477 research outputs found
Detection of the tulip breaking virus (TBV) in tulips using optical sensors
The tulip breaking virus (TBV) causes severe economic losses for countries that export tulips such as the Netherlands. Infected plants have to be removed from the field as soon as possible. There is an urgent need for a rapid and objective method of screening. In this study, four proximal optical sensing techniques for the detection of TBV in tulip plants were evaluated and compared with a visual assessment by crop experts as well as with an ELISA (enzyme immunoassay) analysis of the same plants. The optical sensor techniques used were an RGB color camera, a spectrophotometer measuring from 350 to 2500 nm, a spectral imaging camera covering a spectral range from 400 to 900 nm and a chlorophyll fluorescence imaging system that measures the photosynthetic activity. Linear discriminant classification was used to compare the results of these optical techniques and the visual assessment with the ELISA score. The spectral imaging system was the best optical technique and its error was only slightly larger than the visual assessment error. The experimental results appear to be promising, and they have led to further research to develop an autonomous robot for the detection and removal of diseased tulip plants in the open field. The application of this robot system will reduce the amount of insecticides and the considerable pressure on labor for selecting diseased plants by the crop expert. © 2010 The Author(s
Spatial coherence of thermal near fields
We analyze the spatial coherence of the electromagnetic field emitted by a
half-space at temperature T close to the interface. An asymptotic analysis
allows to identify three different contributions to the cross-spectral density
tensor in the near-field regime. It is shown that the coherence length can be
either much larger or much shorter than the wavelength depending on the
dominant contribution.Comment: 13 pages, 8 graphs, includes Elsevier elsart.cls preprint style.
Submitted to Optics Communications (27 july 2000
Quantum Noise and Superluminal Propagation
Causal "superluminal" effects have recently been observed and discussed in
various contexts. The question arises whether such effects could be observed
with extremely weak pulses, and what would prevent the observation of an
"optical tachyon." Aharonov, Reznik, and Stern (ARS) [Phys. Rev. Lett., vol.
81, 2190 (1998)] have argued that quantum noise will preclude the observation
of a superluminal group velocity when the pulse consists of one or a few
photons. In this paper we reconsider this question both in a general framework
and in the specific example, suggested by Chiao, Kozhekin, and Kurizki [Phys.
Rev. Lett., vol. 77, 1254 (1996)], of off-resonant, short-pulse propagation in
an optical amplifier. We derive in the case of the amplifier a signal-to-noise
ratio that is consistent with the general ARS conclusions when we impose their
criteria for distinguishing between superluminal propagation and propagation at
the speed c. However, results consistent with the semiclassical arguments of
CKK are obtained if weaker criteria are imposed, in which case the signal can
exceed the noise without being "exponentially large." We show that the quantum
fluctuations of the field considered by ARS are closely related to
superfluorescence noise. More generally we consider the implications of
unitarity for superluminal propagation and quantum noise and study, in addition
to the complete and truncated wavepackets considered by ARS, the residual
wavepacket formed by their difference. This leads to the conclusion that the
noise is mostly luminal and delayed with respect to the superluminal signal. In
the limit of a very weak incident signal pulse, the superluminal signal will be
dominated by the noise part, and the signal-to-noise ratio will therefore be
very small.Comment: 30 pages, 1 figure, eps
Complementarity and Young's interference fringes from two atoms
The interference pattern of the resonance fluorescence from a J=1/2 to J=1/2
transition of two identical atoms confined in a three-dimensional harmonic
potential is calculated. Thermal motion of the atoms is included. Agreement is
obtained with experiments [Eichmann et al., Phys. Rev. Lett. 70, 2359 (1993)].
Contrary to some theoretical predictions, but in agreement with the present
calculations, a fringe visibility greater than 50% can be observed with
polarization-selective detection. The dependence of the fringe visibility on
polarization has a simple interpretation, based on whether or not it is
possible in principle to determine which atom emitted the photon.Comment: 12 pages, including 7 EPS figures, RevTex. Submitted to Phys. Rev.
