycle for efficient acetyl-CoA synthesis. This pathway converts a C3 metabolite to two acetyl-CoA by fixation of one additional CO2 equivalent, or assimilates glyoxylate, a photorespiration intermediate, to produce acetyl-CoA without net carbon loss. We first functionally demonstrate the design of the MCG pathway in vitro and in Escherichia coli. We then implement the pathway in a photosynthetic organism Synechococcus elongates PCC7942, and show that it increases the intracellular acetyl-CoA pool and enhances bicarbonate assimilation by roughly 2-fold. This work provides a strategy to improve carbon fixation efficiency in photosynthetic organisms
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