Nonlinear vector prediction using feed-forward neural networks

The performance of a classical linear vector predictor is limited by its ability to exploit only the linear correlation between the blocks. However, a nonlinear predictor exploits the higher order correlations among the neighboring blocks, and can predict edge blocks with increased accuracy. We have investigated several neural network architectures that can be used to implement a nonlinear vector predictor, including the multilayer perceptron (MLP), the functional link (FL) network, and the radial basis function (RBF) network. Our experimental results show that a neural network predictor can predict the blocks containing edges with a higher accuracy than a linear predictor.

Advances in residual vector quantization: a review

Advances in residual vector quantization (RVQ) are surveyed. Definitions of joint encoder optimality and joint decoder optimality are discussed. Design techniques for RVQs with large numbers of stages and generally different encoder and decoder codebooks are elaborated and extended. Fixed-rate RVQs, and variable-rate RVQs that employ entropy coding are examined. Predictive and finite state RVQs designed and integrated into neural-network based source coding structures are revisited. Successive approximation RVQs that achieve embedded and refinable coding are reviewed. A new type of successive approximation RVQ that varies the instantaneous block rate by using different numbers of stages on different blocks is introduced and applied to image waveforms, and a scalar version of the new residual quantizer is applied to image subbands in an embedded wavelet transform coding system.

Pneumatic lithotripsy: a new modality for treatment of ureteric stones

Two hundred and twenty ureteric stones in 214 patients were fragmented intracorporeally by pneumatic lithotripsy under general/regional anaesthesia in a day care set-up. Patients were followed-up weekly and retreatment was done at 4 weeks where necessary. Majority (77%) of patients were in the age group 21-40 years with a male to female ratio of 2:1. Stone location was 86% in the lower third, 11% in the middle and 3% in the upper third ureter. Size of stones was less than 6 mm in 14%, 7-12 mm in 67% and more than 20 mm in 4% cases. All 81% stones of < 12 mm were fragmented in one treatment session while single treatment rate for stones 13-18 mm was 85% and 44% for more than 20 mm size. Overall non-fragmentation rate was 0.9%. Stone free state at four weeks was 95%. Complications were observed in 8.6% cases which included urosepsis, haematuria and perforations. Infrared spectroscopy (IR) in 45 stones showed majority (64%) to be composed of calcium oxalate. Our experience shows that PL is a safe and effective means of performing intracorporeal lithotripsy for both large and hard ureteric stones.

Predictive residual vector quantization [image coding]

This paper presents a new vector quantization technique called predictive residual vector quantization (PRVQ). It combines the concepts of predictive vector quantization (PVQ) and residual vector quantization (RVQ) to implement a high performance VQ scheme with low search complexity. The proposed PRVQ consists of a vector predictor, designed by a multilayer perceptron, and an RVQ that is designed by a multilayer competitive neural network. A major task in our proposed PRVQ design is the joint optimization of the vector predictor and the RVQ codebooks. In order to achieve this, a new design based on the neural network learning algorithm is introduced. This technique is basically a nonlinear constrained optimization where each constituent component of the PRVQ scheme is optimized by minimizing an appropriate stage error function with a constraint on the overall error. This technique makes use of a Lagrangian formulation and iteratively solves a Lagrangian error function to obtain a locally optimal solution. This approach is then compared to a jointly designed and a closed-loop design approach. In the jointly designed approach, the predictor and quantizers are jointly optimized by minimizing only the overall error. In the closed-loop design, however, a predictor is first implemented; then the stage quantizers are optimized for this predictor in a stage-by-stage fashion. Simulation results show that the proposed PRVQ scheme outperforms the equivalent RVQ (operating at the same bit rate) and the unconstrained VQ by 2 and 1.7 dB, respectively. Furthermore, the proposed PRVQ outperforms the PVQ in the rate-distortion sense with significantly lower codebook search complexity.

