Enhancing the absorption capabilities of thin-film solar cells using sandwiched light trapping structures.

A novel structure for thin-film solar cells is simulated with the purpose of maximizing the absorption of light in the active layer and of reducing the parasitic absorption in other layers. In the proposed structure, the active layer is formed from an amorphous silicon thin film sandwiched between silicon nanowires from above and photonic crystal structures from below. The upper electrical contact consists of an indium tin oxide layer, which serves also as an antireflection coating. A metal backreflector works additionally as the other contact. The simulation was done using a new reliable, efficient and generic optoelectronic approach. The suggested multiscale simulation model integrates the finite-difference time-domain algorithm used in solving Maxwell's equation in three dimensions with a commercial simulation platform based on the finite element method for carrier transport modeling. The absorption profile, the external quantum efficient, and the power conversion efficiency of the suggested solar cell are calculated. A noticeable enhancement is found in all the characteristics of the novel structure with an estimated 32% increase in the total conversion efficiency over a cell without any light trapping mechanisms.

Simulating the dispersive behavior of semiconductors using the Lorentzian-Drude model for photovoltaic devices.

Unique light-trapping structures that improve the efficiency of thin-film solar cells require advanced computational methods that can simulate the propagation of light through the thickness of each material in the solar cell. The simulations community that uses the Lorentz-Drude (LD) model cannot precisely simulate the propagation of light through the entire spectrum of the Sun, due to the difficulty in extrapolating the coefficients of each solar cell material. In this paper, a new technique for modeling dispersive and absorptive material over the Sun's entire wavelength range (200-1700 nm) using the LD model is suggested. The new numerical models are used for simulating light propagation through various one-dimensional light-trapping structures, including metal backreflectors and distributed Bragg reflectors. All the numerical simulation results show agreement with previously published theoretical and experimental results. The proposed simulation technique will help the simulations community in using the LD model to simulate the propagation of light in solar cells more accurately.

Non-display applications and the next generation of liquid crystal over silicon technology.

The next generation of applications for liquid crystal (LC) over silicon technology will be non-display oriented systems such as adaptive optical interconnects, optical switches and optical image processors. These new non-display applications have a different set of material parameters, which means that existing display-based materials are not entirely optimal. This is particularly the case when the application is driven by phase modulation at high frame rates (more than 1 kHz). An example of such a non-display application is in adaptive optical interconnects. Optical data transmission between printed circuit boards is becoming more and more important as the data rate in electronic systems increases into the gigahertz region. One way of avoiding the data bottlenecks in board to board interconnects is to use optical links to transmit the data. Recent research into free-space optical links has shown that a high level of manufacturing tolerance must be used to maintain the link. However, one way of avoiding these limitations is to use a reconfigurable LC phase hologram as a beam-steering element to compensate for movement between the boards and maintain the optical data path.

[Left main coronary artery angioplasty: report of five cases illustrating the current indications]. / Angioplastie du tronc commun: a propos de cinq cas illustrant les indications actuelles.

OBJECTIVES: The purpose of our study is to illustrate by five original observations the various situations where the stenting of the left main coronary artery can be proposed in alternative to aortocoronary bridging with encouraging results in short- and long-term. MATERIALS AND METHODS: We report a retrospective study relating to five cases with left main disease treated by stenting between 1996 and 2002 at our institution. In two cases the left main stem was unprotected. In two other cases, the left main trunk was protected. And the last case was an emergency stenting for an iatrogenic dissection of the left main coronary artery. RESULTS: The stenting was carried out successfully among the five patients without major in-hospital complication. During the follow-up of 29 months at mean, no death was deplored, and no target lesion revascularization was required on the left main coronary artery (with a left main trunk permeable on three coronarographic controls). CONCLUSIONS: In the light of these results, and basing on the published data, we conclude that stenting for the left main coronary disease may be a safe and effective alternative to coronary artery bypass surgery in particular cases among "selected" patients (refusal or surgical contraindication, protected left main coronary artery, spontaneous or iatrogenic acute occlusion of the left main coronary artery).

