Investigation of Nanoparticles in High Resolution Scanning Electron Microscopy (SEM) and Low Voltage SEM by Digital Image-Analysis

Small particles (Cu, Ag, In, Sn, Au, also MgO and NaCl) were prepared in the diameter range from 1 nm to 100 nm on different conductive substrates by thermal evaporation in high-vacuum or in an inert gas atmosphere. Imaging of the particles was performed in a high resolution scanning electron microscope (HRSEM) that can also be operated at low beam voltages of a few hundred volts. This mode of operation is called low voltage SEM (LVSEM). Scanning electron micrographs were taken at different beam voltages VO (0.5-30 kV). The micrographs were digitally recorded and analyzed with an image processing system operated on-line to the HRSEM. Grey-value line profiles and densitometric quantities of single particles, as well as the contrast between particle and substrate, changed with VO. The results for tin-particles on a bulk carbon substrate are shown. In all cases considered, only positive contrasts, i.e., particles looking brighter than the substrate, were obtained. The main contrast producing mechanism is, therefore, assigned to effects that include the particle\u27s geometrical properties of size, shape and surface. Sn-, In-, and Ag-particles, imaged in the secondary electron (SE) mode showed significantly larger particle diameters, as did images simultaneously recorded with transmitted electrons; however, Au-particles did not show that difference. This effect may be qualitatively explained by SE resulting from decaying plasmons

Radio Scattering Horizons for Galactic and Extragalactic Transients

Radio wave scattering can cause severe reductions in detection sensitivity for surveys of Galactic and extragalactic fast ($\sim$ms duration) transients. While Galactic sources like pulsars are subject to scattering in the Milky Way interstellar medium (ISM), extragalactic fast radio bursts (FRBs) can also experience scattering in their host galaxies and other galaxies intervening their lines-of-sight. We assess Galactic and extragalactic scattering horizons for fast radio transients using a combination of NE2001 to model the dispersion measure (DM) and scattering time ($\tau$) contributed by the Milky Way, and independently constructed electron density models for other galaxies' ISMs and halos that account for different galaxy morphologies, masses, densities, and strengths of turbulence. For FRB source redshifts $z_{\rm s} \lesssim 1$, an all-sky, isotropic FRB population has values of $\tau$ ranging between $\sim 1\ \mu$s and$\sim 2$ms at 1 GHz (observer frame) that are dominated by host galaxies. For a hypothetical, high-redshift ($z_{\rm s}\sim5$) FRB population,$\tau$ranges from$\sim 0.01 - 100$s of ms at 1 GHz, and is largely dominated by intervening galaxies. About$20\%$of these high-redshift FRBs are predicted to have$\tau > 5$ms at 1 GHz (observer frame), and$\gtrsim 40\%$of FRBs between$z_{\rm s} \sim 0.5 - 5$are predicted to have$\tau \gtrsim 1$ms for$\nu\leq 800$ MHz. The percentage of FRBs selected against from scattering may be substantially larger because our scattering predictions are conservative compared to localized FRBs, and if circumgalactic turbulence causes density fluctuations larger than those observed from nearby halos.Comment: 24 pages, 14 figures, submitted to Ap

The Effects of a Pre-Workout Energy Drink on Measures of Physical Performance

The purpose of this study was to investigate the effects of a pre-workout commercial energy drink on parameters of exercise performance, including anaerobic power, muscular endurance, speed, and reaction time. This study used a randomized, double blind, placebo controlled, parallel design. Participants visited the laboratory on two different occasions. On the first visit, participants were assessed for anaerobic power (via a vertical jump test), muscular endurance, reaction time, reactive sprint test, and aerobic power (via a 1.5 mile run). On the second visit, participants were randomly assigned to ingest four ounces of the energy drink beverage or a similar-tasting placebo beverage 30-minutes prior to engaging in these same physical performance tests. The energy drink treatment had no effect on anaerobic power (vertical jump), reaction time, reactive sprint test, or aerobic power. For the push-up to fatigue test, a significant difference (p = 0.014) was observed with the energy drink treatment enhancing performance by 12% as compared to the placebo treatment (improvement of ~ 4%). For the sit-up to fatigue test, a non-significant difference (p = 0.075) was observed with the energy drink treatment resulting in an enhancement of performance by ~13% as compared to no improvement for the placebo treatment. In light of these findings, individuals whose upper-body muscular endurance performance is part of their physical fitness assessment program may benefit from pre-workout energy drink consumption. In contrast, individuals needing to demonstrate anaerobic/aerobic power, or reactive abilities should not expect an improvement in performance from pre-workout energy drink consumption

Effect of annealing on the interfacial Dzyaloshinskii-Moriya interaction in Ta/CoFeB/MgO trilayers

The interfacial Dzyaloshinskii-Moriya interaction (DMI) has been shown to stabilize homochiral N´eel-type domain walls in thin films with perpendicular magnetic anisotropy and as a result permit them to be propagated by a spin Hall torque. In this study, we demonstrate that in Ta/Co20Fe60B20/MgO the DMI may be influenced by annealing. We find that the DMI peaks at D = 0.057 ± 0.003 mJ/m2 at an annealing temperature of 230 ◦C. DMI fields were measured using a purely field-driven creep regime domain expansion technique. The DMI field and the anisotropy field follow a similar trend as a function of annealing temperature. We infer that the behavior of the DMI and the anisotropy are related to interfacial crystal ordering and B expulsion out of the CoFeB layer as the annealing temperature is increased