Next-state functions for finite-state vector quantization

The finite-state vector quantization scheme called dynamic finite-state vector quantization (DFSVQ) is investigated with regard to its subcodebook construction. In the DFSVQ, each input block is encoded by a small codebook called the subcodebook which is created from a much larger codebook called supercodebook. Each subcodebook is constructed by selecting, using a reordering procedure, a set of appropriate code-vectors from the supercodebook. The performance of the DFSVQ depends on this reordering procedure; therefore, several reordering procedures are introduced and their performance are evaluated. The reordering procedures investigated, are based on the conditional histogram of the code-vectors, index prediction, vector prediction, nearest neighbor design, and the frequency usage of the code-vectors. The performance of the reordering procedures are evaluated by comparing their hit ratios (the number of blocks encoded by the subcodebook) and their computational complexity. Experimental results are presented and it is found that the reordering procedure based on the vector prediction performs the best when compared with the other reordering procedures.

Treatment of ureteric stones. Comparison of laser and pneumatic lithotripsy

OBJECTIVES

To study the treatment of ureteric stones by laser lithotripsy (LL) and pneumatic lithotripsy (PL), and to evaluate the results of the two treatment modalities to assess effectiveness, complications and cost benefits.

PATIENTS AND METHODS

Between January 1993 and February 1994 200 ureteric stones in 194 patients were fragmented intracorporeally, 48 by LL and 152 by PL. The ages of the patients ranged from 31 to 40 years with a male to female ratio of 2:1. All procedures were performed under general/regional anaesthetic in a day-care set-up. Patients were followed at weekly intervals. Re-treatment was carried out at 4 weeks where necessary.

RESULTS

The majority of the stones treated (84%) were in the lower third of the ureter, 69% measured 7-12 mm in diameter, and 61% were composed of calcium oxalate. Ninety-three per cent of the stones were fragmented in one treatment session. The overall stone-free status at 4 weeks was 95% for PL and 84% for LL. The non-fragmentation rate was 10% for LL and 1% for PL. Post-treatment complications were encountered in 8% of the patients treated by LL and 7% by PL.

CONCLUSIONS

Our experience shows that PL and LL both provide a safe and effective means of performing intracorporeal lithotripsy for smaller ureteric stones. However, PL is more effective in fragmenting larger and harder stones. Moreover, PL is more user-friendly and highly cost-effective compared with LL.

Effects of income on drug choice in humans

The effects of income (money available to spend during the experimental session) on human choice were examined in a concurrent-schedule arrangement. Subjects were 7 nicotine-dependent smokers, and reinforcers were puffs on the subject's usual brand of cigarette ("own") and puffs on a less preferred brand of cigarette with equal nicotine content ("other"). Across sessions, income varied and the price of the two reinforcers was held constant, with the other puffs one fifth the price of the own puffs. As income increased, consumption of own puffs increased while consumption of the less expensive other puffs decreased. These effects of income on choice were highly consistent across subjects. For some subjects, however, income had little effect on total puff consumption. Finally, an additional condition examined whether price and income manipulations would have functionally equivalent effects on choice by repeating an income condition in which the price of the other brand was increased. Although the increased price of the other puffs decreased their consumption in 4 subjects, 2 subjects showed increased consumption of the other puffs at the higher price. The results, when defined in economic terms, indicate that the own puffs were a normal good (consumption and income are directly related), the other puffs were an inferior good (consumption and income are inversely related), and the direct relationship between consumption of the other puffs and their price is defined as a Giffengood effect. The latter result also suggests that for these 2 subjects, price and income manipulations had equivalent effects on choice. These results extend findings from previous studies that have examined the effects of income on choice responding to human subjects and drug reinforcers, and provide a framework for further experimental tests of the effects of income on human choice behavior. Methodological and theoretical implications for the study of choice and for behavioral pharmacology are discussed.

Renal stones in children in Pakistan

One hundred and fifty children up to the age of 12 years with documented evidence of renal or ureteric stones were studied between July 1973 and June 1983. The peak age group was between 10 and 12 years, the male to female ratio being 1.9:1. Abdominal pain was the commonest presenting symptom (66.6%). Asymptomatic stones or vague symptoms in 23 patients warrant a higher index of suspicion of renal stone disease in children. Thirty patients had associated renal insufficiency. One third of the children had a positive urine culture, Proteus spp. being the commonest organism. Congenital anomalies of the urinary tract were seen in 12% of patients. In the majority (59%), aetiological factors related to stone formation could not be identified. One hundred and thirty patients underwent surgery for removal of stones. Analysis of calculi by X-ray diffraction and infrared spectroscopy revealed that stones were predominantly of mixed type, calcium oxalate being the commonest compound. The overall recurrence rate following surgical removal was 15%.