139 research outputs found
Effects of process parameters on mechanical properties of abrasive-assisted electroformed nickel
AbstractA cathode mandrel with translational and rotational motion, which was supposed to obtain uniform friction effect on surface, was employed in abrasive-assisted electroforming for revolving parts with complex profile. The effects of current density, translational speed and rotational speed on the deposit properties were studied by orthogonal test. The tensile strength, elongation and micro hardness value were measured to find out how the factors affected the properties. The optimized results show that changes of current density affect the tensile strength of nickel layer most, while translational speed has the most remarkable influences on both elongation and micro hardness. The low rotational speed affects the properties least. In this experiment, a smooth nickel layer with tensile strength 581MPa, elongation 17% and micro hardness 248HV is obtained by the orthogonal test
Nernst effect and dimensionality in the quantum limit
Nernst effect, the transverse voltage generated by a longitudinal thermal
gradient in presence of magnetic field has recently emerged as a very
sensitive, yet poorly understood, probe of electron organization in solids.
Here we report on an experiment on graphite, a macroscopic stack of graphene
layers, which establishes a fundamental link between dimensionality of an
electronic system and its Nernst response. In sharp contrast with single-layer
graphene, the Nernst signal sharply peaks whenever a Landau level meets the
Fermi level. This points to the degrees of freedom provided by finite
interlayer coupling as a source of enhanced thermoelectric response in the
vicinity of the quantum limit. Since Landau quantization slices a
three-dimensional Fermi surface, each intersection of a Landau level with the
Fermi level modifies the Fermi surface topology. According to our results, the
most prominent signature of such a topological phase transition emerges in the
transverse thermoelectric response.Comment: 13 pages, 4 figures and supplementary information; To appear in
Nature Physic
Phonon thermal Hall effect in strontium titanate
It has been known for more than a decade that phonons can produce an
off-diagonal thermal conductivity in presence of magnetic field. Recent studies
of thermal Hall conductivity, , in a variety of contexts, however,
have assumed a negligibly small phonon contribution. We present a study of
in quantum paraelectric SrTiO, which is a non-magnetic
insulator and find that its peak value exceeds what has been reported in any
other insulator, including those in which the signal has been qualified as
'giant'. Remarkably, and peak at the same
temperature and the former decreases faster than the latter at both sides of
the peak. Interestingly, in the case of LaCuO and -RuCl,
and peak also at the same temperature. We also
studied KTaO and found a small signal, indicating that a sizable
is not a generic feature of quantum paraelectrics. Combined to
other observations, this points to a crucial role played by antiferrodistortive
domains in generating of this solid.Comment: Main text: 6 pages, 4 figures, Supplemental Material is included.
Accepted by Phys. Rev. Let
Emptying Dirac valleys in bismuth using high magnetic fields
The Fermi surface of elemental bismuth consists of three small rotationally
equivalent electron pockets, offering a valley degree of freedom to charge
carriers. A relatively small magnetic field can confine electrons to their
lowest Landau level. This is the quantum limit attained in other dilute metals
upon application of sufficiently strong magnetic field. Here, we report on the
observation of another threshold magnetic field never encountered before in any
other solid. Above this field, , one or two valleys become
totally empty. Drying up a Fermi sea by magnetic field in the Brillouin zone
leads to a manyfold enhancement in electric conductance. We trace the origin of
the large drop in magnetoresistance across to transfer of
carriers between valleys with highly anisotropic mobilities. The
non-interacting picture of electrons with field-dependent mobility explains
most results. Coulomb interaction may play a role in shaping the fine details.Comment: 19 pages, 5 figures, Supplemental Material available upon reques
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