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Notes: A theoretical model of fatigue in ferroelectric thin-film memories based upon impact ionization (e.g., Ti+4 to Ti+3 conversion in PbZr1−xTixO3), resulting in dendritic growth of oxygen-deficient filaments, is presented. The predictions of spontaneous polarization versus switching cycles Ps(N) are compared with both Monte Carlo simulations for a two-dimensional Ising model and with experimental data on small-grain (40 nm) sol-gel PZT films. Excellent agreement between theory and experiment is obtained. In addition to modeling the Ps(N) curves, the theory developed explains the observed linear proportionality between switching time ts(N) and polarization Ps(N) during fatigue; other models of aging do not account for this. Earlier theories of switching are also extended to include finite grain sizes, surface nucleation, triangular drive pulses, and dipolar forces. Good agreement with sol-gel PZT switching data is obtained.

Notes: We show that thin-film Ni82Fe18/Ag multilayer structures display multiple peaks in their magnetoresistance curves when biased at current densities above 106 A/cm2. These peaks appear for annealed and unannealed structures, and their number is correlated with the number of NiFe layers. At high bias currents, the peak positions shift linearly with the internal magnetic field created by the bias current. The peak positions extrapolate to nonzero fields at zero bias currents, providing an upper bound on the magnetic layer-layer coupling strength of J0≈10−20 J (kB×700 K). The peak positions do not shift with temperature over the range 200–375 K; their widths narrow with increasing temperature. The single-domain magnetic moment μ is estimated as 10−17 J/T (106 μB) from the peak widths of ∼0.8 kA/m. © 1996 American Institute of Physics.

Notes: Abstract Mediastinal masses are uncommonly encountered in childhood. These tumours are often interesting because of the varied mediastinal tissues from which they arise. Despite extensive investigations, a large percentage of these lesions remain undiagnosed prior to operation. We describe two rare cases of mediastinal lipoma. The first was incidentally diagnosed whereas the second patient presented with respiratory symptoms. The definitive diagnosis was established at surgery, which was curative.

Notes: Abstract Central venous catheters today can be inserted with a remarkable degree of ease due to advances in catheter design and cannulation techniques. This is partly responsible for the increase in the use of this form of venous access. Because of this increase, the occurrence of less well-known complications of central venous cannulation are predicted as illustrated by this report on three infants in whom centrally placed catheters penetrated the pericardial sac, causing tamponade. This complication was associated with the use of one particular type of cannula. The manner in which this described hazard was first detected is highlighted. The realisation that tamponade is not entirely preventable and that the clinical manifestations there of are variable makes the exclusion of a hydropericardium by diagnostic tap an essential step during the resuscitation of any patient who collapses unexpectedly with a central venous catheter in place. The recognition of this fact has altered the poor prognosis previously associated with this complication.

Notes: Abstract A case of ileocaecal atresia is presented. This is an exceedingly rare cause of obstruction in the newborn. The embryology of the ileocaecal valve is described and related to the possible cause of the atresia.

Notes: Abstract A 12-year-old girl with a long history of achalasia and numerous unsuccessful attempts at treatment is discussed. Investigation and management by oesophagectomy are described, with a discussion of achalasia in childhood and of the role of oesophagectomy in achalasia.

Notes: Abstract The use of the sagittal surgical approach to the rectum and urinary fistula in male patients with anorectal agenesis is addressed. Iatrogenic damage to the urethra (1 in 60 cases) and pelvic (2 in 60 cases) occurred when the operator had difficulty identifying the rectum intraoperatively and where inappropriate midline dissection was done. The importance of an adequate preoperative contrast rectogram and the intraoperative identification of the rectum with the aid of a catheter is emphazied. Perirectal blunt dissection is discouraged, the need for deep lateral directed tissue retraction is avoided by applying direct traction onto the freed rectum, and a long and wide portion of rectal wall is left in the midline on the urethra and bladder neck. The anatomy of the autonomic pelvic plexus at risk in the normal and congenitally abnormal case is described.

Notes: Abstract A single neonatal surgical unit treated 42 cases of gastroschisis over a 12-year period (1981–1993). The surgical management of each case was individualised, but every attempt was made to perform a primary repair when possible, based on the premise that this strategy gave the best outcome. The eviscerated intestine was evaluated with the patient under general anaesthesia. Serosal peel was not removed and intestinal atresias were not repaired. Gangrenous intestine was resected. The contents of the bowel were emptied proximally via a large naso-gastric tube and distally via the anus with warm saline lavage. The anterior abdominal wall was stretched and then reduction of the prolapse attempted. Following maximal enlargement of the peritoneal cavity, it was left to the operator to decide whether primary repair was possible and, indeed, permissible in each instance. Staged repairs necessitated the use of silastic pouches. Respiratory and intestinal insufficiency were managed by intermittent positive-pressure ventilation and total parenteral nutrition (TPN). Over one-half of the cases (24 of 42) were under 2.5 kg at birth. Intra-uterine growth retardation was unusual. Ten babies were delivered for obstetrical indications by Caesarean section: 50% were pre-term and in 4 pre-natal diagnosis of a ventral abdominal wall anomaly had been made. The transmural defects were all sited at the umbilicus and were to the right of a consolidated cord in 41 instances. Midgut necrosis due to torsion was encountered in 1 case; 3 further cases with intestinal atresia occurred. Primary closure was obtained in 30 (71%) of the cases reviewed. A prosthetic pouch was used in 12 patients for on everage 10 days in 10 uncomplicated cases. The average length of time in days of tertiary care given to 25 uncomplicated cases treated by primary fascial closure was: ventilatory support 4; intensive care treatment 8; and nutritional source TPN 20. There were 5 deaths (12%): 1 was unpreventable due to prenatal intestinal infarction; 2 were due to abdominal compartment syndrome with renal failure, and, intestinal ischaemia complicating primary and planned staged repairs; 1 caused by intestinal infarction due to torsion of bowel in a pouch; and 1 due to invasive infection. The role played by the strategy taken by the surgeon in the management of gastroschisis is crucial to the outcome. The creation of a compartment-like syndrome produced uncorrectable complications in this series of cases in both primary and staged abdominal wall closures. Minor degrees of this complication proved to be reversible in some patients, which was the reason for the wait-and-see attitude adopted in the management of this problem, often with fatal outcome. Where intra-peritoneal pressure monitoring is not used, the operating surgeon relies on unscientific observations for decision-making at the operating table. The time from birth to operation in 25 of the reviewed cases was on average 5 1/2 h. Of this group, 20 were outborn babies. This is unsatisfactory, but as shown by this review, even in the absence of prenatal management, which should ensure prompt repair, satisfactory results are still possible.