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Non-destructive spectroscopy in the visible and near infrared wavelength range has been introduced for analyzing absorbing compounds in fruit and vegetables. A drawback of the method appears due to the measuring principle, where photons detected in the diffusive tissue are influenced by the sample absorption but also scattering properties leading to variation in the photon pathlength. In the present work, distribution of time-of-flight reading was used to calculate the effective pathlength between source and detector. Using this information in addition to the spectral intensities obtained with common continuous wave spectroscopy, Lambert–Beer law was applied for analyzing absolute pigment contents.The method was tested for liquid phantoms mimicking the optical properties of fresh fruit and vegetables. Lambert–Beer law using a constant pathlength as well as combined application of the intensity at a specific wavelength and the effective pathlength resulted in low calibration errors with r2 > 0.98. Applying the two calibrations on phantoms mimicking changes in the scattering properties resulted in validation results of r2 = 0.47 and 0.64, respectively.Improved results by using the effective pathlength were confirmed on real-world samples. The carrot carotenoids analysis resulted in validation results of r2 = 0.66 and 0.74, respectively, while the measuring uncertainty was reduced from 18.10 to 9.62%.Multivariate calibrations using the entire carrot spectra and data pre-processing aiming the reduction of scattering effects resulted in slightly lower measuring uncertainty by comparison. In the sensor fusion approach proposed, however, no expensive spectrophotometer is required and the phenomenon of varying optical properties of the sample is characterized. 相似文献
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Daniel C. Guariento J. E. Horvath J. A. de Freitas Pacheco P. S. Custodio 《General Relativity and Gravitation》2008,40(8):1593-1602
In this work we extend previous work on the evolution of a primordial black hole (PBH) to address the presence of a dark energy
component with a super-negative equation of state as a background, investigating the competition between the radiation accretion,
the Hawking evaporation and the phantom accretion, the latter two causing a decrease on black hole mass. It is found that
there is an instant during the matter-dominated era after which the radiation accretion becomes negligible compared to the
phantom accretion. The Hawking evaporation may become important again depending on a mass threshold. The evaporation of PBHs
is quite modified at late times by these effects, but only if the generalized second law of thermodynamics is violated. 相似文献
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We investigate several varying-mass dark matter particle models in the framework of phantom cosmology. We examine whether there exist late-time cosmological solutions, corresponding to an accelerating universe and possessing dark energy and dark matter densities of the same order. Imposing exponential or power-law potentials and exponential or power-law mass dependence, we conclude that the coincidence problem cannot be solved or even alleviated. Thus, if dark energy is attributed to the phantom paradigm, varying-mass dark matter models cannot fulfill the basic requirement that led to their construction. 相似文献
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Isabella M. Burtscher Edvin Johansson Stig Holts Freddy Sthlberg 《Magnetic resonance imaging》1999,17(10):351-1519
A new phantom and evaluation method for experimental evaluation of 1H-magnetic resonance spectroscopy single volume localization techniques regarding signal contamination (C), defined as the part of the signal originating outside the volume of interest, is presented. The quality assessment method is based on a spherical phantom with an oil/water interface in order to reduce susceptibility effects, and applied for stimulated-echo acquisition method (STEAM) and spin-echo (SE) sequences, echo times of 270, 135, and 10 ms, and cubic volumes of interest (VOI) of 13, 1.53, 23, 2.53, and 33 cm3. To be able to mimic measurements of the contamination in three dimensions the physical gradients representing the three orthogonal directions for slice selection were shifted in the pulse sequences. Contamination values in one dimension differed between 6.5% and 8.4% in SE sequences, and between 0.7% and 13.8% in STEAM sequences. In STEAM sequences a decrease of C with increasing VOI size was observed while SE sequences showed comparable C values for the different VOI sizes tested. The total contamination in three dimensions were 19% and 18% in SE and STEAM sequences with a TE of 270 ms, and 7% in a STEAM sequence with a TE of 10 ms, respectively. The presented evaluation method is easily applied to the new phantom and showed high reproducibility. 相似文献
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I. DO 《数学年刊A辑(中文版)》1999,20(3):331-336
After reviewing the theory of phantom maps and SNT, the author gives several
general results which relate the theory of phantom maps and SNT and which extend
that of Harper and Roitberg. 相似文献
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We find that the expansion of the universe is accelerating by analyzing the recent observation data of type Ia supernova (SN-Ia). It indicates that the equation of state of the dark energy might be smaller than -1, which leads to the introduction of phantom models featured by its negative kinetic energy to account for the regime of equation of state parameter w < -1. In this paper the possibility of using a non-minimally coupled real scalar field as phantom to realize the equation of state parameter w < -1 is discussed. The main equations which govern the evolution of the universe are obtained. Then we rewrite them with the observable quantities. 相似文献
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We analyze an oscillating universe model in brane world cenario. The oscillating universe cycles through a series of expansions
and contractions and its energy density is dominated by dust matter at early-time expansion phase and by phantom dark energy
at late-time expansion phase. We find that the period of the oscillating universe is not sensitive to the tension of the brane,
but sensitive to the equation-of-state parameter w of the phantom dark energy, and the ratio of the period to the current Hubble age approximately varies from 3 to 9 when the
parameter w changes from −1.4 to −1.1. The fraction of time that the oscillating universe spends in the coincidence state is also comparable
to the period of the oscillating universe. This result indicates that the coincidence problem can be significantly ameliorated
in the oscillating universe without singularity. 相似文献