Optimal control of diffuser shapes for non-uniform flow.

A simplified model is used to identify the diffuser shape that maximises pressure recovery for several classes of non-uniform inflow. We find that optimal diffuser shapes strike a balance between not widening too soon, as this accentuates the non-uniform flow, and not staying narrow for too long, which is detrimental for wall drag. Three classes of non-uniform inflow are considered, with the axial velocity varying across the width of the diffuser entrance. The first case has inner and outer streams of different speeds, with a velocity jump between them that evolves into a shear layer downstream. The second case is a limiting case when these streams are of similar speed. The third case is a pure shear profile with linear velocity variation between the centre and outer edge of the diffuser. We describe the evolution of the time-averaged flow profile using a reduced mathematical model that has been previously tested against experiments and computational fluid dynamics models. The model consists of integrated mass and momentum equations, where wall drag is treated with a friction factor parameterisation. The governing equations of this model form the dynamics of an optimal control problem where the control is the diffuser channel shape. A numerical optimisation approach is used to solve the optimal control problem and Pontryagin's maximum principle is used to find analytical solutions in the second and third cases. We show that some of the optimal diffuser shapes can be well approximated by piecewise linear sections. This suggests a low-dimensional parameterisation of the shapes, providing a structure in which more detailed and computationally expensive turbulence models can be used to find optimal shapes for more realistic flow behaviour.

Correction to 'Homogenized boundary conditions and resonance effects in Faraday cages'.

[This corrects the article DOI: 10.1098/rspa.2016.0062.].

Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line.

Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.

Homogenized boundary conditions and resonance effects in Faraday cages.

We present a mathematical study of two-dimensional electrostatic and electromagnetic shielding by a cage of conducting wires (the so-called 'Faraday cage effect'). Taking the limit as the number of wires in the cage tends to infinity, we use the asymptotic method of multiple scales to derive continuum models for the shielding, involving homogenized boundary conditions on an effective cage boundary. We show how the resulting models depend on key cage parameters such as the size and shape of the wires, and, in the electromagnetic case, on the frequency and polarization of the incident field. In the electromagnetic case, there are resonance effects, whereby at frequencies close to the natural frequencies of the equivalent solid shell, the presence of the cage actually amplifies the incident field, rather than shielding it. By appropriately modifying the continuum model, we calculate the modified resonant frequencies, and their associated peak amplitudes. We discuss applications to radiation containment in microwave ovens and acoustic scattering by perforated shells.

Atypical haemolytic uraemic syndrome treated with the complement inhibitor eculizumab: the experience of the Australian compassionate access cohort.

BACKGROUND/AIM: This study aimed to report the clinical characteristics and outcomes of Australian patients treated with eculizumab for atypical haemolytic uraemic syndrome (aHUS). METHODS: A retrospective cohort study was undertaken of all patients in Australia treated with eculizumab provided in a compassionate access programme for a clinical diagnosis of aHUS using prospectively collected clinical data. RESULTS: A total of 10 patients with a median age of 23.5 years (interquartile range (IQR) 24.83 years) received compassionate access eculizumab for aHUS in Australia. Eight patients were female, and three had a family history of aHUS. Three received eculizumab for an initial acute aHUS presentation, three for relapsing and refractory acute aHUS, two for de novo aHUS post-renal transplantation, and one each for aHUS recurrence post-transplantation and facilitation of transplantation with a history of aHUS. The median duration of eculizumab therapy has been 911.5 days (IQR 569 days) with a cumulative exposure of 9184 days. At baseline all patients had renal and extra-renal aHUS involvement, with up to three non-renal organs affected. All but one patient, who died from uncontrollable gastrointestinal aHUS manifestations, have continued. The nine continuing patients achieved remission of aHUS. Two of the four patients requiring renal replacement therapy (RRT) at eculizumab commencement subsequently ceased RRT. Clinical events occurring in this cohort while on eculizumab treatment included neutropenia (two), posterior reversible encephalopathy syndrome (one), cardiomyopathy (one), pulmonary embolus (one), antibody-mediated rejection resulting in renal graft failure (one), iron deficiency (one), gastrointestinal haemorrhage (one) and death (one). CONCLUSION: Eculizumab has been an effective therapy for aHUS in this cohort, including when other therapies have failed.

The speed of an inclined ruck.

Steady rucks in an elastic beam can roll at constant speed down an inclined plane. We examine the dynamics of these travelling-wave structures and argue that their speed can be dictated by a combination of the physical conditions arising in the vicinity of the 'contact points' where the beam is peeled off the underlying plane and stuck back down. We provide three detailed models for the contact dynamics: viscoelastic fracture, a thermodynamic model for bond formation and detachment and adhesion mediated by a thin liquid film. The results are compared with experiments.

Subclinical rhythmic EEG discharge of adults: SREDA in two children.

Subclinical rhythmic electroencephalogram (EEG) discharge is an uncommon rhythmic EEG pattern that has been reported to occur in adults. It is thought to be a nonspecific finding with little clinical significance. This article reports this EEG pattern in two children and suggests it be called subclinical rhythmic EEG discharge of adults and children.

Indices of renal tubular function in perinatal asphyxia.

AIMS: To determine and compare two urinary indices of renal tubular function, N-acetyl-glucosaminidase (NAG) and beta 2-microglobulin (beta 2 M), in healthy term neonates and babies with perinatal asphyxia. METHODS: In a prospective case-control study using asphyxiated (n = 35) and normal control (n = 55) infants, urinary NAG and beta 2 M were assayed at 24-48 hours of life, 4-6 days, and 4-6 weeks. RESULTS: NAG and beta 2 M were significantly increased at 24-48 hours and 4-6 days in the asphyxiated infants compared with the controls. Increased NAG values reflect the degree of perinatal asphyxia more than do beta 2 M. Gentamicin also increased NAG excretion, but to a lesser extent than did perinatal asphyxia. CONCLUSIONS: NAG (+/- beta 2 M) may be a useful marker of perinatal asphyxia. Urinary NAG concentrations correlate with the severity of perinatal asphyxia.

