We investigate the possibility of a bistable phase in an open many-body system. To this end, we discuss the microscopic dynamics of a continuously off-resonantly driven Rydberg lattice gas in the ...regime of strong decoherence. Our experimental results reveal a prolongation of the temporal correlations exceeding the lifetime of a single Rydberg excitation and show strong evidence for the formation of finite-sized Rydberg excitation clusters in the steady state. We simulate the dynamics of the system using a simplified and a full many-body rate-equation model. The results are compatible with the formation of metastable states associated with a bimodal counting distribution as well as dynamic hysteresis. However, a scaling analysis reveals that the correlation times remain finite for all relevant system parameters, which suggests the formation of many small Rydberg clusters and finite correlation lengths of Rydberg excitations. These results constitute strong evidence against the presence of a global bistable phase previously suggested to exist in this system.
Abstract
Dissipative phase transitions are a characteristic feature of open systems. One of the paradigmatic examples for a first order dissipative phase transition is the driven nonlinear ...single-mode optical resonator. In this work, we study a realization with an ultracold bosonic quantum gas, which generalizes the single-mode system to many modes and stronger interactions. We measure the effective Liouvillian gap of the system and find evidence for a first order dissipative phase transition. Due to the multi-mode nature of the system, the microscopic dynamics is much richer and allows us to identify a non-equilibrium condensation process.
► Characterization of CO2–brine primary drainage on basis of experimental data. ► Criteria for instable displacement in two-phase flow: mobility, capillarity, gravity. ► CO2–brine displacement is ...stabilized on experimental scale by capillary pressure. ► Upscaling to field scale—instable displacement on field scale possible. ► Gravity overrun dominates fingering pattern in gravity-dominated, instable system.
The viscous stability of the primary drainage process is of major interest for the injection of carbon dioxide (CO2) in saline aquifers, since it determines the spread of the CO2 plume in the target aquifer and consequently the initial utilization of the pore space for CO2 storage. In order to analyze the stability of the displacement process, the relative permeability saturation functions must be known; these are usually derived by experiments under conditions representative for the field. It is therefore very important to characterize the flood front stability, not only on the field scale but also on the experimental scale, in order to judge the validity of the experimental results as a precondition for reliable field simulations.
Here we investigate the onset of viscous fingering, thereby studying under what conditions CO2–brine displacement remains stable. We discuss the role of relative permeability and the stabilizing effect of capillary pressure at different length scales by means of numerical simulations. The results allow us to assess different definitions of the mobility ratio and establish criteria for judging the stability of the displacement process. We further show that in cases where gravitational forces are important, the gravity tongue dominates the fingering pattern, and unstable situations can occur where stability would be predicted, by considering viscous and capillary forces only.
In the literature various criteria for the onset of instability have been proposed, but these are inconsistent or inconclusive. Our intention is to bring order into this discussion. In the present study we validate or refute stability criteria by numerical modeling and show that the shock-front mobility ratio correctly describes the onset of fingering. The application of our findings is not limited to CO2–brine displacement. The criteria for stability can be applied to most two-phase flow problems in reservoir engineering in general ranging from water flooding to low interfacial tension surfactant flooding.
Unlike the widely studied ReFeAsO series, the newly discovered iron-based superconductor ThFeAsN exhibits a remarkably high critical temperature of 30 K, without chemical doping or external pressure. ...Here we investigate in detail its magnetic and superconducting properties via muon-spin rotation/relaxation and nuclear magnetic resonance techniques and show that ThFeAsN exhibits strong magnetic fluctuations, suppressed below ~35 K, but no magnetic order. This contrasts strongly with the ReFeAsO series, where stoichiometric parent materials order antiferromagnetically and superconductivity appears only upon doping. The ThFeAsN case indicates that Fermi-surface modifications due to structural distortions and correlation effects are as important as doping in inducing superconductivity. The direct competition between antiferromagnetism and superconductivity, which in ThFeAsN (as in LiFeAs) occurs at already zero doping, may indicate a significant deviation of the s-wave superconducting gap in this compound from the standard s
scenario.Exploring the interplay between the superconducting gap and the antiferromagnetic phase in Fe-based superconductors remains an open issue. Here, the authors show that Fermi-surface modifications by means of structural distortions and correlation effects are as important as doping in inducing superconductivity in undoped ThFeAsN.
Feshbach resonances are a powerful tool to tune the interaction in an ultracold atomic gas. The commonly used magnetic Feshbach resonances are specific for each species and are restricted with ...respect to their temporal and spatial modulation. Optical Feshbach resonances are an alternative which can overcome this limitation. Here, we show that ultra-long-range Rydberg molecules can be used to implement an optical Feshbach resonance. Tuning the on-site interaction of a degenerate Bose gas in a 3D optical lattice, we demonstrate a similar performance compared to recent realizations of optical Feshbach resonances using intercombination transitions. Our results open up a class of optical Feshbach resonances with a plenitude of available lines for many atomic species and the possibility to further increase the performance by carefully selecting the underlying Rydberg state.
We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). ...We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Because of the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems.
