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排序方式: 共有81条查询结果,搜索用时 718 毫秒
51.
F. Bonneau P. Combis J.L. Rullier J. Vierne M. Pellin M. Savina M. Broyer E. Cottancin J. Tuaillon M. Pellarin L. Gallais J.Y. Natoli M. Perra H. Bercegol L. Lamaignère M. Loiseau J.T. Donohue 《Applied physics. B, Lasers and optics》2002,75(8):803-815
In order to resolve problems concerning the understanding and the control of laser-induced damage of silica optical elements,
a collaboration between the CEA and different university laboratories has been undertaken. Ultra-pure silica model samples,
seeded with gold nanoparticles whose diameter did not exceed 5 nm, were prepared. The aim in using these samples was to observe
the mechanism of damage initiation that could be attributed to inclusions of nanometric size. This paper presents the different
steps encountered during this study: preparation of the samples, the laser-induced damage tests, the Nomarski and atomic-force
microscope observations of this damage and a series of experiments using a time-of-flight mass spectrometer at Argonne National
Laboratory. The experimental data are then interpreted, and, in particular, compared to numerical simulations. A very encouraging
result is the existence of a pre-damage phase at very low fluences that is not detectable by classical optical devices. The
experimental means developed for such model samples should be transposable to the analysis of industrial glasses.
Received: 19 July 2002 / Revised version: 23 September 2002 / Published online: 11 December 2002
RID="*"
ID="*"Corresponding author. Fax: +33-1/6926-7106, E-mail: florian.bonneau@cea.fr 相似文献
52.
L. Gallais J. Capoulade F. Wagner J.Y. Natoli M. Commandré 《Optics Communications》2007,272(1):221-226
The damage mechanisms in silica thin films exposed to high fluence 1064 nm nano-second laser pulses are investigated. The thin films under study are made with different techniques (evaporation and sputtering, with and without ion assistance) and the results are compared. The material morphological, optical and structural modifications are locally analyzed with optical microscopy and profilometry, photoluminescence and absorption microscopies. These observations are made for fluences near and above the laser damage threshold, and also in the case of multiple pulse irradiations. An increase in absorption in and around the damages is observed, as well as the generation of different defects that we spatially resolve with absorption and luminescence mappings. 相似文献
53.
M. POPEM. MAGNUSSON R. LUNDSTRÖMC. HULSHOF J. VERBEEKM. BOVENZI 《Journal of sound and vibration》2002,253(1):131-167
There is strong epidemiological evidence that occupational exposure to WBV is associated with an increased risk of low back pain (LBP), sciatic pain, and degenerative changes in the spinal system, including lumbar intervertebral disc disorders. A prototype health surveillance scheme for WBV is presented in this paper. Surveillance is the collection, analysis, and dissemination of data for the purpose of prevention. The aims are to assess health status and diagnose vibration-induced disorders at an early stage, to inform the workers on the potential risk associated with vibration exposure, to give preventive advice to employers and employees and to control whether preventive measures which have been taken, were successful. It is suggested that a pre-placement health examination should be offered to each worker who will be exposed to WBV so as to make the worker aware of the hazards, to obtain baseline health data, and to identify medical conditions that may increase the risk due to WBV. The case history should focus on personal history, work history, and leisure activities involving driving of vehicles. The personal medical history should detail back pain complaints, disorders in the spine, any injuries or surgery to the musculoskeletal system. A physical examination on the lower back should be performed on workers who have experienced LBP symptoms over the past 12 months. The preplacement examination should be followed by periodic health reassessment with a regular interval according to the legislation of the country. It is suggested that periodic medical examination should be made available at least every 2 years to all workers who are exposed to WBV. Any change in vibration exposure at the workplace should be reported by the employer. If an increase in vibration exposure or a change in health status have occurred, the medical re-examination should be offered at shorter intervals at the discretion of the attending physician. There should be a periodic medical examination, which includes recording any change in exposure to WBV. The findings for the individual should be compared with previous examinations. Group data should also be compiled periodically. Medical removal may be considered along with re-placement in working practices without exposure to WBV. This paper presents opinions on health surveillance for whole-body vibration developed within a working group of partners funded on a European Community Network (BIOMED2 concerted action BMH4-CT98-3251: Research network on detection and prevention of injuries due to occupational vibration exposures). The health surveillance protocol and the draft questionnaire with explanation comments are presented for wider consideration by the science community and others before being considered appropriate for implementation. 相似文献
54.
Alajarin M Vidal A Tovar F Ramirez De Arellano MC Cossio FP Arrieta A Lecea B 《The Journal of organic chemistry》2000,65(22):7512-7515
Efficient 1,4-asymmetric induction has been achieved in the highly stereocontrolled intramolecular [2 + 2] cycloadditions between ketenimines and imines, leading to 1,2-dihydroazeto[2, 1-b]quinazolines. The chiral methine carbon adjacent to the iminic nitrogen controls the exclusive formation of the cycloadducts with relative trans configuration at C2 and C8. The stepwise mechanistic model, based on theoretical calculations, fully supports the stereochemical outcome of these cycloadditions. 相似文献
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Morelos A Albuquerque IF Bondar NF Carrigan R Chen D Cooper PS Lisheng D Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Lebedenko VN Li Chengze Li Yunshan Luksys M Mahon JR McCliment E Newsom C Pommot Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Fukun T Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Wenheng Z Zheng Shuchen Zhong Yuanyuan 《Physical review D: Particles and fields》1995,52(7):3777-3780
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In vivo measurement of vascular modulation in experimental tumors using a fluorescent contrast agent
Valentini G D'Andrea C Ferrari R Pifferi A Cubeddu R Martinelli M Natoli C Ubezio P Giavazzi R 《Photochemistry and photobiology》2008,84(5):1249-1256
Abstract We compared the effectiveness of three optical techniques based on fluorescence imaging and spectroscopy with indocyanine green (ICG) contrast agent to evaluate in vivo the disruption of the active vasculature induced by a vascular targeting agent. The blood perfusion of the MDA-MB-435 tumor model transplanted in nude mice was estimated from the signal of the contrast agent measured immediately after its systemic injection in mice. Optical measurements were performed using a fluorescence imaging setup and a fiber-based time correlated single photon counting (TCSPC) apparatus. This latter apparatus was used to measure the tumor fluorescence in transmittance geometry and the change in the basal optical absorption induced by the contrast agent, thus providing an alternative estimation of the blood content in the tumor. Mice were divided into four groups. Three groups were treated with different doses of the vascular disrupting agent ZD6126, the fourth group (control group) received the drug vehicle only. Optical measurements were carried out 3 h after pharmacologic treatment. After 24 h, mice were killed, tumors were excised and the extent of necrosis was evaluated with standard histologic analysis. On fluorescence imaging ICG emission from tumors of mice treated with ZD6126 significantly was lower compared with the emission from control mice. The histologic sections also showed a significantly higher amount of necrosis in tumors of treated mice. Both these findings, which correlate with each other, indicate an effective vascular shutdown induced by the drug. However, ICG fluorescence measured with the TCSPC apparatus in transmittance geometry and the estimate of the change in optical absorption did not allow a statistically significant differentiation between treated and control groups. 相似文献