17,535 research outputs found
Direct-write, focused ion beam-deposited,7 K superconducting C-Ga-O nanowire
We have fabricated C-Ga-O nanowires by gallium focused ion beam-induced
deposition from the carbon-based precursor phenanthrene. The electrical
conductivity of the nanowires is weakly temperature dependent below 300 K, and
indicates a transition to a superconducting state below Tc = 7 K. We have
measured the temperature dependence of the upper critical field Hc2(T), and
estimate a zero temperature critical field of 8.8 T. The Tc of this material is
approximately 40% higher than that of any other direct write nanowire, such as
those based on C-W-Ga, expanding the possibility of fabricating direct-write
nanostructures that superconduct above liquid helium temperaturesComment: Accepted for AP
HST imaging of hyperluminous infrared galaxies
We present HST WFPC2 I band imaging for a sample of 9 Hyperluminous Infrared
Galaxies spanning a redshift range 0.45 < z < 1.34. Three of the sample have
morphologies showing evidence for interactions, six are QSOs. Host galaxies in
the QSOs are reliably detected out to z ~ 0.8. The detected QSO host galaxies
have an elliptical morphology with scalelengths spanning 6.5 < r_{e}(Kpc) < 88
and absolute k corrected magnitudes spanning -24.5 < M_{I} < -25.2. There is no
clear correlation between the IR power source and the optical morphology. None
of the sources in the sample, including F15307+3252, show any evidence for
gravitational lensing. We infer that the IR luminosities are thus real. Based
on these results, and previous studies of HLIRGs, we conclude that this class
of object is broadly consistent with being a simple extrapolation of the ULIRG
population to higher luminosities; ULIRGs being mainly violently interacting
systems powered by starbursts and/or AGN. Only a small number of sources whose
infrared luminosities exceed 10^{13}Lsun are intrinsically less luminous
objects which have been boosted by gravitational lensing.Comment: 16 Pages. Accepted for publication in MNRA
New Limits on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
We update the limit from the 90 GHz PIQUE ground-based polarimeter on the
magnitude of any polarized anisotropy of the cosmic microwave radiation. With a
second year of data, we have now limited both Q and U on a ring of 1 degree
radius. The window functions are broad: for E-mode polarization, the effective
l is = 191 +143 -132. We find that the E-mode signal can be no greater than
8.4 microK (95% CL), assuming no B-mode polarization. Limits on a possible
B-mode signal are also presented.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
CENP-A Is Dispensable for Mitotic Centromere Function after Initial Centromere/Kinetochore Assembly
Human centromeres are defined by chromatin containing the histone H3 variant CENP-A assembled onto repetitive alphoid DNA sequences. By inducing rapid, complete degradation of endogenous CENP-A, we now demonstrate that once the first steps of centromere assembly have been completed in G1/S, continued CENP-A binding is not required for maintaining kinetochore attachment to centromeres or for centromere function in the next mitosis. Degradation of CENP-A prior to kinetochore assembly is found to block deposition of CENP-C and CENP-N, but not CENP-T, thereby producing defective kinetochores and failure of chromosome segregation. Without the continuing presence of CENP-A, CENP-B binding to alphoid DNA sequences becomes essential to preserve anchoring of CENP-C and the kinetochore to each centromere. Thus, there is a reciprocal interdependency of CENP-A chromatin and the underlying repetitive centromere DNA sequences bound by CENP-B in the maintenance of human chromosome segregation
The Power Spectrum of the PSC Redshift Survey
We measure the redshift-space power spectrum P(k) for the recently completed
IRAS Point Source Catalogue (PSC) redshift survey, which contains 14500
galaxies over 84% of the sky with 60 micron flux >= 0.6 Jansky. Comparison with
simulations shows that our estimated errors on P(k) are realistic, and that
systematic errors due to the finite survey volume are small for wavenumbers k
>~ 0.03 h Mpc^-1. At large scales our power spectrum is intermediate between
those of the earlier QDOT and 1.2 Jansky surveys, but with considerably smaller
error bars; it falls slightly more steeply to smaller scales. We have fitted
families of CDM-like models using the Peacock-Dodds formula for non-linear
evolution; the results are somewhat sensitive to the assumed small-scale
velocity dispersion \sigma_V. Assuming a realistic \sigma_V \approx 300 km/s
yields a shape parameter \Gamma ~ 0.25 and normalisation b \sigma_8 ~ 0.75; if
\sigma_V is as high as 600 km/s then \Gamma = 0.5 is only marginally excluded.
