16 research outputs found
Quantum interference induced by multiple Landau-Zener transitions in a strongly driven rf-SQUID qubit
We irradiated an rf-SQUID qubit with large-amplitude and high frequency
electromagnetic field. Population transitions between macroscopic distinctive
quantum states due to Landau-Zener transitions at energy-level avoided
crossings were observed. The qubit population on the excited states as a
function of flux detuning and microwave power exhibits interference patterns.
Some novel features are found in the interference and a model based on rate
equations can well address the features.Comment: 6 pages, 3 figures, comments are welcom
Accumulation of a polyisoprene-linked amino sugar in polymyxin-resistant Salmonella typhimurium and Escherichia coli: Structural characterization and transfer to lipid A in the periplasm
Polymyxin-resistant mutants of Escherichia coli and Salmonella typhimurium accumulate a novel minor lipid that can donate 4-amino-4-deoxy-L-arabinose units (L-Ara4N) to lipid A. We now report the purification of this lipid from a pss- pmrAC mutant of E. coli and assign its structure as undecaprenyl phosphate-α-L-Ara4N. Approximately 0.2 mg of homogeneous material was isolated from an 8-liter culture by solvent extraction, followed by chromatography on DEAE-cellulose, C18 reverse phase resin, and silicic acid. Matrix-assisted laser desorption ionization/time of flight mass spectrometry in the negative mode yielded a single species [M - H]- at m/z 977.5, consistent with undecaprenyl phosphate-α-L-Ara4N (Mr = 978.41). 31P NMR spectroscopy showed a single phosphorus atom at -0.44 ppm characteristic of a phosphodiester linkage. Selective inverse decoupling difference spectroscopy demonstrated that the undecaprenyl phosphate group is attached to the anomeric carbon of the L-Ara4N unit. One- and two-dimensional 1H NMR studies confirmed the presence of a polyisoprene chain and a sugar moiety with chemical shifts and coupling constants expected for an equatorially substituted arabinopyranoside. Heteronuclear multiple-quantum coherence spectroscopy analysis demonstrated that a nitrogen atom is attached to C-4 of the sugar residue. The purified donor supports in vitro conversion of lipid IVA to lipid IIA, which is substituted with a single L-Ara4N moiety. The identification of undecaprenyl phosphate-α -L-Ara4N implies that L-Ara4N transfer to lipid A occurs in the periplasm of polymyxin-resistant strains, and establishes a new enzymatic pathway by which Gram-negative bacteria acquire antibiotic resistance
Population inversion induced by Landau--Zener transition in a strongly driven rf superconducting quantum interference device
This is the published version, also available here: http://dx.doi.org/10.1063/1.3093823.Microwave resonances between discrete macroscopically distinct quantum states with single photon and multiphoton absorption are observed in a strongly driven radio frequency superconducting quantum interference device flux qubit. The amplitude of the resonant peaks and dips are modulated by the power of the applied microwave irradiation and a population inversion is generated at low flux bias. These results, which can be addressed with LandauâZener transition, are useful to develop an alternative means to initialize and manipulate the flux qubit, as well as to do a controllable population inversion used in a micromaser
Population Inversion Induced by Landau-Zener Transition in a Strongly Driven rf-SQUID
Microwave resonances between discrete macroscopically distinct quantum states
with single photon and multiphoton absorption are observed in a strongly driven
radio frequency superconducting quantum interference device flux qubit. The
amplitude of the resonant peaks and dips are modulated by the power of the
applied microwave irradiation and a population inversion is generated at low
flux bias. These results, which can be addressed with Landau-Zener transition,
are useful to develop an alternative means to initialize and manipulate the
flux qubit, as well as to do a controllable population inversion used in a
micromaser.Comment: 4pages, 3 figures; Selected as the cover of the March 9 issue of AP
A Universal Eluent System for Method Scouting and Separation of Biotherapeutic Proteins by Ion-Exchange, Size-Exclusion, and Hydrophobic Interaction Chromatography
Characterization and quality control of biotherapeutic
proteins
commonly require the application of several orthogonal separation
techniques in order to establish product identity and purity. Many
of the techniques used rely on a buffered aqueous mobile phase system
to maintain the native conformation of the protein and its variants.
Optimal pH, buffer substance(s), and chromatography methods vary with
each protein of interest and result in tedious method development
for each new drug product. Linear controlled pH gradient systems from
pH 5.6 to pH 10.2 has been shown to provide a global method for the
separation of charge variants of monoclonal antibodies. This can be
realized using two balanced zwitterionic buffer blends. The pH linearity
of the resulting system, with a cation ion exchange column in place,
can generate any pH value in this accessible pH range. This study
expands the scope of this buffer system and demonstrates its application
in conjunction with a quaternary HPLC pump for several analytical
techniques: the pH optimization of salt gradient-based anion and cation
exchange during method development, as well as performing pH gradient
elution. In addition, the same universal buffers are used for hydrophobic
interaction and size exclusion chromatography. This eluent system
omits the need to prepare different buffers for each method and flushing
of the HPLC system between method changes. The implementation of this
concept is further demonstrated to allow an automated method scouting
approach and selection of different methods that requires minimal
manual intervention
Molecular Dynamics Simulation Study on the Interactions of Mixed Cationic/Anionic Collectors on Muscovite (001) Surface in Aqueous Solution
In this study, the adsorption mechanisms of dodecylamine hydrochloride(DDAHC), sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate(SDBS), and their mixed anionic/cationic collectors at ten different molar ratios on a muscovite (Mcv) surface in neutral aqueous solution were assessed by molecular dynamics simulations (MDS). According to the snapshot, interaction energy, radial distribution function (RDF), and density profile between the Mcv surface and collector molecules, the individual DDAHC collector was an effective collector for the flotation of Mcv. The molar ratio of anionic/cationic collectors was determined to be an essential factor in the flotation recovery of Mcv. The DDAHC collector was involved in the adsorption of the mixed anionic/cationic collectors on the Mcv (001) surface, whereas SDS and SDBS collectors were co-adsorbed with DDAHC. The mixed cationic/anionic collector showed the best adsorption on the Mcv surface in a molar ratio of 2. Additionally, SDBS, which has one more benzene ring than SDS, was more likely to form spherical micelles with DDAHC, thus resulting in better adsorption on the Mcv surface. The results of micro-flotation experiments indicated that the DDAHC collector could improve the flotation recovery of Mcv in neutral aqueous solution, which was in agreement with MDS-derived findings. In conclusion, DDAHC alone is the optimum collector for Mcv flotation under the neutral aqueous conditions, while the mixture of DDAHC and SDBS collectors (molar ratio = 2:1) exhibits the similar flotation performance