596 research outputs found
Visualizing the proteome of Escherichia coli: an efficient and versatile method for labeling chromosomal coding DNA sequences (CDSs) with fluorescent protein genes
To investigate the feasibility of conducting a genomic-scale protein labeling and localization study in Escherichia coli, a representative subset of 23 coding DNA sequences (CDSs) was selected for chromosomal tagging with one or more fluorescent protein genes (EGFP, EYFP, mRFP1, DsRed2). We used λ-Red recombination to precisely and efficiently position PCR-generated DNA targeting cassettes containing a fluorescent protein gene and an antibiotic resistance marker, at the C-termini of the CDSs of interest, creating in-frame fusions under the control of their native promoters. We incorporated cre/loxP and flpe/frt technology to enable multiple rounds of chromosomal tagging events to be performed sequentially with minimal disruption to the target locus, thus allowing sets of proteins to be co-localized within the cell. The visualization of labeled proteins in live E. coli cells using fluorescence microscopy revealed a striking variety of distributions including: membrane and nucleoid association, polar foci and diffuse cytoplasmic localization. Fifty of the fifty-two independent targeting experiments performed were successful, and 21 of the 23 selected CDSs could be fluorescently visualized. Our results show that E. coli has an organized and dynamic proteome, and demonstrate that this approach is applicable for tagging and (co-) localizing CDSs on a genome-wide scale
Epitaxially strained [001]-(PbTiO)(PbZrO) superlattice and PbTiO from first principles
The effect of layer-by-layer heterostructuring and epitaxial strain on
lattice instabilities and related ferroelectric properties is investigated from
first principles for the [001]-(PbTiO)(PbZrO) superlattice and
pure PbTiO on a cubic substrate. The results for the superlattice show an
enhancement of the stability of the monoclinic r-phase with respect to pure
PbTiO. Analysis of the lattice instabilities of the relaxed centrosymmetric
reference structure computed within density functional perturbation theory
suggests that this results from the presence of two unstable zone-center modes,
one confined in the PbTiO layer and one in the PbZrO layer, which
produce in-plane and normal components of the polarization, respectively. The
zero-temperature dielectric response is computed and shown to be enhanced not
only near the phase boundaries, but throughout the r-phase. Analysis of the
analogous calculation for pure PbTiO is consistent with this
interpretation, and suggests useful approaches to engineering the dielectric
properties of artificially structured perovskite oxides.Comment: 8 pages, 5 figure
Testing the Lorentz and CPT Symmetry with CMB polarizations and a non-relativistic Maxwell Theory
We present a model for a system involving a photon gauge field and a scalar
field at quantum criticality in the frame of a Lifthitz-type non-relativistic
Maxwell theory. We will show this model gives rise to Lorentz and CPT violation
which leads to a frequency-dependent rotation of polarization plane of
radiations, and so leaves potential signals on the cosmic microwave background
temperature and polarization anisotropies.Comment: 7 pages, 2 figures, accepted on JCAP, a few references adde
Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon
There are two mechanisms for the generation of an asymmetry between the
strange and anti-strange quark distributions in the nucleon: nonperturbative
contributions originating from nucleons fluctuating into virtual baryon-meson
pairs such as and , and perturbative contributions
arising from gluons splitting into strange and anti-strange quark pairs. While
the nonperturbative contributions are dominant in the large- region, the
perturbative contributions are more significant in the small- region. We
calculate this asymmetry taking into account both nonperturbative and
perturbative contributions, thus giving a more accurate evaluation of this
asymmetry over the whole domain of . We find that the perturbative
contributions are generally a few times larger in magnitude than the
nonperturbative contributions, which suggests that the best region to detect
this asymmetry experimentally is in the region . We find that
the asymmetry may have more than one node, which is an effect that should be
taken into account, e.g. for parameterizations of the strange and anti-strange
quark distributions used in global analysis of parton distributions.Comment: 14 pages, 4 figures, figures comparing theoretical calculations with
NNPDF global analysis added, accepted for publication in EPJ
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Production and Decay of D_1(2420)^0 and D_2^*(2460)^0
We have investigated and final states and
observed the two established charmed mesons, the with mass
MeV/c and width MeV/c and
the with mass MeV/c and width
MeV/c. Properties of these final states, including
their decay angular distributions and spin-parity assignments, have been
studied. We identify these two mesons as the doublet predicted
by HQET. We also obtain constraints on {\footnotesize } as a function of the cosine of the relative phase of the two
amplitudes in the decay.Comment: 15 pages in REVTEX format. hardcopies with figures can be obtained by
sending mail to: [email protected]
Measurement of the branching fraction for
We have studied the leptonic decay of the resonance into tau
pairs using the CLEO II detector. A clean sample of tau pair events is
identified via events containing two charged particles where exactly one of the
particles is an identified electron. We find . The result is consistent with
expectations from lepton universality.Comment: 9 pages, RevTeX, two Postscript figures available upon request, CLNS
94/1297, CLEO 94-20 (submitted to Physics Letters B
Measurement of the Decay Asymmetry Parameters in and
We have measured the weak decay asymmetry parameters (\aLC ) for two \LC\
decay modes. Our measurements are \aLC = -0.94^{+0.21+0.12}_{-0.06-0.06} for
the decay mode and \aLC = -0.45\pm 0.31 \pm
0.06 for the decay mode . By combining these
measurements with the previously measured decay rates, we have extracted the
parity-violating and parity-conserving amplitudes. These amplitudes are used to
test models of nonleptonic charmed baryon decay.Comment: 11 pages including the figures. Uses REVTEX and psfig macros. Figures
as uuencoded postscript. Also available as
http://w4.lns.cornell.edu/public/CLNS/1995/CLNS95-1319.p
Observation of the Charmed Baryon Decays to , , and
We have observed two new decay modes of the charmed baryon into
and using data collected with the
CLEO II detector. We also present the first measurement of the branching
fraction for the previously observed decay mode . The branching fractions for these three modes relative to
are measured to be , , and , respectively.Comment: 12 page uuencoded postscript file, postscript file also available
through http://w4.lns.cornell.edu/public/CLN
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
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