[Apolipoprotein E and angiotensin-converting enzyme gene polymorphisms as risk factors of coronary disease]. / Implication du polymorphisme génétique de l'apolipoprotéine E et de l'enzyme de converstion de l'angiotensine dans l'athérosclérose coronarienne.

The objective of this study was to test the hypothesis that apo E (RFLP, HhaI) and/or angiotensin-converting enzyme (ACE) (ins16del) are associated with higher risk for coronary heart disease. We investigated 250 patients who underwent complete cardiac examination comprising coronary angioplasty and biological analysis (CT, HDLc, LDLc, TG, apo A and apo B). Prevalence of the alleles of apo E and ACE was assessed by molecular analysis. Patients without stenosis or with non-significant stenosis (> 50% of the vascular lumen) were used as reference group (141 patients). Those presenting a significant stenosis of the coronary artery (. 50% of the vascular lumen) were considered as cases (109 patients). The relative frequency of the e 4 allele was significantly higher in cases than in reference group (p > 0.02). A strong association have been found between coronary heart disease and apo E polymorphism (2 = 8.91; p > 0.05). The presence of the e 4 allele increase the risk of atherosclerosis (RR = 2.71; IC95%: 1.25-5.90; p > 0.02) compared to e 3 allele. Also, subjects with D allele were more frequent in cases than in reference group (p > 0.001). A significant association was noted between ACE polymorphism and coronary heart disease (2 = 42.15; p > 0.001). This relationship was positive (rho de Spearman = 0.39; p > 0.01). With D/D homozygotes patients, the RR for coronary heart disease was 19.10 (p > 0.001), while The RR with I/D heterozygotes was 6.91 (p > 0.001) compared to I/I homozygotes. A significant interaction have been shown up between D/D genotype and arterial hypertension (HTA) (2 de Wald = 16.10; p > 0.001). The multivariate analysis showed that the chronic smoking, diabetes, hypoapolipoproteinemia A, interactive effects between D/D and HTA, I/D and obesity, and between D/D and hypertriglyceridemia were the major significant factors to take into consideration in our population. We also note that subjects with both D and e 4 alleles were presenting a high risk to coronary heart disease (RR = 5.93; IC95%: 2.00-17.55; p > 0.01). Thus, those two alleles (4 and D) appears to be important cardiovascular risk factors in the moroccan population.

[Percutaneous transluminal renal angioplasty in hypertension]. / Angioplastie transluminale des artères rénales dans l'hypertension artérielle rénovasculaire.

The aim of our study was assess anatomical and functional results of renal artery angioplasty with and without stenting in 25 hypertensive patients (8 female and 16 male, 42.6 and 61.6 years old respectively) with significative renal artery stenosis (RAS) (atherosclerotic: 22; fibrodysplastic: 3). Eleven patients had simple angioplasty and 13 had stenting. The rate of angioplasty success was 96%. In the stent group, the anatomical result was better: 2% of residual stenosis versus 24% in the other group (p < 0.001). Restenosis occurred in 2 patients. Immediately after revascularisation arterial blood pressure decreased from 195/105 +/- to 150/85 +/- mmHg in-group without stent (p < 0.001) and from 190/100 to 145/85 mmHg in the group (p < 0.001). The value of serum creatinine concentration in patient with renal failure didn't change after revascularization.

[Angioplasty and endoprosthesis of the left coronary artery. Report of a case]. / Angioplastie et endoprothèse du tronc coronaire gauche. A propos d'un cas.

The authors report the case of a 70 year old woman followed up in our Department for ischaemic heart disease since 1991 and admitted to the Intensive Care Unit in November 1996 for unstable angina. Coronary angiography showed significant stenosis of the left main coronary artery, a severe stenosis of the LAD and occlusion of the right coronary artery. Angioplasty of the middle segment of the LAD and left main coronary arteries with implantation of a stent was performed because of resistance to medical therapy and a contra-indication to surgery. Four months later, recurrent anginal pain led to a repeat angioplasty of the LAD with a satisfactory immediate result. The initial procedure on the left main coronary artery was successful and follow up was uncomplicated.

