1,232 research outputs found

    Cell-free prediction of protein expression costs for growing cells

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    Translating heterologous proteins places significant burden on host cells, consuming expression resources leading to slower cell growth and productivity. Yet predicting the cost of protein production for any given gene is a major challenge, as multiple processes and factors combine to determine translation efficiency. To enable prediction of the cost of gene expression in bacteria, we describe here a standard cell-free lysate assay that provides a relative measure of resource consumption when a protein coding sequence is expressed. These lysate measurements can then be used with a computational model of translation to predict the in vivo burden placed on growing E. coli cells for a variety of proteins of different functions and lengths. Using this approach, we can predict the burden of expressing multigene operons of different designs and differentiate between the fraction of burden related to gene expression compared to action of a metabolic pathway

    Controlled Production of Sub-Radiant States of a Diatomic Molecule in an Optical Lattice

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    We report successful production of sub-radiant states of a two-atom system in a three-dimensional optical lattice starting from doubly occupied sites in a Mott insulator phase of a quantum gas of atomic ytterbium. We can selectively produce either sub-radiant 1g state or super-radiant 0u state by choosing the excitation laser frequency. The inherent weak excitation rate for the sub-radiant 1g state is overcome by the increased atomic density due to the tight-confinement in a three-dimensional optical lattice. Our experimental measurements of binding energies, linewidth, and Zeeman shift confirm observation of sub-radiant levels of the 1g state of the Yb_2 molecule.Comment: To be published in Phys. Rev. Let

    INTEGRAL observations of PSR B0540-69

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    PSR B0540-69 is often called an extragalactic 'twin' of the Crab pulsar in the Large Magellanic Cloud. The pulsar is embedded in a synchrotron nebula in the center of SNR 0540-69.3. It was discovered with the Einstein satellite with P~50 ms, spin-down age of ~1500 years and a spin-down luminosity of ~10^38 erg/s. It has since been detected with all major X-ray telescopes. At X-ray energies up to ~40 keV the latest observations were reported from RXTE and from INTEGRAL (only spectrum) in the context of a survey of the LMC. Optical pulsed emission and faint radio emission have also been found from PSR B0540-69. The INTEGRAL analysis presented here is based on observations of the LMC obtained in Jan. 2003 and Jan. 2004 with a total exposure of ~1.5 Ms. In the mosaic maps from the total exposure (JEM-X and IBIS/ISGRI) a source at the location of PSR B0540-69 is clearly visible up to energies of ~200 keV. After barycentric correction and determination of the pulsar phases, based on theephemeris available from contemporaneous RXTE data, the lightcurves show the characteristic shape of a broad pulse up into the 40-100 keV band. At higher energies no significant pulsation is detectable. We derive the spectrum of the total source from the ISGRI data. The photon spectrum can be fitted with a power law of index 2.22, which is compatible with the result found by Goetz et al., 2006.Comment: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany, May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.44-5

    Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75

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    We present Spitzer Space Telescope and Chandra X-ray Observatory observations of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the detected flux at 24 microns and hot gas parameters from fitting spectra from new, deep X-ray observations to constrain models of dust emission, obtaining a dust-to-gas mass ratio M_dust/M_gas ~0.001. We find that a two-component thermal model, nominally representing shocked swept-up interstellar or circumstellar material and reverse-shocked ejecta, adequately fits the X-ray spectrum, albeit with somewhat high implied densities for both components. We surmise that this model implies a Wolf-Rayet progenitor for the remnant. We also present infrared flux upper limits for the central pulsar wind nebula.Comment: 7 pages, 2 tables, 4 figures, uses emulateapj. Accepted for publication in Ap

    Optimisation Of Controller Parameters For Adaptive Building Envelopes Through A Co-Simulation Interface: A Case Study

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    Adaptive building envelopes can dynamically adapt to environmental changes, often supported by a control system. While building performance simulation (BPS) tools can be employed to test different design alternatives, representing control strategies within current BPS tools can be challenging, especially for systems with a fast, dynamic response. Another challenge in current BPS tools is the ability to tune and select parameters for the particular use case. In this study, a modelling approach is presented for the integrated analysis of control strategies of adaptive building envelopes linking thermal performance and control with an optimisation algorithm. The proposed modelling approach was evaluated using a case study with an automated motorised blind with two distinct control strategies. Simulation results suggest that the window heat gains were 72.7 % lower when the controller model was coupled with an optimiser to identify optimised controller parameters compared to a baseline control strategy. The results of this study are suggestive of the benefits that can be obtained from adjusting the dynamic aspects of the building envelope. The results support the thesis of using optimisation as standard building envelope design practice in the future

    Direct measurement of the charge distribution along a biased carbon nanotube bundle using electron holography

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    Nanowires and nanotubes can be examined in the transmission electron microscope under an applied bias. Here we introduce a model-independent method, which allows the charge distribution along a nanowire or nanotube to be measured directly from the Laplacian of an electron holographic phase image. We present results from a biased bundle of carbon nanotubes, in which we show that the charge density increases linearly with distance from its base, reaching a value of similar to 0.8 electrons/nm near its tip. (C) 2011 American Institute of Physics. [doi:10.1063/1.3598468

    Local density of states induced by anisotropic impurity scattering in a d-wave superconductor

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    We study a single impurity effect on the local density of states in a d-wave superconductor accounting for the momentum-dependent impurity potential. We show that the anisotropy of the scattering potential can alter significantly the spatial dependence of the quasiparticle density of states in the vicinity of the impurity.Comment: 8 pages, revtex4, 14 figure
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