415 research outputs found
Multilayer microwave windows for wideband gyro-amplifiers
This paper presents the design and measurement of a HE11 mode multilayer window for a W-band gyro-amplifier. The window acts to seal the vacuum inside the amplifier whilst coupling out microwave power with minimal reflection and absorption. The Gaussian-like HE11 mode is used in order to achieve the lowest reflection through the window. Operating over 90-100 GHz the simulated reflection of this window is better than -30 dB. The design, simulation and microwave measurement of the window is presented
W-band quasi-optical mode converters for gyro-devices
A W-band corrugated horn has been designed, manufactured, and experimentally measured at the University of Strathclyde, for integration into a gyro-device as a quasi-optical launcher. This horn converts a cylindrical TE11 mode into a free space TEM00 mode in a frequency band of 84-104 GHz with a reflection better than-30 dB and a Gaussian coupling efficiency of ∼98% and directivity of 26.6 dB at 95 GHz. The Gaussian output of the horn and small beam waist makes such a horn ideal for integration with applications and for use with a depressed collector system. The measured results are in excellent agreement with the numerical simulations
Outcomes After Bidirectional Cavopulmonary Shunt in Infants Less Than 6 Months Old
AbstractObjectives. We sought to assess the results after bidirectional cavopulmonary shunt (BCPS) in infants <6 months old and to identify risk factors for poor outcome.Background. Although BCPS is a well established procedure for the palliation of patients with a single-ventricle heart, there have been very few reports of outcomes after BCPS in young infants.Methods. Since 1990, 42 infants between 0.8 and 6.0 months of age (mean [±SD] 3.7 ± 1.4) have undergone BCPS for primary (n = 16) or secondary (n = 26) palliation of tricuspid atresia (n = 13), hypoplastic left heart syndrome (n = 10) or other forms of functional single-ventricle heart (n = 19). Accessory pulmonary blood flow was included in 18 patients. Preoperative and perioperative data were gathered on retrospective review of patient records, and follow-up was conducted by means of direct physician contact or record review.Results. The overall hospital mortality rate, including that associated with reoperations, was 4.8% (2 of 42 patients). Seven patients (17%) required reoperation related to the BCPS or pulmonary blood flow in the early postoperative period: Procedures included take-down of the BCPS in four patients, with one early death, and procedures to decrease pulmonary blood flow in three patients. Age <1 month correlated significantly with early death and with early failure of the BCPS (death or take-down). Follow-up of the 37 patients discharged with intact BCPS was obtained at a mean ± SD of 14.3 ± 11.3 months postoperatively, during which time three patients died (at 6.5 ± 2.5 months). The 2-year actuarial survival rate for patients undergoing BCPS at <6 months of age was 86%. Overall freedom from death or take-down (including early and late events) was significantly lower in patients <2 months old than in those >2 months old. Four patients have undergone successful Fontan completion (18.3 ± 2.9 months postoperatively), and one patient whose BCPS was taken down subsequently underwent successful restoration of a BCPS.Conclusions. Outcomes after BCPS in young infants are comparable to those in older infants and children. However, our current preference is to defer this procedure until after 2 months of age.(J Am Coll Cardiol 1997;29:1365–70
Accessory and anomalous atrioventricular valvar tissue causing outflow tract obstruction Surgical implications of a heterogeneous and complex problem
AbstractObjectives. The purpose of this study was to determine the effect of accessory or anomalous atrioventricular valvar apparatus on relief of outflow tract obstruction.Background. Outflow tract obstruction due to accessory tissue or anomalous attachments of the atrioventricular valvar apparatus is an unusual but well-recognized problem. In addition to obstruction, anomalous attachments of the atrioventricular valvar apparatus may interfere with procedures to relieve outflow tract obstruction or perform outflow tract reconstruction.Methods. Since 1992, we have operated on 21 patients (median age 4 years) with systemic (n = 13), pulmonary (n = 5) or bilateral (n = 3) outflow tract obstruction due to accessory atrioventricular valvar tissue and/or anomalous attachments of the subvalvar apparatus. Primary diagnoses were isolated obstruction of the systemic outflow tract or aortic arch (n = 7), transposition complexes (n = 6), previously repaired atrioventricular septal defect (n = 3), functionally