10,056 research outputs found
Forward-backward asymmetry of photoemission in C excited by few-cycle laser pulses
We theoretically analyze angle-resolved photo-electron spectra (ARPES)
generated by the interaction of C with intense, short laser pulses. In
particular, we focus on the impact of the carrier-envelope phase (CEP) onto the
angular distribution. The electronic dynamics is described by time-dependent
density functional theory, and the ionic background of \csixty is
approximated by a particularly designed jellium model. Our results show a clear
dependence of the angular distributions onto the CEP for very short pulses
covering only very few laser cycles, which disappears for longer pulses. For
the specific laser parameters used in a recent experiments, a very good
agreement is obtained. Furthermore, the asymmetry is found to depend on the
energy of the emitted photoelectrons. The strong influence of the angular
asymmetry of electron emission onto the CEP and pulse duration suggests to use
this sensitivity as a means to analyze the structure of few-cycle laser pulses.Comment: 8 pages, 6 figure
Lexical Derivation of the PINT Taxonomy of Goals: Prominence, Inclusiveness, Negativity Prevention, and Tradition
What do people want? Few questions are more fundamental to psychological science than this. Yet, existing taxonomies disagree on both the number and content of goals. We thus adopted a lexical approach and investigated the structure of goal-relevant words from the natural English lexicon. Through an intensive rating process, 1,060 goal-relevant English words were first located. In Studies 1-2, two relatively large and diverse samples (total n = 1,026) rated their commitment to approaching or avoiding these goals. Principal component analyses yielded 4 replicable components: Prominence, Inclusiveness, Negativity prevention, and Tradition (the PINT Taxonomy). Study 3-7 (total n = 1,396) supported the 4-factor structure of an abbreviated scale and found systematic differences in their relationships with past goal-content measures, the Big 5 traits, affect, and need satisfaction. This investigation thus provides a data-driven taxonomy of higher-order goal-content and opens up a wide variety of fascinating lines for future research
Interaction between self-excited oscillations and fuel-air mixing in a dual swirl combustor
A partially premixed gas turbine model combustor close to an industrial design is investigated using Large Eddy Simulation (LES). Two flames, one stable and another unstable with self-excited oscillations are computed. In particular, this study addresses the previously unexplained transition of flame shape in the experiments, from V-shaped to flat when the flame becomes acoustically unstable, suggesting a notable change of the important convective delay in the thermoacoustic feedback loop. The LES results show good agreement with the measured velocities, temperature and mass fractions. The acoustic power spectral density (PSD) obtained from the LES of the unstable flame also agrees well with the measured amplitudes in the air plenum and combustion chamber, and reasonably captures the frequency with a slight under-prediction. A comparison of the stable and unstable cases shows different mixing and reaction behaviours despite similar mean velocity fields. Further detailed analysis shows that the different mixing behaviour is driven by the significantly varying air mass split between the two air passages during a thermoacoustic oscillation cycle. This variation is due to the different impedances experienced by the pressure oscillations propagating through the two swirling injector passages with different internal geometries. This causes a periodic variation of the radial momentum of the fuel jets injected between the two swirling air flows. The resulting flapping of the fuel jets creates an enhanced radial fuel-air mixing that leads to a flattened flame in the unstable case. This provides a new physical explanation for the transitions of flame shape observed in the experiments.ZXC and NS acknowledge the support of Mitsubishi Heavy Industries, Japan. This work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) with the computational time provided by the UKCTRF
Multi-Transition Study of M51's Molecular Gas Spiral Arms
Two selected regions in the molecular gas spiral arms in M51 were mapped with
the Owens Valley Radio Observatory (OVRO) mm-interferometer in the 12CO(2-1),
13CO(1-0), C18O(1-0), HCN(1-0) and HCO+(1-0) emission lines. The CO data have
been combined with the 12CO(1-0) data from Aalto et al. (1999) covering the
central 3.5kpc to study the physical properties of the molecular gas. All CO
data cubes were short spacing corrected using IRAM 30m (12CO(1-0): NRO 45m)
single dish data. A large velocity gradient (LVG) analysis finds that the giant
molecular clouds (GMCs) are similar to Galactic GMCs when studied at 180pc
(120pc) resolution with an average kinetic temperature of T_kin = 20(16)K and
H_2 density of n(H_2) = 120(240)cm^(-3) when assuming virialized clouds (a
constant velocity gradient dv/dr. The associated conversion factor between H_2
mass and CO luminosity is close to the Galactic value for most regions
analyzed. Our findings suggest that the GMC population in the spiral arms of
M51 is similar to those of the Milky Way and therefore the strong star
formation occurring in the spiral arms has no strong impact on the molecular
gas in the spiral arms. Extinction inferred from the derived H_2 column density
is very high (A_V about 15 - 30 mag), about a factor of 5-10 higher than the
average value derived toward HII regions. Thus a significant fraction of the
ongoing star formation could be hidden inside the dust lanes of the spiral
arms. A comparison of MIPS 24um and H_alpha data, however, suggests that this
is not the case and most of the GMCs studied here are not (yet) forming stars.
We also present low (4.5") resolution OVRO maps of the HCN(1-0) and HCO+(1-0)
emission at the location of the brightest 12CO(1-0) peak.Comment: 41 pages, 12 figures, 7 tables; accepted for publication by Ap
Electronic bulk and domain wall properties in B-site doped hexagonal ErMnO
Acceptor and donor doping is a standard for tailoring semiconductors. More
recently, doping was adapted to optimize the behavior at ferroelectric domain
walls. In contrast to more than a century of research on semiconductors, the
impact of chemical substitutions on the local electronic response at domain
walls is largely unexplored. Here, the hexagonal manganite ErMnO is donor
doped with Ti. Density functional theory calculations show that
Ti goes to the B-site, replacing Mn. Scanning probe microscopy
measurements confirm the robustness of the ferroelectric domain template. The
electronic transport at both macro- and nanoscopic length scales is
characterized. The measurements demonstrate the intrinsic nature of emergent
domain wall currents and point towards Poole-Frenkel conductance as the
dominant transport mechanism. Aside from the new insight into the electronic
properties of hexagonal manganites, B-site doping adds an additional degree of
freedom for tuning the domain wall functionality
Effect of electron-electron scattering on spin dephasing in a high-mobility low-density twodimensional electron gas
Utilizing time-resolved Kerr rotation techniques, we have investigated the
spin dynamics of a high mobility, low density two dimensional electron gas in a
GaAs/Al0:35Ga0:65As heterostructure in dependence on temperature from 1.5 K to
30 K. It is found that the spin relaxation/dephasing time under a magnetic
field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an
increasing background with rising temperature. The appearance of the maximum is
ascribed to that at the temperature where the crossover from the degenerate to
the nondegenerate regime takes place, electron-electron Coulomb scattering
becomes strongest, and thus inhomogeneous precession broadening due to
D'yakonov-Perel'(DP) mechanism becomes weakest. These results agree with the
recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying
the importance of electron-electron Coulomb scattering to electron spin
relaxation/dephasing.Comment: 4 pages, 2 figure
Comment on “Intra-abdominal Hypertension and Abdominal Compartment Syndrome after Endovascular Repair of Ruptured Abdominal Aortic Aneurysm”
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