5,447 research outputs found
Additional spectra of asteroid 1996 FG3, backup target of the ESA MarcoPolo-R mission
Near-Earth binary asteroid (175706) 1996 FG3 is the current backup target of
the ESA MarcoPolo-R mission, selected for the study phase of ESA M3 missions.
It is a primitive (C-type) asteroid that shows significant variation in its
visible and near-infrared spectra. Here we present new spectra of 1996 FG3 and
we compare our new data with other published spectra, analysing the variation
in the spectral slope. The asteroid will not be observable again over the next
three years at least. We obtained the spectra using DOLORES and NICS
instruments at the Telescopio Nazionale Galileo (TNG), a 3.6m telescope located
at El Roque de los Muchachos Observatory in La Palma, Spain. To compare with
other published spectra of the asteroid, we computed the spectral slope S', and
studied any plausible correlation of this quantity with the phase angle
(alpha). In the case of visible spectra, we find a variation in spectral slope
of Delta S' = 0.15 +- 0.10 %/10^3 A/degree for 3 < alpha < 18 degrees, in good
agreement with the values found in the literature for the phase reddening
effect. In the case of the near-infrared, we find a variation in the slope of
Delta S' = 0.04 +- 0.08 %/10^3 A/degree for 6 < alpha < 51 degrees. Our
computed variation in S' agrees with the only two values found in the
literature for the phase reddening in the near-infrared. The variation in the
spectral slope of asteroid 1996 FG3 shows a trend with the phase angle at the
time of the observations, both in the visible and the near-infrared. It is
worth noting that, to fully explain this spectral variability we should take
into account other factors, like the position of the secondary component of the
binary asteroid 1999 FG3 with respect to the primary, or the spin axis
orientation at the time of the observations. More data are necessary for an
analysis of this kind.Comment: 4 pages, 3 figures, Accepted in A&A 25 June 201
Design and Testing of a Composite Compressor Rotor
Additive manufacturing (AM) and molding are manufacturing methods known for building representations or replicas of conceptualized engine components, but was considered impractical for manufacturing operating engine components. More recent technology has rendered composite materials (combining high-temperature polymers and fiber reinforcement) capable of withstanding the temperature and structural requirements to compete with conventional turbomachinery metals. This study explores the application of several high-temperature polymers (ULTEM 9085, Onyx-Carbon fiber, and Epoxy-Carbon fiber) and their survivability in the operating conditions of a P400 Engine compressor. The tests conducted for this study determined their viability as compressor materials. This study required conducting tensile specimen testing, FEA modeling, and physical compressor spin testing. The results of each will be discussed
Amplification of surface plasmon polaritons in the presence of nonlinearity and spectral signatures of threshold crossover
We describe effects of nonlinearity on propagation of surface plasmon
polaritons (SPPs) at an interface between a metal and an amplifying medium of
the externally pumped two-level atoms. Using Maxwell equations we derive the
nonlinear dispersion law and demonstrate that, the nonlinear saturation of the
linear gain leads to formation of stationary SPP modes with the intensities
independent from the propagation distance. Transition to the regime of
stationary propagation is similar to the threshold crossover in lasers and
leads to narrowing of the SPP spectrum.Comment: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-34-18-286
Effective spacetime from multi-dimensional gravity
We study the effective spacetimes in lower dimensions that can be extracted
from a multidimensional generalization of the Schwarzschild-Tangherlini
spacetimes derived by Fadeev, Ivashchuk and Melnikov ({\it Phys. Lett,} {\bf A
161} (1991) 98). The higher-dimensional spacetime has
dimensions, where and are the number of "internal" and "external" extra
dimensions, respectively. We analyze the effective spacetime obtained
after dimensional reduction of the external dimensions. We find that when
the extra dimensions are compact (i) the physics in lower dimensions is
independent of and the character of the singularities in higher dimensions,
and (ii) the total gravitational mass of the effective matter distribution
is less than the Schwarzshild mass. In contrast, when the extra dimensions
are large this is not so; the physics in does explicitly depend on
, as well as on the nature of the singularities in high dimensions, and the
mass of the effective matter distribution (with the exception of wormhole-like
distributions) is bigger than the Schwarzshild mass. These results may be
relevant to observations for an experimental/observational test of the theory.Comment: A typo in Eq. (24) is fixe
Transition from decelerated to accelerated cosmic expansion in braneworld universes
Braneworld theory provides a natural setting to treat, at a classical level,
the cosmological effects of vacuum energy. Non-static extra dimensions can
generally lead to a variable vacuum energy, which in turn may explain the
present accelerated cosmic expansion. We concentrate our attention in models
where the vacuum energy decreases as an inverse power law of the scale factor.
