2,452 research outputs found
Structural and dynamical heterogeneities in two-dimensional melting
Using molecular dynamics simulation, we study structural and dynamical
heterogeneities at melting in two-dimensional one-component systems with 36000
particles. Between crystal and liquid we find intermediate hexatic states,
where the density fluctuations are enhanced at small wave number k as well as
those of the six-fold orientational order parameter. Their structure factors
both grow up to the smallest wave number equal to the inverse system length.
The intermediate scattering function of the density S(k,t) is found to relax
exponentially with decay rate Gamma_k ~ k^z with z~2.6 at small k in the
hexatic phase.Comment: 6 pages, 8 figure
Quantum Corrals, Eigenmodes and Quantum Mirages in s-wave Superconductors
We study the electronic structure of magnetic and non-magnetic quantum
corrals embedded in s-wave superconductors. We demonstrate that a quantum
mirage of an impurity bound state peak can be projected from the occupied into
the empty focus of a non-magnetic quantum corral via the excitation of the
corral's eigenmodes. We observe an enhanced coupling between magnetic
impurities inside the corral, which can be varied through oscillations in the
corral's impurity potential. Finally, we discuss the form of eigenmodes in
magnetic quantum corrals.Comment: 4 pages, 4 figure
Plastic flow in polycrystal states in a binary mixture
Using molecular dynamics simulation we examine dynamics in sheared
polycrystal states in a binary mixture containing 10% larger particles in two
dimensions. We find large stress fluctuations arising from sliding motions of
the particles at the grain boundaries, which occur cooperatively to release the
elastic energy stored. These dynamic processes are visualized with the aid of a
sixfold angle representing the local crystal orientation and a
disorder variable representing a deviation from the hexagonal order
for particle .Comment: 3 pages, 3 figure
Binding of holons and spinons in the one-dimensional anisotropic t-J model
We study the binding of a holon and a spinon in the one-dimensional
anisotropic t-J model using a Bethe-Salpeter equation approach, exact
diagonalization, and density matrix renormalization group methods on chains of
up to 128 sites. We find that holon-spinon binding changes dramatically as a
function of anisotropy parameter \alpha=J_\perp/J_z: it evolves from an exactly
deducible impurity-like result in the Ising limit to an exponentially shallow
bound state near the isotropic case. A remarkable agreement between the theory
and numerical results suggests that such a change is controlled by the
corresponding evolution of the spinon energy spectrum.Comment: 4 pages, 5 figures, published versio
spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models
The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site
complete graph extended with on-site repulsion is obtained from the underlying
spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic
ground state is realized for 1 and N+1 electrons only. We identify the large
density of states to be responsible for the suppression of the ferromagnetic
state and argue that a similar situation is encountered in the Kagome,
pyrochlore, and other lattices with flat bands in their one-particle density of
states.Comment: 7 pages, 1 figur
Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-d interfaces
We have studied quasiparticle tunneling into atomically flat a-axis films of
YBa2Cu3O7-d and DyBa2Cu3O7-d through epitaxial CaTiO3 barriers. The junction
heterostructures were grown by oxide molecular beam epitaxy and were carefully
optimized using in-situ monitoring techniques, resulting in unprecedented
crystalline perfection of the superconductor/insulator interface. Below Tc, the
tunneling conductance shows the evolution of a large unexpected asymmetrical
feature near zero bias. This is evidence that superconducting YBCO crystals,
atomically truncated along the lobe direction with a titanate layer, have
intrinsically broken particle-hole symmetry over macroscopically large areas.Comment: 15 pages, 4 figures; v2 includes minor changes in concluding
paragraph to match PRL versio
The Development of Low Activation Ferritic Steels for Fusion Application
