Diffusion trapping times and dynamic percolation in an Ising system.

We address the problem of diffusion through dynamic Ising network structures using random walkers (RWs) whose net displacements are partitioned into two contributions, arising from (1) transport through neighboring "conducting" clusters and (2) self-diffusion of the site on which the RW finds itself, respectively. At finite temperatures, the conducting clusters in the network exhibit correlated dynamic behavior, making our model system different to most prior published work, which has largely been at the random percolation limit. We also present a novel heuristic scaling analysis for this system that utilizes a new scaling exponent theta(z) for representing RW trapping time as a function of "distance" from the dynamic percolation transition. Simulation results in two-dimensional networks show that when theta(z) = 2, a value found from independent physical arguments, our scaling equations appear to capture universal behavior in the system, at both the random percolation (infinite temperature) and finite temperature conditions studied. This study suggests that the model and the scaling approach given here should prove useful for studying transport in physical systems showing dynamic disorder.

Photoplethysmographic waveform characteristics of newborns with coarctation of the aorta.

OBJECTIVE: Fetal echocardiography, physical examination and pulse oximetry detect only half of coarctation of aorta (CoA) cases. We aimed to quantify delayed arrival and diminished amplitude of lower extremity photoplethysmographic (PPG) pulses relative to the right hand in affected patients. STUDY DESIGN: We studied 8 CoA infants and 32 healthy controls. The pulse arrival time difference between foot and hand (f-hTD) and pulse amplitude ratio (F/H) were measured on PPG signal waveforms by digitally-determining maxima and minima of systolic decrease of light transmission. Mann-Whitney test was used for group comparisons. RESULTS: In comparison to healthy newborns, CoA infants' PPG waveforms demonstrated prolonged f-hTD (mean±s.d. of 73.2±26.6 versus 35.2±8.3 ms, P<0.001) and lower F/H (0.57±0.26 versus 0.99±0.58, P=0.014). CONCLUSIONS: F-hTD and F/H are quantifiable from hand- and foot-derived PPG waveforms and are significantly different in CoA versus healthy newborns. Larger studies are needed to validate PPG for improved critical congenital heart disease screening.

Excitonic funneling in extended dendrimers with nonlinear and random potentials

The mean first passage time (MFPT) for photoexcitations diffusion in a funneling potential of artificial treelike light-harvesting antennas (phenylacetylene dendrimers with generation-dependent segment lengths) is computed. Effects of the nonlinearity of the realistic funneling potential and slow random solvent fluctuations considerably slow down the center-bound diffusion beyond a temperature-dependent optimal size. Diffusion on a disordered Cayley tree with a linear potential is investigated analytically. At low temperatures we predict a phase in which the MFPT is dominated by a few paths.

Scaling behavior of cyclical surface growth

The scaling behavior of cyclical surface growth (e.g., deposition/desorption), with the number of cycles, n, is investigated. The roughness of surfaces grown by two linear primary processes follows a scaling behavior with asymptotic exponents inherited from the dominant process while the effective amplitudes are determined by both. Relevant nonlinear effects in the primary processes may remain so or be rendered irrelevant. Numerical simulations for several pairs of generic primary processes confirm these conclusions. Experimental results for the surface roughness during cyclical electrodeposition/dissolution of silver show a power-law dependence on n, consistent with the scaling description.

Congenital aneurysm of the left coronary sinus and left main coronary artery with fistulous communication to the right atrium in pregnancy.

We describe a unique case of a left coronary arteriovenous fistula arising from a left sinus of Valsalva aneurysm in a pregnant woman. The relevant diagnostic contributions of two-dimensional echocardiography, color flow Doppler, magnetic resonance imaging, and angiography are discussed. The hemodynamic manifestations of this anomaly in pregnancy and the eventual surgical correction are reviewed.

Roughness scaling in cyclical surface growth.

The scaling behavior of cyclical growth (e.g., cycles of alternating deposition and desorption primary processes) is investigated theoretically and probed experimentally. The scaling approach to kinetic roughening is generalized to cyclical processes by substituting the number of cycles n for the time. The roughness is predicted to grow as n(beta) where beta is the cyclical growth exponent. The roughness saturates to a value that scales with the system size L as L(alpha), where alpha is the cyclical roughness exponent. The relations between the cyclical exponents and the corresponding exponents of the primary processes are studied. Exact relations are found for cycles composed of primary linear processes. An approximate renormalization group approach is introduced to analyze nonlinear effects in the primary processes. The analytical results are backed by extensive numerical simulations of different pairs of primary processes, both linear and nonlinear. Experimentally, silver surfaces are grown by a cyclical process composed of electrodeposition followed by 50% electrodissolution. The roughness is found to increase as a power law of n, consistent with the scaling behavior anticipated theoretically. Potential applications of cyclical scaling include accelerated testing of rechargeable batteries and improved chemotherapeutic treatment of cancerous tumors.

Echocardiographic findings in Pompe's disease with left ventricular obstruction.

Two infants with Pompe's disease (type II glycogenosis) showing echocardiographic evidence of obstructive cardiomyopathy are described. On M-mode and two-dimensional (2-D) echocardiography there was a severe hypertrophy of the interventricular septum, free, and posterior left ventricular wall with midsystolic closure of the aortic valve. The combined echocardiographic and electrocardiographic findings are helpful in the clinical diagnosis of this severe disease.

The use of calcium gluconate prior to verapamil in infants with paroxysmal supraventricular tachycardia.

Verapamil is a useful drug for treating supraventricular tachycardia; however, severe side effects occasionally have been reported in infants. We describe here our experience with the use of a 10 percent solution of intravenous calcium gluconate prior to the use of verapamil in infants with paroxysmal supraventricular tachycardia. In all the attacks verapamil converted the supraventricular tachycardia to sinus rhythm. We feel that calcium gluconate injected previous to verapamil can avoid the negative inotropic effects without interfering with the antiarrhythmic properties of verapamil.

Transcatheter closure of the patient ductus arteriosus in adults using the Gianturco coil.

BACKGROUND AND HYPOTHESIS: Although results of surgical ligation of the patent ductus arteriosus (PDA) in the pediatric age group are excellent, surgical management of the adult with a PDA may be more problematic. The PDA that presents in adulthood may be calcified and friable, rendering simple ligation via a thoracotomy difficult, inadequate, and hazardous. Patch closure of the ductus arteriosus from either the aortic or pulmonary artery orifice using cardiopulmonary bypass or transient aortic cross-clamping is necessary but increases surgical risk. Furthermore, older patients with diseases unrelated to their PDA and patients with Down's syndrome may have higher risks with intubation, general anesthesia, and surgery. Early results of percutaneous transcatheter occlusion of the PDA with Gianturco coils performed under sedation and local anesthesia are promising. METHODS: Six adults with mean age of 39.1 years (range 23.1-62.0 years) were found to have an isolated PDA with mean minimum diameter of 2.7 mm (range 1.0-5.0 mm) at cardiac catheterization. All underwent percutaneous transcatheter occlusion of the PDA using Gianturco coils. RESULTS: Coil implantation was successful in all patients. There were no complications and all were discharged home within 24 hours. Complete ductal occlusion was seen immediately in 4 of 6 patients (67%) while 2 of 6 (33%) had small residual leaks. However, complete occlusion was achieved in all patients by 6 months following the procedure. CONCLUSION: Transcatheter occlusion of the PDA using coils is safe and efficacious in adults.