14,104 research outputs found
Precision Spectroscopy of Molecular Hydrogen Ions: Towards Frequency Metrology of Particle Masses
We describe the current status of high-precision ab initio calculations of
the spectra of molecular hydrogen ions (H_2^+ and HD^+) and of two experiments
for vibrational spectroscopy. The perspectives for a comparison between theory
and experiment at a level of 1 ppb are considered.Comment: 26 pages, 13 figures, 1 table, to appear in "Precision Physics of
Simple Atomic Systems", Lecture Notes in Physics, Springer, 200
Stable marriage and roommates problems with restricted edges: complexity and approximability
In the Stable Marriage and Roommates problems, a set of agents is given, each of them having a strictly ordered preference list over some or all of the other agents. A matching is a set of disjoint pairs of mutually acceptable agents. If any two agents mutually prefer each other to their partner, then they block the matching, otherwise, the matching is said to be stable. We investigate the complexity of finding a solution satisfying additional constraints on restricted pairs of agents. Restricted pairs can be either forced or forbidden. A stable solution must contain all of the forced pairs, while it must contain none of the forbidden pairs.
Dias et al. (2003) gave a polynomial-time algorithm to decide whether such a solution exists in the presence of restricted edges. If the answer is no, one might look for a solution close to optimal. Since optimality in this context means that the matching is stable and satisfies all constraints on restricted pairs, there are two ways of relaxing the constraints by permitting a solution to: (1) be blocked by as few as possible pairs, or (2) violate as few as possible constraints n restricted pairs.
Our main theorems prove that for the (bipartite) Stable Marriage problem, case (1) leads to View the MathML source-hardness and inapproximability results, whilst case (2) can be solved in polynomial time. For non-bipartite Stable Roommates instances, case (2) yields an View the MathML source-hard but (under some cardinality assumptions) 2-approximable problem. In the case of View the MathML source-hard problems, we also discuss polynomially solvable special cases, arising from restrictions on the lengths of the preference lists, or upper bounds on the numbers of restricted pairs
Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state
In this work, a self-consistent thermodynamic approach to micromagnetism is
presented. The magnetic degrees of freedom are modeled using the
Landau-Lifshitz-Baryakhtar theory, that separates the different contributions
to the magnetic damping, and thereby allows them to be coupled to the electron
and phonon systems in a self-consistent way. We show that this model can
quantitatively reproduce ultrafast magnetization dynamics in Nickel.Comment: 5 pages, 3 figure
Modeling Stable Matching Problems with Answer Set Programming
The Stable Marriage Problem (SMP) is a well-known matching problem first
introduced and solved by Gale and Shapley (1962). Several variants and
extensions to this problem have since been investigated to cover a wider set of
applications. Each time a new variant is considered, however, a new algorithm
needs to be developed and implemented. As an alternative, in this paper we
propose an encoding of the SMP using Answer Set Programming (ASP). Our encoding
can easily be extended and adapted to the needs of specific applications. As an
illustration we show how stable matchings can be found when individuals may
designate unacceptable partners and ties between preferences are allowed.
Subsequently, we show how our ASP based encoding naturally allows us to select
specific stable matchings which are optimal according to a given criterion.
Each time, we can rely on generic and efficient off-the-shelf answer set
solvers to find (optimal) stable matchings.Comment: 26 page
Stability of the hard-sphere icosahedral quasilattice
The stability of the hard-sphere icosahedral quasilattice is analyzed using
the differential formulation of the generalized effective liquid approximation.
We find that the icosahedral quasilattice is metastable with respect to the
hard-sphere crystal structures. Our results agree with recent findings by
McCarley and Ashcroft [Phys. Rev. B {\bf 49}, 15600 (1994)] carried out using
the modified weighted density approximation.Comment: 15 pages, 2 figures available from authors upon request, (revtex),
submitted to Phys. Rev.
The Raman Fingerprint of Graphene
Graphene is the two-dimensional (2d) building block for carbon allotropes of
every other dimensionality. It can be stacked into 3d graphite, rolled into 1d
nanotubes, or wrapped into 0d fullerenes. Its recent discovery in free state
has finally provided the possibility to study experimentally its electronic and
phonon properties. Here we show that graphene's electronic structure is
uniquely captured in its Raman spectrum that clearly evolves with increasing
number of layers. Raman fingerprints for single-, bi- and few-layer graphene
reflect changes in the electronic structure and electron-phonon interactions
and allow unambiguous, high-throughput, non-destructive identification of
graphene layers, which is critically lacking in this emerging research area
Inverse bremsstrahlung contributions to Drell-Yan like processes
The contribution of the sub-process in
hadron-hadron interactions is considered. It is a part of one-loop electroweak
radiative corrections for the Drell-Yan production of lepton pairs at hadron
colliders. It is shown that this contribution should be taken into account
aiming at the 1% accuracy of the Drell-Yan process theoretical description.
Both the neutral and charged current cases are evaluated. Numerical results are
presented for typical conditions of LHC experiments.Comment: 11 pages, 8 figure
Magnetic properties of superconductors with strong spin-orbit coupling
We study the response of a superconductor with a strong spin-orbit coupling
on an external magnetic field. The Ginzburg-Landau free energy functional is
derived microscopically for a general crystal structure, both with and without
an inversion center, and for an arbitrary symmetry of the superconducting order
parameter. As a by-product, we obtain the general expressions for the intrinsic
magnetic moment of the Cooper pairs. It is shown that the Ginzburg-Landau
gradient energy in a superconductor lacking inversion symmetry has unusual
structure. The general formalism is illustrated using as an example CePtSi,
which is the first known heavy-fermion superconductor without an inversion
center.Comment: Published version, 14 pages, minor correction
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