single ventricle (n = 3) and ventricular septal defect with pulmonary outflow obstruction (n = 2). Outflow tract gradients ranged from 20–110 mm Hg (median 58 mm Hg).Results. Complete relief of obstruction due to atrioventricular valvar anomalies was possible in 14 patients. In six patients, the planned procedure either had to be modified or only partial relief of the obstruction was achieved. In the remaining patient, who had borderline functionally single ventricle heart disease (unbalanced atrioventricular septal defect) and systemic outflow obstruction due to accessory and functional valvar apparatus, support was withdrawn because the parents refused univentricular palliation and the valvar anomalies precluded a Ross-Konno procedure. There were two early deaths. At follow-up ranging from 1 to 66 months (median 27 months), there was one death, and there has been no recurrence of outflow tract obstruction or residual atrioventricular valvar tissue.Conclusions. Outflow tract obstruction caused by accessory or anomalous atrioventricular valvar structures is an uncommon and heterogeneous group of conditions that can have significant surgical implications. In the majority of cases, tailoring of surgical techniques will permit complete relief of obstruction. However, such anomalies may limit standard surgical options and necessitate an innovative approach in some patients
Geometric mismatch of pulmonary and aortic anuli in children undergoing the Ross procedure: Implications for surgical management and autograft valve function
AbstractBackground: There is often substantial mismatch between the diameters of the pulmonary and aortic anuli in young patients with systemic outflow tract disease. To implant the autologous pulmonary valve in the aortic position under such circumstances, it is necessary to adapt the geometry of the systemic outflow tract. The effects of such adaptations on autograft function in children are not well known. Methods: To determine factors predictive of autograft regurgitation, we analyzed 41 cases of children who have undergone the Ross procedure. The diameter of the pulmonary valve was greater (by at least 3 mm) than that of the aortic valve in 20 cases, equal (within 2 mm) in 12 cases, and less (by at least 3 mm) in nine cases, with differences ranging from +10 to –12 mm. In 12 patients with a larger pulmonary anulus, aortoventriculoplasty was used to correct the mismatch. In patients with a larger aortic anulus, the mismatch was corrected by gradual adjustment along the circumference of the autograft, rather than by tailoring of the native aortic anulus. Results: At follow-up (median 31 months), two patients had undergone reoperation on the neoaortic valve for moderate regurgitation. In the remaining 38 cases, autograft regurgitation was as follows: none or trivial in 30, mild in seven, and moderate in one. There was no correlation between regurgitation and age, geometric mismatch, or previous or concurrent procedures. Conclusions: Subtle technical factors that may result in distortion of the valve complex are probably more important determinants of autograft regurgitation than are indication for repair, geometric mismatch, or previous or concomitant outflow tract procedures. Significant mismatch of the semilunar anuli is not a contraindication to the Ross procedure in children. (J Thorac Cardiovasc Surg 1998;115:1255-63
Classification using distance nearest neighbours
This paper proposes a new probabilistic classification algorithm using a
Markov random field approach. The joint distribution of class labels is
explicitly modelled using the distances between feature vectors. Intuitively, a
class label should depend more on class labels which are closer in the feature
space, than those which are further away. Our approach builds on previous work
by Holmes and Adams (2002, 2003) and Cucala et al. (2008). Our work shares many
of the advantages of these approaches in providing a probabilistic basis for
the statistical inference. In comparison to previous work, we present a more
efficient computational algorithm to overcome the intractability of the Markov
random field model. The results of our algorithm are encouraging in comparison
to the k-nearest neighbour algorithm.Comment: 12 pages, 2 figures. To appear in Statistics and Computin
Long-term follow-up of truncus arteriosus repaired in infancy: A twenty-year experience
