5,618 research outputs found
Tunneling magnetoresistance in diluted magnetic semiconductor tunnel junctions
Using the spin-polarized tunneling model and taking into account the basic
physics of ferromagnetic semiconductors, we study the temperature dependence of
the tunneling magnetoresistance (TMR) in the diluted magnetic semiconductor
(DMS) trilayer heterostructure system (Ga,Mn)As/AlAs/(Ga,Mn)As. The
experimentally observed TMR ratio is in reasonable agreement with our result
based on the typical material parameters. It is also shown that the TMR ratio
has a strong dependence on both the itinerant-carrier density and the magnetic
ion density in the DMS electrodes. This can provide a potential way to achieve
larger TMR ratio by optimally adjusting the material parameters.Comment: 5 pages (RevTex), 3 figures (eps), submitted to PR
Automatic Differentiation Adjoint of the Reynolds-Averaged Navier-Stokes Equations with a Turbulence Model
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106452/1/AIAA2013-2581.pd
Unexpected intercalation-dominated potassium storage in WSâ‚‚ as a potassium-ion battery anode
Unexpected intercalation-dominated process is observed during K^{+} insertion in WS_{2} in a voltage range of 0.01–3.0 V. This is different from the previously reported two-dimensional (2D) transition metal dichalcogenides that undergo a conversion reaction in a low voltage range when used as anodes in potassium-ion batteries. Charge/discharge processes in the K and Na cells are studied in parallel to demonstrate the different ion storage mechanisms. The Na^{+} storage proceeds through intercalation and conversion reactions while the K^{+} storage is governed by an intercalation reaction. Owing to the reversible K+ intercalation in the van der Waals gaps, the WS_{2} anode exhibits a low decay rate of 0.07% per cycle, delivering a capacity of 103 mAh·g^{-1} after 100 cycles at 100 mA·g^{-1}. It maintains 57% capacity at 800 mA·g^{-1} and shows stable cyclability up to 400 cycles at 500 mA·g-1. Kinetics study proves the facilitation of K^{+} transport is derived from the intercalation-dominated mechanism. Furthermore, the mechanism is verified by the density functional theory (DFT) calculations, showing that the progressive expansion of the interlayer space can account for the observed results
Grain boundary effects on magnetotransport in bi-epitaxial films of LaSrMnO
The low field magnetotransport of LaSrMnO (LSMO) films
grown on SrTiO substrates has been investigated. A high qualtity LSMO film
exhibits anisotropic magnetoresistance (AMR) and a peak in the
magnetoresistance close to the Curie temperature of LSMO. Bi-epitaxial films
prepared using a seed layer of MgO and a buffer layer of CeO display a
resistance dominated by grain boundaries. One film was prepared with seed and
buffer layers intact, while a second sample was prepared as a 2D square array
of grain boundaries. These films exhibit i) a low temperature tail in the low
field magnetoresistance; ii) a magnetoconductance with a constant high field
slope; and iii) a comparably large AMR effect. A model based on a two-step
tunneling process, including spin-flip tunneling, is discussed and shown to be
consistent with the experimental findings of the bi-epitaxial films.Comment: REVTeX style; 14 pages, 9 figures. Figure 1 included in jpeg format
(zdf1.jpg); the eps was huge. Accepted to Phys. Rev.
