5,980 research outputs found
Violation and persistence of the K-quantum number in warm rotating nuclei
The validity of the K-quantum number in rapidly rotating warm nuclei is
investigated as a function of thermal excitation energy U and angular momentum
I, for the rare-earth nucleus 163Er. The quantal eigenstates are described with
a shell model which combines a cranked Nilsson mean-field and a residual
two-body interaction, together with a term which takes into account the angular
momentum carried by the K-quantum number in an approximate way. K-mixing is
produced by the interplay of the Coriolis interaction and the residual
interaction; it is weak in the region of the discrete rotational bands (U
\lesim 1MeV), but it gradually increases until the limit of complete violation
of the K-quantum number is approached around U \sim 2 - 2.5 MeV. The calculated
matrix elements between bands having different K-quantum numbers decrease
exponentially as a function of , in qualitative agreement with recent
data.Comment: 29 pages, 7 figure
Computing in String Field Theory Using the Moyal Star Product
Using the Moyal star product, we define open bosonic string field theory
carefully, with a cutoff, for any number of string oscillators and any
oscillator frequencies. Through detailed computations, such as Neumann
coefficients for all string vertices, we show that the Moyal star product is
all that is needed to give a precise definition of string field theory. The
formulation of the theory as well as the computation techniques are
considerably simpler in the Moyal formulation. After identifying a monoid
algebra as a fundamental mathematical structure in string field theory, we use
it as a tool to compute with ease the field configurations for wedge, sliver,
and generalized projectors, as well as all the string interaction vertices for
perturbative as well as monoid-type nonperturbative states. Finally, in the
context of VSFT we analyze the small fluctuations around any D-brane vacuum. We
show quite generally that to obtain nontrivial mass and coupling, as well as a
closed strings, there must be an associativity anomaly. We identify the
detailed source of the anomaly, but leave its study for future work.Comment: 77 pages, LaTeX. v3: corrections of signs or factors (for a list of
corrections see beginning of source file
Effect of humidity on transonic flow
An experimental investigation of the effects of humidity-induced condensation on shock/boundary-layer
interaction has been conducted in a transonic wind-tunnel test. The test geometry considered was a wall-mounted
bump model inserted in the test section of the wind tunnel. The formation of a λ-shape condensation shock wave was
shown from schlieren visualization and resulted in a forward movement of the shock wave, reduced shock wave
strength, and reduced separation. Empirical correlations of the shock wave strength and humidity/dew point
temperature were established. For humidity levels below 0.15 or a dew point temperature of 268 K, the effect of
humidity was negligible. The unsteady pressure measurements showed that if a condensation shock wave formed and
interacted with a main shock wave, the flow becomes unsteady with periodic flow oscillations occurring at 720 Hz
Microscopic approach to large-amplitude deformation dynamics with local QRPA inertial masses
We have developed a new method for determining microscopically the
fivedimensional quadrupole collective Hamiltonian, on the basis of the
adiabatic self-consistent collective coordinate method. This method consists of
the constrained Hartree-Fock-Bogoliubov (HFB) equation and the local QRPA
(LQRPA) equations, which are an extension of the usual QRPA (quasiparticle
random phase approximation) to non-HFB-equilibrium points, on top of the CHFB
states. One of the advantages of our method is that the inertial functions
calculated with this method contain the contributions of the time-odd
components of the mean field, which are ignored in the widely-used cranking
formula. We illustrate usefulness of our method by applying to oblate-prolate
shape coexistence in 72Kr and shape phase transition in neutron-rich Cr
isotopes around N=40.Comment: 6pages, talk given at Rutherford Centennial Conference on Nuclear
Physics, 8 - 12 August 2011, The University of Mancheste
Shell Model for Warm Rotating Nuclei
In order to provide a microscopic description of levels and E2 transitions in
rapidly rotating nuclei with internal excitation energy up to a few MeV, use is
made of a shell model which combines the cranked Nilsson mean-field and the
residual surface delta two-body force. The damping of collective rotational
motion is investigated in the case of a typical rare-earth nucleus, namely \Yb.
It is found that rotational damping sets in at around 0.8 MeV above the yrast
line, and the levels which form rotational band structures are thus limited. We
predict at a given rotational frequency existence of about 30 rotational bands
of various lengths, in overall agreement with the experimental findings. The
onset of the rotational damping proceeds quite gradually as a function of the
internal excitation energy. The transition region extends up to around 2 MeV
above yrast and it is characterized by the presence of scars of discrete
rotational bands which extend over few spin values and stand out among the
damped transitions, and by a two-component profile in the
correlation. The important role played by the high-multipole components of the
two-body residual interaction is emphasized.Comment: 28 pages, LaTe
Estimation of Continental-Basin-Scale Sublimation in the Lena River Basin, Siberia
The Lena River basin in Siberia produces one of the largest river inflows into the Arctic Ocean. One of the most important sources of runoff to the river is spring snowmelt and therefore snow ablation processes have great importance for this basin. In this study, we simulated these processes with fine resolution at basin scale using MicroMet/SnowModel and SnowAssim. To assimilate snow water equivalent (SWE) data in SnowAssim, we used routine daily snow depth data and Sturmâs method. Following the verification of this method for SWE estimation in the basin, we evaluated the impact of snow data assimilation on basin-scale snow ablation. Through validation against MODIS snow coverage data and in situ snow survey observations, we found that SnowAssim could not improve on the original simulation by MicroMet/SnowModel because of estimation errors within the SWE data. Vegetation and accumulated snowfall control the spatial distribution of sublimation and we established that sublimation has an important effect on snow ablation. We found that the ratio of sublimation to snowfall in forests was around 26% and that interannual variation of sublimation modulated spring river runoff
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