180 research outputs found
MIX DESIGN OF POLYMER CONCRETE FOR POTHOLE REPAIR
The increased traffic load due to rapid urbanization causes pavement distresses resulting reduction of service life of flexible pavement. Pavement distress is harmful to road user and vehicle, and it causes accident. Polymer concrete
having several advantages can be considered as alternative material for pothole repair. Thus, this study has focused on mix design development of polymer concrete through various performances. In this study, orthophthalic unsaturated polyester resin as binder, methyl ethyl ketone peroxide (MEKP) as hardener, acetone and lacquer thinner as diluent, fly ash, silica fume, limestone coarse and fine aggregates, and limestone quarry dust as filler have been used. Three different aggressive solutions such as sodium hydroxide (NaOH), sodium chloride (NaCl) and sulphuric acid (H2SO4) are used to determine resistance capacity of polymer concrete for Mix-1 polymer concrete. The recommended
Mix-1 of polymer concrete is resin with 304 kg, acetone with 16 kg, aggregate with 1,600 kg and fly ash with 320 kg for one cubic meter and the aggregate proportion is 60% coarse aggregate size 10.00 – 5.00 mm and 40% fine aggregate size 3.35 – 1.18 mm. The compressive strength using 100
dia.X200mm cylindrical are 12.12 MPa at age of 7-hour and 44.93MPa at age of 7-day. The resistance capacity of Mix-1 polymer concrete under 90-day continuous immersion in aggressive chemical solutions are noticed through compressive strength test. Polymer concrete has shown strength reduction over 90- day immersion with 31.18% in water, 31.32% in sodium chloride, 34.50% in sulphuric
acid and 44.38% in sodium hydroxide solution compared with control sample
Spherically symmetric relativistic MHD simulations of pulsar wind nebulae in supernova remnants
Pulsars, formed during supernova explosions, are known to be sources of
relativistic magnetized winds whose interaction with the expanding supernova
remnants (SNRs) gives rise to a pulsar wind nebula (PWN). We present
spherically symmetric relativistic magnetohydrodynamics (RMHD) simulations of
the interaction of a pulsar wind with the surrounding SNR, both in particle and
magnetically dominated regimes. As shown by previous simulations, the evolution
can be divided in three phases: free expansion, a transient phase characterized
by the compression and reverberation of the reverse shock, and a final Sedov
expansion. The evolution of the contact discontinuity between the PWN and the
SNR (and consequently of the SNR itself) is almost independent of the
magnetization of the nebula as long as the total (magnetic plus particle)
energy is the same. However, a different behaviour of the PWN internal
structure is observable during the compression-reverberation phase, depending
on the degree of magnetization=2E The simulations were performed using the
third order conservative scheme by Del Zanna et al. (2003).Comment: 11 pages, Latex, 22 Encapsulated PostScript figures, accepted f or
publication on A&
The effects of spin-down on the structure and evolution of pulsar wind nebulae
We present high resolution spherically symmetric relativistic
magnetohydrodynamical simulations of the evolution of a pulsar wind nebula
inside the free expanding ejecta of the supernova progenitor. The evolution is
followed starting from a few years after the supernova explosion and up to an
age of the remnant of 1500 years. We consider different values of the pulsar
wind magnetization parameter and also different braking indices for the
spin-down process. We compare the numerical results with those derived through
an approximate semi-analytical approach that allows us to trace the time
evolution of the positions of both the pulsar wind termination shock and the
contact discontinuity between the nebula and the supernova ejecta. We also
discuss, whenever a comparison is possible, to what extent our numerical
results agree with former self-similar models, and how these models could be
adapted to take into account the temporal evolution of the system. The inferred
magnetization of the pulsar wind could be an order of magnitude lower than that
derived from time independent analytic models.Comment: 11 pages, 7 figures, Accepted for publication on A&
Simulation of the growth of the 3D Rayleigh-Taylor instability in Supernova Remnants using an expanding reference frame
Context: The Rayleigh-Taylor instabilities generated by the deceleration of a
supernova remnant during the ejecta-dominated phase are known to produce
finger-like structures in the matter distribution which modify the geometry of
the remnant. The morphology of supernova remnants is also expected to be
modified when efficient particle acceleration occurs at their shocks. Aims: The
impact of the Rayleigh-Taylor instabilities from the ejecta-dominated to the
Sedov-Taylor phase is investigated over one octant of the supernova remnant. We
also study the effect of efficient particle acceleration at the forward shock
on the growth of the Rayleigh-Taylor instabilities. Methods: We modified the
Adaptive Mesh Refinement code RAMSES to study with hydrodynamic numerical
simulations the evolution of supernova remnants in the framework of an
expanding reference frame. The adiabatic index of a relativistic gas between
the forward shock and the contact discontinuity mimics the presence of
accelerated particles. Results: The great advantage of the super-comoving
coordinate system adopted here is that it minimizes numerical diffusion at the
contact discontinuity, since it is stationary with respect to the grid. We
propose an accurate expression for the growth of the Rayleigh-Taylor structures
