Cadmium sulfide passivation of InGaAs/InP mesa p-i-n photodiodes

A cadmium sulfide (CdS) passivation process was demonstrated for the first time on InGaAs/InP p-i-n mesa photodetectors. The passivated devices produced lower reverse bias leakage currents in comparison to devices that received only a thermally deposited SiO₂ film. The subsequent deposition of SiO₂ on the passivated devices produced virtually no change to the aforementioned leakage currents even after undergoing a 3-h, 300°C thermal treatment. In contrast, similar SiO₂ capped devices, fabricated without the CdS passivating layer, show a large increase in leakage current when subjected to the same thermal cycle. Leakage current versus mesa diameter measurements suggest these results are due to reduce surface recombination at the exposed mesa sidewall. X-ray photoelectron spectroscopy (XPS) results indicate the S:Cd ratio of these films to be 0.77.     

Modelling the abrasive flow machining process on advanced ceramic materials

Abrasive flow machining (AFM) is a unique machining method used to achieve high surface quality on inner, difficult-to-access and on outside contours. Using AFM, it is possible to realise predefined edge rounding on any brittle or hard material. AFM is easy to integrate in an automated manufacturing environment. The abrasive medium applied during AFM is a fluid consisting of a polymer which carries silicon carbide or super-abrasive grains. With a specified pressure and temperature, this fluid flows in alternating directions along the contours of the workpiece resulting in an abrasive effect. AFM is also well suited to process advanced ceramic materials. Especially advanced ceramics are playing increasingly a significant role as a substitute for metals. However the high costs for the inevitable finishing process on ceramics prevent a more frequent use. This paper represents the technological results of a research-project discovering the fundamental principles of AFM on advanced ceramic materials such as a correlation between flow processes, surface formation and edge rounding. Furthermore an insight into a process model is given, which was developed using modern simulation techniques. The overall objective of this approach is to anticipate work results like surface quality and edge rounding on any user-defined geometry.     

Use of cervicothoracic junction pedicle screws for reconstruction of complex cervical spine pathology

STUDY DESIGN: A retrospective review of 21 patients in which cervical pedicle screw fixation was used at C7 with or without upper thoracic pedicle screw fixation. OBJECTIVE: To evaluate the use of pedicle screw placement in the lower cervical spine. SUMMARY OF BACKGROUND DATA: The use of posterior cervical spine fixation, including lateral mass fixation, has become increasingly popular in recent years. However, lateral mass fixation at C7 is often hindered by lack of substantial high quality bone. The end level of long cervical spine constructs is frequently C7 or T1. Dissatisfaction with lateral mass fixation at C7 and T1 led the authors to use lower cervical pedicle screw fixation for several cervical spine disorders. METHODS: Twenty-one patients who had undergone cervical pedicle screw fixation at C7 were reviewed retrospectively. There were 12 males and 9 females, with an average age of 52 years. All pedicle screws were placed, after direct palpation of the pedicle, with a right angle nerve hook after laminoforaminotomy at C7. RESULTS: There were no neurologic complications related to pedicle screw placement, and no patient was symptomatically worse after the operation. Six patients with root pathology improved. Of 14 patients with cervical myelopathy, 12 improved at least one Nurick grade, and 2 had no improvement. There were no failures of fixation or complications related to pedicle fixation at a minimum of 1 year follow-up. CONCLUSION: Pedicle screws in C7 placed with laminoforaminotomy and palpation technique appears to be safe and efficacious. Excellent fixation can be achieved.     

Anterior plate instrumentation for disorders of the subaxial cervical spine

Anterior cervical plate instrumentation is useful in the maintenance of cervical alignment, the prevention of graft extrusion, and the development of late deformity as well as potentially avoiding the need for a secondary posterior cervical procedure in the setting of cervical trauma. Its role in cervical reconstruction after decompression for cervical spondylosis is evolving. The definite risks of anterior cervical instrumentation should be considered, that is, screw and plate displacement or screw violation of neurologic structures, before the implementation of this form of fixation.     

The effect of mannitol and pH of the solution on the properties of sintered magnesium oxide obtained from sea water

In order to reduce the B₂O₃ content in sintered magnesium oxide as much as possible, in precipitation with 80% of the stoichiometric quantity of dolomite lime, the effect of the pH of the agent used for rinsing the magnesium hydroxide precipitate was examined, as well as the effect of mannitol in sea water before precipitation. Mannitol binds orthoboric acid present in sea water into a weakly dissociated complex acid HB(OC)₄. Experiments have shown that the B₂O₃ content in the sintered magnesium oxide samples is satisfactorily low. The lowest B₂O₃ content is obtained when mannitol is added; no B₂O₃ was found in these samples after sintering. Magnesium oxide samples were sintered at 1500°C; duration of isothemal sintering was one hour. Values for density and porosity of individually sintered samples are listed. The ratio CaO/SiO₂ indicates that forsterite (Mg₂SiO₄), monticellite (CaMgSiO₄) and mervinite (Ca₃MgSi₂O₈) are formed during sintering of the samples.     

