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991.
Quirino Majorana (1871–1957) was an outstanding Italian experimental physicist who investigated a wide range of phenomena
during his long career in Rome,Turin, and Bologna. We focus on his experiments in Turin during 1916–1921 and in Bologna during
1921–1934 to test the validity of Albert Einstein’s postulate on the constancy of the speed of light and to detect gravitational
absorption. These experiments required extraordinary skill, patience, and dedication, and all of them confirmed Einstein’s
postulate and Isaac Newton’s law of universal gravitation to high precision. Had they not done so, Majorana’s fame among historians
and physicists no doubt would be much greater than it is today.
Giorgio Dragoni is Professor of History of Physics at the University of Bologna. Giulio Maltese is a Roman member of the Italian
Society for the History of Physics and Astronomy. Luisa Atti is a Bolognese member of the Association for the Teaching of
Physics. 相似文献
992.
Miyoshi Ayama Hiroyasu Ujike Wataru Iwai Masami Funakawa Katsunori Okajima 《Optical Review》2007,14(1):48-56
We examined effects of contrast and character size upon legibility of Japanese text stimuli presented on visual display terminal
(VDT). In the experiment, three different character sizes were employed and the text stimulus was presented under a variety
of conditions where contrast between the text and the background changed. Reading speed and the rate of readable characters
were measured. Subjective rating for legibility was also evaluated. Results showed that legibility increases with luminance
contrast for all character sizes examined here. A strong correlation was found between the subjective rating index and reading
speed. 相似文献
993.
电场对火焰形状及碳烟沉积特性的影响 总被引:2,自引:0,他引:2
建立了三种类型的直流电场分别作用于层流扩散火焰,研究了电场类型、电场强度对火焰形态及所产生的碳烟颗粒在电极上的沉积特性的影响.实验表明,针状电极由于离子风的作用会使火焰高度变短;平板状电极由于电场力的作用可使火焰顶部向阴极板倾斜,证明了有一部分碳烟颗粒本身荷正电.同时,由于环形电极同时产生离子风和电场力,影响火焰形态.而荷正电的中心电极对碳烟颗粒的排放起到抑制作用. 相似文献
994.
Bin Yang 《Proceedings of the Combustion Institute》2007,31(1):555-563
A comprehensive experimental study of the premixed benzene/oxygen/argon flame at 4.0 kPa with a fuel equivalence ratio (?) of 1.78 has been performed with the tunable synchrotron photoionization and molecular-beam sampling mass spectrometry. Isomers of most observed species in the flame have been unambiguously identified by measurements of the photoionization efficiency spectra. Mole fraction profiles of species up to C16H10 have been measured at the selective photon energies near ionization thresholds, and the flame temperature profile is obtained using Pt/Pt-13%Rh thermocouple. Compared with previous studies on benzene flames by Bittner and Howard, and by Defoeux et al., a number of new species are observed in the present work. These new combustion intermediates should be included in the kinetic models of the growth of polycyclic aromatic hydrocarbons (PAHs) and benzene oxidation. Free radicals detected in the flame include CH3, C2H, C2H3, C2H5, C3H, C3H3, C3H5, C4H, C4H3, C4H5, C4H7, C5H3, C5H5, C5H7, C6H5, C6H5O, C7H7, and C9H7. More significantly, isomers of some PAHs have been identified, which should be of importance in understanding the mechanism of soot formation. 相似文献
995.
Development of improved PLIF CH detection using an Alexandrite laser for single-shot investigation of turbulent and lean flames 总被引:1,自引:0,他引:1
We report on the development of planar laser-induced fluorescence (PLIF) for CH imaging with improved detection sensitivity for single-shot investigations of turbulent, lean, premixed flames. A ring-cavity, pulsed Alexandrite laser was frequency-doubled to excite the lines in the R-branch band-head of the B-X (0,0) band and broadband fluorescence from the B-X (0,1), A-X (1,1) and (0,0) bands, overlapping in the spectral range around 431 nm, was collected. The employed Alexandrite laser, which is characterized by its long pulse duration (150 ns), gives a tunable laser beam around 775 nm with a pulse energy for the second harmonic at the CH absorption wavelength of about 70 mJ. Moreover, the laser has the possibility to be operated in narrow bandwidth (100 MHz) or broad bandwidth (8 cm−1). An introductory high resolution excitation scan over the R-branch band-head was performed and, in addition, saturated excitation with the broadband option of the laser was investigated. By simultaneous excitation of several rotational transitions and to bring these transitions close to saturation, high signal-to-noise ratios were reached over a wide range of equivalence ratios. A sharp and thin CH layer was observed in single-shot PLIF images from laminar premixed methane/air flames from Φ = 0.6 to Φ = 1.5. Finally, the impact of the developed CH PLIF technique is demonstrated in a highly turbulent, lean, partially premixed methane/air flame established on a co-axial jet flame burner. 相似文献
996.