that connects smoothly the early growth to the asymptotic self-similar
behaviour. Conclusions: The development of the Rayleigh-Taylor structures is
affected, although not drastically, if the blast wave is dominated by cosmic
rays. The amount of ejecta that makes it into the shocked interstellar medium
is smaller in the latter case. If acceleration occurs at both shocks the extent
of the Rayleigh-Taylor structures is similar but the reverse shock is strongly
perturbed.Comment: 15 pages, 12 figures, accepted for publication in Astronomy and
Astrophysics with minor editorial changes. Version with full resolution
images can be found at http://www.lpl.arizona.edu/~ffrasche/~12692.pd
Compositionally Complex Perovskite Oxides as a New Class of Li-Ion Solid Electrolytes
Compositionally complex ceramics (CCCs), including high-entropy ceramics
(HECs) as a subclass, offer new opportunities of materials discovery beyond the
traditional methodology of searching new stoichiometric compounds. Herein, we
establish new strategies of tailoring CCCs via a seamless combination of (1)
non-equimolar compositional designs and (2) controlling microstructures and
interfaces. Using oxide solid electrolytes for all-solid-state batteries as an
exemplar, we validate these new strategies via discovering a new class of
compositionally complex perovskite oxides (CCPOs) to show the possibility of
improving ionic conductivities beyond the limit of conventional doping. As an
example (amongst the 28 CCPOs examined), we demonstrate that the ionic
conductivity can be improved by >60% in
(Li0.375Sr0.4375)(Ta0.375Nb0.375Zr0.125Hf0.125)O3-{\delta}, in comparison with
the state-of-art (Li0.375Sr0.4375)(Ta0.75Zr0.25)O3-{\delta} (LSTZ) baseline,
via maintaining comparable electrochemical stability. Furthermore, the ionic
conductivity can be improved by another >70% via grain boundary (GB)
engineering, achieving >270% of the LSTZ baseline. This work suggests
transformative new strategies for designing and tailoring HECs and CCCs,
thereby opening a new window for discovering materials for energy storage and
many other applications
Magnetism and Faraday Rotation in Oxygen-Deficient Polycrystalline and Single-Crystal Iron-Substituted Strontium Titanate
Both polycrystalline and single-crystal films of iron-substituted strontium titanate, Sr(Ti[subscript 0.65]Fe[subscript 0.35])O[subscript 3−δ], prepared by pulsed laser deposition, show room-temperature magnetism and Faraday rotation, with the polycrystalline films exhibiting higher saturation magnetization and Faraday rotation. The magnetic properties vary with the oxygen pressure at which the films are grown, showing a maximum at pressures of approximately 4  μ Torr at which the unit-cell volume is largest. The results are discussed in terms of the oxygen stoichiometry and corresponding Fe valence states, the structure and strain state, and the presence of small-volume fractions of metallic Fe in single-crystal films grown at the optimum deposition pressure. Integration of magneto-optical polycrystalline films on an optical-waveguide device demonstrates a nonreciprocal phase shift.National Science Foundation (U.S.) (Grants DMR1419807 and ECCS1607865)Semiconductor Research Corporation. Function Accelerated nanoMaterial Engineerin
A highthroughput infrastructure for density functional theory calculations
a b s t r a c t The use of high-throughput density functional theory (DFT) calculations to screen for new materials and conduct fundamental research presents an exciting opportunity for materials science and materials innovation. High-throughput DFT typically involves computations on hundreds, thousands, or tens of thousands of compounds, and such a change of scale requires new calculation and data management methodologies. In this article, we describe aspects of the necessary data infrastructure for such projects to handle data generation and data analysis in a scalable way. We discuss the problem of accurately computing properties of compounds across diverse chemical spaces with a single exchange correlation functional, and demonstrate that errors in the generalized gradient approximation are highly dependent on chemical environment
Magnetic Rayleigh-Taylor instability for Pulsar Wind Nebulae in expanding Supernova Remnants
We present a numerical investigation of the development of Rayleigh-Taylor
instability at the interface between an expanding Pulsar Wind Nebula and its
surrounding Supernova Remnant. These systems have long been thought to be
naturally subject to this kind of instability, given their expansion behavior
and the density jump at the contact discontinuity. High resolution images of
the Crab Nebula at optical frequencies show the presence of a complex network
of line-emitting filaments protruding inside the synchrotron nebula. These
structures are interpreted as the observational evidence that Rayleigh-Taylor
instability is in fact at work. The development of this instability in the
regime appropriate to describe Supernova Remnant-Pulsar Wind Nebula systems is
non-trivial. The conditions at the interface are likely close to the stability
threshold, and the inclusion of the nebular magnetic field, which might play an
important role in stabilizing the system, is essential to the modeling. If
Rayleigh-Taylor features can grow efficiently a mixing layer in the outer
portion of the nebula might form where most of the supernova material is
confined. When a magnetic field close to equipartition is included we find that
the interface is stable, and that even a weaker magnetic field affects
substantially the growth and shape of the fingers.Comment: 14 pages, 6 figures, accepted for publication in A&
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