A biomechanical model of anther opening reveals the roles of dehydration and secondary thickening.

Understanding the processes that underlie pollen release is a prime target for controlling fertility to enable selective breeding and the efficient production of hybrid crops. Pollen release requires anther opening, which involves changes in the biomechanical properties of the anther wall. In this research, we develop and use a mathematical model to understand how these biomechanical processes lead to anther opening. Our mathematical model describing the biomechanics of anther opening incorporates the bilayer structure of the mature anther wall, which comprises the outer epidermal cell layer, whose turgor pressure is related to its hydration, and the endothecial layer, whose walls contain helical secondary thickening, which resists stretching and bending. The model describes how epidermal dehydration, in association with the thickened endothecial layer, creates forces within the anther wall causing it to bend outwards, resulting in anther opening and pollen release. The model demonstrates that epidermal dehydration can drive anther opening, and suggests why endothecial secondary thickening is essential for this process (explaining the phenotypes presented in the myb26 and nst1nst2 mutants). The research hypothesizes and demonstrates a biomechanical mechanism for anther opening, which appears to be conserved in many other biological situations where tissue movement occurs.

The use of microelectrodes to investigate compartmentation and the transport of metabolized inorganic ions in plants.

Microelectrode measurements can be used to investigate both the intracellular pools of ions and membrane transport processes of single living cells. Microelectrodes can report these processes in the surface layers of root and leaf cells of intact plants. By careful manipulation of the plant, a minimum of disruption is produced and therefore the information obtained from these measurements most probably represents the 'in vivo' situation. Microelectrodes can be used to assay for the activity of particular transport systems in the plasma membrane of cells. Compartmental concentrations of inorganic metabolite ions have been measured by several different methods and the results obtained for the cytosol are compared. Ion-selective microelectrodes have been used to measure the activities of ions in the apoplast, cytosol and vacuole of single cells. New sensors for these microelectrodes are being produced which offer lower detection limits and the opportunity to measure other previously unmeasured ions. Measurements can be used to determine the intracellular steady-state activities or report the response of cells to environmental changes.

Improvement in tangential breast planning efficiency using a knowledge-based expert system.

A knowledge-based expert system was developed for the purpose of improving radiotherapy planning efficiency for a standardized, tangential breast technique. Treatment parameters pertaining to 150 previously planned patients were used for correlating the midplane breast contour of a new patient with an appropriate set of tangential beam weights and wedge angles; other treatment parameters including, planning target volume and isocenter, were specified by a radiation oncologist. Treatment plans generated by the expert system approach and a traditional, dosimetric approach were compared and rated prospectively in 45 patients. In addition, planning time was measured for both approaches. A performance rating of 97% was achieved for the expert system, in which an artificial neural network was used to correlate breast contours to treatment parameters, and approximately 30 minutes per patient was saved in treatment planning time. This high performance rating validated various assumptions concerning the expert system: namely, that the resultant dose distribution was not influenced by tangential field width (within the range of 7 to 12 cm), nominal beam energy (6 MV), or wedge type (physical vs. enhanced dynamic). Hence, the knowledge base may be directly transferable to other cancer centers using the same breast technique, and suggests that a global resource of radiotherapy treatment plans as well as planning strategies, categorized by treatment site, stage, and technique, may be viable.

A medical expert system approach using artificial neural networks for standardized treatment planning.

