3,906 research outputs found
To Wet or Not to Wet? Dispersion Forces Tip the Balance for Water Ice on Metals
Despite widespread discussion, the role of van der Waals dispersion forces in wetting remains unclear. Here we show that nonlocal correlations contribute substantially to the water-metal bond and that this is an important factor in governing the relative stabilities of wetting layers and 3D bulk ice. Because of the greater polarizability of the substrate metal atoms, nonlocal correlations between water and the metal exceed those between water molecules within ice. This sheds light on a long-standing problem, wherein common density functional theory exchange-correlation functionals incorrectly predict that none of the low temperature experimentally characterized icelike wetting layers are thermodynamically stable
Absolute frequency measurement of the 7s S 7s7p P transition in Ra
Transition frequencies were determined for transitions in Ra in an atomic
beam and for reference lines in Te molecules in a vapor cell. The absolute
frequencies were calibrated against a GPS stabilized Rb-clock by means of an
optical frequency comb. The 7s^2\,^1S(F = 1/2)-7s7p\,^1P(F = 3/2)
transition in Ra was determined to be MHz. The
measurements provide input for designing efficient and robust laser cooling of
Ra atoms in preparation of a search for a permanent electric dipole moment in
Ra isotopes.Comment: Accepted for publication in the rapid communication of Physical
review
Self-Organized Dynamical Equilibrium in the Corrosion of Random Solids
Self-organized criticality is characterized by power law correlations in the
non-equilibrium steady state of externally driven systems. A dynamical system
proposed here self-organizes itself to a critical state with no characteristic
size at ``dynamical equilibrium''. The system is a random solid in contact with
an aqueous solution and the dynamics is the chemical reaction of corrosion or
dissolution of the solid in the solution. The initial difference in chemical
potential at the solid-liquid interface provides the driving force. During time
evolution, the system undergoes two transitions, roughening and
anti-percolation. Finally, the system evolves to a dynamical equilibrium state
characterized by constant chemical potential and average cluster size. The
cluster size distribution exhibits power law at the final equilibrium state.Comment: 11 pages, 5 figure
Multiphysics modelling of a hybrid magnetic bearing (HMB) for calculating power loss and temperature with different loss minimization strategies
This paper represents a multiphysics modelling for calculating loss and temperature of a hybrid magnetic bearing (HMB) using finite element method (FEM). It also addresses the different loss minimization strategies for the HMB. The main sources of losses are identified as eddy current loss in permanent magnets, flywheel and copper loss in electromagnet. Due to these losses, the temperature distribution in different portions of HMB is computed using coupled field analysis. To minimize the eddy current loss, slits are fabricated in flywheel plate instead of a solid flywheel. The improvement of the control current is investigated by providing a coating of different metal, like copper, brass and stainless steel on the flywheel. A zero bias current (ZBC) scheme has been introduced where no bias current is required to levitate the rotor or to avoid singularity due to external disturbances, thus reducing the copper loss
Nonfactorization and Color-Suppressed Decays
Using value of the parameter but including a modest
nonfactorized amplitude, we show that it is possible to understand all data,
including polarization, for color-suppressed
decays in all commonly used models of form factors. We show that for decay one can define an effective , which is process-dependent and,
in general, complex; but it is not possible to define an effective for
decay. We also explain why nonfactorized amplitudes do not
play a significant role in color-favored B decays.Comment: 13 pages, Latex, one figure (not included
Surface Hardening and Self-Organized Fractality Through Etching of Random Solids
When a finite volume of etching solution is in contact with a disordered
solid, complex dynamics of the solid-solution interface develop. If the etchant
is consumed in the chemical reaction, the dynamics stop spontaneously on a
self-similar fractal surface. As only the weakest sites are corroded, the solid
surface gets progressively harder and harder. At the same time it becomes
rougher and rougher uncovering the critical spatial correlations typical of
percolation. From this, the chemical process reveals the latent percolation
criticality hidden in any random system. Recently, a simple minimal model has
been introduced by Sapoval et al. to describe this phenomenon. Through analytic
and numerical study, we obtain a detailed description of the process. The time
evolution of the solution corroding power and of the distribution of resistance
of surface sites is studied in detail. This study explains the progressive
hardening of the solid surface. Finally, this dynamical model appears to belong
to the universality class of Gra dient Percolation.Comment: 14 pages, 15 figures (1457 Kb
Interaction of intense vuv radiation with large xenon clusters
The interaction of atomic clusters with short, intense pulses of laser light
to form extremely hot, dense plasmas has attracted extensive experimental and
theoretical interest. The high density of atoms within the cluster greatly
enhances the atom--laser interaction, while the finite size of the cluster
prevents energy from escaping the interaction region. Recent technological
advances have allowed experiments to probe the laser--cluster interaction at
very high photon energies, with interactions much stronger than suggested by
theories for lower photon energies. We present a model of the laser--cluster
interaction which uses non-perturbative R-matrix techniques to calculate
inverse bremsstrahlung and photoionization cross sections for Herman-Skillman
atomic potentials. We describe the evolution of the cluster under the influence
of the processes of inverse bremsstrahlung heating, photoionization,
collisional ionization and recombination, and expansion of the cluster. We
compare charge state distribution, charge state ejection energies, and total
energy absorbed with the Hamburg experiment of Wabnitz {\em et al.} [Nature
{\bf 420}, 482 (2002)] and ejected electron spectra with Laarmann {\em et al.}
[Phys. Rev. Lett. {\bf 95}, 063402 (2005)]
Fusion of Li with Tb} at near barrier energies
Complete and incomplete fusion cross sections for Li+Tb have
been measured at energies around the Coulomb barrier by the -ray
method. The measurements show that the complete fusion cross sections at
above-barrier energies are suppressed by 34% compared to the coupled
channels calculations. A comparison of the complete fusion cross sections at
above-barrier energies with the existing data of B+Tb and
Li+Tb shows that the extent of suppression is correlated with the
-separation energies of the projectiles. It has been argued that the Dy
isotopes produced in the reaction Li+Tb, at below-barrier
energies are primarily due to the -transfer to unbound states of Tb,
while both transfer and incomplete fusion processes contribute at above-barrier
energies.Comment: Phys. Rev. C (accepted
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