3,584 research outputs found
Quantum simulation of frustrated magnetism in triangular optical lattices
Magnetism plays a key role in modern technology as essential building block
of many devices used in daily life. Rich future prospects connected to
spintronics, next generation storage devices or superconductivity make it a
highly dynamical field of research. Despite those ongoing efforts, the
many-body dynamics of complex magnetism is far from being well understood on a
fundamental level. Especially the study of geometrically frustrated
configurations is challenging both theoretically and experimentally. Here we
present the first realization of a large scale quantum simulator for magnetism
including frustration. We use the motional degrees of freedom of atoms to
comprehensively simulate a magnetic system in a triangular lattice. Via a
specific modulation of the optical lattice, we can tune the couplings in
different directions independently, even from ferromagnetic to
antiferromagnetic. A major advantage of our approach is that standard
Bose-Einstein-condensate temperatures are sufficient to observe magnetic
phenomena like N\'eel order and spin frustration. We are able to study a very
rich phase diagram and even to observe spontaneous symmetry breaking caused by
frustration. In addition, the quantum states realized in our spin simulator are
yet unobserved superfluid phases with non-trivial long-range order and
staggered circulating plaquette currents, which break time reversal symmetry.
These findings open the route towards highly debated phases like spin-liquids
and the study of the dynamics of quantum phase transitions.Comment: 5 pages, 4 figure
Epitaxial growth of deposited amorphous layer by laser annealing
We demonstrate that a single short pulse of laser irradiation of appropriate energy is capable of recrystallizing in open air an amorphous Si layer deposited on a (100) single-crystal substrate into an epitaxial layer. The laser pulse annealing technique is shown to overcome the interfacial oxide obstacle which usually leads to polycrystalline formation in normal thermal annealing
Tunable gauge potential for neutral and spinless particles in driven lattices
We present a universal method to create a tunable, artificial vector gauge
potential for neutral particles trapped in an optical lattice. The necessary
Peierls phase of the hopping parameters between neighboring lattice sites is
generated by applying a suitable periodic inertial force such that the method
does not rely on any internal structure of the particles. We experimentally
demonstrate the realization of such artificial potentials, which generate
ground state superfluids at arbitrary non-zero quasi-momentum. We furthermore
investigate possible implementations of this scheme to create tuneable magnetic
fluxes, going towards model systems for strong-field physics
Influence of Additives on the Reversible Oxygen Reduction Reaction/Oxygen Evolution Reaction in the MgÂČâșâContaining Ionic Liquid N âButylâN âMethylpyrrolidinium Bis(Trifluoromethanesulfonyl)imide
The influence of different additives on the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) in magnesiumâcontaining N âbutylâN âmethylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([BMP][TFSI]) on a glassy carbon electrode was investigated to gain a better understanding of the electrochemical processes in Mgâair batteries. 18âCrownâ6 was used as a complexing agent for Mg ions to hinder the passivation caused by their reaction with ORR products such as superoxide and peroxide anions. Furthermore, borane dimethylamine complex (NBH) was used as a potential waterâremoving agent to inhibit electrode passivation by reacting with trace impurities of water. The electrochemical processes were characterized by differential electrochemical mass spectrometry to monitor the consumed and evolved O2 in the ORR/OER and determine the number of transferred electrons. Crown ether and NBH efficiently masked Mg. A stochiometric excess of crown ether resulted in reduced formation of a passivation layer, whereas at too high concentrations the reversibility of the ORR/OER was diminished
Tunneling control and localization for Bose-Einstein condensates in a frequency modulated optical lattice
The similarity between matter waves in periodic potential and solid-state
physics processes has triggered the interest in quantum simulation using
Bose-Fermi ultracold gases in optical lattices. The present work evidences the
similarity between electrons moving under the application of oscillating
electromagnetic fields and matter waves experiencing an optical lattice
modulated by a frequency difference, equivalent to a spatially shaken periodic
potential. We demonstrate that the tunneling properties of a Bose-Einstein
condensate in shaken periodic potentials can be precisely controlled. We take
additional crucial steps towards future applications of this method by proving
that the strong shaking of the optical lattice preserves the coherence of the
matter wavefunction and that the shaking parameters can be changed
adiabatically, even in the presence of interactions. We induce reversibly the
quantum phase transition to the Mott insulator in a driven periodic potential.Comment: Laser Physics (in press
