5,019 research outputs found
Mining the in-use stock of energy-transition materials for closed-loop e-mobility
The decarbonization of transportation is essential to achieve a carbon neutral planetary society. However, the turn to electromobility is based on advanced technologies (e.g., lithium-ions batteries) that tied our development to many functional materials with problematic supply. In this study, we apply prospective dynamic material flow analysis to explore the potentials for closing material cycles while meeting a full transition to electric for a set of energy-transition materials (ETMs) including lithium, cobalt, nickel, manganese, and natural graphite. Three demand scenarios are applied to develop trajectories for ETM demand, their in-use stock, and derive the potentials to which recycling can substitute for virgin material extraction at the global scale to 2065. Our results estimate that ETM inflow to use could increase between 20 and 50 times by 2065. However, secondary supply will hardly enable the achievement of circularity in material cycles in the next decades so that the supply of ETMs will remain mainly based on primary material extraction. Nevertheless, from 2040 onwards, recycling volumes could meet up to more than 80% of demand and represent a viable alternative to mining. If the ideal scenario is realized, government policies could have the potential for achieving the dual goal of decarbonizing e-mobility and securing sustainable access to ETMs already in the middle of 2050s. However, the combined commitment and efforts across the value chain of policymakers, companies involved in the cycle, and consumers will be needed to fully realize the great potential for circular economy to work for e-mobility
Do columnar defects produce bulk pinning?
From magneto-optical imaging performed on heavy-ion irradiated YBaCuO single
crystals, it is found that at fields and temperatures where strong single
vortex pinning by individual irradiation-induced amorphous columnar defects is
to be expected, vortex motion is limited by the nucleation of vortex kinks at
the specimen surface rather than by half-loop nucleation in the bulk. In the
material bulk, vortex motion occurs through (easy) kink sliding. Depinning in
the bulk determines the screening current only at fields comparable to or
larger than the matching field, at which the majority of moving vortices is not
trapped by an ion track.Comment: 5 pages, 5 figures, submitted to Physical Review Letter
Electrochemical machining of stainless steel microelements with ultrashort voltage pulses
An electrochemical pulse technique enables the fabrication of three-dimensional microelements from stainless steel. The method is based on the application of ultrashort (nanosecond) voltage pulses, whereupon electrochemical reactions are locally confined with submicrometer precision. Employing properly shaped tool electrodes enables the machining of freestanding cantilevers or microstructures directly to a metal sheet. Due to gentle removal of the material, the grain structure of the material is revealed without any chemical or mechanical modifications. This is demonstrated by measuring the vibration frequency of a cantilever, and agrees well with the value derived from the bulk material properties
Non-monotonic pseudo-gap in high-Tc cuprates
The mechanism of high temperature superconductivity is not resolved for so
long because the normal state of cuprates is not yet understood. Here we show
that the normal state pseudo-gap exhibits an unexpected non-monotonic
temperature dependence, which rules out the possibility to describe it by a
single mechanism such as superconducting phase fluctuations. Moreover, this
behaviour, being remarkably similar to the behaviour of the charge ordering gap
in the transition-metal dichalcogenides, completes the correspondence between
these two classes of compounds: the cuprates in the PG state and the
dichalcogenides in the incommensurate charge ordering state reveal virtually
identical spectra of one-particle excitations as function of energy, momentum
and temperature. These results suggest that the normal state pseudo-gap, which
was considered to be very peculiar to cuprates, seems to be a general complex
phenomenon for 2D metals. This may not only help to clarify the normal state
electronic structure of 2D metals but also provide new insight into electronic
properties of 2D solids where the metal-insulator and metal-superconductor
transitions are considered on similar basis as instabilities of particle-hole
and particle-particle interaction, respectively
The Effect of Splayed Pins on Vortex Creep and Critical Currents
We study the effects of splayed columnar pins on the vortex motion using
realistic London Langevin simulations. At low currents vortex creep is strongly
suppressed, whereas the critical current j_c is enhanced only moderately.
Splaying the pins generates an increasing energy barrier against vortex
hopping, and leads to the forced entanglement of vortices, both of which
suppress creep efficiently. On the other hand splaying enhances kink nucleation
and introduces intersecting pins, which cut off the energy barriers. Thus the
j_c enhancement is strongly parameter sensitive. We also characterize the angle
dependence of j_c, and the effect of different splaying geometries.Comment: 4 figure
Pseudogap and charge density waves in two dimensions
An interaction between electrons and lattice vibrations (phonons) results in
two fundamental quantum phenomena in solids: in three dimensions it can turn a
metal into a superconductor whereas in one dimension it can turn a metal into
an insulator. In two dimensions (2D) both superconductivity and charge-density
waves (CDW) are believed to be anomalous. In superconducting cuprates, critical
transition temperatures are unusually high and the energy gap may stay unclosed
even above these temperatures (pseudogap). In CDW-bearing dichalcogenides the
resistivity below the transition can decrease with temperature even faster than
in the normal phase and a basic prerequisite for the CDW, the favourable
nesting conditions (when some sections of the Fermi surface appear shifted by
the same vector), seems to be absent. Notwithstanding the existence of
alternatives to conventional theories, both phenomena in 2D still remain the
most fascinating puzzles in condensed matter physics. Using the latest
developments in high-resolution angle-resolved photoemission spectroscopy
(ARPES) here we show that the normal-state pseudogap also exists in one of the
most studied 2D examples, dichalcogenide 2H-TaSe2, and the formation of CDW is
driven by a conventional nesting instability, which is masked by the pseudogap.
