4,961 research outputs found
Increased hydrogen production by Escherichia coli strain HD701 in comparison with the wild-type parent strain MC4100
Hydrogen production by Escherichia coli is mediated by the formate hydrogenlyase (FHL) complex. E. coli strain HD701 cannot synthesize the FHL complex repressor, Hyc A. Consequently, it has an up-regulated FHL system and can, therefore, evolve hydrogen at a greater rate than its parental wild type, E. coli MC4100. Resting cells of E. coli strain HD701 and MC4100 were set up in batch mode in\ud
phosphate buffered saline (PBS) to decouple growth from hydrogen production at the expense of sugar solutions of varying composition. Strain HD701 evolved several times more hydrogen than MC4100 at glucose concentrations ranging from 3 to 200 mM. The difference in the amount of H2 evolved by both strains decreased as the concentration of glucose increased. The highest rate of H2 evolution by strain HD701was 31ml h−1 ODunit −1 l−1 at a glucose concentration of 100 mM.With strain MC4100, the highest ratewas 16ml h−1 ODunit −1 l−1 under these conditions. Experiments using industrial wastes with a high sugar content yielded similar results. In each case, strain HD701\ud
evolved hydrogen at a faster rate than the wild type, showing a possible potential for commercial hydrogen production
Superconductivity and structure in beta-tungsten compounds
Imperial Users onl
Microwave spectroscopy of a carbon nanotube charge qubit
Carbon nanotube quantum dots allow accurate control of electron charge, spin
and valley degrees of freedom in a material which is atomically perfect and can
be grown isotopically pure. These properties underlie the unique potential of
carbon nanotubes for quantum information processing, but developing nanotube
charge, spin, or spin-valley qubits requires efficient readout techniques as
well as understanding and extending quantum coherence in these devices. Here,
we report on microwave spectroscopy of a carbon nanotube charge qubit in which
quantum information is encoded in the spatial position of an electron. We
combine radio-frequency reflectometry measurements of the quantum capacitance
of the device with microwave manipulation to drive transitions between the
qubit states. This approach simplifies charge-state readout and allows us to
operate the device at an optimal point where the qubit is first-order
insensitive to charge noise. From these measurements, we are able to quantify
the degree of charge noise experienced by the qubit and obtain an inhomogeneous
charge coherence of 5 ns. We use a chopped microwave signal whose duty-cycle
period is varied to measure the decay of the qubit states, yielding a charge
relaxation time of 48 ns
- …