1,960 research outputs found
Magnetic ordering, electronic structure and magnetic anisotropy energy in the high-spin Mn single molecule magnet
We report the electronic structure and magnetic ordering of the single
molecule magnet [MnO(2,2'-biphenoxide)Br]
based on first-principles all-electron density-functional calculations. We find
that two of the ten core Mn atoms are coupled antiferromagnetically to the
remaining eight, resulting in a ferrimagnetic ground state with total spin
S=13. The calculated magnetic anisotropy barrier is found to be 9 K in good
agreement with experiment. The presence of the Br anions impact the electronic
structure and therefore the magnetic properties of the 10 Mn atoms. However,
the electric field due to the negative charges has no significant effect on the
magnetic anisotropy.Comment: 4 pages, submitted to PR
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A Review of Hybrid Manufacturing
In recent years the combination of laser-based Additive Manufacturing and Computer
Numerical Controlled (CNC) machining has become increasingly popular, with several machine
tool manufacturers exhibiting products based on different machine tool configurations. This
technology, widely known as Hybrid Manufacturing, generally exploits Directed Energy
Deposition processes using powder feedstock that is fed into a melt pool created by a laser.
Although Directed Energy Deposition processes predate powder bed fusion Additive
Manufacturing (at least in terms of coating and repair applications), commercialization of Hybrid
Manufacturing systems is still very much in its infancy. However, they do offer clear advantages,
combining a high deposition rate together with the accuracy and surface finish associated with
machining. This paper presents the history of the development of Hybrid Manufacturing Systems
(HMS), dating back from work undertaken in the mid 1990s through to the present day. The
relative merits of different material deposition approaches are compared and some of the key
technical challenges which remain are highlighted and discussed.Mechanical Engineerin
Coupling to haloform molecules in intercalated C60?
For field-effect-doped fullerenes it was reported that the superconducting
transition temperature Tc is markedly larger for C60.2CHX_3 (X=Cl, Br)
crystals, than for pure C60. Initially this was explained by the expansion of
the volume per C60-molecule and the corresponding increase in the density of
states at the Fermi level in the intercalated crystals. On closer examination
it has, however, turned out to be unlikely that this is the mechanism behind
the increase in Tc. An alternative explanation of the enhanced transition
temperatures assumes that the conduction electrons not only couple to the
vibrational modes of the C60-molecule, but also to the modes of the
intercalated molecules. We investigate the possibility of such a coupling. We
find that, assuming the ideal bulk structure of the intercalated crystal, both
a coupling due to hybridization of the molecular levels, and a coupling via
dipole moments should be very small. This suggests that the presence of the
gate-oxide in the field-effect-devices strongly affects the structure of the
fullerene crystal at the interface.Comment: 4 pages, 1 figure, to be published in PRB (rapid communication
Spherical Solutions due to the Exterior Geometry of a Charged Weyl Black Hole
Firstly we derive peculiar spherical Weyl solutions, using a general
spherically symmetric metric due to a massive charged object with definite mass
and radius. Afterwards, we present new analytical solutions for relevant
cosmological terms, which appear in the metrics. Connecting the metrics to a
new geometric definition of a charged Black Hole, we numerically investigate
the effective potentials of the total dynamical system, considering massive and
massless test particles, moving on such Black Holes.Comment: 8 pages, 5 figure
DFT calculation of the intermolecular exchange interaction in the magnetic Mn dimer
The dimeric form of the single-molecule magnet
[MnOCl(OCEt)(py)] recently revealed interesting
phenomena: no quantum tunneling at zero field and tunneling before magnetic
field reversal. This is attributed to substantial antiferromagnetic exchange
interaction between different monomers. The intermolecular exchange
interaction, electronic structure and magnetic properties of this molecular
magnet are calculated using density-functional theory within
generalized-gradient approximation. Calculations are in good agreement with
experiment.Comment: 4 page
The algebra of adjacency patterns: Rees matrix semigroups with reversion
We establish a surprisingly close relationship between universal Horn classes
of directed graphs and varieties generated by so-called adjacency semigroups
which are Rees matrix semigroups over the trivial group with the unary
operation of reversion. In particular, the lattice of subvarieties of the
variety generated by adjacency semigroups that are regular unary semigroups is
essentially the same as the lattice of universal Horn classes of reflexive
directed graphs. A number of examples follow, including a limit variety of
regular unary semigroups and finite unary semigroups with NP-hard variety
membership problems.Comment: 30 pages, 9 figure
Velocity of sound in a Bose-Einstein condensate in the presence of an optical lattice and transverse confinement
We study the effect of the transverse degrees of freedom on the velocity of
sound in a Bose-Einstein condensate immersed in a one-dimensional optical
lattice and radially confined by a harmonic trap. We compare the results of
full three-dimensional calculations with those of an effective 1D model based
on the equation of state of the condensate. The perfect agreement between the
two approaches is demonstrated for several optical lattice depths and
throughout the full crossover from the 1D mean-field to the Thomas Fermi regime
in the radial direction.Comment: final versio
Molecular structures and vibrations of neutral and anionic CuOx (x = 1-3,6) clusters
We report equilibrium geometric structures of CuO2, CuO3, CuO6, and CuO
clusters obtained by an all-electron linear combination of atomic orbitals
scheme within the density-functional theory with generalized gradient
approximation to describe the exchange-correlation effects. The vibrational
stability of all clusters is examined on the basis of the vibrational
frequencies. A structure with Cs symmetry is found to be the lowest-energy
structure for CuO2, while a -shaped structure with C2v symmetry is the most
stable structure for CuO3. For the larger CuO6 and CuO clusters, several
competitive structures exist with structures containing ozonide units being
higher in energy than those with O2 units. The infrared and Raman spectra are
calculated for the stable optimal geometries. ~Comment: Uses Revtex4, (Better quality figures can be obtained from authors
Perturbative spectrum of Trapped Weakly Interacting Bosons in Two Dimensions
We study a trapped Bose-Einstein condensate under rotation in the limit of
weak, translational and rotational invariant two-particle interactions. We use
the perturbation-theory approach (the large-N expansion) to calculate the
ground-state energy and the excitation spectrum in the asymptotic limit where
the total number of particles N goes to infinity while keeping the total
angular momentum L finite. Calculating the probabilities of different
configurations of angular momentum in the exact eigenstates gives us a clear
view of the physical content of excitations. We briefly discuss the case of
repulsive contact interaction.Comment: Revtex, 10 pages, 1 table, to appear in Phys. Rev.
On the energy leakage of discrete wavelet transform
The energy leakage is an inherent deficiency of discrete wavelet transform (DWT) which is often ignored by researchers and practitioners. In this paper, a systematic investigation into the energy leakage is reported. The DWT is briefly introduced first, and then the energy leakage phenomenon is described using a numerical example as an illustration and its effect on the DWT results is discussed. Focusing on the Daubechies wavelet functions, the band overlap between the quadrature mirror analysis filters was studied and the results reveal that there is an unavoidable tradeoff between the band overlap degree and the time resolution for the DWT. The dependency of the energy leakage to the wavelet function order was studied by using a criterion defined to evaluate the severity of the energy leakage. In addition, a method based on resampling technique was proposed to relieve the effects of the energy leakage. The effectiveness of the proposed method has been validated by numerical simulation study and experimental study
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