Backpropagation is extended to continuous-time feedforward networks with internal, adaptable time delays. The new technique is suitable for parallel hardware implementation, with continuous multidimensional training signals. The resulting networks can be used for signal prediction, signal production, and spatiotemporal pattern recognition tasks. Unlike conventional backpropagation networks, they can easily adapt while performing true signal prediction. Simulation results are presented for networks trained to predict future values of the Mackey-Glass chaotic signal, using its present value as an input. For this application, networks with adaptable delays had less than half the prediction error of networks with fixed delays, and about one-quarter the error of conventional networks. After training, the network can be operated in a signal production configuration, where it autonomously generates a close approximation to the Mackey-Glass signal.

Articles you may be interested inA field-programmable-gate-array based time digitizer for the time-of-flight mass spectrometry Rev. Sci. Instrum. 85, 045115 (2014); 10.1063/1.4870922 Time-of-flight mass spectrometry for time-resolved measurements Rev. Sci. Instrum. 78, 034103 (2007); 10.1063/1.2712797 Correction of dead time effects in timeofflight mass spectrometry J. Vac. Sci. Technol. A 12, 405 (1994); 10.1116/1.579255 MASTIF: Mass analysis of secondaries by timeofflight technique. A new approach to secondary ion mass spectrometry Rev. Sci. Instrum. 60, 3188 (1989); 10.1063/1.1140550Timeofflight secondary ion mass spectrometry of polymer materials Modulation of an ion beam is crucial to several applications in time-of-flight ͑TOF͒ mass spectrometry, especially for tandem TOF instruments which require selection of a particular precursor m/z ͑mass to charge͒ value prior to fragmentation. Here we present a detailed description of an ''interleaved comb'' ion deflection gate device with suitable electronics which offers a performance advantage over the more commonly used deflection plate devices. We demonstrate unit mass resolution for selection to m/z 167 in the tandem TOF instrument constructed in our laboratory. Calculations suggest that the real time of unit resolution for our experimental arrangement is greater than 300.

An ion trap source has been designed for use with time-of-flight (TOF) mass analysis. Two thin diaphragms make up a segmented ring electrode; the end cap electrodes are planar wire mesh. The potential field produced by the rf voltage applied between the ring and end cap electrodes resembles that of the cylindrical ion trap. The trapped ion population for ions created by electron impact exhibits linear growth against a first-order loss that has a time constant of about 50 µs; no ion loss occurs when the electron beam is off. The observed value of q z at low-mass cutoff for rf ion storage is -0.84. Pulsed extraction of all ions is accomplished by switching the trap electrodes from rf to voltages required to provide a linear dc extraction field. The TOF flight path includes a wide energy range reflectron. Better than unit mass resolution is achieved through m/z 500 without collisional ion cooling. With an extraction rate of 1 kHz and a recording rate of 4 spectra per second, a linear working curve is obtained between 36 pg and 18 ng of chlorobenzene delivered chromatographically. The system has demonstrated the potential to achieve a very high sample utilization efficiency at high spectral generation rates.

Articles you may be interested inQuantitative analysis of transient surface reactions on planar catalyst with time-resolved time-of-flight mass spectrometry Rev.An integrating transient recorder (ITR) has been designed, constructed, and evaluated to accomplish time-array detection in gas chromatography time-of-flight mass spectrometry (GC-TOFMS) applications. The ITR consists of a 200-MHz flash analog-to-digital converter, 16 high-speed 1OOK emitter-couple logic (ECL) summing boards, three parallel processors for real-time data reduction, instrument control and routing functions, and a 300-Mbyte mass storage device. The ITR is capable of recording 80 ,US bursts of transient information with a time resolution of 5 ns. For each transient, up to 16 384 sequential time-resolved channels may be recorded. An operator-selectable number of sequential transients may be summed in a locked time registry creating a summed scan file while maintaining the integrity of the transient time resolution. The information from each transient is read, summed, and stored in one of two summing registers ( 16 x 1024 X 24 bits). While incoming information is being stored in one summing register, the information in the other summing register is processed and read out to disk, thus permitting high-speed data collection continuously for long periods of time. The information from successive transients is summed in order to improve signal-tonoise, dynamic range, and sensitivity, and produces scan files at a rate sufficient to maintain all of the chromatographic information. GC-MS data collected at 1, 20, and 50 spectra per second are presented for a nine-component aliphatic/aromatic mixture. Although the ITR was specifically designed for GC-TOFMS studies, the overall design concepts of the ITR are universal and apply to any situation where information from two or more phenomena occur at the output of a single detector and occur over vastly different time domains.

An experimental speech processing system for extracting acoustic phonetic features from speaker independent continuous speech has been built and tested. The system uses wavelet analysis to pre-process the speech, and a two-layer "receptive field" neural network to recognize the phonetic features. Both training and testing was done on the TIMIT speech database. Preliminary results, using a network trained to recognize voicing and frication, are presented.