231 research outputs found
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 (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 () 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 , an
all-sky, isotropic FRB population has values of ranging between $\sim 1\
\mu\sim 2z_{\rm s}\sim5\tau\sim 0.01 - 10020\%\tau > 5\gtrsim 40\%z_{\rm s} \sim 0.5 - 5\tau \gtrsim 1\nu\leq 800$ 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
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 ms to less than 3.1 ms ( 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 ( 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
B192910 at screen distances spanning of the pulsar's pc
path-length to the observer. Four arcs are observed toward B035554, with one
arc yielding a screen distance as close as au ( 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
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
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
Role of B diffusion in the interfacial Dzyaloshinskii-Moriya interaction in Ta / Co₂₀ Fe₆₀B₂₀/MgO nanowires
We report on current-induced domain wall motion in Ta/Co20Fe60B20/MgO nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient D=+0.06mJ/m2. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta buffer layer during annealing, which was observed by chemical depth profiling measurements. The experimental results are compared to one-dimensional model simulations including the effects of pinning. This modeling allows us to reproduce the experimental outcomes and reliably extract a spin-Hall angle θSH=-0.11 for Ta in the nanowires, showing the importance of an analysis that goes beyond the model for perfect nanowires
Time Scales in Spectator Fragmentation
Proton-proton correlations and correlations of p-alpha, d-alpha, and t-alpha
from spectator decays following Au + Au collisions at 1000 AMeV have been
measured with an highly efficient detector hodoscope. The constructed
correlation functions indicate a moderate expansion and low breakup densities
similar to assumptions made in statistical multifragmentation models. In
agreement with a volume breakup rather short time scales were deduced employing
directional cuts in proton-proton correlations.
PACS numbers: 25.70.Pq, 21.65.+f, 25.70.MnComment: 8 pages, with 5 included figures; To appear in the proceedings of the
CRIS 2000 conference; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
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