837 research outputs found
Direct evidence for charge stripes in a layered cobalt oxide
Recent experiments indicate that static stripe-like charge order is generic to the hole-doped copper oxide superconductors and competes with superconductivity. Here we show that a similar type of charge order is present in La5/3 Sr1/3 CoO4 , an insulating analogue of the copper oxide superconductors containing cobalt in place of copper. The stripe phase we have detected is accompanied by short-range, quasi-one-dimensional, antiferromagnetic order, and provides a natural explanation for the distinctive hour- glass shape of the magnetic spectrum previously observed in neutron scattering mea- surements of La2−xSrx CoO4 and many hole-doped copper oxide superconductors. The results establish a solid empirical basis for theories of the hourglass spectrum built on short-range, quasi-static, stripe correlations
Upper limits for a narrow resonance in the reaction p + p -> K^+ + (Lambda p)
The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and
\Theta = 0 deg with a high missing mass resolution in order to study the Lambda
p final state interaction. Narrow S = -1 resonances predicted by bag model
calculations are not visible in the missing mass spectrum. Small structures
observed in a previous experiment are not confirmed. Upper limits for the
production cross section of a narrow resonance are deduced for missing masses
between 2058 and 2105 MeV/c^2.Comment: 8 pages, 5 figure
Major components of atmospheric organic aerosol in southern California as determined by hourly measurements of source marker compounds
We report the first hourly in-situ measurements of speciated organic aerosol
(OA) composition in an urban environment. Field measurements were made in
southern California at the University of California–Riverside during the
2005 Study of Organic Aerosol at Riverside (SOAR), which included two
separate measurement periods: a summer study (15 July–15 August) and a
fall study (31 October–28 November). Hourly measurements of over 300
semivolatile and nonvolatile organic compounds were made using the thermal
desorption aerosol gas chromatograph (TAG). Positive matrix factorization
(PMF) was performed on a subset of these compounds to identify major
components contributing to submicron (i.e., PM<sub>1</sub>) OA at the site, as
measured by an aerosol mass spectrometer (AMS). PMF analysis was performed
on an 11-day focus period in each season, representing average seasonal
conditions during the summer and a period of urban influence during the
fall. As a result of this analysis, we identify multiple types of primary
and secondary OA (POA and SOA). Secondary sources contribute substantially
to fine OA mass at Riverside, which commonly receives regional air masses
that pass through metropolitan Los Angeles during the summer. Four
individual summertime SOA components are defined, and when combined, they
are estimated to contribute an average 88% of the total fine OA mass
during summer afternoons according to PMF results. These sources appear to
be mostly from the oxidation of anthropogenic precursor gases, with one SOA
component having contributions from oxygenated biogenics. During the fall,
three out of four aerosol components that contain SOA are inseparable from
covarying primary emissions, and therefore we cannot estimate the fraction
of total OA that is secondary in nature during the fall study. Identified
primary OA components are attributed to vehicle emissions, food cooking,
primary biogenics, and biomass burning aerosol. While a distinction between
local and regional vehicle emissions is made, a combination of these two
factors accounted for approximately 11% of observed submicron OA during
both sampling periods. Food cooking operations contributed ~10% of
submicron OA mass during the summer, but was not separable from SOA during
the fall due to high covariance of sources. Biomass burning aerosol
contributed a larger fraction of fine OA mass during the fall (~11%) than compared to summer (~7%). Primary biogenic aerosol
was also identified during the summer, contributing ~1% of the OA,
but not during the fall. While the contribution of both local and regional
primary vehicle OA accounts for only ~11% of total OA during both
seasons, gas-phase vehicle emissions likely create a substantial fraction of
the observed SOA as a result of atmospheric processing
Genome-Wide and Functional Annotation of Human E3 Ubiquitin Ligases Identifies MULAN, a Mitochondrial E3 that Regulates the Organelle's Dynamics and Signaling
Specificity of protein ubiquitylation is conferred by E3 ubiquitin (Ub) ligases. We have annotated ∼617 putative E3s and substrate-recognition subunits of E3 complexes encoded in the human genome. The limited knowledge of the function of members of the large E3 superfamily prompted us to generate genome-wide E3 cDNA and RNAi expression libraries designed for functional screening. An imaging-based screen using these libraries to identify E3s that regulate mitochondrial dynamics uncovered MULAN/FLJ12875, a RING finger protein whose ectopic expression and knockdown both interfered with mitochondrial trafficking and morphology. We found that MULAN is a mitochondrial protein – two transmembrane domains mediate its localization to the organelle's outer membrane. MULAN is oriented such that its E3-active, C-terminal RING finger is exposed to the cytosol, where it has access to other components of the Ub system. Both an intact RING finger and the correct subcellular localization were required for regulation of mitochondrial dynamics, suggesting that MULAN's downstream effectors are proteins that are either integral to, or associated with, mitochondria and that become modified with Ub. Interestingly, MULAN had previously been identified as an activator of NF-κB, thus providing a link between mitochondrial dynamics and mitochondria-to-nucleus signaling. These findings suggest the existence of a new, Ub-mediated mechanism responsible for integration of mitochondria into the cellular environment
Electromechanically active pair dynamics in a Gd-doped ceria single crystal
Oxygen-defective ceria, e.g. Gd-doped ceria, shows giant electromechanical properties related to a complex local rearrangement of its lattice. Although they are not entirely identified, the electroactive mechanisms arise from cation and oxygen vacancy (V-O) pairs (i.e. Ce-V-O), and the local structural elastic distortion in their surroundings. Here, we study the geometry and behaviour of Ce-V-O pairs in a grain boundary-free bulk Ce0.9Gd0.1O1.95 single crystal under an AC electric field of ca. 11 kV cm(-1). The analysis was carried out through X-ray absorption spectroscopy (XAS) techniques at the Ce L-III edge. Using Density Functional Theory (DFT) calculations, we investigated the effects of the strain on density of states and orbitals at the valence band edge. Our research indicates that electrostriction increases at low temperatures. The electromechanical strain has a structural nature and can rise by one order of magnitude, i.e., from 5 x 10(-4) at room temperature to 5 x 10(-3) at -193 degrees C, due to an increase in the population of the electrically active pairs. At a constant V-O concentration, the material can thus configure heterogeneous pairs and elastic nanodomains that are either mechanically responsive or not
Dynamics of the near threshold eta meson production in proton-proton interaction
We present the results of measurements of the analysing power for the p(pol)p
--> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret
these results within the framework of the meson exchange models. The determined
values of the analysing power at both excess energies are consistent with zero
implying that the eta meson is produced predominantly in s-wave.Comment: 3 pages, 3 figures, Presented at the Workshop on the physics of
excited nucleons (NSTAR 2007), 5-8 September 2007, Bonn, German
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