We propose a scheme to realize a heavy Rydberg system (HRS), a bound pair of oppositely charged ions, from a gas of ultracold atoms. The intermediate step to achieve large internuclear separations is ...the creation of a unique class of ultra-long-range Rydberg molecules bound in a stairwell potential energy curve. Here, a ground-state atom is bound to a Rydberg atom in an oscillatory potential emerging due to attractive singlet p-wave electron scattering. The utility of our approach originates in the large electronic dipole transition element between the Rydberg and the ionic molecule, while the nuclear configuration of the ultracold gas is preserved. The Rabi coupling between the Rydberg molecule and the heavy Rydberg system is typically in the MHz range and the permanent electric dipole moments of the HRS can be as large as one kilo-Debye. We identify specific transitions which place the creation of the heavy Rydberg system within immediate reach of experimental realization.
During imbibition, initially connected oil is displaced until it is trapped as immobile clusters. While initial and final states have been well described before, here we image the dynamic transient ...process in a sandstone rock using fast synchrotron‐based X‐ray computed microtomography. Wetting film swelling and subsequent snap off, at unusually high saturation, decreases nonwetting phase connectivity, which leads to nonwetting phase fragmentation into mobile ganglia, i.e., ganglion dynamics regime. We find that in addition to pressure‐driven connected pathway flow, mass transfer in the oil phase also occurs by a sequence of correlated breakup and coalescence processes. For example, meniscus oscillations caused by snap‐off events trigger coalescence of adjacent clusters. The ganglion dynamics occurs at the length scale of oil clusters and thus represents an intermediate flow regime between pore and Darcy scale that is so far dismissed in most upscaling attempts.
Key Points
Ganglion dynamics contributes to nonwetting phase transport
Coalescence of nonwetting phase clusters is triggered by snap off
Ganglion dynamics occurs from 75% nonwetting phase saturation on
•Quasi-static simulation of two-phase flow in porous media agrees with experimental data within experimental uncertainty for drainage.•A morphological approach, which approximates capillary ...displacement, does not represent the imbibition process.•Ultimately for modeling relative permeability in imbibition an approach is needed that captures moving liquid-liquid interfaces which requires viscous and capillary forces simultaneously.•If pore scale fluid distributions are available e.g. from micro-CT flow experiments, relative permeability can be estimated from the connected pathway flow (for low capillary numbers).•The agreement is better at low water saturations where the oil phase is predominantly connected than at higher water saturation where the oil phase is increasingly disconnected.
Pore-scale images obtained from a synchrotron-based X-ray computed micro-tomography (µCT) imbibition experiment in sandstone rock were used to conduct Navier–Stokes flow simulations on the connected pathways of water and oil phases. The resulting relative permeability was compared with steady-state Darcy-scale imbibition experiments on 5cm large twin samples from the same outcrop sandstone material. While the relative permeability curves display a large degree of similarity, the endpoint saturations for the µCT data are 10% in saturation units higher than the experimental data. However, the two datasets match well when normalizing to the mobile saturation range. The agreement is particularly good at low water saturations, where the oil is predominantly connected. Apart from different saturation endpoints, in this particular experiment where connected pathway flow dominates, the discrepancies between pore-scale connected pathway flow simulations and Darcy-scale steady-state data are minor overall and have very little impact on fractional flow. The results also indicate that if the pore-scale fluid distributions are available and the amount of disconnected non-wetting phase is low, quasi-static flow simulations may be sufficient to compute relative permeability. When pore-scale fluid distributions are not available, fluid distributions can be obtained from a morphological approach, which approximates capillary-dominated displacement. The relative permeability obtained from the morphological approach compare well to drainage steady state whereas major discrepancies to the imbibition steady-state experimental data are observed. The morphological approach does not represent the imbibition process very well and experimental data for the spatial arrangement of the phases are required. Presumably for modeling imbibition relative permeability an approach is needed that captures moving liquid-liquid interfaces, which requires viscous and capillary forces simultaneously.
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Background
Oral challenges are the gold standard in food allergy diagnostic, but time‐consuming. Aim of the study was to investigate the role of peanut‐ and hazelnut‐component‐specific IgE in the ...diagnostics of peanut and hazelnut allergy and to identify cutoff levels to make some challenges superfluous.
Methods
In a prospective and multicenter study, children with suspected peanut or hazelnut allergy underwent oral challenges. Specific IgE to peanut, hazelnut, and their components (Ara h 1, Ara h 2, Ara h 3, and Ara h 8, Cor a 1, Cor a 8, Cor a 9, and Cor a 14) were determined by ImmunoCAP‐FEIA.
Results
A total of 210 children were challenged orally with peanut and 143 with hazelnut. 43% of the patients had a positive peanut and 31% a positive hazelnut challenge. With an area under the curve of 0.92 and 0.89, respectively, Ara h 2 and Cor a 14‐specific IgE discriminated between allergic and tolerant children better than peanut‐ or hazelnut‐specific IgE. For the first time, probability curves for peanut and hazelnut components have been calculated. A 90% probability for a positive peanut or hazelnut challenge was estimated for Ara h 2‐specific IgE at 14.4 kU/l and for Cor a 14‐specific IgE at 47.8 kU/l. A 95% probability could only be estimated for Ara h 2 at 42.2 kU/l.
Conclusions
Ara h 2‐ and Cor a 14‐specific IgE are useful to estimate the probability for a positive challenge outcome in the diagnostic work‐up of peanut or hazelnut allergy making some food challenges superfluous.
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