The use of urinary red cell morphology to determine the source of hematuria in children.

Urinary red cell morphology has been used to indicate the source of renal tract bleeding. A double blind study was undertaken to evaluate the reliability of urinary red cell morphology in predicting the source of hematuria in a pediatric population. Two independent observers used phase-contrast microscopy, one also using Nomarski differential interference microscopy, to examine 101 urine specimens from 90 pediatric patients with hematuria. 28 cases were subsequently excluded because the clinical diagnosis was uncertain. In the remaining 62 patients the laboratory diagnosis based on the erythrocyte morphology was compared with the primary clinical diagnosis. Observer 1 documented dysmorphic red cells in 40 of 42 patients with glomerulonephritis, and isomorphic red cells in 19 of the 20 cases of non-glomerular bleeding. Observer 2 documented dysmorphic red cells in 39 of the 42 glomerular lesions, and isomorphic red cells in all of the non-glomerular lesions. This represents a sensitivity for predicting glomerular hematuria of 95% for observer 1 and 93% for observer 2, and a specificity of 95% and 100% respectively. There was no definite advantage in the use of Nomarski compared to phase-contrast microscopy. These results confirm the accuracy of this technique in predicting the source of hematuria in pediatric patients.

The loneliness of the long-distance manager.

Many top managers have been tempted to neglect their own development in the face of massive work agendas. The experiences of 12 senior NHS managers, who were involved in a project designed and implemented by the NHS Training Directorate (NHSTD), bear this out, as Margaret Attwood and colleagues discuss.

Altered in vitro lymphocyte response in childhood nephrotic syndrome.

The immune system, and disturbed T lymphocyte function in particular, has previously been implicated in the pathogenesis of childhood idiopathic nephrotic syndrome. As this disorder is commonly responsive to steroid therapy, we set out to determine whether in vitro suppression of lymphocyte blastogenic response to the mitogen phytohaemagglutinin (PHA) could predict the clinical situation. Comparing nine nephrotic children with nine healthy controls we were able to show the inhibitory prednisolone dose that suppressed lymphocyte blastogenesis by 50% (ID50) at a known concentration of PHA was significantly greater (P < 0.005) for nephrotic individuals. However, the in vitro assay did not reliably predict the clinical response to prednisolone. This study further implicates altered lymphocyte function in the mechanisms underlying idiopathic nephrotic syndrome.

Ureteric sludge syndrome.

Four cases of a form of obstructive uropathy previously unreported in children are described. All presented with oligoanuria and either flank pain or fluid retention and had evidence of crystalline sludge in their lower ureters. Three cases had an underlying crystalluria.

Congenital renal salt-losing syndrome and failure to thrive in infancy.

An infant with congenital renal salt-losing syndrome is reported. The importance of recognizing this rare disorder is emphasized because early detection, and treatment with sodium supplementation, results in marked growth improvement and may prevent volume depletion, electrolyte disturbance, and cardiovascular collapse. The clinical features and biochemical abnormalities seen in the congenital renal salt-losing syndrome are described. In this condition, natriuresis occurs in the face of normal renal and adrenal function and, as the child gets older, spontaneous resolution occurs. Other causes of hyponatraemia in infancy are discussed.

Renal osteodystrophy in children undergoing continuous ambulatory peritoneal dialysis.

Fifteen children undergoing continuous ambulatory peritoneal dialysis for 0.3 to 2.4 years were evaluated longitudinally for renal osteodystrophy. Immunoreactive parathyroid hormone, 25-OHD, total and ionized calcium, inorganic phosphate, and alkaline phosphatase levels were measured regularly. Skeletal radiographic studies were performed at the onset and conclusion of CAPD and at six-month intervals during therapy. All children received 1,25(OH)2D3 and aluminum hydroxide, and nine received supplemental calcium. Plasma 25-OHD concentrations were normal to elevated, and calcium increased steadily to high normal levels despite a trend to persistent hyperphosphatemia. The increased calcium levels suppressed parathyroid hormone overactivity in only one patient. At the onset of CAPD, nine patients had hyperparathyroid bone disease seen radiographically, three of whom also had rachitic lesions. At the end of CAPD, the hyperparathyroid lesions had improved in four patients, completely resolved in three, and deteriorated in two. Rachitic lesions had completely healed in two patients and improved in the third. However, among the six children without radiographically evident lesions at onset of CAPD, hyperparathyroid bone lesions developed in two and rachitic lesions in two others during CAPD. Although CAPD and appropriate therapy benefited most patients with renal osteodystrophy, the benefits were not uniform, and bone lesions deteriorated in some.

Growth in children receiving continuous ambulatory peritoneal dialysis.

Linear growth of 17 children receiving CAPD was compared with growth in 18 patients receiving hemodialysis and 20 who had undergone transplantation, as well as with the previous growth in 11 of the 17 patients. Growth was normal in 10 receiving CAPD, fair in six others, and poor in only one. Growth velocity indexes in those receiving CAPD were significantly better than those of the group receiving hemodialysis (P less than 0.01) but did not differ significantly from those of children who had undergone kidney transplant. All patients grew significantly better after beginning CAPD than before (P less than 0.01). Appropriate management of renal osteodystrophy combined with adequate energy and protein intake were important factors in the growth of patients receiving CAPD.