The study of edge flames has received increased attention in recent years. This work reports the results of a recent study into two-dimensional, planar, propagating edge flames that are remote from solid surfaces (called here, “free-layer” flames, as opposed to layered flames along floors or ceilings). They represent an ideal case of a flame propagating down a flammable plume, or through a flammable layer in microgravity. The results were generated using a new apparatus in which a thin stream of gaseous fuel is injected into a low-speed laminar wind tunnel thereby forming a flammable layer along the centerline. An airfoil-shaped fuel dispenser downstream of the duct inlet issues ethane from a slot in the trailing edge. The air and ethane mix due to mass diffusion while flowing up towards the duct exit, forming a flammable layer with a steep lateral fuel concentration gradient and smaller axial fuel concentration gradient. We characterized the flow and fuel concentration fields in the duct using hot wire anemometer scans, flow visualization using smoke traces, and non-reacting, numerical modeling using COSMOSFloWorks. In the experiment, a hot wire near the exit ignites the ethane-air layer, with the flame propagating downwards towards the fuel source. Reported here are tests with the air inlet velocity of 25 cm/s and ethane flows of 967-1299 sccm, which gave conditions ranging from lean to rich along the centerline. In these conditions the flame spreads at a constant rate faster than the laminar burning rate for a premixed ethane-air mixture. The flame spread rate increases with increasing transverse fuel gradient (obtained by increasing the fuel flow rate), but appears to reach a maximum. The flow field shows little effect due to the flame approach near the igniter, but shows significant effect, including flow reversal, well ahead of the flame as it approaches the airfoil fuel source. 相似文献
997.
Arvind V. Menon 《Proceedings of the Combustion Institute》2007,31(1):593-601
Experiments were conducted on a laminar premixed ethylene-air flame at equivalence ratios of 2.34 and 2.64. Comparisons were made between flames with 5% NO2 added by volume. Soot volume fraction was measured using light extinction and light scattering and fluorescence measurements were also obtained to provide added insight into the soot formation process. The flame temperature profiles in these flames were measured using a spectral line reversal technique in the non-sooting region, while two-color pyrometry was used in the sooting region. Chemical kinetics modeling using the PREMIX 1-D laminar flame code was used to understand the chemical role of the NO2 in the soot formation process. The modeling used kinetic mechanisms available in the literature. Experimental results indicated a reduction in the soot volume fraction in the flame with NO2 added and a delay in the onset of soot as a function of height above the burner. In addition, fluorescence signals—often argued to be an indicator of PAH—were observed to be lower near the burner surface for the flames with NO2 added as compared to the baseline flames. These trends were captured using a chemical kinetics model that was used to simulate the flame prior to soot inception. The reduction in soot is attributed to a decrease in the H-atom concentration induced by the reaction with NO2 and a subsequent reduction in acetylene in the pre-soot inception region. 相似文献
998.
999.
As is distinct from general gas-liquid two-phase flow, a large number of bubbles with different diameters belong to ship wakes.
Feasibility of Laplace equation, used to calculate wake sound speed (WSS), is confirmed based on differential postulation.
Defect for calculating the adiabatic sound speed of gases in references is showed, and a concept of WSS is proposed clearly.
A minimum WSS of 24.5 m/s is got when bubble ratio reads 0.5 according to the calculation when bubble dimension is less than
that of resonance. Also a weak dependence of WSS on pressures is predicted. WSS from calculation corresponds with the experimental
data of references well in high frequency domain, when the actual scale of bubbles is greater than the resonant scale.
Supported by the National Natural Science Foundation of China (Grant No.10274046) and Pre-study Fund of Military Equipment
(Grant No. 51448030101ZK1801) 相似文献
1000.
转镜式高速相机扫描速度检测装置及不确定度评定 总被引:1,自引:0,他引:1
基于光电转换基本原理,设计并研制了用于转镜式高速扫描相机扫描速度的检测装置,包括均匀脉冲光源、精密双狭缝、超快响应光电转换器以及高带宽、高采样率数字示波器等。论述了检测装置的核心部件,用该装置实测了SJZ-15型转镜扫描相机名义扫速为4.5mm/μs的扫描速度,计算出了扫速不均匀性。按照国军标GJB3756,对检测装置的测量不确定度来源进行了分析,给出了该装置的不确定度评定方法及测量不确定度,对检测结果的评定表明,该检测装置的相对测量不确定度不大于0.1%,远低于目前转镜扫描相机的最大扫速不均匀性水平。实验证明,设计的检测装置具有很高的准确度和可靠性。 相似文献