6,050 research outputs found
A light pseudoscalar in a model with lepton family symmetry O(2)
We discuss a realization of the non-abelian group O(2) as a family symmetry
for the lepton sector. The reflection contained in O(2) acts as a mu-tau
interchange symmetry, enforcing--at tree level--maximal atmospheric neutrino
mixing and a vanishing mixing angle theta_13. The small ratio m_mu/m_tau (muon
over tau mass) gives rise to a suppression factor in the mass of one of the
pseudoscalars of the model. We argue that such a light pseudoscalar does not
violate any experimental constraint.Comment: 20 pages, 2 figures; two footnotes and one reference added, final
version for JHE
Simulator study of the low-speed handling qualities of a supersonic cruise arrow-wing transport configuration during approach and landing
A fixed-based simulator study was conducted to determine the low-speed flight characteristics of an advanced supersonic cruise transport having an arrow wing, a horizontal tail, and four dry turbojets with variable geometry turbines. The primary piloting task was the approach and landing. The statically unstable (longitudinally) subject configuration has unacceptable low-speed handling qualities with no augmentation. Therefore, a hardened stability augmentation system is required to achieve acceptable handling qualities, should the normal operational stability and control augmentation system fail. In order to achieve satisfactory handling qualities, considerable augmentation was required
Ground-based and in-flight simulator studies of low-speed handling characteristics of two supersonic cruise transport concepts
Conventional and powered lift concepts for supersonic approach and landing tasks are considered. Results indicated that the transport concepts had unacceptable low-speed handling qualities with no augmentation, and that in order to achieve satisfactory handling qualities, considerable augmentation was required. The available roll-control power was acceptable for the powered-lift concept
Australopithecus afarensis endocasts suggest ape-like brain organization and prolonged brain growth
Human brains are three times larger, are organized differently, and mature for a longer period of time than those of our closest living relatives, the chimpanzees. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear. To study brain growth and organization in the hominin species Australopithecus afarensis more than 3 million years ago, we scanned eight fossil crania using conventional and synchrotron computed tomography. We inferred key features of brain organization from endocranial imprints and explored the pattern of brain growth by combining new endocranial volume estimates with narrow age at death estimates for two infants. Contrary to previous claims, sulcal imprints reveal an ape-like brain organization and no features derived toward humans. A comparison of infant to adult endocranial volumes indicates protracted brain growth in A. afarensis, likely critical for the evolution of a long period of childhood learning in hominins
Electronic Scattering Effects in Europium-Based Iron Pnictides
In a comprehensive study, we investigate the electronic scattering effects in
EuFe(AsP) by using Fourier-transform infrared
spectroscopy. In spite of the fact that Eu local moments order around
\,K, the overall optical response is strikingly similar
to the one of the well-known Ba-122 pnictides. The main difference lies within
the suppression of the lower spin-density-wave gap feature. By analysing our
spectra with a multi-component model, we find that the high-energy feature
around 0.7\,eV -- often associated with Hund's rule coupling -- is highly
sensitive to the spin-density-wave ordering, this further confirms its direct
relationship to the dynamics of itinerant carriers. The same model is also used
to investigate the in-plane anisotropy of magnetically detwinned
EuFeAs in the antiferromagnetically ordered state, yielding a
higher Drude weight and lower scattering rate along the crystallographic
-axis. Finally, we analyse the development of the room temperature spectra
with isovalent phosphor substitution and highlight changes in the scattering
rate of hole-like carriers induced by a Lifshitz transition
Comparison of T1 mapping techniques for ECV quantification. histological validation and reproducibility of ShMOLLI versus multibreath-hold T1 quantification equilibrium contrast CMR
BACKGROUND: Myocardial extracellular volume (ECV) is elevated in fibrosis or infiltration and can be quantified by measuring the haematocrit with pre and post contrast T1 at sufficient contrast equilibrium. Equilibrium CMR (EQ-CMR), using a bolus-infusion protocol, has been shown to provide robust measurements of ECV using a multibreath-hold T1 pulse sequence. Newer, faster sequences for T1 mapping promise whole heart coverage and improved clinical utility, but have not been validated.
METHODS: Multibreathhold T1 quantification with heart rate correction and single breath-hold T1 mapping using Shortened Modified Look-Locker Inversion recovery (ShMOLLI) were used in equilibrium contrast CMR to generate ECV values and compared in 3 ways.Firstly, both techniques were compared in a spectrum of disease with variable ECV expansion (n=100, 50 healthy volunteers, 12 patients with hypertrophic cardiomyopathy, 18 with severe aortic stenosis, 20 with amyloid). Secondly, both techniques were correlated to human histological collagen volume fraction (CVF%, n=18, severe aortic stenosis biopsies). Thirdly, an assessment of test:retest reproducibility of the 2 CMR techniques was performed 1 week apart in individuals with widely different ECVs (n=10 healthy volunteers, n=7 amyloid patients).
RESULTS: More patients were able to perform ShMOLLI than the multibreath-hold technique (6% unable to breath-hold). ECV calculated by multibreath-hold T1 and ShMOLLI showed strong correlation (r(2)=0.892), little bias (bias -2.2%, 95%CI -8.9% to 4.6%) and good agreement (ICC 0.922, range 0.802 to 0.961, p<0.0001). ECV correlated with histological CVF% by multibreath-hold ECV (r(2)= 0.589) but better by ShMOLLI ECV (r(2)= 0.685). Inter-study reproducibility demonstrated that ShMOLLI ECV trended towards greater reproducibility than the multibreath-hold ECV, although this did not reach statistical significance (95%CI -4.9% to 5.4% versus 95%CI -6.4% to 7.3% respectively, p=0.21).