The development of low-activation ferritic/martensitic steels is a key to the achievement of nuclear fusion as a safe, environmentally attractive and economically competitive energy source. The Japanese and the European Fusion Materials programs have put low-activation ferritic and martensitic steels R & D at the highest priority for a demonstration reactor (DEMO) and the beyond. An international collaborative test program on low-activation ferritic/martensitic steels for fusion is in progress as an activity of the International Energy Agency (IEA) fusion materials working group to verify the feasibility of using ferritic/martensitic steels for fusion by an extensive test program covering the most relevant technical issues for the qualification of a material for a nuclear application. The development of a comprehensive data base on the representative industrially processed reduced-activation steels of type 8-9Cr-2WVTa is underway for providing designers a preliminary set of material data for the mechanical design of components, e.g. for DEMO relevant blanket modules. The current design status of FFHR and SSTR utilizing low-activation ferritic steels is reviewed and future prospects are defined
Evidence of Strong Correlation between Instanton and QCD-monopole on SU(2) Lattice
The correlation between instantons and QCD-monopoles is studied both in the
lattice gauge theory and in the continuum theory. An analytical study in the
Polyakov-like gauge, where is diagonalized, shows that the
QCD-monopole trajectory penetrates the center of each instanton, and becomes
complicated in the multi-instanton system. Using the SU(2) lattice with ,
the instanton number is measured in the singular (monopole-dominating) and
regular (photon-dominating) parts, respectively. The monopole dominance for the
topological charge is found both in the maximally abelian gauge and in the
Polyakov gauge.Comment: 4 pages, Latex, 3 figures. Talk presented by H. Suganuma at
International Symposium on 'Lattice Field Theory', July 11 - 15, 1995,
Melbourne, Australi
Near-Ultraviolet and Visible Spectroscopy of HAYABUSA Spacecraft Re-entry
HAYABUSA is the first spacecraft ever to land on and lift off from any
celestial body other than the moon. The mission, which returned asteroid
samples to the Earth while overcoming various technical hurdles, ended on June
13, 2010, with the planned atmospheric re-entry. In order to safely deliver the
sample return capsule, the HAYABUSA spacecraft ended its 7-year journey in a
brilliant "artificial fireball" over the Australian desert. Spectroscopic
observation was carried out in the near-ultraviolet and visible wavelengths
between 3000 and 7500 \AA at 3 - 20 \AA resolution. Approximately 100 atomic
lines such as Fe I, Mg I, Na I, Al I, Cr I, Mn I, Ni I, Ti I, Li I, Zn I, O I,
and N I were identified from the spacecraft. Exotic atoms such as Cu I, Mo I,
Xe I and Hg I were also detected. A strong Li I line (6708 \AA) at a height of
~55 km originated from the onboard Li-Ion batteries. The FeO molecule bands at
a height of ~63 km were probably formed in the wake of the spacecraft. The
effective excitation temperature as determined from the atomic lines varied
from 4500 K to 6000 K. The observed number density of Fe I was about 10 times
more abundant than Mg I after the spacecraft explosion. N2+(1-) bands from a
shock layer and CN violet bands from the sample return capsule's ablating heat
shield were dominant molecular bands in the near-ultraviolet region of 3000 -
4000 \AA. OH(A-X) band was likely to exist around 3092 \AA. A strong shock
layer from the HAYABUSA spacecraft was rapidly formed at heights between 93 km
and 83 km, which was confirmed by detection of N2+(1-) bands with a vibration
temperature of ~13000 K. Gray-body temperature of the capsule at a height of
~42 km was estimated to be ~2437 K which is matched to a theoretical
prediction. The final message of the HAYABUSA spacecraft and its sample return
capsule are discussed through our spectroscopy.Comment: Accepted for publication in PASJ, 22 pages, 7 figures, 6 table
Plastic deformations in crystal, polycrystal, and glass in binary mixtures under shear: Collective yielding
Using molecular dynamics simulation, we examine the dynamics of crystal,
polycrystal, and glass in a Lennard-Jones binary mixture composed of small and
large particles in two dimensions. The crossovers occur among these states as
the composition c is varied at fixed size ratio. Shear is applied to a system
of 9000 particles in contact with moving boundary layers composed of 1800
particles. The particle configurations are visualized with a sixfold
orientation angle alpha_j(t) and a disorder variable D_j(t) defined for
particle j, where the latter represents the deviation from hexagonal order.
Fundamental plastic elements are classified into dislocation gliding and grain
boundary sliding. At any c, large-scale yielding events occur on the acoustic
time scale. Moreover, they multiply occur in narrow fragile areas, forming
shear bands. The dynamics of plastic flow is highly hierarchical with a wide
range of time scales for slow shearing. We also clarify the relationship
between the shear stress averaged in the bulk region and the wall stress
applied at the boundaries.Comment: 17 pages, 15 figures, to appear in Physical Review
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