6,252 research outputs found
Composition Dependence of Glass Forming Propensity in Al−Ni Alloys
Enormous progress has been made over the past decade in developing bulk amorphous alloys with high strength and other mechanical properties while possessing improved glass forming and processing abilities. Particularly important in developing new systems is identifying the compositions most likely to lead to glass formation. We illustrate here for the Al−Ni system how Molecular Dynamics (MD) using a force field derived from first-principles quantum mechanics (QM) can be used to determine the optimum compositions for glass forming ability (GFA). Using the Two-Phase Thermodynamics (2PT) method to extract entropy and free energy directly from MD, we find that the GFA is closely related to (ΔG_(lc))_(Tg), the Gibbs free energy difference between the liquid state and crystal state at the glass transition temperature T_g. We find that the glass phase is preferred at compositions where (ΔG_(lc))_(Tg) is small and where the equilibrium crystal structure is complex. For the AlNi alloys, our calculations suggest that the best glass-forming composition is 87.5% Al and 12.5% Ni. On the basis of the Honeycutt−Andersen type of local structure analysis of alloys in the liquid state, we propose an atomic scale explanation of GFA. Large GFA arises when there is a great difference in the atom bonding preference between different atom species
Charmless Decays in Factorization-Assisted Topological-Amplitude Approach
Within the factorization-assisted topological-amplitude approach, we studied
the 33 charmless decays, where stands for a light vector
meson. According to the flavor flows, the amplitude of each process can be
decomposed into 8 different topologies. In contrast to the conventional flavor
diagrammatic approach, we further factorize each topological amplitude into
decay constant, form factors and unknown universal parameters. By
fitting 46 experimental observables, we extracted 10 theoretical parameters
with per degree of freedom around 2. Using the fitted parameters, we
calculated the branching fractions, polarization fractions, CP asymmetries and
relative phases between polarization amplitudes of each decay mode. The decay
channels dominated by tree diagram have large branching fractions and large
longitudinal polarization fraction. The branching fractions and longitudinal
polarization fractions of color-suppressed decays become smaller. Current
experimental data of large transverse polarization fractions in the penguin
dominant decay channels can be explained by only one transverse amplitude of
penguin annihilation diagram. Our predictions of those not yet measured
channels can be tested in the ongoing LHCb experiment and the Belle-II
experiment in future.Comment: 22 pages, 2 figure
E-Characteristic Polynomials of Tensors
In this paper, we show that the coefficients of the E-characteristic
polynomial of a tensor are orthonormal invariants of that tensor. When the
dimension is 2, some simplified formulas of the E-characteristic polynomial are
presented. A re- sultant formula for the constant term of the E-characteristic
polynomial is given. We then study the set of tensors with infinitely many
eigenpairs and the set of irregular tensors, and prove both the sets have
codimension 2 as subvarieties in the projective space of tensors. This makes
our perturbation method workable. By using the perturbation method and
exploring the difference between E-eigenvalues and eigenpair equivalence
classes, we present a simple formula for the coefficient of the leading term of
the E-characteristic polynomial, when the dimension is 2
An improved method to determine the mixing
We develop an improved method to explore the mixing which
arises from the flavor SU(3) and heavy quark symmetry breaking. In this method,
the flavor eigenstates under the SU(3) symmetry are at first constructed and
the corresponding masses can be nonperturbatively determined. Matrix elements
of the mass operators which break the flavor SU(3) symmetry sandwiched by the
flavor eigenstates are then calculated. Diagonalizing the corresponding matrix
of Hamiltonian gives the mass eigenstates of the full Hamiltonian and
determines the mixing. Following the previous lattice QCD calculation of
and , and estimating an off-diagonal matrix element, we extract
the mixing angle between the and . Preliminary numerical
results for the mixing angle confirm the previous observation that such mixing
is incapable to explain the large SU(3) symmetry breaking in semileptonic
decays of charmed baryons.Comment: 7 pages, 3 figure
Experimental Test of Quantum Jarzynski Equality with a Trapped Ion System
The past two decades witnessed important developments in the field of
non-equilibrium statistical mechanics. Among these developments, the Jarzynski
equality, being a milestone following the landmark work of Clausius and Kelvin,
stands out. The Jarzynski equality relates the free energy difference between
two equilibrium states and the work done on the system through far from
equilibrium processes. While experimental tests of the equality have been
performed in classical regime, the verification of the quantum Jarzynski
equality has not yet been fully demonstrated due to experimental challenges.
Here, we report an experimental test of the quantum Jarzynski equality with a
single \Yb ion trapped in a harmonic potential. We perform projective
measurements to obtain phonon distributions of the initial thermal state.
Following that we apply the laser induced force on the projected energy
eigenstate, and find transition probabilities to final energy eigenstates after
the work is done. By varying the speed of applying the force from equilibrium
to far-from equilibrium regime, we verified the quantum Jarzynski equality in
an isolated system.Comment: 18 pages, 4 figures, 1 tabl
Quantum phase transition of the two-dimensional Rydberg atom array in an optical cavity
We study the two-dimensional Rydberg atom array in an optical cavity with
help of the meanfield theory and the large-scale quantum Monte Carlo
simulations. The strong dipole-dipole interactions between Rydberg atoms can
make the system exhibit the crystal structure, and the coupling between
two-level atom and cavity photon mode can result in the formation of the
polariton. The interplay between them provides a rich quantum phase diagram
including the Mott, solid-1/2, superradiant and superradiant solid phases. As
the two-order co-existed phase, the superradiant solid phase breaks both
translational and U(1) symmetries. Based on both numerical and analytic
results, we found the region of superradiant solid is much larger than one
dimensional case, so that it can be more easily observed in the experiment.
Finally, we discuss how the energy gap of the Rydberg atom can affect the type
of the quantum phase transition and the number of triple points
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