9,234 research outputs found
Radiation safety based on the sky shine effect in reactor
In the reactor operation, neutrons and gamma rays are the most dominant radiation.
As protection, lead and concrete shields are built around the reactor. However, the radiation
can penetrate the water shielding inside the reactor pool. This incident leads to the occurrence
of sky shine where a physical phenomenon of nuclear radiation sources was transmitted
panoramic that extends to the environment. The effect of this phenomenon is caused by the
fallout radiation into the surrounding area which causes the radiation dose to increase. High
doses of exposure cause a person to have stochastic effects or deterministic effects. Therefore,
this study was conducted to measure the radiation dose from sky shine effect that scattered
around the reactor at different distances and different height above the reactor platform. In this
paper, the analysis of the radiation dose of sky shine effect was measured using the
experimental metho
Incommensurate Charge Order Phase in Fe2OBO3 due to Geometrical Frustration
The temperature dependence of charge order in Fe2OBO3 was investigated by
resistivity and differential scanning calorimetry measurements, Mossbauer
spectroscopy, and synchrotron x-ray scattering, revealing an intermediate phase
between room temperature and 340 K, characterized by coexisting mobile and
immobile carriers, and by incommensurate superstructure modulations with
temperature-dependent propagation vector (1/2,0,tau). The incommensurate
modulations arise from specific anti-phase boundaries with low energy cost due
to geometrical charge frustration.Comment: 4 p., 5 fig.; v2: slightly expanded introduction + minor changes. PRL
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Low-degree mantle convection with strongly temperature- and depth-dependent viscosity in a three-dimensional spherical shell
A series of numerical simulations of thermal convection of Boussinesq fluid
with infinite Prandtl number, with Rayleigh number , and with the
strongly temperature- and depth- dependent viscosity in a three-dimensional
spherical shell is carried out to study the mantle convection of single-plate
terrestrial planets like Venus or Mars without an Earth-like plate tectonics.
The strongly temperature-dependent viscosity (the viscosity contrast across the
shell is ) make the convection under stagnant-lid short-wavelength
structures. Numerous, cylindrical upwelling plumes are developed because of the
secondary downwelling plumes arising from the bottom of lid. This convection
pattern is inconsistent with that inferred from the geodesic observation of the
Venus or Mars. Additional effect of the stratified viscosity at the upper/lower
mantle (the viscosity contrast is varied from 30 to 300) are investigated. It
is found that the combination of the strongly temperature- and depth-dependent
viscosity causes long-wavelength structures of convection in which the
spherical harmonic degree is dominant at 1--4. The geoid anomaly
calculated by the simulated convections shows a long-wavelength structure,
which is compared with observations. The degree-one () convection
like the Martian mantle is realized in the wide range of viscosity contrast
from 30 to 100 when the viscosity is continuously increased with depth at the
lower mantle.Comment: 18 pages, 10 figure
Signal and Power Integrity Challenges for High Density System-on-Package
As the increasing desire for more compact, portable devices outpaces Moore’s law, innovation in packaging and system design has played a significant role in the continued miniaturization of electronic systems.Integrating more active and passive components into the package itself, as the case for system-on-package (SoP), has shown very promising results in overall size reduction and increased performance of electronic systems.With this ability to shrink electrical systems comes the many challenges of sustaining, let alone improving, reliability and performance. The fundamental signal, power, and thermal integrity issues are discussed in detail, along with published techniques from around the industry to mitigate these issues in SoP applications
Far-from-equilibrium field theory of many-body quantum spin systems: Prethermalization and relaxation of spin spiral states in three dimensions
We study theoretically the far-from-equilibrium relaxation dynamics of spin
spiral states in the three dimensional isotropic Heisenberg model. The
investigated problem serves as an archetype for understanding quantum dynamics
of isolated many-body systems in the vicinity of a spontaneously broken
continuous symmetry. We present a field-theoretical formalism that
systematically improves on mean-field for describing the real-time quantum
dynamics of generic spin-1/2 systems. This is achieved by mapping spins to
Majorana fermions followed by a 1/N expansion of the resulting two-particle
irreducible (2PI) effective action. Our analysis reveals rich
fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral
states. In particular, we find the sudden appearance of long-lived
prethermalized plateaus with diverging lifetimes as the spiral winding is tuned
toward the thermodynamically stable ferro- or antiferromagnetic phases. The
emerging prethermalized states are characterized by different bosonic modes
being thermally populated at different effective temperatures, and by a
hierarchical relaxation process reminiscent of glassy systems. Spin-spin
correlators found by solving the non-equilibrium Bethe-Salpeter equation
provide further insight into the dynamic formation of correlations, the fate of
unstable collective modes, and the emergence of fluctuation-dissipation
relations. Our predictions can be verified experimentally using recent
realizations of spin spiral states with ultracold atoms in a quantum gas
microscope [S. Hild, et al. Phys. Rev. Lett. 113, 147205 (2014)]
Collective effects in cellular structure formation mediated by compliant environments: a Monte Carlo study
Compliant environments can mediate interactions between mechanically active
cells like fibroblasts. Starting with a phenomenological model for the
behaviour of single cells, we use extensive Monte Carlo simulations to predict
non-trivial structure formation for cell communities on soft elastic substrates
as a function of elastic moduli, cell density, noise and cell position
geometry. In general, we find a disordered structure as well as ordered
string-like and ring-like structures. The transition between ordered and
disordered structures is controlled both by cell density and noise level, while
the transition between string- and ring-like ordered structures is controlled
by the Poisson ratio. Similar effects are observed in three dimensions. Our
results suggest that in regard to elastic effects, healthy connective tissue
usually is in a macroscopically disordered state, but can be switched to a
macroscopically ordered state by appropriate parameter variations, in a way
that is reminiscent of wound contraction or diseased states like contracture.Comment: 45 pages, 7 postscript figures included, revised version accepted for
publication in Acta Biomateriali
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