Two lathyrane diterpenoid stereoisomers containing an unusual trans-gem-dimethylcyclopropane from the seeds of Euphorbia lathyris
Two novel lathyrane-type diterpenoids, the Euphorbia factors L(2a) (1) and L(2b) (2), and their stereoisomer Euphorbia factor L(2) (3) were obtained from seeds of Euphorbia lathyris. Both Euphorbia factors L(2a) and L(2b) possess an unprecedented trans-gem-dimethylcyclopropane as structural feature. Also, the Euphorbia factor L(2a) is the first example of a lathyrane diterpenoid with an endocyclic 12(Z)-double bond. The structures of the molecules and their absolute configurations were elucidated by comprehensive spectroscopic analyses, Cu-Kα radiation X-ray diffraction, and comparison with calculated electronic circular dichroism (ECD) data. The Euphorbia factor L(2b) exhibited an inhibitory effect against U937 cell line with an IC(50) value of 0.87 μM
Super-Eddington Accretion as a Possible Scenario to Form GW190425
On 2019 April 25, the LIGO/Virgo Scientific Collaboration detected a compact
binary coalescence, GW190425. Under the assumption of the binary neutron star
(BNS), the total mass of lies five standard
deviations away from the known Galactic population mean. In the standard common
envelope scenario, the immediate progenitor of GW190425 is a close binary
system composed of an NS and a He-rich star. With the detailed binary
evolutionary modeling, we find that in order to reproduce GW190425-like events,
super-Eddington accretion (e.g., ) from a He-rich
star onto the first-born NS with a typical mass of 1.33 via stable
Case BB mass transfer (MT) is necessarily required. Furthermore, the immediate
progenitors should potentially have an initial mass of in a
range of and an initial orbital period of
from 0.08 days to 0.12 days, respectively. The corresponding mass accreted onto
NSs via stable Case BB MT phase varies from to . After the formation of the second-born NS, the BNSs are expected to
be merged due to gravitational wave emission from 11 Myr to 190
Myr.Comment: 8 pages, 10 figures, updated to add one referenc
Direct <i>Q</i> -Value Determination of the <i>β<sup>-</sup></i> Decay of <sup>187</sup>Re
The cyclotron frequency ratio of 187Os29+ to 187Re29+ ions was measured with the Penning-trap mass spectrometer PENTATRAP. The achieved result of R=1.000 000 013 882(5) is to date the most precise such measurement performed on ions. Furthermore, the total binding-energy difference of the 29 missing electrons in Re and Os was calculated by relativistic multiconfiguration methods, yielding the value of ΔE=53.5(10)  eV. Finally, using the achieved results, the mass difference between neutral 187Re and 187Os, i.e., the Q value of the β-− decay of 187Re, is determined to be 2470.9(13) eV
Revisiting the Properties of GW190814 and Its Formation History
GW190814 was reported during LIGO's and Virgo's third observing run with the
most asymmetric component masses (a black hole and a
compact object). Under the assumption that this event is
a binary black hole (BBH) merger formed through the isolated binary evolution
channel, we reanalyze the publicly released data of GW190814 with the modified
astrophysical priors on the effective spin , and further
explore its formation history using detailed binary modeling. We show that
GW190814 is likely to have been formed through the classical common envelope
channel. Our findings show that the properties inferred using the modified
astrophysical priors are consistent with those inferred by the uniform priors.
With the newly-inferred properties of GW190814, we perform detailed binary
evolution of the immediate progenitor of the BBH (namely a close binary system
composed of a BH and a helium star) in a large parameter space, taking into
account mass-loss, internal differential rotation, supernova kicks, and tidal
interactions between the helium star and the BH companion. Our findings show
that GW190814-like events could be formed in limited initial conditions just
after the common envelope phase: a BH and a helium star
of 8.5 at solar metallicity ( 7.5
at 10\% solar metallicity) with an initial orbital period at around
1.0 day. Additionally, the inferred low spin of the secondary indicates that
the required metallicity for reproducing GW190814-like events should not be too
low (e.g., Z 0.1 ).Comment: 8 pages, 8 figures, 1 table, final version published in MNRAN
Environmental influences on affect and cognition: A study of natural and commercial semi-public spaces
Research has consistently shown differences in affect and cognition after exposure to different physical environments. The time course of these differences emerging or fading during exploration of environments is less explored, as most studies measure dependent variables only before and after environmental exposure. In this within-subject study, we used repeated surveys to measure differences in thought content and affect throughout a 1-h environmental exploration of a nature conservatory and a large indoor mall. At each survey, participants reported on aspects of their most recent thoughts (e.g., thinking of the present moment vs. the future; thinking positively vs. negatively) and state affect. Using Bayesian multi-level models, we found that while visiting the conservatory, participants were more likely to report thoughts about the past, more positive and exciting thoughts, and higher feelings of positive affect and creativity. In the mall, participants were more likely to report thoughts about the future and higher feelings of impulsivity. Many of these differences in environments were present throughout the 1-h walk, however some differences were only evident at intermediary time points, indicating the importance of collecting data during exploration, as opposed to only before and after environmental exposures. We also measured cognitive performance with a dual n-back task. Results on 2-back trials replicated results from prior work that interacting with nature leads to improvements in working-memory performance. This study furthers our understanding of how thoughts and feelings are influenced by the surrounding physical environment and has implications for the design and use of public spaces
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