147 research outputs found
Sea ice strength development from freezing to melting in the Antarctic marginal ice zone
[EN] Sea ice growth in the Marginal Ice Zone of the Antarctic is one of the largest annual changes on earth with a huge impact on the global climate and ecology system. The principles of sea ice growth and melting in the MIZ of the Antarctic is yet not as well researched as its polar counterpart in the north.For this study, pancake ice, consolidated ice and floe ice were analyzed with a compression test in July, October and November 2019 in the marginal ice zone of the Antarctic. Newly formed pancake ice in July showed the highest compressive strength in the bottom layer (3 MPa), whereas consolidated ice was strongest at the top (5 MPa). Consolidated ice in October and November had the highest compressive strength in a middle layer with up to 13.5 MPa, the maximum strength at the top was 3 MPa. Floe ice, consisting of destroyed pack ice, did not show a clear strength development over sea ice depth.The SCALE cruises are funded by the South African National Research Foundation (NRF) through the South African National Antarctic Programme (SANAP), with contributions from the Department of Science and Innovation and the Department of Environmental Affairs. We are very grateful to the teams that have contributed to the success of the SCALE cruise in particular under the guidance of Marcello Vichi and J¨org Schröder.Paul, F.; Mielke, T.; Audh, R.; Lupascu, D. (2022). Sea ice strength development from freezing to melting in the Antarctic marginal ice zone. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 375-385. https://doi.org/10.4995/YIC2021.2021.12249OCS37538
State transition and electrocaloric effect of BaZrTiO: simulation and experiment
The electrocaloric effect (ECE) of BaZrTiO (BZT) is closely
related to the relaxor state transition of the materials. This work presents a
systematic study on the ECE and the state transition of the BZT, using a
combined canonical and microcanonical Monte Carlo simulations based a
lattice-based on a Ginzburg-Landau-type Hamiltonian. For comparison and
verification, experimental measurements have been carried on BTO and BZT
( and ) samples, including the ECE at various temperatures, domain
patterns by Piezoresponse Force Microscopy at room temperature, and the P-E
loops at various temperatures. Results show that the dependency of BZT behavior
of the Zr-concentration can be classified into three different stages. In the
composition range of , ferroelectric domains are visible,
but ECE peak drops with increasing Zr-concentration harshly. In the range of , relaxor features become prominent, and the decrease of
ECE with Zr-concentration is moderate. In the high concentration range of , the material is almost nonpolar, and there is no ECE peak visible.
Results suggest that BZT with certain low range of Zr-concentration around
can be a good candidate with relatively high ECE and
simutaneously wide temperature application range at rather low temperature
Single-shot qubit readout in circuit Quantum Electrodynamics
The future development of quantum information using superconducting circuits
requires Josephson qubits [1] with long coherence times combined to a
high-fidelity readout. Major progress in the control of coherence has recently
been achieved using circuit quantum electrodynamics (cQED) architectures [2,
3], where the qubit is embedded in a coplanar waveguide resonator (CPWR) which
both provides a well controlled electromagnetic environment and serves as qubit
readout. In particular a new qubit design, the transmon, yields reproducibly
long coherence times [4, 5]. However, a high-fidelity single-shot readout of
the transmon, highly desirable for running simple quantum algorithms or measur-
ing quantum correlations in multi-qubit experiments, is still lacking. In this
work, we demonstrate a new transmon circuit where the CPWR is turned into a
sample-and-hold detector, namely a Josephson Bifurcation Amplifer (JBA) [6, 7],
which allows both fast measurement and single-shot discrimination of the qubit
states. We report Rabi oscillations with a high visibility of 94% together with
dephasing and relaxation times longer than 0:5 \mu\s. By performing two
subsequent measurements, we also demonstrate that this new readout does not
induce extra qubit relaxation.Comment: 14 pages including 4 figures, preprint forma
The nature of iron-oxygen vacancy defect centers in PbTiO3
The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy
forms a charged defect associate, oriented along the crystallographic c-axis.
Its microscopic structure has been analyzed in detail comparing results from a
semi-empirical Newman superposition model analysis based on finestructure data
and from calculations using density functional theory.
Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor
center. The position of the iron ion in the ferroelectric phase is found to be
similar to the B-site in the paraelectric phase. Partial charge compensation is
locally provided by a directly coordinated oxygen vacancy.
Using high-resolution synchrotron powder diffraction, it was verified that
lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of
1.0721.Comment: 11 pages, 5 figures, accepted in Phys. Rev.
Bose-Einstein condensation on a superconducting atom chip
We have produced a Bose-Einstein condensate (BEC) on an atom chip using only
superconducting wires in a cryogenic environment. We observe the onset of
condensation for 10^4 atoms at a temperature of 100 nK. This result opens the
way for studies of atom losses and decoherence in a BEC interacting with a
superconducting surface. Studies of dipole-blockade with long-lived Rydberg
atoms in a small and dense atomic sample are underway.Comment: 4 pages, 4 figures. Accepted for publication in Europhysics Letter
Noiseless nonreciprocity in a parametric active device
Nonreciprocal devices such as circulators and isolators belong to an
important class of microwave components employed in applications like the
measurement of mesoscopic circuits at cryogenic temperatures. The measurement
protocols usually involve an amplification chain which relies on circulators to
separate input and output channels and to suppress backaction from different
stages on the sample under test. In these devices the usual reciprocal symmetry
of circuits is broken by the phenomenon of Faraday rotation based on magnetic
materials and fields. However, magnets are averse to on-chip integration, and
magnetic fields are deleterious to delicate superconducting devices. Here we
present a new proposal combining two stages of parametric modulation emulating
the action of a circulator. It is devoid of magnetic components and suitable
for on-chip integration. As the design is free of any dissipative elements and
based on reversible operation, the device operates noiselessly, giving it an
important advantage over other nonreciprocal active devices for quantum
information processing applications.Comment: 17 pages, 4 figures + 12 pages Supplementary Informatio
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