These models agree with the observed accelerating universe, while fitting
simultaneously the observational data for the density and deceleration
parameter. The redshift at which the vacuum energy can start to dominate
depends on the mass density of ordinary matter. For Omega = 0.3, the transition
from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/-
0.20, which is compatible with SNe data. We set a lower bound on the
deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for
Omega = 0.3. The future evolution of the universe crucially depends on the time
when vacuum starts to dominate over ordinary matter. If it dominates only
recently, at an epoch z < 0.64, then the universe is accelerating today and
will continue that way forever. If vacuum dominates earlier, at z > 0.64, then
the deceleration comes back and the universe recollapses at some point in the
distant future. In the first case, quintessence and Cardassian expansion can be
formally interpreted as the low energy limit of our model, although they are
entirely different in philosophy. In the second case there is no correspondence
between these models and ours.Comment: In V2 typos are corrected and one reference is added for section 1.
To appear in General Relativity and Gravitatio
Efficient fiber-optical interface for nanophotonic devices
We demonstrate a method for efficient coupling of guided light from a single
mode optical fiber to nanophotonic devices. Our approach makes use of
single-sided conical tapered optical fibers that are evanescently coupled over
the last ~10 um to a nanophotonic waveguide. By means of adiabatic mode
transfer using a properly chosen taper, single-mode fiber-waveguide coupling
efficiencies as high as 97(1)% are achieved. Efficient coupling is obtained for
a wide range of device geometries which are either singly-clamped on a chip or
attached to the fiber, demonstrating a promising approach for integrated
nanophotonic circuits, quantum optical and nanoscale sensing applications.Comment: 7 pages, 4 figures, includes supplementary informatio
Adoption of E-Payment Systems in the Philippines
Studi ini bertujuan untuk mengeksplorasi faktor-faktor yang memengaruhi konsumen Filipina dalam mengadopsi sistem pembayaran elektronik. Analisis korelasi Spearman digunakan untuk menganalisis data yang dikumpulkan dari 83 karyawan Departemen Pemasaran perusahaan yang menggunakan pembayaran belanja online. Hasil penelitian menunjukkan bahwa signifikansi dari konstruk, yaitu perceived risk, trust, security, use of web-assurance seals, perceived use, dan perceived advantage tidak memadai untuk menentukan hubungannya dengan niat mengadopsi sistem pembayaran elektronik. Oleh karena itu, faktor yang digunakan dalam penelitian ini bukanlah satu-satunya faktor pendorong yang akan memengaruhi keputusan pelanggan
Stars in five dimensional Kaluza Klein gravity
In the five dimensional Kaluza Klein (KK) theory there is a well known class
of static and electromagnetic--free KK--equations characterized by a naked
singularity behavior, namely the Generalized Schwarzschild solution (GSS). We
present here a set of interior solutions of five dimensional KK--equations.
These equations have been numerically integrated to match the GSS in the
vacuum. The solutions are candidates to describe the possible interior perfect
fluid source of the exterior GSS metric and thus they can be models for stars
for static, neutral astrophysical objects in the ordinary (four dimensional)
spacetime.Comment: 15 pages, 8 figures. To be published in EPJ
Revisiting the security of speaker verification systems against imposture using synthetic speech
In this paper, we investigate imposture using synthetic speech.
Although this problem was first examined over a decade ago,
dramatic improvements in both speaker verification (SV) and
speech synthesis have renewed interest in this problem. We
use a HMM-based speech synthesizer which creates synthetic
speech for a targeted speaker through adaptation of a background
model. We use two SV systems: standard GMMUBM-
based and a newer SVM-based. Our results show when
the systems are tested with human speech, there are zero false
acceptances and zero false rejections. However, when the systems
are tested with synthesized speech, all claims for the targeted
speaker are accepted while all other claims are rejected.
We propose a two-step process for detection of synthesized
speech in order to prevent this imposture. Overall, while SV
systems have impressive accuracy, even with the proposed detector,
high-quality synthetic speech will lead to an unacceptably
high false acceptance rate
- ā¦