Scattering variability detected from the circumsource medium of FRB 20190520B

Fast radio bursts (FRBs) are millisecond-timescale radio transients, the origins of which are predominantly extragalactic and likely involve highly magnetized compact objects. FRBs undergo multipath propagation, or scattering, from electron density fluctuations on sub-parsec scales in ionized gas along the line-of-sight. Scattering observations have located plasma structures within FRB host galaxies, probed Galactic and extragalactic turbulence, and constrained FRB redshifts. Scattering also inhibits FRB detection and biases the observed FRB population. We report the detection of scattering times from the repeating FRB 20190520B that vary by up to a factor of two or more on minutes to days-long timescales. In one notable case, the scattering time varied from $7.9\pm0.4$ ms to less than 3.1 ms ($95\%$ confidence) over 2.9 minutes at 1.45 GHz. The scattering times appear to be uncorrelated between bursts or with dispersion and rotation measure variations. Scattering variations are attributable to dynamic, inhomogeneous plasma in the circumsource medium, and analogous variations have been observed from the Crab pulsar. Under such circumstances, the frequency dependence of scattering can deviate from the typical power-law used to measure scattering. Similar variations may therefore be detectable from other FRBs, even those with inconspicuous scattering, providing a unique probe of small-scale processes within FRB environments.Comment: 10 pages, 9 figures, accepted to MNRA

Pulsar Scintillation through Thick and Thin: Bow Shocks, Bubbles, and the Broader Interstellar Medium

Observations of pulsar scintillation are among the few astrophysical probes of very small-scale ($\lesssim$ au) phenomena in the interstellar medium (ISM). In particular, characterization of scintillation arcs, including their curvature and intensity distributions, can be related to interstellar turbulence and potentially over-pressurized plasma in local ISM inhomogeneities, such as supernova remnants, HII regions, and bow shocks. Here we present a survey of eight pulsars conducted at the Five-hundred-meter Aperture Spherical Telescope (FAST), revealing a diverse range of scintillation arc characteristics at high sensitivity. These observations reveal more arcs than measured previously for our sample. At least nine arcs are observed toward B1929$+$10 at screen distances spanning $\sim 90\%$ of the pulsar's $361$ pc path-length to the observer. Four arcs are observed toward B0355$+$54, with one arc yielding a screen distance as close as $\sim10^5$ au ($<1$ pc) from either the pulsar or the observer. Several pulsars show highly truncated, low-curvature arcs that may be attributable to scattering near the pulsar. The scattering screen constraints are synthesized with continuum maps of the local ISM and other well-characterized pulsar scintillation arcs, yielding a three-dimensional view of the scattering media in context.Comment: 20 pages, 14 figures. Submitted to MNRAS and comments welcome. Interactive version of Figure 12 available at https://stella-ocker.github.io/scattering_ism3d_ocker202

Pulsar scintillation through thick and thin: Bow shocks, bubbles, and the broader interstellar medium

Observations of pulsar scintillation are among the few astrophysical probes of very small-scale (≲ au) phenomena in the interstellar medium (ISM). In particular, characterization of scintillation arcs, including their curvature and intensity distributions, can be related to interstellar turbulence and potentially overpressurized plasma in local ISM inhomogeneities, such as supernova remnants, H II regions, and bow shocks. Here we present a survey of eight pulsars conducted at the Five-hundred-metre Aperture Spherical Telescope (FAST), revealing a diverse range of scintillation arc characteristics at high sensitivity. These observations reveal more arcs than measured previously for our sample. At least nine arcs are observed toward B1929+10 at screen distances spanning ~90 per cent of the pulsar’s 361 pc path length to the observer. Four arcs are observed toward B0355+54, with one arc yielding a screen distance as close as ∼105 au (<1 pc) from either the pulsar or the observer. Several pulsars show highly truncated, low-curvature arcs that may be attributable to scattering near the pulsar. The scattering screen constraints are synthesized with continuum maps of the local ISM and other well-characterized pulsar scintillation arcs, yielding a three-dimensional view of the scattering media in context

Magnetic domain wall curvature induced by wire edge pinning

open14In this study, we report on the analysis of the magnetic domain wall (DW) curvature due to magnetic field induced motion in Ta/CoFeB/MgO and Pt/Co/Pt wires with perpendicular magnetic anisotropy. In wires of 20 mu m and 25 mu m, a large edge pinning potential produces the anchoring of the DW ends to the wire edges, which is evidenced as a significant curvature of the DW front as it propagates. As the driving magnetic field is increased, the curvature reduces as a result of the system moving away from the creep regime of DW motion, which implies a weaker dependence of the DW dynamics on the interaction between the DW and the wire edge defects. A simple model is derived to describe the dependence of the DW curvature on the driving magnetic field and allows us to extract the parameter sigma (E), which accounts for the strength of the edge pinning potential. The model describes well the systems with both weak and strong bulk pinning potentials like Ta/CoFeB/MgO and Pt/Co/Pt, respectively. This provides a means to quantify the effect of edge pinning induced DW curvature on magnetic DW dynamics.embargoed_20210815Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D.Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D