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A distributed-origin coupled Hartree-Fock method is used to compute the current density induced in C 60 by an external magnetic field, and hence to plot the π ring currents and obtain ab initio values of the total magnetisability and nuclear magnetic shielding. Paramagnetic ring currents are associated with pentagons, and interpreted as consequences of strong, local circulations about the formal double bonds of the C 60 framework. The calculated total magnetisability of −370 cgs ppm is strongly diamagnetic and in agreement with the previous extrapolated ab initio result and with an experimental measurement. The calculated central shielding of +12 ppm is in qualitative agreement with the previous extrapolation and the measured encapsulation shift for 3 He in C 60 . It is concluded that C 60 is diagmagnetic, but that the interpretation of this diamagnetism as a sing of three-dimensional aromaticity is problematic.

The presence of a three-torus in a seven-mode truncation of the three-dimensional Navier—Stokes equations is investigated numerically by means of cross-section and power spectra. Furthermore, by taking advantage of particular features of the model, rotation vectors, circle maps and torus maps can be computed with high accuracy and used to study the dynamics. In particular, some interesting phenomena of partial phase-locking are described in deep detail. The three-torus, which arises via a Hopf bifurcation and persists in a wide parameter range, is found to break and originate a strange attractor. The onset of chaos and the associated bifurcation point can be defined quite precisely.

N-mode truncations of the three-dimensional Navier-Stokes equations with periodic boundary conditions are considered. The authors show that the solution of the truncated model exhibits, under some assumptions concerning the external force, general properties of symmetry and invariance. A particular seven-mode truncation is then derived and investigated in detail by making use of numerical tools typical of dynamical systems. An intricate phenomenon is found with the significant presence of two- and three-dimensional tori. Among different transitions the one from quasiperiodicity to chaos in a three-torus appears of particular interest.

The basic idea of the Power-Oriented Graphs (POG) modeling technique is to use the power interaction between subsystems as basic concept for modeling. This approach is theoretically supported by the definition and the properties of the port-controlled Hamiltonian systems and allows the modeling of a wide variety of systems involving different energetic domains. Differently from the Bond Graphs technique, based on the same concept, the POG modeling technique solves explicitly the causality problem. By this way, the POG schemes are easily readable, close to the computer implementation and allow reliable simulations using every computer simulator. This paper introduces the properties of the POG technique and presents some examples related to automotive control systems.

One of the main issues of any control strategy for braking systems is to face the many uncertainties due to the strong spread of the system's parameters: road conditions, hydraulic actuators, tire behaviour, etc. Moreover, the need for cheap components limits both the number of sensors and the quality of the actuators. This paper proposes a self-tuning control strategy for braking systems. The proposed control strategy is based on two light assumptions: 1) the tire longitudinal force as a function of the tire slip has always a unique minimum; 2) the hydraulic actuators can increase, decrease and hold the braking pressure within a limited delay. Only the measure of the wheel rotational speed and the estimate of the wheel angular acceleration are required. The control strategy is tested by simulation experiments.

Robust control of AC asynchronous motor drives in the presence of strong parameter uncertainties is considered. Due to the different bandwidths associated with the controlled variables, a cascade structure is used. A multivariable sliding mode closed-loop controller with a hysteresis region is used to transform the voltage source inverter into a current source (CS) one. On the assumption of a CS inverter, the field-orientation principle is adopted for the design of a simplified torque and flux controller. A modified binary controller, ensuring robustness to mechanical parameter variations, is used in the outer velocity loop of the cascade control structure. Modifications to the basic binary controller are introduced to improve tracking capabilities. Performances of the proposed structure are verified by simulating a robotic application. Tracking of a velocity trajectory for a single-link robotic arm is considered. Simulation results show the feasibility and good performance of the robust control structure. >

With regard for the principles that govern the correct application of intramedullary osteosynthesis in the long bones of the lower limb, the authors also support its use in the humerus. After an exhaustive survey of the specific problems at this site, a critical review of 130 cases observed over the last 15 years is reported. Extremely favourable results emerged in the treatment of the humerus with this means of synthesis, thanks to its surgical, mechanical and biological advantages.

Based on more than 20 years experience, the authors support the effectiveness of intramedullary nailing in the treatment of diaphyseal fractures of the femur. They review the history and advantages of this method and discuss the biomechanical principles on which it is based. Recent advances in technique have made it possible to secure proximal and distal anchorage in cancellous bone. This allows the method to be extended to more proximal and distal fractures than in the traditional method which is applicable only to the middle third. It also facilitates progressive axial compression, early loading and early mobilisation of the limb, thus creating the optimum biological conditions for consolidation and joint function. The closed method also reduces blood loss and the risk of infection. The techniques adopted to deal with more complex situations are described. These include moderately comminuted oblique and spiral fractures and certain bifocal fractures. Finally, the results of treating 450 cases are reviewed, with a longterm analysis of 198 patients.

The purpose of this study is to discuss diaphyseal fractures of the tibia treated by intramedullary Küntscher nailing. This is based on 368 cases treated over the last 20 years. Closed intramedullary osteosynthesis favours the healing process, resulting in the early formation of callus which is of good quality and abundant. A careful review of the cases showed a 93.7% incidence of good results.