Detection of the tulip breaking virus (TBV) in tulips using optical sensors
The tulip breaking virus (TBV) causes severe economic losses for countries that export tulips such as the Netherlands. Infected plants have to be removed from the field as soon as possible. There is an urgent need for a rapid and objective method of screening. In this study, four proximal optical sensing techniques for the detection of TBV in tulip plants were evaluated and compared with a visual assessment by crop experts as well as with an ELISA (enzyme immunoassay) analysis of the same plants. The optical sensor techniques used were an RGB color camera, a spectrophotometer measuring from 350 to 2500 nm, a spectral imaging camera covering a spectral range from 400 to 900 nm and a chlorophyll fluorescence imaging system that measures the photosynthetic activity. Linear discriminant classification was used to compare the results of these optical techniques and the visual assessment with the ELISA score. The spectral imaging system was the best optical technique and its error was only slightly larger than the visual assessment error. The experimental results appear to be promising, and they have led to further research to develop an autonomous robot for the detection and removal of diseased tulip plants in the open field. The application of this robot system will reduce the amount of insecticides and the considerable pressure on labor for selecting diseased plants by the crop expert. © 2010 The Author(s
Measurements of the complex dielectric constant of volcanic ash from 4 to 19 GHz
Dielectric data in volcanic ash at weather radar wavelengths (centimeter range) are extremely sparse and are crucial for radar sensing of ash clouds and for imaging of volcanic terrains. This study extends previous data to include a wavelength range of 1.5–7.5 cm and volcanic ash compositions of 50–75% silica. The real part of the complex permittivity, ε′, of volcanic ash is 6 ± 0.5 (1σ) for all wavelengths. The imaginary part, ε″, ranges from 0.08 to 0.27. Both ε′ and ε″ show higher values at lower SiO2 concentration. It is safe to assume in any weather radar applications that the reflectivity factor is K = |(ε − 1)/(ε + 2)|2 = 0.39 ± 0.02 (1σ), regardless of composition or wavelength. The results will help quantify radar observations of volcanic clouds
Super-radiant light scattering from trapped Bose Einstein condensates
We propose a new formulation for atomic side mode dynamics from super-radiant
light scattering of trapped atoms. A detailed analysis of the recently observed
super-radiant light scattering from trapped bose gases [S. Inouye {\it et al.},
Science {\bf 285}, 571 (1999)] is presented. We find that scattered light
intensity can exhibit both oscillatory and exponential growth behaviors
depending on densities, pump pulse characteristics, temperatures, and geometric
shapes of trapped gas samples. The total photon scattering rate as well as the
accompanied matter wave amplification depends explicitly on atom number
fluctuations in the condensate. Our formulation allows for natural and
transparent interpretations of subtle features in the MIT data, and provides
numerical simulations in good agreement with all aspects of the experimental
observations.Comment: 24 pages,16 figures, submitted to Phys.Rev.
Proefresultaten Ziekzoeker 2011 : spectrale en chlorofylfluorescentie beeldanalyse virus- en bacteriezieke pootaardappelen
Een vroege detectie van zieke planten met moderne vision technieken kan de kosten voor selectie in de pootaardappelteelt flink drukken. De nadruk ligt hierbij op de detectie van Erwinia, gezien de grote financiële schade. In 2010 zijn een eerste serie metingen in pootaardappelen uitgevoerd met een bestaande opstelling voor detectie van viruszieke tulpenbollen. De resultaten hiervan waren niet goed genoeg. Daarom is dit onderzoek met name gericht op het vinden van de meest geschikte opnametechniek voor het ziekzoeken, waarmee een eenduidig onderscheid te maken is tussen zieke en niet-zieke planten. Een belangrijk accent ligt op het vroegtijdig herkennen van zieke planten. De nieuwe technologieën hebben vooral meerwaarde als het herkennen mogelijk wordt voordat de symptomen door het menselijk oog waarneembaar zijn
Costs and benefits of smoking
Two recent societal cost-benefit analyses have documented the costs of smoking and the cost-effectiveness of preventing smoking. Smoking costs the Netherlands society EUR 33 billion per year. The majority of this is the monetary value of health loss; these are "soft" euros that cannot be re-spent. There is not a great deal of difference between costs and benefits when expressed in "hard" euros, which means that there is no clear business case for anti-smoking policy. The greatest benefit of discouraging smoking is improved health for the individual and increased productivity for the business sector; however, the benefits cannot be easily realised, because even in the most favourable scenario the number of smokers will decrease slowly. Excise duties seem to offer the most promising avenue for combating smoking. The benefits of anti-smoking policy, therefore, consist mainly of tax revenues for the government. Stringent policy is required to transform tax revenues into health gains
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