Increased plasma viscosity as a reason for inappropriate erythropoietin formation
The aim of this study was to examine whether altered plasma viscosity could contribute to the inappropriately low production rate of erythropoietin (EPO) observed in patients suffering from hypergammaglobulinemias associated with multiple myeloma or Waldenström's disease. We found that the EPO formation in response to anemia in these patients was inversely related to plasma viscosity. A similar inverse relationship between plasma viscosity and EPO production was seen in rats in which EPO formation had been stimulated by exchange transfusion and the plasma viscosity of which was thereby altered by using exchange solutions of different composition to alter plasma viscosity and thus whole blood viscosity independently from hematocrit. Raising the gammaglobulin concentration to approximately 40 mg/ml plasma in the rats almost totally blunted the rise in serum EPO levels despite a fall of the hematocrit to 20%. Determination of renal EPO mRNA levels by RNase protection revealed that the reductions in serum EPO levels at higher plasma viscosities were paralleled by reductions in renal EPO mRNA levels. Taken together, our findings suggest that plasma viscosity may be a significant inhibitory modulator of anemia-induced EPO formation. The increased plasma viscosity in patients with hypergammaglobulinemias may therefore contribute to the inappropriate EPO production, which is a major reason for the anemia developing in these patients
Nonlocal and local models for taxis in cell migration: a rigorous limit procedure
A rigorous limit procedure is presented which links nonlocal models involving adhesion or nonlocal chemotaxis to their local counterparts featuring haptotaxis and classical chemotaxis, respectively. It relies on a novel reformulation of the involved nonlocalities in terms of integral operators applied directly to the gradients of signal-dependent quantities. The proposed approach handles both model types in a unified way and extends the previous mathematical framework to settings that allow for general solution-dependent coefficient functions. The previous forms of nonlocal operators are compared with the new ones introduced in this paper and the advantages of the latter are highlighted by concrete examples. Numerical simulations in 1D provide an illustration of some of the theoretical findings
Interaction-dependent photon-assisted tunneling in optical lattices: a quantum simulator of strongly-correlated electrons and dynamical gauge fields
We introduce a scheme that combines photon-assisted tunneling by a moving optical lattice with strong Hubbard interactions, and allows for the quantum simulation of paradigmatic quantum many-body models. We show that, in a certain regime, this quantum simulator yields an effective Hubbard Hamiltonian with tunable bond-charge interactions, a model studied in the context of strongly-correlated electrons. In a different regime, we show how to exploit a correlated destruction of tunneling to explore Nagaoka ferromagnetism at finite Hubbard repulsion. By changing the photon-assisted tunneling parameters, we can also obtain a t-J model with independently controllable tunneling t, super-exchange interaction J, and even a Heisenberg-Ising anisotropy. Hence, the full phase diagram of this paradigmatic model becomes accessible to cold-atom experiments, departing from the region t _ J allowed by standard single-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show that, by generalizing the photon-assisted tunneling scheme, the quantum simulator yields models of dynamical Gauge fields, where atoms of a given electronic state dress the tunneling of the atoms with a different internal state, leading to Peierls phases that mimic a dynamical magnetic field
Limitations of balloon sinuplasty in frontal sinus surgery
Balloon sinuplasty is a tool that is used to treat selected patients with paranasal sinus pathologies. No studies have investigated the aetiology of failed access to the frontal sinus. The aim of our study was to specify the intraoperative technical failure rate and to analyse the aetiology of the failed access to predict potential technical difficulties before surgery. We retrospectively analysed the charts of patients who underwent balloon sinuplasty from November 2007 to July 2010 at three different ENT-Centres. CT-analysis of the patients with failed access was performed. Of the 104 frontal sinuses, dilation of 12 (12%) sinuses failed. The anatomy of all failed cases revealed variations in the frontal recess (frontoethmoidal-cell, frontal-bulla-cell or agger-nasi-cell) or osteoneogenesis. In one patient, a lymphoma was overlooked during a balloon only procedure. The lymphoma was diagnosed 6months later with a biopsy during functional endoscopic sinus surgery. In complex anatomical situations of the frontal recess, balloon sinuplasty may be challenging or impossible. In these situations, it is essential to have knowledge of classical functional endoscopic sinus surgery of the frontal recess area. The drawbacks of not including a histopathologic exam should be considered in balloon only procedure
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