444 research outputs found
Molecular interactions of carbapenem antibiotics with the multidrug efflux transporter acrb of escherichia coli
The drug/proton antiporter AcrB, engine of the major efflux pump AcrAB(Z)-TolC of Escherichia coli and other bacteria, is characterized by its impressive ability to transport chemically diverse compounds, conferring a multi-drug resistance (MDR) phenotype. Although hundreds of small molecules are known to be AcrB substrates, only a few co-crystal structures are available to date. Computational methods have been therefore intensively employed to provide structural and dynamical fingerprints related to transport and inhibition of AcrB. In this work, we performed a systematic computational investigation to study the interaction between representative carbapenem antibiotics and AcrB. We focused on the interaction of carbapenems with the so-called distal pocket, a region known for its importance in binding inhibitors and substrates of AcrB. Our findings reveal how the different physico-chemical nature of these antibiotics is reflected on their binding preference for AcrB. The molecular-level information provided here could help design new antibiotics less susceptible to the efflux mechanism
Intensity profiles of superdeformed bands in Pb isotopes in a two-level mixing model
A recently developed two-level mixing model of the decay out of superdeformed bands is applied to examine the loss of flux from the yrast superdeformed bands in Pb192, Pb194, and Pb196. Probability distributions for decay to states at normal deformations are calculated at each level. The sensitivity of the results to parameters describing the levels at normal deformation and their coupling to levels in the superdeformed well is explored. It is found that except for narrow ranges of the interaction strength coupling the states, the amount of intensity lost is primarily determined by the ratio of γ decay widths in the normal and superdeformed wells. It is also found that while the model can accommodate the observed fractional intensity loss profiles for decay from bands at relatively high excitation, it cannot accommodate the similarly abrupt decay from bands at lower energies if standard estimates of the properties of the states in the first minimum are employed
Black hole growth and host galaxy morphology
We use data from large surveys of the local Universe (SDSS+Galaxy Zoo) to
show that the galaxy-black hole connection is linked to host morphology at a
fundamental level. The fraction of early-type galaxies with actively growing
black holes, and therefore the AGN duty cycle, declines significantly with
increasing black hole mass. Late-type galaxies exhibit the opposite trend: the
fraction of actively growing black holes increases with black hole mass.Comment: 4 pages, 2 figures. Proceedings of the IAU Symposium no. 267,
"Co-Evolution of Central Black Holes and Galaxies: Feeding and Feedback",
eds. B.M. Peterson, R.S. Somerville and T. Storchi-Bergman
Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.15383.xWe investigate a class of rapidly growing emission line galaxies, known as 'Green Peas', first noted by volunteers in the Galaxy Zoo project because of their peculiar bright green colour and small size, unresolved in Sloan Digital Sky Survey imaging. Their appearance is due to very strong optical emission lines, namely [O iii]λ5007 Å, with an unusually large equivalent width of up to ∼1000 Å. We discuss a well-defined sample of 251 colour-selected objects, most of which are strongly star forming, although there are some active galactic nuclei interlopers including eight newly discovered narrow-line Seyfert 1 galaxies. The star-forming Peas are low-mass galaxies (M∼ 108.5–1010 M⊙) with high star formation rates (∼10 M⊙ yr−1) , low metallicities (log[O/H]+ 12 ∼ 8.7) and low reddening [ E(B−V) ≤ 0.25 ] and they reside in low-density environments. They have some of the highest specific star formation rates (up to ∼10−8 yr−1 ) seen in the local Universe, yielding doubling times for their stellar mass of hundreds of Myr. The few star-forming Peas with Hubble Space Telescope imaging appear to have several clumps of bright star-forming regions and low surface density features that may indicate recent or ongoing mergers. The Peas are similar in size, mass, luminosity and metallicity to luminous blue compact galaxies. They are also similar to high-redshift ultraviolet-luminous galaxies, e.g. Lyman-break galaxies and Lyα emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies. Studying starbursting galaxies as a function of redshift is essential to understanding the build up of stellar mass in the Universe.Peer reviewe
Occurrence and antimicrobial resistance of arcobacter spp. Recovered from aquatic environments
Arcobacter spp. are emerging waterborne and foodborne zoonotic pathogens responsible for gastroenteritis in humans. In this work, we evaluated the occurrence and the antimicrobial resistance profile of Arcobacter isolates recovered from different aquatic sources. Besides, we searched for Arcobacter spp. in seaweeds and the corresponding seawater samples. Bacteriological and molecular methods applied to 100 samples led to the isolation of 28 Arcobacter isolates from 27 samples. The highest prevalence was detected in rivers followed by artificial ponds, streams, well waters, and spring waters. Seaweeds contained a higher percentage of Arcobacter than the corresponding sea-water samples. The isolates were identified as Arcobacter butzleri (96.4%) and Arcobacter cryaerophilus (3.6%). All the isolates showed a multi-drug resistance profile, being resistant to at least three different classes of antibiotics. Molecular analysis of genetic determinants responsible for tetracycline resistance in nine randomly chosen isolates revealed the presence of tetO and/or tetW. This work confirms the occurrence and the continuous emergence of antibiotic-resistant Arcobacter strains in environmental samples; also, the presence of quinolone-resistant Arcobacter spp. in aquatic sources used for water supply and irrigation represents a potential risk for human health
