Distributed gain in plasmonic reflectors and its use for terahertz generation.

Semiconductor plasmons have potential for terahertz generation. Because practical device formats may be quasi-optical, we studied theoretically distributed plasmonic reflectors that comprise multiple interfaces between cascaded two-dimensional electron channels. Employing a mode-matching technique, we show that transmission through and reflection from a single interface depend on the magnitude and direction of a dc current flowing in the channels. As a result, plasmons can be amplified at an interface, and the cumulative effect of multiple interfaces increases the total gain, leading to plasmonic reflection coefficients exceeding unity. Reversing the current direction in a distributed reflector, however, has the opposite effect of plasmonic deamplification. Consequently, we propose structurally asymmetric resonators comprising two different distributed reflectors and predict that they are capable of terahertz oscillations at low threshold currents.

2D metamaterials with hexagonal structure: spatial resonances and near field imaging.

The current and field distribution in a 2D metamaterial consisting of resonant elements in a hexagonal arrangement are found assuming magnetic interaction between the elements. The dispersion equation of magnetoinductive (MI) waves is derived with the aid of the direct and reciprocal lattice familiar from solid state theory. A continuous model for the current variation in the elements is introduced leading to the familiar wave equation in the form of a second order differential equation. The current distributions are shown to exhibit a series of spatial resonances for rectangular, circular and hexagonal boundaries. The axial and radial components of the resulting magnetic field are compared with previously obtained experimental results on a Swiss Roll metamaterial with hexagonal boundaries. Experimental and theoretical results are also compared for the near field image of an object in the shape of the letter M followed by a more general discussion of imaging. It is concluded that a theoretical formulation based on the propagation of MI waves can correctly describe the experimental results.

Increase in size of the pulmonary autograft after the Ross operation in children: growth or dilation?

OBJECTIVE: We sought to assess growth properties of the pulmonary autograft after the Ross operation in children. METHODS: Eight infants with critical aortic stenosis who underwent the Ross operation early in life (median age, 6.4 months) were followed up regarding the possible growth of the autograft. The pulmonary autograft was measured repeatedly by echocardiography during the follow-up, ranging from 6 months to 7 years (median, 5.2 years). Twelve normal children who served as control subjects were similarly followed from 3.9 to 5.8 years (median, 4.9 years). RESULTS: Somatic growth during the follow-up period was significant and was reflected in a doubling of the body surface area, which increased from 0.33 +/- 0.14 m(2) to 0.74 +/- 0.21 m(2). The proximal part of the autograft increased from 13.6 +/- 3.6 mm to 23.3 +/- 3.7 mm (mean +/- SD) and the distal part from 10.5 +/- 2.5 mm to 15.9 +/- 2.8 mm. Growth pattern of the autograft was analyzed by relating measured diameters to predicted normal diameters (ie, Z values). During the first year after the operation, the mean Z value of the proximal autograft increased from 0.2 to 2.2, indicating a more rapid increase than the predicted increase and was also significantly higher than that of the control group (P =.01). After the first year, Z-value changes in patients and control subjects were very similar. CONCLUSIONS: We thus conclude that the pulmonary autograft in the aortic position after the Ross operation does increase in size and that the pattern of this increase is suggestive of passive dilation in the early postoperative period, followed by normal active growth.

Balloon dilation of stenotic aortic valve in children. An intraoperative study.

Ten children in the age range of 3 to 17 years with moderate to severe aortic valve stenosis (gradients of 55 to 109 mm Hg) underwent cardiac operations. At the time of the operation, during bypass, balloon dilation of the stenotic valve was performed and the results were visually assessed by the surgeon. Of the 10 consecutive cases, only three showed dilation results that were comparable to what seems optimal from a surgical point of view. The adverse effects in the remaining seven patients and the corrective measures taken were as follows: (1) too extensive a rupture requiring stabilizing sutures in one patient; (2) too short a rupture, requiring additional commissurotomy in three patients; (3) rupture into the valve leaflet, requiring valve suture and corrective comissurotomy in another three patients. This last, rather serious complication occurred in patients having functionally bicuspid valves with slightly thickened free valve edges, whereas valves with severely thickened edges ruptured in the commissure line but often to an insufficient degree. Because of the high incidence of suboptimal separation of the stenotic aortic valves with balloon dilation, we recommend that further evaluation of long-term results and identification of unsuitable cases should precede widespread use of the technique.

Aortic valve replacement with a pulmonary autograft in infants with critical aortic stenosis.

