14,101 research outputs found
Time-dependent coupled-cluster method for atomic nuclei
We study time-dependent coupled-cluster theory in the framework of nuclear
physics. Based on Kvaal's bi-variational formulation of this method [S. Kvaal,
arXiv:1201.5548], we explicitly demonstrate that observables that commute with
the Hamiltonian are conserved under time evolution. We explore the role of the
energy and of the similarity-transformed Hamiltonian under real and imaginary
time evolution and relate the latter to similarity renormalization group
transformations. Proof-of-principle computations of He-4 and O-16 in small
model spaces, and computations of the Lipkin model illustrate the capabilities
of the method.Comment: 10 pages, 9 pdf figure
Extended nonlocal chiral-quark model for the heavy-light quark systems
In this talk, we report the recent progress on constructing a
phenomenological effective model for the heavy-light quark systems, which
consist of (u,d,s,c,b) quarks, i.e. extended nonlocal chiral-quark model
(ExNLChQM). We compute the heavy-meson weak-decay constants to verify the
validity of the model. From the numerical results, it turns out that (f_D, f_B,
f_{D_s}, f_{B_s})=(207.54,208.13,262.56,262.39) MeV. These values are in
relatively good agreement with experimental data and various theoretical
estimations.Comment: 3 pages, 4 figures, Talk given at the 20th International IUPAP
Conference on Few-Body Problems in Physics (FB20), 20~25 August 2012,
Fukuoka, Japa
Free Energy Approach to the Formation of an Icosahedral Structure during the Freezing of Gold Nanoclusters
The freezing of metal nanoclusters such as gold, silver, and copper exhibits
a novel structural evolution. The formation of the icosahedral (Ih) structure
is dominant despite its energetic metastability. This important phenomenon,
hitherto not understood, is studied by calculating free energies of gold
nanoclusters. The structural transition barriers have been determined by using
the umbrella sampling technique combined with molecular dynamics simulations.
Our calculations show that the formation of Ih gold nanoclusters is attributed
to the lower free energy barrier from the liquid to the Ih phases compared to
the barrier from the liquid to the face-centered-cubic crystal phases
Ultrafast vectorial and scalar dynamics of ionic clusters: Azobenzene solvated by oxygen
The ultrafast dynamics of clusters of trans-azobenzene anion (A–) solvated by oxygen molecules was investigated using femtosecond time-resolved photoelectron spectroscopy. The time scale for stripping off all oxygen molecules from A– was determined by monitoring in real time the transient of the A– rise, following an 800 nm excitation of A– (O2)n, where n=1–4. A careful analysis of the time-dependent photoelectron spectra strongly suggests that for n>1 a quasi-O4 core is formed and that the dissociation occurs by a bond cleavage between A– and conglomerated (O2)n rather than a stepwise evaporation of O2. With time and energy resolutions, we were able to capture the photoelectron signatures of transient species which instantaneously rise (2- for A–O2 and A·O4-·(O2)n–2 for A–(O2)n, where n=2–4. Subsequent to an ultrafast electron recombination, A– rises with two distinct time scales: a subpicosecond component reflecting a direct bond rupture of the A–-(O2)n nuclear coordinate and a slower component (1.6–36 ps, increasing with n) attributed to an indirect channel exhibiting a quasistatistical behavior. The photodetachment transients exhibit a change in the transition dipole direction as a function of time delay. Rotational dephasing occurs on a time scale of 2–3 ps, with a change in the sign of the transient anisotropy between A–O2 and the larger clusters. This behavior is a key indicator of an evolving cluster structure and is successfully modeled by calculations based on the structures and inertial motion of the parent clusters
Propagation of Exchange Bias in CoFe/FeMn/CoFe Trilayers
CoFe/FeMn, FeMn/CoFe bilayers and CoFe/FeMn/CoFe trilayers were grown in
magnetic field and at room temperature. The exchange bias field
depends strongly on the order of depositions and is much higher at CoFe/FeMn
than at FeMn/CoFe interfaces. By combining the two bilayer structures into
symmetric CoFe/FeMn()/CoFe trilayers, and
of the top and bottom CoFe layers, respectively, are both enhanced.
Reducing of the trilayers also results in enhancements of
both and . These results evidence the propagation of
exchange bias between the two CoFe/FeMn and FeMn/CoFe interfaces mediated by
the FeMn antiferromagnetic order
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