3,648 research outputs found
Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals
We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]
OH (1720 MHz) Masers: A Multiwavelength Study of the Interaction between the W51C Supernova Remnant and the W51B Star Forming Region
We present a comprehensive view of the W51B HII region complex and the W51C
supernova remnant (SNR) using new radio observations from the VLA, VLBA,
MERLIN, JCMT, and CSO along with archival data from Spitzer, ROSAT, ASCA, and
Chandra. Our VLA data include the first 400 cm (74 MHz) continuum image of W51
at high resolution (88 arcsec). The 400 cm image shows non-thermal emission
surrounding the G49.2-0.3 HII region, and a compact source of non-thermal
emission (W51B_NT) coincident with the previously-identified OH (1720 MHz)
maser spots, non-thermal 21 and 90 cm emission, and a hard X-ray source.
W51B_NT falls within the region of high likelihood for the position of TeV
gamma-ray emission. Using the VLBA three OH (1720 MHz) maser spots are detected
in the vicinity of W51B_NT with sizes of 60 to 300 AU and Zeeman effect
magnetic field strengths of 1.5 to 2.2 mG. The multiwavelength data demonstrate
that the northern end of the W51B HII region complex has been partly enveloped
by the advancing W51C SNR and this interaction explains the presence of W51B_NT
and the OH masers. This interaction also appears in the thermal molecular gas
which partially encircles W51B_NT and exhibits narrow pre-shock (DeltaV 5 km/s)
and broad post-shock (DeltaV 20 km/s) velocity components. RADEX radiative
transfer modeling of these two components yield physical conditions consistent
with the passage of a non-dissociative C-type shock. Confirmation of the
W51B/W51C interaction provides additional evidence in favor of this region
being one of the best candidates for hadronic particle acceleration known thus
far.Comment: Accepted to Ap
Pressure-induced phase transitions and superconductivity in magnesium carbides
Crystal structure prediction and in silico physical property observations guide experimental synthesis in high-pressure research. Here, we used magnesium carbides as a representative example of computational high-pressure studies. We predicted various compositions of Mg-C compounds up to 150 GPa and successfully reproduced previous experimental results. Interestingly, our proposed MgC2 at high pressure >7 GPa consists of extended carbon bonds, one-dimensional graphene layers, and Mg atomic layers, which provides a good platform to study superconductivity of metal intercalated graphene nano-ribbons. We found that this new phase of MgC2 could be recovered to ambient pressure and exhibited a strong electron-phonon coupling (EPC) strength of 0.6 whose corresponding superconductivity transition temperature reached 15 K. The EPC originated from the cooperation of the out-of-plane and the in-plane phonon modes. The geometry confinement and the hybridization between the Mg s and C p(z) orbitals significantly affect the coupling of phonon modes and electrons. These results show the importance of the high-pressure route to the synthesis of novel functional materials, which can promote the search for new phases of carbon-based superconductors.11Ysciescopu
Dynamic Simulation Methods for Evaluating Motor Vehicle and Roadway Design and Resolving Policy Issues
This study had three objectives: (1) to develop a comprehensive truck simulation that executes rapidly, has a modular program construction to allow variation of vehicle characteristics, and is able to realistically predict vehicle motion and the tire-road surface interaction forces; (2) to develop a model of doweled portland cement concrete pavement that can be used to determine slab deflection and stress at predetermined nodes, and that allows for the variation of traditional thickness design factors; and (3) to implement these two models on a work station with suitable menu driven modules so that both existing and proposed pavements can be evaluated with respect to design life, given specific characteristics of the heavy vehicles that will be using the facility. This report summarizes the work that has been performed during the first year of the study. Briefly, the following has been accomplished: A two dimensional model of a typical 3-S2 tractor-trailer combination was created. A finite element structural analysis program, ANSYS, was used to model the pavement. Computer runs have been performed varying the parameters defining both vehicle and road elements. The resulting time specific displacements for each node are plotted, and the displacement basin is generated for defined vehicles. Relative damage to the pavement can then be estimated. A damage function resulting from load replications must be assumed that will be reflected by further pavement deterioration. Comparison with actual damage on Interstate 80 will eventually allow verification of these procedures
Self-enrichment in globular clusters. I. An analytic approach
By means of analytical calculations, we explore the self-enrichment scenario
for Globular Cluster formation. According to this scenario, an initial burst of
star formation occurs inside the core radius of the initial gaseous
distribution. The outward-propagating shock wave sweeps up a shell in which
gravitational instabilities may arise, leading to the formation of a second,
metal-enriched, population of stars. We find a minimum mass of the
proto-globular cluster of the order of 10^6 solar masses. We also find that the
observed spread in the Magnitude-Metallicity relation can be explained assuming
cluster-to-cluster variations of some parameters like the thermalization
efficiency, the mixing efficiency and the Initial Mass Function, as well as
variations of the external pressure.Comment: 12 pages, 13 figures, accepted for publication in A&
Orbital ordering and enhanced magnetic frustration of strained BiMnO3 thin films
Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on
SrTiO3 substrates, and orbital ordering and magnetic properties of the thin
films were investigated. The ordering of the Mn^{3+} e_g orbitals at a wave
vector (1/4 1/4 1/4) was detected by Mn K-edge resonant x-ray scattering. This
peculiar orbital order inherently contains magnetic frustration. While bulk
BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by
in-plane compressive strains in the films brings about cluster-glass-like
properties.Comment: 8 pages, 4 figures, accepted to Europhysics Letter
SRS: A FRAMEWORK FOR DEVELOPING MALLEABLE AND MIGRATABLE PARALLEL APPLICATIONS FOR DISTRIBUTED SYSTEMS
Selective tumor uptake of a boronated porphyrin in an animal model of cerebral glioma.
Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift
We investigate the star formation history of the central regions of four
Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact
(MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than
-17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the
most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B
< 19.0 mag arcsec^-2) of this population. The observational data used were
obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the
HST/NICMOS first camera. We find evidence for multiple stellar populations. One
of them is identified as the ionizing population, and the other one corresponds
to the underlying stellar generation.
The estimated masses of the inferred populations are compatible with the
dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also
indicate that the first episodes of star formation the presented LCBGs
underwent happened between 5 and 7 Gyr ago.
We compare the stellar populations found in LCBGs with the stellar
populations present in bright, local HII galaxies, nearby spheroidal systems
and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar
populations of LCBGs are similar yet bluer to those of local HII galaxies. It
is also the case that the passive color evolution of the LCBGs could convert
them into local Spheroidal galaxies if no further episode of star formation
takes place. Our results help to impose constraints on evolutionary scenarios
for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with
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