Seven patients with critical aortic stenosis underwent aortic valve replacement with a pulmonary autograft (the Ross operation) between the ages of 5 weeks and 9 months. The operation was considered mandatory for survival because of continued severe heart failure or valve avulsion. Six of the patients had undergone unsuccessful previous palliations, such as commissurotomy, balloon dilation, and transventricular valvotomy, performed singly (n = 1) or in combination (n = 5). The other patient with a severely hypoplastic aortic valve ring underwent the Ross procedure as a primary operation. Two operative deaths occurred. In both cases severe endocardial fibroelastosis was detected at autopsy. One late death 1 year after the operation resulted from progressive hypertrophic cardiomyopathy and pulmonary hypertension. The rest of the patients are doing well, without medications. Apart from trivial regurgitation in two patients, the pulmonary autograft is performing well.

Anticoagulant therapy in children with prosthetic valves.

The purpose of this study was to evaluate the effectiveness and complications of several types of anticoagulant therapy in children with prosthetic valves. During a 7-year period ending April 1985, 130 children aged 1 to 19 years underwent left-sided valve replacement. Operative mortality was 3%, 5%, and 9%, respectively, for aortic, mitral, and aortic and mitral valve replacement. Among the 123 survivors, 32 (26%) had had aortic, 71 (58%) had had mitral, and 20 (16%) had had aortic and mitral valve replacement. Follow-up ranged from 2 months to 8.2 years, a total of 544 patient-years. The survivors were divided into three groups based on anticoagulant treatment: warfarin sodium, aspirin plus dipyridamole, and no anticoagulants. Among the patients who had aortic valve replacement, thromboembolic complications developed in 2.5% (2.5/100 patient-years) of the aspirin plus dipyridamole group and 5% of the group given no anticoagulants. Only the warfarin group (4%) experienced bleeding complications. Among the patients having mitral valve replacement, thromboembolic complications developed in 4% of the warfarin group, 3% of the aspirin plus dipyridamole group, and 11% of the no anticoagulant group. In addition, 2% of patients in the warfarin group experienced severe bleeding. Two fatal cerebrovascular accidents occurred, both in the aspirin plus dipyridamole group. Patients who received a mitral heterograft were not prescribed any anticoagulant medications, and no thromboembolic complications developed. Among patients having double-valve replacement, complications developed in 5% of the warfarin group and 27% of the group given no anticoagulants.(ABSTRACT TRUNCATED AT 250 WORDS)

The forced oscillation technique in children with respiratory disease.

The single-frequency forced oscillation technique was used to estimate the total respiratory impedance, resistance, and reactance at 2, 4, and 12 Hz of children who had cricoid stenosis (CS; n = 11), provoked bronchoconstriction (PB; n = 6), or cystic fibrosis (CF; n = 13). The selection criteria for patients who had CS and CF were abnormal forced expiratory volume in 1 sec (FEV!) and/or maximal expiratory flow at 50% vital capacity (Vmax 50%). Sixteen of the 17 patients who had CS or PB were found to have resistance (Rrs) values outside the normal range at 4 Hz; at 2 Hz, 14 were found to have abnormal values and, at 12 Hz, only 9. The reactance in the CS and PB groups was somewhat less discriminative than Rrs at all frequencies. Of the 13 patients who had CF, only 4 had abnormal Rrs values; in this clinical condition, the reactance at 2 Hz was the most discriminative variable, being abnormal in 6 of the 13 patients. Irrespective of the clinical group, the Rrs was, in absolute terms, highest at 2 Hz, and it decreased with increasing frequency. This pattern of negative frequency dependence was, however, not obviously specific for any of the tested clinical conditions and offered no information in addition to a single low-frequency determination.

Respiratory resistance and impedance magnitude in healthy children aged 2-18 years.

Two hundred eighteen healthy children aged 2 to 18 years were studied using a modification of the forced oscillation technique. Reference values with height as predictor were determined for total respiratory resistance and impedance during inspiration, expiration, and throughout the whole respiratory cycle at an oscillation frequency of 4 Hz and, in a subpopulation of 61 children, at frequencies of 2 and 12 Hz. Mean total inspiratory resistance, determined at 4 Hz, decreased with growth from 1.3 kPa X 1(-1) X s at 2 years of age to 0.3 kPa X 1(-1) X s at 18 years. Variability in the results between individuals, expressed in terms of coefficient of variation, was found to be +27% and -21%, respectively, and within individuals, 9%. Resistance during expiration was on average 16% higher than during inspiration and the variability within individuals was 11%. A marked decrease in resistance was found in small children when the frequency was increased from 2 to 12 Hz. The frequency dependence of respiratory resistance observed in small children changes gradually with growth, in parallel with the reduction of total respiratory resistance, to an adult pattern in which no significant change in resistance can be noted between frequencies of 2 and 12 Hz.