Predictors of outcome in patients with chronic back pain and low-grade spondylolisthesis

STUDY DESIGN: Retrospective case series. OBJECTIVES: To determine the factors influencing symptom relief after uninstrumented posterolateral spinal fusion with or without decompression in adult patients with chronic back pain and previously asymptomatic low-grade isthmic spondylolisthesis. SUMMARY OF BACKGROUND DATA: The role of previously asymptomatic low-grade isthmic spondylolisthesis in chronic adult low back pain is unclear. Operative intervention in this setting is controversial. METHODS: Twenty-four consecutive adult patients with chronic low back pain and low-grade isthmic spondylolisthesis first detected during routine work-up of new onset low back pain underwent spinal fusion with or without decompression. The influence of active worker's compensation or litigation claims, radicular pain, concomitant laminectomy, age, gender, fusion to L4, intervertebral disc bulge, and pseudarthrosis were investigated. RESULTS: All 13 patients involved in worker's compensation claims or pending litigation had fair or poor results. Nine of 11 patients without such issues had good or excellent results. Although the strong association of worker's compensation with poor results made it difficult to assess the importance of other risk factors, the data suggest that good results may be more likely in patients with radiculopathy who undergo laminectomy. CONCLUSIONS: This investigation, although limited by a number of factors including small sample size and retrospective, unblinded review, suggests that active worker's compensation and litigation issues are associated strongly with poor results of operative management for chronic low back pain in adult patients with low-grade spondylolisthesis.     

The ITER EC H&CD upper launcher: Design,analysis and testing of a bolted joint for the Blanket Shield Module

The final design of the structural system for the ITER EC H&CD upper launcher is in progress. Many design features of the preliminary design are under revision with the aim to achieve the built-to-print-status. This paper deals with design and analysis of a bolted joint for the Blanket Shield Module with special perspective on Remote Handling capability. The BSM of the ECH Launcher is attached to the Launcher Main Frame by a bolted joint conceived so that in the Hot Cell Facility, RH maintenance can be performed on internal components. The joint must be capable to resist very high Electro-Magnetic loads from disruptions, while it has to sustain substantial thermal cycling during operation. Thus the need for a rigid and reliable design is essential. Beside the set of pre-stressed bolts the flanges were therefore equipped with additional shear keys to divert radial moments away from the bolts. Main focus of the work performed was the mechanical design of the joint and the assessment of the structural integrity with respect to the loads applied and its capability for maintenance by RH procedures. To fulfill a major aspect of the RH requirements, the bolts were designed as “captive” in order to avoid their accidental removal from the joint. The captive bolt design is based on a concept that uses a dedicated spring ring, a standard spiral spring and a tensioning screw with two threads to secure the bolts in a form-locking stop. The final approval phase of the RH compatibility foresees simulations in Virtual Reality and physical tests on prototypes.     

Pervasive grid for large-scale power systems contingency analysis

Optimal control and management of power systems require extensive analyses of phenomena that can compromise their operation in order to evaluate their impact on the security and reliability levels of the electrical networks. For complex networks, this process, known as power systems contingencies analysis, requires large computational efforts, whereas computation times should be less than a few minutes for the information to be useful. Even though many architectures based on conventional parallel and distributed systems have been widely proposed in the literature, they are characterized by low extensibility, reusability, and scalability, and so, they require a sensible hardware upgrade when more computational resources are necessary. This event is not infrequent in power systems where the constant growth of the electrical network complexity and the need for larger security and reliability levels of the plant infrastructures lead to the need of more detailed contingency analysis in shorter times. To address this problem, this paper proposes a pervasive grid approach to define a user-friendly software infrastructure for data acquisition from electrical networks and for data processing in order to simulate possible contingencies in a real electrical network. The grid infrastructure adopts a brokering service, based on an economy-driven model, to satisfy the quality of service constraints specified by the user (i.e., a time deadline to simulate the contingencies). This paper also discusses the deployment of the infrastructure on a network of heterogeneous clusters and PCs to compute the contingency analysis of a realistic electrical network. The experimental results obtained demonstrate the effectiveness of the proposed solution and the potential role of grid computing in supporting intensive computations in power systems.     

Vertebral artery location in relation to the vertebral body as determined by two-dimensional computed tomography evaluation

STUDY DESIGN: This study analyzed the precise two-dimensional location of the vertebral artery within cervical vertebrae as determined by measurements obtained from axial computed tomographic images of the cervical spine. OBJECTIVE: To determine the margin of safety necessary to avoid vertebral artery laceration during central decompression and lateral nerve root decompression for cervical spinal stenosis. SUMMARY OF BACKGROUND DATA: Laceration of the vertebral artery is a rare but potentially catastrophic complication of anterior decompressive surgery of the cervical spine. METHODS: The mean, standard deviation, and 95% confidence interval of the mean of measurements localizing the vertebral artery within the vertebral body were calculated from 50 transaxial computed tomography images of each of the second through sixth cervical vertebrae. RESULTS: Both the mean interforaminal distance (from 25.90 +/- 1.89 mm at C3 to 29.30 +/- 2.70 mm at C6) and the average distance of the posterior border of the foramen transversarium from the ventral border of the spinal canal (from 2.16 +/- 1.18 mm at C3 to 3.53 +/- 1.56 mm at C6) increased from C3 to C6. CONCLUSIONS: According to our measurements, the risk of vertebral artery laceration is greater at more cephalad vertebrae during lateral extension of central decompressive procedures and lateral nerve root decompression. Because of the variability of these parameters between individuals, accurate individual preoperative localization of the vertebral arteries is recommended.