We study collisional heating in a cold ^{7}Li-^{87}Rb mixture near a broad Feshbach resonance at 661 G. At the high field slope of the resonance, we find an enhanced three-body recombination rate ...that we interpret as a heteronuclear Efimov resonance. With improved Feshbach spectroscopy of two further resonances, a model for the molecular potentials has been developed that now consistently explains all known Feshbach resonances of the various Li-Rb isotope mixtures. The model is used to determine the scattering length of the observed Efimov state. Its value of -1870a_{0} Bohr radii supports the currently discussed assumption of universality of the three-body parameter also in heteronuclear mixtures.
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2.
2020 roadmap on plasma accelerators Albert, Félicie; Couprie, M E; Debus, Alexander ...
New journal of physics,
03/2021, Volume:
23, Issue:
3
Journal Article
Peer reviewed
Open access
Abstract
Plasma-based accelerators use the strong electromagnetic fields that can be supported by plasmas to accelerate charged particles to high energies. Accelerating field structures in plasma can ...be generated by powerful laser pulses or charged particle beams. This research field has recently transitioned from involving a few small-scale efforts to the development of national and international networks of scientists supported by substantial investment in large-scale research infrastructure. In this New Journal of Physics 2020 Plasma Accelerator Roadmap, perspectives from experts in this field provide a summary overview of the field and insights into the research needs and developments for an international audience of scientists, including graduate students and researchers entering the field.
Assessing the factors that have an impact on potential evapotranspiration (PET) sensitivity to changes in different climate variables is critical to understanding the possible implications of ...climatic changes on the catchment water balance. Using a global sensitivity analysis, this study assessed the implications of baseline climate conditions on the sensitivity of PET to a large range of plausible changes in temperature (T), relative humidity (RH), solar radiation (Rs) and wind speed (uz). The analysis was conducted at 30 Australian locations representing different climatic zones, using the Penman–Monteith and Priestley–Taylor PET models. Results from both models suggest that the baseline climate can have a substantial impact on overall PET sensitivity. In particular, approximately 2-fold greater changes in PET were observed in cool-climate energy-limited locations compared to other locations in Australia, indicating the potential for elevated water loss as a result of increasing actual evapotranspiration (AET) in these locations. The two PET models consistently indicated temperature to be the most important variable for PET, but showed large differences in the relative importance of the remaining climate variables. In particular for the Penman–Monteith model, wind and relative humidity were the second-most important variables for dry and humid catchments, respectively, whereas for the Priestley–Taylor model solar radiation was the second-most important variable, with the greatest influence in warmer catchments. This information can be useful to inform the selection of suitable PET models to estimate future PET for different climate conditions, providing evidence on both the structural plausibility and input uncertainty for the alternative models.
The syncytium is a unique plant root organ whose differentiation is induced by plant-parasitic cyst nematodes to create a source of nourishment. Syncytium formation involves the redifferentiation and ...fusion of hundreds of root cells. The underlying regulatory networks that control this unique change of plant cell fate are not understood. Here, we report that a strong downregulation of Arabidopsis (Arabidopsis thaliana) microRNA396 (miR396) in cells giving rise to the syncytium coincides with the initiation of the syncytial induction/formation phase and that specific miR396 up-regulation in the developed syncytium marks the beginning of the maintenance phase, when no new cells are incorporated into the syncytium. In addition, our results show that miR396 in fact has a role in the transition from one phase to the other. Expression modulations of miR396 and its Growth-Regulating Factor (GRF) target genes resulted in reduced syncytium size and arrested nematode development. Furthermore, genome-wide expression profiling revealed that the miR396-GRF regulatory system can alter the expression of 44% of the more than 7,000 genes reported to change expression in the Arabidopsis syncytium. Thus, miR396 represents a key regulator for the reprogramming of root cells. As such, this regulatory unit represents a powerful molecular target for the parasitic animal to modulate plant cells and force them into novel developmental pathways.
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We propose and experimentally investigate a scheme for observing Feshbach resonances in atomic quantum gases in situ and with a high temporal resolution of several tens of nanoseconds. The method is ...based on the detection of molecular ions, which are optically generated from atom pairs at small interatomic distances. As a test system we use a standard rubidium gas (^{87}Rb) with well known magnetically tunable Feshbach resonances. The fast speed and the high sensitivity of our detection scheme allows us to observe a complete Feshbach resonance within one millisecond and without destroying the gas.
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Laser-plasma accelerators, providing high electric field gradients, are promising candidates to drive next-generation compact light sources and high-energy applications. However, conservation of beam ...emittance, a prerequisite for future applications, is very challenging, as the accelerated beam has to be matched to the plasma’s strong focusing forces. Here we derive with simulations ideal laser and plasma density profiles to match an electron beam in and out of a plasma stage, thus relaxing required beta functions for injection and minimizing divergence and emittance growth after the plasma.
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Highly-efficient optical generation of narrowband terahertz radiation enables unexplored technologies and sciences from compact electron acceleration to charge manipulation in solids. ...State-of-the-art conversion efficiencies are currently achieved using difference-frequency generation driven by temporal beating of chirped pulses but remain, however, far lower than desired or predicted. Here we show that high-order spectral phase fundamentally limits the efficiency of narrowband difference-frequency generation using chirped-pulse beating and resolve this limitation by introducing a novel technique based on tuning the relative spectral phase of the pulses. For optical terahertz generation, we demonstrate a 13-fold enhancement in conversion efficiency for 1%-bandwidth, 0.361 THz pulses, yielding a record energy of 0.6 mJ and exceeding previous optically-generated energies by over an order of magnitude. Our results prove the feasibility of millijoule-scale applications like terahertz-based electron accelerators and light sources and solve the long-standing problem of temporal irregularities in the pulse trains generated by interfering chirped pulses.
We prove first-order convergence of the semi-explicit Euler scheme combined with a finite element discretization in space for elliptic-parabolic problems which are weakly coupled. This setting ...includes poroelasticity, thermoelasticity, as well as multiple-network models used in medical applications. The semi-explicit approach decouples the system such that each time step requires the solution of two small and well-structured linear systems rather than the solution of one large system. The decoupling improves the computational efficiency without decreasing the convergence rates. The presented convergence proof is based on an interpretation of the scheme as an implicit method applied to a constrained partial differential equation with delay term. Here, the delay time equals the used step size. This connection also allows a deeper understanding of the weak coupling condition, which we accomplish to quantify explicitly.
The development and application of evolutionary algorithms (EAs) and other metaheuristics for the optimisation of water resources systems has been an active research field for over two decades. ...Research to date has emphasized algorithmic improvements and individual applications in specific areas (e.g. model calibration, water distribution systems, groundwater management, river-basin planning and management, etc.). However, there has been limited synthesis between shared problem traits, common EA challenges, and needed advances across major applications. This paper clarifies the current status and future research directions for better solving key water resources problems using EAs. Advances in understanding fitness landscape properties and their effects on algorithm performance are critical. Future EA-based applications to real-world problems require a fundamental shift of focus towards improving problem formulations, understanding general theoretic frameworks for problem decompositions, major advances in EA computational efficiency, and most importantly aiding real decision-making in complex, uncertain application contexts.
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