Our findings reconcile and explain a number of unusual, as previously believed,
experimental responses as well as disprove many alternative theoretical
approaches. The magnitude, character and anisotropy of the 2D-CDW pseudogap are
intriguingly similar to those seen in superconducting cuprates.Comment: 14 pages including figures and supplementary informatio
Photoconductivity in AC-driven modulated two dimensional electron gas in a perpendicular magnetic field
In this work we study the microwave photoconductivity of a two-dimensional
electron system (2DES) in the presence of a magnetic field and a
two-dimensional modulation (2D). The model includes the microwave and Landau
contributions in a non-perturbative exact way, the periodic potential is
treated perturbatively. The Landau-Floquet states provide a convenient base
with respect to which the lattice potential becomes time-dependent, inducing
transitions between the Landau-Floquet levels. Based on this formalism, we
provide a Kubo-like formula that takes into account the oscillatory Floquet
structure of the problem. The total longitudinal conductivity and resistivity
exhibit strong oscillations, determined by with
the radiation frequency and the cyclotron frequency. The
oscillations follow a pattern with minima centered at , and maxima centered at , where , is a constant shift
and is the dominant multipole contribution. Negative resistance states
(NRS) develop as the electron mobility and the intensity of the microwave power
are increased. These NRS appear in a narrow window region of values of the
lattice parameter (), around , where is the magnetic
length. It is proposed that these phenomena may be observed in artificially
fabricated arrays of periodic scatterers at the interface of ultraclean
heterostructures.Comment: 20 pages, 8 figure
New Lithium Measurements in Metal-Poor Stars
We provide *lambda*6708 Li 1 measurements in 37 metal-poor stars, most of
which are poorly-studied or have no previous measurements, from high-resolution
and high-S/N spectroscopy obtained with the McDonald Observatory 2.1m and 2.7m
telescopes. The typical line strength and abundance uncertainties, confirmed by
the thinness of the Spite plateau manifested by our data and by comparison with
previous measurements, are <=4 mAng and <=0.07-0.10 dex respectively. Two rare
moderately metal-poor solar-Teff dwarfs, HIP 36491 and 40613, with
significantly depleted but still detectable Li are identified; future light
element determinations in the more heavily depeleted HIP 40613 may provide
constraints on the Li depletion mechanism acting in this star. We note two
moderately metal-poor and slightly evolved stars, HIP 105888 and G265-39, that
appear to be analogs of the low-Li moderately metal-poor subgiant HD 201889.
Preliminary abundance analysis of G 265-39 finds no abnormalities that suggest
the low Li content is associated with AGB mass-transfer or deep mixing and
p-capture. We also detect line doubling in HIP 4754, heretofore classified as
SB1.Comment: Accepted for publication in PASP, volume 912 (Feb 2012) 15 pages, 3
figures, 2 table
Geometrical edge barriers and magnetization in superconducting strips with slits
We theoretically investigate the magnetic-field and current distributions for
coplanar superconducting strips with slits in an applied magnetic field H_a. We
consider ideal strips with no bulk pinning and calculate the hysteretic
behavior of the magnetic moment m_y as a function of H_a due solely to
geometrical edge barriers. We find that the m_y-H_a curves are strongly
affected by the slits. In an ascending field, the m_y-H_a curves exhibit kink
or peak structures, because the slits prevent penetration of magnetic flux. In
a descending field, m_y becomes positive, because magnetic flux is trapped in
the slits, in contrast to the behavior of a single strip without slits, for
which m_y =0.Comment: 11 pages, 5 figures, revtex
Flux penetration and expulsion in thin superconducting disks
Using an expansion of the order parameter over the eigenfunctions of the
linearized first Ginzburg-Landau (GL) equation, we obtain numerically the
saddle points of the free energy separating the stable states with different
number of vortices. In contrast to known surface and geometrical barrier
models, we find that in a wide range of magnetic fields below the penetration
field, the saddle point state for flux penetration into a disk does not
correspond to a vortex located nearby the sample boundary, but to a region of
suppressed superconductivity at the disk edge with no winding of the current,
and which is {\it a nucleus} for the following vortex creation. The height of
this {\it nucleation barrier}, which determines the time of flux penetration,
is calculated for different disk radii and magnetic fields.Comment: Accepted for publication in Physical Review Letter
- …