110,406 research outputs found
Concrete: Potential material for Space Station
To build a permanent orbiting space station in the next decade is NASA's most challenging and exciting undertaking. The space station will serve as a center for a vast number of scientific products. As a potential material for the space station, reinforced concrete was studied, which has many material and structural merits for the proposed space station. Its cost-effectiveness depends on the availability of lunar materials. With such materials, only 1 percent or less of the mass of a concrete space structure would have to be transported from earth
On the Tidal Dissipation of Obliquity
We investigate tidal dissipation of obliquity in hot Jupiters. Assuming an
initial random orientation of obliquity and parameters relevant to the observed
population, the obliquity of hot Jupiters does not evolve to purely aligned
systems. In fact, the obliquity evolves to either prograde, retrograde or
90^{o} orbits where the torque due to tidal perturbations vanishes. This
distribution is incompatible with observations which show that hot jupiters
around cool stars are generally aligned. This calls into question the viability
of tidal dissipation as the mechanism for obliquity alignment of hot Jupiters
around cool stars.Comment: 6 pages, 4 figures, accepted at ApJ
Physical properties of concrete made with Apollo 16 lunar soil sample
This paper describes the first phase of the long-term investigation for the construction of concrete lunar bases. In this phase, petrographic and scanning electron microscope examinations showed that the morphology and elemental composition of the lunar soil made it suitable for use as a fine aggregate for concrete. Based on this finding, calcium aluminate cement and distilled water were mixed with the lunar soil to fabricate test specimens. The test specimens consisted of a 1-in cube, a 1/2-in cube, and three 0.12 x 0.58 x 3.15-in beam specimens. Tests were performed on these specimens to determine compressive strength, modulus of rupture, modulus of elasticity, and thermal coefficient of expansion. Based on examination of the material and test results, it is concluded that lunar soil can be used as a fine aggregate for concrete
Toward a Deterministic Model of Planetary Formation IV: Effects of Type-I Migration
In a further development of a deterministic planet-formation model (Ida & Lin
2004), we consider the effect of type-I migration of protoplanetary embryos due
to their tidal interaction with their nascent disks. During the early embedded
phase of protostellar disks, although embryos rapidly emerge in regions
interior to the ice line, uninhibited type-I migration leads to their efficient
self-clearing. But, embryos continue to form from residual planetesimals at
increasingly large radii, repeatedly migrate inward, and provide a main channel
of heavy element accretion onto their host stars. During the advanced stages of
disk evolution (a few Myr), the gas surface density declines to values
comparable to or smaller than that of the minimum mass nebula model and type-I
migration is no longer an effective disruption mechanism for mars-mass embryos.
Over wide ranges of initial disk surface densities and type-I migration
efficiency, the surviving population of embryos interior to the ice line has a
total mass several times that of the Earth. With this reservoir, there is an
adequate inventory of residual embryos to subsequently assemble into rocky
planets similar to those around the Sun. But, the onset of efficient gas
accretion requires the emergence and retention of cores, more massive than a
few M_earth, prior to the severe depletion of the disk gas. The formation
probability of gas giant planets and hence the predicted mass and semimajor
axis distributions of extrasolar gas giants are sensitively determined by the
strength of type-I migration. We suggest that the observed fraction of
solar-type stars with gas giant planets can be reproduced only if the actual
type-I migration time scale is an order of magnitude longer than that deduced
from linear theories.Comment: 32 pages, 8 figures, 1 table, accepted for publication in Ap
Diquarks, Pentaquarks and Dibaryons
We explore the connection between pentaquarks and dibaryons composed of three
diquarks in the framework of the diquark model. With the available experimental
data on H dibaryon, we estimate the Pauli blocking and annihilation effects and
constrain the pentaquark singlet mass. Using the
pentaquark mass, we estimate dibaryon mass
Probing annihilations and decays of low-mass galactic dark matter in IceCube DeepCore array: Track events
The deployment of DeepCore array significantly lowers IceCube's energy
threshold to about 10 GeV and enhances the sensitivity of detecting neutrinos
from annihilations and decays of light dark matter. To match this experimental
development, we calculate the track event rate in DeepCore array due to
neutrino flux produced by annihilations and decays of galactic dark matter. We
also calculate the background event rate due to atmospheric neutrino flux for
evaluating the sensitivity of DeepCore array to galactic dark matter
signatures. Unlike previous approaches, which set the energy threshold for
track events at around 50 GeV (this choice avoids the necessity of including
oscillation effect in the estimation of atmospheric background event rate), we
have set the energy threshold at 10 GeV to take the full advantage of DeepCore
array. We compare our calculated sensitivity with those obtained by setting the
threshold energy at 50 GeV. We conclude that our proposed threshold energy
significantly improves the sensitivity of DeepCore array to the dark matter
signature for GeV in the annihilation scenario and
GeV in the decay scenario.Comment: 19 pages, 5 figures; match the published versio
Using LIP to Gloss Over Faces in Single-Stage Face Detection Networks
This work shows that it is possible to fool/attack recent state-of-the-art
face detectors which are based on the single-stage networks. Successfully
attacking face detectors could be a serious malware vulnerability when
deploying a smart surveillance system utilizing face detectors. We show that
existing adversarial perturbation methods are not effective to perform such an
attack, especially when there are multiple faces in the input image. This is
because the adversarial perturbation specifically generated for one face may
disrupt the adversarial perturbation for another face. In this paper, we call
this problem the Instance Perturbation Interference (IPI) problem. This IPI
problem is addressed by studying the relationship between the deep neural
network receptive field and the adversarial perturbation. As such, we propose
the Localized Instance Perturbation (LIP) that uses adversarial perturbation
constrained to the Effective Receptive Field (ERF) of a target to perform the
attack. Experiment results show the LIP method massively outperforms existing
adversarial perturbation generation methods -- often by a factor of 2 to 10.Comment: to appear ECCV 2018 (accepted version
Matching model of flow table for networked big data
Networking for big data has to be intelligent because it will adjust data
transmission requirements adaptively during data splitting and merging.
Software-defined networking (SDN) provides a workable and practical paradigm
for designing more efficient and flexible networks. Matching strategy in the
flow table of SDN switches is most crucial. In this paper, we use a
classification approach to analyze the structure of packets based on the
tuple-space lookup mechanism, and propose a matching model of the flow table in
SDN switches by classifying packets based on a set of fields, which is called
an F-OpenFlow. The experiment results show that the proposed F-OpenFlow
effectively improves the utilization rate and matching efficiency of the flow
table in SDN switches for networked big data.Comment: 14 pages, 6 figures, 2 table
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