Double-chambered right ventricle in 73 patients: spectrum of the disease and surgical results of transatrial repair.

OBJECTIVE: To review the spectrum of double-chambered right ventricle (DCRV) and the outcome of surgical repair in patients diagnosed between February 1988 and March 1999. DESIGN: The charts of patients with DCRV were studied. SETTING: Tertiary care hospital. PATIENTS AND METHODS: A total of 73 patients were identified. Sixty-nine underwent surgical repair, while four are awaiting surgery. The repair was through a transatrial approach in 61 patients, while in eight an additional ventriculotomy was performed. MAIN RESULTS: An associated ventricular septal defect (VSD) was present in 56 of 73 patients (77%). These patients were significantly younger (P<0.05) than the 17 patients without a VSD. Among patients with a VSD, the 31 requiring patch closure were significantly younger than the 25 patients having direct closure. Five older patients among those with intact septum had impaired right ventricular (RV) function as well as higher intraventricular gradients. At surgery the intraventricular obstruction was relieved by myomectomy. There was no hospital or late mortality. Following surgery, at a mean follow-up of 13.6 months, no increase in the intraventricular gradient was detected by Doppler echocardiography. CONCLUSIONS: The development of DCRV is associated with VSD in early life. The probability of the presence of a VSD decreases with age. The disease is progressive, resulting in increased intracavitary gradient within the RV and in RV impairment if it is not treated in a timely fashion. Transatrial repair is safe with excellent midterm results. In the presence of high gradients within the RV, a ventriculotomy may be necessary to obtain acceptable results.

Transventricular dilation for critical aortic stenosis in neonates.

Critical aortic stenosis (CAOS) is not compatible with life when the ductus arteriosus closes. We have treated 11 consecutive cases with isolated CAOS. Symptom presentation was in the early neonatal period and diagnosis was made noninvasively at a mean age of 4 days. All were operated on with transventricular dilation (TVD) at a mean age of 4.7 days. There was no early mortality. There were two late deaths due to fibroelastosis. Both had the smallest aortic anulus diameter (5 mm). Two other patients had aortic root replacement, one at the age of 6.5 weeks due to intractable heart failure, and the other at the age of 3 months due to increasing gradient. In these two cases elective surgery was made possible by a successful TVD in the early neonatal period. TVD in this material was not associated with any early mortality, which makes this procedure a good alternative in the treatment of CAOS.

Subharmonics in Bi(12)SiO(20) with an applied ac electric field.

The appearance of subharmonics with the aid of an applied square-wave field is reported for the first time to our knowledge. It is shown that the intensity and the order of the subharmonics are dependent on the repetition rate of the square wave.

Spatial frequency filtering in holographic image reconstruction.

We show that reconstructing a hologram by its object beam leads to spatial filtering, namely, to the suppression of spatial frequency components that are perpendicular to the plane of the recording beams. We conduct experiments by rotating the transparencies of Ronchi gratings and crossed gratings and measuring the corresponding diffraction efficiencies. Good agreement is found with a theory based on image reconstruction with a beam that does not quite satisfy the Bragg condition.

Double exposure planar transmission holograms recorded in nonlinear dichromated gelatin.

A coupled wave model is used to describe the replay of two transmission gratings (G(1) and G(2)) which have been recorded in dichromated gelatin at high exposure energies. As a consequence of material nonlinearities, a third grating G(3) , which has a spatial frequency equal to the difference of the two primary recordings, is also recorded. The model assumes multiple interactions between each of the three gratings and is used to match experimental data where the recording angles were (a) far apart so as to minimize interactions and (b) close together to enhance grating interactions. Good theoretical agreement was found with experiment for both cases.

Color-reflection holography: theory and experiment.