CONCLUSIONS: ECV quantification by single breath-hold ShMOLLI T1 mapping can measure ECV by EQ-CMR across the spectrum of interstitial expansion. It is procedurally better tolerated, slightly more reproducible and better correlates with histology compared to the older multibreath-hold FLASH techniques
Persistent detwinning of iron pnictides by small magnetic fields
Our comprehensive study on EuFeAs reveals a dramatic reduction of
magnetic detwinning fields compared to other AFeAs (A = Ba, Sr, Ca)
iron pnictides by indirect magneto-elastic coupling of the Eu ions. We
find that only 0.1T are sufficient for persistent detwinning below the local
Eu ordering; above = 19K, higher fields are necessary.
Even after the field is switched off, a significant imbalance of twin domains
remains constant up to the structural and electronic phase transition (190K).
This persistent detwinning provides the unique possibility to study the low
temperature electronic in-plane anisotropy of iron pnictides without applying
any symmetrybreaking external force.Comment: accepted by Physical Review Letter
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How important are future marine and shipping aerosol emissions in a warming Arctic summer and autumn?
Future sea ice retreat in the Arctic in summer and autumn is expected to affect both natural and anthropogenic aerosol emissions: sea ice acts as a barrier between the ocean and the atmosphere, and reducing it increases dimethyl sulfide and sea salt emissions. Additionally, a decrease in the area and thickness of sea ice could lead to enhanced Arctic ship traffic, for example due to shorter routes of cargo ships. Changes in the emissions of aerosol particles can then influence cloud properties, precipitation, surface albedo, and radiation. Next to changes in aerosol emissions, clouds will also be affected by increases in Arctic temperatures and humidities. In this study, we quantify how future aerosol radiative forcings and cloud radiative effects might change in the Arctic in late summer (July–August) and early autumn (September–October).
Simulations were conducted for the years 2004 and 2050 with the global aerosol–climate model ECHAM6-HAM2. For 2050, simulations with and without additional ship emissions in the Arctic were carried out to quantify the impact of these emissions on the Arctic climate.
In the future, sea salt as well as dimethyl sulfide emissions and burdens will increase in the Arctic. The increase in cloud condensation nuclei, which is due to changes in aerosol particles and meteorology, will enhance cloud droplet number concentrations over the Arctic Ocean (+10 % in late summer and +29 % in early autumn; in-cloud values averaged between 75 and 90∘ N). Furthermore, both liquid and total water path will increase (+10 % and +8 % in late summer; +34 % and +26 % in early autumn) since the specific humidity will be enhanced due to higher temperatures and the exposure of the ocean's surface.
Changes in both aerosol radiative forcings and cloud radiative effects at the top of the atmosphere will not be dominated by the aerosol particles and clouds themselves but by the decrease in surface albedo (and by the increase in surface temperature for the longwave cloud radiative effect in early autumn). Mainly due to the reduction in sea ice, the aerosol radiative forcing will become less positive (decreasing from 0.53 to 0.36 W m−2 in late summer and from 0.15 to 0.11 W m−2 in early autumn). The decrease in sea ice is also mainly responsible for changes in the net cloud radiative effect, which will become more negative in late summer (changing from −36 to −46 W m−2). Therefore, the cooling component of both aerosols and clouds will gain importance in the future.
We found that future Arctic ship emissions related to transport and oil and gas extraction (Peters et al., 2011) will not have a large impact on clouds and radiation: changes in aerosols only become significant when we increase these ship emissions by a factor of 10. However, even with 10-fold ship emissions, the net aerosol radiative forcing shows no significant changes. Enhanced black carbon deposition on snow leads to a locally significant but very small increase in radiative forcing over the central Arctic Ocean in early autumn (no significant increase for average between 75 and 90∘ N). Furthermore, the 10-fold higher ship emissions increase the optical thickness and lifetime of clouds in late summer (net cloud radiative effect changing from −48 to −52 W m−2). These aerosol–cloud effects have a considerably larger influence on the radiative forcing than the direct effects of particles (both aerosol particles in the atmosphere and particles deposited on snow). In summary, future ship emissions of aerosols and their precursor gases might have a net cooling effect, which is small compared to other changes in future Arctic climate such as those caused by the decrease in surface albedo
J/\Psi production, polarization and Color Fluctuations
The hard contributions to the heavy quarkonium-nucleon cross sections are
calculated based on the QCD factorization theorem and the nonrelativistic
quarkonium model. We evaluate the nonperturbative part of these cross sections
which dominates at GeV at the Cern Super Proton
Synchrotron (SPS) and becomes a correction at TeV at
the CERN Large Hadron Collider (LHC). \J production at the CERN SPS is well
described by hard QCD, when the larger absorption cross sections of the
states predicted by QCD are taken into account. We predict an -dependent
polarization of the states. The expansion of small wave packets is
discussed.Comment: 13 pages REVTEX, 1 table, 2 PostScript, corrected some typo
Charmonium suppression from purely geometrical effects
The extend to which geometrical effects contribute to the production and
suppression of the and minijet pairs in general is
investigated for high energy heavy ion collisions at SPS, RHIC and LHC
energies. For the energy range under investigation, the geometrical effects
referred to are shadowing and anti-shadowing, respectively. Due to those
effects, the parton distributions in nuclei deviate from the naive
extrapolation from the free nucleon result; . The strength
of the shadowing/anti-shadowing effect increases with the mass number. The
consequences of gluonic shadowing effects for the distribution of
's at GeV, GeV and TeV are
calculated for some relevant combinations of nuclei, as well as the
distribution of minijets at midrapidity for in the final state.Comment: corrected some typos, improved shadowing ratio
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