578 research outputs found
Characterisation at infrared wavelengths of metamaterials formed by thin-film metallic split-ring resonator arrays on silicon
The infrared reflectance spectra at normal incidence for split-ring resonator arrays fabricated in thin films of three different metals on a silicon substrate are reported. The results are compared with a finite difference time domain simulation of the structures and a simple and novel equivalent-circuit method for the calculation of the first and second resonant wavelengths
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Application of Neural Networks to Flight Test Diagnostics
A system has been designed which can provide summary information about specific noisy electric pulses that are generated during flight testing. This is important from a telemetry viewpoint, since limited bandwidth often rules out transmitting all of the pulse data. The system is based on a neural network processing paradigm. The neural network serves as a mapping between pulse data inputs and pulse category outputs. Output categories correspond to presence or type of component failure. Extensive computer simulations have shown that the system can recognize qualitative pulse features which are useful for diagnostic purposes. A second version of the system, also using a neural network, was designed to perform data compression. In this case, an entire pulse is efficiently coded for transmission and the original signal is reconstructed upon receiving the coded transmission. Successful simulations for both systems have demonstrated feasibility and have led to a hardware development effort aimed at prototyping a fieldable system. Based on these results, it appears that the neural network approach may be applicable to other diagnostic and data analysis problems arising in component or system testing. 3 refs., 16 figs., 2 tabs
Introduction to Loop Quantum Gravity
This article is based on the opening lecture at the third quantum geometry
and quantum gravity school sponsored by the European Science Foundation and
held at Zakopane, Poland in March 2011. The goal of the lecture was to present
a broad perspective on loop quantum gravity for young researchers. The first
part is addressed to beginning students and the second to young researchers who
are already working in quantum gravity.Comment: 30 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:gr-qc/041005
Evolving Lorentzian Wormholes
Evolving Lorentzian wormholes with the required matter satisfying the Energy
conditions are discussed. Several different scale factors are used and the
corresponding consequences derived. The effect of extra, decaying (in time)
compact dimensions present in the wormhole metric is also explored and certain
interesting conclusions are derived for the cases of exponential and
Kaluza--Klein inflation.Comment: 10 pages( RevTex, Twocolumn format), Two figures available on request
from the first author. transmission errors corrected
Towards a formal description of the collapse approach to the inflationary origin of the seeds of cosmic structure
Inflation plays a central role in our current understanding of the universe.
According to the standard viewpoint, the homogeneous and isotropic mode of the
inflaton field drove an early phase of nearly exponential expansion of the
universe, while the quantum fluctuations (uncertainties) of the other modes
gave rise to the seeds of cosmic structure. However, if we accept that the
accelerated expansion led the universe into an essentially homogeneous and
isotropic space-time, with the state of all the matter fields in their vacuum
(except for the zero mode of the inflaton field), we can not escape the
conclusion that the state of the universe as a whole would remain always
homogeneous and isotropic. It was recently proposed in [A. Perez, H. Sahlmann
and D. Sudarsky, "On the quantum origin of the seeds of cosmic structure,"
Class. Quant. Grav. 23, 2317-2354 (2006)] that a collapse (representing physics
beyond the established paradigm, and presumably associated with a
quantum-gravity effect a la Penrose) of the state function of the inflaton
field might be the missing element, and thus would be responsible for the
emergence of the primordial inhomogeneities. Here we will discuss a formalism
that relies strongly on quantum field theory on curved space-times, and within
which we can implement a detailed description of such a process. The picture
that emerges clarifies many aspects of the problem, and is conceptually quite
transparent. Nonetheless, we will find that the results lead us to argue that
the resulting picture is not fully compatible with a purely geometric
description of space-time.Comment: 53 pages, no figures. Revision to match the published versio
Plant Growth Optimization by Vegetable Production System in HI-SEAS Analog Habitat
The Vegetable Production System (Veggie) is a scientific payload designed to support plant growth for food production under microgravity conditions. The configuration of Veggie consists of an LED lighting system with modular rooting pillows designed to contain substrate media and time-release fertilizer. The pillows were designed to be watered passively using capillary principles but have typically been watered manually by the astronauts in low-Earth orbit (LEO). The design of Veggie allows cabin air to be drawn through the plant enclosure for thermal and humidity control and for supplying CO2 to the plants. Since its delivery to the International Space Station (ISS) in 2014, Veggie has undergone several experimental trials by various crews. Ground unit testing of Veggie was conducted during an 8-month Mars analog study in a semi-contained environment of a simulated habitat located at approximately 8,200 feet (2,500 m) elevation on the Mauna Loa volcano on the Island of Hawaii. The Hawaii Space Exploration Analog and Simulation (HI-SEAS) offered conditions (habitat, mission, communications, etc.) intended to simulate a planetary exploration mission. This paper provides data and analyses to show the prospect for optimized use of the current Veggie design for human habitats. Lessons learned during the study may provide opportunities for updating the system design and operational parameters for current Veggie experiments being conducted onboard the ISS and for payloads on future deep space missions
Are Wikis and Weblogs an Appropriate Approach to Foster Collaboration, Reflection and Students’ Motivation?
