6,103 research outputs found
VLA Observations of the Gravitational Lens System Q2237+0305
We report observations of the four-image gravitational lens system Q2237+0305
with the VLA at 20 cm and 3.6 cm. The quasar was detected at both frequencies
(\approx 0.7 mJy) with a flat spectrum. All four lensed images are clearly
resolved at 3.6 cm, and the agreement of the radio and optical image positions
is excellent. No radio emission is detected from the lensing galaxy, and any
fifth lensed quasar image must be fainter than \sim 20% of the A image flux
density. Since the optical quasar images are variable and susceptible to
extinction, radio flux ratios provide the best measurement of the macrolensing
magnification ratios. The radio B/A and C/A image flux ratios are consistent
with the observed range of optical variations, but the D/A ratio is
consistently higher in the radio than in the optical. The radio ratios are
consistent with magnification ratios predicted by lens models, and weaken
alternative interpretations for Q2237+0305. More accurate radio ratios can
distinguish between the models, as well as improve our understanding of both
microlensing and extinction in this system.Comment: 1 postscript file, 13 pages. To appear in AJ (1996.09), Submitted
1996.03.13, Accepted 1996.05.2
How Noisy Data Affects Geometric Semantic Genetic Programming
Noise is a consequence of acquiring and pre-processing data from the
environment, and shows fluctuations from different sources---e.g., from
sensors, signal processing technology or even human error. As a machine
learning technique, Genetic Programming (GP) is not immune to this problem,
which the field has frequently addressed. Recently, Geometric Semantic Genetic
Programming (GSGP), a semantic-aware branch of GP, has shown robustness and
high generalization capability. Researchers believe these characteristics may
be associated with a lower sensibility to noisy data. However, there is no
systematic study on this matter. This paper performs a deep analysis of the
GSGP performance over the presence of noise. Using 15 synthetic datasets where
noise can be controlled, we added different ratios of noise to the data and
compared the results obtained with those of a canonical GP. The results show
that, as we increase the percentage of noisy instances, the generalization
performance degradation is more pronounced in GSGP than GP. However, in
general, GSGP is more robust to noise than GP in the presence of up to 10% of
noise, and presents no statistical difference for values higher than that in
the test bed.Comment: 8 pages, In proceedings of Genetic and Evolutionary Computation
Conference (GECCO 2017), Berlin, German
Lifetime statistics of quantum chaos studied by a multiscale analysis
In a series of pump and probe experiments, we study the lifetime statistics
of a quantum chaotic resonator when the number of open channels is greater than
one. Our design embeds a stadium billiard into a two dimensional photonic
crystal realized on a Silicon-on-insulator substrate. We calculate resonances
through a multiscale procedure that combines graph theory, energy landscape
analysis and wavelet transforms. Experimental data is found to follow the
universal predictions arising from random matrix theory with an excellent level
of agreement.Comment: 4 pages, 6 figure
Explorative investigation of the anti-glycative effect of a rapeseed by-product extract
Formation of Advanced Glycation End-products (AGEs) in biological systems are increased during hyperglycaemia due to higher levels of circulating glucose, as well as carbonyl reactive species. AGEs are causative factors of common chronic diseases. Since synthetic AGE-inhibitors exert unwanted side effects and polyphenols act as potent antiglycative agents, vegetables (fruits, seeds and related by-products) are good candidates for searching natural inhibitors. The aim of this research is to explore the suitability of a polyphenol-rich rapeseed cake extract (RCext) to decrease the formation of AGEs in an in vitro model. Total Phenolic Content, antioxidant, anti-glycative activity, specific inhibition of AGEs (pentosidine and argypyrimidine), and methylglyoxal trapping capacity of the RCext were evaluated. The metabolomic profile of the extract was also analysed through GC-MS. Different phenols, amino acids, carbohydrates, organic acids and fatty acids are identified in the RCE by GC-MS. Results confirm the high concentration of polyphenols correlated with the antioxidant capacity and anti-glycative activity in a dose dependent manner. Rapeseed cake extract (3.7 mg mL−1) significantly reduced the formation of free fluorescent AGEs and pentosidine up to 34.85%. The anti-glycative activity of the extract is likely to be due to the high concentration of sinapinic acid in its metabolic profile, and the mechanism of action is mediated by methylglyoxal trapping. Results show a promising potential for using rapeseed cake extract as a food supplement to ameliorate the formation of AGEs. Rapeseed cake extract should therefore be considered a potential candidate for the prevention of glycation-associated complications of age-related pathologie
Characterisation of damage mechanisms in oxide ceramics indented at dynamic and quasi-static strain rates
Ceramic materials are known to display rate dependent behaviour under impact. Tests to establish the strain-rate dependent variations in damage mechanisms have been carried out on debased alumina, an alumina-zirconia composite, and 3Y-TZP. Materials were indented dynamically and quasi-statically using identical sharp hardened steel projectiles while recording the load profile. Characteristics typical of both sharp and blunt indentation types were observed using scanning electron microscopy and piezospectroscopic mapping. At dynamic strain rates both the depth of the indentation and the residual stress in the material were lower than for quasi-static tests. This was attributed to temperature-induced softening of the projectile. Unusual behaviour was observed in the 3Y-TZP samples due to the reversible transformation from tetragonal to monoclinic crystal structures during mechanical loading. These effects and the observed superior mechanical strength against impact suggest that zirconia or zirconia-composite materials may have advantages over debased alumina for application as ceramic armour materials
Crossover temperature of Bose-Einstein condensation in an atomic Fermi gas
We show that in an atomic Fermi gas near a Feshbach resonance the crossover
between a Bose-Einstein condensate of diatomic molecules and a Bose-Einstein
condensate of Cooper pairs occurs at positive detuning, i.e., when the
molecular energy level lies in the two-atom continuum. We determine the
crossover temperature as a function of the applied magnetic field and find
excellent agreement with the experiment of Regal et al. [Phys. Rev. Lett. 92,
040403 (2004)] that has recently observed this crossover temperature.Comment: 4 pages, 2 figure
Prediction Model for the Life of Nickel-cadmium Batteries in Geosynchronous Orbit Satellites
A mathematical model is described which predicts the service life of nickel-cadmium batteries designed for geosynchronous orbit satellites. Regression analysis technique is used to analyze orbital data on second generation trickle charged batteries. The model gives average cell voltage as a function of design parameters, operating parameters and time. The voltage model has the properties of providing a good fit to the data, good predictive capability, and agreement with known battery performance characteristics. Average cell voltage can be predicted to within 0.02 volts for up to 8 years. This modeling shows that these batteries will operate reliably for 10 years. Third-generation batteries are expected to operate even longer
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