PURPOSE: Many radiotherapy treatment plans involve some level of standardization (e.g., in terms of beam ballistics, collimator settings, and wedge angles), which is determined primarily by tumor site and stage. If patient-to-patient variations in the size and shape of relevant anatomical structures for a given treatment site are adequately sampled, then it would seem possible to develop a general method for automatically mapping individual patient anatomy to a corresponding set of treatment variables. A medical expert system approach to standardized treatment planning was developed that should lead to improved planning efficiency and consistency. METHODS AND MATERIALS: The expert system was designed to specify treatment variables for new patients based upon a set of templates (a database of treatment plans for previous patients) and a similarity metric for determining the goodness of fit between the relevant anatomy of new patients and patients in the database. A set of artificial neural networks was used to optimize the treatment variables to the individual patient. A simplified example, a four-field box technique for prostate treatments based upon a single external contour, was used to test the viability of the approach. RESULTS: For a group of new prostate patients, treatment variables specified by the expert system were compared to treatment variables chosen by the dosimetrists. Performance criteria included dose uniformity within the target region and dose to surrounding critical organs. For this standardized prostate technique, a database consisting of approximately 75 patient records was required for the expert system performance to approach that of the dosimetrists. CONCLUSIONS: An expert system approach to standardized treatment planning has the potential of improving the overall efficiency of the planning process by reducing the number of iterations required to generate an optimized dose distribution, and to function most effectively, should be closely integrated with a dosimetric based treatment planning system.

A neural network representation of electromyography and joint dynamics in human gait.

Optimization theory and other mathematical algorithms have traditionally been used to model the relationship between muscle activity and lower-limb dynamics during human gait. We introduce here an alternative approach, based on artificial neural networks with the back-propagation algorithm, to map two different transformations: (1) EMG-->joint angles; and (2) EMG-->joint moments. Normal data for 16 muscles and three joint moments and angles (hip, knee, and ankle) were adapted from the literature [Winter (1987), The Biomechanics and Motor Control of Human Gait]. Both networks were successfully trained to map the input vector onto the output vector. The models were tested by feeding in an input vector where all 16 muscles were slightly different (20%) from the training data, and the predicted output vectors suggested that the models were valid. The trained networks were then used to perform two separate simulations: 30% reduction in soleus activity; and removal of rectus femoris. Net 2, in which electromyography was mapped onto joint moments, provided the most reasonable results, suggesting that neural networks can provide a successful platform for both biomechanical modeling and simulation. We believe that this paper has demonstrated the potential of artificial neural networks, and that further efforts should be directed towards the development of larger training sets based on normal and pathological data.

Limit of continuous and discrete finite-band Gerchberg iterative spectrum extrapolation.

It is known that the Gerchberg method for iteratively extrapolating the spectrum of an object of finite support has a different limit when the infinite frequency band used in the iterations is replaced by a finite one. It is shown that, for both continuous and discrete data, this limit involves an optimal extrapolation within the finite band to minimize the component of the limit that lies beyond the object support.

Resistance-factors in the hospital and non-hospital environment.

The enteric flora of a group of antibiotic-treated patients and two groups of non-antibiotic-treated individuals were studied for antibiotic resistance patterns and presence of transferable R-factors. The former group consisted of 100 hospitalised patients, the latter two groups consisted of 200 hospitalised patients and 200 individuals from rural communities in Jamaica. The occurrence of multiple-resistant organisms with transferable R-factors was significantly higher in the antibiotic-treated group. R-factors were also more common in the hospitalised, non-treated group than in the non-hospitalised, non-treated group. Follow-up studies on hospitalised patients showed a tendency to increased occurrence of R-factors with duration of hospitalisation, whether the patients were treated with antibiotics or not. These studies have shown that both antibiotic treatment and hospitalisation promote the occurrence of R-factors.

Transmission of infectious drug resistance from animals to man.

The antibiotic resistance patterns of coliforms in faecal specimens from pigs and their human contacts were studied. The ability of the resistant coliforms to transfer their resistance in vitro to antibiotic-sensitive recipients was examined. The results showed that pigs which had received antibiotics carried more multiply-resistant, R-factor bearing coliforms than pigs which had not been given antibiotics. Human contacts of the antibiotic-treated pigs had a higher incidence of antibiotic-resistant coliforms with R-factors than human contacts of pigs which had not been given antibiotics. It is concluded that antibiotic treatment of farm animals may lead to acquisition of antibiotic resistance by gut coliforms of man.