Visualisation of diesel injector with neutron imaging

The injection process of diesel engines influences the pollutant emissions. The spray formation is significantly influenced by the internal flow of the injector. One of the key parameters here is the generation of cavitation caused by the geometry and the needle lift.In modern diesel engines the injection pressure is established up to 3000 bar. The details of the flow and phase change processes inside the injector are of increasing importance for such injectors. With these experimental measurements the validation of multiphase and cavitation models is possible for the high pressure range. Here, for instance, cavitation effects can occur. Cavitation effects in the injection port area destabilize the emergent fuel jet and improve the jet break-up.The design of the injection system in direct-injection diesel engines is an important challenge, as the jet breakup, the atomization and the mixture formation in the combustion chamber are closely linked. These factors have a direct impact on emissions, fuel consumption and performance of an engine. The shape of the spray at the outlet is determined by the internal flow of the nozzle. Here, geometrical parameters, the injection pressure, the injection duration and the cavitation phenomena play a major role.In this work, the flow dependency in the nozzles are analysed with the Neutron-Imaging. The great advantage of this method is the penetrability of the steel structure while a high contrast to the fuel is given due to the interaction of the neutrons with the hydrogen amount. Compared to other methods (optical with glass structures) we can apply real components under highest pressure conditions. During the steady state phase of the injection various cavitation phenomena are visible in the injector, being influenced by the nozzle geometry and the fuel pressure. Different characteristics of cavitation in the sac and spray hole can be detected, and the spray formation in the primary breakup zone is influenced

Dynamic volume magnetic domain wall imaging in grain oriented electrical steel at power frequencies with accumulative high-frame rate neutron dark-field imaging

The mobility of magnetic domains forms the link between the basic physical properties of a magnetic material and its global characteristics such as permeability and saturation field. Most commonly, surface domain structure are studied using magneto-optical Kerr microscopy. The limited information depth of approx. 20 nanometers, however, allows only for an indirect interpretation of the internal volume domain structures. Here we show how accumulative high-frame rate dynamic neutron dark-field imaging is able for the first time to visualize the dynamic of the volume magnetic domain structures in grain oriented electrical steel laminations at power frequencies. In particular we studied the volume domain structures with a spatial resolution of ∼100 μm and successfully quantified domain sizes, wall velocities, domain annihilation and its duration and domain wall multiplication in real time recordings at power frequencies of 10, 25 and 50 Hz with ±262.5 A/m and ±525 A/m (peak to peak) applied field

Visualization of Bulk Magnetic Properties by Neutron Grating Interferometry

The neutron Grating Interferometer (nGI) is a standard user instrument at the cold neutron imaging beamline ICON (Kaestner, 2011) at the neutron source SINQ at Paul Scherrer Institute (PSI), Switzerland. The setup is able to deliver simultaneously information about the attenuation, phase shift (DPC) (Pfeiffer, 2006) and scattering properties in the so-called dark-field image (DFI) (Grünzweig, 2008-I) of a sample. Since neutrons only interact with the nucleus they are often able to penetrate deeper into matter than X-rays, in particular heavier materials. A further advantage of neutrons compared to X-rays is the interaction of the neutron's magnetic moment with magnetic structures that allows for the bulk investigation of magnetic domain structures using the nGI technique (Grünzweig, 2008-II). The nGI-setup and its technique for imaging with cold neutrons is presented in this contribution. The main focus will be on magnetic investigations of electrical steel laminations using the nGI technique. Both, grain-oriented (GO) and non-oriented (NO) laminations will be presented. GO-laminations are widely used in industrial transformer applications, while NO-sheets are common in electrical machines. For grain-oriented sheet, domain walls were visualized individually,spatially resolved, while in NO-sheet a relative density distribution is depicted

Hyperfine Spectroscopy of Optically Trapped Atoms

We perform spectroscopy on the hyperfine splitting of $^{85}$Rb atoms trapped in far-off-resonance optical traps. The existence of a spatially dependent shift in the energy levels is shown to induce an inherent dephasing effect, which causes a broadening of the spectroscopic line and hence an inhomogeneous loss of atomic coherence at a much faster rate than the homogeneous one caused by spontaneous photon scattering. We present here a number of approaches for reducing this inhomogeneous broadening, based on trap geometry, additional laser fields, and novel microwave pulse sequences. We then show how hyperfine spectroscopy can be used to study quantum dynamics of optically trapped atoms.Comment: Review/Tutoria

