SIGNAL SCAN

Figure 5-13. Time resolved 1 + 1 ionization signal scan of the l-naphthol(NH3)3 cluster. Excitation energy, 31,100 cm" ionization energy, 29,000 cm-1. 0, data, solid line, fit. The fit parameters are instrument limited rise followed by a biexponential decay = 60 ps and r2 = 500 ps.

SIGNAL SCAN http //bimas. dcrt.nih.gov/molbio/signal/ IUPAC consensus library... 

Prestridge, D. S. (1991) SIGNAL SCAN a computer program that scans DNA sequences for eukaryotic transcriptional elements. Comp Appl Biosci 7, 203-206. 

Figure B2.1.10 Stimulated photon-echo peak-shift (3PEPS) signals. Top pulse sequence and interpulse delays t and T. Bottom echo signals scanned as a function of delay t at three different population periods T, obtained with samples of a tetrapyrrole-containing light-harvesting protein subunit, the a subunit of C-phycocyanin.

The other application is the flying-spot scanner. In this set up the information of slides or film can be transfonned into electric signals. The election beam excites a phosphor with short decay time. The luminescence signal scans the object point by point and the transmitted radiation is detected with a photomultiplyer. To reduce blurring of the signal, the decay time of the phosphor should be of the order of magnitude of the time the electron beam scans a picture element ( 50 ns). 

Timing related requirements (snch as response time, input signal scanning, synchronization) ... 

Impedance spectroscopy or electrochemical impedance spectroscopy is a powerful electrochemical technique used to investigate the binding events that occur at the electrode surface. The same three electrode systems comprising of a WE, RE and CE are utilized for the EIS experiment. Electrochemical impedance is usually measured by applying an AC sine wave potential with low amplitude (5—10 mV peak to peak) superimposed on a DC potential to the electrochemical system. The AC signal scans the frequency domain, allowing the individual excitation of different processes with different time constants. Therefore, slow processes like chemical reactions and fast reactions Hke ionic conduction can be studied independently this way. 

Fig. 1.22 Heterodyne-detected -Riiiiii fifth-order Raman response of CS2 measured using the crossed-beam geometry and 100 p.m pathlength. Two phase settings are shown solid line is the in-phase signal (A0 = 0), dotted line is the in-quadrature signal (A0 = 7t/2), The signal scans are,/rom top to bottom, probe delay (T4), pump delay (T2), and diagonal scan (t2 = T4) [23], Reused with permission from [23], Copyright 2002, American Institute of Physics...

A novel approach for suppression of grain noise in ultrasonic signals, based on noncoherent detector statistics and signal entropy, is presented. The performance of the technique is demonstrated using ultrasonic B-scans from samples with coarse material structure. 

The 45° transducer was used to inspect side drilled holes, with their centres located 40 mm below the surface. Due to the coarse material structure the echoes from the holes were totally masked by clutter. An example of an ultrasonic response signal, emanating from a hole with a diameter of 8 mm, is shown in the left part of Figure 3. Scanning the surface above the 8 mm and 10 mm holes resulted in the B-scan image shown in the upper part of Figure 4. 

Simulations of that kind result in a wide variety of A-scans and wavefront snapshots. The first screening of this material reveals, that the simulations in which the transducer is coupling partly to the V-butt weld and partly to the steel exhibit quite a number of pulses in the A-scans because the coupling at the interface of the weld results — due to the anisotropic behavior of the weld — in a complicated splitting of the transmitted wavefront. The different parts of the splitted wavefront are reflected and diffracted by the backwall, the interface, and — if present — by the notch and, therefore, many small signals are received by the transducer, which can only be separated and interpreted with great difficultie.s. 

Only the simulations in which the transducer is coupling either to the V-butt weld or to the surrounding steel can be analyzed in a simple and intuitive way, which means that the different pulses in the A-scan signals can be related uniquely to the reflection or diffraction of the wavefront at the weld, the backwall, and/or the notch. 

The upi-SO screen display ( Figure 7 ) shows the A-scan signal (top) and the resulting B-scan image (bottom) for the tandem arrangement of Figure 6. The flaw reflection is seen on the left. 

In addition to the distortions caused by the probes, there were also distortions caused by filtering the signals within the eddy-current test instruments. To achieve the highest possible dynamics with the test instruments, high-pass filters with a high rate of rise, but also a long reverberation time were used. Thus, the recorded C-scan pictures sometimes shows strong echo effects. 

Additional assistance is provided by secondary modification options that allow among others for a depiction of the original signal, the reconstruction of the depiction of the impedance plane of the eddy-current signals or for modifications of phase, amplification or zero point virtually in real time. That way, once C-scan images have been recorded, they can now be evaluated as needed without having to repeat the test. 

The measurements are done at a table with two in X- and Y- direction moveable axes. The measured structures, by an Aluminium-alloy, are situated at the X-axis. The sensor at the Y-axis scans the structure step by step. The position and the electoral signal are measured for every step. A computer controls the movement of the sensor and the data acquisition. 

Fig.l shows the layout of the SPATE 9000 system. It basically consists of a scan unit connected to a signal amplifier. The signals are then correlated with a reference signal derived from a load transducer (e.g. strain gauge, load cell, accelerometer, or function generator). 

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