1,168 research outputs found
Cell-free prediction of protein expression costs for growing cells
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
Characterization of Fe-N nanocrystals and nitrogen–containing inclusions in (Ga,Fe)N thin films using transmission electron microscopy
Nanometric inclusions filled with nitrogen, located adjacent to FenN (n¼3 or 4) nanocrystals
within (Ga,Fe)N layers, are identified and characterized using scanning transmission electron
microscopy (STEM) and electron energy-loss spectroscopy (EELS). High-resolution STEM images reveal a truncation of the Fe-N nanocrystals at their boundaries with the nitrogen-containing inclusions. A controlled electron beam hole drilling experiment is used to release nitrogen gas from an inclusion in situ in the electron microscope. The density of nitrogen in an individual inclusion is measured to be 1.460.3 g/cm3. These observations provide an explanation for the location of surplus nitrogen in the (Ga,Fe)N layers, which is liberated by the nucleation of FenN (n>1) nanocrystals during growth
In Vitro Digestibility of Untreated and Ammonia Treated oat Mill By-Product
Oat mill by-product (OMB, approximately 80% oat hulls) was treated with 0, 1%, 3%, or 5% NH3 and 10%, 20%, 30%, 40%, or 50% H2O (4 x 5 factorial design) and allowed to react for 28 days. Samples were analyzed for in vitro dry matter digestibility (IVDMD), crude protein (CP) and fiber content (NDF, ADF, ADL). Treatment with 3% NH3 and 20% H20 resulted in maximum improvement of IVDMD. CP was increased and NDF decreased due to treatment. Nutritional value of OMB can be improved by NH3 treatment
Data analysis of gravitational-wave signals from spinning neutron stars. V. A narrow-band all-sky search
We present theory and algorithms to perform an all-sky coherent search for
periodic signals of gravitational waves in narrow-band data of a detector. Our
search is based on a statistic, commonly called the -statistic,
derived from the maximum-likelihood principle in Paper I of this series. We
briefly review the response of a ground-based detector to the
gravitational-wave signal from a rotating neuron star and the derivation of the
-statistic. We present several algorithms to calculate efficiently
this statistic. In particular our algorithms are such that one can take
advantage of the speed of fast Fourier transform (FFT) in calculation of the
-statistic. We construct a grid in the parameter space such that
the nodes of the grid coincide with the Fourier frequencies. We present
interpolation methods that approximately convert the two integrals in the
-statistic into Fourier transforms so that the FFT algorithm can
be applied in their evaluation. We have implemented our methods and algorithms
into computer codes and we present results of the Monte Carlo simulations
performed to test these codes.Comment: REVTeX, 20 pages, 8 figure
Observations of X-rays and Thermal Dust Emission from the Supernova Remnant Kes 75
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
Constraints on the luminosity of the stellar remnant in SNR1987A
We obtain photometric constraints on the luminosity of the stellar remnant in
SNR1987A using XMM-Newton and INTEGRAL data. The upper limit in the 2--10 keV
band based on the XMM-Newton data is L<5*10^{34}erg/s. We note, however, that
the optical depth of the envelope is still high in the XMM-Newton band,
therefore, this upper limit does not constrain the true unabsorbed luminosity
of the central source. The optical depth is expected to be small in the hard
X-ray band of the IBIS telescope aboard the INTEGRAL observatory, therefore it
provides an unobscured look at the stellar remnant. We did not detect
statistically significant emission from SN1987A in the 20-60 keV band with the
upper limit of L<1.1*10^{36}erg/s. We also obtained an upper limit on the mass
of radioactive 44Ti M(44Ti)<10^{-3}Msun.Comment: 5 pages, 3 figures, accepted for publication in Astronomy Letter
Accurate determination of blackbody radiation shifts in a strontium molecular lattice clock
Molecular lattice clocks enable the search for new physics, such as fifth forces or temporal variations of fundamental constants, in a manner complementary to atomic clocks. Blackbody radiation (BBR) is a major contributor to the systematic error budget of conventional atomic clocks and is notoriously difficult to characterize and control. Here, we combine infrared Stark-shift spectroscopy in a molecular lattice clock and modern quantum chemistry methods to characterize the polarizabilities of the Sr2 molecule from dc to infrared. Using this description, we determine the static and dynamic blackbody radiation shifts for all possible vibrational clock transitions to the 10−16 level. This constitutes an important step toward millihertz-level molecular spectroscopy in Sr2 and provides a framework for evaluating BBR shifts in other homonuclear molecules
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