There is little evidence for any `preferred scale' in the power spectrum or
non-Gaussian behaviour in the distribution of large-scale power.Comment: Latex, uses mn.sty, 14 pages including 11 Postscript figures.
Accepted by MNRA
Bilateral Isokinetic Torque Differences in Trained Swimmers
Please view abstract in the attached PDF file
Conformational Dependence of a Protein Kinase Phosphate Transfer Reaction
Atomic motions and energetics for a phosphate transfer reaction catalyzed by
the cAMP-dependent protein kinase (PKA) are calculated by plane-wave density
functional theory, starting from structures of proteins crystallized in both
the reactant conformation (RC) and the transition-state conformation (TC). In
the TC, we calculate that the reactants and products are nearly isoenergetic
with a 0.2 eV barrier; while phosphate transfer is unfavorable by over 1.2 eV
in the RC, with an even higher barrier. With the protein in the TC, the motions
involved in reaction are small, with only P and the catalytic proton
moving more than 0.5 \AA. Examination of the structures reveals that in the RC
the active site cleft is not completely closed and there is insufficient space
for the phosphorylated serine residue in the product state. Together, these
observations imply that the phosphate transfer reaction occurs rapidly and
reversibly in a particular conformation of the protein, and that the reaction
can be gated by changes of a few tenths of an \AA in the catalytic site.Comment: revtex4, 7 pages, 4 figures, to be submitted to Scienc
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Heavily reddened z ~ 2 Type 1 quasars - II. H α star formation constraints from SINFONI IFU observations
We use near infrared integral field unit (IFU) spectroscopy to search for
H emission associated with star formation in a sample of 28 heavily
reddened (0.5-1.9), hyperluminous
(47-48) broad-line quasars at 1.4-2.7.
Sixteen of the 28 quasars show evidence for star formation with an average
extinction-corrected star formation rate (SFR) of 32070Myr.
A stacked spectrum of the detections shows weak [NII], consistent with star
formation as the origin of the narrow H emission. The star-forming
regions are spatially unresolved in 11 of the 16 detections and constrained to
lie within 6kpc of the quasar emission. In the five resolved detections
we find the star-forming regions are extended on scales of 8kpc around
the quasar emission. The prevalence of high SFRs is consistent with the
identification of the heavily reddened quasar population as representing a
transitional phase from apparent `starburst galaxies' to optically-luminous
quasars. Upper limits are determined for 10 quasars in which star formation is
undetected. In two of the quasars the SFR is constrained to be relatively
modest, 50Myr, but significantly higher levels of star
formation could be present in the other eight quasars. The combination of the
16 strong star formation detections and the eight high SFR limits means that
high levels of star formation may be present in the majority of the sample.
Higher spatial resolution data, of multiple emission lines, will allow us to
better understand the interplay between star formation and Active Galactic
Nucleus (AGN) activity in these transitioning quasars.The authors thank the Science and Technology Facilities Council (STFC) via the Consolidated Grant awarded to the Institute of Astronomy, Cambridge. SA-Z acknowledges the support from Peterhouse, Cambridge, and the Institute of Astronomy, Cambridge. The narrow-band imaging study is based on observations made with ESO Telescopes at the La Sill a Paranal Observatory under programme ID: 290.A-5062. The IFU study is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs:383.A-0573 (PI:McMahon) and 091.A-0341 (PI:Banerji).This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw68
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