[Percutaneous transluminal valvuloplasty in congenital pulmonary stenosis in adults. Apropos of 34 cases]. / Valvuloplastie transluminale percutanée des sténoses pulmonaires congénitales chez l'adulte. A propos de 34 cas.

Percutaneous pulmonary valvulotomy is the treatment of choice for isolated congenital pulmonary valvular stenosis in childhood. However, experience of this procedure in the adult is much more limited. Between January 1984 and December 1994, 34 patients with severe or moderate pulmonary valvular stenosis underwent percutaneous transluminal valvuloplasty. The age of the patients ranged from 20 to 47 years (mean 22 +/- 4 years). Cardiac catheterisation was performed using the femoral vein in 27 cases and the internal jugular vein in 7 cases. Success was obtained in 28 patients (81% of cases). Pulmonary artery-right ventricular pressure gradient decreased from 113 +/- 35 to 32 +/- 13 mmHg (p < 0.001) after valvuloplasty with one or two balloon catheters. The tolerance of transluminal valvuloplasty was generally good. The poor results were explained by cases of dysplasic valves or of infundibular reactions. There was one death which occurred 24 hours after the procedure. Clinical and echocardiographic follow-up was obtained in 20 patients, 3 to 36 months after valvuloplasty (average: 23 +/- 13 months). No cases of restenosis were observed. Percutaneous transluminal pulmonary valvuloplasty in the adult is feasible and gives good results which are maintained at medium-term; it has become the treatment of choice of valvular pulmonary stenosis and gives good results which are maintained at medium-term, thereby avoiding surgical valvulotomy.

[Syphilitic aortitis and "accelerated" atherosclerosis]. / Aortite syphilitique et athérosclérose "accélérée".

The authors present the case of a 42 year old patient admitted for surgery of massive aortic regurgitation. Investigation of this patient who had no significant cardiovascular risk factors, showed diffuse and accelerated atherosclerosis (severe stenosis at the origin of both subclavian arteries at both superficial femoral arteries). Tertiary syphilis with neurological involvement and aortitis was confirmed by histological examination (peroperative biopsy of the aortic wall). This case is unusual due to the association of early atherosclerosis with tertiary syphilis and raises the question of the causality of syphilis in the generation of these atherosclerotic lesions.

[Coronary aneurysm in Behcet's disease. Report of a case]. / Anévrisme coronaire au cours de la maladie de Behçet. A propos d'un cas.

Cardiac involvement is rare in Behçet's disease. The authors report the case of a young patient with Behçet's disease and multiple cardiac complications. The remarkable feature of this case was the presence of a coronary artery (first diagonal) aneurysm associated with multiple venous thromboses. Anticoagulant therapy was changed for a platelet aggregant. Surgery was not indicated because of the fragility of the vessels.

[Association of coronary-pulmonary fistula and intercoronary fistula. Apropos of a case]. / Association fistule coronaro-pulmonaire et fistule intercoronaire. A propos d'un cas.

The authors present the case of a 30-year-old woman admitted to hospital for investigation of a systolodiastolic murmur. Assessment revealed a fistula between the trunk of the left coronary artery and the pulmonary artery, with an aneurysm on the left anterior descending artery (LAD), associated with an intercoronary anastomosis between the left conus artery and the LAD. Thallium myocardial scintigraphy demonstrated reversible decreased uptake in the anterolateroapical region. Simple coronaro-pulmonary fistulas are a rare disease. The positive diagnosis is suggested by echocardiography and confirmed by coronary angiography. The clinical course is generally favourable, except in the presence of complications such as aneurysm, heart failure or coronary insufficiency. This case raises the difficult problem of the operative indication in these young, usually asymptomatic patients.