Density fluctuations in granular piles traversing the glass transition: A grain-scale characterization via the internal energy

The grain-scale dynamics of the internal energy inside a tapped granular pile is studied, advancing on a kinetic theory of grains.

Structural Heterogeneity of an Amorphous-Nanocrystalline Alloy Fe77Cu1Si16B6 in the Nanometer Range

In this article, an alloy of the Finemet type Fe77Cu1Si16B6 obtained by quenching from a liquid state (spinning method) in the initial state is investigated. The main research methods were scanning and transmission electron microscopy. Methods for describing multiscale structural heterogeneities in amorphous-nanocrystalline alloys have been developed, allowing the structural state to be described and its influence on the physicochemical and technical properties to be determined depending on the technological conditions for obtaining these alloys. Representation of electron microscopic images in the form of Fourier spectra made it possible to reveal the nature of the formation of short- and middle-order in amorphous-nanocrystalline alloys according to the principle of self-similar spatial structures. The analysis of electron microscopic images by integral Lebesgue measures revealed density fluctuations over the alloy volume, which corresponds to the hierarchical representation of structural inhomogeneities in amorphous metallic alloys.

Hybrid simulation of instabilities in capacitively coupled RF CF4/Ar plasmas

Radio frequency capacitively coupled plasmas (RF CCPs) sustained in fluorocarbon gases or their mixtures with argon are widely used in plasma-enhanced etching. In this work, we conduct studies on instabilities in a capacitive CF4/Ar (1:9) plasma driven at 13.56 MHz at a pressure of 150 mTorr, by using a one-dimensional fluid/Monte-Carlo (MC) hybrid model. Fluctuations are observed in densities and fluxes of charged particles, electric field, as well as electron impact reaction rates, especially in the bulk. As the gap distance between the electrodes increases from 2.8 cm to 3.8 cm, the fluctuation amplitudes become smaller gradually and the instability period gets longer, as the driving power density ranges from 250 to 300 W/m2. The instabilities are on a time scale of 16-20 RF periods, much shorter than those millisecond periodic instabilities observed experimentally owing to attachment/detachment in electronegative plasmas. At smaller electrode gap, a positive feedback to the instability generation is induced by the enhanced bulk electric field in the highly electronegative mode, by which the electron temperature keeps strongly oscillating. Electrons at high energy are mostly consumed by ionization rather than attachment process, making the electron density increase and overshoot to a much higher value. And then, the discharge becomes weakly electronegative and the bulk electric field becomes weak gradually, resulting in the continuous decrease of the electron density as the electron temperature keeps at a much lower mean value. Until the electron density attains its minimum value again, the instability cycle is formed. The ionization of Ar metastables and dissociative attachment of CF4 are noticed to play minor roles compared with the Ar ionization and excitation at this stage in this mixture discharge. The variations of electron outflow from and negative ion inflow to the discharge center need to be taken into account in the electron density fluctuations, apart from the corresponding electron impact reaction rates. We also notice more than 20% change of the Ar+ ion flux to the powered electrode and about 16% difference in the etching rate due to the instabilities in the case of 2.8 cm gap distance, which is worthy of more attention for improvement of etching technology.

A poloidal high-k scattering system for NSTX-U

A previous 5-channel tangential high-k scattering system is being replaced by an 8-channel, poloidal high-k scattering system on the National Spherical Torus eXperiment Upgrade (NSTX-U) device located in Princeton, NJ, USA. The 693 GHz poloidal scattering system replaces a 280 GHz tangential scattering system to study high-k electron density fluctuations on NSTX-U, thereby considerably enhancing planned turbulence physics studies by providing a measurement of the k θ -spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Two approaches to generating the 693 GHz probe beam are under development: an optically-pumped far-infrared (FIR) laser that generates ∼50 mW, and a compact gyrotron that can potentially generate in excess of 5 W. Large aperture optics collect radiation scattered from density fluctuations in the plasma core at 8 simultaneous scattering angles ranging from 2 to 15° corresponding to poloidal wavenumbers that extend to >40 cm−1. Steerable launch optics coupled with receiver optics mounted on a 5-axis receiver carriage allow the scattering volume to be placed radially from r/a = 0.3 out to the pedestal region (r/a ∼ 0.99) and translated horizontally as needed to satisfy wavenumber matching.

