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91.
The efficiencies of direct lidars operating at 355, 532, 1064 and 1540-nm radiation wavelengths for early forest fire detection
were compared. For each wavelength, the range for reliable smoke-plume detection was estimated on the basis of a computer
simulation plume using a one-dimensional “top-hat” gas dynamic model for the calculation of the backscattering and extinction-coefficient
profiles within the plume. The agreement between the predicted signal-to-noise ratio (SNR) and experimental results for 532
and 1064-nm wavelength radiation is good. The decrease of the signal-to-noise ratio with distance is maximum for 355 nm and
minimum for 1064 nm. At 1540 nm, the decay of SNR with distance is slightly faster, but the SNR is higher than for other wavelengths,
leading to the highest detection efficiency for the same energy of the probing laser pulse. For a burning rate of 2 kg/s and
a laser beam divergence of 2.5 mr, the maximum distance for reliable detection varies between 6 and 12 km, depending on the
wavelength.
Received: 15 May 2002 / Revised version: 13 September 2002 / Published online: 22 January 2003
RID="*"
ID="*"Corresponding author. Fax: +351-21/841-8120, E-mail: rui.vilar@ist.utl.pt 相似文献
92.
D.M. Kane A.J. Fernandes R.P. Mildren 《Applied Physics A: Materials Science & Processing》2003,77(6):847-853
In earlier work we characterised single-pulse laser cleaning of medium-density (areal coverage 10–20%) alumina particles from glass surfaces with three different lasers. The method of measuring particle-removal efficiency involves optical microscopy imaging (digital) and subsequent image analysis of the area covered by, and/or the number of, particles before and after the single-pulse laser cleaning treatment. The sample-preparation technique used leads to both single particles and agglomerates on the surface. The issues of depth of focus in the imaging and grey-scale thresholding in the image analysis of such samples, with a range of particle and agglomerate sizes, has been systematically investigated. A protocol for optimum imaging and illumination of such samples is described herein. It has been developed based on the results of a systematic investigation of the effect of the image focal plane position relative to the surface also described herein. The image analysis to quantify the particles on the surface involves a judgement of the best threshold grey-scale level in the image to define the boundary between particles and background substrate. A quantitative appraisal of the impact on the laser cleaning efficiency results of a threshold grey-scale level that is set too high or too low, and how these results compare with those obtained for the best-judgement threshold grey-scale level, has been completed. PACS 81.65.Cf; 42.62.Cf; 42.70.Ce 相似文献
93.
U. Köster P. Carbonez A. Dorsival J. Dvorak R. Eichler S. Fernandes H. Frånberg J. Neuhausen Z. Novackova R. Wilfinger A. Yakushev 《The European physical journal. Special topics》2007,150(1):285-291
Refractory elements, i.e. elements with very high melting point and
low vapor pressure, cannot be released in atomic form from an ISOL target.
Therefore most of these elements are presently not available as ISOL beams.
However, when reactive gases are introduced
into the target, they may form volatile compounds with the refractory elements,
allowing for an easier transport to the ion source. Particularly useful are
high-temperature stable fluorides and oxides.
By these chemical evaporation methods so far ISOL beams of the refractory elements
C, Zr, Hf and Ta have been produced. We discuss how ISOL beams of B, Ti, Nb, Mo, Tc,
Ru, W, Re, Os and Ir could be produced in a similar way. 相似文献
94.
95.
96.
97.
Himatkumar V. Patel Kavita A. Vyas Sudhanshu P. Pandey Peter S. Fernandes 《合成通讯》2013,43(21):3081-3087
A novel one-step synthesis of 4-arylazo-1H-1, 3, 5-trimethylpyrazoles is accomplished by reaction of N, N-dimethylhydrazine with 2, 3, 4-pentantrione-3-arylhydrazones via an unusual demethylation. 相似文献
98.
D. G. Beasley A. Alghamdi M. C. Freitas A. Fernandes Z. Révay 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(2):307-311
The epithermal beamline at the Portuguese Research Reactor is being optimized for Prompt Gamma Neutron Activation Analysis
(PGNAA). One of the major changes is to thermalise the beam by the introduction of a sapphire crystal into the beamline. Placing
the sapphire at the exit of the beamline would greatly reduce the alterations and work necessary to the port and make the
crystal easily removable. However, the scattered neutrons from the sapphire would increase both the neutron-induced detector
damage and the background radiation. MCNPX was used to simulate the crystal in the beam port and at the exit of the port. 相似文献
99.
100.
Th. R. Cunningham R. J. Price St. G. Simpson W. C. Schumb P. Klinger O. Schliessmann D. R. Nijk H. Bart G. v. Hevesy R. Hobbie A. Asmanow P. H. M. P. Brinton R. B. Ellestad G. Scagliarini P. Pratesi I. M. Kolthoff J. J. Lingane J. Volmar Mathis J. Perrin E. Bayle R. Fabre H. George H. Gräven G. Canneri und L. Fernandes 《Fresenius' Journal of Analytical Chemistry》1934,99(3-4):113-129
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