10,149 research outputs found
Formulation of a dynamic analysis method for a generic family of hoop-mast antenna systems
Analytical studies of mast-cable-hoop-membrane type antennas were conducted using a transfer matrix numerical analysis approach. This method, by virtue of its specialization and the inherently easy compartmentalization of the formulation and numerical procedures, can be significantly more efficient in computer time required and in the time needed to review and interpret the results
Toy Blocks and Rotational Physics
In this paper we summarize the theory of the "falling chimney," which deals
with the breaking of tall structures in mid-air, when they fall to the ground.
We describe how to reproduce these effects using small-scale models built with
toy blocks. We also present an improved and more effective way to perform and
analyze these interesting experiments, by using video capture software together
with a digital video camera.Comment: 6 pages, including 3 figure
Black hole shadows in fourth-order conformal Weyl gravity
We calculate the characteristics of the "black hole shadow" for a rotating,
neutral black hole in fourth-order conformal Weyl gravity. It is shown that the
morphology is not significantly affected by the underlying framework, except
for very large masses. Conformal gravity black hole shadows would also
significantly differ from their general relativistic counterparts if the values
of the main conformal gravity parameters, and , were increased
by several orders of magnitude. Such increased values for and
are currently ruled out by gravitational phenomenology. Therefore, it is
unlikely that these differences in black hole shadows will be detected in
future observations, carried out by the Event Horizon Telescope or other such
experiments.Comment: 21 pages, including 2 figures. Minor corrections and references
added. Final version to appear in the Canadian Journal of Physic
RBF approximation of large datasets by partition of unity and local stabilization
We present an algorithm to approximate large dataset by Radial Basis Function
(RBF) techniques. The method couples a fast domain decomposition procedure with a
localized stabilization method. The resulting algorithm can efficiently deal with large
problems and it is robust with respect to the typical instability of kernel methods
Probing microplasticity in small scale FCC crystals via Dynamic Mechanical Analysis
In small-scale metallic systems, collective dislocation activity has been
correlated with size effects in strength and with a step-like plastic response
under uniaxial compression and tension. Yielding and plastic flow in these
samples is often accompanied by the emergence of multiple dislocation
avalanches. Dislocations might be active pre-yield, but their activity
typically cannot be discerned because of the inherent instrumental noise in
detecting equipment. We apply Alternate Current (AC) load perturbations via
Dynamic Mechanical Analysis (DMA) during quasi-static uniaxial compression
experiments on single crystalline Cu nano-pillars with diameters of 500 nm, and
compute dynamic moduli at frequencies 0.1, 0.3, 1, and 10 Hz under
progressively higher static loads until yielding. By tracking the collective
aspects of the oscillatory stress-strain-time series in multiple samples, we
observe an evolving dissipative component of the dislocation network response
that signifies the transition from elastic behavior to dislocation avalanches
in the globally pre-yield regime. We postulate that microplasticity, which is
associated with the combination of dislocation avalanches and slow viscoplastic
relaxations, is the cause of the dependency of dynamic modulus on the driving
rate and the quasi-static stress. We construct a continuum mesoscopic
dislocation dynamics model to compute the frequency response of stress over
strain and obtain a consistent agreement with experimental observations. The
results of our experiments and simulations present a pathway to discern and
quantify correlated dislocation activity in the pre-yield regime of deforming
crystals.Comment: 5 pages, 3 figure
The Chemical Evolution of Phosphorus
Phosphorus is one of the few remaining light elements for which little is
known about its nucleosynthetic origin and chemical evolution, given the lack
of optical absorption lines in the spectra of long-lived FGK-type stars. We
have identified a P I doublet in the near-ultraviolet (2135/2136 A) that is
measurable in stars of low metallicity. Using archival Hubble Space
Telescope-STIS spectra, we have measured P abundances in 13 stars spanning -3.3
<= [Fe/H] <= -0.2, and obtained an upper limit for a star with [Fe/H] ~ -3.8.
Combined with the only other sample of P abundances in solar-type stars in the
literature, which spans a range of -1 <= [Fe/H] <= +0.2, we compare the stellar
data to chemical evolution models. Our results support previous indications
that massive-star P yields may need to be increased by a factor of a few to
match stellar data at all metallicities. Our results also show that hypernovae
were important contributors to the P production in the early universe. As P is
one of the key building blocks of life, we also discuss the chemical evolution
of the important elements to life, C-N-O-P-S, together.Comment: Accepted for publication in Astrophysical Journal Letters. 6 pages, 4
figures; reference added to earlier versio
A cloud robotics architecture for an emergency management and monitoring service in a smart cityenvironment
Cloud robotics is revolutionizing not only the robotics industry but also the ICT world, giving robots more storage and computing capacity, opening new scenarios that blend the physical to the digital world. In this vision new IT architectures are required to manage robots, retrieve data from them and create services to interact with users. In this paper a possible implementation of a cloud robotics architecture for the interaction between users and UAVs is described. Using the latter as monitoring agents, a service for fighting crime in urban environment is proposed, making one step forward towards the idea of smart cit
High density limit of the two-dimensional electron liquid with Rashba spin-orbit coupling
We discuss by analytic means the theory of the high-density limit of the
unpolarized two-dimensional electron liquid in the presence of Rashba or
Dresselhaus spin-orbit coupling. A generalization of the ring-diagram expansion
is performed. We find that in this regime the spin-orbit coupling leads to
small changes of the exchange and correlation energy contributions, while
modifying also, via repopulation of the momentum states, the noninteracting
energy. As a result, the leading corrections to the chirality and total energy
of the system stem from the Hartree-Fock contributions. The final results are
found to be vanishing to lowest order in the spin-orbit coupling, in agreement
with a general property valid to every order in the electron-electron
interaction. We also show that recent quantum Monte Carlo data in the presence
of Rashba spin-orbit coupling are well understood by neglecting corrections to
the exchange-correlation energy, even at low density values.Comment: 11 pages, 5 figure
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