Synthetic three-dimensional atomic structures assembled atom by atom

We demonstrate the realization of large, fully loaded, arbitrarily-shaped three-dimensional arrays of single atoms. Using holographic methods and real-time, atom-by-atom, plane-by-plane assembly, we engineer atomic structures with up to 72 atoms separated by distances of a few micrometres. Our method allows for high average filling fractions and the unique possibility to obtain defect-free arrays with high repetition rates. These results find immediate application for the quantum simulation of spin Hamiltonians using Rydberg atoms in state-of-the-art platforms, and are very promising for quantum-information processing with neutral atoms.Comment: 5 pages, 3 figure

Soil respiration at mean annual temperature predicts annual total across vegetation types and biomes

Soil respiration (SR) constitutes the largest flux of CO₂ from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (〖SR〗_MAT), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q₁₀). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SRMAT corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure 〖SR〗_MAT for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO₂ emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle

A Monte Carlo approach for scattering correction towards quantitative neutron imaging of polycrystals

The development of neutron imaging from a qualitative inspection tool towards a quantitative technique in materials science has increased the requirements for accuracy significantly. Quantifying the thickness or the density of polycrystalline samples with high accuracy using neutron imaging has two main problems: (i) the scattering from the sample creates artefacts on the image and (ii) there is a lack of specific reference attenuation coefficients. This work presents experimental and simulation results to explain and approach these problems. Firstly, a series of neutron radiography and tomography experiments of iron, copper and vanadium are performed and serve as a reference. These materials were selected because they attenuate neutrons mainly through coherent (Fe and Cu) and incoherent (V) scattering. Secondly, an ad hoc Monte Carlo model was developed, based on beamline, sample and detector parameters, in order to simulate experiments, understand the physics involved and interpret the experimental data. The model, developed in the McStas framework, uses a priori information about the sample geometry and crystalline structure, as well as beamline settings, such as spectrum, geometry and detector type. The validity of the simulations is then verified with experimental results for the two problems that motivated this work: (i) the scattering distribution in transmission imaging and (ii) the calculated attenuation coefficients.</jats:p

Single-Spin Addressing in an Atomic Mott Insulator

Ultracold atoms in optical lattices are a versatile tool to investigate fundamental properties of quantum many body systems. In particular, the high degree of control of experimental parameters has allowed the study of many interesting phenomena such as quantum phase transitions and quantum spin dynamics. Here we demonstrate how such control can be extended down to the most fundamental level of a single spin at a specific site of an optical lattice. Using a tightly focussed laser beam together with a microwave field, we were able to flip the spin of individual atoms in a Mott insulator with sub-diffraction-limited resolution, well below the lattice spacing. The Mott insulator provided us with a large two-dimensional array of perfectly arranged atoms, in which we created arbitrary spin patterns by sequentially addressing selected lattice sites after freezing out the atom distribution. We directly monitored the tunnelling quantum dynamics of single atoms in the lattice prepared along a single line and observed that our addressing scheme leaves the atoms in the motional ground state. Our results open the path to a wide range of novel applications from quantum dynamics of spin impurities, entropy transport, implementation of novel cooling schemes, and engineering of quantum many-body phases to quantum information processing.Comment: 8 pages, 5 figure

Dryland mechanisms could widely control ecosystem functioning in a drier and warmer world

Responses of terrestrial ecosystems to climate change have been explored in many regions worldwide. While continued drying and warming may alter process rates and deteriorate the state and performance of ecosystems, it could also lead to more fundamental changes in the mechanisms governing ecosystem functioning. Here we argue that climate change will induce unprecedented shifts in these mechanisms in historically wetter climatic zones, towards mechanisms currently prevalent in dry regions, which we refer to as ‘dryland mechanisms’. We discuss 12 dryland mechanisms affecting multiple processes of ecosystem functioning, including vegetation development, water flow, energy budget, carbon and nutrient cycling, plant production and organic matter decomposition. We then examine mostly rare examples of the operation of these mechanisms in non-dryland regions where they have been considered irrelevant at present. Current and future climate trends could force microclimatic conditions across thresholds and lead to the emergence of dryland mechanisms and their increasing control over ecosystem functioning in many biomes on Earth.The support of the Israel Science Foundation is acknowledged by J.M.G. (grant number 1796/19), O.A. (1185/17) and E.M. (1053/17). M.B. acknowledges funding through the ÖAW-ESS project ClimGrassHydro (Austrian Academy of Sciences).Peer reviewe