We present a theoretical and experimental analysis of color-reflection holography. Full parallax three-dimensional color images are obtained by the superposition of wavelength-selective reflection holograms recorded at eight combinations of three laser wavelengths. The test object used was a set of eight Munsell color chips recommended by the Commission Internationale de l'Eclairage (CIE) for color-rendering analysis. The spectral power distributions of all the holographic images are measured using a telespectroradiometer and corresponding points are calculated and plotted on a color diagram. The holograms are modeled by a combination of sinc functions for the diffracted replay signal and an empirically determined function for the replay scatter noise. A new definition of signal-to-noise ratio for color holograms is described. The model is matched to a spectral power distribution by choosing values for relative diffraction efficiencies, bandwidth, signal-to-noise ratio, and wavelength shift components. One spectral power distribution having been matched, theoretical predictions of the remaining colors in the holographic images are obtained. The predictions mapped on the CIE 1976 diagram are shown to agree with experimental results: the average distance between theoretical and experimental points on the CIE diagram for all eight Munsell chips on all eight holograms is 0.0001 CIE 1976 chromaticity diagram unit; the discrepancy of the average gamut area between theoretical and experimental points on the CIE diagrams was < 10%. Good agreement between theory and experiment having been shown, a synthesis of holographic color reproduction at any combination of wavelengths predicts optimum recording wavelengths of 460, 530, and 615 nm for typical replay by a color-reflection hologram.

Transductal balloon angioplasty for coarctation of the aorta in the neonate: preliminary observations.

Transductal balloon angioplasty for coarctation of the aorta is described wherein the balloon dilatation catheter is positioned across the coarctation after having passed into the descending aorta from the main pulmonary artery via a patient ductus arteriosus. This procedure was performed in two neonates with excellent immediate clinical results and objective improvement in the pressure gradient. The mechanism of relief of obstruction appears to be ductal dilatation, which allows bypassing the posterolateral shelf of aortic coarctation. This technique is recommended in neonatal coarctations with open ductus arteriosus, especially if the femoral artery cannot be catheterized for performing conventional transfermoral balloon coarctation angioplasty.

Higher diffraction orders in on-axis holographic lenses.

Lenses are formed in bleached photographic emulsion, and the local diffraction efficiency into the various diffraction orders is determined using a probe beam of small diameter. An analysis of the lens is performed by assuming that both the direction and magnitude of the grating vector are constant over a small area of the hologram, leading to ordinary (in contrast to more rigorous partial) differential equations which may be solved numerically. Comparison of experimental results with numerical analysis shows reasonable agreement.

Angular selectivity of silver halide transmission noise gratings copied into dichomated gelatin.

Transmission noise gratings were copied from silver halide emulsion into dichromated gelatin in an index matching tank. The distance between the two plates was varied to alter the angulars pread of recordeds catter in the dichromated gelatin plate. Results are presented in the form of angular transmittance data and scattering rings which show that the diffraction efficiency and angular selectivity of the transmitted noise decrease with a reduction in noise gratings recorded at high angles.

Transcutaneous-PO2 monitoring for detection of exercise-induced right-to-left shunts in children with congenital heart defects: a case report.

UNLABELLED: A 2-y-old boy with scimitar syndrome underwent surgery involving the redirection of partial anomalous pulmonary venous return to the left atrium. Heart catheterization after the operation did not reveal any significant intra-cardiac shunts. An exercise test performed at the age of 10 y revealed a reduction in working capacity. At the age of 12 y, the patient became unconscious and experienced seizures during heavy physical exercise. EEG and Holter ECG examinations were normal. In a second exercise test, a fall in transcutaneous PO2 was demonstrated at the start of the test. A new heart catheterization revealed communication between the inferior vena cava and the left atrium owing to a misplaced patch. No right-to-left shunt was found at rest, probably as a result of drainage of the inferior vena cava to the superior vena cava by the azygous vein. An exercise test after re-operation revealed normal conditions. CONCLUSION: Haemodynamic studies during heart catheterization in children are usually performed at rest. This could result in exercise-induced right-to-left-shunts being overlooked. The use of PtcO2 monitoring during exercise tests is a non-invasive means of exposing these shunts.

Competition between subharmonic and resonating beams for photorefractive gain in bismuth silicon oxide.

Two beams incident upon a bismuth silicon oxide crystal are shown to give rise to a subharmonic halfway between the incident beams and to an oscillating beam in a ring resonator. It is further shown that the two beams arising are in competition with each other: the subharmonic power rises when the oscillating beam declines owing to damping of the resonator.

Diffraction efficiency limitations of holograms recorded in silver-halide emulsions.

Experimental results are presented of the diffraction efficiencies of holograms recorded in bleached silverhalide emulsions for varying beam ratio and exposure. It is found that for high beam ratios the diffraction efficiency quickly reaches a relatively low limit and remains nearly constant as the exposure is increased. A model is presented which explains this saturation by a simple relationship between the refractive index modulation and the exposure maxima and minima. The effect of noise gratings on the depletion of the transmitted and diffracted beams is also investigated by measurements at different replay directions and at two different wavelengths.