Structures dans l'Emission Photonique de He Provoquée par Bombardement d'Electrons Monocinétiques dans la Région de 60 eV

1973 ◽  
Vol 51 (8) ◽  
pp. 814-819 ◽  
Author(s):  
Pierre D. Marchand
Keyword(s):  
Electron Impact ◽  
Electron Energy ◽  
Energy Resolution ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Photon Intensity ◽  
Noise Ratio

By measuring the photon intensity emitted by He excited by electron impact in the 60 eV region as a function of the electron energy, with an apparatus capable of excellent signal to noise ratio and energy resolution, several structures have been observed, some being entirely new and attributed to levels of the negative He− ion.

Metastable yield of argon between 23 and 37 eV by electron impact

1979 ◽  
Vol 57 (10) ◽  
pp. 1624-1633 ◽  
Author(s):  
P. Marchand ◽  
J. Cardinal
Keyword(s):  
Electron Impact ◽  
Excited States ◽  
Signal To Noise Ratio ◽  
Negative Ion ◽  
Photon Yield ◽  
Large Signal ◽  
Signal To Noise ◽  
Monoenergetic Electron ◽  
Yield Curves ◽  
Noise Ratio

The metastable yield of argon excited by monoenergetic electron impact has been measured between 23 and 37 eV. Thanks to a large signal-to-noise ratio, many very small structures have been detected superimposed on the metastable continuum and are attributed to Ar− negative-ion states and to highly excited states of Ar. The results are compared with broadband photon yield curves and electroionization curves.

Effects of accelerating voltage and thickness on the signal-to-noise ratio in Electron Energy Loss Spectroscopy (EELS)

1989 ◽  
Vol 47 ◽  
pp. 414-415
Author(s):  
Gianluigi Botton ◽  
Gilles L′Espérance
Keyword(s):  
Electron Energy ◽  
Signal To Noise Ratio ◽  
Mean Free Path ◽  
Incident Electron Energy ◽  
Constant Thickness ◽  
Signal To Noise ◽  
Noise Ratio ◽  
Value Changes ◽  
Electron Energy Loss ◽  
External Computer

The advantages of medium accelerating voltages (200-400KV) for EELS have been considered to be an improved jump ratio of edges and an improved signal to background ratio for an increased range of thiknesses. However, very little experimental data of the Signal to Noise Ratio (SNR) as a function of incident electron energy (Eo) can be found in the literature. The interest in performing such measurements is to investigate the effect of accelerating voltage on the detectability limits in EELS since SNR can be related to the minimum detectable fraction. In this paper, measurements made on NiO samples show an improved SNR with increasing Eo at a constant thickness value. Changes in the angular distribution of scattering are considered to be responsible for the improved SNR.The NiO sample studied was prepared by evaporation on a copper supporting grid. Uniform areas of different thicknesses (t) caused by the superposition of the film were analysed. Values of mean free path (λ) for NiO were found in the literature. All analyses were carried out with a Philips CM30 and a GATAN 666 Parallel EEL spectrometer (PEELS) coupled to a Link AN10000 MCA. Spectra were transfered on to an external computer for SNR calculations.

EXCITATION OF N2 BAND SYSTEMS IN AURORA

1964 ◽  
Vol 42 (6) ◽  
pp. 1212-1230 ◽  
Author(s):  
A. L. Broadfoot ◽  
D. M. Hunten
Keyword(s):  
Electron Impact ◽  
Rotational Temperature ◽  
Signal To Noise Ratio ◽  
Ultraviolet Region ◽  
Memory Unit ◽  
Signal To Noise ◽  
Previous Evidence ◽  
Near Ultraviolet ◽  
Vibrational Levels ◽  
Noise Ratio

