Antiproton therapy

Radiotherapy is one of the most important means we have for the treatment of localised tumours. It is therefore essential to optimize the technique, and a lot of effort goes into this endeavour. Since the proposal by Wilson in 1946 [R.R. Wilson, Radiology use of fast protons, Radiology 47 (1946) 487.] that proton beams might be better than photon beams at inactivating cancer cells, hadron therapy has been developed in parallel with photon therapy and a substantial knowledge has been gained on the effects of pions, protons and heavy ions (mostly carbon ions). Here we discuss the recent measurements by the CERN ACE collaboration of the biological effects of antiprotons, and argue that these particles very likely are the optimal agents for radiotherapy.     

A direct method for BBD matrix inversion

Published in Kibernetika i Sistemnyi Analiz, No. 2, pp. 51–64, March–April, 1994.     

Complexity Reduction in SISO Decoding of Block Codes

SISO decoding for block codes can be carried out based on a trellis representation of the code. However, the complexity entailed by such decoding is most often prohibitive and thus prevents practical implementation. This paper examines a new decoding scheme based on the soft-output Viterbi algorithm (SOVA) applied to a sectionalized trellis for linear block codes. The computational complexities of the new SOVA decoder and of the conventional SOVA decoder, based on a bit-level trellis, are theoretically analyzed and derived for different linear block codes. These results are used to obtain optimum sectionalizations of a trellis for SOVA. For comparisons, the optimum sectionalizations for Maximum A Posteriori (MAP) and Maximum Logarithm MAP (Max-Log-MAP) algorithms, and their corresponding computational complexities are included. The results confirm that the new SOVA decoder is the most computationally efficient SISO decoder, in comparisons to MAP and Max-Log-MAP algorithms. The simulation results of the bit error rate (BER) performance, assuming binary phase -- shift keying (BPSK) and additive white Gaussian noise (AWGN) channel, demonstrate that the performance of the new decoding scheme is not degraded. The BER performance of iterative SOVA decoding of serially concatenated block codes shows no difference in the quality of the soft outputs of the new decoding scheme and of the conventional SOVA.     

On-line monitoring of depth of cut in AWJ cutting

Monitoring of the abrasive waterjet (AWJ) cutting process has become increasingly important. The present paper proposes a model for on-line depth of cut monitoring based on the acoustic emission (AE) response to the variation in AWJ depth of cut, instead of the expensive and impractical vertical cutting force monitoring. The main objective is to use the AE technique in order to predict the actual depth of cut in AWJ cutting under normal cutting conditions. It was found that the root mean square of the acoustic emission energy (AErms) increases linearly with an increase in the depth of cut and could be used for its on-line monitoring. The results show that the AE is the most suitable technique for AWJ monitoring, as the AE signal has high sensitivity to the variation in the depth of cut.     

Adaptive Doppler-Kalman filter for radar systems

Time-dependent Fourier transform plays an important role in radar signal analysis. The Doppler frequency carries information about the relative velocity of a moving target regarding the radar antenna. However, because the target movement may be very complex, with temporary high-intensity manoeuvres, the Doppler frequency must be estimated by using a window function. In order to minimise the estimation error, the window function width must be dependent on the target manoeuvre as well as on the signal-to-noise ratio. Here, a system consisting of a Doppler filter and a second-order Kalman filter, connected in an adaptive structure, has been proposed as an efficient solution to this problem. The proposed approach enables the window width adaptation, based on the estimates of target acceleration and signal-to-noise ratio, generated by an adaptive Kalman filter. Simulation results demonstrate the advantage of this structure compared to the fixed-width, window-based algorithms, giving acceptable results even for very bad signal-to-noise conditions.     

Wavelet families of increasing order in arbitrary dimensions

We build discrete-time compactly supported biorthogonal wavelets and perfect reconstruction filter banks for any lattice in any dimension with any number of primal and dual vanishing moments. The associated scaling functions are interpolating. Our construction relies on the lifting scheme and inherits all of its advantages: fast transform, in-place calculation, and integer-to-integer transforms. We show that two lifting steps suffice: predict and update. The predict step can be built using multivariate polynomial interpolation, while update is a multiple of the adjoint of predict. While we concentrate on the discrete-time case, some discussion of convergence and stability issues together with examples is given.     

Modeling of the Effect of Path Planning on Thermokinetic Evolutions in Laser Powder Deposition Process

A thermokinetic model coupling finite-element heat transfer with transformation kinetics is developed to determine the effect of deposition patterns on the phase-transformation kinetics of laser powder deposition (LPD) process of a hot-work tool steel. The finite-element model is used to define the temperature history of the process used in an empirical-based kinetic model to analyze the tempering effect of the heating and cooling cycles of the deposition process. An area is defined to be covered by AISI H13 on a substrate of AISI 1018 with three different deposition patterns: one section, two section, and three section. The two-section pattern divides the area of the one-section pattern into two sections, and the three-section pattern divides that area into three sections. The results show that dividing the area under deposition into smaller areas can influence the phase transformation kinetics of the process and, consequently, change the final hardness of the deposited material. The two-section pattern shows a higher average hardness than the one-section pattern, and the three-section pattern shows a fully hardened surface without significant tempered zones of low hardness. To verify the results, a microhardness test and scanning electron microscope were used.