Minisuperspace Quantization of "Bubbling AdS" and Free Fermion Droplets
We quantize the space of 1/2 BPS configurations of Type IIB SUGRA found by
Lin, Lunin and Maldacena (hep-th/0409174), directly in supergravity. We use the
Crnkovic-Witten-Zuckerman covariant quantization method to write down the
expression for the symplectic structure on this entire space of solutions. We
find the symplectic form explicitly around AdS_5 x S^5 and obtain a U(1)
Kac-Moody algebra, in precise agreement with the quantization of a system of N
free fermions in a harmonic oscillator potential, as expected from AdS/CFT. As
a cross check, we also perform the quantization around AdS_5 x S^5 by another
method, using the known spectrum of physical perturbations around this
background and find precise agreement with our previous calculation.Comment: 22 Pages + 2 Appendices, JHEP3; v3: explanation of factor 2 mismatch
added, references reordered, published versio
Incident cervical HPV infections in young women: Transition probabilities for CIN and infection clearance
Background: We describe transition probabilities for incident human papillomavirus (HPV) 16/18/31/33/35/45/52/58/59 infections and cervical intraepithelial neoplasia (CIN) 1 lesions. Methods: Women ages 16 to 23 years underwent cytology and cervical swab PCR testing for HPV at approximately 6-month intervals for up to 4 years in the placebo arm of an HPV vaccine trial. The cumulative proportion of incident HPV infections with diagnosed CIN, clearing (infection undetectable), or persisting without CIN, were estimated. Results: Most incident infections cleared, without detection of CIN, ranging at 36 months from 66.9% for HPV31 to 91.1% for HPV59. There was little variation in the 36-month proportion of incident HPV16, 18, and 31 infections followed by a CIN1 lesion positive for the relevant HPV type (range 16.7%-18.6%), with lower risks for HPV59 (6.4%) and HPV33 (2.9%). Thirty-six-month transition probabilities for CIN2 ranged across types from 2.2% to 9.1%; however, the number of events was generally too small for statistically significant differences to be seen across types for this endpoint, or CIN3. Conclusions: Some incident HPV types appear more likely to result in diagnosed CIN1 than others. The relative predominance of HPV16, vis-à -vis some other high-risk HPV types (e.g., HPV33) in prevalent CIN2/3, appears more directly associated with relatively greater frequency of incident HPV16 infections within the population, than a higher risk of infection progression to CIN2/3. Impact: Nearly all incident HPV infections either manifest as detectable CIN or become undetectable within 36 months. Some HPV types (e.g., 16 and 33) appear to have similar risk of CIN2/3 despite widely varied incidence. ©2011 AACR
Gauss-Bonnet Black Holes in dS Spaces
We study the thermodynamic properties associated with black hole horizon and
cosmological horizon for the Gauss-Bonnet solution in de Sitter space. When the
Gauss-Bonnet coefficient is positive, a locally stable small black hole appears
in the case of spacetime dimension , the stable small black hole
disappears and the Gauss-Bonnet black hole is always unstable quantum
mechanically when . On the other hand, the cosmological horizon is
found always locally stable independent of the spacetime dimension. But the
solution is not globally preferred, instead the pure de Sitter space is
globally preferred. When the Gauss-Bonnet coefficient is negative, there is a
constraint on the value of the coefficient, beyond which the gravity theory is
not well defined. As a result, there is not only an upper bound on the size of
black hole horizon radius at which the black hole horizon and cosmological
horizon coincide with each other, but also a lower bound depending on the
Gauss-Bonnet coefficient and spacetime dimension. Within the physical phase
space, the black hole horizon is always thermodynamically unstable and the
cosmological horizon is always stable, further, as the case of the positive
coefficient, the pure de Sitter space is still globally preferred. This result
is consistent with the argument that the pure de Sitter space corresponds to an
UV fixed point of dual field theory.Comment: Rextex, 17 pages including 8 eps figures, v2: minor changes, to
appear in PRD, v3: references adde
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