Fundamental Electromagnetic Emissions by a Weak Electron Beam in Solar Wind Plasmas with Density Fluctuations

The generation of Langmuir wave turbulence by a weak electron beam in a randomly inhomogeneous plasma and its subsequent electromagnetic radiation are studied owing to two-dimensional particle-in-cell simulations in conditions relevant to type III solar radio bursts. The essential impact of random density fluctuations of average levels of a few percents of the background plasma on the characteristics of the electromagnetic radiation at the fundamental plasma frequency ω p is shown. Not only wave nonlinear interactions but also processes of Langmuir waves’ transformations on the density fluctuations contribute to the generation of such emissions. During the beam relaxation, the amount of electromagnetic energy radiated at ω p in a plasma with density fluctuations strongly exceeds that observed when the plasma is homogeneous. The fraction of Langmuir wave energy involved in the generation of electromagnetic emissions at ω p saturates around 10−4, i.e., one order of magnitude above that reached when the plasma is uniform. Moreover, whereas harmonic emission at 2ω p dominates over fundamental emission during the time evolution in a homogeneous plasma, fundamental emission is strongly dominant when the plasma contains density fluctuations, at least during several thousands of plasma periods before being overcome by harmonic emission when the total electromagnetic energy begins to saturate.

Dark Energy Survey Year 3 Results: Measuring the Survey Transfer Function with Balrog

We describe an updated calibration and diagnostic framework, Balrog, used to directly sample the selection and photometric biases of the Dark Energy Survey (DES) Year 3 (Y3) data set. We systematically inject onto the single-epoch images of a random 20% subset of the DES footprint an ensemble of nearly 30 million realistic galaxy models derived from DES Deep Field observations. These augmented images are analyzed in parallel with the original data to automatically inherit measurement systematics that are often too difficult to capture with generative models. The resulting object catalog is a Monte Carlo sampling of the DES transfer function and is used as a powerful diagnostic and calibration tool for a variety of DES Y3 science, particularly for the calibration of the photometric redshifts of distant “source” galaxies and magnification biases of nearer “lens” galaxies. The recovered Balrog injections are shown to closely match the photometric property distributions of the Y3 GOLD catalog, particularly in color, and capture the number density fluctuations from observing conditions of the real data within 1% for a typical galaxy sample. We find that Y3 colors are extremely well calibrated, typically within ∼1–8 mmag, but for a small subset of objects, we detect significant magnitude biases correlated with large overestimates of the injected object size due to proximity effects and blending. We discuss approaches to extend the current methodology to capture more aspects of the transfer function and reach full coverage of the survey footprint for future analyses.

Cell-wall fluorescence highlights the phases of xylogenesis

The monitoring of xylogenesis makes it possible to follow tree growth responses to stress factors in real-time, by observing the course of wood cell division and differentiation. Proper microscopy techniques are of key importance to exactly identify the xylem cells during the different phases of differentiation. We aimed to apply epifluorescence microscopy to follow the lignification process during the different phases of xylogenesis in Mediterranean softwood and hardwood. Microcores from trees of Pinus halepensis Mill. and Arbutus unedo L. were collected at a site in southern Italy, during the period June-December. Fluorescence imaging of sections stained with a water solution of safranin and Astra blue clearly highlighted the contrast between lignified and un-lignified tissue. The proposed methodology is useful to quickly and unambiguously detect the different stages of cell differentiation, as well as the progress in the lignification process. Moreover, it proved to be easily applied to demanding wood materials, such as Mediterranean woods and can be helpful to better track stress responses and the development of anomalies during wood formation, such as intra-annual density fluctuations.