810 research outputs found
Numerical Studies on the Magnetism of Fe-Ni-Mn Alloys in the Invar Region
By means of self-consistent semi-empirical LCAO calculations we study the
itinerant magnetism of (Fe_{0.65}Ni_{0.35})_{1-y} Mn_y alloys for y between 0
and 0.22 at T=0 K, neglecting only the transverse spin components. We find that
the magnetic behaviour is quite complicated on a local scale. In addition to
ferromagnetic behaviour, also metastable spin-glass-like configurations are
found. In the same approach, using a direct numerical calculation by the
Kubo-Formalism without any fit parameters, we also calculate the electrical
conductance in the magnetic state and find that the -dependence observed in
the experiments is well reproduced by our calculations, except of an overall
factor of rougly 5, by which our resistivities are too large.Comment: 12 pages (Latex, to be applied 2 times) + 13 figures (eps-files
Relationship between solidification microstructure and hot cracking susceptibility for continuous casting of low-carbon and high-strength low-alloyed steels: A phase-field study
© The Minerals, Metals & Materials Society and ASM International 2013Hot cracking is one of the major defects in continuous casting of steels, frequently limiting the productivity. To understand the factors leading to this defect, microstructure formation is simulated for a low-carbon and two high-strength low-alloyed steels. 2D simulation of the initial stage of solidification is performed in a moving slice of the slab using proprietary multiphase-field software and taking into account all elements which are expected to have a relevant effect on the mechanical properties and structure formation during solidification. To account for the correct thermodynamic and kinetic properties of the multicomponent alloy grades, the simulation software is online coupled to commercial thermodynamic and mobility databases. A moving-frame boundary condition allows traveling through the entire solidification history starting from the slab surface, and tracking the morphology changes during growth of the shell. From the simulation results, significant microstructure differences between the steel grades are quantitatively evaluated and correlated with their hot cracking behavior according to the Rappaz-Drezet-Gremaud (RDG) hot cracking criterion. The possible role of the microalloying elements in hot cracking, in particular of traces of Ti, is analyzed. With the assumption that TiN precipitates trigger coalescence of the primary dendrites, quantitative evaluation of the critical strain rates leads to a full agreement with the observed hot cracking behavior. © 2013 The Minerals, Metals & Materials Society and ASM International
Type-II Interface Exciton in ZnSe/(Zn,Mn)Se Heterostructures
Two emission bands are observed in the photoluminescence spectrum of ZnSe/~Zn,Mn!Se heterostructures. These bands emerge in a magnetic field and are associated with interface excitons formed as a result of a magnetic-field-induced type-I–type-II transition of the band alignment. Time-resolved measurements yield lifetimes in the ns range signifying a relatively large spatial separation of electrons and holes and hence low optical oscillator strength. These features are confirmed by a theoretical analysis of the interface exciton state revealing a reduced importance of the electron-hole Coulomb interaction in comparison with type-II excitons in quantum wells
Thermoelectric three-terminal hopping transport through one-dimensional nanosystems
A two-site nanostructure (e.g, a "molecule") bridging two conducting leads
and connected to a phonon bath is considered. The two relevant levels closest
to the Fermi energy are connected each to its lead. The leads have slightly
different temperatures and chemical potentials and the nanos- tructure is also
coupled to a thermal (third) phonon bath. The 3 x 3 linear transport
("Onsager") matrix is evaluated, along with the ensuing new figure of merit,
and found to be very favorable for thermoelectric energy conversion.Comment: Accepted by Phys. Rev.
Taxonomic diversity and identification problems of oncaeid microcopepods in the Mediterranean Sea
The species diversity of the pelagic microcopepod
family Oncaeidae collected with nets of 0.1-mm mesh
size was studied at 6 stations along a west-to-east transect
in the Mediterranean Sea down to a maximum depth of
1,000 m. A total of 27 species and two form variants have
been identified, including three new records for the
Mediterranean. In addition, about 20, as yet undescribed,
new morphospecies were found (mainly from the genera
Epicalymma and Triconia) which need to be examined
further. The total number of identified oncaeid species was
similar in the Western and Eastern Basins, but for some cooccurring
sibling species, the estimated numerical dominance
changed. The deep-sea fauna of Oncaeidae, studied
at selected depth layers between 400 m and the near-bottom
layer at >4,200 m depth in the eastern Mediterranean
(Levantine Sea), showed rather constant species numbers
down to ∼3,000 m depth. In the near-bottom layers, the
diversity of oncaeids declined and species of Epicalymma
strongly increased in numerical importance. The taxonomic
status of all oncaeid species recorded earlier in the
Mediterranean Sea is evaluated: 19 out of the 46 known
valid oncaeid species are insufficiently described, and most
of the taxonomically unresolved species (13 species) have
originally been described from this area (type locality). The
deficiencies in the species identification of oncaeids cast
into doubt the allegedly cosmopolitan distribution of some
species, in particular those of Mediterranean origin. The
existing identification problems even of well-described
oncaeid species are exemplified for the Oncaea mediacomplex,
including O. media Giesbrecht, O. scottodicarloi
Heron & Bradford-Grieve, and O. waldemari Bersano &
Boxshall, which are often erroneously identified as a single
species (O. media). The inadequacy in the species identification
of Oncaeidae, in particular those from the Atlantic
and Mediterranean, is mainly due to the lack of reliable
identification keys for Oncaeidae in warm-temperate and/or
tropical seas. Future efforts should be directed to the
construction of identification keys that can be updated
according to the latest taxonomic findings, which can be
used by the non-expert as well as by the specialist. The
adequate consideration of the numerous, as yet undescribed,
microcopepod species in the world oceans, in
particular the Oncaeidae, is a challenge for the study of the
structure and function of plankton communities as well as
for global biodiversity estimates
Mathematical modeling of demand in marketing goals by metrods of linear regression
In this paper the mathematical modeling of the demand for marketing purposes. This uses regression analysis and least squares method
Instability of insulating states in optical lattices due to collective phonon excitations
The role of collective phonon excitations on the properties of cold atoms in
optical lattices is investigated. These phonon excitations are collective
excitations, whose appearance is caused by intersite atomic interactions
correlating the atoms, and they do not arise without such interactions. These
collective excitations should not be confused with lattice vibrations produced
by an external force. No such a force is assumed. But the considered phonons
are purely self-organized collective excitations, characterizing atomic
oscillations around lattice sites, due to intersite atomic interactions. It is
shown that these excitations can essentially influence the possibility of atoms
to be localized. The states that would be insulating in the absence of phonon
excitations can become delocalized when these excitations are taken into
account. This concerns long-range as well as local atomic interactions. To
characterize the region of stability, the Lindemann criterion is used.Comment: Latex file, 27 pages, 1 figur
Electronic structure and light-induced conductivity in a transparent refractory oxide
Combined first-principles and experimental investigations reveal the
underlying mechanism responsible for a drastic change of the conductivity (by
10 orders of magnitude) following hydrogen annealing and UV-irradiation in a
transparent oxide, 12CaO.7Al2O3, found by Hayashi et al. The charge transport
associated with photo-excitation of an electron from H, occurs by electron
hopping. We identify the atoms participating in the hops, determine the exact
paths for the carrier migration, estimate the temperature behavior of the
hopping transport and predict a way to enhance the conductivity by specific
doping.Comment: 4 pages including 4 figure
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