241 research outputs found
Colloidal particles at a nematic-isotropic interface: effects of confinement
When captured by a flat nematic-isotropic interface, colloidal particles can
be dragged by it. As a result spatially periodic structures may appear, with
the period depending on a particle mass, size, and interface
velocity~\cite{west.jl:2002}. If liquid crystal is sandwiched between two
substrates, the interface takes a wedge-like shape, accommodating the
interface-substrate contact angle and minimizing the director distortions on
its nematic side. Correspondingly, particles move along complex trajectories:
they are first captured by the interface and then `glide' towards its vertex
point. Our experiments quantify this scenario, and numerical minimization of
the Landau-de Gennes free energy allow for a qualitative description of the
interfacial structure and the drag force.Comment: 7 pages, 9 figure
Shock waves in transonic channel flows at moderate Reynolds numbers
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76375/1/AIAA-9312-844.pd
Change of tRNA identity leads to a divergent orthogonal histidyl-tRNA synthetase/tRNAHis pair
Mature tRNAHis has at its 5′-terminus an extra guanylate, designated as G−1. This is the major recognition element for histidyl-tRNA synthetase (HisRS) to permit acylation of tRNAHis with histidine. However, it was reported that tRNAHis of a subgroup of α-proteobacteria, including Caulobacter crescentus, lacks the critical G−1 residue. Here we show that recombinant C. crescentus HisRS allowed complete histidylation of a C. crescentus tRNAHis transcript (lacking G−1). The addition of G−1 did not improve aminoacylation by C. crescentus HisRS. However, mutations in the tRNAHis anticodon caused a drastic loss of in vitro histidylation, and mutations of bases A73 and U72 also reduced charging. Thus, the major recognition elements in C. crescentus tRNAHis are the anticodon, the discriminator base and U72, which are recognized by the divergent (based on sequence similarity) C. crescentus HisRS. Transplantation of these recognition elements into an Escherichia coli tRNAHis template, together with addition of base U20a, created a competent substrate for C. crescentus HisRS. These results illustrate how a conserved tRNA recognition pattern changed during evolution. The data also uncovered a divergent orthogonal HisRS/tRNAHis pair
Optimization of a solid-state electron spin qubit using gate set tomography
State of the art qubit systems are reaching the gate fidelities required for scalable quantum computation architectures. Further improvements in the fidelity of quantum gates demands characterization and benchmarking protocols that are efficient, reliable and extremely accurate. Ideally, a benchmarking protocol should also provide information on how to rectify residual errors. Gate set tomography (GST) is one such protocol designed to give detailed characterization of as-built qubits. We implemented GST on a high-fidelity electron-spin qubit confined by a single 31P atom in 28Si. The results reveal systematic errors that a randomized benchmarking analysis could measure but not identify, whereas GST indicated the need for improved calibration of the length of the control pulses. After introducing this modification, we measured a new benchmark average gate fidelity of , an improvement on the previous value of . Furthermore, GST revealed high levels of non-Markovian noise in the system, which will need to be understood and addressed when the qubit is used within a fault-tolerant quantum computation scheme
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