The authors discuss the advantages of using intersomatic lumbar fusion with a posterior approach for the treatment of low back pain due to discopathy or grade I spondylolisthesis. After a description of the surgical method used, the long-term results obtained in 16 cases are presented. The clinical and radiographic results are good in cases of discopathy, while in those of spondylolisthesis there is disagreement between the clinical evaluation, which is generally satisfactory, and the radiographic evaluation which is not quite as satisfactory.

Esotropic patients whose angle of strabismus has been corrected by prisms frequently increase their angle deviation to compensate for the prismatic correction. This sensorio-motorial reaction to prism correction has been given the name of anomalous movements (a.m.). Quantification of a.m. has been made according to the amount of prisms that an esotropic patient is capable of compensating for (progressive prism compensation test--p.p. test). Some esodeviation does not compensate for any prisms at all since a.m. have not yet developed. Other cases compensate for as much as 40 or 60 prism diopters and more of over-correction of the angle deviation and they therefore have powerful a.m. The interference of these innervational forces acting on the medial recti to corrective surgery has been studied in 126 operated esotropic patients. A significant decrease from the expected surgical result (p less than 0.001) has been found in patients having powerful a.m., as can be judged by the p.p. test. It is believed that a.m. are an important drawback contributing to vitiate any formula on the amount of muscle surgery to be performed in patients having no possibilities of restoring normal binocular vision. Practical advice on how to eliminate this drawback and theoretical reasoning on the significance of a.m. are offered.

In consideration of the multiple anatomical structures involved in recurrent subluxation of the patella and in external patellar hypertension syndrome, the authors propose an operation which allows for complete realignment of the extensor apparatus by transposition of the anterior tibial tuberosity, division of the external alar ligament, tightening of the internal alar ligament, and correction of the muscular insertions. In particular, removal of a capsulofascial band medially and its reimplantation into the external incision is proposed, thus avoiding the formation of retractive scar tissue. The long-term results, which were overall satisfactory, confirm the effectiveness of the operation proposed.

The authors report their experience in 25 cases of fractures of the shaft of the femur and tibia treated by the Grosse-Kempf method of intramedullary nailing supplemented by screw fixation. They confirm the validity of this technique, which enlarges the indications for intramedullary nailing and offers an alternative method of osteosynthesis in the more severe cases.

It has been demonstrated that, besides sensory adaptation phenomena, sensorimotor phenoma may also develop in concomitant esotropia. The existence of the latter entity can be shown particularly by means of prisms and is interpreted as fusional in origin. It is therefore defined as 'anomalous fusional movements'. The features of these anomalous fusional movements were studied in a group of 30 patients, mainly in order to investigate their finality. Correlations were evaluated between anomalous fusional movements and entities previously described by different names according to the interpretation given them by various authors.

The effectiveness of defibrotide was compared with that of calcium heparin and acetylsalicylic acid (ASA) in the prevention of deep venous thrombosis (DVT) resulting from orthopedic surgery. Sixty-three patients scheduled for elective or traumatological surgery, for the most part involving the hip joint, were recruited. The patients were randomly assigned to one of the following treatment groups: defibrotide (400 mg twice daily), administered intramuscularly (n = 19); calcium heparin (5,000 IU thrice daily), administered subcutaneously (n = 25); and ASA (100 mg on alternate days), administered orally (n = 19). Administration of the drug was started one day before surgery and continued until the seventh day after surgery. Each patient was monitored daily by means of the fibrinogen uptake test. The incidence of increased uptake did not differ significantly in the three groups (defibrotide, ten out of 19; calcium heparin, ten out of 25; ASA, seven out of 19). Conversely, a trend in favor of defibrotide was noted in cases of symptomatic DVT (defibrotide, one out of 19; calcium heparin, two out of 25; ASA, four out of 19) and pulmonary embolism (defibrotide, no cases; calcium heparin, one case; ASA two cases). On the strength of these findings, defibrotide therapy qualifies as a valid alternative to conventional DVT prophylaxis in orthopedic surgery.

The authors discuss the various operations used in the treatment of myelopathy caused by cervical spondylosis. Recently they have used the so-called "open door" operation, which raises the posterior vertebral arch, in place of laminectomy, hemilaminectomy and anterior interbody fusion. The "open door" operation is less radical, less traumatizing and safer, and ensures considerable enlargement of the vertebral canal. This enlargement can be clearly demonstrated by tomography as well as by the traditional radiological methods.

The author's technique of valgus osteotomy is described. The advantages claimed are wide and easy correction combined with distal displacement of the great trochanter, restoration of physiological valgus, lengthening of the limb, and rigid and secure fixation. The indications, contra-indications, technique and results are discussed in an analysis of ninety-eight operated cases.

The Author suggests a technique for surgical equalisation of leg length. When the discrepancy is around 4 cm the Author obtains equalisation by simultaneous shortening and lengthening by removing from the long femur a cylinder of bone equal to half the discrepancy and grafting it into the short femur. Two Küntscher nails are used to obtain fixation. The technique has been successfully used on 4 cases.