AbstractBackground: There have been few reports of long-term follow-up after truncus arteriosus repair in infancy. Methods: A retrospective review was performed to assess long-term outcomes among 165 patients who survived the initial hospital stay after complete repair of truncus arteriosus since 1975. The median age at truncus repair over this 20-year experience was 3.5 months (range 2 days to 36 years), and 81% of patients were less than 1 year of age. Previous pulmonary artery banding had been performed in 15 patients, and two patients had undergone prior repair of interrupted aortic arch. Significant procedures performed along with truncus repair included truncal valve replacement (n = 10) or repair (n = 5) and repair of interrupted aortic arch (n = 4). Results: Patients were followed up for up to 20.4 years (median 10.5 years). Twenty-five patients were lost at cross-sectional follow-up, with a total of 67 patient-years of follow-up available on these patients. There have been 23 late deaths, eight of which occurred within 6 months of repair and 13 of which occurred within 1 year. Ten of the late deaths were related to reoperations. Actuarial survival among all hospital survivors was 90% at 5 years, 85% at 10 years, and 83% at 15 years and was essentially identical for infants alone. A significant independent risk factor for poorer long-term survival was truncus with moderate to severe truncal valve insufficiency before repair. During the follow-up period, 107 patients underwent 133 conduit reoperations. Median time to conduit reoperation was 5.5 years, and the only factor significantly associated with shorter time to conduit replacement was smaller conduit size at initial repair. In addition, 26 patients underwent 30 truncal valve replacements. Six patients required truncal valve replacement before any conduit-related reintervention, with two associated deaths. Actuarial freedom from truncal valve replacement among patients with no prerepair truncal valve insufficiency was 95% at 10 years. Actuarial freedom from truncal valve replacement was significantly lower among patients with truncal insufficiency before initial repair (63% at 10 years). At follow-up, all patients except three were in New York Heart Association functional class I. Conclusions: Ten- to 20-year survival and functional status are excellent among infants undergoing complete repair of truncus arteriosus. Conduit replacement or revision is almost inevitably necessary in this group of patients. (J Thorac Cardiovasc Surg 1997;113:869-79
Results of 102 cases of complete repair of congenital heart defects in patients weighing 700 to 2500 grams
AbstractBackground: Published data suggest that low birth weight is a risk factor for poor outcome in corrective surgery for many cardiac defects. Congenital heart defects in low birth weight infants are typically managed with supportive therapy or palliative operations, with definitive repair delayed. The morbidity associated with such approaches is high. Methods: Since 1990 complete repair of congenital heart defects (other than patent ductus arteriosus) has been performed in 102 infants no larger than 2500 g (median 2100 g, range 700-2500 g), including 16 no larger than 1500 g. Defects included ventricular septal defect (n = 22), tetralogy of Fallot complexes (n = 20), transposition complexes (n = 13), aortic coarctation (n = 12), interrupted arch (n = 10), truncus arteriosus (n = 8), atrioventricular septal defect (n = 6), total anomalous pulmonary venous return (n = 5), and other (n = 6). Results: Preoperative morbidity was more common among patients referred late for surgical correction. There were 10 early deaths (10%) attributable to cardiac failure (n = 4), arrhythmia (n = 1), multiorgan failure (n = 1), sepsis (n = 1), idiopathic coronary artery intimal necrosis (n = 1), foot gangrene (n = 1), and pulmonary hemorrhage (n = 1). No patient had postbypass intracerebral hemorrhage. At follow-up (median 36 months) there were 8 late deaths, and 8 patients underwent 10 reinterventions. There was no evidence of neurologic sequelae attributable to the operation. Conclusions: In general, delaying repair of congenital heart defects in low birth weight infants does not confer a benefit and is associated with higher preoperative morbidity. Complete repair of both simple and complex lesions can be achieved in such cases with good results. Growth after repair approximates the normal curve for low birth weight infants without heart disease. It is recommended that such infants, especially when they have symptoms, undergo early surgical repair rather than prolonged medical management or other forms of palliation. (J Thorac Cardiovasc Surg 1999;117:324-31
Latest development of a W-band Gyro-TWA based on a helically corrugated interaction region
Latest development and experimental study of a W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. With an input seed signal from an 1.5 W, 90-96 GHz solid state source a gain of 27 dB was measured from the experiment. The bandwidth of the gyro-TWA was measured to be at least 5 GH
- …