Giant Thermoelectric Effect from Transmission Supernodes
We predict an enormous order-dependent quantum enhancement of thermoelectric
effects in the vicinity of a higher-order `supernode' in the transmission
spectrum of a nanoscale junction. Single-molecule junctions based on
3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The
nonequilibrium thermodynamic efficiency and power output of a thermoelectric
heat engine based on a 1,3-benzene junction are calculated using many-body
theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure
Unveiling the nature of the "Green Pea" galaxies
We review recent results on the oxygen and nitrogen chemical abundances in
extremely compact, low-mass starburst galaxies at redshifts between 0.1-0.3
recently named to as "Green Pea" galaxies. These galaxies are genuine
metal-poor galaxies ( one fifth solar) with N/O ratios unusually high for
galaxies of the same metallicity. In combination with their known general
properties, i.e., size, stellar mass and star-formation rate, these findings
suggest that these objects could be experiencing a short and extreme phase in
their evolution. The possible action of both recent and massive inflow of gas,
as well as stellar feedback mechanisms are discussed here as main drivers of
the starburst activity and their oxygen and nitrogen abundances.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy
Formation and Evolution", P. Papaderos, G. Hensler, S. Recchi (eds.). Lisbon,
September 2010, Springer Verlag, in pres
Human Computation and Convergence
Humans are the most effective integrators and producers of information,
directly and through the use of information-processing inventions. As these
inventions become increasingly sophisticated, the substantive role of humans in
processing information will tend toward capabilities that derive from our most
complex cognitive processes, e.g., abstraction, creativity, and applied world
knowledge. Through the advancement of human computation - methods that leverage
the respective strengths of humans and machines in distributed
information-processing systems - formerly discrete processes will combine
synergistically into increasingly integrated and complex information processing
systems. These new, collective systems will exhibit an unprecedented degree of
predictive accuracy in modeling physical and techno-social processes, and may
ultimately coalesce into a single unified predictive organism, with the
capacity to address societies most wicked problems and achieve planetary
homeostasis.Comment: Pre-publication draft of chapter. 24 pages, 3 figures; added
references to page 1 and 3, and corrected typ
No Evidence for Evolution in the Far-Infrared-Radio Correlation out to z ~ 2 in the eCDFS
We investigate the 70 um Far-Infrared Radio Correlation (FRC) of star-forming
galaxies in the Extended Chandra Deep Field South (ECDFS) out to z > 2. We use
70 um data from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL),
which comprises the most sensitive (~0.8 mJy rms) and extensive far-infrared
deep field observations using MIPS on the Spitzer Space Telescope, and 1.4 GHz
radio data (~8 uJy/beam rms) from the VLA. In order to quantify the evolution
of the FRC we use both survival analysis and stacking techniques which we find
give similar results. We also calculate the FRC using total infrared luminosity
and rest-frame radio luminosity, qTIR, and find that qTIR is constant (within
0.22) over the redshift range 0 - 2. We see no evidence for evolution in the
FRC at 70 um which is surprising given the many factors that are expected to
change this ratio at high redshifts.Comment: 18 pages, 13 figures. Accepted for publication in Ap
Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?
We present a new study investigating whether active galactic nuclei (AGN)
beyond the local universe are preferentially fed via large-scale bars. Our
investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the
AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disc galaxies
at 0.2 < z < 1.0. We use a novel method to robustly compare a sample of 120 AGN
host galaxies, defined to have 10^42 erg/s < L_X < 10^44 erg/s, with inactive
control galaxies matched in stellar mass, rest-frame colour, size, Sersic
index, and redshift. Using the GZH bar classifications of each sample, we
demonstrate that AGN hosts show no statistically significant enhancement in bar
fraction or average bar likelihood compared to closely-matched inactive
galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above
the control bar fraction by more than a factor of two, at 99.7% confidence. We
similarly find no significant difference in the AGN fraction among barred and
non-barred galaxies. Thus we find no compelling evidence that large-scale bars
directly fuel AGN at 0.2<z<1.0. This result, coupled with previous results at
z=0, implies that moderate-luminosity AGN have not been preferentially fed by
large-scale bars since z=1. Furthermore, given the low bar fractions at z>1,
our findings suggest that large-scale bars have likely never directly been a
dominant fueling mechanism for supermassive black hole growth.Comment: 13 pages, 5 figures, 2 tables, accepted by MNRA
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