The near-ultraviolet region of the auroral spectrum has been observed by a photoelectric spectrometer for the purpose of deriving accurate relative intensities of the N2 band systems. To increase the signal-to-noise ratio with the faint auroras measured, long "exposures" were accumulated in a memory unit. From the band intensities in the Vegard–Kaplan system, the relative populations of the first three vibrational levels of the metastable [Formula: see text] state could be found; the ratios appear to vary significantly. These bands give a rotational temperature of 800 ± 200 °K; they must therefore be emitted from a height of about 220 km. The vibrational populations are most reasonably explained if nearly all the excitation of the A state is by cascading from higher levels. A detailed discussion is given of these processes, supplemented by measurements of the second positive bands. Cascading is found to supply an appreciable fraction of the excitation of the B3Πg state; the C3Πu state seems to be excited purely by electron impact. Previous evidence that the latter is not always true is examined and rejected.

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

Experiments in Bright-Field Imaging with Hollow-Cone Illumination

1981 ◽  
Vol 39 ◽  
pp. 226-227
Author(s):  
W. Kunath ◽  
K. Weiss ◽  
E. Zeitler
Keyword(s):  
Signal To Noise Ratio ◽  
Carbon Support ◽  
Electronic System ◽  
Optic Axis ◽  
Hollow Cone ◽  
Signal To Noise ◽  
Bright Field ◽  
Noise Ratio ◽  
Single Field ◽  
Field Imaging

Bright-field images taken with axial illumination show spurious high contrast patterns which obscure details smaller than 15 ° Hollow-cone illumination (HCI), however, reduces this disturbing granulation by statistical superposition and thus improves the signal-to-noise ratio. In this presentation we report on experiments aimed at selecting the proper amount of tilt and defocus for improvement of the signal-to-noise ratio by means of direct observation of the electron images on a TV monitor.Hollow-cone illumination is implemented in our microscope (single field condenser objective, Cs = .5 mm) by an electronic system which rotates the tilted beam about the optic axis. At low rates of revolution (one turn per second or so) a circular motion of the usual granulation in the image of a carbon support film can be observed on the TV monitor. The size of the granular structures and the radius of their orbits depend on both the conical tilt and defocus.

Information capacity and bandwidth limitations in the SEM

1989 ◽  
Vol 47 ◽  
pp. 84-85
Author(s):  
D. C. Joy ◽  
R. D. Bunn
Keyword(s):  
Signal To Noise Ratio ◽  
Critical Dimension ◽  
Information Capacity ◽  
Acquisition Time ◽  
Signal To Noise ◽  
Sem Image ◽  
Probe Size ◽  
Minimum Number ◽  
Noise Ratio ◽  
Signal Channel

The information available from an SEM image is limited both by the inherent signal to noise ratio that characterizes the image and as a result of the transformations that it may undergo as it is passed through the amplifying circuits of the instrument. In applications such as Critical Dimension Metrology it is necessary to be able to quantify these limitations in order to be able to assess the likely precision of any measurement made with the microscope.The information capacity of an SEM signal, defined as the minimum number of bits needed to encode the output signal, depends on the signal to noise ratio of the image - which in turn depends on the probe size and source brightness and acquisition time per pixel - and on the efficiency of the specimen in producing the signal that is being observed. A detailed analysis of the secondary electron case shows that the information capacity C (bits/pixel) of the SEM signal channel could be written as :

Speech Reception in the Presence of Classroom Noise

1979 ◽  
Vol 10 (4) ◽  
pp. 221-230 ◽  
Author(s):  
Veronica Smyth
Keyword(s):  
Signal To Noise Ratio ◽  
Learning Processes ◽  
Speech Discrimination ◽  
Signal To Noise ◽  
Speech Reception ◽  
Monosyllabic Words ◽  
Noise Ratio

Three hundred children from five to 12 years of age were required to discriminate simple, familiar, monosyllabic words under two conditions: 1) quiet, and 2) in the presence of background classroom noise. Of the sample, 45.3% made errors in speech discrimination in the presence of background classroom noise. The effect was most marked in children younger than seven years six months. The results are discussed considering the signal-to-noise ratio and the possible effects of unwanted classroom noise on learning processes.

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